textproduct: Wilmington

WHAT HAS CHANGED

Flood watch issued for the southern 2/3 of CWA through Wed afternoon due to excessive rainfall.

KEY MESSAGES

1) Higher rainfall amounts within the flood watch will occur along a narrow w-e corridor, with up to 3 inches possible.

2) An unusually high moisture content airmass will be over the region through Thursday, with high temperatures 20-25 degrees above normal and lows 25-30 degrees above normal.

DISCUSSION

KEY MESSAGE 1)

Flooding potential will be encapsulated between I-70 and Ohio River with 1-2 inches expected in the next 24 hours. This band will see an additional inch within a number of points under its narrow axis. In addition, there is some uncertainty on the n-s positioning of the surface boundary, which has a high potential to result in less rainfall along the northern and southern peripheries of the watch. Models are trending south with the sfc front and subsequent axis of heaviest rain. Given an already saturated ground, most rainfall will result in runoff which is the basis that needed to be within this watch area. This is especially true if high end amounts of 2-3 inches occur through this time.

Pwat values are forecast to be 1.1 to 1.2 inches through this next 24 hour period (and beyond). This equals or exceeds the maximum pwat values from ILN sounding climatology for early March, and well above the 90th percentile which sits around .75". The zonal flow in lower levels will keep a continued feed of moisture that will get wrung out on the northern side of this front.

KEY MESSAGE 2)

With the exception of Thursday night where pwat values will drop to near or just above normal, with the remaining time through Friday above the 90th percentile.

Atypically warm and wet conditions continue through the weekend, leading to the development of thunderstorms and a continued threat for flooding.

Temperatures will be well above normal through the period, and overnight lows for the Wed through Fri period have a strong chance to exceed record high minimums.

Zonal w to wsw flow aloft will turn more swly on Thurs with s/w energy crossing at various intervals. On Thurs, an upper low will be digging to the west of the CWA will cross east later in the day Thurs. In the wake of this low occurs some downward motion on the back side, which is the cause of the lull in precip values during this time. After this, flow becomes zonal again with areas of s/w energy crossing ne through the latter part of the forecast.

These vort maxima look to spark some shower activity on Fri, but be quite spotty and generally light in nature. A cold front should pass w-e through the Ohio Valley on Sat, though temperatures behind it will still be above normal and then rise back to well above normal for next week.

With every round of rainfall, the flooding risk will continue to rise. The stronger and deeper convective rainfall on Wednesday and Thursday will increase the flash flooding threat during this time.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Area of rain is laying out along I-70 corridor with slightly lower rainfall rates in broken periods of rainfall closer to the Ohio River. Attm this looks to be the favored location that models are picking up on, and TAF sites are forecast to remain IFR from DAY-ILN- CMH and LCK for the next 24 hour period. Some breaks are expected at CVG/LUK which will bring periods of higher cigs and a lack of precip, but vsbys should remain at least MVFR even without active rainfall.

This w-e line is favored to continue to see rain wrung out along it, though some models have been trying to shift it southward. The models that are doing so are CAMs and my guess is that their southern push is due to a slightly higher area of unstable air along and south of the Ohio. However, this southern nudge of the w-e boundary does not appear to be a likely solution attm.

OUTLOOK...MVFR/IFR conditions are expected to be the prevailing wx through Friday.

ILN WATCHES/WARNINGS/ADVISORIES

OH...Flood Watch through Wednesday afternoon for OHZ060>064-070>074- 077>082-088. KY...Flood Watch through Wednesday afternoon for KYZ089>100. IN...Flood Watch through Wednesday afternoon for INZ050-058-059-066- 073>075-080.