Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 270538 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1238 AM EST Sat Feb 27 2021 .SYNOPSIS... A front will remain stalled south of the region into Saturday as high pressure remains to the north. Gulf moisture will continue flowing north over the front through tonight. The boundary will retreat northward as a warm front through Sunday, with warmer temperatures gradually returning. Another cold front will cross the area from the northwest Sunday night through Monday with abundant moisture. Brief drying is expected Monday night into Tuesday before unsettled weather likely returns to the region through the middle of the week. && .NEAR TERM /THROUGH TODAY/...
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1230 AM Update...No sigfnt changes made to the fcst as the atmos remains fairly steady state with low clouds and weak winds. Periods of IP are persisting across the NC piedmont and foothills with little to no accum over the next few hrs as temps remain in the mid to upper 30s. As of 1000 PM Friday: Rain is still ongoing across much of the cwa, with parts of the southern tier gradually drying out. In coordination with WFO RNK, decided it was best to expire the Advisory due to above freezing temperatures. Expect isentropic lift to allow ongoing precip along the wedge boundary into the overnight period. With the sfc high hovering off the New England coastline, the wedge is still holding strong across the cwa with winds steadily coming out of the N and NE. 850 mb winds are steadily coming out of the S to SW at around 40 kts, but will gradually help erode the wedge as a warm front lifts across the area from south to north overnight into early Saturday. Winds will likely veer to the S and SW tomorrow once the warm fropa occurs. This will set the area under the warm sector and thus, temperatures will rise 10+ degrees compared to today for Max T`s on Saturday as the WAA filters in. The southern stream energy aloft will lift to the north with the sfc low riding underneath as it moves across the lower MS and TN Valleys through the northeastern CONUS tonight into Saturday, which will lead to a much drier conditions compared to today. Cloud cover should remain strong, but a few peaks of sunshine can`t be ruled out during the day Saturday. Some lingering upslope showers should persist across the northern Blue Ridge and southern mountains, as well as the adjacent foothills on Saturday, but should remain mostly dry outside of those locations. Temperatures will remain above- normal for tonight as we stay socked in under cloudy skies, but should slowly rise during the overnight period due to the approaching warm front and eventual fropa. Tomorrow will remain above normal as most locations will end up in the 60s and 70s across much of the cwa for Max T`s tomorrow.
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&& .SHORT TERM /TONIGHT THROUGH MONDAY/... As of 200 pm Friday: The upper air pattern will remain more or less steady-state through the first half of the short term, with ridging persisting off the East Coast and a trough over the interior West, before a complex split flow pattern evolves late in the period. For our forecast area, this means deep SW flow will persist though much of the period, with a warm sector regime yielding well-above normal temps (maxes 10-15 degrees above climo, mins 15-20 degrees above), nocturnal low clouds, and low end shower chances. By Monday, a potent northern stream short wave trough will progress across southeast Canada and the northeast Conus, allowing frontal boundary to sag into the CWA, bringing likely to categorical probabilities of rain from late Sunday night into Monday morning. The latest guidance is in general agreement in depicting a well-forced frontal zones into the TN Valley and southern Appalachians which becomes less so as it sags southeast into the Piedmont. Meanwhile, short term guidance depicts barely >0 values of CAPE in the warm sector. As such, current indications are that any heavy rainfall potential will likely be confined to the NC mountains, while the severe wx threat appears minimal in light of decreasing forcing/unfavorable frontal orientation, very low instability and less than ideal shear parameters given the meager buoyancy. The front will likely sag south of the area by the end of Monday, yielding generally dry and cooler conditions heading into the extended. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 210 pm Friday: Forecast confidence is relatively high for roughly the first 24 hours of the extended range. After that, everything goes to pot in the anticipated complex split flow regime. There are essentially two model camps for the latter half of next week: the GFS camp and the ECMWF/Canadian camp. The latter camp is more potent with a mid-week southern stream disturbance, while the GFS is more sheared/out and suppressed. As such, the GFS is almost completely dry for our area during the Tue night/Wed time frame, while the other model camp develops the next round of widespread precip during this time frame. There`s enough of a signal there to advertise solid chance pops, but would like to see more of a consensus before going any higher than that. If precip does develop early enough Wed, there may be, as usual enough cold air in place to support a brief/low impact winter weather event across the mountains Wed morning. By Day 7, the GFS is more progressive and much stronger with a southern stream upper low originating from the Four Corners region...also maintaining a distinct split flow pattern while the ECMWF/Canadian camp begins to phase the flow be the end of the forecast period. As such, the GFS has a blockbuster storm system impacting the forecast area by next Friday, while the other camp is essentially dry. Again, there`s enough in the guidance to support a small pop, but 20-30% is as far as we`re willing to reach at this point. Temps are forecast to return to more sane levels during the medium range, generally within a category or so of climo through the period. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
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At KCLT and elsewhere: Low-end flight cats will continue or develop this morning across all TAF sites as a shallow sfc wedge begins to weaken and moisture levels remain high. Expect KCLT to remain IFR/LIFR thru late morning and introduced a TEMPO VLIFR aft 08z with light rain affecting the area and likely lowering CIGs. Conds improve slowly by the afternoon, with most sites going VFR, as hipres works across the OH Valley and mixes in llvl dry air. Northeasterly winds will switch to a sw/ly direction by mid morning as the sfc wedge continues to breakdown and the synoptic pattern favors an Atl ridge axis. Outlook: Scattered to numerous showers with associated flight restrictions are expected to return Sunday and linger into early next week. Drier hipres will build back into the area by Tuesday. Confidence Table... 05-11Z 11-17Z 17-23Z 23-00Z KCLT High 100% High 82% High 100% Med 75% KGSP High 100% High 100% High 94% High 85% KAVL High 100% High 100% Med 78% High 95% KHKY High 100% High 100% High 100% High 90% KGMU High 100% High 100% Med 78% High 90% KAND High 100% High 100% Med 72% High 90% 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: www.weather.gov/gsp/aviation
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&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...CAC/SBK SHORT TERM...JDL LONG TERM...JDL AVIATION...SBK

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