textproduct: State College

WHAT HAS CHANGED

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

KEY MESSAGES

1) Periods of rain followed by scattered showers and a few thunderstorms for the last weekend of June

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

DISCUSSION

KEY MESSAGE 1: Periods of rain followed by scattered showers and a few thunderstorms for the last weekend of June

Cloudy/humid/rainy start to the last weekend of June across CPA. Highs today holding in the 70s for most will be 5-10 below the historical average. We tried to emphasize periods of [steadier, mainly light] rain this morning followed by scattered/sparse, shorter duration rain showers for the afternoon and evening. Expect decreasing rain shower activity tonight with 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 /10Z SATURDAY THROUGH WEDNESDAY/

Ceilings will lower west to east today as a low pressure system approaches, with scattered -RA/-SHRA moving across the area. The best forcing is moving through this morning, so we expect the coverage and intensity of rainfall to be highest through midday. Showers will become more scattered this afternoon and the probability of lightning is low.

Ceilings will continue to deteriorate through the day. MVFR or IFR ceilings are favored everywhere except IPT. IFR is a good bet at JST and AOO for much of today, with the next best chance at UNV. Later tonight, calm winds, antecedent moisture from rainfall, and humid conditions will likely lead to widespread restrictions in the form of low clouds/fog.

Outlook...

Sun...Fog and low cigs possible in the morning, then scattered afternoon showers and storms.

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

CTP WATCHES/WARNINGS/ADVISORIES

None.