Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 281319 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 919 AM 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 TONIGHT/...
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920 AM update...went ahead and added a slight chance of thunderstorms across northern mountain zones this afternoon based on latest runs of the HRRR and NAM. Otherwise...previous forecast on track. PREVIOUS DISCUSSION BELOW... Another warm and somewhat humid day on tap with isolated to widely scattered tsra this aftn and early evening. Such is life on the edge of the ridge. It remains difficult to hone in on any specific area for convection later today. However...outside of any isolated mtn convection...NAM model continues to indicate sct convection firing over the Kanawha Valley by 21z and slowly propagating off to the NW early this evening. The previous fcster looks to have handled this well on the day shift and only some fine tuning was made to the pops...mainly to increase to around 40ish for POP flanked with slight chance. Another area to potentially hone in on is across portions of SE OH. Expect downpours in any convection with locally heavy rain given the light flow thru the column and high moisture levels. Added a degree to highs today from observed values yesterday yielding mid to upper 80s in the lower elevations. Suspect a spot 90 will be observed in the urban centers...especially in and around HTS/CRW. Any evening convection will slowly wane as attention turns to low pressure along the SE coast. With an approaching upper trof...models are trying to pull in deeper moisture from the tropical/subtropical system Sat night. This will result in an increase in clouds with a few shra possible toward morning.
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&& .SHORT TERM /SUNDAY 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 /13Z SATURDAY THROUGH WEDNESDAY/...
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SCT/BKN CU field will quickly develop as the morning progresses. Isolated convection will be noted this aftn...primarily over SE OH. Confidence not high enough to put VCTS at any terminal with this issuance. Mid and high clouds will overspread the area from the SE tonight as moisture from low pressure along SE coast advects into the region. As such...not forecasting fog attm. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z SUNDAY... FORECAST CONFIDENCE: Medium. 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 12 13 14 15 16 17 18 19 20 21 22 23 EDT 1HRLY 08 09 10 11 12 13 14 15 16 17 18 19 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 L L H H H H H H H H H H PKB CONSISTENCY M 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 12Z 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...JMV/30 NEAR TERM...SL/30 SHORT TERM...JMV LONG TERM...TRM AVIATION...30 HYDROLOGY...ktb

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