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.

---------------------------------------------------------------

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 /00Z SUNDAY THROUGH THURSDAY/

Winds have started to decrease slightly across the forecast area this evening, which will promote fairly expansive low cloud and/or fog formation across central Pennsylvania. Based on the 12Z HREF 25th/50th percentile members outline all airfields outside of IPT with IFR-to-LIFR conditions. Main reason for leaning towards these members remains to be ample low-level moisture currently in place across the entire region and based on rainfall that has occurred across the area earlier. Recent GLAMP guidance hones onto this trend, thus moderate-to-high (60-80%) confidence in these conditions with timing being the main uncertainty at this time. GLAMP guidance remains fairly sparse in mentions at IPT; however, have included lower ceilings due to current dew point depressions ~6F and heaviest rainfall along the I-80 corridor but slightly lower (~40-60%) confidence.

Fog/low cloud begin to mix out fairly quickly after sunrise on Sunday, with the bulk of IFR/LIFR mentions out by 15Z Sunday with light winds below 10 knots. Main concern in the later half of the TAF package will be some potential for SHRA/TSRA across mainly the southern half of the forecast area after 18Z. The 00Z TAFs go against GLAMP guidance to include some mentions at all airfields outside of BFD/IPT with low-to-moderate (30-50%) confidence given the scattered nature expected of SHRA/TSRA. The most recent HREF 1-hr lightning guidance does indicate lower (less than 30%) probabilities for TSRA, so have kept mentions out at this time.

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.