Archive for December, 2011

Snow or No Snow: The Great Debate
December 21, 2011

The big debate continues…will it snow on Christmas this year? Snow lovers are hoping for “yes”, travelers are hoping for “no”.  Here is where we stand so far…

Latest run of the GFS model still indicates the development of a coastal low this holiday weekend, but the timing has slowed down (precipitation is indicated by the shades of green and blue).  This would make the storm more of a Christmas Day event rather than Christmas Eve.


(6 Z GFS model valid for 4pm on 12/25/11)

A slower moving storm would give the cold air a better chance to catch up to the storm  (notice the blue dashed line over Maryland. This line indicates that the atmosphere may be cold enough for it to snow) 

However, the model is also steering the storm further to our south before moving it offshore.  This means that most of the available moisture would stay to our south as well. So what does this all mean?  Based on this model alone, the forecast would be: rain/snow mix developing Christmas morning, then a change over to light snow.  Drying out by the afternoon.

However, since the computer models are having a difficult time agreeing about this storm, the forecast is still very uncertain at this point.  As always, we’ll know more as we get closer!  For now, be prepared for the possibility of light wintry weather on Christmas day.

On another note:

The National Weather Service released a public information statement about Christmas Weather Statistics for Baltimore and Washington, D.C.  I’ve summarized the information for Baltimore below:

Baltimore, MD — Christmas Statistics

·  10% chance of measurable snow fall on Christmas

·   20% chance of either measurable snow fall or snow already being on the ground from a previous storm

·  35% chance of any type of measurable precipitation

·  Average Christmas Day Weather since 1872: Partly Cloudy, Low: 26 High: 43

Observed Weather during the past 10 Christmases

2010 –> Cloudy with Light Morning Snow, Low: 29 High: 34

2009 –> Cloudy with Afternoon Rain Low 19, High 42

2008 –> Partly Sunny with falling temperatures Low 32, High 59

2007 –> Partly Sunny and Mild Low 30, High 50

2006 –> Cloudy with Afternoon Rain Low 30, High 50

2005 –> Cloudy with Afternoon Rain Low 24, High 42

2004 –> Sunny and Cold Low 17, High 31

2003 –> Mostly Sunny and Blustery  Low 28, High 41

2002 –> Rain mixed with snow/sleet, 1 inch of accumulation Low 32, High 38

2001 –> Partly Sunny and Cool Low 23, High 40

– Ava Marie


A Sliver of Hope for a White Christmas
December 19, 2011

This time of year, we often find ourselves dreaming of one thing…a White Christmas. But what are the odds of this actually happening? Could this year be the year?

A white Christmas is defined as a Christmas morning in which there is at least one inch of snow on the ground. Based on a report from the National Climatic Data Center (NCDC), the probability of a white Christmas in the Baltimore Metro Area is between 12 to 25 percent. These numbers are based on historical data from 1961-1990. For a complete list of all the probabilities across the nation, see the full report by clicking here

(Image source: National Climatic Data Center)

While the odds are stacked against us, a white Christmas is still a possibility this year around Baltimore. Check out this morning’s run of the GFS computer model.

(12Z GFS model run, valid for 4 pm on 12/24/11)

By 4 pm Christmas Eve, it shows the development of a coastal low in Virginia. This low is our one shot at a White Christmas. The moisture is there, the crucial ingredient will be the cold air. Right now, multiple models are in disagreement about the timing of the cold air. If the cold air reaches us in time, we could get accumulating snow. If not, we’ll just get rain.

However, and this is a BIG however, we are still a week away, so there is still a great deal of uncertainty with the forecast, whether a coastal low will even develop at all. The bottom line is that I can neither confirm nor deny a white Christmas, but for all you dreamers out there, at least there is still hope!

– Ava Marie

Two Snow Chances
December 16, 2011

A cold front will shove the unseasonably warm 60F temps off the coast early Friday and a couple of fast moving weather disturbances might have enough cold air to produce a few flakes around here.  The chances aren’t great (20% – 40%), and these aren’t big storms, but at least snow lovers have something to watch.  The first system is associated with a jet streak passing south of Maryland Friday night (see above).  This jet streak should produce a wave of low pressure that will move northeast along the cold front as it settles down into North Carolina Friday night.  This one might be too weak, too far south, and too warm to produce a serious snow threat around here, but there is a slim chance that some moisture will make it far enough north to produce some light rain or snow in areas south of Baltimore between 6pm and 11pm Friday.

The second chance is slightly more promising.  A strong jet streak diving southeast from western Canada is expected to push a fast moving clipper-type weather disturbance through the area early Sunday (see above).  This one will have colder air to work with and it looks a little more energized.  However, clippers are usually very dry and so it might only be able to generate a few flurries or snow showers.

Snow amounts with either of these slight snow chances would be light, but our in-house RPM model does suggest a trace to an inch of snow is possible for parts of northern Maryland by noon on Sunday, and 2-4″ is possible in far western Maryland.

Tom Tasselmyer

on twitter: @ttassel

Southern Snow
December 13, 2011

Arizona Snow!

Coronado National Forest in Arizona is located about as far south as Brunswick, Georgia (around 31 deg. North), but tonight parts of southern Arizona are expecting 15-30″ of snow!  A wet and powerful Pacific storm that produced snow in southern California yesterday, is moving through much of Arizona, New Mexico, and southern Colorado tonight.  The storm is forecast to move northeast, tracking across the plains toward Wisconsin on Wednesday.  That track will keep the mid Atlantic on the warm side of the storm through Thursday, bringing us a chance for rain.  Once the storm passes, cooler air will arrive over the weekend.

Tom Tasselmyer

Low Pressure Deepening
December 7, 2011

3 Hour Pressure Change

NWS Snowfall Forecast

Low pressure is deepening (getting stronger) over North Carolina this evening.  The center of the low is near Henderson, NC at 5pm.  The fast moving storm is forecast to be near Cambridge, MD by 7pm and on the New Jersey Coast by 10pm.  The track brings a chance for a quick burst of snow between 10pm and 3am.  A Winter Weather Advisory is in effect for the Baltimore area.  A trace to 1″ of snow is possible around Baltimore tonight, mainly on colder surfaces such as grass, decks, and tree branches.  In the colder areas of northern Baltimore and Carroll Counties a quick 1-4″ of snow is possible.  Skies will clear before dawn with lots of sunshine on tap for Thursday.

Tom Tasselmyer

Quick Hitting Snow Burst Possible Tonight
December 7, 2011

Upper Level 150 mph Jet Stream

Powerful Upper Level Vorticity Maximum

NWS Snowfall Forecast

The National Weather Service has issued a Winter Weather Advisory for most of central and all of western Maryland tonight.  It’s a Winter Storm Warning in Garrett County.  Strong upper level dynamics will accompany a fast moving area of low pressure racing through the area tonight, changing rain to a period of snow between 10pm and 4am.  Warm and wet ground will limit snow accumulations, but a quick 1-4″ of snow is possible before dawn Thursday, especially across the higher elevations of northern Baltimore, Carroll, and Frederick Counties.  Stay tuned for updates.

Tom Tasselmyer

Snow Threat Update
December 7, 2011

RPM 11pm Wednesday Evening

NAM 1am Thursday

GFS 1am Thursday

NWS Snowfall Forecast ending 7am Thursday

The late morning run of our in-house model (RPM) latched on to the idea of a quick-hitting snow burst Wednesday night into early Thursday.  The U.S. models (NAM and GFS) have had the threat for the past few days.  The RPM is moving things through faster, with rain mixing with or changing to snow in Baltimore area between 10pm and 11pm Wednesday evening.  The NAM and GFS are a little slower, with the changeover happening between 11pm and 1am.  All three models scoot the system up to New England before dawn on Thursday.  A fast moving storm with precipitation falling on warm, wet ground means snow accumulations will be limited.  Still, it’s possible for a 1-3″ snow in the colder northwest suburbs.  The rest of Thursday should be sunny, breezy, and chilly.  Stay tuned to WBAL-TV for updates.

Tom Tasselmyer

Snow Threat Early Thursday
December 6, 2011

NAM 4am Thursday

GFS 4am Thursday

National Weather Service computer models continue to show a possible snow threat developing as  a cold front moves off the coast Wednesday and low pressure moves northeast along the front Wednesday night.  Both the NAM (North American Mesoscale Model) and the GFS (Global Forecast System) show cold air moving into central and eastern Maryland late Wednesday night into early Thursday morning.  If the low is in the right position some snow may impact the Thursday morning rush hour.  With a couple days to go, the track could change, but it’s worth monitoring.

Tom Tasselmyer



Best Chances for Snow & Cold this Winter
December 1, 2011

On the Nov 29th airing of my radio show Weather Talk, we had a guest meteorologist on from WBAL’s sister station WISN in Milwaukee, WI. He introduced us to a new long range forecasting technique called Lezak’s Recurring Cycle or the LRC. They have had such a success with this winter forecasting method over the last few years, that the NWS office in Milwaukee asked the TV meteorologists from the station to give them a seminar! I am just learning how to use this method, but based on what little I know, I have decided to take a crack at forecasting the best time over this winter season for cold and snow around Baltimore. I have only listed what look to me like the significant snow events. My first guess for each month is below. Please keep track, and we’ll see how well this does here in the Mid Atlantic!


Big Snow Possible sometime between the 16th & the 20th. A strong cold snap possible at that time as well.


Moderate Snow Possible between the 1st and the 5th. Temps will be well below average.


Big Snow Possible between the 1st and the 4th. A strong cold snap possible as well.

Moderate Snow Possible between the 16th and the 20th. Temps will be well below average.


Warmest November Since 2003…updated
December 1, 2011

November 2011 will go in the record books as one of the warmest on record in Baltimore.  Official temperature statistics for Baltimore go back to January of 1871, making this the 141st November on record, and only 12 14 of those 141 Novembers were warmer than 2011.  Based on preliminary official numbers from the National Weather Service, the average temperature for the month stands at 50.6° 50.5°, which is 4.1° 4.0° above the 30 year average.  The warmest November on record was in 1931 when the average temperature was 54.7°, the coldest November on record was in 1996 with an average temperature of 40.2°.  For comparison, last year the average November temperature was 47.2° and we have not had a November with an average temperature above 50° since 2003, which came in at 50.6°.  Interestingly, snowfall in the winter after that warm November of 2003 was only a little below normal, 18.3″ compared to the normal amount of 20.2″.

Tom Tasselmyer