Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180823 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 323 AM EST Sun Feb 18 2018 .SYNOPSIS...
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High pressure will move across the area today. A warm front will move north into the southeast tonight into Monday bringing another shot of rain to the area. Afterwards, a strong ridge will set up off the southeast coast providing much above normal temperatures through much of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 310 AM EST Sunday... Expect a clearing trend today, but low clouds are expected to linger in the upslope areas through late morning, with the lower clouds in the piedmont scouring out around 8am. High pressure will be over KY this morning, then shift east off the mid-Atlantic coast this evening. Warm frontal boundary draped over the deep south advances northward tonight as southwest flow increases. Isentropic lift overrunning this boundary should serve to bring a some rain to the area overnight. Temperature profiles stay above freezing and not expecting any ptype issues in our forecast area. Temperatures will be about 10 degrees warmer than Saturday with mid 40s to around 50 west, to lower to mid 50s east, except some upper 50s across the NC piedmont into southside VA. Tonight, the rain will move into the drier air with evap cooling knocking temps into the 30s overnight, except around 40 southwest VA west of Bluefield to Marion, and into the NC foothills/piedmont. Rainfall amounts overnight will be under a quarter inch, with best coverage over southeast WV into the Alleghanys.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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As of 307 AM EST Sunday... Amplified mid-level height pattern through the balance of this period across much of CONUS. The two main large-scale height features being a 2-2.5 standard deviation above-normal subtropical ridge west of Bermuda, and a sharp digging trough into the Desert Southwest/southern Rockies. Given the implied height gradient between the two features, a cold front progged across the mid- Mississippi Valley - serving as the focus for repeated rounds of early-week rain in the middle of the country given a favorable tap of moisture off the western/central Gulf - will be very slow to advance eastward toward the western Appalachians by late Wednesday. Main highlights in the period are well above normal high/low temps Tuesday and Wednesday with springlike humidity levels. Couple chances for precip in the period - as a warm front makes northeastward progress Monday, and in a weakly unstable environment Wednesday. Warm front from Sunday night will make a slow advance northeast, with leftover showers continuing into the early afternoon north of Route 460. Given the timing of the front and the likelihood of leftover clouds behind the front, am not optimistic that the Piedmont in VA/NC gets out of the mid 50s in terms of highs, despite 850 temps pushing +11C. Southeast WV and into the New River Valley stands the best chance of reaching the low/mid 60s given southwest surge of milder air from the TN Valley. Any afternoon showers would be mainly in the southern Blue Ridge in NC/VA and would depend highly on enough southeast-south wind convergence to generate any showers. Am not optimistic this will occur but kept a token 15-20% PoP in for these areas. Warming trend areawide begins Tuesday where guidance has begun to trend less cloudy. It will begin to turn more humid by mid-Feb standards as well w/dewpoints commonly in the 50s. Subsidence again largely keeps the forecast area dry. Partly cloudy skies should push most areas into the lower 70s, except along the ridges with mid 60s. While the first half of Tuesday night looks dry, moisture begins to increase per 00z NWP against the Blue Ridge and have carried 15-30% PoPs for the after-midnight period. Still looks like the best chance at rain Tuesday night is into the southern Appalachians. Cold front begins to approach central/eastern KY on Wednesday, with another day of anomalously mild, humid conditions by mid-Feb standards. Noticed the 00z ECMWF and 00z GFS generate warm-sector QPF mainly from the Blue Ridge foothills west, in a regime of weak instability (LI`s of -1 and showalters of -1 per GFS) with PWATs of 1-1.25". Kept PoPs at Chance levels Wednesday, but opted to introduce slight chance thunder. And by slight chance thunder, this really translates to a few rumbles here or there. Best convergence still lags the region but given the progged thermo environment, couldn`t say thunder is out of the question. Rain chances diminish the further east of the Ridge one goes, with QPF a few hundreths to as much as a quarter-inch. Highs should again top out in the lower 70s with mid 50s to lower 60s dewpoints.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
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As of 300 PM EST Saturday... Synoptic pattern features a strong subtropical ridge of high pressure parked along the southeast Atlantic Coast with 590+ heights at 500 mb. Relative to climatology, this is 2 to 2.5 standard deviations above normal. This set-up favors much above normal temperatures for the Southeast States with the baroclinic zone forced to reside on the west side of the Appalachians from East Texas to the Ohio Valley and into the eastern Great Lakes. Repetitive rainfall is likely within this corridor during the second half of the week with our forecast area far enough east of the boundary to escape anything significant. Toward the end of the week, models hint that a surface front will impinge on the forecast area, but overall weather conditions for mid week feature above normal warmth and only a chance for showers pending any instability within the warm subtropical airmass. Temperatures Wednesday night are expected to be 10-20 degrees above normal with lows in the 40s. Models suggest potential for a backdoor front to impinge from the north-northeast Thursday, so somewhat cooler/wetter conditions are favored for Thursday.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/... As of 1145 PM EST Saturday... Short wave crossing through the Ohio Valley will keep low clouds on the west slopes of the central Appalachians overnight. As a surface low develops off the Delmarva coast winds will become northwest and erode low clouds east of the Blue Ridge. Medium to high confidence on timing of improvement to VFR at KROA, KLYH and KDAN before 09Z/4AM. MVFR clouds will linger until around sunrise for BLF/LWB. Weak high pressure building into the region Sunday will maintain VFR conditions through the day. Winds will gusts up to 25 knots overnight but will diminish by afternoon. As the high moves offshore Sunday night, return flow of deeper moisture will bring rain back into the Mid Atlantic region after 00Z. Most area TAF sites will remain VFR through the 06Z end of the TAF forecast period. Extended Aviation Discussion... A warm front lifts back north into the area on Sunday night and Monday with another round of sub-VFR ceilings and visibilities with rain, especially mountains. High pressure strengthens offshore resulting in a return to overall VFR Tuesday ahead of the next cold front well west of the Appalachians. Scattered MVFR showers are expected Wednesday into Thursday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...AL LONG TERM...PM AVIATION...AMS/JR

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