Area Forecast Discussion
Issued by NWS Wilmington, OH
Issued by NWS Wilmington, OH
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091 FXUS61 KILN 041736 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 136 PM EDT Thu Jul 4 2024 .SYNOPSIS... Multiple rounds of showers and thunderstorms remain in the forecast through Friday. The area looks to dry out over the weekend as high pressure builds across the Ohio Valley. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Update (Severe Thunderstorm Watch)... A Severe Thunderstorm Watch was recently issued for portions of northern Kentucky. Although thunderstorms extend northward into southwest and west-central Ohio, the best instability remains consolidated along the southern border of the ILN CWA. The Kentucky Mesonet shows a 10 to 15 degree temperature difference is present across only 1 or 2 counties from north to south. With increasing southwesterly flow, the better heating/moisture will likely nudge northward into the watch area ahead of the thunderstorm line. Damaging winds remain the greatest threat with these storms with an isolated spin-up tornado possible. Otherwise, behind the line, the atmosphere is beginning to recover as mostly clear skies are allowing for efficient heating. The amount of recovery will be critical for the potential second round severe threat later on this evening. This would be handled through a completely different watch, if necessary at all. Previous discussion... Regional radar mosaic is quite active this morning as thunderstorms continue to develop and persist across much of southern/south-central Indiana. A pseudo-warm front wing is also developing thunderstorms into portions of northern Kentucky and soon, southeast Indiana. PoPs have been adjusted to the latest radar trends and mesoscale factors through the early afternoon. The latest 12Z HRRR is likely too quick with the erosion of the thunderstorm activity, so this increases uncertainty for the overall CAM projections for the next, more concerning round of development later this afternoon and early evening. With the 13Z update, SPC introduced a Level 2 of 5 risk (Slight Risk including 5% tornado) into southeast Indiana, northern Kentucky, and portions of southwest Ohio. This scenario becomes more plausible the faster the ongoing thunderstorm activity clears, allowing for mass support northward ahead of an approaching MCV. If enough clearing can occur, the potential exists for discrete storms to persist within an environment of strengthening deep- layer flow and backed low- level flow. The magnitude of the backed flow may be largely dependent on the remnant cold-pool air mass left behind modifies with afternoon heating and moisture transport. To the north of this morning`s thunderstorm activity, a broad shield of light-moderate rain with embedded thunder is expected through the rest of the morning. This should gradually decrease in coverage as the thunderstorm activity to the south shifts east. Additional, scattered thunderstorm activity will be possible late this afternoon into the evening hours, but the overall severe threat is limited. While much of the previous discussion was focused on the severe weather threat, the east to west corridor of thunderstorms this morning may bring cause for locally heavy rainfall depending on how quickly it propagates eastward. Southeast Indiana and portions of northern Kentucky currently stand the best chance of observing the locally heavy rainfall. This could lead to high water in a few spots. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Mid level shortwave and thunderstorm complex to be moving thru the area thru the evening. Some additional fog development will be possible in the moist environment overnight. Mild lows are expected generally in the lower 70s. More significant mid level low to track thru the Great Lakes Friday. Associated surface cold front to sweep thru the area during the afternoon. Some uncertainty remains regarding the degree of instability Friday with residual cloud cover from Thursday night`s pcpn. Given that effective shear increases to around 40 kts, even low end moderate instability will support a threat for severe storms mainly in the east. The main threat will be damaging winds. Expect highs to range from the mid to upper 80s. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... A cold front will be progressing east of the Ohio Valley on Friday night. Cooler, drier air moves in behind the front for the weekend as high pressure builds in from the west through Sunday. This will signal an end to the hot, humid, and unsettled weather setup from this past week. Forecast highs on Saturday remain in the lower 80s and lows Saturday night will be in the lower 60s. Highs on Sunday reach back into the middle 80s. Surface high pressure shifts east of the area by Monday. Southwesterly flow redevelops west of the high which will allow heat, humidity, and afternoon rain chances to return midweek. A weak surface boundary and upper level shortwave may increase rain chances on Tuesday before diurnal shower/storm chances return to lower probabilities by Wednesday and Thursday. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... Scattered, disorganized thunderstorms continue to form and dissipate across the area this afternoon. This has made timing challenging. To the south, a more organized line of thunderstorms will pass to the south of the area. Behind the line, temperatures are beginning to warm following this morning`s thunderstorms/stratiform rain. Therefore, left VCTS mention in through the rest of the afternoon and into the evening (00Z-02Z) as additional thunderstorms are forecast. Confidence on timing and coverage are low so no TEMPO groups were added. Following the thunderstorm/shower activity this evening, another period of MVFR/IFR CIGs is expected through the overnight into Friday morning. Some VIS restrictions are also forecast. Improvement is expected through the mid-morning with VFR expected by the afternoon. The front will still not have passed through until after 00Z Saturday so some thunderstorms will once again be possible. Surface flow will be less than 10 knots except for influences from thunderstorms. Westerly winds increase to above 10 knots Saturday afternoon. OUTLOOK...Thunderstorms possible on Friday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...AR NEAR TERM...McGinnis SHORT TERM...AR LONG TERM...Campbell AVIATION...McGinnis