Area Forecast Discussion

WHAT HAS CHANGED

No significant changes

KEY MESSAGES

1) Showers and thunderstorms expected into Saturday morning. Some storms may be strong to severe this afternoon and evening. The potential for heavy rainfall will increase Friday into Friday night.

2) Hot and humid next week.

DISCUSSION

KEY MESSAGE 1)

A weak front stretching across the lower Great Lakes will sag south into the region tonight and then stall. A jet streak associated with a disturbance passing north of the area has resulted in a strongly sheared environment with 0-6 km shear of 40 to 60 kt. Instability is forecast to settle in the 1000 to 1500 J/kg range but mid level lapse rates are expected to remain 5.5 to 6 C/km, which may limit the intensity and coverage of storms this afternoon into the evening. Certainly, many of the convective allowing models have been modest in their depiction of storms this afternoon. Nonetheless, if robust updrafts can develop and sustain themselves, then there will be the potential for storms to become severe with damaging wind the primary threat. There could also be some hail. The best juxtaposition of instability and hail will be in central Ohio, so the threat of severe storms is relatively greater there. In addition, there may be a brief period when low level shear could become favorable for tornadoes in central Ohio.

Storms will diminish this evening, although the scope may not quite become echo free. Increasing lift from a short wave moving out of the mid Mississippi Valley will cause showers and some storms to start to blossom, primarily near the stalled boundary, on Friday morning. Precipitation will increase in coverage area wide in the afternoon as the short wave moves across the area. A modest west southwest low level jet associated with this will advect in a very moist airmass with precipitable water approaching 2 inches. In addition, warm cloud depth will increase to 4 km or more allowing for efficient warm rain processes. Thus heavy to torrential rainfall will be possible with stronger convective elements. The potential for strong to severe storms will be less than today but non-zero. That will be contingent on how much instability is able to be realized with a relative maximum near and south of the boundary. The heavy rain threat will continue, and may even increase, on Friday night. Mid level forcing will be subtler but the low level jet will strengthen as it slowly translates eastward. There is the potential for repeated rounds of heavy rain. This will all wind down late Friday night into Saturday morning.

KEY MESSAGE 2)

Strong mid level high will expand northward early next week and then predominate through mid week and likely beyond. This will bring hot and humid conditions with a very low chance of any convection. Probability of the heat index exceeding 100 is only about 25 percent on Monday along and west of I-75. But those probabilities increase to 40 to 60 percent area wide on Tuesday and then peak at 70 to 80 percent on Wednesday. But the probability of a 105 or higher heat index is less than 15 percent. So there is a pretty high likelihood of a heat advisory at some point next week but very low that it will reach excessive heat warning thresholds.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Scattered showers and thunderstorms will develop and move across the region during the early part of the period. Given uncertainties, have continued with PROB30 with the initial issuance and will amend if it becomes clearer that any of the terminals will be impacted.

After 00Z, winds will become light as a boundary stalls across the region. This could become the focus for low level moisture, although it is still very uncertain whether that will lead to visibility restrictions or low ceilings or both. Have continued with some reduced visibility after 06Z, but only to MVFR given the lower confidence. There is potential for at least some sites to drop to IFR visibility or ceiling. Most likely there will be improvement late in the period, although showers and embedded storms will be moving into the region before 18Z. Highest probability of precipitation occurring before the end of the TAF period is at KDAY.

OUTLOOK...Thunderstorms are possible through Saturday. MVFR ceilings and visibility are possible Friday afternoon into Saturday morning.

ILN WATCHES / WARNINGS / ADVISORIES

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