March 28, 2013: One More Shot of Cold Next Week

In my earlier post, the models were suggesting that a new coastal storm would develop around the middle of next week, on the heels of an arctic air mass dropping south out of Canada.

Over the past couple of days, the models have trended away from a storm...but maintain a strong late-march surge of arctic air.  The arctic front will sweep south across the Mid Atlantic early next week, pushing all the way offshore into the Gulf of Mexico by Thursday morning:

With strong high pressure in control of the Mid Atlantic's weather next week, it does not appear that any storminess will develop.  After highs near 65 F on Monday, temps will drop into the mid-upper 40s on Wednesday-Thursday, but weather will remain fair.

March 26, 2013: Spring Ain't Here...Not By A Long Shot

Enjoy the slow ramp up to temps in the low 60's this weekend - because another blast of arctic air will likely arrive around Monday of next week.  And...two of the major medium-range prediction models are creating yet ANOTHER coastal low scenario around Wednesday of next week (April 3)...with the suggestion of more wintry weather/snow for our region.  Nothing like receiving the dead of winter three months late!

Here is the latest ECMWF model forecast, next Thursday morning:

Another snowstorm?  Courtesy Weatherbell Analytics.

Don't let the mild weather this weekend fool you!  The NAO (North Atlantic Oscillation) is still negative, the Greenland Block is still in place, and Mother Nature is reloading the Siberian Express for our region. 

Here is the latest GFS model forecast for snow accumulation, valid next Tuesday:

Not a lot of snow for D.C. - Baltimore, but the presence of an Arctic Front in the Mid Atlantic makes me nervous.  Courtesy of Weatherbell Analytics.

As they always say...it's gonna get worse around here, before it gets any better.   Look for persistent, mild, springlike weather around the 3rd week of April. 

March 23, 2013: Slushy Mess Still On Tap Monday

***10 PM UPDATE***
See the latest NWS snow accumulation map for our region, below, through 8 pm Monday night.

My forecast is still on track, based on all the reasons I gave in my blog yesterday (March 22).

Here are some accumulation numbers.

First - the probability, according to the NOAA Weather Prediction Center, that D.C.-Baltimore will see > 4" of snow is about 30%.  There is zero probability that the Metro region would see at least 8".  The probability of at least 4" is much higher in the elevated terrain to our west and north:

Probability of at least 4" of snow.  Blue = 10%, green = 40%, red = 70%.

Second - the NWS forecast office in Sterling, VA is beginning to issue snow accumulation maps.  Their latest (10 pm) is shown below. 

22 March, 2013: A Slushy Monday AM Commute

We are on track for an East Coast storm Sunday afternoon through Monday morning.   This is not expected to be a high impact storm for several reasons:

1)  The storm is split into two parts - a vortex over the Ohio Valley and a coastal low.   As the Ohio Valley storm weakens, the coastal takes over.  Anytime this transfer process occurs i.e. one storm robs energy and moisture from the other, the result is often a disorganized, weak field of precipitation left in between the two systems - conincident with the D.C.-Baltimore corridor;

2)  The coastal low, while intensifying, will be pulling its precipitation and energy away from the coast fairly rapidly;

3)  There is no deep, subfreezing air mass to our north, and thus no feed of intensely cold air into either storm system.   This has been a major reason why coastal storms have failed to produce measurable snow in our region all winter;

4)  Enough mild air may be pulled in off the warm Atlantic to keep the lowest few 1000 feet of atmosphere above freezing for some of the time - thus facilitating more of a wintery mix;

5)  The coldest air will be over the higher elevations to our west and northwest...and as usual this winter, these regions will likely experience the most prolonged period of all snow;

6)  There is limited moisture inland in between this complex of systems, generally 0.5" of total precipitation...this does not translate into large snow accumulation particularly with rain and sleet mixing in.

Many government and private forecast agencies are starting to issue snow accumulation maps.  The one I feel most comfortable with thus far, in terms of painting the general snow accumulation across the Mid Atlantic, comes from Accuweather:

Accuweather

March 21, 2013: Wintry Mix Likely Sunday-Sunday Night-Monday

We are now 3 days out from this next winter weather event - even though it is now Spring :)

The various models (ECMWF, GFS, Canadian) continue to portray different evolutions of a complex, double-barrel storm system forming over the East.   All models develop heavy snow within the Mid Atlantic as the primary low over the Tennessee Valley transfers its energy to a coastal low Sunday night.  A shallow layer of cold air will remain wedged in between the systems, dammed up against the Appalachians.

However, the trends and consensus among the models support the notion that the D.C.-Baltimore region will NOT be in the heavy snow bulls eye;  that will unfold over the higher elevations either to our west, or to our north and west.   Warm enough air will invade on east winds off the Atlantic to prevent an all-out heavy snow storm.  What appears to be on tap for here is a 12-18 hour period of "wintry mix" meaning rain, sleet, and wet snow.

Here are two of today's model runs, and their snow accumulation predictions:

WeatherBell Analytics

This one is from the GFS model.   The snow bulls eye, up to 1 foot, is over Garrett County and he WV Panhandle.   D.C. and Baltimore pick up about 3".

Here is the Canadian model's forecast snow accumulation:

Weatherbell Analytics

Note the heavy snow bulls eye (again, 1 foot) over the PA Poconos and Delaware Water Gap region.  Zero frozen precipitation occurs over our Metro region.

The NOAA Weather Prediction Center states that the chance of a major D.C. - Baltimore - Philadelphia snow storm is 10%.

Again, there is a complex storm evolution involved here, so future refinements to this scenario are probable.

March 20, 2013: A Storm Looking More Certain Sunday Night

A consensus is emerging that a complex coastal storm will develop off the Eastern Seaboard this Sunday into Monday.

However, most computer models suggest that there will be two pieces of energy - a primary system over the Tennessee Valley, and a secondary or coastal piece of energy off Cape Hatteras. 

There are significant differences in the models on which storm will predominate, and in particular their tracks and intensities. 

For now, a wintry mix is on the table for the D.C. - Baltimore metro region, with elevation-dependent snow (possibly heavy) over the mountains to our north and west. 

Once the storm departs Monday morning, a reinforcing blast of chilly arctic air returns to start the first week of April.

Here is the best guess concerning positions and intensities of the two storms, from the NOAA Weather Prediction Center:

Forecast Map, Sunday Morning

In this map, note the two areas of low pressure (Tennessee Valley and Georgia).   A weak wedge of cold air damming remains in place between the two systems, over the Mid Atlantic (blue "H" over NY-PA).

Forecast Map, Monday Morning

Note how the two systems remain separate. Eventually the primary storm over the Tennessee Valley weakens, drifting northeast, while the secondary of coastal system deepens as it moves northeastward away from Cape Hatteras.  Neither storm is very intense.  This is a bit of an "outside track" for a coastal low to clobber us with heavy snow.  However, with the western piece of energy and enough cold air in place, we could still pick up accumulating snow in some parts of the region.

Bottom line:  I expect a rain-sleet-snow mix here overnight Sunday, with a low chance of a major snowstorm. 

Stay tuned as the details of this complex forecast continue to get better resolved.

March 19: Next Potential Storm Still Highly Uncertain

In year’s past, I have blogged about the lessons learned from the 1942 Palm Sunday (March 29) snowstorm, which buried Baltimore in 22 inches of heavy, wet snow.    It was outright crippling in terms of downed trees, broken utilities and clogged transportation arteries.    There was a real “shock and awe” factor with this one – as the following pictures attest:

Library of Congress

Library of Congress

So, even though this is an extreme “outlier” event, there is precedent;  it could happen again.    Today, the computer models continue to advertise a significant coastal low or Nor’easter in the March 25-26 timeframe.    This, thanks to an unusually cold late-March air mass coming down from Canada.    When air this cold moves along the warm Atlantic’s Gulf Stream the Polar Front becomes prime breeding ground for a coastal storm.

With the possible storm still about a week out, there continues to be a lot of uncertainty in the model projections…in terms of storm location, intensity, track and manner in which it taps the cold air.    Odds are against a major snow storm during early spring, due to high Sun angle and warmer air masses to our south and east.  Also, the western Atlantic water is very warm, and if this air invades the D.C. – Baltimore region (in the lowest few thousand feet), it means a rainy day, not snow. 

At this point, I give equal probability to all of the following options:  All rain, mix of rain and snow, a big snow, nothing at all – which means I have about zero confidence in what may happen seven days from now.

Stay tuned, and as usual, this next “event” will probably have everyone on edge as the weekend draws near.