Mild this week, then winter comes roaring back next week into March

cwg_JunkerFinally, a break in winter is coming!  Warmer than normal temperatures are expected this week with maximum temperatures running in the 50s to low 60s. Lows in the 30s over the next two nights probably climb into the 40s Thursday night.  No snow is expected which is good news for those with sore backs.  Showers are possible Wednesday and then again Friday and Friday night, when thunder is even possible with the passage of a strong front.

If you hate winter, next week through the first couple of days of March may have you hating life or at least hating how resilient winter has been this season.  This week’s warm spell will probably be history as another shot of cold arctic air spreads into the area.  The pattern from roughly February 24 through March 3 is expected to average colder than normal with above normal chances of seeing additional accumulating snow.

Instead of our highs running in the low 50s – normal for this time of year – they are likely to average in the upper 30s to mid-40s.  However, any cloudy day with a storm to our south could cap daytime temperatures below freezing.   However, I doubt every day will end up colder than normal as there usually is at least one sneaky warm day when looking at a period encompassing 8 days.  Still temperatures should average well below normal.

Why do you expect the warmth to end?

The box and whiskers diagram below illustrates how this week is likely to feature above normal temperatures but starting around next Monday maximum temperatures are likely to close out the month on the cold side.  Note on the figure below that the average of model simulations or “ensemble mean” (green line) actually predicts several days this week with temperatures nudging into the 60s.  Enjoy the warmth, it won’t last much beyond this weekend. Unfortunately, colder than normal temperatures are expected to return next week as the pattern reverts to the one that has held dominion over our weather most of this winter.

(WeatherBell.com, adapted by author)

(WeatherBell.com, adapted by author)

The ensemble mean (green line) and operational European model (black line) temperature forecast never rises above 45 F next week, with a couple of days staying in the 30s.  The various ensemble members (different simulations) show increasing uncertainty beyond this week concerning temperatures which can give cold haters a little hope that maybe they don’t end up as cold as the mean each day. However, most ensemble members still hold the temperatures quite a bit colder than normal.

Pattern discussion for the February 27-March 3

analog-coldThis 5-day period looks much colder than normal.  The one saving grace is that average daytime highs by the end of the month into the beginning of March sneak into the low 50s.  Unfortunately, our air masses are again likely to be of arctic origin so our highs are more likely to be in the mid-to-upper 30s into the 40s during the period.  The period also offers above normal chances of getting another 1 inch or greater snowstorm at Reagan National Airport.

The 5-day mean 500 mb pattern (weather pattern at around 18,000 feet) to the right helps explain why our temperatures are likely to be cold during the last few days of February and the first three days of March.   Again, the pattern features a strong ridge (red area) across western North America like we’ve had most of the winter.   Such a strong upper level ridge forces a downstream trough (dip in the jet stream) leading to the southward displacement of the polar vortex.

More important to us is that the steering flow is generally parallel to the thin black lines on the map.  I’ve added a thick black arrow to approximate the steering flow.  With such a pattern, cold high pressure systems are likely to build over northern Canada and then plunge southward into the U.S.

Examining similar patterns from the past, or analogs, can offer a sense of how cold it might be.  Using a set of analogs, I averaged temperatures over similar 5-day periods in recent decades. All of the analogs were colder than average.  At least one day averaged more than 14 degrees below normal – extremely cold for an average.

The analogs suggest there is potential for a day when we don’t even reach 30. Multiple days with highs in the 30s are possible despite how late it’s getting in winter.  This analysis doesn’t guarantee that every day will be colder than normal as the sun is getting higher in the sky and the days are getting longer – air masses tend to moderate more quickly than earlier in the season.  Still, more days will be colder than normal than warmer during that 5-day period.

cold-cold-cold

What about snow?

While the pattern is not a really wet one, it’s also not an extremely dry one.  The pattern offers snow lovers hope that upper level disturbances will dive southward out of Canada and slide to our south.  Light to moderate snowstorms are more likely in this kind of pattern than another behemoth like we just had.  Four of the 10 analogs had 1 inch or greater snowstorms during this 5-day window.   When you increase the analog period by a day on either side, another two snow events were noted.  One of the storms was a really notable one just to our south and still gave us almost 5 inches. So despite my feelings about the pattern being more favorable for clipper-type systems, a similar pattern did produce a significant snowstorm for the southern Mid-Atlantic.

The bottom line

 Enjoy the warm weather this week. You may have to dodge showers Wednesday and even a thunderstorm Friday but the warm weather will be a welcome change.  Next week starts another stretch of winter-like weather, colder than normal with above normal chances of a snowstorm cropping up.  Right now, it’s too early to give snow specifics but the pattern is a pretty good one for snow.

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