textproduct: State College

WHAT HAS CHANGED

* Flood Watch issued for the southern Alleghenies & Laurel Highlands until 12AM Wednesday

KEY MESSAGES

1) Isolated to scattered areas of flash flooding possible in south central PA this afternoon into tonight

DISCUSSION

KEY MESSAGE 1: Isolated to scattered areas of flash flooding possible in south central PA this afternoon into tonight

Considerable breaks in the clouds has allowed for convective development over southwest PA late this morning into the early afternoon. High moisture content environment remains in place with slow moving showers/storms capable of producing intense rain rates. Cumulative rainfall over the past few days has lead to increased soil sensitivity and significantly reduced FFG. Hires ensemble guidance (HREF/REFS) shows the southern Alleghenies and Laurels Highlands with the highest odds for localized 2-3" rainfall amounts. WPC has maintained a level 2/4 excessive rain risk for this area and we issued a flood watch until 12AM Wed to highlight the short-term flooding threat.

Daily chances for showers and thunderstorms will continue through the end of the week, especially Thursday and Friday. Temperatures will be seasonable with highs generally in the low to mid 80s.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Current radar outlines showers and isolated thunderstorms across the south-central Pennsylvania mainly south of AOO/JST as of 18Z. The bulk of model guidance continues to suggest that precipitation will fill back into the aforementioned airfields and bring about MVFR ceilings/visibilities within showers and thunderstorms. Brief restrictions towards IFR thresholds will be possible within thunderstorms given the ample moisture in place; however, this remains a lower confidence solution to include into the 18Z TAF package with model solutions outlining different timing of these heavier showers/storms. Thus, have included PROB30s outlining lower visibilities, especially at JST where the signal is slightly more favorable, around the timeframes best progged by HREF/GLAMP model guidance. Elsewhere, removed mentions of showers in the 18Z TAF package due to lower confidence (< 30%) of impacts at the terminals.

After 00Z Wednesday, there remains a good signal for low-level clouds dropping below IFR thresholds based on the 25th and 50th percentile members of HREF ensemble guidance. Overall, the best signals for this potential exists at JST/AOO due to the potential for heavy rainfall and potential for calm winds overnight. BFD/UNV/IPT also exhibit this potential albeit to a smaller magnitude compared to JST/AOO. Given more recent HREF and GLAMP model guidance, have decided to include mentions at BFD/UNV but have been slightly more optimistic at IPT given 50th percentile members of the HREF outlining ceilings remaining over IFR thresholds. IFR thresholds will still be possible although it is a less confident solution between 08-12Z.

Model guidance does indicate a slow improvement trend after 12Z Wednesday, thus have started to introduce incremental increasing in visibilities and ceilings towards the end of the 18Z TAF package. More recent HREF guidance does indicate the improvement trend might be more rapid than current TAF package indicates; however, decided to take the route that outlines slower improvement based on GLAMP/NBM model guidance and a touch of persistence forecasting as would like to see current observations closer to the time and gather some insight on the exact area of high pressure that could bring quick improvement before outlining these explicitly in the TAF package.

Outlook...

Thu-Fri...Mainly dry early. Numerous showers/tstorms during the afternoon. Intermittent impacts likely.

Sat-Sun...Chance of showers and a few storms.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch until midnight EDT tonight for PAZ024>026-033>035.