Tuesday, March 24, 2015

Cloud "Mystery" Solved

If you are interested in weather phenomena and like a good detective story, then this is for you.

About two weeks ago people noticed strange cloud formations in the skies above San Antonio, TX. A deck of altostratus clouds were moving across the area, and people noticed wide, winding openings in the cloud deck and in some cases large circular openings. Photos began being posted to the NWS San Antonio Facebook page with inquiries about what caused these unusual formations.

Cloud formation seen above San Antonio on March 13, 2015

The phenomenon is known as "hole punch" clouds, or fallstreak holes. They are not that uncommon, especially near major airports and along air traffic routes, but the conditions have to be just right for them to occur. What happens, in simple terms, is that aircraft cause precipitation to occur as they fly through these clouds of supercooled droplets. The precipitation falls out of the cloud, but evaporates in the typically dry air underneath. When the cloud layer is thin and there is no supply of moisture to replace that which precipitated out, a hole remains.  The wispy streaks you often see beneath the hole are ice crystals precipitating out of the cloud. The difference between a "canal" in the clouds or a circular hole depends on whether the aircraft was cruising through the cloud layer or descending or ascending through the layer.

This is a photo of a "hole punch" cloud I took over western Indiana
on October 17, 2014

What is really neat about the San Antonio occurrence is that the forecasters at the National Weather Service, through a little "detective" work, were able to determine which individual airplane caused these hole punch clouds using sounding, satellite, and air traffic data! You can read the details about "The Mystery of the 'Cloud Hole Punch'" at the NWS San Antonio web site.

There is also more information about hole punch clouds at from NASA at this link. Some striking photographs and more explanation of hole punch clouds can be found at EarthSky.

There are more spectacular photos and explanation on the Cloud Appreciation Society web site. Keep your eyes to the sky - you never know what you may see.

Wednesday, March 11, 2015

The Yin and Yang of the Winter of 2014-2015

Yin and yang. Warm and cold. Buried and barren. Winners and losers.

There are a number of ways to describe this past winter, but my pick for a description would be something along the the lines of "sudden and weird".

The winter of 2013-2014  was a severe winter in many parts of the country, especially in the Northern Plains, Great Lakes, Midwest, and parts of the Northeast. Winter weather settled in during December and it was pretty consistently cold and snowy in the aforementioned areas until mid-March. Winter was relentless.

This year, however, Old Man Winter toyed with us. A typical first 10 days of November gave way to record cold and snow . On November 17 more than half of the lower 48 states had snow on the ground and was the highest level for the season until January 4.  Then came December, which was warmer than average across the entire country. The northern and central Rockies, some Great Lake snow belts, and western Maine were the only areas to see average to above average snowfall.

January's temperature departure pattern had hints of the warm west, cold east pattern that ultimately defined the winter. Snow was above normal in the northern Rockies, the southern Rockies, higher elevations of Arizona, New Mexico, and west Texas through the first three weeks of the month. Other than the dramatically cold and snowy weather for a couple of weeks in November, winter failed to materialize for much of the country.

Mean 500 millibar pattern
for January 24-February 28, 2015
Everything changed the last week of January. A building upper level ridge in the western U.S. was complemented by a deepening trough over the central and eastern U.S., a pattern that would remain more or less the same through February. For much of the country east of the Mississippi River winter began that week, and it came in at full speed with no let up. The start of that week saw much warmer than normal weather extended into the northern Plains under a building upper ridge, while to the east the stage was being set for the first of what would be several major snowstorms of the season to hit the Northeast.

For the six-week period ending March 7 snowfall was much above normal in a wide band from the southern Rockies eastward to the Carolinas, north to the southern Great Lakes and northern New England. Late February and early March storms brought one to two feet of snow to Kentucky, and damaging ice storms from Tennessee east to the Carolinas and south into the northern Gulf States.

February was an incredibly cold month for the country east of the Rockies, with temperatures averaging 10 to 18 degrees below normal across the northeastern third of the country. There were 23 states that recorded a top-ten coldest February. Much warmer and drier than normal weather continued over the western U.S. with record warmth in six states.

For the period beginning December 1 snow cover across the U.S. reached it's season low on December 12 at 17.5 percent. (It had dropped to 16 percent on November 24 after the mid-November peak of 50.4 percent). It rose to 53 percent on January 4, then fluctuated up and down before dropping to 21 percent in early February. The storms the last three weeks of February led to a peak snow cover of 63.4 percent on March 1.

Chart showing percent of U.S. (lower 48 states) covered by snow each day since November 1.

Today, after several days of mild weather and some rain, snow cover has plunged to 16.1 percent. Much of that snow cover is in the Northeast which is still 98 percent snow covered with an average depth of 21 inches. It will be a few weeks before the last vestiges of the Sudden Winter of 2014-2015  disappear from the landscape there.

Snow depth and extent on March 1, 2015 (left) and March 11, 2015 (right).
Source: NOAA National Operational Hydrologic Remote Sensing Center

Tuesday, February 24, 2015

Hang On - The Icy Grip of Winter Is Not Ready to Let Go

For those winter-weary folks who are ready for spring, it looks like you will have to hang in there a little longer.

This has been an unusual winter so far in most parts of the country. It got off to an unseasonably early, cold, and snowy start in November. By mid December it was clear that winter was pretty much a no-show for much of the country. December temperatures were above normal across the country, and snowfall was below normal in many locations, especially the Northeast.

 The first three weeks of January were colder than normal across the eastern U.S., but snow was surprisingly lacking. The locations with higher than normal snowfall were Arizona and New Mexico, the northern Plains and Rockies, and the snow belt areas around the Great Lakes.

So for the most part, real winter weather has only been with us for about four weeks. The four weeks of unrelenting cold, snow, and ice in the Northeast and the cold, snow, and ice in the southern Midwest and Southeast seems like it been around a lot longer. 

Snow cover across the U.S. was at a season-high 53.4 percent this morning. The continuous flow of Arctic air into the central and eastern U.S. has hastened the ice formation on the Great Lakes. It stands at 85.9 percent as of Monday, compared to 38.6 percent at the end of January, and 61.9 percent at this time last year. Last year ice cover on the Great Lakes peaked at 92.5 percent on March 6, the second greatest amount since the maximum of 94.7 percent in 1979.

Minimum temperature records were shattered across the eastern Midwest and Northeast yesterday morning and this morning, too numerous to list. Subzero temperatures occurred as far south as the Ohio River and east to Maine. Some of the coldest air was in east-central and central Illinois, and in northern New York through New England. It dropped to -20°F in Neoga in the south-central part of Illinois. Montpelier, VT set a new record low of -23°F. The lowest temperature in the lower 48 this morning was -34°F at Mount Washington, NH.

Minimum temperatures for the 12-hour period ending at 6:00 a.m. CST February 24.

The latest storm system that began over the weekend in the Southwest and affected the Rockies and all the way through the Deep South with snow and ice is moving out to sea off the Carolinas. It left two to three feet of snow in the Arizona and Colorado mountains and snow from Texas to North Carolina. Freezing rain glazed parts of Texas, Oklahoma, Alabama, and Mississippi. Sleet affected locations as far south as Louisiana and Mississippi.

72-hour snowfall ending the morning of February 24.

The 6-10 day and 8-14 day outlooks issued by the Climate Prediction Center today don't have a lot of good news for the winter-weary. Temperatures are likely to be below normal over much of the country through the first 10 days of March.

6-10 day (left) and 8-14 day (right) temperature outlooks issued February 24 by the Climate Prediction Center.

In addition, over the weekend one weather system could bring snow to much of the Midwest, and on Tuesday and Wednesday the Midwest, Ohio Valley, and Tennessee Valley may see rain or a wintry mix of precipitation. Both systems bear watching, so stay in touch with the forecast from your local National Weather Service office.

 (Left) Quantitative precipitation forecast for the period from 6:00 p.m. CST Friday, February 27 to 6:00 p.m. Sunday, March 1.  (Right) Quantitative precipitation forecast for the period from 6:00 p.m. CST Sunday, March 1 to 6:00 p.m. CST Tuesday, March 3.

Thursday, February 19, 2015

Brrrutal Cold

Surface temperatures at 6:00 a.m. CST on February 19.
Low temperature records were falling from the upper Midwest to Florida this morning as the leading edge of a Arctic cold air mass surged as far south as the Gulf Coast and central Florida. Watertown, NY plunged to -36°F this morning, shattering the previous record of -24°F set in 1963. The temperature at Chicago's O'Hare International Airport dropped to -8°F this morning, beating the previous record of -7°F set in 1936. In addition, today's high temperature only made it 4°F, a record low maximum high for this date. The previous record was 9°F degrees in 1936. A record low (-24°F) and record low high (-4°F) were also set in Marquette, MI today. Record low maximum temperatures were set in Binghamton, NY (10°F), tied in Syracuse (11°F), broken at Bridgeport, CT (24°F), broken at Islip, NY (24°F), and on and on. A number of these locations in New York broke records on several days this week. Record low temperatures and record low maximum temperatures were set as far south as Alabama, Georgia, South Carolina, and northern Florida. Daytona Beach reached only 50°F today, a record low maximum temperature for today, breaking the previous record of 53°F set in 1958 and 1972.

The lowest temperature this morning in the lower 48 states was -42°F in Cotton, MN, about 36 miles north of Duluth. Duluth's high temperature of -5°F today tied the record low maximum first set in 1941.

Minimum temperatures for the 12 hr period ending at 6:00 a.m. CST February 19.

Surface temperatures at 3:00 p.m. CST February 19.

The wide extent of the cold air is due to a huge upper level trough over the eastern two-thirds of the country. As can be seen on the chart below, the air, which flows parallel to the lines on the map, is coming straight over the Arctic and into Canada and the U.S.

500 millibar map for 6:00 p.m. CST February 19.

More records are likely Friday morning especially across the eastern U.S. where clear skies and snow cover will allow the temperature to plummet. Clouds spreading across the Midwest will slow the temperature drop there. Hard freeze warnings are in effect from southern Alabama through the northern half of Florida.

Forecast minimum temperatures for Friday, February 20.

While the intensity of the cold air is bad enough, the persistence of the cold air is a real problem for an area from the Ohio Valley southeast into Tennessee, Georgia, and western North Carolina where freezing rain from the storm earlier this week caused power outages. Unfortunately, it appears that more icing could occur this weekend from Ozarks east through Tennessee into North Carolina and Virginia.

Forecast for the period from 6:00 p.m. CST February 19 to 6:00 p.m. CST February 22.
It's likely that colder than normal weather will continue through the rest of the month for the eastern half of the U.S. The weather will moderate some next week, but temperatures will still be well below normal.

Minimum temperature forecast for Thursday, February 26.

Tuesday, February 17, 2015

New England, Canadian Maritimes Get PHD in Snow

That's PHD as in "piled higher and deeper".

The amazing thing about this winter is that the winter pretty much has been compressed into the last three weeks. In 1995-1996 Boston's record snowfall of 107.6 inches accumulated beginning in November and ending in April. This year that same amount of snow has almost accumulated in the last three weeks.

Last week about this time Boston had tallied 78.5 inches of snow for the season, but another foot has been added to that since then. As of today the season's snowfall for Boston was up to 96.0 inches, just 11.6 inches short of the record snowfall in 1995-1996. All but 5.5 inches of that, 91.5 inches, has fallen in the past 25 days. South of Boston snow amounts are higher, with Blue Hill up to 109.3 inches (more than 9 feet!)since January 24. The season total at Blue Hill stands at 131.4 inches. AS of today there was 36 to 42 inches of snow on the ground in Plymouth, Suffolk, and Norfolk counties in Massachusetts. Up the coast in Eastport, ME our CoCoRaHS observer there reported 78.5 inches on the ground today.

Snow piled up along the right field wall in Fenway Park in Boston.
Photo credit:  Jim Cantore via Twitter

You can see some spectacular "before and after" photos of  the snow in Boston in this Mashable article.

While a lot of attention has been on New England, the Canadian Maritime provinces have been getting hit just as hard by the snow. Three to four feet of snow blanket New Brunswick, and CoCoRaHS observers on Prince Edward Island reported as much as 55 inches (140 cm) of snow on the ground today.

Snow depths on February 17 for New England and Canadian Maritime provinces, including CoCoRaHS observations.

Digging out in Summerside, Prince Edward Island.
Photo from Twitter

8-14 day temperature outlook
All indications are that the cold weather will continue through the end of the month for the eastern half of the country. There appears to be a chance of snow every few days in the Northeast and New England, but right now nothing major appears to be in the cards. It looks like the expanse of cold air over the eastern two-thirds of the country will suppress the storm track south of New England keeping any major lows from developing off the New England coast. That's not to say it won't snow, but hopefully snowfalls will be measured only inches and not in feet. There is little doubt in my mind that Boston and many other locations will set new season snowfall records this year.

U.S. snow cover has jumped to almost 49 percent after the storm that affected the Midwest, mid-Atlantic, and Southeast yesterday. It had been down to 24 percent on February 14. What is also evident on the map is the lack of snow in the western U.S., but that's another story.

Thursday, February 12, 2015

Buried in Boston

Last week I wrote about the incredible amounts of snowfall in the Northeast, especially in Downeast Maine. Since last week's post Eastport has picked almost another foot of snow. Winter's onslaught has not let up, and this week Boston takes the spotlight.

The Boston area has received more snow in the past two and a half weeks than most locations, outside of the lake-effect snow belts, receive in one season. Winter really kicked in on January 24 with the blizzard, and it has been "pedal to the metal" ever since.  In the last week of January Boston's Logan Airport measured 31.7 inches of snow. In the first 11 days of February another 41.3 inches accumulated, bringing the total to 73 inches (more than six feet!) of new snow since January 24!  Boston set a record for the most snow recorded in a 30-day period, with 71.8 inches, breaking the record of 58.8 inches set in February 1978. The average season snowfall for Boston is 43.8 inches. The latest "frosting on the cake" was 14.8 inches of snow on Monday February 9, which tied the daily maximum snowfall record set in 2013. However, there were reports of 20 to 31 inches of snow at locations in Norfolk and Plymouth Counties south and southeast of Boston.

Daily snowfall for Boston since January 16, 2015 through February 12, 2015

The total snowfall in Boston so far this season is 78.5 inches, which is far from the record of 107.6 inches in the winter of 1995-1996. However, winter looks to be far from over.

The U.S. Cooperative observer at Blue Hill, MA, just south of Boston, tallied 36 inches of new snow the last week of January and another 47.7 so far this month, for a total of 83.7 inches!  Yesterday morning Blue Hill reported 38 inches of snow on the ground. CoCoRaHS observers around the Boston area are reporting anywhere from 26 to 39 inches of snow on the ground.

Snow depths reported by CoCoRaHS observers in Boston, February 12, 2015

Snow depth across the Northeast February 12, 2015.
Note that the highest amounts are along the Massachusetts and Maine coasts

Sledding off the roof in Boston.
Photo by Eric Fisher via Facebook.
If you have been following the news then you know that the snow has caused no shortage of problems in the Boston area. Collapsed roofs, awnings, and even entire buildings have occurred. Public transportation has been hampered, and the city has run out of places to put snow. City workers are trying to melt snow using large snow melters but can't keep up with the snow that has fallen.

Interestingly, winter in the Northeast was rather tame and mild up until January 24. Through January 23 Boston had received only 5.5 inches of snow, which at that point was 14.5 inches below normal. Temperatures were running near to slightly above normal. To give you an idea of how much things have changed in two weeks, take a look at this plot of the Accumulated Winter Severity Index (AWSSI) for Blue Hill, MA. The AWSSI is an index that a colleague, Barbara Mayes-Boustead, and I developed to measure the severity of a winter using readily available daily temperature and snow data. You can read more about this index here. What's interesting is that the plot of the index shows that the Boston area was bordering on a mild winter until January 24, but since then the winter has moved into the Extreme category (the top 20 percent of severe winters). The average AWSSI for the Boston area is 674, and the record (since 1950) is 1196 in the winter of 2002-2003. The value as of February 11 is 827.

Plot of the Accumulated Winter Season Severity Index for Blue Hill, MA.

Plot of the 2014-2015 AWSSI for Blue Hill. The solid black line is the average,
and dashed lines are one standard deviation above and below.

The steep climb of the AWSSI is likely continue based on the current upper air setup. A strong upper level trough is forecast to establish over the eastern two-thirds of the country, and that means a steady flow of Arctic air into the central and eastern U.S.

500 millibar forecast for 7:00 a.m. Wednesday, February 18.

6 to 10 day temperature outlook issued February 12, 2015
for the period February 18-22.

Disturbances moving through this trough are likely to result in storm development at some point next week, but exactly when and where is hard to pin down right now. However, the Quantitative Precipitation forecast chart for the 7-day period does show where it's possible that precipitation will fall and how much. You can follow developments on the NWS Weather Prediction Center website.
7-day Quantitative Precipitation Forecast for the period
7:00 p.m. EST February 12 through 7:00 p.m. EST February 20.

Since last week U.S. snow cover has dropped to 24.9 percent, but a significant portion of the snow is in the Northeast. It's not likely to go anywhere soon.

Wednesday, February 4, 2015

Winter's Resurgence and the Maine Event

Snowstorms have been in the news regularly the last week or so. First was the Northeast blizzard which left two three feet of snow across much of eastern New England. Then there was the storm this weekend which produced blizzard conditions in northeastern Illinois and northern Indiana, and dropped 12 to 18 inches of snow from Iowa through northern Illinois into northern Indiana and southern Michigan. As that storm marched east it compounded problems in the Northeast by laying down another 6 to 12 inches of snow from eastern New York across New England. Higher amounts, up to 18 inches, occurred in eastern Massachusetts to Downeast Maine.
Snowfall for the 72-hour period from 7:00 a.m. January 31 to 7:00 a.m. February 3, 2015

Many locations in the Midwest and Northeast doubled their season-to-date snowfall this week. Chicago piled up 19.3 inches of snow from January 31-February 2, making it the fifth largest snowstorm in Chicago's history. The largest snowstorm is 23.0 inches from the Big Snow of January 26-27, 1967. So far this week Chicago has measured 22.6 inches of new snow, and more fell today. The total for the season so far is 36.3 inches. The average for Chicago for the season is 38.0 inches.

Detroit, MI had been enjoying a fairly tame winter until this week as well. However, the big storm last weekend dumped 16.7 inches on Detroit with 18.4 inches in the last week. That brings their seasonal total to 35.8 inches. The average seasonal snowfall for Detroit is 44.1 inches.

Much of New England was just getting back to normal when the weekend storm brought more snow to the region. Boston picked up another 15.9 inches of snow, making it 42.5 inches for the week.

However, the most impressive and spectacular snowfalls occurred in Downeast Maine. Our CoCoRaHS observer at Eastport 1.5 SE (ME-WS-24) has measured 76.0 inches of snow since January 24! As of this morning the snow cover was 60.5 inches deep! This is far and away a record for a ten day period.

Daily snow fall and snow depth values for the CoCoRaHS station at Eastport, ME (ME-WS-24)
There was a U.S. Cooperative Network station in Eastport from 1895 to 2013, and the most snow recorded in a 10-day period at that location was "only" 37.5 inches. Other locations in Downeast Maine also tallied some impressive ten-day totals. Bangor had 44.5 inches, Machias, ME measured 62.1 inches (old record 35.5 inches in December 1964, records go back to 1893), and Robbinston, ME received 54.7 inches, breaking the records of 32.7 inches in March 1999 (records go back to 1994). You can view the individual storm maps for the entire season for Maine on the NWS Bangor web site. The average seasonal snowfall in the Eastport area is about 72 inches. The maximum snowfall since 1951 is 132.4 inches in Machias, ME in 1955-56 (there were five years missing in the 1980s).

Snow piled up in Eastport, ME. Photo by Wayne Tripp.
Wayne Tripp, the CoCoRaHS observer at ME-WS-24 (Eastport 1.5 SE), said that the last two weeks have been tiring. He's had to move his rain gauge to a new location because the normal spot is under a seven foot drift. "As you can imagine, measuring the snowfall has gotten quite challenging - between drifts of up to 10 feet from the blizzard, huge snowbanks from removing the snow and the pure challenge of getting away from the roads to do any measurements, have had to rely on common sense." Wayne said.  "I try to measure snow in many locations that I can access around the house - have found that there are some nicely sheltered sections where there is minimal drifting or blowing, and the deck (usually) is a good surface.  As the snow was piling up recently, it got progressively more difficult to find areas to measure - the latest storm with 18.1" had a great deal of drifting even on the deck.  I have resorted to slogging to a neighbors yard (they are summer folk) and taking a transect - almost like a geology task - through the snow.  Each storm has a very discrete layer, so I can dig into the yard and get a measurement for the most recent storm.  I may need to resort to snow shoes soon, though, as my stature is decidedly less than the current snow depth!"

Looking down the street toward the shoreline in Eastport. Campobello Island (Canada) is nearly obscured by the sea smoke. Photo by Wayne Tripp

Despite the regular sequence of winter storms the past two weeks, only 37.4 percent of the U.S. has snow cover as of this morning. Last year the figure was 61.2 percent.

Snow cover over the U.S. on February 4, 1014 (left) and February 4, 2015.
Maps from the NOAA/NWS National Operational Hydrologic Remote Sensing Center

The highest percentage this season so far was on January 4 when 54.1 percent of the U.S. had snow cover. On November 17 snow cover was 50.1 percent as a result of the unusually cold and snowy period the middle of that month. Note that the largest difference on these maps is the lack of snow in the western U.S. this season. The chart below shows the daily percentage of the U.S. covered by snow since November 1.
U.S. covered by snow as of February 4, 2015.

For the Northeast sector of the country, snow cover is 99.2 percent with an average depth of 20.3 inches

Wednesday, January 28, 2015

...and Now for Something Completely Different

The big news in the weather world this week, of course, has been the huge nor'easter that dumped three feet of snow on eastern Massachusetts, and not so much on New York City. There's plenty to read about that on the web right now, so I'd like to focus on  another weather "event" that has been taking place this week in the central and western U.S. - warm weather.

Temperatures the last few days have been more than 20°F above normal throughout the Central and Northern Plains, and and 10°F to 15°F above normal across the western U.S.

High temperatures have been running 18°F to 25°F above normal from Oklahoma north to the Dakotas and Montana. Low temperatures have been 10°F to 25°F above normal across the same area.

High temperatures yesterday were in the upper 70s and low 80s in Oklahoma and Kansas and in the low 70s as far north as South Dakota. Hard to believe it's late January.  There were 138 max temp records broken and 24 tied on January 26, and more were likely recorded on January 27 but weren't yet available at the time of this writing.

Maximum temperatures for January 27, 2015.

The reason for the warm weather is a strong upper level ridge over the western U.S., a complement to the trough over the eastern U.S. associated with the nor'easter. The ridge trough pattern is clearly evident in this water vapor satellite image from January 27.

Water vapor image at 6:45 a.m. CST January 27, 2015

Residents of the Central and Northern Plains should enjoy the warm weather while it lasts, because it wont last long. A surge of cold air will spread south across the Plains and Midwest this weekend, and by early next week it will definitely feel like it's February.

The 6 to 10 day outlook issued on January 28 for the period February 3-7, 2015.