Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011547 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1050 AM EST Wed Mar 1 2017 .SYNOPSIS... Warm southwest flow will continue across the region today ahead of a strong cold front approaching from the west. The cold front will cross the area tonight, followed by cool high pressure for the latter half of the week. && .NEAR TERM /THROUGH TONIGHT/... As of 1050 AM Wednesday... Potential for severe storms with damaging wind gusts appears slightly higher, primarily west and north of Raleigh late this afternoon into the evening hours. Early morning analysis depicts a conditionally stable air mass as 12Z GSO sounding depicts a strong cap between 850-750mb. In addition, very strong winds noted just off the surface with 40kts observed at 1000 ft. As temperatures rise to around 70, breaking the sfc based inversion, should see an increase in the sfc winds with gusts 30-40 mph. Plan to handle gusts with a SPS but may need to issue a short fuse wind advisory by mid day. While a few showers may skirt the northwest Piedmont early this afternoon, the better forcing for scattered-numerous showers and storms appears to arrive in our region after 21Z. Sfc dewpoints this morning are in the upper 50s-lower 60s west and low-mid 60s east. These values are a few degrees higher than projected. In addition, low stratus absent across much of the northwest Piedmont, allowing this region to warm faster than earlier thinking. The expected string heating late this morning-early afternoon along with the approach of a slightly cooler air mass aloft may be enough to erode/break the 850-750mb cap, leading to a better potential for strong/severe storms. This threat appears most likely across the western piedmont into the far northern Piedmont along the Virginia border counties. Still some uncertainty as to the probability of severe storms in the RDU metro area and points east-se as system projected to go through mid-late evening hours when the near sfc air mass will begin nocturnal stabilization. If storms arrive in the Raleigh area closer to 7 or 8 PM, the threat for locally damaging winds will increase. Afternoon temperatures near 80 NW to the low-mid 80s SE still appear on track. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... As of 400 AM Wednesday... After lingering mid level ceilings and perhaps a few sprinkles over the far sern counties early Thu, cirrostratus within the axis of a 150 kt WSWly gradually edge Swd and out of central NC throughout the day. Downslope NWly flow will help offset waning CAA. Highs in the upper 50s to lower-middle 60s, with gusts up to 25 mph until midday- early afternoon, before CAA diminishes by afternoon. Surface high pressure will ridge overhead from the SW in advance of a clipper frontal system approaching from the NW, so temperatures will have the potential cool into the upper 20s to lower-middle 30s. Thu night. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 355 AM Wednesday... A progressive pattern aloft will result in a transition from a departing trough in the eastern U.S. Fri-Sat, to ridging through early next week. The trough will reach maximum amplitude as a shortwave trough in NW flow aloft amplifies across the Middle Atlantic states during the day Fri. This trough will be followed by a less amplified/shear vorticity maximum that will migrate through the NW flow, with a brief period mid level WAA cloudiness, on Sat. At the surface, a clipper surface wave accompanying the aforementioned shortwave trough in NW flow aloft will track across the nrn Middle Atlantic states, while the trailing nrn stream surface cold front will sweep across central NC during the day Fri. Given both 1) a tendency for the models to advect cold air across the Appalachians too quickly, and 2) the prevalence of a downslope/compressional warming flow component throughout the day, temperatures are expected to recover into the middle 50s to lower 60s. Cold and dry advection within a deeply mixed (800-750 mb) boundary layer will support afternoon wind gusts up to 25-30 mph, which will make it feel cooler. Incoming cP surface high pressure behind the front on Fri will result in a hard freeze Fri night-Sat morning, when temperatures are expected to fall into the lower-middle 20s over the Piedmont, to upper 20s to around 30 degrees over the Sandhills, srn Coastal Plain, and urban areas. Temperatures will gradually moderate thereafter, as the surface ridge moves E and modifies, with 50s on Sat replaced by 60s-70s by early next week. After a dry weekend as the ridge moves overhead and offshore, the approach of the next frontal system will result in a chance of showers late Mon-Tue. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 640 AM Wednesday... Strong winds expected today, with storms late this evening... MVFR and IFR ceilings from RCZ to FAY to RWI will continue to drift slowly north and lift through mid morning, evolving into a deck of MVFR to low end VFR cumuli by midday. Confidence in sub-VFR ceilings this afternoon is medium and strongest at INT and GSO based on latest hires model guidance. Meanwhile, southwesterly wind gusts to 30-35kt are expected, with winds increasing after 15Z as a cold front moves through the Tenn Valley and across the mountains this afternoon. A line of storms will cross central NC this evening, likely at INT/GSO by 00-02Z, RDU by 02Z and RWI/FAY by 03-05Z. The storms have the potential to be severe with gusts to 50kt or higher. Behind the convection, low-level drying will return conditions to VFR as winds turn to northwesterly, though winds may continue to gust to around 20kt. Outlook: Skies will clear out for Thursday with VFR conditions and NW winds. VFR conditions will continue through Sunday under high pressure. && .FIRE WEATHER... As of 550 AM Wednesday... Critical, or nearly so, fire weather conditions still probable Thu and especially Fri. Much drier air will overspread central NC following a cold frontal passage, and accompanying line of showers and storms, tonight. The drier air, combined with afternoon temperatures in the upper 50s to middle 60s on Thu, will result in minimum relative humidity values between 20 and 25 percent Thu afternoon. However, NWly winds, which will gust between 20-25 mph through 1 PM, will subside during the afternoon (when critical RH values are met). Nonetheless, there may be a several hour period centered around noon Thu when marginally critical relative humidity values between 25-35 percent overlap with the aforementioned stronger winds; and increased fire danger may result. These conditions will also set the stage for Fri, when daytime heating and a secondary cold frontal passage during the afternoon will result in critical RH values for several hours during the afternoon. In addition, breezy Wly to NWly surface winds are forecast to be sustained between 15-20 mph, with 25-30 mph gusts. These conditions for increased fire danger to red flag will likely be coordinated with the NCFS later today and/or on Thu. && .CLIMATE... Record highs for March 1st: RDU: 82 (set in 1997) GSO: 77 (set in 2012) FAY: 87 (set in 1918) && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...WSS SHORT TERM...MWS LONG TERM...MWS AVIATION...SMITH FIRE WEATHER...MWS CLIMATE...RAH

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