Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 100010 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 810 PM EDT Sun May 9 2021 .SYNOPSIS...
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A cold front will approach from the northwest tonight, then cross the region Monday. Strong high pressure over the upper Midwest will build south and east into the eastern United States behind the front Tuesday and Wednesday. A turn to chilly temperatures can be expected with this high pressure.
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&& .NEAR TERM /TONIGHT/...
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As of 805 PM Sunday... ...Prefrontal conditions will mean a breezy south to southwest wind and warm temperatures tonight. A strong system will lift out to the NE through the Ohio Valley into the NE states tonight. The trailing cold front will approach the Appalachians overnight. Numerous showers and thunderstorms were noted along the front over TN/AL/MS at the moment. However, the convection has been weakening quickly as it approaches the spine of the Appalachians of western NC. Cirrostratus had overspread much of NC (to the coast) just before sunset. Lower clouds were hard to find in the dry subcloud later east of the Blue Ridge. The forecast overnight will be for outflows to make it across the Mountains in a greatly weakened fashion - but all the convection is expected to dry up before reaching the Western Piedmont. A few sprinkles may fall from the residual mid cloud layers - but essentially trace amounts expected, if that. Otherwise, it will be warm overnight with the SSW winds at 10-20 mph continuing. In addition, the considerable high level overcast will put a lid on cooling, as well. Lows in the lower to mid 60s appear reasonable. The outflows should make for a pre-frontal trough that should position along or near the Triad by around daybreak. This is the trough that will then work with heating and finally upper support scattered to numerous showers/storms from 15z-20z in the west, and 18z-23z in the east Monday. There is still a Marginal Risk for a severe storm or two - but this will be tied to the amount of heating and instability that can be attained (which will be in question given the expected cloudiness) along and ahead of the trough, then the cold front that will follow. It appears that areas from the Albemarle east to the Triangle Area - then south and east will have the highest PROB of heating/destabilizing and thus thunderstorms. The initiation of convection should be near a weak meso-low / trough position over the central Piedmont by early afternoon, spreading ESE with time. This may very well change and expect a much better and possibly higher PROB forecast by Monday morning!
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&& .SHORT TERM /MONDAY and MONDAY NIGHT/... As of 310 PM Sunday... The cold front will move across the region Monday. Although the Carolinas will be well removed from the best forcing as the parent low will be to the north, an upper-level shortwave should help to provide additional forcing for lift. High-resolution models in the HREF indicate that thunderstorms may not develop until after the front moves through the Triad, although the entire forecast area does have likely pops tomorrow. Modest values of both shear and instability warrant the SPC marginal risk (level 1 of 5) for thunderstorms tomorrow. May have been a little too aggressive in lowering high temperatures for tomorrow by following high-resolution guidance, but now have highs ranging from the mid 70s in the Triad to the low 80s in the southeast. Thunderstorms will continue generally south of US 1 after sunset, though any severe thunderstorm risk should wane quickly. Even with the front pushing through, can`t rule out a shower most locations through the night. Lows will drop into the 50s behind the front. && .LONG TERM /TUESDAY THROUGH SUNDAY/... As of 255 PM Sunday... Tue/Tue night: The cold front will be settling to our S Tue morning, although only portion of the incoming frigid air mass -- the large Arctic high centered over the Upper Midwest -- will be allowed to spill into NC, with the most dense and chilliest air holding NW of the mountains. This small portion of the surface ridge will shift to our E during the afternoon as an inverted trough develops over the foothills. The low levels should mix with heating, but with more stable air just above the BL, lingering moisture within that depth will tend to stay locked in with light easterly flow below, and skies should range from partly cloudy N to mostly cloudy across the S. With the delay in the most pronounced CAA, will trend toward the higher end of model-suggested thicknesses and temps, yielding highs of 68-74. Strong sheared shortwave energy diving S and SSE through the Great Lakes and St Lawrence Valley Tue and through the Ohio Valley and Northeast states Tue night will help draw the colder air into NC from the NNW and N, resulting in both falling surface dewpoints and low level thicknesses, the latter of which is likely to bottom out around 50 m below normal by Wed morning. Expect chilly lows in the low 40s N to around 50 S. Skies will trend toward mostly cloudy to cloudy areawide with increasing moisture and forcing for ascent in the mid to upper levels, in large part a function of the falling mid level heights and accelerating flow over and just off the Mid Atlantic coast. While NC will be squarely in the RRQ of this jet, the low levels (<4kft AGL) may remain sufficiently dry so as to limit QPF (although particularly vigorous lift could overcome this anyway). And if the strong mid-upper lift induces surface low genesis along the front to our SW (as most models indicate), the isallobaric contribution to an enhanced NE flow may draw in even drier air initially in the N. For now will keep pops muted, a 20-40% chance across the S and extreme W overnight. Wed/Wed night: The aforementioned lift mechanisms continue into Wed, as the surface low tracks along the front to our S. Expect good chance pops across the S Wed morning, much lower N, trending down and out through the afternoon as the upper jet decelerates and shifts out over the NW Atlantic with the surface low pushing off the SC coast. The ECMWF trends back to dry much more quickly as it drops the broad shear axis further S over the NW Atlantic, allowing more and deeper low level dry air to penetrate further S, while the less amplified GFS retains deeper moisture and lingering lift over NC with a much slower surface low closer to the SC coast into Wed night. The ECMWF solution makes more sense in this respect, and most of its ensemble output skews dry, so will trend toward drier weather Wed night. Highs will be anomalously chilly Wed, in the mid-upper 60s, followed by lows in the 40s. Thu through Sun: The end of the week will feature split flow over S Canada and the northern CONUS, with the western portion of the elongated shear axis deepening gradually into a low or pronounced shortwave trough over the Midwest by Thu. This wave drifts ESE and amplifies over the Ohio Valley down through the Mid South Thu then swings through our region Thu night/Fri, inducing another surface low along the front to our S. This all points to a quick return to unsettled weather for NC, esp across the S. Will bring in pops late Thu, peaking Thu night/Fri then decreasing Fri night as the trough moves offshore with rising heights aloft over NC. Broad NW mid level flow with the modifying surface high still sitting over the Midwest/Ohio Valley/Great Lakes will follow, with dry weather and somewhat cool but moderating temps over the weekend. -GIH && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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As of 810 PM Sunday... Through 00Z Tuesday: S-SW gusty winds are expected through the entire period, including overnight. Near surface winds will be around 10-20 knots overnight, but LLWS may still be a concern as the winds at 2k feet AGL are forecast to increase to near 45 knots between 05z and 09z, lingering through daybreak, or so. A pre-frontal trough will bring widespread VFR CIGS overnight. The showers over TN should die out and only bring VFR mid level CIGS to the KGSO/KINT areas between 06z-12z. MVFR to IFR CIGS with MVFR VSBYS with scattered to numerous showers and storms are expected, especially east of the Triad TAF sites between 18z?mon and 00z/Tue. This will be with a trough and cold frontal passage. Winds will become northern after the fropa. After 00Z/Tuesday: A return to VFR conditions is expected Monday evening, with VFR conditions expected Tuesday and possibly into Wednesday with a NNE low level flow associated with high pressure to the NW-N (Midwest to Great Lakes to New England).
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Badgett SHORT TERM...Green LONG TERM...Hartfield AVIATION...Badgett/Green

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