textproduct: State College

WHAT HAS CHANGED

* Reorganized the heat products/timing, mainly extending things a bit. * Days 2 and 3 now carry a slight risk of severe thunderstorms for much of the CWA. * Days 3, 4 and 5 also hold a marginal risk for excessive rainfall/flooding.

KEY MESSAGES

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

Tried to keep temps and dewpoints very similar to what we've had running for many days. However, we did extend the heat products out in time on the whole. The biggest change was to upgrade the Lower Susq to a warning for Sat - which basically just extends what is running right now. While HI values do lower some on Sat all across the CWA, those SE zones will still be capable of hitting 105 Sat aftn. That has looked to be the case for at least a day, and we're now more confident in that outcome.

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

We should be sufficiently capped today (Thurs) to preclude all but the very isolated of storms. We could see one pop up near the NY border late in the day. But, we'll likely not see any deep convection until later tonight when a bit of upper forcing rolls W-E on the zonal flow just to our N. As we will still be under the influence of the strong upper ridge, we may not become unstable enough at night to pop anything, but some showers/storms may slide in from the NW into the nrn mtns overnight.

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. Lots of the guidance keeps the area rain-free for all of the day on Fri and only 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. SPC has placed almost our entire area in the slight risk category, mainly for wind damage. However, we'll have to wait and see just how much instability we can generate and find some lift in order to overcome the CINH. 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 /07Z THURSDAY THROUGH MONDAY/

High pressure at the surface and aloft which is delivering unseasonable heat and humidity will expand and center more closely to Pennsylvania over the next 48 hours.

This will push any ridge-edge convection further north and east of Pennsylvania Thursday and Friday. Good VFR will prevail at all locations through the forecast period. Winds will remain generally light and westerly with just isolated areas (20%) topping 10 knots during the afternoon hours.

Biggest concern will be density altitude over the next two days. High resolution short term models forecast dewpoints to drop overnight and then fall into the 50s during the afternoon Thursday. This should keep any widespread fog from forming overnight (<10%), but will help surface temperatures climb a few degrees higher than today. 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.

CLIMATE

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.