Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201448 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1045 AM EDT Wed Mar 20 2019 .SYNOPSIS... Continental polar high pressure will extend southwestward across the middle Atlantic and interior Carolinas today. Meanwhile, coastal low pressure now developing off the north-central SC coast will track northwestward and inland across eastern NC tonight, then rapidly deepen up the middle Atlantic coast on Thursday. A pair of strong shortwave troughs aloft and related surface cold fronts will follow and cross central NC Thursday afternoon and Thursday night. && .NEAR TERM /THROUGH TONIGHT/... As of 1045 AM Wednesday... Little adjustment required to the near term forecast. Presence of a sfc ridge in the vicinity of the far NW Piedmont and attendant dry air will delay precip onset until later today, so have adjusted PoPS accordingly. 12Z upper air analysis depicts a narrow region of low level moisture advection focused across the NC Coastal Plain in association with a developing area of low pressure off the SC coast. The approach of a modest mid level perturbation lifting east-northeast from the SE U.S./northern FL peninsula should serve to strengthen this low this afternoon. This, in turn should strengthen the onshore flow into the NC Coastal Plain, leading to deeper moisture and lift. Thus, still expect areas of light rain to blossom over the Coastal Plain and Sandhills, and possibly as far west as the Triangle region between 5 PM and 8 PM. Increasing/thickening cloud cover and patchy light rain expanding in coverage will limit insolation, inhibiting temperature recovery. Anticipate highs this afternoon along and east of highway 1 in the 40s. Based on expected arrival of the deeper cloud coverage over the Triad, still expect highs to reach the low-mid 50s over the far western-NW Piedmont. Tonight, lift through the column will increase thanks to a s/w pivoting newd from the TN Valley into the southern Appalachians. In addition, central NC will be in the left exit region of a upper jet streaking across the Deep South. Meanwhile low level moisture will continue to advect into the eastern sections of our forecast area as a sfc wave lifts nwd through the NC Coastal Plain. This will lead to categorical PoPs over the northeast Piedmont-northern Coastal Plain, with likely PoPs over the remainder of the Sandhills and southern Coastal Plain, especially this evening. PoPs will quickly dwindle farther west as moisture depth will not be as great as compared to the east plus low level convergence will be weaker. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 415 AM Wednesday... Thursday morning the area of banded precipitation will be heading well north into Virgina as the dry conveyor belt punches north across central North Carolina. Most of the area will remain overcast at this time though as low level saturation remains trapped underneath the inversion. The brief break in the precipitation will be short lived as a stronger wedge of DCVA approaches from the west. A nice fall/rise height couplet will accompany the wave and cross the zones Thursday afternoon. Mid level thermal profiles will also begin to collapse as the wave moves overhead allowing showers to develop across central North Carolina. Further enhancing the already impressive lift will be a surface cold front. PWATs at this time are slightly elevated or around 0.58" (just above the mean for this time of year). Central NC also remains on the divergent side of the trough axis. Given the above have increased PoPs for Thursday. Temperatures for Thursday will again be extremely tricky as the low level clouds hanging around will likely limit highs. The NAM has highs struggling to get out of the lower 50s with the GFS showing lower 60s possible. The ECMWF splits the difference. For now have trended high temperatures down across the area for Thursday, but this might need to be further lowered. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 345 AM Wednesday... Dry weather with temperatures slightly below to near normal can be expected Friday with breezy conditions. Friday morning an upper level trough axis will be centered over central North Carolina as the DCVA from the exiting surface low ejects northeast. CAA and deep mixing are forecast on both NAM and GFS forecast soundings as the trough axis swings east. A breezy northwest wind Friday afternoon is indicated as forecast soundings show gusts in the upper 20 mph range via momentum transfer techniques. Friday night a vertically stacked upper level low over New England will continue to deepen and push a reinforcing cold front through the area. Low temperatures Saturday morning will be in the mid to upper 30s. During the day Saturday the stacked low over New England will pull northeast with low level thermal profiles moderating. Given the slightly further west placement of the low (and therefore trough axis) have lowered high temperatures a bit for Saturday. Dry weather will then continue into Sunday as the upper level low exits east. Right on the heels of the exiting upper level low will be another potent upper level low diving southeast of the Hudson Bay. This low will then absorb a weaker upper level low over the Midwest United States. The GFS is slightly stronger and less progressive with the upper level low in Quebec than the ECMWF. The CMC is even more progressive than the Euro. The stronger and less progressive solution allows the low over the Midwestern United States to be absorbed with the remnant energy swinging south around the base of the trough axis. The CMC/ ECMWF solution doesn`t absorb all of the energy across the Midwest and actually brings a closed low across the Mid-Atlantic States. The cold front in association with the low over Quebec crosses central NC the quickest with the GFS solution (early Tuesday morning) and the slowest with the CMC solution (Wednesday afternoon). For now have trended the forecast slightly towards the slower ECMWF and CMC solutions. The next chance of precipitation (after today/ Thursday) now looks to be delayed until Monday afternoon. This could be delayed even further if models trend further towards the CMC solution. && .AVIATION /11Z WEDNESDAY THROUGH SUNDAY/... As of 715 AM Wednesday... An area of 3-8 thousand ft ceilings and light rain will continue to blossom nwwd into cntl NC today, on the northwest side of a coastal low now developing off the n-cntl SC coast. As lift and moisture increase/deepen through the afternoon and early tonight, ceilings will likely lower into MVFR range at KFAY and KRWI prior to 18Z and KRDU between 18Z-00Z, also roughly coincident with the onset of a steady light rain. Conditions will lower to IFR or LIFR as the rain increases in intensity by early tonight; and while the heaviest steadiest rain will end from ssw to nne between 03Z-06Z, widespread IFR-LIFR overcast and periods of drizzle will remain through early Thu. Meanwhile, the wrn edge of the rain and sub-VFR conditions is likely to bisect the wrn NC Piedmont, including the GSO and INT vicinity. As such, rain and sub-VFR conditions will occur later (after 00Z) at those sites, and likely no worse than MVFR at INT. Outlook: Low overcast and areas of light rain or drizzle will scatter and lift to VFR from sw to ne Thursday morning to early afternoon. Thereafter, a pair of strong shortwave troughs aloft and related surface cold fronts will cross central NC Thursday afternoon and Thursday night, the former of which will likely be accompanied by a band of showers and sub-VFR conditions. Breezy to windy conditions will follow for Fri into Fri night. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...WSS SHORT TERM...Haines LONG TERM...Haines AVIATION...MWS

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