Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201753 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1255 PM EST Sat Jan 20 2018 .SYNOPSIS... High pressure will drift across the southeastern United States through tonight, then offshore on Sunday. A cold front will approach from the west Monday, and cross central NC on Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 1010 AM Saturday... Little change required to the near term forecast. 12Z upper air analysis depicts a deep westerly flow over the Carolinas thanks to high pressure positioned across the eastern Gulf and the FL peninsula, and an elongated west-to-east trough over the Great Lakes into New England. This mild flow will aid to push temperatures back to or slightly above normal across most of central NC this afternoon. The exception will be where a snowpack of several inches still exists, which will deter/slow temperature recovery. Seeing evidence of this at mid morning as temperatures in the snowpack hovering close to freezing while locations with bare ground reporting temperatures in the upper 30s to the lower 40s. Will likely see a similar disparity this afternoon as temperatures will generally be in the 55-60 degree range except the lower 50s where snow depth of more than 2 inches exists. ~WSS 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. ~MWS && .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 /18Z SATURDAY THROUGH THURSDAY/... As of 1255 PM Saturday... There is a high likelihood that VFR parameters will persist across central NC through 03Z Sunday as high pressure to our south maintains good to excellent aviation conditions. Some model members are still suggesting that areas of fog will develop over/in vicinity of the snowpack region overnight with visibilities as low as IFR. Will error on the side of caution and depict similar scenario with MVFR/IFR visibilities overnight through early Sunday morning. Several other model members, however, suggest little if any fog development overnight so this made need adjustments as the time approaches. Otherwise, expect VFR parameters through Monday afternoon, aside from a threat for early morning fog and low clouds across the Piedmont early Monday morning. An approaching cold front will cause ceilings to thicken and lower Monday though VFR ceilings expected through 00Z Tuesday. After 00Z Tuesday, shower coverage will gradual increase west-to-east, along with the threat for MVFR ceilings. Low end VFR/MVFR ceilings are highly probable late Monday night through early Tuesday morning along with scattered rain showers. Aviation conditions are expected to rapidly improve southwest-to-northeast across central NC late Tuesday morning through Tuesday afternoon as the cold front exist the region. VFR parameters will return to the area, and linger into Wednesday and Thursday. While sfc winds will generally be less than 10kts through Monday morning, the approach of the cold front Monday afternoon will cause sfc winds to increase, with sustained sly winds 10-15kts probable late Monday into Monday night and gusts around 25kts. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS/MWS SHORT TERM...MWS LONG TERM...KC AVIATION...WSS

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