Rain, to ice, to heavy snow overnight; hazardous conditions Monday morning

* Winter storm warning for entire area late tonight through Monday afternoon | Delays/closings *

8 p.m. update: Here’s a great visualization showing the storm move in overnight and the transition from rain to ice to snow, from the HRRR model, through 8 a.m.: Radar simulation (future-cast).

Reminder: We’ll be live blogging the latest models coming in this evening starting around 9 p.m. Follow this link. Scroll down for current accumulation forecast, storm timeline, FAQs, and more.

Temperature Map

Temperatures: Latest D.C. area temperature map. See interactive map on our Weather Wall.

7 p.m. update: Federal offices in the D.C. area are closed Monday due to the storm.  Several school systems have decided to close and it’s only a matter of time until most others follow suit.

4:40 p.m. update: The arctic front has come through and temperatures have begun a steady decline as rain falls (precipitation probably takes a brief break between around 6 and 10 p.m. or so). After they reached the balmy 50s early this afternoon, temperatures have fallen into the upper 30s and low 40s – falling even a bit faster than forecast.

The latest modeling now suggests our northwestern and western suburbs could dip to freezing between 10 p.m. and 1 a.m. while still taking until between 1 and 3 a.m. around the city and south and east. So locations in western Fairfax and western Montgomery counties, and points west, should be prepared for some possible slick spots even prior to midnight tonight. And locations from western Loudoun County into Frederick (Md) and Carroll counties, may see rain and the wintry mix change to snow before midnight. See revised timeline below.

HRRR model shows 32 degree line (in blue) into our northwest suburbs by midnight and the rain having changed to snow in northwest Loudoun County into northern Maryland (WeatherBell.com)

Midnight radar simulation: HRRR model shows 32 degree line (in blue) into our northwest suburbs and the rain having changed to snow in northwest Loudoun County into northern Maryland (WeatherBell.com)

In terms of snow amounts, the latest models run this afternoon have not changed our thinking and we continue to expect 5-9 inches in the region, although locations just south of D.C. have a good chance to be at the high end of that range and a shot to go a little above it.

From 2:00 p.m.: Don’t be fooled by Sunday afternoon’s mild weather. An arctic cold front – responsible for record-shattering cold in the northern U.S. – steam rolls south tonight while a moisture-infused southern storm makes its approach. The result is crashing temperatures, and rain changing to ice and then heavy snow. We expect 5-9 inches of snow to fall across the region through Monday afternoon on top of a slick layer of sleet.

Capital Weather Gang snowfall forecast for Monday, issued 2 p.m. Sunday.

Capital Weather Gang snowfall forecast for Monday, issued 2 p.m. Sunday.

Key points

  • Travel Monday morning will be extremely difficult and is discouraged. Snow will be falling on top of a layer of ice, as temperatures fall through the 20s.
  • The worst of the storm is expected from roughly 4 a.m. to 10 a.m.
  • We expect total accumulations of 5-9 inches, although locally higher amounts are possible (into double digit territory), especially south of the District.  Locally lower amounts are possible, especially north of Baltimore and Frederick.
  • It will be extremely and unseasonably cold following the storm with the mercury dipping to the teens by late Monday afternoon.  Temperatures fall to near 10 degrees Monday night downtown with single digits in the suburbs.  Everything will be frozen solid.

Timeline, updated at 4:40 p.m.


Radar & lightning: Latest regional radar shows movement of precipitation and lightning strikes over past two hours. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.
  • 2-9 p.m. Sunday: Areas of light rain develop, west to east. Temperatures falling from near 50 to 32-38 (northwest to southeast).
  • 9 p.m. Sunday – 2 a.m. Monday: Areas of rain, changing to sleet and freezing rain and then snow in north and west suburbs between 10 p.m. and 1 a.m. Rain changes to a mix elsewhere between midnight and 2 a.m. Temperatures falling from 32-38 to 28-33 (coldest in northwest suburbs).
  • 2 a.m.-7 a.m. Monday: Snow in north and west suburbs. Mixed precipitation elsewhere rapidly changes to snow by 4 a.m.  Snow becomes moderate to heavy at times.  Temperatures fall from 28-33 to 22-27 (coldest in northwest areas).
Canadian model shows precipitation transition from ice to snow around 4 a.m. across D.C. area. (Environment Canada)

Canadian model shows precipitation transition from ice to snow around 4 a.m. across D.C. area. (Environment Canada)

  • 7 a.m. to noon Monday: Snow, moderate to heavy at times. Temperatures falling towards 20 degrees.
  • Noon to 3 p.m. Monday: Snow diminishes in coverage and intensity from northwest to southeast. Temperatures steady around 20 degrees.

SchoolCast

schoolcast-3.5-apples

3.5 apples: It’s pretty safe to blow off the homework, but your day off will be more enjoyable if you do it now.

FedCast

fedcast-3.5-domes

3.5 domes: Greater than 90% chance of unscheduled leave policy and/or delay. Greater than 50/50 chance of shutdown. [FROM 2:00 p.m.]

UPDATE, 7 p.m.: Federal offices are in the D.C area are closed.

Frequent questions

How will the snow stick with temperatures so warm this afternoon?

Thanks to the arctic front, temperatures will fall steadily and rapidly overnight, into the 20s by dawn.  The combination of falling temperatures and steady sleet and then snow will sufficiently freeze the ground to enable accumulation.  The sleet which precedes the snow may actually help the snow stick more readily, acting as an icy primer.

Look how cold temperatures are to D.C.’s northwest, where the front is coming from (map below) as of early Sunday afternoon.

Temperatures early Sunday afternoon across Lower 48 (Oklahoma Mesonet)

Temperatures early Sunday afternoon across Lower 48 (Oklahoma Mesonet)

Could there be power outages due to ice and snow?

The National Weather Service mentions the possibility of outages in its warning statement, but we view it as just a slight risk.  The period of icing should be relatively brief and ice accumulation on trees and power lines will be minimized by both this short duration as well as the fact temperatures will be 30-32 when it’s falling, which should reduce accretion.

Although the snow will be wet for a brief time – when it begins – it should change to a more powdery consistency as temperatures fall into the 20s – reducing the potential it builds up on trees and power lines.

How will air travel be affected?

Expect major air travel delays and cancellations Monday morning. It’s possible all of the airports in the region will be forced to closed for a period of time. The travel window with the largest potential for disruption is between roughly 5 a.m. and noon Monday.

As of 2 p.m., 578 U.S. flights already have been canceled ahead of Monday’s snowstorm, including 232 arrivals and departures at 3 D.C.-area airports.

Check your flight status before heading to airport.

How could the storm produce more snow than expected?

If it slows down some and/or a heavy band sets up over the region, snow totals could approach double digits – our boom scenario.  We give this a 20 percent chance.

How could the storm produce less snow than expected?

If the storm speeds up and/or the arrival of cold air takes longer than expected, snow totals could be less than 5 inches in the region.  We give this a 20 percent chance.

How will Monday afternoon’s commute be?

Hopefully people stay off the roads in the morning, so there isn’t much of an afternoon commute to speak of. Having said that, snow should end by mid-afternoon, which will give crews the opportunity to clear the major arteries. The side roads, however, will remain a hazardous mess probably well into Tuesday.

Why was the National Weather Service forecasting more snow than you?

The National Weather Service’s forecast had been for 10-14 inches of snow across the metro region as of this morning based on some of the more aggressive model snow forecasts over the last day, which were in the minority.  Early this afternoon, it lowered its forecast to 6-8″ for the D.C. metro region, very much in line with our forecast.

National Weather Service snowfall forecast.

National Weather Service snowfall forecast.

How much are the different models forecasting?

 Canadian model

Canadian model snowfall forecast (WeatherBell.com)

Canadian model snowfall forecast (WeatherBell.com)

High resolution NAM model

High resolution NAM model snow forecast (WeatherBell.com)

High resolution NAM model snow forecast (WeatherBell.com)

GFS model

GFS model snowfall forecast (WeatherBell.com)

GFS model snowfall forecast (WeatherBell.com)

European model

European model snowfall forecast (WeatherBell.com)

European model snowfall forecast (WeatherBell.com)

Technical model discussion by Capital Weather Gang winter weather expert Wes Junker

cwg_JunkerLast night’s and today’s European model and the GFS continue to be bullish on the idea of a band of moderate to heavy snow setting up across the area and gradually sinking southward with time.  Such bands often set up when there is a strong temperature contrast across the area with the temperature lines getting squeezed together with time (this is called frontogenesis).

The models still differ somewhat on exactly where the heaviest band will set up.  This morning’s NAM model focuses the heaviest snow south of D.C. but still hits the region with a decent snowfall at the lower end of our forecast range.  The European model would argue for the higher end of our range.  Today’s Canadian model is a little north of the NAM forecast and would keep D.C. in the accumulating snow a little longer.  The snowfall totals will not depend as much by the time of the changeover  - now pretty similar on the models (between 1-4 a.m. northwest to southeast) – but on how long D.C. sits under the heavy snow band.  The models continue to differ on that aspect of the forecast though all support a pretty significant snowfall across the area.

The Short Range Ensemble Forecast (SREF) members (below) reflect the various model scenarios possible with the storm.  Remember the various lines represent model runs with either their initial conditions or physics tweaked a bit.  When the lines are climbing fastest the precipitation is heaviest.

Simulations from the Short Range Ensemble Forecasting System.  Each line is a different simulation.  When the line is green, it indicates rain, when it's red ice, and when it's blue snow.  When the lines are rising, it indicates falling precipitation, when they're flat, no precipitation is falling.

Simulations from the Short Range Ensemble Forecasting System over time, 00z indicates 7 p.m. local time, 12z indicates 7 a.m. local time. Each line is a different simulation. When the line is green, it indicates rain, when it’s red ice, and when it’s blue snow. When the lines are rising, it indicates falling precipitation, when they’re flat, no precipitation is falling.

 

The big thing to take away from the ensembles is that all the members predict the precipitation to transition to snow at Reagan National Airport well before 7 a.m.  The lowest member forecasts 0.39” of liquid equivalent and the highest 0.88” .  Snow to liquid ratios would probably be higher than 10-1 more in the 12-1 to maybe even 15-1 range so the members pretty much support our current forecast or 5-9” across the area.

Despite its edging southward today with its heaviest band of precipitation, the NAM fits easily in the range of SREF solutions.  Today’s GFS is very similar to last night’s run which would suggest 6 to 9 inches of snow.   The European model is in the 7-10 inch range.  The bottom  line is all the models continue to support a significant storm across the area.

Also on Capital Weather Gang

D.C. area forecast: Disruptive winter storm brings wintry mix tonight, then a cold and snowy Monday