Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250012 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 710 PM EST Fri Jan 24 2020 .SYNOPSIS... Low pressure will track across the west-central Carolinas to south- central VA this evening. A trailing cold front will sweep east across central and eastern NC through Sat morning. High pressure will then build from the lower MS Valley eastward across the Southeast through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 445 PM Friday... A closed mid-upr low centered over the cntl IL/IN border this afternoon will wobble newd into swrn MI by 12Z Sat. An elongated axis of vorticity around the base of the low, including an observed ~90 kt mid level jet at SHV and JAN at 12Z, will stream newd and overspread the srn Appalachians and wrn Carolinas tonight, with related strong height falls (60-120 m)/forcing for ascent focused over cntl NC between 06-12Z Sat. At the surface, an occluded low over the nrn IL/IN border at 21Z will move slowly nwd across Lake MI tonight, generally beneath the aforementioned mid-upr low. Meanwhile, an elongated, 1012 mb low along an in situ cold air damming/wedge front from Forsyth and Davie Co. sswwd across w-cntl SC and e-cntl GA, will consolidate while tracking newd across the wrn and nrn NC Piedmont, into s-cntl VA, through 06Z. The trailing cold front and elongated low will sweep ewd across cntl NC through 08-09Z. A strongly confluent llj and related band of convection across the w- cntl Carolinas and swrn VA, still entirely devoid of lightning at 2145Z, will intensify beneath the strengthening forcing aloft and low level frontogenesis, while shifting east across cntl NC tonight. Previous timing and intensity thoughts remain relatively unchanged - across the srn and wrn Piedmont through 02Z, the Sandhills and ne Piedmont between 03-06Z, and the Coastal Plain between 06-08Z. A shallow plume of modified EML, sampled in the 850-700 mb layer by the BRO RAOB last evening, has nosed from the nrn GOM newd into srn GA this afternoon, per both RAP-based (SPC) Mesoanalysis and GOES 16 wv satellite (7.3u) data. The models indicate this EML plume, and relatively steeper mid level lapse rates, will advect newd into the ern Carolinas roughly coincident with the foregoing convective line and contribute to mostly elevated instability of up to 500-750 J/kg of MUCAPE over the Sandhills and srn Coastal Plain between 03-06Z. And while low and deep layer shear will be strong, enhanced by the arrival of the exit region of the mid level speed max noted above, related convective organization/rotation will likely remain rooted above a shallow layer of stability near the surface. Nonetheless point forecast soundings suggest this stable layer will be sensitive to even subtle changes to surface theta-e, so surface-based (or nearly so) cells --and related surface wind hazards (e.g. damaging wind/isolated tornado)-- cannot be ruled out early tonight. This threat will be roughly from MEB to FAY to GSB and points south, where surface dewpoints are likely to maximize in the upr 50s to around 60 degrees and contribute to parcels rooted nearer the surface, with a relative minimum of CINH. Additional rainfall amounts are expected to range from around an inch over the nw Piedmont (where around a half an inch fell this morning), along the track of the surface wave and where deep forcing for ascent will be strongest and longest, to a half an inch in the srn and cntl Coastal Plain. Individual convective elements will race nnewd (motion ~200/45-50kts) and briefly train within the parent band that will edge more slowly ewd. Locally heavy rain and minor flooding may result, primarily in urban/areas, since the brunt of the rain will fall in just a couple of hours time. Lastly, areas of low overcast and fog --some dense-- may develop and expand from the Foothills to the Piedmont of NC overnight, beneath clearing skies aloft, with low temperatures mostly in the 40s. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 250 PM Friday... Sat: A closed mid-upr low will wobble newd across MI Sat, while a negative tilt trough at the base of the trough, initially over the Carolinas, will pivot off the middle Atlantic coast. Height rises will consequently overspread the srn Appalachians and Carolinas, with related subsidence, through 00Z Sun. At the surface, a cold front along the srn middle Atlantic coast at 12Z Sat will move offshore, while a lagging occluded front will cross the ne Piedmont and nrn Coastal Plain through 14Z. Appalachian- lee troughing will otherwise persist beneath cyclonic, wly flow aloft influenced by the features noted above. While there may be a few shallow showers along the occluded front during the morning, the day should be dry. Otherwise, after lingering low overcast and areas of fog focused over the srn Piedmont during the morning, a scattering of flat cumulus at the base of a developing subsidence inversion will yield partly to mostly sunny conditions - and mild ones, with high temperatures in the 50s, to near 60F in the Coastal Plain. Sat night through Sun night: Westerly flow and a brief period of cold advection will set in Saturday night, while modified high pressure migrates along the gulf coast. Broad westerly flow aloft and limited moisture between the exiting system and next in a series of shortwaves moving through the southern US will keep skies mostly clear Sunday. The airmass change behind the early weekend system is minimal, and LL thicknesses on Sunday support highs rebounding back in the lower 50s and near normal lows in the low to mid 30s Saturday and Sunday nights. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 250 PM Friday... The forecast for the upcoming week is fraught with uncertainty as low amplitude shortwaves move through a broader longwave trough before perhaps carving out a deeper longwave trough by next weekend. Early in the week a pair of shortwaves look to phase over TN valley to SE US on Monday, with weak cyclogenesis along the polar front across FL. However, models have trended stronger with the shortwave dynamics and have some qpf blossoming across the Carolinas, particularly near the arctic front which should lie across VA. Per forecast soundings most of the moisture is mid-level, but a period of showers are possible Monday afternoon. Have lowered highs a few degrees given the expected cloud cover and possible showers and virga as the shortwave passes overhead. The arctic front will trail on Monday night with temps falling into the upper 20s and lower 30s. Another shortwave is forecast to cross the region Wednesday/Thursday, but models have been all over the place with the amplitude of this wave and potential for precip. Most recent runs have been weaker with limited moisture, so will keep the forecast mostly dry with just a flight chance on Wednesday night. The ECWMF squeaks out a few hundredths of qpf, and thermal profiles are a bit cooler and supportive of frozen precip with the frontal zone to our south, but forcing and moisture look to be too limited at this time. Have kept temps mostly near normal in line with LL thicknesses around 1300-1310m, though Wednesday could be another cooler day given increase mid and high clouds. Finally the next and deeper system forecast for the weekend has the potential to bring more substantial rain with a digging trough and coastal low by Saturday. Forecast confidence is low at this time given run to run inconsistencies, but the signal is certainly there in the deterministic runs and GEFS/EPS means. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... As of 710 PM Friday... Restrictions have already developed at INT/GSO/FAY as a front moves into the region with showers and lower ceilings. A band of heavy showers with an isolated thunderstorm possible will move from west to east. Have included a tempo group for each terminal when the most intense rain is expected as well as the possibility of mixing down some stronger wind gusts. Once the rain departs the Triad, conditions should briefly rise to MVFR before IFR conditions become predominant until sunrise. At RDU, conditions should remain steady- state, MVFR, for a few hours after the rain. Meanwhile, FAY/RWI should both see conditions improve quickly after rain departs. All terminals are expected to return to VFR by 15Z, with clouds scattering out. Outlook: A passing mid to upper level disturbance will result in a chance of light showers and MVFR ceilings on Mon. Mainly VFR conditions are otherwise expected through mid next week. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS/BS LONG TERM...BS AVIATION...Green/MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.