textproduct: State College

WHAT HAS CHANGED

Level 2/5 severe T-storm risk expanded over the southern tier of central PA for this afternoon and evening

KEY MESSAGES

1) Scattered severe thunderstorms with locally heavy rainfall are possible across the southern tier/third of central PA this afternoon and evening

DISCUSSION

KEY MESSAGE 1: Scattered severe thunderstorms with locally heavy rainfall possible across the southern tier/third of central PA this afternoon and evening

Steady warm advection rain has expanded across the northern tier early this morning. This leading edge rain is likely tied to 850mb wind max downstream of dampening mid level shortwave trough/remnant MCV in the Ohio Valley. Hires guidance focuses mean QPF in the 0.50-0.75 inch range to the north of I-80 through 18Z with local rainfall amounts possibly exceeding 1 inch by early afternoon.

Attention shifts to the south this afternoon and evening as a warm front will lift north of the MD line to a position somewhere between I-80 and US-22. Sfc dewpoints are projected to surge into the upper 60s to the south of the warm front where some cloud breaks should allow for at least modest destabilization. The moderately sheared and conditionally moist/unstable convective environment should promote scattered t-storm ignition into peak diurnal heating. The initial storm development is expected to evolve into forward propagating clusters with a strong to locally damaging wind threat. As convection intercepts the northward moving warm front over the southern tier of CPA, locally backed flow and more favorable low level shear may support the development of at least transient supercells with some tornado potential. SPC has expanded the level 2/5 slight risk to include the entire southern tier/third of CPA (areas near and south of US-22) along with corresponding severe wind and 2% tornado probs.

Heavy rainfall will also be a concern with pwat values between 1.5 and 2 inches. This is around the 95th percentile for this time of year and would support intense rain rates perhaps as high as 2-3"/hr. A warm cloud depth in excess of 11,000 feet and tall, skinny CAPE profiles also support a heavy rain signal. WPC has maintained a level 2/4 slight risk for excessive rainfall (ERO) over roughly the southern third of the forecast area where isolated instances of flash flooding will be possible, particularly in training/repeat storms over urban areas. The two limiting factors going against a more considerable flash flood threat are the ongoing dryness/drought conditions focused over the LSV and fairly progressive storm motions.

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Much drier conditions are expected for Tuesday and Wednesday as high pressure builds into Pennsylvania. A slight warming trend is expected, with high temperatures expected to be in the 70s and low 80s through the end of the week. An upper level disturbance moving through the region on Thursday and Friday will bring the next chance for showers and thunderstorms to Central PA, though there are still some timing differences in the models as to when rain will be most likely.

Temperatures continue to warm up into the weekend, with most of the area expected to see highs in the 80s by Sunday. A major pattern change upstream over the Pacific/Intermountain West this weekend could spell a return of more typical hot and humid conditions to close out June and begin July.

AVIATION /09Z MONDAY THROUGH FRIDAY/

Low pressure over the Lower Ohio Valley early today will move northeast this morning and reach South-Central PA by early this evening.

Rain associated with warm air advection (WAA) ahead of this low will continue to move ENE and expand across the NW half of PA this morning.

Initial lack of any appreciable SFC or ML instability will support showers of varying intensity and mainly VFR flying conditions prior to 16Z.

SHRA/TSRA becoming more numerous through the midday and afternoon hours. Embedded thunderstorms are possible within the WAA rainband as overrunning warm/moist air introduces instability within the mixed-phase layer (~50 J/kg MUCAPE between -10C to -30C), enabling lightning production.

Ceilings will trend lower during the daylight hours today as the aforementioned low tracks over the Commonwealth & showers/storms grow more widespread, with lower confidence in ceiling restrictions across the Lower Susquehanna Valley (KMDT/KLNS) deeper into the warm sector.

Restrictions in visibility will become likely with the passage of any heavier showers/storms this afternoon as precipitable water values climb to anomalously high values (PWATs >1.5") supporting locally heavy rain, especially where 2 or 3 TSRA train over the same area.

Another factor to flight ops will be LLWS as a result of a fairly strong southerly/southwesterly LLJ ahead of the system, High confidence of lower cigs and vsbys at KBFD/KJST at this time.

Lastly, Convection-Allowing Models (CAMs) suggest a line of thunderstorms may develop along a pre-frontal trough this afternoon, with potential impacts at KMDT/KLNS between roughly 18Z-21Z.

Decent deep-layer wind shear (0-6 km shear around 40 kts) + adequate instability (MLCAPE between 750-1000 J/kg) will support organized convection with this trough, along with the possibility for gusty winds and perhaps some locally severe weather.

Outlook...

Tue...Lower chances of showers, mainly VFR.

Wed...Mainly VFR, watching for precipitation chances though in the evening/overnight.

Thu...Restrictions possible in another round of evening/overnight.

Fri...Restrictions possible in another round of daytime/evening showers.

CLIMATE

5th driest June 2026 (MTD) on record (of 132 years) at Williamsport with total monthly precip 0.73"

9th warmest average high temperature of 84.4 degrees at Harrisburg for June 2026 (MTD) on record (of 138 years) 10th driest June 2026 (MTD) on record at Harrisburg with total monthly precip of 0.58"

CTP WATCHES/WARNINGS/ADVISORIES

None.