Area Forecast Discussion
Issued by NWS Blacksburg, VA

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875 FXUS61 KRNK 201951 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 351 PM EDT Wed Jul 20 2016 .SYNOPSIS...
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High pressure was over the mid Atlantic region today and will remain over the area through Thursday night. Two weak cold fronts will approach the area later this week into early next week. The first front crosses the Ohio valley and northeast United States on Friday night and Saturday, and the next on Monday night and Tuesday.
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&& .NEAR TERM /THROUGH THURSDAY/...
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As of 345 PM EDT Wednesday... Good mixing has lowered dew points into the 50s over the mountains this afternoon. Water vapor loop showed a pocket of mid level dry air over the Carolinas today. Environment is dry and stable enough to keep precipitation out of the forecast until Thursday afternoon. Hi-res NMM guidance had a reasonable placement along the southern Blue Ridge after noon for the most likely area where isolated thunderstorms will develop. Temperatures will be near normal tonight and Thursday.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
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As of 330 PM EDT Wednesday... Will be increasing maximum temperature on Friday based on rising 500mb heights and forecast 850mb temperatures around +22C. Heat index values will be at or just above 105 in the far eastern county warning area on Saturday afternoon. A cold front will move gradually south through Ohio and Pennsylvania on Friday night and may continue to drift into Virginia on Saturday. While the front may not be much of a change of air mass it will be an area of better low level convergence and deeper moisture and when combined with the upper support will result in an increases probability of showers and thunderstorms. Even without the boundary passing south of the forecast area, it will be close enough that convergence along the boundary or along outflow boundaries will aide in storm initiation. Precipitable water values are back up over 1.0 inch on Friday afternoon then closer to 1.75 inches on Saturday.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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As of 230 PM EDT Wednesday... Upper ridge will extend from coast to coast Sunday through Wednesday. In the northern stream the next synoptic scale wave crosses through the northeast United States on Tuesday. Models were similar bringing moisture back into the region on Monday and Tuesday ahead of the front. Therefore this will be the time frame with the highest probability of showers and thunderstorms.
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&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... As of 215 PM EDT Wednesday... With some upper level short wave energy moving through the region in northwest flow aloft combining with diurnal instability, believe Cu field will be rather extensive but remain essentially as sct/v/bkn with VFR heights. There may be an isolated shower/storm along and east of the Blue Ridge but coverage will not warrant any mention in TAFs. NAM has been an outlier solution in generating convection across the piedmont into early tonight but currently do not see a lot of support for this as the best instability will likely be further to the south and east. Will continue to monitor to see if later runs of meso models start to support something along these lines, and may adjust KDAN and KLYH if needed. Surface high will be sliding off to our east and return flow of moisture will be working in from the east. With good radiational cooling expected this will aid in fog formation and there is the possibility of some lower clouds working in across the piedmont. Will advertise SCT lower clouds overnight at KLYH and KDAN but these clouds may need to be increased/lowered if clouds are more robust than anticipated. Fog will generally be MVFR with a tempo to IFR at KLWB and KBCB, and no OBVIS currently expected for KROA. After any fog/stratus burns off, Thursday looks to feature VFR conditions with the possibility for diurnal convection mainly from the Blue Ridge eastward. Winds will be light through the period. Extended aviation discussion... Strong high pressure aloft will move east across the region into next weekend. Cannot totally rule out an isolated storm each afternoon/evening through the period but appears overall VFR outside of the typical late night valley fog in spots. Hot and humid conditions east of the Blue Ridge this weekend which may impact density altitude, and also slightly better thunderstorm chances across the Appalachians. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS/MBS SHORT TERM...AMS LONG TERM...AMS AVIATION...MBS/SK

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