1/31/11: Some Ice, Then Rain

Expect light snow and sleet to continue to develop over the area tonight, transitioning to freezing drizzle.  The freezing drizzle will continue, off and on into Tuesday morning, before possibly changing to plain rain and ending tomorrow afternoon.

A heavier batch of precipitation will move in late tomorrow night.  This batch will likely be freezing rain for most areas Tuesday night.  The freezing rain will continue into Wednesday morning for the northern and western counties, while it changes to rain in central and Southern MD.

Up to a half inch of ice accumulation is possible in the Northern and Western counties (those under the Winter Storm Watch), but significant icing should not be a concern for the rest of the area.

Rain/freezing rain will continue into Wednesday afternoon, before the cold front moves through.

Be sure to check the website for updates on the progress of the storm and surface temperatures, as well updates on Watches and Warnings.

1/30/11: Forecast - Another Midweek Threat

Another week, another significant storm threat

We are in a very active pattern right now and it continues to produce major storms in the Eastern US.  This week's storm will not be a coastal storm however, as all model guidance take it west of the Appalachians.  This storm track will ultimately mean rain for the area, but there looks to be frozen precipitation for a period, before we change over.

Take a look at the following GFS model graphic for 1am Tuesday morning:

If you look along the east coast, you can see the isobars (black lines) and the isotherms (red and blue lines) bending south.  This is a classic representation of cold air damming.  As the storm moves in, it is bringing a surge of warm air.  This warm air runs over top the cold air that is trapped near the surface.  The high pressure to the north of us keeps the cold air locked in east of the mountains.

This map also shows some light precipitation over the area.  This is a result of the rush of warm air ahead of the system.  At this time (1AM) it should be cold enough for this precip to be all snow, but as we head into the morning afternoon hours on Tuesday, it will change to sleet and then freezing drizzle.  

Here is the map for 7am Tuesday morning:

 This map continues to show the cold air damming and the freezing line down to near the VA/NC border.  Surface temperatures are still below freezing, but the warm air continues to surge northward aloft.


1PM on Tuesday:

Here we see the freezing line moving back north and basically right through the state. As the storm continues its northward trek, the warm air continues to surge and displaces the sub-freezing temperatures at the surface and changing the precip to just plain rain.

The good news is that most of the precipitation that falls from this storm will indeed be plain rain.  The bad news is, most models do a fairly poor job at handling cold air damming situations and tend to erode the cold faster than it actually does.  What this means is, we could see a fairly long period of light sleet and freezing rain into Tuesday evening.

By Tuesday night, the transition should be well underway and temperatures will continue to climb all the way to the mid-40s on Wednesday. The bulk of the precip will fall late Tuesday night and Wednesday so there is no concern of a major ice event for our area.

7AM Wednesday morning:

The freezing line has moved well to our north by 7AM Wednesday morning, while the heavier precip is falling as rain.  Expect Wednesday to be a relatively mild day, with rain lasting into the late afternoon, early evening hours.  When all is said and done the GFS shows us ending up with an inch of liquid precip, but again this will fall mostly as rain:

While it will be mostly rain for us east of the track, those west of it appear to be line for a heavy snowstorm.  Illinois and Indiana appear to be in the jackpot zone, where Winter Storm and Blizzard Watches are already posted for snowfall totals in "feet" not inches.

Looking ahead


Several models are hinting at yet another coastal low possibly affecting the area by the end of the week.  It will take a few days to sort through everything to see how it may affect us, if at all.  For now, it is just something to keep an eye on.

1/27/11: Snow Totals and Next Possible Storm

Here is a map of reported snow totals from the NWS:

Here is the forecast I made on Tuesday afternoon:

As you can see, my forecast was a bit low.  The morning snow was unexpected.  I didn't anticipate that accumulation as I thought we would have more of a rain/snow mix overnight Tuesday night.  That gave the area a 1-4" head start and snarled the morning commute.

I also didn't anticipate the snow being able to stick as fast as it did.  Most areas saw a period of very heavy sleet that provided a crusty ice base for the snow once it started so not much was lost to melting on wet surfaces.  I also didn't anticipate the widespread thundersnow.  Like storms in the summer, these quickly upped the snow rate (over 2+ inches an hour) and allowed for the localized amounts near a foot.  I knew that thundersnow would be possible, I just didn't think it would be as prevalent as it was.

Overall, I believe I still had the right idea and without the morning snow, numbers would fall more in line with my thinking.


Next Snow Chances?

We could see some snow showers tomorrow and Saturday from a series of weak clippers, with minor (half inch) accumulations.  Our next chance of significant snow appears towards the middle of next week.

The GFS model is advertising a Groundhog Day special with another coastal storm potentially affecting the area:

It is still a long way away and things will definitely change, but I wanted to give a heads up that this is the next snow possibility.

1/26/11: Storm Update

Everything continues to unfold about as expected... the NWS has expanded the Winter Storm Warning back to the east to include the central Maryland counties that were previously under an Advisory.  Southern MD and the lower Eastern Shore remain under the Advisory for 2-5 inches.

I am sticking with my original forecast from last night:

Here is the text of the Winter Storm Warning:

WWUS41 KLWX 262014

WSWLWX


URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC

314 PM EST WED JAN 26 2011


DCZ001-MDZ004>007-009>011-013-014-VAZ036>040-042-050>056-501-502-
270415-

/O.CON.KLWX.WS.W.0003.000000T0000Z-110127T0900Z/

DISTRICT OF COLUMBIA-FREDERICK MD-CARROLL-NORTHERN BALTIMORE-
HARFORD-MONTGOMERY-HOWARD-SOUTHERN BALTIMORE-PRINCE GEORGES-
ANNE ARUNDEL-NELSON-ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-LOUDOUN-
ORANGE-CULPEPER-PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX-
ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA-
NORTHERN FAUQUIER-SOUTHERN FAUQUIER-
INCLUDING THE CITIES OF...WASHINGTON...FREDERICK...WESTMINSTER...
GAITHERSBURG...COLUMBIA...BALTIMORE...ANNAPOLIS...
CHARLOTTESVILLE...LEESBURG...CULPEPER...MANASSAS...
MANASSAS PARK...FAIRFAX...ALEXANDRIA...FALLS CHURCH...
FREDERICKSBURG...WARRENTON
314 PM EST WED JAN 26 2011

..WINTER STORM WARNING REMAINS IN EFFECT UNTIL 4 AM EST
THURSDAY...


A WINTER STORM WARNING REMAINS IN EFFECT UNTIL 4 AM EST THURSDAY.

* PRECIPITATION TYPE...SNOW. SNOW MAY MIX WITH RAIN AND SLEET
 THROUGH THE MID AFTERNOON.

* ACCUMULATIONS...4 TO 8 INCHES.

* TIMING...RAIN AND SLEET CHANGING TO SNOW DURING THE MID TO LATE

 AFTERNOON. SNOW WILL END AFTER MIDNIGHT FROM SOUTHWEST TO
 NORTHEAST. THE HEAVIEST SNOWFALL IS EXPECTED BETWEEN 4PM AND 10

 PM...IMPACTING THE AFTERNOON AND EVENING RUSH HOUR.

* TEMPERATURES...LOWER TO MID 30S...DROPPING INTO THE LOWER TO MID
 20S OVERNIGHT

* WINDS...NORTHEAST 10 TO 15 MPH...BECOMING NORTHWEST THIS

 EVENING.


PRECAUTIONARY/PREPAREDNESS ACTIONS...


A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW...
SLEET...AND ICE ARE EXPECTED OR OCCURRING. STRONG WINDS ARE ALSO
POSSIBLE. THIS WILL MAKE TRAVEL VERY HAZARDOUS OR IMPOSSIBLE.


&&


$$

1/25/11: Snowfall Forecast

I disagree a bit with the National Weather Service forecast for this storm.  I do not think we will see Winter Storm Watch level snows (5+ inches) in the DC/Baltimore Metro areas.  I think the snow will have a difficult time sticking at first, and the shot of heavier snow they expect tomorrow evening will be of short duration, as the storm races northeast.  

Nonetheless, I expect a few inches in Central Maryland with higher amounts north and west of the cities, where the changeover will happen sooner (mid-morning vs. early afternoon).

My Forecast:

NWS Forecast:

1/25/11: NWS Bumps Snow Totals

There is a possibility of snow accumulation tomorrow evening as colder air begins to filter back into the area, changing the rain back to snow.

Snow totals will be cut down, due to the rain and wet surfaces but a few inches along the I-95 corridor isn't out of the question.

EDIT:  The entire state, except for the lower Eastern Shore is now under a Winter Storm Watch for 5 inches or more of snow:

Winter Storm Watch

Predicted Snow Totals

1/24/11: Near Perfect Track... Imperfect Pattern

For the first time this winter, the models are converging on almost a perfect storm track to bring a significant snowfall to our area.  The only problem (for snow lovers) is that the cold airmass that is currently in place will move out to sea before it arrives.

The blue line is the freezing line.  As you can see, central MD and points east are above freezing.

With no strong cold air source to the west or north, and the storm bringing plenty of warmer air with it, our perfect storm track looks to bring mostly rain to areas east of the mountains.

As it looks right now, this should be a mostly rain event, with snow mixing at times and ending as a bit of snow.  Here is the NWS forecast for central MD:

Tuesday Night	A chance of rain and snow after midnight. Mostly cloudy, with a low around 30. East wind between 3 and 7 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.
Wednesday	Rain and snow likely, becoming all rain after noon. Cloudy, with a high near 37. North wind between 9 and 15 mph. Chance of precipitation is 70%. New precipitation amounts between a quarter and half of an inch possible.
Wednesday Night	Rain and snow likely before midnight, then a chance of snow. Mostly cloudy, with a low around 27. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

The one certainty is that as this system pulls away, it will drag in another reinforcing shot of cold air for next week.

1/22/11: Midweek Snow Threat

Another coastal storm system will approach the area Tuesday and Wednesday of this coming week.  As it has been all season, the models continue to have disagreements as to where the system will fully develop and where exactly it goes after doing so.

Currently, the GFS model is trending towards a storm that develops to our south, then moves Northeast, bringing very little precipitation to the area.  The ECMWF (a European model) has the low much closer to the coast and more precipitation for the area.

Latest GFS for Wednesday Evening (00z Thursday):

Latest ECMWF for Wednesday Evening (00z Thursday):

As you can see, the GFS has the low about 500 miles further east than the ECMWF, which has the low just off the Delmarva coast on Wednesday evening.  This gap is significant, as is the difference in the resulting weather for our area.

Given the seasonal trends, I am leaning towards the GFS solution and little to no snow.  This is a low confidence forecast, and things will most certainly change.  I will update as things (hopefully) come into better focus over the next few days.