Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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041 FXUS62 KRAH 052049 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 350 PM EST Mon Dec 5 2016 .SYNOPSIS... High pressure will build across the Middle Atlantic states through tonight, ahead of a Miller B low pressure system and associated cold air damming, which will result in the development and deepening of an area of low pressure through the eastern Carolinas on Tue. Another area of high pressure will build overhead for the middle of the week. && .NEAR TERM /THROUGH TONIGHT/... As of 1000 AM Monday... Today: The trend to a prominent downslope-directed component to the low level flow will help scour out the lingering low clouds within the trailing cool stable pool, to the northwest of the surface frontal zone stretching across the southern Gulf states, GA, and the coastal Carolinas. But the continued presence of the upper jet core to our NW and N and steady elevated integrated WV transport to our SW and S will keep a flow of mid and high clouds over the area today, yielding milky sunshine at best over much of the area, thicker across the south and a bit thinner in the north. Given the lull in forcing for ascent today --including a brief uptick in mid level heights in the wake of the shortwave trough shifting NE into the Mid-Atlantic/Northeast as well as the weak surface high nosing in from the NNW -- dry weather is expected, after a period of chance pops in the southeast portion of the forecast area for a couple of hours near and soon after daybreak. The period of fair skies today balanced with above normal thicknesses should help push temps up to near normal readings today, with highs mostly in the upper 50s. Tonight: The respite in the rain will be short-lived, as lift and deep moisture spread back in from the SW this evening. The mid level shortwave trough tracking NE over TX today will de-amplify but remain potent as it moves NE through the western Gulf States tonight. This wave will coincide with a strengthening surface low that moves from LA into the Mid South tonight, forcing strengthening and deepening moist isentropic upglide from SW to NE during the evening hours. Strong upper divergence in the right entrance region of an accelerating jet to our north will also contribute to vigorous deep lift. With a minor speed-up in timing, I have retained the ramp-up in pops from SW to NE to categorical areawide by midnight. Expect gradually increasing NE winds, especially across the south half, as the MSLP gradient tightens between the exiting surface high and the incoming low. Lows 41-47. -GIH && .SHORT TERM /Tuesday through Tuesday night/... As of 255 AM Monday... Widespread rain will persist through much of Tue with chilly temps. The mid level wave will continue moving NE through the southern Appalachians and VA, as a Miller "B" surface pattern develops, featuring the primary low losing steam over TN into WV while secondary low pressure forms along the front over SC early Tue and tracks NE across SE and coastal NC through Tue evening, then offshore Tue night. Lift will be its deepest and strongest Tue morning with the vertical juxtaposition of the peak upper divergence, strongest PW flux and IVT, and intense mass convergence in the nose of the large 45-50 kt 850 mb jet. Total rainfall amounts of 1-2" are likely, according to model consensus. Temps are likely to budge little on Tue given thick clouds, steady rain, and a wedge regime in place, so expect highs of just 43-49 over much of the area, with highs of 50-53 in the far SE CWA, through which the models show the warm sector edging northwestward during the day. An end in precip from SW to NE is expected during the mid to late afternoon as the mid level wave shifts to our north and NE, with an eastward departure to the 850 mb jet, and as the secondary low (which will have taken over as the primary low by that point) shifts just off the northern Outer Banks by 00z Wed, rain chances should be ending by mid evening or so, with dry weather overnight. We should see a low level residual cool stable pool behind the low, however, covering much of interior NC, suggesting a very slow dissolution of the low level clouds Tue night as this air mass should be resistant to dispersion either horizontally or vertically. Will taper down sky cover gradually overnight. Expect lows from the upper 30s NW to lower 40s SE. -GIH && .LONG TERM /Wednesday through Monday/...
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As of 350 PM Monday... In the wake of the departing low pressure on Tuesday, and preceding a strong arctic front moving through the Midwest, the flow will be weak over central NC on Wednesday. Forecast soundings show enough drying to erode the lingering low clouds and/or fog early Wednesday, with daytime heat into the mid 50s (per statistical guidance) likely to result in a cu field, mainly east. Weak but moist southerly flow should redevelop late Wednesday in response to weak height falls and an intense upper jet associated with the aforementioned cold front and result stratus Wednesday night. Lows 39-44. The cold front, progged to be just west of the Yadkin early Thursday morning, will will cross the area during the first half of the day, with strong cold advection behind it Thursday evening and overnight. The front itself is not expected to produce much precip, if any, though the GFS cranks out some light qpf, owing likely to a period of strong low-level FGEN and sufficiently deep moisture across the northern half of the area. The current slight chance POP will be maintained. Highs in the upper 40s to mid 50s. Strong cold advection Thursday night should result in gusts to 15- 20kt and wind chills in the upper teens, as lows drop into the mid to upper 20s. Arctic high pressure will then build in over the weekend, with forecast thicknesses progged to approach 1270m Sat/Sun morning. Lows should have little problem hitting the upper teens and lower 20s. The high then quickly moves offshore and the synoptic front return north with the next chance of rain early next week.
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&& .AVIATION /18Z Monday through Friday/... As of 330 PM Monday... Initially VFR conditions through this evening will yield to progressively lowering ceilings tonight, into IFR-MVFR range late tonight-early Tue, as lift and moisture increase downstream of a complex low pressure system approaching from the SW. Patchy light rain will also begin to fall from the VFR ceilings this evening, then increase in coverage and intensity through early Tue. A few rumbles of (elevated) thunder, whose cloud bases would be rooted around 5000 ft owing to a cold and stable low level air mass, will be possible roughly between 14-18Z Tue, as lapse rates aloft briefly steepen with the passage of a mid-upper level trough. The passage of the trough axis will also cause widespread rain to end, and clearing to commence, from SW to NE throughout the afternoon and early evening hours. The clearing, in conjunction with wet soil, will result in the development of patchy fog Tue night. Outlook: Chance of MVFR ceilings ahead of an arctic cold front Wed night-Thu, and blustery NW winds behind the front late Thu-Thu night. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Smith AVIATION...MWS

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