Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201055 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 655 AM EDT SAT AUG 20 2016 .SYNOPSIS... An upper level trough and attendant cold front will approach the region from the west tonight, then progress east across the Mid- Atlantic and Carolinas Sunday into Sunday night. && .NEAR TERM /TODAY AND TONIGHT/... As of 330 AM Saturday... Expect similar conditions to yesterday given little overall change in the synoptic pattern, characterized by unidirectional flow aloft in advance of an upper level low expected to progress from the upper Midwest to the upper great lakes. Expect the location and coverage of convection to depend upon several factors including diurnal heating/destabilization, DPVA attendant small amplitude waves in unidirectional flow aloft, a NW-SE oriented PWAT gradient characterized by PWAT values ~1.80" in the Triad and 2.20" from the Triangle south and east, and a much drier H85 airmass in central/northern VA that could advect into portions of the N/NW Piedmont this afternoon via weak N/NE H85 flow. Should this occur, diurnal heating/mixing could result in a drier boundary layer, weaker destabilization, and lower chances for convection in the N/NW Piedmont. With the above in mind, expect the best potential for convection to remain from the Triangle south and east. Highs near 90F, lows in the lower 70s. Flow aloft (well aloft at H3-H4) will be strengthening Saturday aft/eve, however, with moderate destabilization expected, updraft depth/intensity should be insufficient to yield anything organization beyond that of multicellular. Weak DCAPE and weak mid-level lapse rates suggest sub- severe convection in general, with any isold/brief wet downburst potential smaller than the potential for locally heavy rainfall and isolated flash flooding, primarily from the Triangle south and east into the coastal plain. -Vincent && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 345 AM Saturday... Flow aloft will further strengthen Sun/Sun night as the aforementioned upper low progresses ENE into southern Canada and additional shortwave energy digging southeast through the central MS river valley amplifies an upper level trough over the OH valley and Great Lakes, and an attendant surface cold front approaches from the NW Sunday afternoon, progressing through central NC sunday evening/ night. Expect the best overall potential for convection this weekend to occur late Sunday afternoon through Sunday evening as the surface cold front /low-level trough/ progresses into the region in vicinity of peak heating in the presence of above normal moisture, marginal to moderate destabilization, and small amplitude waves embedded within relatively speedy westerly flow aloft. Deep moisture /cloud-cover/ and weak mid-level lapse rates may temper instability such that more favorable deep layer shear attendant stronger flow aloft may not be fully realized/capitalized upon by updrafts at this latitude. Weak DCAPE suggests weak cold pools, though ~20 kt westerly flow in the lower-levels may support upscale growth /downdraft consolidation/ and eastward propagation, perhaps evolving into a multicells line along/east of hwy 1 with an isolated potential for damaging winds via precip loading and downward momentum transport. Regardless, expect the best potential for convection in the late afternoon and evening, ending from west-east Sunday evening/night as the surface front low-level trough progress east toward the Carolina coast. Expect highs in the upper 80s to lower 90s and lows Sunday night driven by cold advection, ranging from the lower/mid 60s far NW to lower 70s far SE. -Vincent && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 245 AM Saturday... Surface high pressure will build into the area behind the cold front early next week, resulting in much lower afternoon humidity values and temps near to below normal along with dry weather. The surface high will slowly shift off the Mid-Atlantic coast mid to late week, allowing for moisture and temps to slowly increase. However, dry weather is generally expected to continue through the end of the workweek. High temps are expected to be in the 80s early to mid week, before increasing into the upper 80s to lower 90s by late week. Low temps will follow a similar trend, with lows generally in the 60s throughout the week though (with possibly a few 50s in the usual rural cool spots early to midweek). && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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As of 655 AM Saturday... 24-hr TAF period: Sub-VFR conditions associated with low ceilings will affect eastern terminals, primarily in the form of IFR/LIFR ceilings for several hours around sunrise. Otherwise, expect VFR conditions to prevail through the remainder of the morning, with sub- VFR conditions attendant scattered convection during the afternoon and evening hours. Looking ahead: Expect a continued potential for low ceilings Sunday morning (at all terminals), with an excellent chance for convection at all terminals Sunday aft/eve in association with a cold frontal passage. VFR conditions will return in the wake of the front Sunday night through mid next week. -Vincent
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...ND AVIATION...Vincent

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