Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 221125 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 725 AM EDT Sat Jul 22 2017 .SYNOPSIS... A frontal boundary draped from the midwest-lower Great Lakes east to the mid-Atlantic will stay situated around this area into Sunday. Low pressure and attendant cold front finally pushes east into the central Appalachians and across our area by Monday. High pressure builds across the mid-Atlantic Tuesday into Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 304 AM EDT Saturday... GFS seems the odd model out this forecast period as its the only one blowing up organized convection this afternoon/evening across southside VA into NC foothills/piedmont. Majority of the high-res and synoptic models are in line with current conditions across the Ohio Valley and trend convection across the eastern Ohio Valley into the mid-Atlantic today into this evening. That is not to say to organized storms will not impact our forecast area. Outflow from upstream convection, combined with weak/no cap and SBCAPES in the 1500-2000 J/KG, and some modest 30-40kt bulk shear mainly north of a Greenbrier to Buckingham line suggest severe convection potential exists in an organized state. Meanwhile further south convection should be more widely scattered in nature but could develop into a multicellular broken line late in the day toward the piedmont. Another question will be how much blowoff from upstream convection impacts heating. Given what happened yesterday, and looking at the model 300-500 mb field flow suggests that any high clouds will be over the northern CWA, so heating should not be compromised too much. For Pops today, kept them below likely with higher chance north of I- 64, southeast toward Roanoke/Lynchburg, and along the southern Blue Ridge, where low level convergence will favor a little more coverage. Lowest pops are going to be over the NC piedmont. The cloud cover also plays a role in the heat advisory, and seeing no changes to that, with mainly 1 hour of 105F heat index values being reached in the piedmont around 4pm. Obviously convection could have an impact on how hot this gets. Still looking at highs from the mid 80s to near 90 mountains, to mid to upper 90s east. Tonight, models sans GFS continue to string along a couple of upper waves from the midwest into the mid-Atlantic. NAM/ECWMF favor and even the GFS favor another MCS potentially rolling into the central Appalachians by dawn Sunday. Given time of day severe threat will be limited but some stronger gusts are possible. Still keeping higher chance pops tonight mainly north of a line from Bluefield, WV to Roanoke to Lynchburg with less coverage in NC. Expecting a little more clouds tonight and higher dewpoints so lows will be in the upper 60s west, to lower to mid 70s east. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 AM EDT Saturday... A couple of mesoscale convective systems will track across to the north along a frontal boundary from West Virginia and Maryland. An upper level trough will travel eastward over the Great Lakes Sunday as a broad upper level ridge remains over the Southeast. The tenacious upper ridge will keep the heat and humidity over the Mid Atlantic on Sunday with heat indices reaching over 100 degrees in parts of the Piedmont. With LIs of minus 4 to minus 6 and CAPE around 2,000 J/kg Sunday afternoon. SPC day 2 convective outlook placed most of the forecast area in slight risk for severe thunderstorms. There is the potential for damaging winds and possibly hail with stronger thunderstorms across the area. High temperatures Sunday afternoon will range from the lower 80s in the mountains to the mid 90s in the piedmont. Expecting convection to spread east Sunday night and taper off to a few showers overnight. Low temperatures Sunday night into Monday morning will vary from the mid 60s in the west to the mid 70s in the east. Depending on how well the convection can push the frontal boundary southward over our CWA will play a key role for Mondays forecast. Kept scattered showers and thunderstorms for Monday afternoon. The highest chance appears to be along the southern Blue Ridge and through the northwest North Carolina mountains. High temperatures Monday will be a couple of degrees cooler than Sunday with readings from around 80 degrees in the mountains to the lower 90s in the piedmont. Drier air moves in Monday night as high pressure approaches from the north. Low temperatures Monday night into Tuesday morning will generally be from around 60 degrees in the northwest mountains to the lower 70s in the Piedmont. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 330 PM EDT Friday... High pressure should build over the Northeast by Tuesday. The frontal boundary will be shoved southward southward toward the North Carolina coast by this time. Lingering moisture may still spark a few diurnally-driven showers and thunderstorms during each afternoon through this period. The best chances appear confined to the VA/NC border on Tuesday, but more potential exists for Wednesday with easterly to southeasterly flow from high pressure offshore. There could be some wedging possible east of the Blue Ridge, so high temperatures were pushed downward for Wednesday to allow for the potential of upslope flow along the Blue Ridge and more cloud cover. Temperatures should bounce back upward by Thursday as high pressure heads further out into the Atlantic Ocean. Long range models hint at another frontal boundary approaching our CWA by Friday. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... As of 720 AM EDT Saturday... Going to see showers and storms fire up by midday/early afternoon, especially along the Blue Ridge northwest to the Alleghanys. At the moment models still not showing enough coverage to have thunderstorms as the main wx type but enough of a threat for VCTS. Still looks like best coverage stays north of a BLF-BCB-ROA-FVX line so took VCTS out of DAN`s taf. As the case is in these patterns a cluster of storms could sink further south impacting LWB-LYH, but at the moment it looks like best coverage will be north. VFR through the period outside storms. Severe threat exists so turbulence will be an issue this afternoon/evening. Another cluster of storms may arrive by 12z Sunday near BLF/LWB but too far out to have in the tafs. With more high clouds expected tonight have not included any fog. Confidence is high on cigs/vsbys through this evening, but low on vsbys late tonight as fog could form if less cloud cover occurs. Aviation Extended Discussion... Confidence is growing in a potential more active extended aviation forecast period for Sunday into Sunday night with multiple opportunities for thunderstorms. May see coverage shift into southern sections by Monday afternoon as residual outflow from Sunday jumps into North Carolina so appears more in the way of overall VFR possible Monday based on latest guidance. Otherwise most of the period will be VFR but with better chances for storms in more locations, mainly afternoon and evening late in the weekend, and with better coverage of rainfall the chances for IFR fog in the early morning hours increases again especially for KLWB and KBCB. A weak cold front is likely to push some of this moisture off to the southeast by Tues or Wed for at least a couple of relatively dry days. Overall, confidence of all weather parameters is moderate during the extended portion of the forecast. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for VAZ044>047-058-059. NC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for NCZ005-006. WV...None. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...KK LONG TERM...PW AVIATION...JH/MBS/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.