Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201232 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 732 AM EST Sat Jan 20 2018 .SYNOPSIS... High pressure will drift across the southeastern United States through the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 730 AM Saturday... WV satellite imagery and 00Z upr air depict a split flow pattern across the CONUS, with the main nrn stream jet extending from a trough along the West Coast, ewd across the nrn tier of the country. A formerly nrn stream trough has separated from that flow and become a closed mid-upr low over the lwr MS Valley. Meanwhile, the srn branch of the jet extends from cntl Mexico newd across cntl FL; and the presence, proximity, and influence of this jet will cause the mid-upr low to shear ewd and become an open wave over srn GA/nrn FL by 12Z Sun. A thin veil of cirrus associated with this wave may consequently skirt srn NC tonight. While the majority of the upstream stratocumulus now banked against the west side of the cntl Appalachians will remain so, in a strong 925-850 mb WAA regime directed there from the lwr MS Valley, a scattering of this cloudiness may squeeze through the peaks and into the nrn NC Piedmont late this afternoon and evening. At the surface, 1026 mb high pressure analyzed at 12Z over srn GA will drift slowly newd, into the Savannah basin by 12Z Sun, while a lee trough remains in the immediate lee of the Appalachian. Modification of the high, and the associated air mass, will yield warmer conditions over cntl NC today, with highs mostly in the mid- upr 50s. Strong radiational cooling conditions tonight will favor lows mostly in the lwr-mid 30s, though if any snow cover remains after another mild day, then those locations are apt to dip into the upr 20s. Areas of fog will be possible late, mainly over the Piedmont, where near surface moisture, especially from recently melted snow, will be maximized.
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 359 AM Saturday... The trough aloft now along the West Coast will migrate ewd, to the Plains, with an associated exit region of a strong, ~130 kt upr jet forecast to nose into the cntl Appalachians by 12Z Mon. The surface ridge initially over the sern US will migrate across the Carolinas and off the srn middle Atlantic coast. Temperatures will consequently continue to modify, with a scattering of stratocumulus, ~850 mb, that will have spilled east of the Appalachians by that time. Highs are expected to climb into the lwr-mid 60s. Lows, with a good chance of radiation fog, and associated low overcast by Mon morning, mostly in the mid-upr 30s. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 200 AM Saturday... Monday and Tuesday: Fairly high confidence in the low pressure system approaching and moving through Central NC as all medium-range models are in good agreement. An upper low will develop off the Rockies on Monday, progressing east-northeastward through the Midwest and into the Great Lakes region through Tuesday. Meanwhile, the surface cold front will move eastward toward the Mid-Atlantic. With the increasing southerly flow over Central NC Monday into Tuesday, high temperatures will range from mid 50s NW to mid 60s SE. Lows Monday night in the mid 40s NW to low 50s SE. Of bigger concern than temperatures is the chance for precipitation and possibly some thunderstorms as the line of pre-frontal convection moves into and through the area. As of the latest model runs, MUCAPE appears to be less than 500 J/Kg and the surface low is displaced well to the north over the Great Lakes. There are still slight timing and intensity/amount of precip differences between the models, which will play a role in forecast for possible thunder. For now, given the uncertainty, will keep mention of thunder out of the forecast. Both models do indicate precipitation exiting the area by Tuesday night, with cold air starting to filter in behind the front. As a result, Tuesday night will likely be dry and temperatures quite a bit lower than the previous night, in the low to mid 30s. Wednesday through Saturday: This part of the forecast is likely to be dry, with a reinforcing dry cold frontal passage on Wednesday night/Thursday. Surface high pressure is expected to build into the area in the wake of the secondary cold front and remain over the area into Saturday. Chances for precipitation will increase over the weekend, but details are still far from nailed down. Highs will be generally in the 50s and lows in the upper 20s to low 30s Wednesday and Thursday night, increasing into the 30s Friday night. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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As of 720 AM Saturday... High pressure over the southeastern US will result in mainly VFR conditions through the weekend. The exception will be a medium chance of fog and associated ceilings/visibility restrictions between 05Z-14Z Sun, with some lingering sub-VFR ceilings possible through the midday hours on Sunday, as that moist layer lifts and disperses with diurnal heating. Outlook: The threat of persistence fog and low ceilings will exist for Sun night-Mon morning. Sub-VFR conditions, and showers, are expected to affect cntl NC along and ahead of a cold front Mon evening through early Tue.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...KC AVIATION...MWS

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