Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250238 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 935 PM EST Wed Feb 24 2021 .SYNOPSIS... A dry cold front will settle southeastward across central NC Thursday morning. Cooler high pressure will follow and build across the middle Atlantic and into central NC Thursday through early Friday. Meanwhile, a warm front will retreat northward toward the region late Friday and Friday night, with associated lift and moisture that will promote the development of cold air damming over the middle Atlantic, later Fri into Sat. && .NEAR TERM /THROUGH TONIGHT/... As of 935 PM Wednesday... A mild night out ahead of the approaching dry cold front... Not a cloud in the sky was noted across the entire length of NC as of mid-evening tonight. In addition to the clear skies, it continued very mild with a SSW flow at 10 mph or so, throughout our region. 900 PM temperatures ranged in the mid 50s to mid 60s. Dew points were in the 30s indicating the extent of the dry air (even at the surface). 00z/25February - GSO and RNK RAOB information - indicated very dry air aloft, as well. The high pressure to our east will give way to the cold front over pulling southeast through KY/WVA later tonight and early Thursday. The front was producing a line of light rain showers over KY and WVA, but will lose any lift/moisture as it approaches our region as the dynamics pull out to our NE. The only thing that we will note will be an increase in mid level cloudiness late tonight in the NW, then this cloudiness will push into much of central VA and north-central NC from daybreak to 900 AM as the front seeps into the northwest third of the state then. Expect the SSW wind at 8-12 mph to gradually become more westerly and diminish just prior to dawn. Lows will continue to be mild in the pre-cold frontal resume. Expect mostly mid 40s with some readings near 50 possible in the urban areas for minimum temperatures. Previous discussion issued 215 PM Wednesday... A positive tilt shortwave trough will continue to shear enewd across the Great Lakes and Northeast tonight, to NB by 12Z Thu. An accompanying narrow mid level moist axis and surface cold front -- the latter stretching at 18Z from a 1001 mb low over Lake Huron swwd from DET to DAY to LIT to SAT-- will settle sewd and into the nrn NC Piedmont between 08-12Z Thu. Clear skies through most of the night will become filled with scattered to broken, and possibly briefly overcast, 8-10k ft altocumulus over the nrn half of cntl NC during that time. Overnight lows are expected in the lwr-mid 40s, with late night-early morning rising temperatures possible as the aforementioned mid level clouds arrive across the north. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 305 PM Wednesday... Upstream of broadly cyclonic and confluent flow at the base of a positive tilt trough that will stretch from Atlantic Canada wswwd into the OH and mid MS Valleys, a shortwave trough will pivot ewd from the Southwest to the lwr-mid MS Valley by 12Z Fri. Beneath that confluent flow aloft, cP high pressure now building across the cntl High Plains will strengthen to between 1030-1035 mb while building ewd across the mid MS and OH Valleys Thu and middle Atlantic Thu night. So while initial CAA and nly low level flow behind the cold front forecast to cross cntl NC Thu morning will result in temperatures about 10 degrees cooler than the warm ones of Wed, the brunt of colder air and MSL pressure rises will be initially blocked by the Appalachians until the high builds across PA/MD late Thu night, with associated dry air ridging that will extend swd into cntl NC by the end of the forecast period. A narrow band of scattered to broken, to briefly overcast, altocumulus will settle sewd and out of cntl NC through midday, or early afternoon across our southeast zones, with following mostly sunny-clear conditions during the afternoon and evening. Multi- layered cloudiness and associated cloudy or mostly conditions will then arrive from the west overnight-Fri morning, some of which may produce a little light rain over the far srn and wrn NC Piedmont by 12Z Fri, with temperatures mostly in the upr 30s to around 40F. Even if the precipitation were to arrive earlier and with more complete low level saturation/wet-bulb effect, above freezing wet bulb temperatures in at least the lowest 750-1000 ft suggest the predominant precipitation type would be rain, with perhaps a little nuisance sleet at onset. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 250 PM Wednesday... In a sentence, every 12 hour period of the extended forecast has a chance of rain. So there`s that. More specifically, Friday morning will start with high pressure near Washington DC providing cool northeasterly flow into the Carolinas while the front moving through tonight will be nearly stationary to the north of the Gulf Coast. The main low pressure along the stationary front will be across east Texas, and that low is expected to move northeast to eastern North Carolina by Saturday morning. Precipitation is expected to move in late Friday and continue through the night. Despite the cooler air that will be in place when the precipitation starts, temperatures should be warm enough to allow all precip to fall as rain, with temperatures in the 40s and lower 50s through the day and night. As the low moves northeast Saturday, showers will continue to the south and west of the low, and models are still showing some variation in how much of that precipitation shield will extend over North Carolina. Showers appear as if they will be more scattered in coverage Saturday. However, another low pressure system will move into the Ohio River Valley by Saturday and move northeast, with a cold front extending to the south. Rain from the front will begin to move into the region late Sunday and continue both Sunday night and Monday. The 12Z GFS is more optimistic in pushing the cold front through the area by Monday evening and allowing high pressure to build into the Ohio River Valley Tuesday and North Carolina by Wednesday. On the other hand, the 12Z ECMWF temporarily clears the front Monday night, then has another wave of low pressure develop along the front and brings rain all the way into Wednesday. Will stick with slight chance to chance pops through this entire time period. and will hope that the models begin to come into better agreement for the beginning of the next work week. Temperatures will be a bit of a roller coaster. The warmest day will be Sunday, with highs ranging from the mid 60s to the mid 70s, but Tuesday`s highs will be back in the 40s and 50s, similar to Friday. The coldest lows will be Monday and Tuesday nights, with temperatures in the mid to upper 30s. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... As of 640 PM Wednesday... VFR conditions expected at all sites through the TAF period. The development of a 35-40 kt, swly low level jet later this evening, atop the very light flow at the surface, will favor a short period of low level wind shear overnight primarily at Piedmont sites and RWI. Meanwhile, a cold front will approach from the northwest and settle sewd across cntl NC, with an accompanying narrow band of altocumulus (~8-10k ft) and associated brief ceilings, Thursday morning. Outlook: Periods of IFR-MVFR conditions and rain are expected to occur along and to the north/cold side of a frontal zone forecast to waver over the Carolinas and srn middle Atlantic Fri through early next week, with the relative highest probability of those sub-VFR conditions and related cold air damming over cntl NC Fri through early Sat. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett/MWS NEAR TERM...Badgett/MWS SHORT TERM...MWS LONG TERM...Green AVIATION...Badgett/MWS

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