196 FXUS62 KRAH 232313 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 610 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 PM Thursday... A closed mid-upr low initially over sern MO/nern AR at 12Z Fri will wobble newd across IL/IN, to srn MI, by 12Z Sat. Mostly shear vorticity in nnwly flow from that low, nnwwd across the nrn High Plains and srn SK, will stream around the base of the low will overspread the srn Appalachians and wrn Carolinas Fri night, with related strong height falls (50-100 m)/forcing for ascent focused there between 06-12Z Sat. At the surface, an occluding low will track well west of the Appalachians, generally beneath the mid-upr low, Fri-Fri night, while a triple point low will develop around the srn rim of the Appalachians from n-cntl GA newd across the cntl Carolinas and srn middle Atlantic. That latter feature will track along a retreating wedge front, resulting from in-situ cold air damming over the Piedmont, owing to the initial presence of weakening high pressure and a related dry air ridge that will initially extend swwd across the Piedmont while drifting offshore. After the initial area of rain early in the day, deeper lift and saturation will pivot newd across the middle Atlantic with the passing shortwave trough now over the lwr MS Valley. As such, the majority of the day will be a mostly dry one away from the wrn Piedmont and heart of the in-situ CAD regime, where light rain and drizzle are likely to continue. The character of the rain will then transition from stratiform rain/drizzle over the wrn Piedmont during the day to increasingly showery/heavier character as warm conveyor belt convection/band of showers --along a confluent llj axis-- intensifies and shifts east across the region early Fri night. Individual convective elements will race nnewd (motion ~200/50kts) and briefly train within the parent band that will edge more slowly ewd. Locally heavy rain and minor flooding may result primarily in the urban/Triad region, where storm total amounts are expected to maximize beneath the aforementioned strongest large scale forcing for ascent, and along and west of the wedge front and triple point wave and low level lift, with around one and a half to one and three quarters inches there - most of which will fall in just 2-3 hrs. Rainfall amounts are forecast to range to just a quarter to half inch in the Coastal Plain. While surface theta-e advection will strengthen immediately preceding the triple point late Fri-early Fri night, it will be an incompletely modified, Arctic-origin airmass that plunged all the way through FL and into the Caribbean. As such, surface dewpoints are likely to climb only into the 40s over the wrn Piedmont to perhaps mid-upr 50s over the Sandhills and srn-cntl Coastal Plain, with limited buoyancy amidst weak low to mid-tropospheric lapse rates. The threat of thunder, even elevated, and severe potential, will consequently be very low. The theta-e advection will, however, result in some warming of surface temperatures and erosion of the preceding CAD, with highs expected to range from mid-upr 40s over the nw Piedmont to around 60-65F in our southeast zones. Lastly, areas of low overcast and fog --some dense-- will likely expand across the residual CAD regime over the Piedmont overnight, beneath clearing skies aloft. Both the heavy rain and dense fog potential have been highlighted in the HWO over the Piedmont. && .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 /00Z FRIDAY THROUGH TUESDAY/... As of 610 PM Thursday... The 00Z TAF period will start under VFR conditions with broken high clouds. MVFR ceilings will develop after midnight, with enough low- level moisture expected to allow for all locations to drop to IFR ceilings. Showers are expected in the Triad, with chance pops expected farther east. Cold air damming will help to keep low ceilings throughout the day, although IFR cigs should manage to rise up to MVFR levels by the afternoon. In addition, low level wind shear is expected to develop in the Triad by mid morning and continue through the afternoon hours. 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 00-01Z 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..MWS LONG TERM...BS AVIATION...Green