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Frigid blast AGAIN next week, possibly stormy in early February

cwg_Junker

Extreme cold is expected to dominate during the next week as disturbances zip by to our north but drag down more arctic air in their wake.

The first disturbance arriving Saturday could bring another light coating of snow on the order of a dusting to an inch to the area.  Behind the second disturbance, passing through Monday, a major jolt of arctic air is expected which may keep maximum temperatures in the teens to low 20s on Tuesday and Wednesday while dropping low temperatures back in the single digits. Some locations again could flirt with or even drop below zero again.

Even after that,  the colder than normal weather is expected to continue through the end of the month.

Subtle changes to the pattern suggest there could be some moderation of temperatures during the first week of February (normal daily highs and lows of 45 and 29). Temperatures probably average near or slightly below normal with some warmer than normal days entering the mix with the colder than normal ones. Flow from the west and south is forecast to develop which could result in increased chances of getting moisture from the Gulf of Mexico into the area – possibly (but not necessarily) interacting with another polar air mass.  This favors above normal precipitation and the potential for wintry weather.

Overall, the pattern still is a little above normal for getting a 1 inch or greater snowstorm in Washington, although not on the immediate horizon.

Technical discussion

Temperature overview for the next 10 days

The two figures below display the range of ensemble forecasts for the next 10 days. The top panel shows the maximum temperatures being forecast during each 6-hour period for the next 10 days from 50 European model runs having lower resolution than the operational model runs. The green line and circles displays the average of those 50 models, the black line shows the forecast for the high resolution European model run and the blue line indicates is the forecast of a lower resolution European model run having the same initial conditions as the European model. It’s considered a control to see what impact using lower resolution might have on the forecast. The vertical bracketed blue lines indicate total range of the ensemble model solutions. The greenish gray vertical lines show where around 68% of the members are clustered. The bottom figure is the same except that it is displays the minimum temperatures each 6-hour period.

The ensembles are pretty adamant that next week during the period from Tuesday into Friday (the period marked 108 to 156) daytime temperatures are likely to struggle to get out of the teens (top panel) and minimum temperatures will likely be in the single digits to low teens. The shortness of the vertical blue lines indicates that during that period the models are in strong agreement that temperatures will be frigid.

(WeatherBell.com)
(WeatherBell.com)

 

Towards February, the uncertainty in the temperature forecasts increases as we get into early February. Note how the vertical blue lines get longer.

Pattern discussion for Jan 28.-Feb 2.

The 5-day European ensemble mean 500 mb height pattern (below) helps explain why temperatures are still expected to remain colder than normal on average through the next 10 days. When dealing with time periods beyond 5 days forecasters generally like to look at a 5-day mean pattern as it tends to preserve the larger scale features which generally are easier to predict. The massive upper level ridge (red area) over Alaska forces a downstream trough or dip (blue area) in the jet stream. The steering currents are generally parallel to the black lines on the maps below. During the period, systems are expected to plunge from northern Canada into the Plains and then progress to the East Coast. The arctic origins of the various weather systems should generally keep our temperatures below normal.

(WeatherBell.com)
(WeatherBell.com)

What about snow potential?

StormVista (a private company) and NOAA’s Climate Prediction Center have products that identify the ten closest 5-day average patterns to this one since 1950. 40 percent of the StormVista analogs had a snowstorm within 3 days of the centered mean. Three of the snowstorms were in the 6-8 inch range. There is no guarantee that this pattern will result in a major snowstorm, most of the time the pattern did not result in a significant snowstorm. However, similar patterns in the past have sometimes produced snow.

On the back side of arctic air masses during periods of retrogression (the trough over the U.S. will be shifting west) are usually periods to watch fairly closely as moisture will be increasing and arctic air is sometimes hard to displace. The threat of winter weather in the form or snow or freezing rain looks above normal during the late January through the first week of February. It’s way too early to try to identify possible dates of any storms.

During the Feb. 2-7 period the pattern subtly changes

Retrogression is taking place in the pattern. That means the larger scale waves in the atmosphere are shifting west.

Note the differences between the 5-day mean during the period ending Feb. 2 and the map below. The trough and below normal heights (blue area) has shifted west and some above normal heights (orange) has crept westward into the Southeast. However, heights still are higher than normal across Alaska and the arctic regions to its east. Arctic air will still be plunging into the northern Plains but will take a more roundabout route getting to the east coast.

(WeatherBell.com)
(WeatherBell.com)

This evolved pattern favors short waves (weather systems) possibly coming into the U.S. from the Pacific suggesting the weather will not be exclusively one of unrelenting cold. Rather it suggests the potential for a brief period of moderation. The pattern also favors a day or two with temperatures rising to normal or a little above as lows will tend to track to our north. The above normal heights over the southeast also increase the chances of Gulf moisture making it into our region.

I’ve averaged the temperature anomalies (departures from normal) in the figure below. The retrogression of the trough causes the cold air to plunge southward a little farther west than during the past couple of arctic episodes. We never get real warm but do have a couple of days with near or slightly above normal temperatures in the mean before the air pushes east into the region. A few of the analogs actually had a day or two with temperatures nudging 60. They were the outliers but are indicative of how uncertain temperature forecasts are for any warm days during the period.

wes1-4

The analogs also favored wetter than normal period due the flow becoming west-southwesterly over us. The pattern is a really good one for getting overrunning of the cold air once it gets to us which introduces the potential for all kinds of winter weather possibilities including snow, sleet or freezing rain. . One notable snowstorm showed up in the analogs (Feb 2, 1996). Three other snowstorms also were identified by the 10 analogs identified above. For those hating snow, there were also several analogs that gave rain and no snow. The bottom line is that favors above normal precipitation and near normal to slightly below normal temperatures. The chances of getting some winter weather are above normal.

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