Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230624 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 224 AM EDT Mon Oct 23 2017 .SYNOPSIS...
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A potent upper level trough and accompanying surface frontal system will approach from the west and cross the Appalachians and middle Atlantic states this afternoon through tonight. A secondary cold front will follow and cross our region late Tue and Tue night.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 1020 PM Sunday... Closed upper low over the Lower/Middle Ms Valley this evening will progress east and become increasingly negatively tilted as it moves into the TN Valley by daybreak. Strengthening SELY 925- 850mb moist upglide in advance of the low will be maximized across western NC, leading to the expansion and lowering of the 3 to 4 kft stratus deck across upstate SC into western Piedmont counties overnight, that will then spread east central and eastern NC between 12 to 18z Monday. Can`t rule out an isolated shower/sprinkles within the low-level warm moist air advection, but measurable rain chances should largely remain along and west of the Yadkin River, near the upslope areas. Dewpoints have recovered into the upper 50s to lower 60s this evening, which will result in significantly milder temperatures overnight. Lows generally in the upper 50s to lower 60s, with some mid 50s possible across the NE. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 335 PM Sunday... Model difference from 24 hours ago is that the models are trending faster with system crossing our region Monday night. S/w over the TN Valley early Monday will lift newd into the lower OH Valley by Monday evening. This system takes a negative tilt, thanks to strong jet digging on the backside of the system, resulting in upper level heights of of 60-80m over central NC. Low level jet on the order of 40-50kts will supply abundant warm moist air, with precipitable water values of 1.5-1.8 inches expected by late Monday. Additionally, near term model guidance now depicting a sfc wave lifting nwd across the foothills/western Piedmont Monday evening. Expect shower coverage to increase Monday afternoon west of highway 1, encroaching upon the highway 1 corridor after 21Z, more likely toward 00Z, then crossing the coastal plain in the late evening/first half of the overnight. Now appears that the bulk of the showers will exit our far east-ne counties prior to 09Z. While kinematics quite impressive with bulk shear 40-50kts (highly supportive of organized convection), model guidance remains weak/anemic when it comes to low level instability as MLCAPE on the GFS are below 500 J/kg. Storm relative helicity (0-1km) on the order of 150-300 m2/s2 by Monday evening raises concerns for rotating updrafts. Expect a band of heavy showers to progress east-ne across central early Monday evening with isolated thunder probable close to the SC border. Due to strength of the low level flow, strong/locally damaging wind gusts expected along the band of showers, especially where any bowing occurs. Lack of low level instability may deter tornadic threat, though if this parameter were to increase closer to 800-1000 j/kg MLCAPE, then tornadic may be realized. If low level instability achieved, believe tornadic threat will be greatest over the southern and western Piedmont, since this region in closer proximity to the sfc wave. High temperatures Monday highly dependent upon shower coverage. If shower coverage becomes widespread by early afternoon across the west, then high temps may end up being a couple of degrees cooler. Due to expectation that showers will occur late in the day/early evening in the east, potential for temperatures along and east of highway 1 reaching well into the 70s. Expect warm/breezy conditions Monday evening, with cooler air not reaching the western Piedmont until after midnight, and likely not reaching the coastal plain until close to daybreak. && .LONG TERM /TUESDAY THROUGH SUNDAY/... As of 220 PM Sunday... Low level jetting and the associated deep moisture plume will be moving east of the Coastal Plain early Tuesday morning, with drier and cooler air beginning to filter in as the moisture tap cuts off. Cloudiness will be diminishing, with stratocumulus lingering primarily across the northern tier associated with the H85 trof which will be moving across during the afternoon/evening. Cold air advection will be delayed until the surface front exits the area towards sunset, allowing highs to reach mostly lower 70s, with some upper 60s in the northwest. The cool air settles in Tuesday night and Wednesday, with mins mostly in the mid 40s Wednesday morning warming to mostly low and mid 60s in the afternoon. The main long wave trof axis will cross the area Wednesday night as it rotates across the Great Lakes into New England. The ensuing northwest flow will reinforce the cool air and perhaps produce some scattered very light showers in the lee of the mountains, but it will be short-lived as the progressive pattern rapidly transitions to a short wave ridge and rising heights in the late week. Lows Thursday morning will be our coolest of the period, falling to the upper 30s to lower 40s, with highs Thursday topping out 5-7 degrees below normal in the 60 to 65 range. The short-lived ridging shifts offshore and ensuing southerly return flow induces a modest warming trend into the weekend, with highs from 65 to 70 on Friday, and upper 60s to lower 70s on Saturday. Our next front will be approaching from the west, perhaps as early as Saturday night, with associated showers and a cool down into the 60s likely on Sunday. && .AVIATION /00Z MONDAY THROUGH SATURDAY/...
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As of 215 AM Monday... In strengthening and increasingly moist east to sely low level flow off the Atlantic ocean, an axis of MVFR ceilings and showers extending from se to nw across SC, will gradually edge ewd and into the Triad vicinity (INT/GSO) between 12-15Z this morning, then continue, with periods of IFR ceilings, today through this evening. Meanwhile, radiation fog, and perhaps some associated ceilings, will occur at RWI, where radiational cooling potential will linger in closest proximity to the ridge of high pressure that has extended across NC in recent days, which has since moved offshore. Aside from a brief instance of an MVFR ceiling at RDU and FAY, generally VFR conditions are expected to persist at those locations until this evening. An approaching frontal system will then result in the ewd progression of a band of IFR-MVFR ceilings, heavy showers and isolated storms with strong and gusty sly to sswly winds --including some severe with isolated tornadoes and straight line wind gusts aoa 50 kts-- between 22Z/23rd and 05Z/24th. Sely surface winds will otherwise increase after daybreak today, and become strong and gusty by late morning to midday, ahead of the expected line(s) of convection. West to east clearing will occur with the passage of the associated cold front this evening-early tonight. Outlook: Lessening winds and lingering low level moisture late tonight may result in the development of fog and low stratus primarily at INT and GSO between 08-12Z/24th, with VFR conditions anticipated otherwise and elsewhere for at least the next several days.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...CBL SHORT TERM...WSS LONG TERM...mlm AVIATION...MWS

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