Scientific Forecaster Discussion

Area forecast discussion National Weather Service Greenville-Spartanburg SC 302 PM EST Friday Jan 30 2015 Synopsis... in the wake of a cold front...cool high pressure will build into the region and linger through most of the weekend. Moisture should return later Sunday ahead of a developing low pressure system... with the associated cold front crossing the region early Monday. Cold and dry high pressure will then set up through the first half of next week. && Near term /through Saturday/... as of 230 PM EST Friday...a tight surface pressure gradient over the region between a low off the middle-Atlantic coast and a 1035mb cp high centered over the Midwest has resulted in gusty north/northwest winds across much of our County Warning Area today. Stronger wind gusts of 40-50 miles per hour will continue to affect the northern NC mountains through tonight. Hence...will continue the Wind Advisory for Avery...Mitchell and Yancey counties through mid-night. The winds should die down towards the late evening as the pressure gradient relaxes over the area. Any lingering snow showers along the Tennessee line should taper off through the late afternoon hours as appreciable low level drying continues. With Stout cold air advection northwesterly flow...overnight temperatures will drop into the 10s/low20s across the mts/valley zones...l20/m20s over the NC Piedmont/eastern upstate SC and m20/u20s elsewhere. Tomorrow...a rather flat upper ridge will build in from the west allowing the surface high to settle across the region. Therefore...we will see continued dry weather and temperatures should stay 3-5 degrees below normal for most locations. Mostly clear skies tomorrow morning will give way to partly to mostly cloudy skies towards the late afternoon as considerable middle/high clouds ahead of an approaching upper trough from The Rockies overspread the area. && Short term /Saturday night through Monday/... as of 245 PM Friday...short range models indicate that low pressure will likely organize across the central Mississippi River valley Sunday morning. Moisture is expected to increase from the top down Sunday am...but forcing and moisture appear too limited to support measurable precipitation before middle morning. Based on a blend of the models...I will increase rapidly into the likely range by middle day...reach cate across the mountains by evening. The timing of the probability of precipitation should allow freezing morning temperatures to warm well above freezing before precipitation onset. High temperatures on Sunday should range from middle 40s to near 50 across the mountains to low 50s east. Sunday night...the center of the low is timed to pass across the Middle Atlantic States around daybreak. A strong cold front associated with the low is forecast to sweep east across the County Warning Area early Monday. East of the front...temperatures across the mountains should remain above freezing Sunday night...supporting generally rainfall. However...strong cold air advection behind the front should result in a fast transition to snow around sunrise Monday. In fact...temperatures across the mountains are forecast to continue to fall through the daylight hours. The precipitation will become supported by moist and cold northwest winds along the Tennessee border by middle day Monday. Areas east...should experience strong downsloping flow with decreasing moisture. It appears that the best overlap of moisture...winds...and snow supporting temperatures will occur during the early daylight hours...then gradually decrease through the rest of the day. The later arrive of cold air will result in a decrease in storm total snowfall...however...we will continue to highlight in the severe weather potential statement. && Long term /Monday night through Friday/... as of 255 PM Friday...there is good agreement at the start of the period as cold and dry high pressure builds into the area Tuesday. Below normal temperatures are expected. After Tuesday...confidence drops significantly. Guidance still shows a pattern where an upper low over the Baja California peninsula opens up and moves toward the southeastern Continental U.S. In the southern stream flow toward middle- week...while a short wave drops into across the area in the northern stream flow toward the end of the period. However...the surface pattern differs greatly with the GFS bringing a Miller-a type low to the Florida Panhandle Gulf Coast Wednesday and moving to Cape Hatteras Wednesday night... bringing widespread moisture and precipitation to the area. The low moves NE away from the area Thursday...as cold high pressure builds in from the NE through Friday. Low level moisture and isentropic lift over the developing cad then produce widespread precipitation across the area from late Thursday into Friday morning. The European model (ecmwf) on the other hand...has a Gulf low. However...it is much farther south...keeping any moisture and precipitation well south of the County warning forecast area. It brings a cold front across the area Thursday...with maybe some northwest flow precipitation...but mainly a much colder air mass. The gefs ensemble mean does have precipitation during this time...but it is limited to the low chance range. Therefore...have taken this track and limited pop to low chance for late Wednesday and Wednesday night...with slight chance on Thursday. Precipitation is late enough and temperatures are warm enough for the Wednesday precipitation to be mainly rain. Temperatures are cold enough on the back side of the precipitation to be snow...but precipitation ending would limit any snow outside of the mountains temperatures will be near normal Wednesday and Thursday...but back below normal for Friday. && Aviation /20z Friday through Wednesday/... at kclt...VFR through the period under the influence of high pressure. A tight surface pressure gradient over the region will continue to yield gusty northwest winds of 15-25kts through the afternoon. Winds will decrease after around 22z as the gradient relaxes. As the center of high pressure shifts east of the area...northwest winds will veer to the west-southwest by Friday morning. Skies should remain mostly clear throughout the period. Elsewhere...expect VFR conditions to persist throughout the taf period under the influence of the cp high pressure. Gusty northwest winds of 15-25 kts will continue at least through late this afternoon across much of the region. Kavl will continue to see stronger gusts to around 25-35kts lasting through the evening. As the high pressure gradually shifts east tonight through tomorrow...northwest winds will veer to the west/west-southwest by Friday morning. The exception will be kavl where north winds should persist through the period. Skies should remain mostly clear through tomorrow for most locations. Outlook...mainly VFR conditions are expected across the area Saturday. Moisture then begins to return Sunday ahead of another low pressure system...which is likely to bring precipitation and restrictions. Drying is expected by late Monday in the wake of that system. Confidence table... 20-02z 02-08z 08-14z 14-18z kclt high 100% high 100% high 100% high 100% kgsp high 100% high 100% high 100% high 100% kavl high 100% high 100% high 100% high 100% khky high 100% high 100% high 100% high 100% kgmu high 100% high 100% high 100% high 100% kand high 100% high 100% high 100% high 100% The percentage reflects the number of guidance members agreeing with the scheduled taf issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: (must be lower case) Www.Weather.Gov/gsp/aviation_tables && Gsp watches/warnings/advisories... Georgia...none. NC...Wind Advisory until midnight EST tonight for ncz033-049-050. SC...none. && $$ Synopsis...csh near term...joh short term...Ned long term...rwh aviation...joh

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