Area Forecast Discussion
Issued by NWS Blacksburg, VA

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234 FXUS61 KRNK 262356 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 756 PM EDT THU MAY 26 2016 .SYNOPSIS... A southwest flow of moisture around high pressure will push warm unstable air into our region. High pressure staying off the coast through Friday with typical summer like weather impacting us increasing humidity. This weekend, a potential tropical low may arrive toward the South Carolina coast and linger in the general area into early next week. && .NEAR TERM /THROUGH FRIDAY/... As of 347 pm EDT Thursday... An upper air disturbance rotating across our area will trigger scattered showers and thunderstorms this afternoon into this evening. SPC mesoscale analysis at 18z showed best moisture convergences along the southern Blue ridge mountains. SBCAPE values have climb into the 1000 to 1500 j/kg range in the east. Surface based LIs were minus 2 to minus 4 across our region. Looks like the best chance for convection will be along the Blue Ridge. SPC has our area in general thunderstorms in the day one convective outlook. Limited instability and weak shear will hinder severe weather potential. For pops this afternoon leaned towards the HRRR, then blended NAM and ECMWF for tonight. With the loss of solar heating expect storms to diminish this evening and end by Midnight. Areas of fog will develop overnight into Friday morning especially in the river valleys. Low temperatures tonight will drop into the upper 50s in the mountains to the mid 60s in the Piedmont. Surface high over the western Atlantic strengthens Friday as a cold front approaches from the west. A deep conveyor belt of Gulf moisture will be tracking northward into our area around the high. An upper disturbance will moved into New England, leaving little triggering mechanism to work with Friday. A very moist summerlike atmosphere will be present across the region with PWATS in around 1.5 inch. Scattered convection should develop...especially across the Alleghanys and western mountains in association with differential heating. Steering currents will be weak and limited dynamics. High temperatures Friday will climb into the mid 70s in the mountains to the mid 80s in the Piedmont. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... As of 330 pm EDT Thursday... Scattered showers and thunderstorms Friday afternoon especially in the northwest will diminish with the loss of solar heating Friday evening. The combination of low level moisture and light winds will result in areas of fog Friday night into Saturday morning. The remainder of the forecast period continues to hinge heavily on the track...intensity...and duration of a tropical system developing across the Bahamas. The models move the coastal upper low to the SC coast by Saturday evening, while the upper ridge weakens over the Southeast. The upper low is shown to move very little over coast SC through Sunday. The 27/12Z ECMWF/GFS were in very good agreement until 30/12Z along the SC Coast. Then, there are differences on how the models handle the low and its associated moisture. WPC was leaning towards the ecmwf solution over the aggressive and inland GFS solution. The GFS solution would bring heavy rain into the CWA and arouse flooding concerns...while the other models suggest much less potential...barring a predecessor rain event (PRE). Will need to watch closely...but the consensus among most models is for scattered to numerous showers/thunderstorms by Sunday across the region...especially east of the Blue Ridge...requiring at least high chance pops. It will not be widespread continuous rain event...but largely diurnally driven. A very moist summerlike atmosphere will expected across the region with PWATS in around 1.0 to 2.0 inches. Moisture/humidity will increase through the period and overall it will feel very muggy and summerlike with mild to warm nights and warm/humid days. Looks for low temperatures to be mainly in the 60s with high temperatures in the the 70s for the mountains. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 345 pm EDT Thursday... There remains a lot of uncertainty in the medium range forecast. The forecast challenge through the period will depend on the track of an area of tropical low pressure across the Southeast states. The Question is whether it linger across the region through the period thanks to a stagnant upper atmospheric pattern with an upper high to our north and a broad upper low continuing in the western U.S. If the tropical system does linger for several days with non- existent steering currents and blocked upper flow, rainfall may become a concern as a result. The other key player in the extended period is a cold front to the west, which travels eastward during the period. The strength of the ridge will determine how far the front makes it. In any case, we can expect scattered diurnal convection with warm/humid conditions through the period. used the superblend for temperatures. In general, High temperatures will remain mostly in the 70s mountains to the 80s elsewhere. Low temperatures will be mainly in the 60s. The details of the extended forecast will become clear during the next couple of days. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... As of 750 PM EDT Thursday... Areas that had rain this afternoon into this evening will have a better chance of seeing late night/early morning fog with IFR to LIFR ceilings and visibilities Friday morning. Highest confidence of IFR is at LWB/BCB for now. Areal coverage of any showers and thunderstorms Friday afternoon will be better west of the Blue Ridge. The most likely time frame for storms at KBLF, KLWB, KROA, and KBCB will be from 19Z/3PM until 00Z/8PM. Extended discussion... Saturday the region will be in between systems with the upper low remaining west of the region and a tropical system developing off the SC coast. Little forcing and lift plus increased subsidence should confine any convection to the mountains...isolated to scattered diurnal activity at best. For the remainder of the period...the forecast will hinge heavily on the track of the tropical low pressure area...which at a minimum will bring increased moisture and shower chances to the area...which could linger well into next week. This will result in periods of mvfr- ifr cigs and greater potential for late night/early morning fog as well. Confidence in the evolution of the forecast past Sunday is low. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK/WP NEAR TERM...KK SHORT TERM...KK LONG TERM...KK AVIATION...AMS/KK is the U.S. government's official web portal to all federal, state and local government web resources and services.