Wednesday, January 31, 2018

Winter 2017-2018 Update - It's Not Over Yet

We are two-thirds of the way through climatological winter (December-February), and it has been a rather unusual one so far in many different ways. Winter weather won't necessarily stop in March, or even April (or in one or two recent cases, May), but for statistical purposes December through February is our target period.

Winter weather got off to a late start in most of the country as much warmer than normal weather prevailed in much of the country. The big news in December prior to Christmas was the tinder dry weather in the west and the devastating wildfires in California. There was also some heavy snow across parts of the southeast the second week of December.

The weather pattern changed dramatically the last week of December, and cold Arctic air spilled into much of the eastern half of the country. It persisted through the the middle of the month with one or two brief breaks. This pattern change also brought much needed rain to California. Unfortunately the rain triggered deadly mudslides as it washed away hillsides left bare by the earlier wildfires.

It was during this period the snow cover across the U.S. was at the highest of the season so far with 53.6 percent of the lower 48 states with snow on the ground. This was also the time when all 50 states had measurable snow on the ground. There was a notable lack of snow in the Cascades and Sierra Nevada.

The Accumulated Winter Season Severity Index (AWSSI) in mid-January depicted a severe to extreme winter in much of the eastern U.S. as well as in the northern Rockies. Below normal snowfall in the Midwest and Plains contributed to the average to moderate categories there, despite cold weather.

So, here is how we stand at the end of January. Temperatures have been normal to below normal across most of the country east of the Rockies., while it remains warm in the western U.S.

Season-to-date snowfall is an odd picture, with much above normal snowfall in the Gulf Coast states the southeast, and in the northern Rockies. Snowfall is near to above normal around the Great Lakes and New England. Snowfall is well below normal in the northern Plains, central and southern Rockies, and much of the Midwest.

As of today snow cover was down to about 25 percent across the U.S., half of what it was two weeks ago.

The precipitation map demonstrates the disparity in winter precipitation across the country to date. It has been dry in much of the west, and very dry from eastern New Mexico through the Texas and Oklahoma panhandles.

The dry weather in California, in what is normally the wet season, is having a significant impact on snow in the Sierra Nevada, crucial for water supplies the rest of the year. Snow water equivalent (SWE) is approaching record lows for a number of locations for this time of the season. SWE is also very low further east in the central and southern Rockies.

The last two weeks of mild weather is also reflected in changes in the AWSSI with a drop of one category in the Midwest and in the east.

Winter weather looks like it will make a return during the first two weeks of February, at least, so there will be more to factor in before this winter is over. A broad scale trough is forecast to reestablish over much of  the U.S. in the next week, funneling more Arctic air into the country.

500 millibar forecast map for 6:00 p.m. Thursday, February 8, 2018.

Monday, January 15, 2018

Singing Ice

Many people don't find a lot to like about winter weather. I'm good with everything about winter except the occasional howling winds, and freezing rain. Even if you aren't a fan of winter weather, there are a lot of interesting phenomena to observe during cold weather. Many of you have probably seen the "throw boiling water into the air when it's -20°F" video as one example. Here is a video I came across the other day which describes the physics behind the phenomenon of "singing ice".  This video was produced by National Public Radio science and hosted on their Skunk Bear YouTube channel. It's a worth a watch!

Thursday, October 26, 2017

You Won't Regret Spending 8 Minutes of Your Time on This

Lightning. Dust storms. Hail shafts.  Explosively developing thunderstorms. Microbursts. Shelf clouds. Rainbows. Spectacular Southwest scenery.

If any of these things interest you, then you will want to be sure to view photographer Mike Olbinski's latest film, "Monsoon IV".

Olbinki is a professional photographer from Phoenix, AZ. His main business is as a wedding and family photographer, but he also spends a good amount of time chasing weather, the Southwest Monsoon in particular, and storms in general. I wrote a blog post about Olbinski's first monsoon video in 2014.

He wrote a short blog post about his activities this past summer, and you can view the video there as well. His Storm Blog contains amazing photos accompanied by description of his chasing activities associated with that particular photo.

This is best viewed full screen on your computer, but for the full experience view it on a large screen HDTV if you can.

Monday, September 18, 2017

Notes on Hurricane Irma

Hurricane Irma on September 8.
Five days ago the last remnants of what was once Hurricane Irma fizzled over the eastern U.S. Attention is now focused on dangerous Hurricane Maria, which at this writing is slamming the island of Dominca. For the most up to date information on Maria, Jose, and Lee visit the National Hurricane Center web site.

As Hurricane Irma gained strength I and many others were riveted to web sites, social media, and news programs tracking the progress of the storm. In this day of nearly instant communication of information it's not hard to get immersed in following the progress of a storm like this. Periodically I grabbed images and information to save in anticipation of a blog post or two about this storm. Irma and its aftermath has been well-documented so I won't rehash Irma's history here. What I would like to do is share some of the images and information I collected during the storm that you may not have seen.

The first land Irma slammed into was the island of Barbuda. Barbuda is one of two major islands that make up the Caribbean nation of Antigua and Barbuda in the middle of the Leeward Islands. Irma made a direct hit on Barbuda.

Here is the radar image from Guadalupe showing the eyewall of Irma over Barbuda at 0100 local time. Winds were likely gusting to 170 mph or more over the island.

Here is the series of weather observations from Barbuda for the two hours prior to the arrival of the eye.  Sustained hurricane force winds with gusts as high as 155 mph were recorded at this station on the southwest side of the island. Note that the CALM winds reported for the last two observations were not from being in the eye, but were due to the destruction of the anemometer.

Weather observations from Barbuda as Irma made landfall September 6.

This radar image at 1:30 a.m. local time shows the entire island of Barbuda in the calm eye of the hurricane.

Irma left widespread destruction across Barbuda. The island was evacuated after the hurricane moved on, leaving the island uninhabited for the first time in 300 years.

Irma's path then took it through the Virgin islands, producing destruction across St. Thomas, St. John, and St. Maarten.

Damage in St. Maarten.
Photo: Dutch Defense Ministry

Irma continued WNW and passed to the north of the Dominican Republic and Puerto Rico.

Hurricane Irma approaches Puerto Rico on September 6.

Irma was able to maintain its strength due to the very warm water in the southern Atlantic and Caribbean, especially the area between Cuba and the Bahamas. Sea surface temperatures in this region were in the range of 85°F to 90°F

Sea surface temperatures on September 6.

One interesting image is this one of all the marine traffic around Florida on Saturday, September 8, heading south and east. It's interesting to note the number of cruise ships.

Marine traffic near Florida on the morning of September 8.

After brushing along the north coast of Cuba on Saturday, September 9, Irma turned north toward the Florida Keys. The eye of the storm made landfall in the Florida Keys, east of Key West, around 8:00 a.m EDT, Sunday, September 9.

Radar image from the NWS Key West radar at 8:02 a.m. EDT September 10.

After crossing the keys, the eye of Irma was over open water and headed to another landfall on the Florida west coast. Irma made its final landfall near Marco Island, FL at 3:35 p.m. EDT on Sunday.

Radar image from the NWS Key West radar at 3:35 p.m. EDT September 10.

Hurricane Irma was certainly a storm of record. No doubt the name Irma will be retired. Philip Klotzbach, a tropical storm researcher at Colorado State University, compiled a list of of records and notable facts about Irma.
Josh Morgerman (iCyclone on Facebook and Twitter), a professional hurricane chaser, was in Naples, FL when Irma made landfall. He produced a video of his experience which you can view here.

Wednesday, September 6, 2017

Montana is Burning...

The sky over Butte, MT on September 3.
Source: Facebook
and so is Oregon, California, and Idaho.

Much of the "weather attention" is now on Hurricane Irma, still a few days away from affecting the U.S. Smokey skies from the Pacific coast to the Midwest call attention to another disaster - wildfires in the west, particularly in Montana, Oregon, and California.

Eighty-one large fires have burned 1.4 million acres in nine western states. Hot weather on Labor Day caused fires to gain thousands of acres in Montana, Oregon, & California. Of the nine western states with wildfires, Montana tops the list with 28, the largest being the Rice Ridge fire in the Lolo National Forest at 108,126 acres. Two other fires in the Miles City area are at 99,735 and 73,797 acres. Of the 28 fires (total of 574,552 acres) only one is completely contained. The Rice Ridge fire is only 2 percent contained. California (17 fires, 244,066 acres). Sadly, two fire fighters have lost their lives fighting the wildfires in Montana.

Wildfires in the northwestern U.S. as of September 5.

In Oregon, there are 19 active fires encompassing 353,029 acres and none are contained. Almost half of that acreage is one fire - the Chetco Bar fire in the Siskiyou National Forest. The Chetco Bar fire is 167,513 acres and is only five percent contained. The Eagle Creek fire straddles the Oregon-Washington border and is now burning more than 30,000 acres.

Eagle Creek in Oregon.
Photo credit: @tristanCF on Twitter

So far this year 47,094 fires consuming 7.8 million acres.It's the most fires since 2011. but so far third in acreage as of this date behind 2015 and 2012. There is still a long way to go. For the ten-year period from 2006 through 2016, the was an annual average of 50,129 wildfires and an average of 5,458,817 acres affected. For 2017 there are fewer fires but a 14 percent increase in acreage as of September 5.

GOES-16 loop of wildfires in western Montana and Idaho late on September 3.
Source: NOAA

At first glance one might think that the fires are just burning grasslands and forest. However, much of that grassland in some areas is grazing land  In Montana, for example, the impact from the fires will be long-lasting. Fires have burned thousands of acres of grazing land. The price of hay was already 30 to 40 percent higher or more because of the drought. Donated hay may help ranchers make it through this year, but there is next year to worry about. In some cases the fires will have impacts for years to come, as ranchers may have to sell off cattle to survive. Cattle have perished in the fire, and others that survived may be affected by heat and smoke inhalation. or burned hooves from walking over smoldering ground. In addition to the grass and trees, an estimated 1400 miles of fencing has been destroyed, costing an estimated $15 million to replace.  It has been estimated that 80 to 100 percent of the acreage affected by the Lodgepole Complex of fires in east-central Montana suffered a complete loss of grass, most of which was grazing land.

Fires in and around Glacier National Park in northwestern Montana have destroyed one structure and threatened others. Firefighters lost the battle to protect the Sperry Chalet on August 31st as the Sprague fire spread into the area.

The Sperry Chalet main building ablaze in Glacier National Park.
Photo credit; National Park Service

Moisture conditions coming into the summer were not bad in Montana. At the end of the May much of the eastern third of Montana was classified as D0 (Abnormally Dry). By the end of June drought had intensified and D3 (Extreme Drought) was established in northeastern Montana. At the beginning of August D4 (Exceptional Drought) covered the northeastern quarter of Montana. As of last week Extreme to Exceptional Drought covered almost 40 percent of the state.

The lack of rainfall has been well-documented by our Montana CoCoRaHS observers.There have been lots of gray dots on the Montana map the past few months. The CoCoRaHS observer at MT-LC-14 Helena 2.0 NNW has measured only 1.36 inches of rain since June 1st. There have been only eight days with measurable rain, and 0.79 inch is the largest daily amount. The observer also measures evapotranspiration, and the water balance since June 1st (precipitation minus evaporation) is -21.26 inches.

The observer at MT-LN-6 Troy 26.9 NNE has tallied only 0.97 inch of rain since June 1st, and today commented that this marks "63 consecutive days with no measurable rain." (the number is actually 52 days - the last measurable rain, 0.01", was on July 16).

Many CoCoRaHS observers are reporting low visibility from smoke and even ashfall. Ash was falling in Seattle Tuesday morning morning, the first time since Mount St. Helens erupted in 1980. Ash was also reported in Portland, OR.

Smoke from the western fires is causing serious air quality issues in the west with visibility reduced to less than a mile in some locations. The smoke has also hazed the skies over the Plains and Midwest making for some spectacular sunrise, sunsets, and coloring the moon orange.

The combination of dry and hot weather this summer has exacerbated fire conditions from Montana to the Pacific coast. Dryness increased across the west during the summer, while the heat has been fairly persistent especially in the Pacific Northwest south through California.

Some showers could move through western Washington, Oregon, and perhaps Idaho by the end of the week which may help a little. However, most of Montana will remain dry.

Quantitative precipitation forecast for the three-day period ending at 6:00 p.m. MDT Saturday, September 9, 2017

Thursday, August 31, 2017

CoCoRaHS Observers Document Record Tropical Rain from Harvey

There are more than 20,000 CoCoRaHS observers across the U.S., Canada, Puerto Rico, the Bahamas, and the U.S. Virgin Islands. So when a weather disaster occurs, some of our observers are bound to be affected. We have seen that in the past, and it happened again this past week when Harvey slammed into the coast of Texas. Often we don't always know how observers have been affected. Some will post comments with their observations when they get back online or post to the CoCoRaHS Facebook group, and some drop an email to headquarters or their state coordinator let us know their situation. Most of the time, however, we just see the observations disappear from the map.

Texas CoCoRaHS maps for August 24 and August 28, 2017

The comparison might not be obvious at first glance, but there are a lot of gray dots on the August 24 map, and many fewer dots on the August 30 map. The area outlined in yellow is where Harvey came ashore with winds of 120 mph. I looked at the reports from six counties along the coast (Nueces, San Patricio, Aransas, Refugio, Calhoun, and Victoria). On August 24 there were a total of 35 reports submitted for those counties. On August 28, there were only nine. We are all hoping that all of our Texas and Louisiana observers affected by the winds and flooding from Harvey are safe and well.

8/25/2017  TX-VC-39   Getting ready for Harvey. I wont be able to record the rain unfortunately... my gauge is not secure enough to maintain integrity, so I brought it inside. It is now 1:00pm and it has just really started coming down. Pray for me... it's me, my husband and my 88 year old dad, hunkered down in Victoria..I'll be back when the power comes back on.

Further north from landfall,in Harris and surrounding counties, torrential rain and flooding hampered rainfall observations. In some cases the rain came down so hard and fast that observers could not get their gauges before they overflowed (the 4-inch gauge holds approximately 11 inches of rain). We had a few reports of gauges being blown over, and numerous comments about overflowing rain gauges. In places where the flooding was minor observers were able to regularly get out to their gauges and make measurements. Here is an example of a great report from the observer at TX-SJ-12 Oakhurst 3.6 SSE on August 28 detailing his measurements. The total measurement was 16.50 inches, and the comment was as follows:

Measurements and times breakdown: 1.28 was one hour period 7am-8am (8/27/17) 7.84 was 12 hour period 8am-7pm (8/27/17) 7.38 was overnight 7pm (8/27/17)-7am (8/28/17)

Neil Bradley (TX-HRR-116) with
his rain gauge on August 30.
There were 168 Significant Weather Reports submitted by Texas CoCoRaHS observers between August 25 and August 30. All of those were immediately routed to the nearest National Weather Service Office and aided forecasters in their real-time assessment of the storm. One CoCoRaHS observer in Harris County, Neil Bradley (TX-HRR-116, Katy 1.0 NNE) submitted hourly Significant Weather Reports on August 27 and 28. By the time the rain ended on August 29 he had measured 34.52 inches of rain. He also posted regular updates to the CoCoRaHS Facebook group. Greg Story, a meteorologist with the NWS West Gulf River Forecast Center commented "Neil, on behalf of all of us at the NWS West Gulf River Forecast Center, thank you for your timely, invaluable reports. Much appreciated!!"

The rain bands and convective clusters with Harvey resulted in some striking differences in rainfall amounts over short distances. Here is an example showing the bands of rain in the hours after Harvey made landfall. This image is the Storm Total Precip product (radar estimated rainfall) on August 26 at 9:40 a.m. from the Corpus Christi radar.

Radar estimated precip from Corpus Christi radar on 8/26/17 at  9:40 am.
The blue band >10". Sfc reports confirmed 14.46" near Austwell, TX

This is a composite image from three weather radars (Corpus Christi, San Antonio, and Houston) of the storm total precipitation on 8/26 at 2:00 p.m.

Storm Total Precipitation at 2:00 p.m. CDt 8/26/17.
Image is indicating there is already 10"+ west of Houston.

Looking at the colors and pattern is one things, but looking at actual numbers is another. Here is the total rainfall recorded by CoCoRaHS observers over the course of the storm. This only lists amounts greater than 32 inches for Texas and greater than 10 inches for Louisiana, otherwise it would be pages long.

Total precipitation for 8/25/2017-8/31/2017 for Texas and Louisiana

It's no secret the the Houston area is flood-prone, and to monitor conditions in the area the Harris County Flood Control District has automated rain gauges and stream gauges throughout Harris County. With the addition of CoCoRaHS and NWS Cooperative observations the character of precipitation is well captured. The map below is the total precipitation measured by these automatic gauges for through August 29.

Map of precipitation amounts from Harris County Flood Control District rain gauges.
The Cedar Bayou gauge with 51.88 inches is circled in green
This chart shows the 12 hour precipitation amounts measured by the HCFCD rain gauge at Cedar Bayou.

When all was said and done and Harvey finally pulled to the northeast, more than 50 inches of rain had been measured in the Houston area, and more than 45 inches of rain in eastern Texas near Beaumont/Port Arthur. Beaumont, TX received 26 inches of rain in 24 hours Tuesday into Wednesday.

To get some perspective on how incredibly unusual this amount of rain was, check out this map from climatologist Brian Brettschneider.

Hats off to all of our observers in Texas and Louisiana who were able to make measurements through the storm. Thank you for your dedication to CoCoRaHS. There are likely a number of observers who were not able to submit measurements because of wind damage, flood damage, or power outages. We hope you are all safe and that recovery is underway.

Finally, here is the list of precipitation amounts and wind gusts associated with Harvey as compiled by the NWS Weather Prediction Center. This list is long but I wanted to include it before it disappeared from the web.

1000 PM CDT WED AUG 30 2017





BONSECOUR                             7.91                   
GASQUE                                7.45                   
GRAND BAY 10.5 NE                     6.81                   
FOLEY 7.4 SW                          6.44                   
ELBERTA                               6.31                   
ORANGE BEACH                          6.03                   
TILLMANS CORNER 4.3 WNW               6.01                   
MOBILE REGIONAL AIRPORT               5.83                   
FAIRHOPE                              5.77                   
GULF SHORES                           5.60                   
MOBILE 11.2 WSW                       5.44                   
MOBILE/BATES FIELD                    5.02                   
SUMMERDALE                            4.73                   
MONTROSE                              4.52                   
DAPHNE 0.4 SW                         4.42                   
FISH RIVER NEAR SILVERHILL 3W         4.35                   
SONNY CALLAHAN ARPT                   4.32                   

MAMMOTH SPRINGS 2 SSE                 6.42                   

MILTON                                6.92                   
PENSACOLA REGIONAL AIRPORT            6.84                   
UNIVERSITY WEST 2.0 WNW               6.36                   
PACE                                  5.35                   
GULF BREEZE                           5.28                   
ORIOLE BEACH 2 WSW                    3.01                   

BAYOU CONWAY                         22.25                   
BAYOU TORO NEAR TORO                 20.62                   
KENNER GULLY AT MARK LEBLEU          18.23                   
CALCASIEU RVR AT OLD TOWN BA         18.15                   
W-14 AT JOE SPEARS RD                17.85                   
W-6 AT WARD LINE ROAD                17.24                   
MOSS BLUFF                           16.70                   
BELFIELD DITCH AT BELFIELD ROAD      16.37                   
IOWA 0.9 ESE                         16.36                   
GOLDSMITH CANAL AT GOOS RD           16.02                   
BAYOU ARSENE AT HECKER ROAD          15.84                   
GOLDSMITH CANAL AT HWY 171           15.74                   
LAKE CHARLES 11.5 SSW                15.41                   
RAGLEY 5.0 SE                        15.18                   
EB L-14 AT IOWA BASEBALL FIELD       14.85                   
INDIAN BAYOU AT COFFEY ROAD          14.10                   
TOPSY 4 NNW                          14.08                   
LACASSINE BAYOU AT LORRAIN BRIDGE    13.04                   
ZAVALLA 2 ENE                        12.87                   
SULPHUR 2.2 E                        12.54                   
BON WIER 2 ENE                       12.44                   
HACKBERRY 5 SSE                      12.33                   
CONTRABAND BAYOU AT 18TH STREET      12.28                   
WELSH 0.7 W                          12.26                   
W-4 AT NELSON ROAD                   12.12                   
GILLIS 4 WSW                         12.11                   
FORT POLK                            11.96                   
BUXTON CREEK AT DOUGLAS ROAD         11.21                   
CHOUPIQUE BAYOU AT HWY 90            11.02                   
LACASSINE NATIONAL 2 ENE             10.55                   
BAYOU DINDE AT PICARD ST              9.76                   
LEBLEU SETTLEMENT 2 WNW               9.64                   
FORKED ISLAND 5 ENE                   9.37                   
BUNDICK CREEK NEAR DE RIDDER          9.26                   
PECAN ISLAND 2 E                      9.14                   
LAKE CHARLES MUNI ARPT                9.08                   
NEW IBERIA/ACADIANA                   8.92                   
VERNON - FTS                          8.77                   
LAFAYETTE RGNL ARPT                   7.14                   
NEW ORLEANS/MOISANT                   5.88                   
NEW ORLEANS/LAKEFRONT                 5.33                   
ENGLAND AFB/ALEXANDRIA                4.84                   
SLIDELL AIRPORT                       3.82                   
BATON ROUGE/RYAN MUNI ARPT            3.17                   

GAUTIER                               8.27                   
SANDHILL CRANE - FTS                  7.90                   
GRAND BAY                             6.06                   
OCEAN SPRINGS 3.6 ESE                 4.61                   
MOSS POINT - TRENT LOTT INTL ARPT     4.55                   
PASCAGOULA                            4.52                   
PEARLINGTON 4.4 N                     3.99                   
JOURDAN RIVER NEAR KILN               3.35                   
TANGIPAHOA RIVER AT OSYKA             3.15                   
TYLERTOWN 9 WNW                       3.08                   
NATCHEZ/HARDY                         2.91                   
KEESLER AFB/BILOXI                    2.55                   

CEDAR BAYOU AT FM 1942               51.88                   
CLEAR CREEK AT I-45                  49.40                   
DAYTON 0.2 E                         49.23                   
MARYS CREEK AT WINDING ROAD          49.20                   
BEAUMONT/PORT ARTHUR                 47.35                   
SANTA FE 0.7 S                       46.70                   
PASADENA 4.4 WNW                     45.74                   
HORSEPEN CREEK AT BAY AREA BLVD      45.60                   
SOUTH HOUSTON 4.0 SSW                44.91                   
BERRY BAYOU AT FOREST OAKS BLVD      44.80                   
BERRY BAYOU AT NEVADA                44.44                   
FRIENDSWOOD 2.5 NNE                  44.05                   
LITTLE VINCE BAYOU AT BURKE RD       43.52                   
HOUSTON WEATHER FORECAST OFFICE      43.38                   
LEAGUE CITY 2.7 NE                   43.32                   
WEBSTER 0.4 NW                       43.32                   
LNVA CHEEK CANAL AT DITCH 407        43.11                   
LITTLE CEDAR BAYOU AT 8TH ST         42.32                   
ARMAND BAYOU AT GENOA-RED BLUFF RD   42.16                   
TURKEY CREEK AT FM 1959              42.12                   
BOONDOCKS RD AT TAYLORS BA           41.86                   
ARMAND BAYOU AT PASADENA LAKE        41.20                   
TAYLOR LAKE AT NASA ROAD 1           40.44                   
SH 124 AT HILLEBRANDT BAYOU          38.18                   
MAHAW BAYOU AT ENGLIN RD             37.75                   
JACINTO CITY                         37.60                   
HUNTING BAYOU AT LOOP 610 EAST       37.00                   
TELEPSEN                             36.60                   
MAHAW BAYOU AT BRUSH ISLAND ROAD     36.53                   
FIRST COLONY 4 WSW                   36.34                   
BEAMER DITCH HUGHES RD               36.32                   
LA PORTE 1 N                         36.24                   
BAYTOWN 2 NW                         35.64                   
MOUNT HOUSTON                        35.60                   
HOUSTON/CLOVER FIELD                 33.37                   
HOUSTON/INTERCONTINENTAL             31.26                   
KATY 6 NE                            31.23                   
HOUSTON/WILL HOBBY                   27.88                   
HOUSTON/D.W. HOOKS                   27.01                   
GALVESTON/SCHOLES                    22.84                   
COLLEGE STATION 2 SSW                19.64                   
VICTORIA 3.8 NW                      15.60                   
AUSTIN 4 SSE                         10.28                   
AUSTIN/MUELLER MUNI ARPT             10.07                   
CORPUS CHRISTI 3.6 S                  6.23                   


PORT ARANSAS 2 ENE                   132                   
COPANO VILLAGE 1 ENE                 125                   
LAMAR 2 SSW                          110                   
ROCKPORT 1 S                         108                   
TAFT 5 NNE                            90                   
MAGNOLIA BEACH 8 ESE                  79                   
EDNA                                  73                   
FLOUR BLUFF 4 ESE                     72                   
ARANSAS PASS 7 SE                     71                   
CLEAR LAKE SHORES 1 WSW               71                   
BRAZOS 451                            70                   
PALACIOS MUNICIPAL AIRPORT            69                   
CORPUS CHRISTI NAS 5 SE               65                   
GANADO 7 S                            64                   
LA WARD                               64                   
BAYOU VISTA 13 E                      61                   
NEW BRAUNFELS MUNICIPAL AIRPORT       58                   
QUINTANA 1 NE                         58                   
SUGAR LAND MUNICIPAL AIRPORT          58                   
JONES CREEK 9 SW                      55                   
LA MARQUE 2 E                         55                   
FREEPORT 1 ESE                        54                   
SAN LEON 19 E                         54                   
MISSOURI CITY 1 SE                    53                   
SAN ANTONIO INTL ARPT                 53                   
WEBSTER                               53                   
BERGSTROM INTL AIRPORT                52                   
GONZALES AIRPORT                      52                   
NASSAU BAY                            52                   
TEXAS CITY 4 ENE                      52                   




Wednesday, August 30, 2017

A Brief History of Harvey

"Local rainfall amounts of 50 inches would exceed any previous Texas rainfall record. The breadth and intensity of this rainfall are beyond anything experienced before. Catastrophic flooding is now underway and expected to continue for days."
 NWS Weather Prediction Center, Sunday, August 27

Harvey started out as a rather innocuous disturbance in the Caribbean more than 10 days ago. It was disorganized and at times looked like it was going to fall apart. On Thursday, August 17 the disturbance was promoted to Tropical Storm Harvey. By late on Saturday August 19 Harvey had weakened into a tropical wave. There were no advisories issued Sunday through Tuesday as what was left of Harvey drifted west. On Wednesday, August 23  a Hurricane Hunter found that Harvey had regenerated in the Bay of Campeche, and advisories were issued. At that time Harvey was expected to make landfall along the southern Texas coast by Saturday morning. It was also expected that Harvey might slow down or stall out over southeast Texas,

Harvey intensified quickly on Thursday morning and was forecast to become a hurricane before landfall. By early afternoon on Thursday the storm had become Hurricane Harvey, with further intensification expected. By midnight Harvey was a Category 2 storm with winds near 100 mph. In the 4:00 a.m. advisory on Friday the National Hurricane Center expected further intensification and expected Harvey wander slowly through southeast Texas for the next five days. It also included this statement:

"Devastating and life-threatening flooding is expected across the middle and upper Texas coast from heavy rainfall of 15 to 25 inches, with isolated amounts as high as 35 inches, from today through next

The 4:00 p.m. advisory on Friday indicated Harvey's winds had increased to 125 mph, and by 7:00 p.m. Harvey was a category 4 storm with winds of 130 mph. Hurricane Harvey made landfall just before 10:00 p.m. CDT on the Texas coast over the northern end of San Jose Island about 4 miles east of Rockport. The storm stalled about 60 miles east of San Antonio for awhile, then gradually drifted southeast back into the Gulf of Mexico. Early this morning (August 30), Harvey made landfall for a second time just west of Cameron, Louisiana. The excellent graphic below shows Harvey's travel from the Atlantic to this morning's second landfall.

The path of Hurricane Harvey.
Credit: Brandon Moses (via Twitter)

Josh Morgerman (@iCyclone), a hurricane chaser, was in Rockport, TX when Harvey made landfall. You can read his interesting account of his "chase" of Harvey at this link.

 Initially the high winds and storm surge were the focus of attention. The Texas coast from Rockport to Port Aransas was raked by 100+ mph winds, and storm surge quickly flooded coastal areas. As Harvey drifted inland the winds weakened, but the worst of the storm was starting to take shape.

This is the  storm relative velocity image (SRV) out of Corpus Christi radar at 4:10 p.m. CDT on Friday, August 25. Max winds outbound ~140 mph (brown), inbound ~115 mph (blue).

With a few exceptions (Hurricane Andrew, for one) winds usually aren't the worst of a hurricane or tropical storm. Torrential rain and resultant flooding (as well as flooding from storm surge) usually result in the most damage. As Harvey moved ashore late on Friday feeder rain bands on the east side of the storm were starting what was to be an epic and unprecedented tropical rain event. The astounding forecasts of up to 50 inches of rain verified by Tuesday afternoon. Though the rain ended in Houston, it was unrelenting in eastern Texas and western Louisiana. 26 inches of rain fell in 24 hours in Beaumont, TX, and radar estimated rainfall as of early afternoon today was in excess of 50 inches there as well.

Radar estimated rainfall from the Lake Charles, LA radar at 10:50 a.m. CDT Wednesday, August 30. Rain continued for several hours after this image. Max value indicated by radar was 50.80". The white to gray shading is 40 to 50 inches.
Tonight Harvey was downgraded to a tropical depression. The storm is expected to continue moving northeast and into Ohio by Saturday.producing heavy rain in the Tennessee and Ohio Valleys and south.

Next post: CoCoRaHS Observers, Rainfall, and Hurricane Harvey

Tuesday, June 20, 2017

New National Hurricane Center Advisory Policy in Play this Week

For days meteorologists have been watching a disturbance in the Gulf of Mexico. Today that disturbance became Tropical Storm Cindy, the third storm of this young season and concurrent with T.S. Brett in the Caribbean. This year the National Hurricane Center has the option of issuing the full range of advisories, watches, and warnings for disturbances that not yet a tropical cyclone but which  pose the threat of bringing tropical storm or hurricane conditions to land areas within 48 hours. Under previous longstanding NWS policy, it was not been permitted to issue a hurricane or tropical storm watch or warning until after a tropical cyclone had formed. The purpose of these potential tropical cyclone advisories, watches, and warnings is to provide more lead time to those that will be impacted, hopefully minimizing injuries and saving lives.

Monday at 4:00 p.m. CDT the first advisory was issued for Potential Tropical Cyclone Three, now Tropical Storm Cindy. That advisory, which included a tropical storm warning and watch, was issued 18 hours earlier than would have been allowed in previous years.

Here is the forecast track of the storm as of 10:00 p.m. CDT. As the graphic states, hazardous conditions can occur outside the probable path of the storm. Typically with systems like this one, heavy rainfall and flooding is the biggest threat. 

To give you an idea of the extent of the storm, here is the Quantitative Precipitation Forecast for the next five days. Note that the heavy rain and likely most of the impacts, including some storm surge, will be well east of the storm track.

Over the next 72 hours the heaviest rain is expected over the Mississippi and southwest Alabama coast.

A complicating factor for the southeast is a frontal system which will likely slow to a crawl or stall out as it moves into the Tennessee Valley late in the week providing additional lift in the moisture-laden atmosphere associated with the remnants of Cindy. CoCoRaHS observers from eastern Texas to West Virginia will be busy measuring rain the rest of this week.

Forecast surface weather map for 7:00 a.m. CDT Saturday, June 24, 2017.

Only three previous Atlantic hurricane seasons on record have had two concurrent named storms in June prior to this year: 1909, 1959, 1968, and now 2017. In addition, T.S. Bret and T.S. Cindy became named storms only 21 hours apart, the shortest time between two June named storm formations in Atlantic on record. Late this afternoon Brett was downgraded to a tropical depression.