Area Forecast Discussion
Issued by NWS Blacksburg, VA

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001 FXUS61 KRNK 251748 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 148 PM EDT Mon Jul 25 2016 .SYNOPSIS...
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Strong high pressure aloft will continue to result in hot and humid weather early this week. A weak cold front approaching from the north should bring increasing chances of showers and thunderstorms over the mountains this afternoon, and across the region on Tuesday. This boundary looks to linger over the area through the rest of the week with added showers and storms possible each day.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 100 PM EDT Monday... Increased pops for this afternoon matching closer to HiResw-arw and the NAM. Regional WSR-88d showed scattered convection forming across the mountains in the unstable air with li around minus 4. more changes later this afternoon... As of 956 AM EDT Monday... Made some minor adjustments in temperatures for this morning into this afternoon utilizing sfc obs,and their trends, then leaned temperatures towards lamp guidance. As supported by Highres models, allowed for some isolated cooling convection, mainly in the mountains. May still have to adjust pops up for this afternoon depending on the evolution of convection early this afternoon. There is a slight risk to our north across northern West Virginia and northern Virginia associated with shortwave rotating east. Another hot and humid afternoon expected...with high temperatures ranging from the mid 80s in the mountains to around the century mark in the Piedmont. Heat advisory look good with heat indices as high as 105 in the far east. More changes later... As of 300 AM EDT Monday... Upper ridge will continue to hold for the most part for one more day before slowly weakening/flattening overnight as shortwave troughing passes to the north. This continued subsidence along with progged 850 mb temps of around +24C espcly east will make for another very hot afternoon. Still appears that dewpoints may again fall with mixing later on but given more of a southwest trajectory and slowly rising pwats, may see values out east stay a bit higher than the last few days. This supports, espcly for impact, keeping the heat advisory headlines going where in place with indices even around 100 back west to the Blue Ridge. Expect actual high temps again in the 95-100 range just east of the Blue Ridge, per latest slightly higher forecast thickness, with 87-92 west where a bit more cloudiness and convection could occur. Again appears that BCB and BLF have the best shot at high temp records today. Expanse of afternoon shra/tsra still a bit iffy given faint late day cooling aloft far west/nw and slightly better moisture under strong instability/theta-e. However forcing to remain well to the north closer to the upstream front with orographics aided convection more likely espcly I-77 corridor and perhaps southern Blue Ridge to start. Expect some of this to slowly spread north/east with possible better coverage and stronger storms affecting the far north late where closer to the front/wave per latest WRF/Cam solutions. Otherwise still mainly chance pops with little coverage southeast where will remain under the ridging aloft for now. Boundary sinks southward to just north of the area late tonight with the axis of higher pwats and weak lift strung out from the western slopes to across the north overnight. This may allow a corridor for added convection to track along espcly during the evening given likely leftover CAPE from such a hot afternoon. This seen in a few models in showing weak low level convergence under diffluence aloft far west and along the swath of higher theta-e exiting the east. Will also have more shearing energy aloft across the north along the bottom of the passing mid level trough, so likely need to keep some pops in north-west overnight. Otherwise partly to mostly cloudy and very muggy/warm with lows mostly in the 70s, except for a few 60s in the cooler valleys, including where earlier showers occurred.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... As of 330 AM EDT Monday... The frontal boundary will wash out across the area tonight, then linger across the region through the middle of the week. Meanwhile quasi zonal flow aloft will keep pieces of short wave energy streaming in our direction, followed by a more significant short wave that will bend the flow to more of an eastern trof by the end of the week. There are also indications that we will be in the right rear quad of a series of jet streaks moving by to our north, providing us with some enhanced synoptic lift. This all makes for unsettled weather with a good chance for thunderstorms through midweek. Individual upstream short waves will play a large role in triggering and maintaining convection but there is too much uncertainty to get very specific deep into the forecast, so will bias the POPs with a typical diurnal peak in the late afternoon and will linger activity a bit linger into the night time periods. While there will be ample instability to support vigorous convection, the absence of significant shear will continue to limit our chances for large scale organized severe weather, making pulse storms/clusters our main threat. PWATs will also be climbing into the 1.5 to 2 inch range so locally heavy rain will be an increasing concern, though the warm and relatively dry antecedent conditions will be a limiting factor. Temperatures will continue to a few degrees above normal through the period. Highs will be in the low to mid 90s east of the Blue Ridge with mid/upper 80s to the west. && .LONG TERM /FRIDAY THROUGH SUNDAY/... As of 315 PM EDT Sunday... Amount of troffing in the eastern United States for the end of the week is questionable. GFS was the more amplified while the ECMWF was slightly flatter. Friday looks to be the next day with any potential for decent upper support. Will have the higher probability of precipitation on Friday and Saturday afternoon and evening. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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As of 148 PM EDT Monday... SCT to BKN MVFR clouds this afternoon with isolated to widely scattered IFR conditions near thunderstorms. Ridging aloft will remain in place this afternoon into tonight, with a bit better low level convergence developing over the mountains ahead of a weak cold front to the northwest. Given strong instability would expect somewhat better tsra coverage mainly west of the Blue Ridge this afternoon, with perhaps some of this shifting slowly east by late in the day. Still overall coverage appears scattered to widely scattered but more clustering potential mountains given slow movement. Will keep VCTS at most western sites including KBLF/KBCB and KLWB this afternoon into tonight. Added the mention vcsh for KROA with nearby convection. Despite loss of heating the approach of an upstream cold front and leftover instability/outflow may keep at least isolated convection going this evening into tonight. The best chance for any storms will occur across the north and west. Otherwise should return to VFR outside of any leftover tsra this evening prior to patchy fog formation again late. Ridge is slowly breaking down Tuesday with scattered MVFR/IFR showers and thunderstorms possible mainly during the afternoon and evening hours. Medium to high confidence in ceilings, visibilities and winds during the taf period. Extended aviation discussion... The ridge will weaken through mid week as an initial cold front sinks toward the area from the northwest. This should bring about an increase in daily convective coverage Tuesday late afternoon and evening into Friday with periodic MVFR/IFR possible depending on exactly how far south the front makes it. Late night and early morning fog will likely occur at the usual valley locations, and those chances increase across the entire region if any rain occurs during the afternoon or evening at any site.
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&& .CLIMATE... Record high temperatures for Monday (7/25) Roanoke.....100 in 1934 Lynchburg...102 in 1934 Danville....102 in 2010 Blacksburg...92 in 1987 Bluefield....90 in 1987 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Heat Advisory until 8 PM EDT this evening for VAZ046-047-058- 059. NC...None. WV...None. && $$ SYNOPSIS...JH/RCS NEAR TERM...JH/KK SHORT TERM...MBS LONG TERM...AMS/MBS AVIATION...JH/KK CLIMATE...JH

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