Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 131734 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1235 PM EST Fri Jan 13 2017 .SYNOPSIS... A cold front will push south through the area this evening and overnight. Cool high pressure will briefly build in from the northeast on Saturday, followed by a secondary cold front on Sunday, and then another reinforcing high pressure Sunday night. && .NEAR TERM /THROUGH TONIGHT/... As of 1040 AM Friday... Main adjustments to the near term forecasts was to adjust max temps this afternoon up couple of degrees, and to mention a few sprinkles across the north late this morning. Strong sfc cold front orientated west/nw-east/se across southern VA poised to enter our northern coastal plain. Due to a fairly deep wly flow, the sfc front will initially have difficulty moving southward. However, expect a more substantial surge southward by early evening as an arctic high pressure over the Great Lakes moves east into southern New England and builds southward along the East Coast. With temperatures already close to forecast max temps across the far north-northeast, have raised max temps in this region into the mid 60s. These high temps will occur by early afternoon with falling temps anticipated during the mid-later afternoon as low level ne flow advects in the the much cooler air. Elsewhere, expect another afternoon with much above normal temperatures (on the order of 20-25 degrees above normal) as temps should range between 70-75, warmest across the southern Piedmont-Sandhills. Temps across the Triad region may need some adjustments downward due to the presence of a fairly solid deck of stratocu, inhibiting insolation. High temps more in the 62-65 degree range may occur here rather than upper 60s. ~WSS By all accounts the front and it`s low-level moisture will be through the area by 03Z, followed by a fairly substantial surge of dry air from the northeast below 3k ft, though moisture between 3k and 10k ft will keep skies overcast. The flow quickly veers to southeasterly in the low-level, and the induced isentropic lift should result some areas of light rain after midnight, focused mostly west of US 1 per hi-res WRFs. The combination of cold advection and evaporation cooling (across the Piedmont) will drive lows into the mid 30s to lower 40s. -SMITH && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... AS OF 350 AM Friday... High the parent high supporting the onset of CAD tonight will quickly shift offshore on Saturday, southerly low-level flow and light rain atop the cold dome should maintain the wedge airmass, especially across the north as the best isentropic lift shifts north throughout the day. Temperature recovery will be weak, and guidance is likely too warm with mid 40s to lower 50s, so will undercut statistical guidance and flavor a NAM-like temperature range of 40-49. The H9 flow will swing all the way around to westerly by Saturday night ahead of a secondary front moving into VA. Models indicate some drying above the boundary layer and even hint at some clearing of low clouds, but this seems overdone given that it`s overnight. Some low clouds should remain, and lows will be in the low to mid 40s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 400 AM Friday... Little change in overall forecast rationale during the medium range, in a pattern that local expertise can demonstrate significant value --and better accuracy-- versus national blended data sets. A shortwave trough will migrate through the base of a broad trough over central and Ern Canada, and off the NErn U.S., coast early Sun. Following height rises and subsidence will maintain strong, 1030- 1035 mb arctic surface high pressure over the Northeast and Middle Atlantic, whose leading edge will be marked by a cold front, now draped from the Great Lakes to the Central-Srn Plains, that will move SWwd through central NC during the Sun. Both low and mid level cloudiness, the former of which will become a widespread OVC in post- frontal NEly flow, will limit the degree of heating prior to frontal passage, which is forecast to occur during the morning in the NE Piedmont/Nrn Coastal Plain; midday to early aft in the Triad and Triangle; and late afternoon in the Sandhills and Srn Piedmont. Highs in the mid 40s NE to around 60 SW. Low level CAA will continue in earnest through the night Sun and day Mon, with a pronounced 1030 mb ridge over NC "overrun" --isentropically-- by warmer air just above the surface - a pattern that will promote stability and associated CAD that will be enhanced by widespread low OVC, and light rain/drizzle over the Wrn Piedmont. Some afternoon erosion of the low OVC may occur on the SE flank, typical in these patterns, but mid level ceilings even there will keep temperature from climbing much. As such, it will be a cool day, with highs in the 40s, to perhaps low to mid 50s in the S if low clouds indeed break. If not, 40s areawide. Guidance temperatures, and associated blended national data sets, have (not surprisingly) been steadily trending toward our cooler official forecast. A subtropical ridge will become increasingly amplified/dominant over the SErn U.S. during the middle of the week. While associated deep layer SWly flow will favor warming and increasingly humid conditions for January (surface Td`s in the 50s), the warming will be somewhat muted by both multi-layered cloudiness, and lingering in-situ CAD over the Wrn Piedmont through at least Tue. After a chance of drizzle or light rain along and behind the aforementioned backdoor cold front on Sun, which will continue within the heart of the wedge /low OVC/ over the Wrn Piedmont through Tue, the best chance of any appreciable precip --in the form of rain showers-- will be with the approach and eventual passage of a slow-moving cold front mid to late week. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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AS OF 1235 PM Friday... VFR conditions across central NC will gradually deteriorate northeast to southwest this afternoon and this evening as a strong cold front drops southward. Low level northeast flow will usher in a moist air mass, resulting in the formation of a stratus layer and associated MVFR/IFR ceilings. These adverse ceilings should be areawide by 03Z. An intrusion of drier air in the 1000-2500 ft layer may allow ceilings to lift temporarily into the VFR category at KRWI and possibly KRDU during the overnight hours before ceilings lower back to the IFR/MVFR categories by daybreak Saturday. Pockets of very light rain should develop over sections of the Piedmont this evening and persist into the overnight hours. This probability appears greatest in vicinity of the Triad terminals, and less so toward KFAY. In addition, a stout ne sfc wind will occasionally gusts between 18-23kts tonight. The patchy light rain will gradually diminish Saturday morning though widespread IFR/MVFR ceilings will linger Saturday and Saturday night. An unsettled aviation weather period is expected Sunday through Wednesday as abundant moisture in the lower half of the atmosphere and a series of perturbation aloft will maintain extensive cloudiness and instances of light rain. This suggest prolonged periods of MVFR/IFR ceilings are likely Sunday through Wednesday.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...WSS/SMITH SHORT TERM...SMITH LONG TERM...MWS AVIATION...WSS

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