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Area Forecast Discussion
Issued by NWS Wilmington, OH
Issued by NWS Wilmington, OH
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069 FXUS61 KILN 190153 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 953 PM EDT Thu Jul 18 2024 .SYNOPSIS... Dominant high pressure centered over Iowa this evening will influence the weather over the Ohio Valley into and through the weekend with dry conditions, and below normal temperatures as it shifts slowly across the Great Lakes. Increasing warmth and moisture is on tap late in the weekend into most of next week with warm and humid days returning, and increasing chances for showers and storms as a moist southwesterly flow sets up and persists on the backside of the departing high pressure system. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Skies already mostly clear, with temperatures falling a little faster than expected. Still thinking that mid/upper 50s for overnight low looks good, just tweaked hourly temperatures. Still expecting some valley fog, with clear skies and light winds increasing the potential. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... Strong 1020mb high pressure will elongate and sprawl from the Mid Mississippi River Valley into and across the Great Lakes on Friday. Light north/east winds will continue, and widespread subsidence will guarantee ample sunshine outside of more fair weather cumulus which will develop in few/scattered fashion. PWAT anomalies will remain 1.5 to 2.0 sigma below climatology as surface dewpoints remain the 50s. Winds overall will decrease considerably in the lower troposphere as the high exerts its influence as the day wears on. Under clear skies Friday night, overnight lows will drop back down into the 50s to around 60. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... This period will be characterized by a warming, moistening, and destabilizing airmass over the Ohio Valley that will end up becoming quite unsettled from late in the weekend through all of next week. From a hazard assessment standpoint - despite temperatures largely remaining below normal - instability will be on the increase owing to increased moisture and relatively cool temps aloft. Experimental machine learning probabilities of severe storms based on the 18.00 GEFS pattern from both CSU and NSSL show slowly increasing /albeit still quite low and perhaps climatologically normal/ probabilities of severe storm and heavy rain hazards in this pattern. The signal is broad/muted, which is interpreted right now as a pretty typical mid-summer pattern where most storms contain low end threats of pulse downburst wind and/or localized torrential rain. So no significant concerns of anything looking atypical from what we normally see during a normal late July week, but certainly could be several days where low end threats of strong storms /wind/ or heavy rain could develop. In the details...beginning on Saturday morning...an amplified height pattern aloft is present over the CONUS with anomalous western US ridging, and deep troughs anchored in the northeast Pacific and across eastern North America...an omega-like blocking pattern. Shortwave energy will be dropping down the backside of this ridge into the Mid Mississippi River Valley on Saturday and into Sunday, and this will further re-develop / re-center the upper trough axis in the eastern half of the CONUS back over Iowa/Missouri/Arkansas. By Sunday evening, this trough to our southwest will continue to deepen owing to amplification/retrogression of the Bermuda/subtropical anticyclone off the southeast coast. The net effect of this process - in combination with the strong surface high from Friday/Saturday slipping southeast of the area - will be a uniform increase in low-mid level southwesterly flow into the Ohio Valley which begins Saturday night and just continues to increase slowly Sunday into Monday. This will continue in steady-state / stagnant continuation through Tuesday/Wednesday/Thursday as the once-Omega-block construction of the upper air pattern becomes somewhat Rex-blockish with very strong western Canada height anomalies trying to overtop retrograding negative anomalies now moving westward into the Southern Plains as the subtropical ridge to our southeast tries to build north/west. Sensibly speaking - all of this means increasing dewpoints/deep moisture on southwesterly flow which manifests with slowly increasing rain/storm chances from south to north with time. Initially focused over northern Kentucky (weekend), the rain chances become more widespread Monday as southwesterly flow and PWAT anomalies increase. Forcing Monday/Tuesday will be weak, but deterministic soundings from most ensemble members suggest an uncapped airmass as dewpoints press toward 70F. Just enough deep layer southwesterly flow /30kts at H5 within the PWAT ribbon/ suggests this environment may able to wring out a few organized storms each afternoon with tall skinny CAPE profiles seen amidst PWATs pushing past 1.75". A more appreciable shortwave trough is evident in the ensemble members sometime (poor timing agreement) Wednesday or Thursday, which may help focus higher rain chances, and a little higher hazard chance via traditional late July thunderstorm clusters. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... With VFR clear skies overnight, winds will generally be in the 05-10kt range. However, in the valley area near KLUK, lighter winds will bring on MVFR and occasional IFR conditions from about 8 to 13z. Light winds become northeast for Friday, with slightly fewer VFR cumulus expected than Thursday. OUTLOOK...No significant weather is expected at this time. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Binau/JDR NEAR TERM...JDR SHORT TERM...Binau LONG TERM...Binau AVIATION...JDR