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Posted at 01:40 PM ET, 01/31/2013

Snow hunt: three chances for flurry-fests next 5 days, then milder


It’s hard to believe it was over 70 degrees yesterday. A series of clipper systems presents three chances for a little snow between now and Wednesday.

The first is expected late tonight or early Friday morning (most likely timing: 5-10 a.m.) and the second may affect us Sunday. The third possibility would be on Tuesday but the models are at odds on whether that clipper will pass harmlessly to our north or track just to our south offering us snow.

More often then not, clipper systems only give us a dusting. However, clippers are tricky little systems that sometimes produce narrow stripes of accumulating snow so we’ll be closely monitoring them during the next several days.

Right now it looks like tonight’s clipper would give us a dusting to half an inch at most. It’s too early to speculate about how much snow the other clippers might produce, but it won’t be a lot.

Longer term snow prospects dim

After next Tuesday, temperatures next week look to be fairly seasonal through Thursday or Friday with high temperatures probably being mostly in the low-to-mid 40s and lows being in the upper 20s to low 30s. Right now, it looks mostly dry (maybe some light precip Friday).

Beyond Friday, temperatures should start creeping up as southwesterly flow is eventually established. Enough warming is expected for temperatures to rise into the upper 40s and 50s during most days of the February 8-13 period. I wouldn’t be surprised if thermometer nudged 60 one day.

During that Feb 8-13 period, any storms are expected to stay to our north. However precipitation accompanying trailing cold fronts are likely to keep rainfall near or slightly above normal. Unless we get some snow with our clippers in the next 3 or 4 days, the area’s snow drought is likely to continue. The pattern is not a good one for snow lovers.

Technical discussion

Clippers

Tonight’s clipper

Tonight’s clipper will probably produce some light snow across the area starting perhaps pre-dawn and ending by mid-morning. Both the NAM (below) and GFS bring an upper level disturbance across the area.

The track of the impulse is far enough south to threaten the area with a brief period of snow showers or light snow. Both models are now forecasting enough precipitation to suggest the potential of a dusting to a half inch. The lack of a decent surface wave makes getting an inch out of the clipper a long shot.

Sunday’s clipper

This morning’s GFS and NAM dig a vigorous upper level impulse southeastward towards the region Sunday. The GFS tracks the upper level vorticity (spin) center just to our south, a track favorable for producing some snow as a new low develops off the Delmarva coast. The NAM track is a little farther to the north just skirting us which would probably help put us in a dry slot. Right now either scenario is plausible.

Tuesday’s clipper

The potential for snow Monday night or Tuesday is worth discussing in a little more detail.

Last night’s European model (below right panel) and its ensemble mean forecast enough digging of a shortwave southward to take a low to our south. Such a track would lead to a period of snow across the region. Today’s European looks a little stronger even, suggesting - if things came together - we could squeeze out an inch or two of snow.

By contrast the GFS (left hand panel below) model at the same time tracks the low well to north giving us a warmer setup. Its track would tend to keep any significant precipitation well to our north.


GFS (left) and European (right) models forecasts of sea level pressure valid 7 p.m. Tuesday, February 5.

Note how much farther south the trough (southward dip in the blue shading) extends on the European model forecast than on the GFS in the above graphic. The bulk of the GFS and European model ensemble members each follow their parent model providing little help in trying to resolve which forecast is more likely to be right. However, the Canadian and UKMET models simulate the northern track of the GFS though with considerable timing differences.

Although the GFS model takes the clipper to our north, today’s run brought the clipper considerably south of last night’s run.

The Hydrometeorological Prediction Center (HPC) prefers the more northerly GFS-like track. I side with HPC but not with much conviction. Obviously, today’s Euro and the shift of the GFS further south suggest that the evolution and track of this clipper is still in flux. The models will probably need several more days to sort out which solution is correct.

Discussion of the February 7-13 period

Today’s Day 11 superensemble mean illustrates (below) some of the features that are expected to in place to produce another warmer than normal period for our region.


The two most significant features are the return of trough into the southwest (blue area) and the large area of above normal heights across eastern North America. Couple those two features with much less amplified flow across western Canada than we’ve had during our cold shots and the result is a warm look across much of Canada and the U.S.

Remember that the steering currents are almost parallel to the height lines (black lines) so the flow travels across Canada and much of U.S. from the west to east with air masses originating over the Pacific Ocean. The fast westerly flow cross Canada also will make it difficult to build cold high pressure systems that help bring cold air south. For these reasons, NOAA’s Climate Prediction Center is calling for warmer than normal temps across much of the U.S. during the 6-14 day period. Not every day is guaranteed to be warmer than normal but more days should be warmer than colder.

The lack of any true blocking across Greenland or a vortex (low pressure) near the Canadian Maritimes suggest storms that come out of the southwest will track northeastward towards the Great Lakes or Ohio Valley rather than will be tracking to our south.

I composited the temperatures for the ten 7-day periods provided by the super ensemble analogs (similar 500h patterns to the one above) and got a uniformly warmer than normal look across our area for the Feb 7-14 period.

I also looked at each of the 10 analog periods that were identified by the yesterday’s and today’s super ensemble mean patterns to see how many supported snow and found only one storm from yesterday’s grouping and none from today. That’s a discouragingly low number for this time of year if you are a snow lover.

Bottom line: the upper level flow pattern forecast for the February 8-14 period is an unfavorable one for snow. Any winter weather would likely come from warm advection out ahead of a low passing to our north. That usually ends up producing a mix to rain scenario.

The North American Ensemble Forecast System (NAEFS, see below) also supports the idea that warmer than normal temperatures are more likely across most of the country than colder than normal ones.

The product below assesses the probability of different temperature classifications based on the percentage of ensemble members that fall into the different categories.


The NAEFS forecast indicates that there is more uncertainty about the inevitability of temperatures across our region ending up warmer than farther to the west. Warmer than normal temperatures are highly likely to our west while our temperatures chances of having above normal temperatures are in the 60 to 70 percent range. I’d lean more towards 70% than 60% but there is enough uncertainty in the forecast to conclude that the expected warmer than normal scenario, while favored, is not a slam dunk.

Conclusion

A series of clippers will be tracking towards our area between now and next Wednesday providing several opportunities for light snow. After Wednesday, temperatures will slowly start to warm to above normal by Feb 8 or 9. Most days from February 8th through the 14th are expected to be either in the high 40 or 50s.

After our series of clippers, the pattern becomes favorable for a northern storm track putting us on the warm side of storms. This unfavorable track and temperatures averaging above the seasonal average suggest that our record breaking snow drought (for two inch or greater snowstorms) will continue.

By  |  01:40 PM ET, 01/31/2013

Categories:  Latest, Winter Storms | Tags:  latest

 
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