Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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021 FXUS62 KRAH 051801 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 201 PM EDT Wed Jun 5 2024 .SYNOPSIS... A series of mid-level disturbances will move east and interact with an unseasonably moist airmass over NC through Thursday. A pre- frontal trough and cold front will move across the area Thursday evening through early Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 1100 AM Wednesday... Forecast seems to be on track, thus no major updates needed with the morning update. Adjusted PoPs slightly to blend in the latest Hi-Res guidance which kept the NW Piedmont in a slight chance for the rest of the morning and then increasing to chance PoPs for areas along and west of the US1 corridor. Scattered showers and storms are expected to be pulse-type again today with the best chance for storms over the western and northern Piedmont regions. The Coastal Plain could also see some showers and storms but the timing would most likely be later in the evening. Highs temps today are on track to be in the low to mid 80s NW to upper 80s SE with a few of the hot spots hitting 90 degrees. As of 420 AM Wednesday... Although it will again be seasonably hot, with above average chances of showers/storms, confidence in timing, coverage, and intensity of that convection remains low. The basal portion of a synoptic trough, now stretching from a cyclone over the cntl SK/MB border ssewd through the upr/mid MS Valley then swwd into the srn Plains, will move ewd in positive tilt fashion and reach the cntl/srn Appalachians and TN Valley by 12Z Thu. Preceding that trough and more influential for cntl NC this period, a couple convectively-generated mid-level troughs and vorticity centers/MCVs will move generally enewd across the Middle and South Atlantic states. The first/lead one stretched this morning from a well-defined MCV over ern KY ssewd across the w-cntl Carolinas and should move ewd across cntl NC through early this afternoon. The second, centered over the TN Valley and which includes a couple of equally as prominent MCVS over wrn TN and w- cntl AL, should extend from the OH Valley to the srn Appalachians by this evening and move across the srn Middle Atlantic and Carolinas overnight. Net, ~20-30 meter mid-level height falls will become maximized over cntl NC tonight. Upstream VWP data this morning depict modest, 25-35 kts of 700-500 mb mb flow centered over the TN Valley; and this enhanced flow should move downstream and across the srn Middle Atlantic/Carolinas later today and tonight. At the surface, high pressure will persist and extend from near and south of Bermuda wwd and across the South Atlantic states, while a differential heating zone preceding the lead mid-level vorticity lobe and associated cloud canopy, and a loosely-organized outflow boundary from related rain/storms ongoing from the wrn NC Piedmont swd into ern GA, will move east across cntl NC through early this afternoon. Given generally poor representation of the ongoing convection in CAMs, generally non-existent in the HRRR, it remains unclear to what degree this ongoing convection now moving across the srn and wrn NC Piedmont will be maintained or intensity as it moves ewd through the morning and early afternoon, and subsequently how unstable the environment over cntl NC will be ahead of the trailing mid-level trough/MCVs later this afternoon-tonight. It seems plausible that this convection will increase in intensity as it, and its associated differential heating zone and frontal-like circulation, encounters a partly sunny and quickly, diurnally-destabilizing environment over the NC Sandhills and Coastal Plain through early afternoon, with a secondary instability maximum developing in its wake today over the srn and wrn Piedmont and ahead of the trailing mid-level trough. The relative greatest coverage and intensity of convection would then be maximized over those wrn counties this evening. On the other hand, the CAMs generally depict little coverage with this lead, ongoing activity and dissipates that which it is initialized, and instead tends to focus scattered to locally numerous showers/storms over the wrn half of cntl NC this evening, with very little in the ern Sandhills and Coastal Plain. Regardless, the aforementioned modest, wly/wswly mid-level flow will favor clustering and preferential multi-cell development on the ern flank of outflow, with an associated risk of strong to severe outflow wind gusts. It should otherwise be persistently hot in the mid 80s to around 90 F ahead of the differential heating zone, and up to several degrees cooler to its west (ie. most likely the srn/wrn Piedmont and perhaps wrn Sandhills). Given the uncertainties in convective evolution described above, a broad, slight to low chance of convection will be maintained overnight, with low temperatures again in mainly the mid-upr 60s. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 300 AM Wednesday... A surface low will be north of the Great Lakes Thursday morning with a cold front arcing southeast towards Buffalo, then curving back to the southwest across Tennessee and into Texas. This front will be the primary weather maker on Thursday, bringing showers and thunderstorms to the region. The established air mass over the region has plenty of moisture, and CAPE values should range between 1000-2000 J/kg. Effective bulk shear does not appear to be too strong, but could be strong enough to provide a little bit of organized convection along the front. Frontal timing should be late afternoon/early evening, with the bulk of the rain moving through by sunset. Considering the timing of the front, reduced high temperatures across the Triad which should have the thunderstorms moving through before peak heating, keeping highs in the low 80s. Elsewhere, highs should range from the mid 80s to the low 90s. The cold front will not bring much of a change in air mass, so another night of low temperatures in the 60s and low 70s is forecast Thursday night. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 200 PM Wednesday... Friday and Saturday: Aloft, an upper low will meander slowly eastward through southern Ontario/southern Quebec, Canada Fri and Sat. The attendant trough will progress eastward through the East Coast states Fri as a s/w passes over central NC within the trough. The trough will continue offshore Fri night. Nearly zonal flow should prevail Sat/Sat night, with a weak s/w or two passing overhead. At the surface, the cold front should be through central NC Fri morning and continue eastward offshore through the aft/eve. Cool high pressure centered just west of the southern Appalachians will ridge eastward into the area Fri night. A trough may develop over the area Sat and amplify Sat night, while the high weakens. For now the forecast remains dry. Highs Fri ranging from low/mid 80s NW to mid/upper 80s SE, with lows ranging from mid 50s north to mid 60s south. Temps should be similar Sat/Sat night, highs a degree or two lower and lows a couple/few degrees higher in some spots. Sunday onward: There is still some uncertainty in this part of the forecast, so confidence is on the low side. Aloft, as the parent low swings through Quebec, Canada and the Northeast US a potent s/w will drop south out of central Canada, through the northern Plains/upper MS Valley Sat night/Sun, then continue around the parent low through the Great Lakes/OH Valley Sun, amplifying the attendant trough in the process. As the low lifts northward Sun night/Mon, the trough should swing eastward into (GFS)/toward (ECMWF) the mid-Atlantic. The s/w should move through central NC Mon night or Tue/Tue night. At the surface, with the trough over central NC, a warm front may briefly lift through the area Sun aft/eve, before another cold front pushes through the area Sun eve/night. The front should stay east of the area, with high pressure over the Plains/MS Valley through Mon night. Beyond that, the medium-range guidance varies greatly, with the ECMWF showing a low tracking along the Southeast US/Carolina coast Mon night and Tue, while the GFS slowly develops a westward retreating, inverted coastal trough Tue/Wed. The best chances for showers/storms will largely be tied to the initial s/w sometime between Sun eve and Mon night. Additional showers/storms will be possible through mid-week, but confidence is low at this time. Temperatures should be within a category or two of normal. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 200 PM Wednesday... MVFR conditions have lingered in the NW Piedmont for most of the day and expected to become VFR later this afternoon. Although VFR conditions may not last very long at the NWern terminals as isolated to scattered thunderstorms could produce sub VFR conditions at anytime. While the rest of the terminals are currently VFR, Hi-Res models do suggest that a period or two of TSRA could be in the vicinity of the terminals through the afternoon and early evening. Generally ceiling are expected to be 2k ft in the NW and 3k to 4k feet elsewhere overnight before another round of low stratus develops over much of the region. Conditions are expected to improve by mid morning to VFR conditions before the next chance of storms move into the area ahead of an advancing frontal passage. Outlook: Showers and storms associated with a cold front that is expected to come through the region late Thursday will result in flight restrictions of MVFR or lower in some areas. VFR conditions are expected to return Friday through the weekend before another disturbance moves into the region early next week. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...Green LONG TERM...KC AVIATION...CA