448 FXUS62 KGSP 131450 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 950 AM EST Mon Jan 13 2020 .SYNOPSIS... A wet and unsettled weather pattern returns for the first half of the work week. Cooler and drier high pressure will spread back over the area for Thursday and Friday, with another wet system arriving on Saturday. && .NEAR TERM /THROUGH TONIGHT/... As of 945 AM: Showers have been more widespread across the area this morning, some with heavy rainfall, especially across the southern CWFA border. There have even been a few thunderstorms, with good muCAPE across the area. Therefore, have expanded the categorical PoP to cover most of the area outside of the TN border counties where showers will be more spotty. Have upped QPF across portions of the area as well. Will need to consider a Flood Watch for the afternoon update. Have adjusted highs some based on current temps. Otherwise, rather diffuse, slow-moving warm front currently extends from central GA through the Carolina Piedmont. The 00Z MHX Raob, which appears to have sampled the associated deep moisture plume well, sported a PWAT of 1.5", which is very near the daily maximum (per SPC sounding climatology), and is about where the PWAT typically is during the dog days of late July/early August. Add in a little increasing upper divergence per the latest short term guidance, some (mostly) elevated instability, and it's no surprise that convection remains widespread from central GA through the SC Piedmont this morning. Hourly rainfall rates of .25-.5 inch, with locally higher amounts have been common, especially from central Georgia into the lower SC Piedmont and as much as 3 inches of rain has fallen across portions of this area since midnight, confirming that the ingredients are in place for heavy, and perhaps locally excessive rainfall, with rather high training potential along the slowly retreating boundary. However, as convection has pushed farther north into the forecast area, further displaced from higher elevated instability, rainfall rates have continued to show a tendency to diminish. Thus, while there appears to be a gradually ramping-up excessive rainfall concern across our lower Piedmont (mainly Greenwood County), the remainder of the southeast half of our forecast area will see just a soaking rain this morning. That may change later today into this afternoon and evening as elevated instability makes a little more inroads. It is also not clear how much northward progress the boundary and associated moisture plume will make throughout the day, and any stalling of the front/slowing of the northward progress of the ongoing convection will only enhance the training potential. Needless to say, confidence in QPF is lower than normal, and that leads us to the elephant in the room, which is the very high qpf offered by the NAM: (a large swath of 4.5 to 5.5 inches across the SC and GA Piedmont by the end of Tuesday. In a way, the NAM has shown some run-to-run consistency in these amounts. However, it has not been consistent in the placement, nor has it been consistent in the timing. For instance, the 00Z run suggested today would be the time frame for the heaviest rainfall, the new 06Z run more of a late tonight and Tuesday event. Additionally, The NAM has also depicted similar rainfall swaths during prior rainfall events this cool season, with limited success at best. As such, the NAM's qpf has been disregarded, but it can probably be considered as another stark reminder that the potential for localized excessive rainfall exists. Otherwise, likely-to-categorical pops spread slowly north throughout the day and into tonight, with the highest probs becoming increasingly focused across the mountains and the northern zones by the end of the period. Total qpf during the near term period ranges from around 2 inches across the lower SC Piedmont, to 1-1.5 inches across the I-85 corridor, to around one half inch across the northern zones, but again confidence in these amounts is low and locally higher amounts are likely, with excessive rainfall possible esp across the SC Piedmont. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 325 AM Monday: the short-term fcst picks up at 12z on Tuesday with flat upper ridging still in place and centered to our SE. Over the next 24 to 48 hrs, the center of the upper ridge will gradually shift westward and end up over the Gulf of Mexico by the end of the period 12z Thursday. At the surface, a rather poorly defined moist, baroclinic zone will be in place over the Southeast as we begin the period and is expected to linger over the region thru most of the short-term period. At this point, it's still difficult to have much confidence wrt the specifics of the flooding threat. Locally heavy rain is still the main concern with the deep bndy-parallel flow and elevated PWAT values. This along with elevated instability over much of the CWFA on Tues and Wed could certainly enhance rain rates. For Tues and Wed, the area of greatest QPF is still over the far western and southern mtns, with just over 2 inches expected for most of that region. With the poor run-to-run consistency among the models (especially the operational NAM), storm total QPF amounts could change appreciably over the next few fcst cycles. Otherwise, temps will remain well above normal thru the period with highs approaching 70 degrees for most of the lower terrain. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 305 AM Monday: the extended forecast picks up at 12z on Thursday with flat upper ridging still in place over the Southeast as a broad, low amplitude upper trof moves east of the Great Lakes. The trof is expected to amplify as it moves over New England and then offshore. As it does, upper ridging will briefly amplify over the Eastern CONUS on Friday. The upper pattern remains progressive as we go into the weekend, with another upper trof moving across the Central CONUS early Sat. The latest long-range guidance has the trof lifting just to our north late Sat, and eventually off the New England Coast on Sunday. In its wake, the pattern flattens out over our area as the period ends. At the sfc, a low pressure system and its associated cold front will be moving into the fcst area from the west as the period begins late Wed. Behind the front, strong Canadian high pressure will push into the area on Thursday bringing cooler and drier air to the CWFA. Much like the upper pattern, the sfc pattern will remain progressive for the rest of the period. On Friday, the high will quickly move eastward setting up a brief, wedge-like pattern over the Carolinas. At the same time, a powerful low will eject out of the Plains and bring a strong cold front to our doorstep on Sat. The front is expected to push thru the CWFA quickly on Sat and move offshore by early Sunday with cold and dry high pressure spreading over the area in its wake. Temperatures start out well-above normal on Thurs and cool to just above normal for Fri. They warm again briefly on Sat and then cool to below climatology by early next week. && .AVIATION /15Z MONDAY THROUGH FRIDAY/... At KCLT and elsewhere: A warm front will continue to lift slowly north across the terminal forecast area (TFA) through the period. IFR/LIFR cigs will persist/redevelop near the front at KCLT/KAND and continue through much of the period, eventually spreading to the other terminals during the afternoon and evening (other than tempos for brief IFR this morning at KGMU/KGSP). In the interim, convection (mainly heavy rain showers, but with isolated/widely sct TSRA as well) continues to impact locations roughly along and south of a line from KAND->KGSP->KCLT, and this is forecast to continue lifting slowly across the TFA through the day. In general...where it's already raining, it's not going to stop anytime soon, and TAF precip trends are handled with categorical 6SM/-SHRA through the entire forecast period with tempos for lower visby this morning. At KAVL/KHKY, a 3-4 hour tempo window prior to arrival of categorical -SHRA this afternoon, followed by categorical -SHRA this evening. As far as the thunder potential, at least isolated TSRA is are expected near the SC terminals and KCLT, esp this morning, but based upon current radar trends, we opted to leave out a mention at this time. Outlook: Moisture, precip, and associated restrictions will persist through much of the work week. Brief period of dry weather may occur on Thursday into Friday. Confidence Table... 15-21Z 21-03Z 03-09Z 09-12Z KCLT Med 70% Med 61% High 83% High 81% KGSP Med 65% Low 51% Med 66% High 81% KAVL High 100% High 95% Med 71% High 84% KHKY High 81% Med 76% Med 66% High 83% KGMU Med 78% Low 51% Med 71% High 88% KAND Med 71% Low 45% Med 70% High 84% 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...JPT NEAR TERM...JDL/RWH SHORT TERM...JPT LONG TERM...JPT AVIATION...JDL