Area Forecast Discussion
Issued by NWS Blacksburg, VA

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901 FXUS61 KRNK 270527 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 127 AM EDT Tue Sep 27 2016 .SYNOPSIS... A cold front will move east tonight into Tuesday across the region with scattered showers and thunderstorms. A wave of low pressure moving along this front will stall the convection across eastern sections of the area on Wednesday, before finally exiting Wednesday evening into Wednesday night. && .NEAR TERM /THROUGH TODAY/... As of 1050 PM EDT Monday... Made some fairly significant changes to pops and weather once again. As expected pre-frontal activity slowing in its eastward progression across the eastern parts of the forecast area, but the more intense activity has moved east of the CWA border. With the wave of low pressure riding along the front from the southeast states, do not expect this activity to make much further eastward progress overnight, so will continue to hold onto likely to categorical pops east of the Blue Ridge overnight. Back to the west, the front is near an LWB-BLF-JFZ line, along which a broken line of showers persists with an isolated thunderstorm. Have increased pops across this area as a result. After this passes by, it is likely that fog and drizzle will develop across areas west of the Blue Ridge overnight before a better northwest takes effect after 14Z Tue. No significant changes to T or Td readings this hour. As of 800 PM EDT Monday... Initial line of pre-frontal convection slowly moving east of the Blue Ridge. Thunderstorms and heavy rain showers likely for the next couple of hours from KLYH to KROA to KDAN. Redevelopment of convection back along the front in eastern WV. HRRR seems to have a good handle on the overall progression and development of convection through the evening, although the placement may be a bit off, namely too far north. Heavier convection developing across northwest/north central NC may cutoff convection back to the north somewhat. At any rate, will continue with likely to categorical pops across much of the area through 06Z...tapering to chance thereafter. Temperatures were running several degrees cooler in rain cooled areas west of the Blue Ridge and were adjusted downward. Otherwise, no significant changes were needed. As of 259 PM EDT Monday... A strong cold front will move east across the region tonight into Tuesday. An axis of moderate instability just ahead of the front will fuel scattered to numerous showers and thunderstorms, some of which could contain heavy rains and gusty winds. Lack of deep-layer shear and poor mid-level lapse rates will limit severe potential. These storms are expected to weaken tonight after they cross the mountains and encounter the cooler stable airmass east of the Blue ridge. Leaned tonight pops towards the HRRR which captured the convection best this afternoon. A period of moderate to heavy showers are possible with convection this evening into tonight. There is the potential for a half inch of rain as the front moves over and east of the Blue Ridge. However, the forward progress of the cold front will slow with the upper level support lagging overnight. With low level moisture and light winds expected patches of fog overnight. Low temperatures tonight will range from the upper 40s in the northwest mountains to the mid 60s in the Piedmont. On Tuesday, the cold front will slowly move east across the region in advance of a closing upper low rotating through the Great Lakes. Elected to slow down the timing of the frontal passage. Considerable cloudiness and scattered showers will continue Tuesday, especially east of the Blue Ridge mountains. An isolated thunderstorm is possible in the east if enough daytime heating is allowed. The day two convective outlook supports this with its general thunderstorm area. High temperatures on Tuesday will vary from the mid 60s in the mountains to the mid 70s in the Piedmont. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... As of 1230 PM EDT Monday... At the beginning of this portion of the forecast, a cold front will be making slow progress eastward through the central and eastern portions of the forecast area. A wave moving along this front will stall the activity across the far eastern sections of the area on Wednesday, finally exiting Wednesday evening. We also will be watching a slow progression southeastward of a closed upper low from Wisconsin to either eastern Kentucky or West Virginia. Showers will be on the increase across the area with the approach of this system, especially by the time Wednesday night into Thursday arrives. Steep cold pool lapse rates will allow for decent shower development. Isolated thunderstorms will be possible thursday afternoon, mainly east of the Blue Ridge. Models place the freezing level around around 5000 to 7000 ft AGL across the mountains and 8000 to 10000 ft AGL across the Piedmont. Small hail will be possible given the expected convective nature of the day, even from strong showers, and the relatively low freezing levels. Previously on Wednesday, freezing levels are expected to be about 2000 to 3000 feet higher, thus small hail is less likely, but not impossible, on Wednesday, especially across western sections, as compared to Thursday. Temperatures during this portion of the forecast will turn slightly cooler as compared to Tuesday, but average within a degree or two plus or minus of normal conditions for this time of the year. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 130 PM EDT Monday... The slow moving upper low will continue to impact our forecast into Friday, however, the trend will be for the low to start heading north in response to a building upper ridge across the center portion of the nation. Progressively each day through Sunday, the concentration of showers will will trend more toward the northern sections of the forecast area, following the track of the low. While no thunderstorms are forecast, isolated hail will again be possible within the stronger showers given a continuation of a relatively low freezing level through Saturday. Sunday into Monday, a dry forecast is expected along with moderating temperatures as the upper ridge strengthens and its axis shifts eastward. At best some isolated showers may be possible across the Northern Mountains of North Carolina on Monday where Temperatures during this portion of the forecast will trend only slightly milder on average than the early part of the week. While highs may climb a bit higher, lows are expected to trend slightly cooler as the diurnal range increases thanks to decreasing dew point values across the region. && .AVIATION /05Z TUESDAY THROUGH SATURDAY/...
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As of 120 AM EDT Tuesday... Generally poor aviation conditions expected through this morning. A cold front was moving across the mountains early this morning with a broken line of showers. Ahead of the front are some prefrontal showers across Southside (KDAN), but mostly MVFR-IFR low clouds and fog from the Blue Ridge eastward. For the TAF valid hours after 14Z Tuesday, look for variable clouds as an upper low begins to drift southward from the Great Lakes region. Ceilings will range from high end MVFR or low end VFR by afternoon. Showers remain possible across the Piedmont, including Danville, as a wave of surface low pressure rides northeast along the slow moving frontal boundary located over the coastal plain. Extended aviation discussion... The front will be located across the coastal plain into Wednesday awaiting additional upper support from an approaching upper low. Conditions will becoming increasingly unsettled as a deep upper low sags southward from the Great Lakes into the Central Appalachians. This will keep variable clouds, MVFR cigs, and periods of -SHRA across the region through much of the period.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK NEAR TERM...KK/RAB SHORT TERM...DS LONG TERM...DS AVIATION...RCS

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