Area Forecast Discussion
Issued by NWS Blacksburg, VA
Issued by NWS Blacksburg, VA
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358 FXUS61 KRNK 181832 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 232 PM EDT Wed Sep 18 2024 .SYNOPSIS... Low pressure centered over the southern Appalachians will drift northeast through Thursday, bringing additional clouds and precipitation. The low moves offshore by Friday, lowering the probability of precipitation. Dry weather and seasonal temperatures are expected for Saturday and Sunday. && .NEAR TERM /THROUGH THURSDAY/... As of 230 PM EDT Wednesday... Key Messages: 1) Light showers/isolated storms possible through this evening. 2) Localized urban and small stream flooding possible tonight, with a lower flash flood threat compared to yesterday. A vertically-stacked low pressure system was centered near Greenville, SC. Moisture from the Mid Atlantic continued to be drawn westward towards the Appalachians. Lift provided by energy rotating around the low was generating convection for parts of the piedmont of VA and the southern Shenandoah and Greenbrier Valleys. Precipitable water had backed off some here (1.23 inches on this morning`s RNK sounding) compared to last night. The better moisture and instability was pooling to our east, but breaks in cloud cover should generate enough instability for showers and isolated storms this afternoon and evening, generally NE of a line from Hinton, WV to Danville, VA. Heavy rain leading to localized flooding appears to be the main concern once again through this evening, especially if any convection forms in areas which received substantial rains last night. Showers and storms should diminish overnight, with lows again in the 50s and 60s. Abundant low level moisture remains in place across the region through Thursday. Any skies that have scattered out will quickly fill back in tonight through mid morning tomorrow with low clouds and ground fog. Another round of convection is likely tomorrow afternoon and evening. Highs Thursday should warm into the low to upper 70s. Confidence in the near term is moderate, but lower for QPF. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 215 PM EDT Wednesday... Key Messages: 1) Rain will begin to wind down Thursday night into Friday as the upper-low moves east and offshore. 2) Confidence is high that mostly dry conditions will occur on Friday and Saturday with temperatures increasing with more sunshine. Scattered rain chances will continue for Thursday night, but will dissipate into the overnight hours. On Friday, drier weather will be in store across most of the CWA with mid-level RH values lowering due to the upper-low moving offshore. However, showers and a slight chance of storms will remain possible in far southwest Virginia and in the mountains of North Carolina due to the increased instability from less cloud cover along with a light upslope flow. Any convection will be short- lived, and quickly dissipate after sunset. Due to the limited cloud cover, high temperatures will be near to slightly above normal, with highs in the 70s and low 80s while lows will be mainly in the 50s as radiational cooling will allow temps to fall at night. Similar conditions are expected on Saturday, though lower dewpoints will reduce rain chances across the RNK CWA, with most areas likely seeing no rainfall. Model ensemble means have QPF totals around 0.10 inches through late Saturday. Overnight Saturday will see a very slight increase in rain chances as mid-level moisture increases briefly, but any showers will remain very isolated. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 200 PM EDT Wednesday Key message: 1) An upper level trough and associated cold front will approach the region early next week, and provide daily chances for isolated shower and thunderstorm activity. Starting Sunday, there is good ensemble guidance between the GEFS and EPS suggesting that the region will be wedged between an upper level troughs centered off the Northeast coast, and the northern Great Lakes region. This will keep the region temporarily under the influence of upper level ridging. This will keep temperatures above normal across the region on Sunday, with highs climbing into the low to mid 80s. Models do seem to diverge starting Monday, as the timing of the upper level trough across the Great Lakes approaching the area is still uncertain. Regardless of the timing of the upper level trough and associated cold front early next week, some prefrontal shower and thunderstorm activity looks possible as appreciable PWATs in the 1.4-1.6 inch range look to linger across the region. With surface high pressure centered over southeast Canada, weak wedging down the eastern Appalachians look to create some easterly flow across the region, which may enhance the aforementioned shower and thunderstorms on Monday and Tuesday. The upper level trough across the upper Great Lakes region looks to lift north late Monday and into Tuesday, which may leave a stalled cold front across the western Blue Ridge, and provide a focus for shower and thunderstorm development through the middle of the week. These showers will generally be diurnally driven, and should diminish after sunset. Temperatures each day will generally climb into the low to mid 70s, and lows look to fall into the low to mid 50s. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 205 PM EDT Wednesday... Ceilings are ranging from IFR to VFR this afternoon, with BLF being the only site currently VFR. High pressure wedging and plenty of moisture in the area/light easterly flow will keep stratus, ground fog, and some -DZ/-SHRA in the area through tomorrow. Tonight, IFR/LIFR will be common again, improving to MVFR around 18/15-16Z. Scattered showers and isolated thunderstorms are possible in areas that get solar heating, resulting in better instability. However, chances for thunder look low for our TAF sites, and better east of LYH/DAN. Northeast winds of less than 10 kts will drop to light and variable to calm overnight. Average confidence for ceiling and wind. Below average confidence for coverage of any thunderstorms this afternoon and evening. EXTENDED AVIATION OUTLOOK... For Friday, less coverage of showers is expected. Ceilings will improve to VFR by Friday. We may still see residual moisture trapped under an inversion Thursday night into Friday morning, leading to patchy fog and stratus. VFR conditions and dry weather is expected to return for Saturday and Sunday. By Monday, -SHRA will be possible for the mountain terminals (BLF/LWB) as a warm front lifts north. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...SH NEAR TERM...SH SHORT TERM...EB LONG TERM...JCB AVIATION...SH