textproduct: Wilmington

WHAT HAS CHANGED

Confidence increasing in chances for excessive rainfall late this week.

KEY MESSAGES

1) Showers and thunderstorms expected at times from Thursday through Saturday, some potential for heavy rainfall and flooding, and possibly some severe weather.

2) Temperatures increasing going into early next week.

DISCUSSION

KEY MESSAGE 1) Showers and thunderstorms expected at times from Thursday through Saturday, some potential for heavy rainfall and flooding, and possibly some severe weather.

Surface high pressure will be in control of the weather over the ILN CWA for Wednesday. This is a relatively cool and dry air mass, supporting max temps around 80 (slightly below normal) and dewpoints in the mid 50s. By late tonight, the high will be moving off to the east, and the overall weather pattern will be switching to one with more southerly flow -- and theta-e advection into the Ohio Valley. Some showers and thunderstorms developing over the Great Lakes may drift into the northern sections of the ILN forecast area early Thursday before dissipating.

The westerly flow pattern will become active from Thursday through Saturday, with occasional showers and thunderstorms expected. Although temperatures will remain below normal during this period, moisture will be on the increase, with dewpoints getting into the 60s to near 70. It is expected that there will be a surface frontal zone somewhere over the ILN CWA during this time frame, providing some convergence and a gradient in temperatures, which may act as a focus for thunderstorm development. Broader forcing will occur as shortwaves in the westerly flow move across the region. Some of the bigger sources of uncertainty in the forecast are instability (lapse rates are not impressive, and SBCAPE/MLCAPE north of the boundary will be low) and timing of the shortwaves, especially Friday and Saturday.

For Thursday, confidence is fairly strong on a wave sparking thunderstorm development over the ILN CWA during the afternoon, perhaps becoming more focused as the activity moves east into PA/WV. With some decent deep-layer shear, could not rule out a stronger storm, but instability appears marginal (around 1000 J/kg MLCAPE).

A greater potential for storms will occur at some point Friday and possibly into Saturday. Most models depict some degree of widespread precipitation moving into the area Friday, though with varying timing. Some models also depict a weak surface low associated with the shortwave, which could increase both forcing and low-level shear if one were to develop. Neither instability or shear appear to be on the higher end of the scale for Friday, but a few strong to severe storms appear possible. If an organized MCS were to develop and ride along the temperature / CAPE gradient, a slightly greater damaging wind potential could occur. For now, confidence in any exact severe scenario is low. Confidence is a bit higher in the heavy rainfall potential, especially if multiple rounds of storms progress in the westerly flow over the west-to-east surface boundary. Precipitable water values may be approaching 2" by Friday, so not only will storms have the potential to train, but rain rates may also be quite high.

Convection should generally trend southward from Friday to Saturday, and confidence is very low in any specifics, but some additional strong storms and heavy rain could occur Saturday as well. This would be more likely for the southern sections of the ILN CWA.

KEY MESSAGE 2) Temperatures increasing going into early next week.

Precipitation chances will be diminishing by the second half of the weekend, with a big pattern change forecast to take place. Ridging is forecast to build through the eastern CONUS, putting the Ohio Valley in an air mass that will be increasingly hot and humid. Thus, the main concern for next week will be the potential for heat to reach hazardous levels. There is high confidence that surface temperatures will at least reach the upper 80s across the area by Monday and Tuesday, and medium confidence that temperatures will get into the 90s. With dewpoints in the lower 70s, heat index values near or above 100 will be possible.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

VFR conditions are generally expected through the TAF period. Scattered cumulus clouds, and a few high clouds, are expected today. Some mid level clouds will move into the area tonight. Winds will be light this morning, and then out of the southwest at under 10 knots this afternoon.

OUTLOOK...Thunderstorms are possible at times from Thursday through Saturday. MVFR conditions are possible Friday.

ILN WATCHES/WARNINGS/ADVISORIES

OH...None. KY...None. IN...None.