textproduct: State College

WHAT HAS CHANGED

Day 2 SPC SLGT RISK Area now covers all but a small sliver of PA.

Day 4 - 15% Prob of SVR Weather within 25 miles of a location extends into Southern Adams, York and Lancaster counties from a fairly large area that covers much of the Delmarva, I-95 corridor in VA and MD and the Blue Ridge Mtn region.

KEY MESSAGES

1) Significant, long duration, and dangerous heat wave will persist into Independence Day.

2) A rather conditional severe weather threat will exist for Friday afternoon into Saturday night.

3) A lazy front over the area will result in a multi-day threat for thunderstorms. This could lead to flash flooding over the weekend and into next week.

DISCUSSION

KEY MESSAGE 1: Significant, long duration, and dangerous heat wave will persist into Independence Day.

We will see another few-several deg F of warming this afternoon, especially thanks to full sun and adiabatic warming (across the Central Ridge and Valley Region and Susq Valley) as a result of the downsloping westerly llvl flow that's currently gusting into the mid and upper teens (KTS).

Earlier cu field mixed-out/dissolved as anticipated with clear skies and some light haze over the bulk of the CWA for the rest of the day.

Extreme Heat Warnings (Central CWA and the Susq Valley) and Heat Advisories (Northern and Western Mtns of PA) Continue through Friday, then become focused in the Central Mtns and Susq Valley as heights aloft/thicknesses fall and max temps slip by a few degrees F.

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KEY MESSAGE 2: A rather conditional severe weather threat will exist for Friday afternoon into Saturday night.

We won't have any chance for deep convection until later tonight (at the earliest) when a bit of upper forcing rolls W-E on the zonal flow just to our N.

Since we'll still be under the influence of the strong upper ridge, we may not become unstable enough at night to pop the very warm mid level temps unless some significant outflow boundaries can be driven SE into the CWA form upstream TSRA/MCS.

Some showers/storms may slide in from the NW into the nrn mtns overnight, but the bulk of hi res guidance suggests a very low probability anywhere south of the Northern Tier.

A lot of CAPE is still expected on Friday due to the heat and humidity, and the cap may get weaker through the day, esp in the north as the ridge could get suppressed to the south slightly.

SPC expanded the SLGT RISK to cover all of PA Friday (Except for a small sliver over far SW PA). Pulse severe storms with localized damaging downburst winds are the primary threat considering very warm temps aloft and weak to marginal deep layer shear.

Most of the guidance keeps the vast majority of the area rain- free for all of the day on Fri and brings in some convection from the west Fri night. The Hi-res WRF members of the HREF do make more daytime convection than the others (specifically after 19z across the NW/Ncent Mtns - apparently initiated by the Lake Erie Breeze).

Saturday looks similarly marginal/tenuous. The best instability and shear will be in the nrn mtns in the aftn Sat and then it looks better for the srn half of the area Sat night.

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KEY MESSAGE 3: A lazy front over the area will result in a multi-day threat for thunderstorms. This could lead to flash flooding over the weekend and into next week.

A slow-moving cold front could languish over or very close to the state over the weekend and into early next week. The CWA will be in the warm sector Sat when scattered strong/severe storms will threaten. But, the front will then dip into PA from the north and should bring repeated bouts of thunderstorms and heavy rain. This is looking very much like a typical Maddox frontal heavy rainfall scenario with the front draped W-E and ample moisture flowing in from the S/SW. An upper low moving down from the Upper Great Lakes in the first to middle part of the week could finally shove the front far enough to the south to alleviate our worries for flooding.

AVIATION /21Z THURSDAY THROUGH TUESDAY/

High pressure at the surface and aloft will continue to bring the entire region unseasonable heat and humidity over the next 36-48 hours.

VFR will prevail at all locations through the forecast period. Winds will remain generally light and westerly, though the next several hours (through 22Z) will see some gusts in the mid to upper teens across the Central Mtns and Susq Valley airfields.

Patchy valley fog is expected again late tonight across Northern PA.

Biggest concern will be density altitude over the next two days. If you're flying on the heavy side and/or taking off from a runway on the shorter side, double check that value and its effect on your performance.

Outlook...

Fri-Sat...Patchy AM fog; otherwise VFR. Hot & humid with PM t-storms psbl. High density altitude concerns possible.

Sun...Restrictions possible in afternoon t-storms.

Mon...Restrictions possible in afternoon t-storms.

Tue...Still a chance of a shower or storm.

CLIMATE

Bradford reached 90 degrees this Thursday afternoon. This tied the old record of 90 degrees set back in 1966.

Williamspot reached 100 degrees, breaking the old record of 99 degrees set back in 1911 and 1931.

Harrisburg did reach 102 degrees, just short of the record of 104 degrees set back in 1966.

Many record highs were set in 1966 around this time of year, while record lows were common back in 1982.

Earlier information below.

Bradford reached 89 degrees Wed, breaking the old record of 88 degrees set in 1963. Harrisburg came up one degree short of tying their own record max Wed.

Triple digit max temps are forecast in the Lower Susq Valley (LSV) today and Friday, and 90s for Saturday.

The last time Harrisburg observed consecutive days with maxT greater than or equal to 100F was back in 2011 on July 21-22.

The record number of consecutive days with maxT >= 100F is 3 and has occurred 5 times: (all in the month of July)

1999-07-16 to 1999-07-18 1999-07-04 to 1999-07-06 1991-07-19 to 1991-07-21 1966-07-02 to 1966-07-04 1936-07-09 to 1936-07-11

The last time Harrisburg hit the century mark was July 16th in 2024. Prior to that, it was July 19th in 2020.

Harrisburg averages 1 day annually with a maxT >100F. The most number of days observed in a year is 6 in 1999.

The record maxes for the next few days are in jeopardy:

Station/Date...07/02...07/03...07/04...07/05. MDT.............104.....107.....104.....102.. IPT..............99.....100.....100.....100.. AOO..............97......97......97......94.. JST..............98.....100.....100.....101.. BFD..............90......91......91......91..

CTP WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM EDT Friday for PAZ004>006-010>012-017- 018-024-033-037-041-042. Extreme Heat Warning until 8 PM EDT Friday for PAZ019-025>028- 034>036-045-046-049>053-056-058-063. Heat Advisory from 8 PM Friday to 8 PM EDT Saturday for PAZ019- 026>028-036-045-046-049>053-056-058-063. Extreme Heat Warning until 8 PM EDT Saturday for PAZ057-059- 064>066.