textproduct: Wilmington

WHAT HAS CHANGED

A Flood Watch for flash flooding has been issued for parts of southeast Indiana and northern KY tonight through Wednesday morning.

KEY MESSAGES

1) Showers and thunderstorms are expected this evening into the overnight, with the potential for heavy rain and flash flooding, mainly in far southwest parts of the local area in northern Kentucky and far southeast Indiana.

2) Hot and humid conditions are expected Wednesday and Thursday.

3) A cold front will move through the area on Friday bringing the chance for severe storms on Friday. Cooler, drier air works in for the weekend.

DISCUSSION

KEY MESSAGE 1) While skies have trended mostly clear locally, focus has shifted to the development of storms currently upstream in IL, which will progress to the east/southeast this evening through tonight. The current local environment continues to destabilize, with clearing working its way E behind the departing MCV. The main concern with this activity as it progresses into an unstable environment (MLCAPE >2000 J/kg) through midnight will be gusty to isolated damaging winds and isolated large hail, mainly near/west of the I-75 corridor through midnight.

The clusters of storms will likely grow upscale into more of a pivoting line late this evening into early tonight as it nears the I-71 corridor. With time, this activity is expected to track into the pooling of better instby to our S across parts of KY, with a decrease of diurnally-driven instby with eastward extent. With this, the storms should gradually pivot more to the S, opposed to the E, with the potential for slower moving/training storms developing into parts of northern KY and far southeast IN after midnight. This will especially be the case between about 1 AM and 7 AM, with a NW-to-SE axis of torrential rainfall possible in these areas during this time. There is still /quite/ a bit of uncertainty in exactly where this axis will set up, with the potential for it to become established further to the SW closer to Louisville (out of the ILN CWA). Nonetheless, there are at least some indications for locally heavy rainfall in far SW parts of our area, especially with the prospect of training storms in a NW-to-SE fashion in the middle of the night.

Anomalously-high PWs on the order of nearly 200% of seasonal norms, along with some LL moisture/mass convergence along the flanking line of organized storms, presents a concern for very heavy/localized rainfall in far SW parts of northern KY and far southern/SE IN tonight into early Wednesday morning. Rain rates in excess of 2" per hour are possible in the heaviest/most persistent activity, mainly in Carroll/Owen Counties in KY and points further to the SW.

KEY MESSAGE 2) Persistent southerly low level flow stretching to the Gulf remains in place on Wednesday and Thursday. Low level moisture is continuously advected to the Ohio Valley allowing dew points to reach into the lower and middle 70s. Afternoon temperatures are also forecast to top out in the upper 80s both afternoons which supports the heat index reaching into the upper 90s to near 100 across the area. Forecast lows offer little relief only dropping into lower and middle 70s Wednesday and Thursday nights.

There is a chance that some patchy, brief relief from the heat could occur if diurnal thunderstorms develop each afternoon. However, with lack of forcing, storm coverage may remain low.

KEY MESSAGE 3) A surface low forms in Canada on Friday in response to a trough ejecting east out of the northern Plains. A trailing cold front attached to the low progresses through the Ohio Valley on Friday. The timing of frontal passage will be important for our area since showers and storms are likely to form ahead of the front Friday afternoon. Some of the showers and storms could be severe since instability and shear are forecast to be sufficient for storm organization. Currently, it appears that the front may be at least partially through the area by Friday afternoon which supports better severe chances along and southeast of I-71.

Behind the front, shower and storms chances end. Drier and slightly cooler air arrives behind the front for the weekend and into early next week.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

The expansive cloud cover associated with the departing MCV continues to clear from W to E, leaving in its wake SCT VFR Cu amidst an unstable environment.

The main focus for the TAF period is going to be the progression of a linear cluster of storms, which will progress through the terminals between about 03z (near KDAY) to about 07z (KCVG/KLUK/KCMH/KLCK). The highest confidence in at least TEMPO TSRA is going to be across western sites of KDAY/KCVG/KLUK/KILN, but suppose it will be possible at KCMH/KLCK as well. There will also likely be a sudden changes to wind direction/speed with the arrival of the storms, especially at KDAY/KCVG/KLUK where storms will be more organized upon arrival. But this will be handled with amendments as needed. These storms will likely bring sudden reductions to VSBY as well and will introduce expanding MVFR CIGs in their wake through most of the morning.

Widespread 1-2kft clouds are expected from about 09z through the remainder of the morning before slowly scattering into early afternoon, with conditions returning to VFR by 18z.

SSW winds around 8-10kts will gradually go more out of the WSW toward daybreak and beyond, increasing to around 10-12kts for the daytime.

OUTLOOK... Thunderstorms are possible for eastern sites Friday afternoon.

ILN WATCHES/WARNINGS/ADVISORIES

OH...None. KY...Flood Watch from 10 PM EDT this evening through Wednesday morning for KYZ089-090-094-095. IN...Flood Watch from 10 PM EDT this evening through Wednesday morning for INZ080.