textproduct: State College

WHAT HAS CHANGED

* WPC MRGL excessive rainfall risk level 1 added for Wed. (9/2)

KEY MESSAGES

1) Late summer heat+humidity to close August and open September 2) Bouts of heavy rain & severe storms possible Monday-Wednesday

DISCUSSION

KEY MESSAGE 1: Late summer heat+humidity to close August and open September

The latest available model guidance has a fairly good handle on the overall large scale pattern through the middle of next week. The dominant synoptic feature will be a sprawling 500mb anticyclone gradually expanding to the east northeast from the central/southern Plains to the southern Mid Atlantic and Southeast. This will deliver a stretch of very warm and humid conditions with temperatures rising several degrees above the historical average from Sunday (last day of August) through Wednesday (first few days of September).

The heat will peak Tuesday and Wednesday with temperatures ranging from the mid 80s to mid 90s. Heat index values could approach the century mark across the south central mountains each afternoon as well. Overnight lows in the 60s and 70s will provide little relief from daytime heat. This warm/humid air will also provide ample fuel for thunderstorms as the week wears on.

KEY MESSAGE 2: Bouts of heavy rain & severe storms possible Monday-Wednesday

A series of dynamic shortwaves and frontal systems tracking eastward along the northern periphery of the elongated upper ridge will interact with high humidity/very high PWs, strong mid level flow/favorable jet streaks, and instability to produce a few episodes of heavy rainfall and possible severe weather during the middle part of next week. There are typical timing and amplitude differences of the smaller scale disturbances that will need to be resolved, but the convective signal is supportively bullish for a couple rounds of strong to severe storms and at least localized areas of potentially excessive rainfall. WPC has continued to highlight portions of north central PA with a marginal risk for Monday & Tuesday followed by a new, broader coverage for Wed/D5. SPC has maintained the 15% or level 2/5 equivalent severe probs on Wednesday while acknowledging additional probs will likely be needed on either side of Day 5 based on medium range ML and AI generated guidance.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

1025 mb surface high pressure will drift slowly to the East- Southeast today, bringing VFR with light wind, excellent visibility and variable amounts of mainly thin cirrus clouds drifting SE from the Great Lakes region. Winds will be light and variable during the daylight hours today and will once again diminish to near calm tonight/early Sunday. Air/water temp differences tonight and early Sunday should be 10-12 deg F less than what we just had this morning, which didn't produce much fog. Therefore, won't consider anything lower than 6SM BR at this point at KBFD and KIPT, considering that deterministic and ensemble numerical guidance keeps sfc temp/dewpoint spreads of 4 deg F or more late tonight/early Sunday.

Late tonight, low level southeasterly flow may lead to the development/NWWD advection of a stratocu deck, based mainly between 2500 - 4000 ft AGL. This could lead to a couple hours of MVFR restrictions at LNS and MDT toward daybreak Sunday.

Outlook...

Sun...Mainly VFR. Isolated SHRA/TSRA possible.

Mon-Tue...Rounds of SHRA/TSRA with brief restrictions possible. Morning fog.

Wed-Thu...Sct SHRA/TSRA with brief restrictions possible.

CTP WATCHES/WARNINGS/ADVISORIES

None.