Thursday, January 28, 2016

The Nor'easter Blizzard 2016 - One for the Record Books

I spent much of last Saturday vicariously experiencing the winter storm along the east coast through the various weather web sites, radar, and social media. From a media standpoint this storm was well-covered, and there is plenty of information online about this storm and its impacts, including dozens of photos and videos. Rather than try to recap everything related to this storm, I'd thought I'd touch on some highlights and interesting aspects of this system.

Storm total snowfall from the January 22-24 storm.

There is no reason anyone in the storm's path should not have been prepared for what occurred. The potential for significant winter weather along the storm's projected path started coming into focus a week out. By Wednesday it was pretty clear that the mid-Atlantic region was the bullseye. The various atmospheric models were being remarkably consistent, increasing confidence in the forecast of heavy snow over a large area from the Appalachians to the coast. One of the major uncertainties in the forecast was how far north the snow would develop. Most of the models kept significant snow accumulations south of New York City, though by late in the week one model was indicating heavy snow in New York City. It was the outlier at the time, and while forecasters were aware of the possibility of this occurring other data seemed to contradict this solution. That being said, one message forecasters did consistently convey was that the northern edge of the heavy snow would be sharply defined, and that a shift of just a few miles could significantly change the forecast for locations along the northern edge of the snow shield.

 This is a loop of the radar during the Blizzard of 2016 starting at 10:00 p.m. EST January 21 through 7:00 p.m. EST January 24.

As it turned out that one model ended up being mostly correct, and the other models eventually caught on. The result was two feet of snow in New York City. What about the sharp northern edge? It was. Fishkill, NY in Dutchess County received no measurable snow from this storm, while about 12 miles to the east southeast is the town of Lake Carmel in Putnam County, NY received 12" of snow.
This storm was fairly intense and slow-moving. The pressure gradient (the change in pressure over a given distance) was rather steep, producing strong winds. The onshore easterly winds circulating around the low on the north side of the storm track generated a storm surge at high tides which in some areas exceeded the surge experienced during Hurricane Sandy. The winds persisted through three high tide cycles and helped produce major coastal flooding. The tidal flooding exceeded that of Hurricane Sandy from Stone Harbor, NJ south to Cape May, and also at Lewes, DE located at the entrance to Delaware Bay.

Wind gusts recorded during the January 22-24, 2016 storm.
Credit: NWS Mt. Holly

Winds were a major feature of this storm and were the reason for the Blizzard Warnings that were issued  for the area from Washington, DC to New York City. The highest wind gust recorded was 68 mph at the mouth of Chesapeake Bay, with gusts from 60 to 65 recorded along the coasts. Was the blizzard warning justified? This map shows the number of hours that various locations experienced visibility 1/4 mile or less and winds gusts equal to or greater than 35 mph.

The consecutive hours of heavy snow where driven by the the very strong upward vertical motion within this storm system and a basically unlimited supply of moisture from a warmer-than-normal Atlantic Ocean. Thundersnow was observed in a number of locations from Washington DC northward during the storm, indicative of strong convection.

This photo was taken by astronaut Scott Kelly from the International Space Station on January 23. The bright spot in the middle of the photo is a lightning flash over eastern Virginia during the snow storm.

The mid-Atlantic and the northeast had everyone's attention over the weekend, but as the storm approached Thursday and Friday winter weather spread from the lower Ohio Valley into the southeast. Sleet and snow occurred as far south as Georgia, Alabama, and the Carolinas. Parts of North Carolina received several inches of sleet while western mountains got a foot of snow or more.

How did this storm measure up to past nor'easters? According to the Regional Snowfall Index  produced by the National Centers for Environmental Information (NCEI), this storm ranks 6th on the list of major snowstorms with an RSI of 17.758. The area covered by 30 inches of snow or more was 1220 square miles, with an affected population of 1,121,182. The population affected by 4 or more inches of snow was 47,293,970. The highest ranking storm for the Northeast Region was the storm of February 21-27, 1969 with and RSI of 34.026.

There were many daily snowfall records set during the storm, too many to list here. Central Park totaled 26.8in inches of snow, falling a tenth short of the record28.9 inches in February 1-2, 2006. 24-hour snowfall records ere set at Kennedy Airport (30.3"), LaGuardia Airport (27.9"), Islip (23.4"), and Newark, NJ (27.5"). The official (so far) total for Washington DC is 17.8 inches (at Reagan National Airport), but there is some question about that amount due to measurement procedures. You can read more about this in this article by the Capital Weather Gang.  The CoCoRaHS station at the White House (DC-DC-19), measured a total of 21.9 inches of snow during the storm.

The observations from CoCoRaHS station DC-DC-19, the White House.

CoCoRaHS observers did a great job during this storm. The heavy snowfall rates and high winds made for very challenging measurement conditions. 33 CoCoRaHS observers reported 30 or more inches of snow for the two-day storm from Maryland,Virginia, West Virginia, Pennsylvania, New York, and New Jersey.

Once the nor'easter ended the snow cover across the U.S. was at 53 percent with an average depth of 5.6 inches. The relatively mild and quiet weather since the storm has rapidly decreased the snow cover in the Midwest, south, and reduced the depth substantially in the east. Today snow cover was down to 38.5 percent with an average depth of 4.6 inches. Last year on this date it was 27.5 percent.

Snow cover on the morning of January 25, 2016.

Snow covr on the morning of January 28, 2016

Wednesday, January 20, 2016

Some Thoughts on Snow - Past, Present, and Near Future

This has been a down year for snow lovers, unless you are in the Pacific Northwest, Sierra Nevada, or the Rockies. The eastern two-thirds of the country has been experiencing a very mild winter in terms of both temperature and snowfall.

This map shows the status of the Accumulated Winter Severity Index as of January 19. The index characterizes the severity of winter using temperature, snowfall, and snow depth data.

We are now probably in one of the more "snow active" periods of this winter so far. Storms continue to pound into the west coast, increasing the snowpack in the Cascades and Sierras. Cold Arctic air streaming across the warm and open waters of the Great Lakes flipped the lake-effect snow machine to "on", resulting in feet of new snow in the lee of the lakes from Michigan to New York.

72-hour accumulated snowfall ending 7:00 a.m. EST January 20.

A relatively weak upper wave crossing through the Midwest dropped from one to six inches of in a band from eastern Nebraska east-southeast into northern Kentucky on Tuesday night, and light snow occurred further southeast into Tennessee, northern Alabama, and Georgia today. Highlighting the winter weather this week is the chatter the past two to three days about the impending winter storm along the east coast.

As of today snow cover across the U.S. stands at 52.6 percent with an average depth of 5.2 inches. That's not bad considering the first part of the winter.

Snow depth and extent across the U.S. as of January 20, 2016

A year ago snow cover was half of this, sitting at 25 percent with an average depth of 2.5 inches. The largest and most welcome changes since last year are in the western U.S. In the western coastal region, which includes the Sierra Nevada mountains, snow extent is 17 times greater than last year (8.6 percent this year vs. 0.5 percent in 2015), and the average depth is 2.6 inches compared to a measly 0.1 inch last year. This is critically important for California's water supply and recovery from drought. Snow water equivalent, the amount of water in the snow, ranges from 95 percent of normal in the southern Sierra to 125 percent of normal in the northern Sierra. However, there is a ways to go before SWE reaches what's normal for April 1. The snow melt and runoff in the spring and summer is the water source during the dry season.

Status of the snow water equivalent in the California Sierra Nevada mountains.

In the Pacific Northwest, snow extent is 48.6 percent at this time, compared to 31.2 percent a year ago. Average snow depth is 25.4 inches compared to only 10.3 inches last year.

You can find more of this information for other parts of the country as well as maps at the National Operational Hydrologic Remote Sensing Center web site.

As I mentioned earlier, the buzz so far this week has been the impending winter storm in the eastern United States. The forecast models have been pretty consistent this week with the overall picture. There have been some run-to-run shifts in the track and position of the low, but generally the mid-Atlantic region has remained under the gun. The finer details have yet to be worked out, as the upper level disturbance that will spawn this storm just came ashore Tuesday night in the Pacific Northwest and today was over the central Rockies. This morning a Blizzard Watch was issued for the District of Columbia north through Baltimore for Friday through Saturday night.

If it plays out as forecast, this will be a paralyzing storm for the region. As much as 10 inches to two feet of snow may occur before it's all over, all whipped around by winds from 20 to 30 mph and gusts to 40 mph. Heavy snow could extend as far north as New York City. There is likely going to be a sharp cutoff in snow amounts at the northern edge of the system so a slight shift in track north or south could make a big difference in snow amounts. In addition, onshore winds will likely result in some coastal flooding. While most of the attention will be on the snow, a potentially damaging ice storm could be in store for the western half of North Carolina into southern Virginia. Further south along the Gulf coast sever weather is a possibility.

Impacts won't just be related to snow. For a good take on the likely impacts from this storm, check out Gary Szatkowski's blog, "Winter Weather Impacts Are About More Than Snowfall Totals".
Gary is the Meteorologist-in-Charge at the National Weather Service Office in Mt. Holly, NJ which covers the Philadelphia area.

Stay up to date with the last information, watches, and warnings at your local National Weather Service Office web site. The first round of snowfall forecasts were issued this afternoon and will be updated as more information comes in and details come into more focus.

Watches, warnings, and advisories in effect as of 8:00 p.m. EST January 20.

A message to CoCoRaHS observers - as part of your preparations for this storm try and take some time to review snowfall measurement and reporting procedures. It's been a long time since there has been a significant snow to measure in the eastern U.S., and the snow amounts and winds expected will present some challenges. The short videos (~2-4 minutes) on the CoCoRaHS YouTube channel are a great way to review this material. You can find them  under Training Animations.

One last thing - be safe. No observation is worth risking life and limb. If it is too icy or otherwise too hazardous for you to get out to your gauge, wait until the next day and submit a multi-day report.

We'll be looking forward to seeing all of your reports.

Sunday, January 3, 2016

A December to Remember

To say there was a lot going with the weather in December would be a gross understatement. The country seems to be catching  its collective breath this week after the conclusion of a truly amazing December. Unfortunately the frequency of events, a busy schedule, and the holidays made it tough to get any meaningful blogging done. Rather than concentrating on any one event this post will summarize the weather that made this a December to remember.

During the first weekend in December 10 to 15 inches of rain fell in southeast Florida, with nine to ten inches falling in 12 hours Miami-Dade County.

Heavy rain (and snow) also continued to fall in Washington and Oregon the first two weeks of the month. Rain totaled 16 to 25 inches in northwest Oregon and western Washington. This caused many flooding issues as might be expected. On the positive side, snowpack in the Cascades continued to increase, and by the end of December was well above normal across Washington and Oregon and near to above normal in the California Sierra.

A storm system that slowly lifted through the central U.S. the middle of December brought winter weather to the Rockies and central and northern Plains, while springtime warmth and rain spread across the central U.S. Three-day rainfall topped six inches in eastern Texas and Oklahoma and three to four inches in the upper Midwest.

A few days of fair weather followed this system. As a large high pressure system moved off the east coast strong southwesterly flow set up over the central U.S. on December 22. High temperatures reached A cold front helped trigger severe thunderstorms from Illinois south to the Gulf Coast. A number of tornadoes resulted from the severe storms, including one long track tornado in Mississippi which resulted in two fatalities.

The parade of storms continued over Christmas, with the next major system taking shape over the southern Rockies on December 26. This would end up being the defining storm of the month. Severe weather developed from Texas into Oklahoma, including tornadoes in the Dallas area. The communities of Garland and Rowlett were particularly hard-hit. A total of 11 people lost their lives in the storms, with eight killed when an EF-4 tornado tore through and interchange on Interstate 30. Severe weather continued on December 27 with tornadoes touching down in northeast Texas, southern Arkansas, and Louisiana.

Meanwhile, in the wake of the severe thunderstorms, blizzard conditions spread into eastern New Mexico and the Texas Panhandle. Winds and snow reduced visibility to zero and closed miles of Interstate, bringing post holiday travel to a standstill. The severe winter weather had a serious impact on cattle in the region, with an estimated 40,00 dairy cattle lost to the storm.

72-hour snowfall for the period ending 6:00 a.m. CST on December 29.

Back in the eastern half of the country, waves of rain were moving north through the Midwest as the storm slowly lifted north through Missouri and Illinois. Strong southerly flow pumped unseasonably warm and moist air into the eastern U.S.  In a three day-period in Missouri and Illinois rainfall topped 5 to 12 inches, with the heaviest rain in central Missouri.

The widespread heavy rain and saturated soils led to high runoff and severe flooding along many rivers in Missouri and Illinois. The Mississippi River in St. Louis reached its third highest crest on record, a phenomenon usually confined to the spring and summer. Record high temperatures were recorded from Florida to Maine.

Records Galore

There was so much going on this December that it's difficult to pick on specific thing to characterize it. However, all things considered it has to be the record warmth in the eastern half of the country. The warmth wasn't limited to the U.S., either. Eastern and central Canada were equally as warm.

December temperature anomalies for Canadian locations, in degrees Celsius

Temperature departures December temperatures averaged from 9 to 16 degrees above normal, a remarkable amount for a monthly average. There were more than 5,000 record daily high temperatures set in the U.S. and more than 6,700 record high minimum temperatures. To date 111 monthly record highs were set and 469 monthly record high minimums. Many of the old records were not broken by one or two degrees but several degrees and more.

Precipitation was much above normal in the eastern U.S. and the Pacific Northwest. The pattern was much different than in December 1997 during the last strong El NiƱo, and clearly there were other factors in play this year.

Comparison of precipitation between December 2015 and December 1997

December tornadoes put an exclamation point on what was otherwise a fairly quiet year for severe weather. Texas recorded 15 tornado fatalities in 2015, 11 of which occurred in the December 23rd tornado outside Dallas.

Flash flooding from the December rainfall resulted in multiple fatalities, and river flooding to record and near record levels is causing extensive damage in the Midwest.

The abundant snow in the west was good news not only for water supplies but also for ski resorts. This year was a welcome turnaround from the snow drought last year. In contrast, ski areas in the eastern U.S. suffered with little snow and little cold air to work with until the very end of the month..

I've only touched on the events in this post, and there is still a lot to be written about December 2015. The National Centers for Environmental Information (NCEI) will have more information compiled later this week.

It remains to be seen what the rest of winter 2015-2016 will bring, but it is bound to be interesting.