Scientific Forecaster Discussion

Area forecast discussion National Weather Service Greenville-Spartanburg SC 935 am EDT Wednesday Oct 1 2014 Synopsis... drier high pressure will linger over the region through Thursday. A strong cold front will then arrive from the northwest on Friday and move offshore by early Saturday. In the fronts wake...a cool and dry airmass will move back over the southeast and remain in place over the weekend. Another cold front will approach the southern appalachian region from the northwest on Tuesday. && Near term /through tonight/... as of 930 am...current satellite pics show patchy high clouds moving from west to east over the region. Some ac is noted...but soundings indicate that middle level inversion should cap off any deep convection. Therefore...will maintain a dry forecast. Made only minor adjustments to temperature/dp/wind fields. As of 630 am...a few patches of fog across the Piedmont...but the visibility trend has been upward over the last bit...even in the mountain valleys. The fog should dissipate quickly an hour or two after sunrise. The next 24 hours should be relatively quiet across the western Carolinas and northeast Georgia. An upper ridge will build overhead today and then the axis of the ridge will move eastward tonight as an upper low along the New England coast moves farther offshore. The ridge will support weak high pressure at the surface...and a fairly substantive subsidence inversion. The NAM in particular develops widely scattered showers this afternoon on the Blue Ridge and moves them east this the cap is broken over parts of the Piedmont. This seems unlikely and suspect the NAM surface dewpoints are too high as usual. Think the GFS/European model (ecmwf) have the right idea that the cap will be far too strong and that it will remain dry. Have removed all mention of showers for that reason. Temperatures should be a degree or two warmer than Tuesday. High pressure remains in control tonight with patchy fog possible again around daybreak Wednesday. && Short term /Thursday through Friday night/... as of 3 am Wednesday...on Thursday...a ridge of surface high pressure will remain across the region...under the axis of a 500 mb ridge. 850 mb temperatures are forecast to range from 16c across the mountains to 15c across the Piedmont. The combination of mild low level thicknesses and plentiful insolation should support high temperatures near 80 within the mountain valleys to middle 80s across the Piedmont. Forecast soundings indicate that a significant h65 inversion will linger through Thursday. A layer low level cin should remain through the day...capping surface based parcels. On Friday...a deep middle level closed low will track SW across the northern plains and western Great Lake region. South of the low...the axis of the middle level trough will dig east across the southeast region. At the surface...a strong cold front will push from middle Tennessee 12z Friday to the Carolina coast by 12z Saturday. Middle and upper level forcing will increase as a short wave and band of jet divergence crosses the southern Appalachians after 12z Saturday. The low level environment will feature convective available potential energy between 1000-1500 j/kg with helicity values between 50-100 m2/s2. This environment should support the daytime passage of a pre frontal band of convection across the high terrain. I will increase probability of precipitation to cate to high likely across the County Warning Area...especially Friday afternoon. Given the is possible that well organized qlcs could develop Friday afternoon or evening. However...the possibility of severe weather appears too limited to highlight in this mornings severe weather potential statement. Temperatures will be limited by thick clouds and rainfall...highs should remain around 5 degrees below normal. && Long term /Saturday through Tuesday/... as of 330 am Wednesday...on Saturday...strong 850 mb cold air advection will occur across the region...falling from 10c over avl at 6z to 3c by 12z. Low temperatures are forecast to range from the middle 40s across the high terrain to the middle 50s across the Piedmont. High temperatures will likely range 5 to 8 degrees below normal. Sunday should see the coolest temperatures of the period. The center surface high pressure is forecast to reach the Alabama/Georgia line by 12z Sunday. Conditions across the region will feature dry...calm...and limited sky cover. In addition...cold air advection may push 850 mb temperatures across the northern mountains from 0c to -1.5c. Sunday morning...mins in the middle 30s should be common across mountain ridges. Elsewhere....values are forecast to range in the middle to u40s. Early next week...the center of high pressure will push off the Carolina coast as another cold front approaches from the west. This pattern should advect warmer temperatures and moisture across the southern appalachian region. Temperatures will modify through the late extended period...return to near normal by Tuesday. In addition...I will mention developing widely scattered showers across the County Warning Area on Tuesday. && Aviation /14z Wednesday through Sunday/... at kclt...fog was noted across parts of the NC Piedmont as of issuance time...think that MVFR visibility will surround kclt and will probably be IFR/LIFR at outlying spots. However...think kclt will see at worst a brief MVFR visibility...but confidence not high enough to be included in the taf. Expect few/scattered stratocu with bases around 050 and a light S/SW wind bu midday. Kept those conditions through the end of the current period. Elsewhere...similar conditions as kclt...especially kgsp/kgmu. Kavl will see an upvalley wind during the morning and into the afternoon... becoming downvalley in the late afternoon and evening. Expect some Mountain Valley fog yet again early Thursday morning. Outlook...VFR still expected Thursday. A front will approach on Friday which could trigger some showers and thunderstorms...with associated restrictions it moves across the region Friday afternoon and night. VFR returns on Saturday through the rest of the weekend. Confidence table... 13-19z 19-01z 01-07z 07-13z kclt high 100% high 100% high 100% high 100% kgsp high 100% high 100% high 100% high 100% kavl high 88% high 100% high 100% medium 77% 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...none. SC...none. && $$ Synopsis...Ned near term...lg short term...Ned long term...Ned aviation...PM

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