Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 251753 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 153 PM EDT Thu May 25 2017 .SYNOPSIS... A weak cold front will pass east of the region this morning. An area of upper level low pressure will then swing across the area this afternoon before exiting tonight. Weak high pressure spills in on Friday with a brief return to drier weather before more showers and storms arrive this weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1250 PM EDT Thursday... Updates for this afternoon include a lowering of forecast high temperatures across the far western sections of the region where cloud cover has been ongoing, and is expected to remain that way the remainder of the afternoon. Also, have refreshed the timing and location of after showers and storms. Plenty of sunshine has been across central and eastern portions of the area, allowing for surface warming. Anticipating convection to become more robust across the area with both the upper cold pool lapse rates passing overhead in alignment with the surface heating. Small hail is still possible with almost any thunderstorm, and even the stronger showers given the relatively lower freezing level this afternoon. Issuing a wind advisory for the mountain region for late this afternoon through noon Friday. 850mb flow around the backside of the upper low is expected to increase to around 40kts this afternoon and remain that way through the overnight hours. Translated surface wind speeds and gusts are not expected to reaching official wind advisory thresholds, at least not many. However, this advisory will be impact based upon the concerns the gusty winds will be encountering trees with plenty of leaves on them resting in a very saturated soil. Trees are expected to come down with wind speeds lower than those typically expected to do so. As of 955 AM EDT Thursday... Forecast update this morning will reflect the ongoing precipitation coverage across the region. Some scattered showers and isolated thunderstorms are between roughly Martinsville, VA and Ellisboro, NC and moving northeast. Patchy light rain showers extended north of this primarily showers into parts of the Alleghany Highlands. This activity will gradually head towards the northeast as the morning progresses. We are still anticipating greater development as we head into the afternoon during the heating of the day as an elevated cold pool with steep lapse rates shifts eastward across the area today. With a freezing level around 9000 feet MSL, even some of the stronger showers may grow tall enough to produce some small hail, especially across central and eastern parts of the area. Updated hourly temperatures, dew points, and sky cover grids to reflect the latest observations and expected trends into the early afternoon. As of 245 AM EDT Thursday... Ongoing showers producing heavy rainfall slow to exit as waiting for the upstream dry slot seen on water vapor to kick through which guidance shows taking shape by daybreak. Thus will continue high pops north-east early on before seeing a brief lull as we slide in between deep moisture with the front and the upper low to the west. Core of this cold pool aloft then looks to pivot east through the far western zones around midday with the associated vort lobe swinging across the east during the afternoon. This should bring another round of showers to the western mountains by early afternoon before clusters of deeper convection develop on the leading edge and points east during the afternoon. Secondary wave sliding around the base should aid lift with perhaps some organization into a broken line over the piedmont by late in the day as hinted at by a couple short term solutions. Main aspect will be with cooling aloft and subsequent steep lapses capable of producing hail and even some downburst potential given lingering shear aloft. Also given a bit slower scenario, have pushed thunder chances back to at least the Blue Ridge where will mention small hail per latest SWODY1 with all seeing a period of likely pops this afternoon. Other issue with possible heavy rain and added flooding given saturated conditions and high water levels. However at this point appears far western coverage may be more showery with lower rates while stronger storms to the east will be more capable of producing at least isolated flash flooding. Since still dealing with the current event and given uncertainty with coverage this afternoon, opting not to include another flood watch headline at this point and give the dayshift a chance to issue a short term FFA if needed. Otherwise thinking will see some sun espcly Blue Ridge east as the wedge breaks down and downsloping kicks in. This should help push highs above 70 out east while 60s prevail elsewhere over the west. Upper low finally exits to the northeast this evening with subsidence spilling in on a rather strong 850 mb jet at 30-40 kts that will make for a gusty evening/overnight. However latest soundings suggest speeds to stay below advisory levels over the ridges at this point. Otherwise appears any residual pops will be confined mainly to upslope areas across the northwest where some wrap around showers may persist. Thus keeping in chance pops northwest third with a gradual decrease in coverage late. Elsewhere expecting downslope drying to limit much in the way of added showers with clearing skies east. Lows on the cool side with most seeing 50s overnight if not a few 40s in the valleys. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... As of 305 AM EDT Thursday... On Friday, we will gradually lose the upslope scattered showers, and associated cloud cover, as low level winds start to back more westerly through the day with the approach of an upper level shortwave ridge. The arrival of drier air will also yield a decreasing trend in coverage. The best chances will still be over parts of southeast West Virginia, mainly during the morning hours. The vast majority of the forecast area will experience limited cloud cover and weak winds. Our period of drier weather will be short lived. Friday night into Saturday we will be watching a cold front approach and then enter the region. Isolated showers may develop by sunrise Saturday in the northwest portions of the area, but the better chances will be during the day Saturday with the arrival of the front combined with daytime heating. Guidance varies on what extent the front makes it through the region before stalling. Model are leaning towards a thunderstorm complex potentially riding along this stalled front late Saturday night and entering the area by Sunday morning. This supported by the 00z ECMWF which has multiple complexes riding the boundary from late Saturday through Sunday. Temperatures during this portion of the forecast will start near normal, but trend to a little over five degrees above normal by Saturday. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... As of 205 PM EDT Wednesday... During this part of the forecast, a broad, slow moving upper low will transition from the Great Lakes region to over southeast Canada. This will keep our region in a pattern dominated by a persistent trough of low pressure across the eastern portion of the U.S. Within this trough pattern a series of cold fronts are expected to enter, and then move through the forecast region. Guidance offers the first of these two to have a Sunday night into Monday time frame, with a second during late Tuesday night into Wednesday. Both of these time frames will be periods with a greater potential for showers and storms, with the first being more robust than the second. However, while the area is within the overall trough pattern, daytime heating will be enough to produce at least isolated showers during other parts of this time period. Temperatures during this portion of the forecast will start the period about ten degrees above normal. By Wednesday, readings within a degree or two of normal are forecast. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 140 PM EDT Thursday... Upper low was making progress eastward across northern Virginia. Associated cold pool lapse rates and daytime heating will lead to convection this afternoon, mainly in areas along and east of the crest of the Blue Ridge. Broad area of IFR/MVFR cloud cover over KY/WV will advance into the region from the west, and impact areas in the west late this afternoon through the overnight hours. Visibilities will mainly be VFR, but pockets of MVFR visibilities are possible across the mountains. Low level winds will become northwest by this evening and allow for subsidence clearing in areas east of the Blue Ridge. Wind gusts across the higher elevations will be in the neighborhood of 25 to 35 kts. These prevailing winds allow for a continuation of upslope rain showers in the west, and these will continue into the day Friday. However, coverage during the day Friday will be on the decline. Extended Aviation Discussion... VFR conditions are expected on Friday as a shortwave ridge builds into the region. We will transition back into a wet pattern over the weekend as a frontal boundary enters and stalls over the area. A series of disturbances will bring showers and storms to the area. Anticipate at least some pockets of sub-VFR conditions. The coverage of showers and storms decrease early next week, but remain at least scattered in coverage. && .HYDROLOGY... As of 100 PM EDT Thursday... Small streams and creeks have been receding and most are below flood stage. We are in a river flooding scenario for portions of the Roanoke and Dan River basins. The New River and Greenbrier river are expect to stay below flood stage. The upper level system moving in from the west will bring scattered to numerous showers and possible thunderstorms. Overall rainfall amounts on average will be under a quarter to half inch, in this scenario. Will have to watch for any training or heavier downpours, as it will not take much to cause flooding again given the saturated grounds and swollen creeks and rivers. Currently, we are not expecting enough for a flood/flash flood watch and activity should diminish/weaken after sunset. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Wind Advisory from 6 PM this evening to noon EDT Friday for VAZ007-010>014-016>020-022>024-032>035. Wind Advisory until noon EDT Friday for VAZ009-015. NC...Wind Advisory until noon EDT Friday for NCZ001-002-018. WV...Wind Advisory from 6 PM this evening to noon EDT Friday for WVZ042>044-507-508. && $$ SYNOPSIS...JH NEAR TERM...DS/JH SHORT TERM...DS/JH LONG TERM...DS AVIATION...DS HYDROLOGY...WP

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