textproduct: State College

WHAT HAS CHANGED

* The day 6 SPC outlook clips our SWrn counties with a 15% chance of severe weather.

KEY MESSAGES

1) Isolated showers popping up, but are not sustained and should die off with loss of heating. Some fog overnight.

2) Hot and humid pattern set to return for the middle of the week.

3) Day 6 (Fri-Fri night) SPC Outlook paints a 15% chc of severe weather for the SWrn quarter of the CWA.

DISCUSSION

KEY MESSAGE 1: Isolated showers popping up, but are not sustained and should die off with loss of heating. Some fog overnight.

Afternoon radar loop showing that the forecast is working out with isolated returns that pop up, grow just a little and drop out of existence quickly. Capping inversion around 12kft aloft is keeping convection from getting tall enough to sustain. Little to no shear means the organization should continue to be poor with terrain and previously cooled-air outflow boundaries dominating the list of lifting mechanisms today. Expect these showers to die off with the loss of solar heating. But, some could still get tall enough to produce a CG before dying off.

Dewpoints are still in the 60s for much of the CWA, blowing up the manual modification made to the guidance Td by some poor forecaster yesterday at this time. Only terminal with Td <60F is BFD, with m60s the most common reading. Thus, with the loss of most of our clouds tonight, cooling should help the Ts get close to or even below current Tds. That trick usually means fog especially in the valleys. Have expanded mentions of valley fog for later tonight and early Mon AM.

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KEY MESSAGE 2: Hot and humid pattern set to return for the middle of the week.

Dry conditions are expected to prevail for the first half of the week with a strong ridge expected to develop over the middle of the country. Increasing heat/humidity is forecast across central Pennsylvania although there remains some uncertainty with respect to how warm temperatures and/or humidity get across the region. Current forecast favors the hottest temps returning Tue to Thu with highs 85-95F and max heat index 90-100F, potentially rising above 100F on Wednesday. Rain chances show up Thursday and into the weekend, but PoPs remain low at this time as the occurrence of rain will depend on the timing and proximity of fronts and upstream convective systems.

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KEY MESSAGE 3: Day 6 (Fri-Fri night) SPC Outlook paints a 15% chc of severe weather for the SWrn quarter of the CWA.

A weak cold front may dip across the CWA on Thursday, but provide little relief to the heat of Wed, mainly lowering the Ts and Tds by a few degs each. But, the different airmass may not get shoved completely out of the CWA. With plenty of heat and moisture available along and S of the boundary, thunderstorm chances are high wherever the boundary finally sets up. Shear (deep and lowest-layer) can be maximized right there, too. NBM guidance mean and WPC forecast keeps PoPs at 30-40pct with low confidence in timing and overall placement of storms at such a long range. So, it doesn't seem out of line to me for us to have the 30-40% PoPs with the 15% severe chances. The 15% outlook for day 6 rarely gets painted over Central PA - only a handful of times per year. So, the day could be very active, but we'll have more confidence as time gets closer. For now, it will be enough to take note of the higher possibility of severe thunderstorms/tornadoes. Things can, and usually do, change with a Day 6 forecast.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

High pressure over southern Ontario will keep a weak easterly flow over the area into Monday.

Still an isolated shower possible into this evening, but left out of the 18Z TAF package.

With weak winds and still wet ground, some potential for low clouds and fog tonight, but left out for now. Models don't indicate much potential. Also quite dry aloft as one gets into northern PA, so mixing this afternoon should help dry things out some.

Next chance of widespread showers and storms late Thursday into next weekend. Perhaps a few showers and storms late Wednesday across the north and west, but this activity more limited in area and time.

Outlook...

Tue-Thu...Mainly VFR, with areas of late night/AM fog.

Fri...Chance of showers and storms.

CTP WATCHES/WARNINGS/ADVISORIES

None.