Area Forecast Discussion
Issued by NWS Blacksburg, VA

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112 FXUS61 KRNK 251102 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 702 AM EDT Mon Jul 25 2016 .SYNOPSIS... 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 today, 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. && .NEAR TERM /THROUGH TONIGHT/... 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. && .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 /12Z MONDAY THROUGH FRIDAY/... As of 640 AM EDT Monday... Other than for patchy fog/stratus in the valleys, mainly VFR to start this morning under increasing high cloud canopy that will likely be over the region this morning. Thus may need to include brief IFR/MVFR at KLWB/KBCB pending release observations. Otherwise ridging aloft will remain in place today with a bit better low level convergence developing over the mountains in the afternoon ahead of a weak cold front to the northwest. This should lead to a scattered to broken VFR cu field by afternoon with cigs most likely across the far west where moisture is a bit better. Also given strong instability would expect somewhat better tsra coverage mainly west of the Blue Ridge during the 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. Thus confidence remains high enough to keep VCTS at most western sites including KBLF/KBCB and possibly KLWB by mid to late afternoon at this point. Despite loss of heating the approach of an upstream cold front and leftover instability/outflow may keep at least isolated convection going into late this evening. Looks like best coverage would be across the north and west but too iffy to include additional shra/tsra mention into late tonight for now. Otherwise should return to VFR outside of any leftover tsra this evening prior to patchy fog formation again late. Extended aviation discussion... Ridge will finally 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 into Friday with periodic MVFR/IFR possible especially Tuesday afternoon and again Wednesday pending 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. && .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 from noon today to 8 PM EDT this evening for VAZ046-047-058-059. NC...None. WV...None. && $$ SYNOPSIS...JH/RCS NEAR TERM...JH SHORT TERM...MBS LONG TERM...AMS/MBS AVIATION...JH/RCS/WP CLIMATE...JH is the U.S. government's official web portal to all federal, state and local government web resources and services.