Scientific Forecaster Discussion

Area forecast discussion National Weather Service Greenville-Spartanburg SC 652 am EDT Tuesday Jul 28 2015 Synopsis... high pressure will persist over the region through Wednesday...with continued warm temperatures. A weak cold front will approach the area from the northwest on Thursday and settle just south of the region on Friday. The front will likely remain stalled just south of the area through the weekend...with cooler temperatures expected. Moisture should increasingly return northward over the front the latter half of the weekend into early next week. && Near term /through tonight/... as of 650 am...patchy fog and low clouds have develop across most of the County Warning Area this morning. I will update the forecast to increase sky cover and indicate limited visible across areas of fog. Radar trends indicate a isolated rain showers across the lower French Broad valley...otherwise...conditions appear dry. As of 320 am...radar indicated weak isolated showers across the NC Piedmont with another cluster sliding east toward the north four NC counties. Cams indicate that the convection will gradually dissipate across the mountains...with a few rain showers lingering across the Piedmont through sunrise. This afternoon...near term models show the center of the 500 mb high over the Central Plains...with northwest to southeast heights across the western Carolinas. Recent west/v images indicated that well develop vorticity maximum was moving over the western Ohio River valley. 0z runs of the near term models did resolve this feature very well...but the NAM appears the best initialized with the feature. The vorticity should track southeast through the day...reaching the southern Appalachians by early this evening. Forecast soundings show greater instability and lower level of free convection this afternoon compared to the past several days. Given the approach of the middle level feature and more supportive thermal profiles...I will forecast 40 probability of precipitation across the mountains and 30 probability of precipitation east. The center of the vorticity is expected to pass to the SW...however...convection across the forecast area may remain well into the evening. I will keep scattered probability of precipitation in the forecast until midnight. High temperatures this afternoon will remain comparable to the past two days...slightly cooler than yesterday. Tonight...convection after midnight is forecast to remain sparse...but enough to support schc probability of precipitation. Periods of debris clouds...mild thicknesses...and light south low level winds should keep min temperatures mild. Using a blend of preferred guidance...I will forecast lows in the upper 60s within the mountain valleys to low 70s east. && Short term /Wednesday through Thursday night/... as of 245 am EDT Tuesday...a broad upper ridge will stretch across the southern tier of the United States on Wednesday. Weak lobes of vorticity may drop southward through the western Carolinas Wednesday afternoon along the eastern periphery of the ridge. Mountain triggering of convection is likely early Wednesday afternoon...especially along the eastern slopes where low level convergence will be best. Any early to middle afternoon mountain activity may develop eastward off the higher terrain into the Piedmont through the evening and early overnight hours. Gradual height falls are then expected through Thursday...but with the best shortwave energy associated with a vigorous northern stream wave passing north of the area from the Ohio Valley to the middle Atlantic through Thursday night. The developing trough will allow a cold front to arrive in the southern Appalachians from the northwest Thursday afternoon...but it will likely stall over the lower Piedmont through early Friday morning. Above climatology temperatures will persist through the period. && Long term /Friday through Monday/... as of 245 am EDT Tuesday...more prominent height falls are expected on Friday...with an eastern Continental U.S. Trough developing and lingering over the region through the weekend into early next week. The stalled boundary along the southern periphery of the area will allow deeper moisture to remain close by...but with some measure of drying arriving from the north Friday into Saturday. A decent north to S gradient of slight chance to solid chance probability of precipitation will be warranted both afternoons. Maximum temperatures will fall to or below climatology values. There is some potential for a weak disturbance in the NE Gulf of Mexico to get entrained into the trough and feed even better moisture northward through the Piedmont of the Carolinas Sunday through Monday. Will keep associated probability of precipitation fairly conservative in the chance category given the uncertainty...but continued cooler maximum temperatures looks more likely with no 90s expected anywhere in the County Warning Area Sunday to Monday. && Aviation /12z Tuesday through Saturday/... at kclt...recent satellite images and observations indicated widespread low clouds and patchy fog across the I-77 corridor. Forecast soundings and several MOS guidance indicates that MVFR ceilings may thicken one to two hours after sunrise...remaining through most of the morning. I will use a tempo during the 12z to 15z period...followed by a from group for bkn035 at 16z. Cams and persistence support a tempo between 19z to 23z for thunderstorms and rain. Winds should remain between 160-180 degrees around 5 kts through the period. Elsewhere...kavl and khky may see vlifr to LIFR conditions through middle morning. Elsewhere...MVFR ceilings may linger at kgsp and develop at kgmu during the early daylight hours. The afternoon approach of a weak middle level disturbance should yield a round of rain showers/thunderstorms and rain late this afternoon and evening. I will include a prob30 or tempo in each taf...generally between 20z to 24z. Mountain MVFR ceilings may redevelop late tonight...especially over areas that see rain this afternoon and evening. Outlook...a middle level ridge will remain across the western Carolinas through middle week. A longwave trough will amplify across the Atlantic state late in the week...with the likely passage of a cold front on Friday. The potential for convection will increase each day this week. Confidence table... 11-17z 17-23z 23-05z 05-06z kclt high 100% medium 60% high 100% high 100% kgsp high 100% medium 60% high 100% high 100% kavl medium 61% high 100% high 100% high 100% khky medium 78% medium 65% high 100% high 100% kgmu high 100% medium 60% 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...none. SC...none. && $$ Synopsis...hg near term...Ned short term...hg long term...hg aviation...Ned

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