Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170616 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 115 AM EST THU Jan 17 2019 .SYNOPSIS... A weak front stalled across southern NC this morning will lift back north as a warm front today. A fast moving upper level trough will cross the region Thursday evening, producing unsettled weather. Weak high pressure will bring dry weather Friday, then a strong storm system will move through Saturday through early Sunday. Sharply colder air will arrive Sunday into Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 1005 PM Wednesday... A dry backdoor cold front has pushed south through much of central NC this evening. High pressure will continue building into the area behind it. As a result, expect generally light northerly winds and dry weather overnight. Skies will start off clear, but expect increasing high clouds from the northwest later tonight through daybreak. Lows will bottom out in the low 30s. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 240 PM Wednesday... A low-amplitude shortwave trough, comprised of several pieces of shortwave energy, will progress quickly east from the Mid MS Valley early Thursday to moving off the Mid-Atlantic Coast shortly after midnight Thursday night. In advance of this system, the weak back- door front will return north as a warm front during the afternoon. While associated rain showers are not expected to arrive into the western Piedmont until the late afternoon/early evening, thickening/lowering clouds prior to the arrival of the rain will greatly temper insolation. Have continued to trend the high temperatures lower, especially across the northern Piedmont counties which will likely see little to no sunshine during the day. Highs will range from mid 40s north to lower/mid 50s south. Area of showers will quickly traverse the area Thursday evening, with the best shower coverage expected across the northern half of the forecast area, where deeper moisture profiles are projected. Both the NAM/GFS modeled thermal profiles also hint at the slight possibility of a brief period of no impact sleet/rain mix at the onset of the showers, primarily between 23z (6pm) - 03z (10pm). With sfc temps remaining 5 to 10 degrees above freezing, this occurrence, if it happens, will have little to no sensible impact and likely only persist for a short amount of time. Due to the fast movement of this system, along with rather modest forcing, precip will be light, generally less a tenth of an inch or less in terms of accumulation, with the highest amounts near the Va border. Thursday night/Friday morning lows will remain in the upper 30s to low 40s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 300 PM Wednesday... A cold front, related to the passing, Thu night shortwave trough, will settle sewd across cntl NC Fri afternoon-early Fri night. The development and presence of a subsidence inversion, amidst height rises aloft, should generally cap any weak instability and shallow cumulus ahead of/along the front. Milder, with highs in the mid 50s north to low-mid 60s south. Continental polar high pressure will follow and extend swd across NC Fri night, with lows in the upr 30s to lwr 40s. Significant flow amplification, spanning multiple streams, is forecast this weekend into early next, with a resultant full latitude trough forecast to migrate from the cntl US on Sat to the East Coast by Mon, and following cross polar, nwly flow delivered all the way to the Sunshine State. Deepening low pressure will accompany the trough aloft and cross the srn-cntl Appalachians and middle Atlantic states late Sat through early Sun. While preceding mild, warm sector flow should envelop much of the sern US and Carolinas, some degree of cold air damming, from clouds and rain that will overspread the nrn and wrn Piedmont on Sat, may hold those areas in a cooler regime (upr 40s), versus the growing warm sector 50s-60s elsewhere late Sat-early Sun. A half an inch to an inch of rain-soaking and leading shallow convection, likely devoid of lightning owing to pseudo-moist adiabatic level lapse rates and limited CAPE, appears likely Sat night-early Sun. Strong wind gusts may accompany that shallow convective line, should it indeed materialize. Sharply colder temperatures, and the leading edge of 1040`ish mb Arctic high pressure, will plunge across cntl NC Sun afternoon and night. The incoming Arctic airmass will likely produce the coldest temperatures of the season, and a legitimate risk of sub-zero wind chill values over the Piedmont, to single digit ones elsewhere, by Mon morning. Cold highs in the 30s on Mon will then be followed by strong radiational cooling of a single digit to sub-zero surface dewpoint airmass accompanying the Arctic high Mon night, with lows mostly in the teens. Ridging aloft and moderating temperatures will then occur over the sern US Tue-Wed, ahead of the next amplified system approaching from the west - one which will increase shower chances in cntl NC late Wed-Wed night. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... As of 115 AM Thursday... A fast moving, low-amplitude shortwave trough over the Mid MS Valley this morning will cross the southern Appalachians late this afternoon and then through the area between 00 to 06z. In advance of this system, top-down moistening will result in lowering ceilings through the day, but should remain predominately VFR through 00z Friday. After 00z, there are some significant model differences with how low ceilings will fall as an area of spotty light rain showers move east across the area between 00 to 06z. At this time, confidence in sub-VFR conditions is highest at KINT and KGSO, where highest rain chances/pops are expected. For now will leave all other TAF sites low end VFR. Outlook: In the wake of the exiting system, VFR conditions are expected to return on Friday. The risk for sub-VFR conditions increases starting late Fri night as a strong storm system approaches from the west, with widespread rain likely to arrive late Sat through Sat night, along with strong/shifting winds. VFR conditions should return Sun into Mon with brisk winds and sharply colder air. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...KC SHORT TERM...JJM/CBL LONG TERM...MWS AVIATION...CBL/Hartfield

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