218 FXUS62 KRAH 232046 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 346 PM EST Thu Jan 23 2020 .SYNOPSIS... High pressure will continue to extend across the middle Atlantic and Carolinas tonight. A wave of low pressure will then develop northeastward across the Carolinas, along a retreating wedge front, Fri and early Fri night, then off the middle Atlantic coast early Sat. && .NEAR TERM /TONIGHT/... As of 340 PM Thursday... Earlier, considerable mid-high level cloudiness/overcast will continue to thin and lead to a brightening sky through sunset, behind a srn stream shortwave trough now crossing the Carolinas. Upstream, another shortwave trough, now evident in wv imagery over the lwr MS Valley, will pivot newd across the TN Valley and srn Appalachians tonight, with related weak height falls (10-30 m) and forcing for ascent that will overspread the wrn Carolinas late tonight-Fri morning. Much stronger and focused forcing for ascent will remain west of the Appalachians, associated with and preceding a mid-upr low forecast to deepen while digging from cntl KS this afternoon to sern MO/nrn AR by 12Z Fri. The associated low level mass response related to these features above will result in the strengthening of a low level jet and maximum of warm, moist advection analyzed over the lwr MS Valley at 12Z, nwd into the wrn Carolinas through the 12Z Fri. At the surface, 1029 mb high pressure along and offshore the nrn middle Atlantic coast this afternoon will continue to extend swwd across the Carolinas tonight, while a 1012 mb low analyzed over ern LA/swrn MS at 20Z will migrate enewd into the TN Valley by 12Z Fri. After the aforementioned brief thinning of mid-high level overcast through early this evening, thickening and lowering clouds at that level will occur from the southwest overnight. Additionally, the development of the llj, moistening, and ascent, will promote the nwd development/expansion of low clouds into w-cntl NC after midnight. Temperatures will consequently fall most abruptly early this evening, steady or fall more slowly overnight, then begin to rise with the development/arrival of the low clouds late. Low temperatures generally in the mid 30s to around 40 degrees will result. A lead area of rain/showers will also accompany those low clouds, as that moistening and lift strengthen beneath deeper layer forcing and saturation accompanying the approaching shortwave trough aloft. A chance of rain will accordingly increase over the wrn half of cntl NC through Fri morning, with likely to categorical probabilities over the srn and wrn Piedmont by 12Z Fri. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... As of 425 AM Thursday... The strong mid level low is expected to wobble from SE MO to near Fort Wayne IN from early Fri through Fri night, bringing 100+ m height falls across the Ohio Valley and Appalachians. At the surface, the last vestiges of the high pressure ridge will be slowly eroded from the S and E within the increasing low level moisture advection resulting from the onshore-directed flow. But as the band of deeper forcing for ascent (including bouts of upper divergence associated with a strong jet core on the SE side of the low, deepening low level moist upglide accompanying a 40-50 kt southerly low level jet, and mid level DPVA) shifts into the Piedmont Fri within a surge of 1"+ PW, the resulting showers should help lock in the surface based stable layer over the NW Piedmont. These showers will move in ahead of and with the corresponding surface cold front which is expected to ease slowly into W NC Fri morning, crossing central NC late Fri afternoon through the evening and early overnight hours. Factoring in the models' slightly faster precip arrival and end in recent runs, expect pops to peak mid-late Fri afternoon in the W half and in the 00z-06z window E half, with pops tapering down and out W to E overnight. The highest precip amounts for this event should be over NW NC, where the strongest dynamics and deepest moisture line up, and we expect to see storm totals of 1- 2" in the Triad region ranging to one half to one inch elsewhere. Regarding thunder chances, models generally depict a few hundred J/kg of mostly elevated CAPE working into the warm sector over the Sandhills and central/southern Coastal Plain E to the coast, although a boundary to focus deep convection is lacking, and the best kinematics appear to track to our NW. Will including a few hours of an isolated thunder threat in the SE late in the day, but nothing approaching severe limits is anticipated. Temps will be tricky with expectations of a lingering stable pool in the NW, and as usual in events like these, the statistical guidance may not adequately capture the stable pool or the warm sector. Expect highs in the mid-upper 40s in the NW Piedmont including the Triad with the earlier precip arrival, while elsewhere, with WAA and the steady showers holding off until the afternoon, will have highs in the 50s to lower 60s. Lows from the upper 30s W (with precip ending overnight) to the upper 40s E. -GIH && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 245 PM Thursday... The occluded cyclone over the Great Lakes Saturday morning will continue to move slowly toward New England, with the trailing cold front pushing further off the east coast. The airmass change in its wake will be subtle, with mostly westerly tropospheric flow and weak high pressure migrating along the gulf coast. Another shortwave will dive south across the Southeast US by Monday, but the mean frontal zone will remain suppressed well to our south and limit the brief frontal interaction to FL, keeping NC dry and mostly cloud free. The next shortwave cross the central Rockies should reach the central US by Tuesday, but in split flow the medium range guidance has shown varying amplitudes with this wave, leading to below normal confidence in when it reaches NC or how much precip there will be. The outlying and more amplified ECWMF deterministic runs have trended toward a lower amplitude and more suppressed wave, which agrees a bit more with a loose model consensus, which would favor a faster and more southern track with precip Wednesday night into Thursday. Have adjusted POPs and temps to reflect slightly higher chances across the south and slightly cooler mid week temps, though still near normal, which will be the trend for most of the week as highs each day should be in the 50s (overnight lows in the 30s). && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... As of 220 PM Thursday... Initially VFR conditions, under the influence of lingering, chilly and dry high pressure, will yield to the development and newd expansion of MVFR ceilings tonight. Those ceilings will subsequently lower into IFR-LIFR range Fri morning, at which time a lead area of rain/showers is forecast to overspread the wrn NC Piedmont, including INT/GSO. While resultant well-entrenched cold air damming and continued LIFR overcast and drizzle or light rain will persist throughout the TAF period there, along with the development/ occurrence of low level wind shear after 14Z, mainly dry conditions and lifting and scattering through MVFR range will be likely across the remainder of cntl NC through early Fri afternoon - first and most likely at FAY and RWI. Outlook: A band of heavy showers will strengthen and approach slowly from the southwest late Fri, before edging ewd across cntl NC TAF sites in the several hours centered around 23-00Z at INT/GSO, 03Z- 05Z at RDU and FAY, and 06-07Z at RWI, respectively. An embedded thunderstorm will also be possible, primarily at FAY and RWI. Otherwise, clearing/drying behind the band of showers will promote the development of areas of fog and continued low overcast mainly at Piedmont sites overnight-early Sat, with following VFR conditions Sat through early to mid next week. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM..Hartfield LONG TERM...BS AVIATION...MWS