Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230635 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 235 AM EDT Thu Mar 23 2017 .SYNOPSIS... Continental polar high pressure will continue to modify over the Srn Middle Atlantic states through tonight. A warm front will retreat north across the region on Fri, as the high drifts east toward Bermuda. && .NEAR TERM /THROUGH TONIGHT/... As of 945 PM Wednesday... Forecast is on track. The opaque high clouds which covered the southern half of the forecast area for much of the afternoon have been shunted southward with the push of deep dry air into the area. Skies should remain clear for the next several hours, although high level moisture to our NW (evident on upstream soundings) should lead to increasing high clouds late, and these may be orographically enhanced yielding thicker cloud cover over the western CWA. Temps are running a degree or two warmer than the forecast pace, although as northeasterly surface winds die off later tonight, readings should plunge given the low dewpoints and expectation of good radiational cooling. Lows in the upper 20s to lower 30s. -GIH Earlier discussion from 250 pm: An upper level ridge over the central U.S. and a l/w trough along the eastern seaboard will funnel cold dry air into central NC tonight. This drier air already made evident by sfc dewpoints in the teens across the western Piedmont at 18Z. This drier air will continue to spread south and east through this evening. Orographic induced high clouds will slowly fade/dissipate through early evening as the atmosphere aloft dries out and the winds field weakens. Sfc winds will remain 4-8kts after sunset, though should decouple after midnight. With the cold dry air mass in place and near calm sfc winds, should see temperatures drop into the upper 20s- lower 30s overnight. Patchy frost possible in the well sheltered areas though most places will see little if any frost due to the dry low level air mass. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 250 PM WEDNESDAY... Thursday, 850mb thermal trough overhead signals a day of well below normal temperatures. While skies will be sunny, the cold dry air mass deposited by the high pressure system will yield max temps in the low-mid 50s, a solid 10-12 degrees below normal. Thursday night, l/w trough will lift to the ne while the upper ridge will extend across our region. This set-up will maintain mostly clear skies and chilly overnight temperatures. Under clear skies and a light wind regime, temperatures will quickly fall after sunset with overnight temperatures generally near 30 to the lower 30s with the coldest temperatures across the far northeast Piedmont and the northern coastal plain. && .LONG TERM /Friday through Wednesday/... As of 305 PM Wednesday... Expect above normal temps and below normal precip chances at least into Tuesday, with high confidence. Divergence in model solutions beyond this time leads to increased uncertainty Tue night/Wed. Fri/Sat: Deep troughing featuring a closed low over SE CO early Fri will continue to build downstream ridging over the Gulf into the Mid South and Southeast heading into the weekend as it tracks slowly eastward into the S Plains, while surface high pressure along the East Coast shifts east out over the ocean. A batch of elevated moisture now over the N/C Plains is poised to ride atop the ridge Fri, bringing some mid and high cloudiness, but otherwise the column will be sufficiently dry and stable for a precip-free forecast and partly to mostly sunny skies, dominated by scattered to broken flat cumulus, within light but long-fetch onshore-directed low level Atlantic flow. Thicknesses start out a bit below normal Fri then rise through Fri/Sat, indicating highs of 64-71 Fri and 71-76 Sat, with lows of 46-50. Sat night-Sun night: The aforementioned deep low will move from the mid Miss Valley Sat evening northeastward with a negative tilt as is opens up over the Great Lakes region Sun night. This system will be reflected at the surface as an occluding front passing to our NW, dragging only a weak trough into N/W NC, so we`ll stay in the warm sector of this system as weak ridging begins to build in anew from the SW by Sun night. Low level moisture transport will steadily increase through this period, as PW surges from the SW to over 1 inch, focusing on the W CWA Sun morning before shifting east to central and E NC late Sun through Sun night, corresponding with passage of the broadening mid level trough axis and weak DPVA, as well as a zone of enhanced upper divergence and erosion of the 850- 700 mb cap. With minor changes to delay onset, will keep the trend to good chance pops Sun morning, spreading east through Sun night, with partly to mostly cloudy skies. Lows in the low-mid 50s, highs 70-78 Sun, followed by lows in the mid-upper 50s Sun night. Mon-Wed: The overall pattern becomes increasingly active, wavy, and progressive next week. The open wave will move ENE through the Northeast states then offshore to the ESE, as a mostly phased trough shifts eastward through the E CONUS. The GFS greatly amplifies the northern portion of this trough over the NE on Wed, while the ECMWF is weaker with a later amplification over the NW Atlantic late in the week and, as a result, it builds ridging back into the Gulf States and Southeast from the west on Wed. The result is a cold frontal passage and cooler temps Wed with the GFS, and much warmer temps Wed with the ECMWF. Given the dominance of the southern stream, with less polar air injection through mid week, will lean toward the ECMWF and keep temps above normal. Will have low chance pops over the SE on Mon near the sea breeze, then better chances areawide Tue as the trough axis moves through. Dry/warm Wed. -GIH && .AVIATION /06Z Thursday through Monday/... As of 230 AM Thursday... Continental polar high pressure will result in VFR conditions through the TAF period. Surface winds around the high will generally be light and gradually veer from NEly/ENEly this morning to Ely/ESEly by this afternoon. The exception will be at FAY and RWI for a few hours mid to late morning, when winds may briefly increase to around 10-15 kts, with occasional gusts between 15-20 kts. Skies will be clear, aside from periods of thin cirrus. Outlook: There will be a chance of MVFR-IFR visibility restrictions in radiation fog in SErn NC (FAY and possibly RWI) Fri morning, then with patchy coverage throughout central NC Sat morning. A chance of showers and storms and sub-VFR conditions mainly at Piedmont TAF sites will follow for Sun. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...Hartfield/WSS SHORT TERM...WSS LONG TERM...Hartfield AVIATION...MWS

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