Louis A Grant Inc, PA Hourly Weather Updates

Key Messages

1) The next thunderstorm cluster is favored to cross late Saturday night into Sunday morning, posing a flash flood and limited wind threat.

2) Varying storm and hazardous weather risks for Sunday afternoon/evening.

3) After lingering rain chances dissipate Monday, there is fairly high confidence in dry weather until the next system arrives Wednesday/Thursday.

Discussion

... KEY MESSAGE 1... A thunderstorm cluster is expected to develop near northern IL tonight into Saturday morning that will eventually travel ESE through the lower Great Lakes in conjunction with a mid-level shortwave. 12z guidance appears to be coalescing around a late Saturday night into Sunday morning timeframe for this system in the Upper Ohio River Valley, though variations in path ranging from southern OH/central WV to northeast OH/northwest PA remain.

Any severe risks associated with damaging wind reside in an earlier arrival (Sat aftn/eve) that sees the MCS driving SE through the far eastern OH zones (Muskingum/Coshocton Counties) along the CAPE gradient. Given where latest trends are heading, this risk appears increasingly unlikely, especially with a potentially stable environment in place if it arrives later in the night. More likely, the hazardous weather risk will be flash flooding as strong warm/moist advection (which is partially responsible for its eastward drive) pushes PWAT values near or even exceeding the 99th percentile. Combined with warm- rain processes and strong ascent, rainfall rates of 1-2" may be common (and potentially exceeded) that could result in flash flooding, especially on saturated grounds. The potential lack of notable elevated buoyancy and faster storm motion (more on the 25-35kts realm) could limit rainfall duration to just stay under FFG amounts. As mentioned, favored locations and timing remain variable enough to preclude Flood Watch at this time, but could be needed if confidence increases.

KEY MESSAGE 2... Stable air develops in the wake of the morning MCS Sunday that could generally last most of the day and limit any activity in the afternoon/evening to spotty, sub-severe coverage.

However, there remains a low probability that enough clearing occurs in the wake for afternoon destabilization resulting in SBCAPE values rising to 1000-1800 J/kg in a 25-30kt sheared environment. If there is enough lift in the lingering NW flow, a few instances of severe storms with damaging wind can`t be ruled out along with non-zero flood risks where rain previously fell.

KEY MESSAGE 3... Scattered showers and low probability thunderstorms may linger within the increasingly stabilizing environment Sunday night into Monday. However, high pressure building in from the west under drier NW flow favors a drying trend in storm activity by Monday evening that lasts generally til Wednesday.

Though timing can change, the next system featuring shower/thunderstorm chances favors the mid to latter week period next week.

Aviation

/00Z SATURDAY THROUGH WEDNESDAY/... Areawide VFR continues into tonight, though early morning fog development is favored for areas that see the heaviest rain today (HLG, ZZV, MGW) and the usual suspects (DUJ/FKL). Fog is generally low confidence elsewhere. Fog could be dense at times, most likely during the pre-dawn hours. Improvement to VFR is expected later Saturday morning.

Generally quiet VFR conditions with light and variable wind are expected Saturday afternoon as clouds thicken and slowly lower. An MCS is expected to track across the area late Saturday evening into the overnight, though exact timing and location remains lower-confidence. Restrictions with heavy rain and possibly strong winds are expected.

Outlook... Restrictions with rain will likely linger through Sunday with general improvement on Monday.

Watches / Warnings / Advisories

/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None.