Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 170811 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 311 AM EST Sun Nov 17 2019 .SYNOPSIS... A deep low pressure system will lift away from the Carolina coast today. A couple of weak cold fronts will move through the area Monday and Tuesday but temperatures will gradually warm Wednesday and Thursday ahead of the next cold front expected late in the week. && .NEAR TERM /THROUGH TONIGHT/... As of 230 AM: A coastal low will continue to slowly drift east off the Carolina coast today, as a shortwave upper ridge builds in ahead of an approaching deep trough to our west. Moist NELY low-level flow is maintaining/expanding a stratocu deck, and it may be stubborn to scatter out due to a fairly strong inversion in the 850-700 mb layer. The NAM is much more bullish on this cloud cover (and so far is the closest to reality). So have blended in the NAM and keep a little more cloud cover today, especially across the south and eastern zones. This, in combination with ongoing low-level CAA, should keep max temps below normal today, especially east. Fortunately, the pressure gradient is relaxing with the departing low, so it shouldn`t be as breezy as yesterday. Tonight, a deep H5 trough will enter the OH/TN valleys and pivot into a negative tilt. This will provide strong mid to upper level forcing atop the forecast area. The thinking over the last few days has been for this wave to have little moisture to work with. Overall, model trends are for a little more moisture and possibly some light precip being able to break out late tonight. The 00z NAM looks overdone, but has some support from the SREF and ECMWF. Meanwhile, the GFS is still dry. So have introduced a slight chc of light rain across most of the area (best chances will be along and south of I-85). Even with this trend, I think most people will see a trace of precip, if anything. Temps were bumped up tonight a category or so, due to the expected increase in cloud cover (Lows near to slightly above normal). && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 225 AM EST Sunday: The guidance continues to differ with the strength, location, and resulting precip associated with two short waves rotating through the longwave trough over the eastern CONUS. The NAM has trended toward the ECMWF, which has been consistent with its last three runs, of bringing some light showers across the area Monday morning. The GFS is dry while the SREF has some precip. Therefore, have added slight chance PoP to the southern and eastern sections of the CWFA Monday. Dry conditions return Monday night as the first short wave moves east. Some of the guidance shows light precip Tuesday with the second short wave, however they continue to differ from run to run. Have kept the forecast dry for now until some consistency develops. Highs will be around 5 degrees below normal both days, with lows a few degrees below normal. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 245 AM EST Sunday: Guidance in good agreement early as short wave ridge moves over on Wednesday keeping a dry forecast in place and temps near normal. The guidance is now trending toward better agreement for the rest of period. Zonal flow develops Thursday as a northern stream short wave moves into the Upper Midwest. The GFS is trending toward the ECMWF and not phasing this wave with an upper low over the Four Corners region. That said, the GFS is still faster than the ECMWF in moving the northern stream short wave east across the Great Lakes into Quebec. The GFS is also faster moving the southwestern upper low into the area by Saturday. The ECMWF shows a similar trend but 12 to 24 hours slower. At the surface, the cold front associated with these systems moves toward the area Thursday and into the area Friday. The GFS brings the trailing surface low into the area Saturday with little break between the initial frontal precip and precip with the low. The ECMWF shows a break in the precip Friday night and a slower onset Saturday as the trailing low moves slower. As usual, went with a model blend due to these differences. This limits chance PoP to mainly the mountains late Thursday into Friday and the western CWFA on Saturday. Slight chance PoP is featured elsewhere. Temps go above normal Thursday, remain nearly steady Friday, then drop to a little below normal Saturday. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... For KCLT and elsewhere: A coastal low will slowly drift further east off the Carolina coast today, but lingering low-VFR cigs expected thru the morning. Guidance is mixed on how much dry air filters in from the north this aftn, but overall, expect most of the cigs to scatter out today. An increase in low clouds is expected this evening ahead of an approaching cold front. Depending on how much moisture there is to work with, spotty light rain may develop overnight, but confidence is low. Otherwise, NE winds should remain gusty thru late morning at KCLT, then become light this aftn and somewhat variable this evening. Outlook: Brief low cigs possible early Monday with the passage of a mainly dry front. The dry high pressure dominate the region for most of the work week, resulting in VFR conditions. Confidence Table... 08-14Z 14-20Z 20-02Z 02-06Z KCLT High 98% High 97% 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 97% 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: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...RWH NEAR TERM...ARK SHORT TERM...RWH LONG TERM...RWH AVIATION...ARK

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