Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 240112 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 912 PM EDT Sun Jul 23 2017 .SYNOPSIS... A slow-moving cold front will drift southward over the Mid Atlantic during tonight into Monday. This frontal boundary will stall and eventually head back north as a warm front later in the week. && .NEAR TERM /THROUGH MONDAY/...
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As of 910 PM EDT Sunday... Ill defined weak frontal boundary being pushed along by shortwave energy aloft is helping to trigger convection in a pool of residual instability extending from far southwest Virginia back through Tennessee. HRRR meso guidance has been handling the situation quite well and will lean heavily on it to structure POPs overnight. Expect the showers and thunderstorms to spread eastward early tonight, then fade after crossing the Blue Ridge after Midnight. The threat for severe weather will be quite low and rely on outflow boundary interactions in clusters of storms. Lows tonight will remain warm with low/mid 70s east of the Ridge and mid/upper 60s west. Previous discussion... Chances of showers and thunderstorms appear lower for Monday afternoon, and any activity that does develop will be isolated at most. The best chances for any development appear to be in the northwest North Carolina mountains. Most locations should remain dry on Monday, but it will be hot and humid once again by the afternoon. Roanoke will more than likely reach its 15th consecutive day of having a high temperature of 90+ degrees on Monday. At that point, this streak would take sole possession of fifth place for the all-time longest streak of 90+ degrees since records began in 1912. However, this streak would have to reach 22 consecutive days to tie the longest streak on record that occurred during June 23rd through July 14th back in 1966.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 300 PM EDT Sunday... Upper trough over the Northeast at the outset of this period will be lifting out with a trailing cold front stretching from just off the Atlantic coast back though central VA. This front is expected to make progress to the south and east over the ensuing 24-hour period reaching to about South Carolina where it is expected to stall out. The surface high over the Great Lakes will also slide toward the east and should usher in a slightly drier and cooler air mass into the region. Did not go quite as aggressive as the model blend in lowering dewpoints but possibly a 3 to 5 degree F drop by Tuesday night into early Wednesday, which should be noticeable. Overnight lows Monday range from low 60s NW to low 70s SE. Highs Tuesday near climo norms for late July l/m 80s NW and low 90s SE. Chances for rainfall will be low with the only PoPs at slight or higher compressed to the far southern reaches of the CWA where somewhat better moisture/instability will reside. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 1100 AM EDT Sunday... Wind flow around high pressure centered over New England will result in an easterly breeze on Wednesday, bringing cooler Atlantic air into the region. As such, afternoon high temperatures will likely be the coolest of any day this week, ranging from the mid/upper 70s west to low/mid 80s east. The upslope wind flow will also support spotty showers/thunderstorms during the afternoon and evening, with greater coverage across the mountains and foothills. High pressure will shift off the New England coast Wednesday night, allowing winds to turn more southerly across the mid- Atlantic by Thursday, making for a return of warmer, more humid air. Strong daytime heating will support pulse variety showers and thunderstorms, a few of which will likely become strong for brief periods of time during the afternoon and evening. A cold front will make its way across the mid Atlantic on Friday, triggering more organized/widespread shower and thunderstorm activity. Latest run of the weather forecast models indicate that the front will clear our area to the south by Saturday morning, bringing drier air in its wake. Have therefore lowered rain chances for next weekend, though isolated showers/storms cannot be ruled out. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... As of 735 PM EDT Sunday... The main short wave associated with the upper trough moving slowly across the Great Lakes was moving into the CWA from the west this evening, triggering another more significant round of convection. Following the HRRR and other short range/HIRES models, would expect convection to track into far southwest VA/southern WV over the next few hours before dissipating toward midnight near the Blue Ridge. Will include VCTS at BLF and BCB and VCSH at LWB/ROA until better expectation of how far thunder will go before including further east. Expect mostly VFR ceilings, except brief basically unpredictable MVFR-IFR ceilings in evening thunderstorms. Overnight, upslope westerly flow behind the upper trough should result in MVFR cigs developing from LWB to BLF and possibly BCB as well, breaking up and becoming scattered 14Z-15Z with VFR expected the rest of the day. Confidence in any convection Monday afternoon is too low to include in the TAFs at this time. Have not included fog at this time because of cloud cover, wind, and precipitation expected overnight. Will need to watch across the Piedmont. Winds will remain WSW-WNW 5-10kts through most of the TAF valid period, but low end gusts are expected after 14Z Monday mainly west of the Blue Ridge. Medium confidence in ceilings through the TAF valid period. Medium to high confidence in visibilities through the TAF valid period. High confidence in wind speed/direction through the TAF valid period. Aviation Extended Discussion... A slow-moving cold front should slowly sag south of our region by Monday afternoon into Monday night. This frontal boundary should stall to the south by Tuesday and eventually return northward as a cold front later in the week. Although convection should become more isolated for most of this period, the weather patten will still remain unsettled to some extent. High pressure wedging southward on Wednesday could bring some MVFR/IFR ceilings, which should quickly vanish by Thursday. Aside from any early morning fog and isolated convection, VFR conditions should prevail through most of this week. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PW NEAR TERM...MBS/RAB SHORT TERM...WP LONG TERM...NF AVIATION...PW/RAB

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