Area Forecast Discussion

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

1) Warm and humid conditions move in on Tuesday, with an initial chance of storms on Tuesday night.

2) Heat and humidity continue through the week, with occasional chances for storms through the forecast period.

DISCUSSION

KEY MESSAGE 1)

Surface high pressure is drifting off the east coast. Meanwhile, a closed mid-level high is setting up over the southeastern states. This will result in a pattern change and deep-layer theta-e advection coming into the Ohio Valley starting today. This change in air mass will result in highs in the mid 80s to lower 90s, and dewpoints reaching the upper 60s to around 70. Not out of the question that head indices could briefly approach 100 in the far southwestern ILN CWA.

While an initial shortwave today will remain well north of the region, a frontal zone will set up over the Great Lakes, eventually leading to increasing precipitation chances across the ILN forecast area. For tonight into Wednesday morning, the convective forecast for the ILN CWA is not particularly high confidence. Storms are expected to initiate over Illinois and northern Indiana during the evening, moving east toward the northwestern corner of the ILN CWA in the late evening through the overnight hours. The SPC Day 1 MRGL risk area indicates the area where this may occur. It is not entirely sure if the storms will hold together -- some CAMs are quite spotty with coverage. If they do, while parameters are not overly impressive, there appears to be just enough CAPE and shear to support a marginal severe threat.

KEY MESSAGE 2)

Most of the rest of the week will be characterized by high theta-e values (with heat and humidity) on the northern periphery of the ridge, with convective chances initiating from the frontal zone on the northern edge of the warm sector. Timing on convective chances remains somewhat uncertain, as antecedent convection may play a role, as will fast-moving shortwaves moving through the westerly upper flow.

Although convection could disrupt the temperature forecast, as of now it appears both Wednesday and Thursday will feature highs in the mid 80s to lower 90s. With dewpoints getting into the lower 70s, some areas in the southern half of the forecast area may approach heat advisory criteria (100 degree heat indices).

As of now, it appears heavy rain will be the main convective threat. Shear will be marginal, though a strong storm or two could not be totally discounted given the expected instability (SBCAPE of 1000-2000 J/kg). Rather, it will be the potential for repeated rounds of storms that create greater concern for flooding -- especially in an environment with precipitable water values of around 2 inches.

Might have some additional storm chances on Friday and into the weekend, but confidence in the forecast decreases considerably once the ridge begins to break down. Slightly cooler temperatures look likely for Friday, Saturday, and Sunday, compared to the middle of the week.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

VFR conditions are expected through the TAF period, with the exception of some fog at KLUK.

Winds today will be out of the SSW, generally 10 knots or less. High and mid clouds will thicken up during the overnight into early Wednesday morning. As of now, it looks like precipitation chances will remain outside of the TAF sites through the valid forecast period.

OUTLOOK...Thunderstorms are possible in some locations at times from Wednesday through Friday.

ILN WATCHES / WARNINGS / ADVISORIES

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