April 13, 2021

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WINTER WEATHER SYNOPSIS…ISSUED DEC. 21, 2020…9:00 P.M. EST

5 min read


Disclaimer:  This site is not affiliated with the National Hurricane Center, Hurricane Hunters, Storm Prediction Center, or National Weather Service.  ALL forecasts herein are the result of my analysis, and I am solely responsible for the content.  As ALWAYS, follow the National Hurricane Center, National Weather Service, and your local Emergency Management officials for emergency decisions.  In addition, this is strictly a FORECAST OFFICE.  I CANNOT make decisions regarding travel plans, etc.  My purpose, is to provide you the information, based solely on information I analyze, and the accuracy of the information at hand of the time of analysis, so you may make informed decisions.
(T. F. “Storm” Walsh)

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Greetings to everyone!
Please be aware, even though I do not post every night, rest assured I am continuously monitoring various areas for any significant weather.  I will be taking Sundays off (family time), unless we have active systems that may be posing a threat (i.e. Tropical, Winter Weather, Coastal Storms, etc.).

Good evening,
Looks like more snow, wind, wintry precipitation and dangerous sea conditions ahead, along the U.S. East coast, and possible blizzard conditions for portions of the Great Lakes and Ohio valley.  Currently, low pressure is located over a portion of the Great Lakes, and will move out of the picture during the next 24 hours.  Another low pressure system will make its way out of the Pacific NW, slide SEWD, then East and North, eventually moving north of the Great Lakes region.  The system is forecast to deepen to around 986 mb – 983 mb.  The tightening of the isobars indicate an decent increase in wind speed withe the tightening of the pressure gradient.  Based on analysis of the 1000 – 500 mb thickness charts, snowfall may begin around the upper Midwest late Wednesday evening to very early Thursday morning, based on the analyzed area of precipitation and the 540 line (5400m on the 50 mb level). 

Rain/Snow Line (From NWS Jetstream)

The 1000-500 mb thickness value of 540 (5,400 meters) is the traditional line to determine rain verses snow. The 540-contour closely follows the surface freezing temperature (32°F/0°C).

The 540-thickness line (5,400 meters deep) is approximately the point where precipitation changes from liquid to frozen or vice versa.

If precipitation is expected for locations poleward of the 540-thickness line, the rule of thumb is to predict snow.

If precipitation is expected on the equator side of this line then the precipitation would be liquid. In the example below, the 540 (and lower) thickness lines are colored blue and 546 (and higher) thickness lines and greater are colored red.

As with everything else in meteorology there are always exceptions, especially with seasons and terrain. But the 540-thickness line is a good first guess for determining rain verses snow.

The following MSLP anomaly maps will allow you to view the progress of the current system in the east, and the approaching system.  The approaching system eventually begins to weaken, and a second low develops at the southern end of the frontal / trough system, moving up the U.S. East coast.
ECMWF AND GFS MSLP ANOMALIES FORECAST GIF


Surface winds over the Great Lakes are forecast to attain tropical storm force, and surface winds along the U.S. East coast reach strong tropical storm force winds.  The forecast winds over the Great Lakes region could cause blizzard conditions over portions of the upper Midwest / Ohio valley regions.  The winds along the East coast area of the U.S. could cause some beach erosion and coastal flooding due to the forecast of high seas.  Small craft should remain inport, and commercial shipping should take appropriate actions.
ECMWF AND GFS 10M WIND FORECAST GIF


WAVEWATCH WAVE HEIGHTS AND DIRECTION FORECAST GIF

The following are projected snowfall totals using the Kuchera values, from both the ECMWF and GFS global models from 12/23 to 12/27.


Once again, along with the combination of the lows mentioned, much colder air will be forced south, with low temperatures in the 30’s forecast all the way into central Florida.  Based on analysis of forecast minimum temperatures near Christmas, it appears we get a shot of Arctic air (up until now, everything has been polar air).  Minimum temperatures in the northern portion of the country are forecast to slide into the single digits around the 25th – 27th, with some temperatures reaching below zero.
ECMWF AND GFS TEMPERATURE FORECAST GIF


Based on analysis of the stratospheric level, I do not see a “real” SSW event, however analysis of both the 10 and 50 mb temperature and pressure anomalies indicates that warmer stratospheric temperature anomalies displace the colder anomalies far enough east, and higher pressure anomalies displace lower pressure anomalies enough, to allow the Arctic Oscillation to become negative enough to allow Arctic air to push south.
50 MB TEMPERATURE ANOMALY FORECAST

10 MB TEMPERATURE ANOMALY FORECAST

50 MB PRESSURE ANOMALY FORECAST

10 MB PRESSURE ANOMALY FORECAST

ECMWF AND GFS ENSEMBLE AO FORECAST


The following NWS Watch / Warning map will provide local NWS information for your area.  Click the image, then once it refreshes, click on your area of interest.
NWS WATCH / WARNING DISPLAY (LINKED)

WSI DOPPLER RADAR LOOP (LINKED)

I will try to update again before Christmas.  IF I am unable to do so, please use the NWS MAP and RADAR LOOP to your advantage.

You may direct any questions by contacting me personally, ANYTIME, at: twalsh22000@yahoo.com

Have a blessed evening!

T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST



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