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Winter storm warning for several inches of snow in D.C. area Monday, falling heavily at times

We expect 3 to 6 inches of snow in the immediate area, with more to the south. Travel could be very difficult in the morning.

* Winter storm warning for the District and adjacent counties from 1 a.m. to 4 p.m. Monday; winter weather advisory for Loudoun County and western Montgomery and western Howard counties and points north *

Key points

  • Precipitation to move in between midnight and 3 a.m., starting as rain but changing to sleet and then snow during the predawn hours as temperatures quickly drop.
  • Snow may fall heavily, especially from the District south, between around 5 a.m. and midday with temperatures falling below freezing. Travel may become very difficult with limited visibility and roads becoming snow-covered. Gusty winds are also expected.
  • The snow should taper off during the mid-afternoon hours from northwest to southeast. Total amounts of 3 to 6 inches are most probable in the immediate area, with more south and less north.

11 p.m. — Be prepared for heavy burst of snow in the morning, very difficult driving conditions. Chance of “boom” snow scenario increasing.

After reviewing all of the evening model projections, we’re confident that there will be a period of heavy snow Monday morning, probably starting around 6 or 7 a.m. and continuing through midday. Don’t be surprised to wake up with not much on the ground but conditions will change rapidly after sunrise. Snow could fall at rates of at least one to two inches per hour for a time with visibility below half or even one-quarter mile. Roads could quickly become slick and snow-covered. We would strongly encourage staying home and off the roads if possible.

While we are not altering our snow accumulation forecast of 3-6 inches in the immediate area, we think the likelihood of a boom scenario of over 6 inches is now more likely than a bust scenario of less than 3 inches. The one thing holding us back from increasing totals is the possibility that temperatures cool slowly enough that a lot of the initial snow that falls melts.

Here are the latest projections from different models (with the caveat that about 25 to 33 percent of these amounts may be lost due to melting and/or sleet): NAM: 14 inches | American (GFS): 10-14 inches | HRRR: 10-13 inches | High-resolution NAM: 11-12 inches | HIgh-resolution Canadian: 5-6 inches

We’ll be back with coverage starting at 5 a.m. Monday.

7:15 p.m. — We’ll have a panel discussion of the evening computer models on Facebook live at 9 p.m.

Tune in at facebook.com/jason.samenow

5:30 p.m. — We are slightly increasing our snowfall forecast

Based on the consistency of model forecasts and the likelihood of a corridor of heavy snow just south of Washington, we’ve increased amount to 5 to 9 inches in that area (from 4 to 8 inches previously). In the immediate area, we’ve increased totals from 2 to 6 inches to 3 to 6 inches as models continue to suggest several hours of heavy snowfall tomorrow morning; however, there may be a sharp cutoff in where snowfall of at least 2 or 3 inches occurs so confidence in amounts decreases from the District northward.

The latest afternoon model simulations project the following amounts for the District:

  • American (GFS): 10-15 inches
  • European: 9-10 inches
  • High-resolution Canadian: 7-8 inches
  • High-resolution NAM: 4-8 inches
  • HRRR: 6-8 inches
  • NAM: 2-4 inches

As noted earlier, these models incorrectly assume all snow will stick so we need to cut them back by about at least 25 to 33 percent to gain a more realistic sense of how much will actually accumulate.

2:55 p.m. — Winter weather advisory upgraded to winter storm warning for District and surrounding counties

The National Weather Service has upgraded the winter weather advisory in effect for the immediate D.C. metro area Monday to a winter storm warning. It is now predicting 4 to 8 inches of snow along with wind gusts up to 35 mph. Previously, it had been predicting 2 to 6 inches. The warning zone includes the District along with Fairfax, Prince William, Fauquier, southern Montgomery, Prince George’s, eastern Howard and Anne Arundel counties.

A winter storm warning is also in effect farther south in north central Virginia and southern Maryland, where 5 to 8 inches of snow is predicted.

A winter weather advisory covers our northern and northwest areas, including Loudoun, western Montgomery, western Howard and Frederick counties, where 1 to 3 inches are most likely.

Our forecast, explained below (and shown above), is generally consistent with the National Weather Service’s warnings and advisories and anticipated amounts. Our predicted totals are slightly less but not meaningfully.

Original story from 1:30 p.m.

Temperatures will soar into the mid-60s on Sunday afternoon in the Washington area, but it may be blanketed in snow less than 24 hours later, with temperatures below freezing. Snow could fall heavily Monday morning, making travel very difficult across portions of the region. In most areas, snow should taper off by early to midafternoon Monday.

We’re projecting about 2 to 6 inches of snow in the immediate area, but amounts could easily end up above or below that range. The heaviest amounts, potentially topping 6 inches, are most likely south of Washington.

There may be a sharp cutoff in meaningful snow amounts somewhere between the Beltway and northern Maryland; model simulations differ as to exactly where the northern edge of significant snow will end up. It’s possible that snow totals could differ by 6 inches or more over a swath spanning 50 miles or less. This makes the forecast particularly difficult from the Beltway area northward.

The storm has the potential to bring the most snowfall to parts of the region since January 2019, when 6 to 12 inches fell.

A strong cold front will push toward the East Coast late Sunday, with Arctic air spilling southward. A storm will form along the southern end of the front and ride northeastward Sunday night and Monday, from roughly Georgia to the North Carolina Outer Banks, throwing back precipitation into the cold air. Such a storm track is historically quite favorable for snowfall in our region.

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The precipitation will probably begin as rain or sleet between midnight and 4 a.m. before transitioning to snow during the predawn hours. The potential for heavy snow, possibly falling at rates of up to 1 to 2 inches per hour for a time, will probably occur between about 5 and 11 a.m. Monday.

Although air and ground temperatures may initially be too warm for snow to stick, especially on paved surfaces, they are forecast to fall to between 26 and 30 degrees for a time Monday morning. The combination of heavy snowfall rates and freezing temperatures would eventually cause roads to become slick and hazardous, despite the 60-degree weather just 18 to 24 hours earlier.

We would anticipate road condition rapidly deteriorating between 5 and 8 a.m. in most areas. In the hardest-hit areas, especially in the southern part of the region, we can’t rule out thundersnow, very low visibility (below one-quarter mile) and extremely difficult travel conditions. Gusty winds, topping 25 mph, also could reduce visibility at times.

Amounts

While we’re forecasting 2 to 6 inches in the area, model simulations present a range of between an inch and more than a foot in portions of the region.

The models generally indicate that the heaviest amounts and the greatest potential for at least 4 to 6 inches should focus south of the District into north-central Virginia and Southern Maryland. Wherever the heaviest snow sets up, totals could even balloon into the double digits.

Just a slight nudge north in the storm track could even bring such totals into the immediate D.C. area and northern suburbs. This possibility is reflected in our boom scenario.

January should bring colder weather and snow chances to D.C. area

However, it’s possible that the northern edge of significant precipitation ends up near or just south of the Beltway. Areas that do not see heavy precipitation will not see temperatures drop enough for snow that falls to accumulate much, especially on roads. This would greatly limit snowfall potential in the immediate area, with amounts generally below two inches.

Here’s how much snow different models project for the District:

  • American (GFS): 16-18 inches.
  • HRRR: 10-12 inches.
  • European: 10-12 inches.
  • Canadian: 10 inches.
  • High-resolution Canadian: 8-10 inches.
  • NAM: 2-4 inches.
  • High-resolution NAM: 1-3 inches.

Note that these model forecasts assume all snow that falls will stick, which isn’t correct. Much of the snow that falls during the initial hours of the storm will melt. So we would generally cut these amounts by about 25 to 33 percent to be more realistic. That said, if the snowiest models are correct, that would still mean the potential for double-digit amounts in the hardest-hit areas.

Storm timeline

11 p.m. to 2 a.m.: Rain moves in from south to north. Temps falling to near 40.

2 a.m. to 6 a.m.: Rain changing to sleet and snow. Temps falling toward the low 30s.

6 a.m. to 10 a.m.: Snow, moderate to heavy at times. Temps in the upper 20s to low 30s.

10 a.m. to 2 p.m.: Snowy with gusty winds over 25 mph. Temps in the upper 20s to low 30s.

1 to 4 p.m.: Snow tapers to flurries from northwest to southeast. Breezy with clearing skies to the west. Temps in the low to mid-30s.

Storm impacts and SchoolCast

Using our Capital Weather Gang winter storm impact scale, we rate this event around a Category 3 “significant” winter storm. This means travel will be difficult during periods of heavy snow; neighborhood roads will become hazardous to navigate first, and even main roads could become challenging during heavier bursts. Flight delays and cancellations are likely Monday morning.

It’s possible our southern areas could face a Category 4 “major” event, while it’s more of a Category 2 “disruptive” event in our northern suburbs.

The snow will initially be heavy, wet and pasty, great for snowballs and packing, but should transition to a somewhat drier consistency as temperatures fall toward 30 degrees.

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As for schools, we are not issuing formal county-by-county predictions (or what we previously called SchoolCast) due to the fact they all have different snow-day policies and some have remote-learning options during inclement weather. We would expect few counties to proceed with in-person learning, given the forecast.

Forecast challenges and uncertainty

The dip in the jet stream and strong disturbance riding along it to our south give the system the potential to produce a significant snowstorm. It would draw moisture from the Gulf of Mexico and Atlantic Ocean into the region. But in terms how much snow falls and where, the devil is in the details.

The major forecast problems that will affect how much snow falls and where are:

1) How much the warm ground and initially mild temperatures hold down accumulations.

2) Where and whether the heavy snow actually materializes and can overcome the mild temperatures. This system has the potential to generate a narrow corridor of intense snowfall rates exceeding one inch per hour. Right now, it seems that corridor may set up just south of Washington.

3) Whether the sharp cutoff in significant snow accumulation occurs near the Beltway or closer to the Mason Dixon line. The models have been jumping around on how far north the northern edge of that corridor may set up.

Snowfall totals will be at or below the low end of projections if we have a storm that travels farther south with warmer temperatures and lighter precipitation. But if the storm is strong, edges north and the precipitation is heavy, this becomes a serious snowstorm for the immediate area and even into our northern suburbs.

Why predicting winter storms in Washington is so hard

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