Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 130839 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 439 AM EDT Sun Aug 13 2017 .SYNOPSIS...
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A weak frontal boundary will remain stalled just to our south for the next several days. A broad area of low pressure aloft, located across the Great Lakes, will continue to send a series of upper-level disturbances toward the region from the west. These disturbances will interact with the front helping to enhance periods of showers and thunderstorms at times through the week. A new frontal system will move into the region from the west Friday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 415 AM EDT Sunday... What was appearing to be relatively dry day compared to the past few and the upcoming several, does not appear so dry now. Model trends continue to stall the frontal boundary, which moved through the area slowly late Friday and yesterday, further north. This will leave the associated moisture further north as well. Lingering showers and isolated thunderstorms early this morning across the far southeastern portions of the CWA, associated with an upper-level disturbance, are moving east and will move out of the region before daybreak. By afternoon, moisture will return northward through especially the southwest and western parts of the CWA as surface high pressure drifts from the eastern Great Lakes toward New England. This will help to set up easterly flow and enhance moisture and lift along the Blue Ridge going into Monday. Would look for rain showers, and possibly even a thunderstorm in the far southwestern areas, during the afternoon/evening hours. Moisture will continue to closely creep northward overnight as the east-southeast flow further enhances lift along the Blue Ridge. Rain chances will increase from the south overnight. There may also be areas of drizzle and fog, especially along and near the Blue Ridge from northwest NC into southwest VA overnight. So, this may leave a period this morning where much of the CWA, especially the northern sections, will have a rain free period, but still lots of clouds. Throughout this section of the forecast, the best rain chances will be located east and south of the Blue Ridge, with the lowest chances toward the I-64 corridor. 850mb temps drop back into the +12C north to +14C south range today. This combined with the developing northeast to east flow, hence weak wedge, should result in similar or cooler daytime max times than what was observed Saturday. The air mass will be slightly drier with lower dewpoints northern areas today. A few glimpses of sun may help warm northern areas a bit more than southern areas where clouds will be more solid. MET MOS seemed to have the best handle on the cooler temperatures as it was generally a full category lower on max temps than the GFS or ECMWF MOS. Thus, given the synoptic situation in place, leaned heavily toward the MET MOS. This will yield highs near 80 across the Piedmont, with mostly 70s elsewhere. Lows remain muggy at night with increasing humidity again, mainly in the 60s, but near 70 across the eastern and southeastern parts of the Piedmont.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
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As of 245 AM EDT Sunday... High pressure centered over the northeastern states will wedge south into the Carolinas Monday. The parent high will move off the New England coast Monday night with a bubble high remaining over southern Virginia and western North Carolina. A series of mid level short waves, being ejected out of an upper level trough over the Midwest, will move over the wedge keeping the chance for showers along and east of the Blue Ridge Monday. The highest probability for showers through the day will be along the NC/VA border. Northeasterly flow may keep the morning dry for areas north of hwy 460. As the parent high shifts towards the New England coast, low level flow will become more east to southeast, increasing the chances for showers to the north Monday afternoon and evening. Downsloping southeast flow should help deter rain from falling across extreme southwestern Virgina and southeastern West Virginia. However, the wedge will partially erode across the Mountain Empire to the Bluefield area. This area may see some late day thunderstorms that will fade during the evening. All in all, Monday will be a damp cool day with highs generally in the 70s. Areas outside of the wedge may touch 80F. Rain chances and areal coverage decrease Monday night. Areas not seeing rain overnight will see fog developing and hanging around into Tuesday morning. The wedge is expected to erode Tuesday as the upper level trough approaches from the west. Areas across south-central Virginia may not see the wedge erode until mid to late afternoon. Forecast soundings still showing a moist environment when the wedge breaks. So, as the sun peeks through the clouds, afternoon heating will lead to showers and thunderstorms Tuesday afternoon and evening. Afternoon temperatures should warm towards normal levels with near 80F west of the Blue Ridge to the low to mid 80s east. Fog is again possible Tuesday night, especially in mountain valleys.
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&& .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 130 PM EDT Saturday... Overall not a lot of change in the pattern from the past couple of weeks as any mid week ridging looks to evolve back into a weak upper trough pattern by next weekend. This will again force weak surface ridging Tuesday night into Wednesday to give way to return flow by the end of the week with a residual front to the south lifting back north as a warm front into Thursday. Upper flow then briefly amplifies with a surface low near the Great Lakes pushing another weak cold front southeast toward the region by Saturday. This should result in less shower activity to start the period, per lower PWATs off extended guidance, followed by increasing coverage with the warm front espcly southern/western sections Thursday, and then ahead of the cold front Friday into Saturday. Appears best coverage likely Friday as deeper moisture returns behind the passing warm front and ahead of the pre-frontal axis in advance of the cold front. Temps to rebound to more normal levels through the week under increasing 850 mb temps as a more predominate west to southwest flow aloft takes shape ahead of the next weak upstream cold front. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... As of 200 AM EDT Sunday... Poor aviation conditions expected through much of the TAF valid period. A weak front appears to be stalled from western NC into southeast VA, along which showers and a few thunderstorms continue at this hour, especially in the KDAN and KSIF areas. Per HRRR, this activity should diminish and shift east of the RNK CWA around 08Z. Otherwise, looking for mainly MVFR to low end VFR ceilings overnight with areas of fog developing toward daybreak. Given rain at many locations during the day Saturday, the potential exists for late night/early morning fog to develop in a very moist low-level atmosphere with light winds. Will anticipate IFR-LIFR BR/FG developing at KLWB and KBCB as well as similar locations, with MVFR BR possible at most other sites such as KLYH and KDAN. Expect light east wind to evolve at KBLF before daybreak with potential for IFR-LIFR cigs/vsbys developing there as well. Throughout most of the day after 14Z, expect low end VFR ceilings. This will lower to MVFR levels around sunset and into the evening as a bonafide wedge develops with a good northeast flow. Expect areas of drizzle to develop, especially west of the Blue Ridge. Visibilities and ceilings could well drop into the MVFR range after 00Z at many TAF sites, especially west of the Blue Ridge. Winds will be light northwest or calm this morning, then becoming light east to northeast 4-7 mph through the day Sunday at most TAF sites. Medium confidence in ceilings through the TAF valid period. Medium confidence in visibilities throughout the TAF valid period, except medium to high during the 15Z-20Z time frame. Medium confidence in wind direction, high confidence in wind speed through the TAF valid period. Extended Aviation Discussion... Widespread IFR or worse ceilings/visibilities expected Sunday night/early Monday as a weak wedge persists across the area with accompanying east-northeast low level winds. The wedge may be slow to erode Monday with the potential for widespread low-mid clouds and a few showers Monday. Late in the day Monday, a cold front will move into the region from the west resulting in a better chance for showers and thunderstorms and accompanying sub-VFR conditions. The front will stall, as the past several have done so, and linger just to our south through Wednesday until another frontal system arrives and moves the stalled front out of the area. Another frontal system is slated to arrive by Thursday. All-in-all look for unsettled week with scattered to numerous showers, with thunderstorms possible during the afternoon and evening hours. && .EQUIPMENT... As of 755 PM EDT Saturday Aug 12th... KFCX doppler radar will continue to be down for the rest of the month due to a failing bull gear. It will only be operational during this time frame for brief periods if an imminent significant widespread severe weather and/or hydrologic event occurs. Operating the system for any amount of time until the bull gear is replaced risks a catastrophic failure that would further extend system downtime. From the 17th through the 27th the radar will most likely be down completely as the repairs are expected to be made during this period. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...RCS LONG TERM...JH AVIATION...AMS/RAB EQUIPMENT...RAB/WERT

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