Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 221221 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 721 AM EST Mon Jan 22 2018 .SYNOPSIS... High pressure will drift offshore this morning, and subsequently allow a warm front to retreat north across the southeastern U.S. today. The warm front will lift across NC and VA tonight, immediately ahead of a lead cold front that will cross the region on Tuesday. A secondary cold front will follow and cross the region Tuesday evening. && .NEAR TERM /TODAY/... As of 340 AM Monday... A mature, deep layer cyclone over the cntl Plains this morning will migrate newd across the mid MS Valley today. At the base of the cyclone, a powerful srn stream jet observed at 00Z/22nd across nrn Mexico, s-cntl TX and the lwr MS Valley --including 145 kts at 200 mb at Del Rio-- will meanwhile stream enewd across the sern U.S. Satellite imagery indicates cirrus and cirrostratus, in strongly difuent upr level flow between the srn stream jet axis and the aforementioned cyclone/closed low, has already started to overspread w-cntl NC this morning; and it will continue to expand newd across the state today. It appears to be relatively thin enough to allow filtered sun to shine through it, although it`s always difficult to determine the opacity of high cloudiness without the benefit of the visible channel. At the surface, 1024 mb high pressure analyzed just offshore the NC coast at 09Z will continue to drift ewd, and allow a light sly return flow to envelop the Carolinas. Within that return flow, a developing coastal front, evident in surface and buoy data from the nern GOM and cntl FL, newd along the Gulf stream, will retreat nwd across the sern U.S. today, and into nrn SC and srn NC by 00Z. The approach of that boundary and associated low level warm/moist advection will result in the continued nwd development of a shield of stratocumulus now developing along and north of the coastal front, into srn NC with associated cloudy or mostly so conditions by late afternoon. A slight chance of an afternoon shower will also result over the srn-cntl Coastal Plain. High temperatures mostly in the 60s are expected, though a few persistence lwr 70s will be possible across the srn Piedmont, Sandhills, and srn Coastal Plain, particularly if the aforementioned high cloudiness indeed allows filtered sunshine through. && .SHORT TERM /TONIGHT AND TUESDAY/... As of 400 AM Monday... Tonight: The warm front and associated leading edge of surface dewpoints in the 50s will surge nwd across cntl NC tonight, with low temperatures likely to occur during the mid-evening hours, before slowly rising overnight. Despite the increasing surface theta-e, bufr forecast soundings suggest a shallow, near-surface stable layer will likely remain in place, thereby muting surface-based instability and threat of severe weather overnight. Nonetheless, HREF mean MUCAPE values are forecast to climb to around 250 J/kg between 06-12Z, in a strong WAA regime driven by a 45-60 kt sswly llj at 925-850 mb. As such, scattered to numerous (slightly elevated) showers are apt to develop and overspread cntl NC, along the axis of the llj, overnight. Tuesday: The warm front will be quickly followed by an effective (lead) cold front forecast to cross cntl NC between 12-15Z over the nw Piedmont and between 18-20Z over the Coastal Plain. The passage of this cold front --one that may be better characterized as a dry line, and accompanying broken line of convection-- will result in clearing, drying the in the low levels, and the deepening of a diurnal mixed layer that will promote the development of strong sswly winds and associated gusts that will peak in the 30s kts per bufr forecast soundings. In addition, some realization of weak surface-based instability may occur ahead of the convective line with diurnal heating, mainly east of Hwy 1, though widespread pre-frontal cloudiness will limit this heating and associated destabilization, to a several hundred J/kg or less. Nonetheless, a few strong convective wind gusts will be possible as the line moves east. Any appreciable cooling will lag this feature and not occur until a secondary front settles sewd across cntl NC after 21Z. High temperatures will consequently again climb into the 60s, to lwr 70s over the sern CWFA. Storm total precipitation amounts are expected to be around a tenth to quarter inch on average, and scattered, so a widespread soaking rain is not anticipated. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... As of 210 AM Monday... Expect dry weather through Friday night. An upper level shortwave and a reinforcing dry cold frontal passage is expected Wednesday night/Thursday. Surface high pressure is expected to build into the area in the wake of the secondary cold front and remain over the area into Saturday. The upper level ridge will move eastward over the Carolinas through Friday night. Another upper level trough and surface cold front will develop over the Midwest and progress eastward toward the Mid-Atlantic over the weekend. As southwesterly flow increases, so will the warm, moist advection into the region. As a result, cloud cover and chances for precipitation will increase late Saturday into Sunday as the cold front approaches. As of the latest forecast cycle, the front progresses through Central NC by Sunday night, with cool high pressure building in behind it. Highs will be generally in the upper 40s north to mid 50s south through Friday and lows in the upper 20s to low 30s Wednesday and Thursday nights. Temperatures will moderate through Sunday, cooling down once again in the wake of the front. && .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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As of 720 AM Monday... The flow around high pressure off the NC coast will allow a warm front and associated leading edge of more humid/moist air to surge into cntl NC from south to north between 22Z-06Z. A lead band of 2500-4000 ft stratocumulus will accompany the warm front; and this may result in an MVFR ceiling and a widely scattered shower around FAY as early as 22Z. Sly flow will strengthen, particularly just above a shallow layer of stability near the surface, to around 40-45 kts at 1500 ft late this evening-early tonight; and this will result in both the newd development of widespread 500-1200 ft ceilings and low level wind shear conditions between 02Z-07Z. Initially scattered showers will also become more numerous overnight, with a few thunderstorms possible Tue morning. Outlook: The above-referenced IFR-MVFR and llws conditions, and showers and isolated thunderstorms, will persist until a cold front crosses cntl NC from west to east on Tue. A subsequent return to VFR will result behind the cold front, generally between 12Z-15Z at Triad sites and around 18-20Z at ern ones. A very breezy swly wind will also develop behind the front, with gusts to around 35 kts probable for at least a few hours on Tue.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...KC AVIATION...MWS

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