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Posted at 03:12 PM ET, 02/05/2013

Volatile weather pattern *could* turn snowier by Valentine’s Day


The last several weeks have been a roller coaster ride alternating between cold and warm periods but the cold has yet to produce any significant snowstorms. That roller coaster ride is expected to continue during the next couple of weeks.

We’re now exiting a cold period and entering a period where temperatures will rise into the mid-to-upper 40s by later this weekend and into the 50s early next week. However, a cold rain looks like it could be in the offing for Friday with Saturday probably remaining on the chilly side.

How warm it gets next Sunday through Tuesday will depend on whether we are stuck in clouds or not. If it’s cloudy, maximum temperatures will stay in the low-to-mid 50s. If somehow we break out of the clouds on Monday, we might even nudge 60. Right now, it looks like cloudiness will prevail.

The period from February 13-18 has an unusually high level uncertainty associated with it. Another front will be crossing the area in the next Tuesday or Wednesday timeframe ushering in the next cooler than normal spell. The models differ quite a bit on the timing of this front and on how quickly the cold air will get into the area. The magnitude of the cold and how long it might stay is more of a question than during the last two cold spells.

Snow looks very unlikely before February 13. Then the picture becomes cloudy as there is some southern stream energy showing up on the guidance which raises the potential for a wave to form on the front Such a wave raises the odds slightly of breaking out of our 2 inch or greater snowstorm drought.

Technical discussion

The two maps below give a feel for some of the issues involved in today’s outlook. Remember that winds aloft are roughly parallel to the contours (black line) on the map at left.


144 hour GFS ensemble mean 500 mb heights and anomalies (left) and selected contours from the ensember members valid at 1 a.m. February 11 (right).

By 1 a.m. Monday morning deep southwesterly flow is present across the eastern half of the country. Above normal heights and s ridge (northward bulge in the flow) extends across the easterly U.S. That ridging and the southwest flow promise to deliver warmer than normal air ahead of a cold front.

Most of the guidance is forecasting a low to track northeastward in that flow towards either the Great Lakes or Ohio Valley with the low passing to our north. That puts us on the warm side of the storm. However, the models also are suggesting that a trough will be left behind over the Southwest (the blue area). The latter feature and the subtropical jet associated with it are what makes the coming period interesting. How quickly this feature comes eastward and how it interacts with the cold front that will be crossing the area will determine our chances at a snowstorm.

How we could get a southern stream storm

Last night’s 240 hour European model forecast for Valentine’s Day offers an example of how the front might interact with the remains of the southern stream energy to produce a coastal low that could threaten us with winter weather.


I’m not showing the map because I think it is correct. The odds of a 10 day forecast from any model being right is even less than the probability that Wizards will make the playoffs this season. However, the remains of the southern stream upper trough lifting northeastward towards our region would give us a chance at a frontal wave sometime during the Feb. 13-15 period.

Pattern uncertainty


500 mb forecast from the 8 GFS ensemble members at the same time as the European model above
The trouble with getting too enamored with any solution especially one that might produce a relatively rare event (a snowstorm) is that the models have been all over the place in that time Feb. 13-18 range.

Eight different ensemble solutions are offered to the right valid at the same time as the European model shown above. Note how different the 500 mb heights are below to the 500 mb pattern of the European model (above right). That doesn’t mean the European model is wrong but rather, in this case, there is tremendous uncertainty about the pattern. Note that a couple of members still are forecasting that another trough will be located over the Southwest while keeping the east under southwest flow. They seem to be outliers but are a testament that this pattern will be a tough one for the models to resolve.

A little more about the pattern

Despite the uncertainties, today’s Day 11 super ensemble composite mean pattern analogs suggest that the pattern will trend to colder beyond Valentine’s Day. That’s a large part of why I’ve leaned towards a colder than normal look in the Feb. 14-18 time range despite the uncertainty expressed by the individual ensemble members. Three of the ten analog periods identified in the pattern produced a snow event. All three of the events produced over 2 inches.

Snow lovers can pin their hopes on a long shot like the 8 inch-plus February 11-12, 2006 storm identified by the analogs. I’m still not sold on this being a great pattern for a significant snowstorm but it does look more promising than what we’ve had so far this winter and certainly looks like any potential snowstorm would be more than a clipper.

Conclusion

Temperatures will slowly moderate during the next week but still will remain seasonal through Saturday with a cold rain possible on Friday.

Sunday through Tuesday of next week temperatures should average above normal. How cloudy we get Monday and Tuesday will determine how far we climb into the 50s.

There is an unusually high level of uncertainty about the pattern beyond next Wednesday. Overall the pattern looks it will revert to a cooler than normal one but the details about any storms or cold spells are very muddled. Introducing a southern stream into the mix complicates the pattern making it a tougher one for the models to resolve but also offering more potential for a two inch plus snowstorm than we’ve had previously this year.

By  |  03:12 PM ET, 02/05/2013

Categories:  Latest, Winter Storms | Tags:  latest

 
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