Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 281720 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 120 PM EDT SAT MAY 28 2016 .SYNOPSIS... Slow moving convection with heavy downpours again today. Moist southeast flow will raise shower chance Sunday in the mountains. Upper level ridge rebuilds next week. && .NEAR TERM /THROUGH SUNDAY/... Overall...no significant changes were necessary to the previous forecast. As expected...sct showers and thunderstorms have started to develop across Ohio...and am expecting sct showers and thunderstorms to develop across southeast Ohio...NE KY...and adjacent WV counties this afternoon...as upper disturbances moving north out ahead of an approaching upper trough affect the area. In addition...isold convection has developed across the northern mountains just outside the CWA due to differential heating...and will maintain a slight chance across northern mountain zones this afternoon. As with yesterday...overall flow is light...and storms will be slow to move and contain heavy downpours. Bulk of convection will briefly die down tonight...however...things will ramp up again towards morning...as a combination of moisture from a tropical depression...which will move inland towards South Carolina...and upper trough moves in from the west. Models seem to be backing off a bit on how much moisture and energy will actually make it into our CWA from the tropical depression...and elected to back off the pops a bit tomorrow across the east as a result. Still...looking at overall higher pops across the east...with lower pops across the central and western counties as upper trough pushes east into region. With the expected cloud cover and shower activity on Sunday...temperatures will be several degrees cooler than in recent days...particularly across the east. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... There are only very minor models differences in the exact track and timing of the two synoptic scale systems affecting our area this period...with the biggest forecast challenge coming in the QPF fields...as the models have trouble with convection in the summer like moist and unstable atmosphere. Handling of the QPF will again be handled on a diurnal basis outside of the main synoptic features. First is the tropical/subtropical low pressure system that tracks northwestward to the South Carolina coast this weekend...and then just sits there through early next week...as the supporting upper trough is sheared north and northeast thru the Mid Atlantic states on Sunday. This shearing out of the upper trough on Sunday is caused by the current Plains upper low opening up and moving east across the Great Lakes. This second system is strong enough to drive a weak front across the area Sunday night and Monday morning. The best chance of showers and storms comes with the upper trough on Sunday...mainly in the mountains...as the upper trough lifts north and then northeast through the Mid Atlantic states. Just diurnally driven low pops mainly in the afternoon over much of the low lands...as the deepest moisture and lift remains in the east. This swath of precip then shifts east early Sunday night with the upper trough. The following frontal system that comes across Sunday night and Monday morning has less moisture to work with...thanks to the previous system taking the deeper moisture with it. So we will play low pops with this front...especially given the loss of heating to support convection. Behind the front...look for drying and some clearing from northwest to southeast with any lingering showers ending in the mountains Monday afternoon. Thereafter...weak high pressure and upper ridging will bring dry weather Tuesday. Only minor changes to high temperatures this period...with no really cooler air moving in behind the front. However...behind the front...the muggier air will exit with lows Monday night and Tuesday night somewhat cooler. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... Upper level ridging over the central Appalachians and middle Atlantic seaboard leads to a dog day summer pattern for the middle portion of the short work week, with increasing diurnally driven thunderstorms tending to favor the mountains per elevated heat source. Models begin to diverge on the strength and timing of the ridge, which is stronger and peaks later, on Thursday, in the GFS solution, while weaker and peaking on Wednesday in the ECMWF solution. This model divergence continues on Friday, as the ECMWF rolls an upper level low across southern Canada during the week, which then pushes a cold front through the area on Friday. The GFS has divorced itself from this solution, instead shearing out the southern Canadian low, and dropping another southeastward through the plains states toward the lower Mississippi valley. The forecast does not bite on the left turn taken by the GFS, and instead picks up on an increasing chance for showers and thunderstorms Thursday into Friday, before turning slightly drier and cooler late Friday and Friday night. Temperatures close to central guidance with little change through day 6, and then the trend toward slightly lower values. && .AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
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ISOLD to SCT showers and thunderstorms...mainly across southeast Ohio...WV lowlands...and northeast Kentucky through 02Z. Otherwise...increasing bkn-ovc vfr sky cover overnight...as moisture from a low along the Carolina coast advects into the region. Thinking this should to keep much fog development tonight at bay. After 12Z...sct showers and thunderstorms will develop again...with heavy downpours...and brief mvfr/ifr conditions in vcnty of storms. Elsewhere...VFR with light surface winds. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z SUNDAY... FORECAST CONFIDENCE: High. ALTERNATE SCENARIOS: Extent and coverage of convection this afternoon remains in question...especially regarding any location that may be affected. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. UTC 1HRLY 15 16 17 18 19 20 21 22 23 00 01 02 EDT 1HRLY 11 12 13 14 15 16 17 18 19 20 21 22 CRW CONSISTENCY H H H H H H H H H H H H HTS CONSISTENCY H H H H H H H H H H H H BKW CONSISTENCY H H H H H H H H H H H H EKN CONSISTENCY H H H H H H H H H H H H PKB CONSISTENCY H H H H H H H H H H H H CKB CONSISTENCY H H H H H H H H H H H H AFTER 18Z SUNDAY... No widespread IFR conditions expected.
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&& .HYDROLOGY... The river gauge...and forecast point...at the South Side Bridge in downtown Charleston has not be reading correctly. The NWS hydrologist is working to correct this problem. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...ARJ/SL NEAR TERM...SL SHORT TERM...JMV LONG TERM...TRM AVIATION...SL HYDROLOGY...ktb

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