Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 222004 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 400 PM EDT Tue May 22 2018 .SYNOPSIS... A lee trough will linger over the srn middle Atlantic states ahead of a cold front that will settle southeastward into the area late Wednesday and early Wednesday night. Following high pressure will ridge south across the region on Thursday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 400 PM Tuesday... A shear/trough axis evident from the Northeast swwd across the mid MS Valley and cntl Plains, and immediately preceding band of convection from the nrn middle Atlantic and lwr OH Valley swwd into the mid-South, will move ewd to the lee of cntl Appalachians through this evening. At the surface, a cold front was analyzed from a 1012 mb low over Lake Huron swwd across cntl OH and srn IL/MO. This boundary will move east to the srn New England coast swwd into MD and ern WV by Wed morning. An Appalachian-lee trough will meanwhile remain quasi- stationary over w-cntl NC. The aforementioned upstream convection centered over the cntl Appalachians and associated convectively-enhanced shear axis will drift east into cntl NC, likely in a weakening state owing to nocturnal stabilization, late this evening-early tonight. As such, some showers and storms may drift into the nrn and nwrn Piedmont through the first half of the night, before dissipating. Lows generally 65-70 degrees.
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&& .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
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As of 345 PM Tuesday... At the base of a mid-upr low migrating ewd across Hudson Bay and Quebec, a series of minor perturbations will sweep across the Northeast and middle Atlantic Wed, then offshore by Wed night. Mid- upr lvl flow will consequently strengthen slightly and veer to nwly over cntl NC, with effective bulk shear values likely to increase into the 25-30 kt range. At the surface, a cold front will settle swd, in backdoor fashion, across VA during the day, then into the nrn NC Piedmont very late Wed afternoon and evening, where it will overtake a preceding, quasi- stationary lee trough over w-cntl NC. The front, modulated by convective outflow, will settle swd through cntl NC overnight. A somewhat drier/lee humid/cooler air mass will follow, as post- frontal high pressure ridges swd across the middle Atlantic region. Initially scattered showers and storms are likely to focus along remnant outflow from convection from the previous day/night; and also along the lee trough. This activity is expected to become numerous by late afternoon and early evening, as convergence/lift increase with the arrival of the surface front. Storms are likely to become semi-organized in a multi-cellular storm mode along common outflow, with an associated strong to isolated damaging wind threat as storm clusters propagate sewd, with the relative greatest potential where the aforementioned bulk shear should be maximized over the nrn Piedmont and nrn Coastal Plain. The chance of showers and storms will linger overnight, particularly over the srn half of the CWFA, as the (effective) frontal zone settles swd. Any earlier severe threat will have diminished owing to both nocturnal cooling and prior convective overturning. Generally persistence temperatures in the mid-upr 80s are expected on average, though modulated and shortened by convection/clouds, with lows in the mid 60s to around 70 degrees.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 235 PM Tuesday... Progressive high pressure over the Great Lakes will make a stab at drying us out, pushing a front south of the area early on Thursday. With the front along or south of the area, will have only small chance PoPs along the southern tier counties Thursday into Thursday night. Highs will be only mildly influenced by the front due to strong insolation and should reach mostly mid 80s. The high moves off the New England coast, with return flow beginning to spread into the west Friday into Saturday. As such, chance category PoPs in the west Friday taper off eastward, with all areas in the low chance category on Saturday as we sit beneath an upper ridge conducive to airmass thunderstorms in the resulting unstable, but weakly forced environment. Highs both days will mostly reach mid 80s after mild morning lows in the mid and upper 60s. The moisture transport from the south returns once again for the late weekend aided by the Bermuda high and a developing low pressure system in the Gulf of Mexico. The moisture return will increase precip coverage Sunday and into early next week, and while there is a lot of uncertainty as to the timing of forcing mechanisms driving heavier convection, it will be diurnally influenced, and will maintain high chance to likely PoPs Sunday through Tuesday. Highs will show little variation from previous days, mostly mid 80s, with morning mins in the soupier airmass closer to 70 each morning. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... As of 155 PM Tuesday... Scattered showers and storms, with associated brief sub-VFR conditions and gusty winds, will focus in the RDU and RWI vicinity this afternoon, in association with an upper level disturbance now crossing that region. Another relative maximum in shower and storm coverage will be possible at INT and GSO this evening, related to the approach of a mid level trough and band of upstream convection now over the cntl Appalachians. Storm coverage is otherwise expected to remain isolated and/or of limited predictability (for inclusion in the TAFs). Similar to Tue morning, IFR-MVFR ceilings will be possible in the several hours centered around 12Z. Outlook: Scattered showers and storms will focus along a lee trough Wed afternoon, then become more numerous with the arrival of a cold front from the northwest late Wed and early Wed night. Sub-VFR conditions and strong wind gusts will result where storms occur. Otherwise, another round of sub-VFR ceilings will probably result late Wed night-early Thu, owing to low level moisture convergence along and ahead of the aforementioned frontal zone. After relatively dry/VFR conditions Thu-Sat, moisture will increase by Sun-Mon, with resultant increasing probabilities of convection and morning stratus and/or fog during that time. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...mlm AVIATION...MWS

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