Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230043 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 840 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 /TONIGHT THROUGH FRIDAY NIGHT/... As of 245 PM Thursday... Through tonight: Mid cloudiness associated with the passing shortwave trough will gradually dissipate as the wave moves off the Carolina coast early tonight, as the surface ridge to our W/NW builds in. With overall sinking motion through the column and a light NW wind overnight, expect clear skies with decent radiational cooling. Lows 28-33. Fri/Fri night: The mid level trough takes on a negative tilt out over the Atlantic Fri, keeping NC beneath northwesterly mid level flow as the surface ridge extends through the area. With a continued lack of moisture and descent through the column, expect fair to sunny skies Fri. Temps should top out a few degrees warmer than today, 53-60. A mid level shortwave trough over the Rockies Fri morning will top the ridge through Fri night, moving through the Midwest. An associated surface low will move E over the central Plains, while the preceding southerly flow out of the Gulf will prompt deepening moist upglide to our west and NW. As this moist ascent spreads eastward late Fri night, low chance pops will spread into W NC, and based on the average timing from the models, will bring in isolated precip chances late. The vertical thermal and moisture profiles (including the near-surface wet bulb trace) suggest that this may fall as a little light snow or sleet in the Triad late Fri night at onset, but impacts will be minimal to nothing. Given that clouds will be increasing from the west overnight, temps in the Triad may level off at milder readings, such that even low level wet bulbs may be at or above freezing. Expect lows of 28-37 with increasing clouds. -GIH && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 330 PM Thursday... A low pressure system forming over Missouri will drop southward through the Carolinas over the weekend bringing a fair amount of rain and possibly some winter P-Types to the northern portions of our forecast area. Synoptically this system is neither a true Miller A or B scenario as the low drops in from the northwest instead of from the southwest and true secondary low never forms west of the mountains. Most of the jet dynamics with this system remain well to the north of the area, but as the low comes through Early Sunday morning an upper level jet streak passes to the southwest which will help bring some lift to the area. There is high confidence that this event will bring a good amount of rain to the area through the weekend, which won`t be favorable for any outdoor plans. At this time, models are predicting up to an inch of rain for this event with higher amounts across the northern half of the forecast area. Winter P-Types: There are many factors that make this a low confidence event for winter p-types at this time. An analysis of surface wetbulb temperatures show period Saturday morning of below zero wetbulbs across the Triad and VA border counties. The best chance for some snow mixing in would be right around 12z but the precipitation may not actually be in the Triad yet at that time or just arriving. When it does, it will have a lot of dry air to overcome in the low levels making sublimation a possibility for any snow. By the time those surface layers moisten up, temperatures may be too high to support snow. At that point, expect much if not all of the precipitation on Saturday to fall as rain. Expect high temperatures in the low to mid 40s across the north with mid 40s to low 50s in the south. Sunday morning will be the best chances for some accumulating snow as thermal profiles are more supportive of it and moisture and cold air are in place simultaneously. The problem is that forecast soundings lose a lot of the lift at this time and moisture in the dendritic growth zone is drying out. That would favor more sleet than snow. Therefore have added very small accumulations north of I- 85 and east to Halifax of less than a half of an inch on Sunday morning. Otherwise this should be a rain or rain/sleet event for points south. Sunday, temps will be in the low 40s across the Triad for highs with closer to 50 degrees in the south. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 130 PM Thursday... Mostly dry weather is expected during the beginning and mid part of the work week, although the clouds should hang on through at least Mon evening (and perhaps into Tue in the western CWA) as a semi- anchored surface high, centered over SW Quebec into the Maritimes, ridges SSW through NC, locking the wedge air mass over central NC. Mid level ridging will steadily build over the eastern CONUS through mid week, between deep closed lows over the Desert Southwest and over the NW Atlantic, ensuring a lack of forcing for ascent and continued tranquil weather (albeit with periodic cloudiness). Model solutions start to diverge Wed/Thu with the GFS trending more progressive, weakening and lifting out the NW Atlantic low, which allows the E Coast ridge to weaken and move east. The ECMWF and Canadian keep the Atlantic low in play with a southward drift, which keeps the mid level ridge over the Southeast. The slower blocking pattern is preferred, which will mean a trend to increasing sunshine and warming temps starting Tue and especially Wed/Thu, when low level thicknesses will reach or exceed seasonal normals with a modifying surface air mass. -GIH && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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As of 840 PM Thursday... 24 Hour TAF Period: VFR conditions are expected to continue through the 24 hour TAF period as surface high pressure moves across the Southeast U.S. This will lead to continued VFR conditions with generally mostly clear/mostly sunny skies through early afternoon Friday. However, a few mid/high clouds will affect KRWI and KRDU this evening as the departed mid/upper level trough continues to shift further to the east of the area overnight and some flat cumulus at around 5 to 7 kft areawide Friday afternoon. Otherwise, VFR conditions will continue, with possibly some wind gusts of up to 20 kts out of the WNW on Friday afternoon. -BSD Outlook: 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
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...Hartfield SHORT TERM...Ellis LONG TERM...Hartfield AVIATION...BSD/Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.