Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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662 FXUS62 KRAH 051122 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 622 AM EST Mon Dec 5 2016 .SYNOPSIS... Low pressure will move off the Southeast coast this morning. High pressure will build in briefly from the northwest this afternoon, then a second stronger low pressure system will cross the Gulf States and Carolinas Monday night through Tuesday. This system will shift off the coast Tuesday night, followed by high pressure building in for Wednesday into Thursday. An arctic cold front will cross the area Thursday night. && .NEAR TERM /Today through Tonight/... As of 240 AM Monday... Through today: Widespread light rain and drizzle over the area will taper off by mid morning, followed by a fairly quiet and dry day. Deep moist isentropic upglide from 285K through 305K will drop off rather swiftly from west to east this morning as the 850 mb trough sweeps through the Mid-Atlantic and Northeast, pushing a 40-50 kt southwesterly low level jet to our east. 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 Sunday/... As of 355 AM Monday... Wed-Thu Night: Although some drying will occur in assoc/w cold advection in the wake of a low pressure system progged to track offshore the Carolina coast Tue night, enhanced low-level moisture (relatively speaking) is expected to linger over the region Wed/Wed night as low-level flow quickly backs to the south/southwest (giving rise to weak warm advection) in response to upstream height falls as potent shortwave energy ejects E/ENE from the Rockies into the OH valley and the leading edge of an arctic cold front progresses eastward to the southern Appalachians by 12Z Thu. Light rain or sprinkles will be possible in the wake of the leading edge of the arctic front Thu morning, assuming a favorable juxtaposition of low- level fgen/ strengthening cyclonic flow aloft and lingering low- level moisture. The 00Z ECMWF shows little if any measurable precip over central NC Thu morning, while the GFS indicates a hundredth or two across most of the area. With the above in mind, will continue to indicate a slight chance of showers or sprinkles progressing from west-to-east across central NC Thu morning. Expect highs in the 50s on Wed, lows in the upper 30s to lower 40s Wed night. Highs on Thu will depend on fropa timing and whether or not anafrontal precipitation /evap cooling/ occurs. At this time, will indicate highs on Thu ranging from the upper 40s far NW to mid 50s far SE, with temperatures falling west of Hwy 1 during the afternoon. Lows Thu night will depend on fropa timing and ensuing cold advection . Expect lows ranging from the mid 20s NW to lower 30s SE. Fri-Sun: Expect cold/brisk conditions on Friday with highs in the mid/upper 30s to lower 40s and a NW breeze assoc/w strong cold advection as 1040 mb arctic high pressure builds eastward from the central plains toward the Appalachians in the wake of the cold frontal passage on Thu. Expect very cold lows in the upper teens to lower 20s Sat morning as the arctic high settles over the Carolinas late Friday night. Expect highs a few degrees warmer on Sat, further rebounding on Sun when the modified arctic high shifts offshore, though insolation may be offset to some degree by increasing mid/upper level cloud cover from the west. -Vincent && .AVIATION /12Z Monday through Friday/...
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As of 622 AM Monday... Conditions are currently improving to VFR at INT/GSO, but elsewhere, poor aviation conditions will dominate for another few hours, until mid morning. An upper level disturbance passing through the region combined with low pressure tracking SW to NE over the Southeast states brought widespread IFR/LIFR conditions in steady light rain and drizzle to the area overnight. This rain and IFR/LIFR conditions have moved out of the NW sections, but will linger until 13-15z at RDU/RWI/FAY, when a trend to VFR will occur as the low pressure area moves offshore. VFR conditions and dry weather will then hold areawide today into early evening. The approach of another stronger disturbance and a stronger surface low tracking ENE toward the Mid South and Southeast states will bring an increase in clouds this evening, with a trend to MVFR then IFR after 06z tonight (06z Tue), occurring around 06z-09z at INT/GSO, 07z-10z at RDU/FAY, and 08z-11z at RWI, with steady rain spreading in from the SW. Surface winds will be light mainly from the north this morning, becoming NE this afternoon into tonight. Looking beyond 12z Tue, IFR/LIFR conditions in on-and-off rain will persist through much of Tue, with gradual improvement from west to east Tue night as this storm system moves east off our coast, although areas of fog may linger into early Wed morning in the east. VFR should dominate much of Wed, then sub-VFR conditions may return Wed night through much of Thu as an arctic cold front approaches from the NW. Much colder air and VFR conditions are expected Thu night through Fri. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Vincent AVIATION...Hartfield

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