Area Forecast Discussion
Issued by NWS Blacksburg, VA

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101 FXUS61 KRNK 232338 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 738 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/... As of 645 PM EDT Sunday... Have lowered pops across the CWA drastically for this evening as earlier morning convective complex debris has generally put a lid on convection across the area today. Activity has been on the periphery across far northern VA/MD, eastern shore, and down in NC mostly along and south of the I-40 corridor. Focus now will be on potential for activity to redevelop upstream in association with main short wave approaching from the northwest. Look for activity to redevelop across eastern KY, southwest VA, eastern TN in the next few hours, then spread into our CWA in the 00Z-02Z time frame before dissipating as it moves eastward during the remainder of the evening. Have shaped pops accordingly. Marginal risk for tomorrow in my opinion is questionable as convective coverage will be minimal. Focus for widespread convection is further south across GA/SC/NC where lingering boundary will be found along with numerous convective outflow boundaries. Marginal risk seems to hinge on short wave on back side of upper trough moving across eastern Great Lakes. Confidence is low in much convection east of the Alleghany front in my opinion at this time, but we shall see. Pops are minimal at this time and generally confined to far western/northern/southern areas. Adjust T/Td readings and Min T slightly. Still looking for a warm night across the area, but should be a few degrees cooler, especially in the west, than last night. As of 310 PM EDT Sunday... Convection from earlier mesocyclone convective systems has dissipated during the past few hours, which has left our region in a lull of activity. That quietness is due to earlier cloud cover and the extra time needed to reload on instability for later this afternoon. High temperatures were bumped upward and POPs were lowered to account for the clouds clearing out earlier than anticipated. Thus, it will be another hot and humid afternoon with 80s and 90s for highs. Heat indices will likely cross 100 degrees again in the Piedmont but fall shy of advisory criteria. The Storm Prediction Center downgraded the slight risk for our region to just a marginal risk. Any new showers and thunderstorms that develop later today will be scattered at most and only provide a threat of damaging winds south of Route 460 based on the latest mesoscale models. Convection could linger into the early overnight hours due to late initiation. Models indicate that it should decay before midnight. The slow-moving cold front trailing behind an upper level trough over the Northeast has been responsible for the unsettled weather lately, and it should eventually drift southward overhead tonight. With lingering cloud cover and the front expecting to stall on Monday, it will remain muggy with lows in the 60s and 70s. 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. With Roanoke already above 90 degrees today, the city 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. && .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 /00Z 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...PW/RAB SHORT TERM...WP LONG TERM...NF AVIATION...PW/RAB

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