textproduct: State College

WHAT HAS CHANGED

* Severe thunderstorm risk upgrade to level 3/5 (Enhanced) for Saturday afternoon through Saturday evening

KEY MESSAGES

1) Wildfire smoke will result in unhealthy air quality and reduced visibility today and into early Saturday

2) Severe thunderstorms with damaging winds and heavy rainfall are possible Saturday afternoon through Saturday evening

DISCUSSION

KEY MESSAGE 1: Wildfire smoke will result in unhealthy air quality and reduced visibility today and into early Saturday

Visible satellite shows main smoke layer over the southwest quadrant of the CWA this afternoon. Hires model data shows this layer slowly pivoting and retreating to the north/east late tonight through early Saturday as the mean flow shifts to the southwest. The worst/unhealthiest air quality will impact the area from this afternoon through early Saturday morning before conditions improve by Saturday afternoon.

Statewide code PURPLE Air Quality Alert for July 17th

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KEY MESSAGE 2: Severe thunderstorms with damaging winds and heavy rainfall are possible Saturday afternoon through Saturday evening

SPC upgraded most of central PA to level 3/5 severe t-storm risk driven by 45% damaging wind probability.

As the smoke clears, scattered to numerous thunderstorms are forecast Saturday. The latest model projections support an increasingly favorable severe storm environment including strengthening deep layer wind fields and rich low level moisture. A remnant surface front initially draped from southern NJ into western PA will lift northeastward as an effective warm front, in advance of a cold front trailing low pressure tracking across southern Quebec toward northern Maine.

The departing/exiting smoke layer would be helpful in allowing for strong diurnal heating and moderate instability. However, it's unclear how much early day, warm advection/elevated convection and associated cloud cover will complicate future convective rounds during the afternoon and evening hours. Should adequate clearing/heating occur, steep low level lapse rates on sounding profiles will support a rather favorable wind damage threat. In addition to the wind-damage threat, some hail and tornado potential may also evolve with any supercell development, particularly in the vicinity of the warm front given the presence of favorable effective SRH. The southward advancing cold front should be a catalyst for second or third round late day/evening storms with duel wind/tornado threat especially near remnant outflow boundaries.

Southwesterly low-level flow ahead of the front will transport a high PW (>2") airmass into CPA. Strong synoptic forcing, driven by an amplifying trough over the Northeast and favorable upper jet dynamics, and deep warm-cloud depths will support the potential for very heavy rain rates to produce isolated flash flooding concerns. WPC has kept all of central PA in a level 1/4 MRGL excessive rain outlook for Sat PM. Some considerations were discussed for potential flood watch with PHI/LWX, but decided to hold off for now given fairly progressive storm motions and somewhat localized spatial FF risk. A drying trend is expected Sunday with noticeably lower humidity allowing for a pleasant day and relatively cool night. However, latest RRFS shows some near sfc smoke returning to CPA from the Great Lakes. This could result in reduced air quality and hazy sky conditions.

Additional bouts of rain/t-storms are possible into the workweek. The next severe wx focus will be on Tuesday 7/21 with SPC already highlighting a 15% prob (equivalent to SLGT risk level 2/5). Forcing for this medium range severe outlook appears fairly robust and would take stock in this risk manifesting at shorter ranges.

Temperatures will trend near to slightly below historical averages through late week into month-end with some noticeably cooler nights possible.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Ongoing visibility restrictions due to wildfire smoke (primarily MVFR-IFR) will gradually extend back into our northern/eastern terminals (KBFD/KIPT) as light winds trend southwesterly ahead of a system moving across the Great Lakes. These winds will increase to around 10 kts through Saturday morning, allowing for the plume of smoke to fully push northeast of our area by the afternoon. A return to VFR is expected once the smoke is scoured out, with exceptions being temporary restrictions in any heavier showers/thunderstorms that develop tonight/tomorrow, along with possible MVFR ceilings in the morning and afternoon given increasing moisture & cumulus field development.

Later tonight and into Saturday morning, a cluster of showers will develop along the leading moisture edge (PWATs increasing to 1.5"-2.0") as moisture filters in out ahead of the Great Lakes system, with a few thunderstorms being possible as this activity progresses west to east across the Commonwealth. Additional thunderstorms will develop within the warm sector of this system across our region Saturday afternoon and evening, some of which may produce gusty winds, heavy rain, and flight restrictions.

Outlook...

Sun...Lingering -SHRA with restrictions possible early (primarily driven by low ceilings), with VFR favored otherwise.

Mon...Mainly VFR.

Tue-Wed...Restrictions possible in showers/t-storms with cold FROPA expected between Tuesday/Wednesday.

CTP WATCHES/WARNINGS/ADVISORIES

Air Quality Alert until midnight EDT tonight for PAZ004>006- 010>012-017>019-024>028-033>037-041-042-045-046-049>053- 056>059-063>066.