textproduct: State College

WHAT HAS CHANGED

* Dense Fog Advisory issued early this morning for the western and central Alleghenies * Targeted Moderate Risk Excessive Rainfall Outlook (level 3/4) for east-central Pennsylvania through tonight * Flood Watch issued this afternoon through Monday for east- central Pennsylvania

KEY MESSAGES

1) Breakdown of heat wave pattern gives rise to severe storms and torrential downpours today and Monday

DISCUSSION

KEY MESSAGE 1: Breakdown of heat wave pattern gives rise to severe storms and torrential downpours today and 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.

In the very near term, clearing sky and nearly calm wind following last evenings widespread rainfall has resulted in areas of dense fog over the western and central Alleghenies. IR sat shows the fog expanding as higher clouds peel away. We issued a DFA through 13Z/9AM with several ASOS and RWIS sites already reporting 1/4 mile visibility.

Another active wx day ahead with dual severe T-storm and flash flood risks to manage. 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. SPC placed the highest damaging wind probs near/southeast of I81/78 where max temps should reach 90F.

Focus will should 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 and 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 /12Z SUNDAY THROUGH THURSDAY/

Fog and low clouds are producing a mix of MVFR and IFR conditions this morning across much of Central PA. The fog will dissipate by 15Z and VFR conditions will return for the rest of the morning and into the afternoon.

Showers and thunderstorms will develop during the afternoon and are once again likely to impact all TAF sites through the evening. PROB30s have been included to highlight this potential, though the timing will need to be adjusted as confidence increases. Storms will be capable of producing strong wind gusts, intense rainfall rates, and frequent lightning. Any storms that move directly over an airfield will likely lead to brief periods of IFR conditions.

Rain comes to an end from west to east after 00Z, though showers and storms may linger at MDT and LNS past 06Z. Fog and low clouds appear likely behind these showers and widespread IFR conditions will be possible into Monday morning.

Outlook...

Mon-Tue...Restrictions possible in A.M. fog and P.M. T-storms. Wed-Thu...Improving conditions expected.

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

Dense Fog Advisory until 9 AM EDT this morning for PAZ004>006- 010>012-017>019-024>027-033>035-037-041-042-045-046. Flood Watch from 2 PM EDT this afternoon through Monday evening for PAZ019-026>028-036-045-046-049>053-056>059-063>066.