Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 291748 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 148 PM EDT Thu Sep 29 2016 .SYNOPSIS... A large area of low pressure will remain in place over the Ohio Valley through the rest of the week, providing cool and occasionally rainy conditions. Chances for rain will begin to diminish on Saturday, as the low gradually begins to move to the northeast. Drier and warmer conditions are expected for Sunday and Monday, with surface high pressure building in from the west. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1245 PM Update > Refined forecast a little while ago with a healthy blend of previous forecast and HRRR ensemble data which has a good handle on batch of rain/few storms along/west of the Scioto Valley. This should continue to peel slowly northwest into central/southwest Ohio as it continues to slowly weaken/erode on the nrn edge as it gets removed further from stronger flows and forcing. Other showers/storms developing along old occluded front in ern OH and these have a trajectory NW back toward cntl OH for mid/late afternoon. As we approach peak heating over the next couple of hours...other showers/storms will form in isold/sct fashion across nrn KY/swrn OH. Still looks like primary threat for stronger updrafts is east of the ILN area - though a stronger cell could wander into the Scioto Valley between 3PM and 5PM. Also increased rain chances this eve along/south of Ohio River...recent HRRR runs and new 29.12Z NSSL WRF have been showing this area lighting up in a narrow band of rain/storms as stronger shortwave dynamics rotate NW across nrn KY this evening. Another large band/arc of showers and storms will likely develop later this evening into the overnight across the area but timing of this is not good among the hi-res guidance. Most concern for impact through tonight will be localized flooding with narrow bands of moderate/heavy arcs of rain rotating around the upper low. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... Overnight, a swath of showers (associated with the upper forcing and whatever is leftover from afternoon convection) is forecast to move westward through the ILN CWA. If nothing else, this forecast for rain makes the potential for fog tomorrow morning a little more uncertain, even if conditions would otherwise be favorable. Patchy fog wording will be included in the forecast, along with 50-70 percent chances of precipitation. As the mid-level low starts to swing northward again on Friday, there is reasonable model agreement in a relatively dry wedge entering the south-central section of the ILN CWA during the afternoon, with little in the way of forcing. PoPs on Friday afternoon and evening will range from 20-50 percent, with the highest values in the northern and northeastern sections of the forecast area. With systems like this, and still plenty of room for error in timing out the vorticity maxima rotating around, this PoP forecast should still not be seen as an explicit forecast of specific timing and placement. Precipitation chances will begin a more significant decrease on Saturday, as the low starts a quicker motion out of the Ohio Valley and back into the Great Lakes from whence it originated. Early on Saturday, the western half of the ILN CWA will be most likely to receive additional precipitation, but a gradual drying from south to north is expected by afternoon. The relatively small diurnal temperature ranges will begin to expand a little by Friday, and especially by Saturday, as slightly drier overall conditions allow for a little more heating in the afternoons. In fact, the forecasted highs on Saturday (upper 60s to lower 70s) are only a little bit off from normals for early October. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... This period will be characterized by a much warmer drier/period vs the short term. On Sunday morning...the closed low will be drifting northeast...weakening...and opening up into a more progressive shortwave trough over New England by Monday. Thus...there is still a small threat of showers into Sunday but right now the timing/placement of this threat is very tough but seems focused north of I-70 closer to mid level cold pool. Large scale ridging ahead of the next longwave trough over the west will allow for dry weather Monday thru Wed as high pressure at the surface moves across the eastern U.S. Temperatures will be warming steadily and by the middle of next week should be well into 70s if not the lower 80s with dewpoints hanging tough in the 50s. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... Low confidence TAF forecasts this cycles due to variable cigs amidst moist/unsettled pattern under upper low. Bands of rain/embedded storms should affect all sites from time to time but timing/placement of rain bands is problematic at best. Bottom line...a good deal of shower mention are in the TAFS...either in VCSH fashion or predominant weather. Thunder is highlighted through this afternoon in the Columbus area terminals closer to old/weak occluded boundary and nearest best moisture transport this afternoon/evening. Trended vsbys from VFR down to MVFR in the overnight and with associated showers. Cigs are all over the place...though generally lifting to VFR this afternoon but occasionally down to MVFR in showers or in tempo groups. With the onset of stronger moisture push and rain this afternoon and night across the TAF sites...am bringing vsbys and cigs down well into MVFR and even IFR late in the night given weak/convergent flows in the boundary layer near weak low pressure to the south. OUTLOOK...MVFR ceilings and visibilities possible with showers Friday afternoon through Saturday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Binau/Hatzos SHORT TERM...Hatzos LONG TERM...Binau AVIATION...Binau

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