Hosed by the Thursday Anafront

7:00AM 3/5/2015 Update:

Based on the reports of snow mixing in Germantown, we'll probably be all snow by 8AM

6:45AM 3/5/2015 Update:

I have some pretty maps for you

First of, the HRRR:

Changeover around 9AM

 Around 7 inches of snow

 The 1.33km NAM Nest:
Changeover around 10AM
Around 6 inches of snow


The RAP
Around 6 inches of snow too

6:30AM 3/5/2015 Update:

Well. MCPS closed at 4:25 AM. I think they were messing with us. In line with their worries that the snow well never materialize, we're still raining at 6 AM and will keep raining the whole day. JK, most of that "rain" will be frozen and fluffy. 

Snow totals will go as forecasted. The latest short term and global models almost unanimously give us 6-10 inches (at 10:1 ratios), like 4-8 accounting for low ratios and sleet. The sleet line has made it down to DC (it started sleeting as I was typing this) Expect light sleet until around 9-10 AM, when the next batch of heavy precip is expected to cross the area, removing the elevated warm layer. Do not panic-yet.

3:00 PM 3/4/2015 Update:

The NWS upgraded us to a Winter Storm Warning for 6-10 inches of snow.

...WINTER STORM WARNING REMAINS IN EFFECT FROM 10 PM THIS EVENING
TO 7 PM EST THURSDAY...

* PRECIPITATION TYPES...WINTRY MIX LATE THIS EVENING...THEN
  SNOW... HEAVY AT TIMES.

* ACCUMULATIONS...SNOW ACCUMULATION OF 6 TO 10 INCHES.

* TIMING...RAIN CHANGES TO WINTRY MIX LATE THIS EVENING THEN ALL
  SNOW THROUGH THURSDAY. SNOW HEAVIEST THURSDAY LATE MORNING
  THROUGH MID AFTERNOON.

* TEMPERATURES...IN THE LOWER 30S...DROPPING INTO THE LOWER 20S.

The timing of the changeover to freezing precip has been delayed by a couple of  hours but no worries, the precip will hang around longer too.

Final Call:
Temps: dropping below freezing when precip flips and dropping throughout the day into the low 20s and then into the single digits by dawn Friday.
Accumulation: 4-8 inches overall, up to 10 inches where banding sets up.
Timeline (+/- 1 hour): 3AM Thurs Rain to sleet, 6AM Thurs-sleet to snow, 8PM Thurs-Snow stops
School (or no school): No school Thursday. Probably no school Friday too depending on accumulations

9:15 PM 3/3/2015 Update:

Whoops forgot to mention that the NWS has issued a Winter Storm Watch for our area

Here it is:

...WINTER STORM WATCH REMAINS IN EFFECT FROM WEDNESDAY EVENING
THROUGH THURSDAY EVENING...

* LOCATIONS...THE BALTIMORE AND WASHINGTON METROPOLITAN AREAS.

* HAZARD TYPES...FREEZING RAIN THIS EVENING. SNOW... HEAVY AT
  TIMES...WEDNESDAY NIGHT INTO THURSDAY.

* SNOW ACCUMULATIONS...POTENTIAL FOR 5 OR MORE INCHES.

* TIMING...ICING THROUGH SUNDOWN. RAIN CHANGING TO SNOW
  WEDNESDAY EVENING. SNOW MAY BE HEAVY AT TIMES WEDNESDAY NIGHT
  INTO THURSDAY MORNING.

* IMPACTS...ROADS MAY BECOME ICY LATE THIS EVENING. ROADS WILL
  BE SNOW COVERED WITH VISIBILITY REDUCED TO NEAR ONE-QUARTER
  MILE AT TIMES WEDNESDAY NIGHT INTO THURSDAY. TRAVELING
  POTENTIALLY WILL BE DANGEROUS.

Apparently it includes details about the icing event today. That information is crossed out.

Original Text:

First off, a beautiful image showing the moisture feed of our upcoming storm reaching all the way into the tropical Pacific.

A cold front will slowly sag south tomorrow (Wednesday), with a wave of low pressure riding along the front. As the cold air pours in Wednesday night and into Thursday, precipitation is expected to change from rain to snow. Temperatures will plummet Thursday and precip will shut off by Friday morning. This much we are sure of. What is left to determine is the speed and strength of the cold air infiltration and how much of what will fall out of the sky.

Models look to all be hits. There are some pretty significant variations on the time of the switchover. The globals (GFS, Euro, CMC, UKMET) all show 6-10+ inches(10:1 ratios) across the region, not accounting for loss of accumulation due to sleet, low ratios, ect. The lowest end accumulation is from the NAM, around 4-8 inches at 10:1 ratios. The NAM has a long period of sleet and a farther north track. We are not yet in range of the short range models.

First Call:
Temps: dropping below freezing when precip flips and dropping throughout the day into the low 20s and then into the single digits by dawn Friday.
Accumulation: 4-8 inches
Timeframe (all +/- 1 hour): 1AM Thurs- Rain to sleet, 5AM Thurs -sleet to snow, 7PM Thurs -Snow  stops
School (or no school): No school Thursday perhaps Friday too  depending on accumulations

This looks to be the last major storm of the season (at least for the next 2 weeks or so). Once we get out of early March, snow  hard to come by. Things also look to warm up a bit next week. Maybe spring will arrive. Thanks for reading, and I will try to update as much as possible

Tuesday Potential for a Rush Hour Mess

10:30 PM 3/2/2015 Update:
The NWS has issued a winter weather advisory. Starts early at 9AM. Not sure why. Overall seems a little out of sync with model guidance but maybe they know something I don't. The rush hour timing certainly won't help with minimizing impact. But the March sun will hopefully keep pavement temps high enough to prevent glaze from forming on the roadways.

...WINTER WEATHER ADVISORY REMAINS IN EFFECT FROM 9 AM TO 10 PM
EST TUESDAY...

* LOCATIONS...THE BALTIMORE AND WASHINGTON METROPOLITAN AREAS
  AND NORTH CENTRAL MARYLAND.

* HAZARD TYPES...SNOW...SLEET AND FREEZING RAIN.

* ACCUMULATIONS...SNOW AND SLEET ACCUMULATION OF UP TO 1
  INCH...ALONG WITH UP TO ONE TENTH OF AN INCH OF ICE.

* TIMING...TUESDAY MORNING THROUGH LATE TUESDAY EVENING.

* IMPACTS...ROADS WILL BE SNOW AND ICE COVERED. TRAVELING WILL BE
  DANGEROUS.

Final call (based on what I see): 
Trace sleet/freezing rain.
Changeover to rain around 7PM
Early release possible. The start time of precip is forecasted to be around noon.

Original Text:
Today we'll get some pretty decent ice melt which is a good thing since the load needs to be taken off the tree branches and power lines before the possible next round Tuesday afternoon. High pressure building in today will keep us cool, in the 30s to near 40. We will drop to the low 20s tonight. Tomorrow will dawn cold and cloudy and we will struggle to climb above freezing. Starting mid afternoon, snow and sleet will move in and fall through rush hour before possibly changing to freezing rain if temperatures drop. Temps are expected to rise above freezing overnight.

Since there are significant variations between the models regarding impact, we are waiting for the 12z models to come out before going forth with the final call.

First call: 
Half inch sleet, trace freezing rain.
Temps in the low 30s
Perhaps an early release if the radar lights up earlier than expected, which has been the pattern lately.