Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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718 FXUS62 KRAH 180052 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 752 PM EST Tue Jan 17 2017 .SYNOPSIS... A cold front will approach from the northwest this evening, then track southeast through central North Carolina Wednesday morning. In the wake of the front, high pressure will build into the region from the northwest Wednesday night and Thursday. && .NEAR TERM /THROUGH TONIGHT/... As of 100 PM Tuesday... Surface observations indicate visibilities have risen above 3 miles in most locations as of 16Z, indicating that top-down erosion of the CAD wedge has commenced in assoc/w insolation and strengthening SW low-level flow in advance of a shortwave trough /DPVA/ approaching the Mid-Atlantic from the W/NW. Overcast skies should thin and may become broken this afternoon, though current trends would suggest breaking out entirely is unlikely except near the NC/SC border. As such, expect highs ranging from the upper 50s to ~60F in the North to mid 60s in the far SW Piedmont. Forcing this aft/eve will be limited to weak low-level warm advection, primarily in the NW Piedmont and VA border counties where a few periods of light rain will be possible through this aft/eve. Precipitation chances overnight remain difficult to ascertain. Low-level forcing will largely be absent overnight, with central NC in a relatively homogeneous warm sector characterized by unidirectional /SW/ flow. As a result, expect dry conditions with the best chance of rain between 06-12Z to the north in southern VA. Broken to overcast cloud cover and a 10-15 mph SSW/SW breeze should result in mild temperatures tonight, i.e. little diurnal variation from this afternoon. -Vincent && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 115 PM Tuesday... Expect some chance for showers along the cold front progressing into central NC Wed morning given a modest plume of SFC-925 mb moisture in the presence of low-level convergence within the low-level trough. In the immediate wake of the front late Wed morning through early Wed afternoon, strong DPVA progged to track ESE through VA into northeast NC may encounter lingering low-level moisture across central/eastern NC. As a result, a period of anafrontal precipitation will be possible in central NC, primarily from the Triangle east into the Coastal Plain. Expect a clearing trend mid/late afternoon in assoc/w subsidence in the wake of the shortwave and the onset of low-level cold advection in the wake of the front. Given the timing of the front and the potential for precipitation /evap cooling/ late Wed morning through early Wed afternoon, high temps on Wed will vary little from overnight lows except perhaps in the far S/SE where temps may reach the mid 60s prior to cold advection post-fropa. Lows Wed night will be driven by a combination of cold advection and radiational cooling, ranging from near 40F at the VA border to the mid 40s SC border. -Vincent && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 244 PM Tuesday... There is fairly good model agreement through this period. The general pattern is a series of weather systems swinging through the region, resulting in alternating wet and dry periods. Thursday through Friday Night: Thursday will be largely dry with a surface high briefly moving over and away from the area and an upper level ridge over the Southeast U.S. Meanwhile, an upper low that developed over the Southwest U.S. will lift northeast and get absorbed into the northern stream. This low will then transition into a shortwave trough extending southeast into the Carolinas from the Plains. A warm front will lift northward through Central NC Thursday night into Friday. Strong southerly flow advecting warm moist air into the region, combined with the upper forcing from the s/w aloft, will result in a period of rain moving through the area Friday aft/eve and clearing out Friday night. Highs will increase slightly from Thursday (mid to upper 50s) to Friday (mid 50s north to mid 60s south), but lows will be mainly in the mid to upper 40s. Saturday through Monday: Saturday should be dry with highs in the low to mid 60s with continued advection of warm air into the region. The weather gets increasingly more interesting for the rest of the weekend and model agreement remains above normal, especially for this far out in the forecast period. A strong low pressure system moves off the Rockies Saturday night and quickly moves east through the ARKLATEX on Sunday. With continued advection of warm moist air off the Gulf ahead of the low, PWATs and precip chances will increase Saturday night. The trough will become increasingly negatively tilted Sunday night into Monday as the upper low swings toward and along the Appalachians. This system will bring our first chance for potentially strong storms to move through the area, though for now will indicated the chance for some isolated thunderstorms until it gets closer in time we get a better handle on the instability, shear, and lapse rates that will largely determine what type and strength of convection we can expect. Temps will increase Sunday through Monday, especially across the southeast, before decreasing again Monday night on. The weather should dry out on Tuesday, though the negatively tilted trough will remain over the Mid-Atlantic as the low lifts northward through NY into Canada. Highs in the mid 50s and lows in the upper 30s to mid 40s expected. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 740 PM Tuesday... 24 Hour TAF period: Isolated to scattered showers (with possibly MVFR visbys with the showers) will be possible this evening into Wednesday morning ahead of an approaching cold front that is expected to move through the area near daybreak Wednesday through around 15/16Z or so (in a NW to SE fashion). We may see some sub-VFR cigs develop after midnight in advance of the front, along with the potential for a few showers, though confidence in the coverage and how low cigs will be is much in question. For now will go with low- end MVFR cigs developing at all TAF sites in the 07-09Z time range, then continuing until fropa (low confidence though). Winds will switch around from southwesterly to northwesterly behind the front on Wednesday, with possibly some gust into the 18 to 25 mph range. Outlook: Expect a clearing trend in the wake of the front with a brief return to VFR conditions Wed night/Thu. A pattern similar to the one affecting the region today is progged to develop over the region again late this week. With this in mind, expect ceilings to begin deteriorating Thu night/Friday, with unsettled weather expected into the weekend.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...KC AVIATION...BSD/Vincent

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