2:00 PM | ***Snow or a wintry mix likely arrives tomorrow afternoon…ice/rain tomorrow night…brutal cold later Sunday into Monday…power outages are a threat***
Paul Dorian
Bitter cold will grip the Mid-Atlantic region come early Monday morning; courtesy NOAA, tropicaltidbits.com
Overview
A significant winter storm will impact the DC metro region from Saturday afternoon into Sunday with snow, ice and rain. Snow or a wintry mix is likely to arrive during the early-to-mid afternoon hours and continue into the early evening. The wintry mix is likely to change to rain tomorrow night and it can come down hard at times, but there can be some freezing on various surfaces into the overnight hours in far northern and western suburbs where temperatures will struggle to climb above freezing. On the backside of the storm, much colder air will pour into the region on Sunday and rain or a wintry mix early Sunday may end briefly as snow with only minor additional accumulations likely. As the Arctic air floods the region later Sunday, N-NW winds will intensify, temperatures will plunge and any slushy or wet surfaces may quickly ice-up. The plummet in temperatures will continue on Sunday night and overnight lows will likely be in the single digits come early Monday – easily the coldest day of the year so far - and afternoon temperatures may not escape the teens.
The beginning stages of the weekend storm as depicted by the 12Z NAM; courtesy NOAA, tropicaltidbits.com
Discussion
This unfolding pattern reminds me of the November snowstorm in which low-level cold air was very reluctant to give up its ground and the next thing you know there were 6+ inches of snow on the ground from the suburbs of Philly to NYC and small amounts in the DC area. Low-level cold air during the upcoming weekend will also be slow to retreat and this could lead to accumulations of snow and/or ice in at least parts of the region. By early Saturday, low pressure will be intensifying over the Mississippi Valley and it’ll feature lots of snow to its north/west and rain to its south/east. At the same time, an important factor will be strong high pressure that will be building over southeastern Canada and this will push a reinforcing cold, dense air mass into the Northeast US. It is likely the surface low pressure system will advance as far north and east as West Virginia this weekend before jumping towards the Mid-Atlantic coastline and likely located not far from Long Island, NY by early Sunday morning.
Strong upward motion late tomorrow afternoon can cause intense precipitation bands across the DC metro region; courtesy NOAA, tropicaltidbits.com
Precipitation should arrive in the DC metro by the early-to-mid afternoon hours on Saturday and, with the reinforcing cold air mass in place, it is quite likely to be in the form of snow or perhaps a wintry mix. The snow/wintry mix will continue into the early evening hours and then transition to rain tomorrow night; however, there can still be some freezing on various surfaces across the far northern and western suburbs. Snow and ice accumulations before the changeover should be on the order of a coating to an inch or two. There will be tremendous “frontogenesis” late tomorrow afternoon leading to upward motion across the DC metro region (see 12Z NAM forecast map) and this is likely to contribute to an intense burst of precipitation in the early stages of the weekend storm. On Sunday, cold air will be advancing southward as the storm pulls off the Mid-Atlantic coastline and the precipitation may change back to snow for a brief period of time before it winds down.
12Z NAM surface forecast maps for late Saturday evening (left) and late Sunday night (right); courtesy NOAA, tropicaltidbits.com
An influx of Arctic air will cause temperatures to drop sharply later Sunday and Sunday night and winds will pick up in intensity out of the N-NW. Any slush or residual wet surfaces will freeze rather quickly late in the day on Sunday. The plunge in temperatures will continue on Sunday night and overnight lows could end up in the single digits by early Monday – easily the coldest day so far – and highs on Monday will do no better than the teens. One of the reasons this Arctic air mass will be so cold around here is the fact that it’ll be coming from the continental part of southeastern Canada and not able to get modified by the more typical crossing of the still-not-completely-frozen Great Lakes.
One final note of concern, the intensification of the winds to 40 mph or so late Sunday and Monday as Arctic air pours into the region may not work too well with potentially ice-covered or snow-covered branches and limbs (i.e., possible power outages) – this is a terrible prospect given the bitter cold.
12Z Euro surface forecast map for January 27th…wow; courtesy WSI, Inc., ECMWF
Looking ahead
This will certainly not be the end of the storminess and the bitter cold air masses for the eastern US. Another storm may impact the Mid-Atlantic by the middle or latter part of next week - perhaps again resulting in mixed precipitation. Beyond that, there are signs for an even colder air mass to invade the central/eastern US in about ten days or (1/27-2/28 or so) and that could be accompanied by a snowstorm in parts of the Northeast US…stay tuned.
12Z Euro forecast map of 100-500 mb thickness for January 27th…wow; courtesy WSI, Inc., ECMWF