textproduct: State College

WHAT HAS CHANGED

* Enhanced Risk Area for Severe Storms Tuesday afternoon and evening was expanded to cover almost all of PA. * Thin layer of generally elevated smoke will be mainly over western PA through late today

KEY MESSAGES

1) Severe thunderstorms are a near-certainty for Tuesday afternoon and evening. Some areas of flash flooding are also expected.

2) Wildfire smoke should stay mainly over western PA, with levels barely noticeable in the east.

DISCUSSION

KEY MESSAGE 1: Severe thunderstorms are a near-certainty for Tuesday afternoon and evening. Some areas of flash flooding are also expected.

For tonight, PWAT values will increase from the south by 0.5 to 0.75 of an inch leading to notably more humid late night/Tuesday.

Severe weather is once again on the slate for Tuesday afternoon and evening as an amplifying upper level trough heads SE across the Great Lakes region and a strong, sub-1000 mb sfc low (just south of James Bay Canada Tuesday afternoon) pushes a potent cold front SE across PA late Tuesday/early Wed.

Tuesday (Day 2) has been consistently highlighted by SPC for many days as a potentially active and dangerous weather day. The DY2 ENH Risk area has been expanded to cover the entire state of PA except for a sliver near the NY border.

The threat for pockets pf damaging wind is near certain, and could occur anywhere over the CWA Tuesday afternoon and evening.

Additionally, the threat for hail is higher than it was this past Saturday, and the potential for tornadoes is similar, with a mix of supercells and line segments with mini bow echoes expected to be the primary storm modes given the presence of likely low level boundary from some morning convection across the east, followed by a several hour period of subsidence/partial clearing beneath and juicing up of the instability and deep layer shear as the nose of a 100+ kt 300 mb jet approaches from the Ohio Valley late in the afternoon/evening.

0-1KM EHIs of 2-3.5 M2/S2 with leftover llvl outflow boundaries and one or more prefrontal/lee-side troughs point toward a distinct threat for some long-lasting supercells and potentially a few to several EF1-2 tornadoes across our CWA.

It looks like a pre-frontal trough will charge in from the NW and cross the CWA in the afternoon hours. The real cold front will arrive in NW PA later in the evening/early Tuesday night. It may arrive too late (some stabilization could already happen) and have little left to work with by the time it gets into the CWA to make much of a severe threat.

There is also a threat for localized flash flooding, but only in places that receive multiple rounds of heavy rain. There should be a fairly fast movement to the storm cells (ENE at about 40 kts), limiting the threat somewhat. However, moisture is expected to be very high, PWATs 1.5-2".

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KEY MESSAGE 2: Thicker wildfire smoke should stay mainly over western PA, with levels barely noticeable in the east.

An air quality alert/action day remains in effect for most of southwestern PA where levels are expected to be unhealthy for sensitive groups. HRRR smoke plume progs keep the thicker smoke over western PA with much less over the east. The light wind this morning will turn from easterly to southerly through the day which will help to keep the near-sfc smoke from spreading to the east.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Mostly clear skies and dry conditions means VFR is expected to prevail for the next 12-15 hours across much of Central and Western PA airfields, while some lower MVFR cigs between 2-3 kft AGL in showers and TSRA are expected to move south to north very late tonight into Tuesday morning, especially across the Susq Valley and points east as the axis of a strengthening southerly LLJ shifts east into that area.

Outlook...

Tue-Wed...Periods of brief restrictions possible in showers/t-storms with cold FROPA expected Tuesday/Tuesday night with lingering showers possible Wednesday morning.

Wed afternoon-Sat...VFR Conditions.

CTP WATCHES/WARNINGS/ADVISORIES

Air Quality Alert until midnight EDT tonight for PAZ024-033.