Area Forecast Discussion
Issued by NWS Blacksburg, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
407 FXUS61 KRNK 290843 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 443 AM EDT WED JUN 29 2016 .SYNOPSIS... A weak cold front will drift east through the region this morning before stalling southeast of the area tonight into Thursday. Weak high pressure following the front should bring somewhat drier air to the area by this afternoon. However, as the high shifts east, moisture will quickly return for the end of the week ahead of another cold front that will affect the region into the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM EDT Wednesday... Surface cold front continues to slowly ooze across the mountains early this morning while the actual 850 mb boundary lags back just west of the mountains closer to earlier showers that were over the far west. Should see somewhat drier air make some inroads later this morning into the afternoon as the upper trough to the north pivots by and gives the dewpoint front a nudge eastward. However given such weak features aloft in late June and added upstream shortwave energy approaching later today, questions about the degree of drying that will take place espcly south/east this afternoon. Latest guidance varies with some solutions much drier aloft, while others hang onto just enough low level moisture to pop convection given decent instability mainly southern Blue Ridge east. This looks a bit overdone under developing west/nw flow aloft, but since the flow is quite weak near the surface under a lingering theta-e ridge, and slight cooling aloft under the trough, will lean a little higher with pops southern third later on. This more in line with the latest Cam and ensemble solutions so including 20/30 pop mainly south-sw this afternoon. Otherwise should see more sunshine take shape elsewhere once fog fades and without pop mention given dry advection under weak high pressure building in from the west. Any brief cooling at 850 mb will be short as another impulse approaches and given weak downsloping under insolation, bumped up highs closer to current warmer Mav mos values. Weak surface high continues to slide in overnight while impulses aloft slide by just north of the residual surface front just to our southeast. Seeing some weak backing aloft taking place while overall deep moisture lacking with the majority of better lift to the east. However models do show some lingering low level convergence southern sections that may translate east with a weak wave to the south overnight. Thus left in low pops this evening, tapering to isolated southeast late. Otherwise partly cloudy with another round of fog and lows a bit cooler, but more toward the milder Met mos espcly Blue Ridge east where have doubts about seeing dewpoints drop a lot. && .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... As of 400 AM EDT Wednesday... Rather complicated forecast and no really rain free periods as a weak frontal boundary/baroclinic zone lingers near the NC/VA border Thu-Fri, while somewhat of an inverted trough is evident across the Piedmont/Coastal Plain, delineating an area of deeper moisture with PWATS near 2.00 inches from PWATS across western areas less than 1.5 inch. Meanwhile, a fairly unstable W-WNW flow remains in place aloft, although more southwest across the eastern part of the CWA as a broad trough axis lingers over the region, with several upstream disturbances emanating from the parent low above the Great Lakes. Several fairly notable disturbances are slated to traverse the region during the period. For Thursday, a disturbance laden with tropical moisture will likely ride northeast from GA/SC along the inverted trough axis. This will likely trigger scattered to numerous showers/thunderstorms during afternoon heating, with perhaps even a few showers even in the morning hours as well as lingering well into the evening. This precipitation should remain mostly along/southeast of the Blue Ridge with drier air, westerly flow, and less forcing west/north of the Blue Ridge. By Friday, a trough associated with the aforementioned upper low will drift southward into the region. The earlier inverted trough will be pushed to the coast along with the deeper moisture. However, the upper trough combined with diurnal heating should be enough to trigger scattered showers/thunderstorms across much of the CWA Friday afternoon/evening. As with most recent systems, the front will stall across the CWA, most likely near the NC/VA border and then begin to drift back north Saturday as the upper trough and support lifts off to the northeast. This will leave a baroclinic zone across the region Saturday with a delineating zone of deeper moisture and better instability evident in all models between the north and south parts of the CWA. Again, expect scattered showers and thunderstorms across mainly southern/eastern parts of the CWA Saturday, especially along and south of U.S. 460. Fortunately, through Saturday the heaviest rain should remain across areas that were not so hard hit last week. WPC and model QPF through Saturday does not appear to be a problem anywhere with generally less than 1/4 inch advertised across the recently flood ravaged northern part of the CWA. 850mb temps hold in the +16C to +20C range through the period, which should keep max temps close to 90 across the Piedmont, with mostly 80s elsewhere outside mid to upper 70s in the mountains. These temperatures are about 5 degrees above normal. Min temps will also average about 5 degrees above normal, mainly upper 50s mountains to mid 60s Piedmont. && .LONG TERM /SUNDAY THROUGH TUESDAY/... As of 420 AM EDT Wednesday... Sunday, the weak front lingers near the NC/VA border as weak high pressure slides across the Ohio Valley toward the Mid-Atlantic. The front will continue to serve as a baroclinic zone and serve as a focusing mechanism for showers/thunderstorms, most numerous during the afternoon/evening, but given the very moist airmass and instability in place, cannot completely rule out showers and isolated thunderstorms even during the nighttime hours. Monday brings about concerns for both severe weather and flooding once again. A vigorous short wave is progged by all models to move out of the central Plains and ride along the persistent baroclinic zone from KS/MO toward the central Appalachians. During the day Monday, the baroclinic zone/cold front will begin to return north as a warm front in response to the approaching short wave. Most models have a clear MCS signal progged to traverse the region and which unfortunately appears to focus on and track across the recently flood ravaged areas of WV and central VA. This situation will have to be watched very closely as most models have a swath of very heavy precipitation, 3-4 inches in 24 hrs, tracking from KS/MO into KY, then 2-3 inches into WV/VA. Again, this will need to be watched very closely as this type of rainfall could quickly result in flooding/flash flooding across southeast WV and the I-64 corridor. The severe weather threat Monday is less certain as the best instability appears to remain further south, not in line with the projected track of the MCS/best forcing. Again, it appears that heavy rain/flooding would be the main concern, but there does appear to be at least some severe threat, mainly in the form of wind gusts. Temperatures, outside cloudy/rainy periods will be warm and humidity levels will be high, increasing beyond Monday as the warm front lifts north of the region and heights aloft rise in response to a building upper ridge across the southeast states. 850mb temps are currently progged, especially on the GFS, to reach the highest levels of the year so far by the mid part of next week, namely in toward +23C across parts of the CWA. Thus, temperatures will likely be several degrees above normal, especially min temps. && .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/... As of 1255 AM EDT Wednesday... Cold front slowly making its way across the Blue Ridge should continue to edge east of the region by daybreak. This looks to bring in slightly lower dewpoints across the mountains through morning while soupy conditions linger out east. Otherwise looking at mainly VFR cigs to start with potential for areas of dense fog in the valleys as well as across the east during the next few hours. However just how widespread fog will be remains iffy given residual mid clouds so keeping trend of prevailing MVFR to IFR in fog/stratus with tempo to LIFR at times outside of KROA. Wednesday morning will see fog/stratus dissipate with a return to VFR conditions expected by midday with mainly broken 4-6k cumulus fields Wednesday afternoon. Also cant totally rule out isolated convection Wednesday afternoon espcly southern sections but just to iffy to include for now. Extended discussion... Thursday into Sunday, the high will shift to the east and the region will be within southerly flow again. This pattern will have the potential of advecting moisture back into the area. Showers and storms will again be possible yielding areas of sub-VFR conditions espcly during the afternoon/evening hours. This likely followed by late night and early morning patchy fog with localized sub-VFR possible. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...RAB LONG TERM...MBS/RAB AVIATION...JH/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.