Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 181351 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 951 AM EDT Fri May 18 2018 .SYNOPSIS...
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A frontal boundary across the region will remain in place today and tonight before lifting north as a warm front Saturday. Several waves of low pressure will ride north along the front acting to enhance showers and storms into tonight. Warm and humid conditions will continue into the weekend with showers and thunderstorms becoming more scattered over the weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 945 AM EDT Friday... Deep tropical moisture remains in place this morning per observed PWATS near 1.5 inches and continued shower bands within a highly diffluent environment aloft east of the mid level low off to the west. Main convergence axis remains across southern sections where the residual front remains with deeper convection forming south of the boundary with showers overrunning the cool pool north of the NC/VA border. Latest short term guidance tending to weaken current coverage before redeveloping another band of heavier rain from north to south along the Blue Ridge this afternoon. This also supported by forecast of more instability over the far south with this swath of heavier rain sliding east later in the afternoon per latest HRRR. Thus have adjusted pops up across the central/east with likely/categorical pops continuing most spots with at least localized heavy rain likely. Thus keeping the watch going and may need to extend overnight pending later model guidance. Appears high temps wont rise much espcly northern half per weak wedge/showers with warmest values south where more heating could push values into the low/mid 70s. Previous discussion as of 355 AM EDT Friday... Flash Flood Watch remains in effect through this evening. The heavy rain threat continues with deep southerly flow of moisture, quasi-stationary front and wet antecedent conditions. The frontal boundary will linger over the region today with a gradual drift to the north as weak impulses of shortwave energy aloft move up form the south in deep, moist tropical flow. This morning the frontal boundary combined with a weak shortwave is focusing low level convergences and instability mainly in the south and east. With pockets of light rain, drizzle and fog in the west. Later today an upper low will travel into our forecast area. This create favorable QG ascent, along with the persistent southerly upslope flow induced by the Bermuda High. Scattered showers and thunderstorms with rain heavy at times are expected this afternoon into tonight. Rainfall will continue to be very efficient and it will not take long for slow moving cells to produce excessive rainfall. The FFG is quite low in several places and widespread heavy rain fall Thursday night. High temperatures this afternoon will range from the mid 60s in the northwest mountains to the mid 70s in the piedmont. Rain chances will decrease tonight mainly in the west. Cloudy skies will persist with lingering showers along and east of the Blue Ridge. Low temperatures tonight will vary from the upper 50s in the mountains to the mid 60s in the piedmont.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 415 AM EDT Friday... Wet weather is expected to continue through the weekend and into early next week. A broad upper trough infiltrated with deep tropical moisture will remain over the area through the weekend. The frontal boundary that has been lingering across central WV/VA will drift back to the north over the weekend. While this will take the better dynamics and focus for heavy rainfall and thunderstorms further north, it will leave a tropical laden air mass firmly in place across the region. All of the various models indicate potential for scattered to numerous showers and thunderstorms each day. The activity will be largely diurnally driven with no organized convection likely given the lack of dynamics and upper ridging from the south central U.S. Locally heavy rainfall will remain possible with a very low end severe threat mainly confined to wet downbursts. As we move into Monday, activity will likely tend to become a bit more numerous again as a weak frontal boundary approaches from the north and then again stalls near the I-64 corridor. Simultaneously, there is evidence of another tropical type disturbance spreading north from the southeast states which could also enhance rainfall. Warm and humid conditions will continue through the period with above normal temperatures, especially minimum temperatures will be some 15 to 20 degrees above normal. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 430 AM EDT Friday... Monday night into Tuesday, a surface low is expected to have reached KY/OH/WV with the stationary front over PA sinking south as a backdoor cold front. The cold front associated with the surface low is progged to stall and take on warm front characteristics from roughly Missouri into Kansas. While there initially will be a decrease in coverage of precipitation across the region Monday night, most of this decline will be due to loss of heating. Western sections of the area, closer to the approaching low, will be the most likely to continue to see some isolated to scattered showers, and few storms, through the night. On Tuesday, coverage is expected to increase again with the return of daytime heating, and increased dynamics as the system draws closer. Tuesday night night into Wednesday, look for the low to wash out, but the back door cold front will continue to inch south through, then south of the area, stalling over GA/SC by Thursday morning, and remaining there into Friday. Behind the front, high pressure will build into our region. The result for our region will be another decrease in coverage Tuesday night with the loss of heating. On Wednesday, scattered showers will be confined to primarily the southern third of the area. Wednesday night into Thursday, limited, if any, precipitation is forecast for the area with the push of high pressure into the area. Temperatures during this portion of the forecast will average about ten degrees above normal on Monday, and trend cooler each day. By Thursday, temperatures will average around five degrees above normal. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... As of 556 AM EDT Friday... Poor flight conditions will continue at TAF sites this period with low clouds, rain, drizzle and convection. Lingering frontal boundary combined with impulses of short wave energy in a tropical airmass will generate showers and a few thunderstorms with heavy rain. Adjusted timing of features with latest mesoscale models, and will amend as necessary with a preference to leave lower conditions prevailing when more activity is expected to move in. Believe that the HiResw-arw-east and HRRR capture this morning the best. Light rain and drizzle expected early this morning in the west with IFR cigs (isolated LIFR) to remain in place. Another wave of showers and isolated thunderstorms will advance north across the region this morning into this afternoon. This convection will continue to effect TAF sites this afternoon into tonight as the frontal boundary starts to push back to the north. Cloud skies with scattered showers will continue tonight into Saturday morning. Medium confidence in ceilings, visibilities and winds during the taf period. .Extended Aviation Discussion... The pseudo-tropical low and the lingering frontal boundary will begin to drift north of the CWA into the weekend. This should bring about a slight decrease in rain coverage with activity trending more scattered and diurnal in nature as we go into the weekend and high pressure ridging is noted across the southeast states. However, still feel that chances for showers/thunderstorms and associated aviation issues will be greater than normal for this time of the year, at least through Saturday with periods of sub-VFR possible. Fog and low clouds will be common during the late night and early morning hours as well. After more isolated storms on Sunday, appears another weak cold front may bring increasing coverage of showers and thunderstorms again on Monday. Monday night into Tuesday, a surface low is expected to have reached KY/OH/WV with the stationary front over PA sinking south as a backdoor cold front. Scattered MVFR showers and thunderstorms are possible monday night into Tuesday. && .HYDROLOGY... As of 458 AM EDT Friday... A Flash Flood Watch remains in effect for the entire CWA through this evening. The main concern through this evening will be for localized flash flooding, as well as flooding on small creeks, streams, and smaller rivers as a result of heavy tropical rain showers and thunderstorms expected across the area. Rainfall amounts Thursday evening into Thursday night averaged from one to 4 inches. Some of the worst flooding occurred in central Monroe county in West Virginia, Roanoke, Bedford and Franklin counties in Virginia. With the wet antecedent conditions and a tropical airmass, scattered showers and thunderstorms with heavy rains can produced flooding. WPC has placed much of our forecast area under a light to moderate risk of excessive rainfall today. The highest rain totals will be along and east of the Blue Ridge. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Flash Flood Watch through this evening for VAZ007-009>020- 022>024-032>035-043>047-058-059. NC...Flash Flood Watch through this evening for NCZ001>006-018>020. WV...Flash Flood Watch through this evening for WVZ042>044-507-508. && $$ SYNOPSIS...KK/PM NEAR TERM...JH/KK SHORT TERM...RAB LONG TERM...DS/RAB AVIATION...KK/MBS HYDROLOGY...KK/RAB

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