Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 281656 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1256 PM EDT Thu Jul 28 2016 .SYNOPSIS... Low pressure will move along a stalled front from the mid Mississippi Valley to the Ohio Valley today and tonight. This wavy frontal system will remain across the region through Monday. The front is expected to drift south and dissipate next Tuesday and Wednesday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1255 PM EDT Thursday... Expect no significant changes to the forecast through the remainder of the afternoon. Isolated to scattered convection is expected to start to develop within the hour across primarily the mountains. After roughly 400 PM or 500 PM a more organized band of showers and storms is expected to progress into the area from the west and make progress eastward through the evening. Forecast highs are on track for most areas. Added a degree or two to the forecast highs around the Roanoke region based upon the latest observations. As of 1215 PM EDT Thursday... Have decided to hoist a Flash Flood Watch for our southeast West Virginia counties and Tazewell County Virginia. Latest one hour flash flood guidance values for parts of these counties is in the one to one and one-half inch range. These values will be obtainable from late this afternoon into tonight with the potential of multiple thunderstorms training across the same location. As of 1020 AM EDT Thursday... Adjustments to the forecast for this afternoon will reflect a slightly slower arrival time of the main band of showers and storms that will enter the region from the west. While isolated to scattered coverage of showers and storms are expected across the mountains starting around noon, the main swath of potentially strong storms is more likely going to arrive in the west closer to 400-500 PM EDT and spread eastward into the evening hours. The storm prediction center has expanded the Slight Risk for today farther west into southeast West Virginia. If severe weather is to occur, the greatest potential will be damaging winds rather than large hail. Will continue to monitor and assess any potential for flash flood watches for any portion of the forecast area. The latest guidance suggests portions of southeast West Virginia may have the best potential. As of 430 AM EDT Thursday Cluster of showers and thunderstorms was tracking northeast through western part of the county warning area at 400AM. High resolution guidance has a majority of this precipitation north of the forecast area at 13Z/9AM. There will be some residual cloud cover this morning which will cut back on the potential heating and instability. Temperatures will still climb into the 80s today in the mountains and into the 90s in the piedmont. Starting with muggy conditions this morning in part due to surface dew points in the upper 60s to lower 70s. Heat index will top out around 100 in the east of the Blue Ridge this afternoon but will fall short of advisory level values. Short waves over the mid Mississippi valley early this morning are forecast to track into the Ohio Valley by Friday morning. This will provide better synoptic scale lift plus forecast area will be in the right entrance region of the upper jet this afternoon and evening. low and mid level winds increase from the southwest to west by late this afternoon which will increase the helicity. Bufkit forecast soundings were showing some decent speed shear. Directional shear becomes stronger this afternoon too as the surface low that was over southeast Missouri this morning moves east and backs the surface winds to the southeast. Once the short wave moves east...surface through mid level winds turn to the northwest and best lift will be confined to the western county warning area. No change in air mass overnight so minimum temperatures will be similar to past few mornings.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 330 AM EDT THURSDAY... A shallow slow moving upper trof will remain across the eastern part of the country through the weekend. This will keep a steady stream of short waves moving through the region, along with deep moisture and a lingering frontal boundary just off to our southeast. This pattern will produce broad synoptic lift and enhance convective activity that develops in the unstable environment, and give us increasing chances for showers and thunderstorms each day through the weekend with the best chances mainly along and west of the Blue Ridge. Shear will be limited so any marginal severe threat will be with pulse storms/clusters, and the concern for hydro issues will be growing as successive rounds of locally heavy rain will start to add up. Temperatures will be right around normal for late July with highs generally around 90 east of the Ridge, low/mid 80s west. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 1150 AM EDT Thursday... Belt of westerlies will be laying across the area Sunday night into Monday, with front situated across the mid-Atlantic. Afterward the upper flow takes on a more NW to SE orientation across our area as ridge builds over the Central Plains. The front weakens but convergence along it to remain through midweek. In addition, the upper pattern favors potential ridge runners, where convective clusters form over the upper midwest and shift southeast over our area. Overall, will keep threat of showers and storms in the forecast all periods but looks like Sunday-Monday have the better chance for measurable rainfall. May see slight nudge downward in temps early but overall humidity levels should stay the same, so no appreciable dry air expected thru Thursday. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 745 AM EDT Thursday... Lingering LIFR clouds and fog at KLWB and in the western Appalachian mountains this morning will dissipate by 14z/10AM. Storms will develop over the mountains during the early afternoon and then move east into the foothills and piedmont during the mid- late afternoon. High confidence of a couple hours of MVFR conditions due to the storms at all the airports in the central Appalachians but timing is still uncertain. Bufkit showed a favorable shear profile for more organized storms and the potential for microburst winds within the thunderstorm cores leading to isolated surface gusts of 30-50kts. Coverage of thunderstorms will diminish after sunset in the piedmont. Scattered showers will continue in the mountains overnight. Models bring in IFR ceilings with deep westerly winds after 06Z/2AM in the western mountains. Have added this with medium confidence of occurrence. Extended aviation discussion... An upper ridge of high pressure will remain just south of the area and a residual frontal boundary will remain over the area through Monday. This will allow for periodic, mainly diurnally driven, deep convection. A more widespread sub-VFR potential exists into Friday per a strong wave of low pressure which will ripple east along a stalled front. After the passage of this wave, some decrease in coverage of precipiation is expected over the weekend. In addition to the thunderstorm threat, late night and early morning fog will likely occur at the usual valley locations. && .CLIMATE... Record warm minimum temperatures for July 28 Bluefield WV.....69 in 2010 Danville VA......76 in 1997 Lynchburg VA.....77 in 1930 Roanoke VA.......80 in 1930 Blacksburg VA....68 in 1987 && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Flash Flood Watch from 4 PM EDT this afternoon through Friday morning for VAZ007. NC...None. WV...Flash Flood Watch from 4 PM EDT this afternoon through Friday morning for WVZ042>044-507-508.
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&& $$ SYNOPSIS...AMS NEAR TERM...AMS/DS/WP SHORT TERM...MBS LONG TERM...WP AVIATION...AMS/PM CLIMATE...PM

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