Area Forecast Discussion
Issued by NWS Blacksburg, VA

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299 FXUS61 KRNK 241702 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 102 PM EDT Sat Jun 24 2017 .SYNOPSIS... The remnants of former T.S. Cindy, located over northern Virginia this morning will accelerate northeast of the Mid- Atlantic coast by evening as upper troughing deepens across the Great Lakes. A weak cold front will push slowly southeast through the day, then southeast of the area by Sunday morning. Upper troughing will remain in place through much of the upcoming week, but at the surface weak high pressure will hold until late week, leaving the area with mostly dry conditions until late week with slightly below normal temperatures. && .NEAR TERM /THROUGH TONIGHT/... As of 1255 PM EDT Saturday... The biggest adjustments to the forecast for this afternoon is an increase in forecast high temperatures by roughly two to four degrees across the eastern parts of the area. A bit more sunshine was received than earlier anticipated across the region which allowed the increase. Clouds are now advancing into that area, so the rate of increase should start to decrease, but there will still be enough sunshine to warrant the forecast high increase. Adjusted precipitation forecast from this morning is on track with isolated showers now located across North Carolina generally along and west of I-77. As of 955 AM EDT Saturday... The biggest forecast adjustment for today is a increase in arrival time of clouds and isolated to scattered showers over and east of the Foothills and neighboring sections of southwest Virginia. Latest radar trends and the most recent meso-scale models suggest arrival about three to four hours later than those earlier advertised. Have adjusted the forecast accordingly. The only other adjustment is a reflection of the current observations of temperature, dew point, and wind with expected trends into the early afternoon. As of 415 AM EDT Saturday... Surface pressure analysis shows that the remnants of T.S. Cindy tracked through the heart of the CWA overnight and early this morning were located over Loudon county VA, just west of D.C. Any area of showers and gusty winds moved quickly through the CWA just after midnight blowing a few trees down in the Henry County VA/Rockingham County NC area, but other than that it was just a breezy and muggy night, albeit about 10 degrees cooler with the passage of the showers and Cindy. So, we are done with problems associated with Cindy now as it is progged to continue racing off quickly to the east-northeast amidst strengthening 500mb flow thanks to a trough deepening over the Great Lakes. A trailing cold front, will be much slower to push south of the area, as the flow aloft is largely parallel to the front. With the trough deepening, the front will eventually sag south of the CWA later tonight and early Sunday. Convective allowing models in addition to most of the synoptic scale models, indicate good potential for showers and thunderstorms to develop across eastern TN/western NC and perhaps even into far southwest VA, such as the Grayson/Carroll county area, this afternoon, before drifting east-southeast through the evening. Brooks-Craven parameters suggest that there is even some potential for a few severe storms, but mainly closer to the I-40 corridor just south of the CWA. SPC has indicated a marginal risk for severe this afternoon/evening, but has kept it just south of our CWA with general thunder indicated to the northwest into most of the areas previously mentioned. With the wind fields much weaker than was the case earlier with the passage of the remnants of T.S. Cindy, main threat would be locally heavy downpours, CG lightning, and perhaps small hail/localized wind gusts. Any threat of convection will end very quickly after sunset with the boundary shifting southeast of the area under the deepening upper trough. Cooler/drier air will start to filter further southeast overnight and Sunday morning will start off quite a bit cooler than we have seen in the past few days with lows ranging from the 50s in the northwest to the 60s in the southeast with dewpoints dropping into the 50s northwest to the 60s southeast. This will end the daily thunderstorm threat for the next few days. The passing remnants of T.S. Cindy and the deepening upper trough/lower heights will lead to fairly breezy conditions today, so some wind gusts into the 20-25 mph range not out of the question at all. But for most of us, especially north and west of the Blue Ridge, it will be a very pleasant Saturday. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... As of 330 AM EDT Sunday... A broad upper level trough will reside over the eastern half of the US through early next week. Northwest winds will usher in cooler drier air both Sunday and Monday. Besides some fair weather cumulus clouds forming in the afternoon, both days look very comfortable. Afternoon temperatures will average 3F-5F cooler than normal. Dew points will range from the upper 40s across the mountains to upper 50s in the piedmont. No rain is expected until Tuesday afternoon. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 339 PM EDT Friday... The long range models are in good agreement with the overall upper air pattern during this period with an anomalously deep upper trof over the eastern U.S. early in this period, with 500mb heights 2-3 standard deviations below normal,transitioning to a zonal flow by mid week, with ridging building by the end of the week. The 12Z GFS is still fastest with the eastward progression of the upper trof Tuesday night into Wednesday, but this has little impact on the tranquil weather expected during this time. A weak frontal boundary moving through early Tuesday morning may generate some spotty showers in the mountains, but forecast RAOBS indicate there will be very little moisture available. Otherwise, PWAT values will remain below average until Thursday night/Friday so expect a prolonged period of dry weather. By late in the week...a deep southwest flow developing on the west side of an upper ridge and ahead of an approaching upper trof in the upper mid west will increase moisture and provide the opportunity for weak upper level disturbances to pass over our area. This will result in increase chances for scattered thunderstorms during this period. As for temperatures, forecast 850mb temps from the GEFS are 2-3 standard deviations below average, which will lead to some cool mornings Tuesday and Wednesday. Adjusted low temperatures down a couple of degrees below guidance during this period. Temperatures will moderate late in the week. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 745 AM EDT Saturday... Remnants of T.S. Cindy have moved well northeast of the area and its effects, which moved through very rapidly overnight, are gone and it will no longer be a factor in our weather going forward. Concern through the day today is a weak cold front sagging slowly southward being supported by increasing broad upper troughing across the Great Lakes. The front will combine with residual moisture and afternoon heating to likely support thunderstorms across northwest/north central NC and Southside VA later this afternoon. HRRR supports some pretty robust thunderstorm development in those areas after 17Z, moving southeast of the area after 00Z. Included a VCTS at KDAN, but this is the only TAF site that could potentially be impacted. Otherwise, lingering upslope MVFR to briefly IFR cigs across eastern WV, with mostly VFR cigs elsewhere. Would expect cigs to improve to MVFR or better in eastern WV after 16Z with VFR conditions holding in most areas from mid-afternoon onward. Air mass is drying, so do not expect fog development overnight or Sunday morning. Winds will be WSW veering more toward the WNW with time as high pressure builds southeast from the Midwest and the remnants of T.S. Cindy move further away. Low end gusts can be expected in the 16Z through 22Z time frame at most sites. On average, look for speeds of 7-10kts with gusts 18-20kts. Medium to high confidence in ceilings through the TAF valid period. High confidence in visibilities through the TAF valid period. Medium to high confidence in wind direction/speed through the TAF valid period. Extended Aviation Discussion... VFR conditions expected to prevail most of the Sun through Wed period. A weak front may provide a few clouds early in the week, but little sensible weather. Potential for radiation fog and related visibility restrictions will increase later in the week as moisture levels increase. Showers and thunderstorms will return in earnest late in the week as southwest flow returns to the area. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...DS/RAB SHORT TERM...RCS LONG TERM...PH/RCS AVIATION...JH/RAB is the U.S. government's official web portal to all federal, state and local government web resources and services.