textproduct: State College

WHAT HAS CHANGED

Threat for isolated strong storms with heavy rainfall has ended in the Lower Susquehanna Valley

KEY MESSAGES

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

DISCUSSION

A couple of persistent, slow moving T-storms pushed both severe and flash flooding warning limits late this evening in the Lower Susquehanna Valley. Upper shortwave progressing through the Mid Atlantic could linger isolated convection early into the overnight hours. Areas of fog should expand in coverage through predawn into daybreak early Monday morning.

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

There is still some uncertainty regarding the coverage of storms during the day on Monday as upper level forcing is expected to remain weak. 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 show an MCS diving south from the Great Lakes Monday night 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 as 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 Monday 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 /06Z MONDAY THROUGH FRIDAY/

Widespread VFR conditions currently across central Pennsylvania based on observations; however, recent ECONUS Nighttime Microphysics outlines the typical dendritic valley fog across portions of northern Pennsylvania that will bring IFR/LIFE concerns in the near-term. Airfield most likely to receive restrictions will be BFD with HREF/GLAMP/NBM guidance all in fair agreement that LIFE conditions are imminent by 09Z, with some potential at JST also based on HREF model guidance. In general, have continued with the optimistic approach that BFD/JST will be the only airfields with restrictions overnight, with JST most likely honed in on a one-two hour timeframe just ahead of sunrise. Similarly to yesterday morning, 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 this past afternoon; however, overall confidence in airfield impacts remain low outside of BFD/UNV/JST where model guidance does outline some agreement in showers/storms firing but quite different on placement at this time. Given this potential, have outlined 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 at this time. Rain moves into the western terminals towards the end of the TAF package so have also outlined some showers at BFD/JST towards the end of the 06Z TAF package with moderate (50-60%) confidence on rain occurring but lower (30-40%) confidence on timing, which could trend slightly later than current forecast.

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.