textproduct: State College

WHAT HAS CHANGED

* Tweaks to match near term radar and sky trends.

KEY MESSAGES

1) Showers/storms affect some of the area tonight as a warm front lifts across the state.

2) Severe thunderstorm risk for Wed night/Thursday 6/17-18, with a gusty westerly gradient wind of 30-35 mph in the afternoon across the NW half of the state.

DISCUSSION

KEY MESSAGE 1: Showers/storms affect some of the area tonight as a warm front lifts across the state.

Storms associated with the advance of an upper trough and warm front are starting to impact the NW mtns. Some gusts into the 30+KT range have been noted across wrn PA. Lightning is decreasing slightly as the cluster of storms moves into the CWA. Cannot see any significant downdraft potential from these storms, but a gust to 40KT across Warren/McKean/Elk Cos is possible.

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KEY MESSAGE 2: Severe thunderstorm risk for Wed night/Thursday 6/17-18, with a gusty westerly gradient wind of 30-35 mph in the afternoon across the NW half of the state.

Latest model guidance is a bit concerning regarding the potential for an Eastward/SEWD moving MCS late Wed night and Thursday AM. The area most prone to seeing this will be the NW Mtns of PA where a surge of llvl moisture and warmer temps will lead to at least several hundred J/kg of MU CAPE - mainly across the NW half of PA.

We'll be monitoring the potential timing for severe weather closely. It could be one of those rare nights where the number and timing of storms makes it a rather noisy night to sleep undisturbed.

The severe threat shifts to the southeastern half of the CWA for Thursday, though there still remains some uncertainty regarding how much the airmass will be able to recover behind any morning convection and cloud cover.

The nose of a very strong, 40-50 KT swrly 850 mb jet 50+ KT at 700 mb (both being 3-4 sigma on the standardized anomaly scale), the the left exit region of a 100 KT 250 mb jet and PWATS around 1.5 inches (with the potential for a narrow tongue of an EML surging east ahead of a strong sfc cold front) will create a favorable synoptic setup for severe weather (High Shear Low CAPE Environment).

Another notable weather factor for the bulk of the daylight hours Thursday will be the likelihood of 30-35 kt gradient, westerly wind gusts focused mainly across the NW half of the CWA.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

A weak shortwave moving northeastward across the Great Lakes will continue to bring scattered showers and thundershowers over the Commonwealth through Wednesday afternoon. Although VFR will prevail, brief MVFR/IFR visibility restrictions are possible in the heaviest showers (for example, 04:37Z observation at KBFD showed 2 1/2 SM visibility in SHRA). Modest CAPE within the mixed-phase zone (~50 J/kg of CAPE between -10C and -30C) will support occasional lightning in the strongest cells, with mentions to be handled by TEMPOs wherever confidence in lightning is higher.

Shower activity will generally wane between 14Z-18Z Wednesday, with a SCT-BKN VFR cumulus deck in place during the afternoon. A few diurnally driven showers/thundershowers may develop (PROB30) between 17Z-21Z over the eastern terminals (KIPT/KMDT/KLNS) as the shortwave continues exiting the region, though most areas will remain dry. Otherwise, southwest winds will increase to around 10 kts, with gusts of 15 to 20 kts likely during the day.

High clouds will filter overhead Wednesday evening ahead of a potent low pressure system moving across the Great Lakes. A band of -SHRA/-RA will overspread much of the Commonwealth from west to east overnight, followed by the passage of a decaying MCS. While the MCS will be weakening as it encounters more stable air across central Pennsylvania, it will be coincident with an unseasonably strong nocturnal LLJ (~65 kts at 850 mb, above the 99th percentile for this time of year). As such, a period of LLWS concerns + southerly ridgetop wind gusts are likely overnight, along with the potential for gusty winds to be transported within the weakening MCS.

Outlook...

Wed...Higher chances for -SHRA/-TSRA, restrictions more likely late. High probability (90+ percent) for LLWS Wed night into Thursday morning as the axis of an anomalously strong south/southwesterly LLJ slides east across the Commonwealth.

Thu...Restrictions possible in -SHRA/-TSRA.

Fri...Showers ending.

Sat-Sun...Chance of afternoon showers and thunderstorms over the north and west.

CTP WATCHES/WARNINGS/ADVISORIES

None.