Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 030259 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 959 PM EST Wed Dec 2 2020 .SYNOPSIS... A moderating high pressure area will be in control of our weather through Thursday. A low pressure system will cross the area this weekend. A return to cool and dry weather is expected next week. && .NEAR TERM /THROUGH THURSDAY/... Evening Update...Expect quiet conds overnight with temps cooling efficiently in a deeply dry and stable airmass. Current obs are running close to the fcst curve, so no changes will be made to min temps. Some mtn valley and lake fog is possible arnd daybreak, other than that most areas will remain fog free. Quiet weather continues into Thursday. A closed low that was dropping into the Southern Plains will be come elongated while drifting our general direction. Weak surface high pressure will settle into the area tonight supporting nearly ideal radiational cooling conditions with the dry air in place, light winds and mostly clear skies. Have under model guidance a bit for overnight lows as a result, yielding lows generally in the 20s. These conditions may also be favorable for lake fog development. Added a fog mention for now for larger lakes, although dense fog may also be possible. West southwest flow aloft Thursday associated with a progressive short-wave ridge will shut off any lingering cold air advection atop the region, allowing temperatures to continue to rebound, with near normal high temperatures well into the 50s. Mid to high level clouds will increase from the west in earnest through the afternoon, perhaps curtailing putting a lid on afternoon heating for far western areas. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... As of 200 pm Wednesday: Model guidance continues to exhibit improving agreement regarding southern stream upper low that is expected to begin wobbling east from the southern Great Plains near the start of the short term period. It is looking increasingly likely that this feature will accelerate across the lower Miss and TN Valleys in response to a digging northern stream wave Friday through early Saturday, possibly phasing into the northern stream before it moves off the Mid-Atlantic coast late in the period. With this evolution, cyclogenesis is expected across the inland Southeast Friday, with surface low likely tracking quickly from the Deep South through the Carolinas late Friday through early Saturday. This will place the best deep layer forcing and moisture profiles very close to our CWA, warranting increasing pops beginning around daybreak Friday, reaching categorical by late Friday evening. Based upon the forecast track of the cyclone center across, or very close to the CWA, it will be a struggle for the warm sector air mass to make significant headway into the forecast area, and as such, instability will be weak to non-existent, with what little there will be likely confined to the far southern periphery of the CWA. Having said that, there will be a non-zero threat of high shear/low CAPE severe convection in that area Fri night. The absence of instability along with quick movement of the system should result in respectable, but hardly excessive rainfall, with most locales likely seeing .5-1.0 inch. As the cyclone becomes increasingly wrapped up as it moves away from the area, cold advection and lingering moisture from the TN Valley into the southern Appalachians should result in at least a brief period of northwest flow snow showers on Saturday morning, with minor accums appearing to be a possibility across the higher elevations near the TN border. Max temps will be near to a little below normal, and mins a little above normal through the period. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 220 pm Wednesday: A rather complex/split upper air flow pattern will persist through the medium range, with troughing generally predominating over the East. As such, temps are forecast to be a handful of degrees below normal through the period. Dry conditions will predominate, although a very potent clipper system/ upper low is forecast to dig well into the Southeast on Monday. This will undoubtedly bring another round of northwest flow rain/snow showers to the mountains. Interestingly, because they are digging the trough so far to the south, with the speed max actually passing south of the forecast area based on some solutions, the global models are beginning to depict some precip breaking containment into the Piedmont and foothills Mon afternoon/evening. IF this were to happen, p-type east of the high terrain could be very interesting, as it appears mid-level thickness values would be more than adequate for frozen precip. For now, we are opting to continue a dry forecast for much of the area Mon/Mon night. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... At KCLT and elsewhere: VFR conds will continue thru the period over all sites. Strong and deeply dry hipres will build across the fcst area and make for steep sfc-based inversions overnight, however, any fog development will likely be held to areas near lakes and a few valley drainage locales. KAVL should maintain VFR VSBY. Winds go calm overnight, then setup after inversion mixes out to weak s/ly to se/ly across the non mtns and nw/ly at KAVL. Outlook: VFR conditions will prevail until the next system approaches the area Thursday night into Friday. Confidence Table... 03-09Z 09-15Z 15-21Z 21-00Z 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 are available at the following link: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...JDL NEAR TERM...Munroe/SBK SHORT TERM...JDL LONG TERM...JDL AVIATION...SBK is the U.S. government's official web portal to all federal, state and local government web resources and services.