Area Forecast Discussion
Issued by NWS Blacksburg, VA
Issued by NWS Blacksburg, VA
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567 FXUS61 KRNK 050028 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 828 PM EDT Sat May 4 2024 .SYNOPSIS... An upper level trough of low pressure will move across the Mid- Atlantic Region through Sunday, resulting in mostly cloudy skies, widespread showers, and a few thunderstorms. Rainfall amounts will be highly variable, ranging from a quarter of an inch, to more than an inch. Temperatures rebound into the 70s for Sunday. Daily afternoon showers and thunderstorms are possible through the week. && .NEAR TERM /THROUGH SUNDAY/... As of 815 PM EDT Saturday... For the near term update this evening, expecting areas of light rain and showers to continue through much of the overnight as strong isentropic upglide overrides the CAD wedge. Any attainable instability should be mainly confined to the south and west of the CWA so there is no thunder mention through tonight. Areas of fog should also develop across much of the area. Not expecting much dense coverage but there could be some spots that bounce around the 1/4 SM vsby at times. Forecast largely on track and previous discussion follows... As of 200 PM EDT Saturday... Key Messages: 1. Isolated thunder possible mainly for western and southern sections of the forecast area this afternoon/evening. 2. Rainy and foggy conditions continue, with a large area of rain moving through tonight. 3. Wedge of cool/damp air begins to erode slowly on Sunday with scattered showers and thunderstorms. Scattered to numerous rain showers continue through this evening. The eastern portion of our VA counties were embedded in a wedge of high pressure supported by easterly surface winds. This was keeping temperatures cool and thunderstorms out of that region. The western side of the wedge was bounded by a warm/backdoor front, and to the west of this we were seeing heavier showers and an uptick in thunderstorms this afternoon. The western edge of the forecast area will see the best chance for thunder where there have been breaks in cloud cover. Elsewhere, the wedge stays in place and will keep the weather damp and foggy. Tonight, isentropic lift increases as moisture rides over the wedge ahead of a short wave, as does frontogenesis associated with the residual warm/backdoor front. This will culminate in a large area of stratiform rain moving from the Deep South north towards the Mid Atlantic. As this occurs, PWATs will hover around 1.5 inches, and warm cloud depths will reach 10 kft. A LLJ of about 20 to 25 kts and slow storm motion will support training and urban and small stream flood concerns. So far, precipitation amounts have varied widely, but southern and southeastern sections of our area have seen close to an inch or more. These locations will be monitored for flood/flash flooding potential. As this large slug of rain moves out in the morning, the wedge of cool air begins to retreat to the northeast. Tomorrow`s rain and thunderstorm chances look more widely scattered and centered on the higher terrain. Temperatures should rebound somewhat in southerly flow tomorrow, reaching the upper 60s to mid 70s. Confidence in the near term is moderate. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 130 PM EDT Saturday... Key Messages: 1. Warming trend in temperatures for beginning of the week. 2. Chances for showers and storms each day. Rain and thunderstorm chances continue each day through this short term period of the forecast as a front stalls to the north and west of the area. Late Monday, a 500mb shortwave rides over the ridge and provides some additional upper forcing for ascent over the area, which could result in some showers and storms. The surface front lifts northward Tuesday, putting the area in a broad warm sector, with the surface low still over the north central US, bringing in warmer air and more moisture. With the front moving farther from the area early Tuesday, expecting more breaks in the clouds than on Monday, and so daytime heating will increase the instability over the area later in the day, and will lead to showers and thunderstorms again Tuesday afternoon. Weak ridging at 500mb will spread over the southeast US and Mid Atlantic into the beginning of the work week. Increasing heights will lead to a warming trend in temperatures through Tuesday, with increasing positive 850mb temperatures anomalies through the middle of the work week. High temperatures will gradually increase from the low 70s to upper 70s in the west, near 80 to mid 80s in the east, through Tuesday. Lows will be mild, in the mid to upper 50s in the west and low 60s in the east. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 200 PM EDT Saturday... Key Messages: 1. Showers and storms possible each day, highest probability Thursday. 2. Warming temperatures through Wednesday, cooler for the weekend. Mid level ridging builds back in over the southeast and Mid Atlantic in response to a trough deepening over the central US. This keeps broad southwesterly flow at mid levels over the area into the second half of the work week, but slowly flattening and becoming more zonal into the weekend, as the main 500mb low tracks across southern Canada. A surface low pressure system moves eastward across the Great Lakes by Thursday, with a cold front extending south and another boundary extending west-east across the upper Mid Atlantic. With this increased large scale forcing, probabilities for thunderstorms are highest on Thursday. Deterministic long range models show some differences in the timing of the actual frontal passage, some bringing it through the area late Thursday and others not until Friday, which brings some uncertainty into duration of precipitation with the front. The warming trend in temperatures will continue through the middle of the work week. Rain and cloud cover will keep Thursday a couple degrees cooler as well, but not quite as cool as the weekend, as a cooler and drier airmass settles into the area behind the front. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... As of 820 PM EDT Saturday... Most sites should stay with LIFR cigs and IFR/LIFR vsbys (possibly lower) through the overnight along with areas of RA/SHRA and possible fog. There could be a lull in precip coverage Sunday morning after sunrise though the low cigs and vsbys could continue through much of the morning with eventual improvement after about 17/18z (perhaps sooner for the western sites). TSRA chances could increase for Sunday afternoon but coverage of precip overall should be less than today. Winds initially east to SE under 10 kts then mainly shift more south to SW/west during the day Sunday. Extended Aviation Outlook... SHRA/TSRA with periods of BR yielding MVFR/IFR/LIFR conditions continue through Sunday evening. More diurnally driven -SHRA/TSRA are expected Monday through Wednesday. This will bring periods of MVFR ceilings and visibilities at times. Winds Monday through Wednesday will be SSW and gusty at times. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM/SH NEAR TERM...SH/AB SHORT TERM...AS LONG TERM...AS AVIATION...SH/AB