Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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224 FXUS62 KRAH 221630 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1230 PM EDT Thu Mar 22 2018 .SYNOPSIS... Cool high pressure will build in from the northwest through Friday, before moving east and offshore Friday night. An area of low pressure will approach from the west Saturday and cross our region Saturday night, bringing a period of unsettled weather. && .NEAR TERM /TODAY/... As of 905 AM Thursday... Little change to forecast. A potent but moisture-starved mid level shortwave trough will move southeastward through the region today, resulting in scattered to broken mid clouds across northern and NE sections of the CWA. Otherwise, sunshine will be plentiful. Morning thicknesses around 40 m below normal support highs of 51-57. -GIH Previous discussion as of 330 am: Cloudiness will continue to diminish slowly from the southwest with lingering wrap-around cloudiness mainly across the north and east through the morning as the stacked low off the mid Atlantic coast lifts northeast. Mins this morning will benefit from the lingering cloudiness and modest mixing overnight with northwest winds 4 to 8 mph, bottoming around 30 across the north to mid 30s south. The increasing sunshine will be largely offset by cold air advection in breezy northwest flow today, with highs only reaching low 50s across the north to mid 50s across the south. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... As of 330 AM Thursday... Cold and dry surface high pressure will continue to spill southeast into the area in deep northwest flow as the upper east coast trof axis shifts east and offshore Thursday night. Loosening pressure gradient will allow atmosphere to decouple and temps will again fall to the 30 to 35 range, with some upper 20s across the northern tier. The cool northwest flow will be maintained on Friday, with highs edging up slightly into the mid and upper 50s. We will see cloudiness increase rapidly in the west Friday night as a developing low pressure system begins spreading moisture out of the Gulf northeastward. This moisture will be lifted orographically and isentropically late Friday night, with light rain expected to hold off until early in the day Saturday. Lows will benefit from the onset of cloud coverage in the west and south with mins mostly in the 30s, while the clearer northeast will see lows below freezing northeast of the Triangle. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 330 AM Thursday... Complex weather pattern Saturday into Sunday across central NC with another potential for accumulating light wintry precipitation across the northern counties. A s/w exiting the upper Midwest early Saturday will track sewd and cross the central Appalachians Saturday night, and exit off the NC coast Sunday. This s/w projected to weaken/dampen with time as it encounters strong confluence associated with the deep low off of the New England coast. The associated sfc and 850mb low expected to remain west of our region through late Saturday night, with a secondary low developing early Sunday along the NC coast (Miller "B" scenario). Initial lift over our region will be induced by isentropic upglide Saturday, and this is primarily focused across our NW Piedmont counties. Currently appears that light precipitation may develop around daybreak Saturday. The atmosphere, aided by evaporative cooling, will be cool enough to support light snow early Saturday across the far NW Piedmont before transitioning to rain later Saturday morning. If the light snow does develop, no accumulation is expected as the precip rates appear marginal/weak at this time. As the s/w and associated low level wave gets closer and the atmosphere moistens, expect widespread rain to develop over roughly the northern two-thirds of central NC Saturday afternoon, continuing into Saturday night. As the low level low develops near the NC coast late Saturday night-early Sunday, circulation around this feature will begin to advect a colder low level air mass into central NC, especially the northern-ne counties. Also, the cool pool associated with the passing of the s/w will further cool the column. These combined actions should lead to the rain becoming a rain/snow mixed late Saturday night-early Sunday, primarily across the far northern counties. During times of heavier precip rates, snow will become the dominate precipitation type, with a mixture of rain/sleet/snow during lighter rates. Way too early to determine with a high degree of confidence if any accumulation of significance will occur, though a light dusting on grassy areas does appear possible by early Sunday near the Virginia border. At this time will highlight the potential for light wintry accumulation in the HWO. As the sfc low exits off the coast Sunday afternoon, should see a decrease in precipitation coverage and intensity. Temperatures Saturday into Sunday have been adjusted downward based on potential for overcast skies and widespread precipitation. Central NC should see improving weather conditions Monday through Wednesday as a deep low off of the eastern seaboard and a digging l/w trough over the western U.S. will amplify an upper ridge from the Deep South into the Great Lakes. Associated subsidence with this feature should result in dry conditions across our region with a warming trend. temperatures early next week will start out 6-9 degrees below normal. As the air mass modifies, temperatures should return to near normal levels (highs in the mid 60s NW-near 70 south). Min temps in the low-mid 30s Monday and Tuesday mornings with frost probable. Min temps Wednesday morning should moderate into the upper 30s-lower 40s. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 1230 PM Thursday... VFR conditions will hold through the next 24 hours. A deep trough along the Eastern Seaboard today will shift eastward this afternoon through Fri, with drying and sinking air through the column. An expansive surface high building in from the NW through Fri will ensure dry low level air within a downsloping low level flow from the NW. A few gusts to 15 kts are possible this afternoon, otherwise light NW surface winds are expected. Looking beyond 18z Fri, VFR conditions will hold through Fri night, although an approaching storm system from the NW will result in a trend to MVFR Sat morning at INT/GSO/RDU, and Sat afternoon at RWI/FAY, with precip moving in from the NW. INT/GSO will likely trend to IFR Sat afternoon. Precip is expected to start off wintry at all sites except FAY Sat morning before trending to mostly rain. Low level wind shear may also be a concern Sat afternoon/Sat night at FAY. IFR conditions should dominate at all terminals Sat night, followed by a slow trend to MVFR Sun, although IFR cigs may redevelop late Sun night at INT/GSO and persist through Mon, while other sites trend to VFR Mon. A trend to VFR is expected at all sites Tue. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...mlm/Hartfield SHORT TERM...mlm LONG TERM...WSS AVIATION...Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.