textproduct: State College

WHAT HAS CHANGED

* All the CWA is now in the Day2 (Sat/Sat night) SPC severe slight risk category and the WPC excessive rainfall marginal risk. * Added smoke into the wx grids for Sat (AM for W and all day for the E).

KEY MESSAGES

1) Wildfire smoke will result in very unhealthy (purple) air quality and reduced visibility today and into Saturday.

2) Strong to severe thunderstorms with damaging winds and heavy rainfall are possible Saturday afternoon and the first half of Sat night.

DISCUSSION

KEY MESSAGE 1: Wildfire smoke will result in very unhealthy (purple) air quality and reduced visibility today and into Saturday.

Widespread smoke continues to reduce visibility, even overnight, (generally 1-3 miles in FU and HZ) and degrade air quality across much of the region. The PA DEP has placed all of the state into a Code Purple (very unhealthy) alert as PM2.5 (particulate matter) remains high, especially in the southern tier of the state. Somewhat of a dip in smoke density/concentration is possible for the northeastern counties today. But, it waggles right back into there out of the south overnight. RRFS progs continue to press the highest near- surface smoke to the north and east during the day Sat. The precipitation Sat/Sat night may temporarily help by literally precipitating the smoke out of the air, but the concentrations rise again on Sunday as the plume of higher smoke is progged to come back in from the west.

Kept on with a 2F nudge downward on the daytime temps vs straight NBM mean today. Made no adjustments to T for Sat as warm advection and sct-nmrs SHRA offer no clear direction to tilt away from NBM temps.

-------------------------------------------------------------

KEY MESSAGE 2: Strong to severe thunderstorms with damaging winds and heavy rainfall are possible Saturday afternoon and the first half of Sat night.

A potent cold front trailing a deepening sfc low tracking up the St. Lawrence River Valley is expected to trigger one or more rounds thunderstorms Saturday afternoon and evening.

severe... SPC level 2/5 severe thunderstorm risk continues cover most of central PA for day 2/Saturday into Saturday night. A warm front will attempt to lift north-east across the area during the daytime. A potent cold front will cross the area Sat night. Storms will likely initiate before and along the front. Some storms ahead of the cold front will have the chance to spin as the shear from the warm front and other boundaries could contribute to localized higher helicity values. However, the bigger worry is for damaging wind gusts as clusters could organize better and produce long-lived bow(s). Reduced instability may be a limiting factor if clouds and showers persist from early in the day. How the smoke may play into all of this is unclear. No pun intended. It could help keep temps and instability down. But, the extra condensation nuclei could make it more efficient at producing rainfall and evaporative cooling. On the other hand, the smoke does seem to get pushed NE thru the day, and may not play any role in the precipitation and severe threats.

rain... Southwesterly low-level flow ahead of the front will transport a high PW airmass into CPA. Strong synoptic forcing, driven by an amplifying trough over the Northeast and favorable upper jet dynamics, will support the potential for heavy rain rates to produce isolated flash flooding concerns. WPC has the entire area in the MRGL risk for ex rainfall on Day 2 (Sat-Sat night). Convection earlier in the day will be followed by more SHRA/TSRA later in the day and through the first half or more of the night. A drying trend is expected Sunday with noticeably lower humidity allowing for a pleasant day and relatively cool night. But, the RRFS progs of smoke do bring some back into the state from the W on Sunday. That may keep it from being a refreshing day. Additional bouts of rain/t-storms are possible into the workweek. Temperatures will trend near to slightly below historical averages through late week with some noticeably cooler nights possible.

AVIATION /07Z FRIDAY THROUGH TUESDAY/

The primary concern for the next 24 hours continues to be visibility restrictions due to wildfire smoke from Canada and northeastern Minnesota. Tonight may bring the most widespread restrictions as winds lighten behind the front with high pressure moving in, with the HRRR/RRFS models showing IFR to LIFR visibilities across much of Central PA. Improvements from overnight IFR-LIFR on Friday is favored across the northeastern edge of the smoke plume (currently forecast to be KBFD/KIPT), where the wind's northerly component may linger enough to bring smoke south of those sites, with improvements looking less likely over southwestern Pennsylvania (KJST/KAOO) where the winds may lighten as the core of the smoke plume moves overhead.

As of right now highest confidence remains in smoke hanging on until after 06Z on July 18th. A frontal system will approach us very late Friday night into Saturday morning and usher the smoke out, only to replace it with showers and thunderstorms through the day on Saturday.

Outlook...

Sat-Sun...Chance of showers and t-storms, mainly during the afternoon hours on Saturday into early Sunday aft. Smoke moving out.

Mon...Mainly VFR.

Tue...Restrictions possible in showers/t-storms.

CTP WATCHES/WARNINGS/ADVISORIES

Air Quality Alert until midnight EDT tonight for PAZ004>006- 010>012-017>019-024>028-033>037-041-042-045-046-049>053- 056>059-063>066.