textproduct: State College

WHAT HAS CHANGED

Increasing confidence in a significant, potentially dangerous heat wave to start the month of July.

KEY MESSAGES

1) Drying trend for this afternoon and tonight with just spotty light showers. Another few to several hour round of afternoon showers is likely Sunday.

2) Significant, potentially dangerous heat wave to start the month of July

DISCUSSION

KEY MESSAGE 1: Drying trend for this afternoon and tonight with just spotty light showers. Another few to several hour round of afternoon showers is likely Sunday.

Thick, layered clouds were holding tough across all of the CWA outside of the Northern Tier of Penn where a mix of sun and clouds and slightly lower sfc dewpoints in the upper 50s were found.

The clouds and area of steady light to moderate rain exiting east across the Middle Susq Valley and Poconos along with showers over the Lower Susq Valley will be followed by just isolated to scattered -SHRA this afternoon as the earlier area of moderately strong, southerly isentropic lift is replaced by much weaker lift within the 925-850 mb layer.

HREF cloud panels indicate that we should see brightening skies this afternoon across the aforementioned overcast area of Central and Western PA with temps climbing another 7-8 deg F from their 15Z values.

Areas of fog to precede another diurnal uptick in rain showers and a few t-storms through Sunday afternoon, mainly to the south of I-80. Max temps on Sunday will be ~5 degrees warmer vs. Saturday with fcst highs in the mid 70s to low 80s. Total rainfall over the weekend ranges from <0.10" in the northern tier to 0.25-0.50" across south central PA.

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KEY MESSAGE 2: Significant, potentially dangerous heat wave to start the month of July

Confidence and predictability remains high for a large and anomalous upper level ridge to deliver a significant, potentially dangerous heat wave to start the month of July. Widespread temperatures in the 90s to near 100F, combined with high humidity, will result in fcst max heat indices approaching or exceeding 105F. This equates to widespread Major to Extreme HeatRisk and high probability of heat WWA headlines. Thursday 7/2 looks to be the hottest day at this time. The heat wave could last into the July 4th/Independence Day weekend, although ridge riding shortwaves may act to suppress/weaken the heat dome to some extent. Overnight lows will also be quite warm, bringing little to no relief from the heat in the nighttime hours.

Latest QPF trends favor little to no rain Monday-Friday next week given close proximity to the upper ridge. However, can't rule out isolated airmass/terrain-driven diurnal convection or possible MCS activity (thunderstorm complexes) on the northern periphery of the ridge within a classic ring of fire synoptic pattern. This setup appears more likely to unfold during the second half of next week.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Scattered showers/mist and low clouds due to broad low pressure across the Ohio Valley and Mid-Atlantic will tend to maintain current flight restrictions this afternoon, though breaks in clouds may permit slight improvements before sunset. Scattered showers are expected for the remainder of today given ample moisture (PWATs AoA 1.5"), albeit with lower coverage as best mid-level moisture presses eastward, with heavier showers possible around (and mainly south of) the Mason-Dixon line where SPC Mesoanalysis shows MUCAPE >500 J/kg (lightning possible, though tall/narrow CAPE profile primarily favors rainfall efficiency over lightning).

High confidence in regionwide IFR-LIFR overnight given moist air mass in place + recent rainfall and light/variable winds, especially along the Appalachian Mountains. Lingering showers and drizzle are possible overnight, though shower coverage is favored to increase Sunday afternoon with development of modest instability (MLCAPE up to around 500 J/kg). Otherwise, weather conditions will improve through Sunday morning through diurnal boundary layer mixing, though stubborn low-level moisture and stratus may tend to make improvements more gradual through the morning.

Outlook...

Mon-Thu...AM fog; otherwise VFR. Trending hotter with isold PM t-storms psbl. High density altitude concerns possible.

CTP WATCHES/WARNINGS/ADVISORIES

None.