Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 210158 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 958 PM EDT Fri Apr 20 2018 .SYNOPSIS...
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Continental polar high pressure will extend across the middle Atlantic states through the weekend.
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&& .NEAR TERM /TONIGHT/...
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As of 955 PM Friday... A longwave ridge over the MS Valley this evening will build slowly ewd tonight, with associated dry nwly flow and height rises aloft forecast over cntl NC. At the surface, a parent 1032 mb ridge centered over the Great Lakes will continue to extend sewd across the middle Atlantic states and Carolinas, with a lee trough in the immediate lee of the cntl and srn Appalachians again separating this parent high from a smaller/ weaker ridge centered along the VA/NC coast. Surface winds went calm in most areas after sunset, with resultant radiational cooling occurring much earlier than last night. This associated calm, and mostly clear owing to only thin cirrus evident in satellite imagery in the aforementioned dry nwly flow aloft, will result in another cold night, with lows mostly in the middle 30s to around 40 degrees. However, lwr to middle 30s will be possible over the ne Piedmont and nrn Coastal Plain, in closest proximity to the surface ridge axis and low level thermal trough, and otherwise in the typically colder areas of the Piedmont (SCR, TDF, TTA). Patchy frost can be expected in those areas.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY/... As of 310 PM EDT Friday... Saturday through Sunday, sfc ridge will drift slowly east and lie just offshore by Saturday evening where it is forecast to stall through Sunday. This feature becoming stationary a result of confluent flow at 500mb over southern New England aiding to anchor the parent sfc high over that region. This stalled sfc high/ridge will aid to block/slow the eastward translation of moisture ahead of a deep upper level low projected to move from the southern Plains into the lower MS Valley. With the better moisture return expected to our south-southwest through Sunday, anticipating dry and seasonably cool conditions to persist across central NC through Sunday afternoon. Expect abundant sunshine Saturday, with a notable increase in high level cloudiness Saturday night into Sunday. The mid-high clouds Saturday night will be attributed to a minor disturbance passing across VA while the high clouds Sunday will be more closely tied to the upper level well to our southwest. Temperatures through the period will remain seasonably cool for late April. Highs Saturday should average in the mid-upper 60s, about 3 degrees warmer than highs expected this afternoon. Comparable temperatures expected Sunday as the thickening high clouds will deter warming, especially in the afternoon. If thicker clouds are slow to arrive, potential for high temperatures Sunday to be a couple of degrees warmer forecast. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... As of 245 PM EDT Friday... ...Unsettled weather for the first half of next week... Upper low over the Deep South Monday morning will begin to gain some latitude Monday night and Tuesday, lifting slowly NNE into the southern Appalachians before eventually becoming absorbed by the kicker shortwave trough diving east/southeast through the central and eastern US. Owing to the slow movement of the upper low across the region, along with early depictions of a very strong Atlantic maritime feed into the area, central NC has the potential to see a widespread soaking of 1 to 2 inches, with localized higher amounts possible, across central NC Monday through Tuesday night. With area rivers and creeks running high from recent heavy rainfall over the past week, this additional rainfall may be enough to result in some localized/minor flooding. Meanwhile, the severe threat at this time,appears to be low with much of the forecast area expected to stay in the cool stable low-level NELY flow, north/northwest of the surface low as it tracks along the coast. If future model runs trend farther inland/westward with the track of the low, there will be a greater convective threat across eastern/southeastern portions of the forecast area. Rain chances should decrease on Wednesday, but the approach of the aforementioned shortwave trough into the eastern US, followed by yet another shortwave trough dropping southeast into the region will support scattered showers through Thursday. Insitu CAD in place east of the mountains, along with widespread rain and extensive cloud cover will hold temperatures down into 60s Monday and Tuesday, with it definitely plausible that highs Tuesday across the the heart of the damming region across the NW Piedmont, could struggle to climb out of 50s. Although rain chances should decrease significantly on Wednesday, without a well-defined mechanism to erode the lingering low-level wedge/low clouds, temperatures could be slow to recover/moderate through the remainder of the work week. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... As of 825 PM Friday... 24 Hour TAF Period: VFR conditions are expected to continue through the 24 hour TAF period, high confidence. Surface high pressure will continue to extend into the area from the north through Saturday resulting in mostly clear/mostly sunny skies and calm to light and variable winds. Outlook: An approaching low pressure system early next week will increase the threat for sub VFR ceilings and MVFR/IFR visibilities due to rain and/or fog persist across central NC. The threat for adverse aviation conditions appears greatest from late Monday through Wednesday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...WSS LONG TERM...CBL AVIATION...BSD/WSS

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