Monday, November 3, 2014

Wild Windy Wintry Weekend

A rapidly deepening upper level trough brought three days of wild weather to the eastern half of the country from the end of last week through this weekend.

An intensifying surface low and cold front brought cold, windy, and snowy weather to much of the eastern Midwest on Thursday and Halloween.

500 millibar map (left) and surface map (right) for 7:00 a.m. CDT October 31, 2014

Winds gusted to 69 mph in Gary, IN on Friday and 67 mph at the Chicago Harrison-Dever Crib and Michigan City, IN.  Wind damage was common, and the winds drove large waves from Lake Michigan onto Lake Shore Drive in Chicago and caused damage to Chicago's lakefront bike path. Heavy snow fell in northern Wisconsin and the Michigan U.P. and measurable snow was recorded as far south as northern Illinois and Indiana. Snow showers occurred even farther south through central Illinois and Indiana.

Snowfall in northern Wisconsin and part of the Michigan U.P. as of the morning of October 31
 The mid-lake south buoy, located about 43 miles east of Milwaukee recorded a wave height of 21.7 feet.  This was tied for the second highest wave height on record at the south buoy, after only 22.9 feet on September 30, 2011.

Snow in Asheville, NC
Photo by Mike Palecki
As the upper level trough deepened a second low developed over western South Carolina, with another low off the Virginia coast Friday night. Plenty of moisture and now cold air was available to the low over South Carolina and heavy snow fell in the Appalachians. Snow piled up to 22 inches in both Spring Creek, NC and Gatlinburg, TN. Measurable and often heavy snow accumulated in higher elevations of Kentucky, Tennessee, Georgia, South Carolina, North Carolina, Virginia, and West Virginia.

500 millibar map (left) and surface map (right) for8:00 a.m. EDT November 1, 2014
Snow in Morristown, TN.  Photo by the NWS Morristown

By midday Saturday the South Carolina low moved out over the Atlantic while continuing to intensify. By late afternoon it began to merge with a second low to its north. By 1:00 a.m. EST on Sunday morning the low was located east of Norfolk, VA at pressure had dropped to 988 millibars. Twelve hours later (1:00 p.m. EST) the strong storm was centered east of Nantucket, MA.

500 millibar map (left) and surface map (right) for 7:00 a.m. EST November 2, 2014

Some snow fell in Massachusetts, but the heaviest snow on Sunday (10 to 21 inches) fell in the eastern portions of Maine. Bangor (12 inches) and Caribou (10.1 inches), ME both set their record earliest day (November 2) with snowfall 10 inches or more. The largest snow accumulation was 21 inches in Cary, ME near the Canadian border. The heavy wet snow and howling winds brought down power lines cutting off power for 130,000 customers. Power may be out in some areas several days.

72 hour snowfall accumulation ending the morning of November 3.

Thursday, October 30, 2014

Fall Bird Migration Caught on Weather Radar

On Tuesday evening I noticed some peculiar radar returns developing on the Lincoln IL radar beginning about 6:45 p.m. CDT. The returns appeared to develop along the Illinois River, and my first thought was that it might be biological. I checked the satellite image for the region and there were a band of clouds over central Illinois, so I attributed it to precip, even though none was expected.

While working in my home office last night I glanced at the radar and similar returns were starting to show on the radar at the same time as the night before!. For a moment I thought that perhaps I was looking at an image from the previous night. The returns developed along the Illinois River, and then moved to the southeast. After some inquiries of friends and colleagues, it appears what we were seeing on radar was the fall migration of thousands of birds, probably mostly waterfowl. The birds took flight about 50 minutes after sunset.

Lincoln, IL radar images for Wednesday night, October 29.
Tuesday, October 28. Click on image to view a two hour loop of the radar.

Reports and forecasts of fall migration are available on BirdCast, part of the Cornell University Lab of Ornithology web site. Regarding the migration through the central U.S. on Wednesday BirdCast indicated that

"This night will surely represent one of the last large movements of the fall of both landbirds and waterbirds. Species on the move this week will include Hooded Merganser, American Tree Sparrow, Lesser Scaup, Common Loon, Red-breasted Merganser, Lapland Longspur, Canvasback, Bonaparte’s Gull, Fox Sparrow, Greater Scaup, Ring-necked Duck, Common Goldeneye, Redhead, Dark-eyed Junco, and Ruddy Duck."

Credit: U.S. Fish & Wildlife Service
A colleague of mine who is a birder reported that he had seen a report of thousands of waterfowl at Chautauqua National Wildlife refuge near Havana on the Illinois River. There are other National Wildlife Refuges along the Illinois River as well.

The Illinois River is a major flyway for migratory birds and the most striking radar images I found came out of Lincoln. However, birds taking flight were also captured by the Des Moines, IA and Kansas City, MO radars on Tuesday night.

Des Moines, IA radar at 7:11 p.m. CDT Tuesday, October 28. The dark blue and green returns are likely birds taking flight.
Kansas City, MO radar at 7:27 p.m. Tuesday, October 28. Note how the bird returns are along the Missouri River.

Birds use a variety of means to navigate during migration, including the sun, stars, and magnetic fields. It is thought that nighttime migration is advantageous for birds because of the lower temperature. Birds generate a lot of heat while flying, and lower temperatures (and lack of sun) help them maintain and optimum body temperature as they travel.

You can learn much more about bird migration at the following web sites:

Northern Prairie Wildlife Research Center
Cornell University Lab of Ornithology  

Tuesday, October 28, 2014

Big but Short-Lived Chill on the Way

Temperatures have been mild for much of October throughout the U.S., with near normal temperatures across the central U.S. and Southeast. The mild weather along with extended periods of dry weather have made for nearly ideal harvest conditions.

Freezing and sub-freezing temperatures have occurred across the Northern Plains, Minnesota, Iowa, and Wisconsin, but killing freezes so far have been restricted to the northern tier of states.

Lowest minimum temperatures since August 1.

The first freeze across the central U.S. is running later than normal, but that could change this weekend.

A strong upper level trough will deepen over the eastern U.S. at the end of this week and the resulting northwesterly flow on the west side of the trough will bring frigid air deep into the central U.S.

500 millibar map forecast for 7:00 a.m. CDT Saturday, November 1

 A strong surface high pressure system will drop out of Canada and by Saturday morning will be centered over the upper Great Lakes. Under clear skies and calm air temperatures will drop into the low 20s and perhaps lower over the upper Midwest, mid 20s over the central Midwest and below freezing as far south as the Ohio River. The Northern and Central Plains will remain on the periphery of the coldest air.

Minimum temperature forecast for Saturday morning, November 1.
Recovery from the cold air will be quick. By next Monday the amplified upper level pattern will be flattening out and relatively mild Pacific air will be streaming across the U.S.

500 millibar map forecast for Tuesday, November 4 at 12:00 CST
That means the first week of November is likely to be warmer than average throughout much of the country east of the Rockies.

Maximum temperature anomaly for Tuesday, November 4.
The outlook from the Climate Prediction Center is for a higher probability of warmer than normal temperatures through the first half of November for most of the U.S.  However, accompanying the mild weather is a likely wet pattern in the Pacific Northwest and in the eastern half of the country.

Wednesday, October 22, 2014

Changes to Severe Weather Outlooks

The Storm Prediction Center has instituted several changes to it's severe weather outlook products effective today.

If you are familiar with the convective outlooks that the SPC issues several times per day you know that the outlooks indicate where general thunderstorms are expected, where there is a low probability of severe weather (the "See Text" category), and where there is a Slight, Moderate, or High Risk of severe weather. Effective today there is one change and one additional category being used in the Day 1 through Day 3 outlooks.

There are real numbers behind the determination of each of the former and current risk areas. A 15 percent probability of a tornado (Moderate Risk category) may seem low, but the normal probability of a tornado, for example, during the peak of the season on May 13 in central Oklahoma is only about 1.5 percent. A Moderate Risk in  in this case would indicate about 10 times of the normal probability for a tornado.

The probability for a tornado changes by season.The probability of a tornado in central Oklahoma this week in October is normally about 0.15 percent, ten times lower than in mid-May.

Here are the new/revised categories and what they describe. The probabilities for Day 1 are more detailed than Days 2 and 3.

Day 1
General Thunderstorms
    10 percent or greater probability of non-severe or near severe thunderstorms

    - 2% tornado probability, or
    - 5% severe hail or severe wind probability.
    - 5% tornado probability, or
    - 15% severe hail or severe wind probability WITH OR WITHOUT 10% or greater probability
      of hail 2 inches or greater in diameter, or wind gusts 75 mph or greater.
Enhanced (the upper end of the former SLIGHT category)
    - 10% tornado probability WITH OR WITHOUT 10% or greater probability
      of an EF2 or greater tornado, or
    - 15% tornado probability, or
    - 30% severe hail or severe wind probability WITH OR WITHOUT 10% or greater probability
      of hail 2 inches or greater in diameter, or wind gusts 75 mph or greater, or
    - 45% probability of severe hail or wind.
    - 15% tornado probability AND 10% or greater probability
      of an EF2 or greater tornado, or
    - 30% tornado probability, or
    - 45% severe wind probability AND 10% or greater
      probability of a wind gusts 75 mph or greater, or
    - 45% severe hail probability AND 10% or greater
      probability of hail 2 inches or greater in diameter, or
    - 60% severe wind probability, or
    - 60% severe hail probability WITH OR WITHOUT 10% or greater probability
      of hail 2 inches or greater in diameter.
    - 30% tornado probability AND 10% or greater probability
      of an EF2 or greater tornado, or
    - 45% or greater tornado probability WITH OR WITHOUT 10% or greater probability
      of an EF2 or greater tornado, or
    - 60% severe wind probability AND a 10% or greater
      probability of a wind gust 75 mph or greater.
Days 2 and 3
General Thunderstorms
      - 10% or greater probability of non-severe or near severe thunderstorms.

      - 5% total severe probability.

      - 15% total severe probability WITH OR WITHOUT 10% or greater probability
        of significant severe.

      - 30% total severe probability WITH OR WITHOUT 10% or greater probability
        of significant severe, or
      - 45% total severe probability.

      - 45% total severe probability AND 10% or greater
        probability significant severe, or
      - 60% total severe probability (Day 2 only).

High (Day 2 only)
      - 60% total severe probability AND 10% or greater
        probability of an EF2 or greater tornado or a wind gust 75 mph or greater.

The SPC has a number of examples of the new vs. old  categories on its web site. Here is an example of the difference in outlooks for the day of the Southeast tornado outbreak on April 27, 2011.

The Day 1 convective outlook for April 27, 2011 in the new format (left) and old format (right)

The Storm Prediction Center is also considering changes to the Day 4 to 8 outlook product. This is still in experimental mode and more information can be found here.

Although much of the country is currently enjoying pleasant fall weather, we have entered a ramp-up period to a secondary peak in severe weather season. October through December is a period of increased frequency of severe weather and tornadoes from far eastern Texas through Alabama, an area dubbed "Dixie Alley", with a peak in the frequency of tornadoes in mid to late November.

Mean number of tornadoes for October through December in Dixie Alley.

If you would like to explore the climatology of severe weather the SPC has an interactive web page where you can view the probabilities for tornadoes, significant wind, and significant hail for 52 one-week periods. You can animate the maps to see how the severe weather shifts through the country and how the probabilities change from week to week.

Thursday, October 9, 2014

Super Typhoon Vongfong - An Impressive Storm

Not only has the eastern Pacific tropical season been above normal, but storms have been frequent in the central and western Pacific as well. Super Typhoon Vongfong has been in the news lately partly because of some of the spectacular photos and satellite images that have been collected as this typhoon has crossed the Pacific but also because it is the strongest storm of 2014 in any basin.

Vongfong was born as a weak depression just south of the Marshall Islands on September 30. By October 3 it had strengthened into a tropical storm, and 30 hours later a typhoon. It reached super-typhoon strength on the morning of October 7 with winds of 155 knots (178 mph).  Winds are currently down to 130 kts, still a strong,dangerous, and massive storm. Gale force winds (>34 knots/39 mph)associated with this storm cover an area of 340,00 square miles.

The track of Super Typhoon Vongfong.
While here in the U.S. we are familiar with the terms tropical storm and hurricane, terminology differs in other parts of the world. A typhoon is the same as a hurricane west of the International dateline. A "super-typhoon" is a term utilized by the U.S. Joint Typhoon Warning Center for typhoons that reach maximum sustained 1-minute surface winds of at least 130 kt/150 mph). This is the equivalent of a strong Saffir-Simpson category 4 or category 5 hurricane in the Atlantic basin.

One of the more interesting and spectacular images of Super Typhoon Vongfong was this visible image from NASA illuminated only by moonlight . Note the thunderstorms on the west and northwest outer bands of the storms identified by the bubble-like cloud tops.

This image is one hour earlier than the last position labeled on the chart above when the winds were 178 mph.

The Capital Weather Gang at the Washington Post assembled images of Super Typhoon Vongfong for their column today. Rather than reproducing them here, visit their web page "Twelve incredible images of most powerful storm of the year, Super Typhoon Vongfong".

As you can see on this image of the current and projected track, Vongfong is forecast to weaken as it moves north. It will reach Okinawa as a category 3 equivalent storm, and by late this weekend will be entering southern Japan as a category 1 equivalent storm with top winds of about 90 mph.

Current and projected track of Super Typhoon Vongfong.

Tuesday, October 7, 2014

Pacific Tropical System Injects More Moisture into U.S.

It has been an active tropical weather season in the eastern Pacific.  As of today there have been 18 named storms, with 13 of those reaching hurricane strength. The eastern Pacific season is above normal so far this year. At this point in the season the average number of named storms is 13 and hurricanes seven.

The increase in storms has been a "good news, bad news" situation for the southwestern U.S. It has been good because there has been significant improvement in (but not elimination of) drought conditions in much of New Mexico, the southern half of Arizona, and western Texas since early July. The bad aspect is the amount of flooding and flash flooding that has occurred as a result of heavy rains from the enhanced moisture.

As of noon Tuesday Simon was a minimal tropical storm located just off the central coast of the Baja California peninsula, and by evening Simon was downgraded to a tropical depression. Over the next few days moisture associated with Simon will cross through the Desert Southwest and then eastward across the country.

Quantitative precipitation forecast for the 72-hour period ending 7:00 p.m. CDT on Friday, October 10.
A large high pressure system over the upper Midwest will keep most of the precipitation associated with this moisture in the southern half of the country. A wave of low pressure moving across the frontal boundary dividing cool dry air to the north from the warmer, moist air to the south will provide the trigger for widespread and potentially heavy rain. Heavy rain is expected across Arizona - again - , and presenting a threat for flash flooding the next couple of days. The threat for heavy rain will then shift to the Central Plains and Midwest.

Surface weather map forecast for 7:00 p.m. CDT Wednesday, October 8.

Surface weather map forecast for 7:00 p.m. CDT Thursday, October9

Unfortunately very little, if any of that rain will reach parched California, where severe to exceptional drought encompasses 83 percent of the state.

Status of California drought as of September 30.

The rain through southern southern half of the U.S. will slow up fall harvest which has been progressing very nicely with the long stretch of dry weather at the end of September.

Monday, September 22, 2014

The 2014 Southwestern Monsoon in 8 Minutes - Spectacular Video

I've written a couple of posts this year and in the past about the southwestern monsoon season in the U.S. Even with maps, charts, and photos it's difficult for those who have never experienced that part of the country to imagine the scope of the weather that occurs during this important season. Today I came across a video that condenses the 2014 monsoon into eight minutes of boiling cumulus clouds, intense rain shafts, hail, haboobs, lightning, and desert scenery. Photographer Mike Olbinski spent the summer driving 14,000 miles to capture the images that make up this time lapse video.

Maps and charts really only tell the technical part of the story. A video such as this one easily explains why so many are fascinated with the weather.

Be sure to watch this full screen and turn up your speakers. You will want to view this more than once to catch all of the details.

By the way, if you do want a "technical" explanation of the southwestern monsoon see a previous post here.

Wednesday, September 17, 2014

Tropical Weather in the Desert Southwest - Odile is a Big Deal

A few days ago Odile was a Category Four Hurricane off the west coast of Mexico, and as of this morning was still a weak tropical storm. Odile fell apart over northwestern Mexico during the day, and is now just a shell of its former self.  However, the remnants of Odile will still have quite an impact on weather for the next few days, first across the southwestern U.S. and then perhaps across the extreme southern U.S.

Map shows the expected position of the remnants of Odile [D] at 11:00 p.m. PDT September 17.

The remnants of Odile were already feeding plenty of moisture into the Desert Southwest. Storms were bubbling up today across Arizona and New Mexico while some isolated storms popped up in southern California.

Yesterday there were some rare severe thunderstorms in southern California. Wind damage was reported in and around San Diego, where numerous trees and light poles were toppled and small planes were flipped over at Montgomery Field Airport. One inch hail was reported near Joshua Tree, CA in San Bernadino County.

San Diego radar image for 3:15 p.m. PDT September 16. Storms were moving to the west.
Conditions across southern Arizona and New Mexico today were decidedly tropical. It was quite humid with dewpoints generally in the mid to upper 60s. The dewpoint in Phoenix this afternoon reached 72°F, a level that is rarely seen there. Swamp coolers (evaporative air conditioners) don't work very well when the dewpoint is high. 

There are a combination of factors that will make the next few days messy, to say the least, in the Desert Southwest. CoCoRaHS observers in the region will be getting a lot of measurements in over the next several days.  Although we are the tail end of the summer monsoon season, there will be heavy showers and thunderstorms because of the plentiful moisture being fed into the region. Weak flow in the upper atmosphere will provide for little steering of the showers and thunderstorms, and those that develop could remain over a relatively small area for much of the storm's lifetime. That means potentially heavy rain for a long period of time.  That same weak upper flow also means that the leftovers from Odile will be slow to move out of the region.

500 millibar map for 5:00 a.m. PDT this morning. The circulation of Odile is caught in a ridge over the Southwest.

The NWS Weather Prediction Center is expecting as much as 4 inches of rain from southeastern Arizona through southern Arizona and into western Texas, with some locally higher amounts possible.

Rainfall forecast through 5:00 p.m. PDT Saturday, September 20.

Flood watches are in effect for large portions of Arizona and New Mexico.

Flood watches (dark green) and flood advisories (light green) in effect as of 5:00 p.m. PDT

Here is a broader picture of the rainfall expected in the southwest and across the country the next three days.

Quantitative Precipitation forecast for the 72-hour period ending 5:00 p.m. PDT Saturday, September 20.

The showers and thunderstorms are most numerous tonight south of the Arizona-Mexico border but are steadily feeding northward. The Tucson NWS office has a nice summary of daily and monthly rainfall records for a number of locations in southern Arizona on their web site. 

Tucson, AZ radar at 5:39 p.m. MST September 17

Monday, September 15, 2014

Snowtember Recap - the Snow and Cold Weather

Unless you weren't paying attention at all to the weather last week you have heard about the snow in the Rockies and northern Plains as well as the unseasonably cool weather that followed for much of the eastern three-quarters of the country. So how bad was it?

The snow forecasts were pretty much on target, though amounts in a few places (notably mountain areas) were a little higher than expected.  The CoCoRaHS observer at WY-SH-33, Sheridan 15.7 W on the east slopes of the Bighorn range measured a storm total of 19.0 inches of snow. Snow fell along the Front Range in Colorado as far south as Denver, with a half inch of accumulation in Boulder northwest of Denver. The accumulating snow reached as far east as Rapid City, SD with 3.5 inches, the earliest measurable snow on record. The old record for Rapid City was 2.8 inches on September 15, 1903. Six to 8 inches of snow fell in the Black Hills during this storm. North Platte, NE picked up a trace of snow, the earliest on record there.

72-hour snowfall accumulation for the period ending 7:00 a.m. local on September 12

From the National Weather Service:


CASTLE ROCK 5.2 SW                    1.0                   
HORSETOOTH MOUNTAIN 3.2 NNW           1.0                   
NEDERLAND 4.8 ENE                     0.9                   
ASPEN PARK 5.2 ESE                    0.7                   
BOULDER 1.6 S                         0.5                   

HEART BUTTE                           8.0                   
MELVILLE 4.7 W                        7.5                   
RED LODGE 4.2 W                       6.0                   
WYOLA 17.3 WSW                        6.0                   
ZORTMAN                               6.0                   
LIVINGSTON 6.6 ESE                    3.5                   


DOWNTOWN CUSTER                       8.0                   
MOUNT RUSHMORE                        7.0                   
HILL CITY 5 S                         6.0                   
LEAD 5.5 SSW                          6.0                   
RAPID CITY 6.9 W                      3.5 -- EARLIEST ON RECORD

LITTLE GOOSE                         18.0                   
SHELL CREEK                          14.0                   
STORY 0.8 W                          14.0                   
SHERIDAN 15.7 S                      13.0                   
BIG HORN                             12.0                   
BURGESS JUNCTION 4 NW                12.0                   
SOLDIER PARK                         11.0                   
BUFFALO 1 E                          10.0                   
BANNER                                7.0                   
CODY 5 ESE                            7.0                   
SUNDANCE 1 ENE                        6.0                   
DOUGLAS 6 S                           3.0  

Obviously that snow would not have been possible without some pretty cold air for this time of year. The cold air spilled south behind this storm system. On Friday, September 12 Cloud Peak, WY in the Bighorn Mountains recorded the nation's lowest temperature of 4°F.  By Saturday morning, September 13 the cold air had pushed as far south as central Texas and New Mexico.

Minimum temperatures for the period from 7:00 p.m. CDT September 12 to 7:00 a.m. September 13

Temperatures for September 12-14 were as much as 20°F below normal in the Central Plains, with much of the middle third of the country from 10°F to 15°F below normal.

In the northern tier of states the first freeze of the season was recorded from Wyoming east into northern Kansas and northwestern Wisconsin and northern lower Michigan.

Map of locations recording first 32°F freeze

Fortunately, a hard freeze (28°F) was limited to Wyoming, Colorado. the far western Dakotas, western Nebraska, and scattered areas in northern Minnesota.

Map of locations recording first 28°F freeze

For most areas the first occurrence of 32°F was about two to four weeks early.

Median date of first occurrence of 32°F in the fall.

The weather will gradually warm this week and it looks like we'll enjoy some "normal" September weather for the next week to ten days

Wednesday, September 10, 2014

It's Snowtember in the North

Snowy Calgary on September 8.
The forecast for much of the central and eastern U.S. has been calling for much cooler weather over the next few days. The cold air that will spread over the U.S. the rest of this week has already plunged into southern Canada and the northern U.S. Rockies. Calgary, Alberta has been hit hard by heavy, wet snow this week. On Monday Calgary picked up 11.8 cm (4.5 inches) of new snow, and on Tuesday an additional 1.3 cm (0.5 inch), and had 10 cm (4 inches) on the ground. This was all following a weekend with temperatures in the mid 70s Fahrenheit. The heavy, wet snow brought down trees that still were leafed out, and those in turn took down power lines. This morning an estimated 30,000 customers were without power. In addition to downed trees and power lines there were numerous traffic accidents, sort of typical for the first snow of the season, even in Canada. Some flights were delayed or cancelled at Calgary International Airport. Interestingly, schools remained open except for a few that had power outages.

This probably was a common sentiment
in Calgary. Photo by Deanna Allen
September snow is not that unusual for Calgary, with about 2 days of measurable snow on average. The snow Calgary has received this week is what they would normally receive for September and October combined. The snow continued today, and this morning Environment Canada issued a Snowfall Warning for the City of Calgary today with another 10 to 15 cm (4 to 6 inches) of snow expected. Except for damaged trees the snow will soon be a memory as a warmup is expected through the weekend and temperatures will be in the 70s Fahrenheit by early next week.

The cold air doesn't stop at the border, of course. Snow was falling in higher elevations in northern Montana today and Winter storm Warnings and Winter Weather Advisories are in effect until midday Thursday for areas on the east side of the Rockies as far south as northeastern Wyoming. Some snow also dusted the higher elevations in northern Colorado today.

View from Montana DOT camera at Two Medicine River  Bridge (elevation 4900 ft) near East Glacier at 6:19 p.m. MDT September 10
The higher mountains and passes could receive 6 to 12 inches of snow while the north-central plains pick up 1 to 3 inches. The southwestern valleys of Montana and lower elevations in Wyoming will see mostly a rain/snow mix.

Watches, warnings, and advisories in effect as of 6:27 p.m. MDT

As this cold air continues to spill south and east it will usher in an extended period of cooler than normal weather for the eastern two thirds of the country.

Minimum temperature forecast for Saturday, September 13

Maximum temperature forecast and departure from normal for Wednesday, September 17.