textproduct: State College

WHAT HAS CHANGED

* Severe threat has ended for the most part, but flash flood threat will continue through at least midnight.

KEY MESSAGES

1) Thunderstorms are weakening/losing vertical development. Flood threat remains.

2) Breakdown of heat wave pattern gives rise to severe storms and torrential downpours today and tonight; flood risk lingering in the east on Monday.

DISCUSSION

KEY MESSAGE 1: Thunderstorms are weakening/losing vertical development. Flood threat remains.

Current (930 PM EDT) assessment of environment over Central PA is that the severe threat is just about over. Most places have stabilized at the lowest layer. This will make it difficult for additional wind damage to occur. Will leave the watch up for just another 30 mins, but should be able to clear the rest of it shortly.

As anticipated, the threat is now flash flooding. Many places have picked up >1" of rain across the CWA, with 3-5" amounts reported in the Harrisburg area. Considerable flash flooding has been on-going for a few hours, starting in Tyrone/Blair Co, and shifting to the east. The flooding in the SE will continue for a few more hours with a few new instances of flooding before midnight. What should be the last batch of very heavy rainfall is moving through the SE now. Lone FFW over State College should see the water start to go down in an hour or so.

High moisture and light wind will cause fog over most of the CWA overnight. Will likely need a dense fog advisory at some point.

KEY MESSAGE 2: Breakdown of heat wave pattern gives rise to severe storms and torrential downpours today and tonight; flood risk lingering in the east on Monday.

40 severe thunderstorm warnings issued in the past 2 days. The days following a transition from an extreme heat pattern are often marked by severe/active weather, and that trend continues through at least Monday. As the heat dome shifts to the west and troughing develops over the Great Lakes/Ohio Valley/Northeast, the upcoming week will feature relatively cooler (more seasonal) temperatures with a bullish signal for almost daily rain chances particularly early and late in the week.

Another active wx day ahead with dual severe T-storm and flash flood risks. We anticipate another diurnal uptick in convective development within a very warm, moist and increasingly unstable environment indicative of steep low-mid level lapse rates. Pockets of stronger deep layer shear 30+ kt may exist in the upper OH Valley and eastern PA, but the general expectation is for pulse to multicell storms to once again merge/form into line segments with some cold pool organization to promote damaging wind potential from mid afternoon into the evening. Terrain boundaries will also play an important role in initiating/organizing convection given lack of other strong forcing. SPC placed the highest damaging wind probs near/southeast of I81/78 where max temps should reach 90F.

Focus will evolve from severe to flash flood/hydro ops by later this evening and continue into Monday as a robust +RA signal continues to manifest over east-central PA. Atmos conditions will be quite favorable for heavy rainfall and flash flooding potential with 2+ inch pwats correlating to intense rain rates >2 in/hr. Still some question on degree of repeating/back- building storms along q-stnry/wavy frontal zone. Latest HREF/REFS mean QPF guidance is signaling 1-3" in the 24hr period ending 00Z Tue with PMM/LPMM max values exceeding 5 inches. WPC coordinated a targeted and relatively small moderate excessive rainfall outlook (level 3/4) within a broader level 2/4 or SLGT risk area. We issued a relatively large/broad flood watch along with WFO PHI as there remains some spatial uncertainty to exactly where the greatest rainfall will occur. The setup (multiple rounds of slow moving/torrential downpours) favors locally significant flash flooding particularly in terrain areas and highly urbanized corridors. One limiting factor is obviously the drought conditions and corresponding elevated FFG values that may offset the overall risk to some extent.

AVIATION /01Z MONDAY THROUGH FRIDAY/

Convection generally confined to the eastern half of Pennsylvania to begin the forecast. Tried to time the arrival of the main areas but there will be additional -TSRA through midnight over the eastern airfields.

The remainder of the night will see MVFR to IFR with lingering light rain. Dewpoints near 70 combined with earlier rainfall will result in patchy BR/FG. Confidence of LIFR in FG is around 40% in any one location.

Precipitation returns during the afternoon Monday with isolated TSRA through the remainder of the forecast period. Expect MVFR to IFR during this time.

Outlook...

Tue...Restrictions possible in A.M. fog and P.M. T-storms. Wed- Fri...Restrictions possible in showers/storms, most widespread on Friday.

CLIMATE

Rare Heat at Harrisburg: 3 consecutive days with maxT >= 100F from July 2-4, 2026. The last time this streak occurred was July 1999 (2x) and is only the 6th time on record going back to 1888.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch through Monday evening for PAZ017>019-024>028- 033>036-042-045-046-049>053-056>059-063>066.