textproduct: State College

WHAT HAS CHANGED

Trying to better depict the late afternoon/evening timing of a first cluster of TSRA with a second occurring very late tonight/early Tuesday (and possibly a third distinct round of SHRA/TSRA Tues afternoon/early evening across the far SE part of the CWA).

KEY MESSAGES

1) Severe thunderstorms capable of damaging winds and heavy to potentially excessive rainfall are possible this afternoon and Tuesday.

DISCUSSION

Areas of valley fog should stay mainly light through about 12Z today with vsbys AOA 2SM.

KEY MESSAGE 1: Severe thunderstorms capable of damaging winds and heavy rainfall are possible this afternoon and Tuesday

There is still some uncertainty regarding the coverage of storms during the day today as high res models have quite a wide spread w/respect to the timing, location and apparent intensity of several small areas of preferred CI and movement of the individual cells or clusters of SHRA/TSRA.

On the larger scale we're looking at weak ridging sliding over the state from the NW at the surface and aloft today, which will almost certainly create an unfavorable environment for anything more than a stray shower/TSRA through 19Z if not longer today.

We should see at least scattered thunderstorm development during the afternoon as modest instability develops, but shear will remain weak. The severe threat appears to be low, but a few strong to severe wind gusts will be possible with any stronger storms.

Some models still continue to highlight a MCS diving south/SE from the Great Lakes later tonight which could impact western portions of the area, but confidence is low on timing and placement of this feature.

Tuesday will likely see the most widespread showers and thunderstorms of the week coming in one or two distinct rounds.

A potent shortwave approaches from the west and its associated surface low tracks over the region. Showers and storms will likely be ongoing across parts of Central PA Tuesday morning and should continue through the rest of the day. The potential for severe weather remains uncertain as it will depend on much we are able to destabilize behind the morning showers and storms. SPC has areas roughly along and south of I-80 in a marginal risk for severe weather and they have included far southern portions of the area in a slight risk.

Heavy rain will also be a concern this evening into Tuesday with any storms that develop as PWAT values will climb to around 1.8 inches. Storms will be very efficient rainfall producers and areas that see repeated rounds of thunderstorms may see some flash flooding concerns develop. WPC has placed nearly all of Central PA in a marginal risk for excessive rainfall for both Monday and Tuesday.

AVIATION /12Z MONDAY THROUGH FRIDAY/

Restrictions are limited to BFD/JST this morning with fairly high confidence on rapid improvement in conditions with airfields likely prevailing VFR by 13Z Monday at the latest. Showers and some isolated thunderstorms will once again be possible with another day of the pulse-storm mode expected across the region. Coverage *might* be slightly higher compared to yesterday; however, overall confidence in airfield impacts remain low outside of BFD/UNV/JST/IPT where model guidance does outline some agreement in showers/storms firing. Actual locations remain the most uncertain aspect of the forecast, so near-term trend will need to be continued to be monitored. Given this potential, have continued PROB30s for the main timeframe of convection occurring as they will need to fire close to the airfield in order for restrictions to be realized. In terms of IFR-and-below conditions from these, would have to be due to a heavier thunderstorm with visibility restrictions as cloud bases do not look extremely low with these showers/storms.

Rain moves into the western terminals close to 06Z and have outlined more widespread shower mentions towards the end of the 12Z TAF package. At this time, HREF/NBM model guidance shows fair agreement in sub-VFR conditions across the western terminals; however, have taken a slightly more optimistic approach at AOO where there will be some low-level dry air that could limit these concerns.

Outlook...

Tue...Restrictions likely with scattered -SHRA/-TSRA.

Wed-Thu...Restrictions possible as -SHRA/-TSRA becomes less numerous. Patchy overnight fog possible.

Fri...VFR favored with slight chance for -SHRA. Patchy overnight fog possible.

CTP WATCHES/WARNINGS/ADVISORIES

None.