Wednesday, August 24, 2016

Fire and Rain

A lot of attention is being paid to the tropical Atlantic where Fiona is now history, Gaston is strengthening, and a third disturbance, which could end up being Hermine, is being watched closely. Although there were five previous systems, including two hurricanes (Alex and Earl), only two, Bonnie in late May and Colin in early June, directly affected any part of the U.S., mostly with heavy rain.

In the meantime, resident of south-central Louisiana are still trying to clean up after a no-name tropical-like system dumped two feet of rain on them just 10 days ago.

7-day precipitation for Louisiana ending August 16. However, most of this fell in just two days (August 12-13).

The public and the news media don't get quite as excited about things when they aren't being talked about days in advanced (hyped, if you wish), and don't seem as interested in the aftermath when there is no "name" (e.g. Katrina, Sandy, Andrew) to blame it on. With or without a name, the destruction is the same.

Flooding in Baton Rouge.
Credit: U.S. Department of Agriculture - https://www.flickr.com/photos/usdagov/28426228294/


In Louisiana an estimated 60,000+ homes are damaged, to say nothing of businesses, schools, and other buildings. The US Coast Guard, National Guard, local emergency responders, and citizens helped rescue more than 30,000 residents and 1,400 animals. Thirteen people lost their lives in the flooding. At least 7,000 people are in shelters, and more than 100,000 people in the state have registered for federal emergency aid. Twenty parishes (counties) have been declared federal disaster areas.

Two photos showing flooding in a Baton Rouge neighborhood on August 14 (top) and five days later on August 19.
Credit:Twitter @JesseWeather


In the western U.S. wildfires have been in the news. Much of the west, but California in particular, is tinder dry, and wildfires are everywhere.


Almost all of the western states are dealing with fires at the present time.  Large fire activity picked up with seven new large fires reported Monday. Currently, 32 large fires have burned more than a half million acres. Some of these fires have been burning for well over a month. The fires have destroyed numerous homes, disrupted truck and rail transportation, and caused air quality issues throughout the west.


Although fire activity is high, the number of fires and the acres involved are less than last year. According the the National Interagency Fire Center, the states currently reporting large fires and their number are: California (6), Colorado (1), Idaho (7), Montana (2), Nevada (1), Oklahoma (1), Oregon (5), Utah (6), Washington (6), and  Wyoming (6).



In Alaska 52 wildfires are currently being monitored. Alaska wildfires have burned more than 384,000 acres, substantially less than last year.

Active Alaskan wildfires as of 8/24/2016.
Credit: University of Alaska Fairbanks Arctic Region Supercomputing Center as part of the UAF SMOKE forecast project.
The outlook for the next month or so is for continued above normal fire risk in California and a return to normal fire risk in the intermountain west.

 
While Louisiana residents continue to recover from the rain and flooding almost two weeks ago, they are also keeping a watchful eye on the developments in the Atlantic. The tropical disturbance now labeled #99L is showing signs of organization and there is a 50 to 80 percent likelihood it will develop into a tropical cyclone in the next 3 to 5 days. It is way to early to determine a confident track for this potential cyclone, so those with interest from the Gulf Coast to the Florida east coast should be staying abreast of the latest information and advisories from the National Hurricane Center.


Friday, August 12, 2016

Louisiana Deluge

A flooding disaster of major proportions is underway in Louisiana and is likely to get worse over the next few days.

As of early Friday morning up to 15 inches of rain had accumulated during  the preceding 24 hrs. A westward moving low pressure system that is tropical in nature had been producing torrential rains from western Mississippi through eastern and  south-central Louisiana.

24-hour precipitation valid at 7:00 a.m. CDT 8/12/2016

Amounts reported by CoCoRaHS observers topped 11 inches this morning, and a late report at 7:00 p.m. tonight reported 14.65 inches (this is likely a 36 hour total).

CoCoRaHS reports >7.00 inches for Louisiana and Mississippi 8/12/2016

The U.S. Cooperative observer in Livingston, LA reported 10.55 inches of rain this morning, and then  another 6.54 inches as of 3:00 p.m. this afternoon. The observer reported rainfall rates of 3 inches  per hour for an extended period this morning. Rainfall totals exceeding 20 inches will be common by Saturday morning across Louisiana.

The low pressure system responsible for this rain has been hanging along the Gulf coast the past several days and become somewhat more organized as it drifted east. It was located over western Mississippi this morning, and slowly drifted westward during the day today.

Surface map at 1:00 p.m. CDT 8/12/2016 showing low pressure center over western Mississippi.

Visible satellite image for Louisiana at 4:15 p.m. CDT 8/12/2016. The bulging clouds over north-central Louisiana are indicative of strong convection.
 The low is expected to eventually begin drifting to the east and northeast this weekend. The potential for additional heavy rain remains high through the weekend.

Excessive rainfall outlook for the period from 7:00 a.m. CDT Saturday 8/13 to 7:00 a.m. CDT Sunday 8/14/2016.

The 3-day Quantitative Precipitation Forecast for the period from 7:00 p.m. CDT Friday, 8/12 to 7:00 p.m. CDT Monday, 8/15/2016.

Flooding is extensive. Rivers and streams rose rapidly with the high rainfall rates. Numerous rivers in southeast Louisiana and southern Mississippi were overflowing their banks and threatening widespread flooding and most rivers are expected to reach major flooding levels.

River levels and forecasts for southwest Mississippi and southwest Louisiana.
There have been two fatalities reported as a result of the flooding, and another person was reported missing at the time of this writing. Louisiana Gov. John Bel Edwards declared a state of emergency today because of the severe flooding and additional heavy rain expected.

Update Saturday, August 13  10:30 a.m.

Here are two-day rainfall totals for Louisiana. Radar rainfall estimate of 27.47" near Brownfields, LA corresponds well with observed rainfall.

48 hour rainfall totals for stations reporting >10" in Louisiana for period ending 7:00 a.m. CDT August 13.

Wednesday, July 13, 2016

A Different Spin on Vorticity

"Vorticity" is the name of the latest video from Phoenix-based photographer Mike Olbinski. I've featured Mike's work in a past blog post on the southwestern monsoon.

This film  is a time-lapse summary of many of the features Olbinski photographed this spring while chasing weather for 18 days and 20,000 miles over a period of two months. He records many "spinning" features in the atmosphere: rotating mesocyclones, roll clouds, tornadoes, downpours, dust, and churning skies. The film is dramatic and awe-inspiring, and the music by Kerry Muzzey gives the film an epic feel.

 
                                       Vorticity (4K) from Mike Olbinski on Vimeo.

If you have a good Internet connection be sure to view this in full screen HD. I've viewed this several times already and each time I see something new I didn't notice before.

You can see some more of Mike's work (including Monsoon II) at http://www.mikeolbinski.com/timelapse/

As for the title of the film, vorticity is a clockwise or counterclockwise spin in the troposphere. We typically look at vorticity at the 500 millibar level, which is about 20,000 feet. If you have followed this blog you have seen vorticity depicted on some of the 500 millibar maps I've included, like this one. The orange and yellow shading depict areas of vorticity, spinning that produces upward motion, and thus usually clouds and precipitation.

500 millibar showing areas of vorticity

Wednesday, July 6, 2016

Waters Have Receded, but the Mess in West Virginia Remains

The I-79 Clendenin exit in Kanawha County, WV, on June 24, 2016.
Credit: Facebook/West Virginia Department of Transportation
Two weeks ago Friday residents of West Virginia woke up to a disaster in the making. Heavy thunderstorms trained over the mountainous terrain of southeastern West Virginia dumping almost ten inches of rain in less than 12 hours over parts of two counties.

The flooding washed out many roads, caused landslides, destroyed numerous bridges, and left behind a thick layer of mud and debris in many communities. The death toll from this flood stands at 26, making it the third most deadliest flood in the state's history. In the days following the flood at least 32,000 homes and businesses were without power and more than 60 secondary roads in the state were closed.

The Elk River soared to a record crest of 33.37 feet on the morning of June 24, rising about 27 feet above the level it was on June 23.



Heavy rain occurs frequently during this time of the year in many parts of the country, but why was this particular event the disaster it was?

Geography plays a big part. The topography of West Virginia is mountainous, and the steep hills and long narrow valleys are conducive to flooding in very heavy rain events, particularly in the southeastern part of the state. In this particular situation, the heavy rain fell in a relatively short period of time (hours, not days) rushed down the hillsides and was funneled down the valleys. Rivers rose quickly and in some cases cut off escape routes.



The second major factor were training thunderstorms - thunderstorms that repeatedly move over the same area. There were actually two rounds of rain that moved across the state, but the second round that occurred beginning on the afternoon June 23 was the straw that broke the camel's back.

The surface weather map at 8:00 a.m. on June 23 showed a cold front extending from a low over Indiana through the Midwest, and a warm front extending east from the low through Ohio and Pennsylvania.

8:00 a.m. EDT June 23, 2016

By 8:00 p.m. on June 23 the front extended from Missouri east into southern Ohio. It stalled out there as a series of low pressure waves rippled along the boundary. These ripples along with warm, humid air south of the front was the ingredients needed for the heavy rain.

8:00 p.m. EDT June 23, 2016


As of 12:30 a.m. on June 23 there were only a few thunderstorms developing in western West Virginia, with most of the activity further north along the front.



However, during the pre-dawn hours thunderstorms rapidly developed and were producing some heavy rain. Showers and thunderstorms continued during the morning hours.



By late afternoon and evening thunderstorms were numerous and oriented west to east across central and southern West Virginia. There was only a slow southward advancement so the thunderstorms essentially trained across the same area.


By 10:30 p.m. EDT the line of storms finally pushed south, leaving widespread flash flooding in their wake.

Counties outlined in green are under flood warnings.


Nicholas and western Greenbrier Counties in West Virginia received the most rain, though heavy rain also occurred in western Virginia and flood warnings were issued for several counties there. Radar estimated up to 10 inches in Greenbrier County, with up to seven inches falling in only three hours.

24-hour rainfall ending at 8:00 a.m. EDT on June 24
 
36-hour rainfall amounts end the morning of June 24, 2016
Measured amounts included 8.29 inches in White Sulphur Springs and 8.00 inches in Lewisburg, both in Greenbrier County. The CoCoRaHS observer at Runa 0.1 W in Nicholas County measured 7.20 inches of rain. 24-hour amounts this high have one a 1 in 1000 probability of occurring (0.1 percent).




Credit: NWS Blacksburg, VA

Fifteen of the fatalities occurred in Greenbrier County. Damage was extensive. The Greenbrier GolfClassic scheduled to start July 7 was canceled. The President declared central and southeast West Virginia major disaster areas.



Below are two links that contain slideshows of the flooding and damage in West Virginia and Virginia.

WVVA-TV  
The Weather Channel

While the floodwaters have receded, residents affected by the flooding will be dealing with the aftermath for some time to come. 

Wednesday, June 15, 2016

The Backdoor Cold Front


At the beginning of this week there was a good example of what is called a backdoor cold front in the Midwest. What was striking about this particular front was the contrast between the air behind the front and ahead of it.

A cold front is the leading edge of a mass of cold air that is cooler and/or drier than the air it is replacing, and usually marked by a wind shift. Typically in North America cold fronts move from northwest to southeast, from west to east, or north to south. The system moving through the central U.S. today is your "typical" cold front. The front is moving from northwest to southeast across the Plains and Midwest.

Surface map for 1:00 p.m. CDT June 15, 2016

A backdoor cold front is a cold front that moves to the west or southwest (from the east or northeast), typically in the Great Lakes or along the Atlantic seaboard. These are commonly occur in the spring along the Atlantic coast when colder air is pushed inland as high pressure builds over new England or the North Atlantic. These fronts can also move south along the eastern seaboard as well.

The cold front that pushed in the backdoor of the Midwest early this week was pretty impressive.

In the sequence of surface maps below you can see how the cold front went from an west-east orientation in the first map to a northwest-southeast orientation on the west end of the front. The cool, very dry air pushed from Michigan and Wisconsin across northeastern Illinois, eventually orienting on a line roughly fronm Des Moines, IA to St. Louis, MO to Evansville, IN.


Surface maps for 10:00 p.m. CDT Saturday, June 11 (top), 7:00 a.m. CDT Sunday, June 12 (middle) and 10:00 p.m. CDT Sunday, June 12

Dewpoints in the air behind the front reached the low 30s, not something you see very often in June in the Midwest. Southeast of the front, dewpoints were in the muggy upper 60s and low 70s. Here is a graph of the temperature and dewpoint at Chicago's O'Hare Airport prior to, during, and after the cold front passage. The front moved through the station between 6:00  and 7:00 a.m. CDT on June 12, and in the next hour the dewpoint dropped 16 degrees, and 24 degrees in the first two hours.



Below is an animation of dewpoint maps every three hours that shows the push of the drier air from northeast to southwest.

Loop of surface dew point maps from 10:00p.m. CDT Saturday, June 11 to 10:00 p.m. CDT Sunday, June 12

I watched with anticipation as the cold front pushed south and west during on Sunday, hoping for some of that dry air to clear out the humidity. Winds shifted to the northeast during the late afternoon, but it was almost sunset before the really dry air pushed in. It was, however, only a brief respite from the high dewpoints, and by the morning of June 13 dewpoints were beginning to climb back into the 60s as the muggy air mass to the south replaced the retreating cooler, drier air.

Wednesday, June 1, 2016

Torrents in Texas

If you watch the CoCoRaHs national precipitation map each day no doubt you have noticed that most of the highest amounts in the past two months - anywhere from 8-16 inches - have occurred in Texas. One of the locations impacted by the heavy rain (by no means the only one) is Houston. The Houston area has received an astounding amount of rain in the past 60 days, largely from two big events. One of these occurred in April, and the other within the past week. Now, any location receiving 12 to 16 inches of rain in 8, 12, or even 24 hours would experience some type of flooding. What is it about Houston that seems to make it susceptible to severe flooding?

One reason is geography. The landscape around Houston is criss-crossed by web of bayous. Bayous are slow-moving rivers or streams generally in flat, low-lying areas. There are often associated with marshes or wetlands and are a tributary to a larger body of water. Houston was founded the Buffalo Bayou, 52-mile long waterway that winds through Harris County, in 1836. The waterways are an integral part of the landscape supporting wildlife, recreational activities, and providing drainage.

Map of the bayous and drainage areas in Harris County, TX.
Credit: Harris County Flood Protection District.


Another reason - the Houston area is becoming a bowl. In the past 100 years the withdrawal of groundwater, oil, and gas has caused the land to sink. The situation is particularly critical in northwest Houston, where wells are tapping the groundwater to supply new residential areas. In the area northeast of two major reservoirs (Addicks and Barker) the land has dropped seven feet since 1906 and continues to do so.

Population increase, population density, and its attendant urbanization is another reason contributing to flood vulnerability. The natural landscape was once dominated by marshes, prairies, and wetlands which helped buffer floods. Much of that has now been replaced by impervious surfaces - buildings, roads, and other paved surfaces - that increase runoff.

The heaviest rain amounts during the heavy rain event of April 17-18 in the Houston area were found north and northwest of the city. The storms were slow-moving and often training over the same areas. The rainfall amounts were bad enough, but the rainfall rates were astounding. A gauge in Pattison, TX in Waller County which lies at the head of Cypress Creek measured 23.50 inches of rain in only 14.5 hours.

Quantitative Precipitation Estimates for the 24 hr. period ending the morning of April 17 (left) and April 18, 2016 (right).

Rainfall amounts (light blue) and flooding in Harris County for the April 17-19, 2016 storm.


The rain gauge at TX-MG-49 Magnolia 10.6 ENE
with 8.47 inches of rain on May 27.
Final total was 11.35". (via Facebook)
This was a particularly challenging storm for CoCoRaHS observers for several reasons. The heavy rainfall occurred overnight, and many were sleeping when their gauges started to overflow resulting in a loss of an actual measurement. Those who attempted to empty the gauge before it filled to capacity were thwarted by nearly continuous lightning which made it extremely dangerous to venture outside. It's not really possible to even estimate the amount of rain once the gauge overflows. The gauge holds from 11.3 to 12 inches (depending on if the tube and funnel are in place), so the most we know from the overflow gauges is that at least 11 inches of rain fell.










The most recent heavy rain event on May 26-27 repeated the April scenario from 6 weeks ago, with the heaviest rain north and northwest of Houston.

Quantitative Precipitation Estimates for the 24 hr. period ending the morning of May 27 (left) and May 28, 2016 (right).

Flood warnings are still in effect from this rain. CoCoRaHS observers in Waller County had the highest two-day rainfall amounts with amounts from 16 to 22 inches. The highest was reported at TX-WA-17 Brenham 9.9 N with a two-day total of 22.41 inches, and TX-WA-24 Brenham 0.7 E with 20.97 inches.

CoCoRaHS 48-hour precipitation amounts for the period ending the morning of May 28, 2016.
Only amounts in excess of 12 inches are shown.


The automated station (AWOS) at Brenham recorded 16.62 inches of rain on May 26, making it the wettest day in the city's history by more than six inches. The Brazos River in Texas surged to a record high 54.76 feet early this evening at Richmond, TX, northwest of Houston. The river is at  4.46 feet above the previous record (50.3 feet) set on October 21, 1994.

Hydrograph for the Brazos River as of 9:20 p.m. CDT June 1. The river reached a record 54.76 feet about 6:15 p.m.

The flooding from this latest storm has resulted in six fatalities and damage to hundreds of homes and buildings. Seven people lost their lives in the April flood. Most of these were in vehicles.

Not a river, but a flooded road in Fort Bend County (west of Harris County).
Note the swimming alligator in the lower right hand corner.
Credit: Fort Bend Sheriff Office via Twitter.


There's no rest for the weary, either. Thunderstorms have been frequent the past several days, and thunderstorms rolled through Harris County and surrounding areas today. The outlook for the next five days paints a wet picture for the Houston area.

Quantitative Precipitation Forecast (QPF) for the 5-day period ending 7:00 p.m. CDT Monday, June 6.


Flooding is the most frequent and dangerous natural hazard in the Houston area, but they are prepared to deal with it. The Harris County Flood Control District continuously monitors stream flow and precipitation to asses the flood potential. It also controls the releases from the reservoirs that hold the runoff from storms, maintains the infrastructure, and develops and implements flood damage reduction plans.You can learn more about the flooding issues in the Houston area on their web site  and view the real-time Harris County Flood Warning System at http://www.harriscountyfws.org/.

Screen capture of the Harris County Flood Warning System web page.

Monday, May 9, 2016

Ingredients for a Wildfire - Fort McMurray, Alberta

The Fort McMurray fire in Alberta, Canada ignited sometime on May 1, very likely human-caused. It was quickly news on social media, but it was a couple of days before it was widely reported in the news. Spectacular video taken by evacuees quickly went viral on the Internet.


The spring fire season in the boreal forests in British Columbia and Alberta got off to an early start this year. A dry winter and early spring was one of the main factors.


This map shows the status of drought across Canada. Higher values indicate drier conditions

The very warm spring resulted in a faster than normal spring melt. In a normal spring the snow melts gradually keeping the forest floor moist. With the warm dry winter the forest floor was covered in dry leaves and pine needles. The premature spring warmth and low humidity dried things out even further.Deciduous trees, such as aspens, hadn't yet sprouted leaves. Leaves transpire moisture into the forest and help cool the forest environment.

The end of April and early May was unseasonably hot. The maximum temperature last Wednesday (May 4) in Ft. McMurray reached 91°F (32.6°C), with the humidity about 15 percent. Ft. McMurray is located at 56.6° North, about the same latitude as the Aleutian Islands. Several dozen Canadian record high temperatures were set that day. The hot weather last week was caused by an upper ridge of high pressure that extended through western Canada and into the Arctic Circle. High temperatures reached the 80s to low 90s from the Dakotas north through Alberta and Saskatchewan.

500 millibar map for Wednesday, May 4, 2016

With plenty of tinder dry fuel, hot dry weather, and strong winds it was no surprise the Fort McMurray fire took off like it did. It was far from the first fire of the season. Fire activity across British Columbia and Alberta was already well above average.

Number of Canadian wildfires by province in 2016 compared to normal


The Fort McMurray fire was intense and produced smoke that turned day into night. It also generated pyrocumulus clouds with lightning.

This video gives you a sense of what it was like evacuating from Ft. McMurray. It's both frightening and mesmerizing. Note that this was recorded during the middle of the afternoon.



This animation shows the extent of the Fort McMurray fire as it spread over the past nine days. As of today the extent of the area affected by the fire was more than 200,000 hectacres (2000 sq km). The good news is that latest reports indicate that about 85 to 90 percent of the structures in Fort McMurray were saved. Unfortunately, neighborhoods in the path of the fire, such as Beacon Hill in the video above, were largely destroyed. It's estimated that the fire destroyed 2,400 structures.

The fire danger last week across most of Alberta and southern Saskatchewan was Extreme.

Fire Danger across Canada on May 5, 2016


Conditions improved yesterday and last night as cooler weather and rain fell across the province.

Fire Danger on May 9, 2016

Amounts were light (5 to 10 mm, about 0.25 to 0.30 inch) but most welcome. One CoCoRaHS location on the Alberta/NWT border (CAN-NT-7) reported 34.3 mm (1.35 in.) of rain indicating a "steady cold rain all day and evening".


Wildland fire activity in Alberta has been well above average the last three years and is well on its way to another above average year. Last year fires burned 491,000 hectacres of land, well over twice the ten-year average of 179,000 hectacres. The Fort McMurray fire alone has already exceeded the average.