Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 180816 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 416 AM EDT Mon Mar 18 2024 .SYNOPSIS... A cold front pushing southeast through the region will settle to our southeast this morning. A stronger second cold front and upper level disturbance will cross the area late today, bringing cooler air for tonight through Tuesday as Canadian high pressure builds in from the west and southwest. Milder temperatures return for Wednesday as the high shifts to our south. && .NEAR TERM /TODAY THROUGH TONIGHT/...
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As of 400 AM Monday... ...A Freeze Warning has been issued for portions of the Southern Piedmont and Sandhills for sub-freezing temperatures tonight... Surface observations as of 07z show a cold front extending from southeast VA through the Triangle and down towards the Charlotte area. This front marks a sharp gradient in dew points with low 50s ahead to mid 20s behind. This front along with periodic winds gusts 15 to 20 mph will continue to march through central NC through early this morning before shifting offshore by sunrise. This initial surge of noticeably drier and slightly cooler air will be a precursor to a secondary surge of cold air and another cold frontal passage expected this evening through early tonight (See Fire Wx section below for more information related to fire concerns). A deep and positively tilted trough axis will pivot across the Ohio Valley this morning and begin taking on a neutral tilt as the base of a significant PV anomaly swings through the southern Mid-Atlantic this evening through midnight. The core of the PV anomaly will have a favorable track right over central NC to produce strong synoptic forcing for ascent which will lift the inversion at 700mb and result in mid-level clouds blossoming over central NC. Mid-level ascent will be amplified by 700-500mb FGEN during this time, but should result in mostly virga across the area with only isolated locations able to sufficiently measure precipitation thanks to a deep inverted- V signature in the boundary layer and large dew point depressions. Much cooler air will filter in behind the Arctic cold front throughout the night and allow for temperatures to drop well into the 30s by early Tuesday morning. Yesterday marked the first day of the growing season for the southern Piedmont, Sandhills, and central/southern Coastal Plain. As such, the Freeze Watch has been upgraded to a Freeze Warning over the areas where confidence is sub- freezing temperatures is highest. Although not in the Freeze Warning, a large portion of the Northwest Piedmont, Northern Piedmont will also likely see sub-freezing temperatures and any early-budding vegetation will also be at risk of damage from sub-freezing temperatures.
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&& .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... As of 200 AM Monday... The potent mid level PV max will have shifted offshore by Tue morning, and while another much weaker perturbation will shift ESE through the Mid Atlantic Tue afternoon, it won`t have any moisture to work with, as the mid levels continue to warm and stabilize within deep subsidence. Little more than a streak of high thin clouds is expected Tue afternoon, with the remainder of the area and of the period largely cloud-free as surface high pressure builds across the Gulf and Southeast states and eventually spreads E off the Southeast coast. Our NW or WNW surface flow early Tue will back quickly to SW and remain rather stout and gusty, given the MSLP gradient between the W-E surface ridge to our S and a northern stream cold front dropping into the Ohio Valley and approaching our area from the NNW late Tue night. This will set up a lee trough over the W Piedmont that will persist Tue/Tue night, but again, the lack of moisture will make this inconsequential. With low level thicknesses having bottomed out around 50 m below normal Tue morning, some recovery will begin Tue as the SW flow develops, however Tue will be our coldest day of this stretch, given the cold start and the somewhat shallow BL beneath the growing subsidence inversion aloft. Expect highs in the 50s. Radiational cooling should be better, although not ideal, Tue night with clear skies and lighter winds, supporting decoupling by late evening. Expect lows in the mid 30s to around 40, with the risk of another freeze night rather low and confined to just the typically cooler rural/outlying central Piedmont for which the growing season has not yet officially begun. -GIH && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 230 AM Monday... Overview: Some uncertainty persists regarding late-week rain chances, but late Thu night through late Sat appears to be the time frame with the better chances, likely peaking Fri/Fri night across the S and E. Forecast confidence in both temps and rain chances plunges over the weekend. Near to above normal temps Wed will drop to below normal then persist through the weekend, with Thu/Fri as the coolest days. Wed/Wed night: Very nice day expected. With a dry and stable column persisting through Wed, expect lots of sunshine with WAA, which should push temps up to the upper 60s to mid 70s, with gusty SW winds, meaning the early-season pollen will be flying. Models continue to depict a backdoor cold front dropping SSE into or through NC Wed night, driven by a passing shortwave trough through the Northeast/New England and incoming dense air associated with the cold high pushing from Manitoba/W Ontario into the Upper Midwest and Great Lakes. Thus, our temps should drop back to near to slightly below normal Wed night, esp across the N, with lows from the mid- upper 30s near the VA border to the low-mid 40s S. Thu-Sun: Conditions become increasingly unsettled late in the week as the upper low over the Desert Southwest this morning will have finally opened to a shortwave trough and begun to shift eastward, tracking from OK/N TX Thu morning across the lower Miss Valley through Fri morning and into the Southeast and Carolinas by Fri night. While most models depict this wave starting to dampen by this time, their solutions diverge Fri-Sun in terms of timing and amplitude, producing sensible weather differences. The latest GFS/GEFS are deeper and faster (a result of a deeper polar low crossing S Ontario, causing our wave to shift quickly off the Mid Atlantic coast Sat morning, albeit with a lagging trailing trough over/off the FL E Coast), while the Canadian/ECMWF and older GEFS/GEPS also maintain some amplitude but are slower, reasonable given their weaker and further-north polar low, resulting in an overall weaker steering over the SE quarter of the CONUS as longwave troughing starts to dig down the West Coast. The latter camp and its weak upper low holding over the E Carolinas suggests lingering clouds and rain chances persisting, mainly E, while the faster GFS indicates clearing/drying and warming over the weekend. The newer GEPS/ENS are a good compromise, showing a slowing wave over the Carolina coast through Sat followed by an eastward push with incoming shortwave ridging Sun, and will follow this path with the forecast. Will have fair skies Thu with dry weather through the evening, then spread chance to low-end likely pops (highest S/E) Fri morning, peaking in the afternoon through night, before shifting pops to mainly in the Coastal Plain Sat with drying late Sat night through Sun. Expect slightly below normal temps Thu behind the backdoor front. As the rain arrives Fri, the surface high to our N and NE will have pushed off the Mid Atlantic coast but still extend back into the Piedmont with lower pressures over GA/FL/SC. This should set up a brief CAD event as the rain locks in the stable air, and as such, have knocked temps down over much of the Piedmont Fri. Will have highs in the lower 50s NW ranging to the low-mid 60s SE. These NW readings are several degrees below most guidance, and may not even be cool enough, however the high is not centered in a good spot (off the Mid Atlantic coast) to provide a steady feed of cooler air/lower dewpoints, so will stick with these more modest adjustments for now. After low pops mainly E Sat, will trend them E and out Sat night/Sun, with temps slightly below normal. -GIH && .AVIATION /08Z MONDAY THROUGH FRIDAY/... As of 200 AM Monday... VFR conditions are expected through the 24 hour TAF period. A cold front and wind shift is currently making its way through central NC and is forecast to reach RDU by 07-08z and RWI/FAY by around 09z. Winds will increase out of the NNW 10-15 kts for a couple hours post fropa. Winds will shift back generally out of the west Mon afternoon ahead of another stronger cold front forecast to move through central NC from 22-03z. Surface winds will again veer out of the NW around 15 kts sustained with gusts 20-30 kts. Gusts will gradually weaken, but should continue through most of the night into early Tues morning. Some light rain, but mostly virga, will be possible as a 5-8k ft cloud deck blossoms over most of central NC Mon evening through midnight. Outlook: LLWS will be possible Tues night into early Wed as winds at 2k ft increase to 30-40 kts. A dry cold frontal passage will bring a wind shift out of the NW late Wed into early Thurs. A storm system approaches the area Fri into Sat bringing a high chance for sub-VFR conditions. && .FIRE WEATHER...
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Mon evening: Take extra precaution to extinguish any fires this afternoon ahead of the frontal passage this evening into tonight. Dew points in the low 20s to teens with temperatures still in the 50s late this afternoon will result in RH values in the low to mid 20s with westerly winds increasing to 10-15 mph and gusts up to 20 mph. Any fires that start today will be at risk for spreading and rapid change in direction as the strong cold front moves into the NW Piedmont this evening with sustained winds around 15 mph and gusts up to 30 mph behind the front. Wed: Ahead of a dry cold frontal passage, southwest winds will increase to 10 to 15 mph sustained with gusts up to 25 mph Wed afternoon. Temperatures rising into the upper 60s to mid 70s with dew points in the upper 20s to low/mid 30s will result in Min RH in the 20s.
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&& .RAH WATCHES/WARNINGS/ADVISORIES...
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Freeze Warning from midnight tonight to 9 AM EDT Tuesday for NCZ073>076-083-084.
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&& $$ SYNOPSIS...GIH NEAR TERM...Swiggett SHORT TERM...GIH LONG TERM...GIH AVIATION...Swiggett FIRE WEATHER...Swiggett

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