Windspeed Posted February 13, 2015 Share Posted February 13, 2015 A thread to discuss the potential for a Southern winter storm affecting portions of the Tennessee Valley. SHORT WAVE ENERGY TRACKING FROM THE NORTHERN ROCKIES CARVES OUT APOSITIVELY TITLED LONG WAVE TROUGH ACROSS THE SOUTHWEST STATES ANDSOUTHERN PLAINS ON DAYS 2 AND 3. WHILE THERE WAS GENERALLY DECENTAGREEMENT ON THE PLACEMENT OF THE LONG WAVE TROUGH...THERE WASSPREAD ON THE TRACK OF THE SURFACE LOW AND THE AMOUNTS OF MOISTUREDRAWN NORTH FROM THE GULF OF MEXICO. THESE FACTORS INFLUENCE THENORTHERN EXTENT OF THE PRECIPITATION SHIELD AND PRECIPITATIONTYPE. AT THIS POINT...THE 12Z NAM/00Z ECMWF/ECMWF ENSEMBLE MEANBLEND APPEARS TO HANDLE THE MOISTURE FOR DAYS 2 AND 3 (THE 12Z GFSSEEMS TOO SUPPRESSED WITH THE MOISTURE).. Area forecast discussionNational Weather Service Morristown Tennessee307 PM EST Friday Feb 13 2015Short term...(tonight through Saturday night)...high pressure overthe area shift east tonight and early Saturday. An Arctic frontwill move through late in the day Saturday...followed by a surge ofbitter cold air. Precipitation will move in Saturdayafternoon...especially north...and will likely start as some lightrain showers in valley areas before transitioning to snow showers bySaturday night. However...freezing levels will be low enough formost of the precipitation to fall as snow in the higher elevations...andsome light snow accumulation is expected there. Winds will increaseahead of the front and will continue as winds shift to the northwestbehind the front. Winds will be stronger in the higher elevationsof the east Tennessee mountains...and will issue a Wind Advisory for themountains from Monroe north. The very cold air will combine withthe winds to produce wind chill values that reach warning criteriain these same mountain areas...so will issue a wind chill watch aswell for Saturday night. May end up needing a Wind Chill Advisoryfor some other parts of the area as well...especially the plateauand SW Virginia...but will let later shifts evaluate this. Will issue anSpecial Weather Statement highlighting the snow and cold potential.Long term...(sunday through friday)... very interesting forecastin the extended period...with a possible significant winter weatherevent occurring on late Sunday night and Monday. However...this isstill an uncertain forecast given the fluctuations between forecastmodels regarding the timing of the system and the amount of quantitative precipitation forecastthat will occur. Currently...my feeling is that the European model (ecmwf) /and itsemsembles/ has been more consistent in showing timing/track and quantitative precipitation forecastfor this event. To a lesser extent...the NAM is on board with thisEuropean model (ecmwf) wetter solution...though its timing is earlier by around 12hours. Combined with the sunfreezing air...this would supportwidespread snowfall across the region during this time period. TheGFS also shows a snow solution...but is much weaker with quantitative precipitation forecastamounts. Given its very erratic run to run track record oflate...have opted to weigh the European model (ecmwf)/NAM solutions more heavily forthis forecast package. At any rate...all model guidance suggeststhat some snowfall /possibility significant/ will occur across theTennessee Valley and southern appalachian region from 06z Monday to06z Tuesday.The primary factor for generating this snowfall will be the verycold temperatures in place at the surface and aloft Sunday night...with lows /even with some cloud cover/ bottoming out in the teensacross the nearly the entire Tennessee Valley. Lift will alsoenhanced by a fairly Stout 700 mb jet rotating over the region. Themain questions will be much moisture will be available to work withand the timing of the precipitation. As mentioned...the NAM isearlier with its timing and shows the heaviest precipitation movingthrough the area faster...during a 06-18z Monday time period. TheEuropean model (ecmwf)/Canadian shows a slower solution during the day and more of a12z Monday to 00-06z Tuesday time frame. In each case though...quantitative precipitation forecastamounts are high which would generate a good measurable snowfallareawide. As a result...have introduced snowfall amounts for thistime period...though as mentioned timing is still a big question.At this time...have favored the European model (ecmwf) solution more and show accumulationoccuring toward the late morning and afternoon on Monday. Althoughit will most definitely be possible to see higher amounts should theforecast continue to trend this way...have gone a littleconservative in snowfall amounts for now give the model flucuation.This will allow for some flexibility and fine-tuning as more modelruns come...and confidence increases one way or the other. Asmentioned...models have wavered with this system quite a bit...soexact totals/timing are still uncertain at this time. However...confidenceis high for some valley and mountain snowfall accumulations onMonday. As such...have added a broad 1-2 inches in the grids acrossthe entire forecast area...with very slightly higher amounts acrossthe southern valley/plateau and mountains. The potential for awidespread heavier snow event is possible for Monday...but do wantto see a couple more model runs before having enough confidence toplace this in the forecast.Thereafter...the forecast remains somewhat in question...though thefavored European model (ecmwf) shows a drier period for Tuesday into Wednesday as thebase of the trough rotates across the region. Other than some lightsnow showers across the mountains Tuesday night...the secondary lowthat will form on the leeside of the mountains will track furthereast and thus keep any additional precipitation to the east of themountains. The GFS shows some moisture working in on Tuesday...butgiven its aforementioned back and forth track record have beencautious with trusting this for now. Models do hint at the potentialfor another round of precipitation moving southeast into theTennessee Valley early Thursday...though the magnitude and track arestill uncertain this far out. Overall...this upcoming week will bevery cold and much below normal for this time of year. Some reliefmay occur by Friday into the weekend as southerly winds and perhapssome weak ridging start to return. Link to comment Share on other sites More sharing options...
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