Area Forecast Discussion

WHAT HAS CHANGED

Additional enhancement of forecast rain amounts for Poconos- Catskills Monday-Tuesday from topographical influences. Slight Risk for excessive rainfall by Tuesday-Tuesday night generally east of I-81 in PA and south of I-88 in NY.

KEY MESSAGES

1) Though just a few scattered showers and isolated thunder are bringing the weekend to a close, our pattern is turning more active with several rounds of showers and occasional thunderstorms through at least midweek. Locally heavy rainfall, and isolated gusty storms, could occur.

2) A relatively drier period is anticipated late this week, but there is uncertainty for how long it takes for a low pressure system to finally exit the region to take away lingering showers.

DISCUSSION

KEY MESSAGE 1...

Weak passing waves will continue to interact with a gradually moistening environment this afternoon through Monday, as a broader upper trough gradually digs over the Northeast. A more significant low pressure system will then develop over our region Tuesday with increasing potential impacts, which could linger into Wednesday.

This afternoon-early evening, flow is weak and instability limited. Diurnally-driven showers will be scattered and thunder isolated non-severe. Dewpoints have crept up which will lead to areas of fog formation tonight-early Monday as cloud cover aloft decreases and allows some radiational cooling.

For Monday, Precipitable Water Values continue to gradually increase, yet some ridging will also occur aloft ahead of the more significant low approaching from the west. This may limit coverage of diurnal showers-thunderstorms. That said, there will still probably be small shortwaves embedded within the ridge. There will also be modestly more Convective Available Potential Energy, especially in Northeast PA and thus the marginal risk for Severe for the threat of isolated downbursts from cores. Timing of modeled shortwave and orographic effects will favor Poconos-Catskills coverage-wise for showers and storms. Things should be more scattered to the west.

Locally heavy rainfall cannot totally be ruled out Monday, though recent dry weather should allow our area to generally take initial rains well. However, as additional waves occur into Tuesday it could be more of an issue. Models generally cut off an upper low and gradually stack it with the incoming surface low, to cause slow movement of features with elevated precipitable Water values around 1.75 inch Tuesday-Tuesday night. It could even linger into Wednesday. From I-88 southward in NY, and from I-81 eastward in PA, Weather Prediction Center has Slight Risk for excessive rainfall and at least Marginal Risk for the rest of the area. The forecast has areal averages of 1.5-2.5 inches with locally higher amounts for Wyoming Valley-Poconos-Catskills; more like 1-1.5 inches to the west. Orographic enhancements, and slow-movement or training of heavier showers, will have to be monitored closely for localized flooding potential. For Tuesday-Wednesday, severe risk is more likely to be shunted to our south in the warm sector of the low, as things become progressively cooler and stratiform with time in our region. Still, a gusty few cells could occur Tuesday in Northeast PA before the low translates overhead.

KEY MESSAGE 2...

Cutoff stacked lows often take longer than expected to break down. Thus we still have a lingering chance of showers and thunderstorms Thursday, especially east of I-81. There is uncertainty but these chances could easily go higher given the trend in the latest models to keep the upper low in our region for a longer time. Eventually the low departs in favor ridging which will bring at least a window of drier and warmer weather Friday-Saturday.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Mainly VFR conditions are expected through this evening. Isolated showers and thunderstorms are expected to start to bubble up around the area over the next hour or two and linger through about 00Z in most places. AVP can see something spotty around through about 01Z-02Z. Looking at the current mesoanalysis, the best chance for any thunder looks to be at ITH, ELM, BGM and AVP, so this has been covered via TEMPO, and will be amended in if needed for the northern terminals.

Areas of fog are expected to form around most of the terminals later tonight into tomorrow morning with a mix of MVFR/IFR restrictions. Confidence is highest in LIFR restrictions at ELM, but can't be ruled out elsewhere, especially if there is enough clearing prior to daybreak. While the GFS seems to hold onto some mid and high level clouds overnight, most other guidance clears things out allowing for the widespread fog to form. After the morning fog clears tomorrow, isolated to scattered showers and storms are expected to develop after 18Z with daytime heating.

Outlook:

Monday afternoon through Thursday...Scattered showers and/or thunderstorms resulting in occasional restrictions, especially during the afternoon and evening hours. Valley fog possible, especially at KELM during the late-night and early morning hours.

Friday...Mainly VFR; low chance of a shower or thunderstorm.

BGM WATCHES / WARNINGS / ADVISORIES

PA...None. NY...None.