textproduct: State College

WHAT HAS CHANGED

* A Heat Advisory has been issued for much of central PA for Tuesday. Expansion toward the southeast is possible for Wednesday as another hot day looks increasingly likely.

KEY MESSAGES

1) Isolated showers and thundershowers possible along a sfc trough across the northern tier this afternoon.

2) A Heat Advisory has been issued for much of central PA for Tuesday. Expansion toward the southeast is possible for Wednesday as another hot day looks increasingly likely.

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 and thundershowers possible along a sfc trough across the northern tier this afternoon.

Patchy morning valley fog will give way to another mostly sunny, mostly dry day. The exception will be isolated showers and thundershowers possible along a sfc trough across the northern tier this afternoon within a narrow corridor of SBCAPE near 1000 J/kg. Most convection should produce fairly narrow swaths of less than 0.50 inch of rain, so we are not anticipating any hydro concerns. Light winds aloft and modest CAPE profiles also suggest the threat for any severe weather is minimal. Convection will likely dissipate around sunset.

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KEY MESSAGE 2: A Heat Advisory has been issued for much of central PA for Tuesday. Expansion toward the southeast is possible for Wednesday as another hot day looks increasingly likely.

Temps will begin to warm across central PA today and jump several more degrees into Tuesday, as a warmer airmass spills in from the northwest. Compared to the tropical heat wave we experienced in early July, where that airmass originated in the deep tropics, this airmass over us on Tuesday will have spent the past 7+ days in northern Canada with midlevel source regions from the Pacific. Therefore it will not be quite as juicy. Expect dewpoints on Tue mostly in the mid 60s (vs mid 70s early July). There's some possibility for lower dewpoint air to mix down from aloft during the peak of the heat, but evapotranspiration off a ground that has seen much rain over the past week should at least somewhat compensate and keep dewpoints high enough to have a positive contribution to the heat index.

We issued a Heat Advisory for much of central PA valid Tuesday. For places like BFD, where the record high for Tuesday is 89 set in 1979, the forecast of 90 degrees would not only break the daily record but also match the hottest observed temperature YTD. This was a contributing factor in our decision to issue the Heat Advisory even for places where the heat index doesn't quite exceed 100 degrees. The higher chances for Heat Index over 100 degrees appear to be at lower elevations within the central ridge/valley region, as well as within the Susquehanna Valley (places like Selinsgrove and Williamsport). We excluded the Lower Susq Valley and the Laurel Highlands from the advisory on Tuesday because their forecast Heat Index is forecast below 100 degrees and temperatures substantially below their daily records (by 5-10 degrees).

Expansion of the Heat Advisory to the south and east is possible for Wednesday. Hot air will continue spilling over the ridge from the northwest, with the max anomalies shifting toward the south and east. Heat index values above 100 degrees are possible for much of the Lower Susq Valley and as far north/west as Williamsport/State College/Altoona. One complicating factor is the arrival of drier air with a cold front pushing in from the north. Latest NBM guidance has Td dropping from the mid 60s at 12z to the mid 50s F by 21z across the northern tier. Places south of Interstate 80 are more likely to see Td remain in the mid 60s to low 70s through the peak heating Wed afternoon.

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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.

Behind the cold front on Thursday, expect T and Td to both be a few degrees lower than Wed. But, there is still uncertainty with the exact placement of this front, and it may be close enough on Thursday and Friday to touch off some showers and thunderstorms esp across the southern tier. Day 6 (Fri-Fri night) SPC Outlook paints a 15% chc of severe weather for the SWrn quarter of the CWA. PoPs increase into the weekend as active weather remains possible within a thermal gradient between hot air to our southwest and much cooler air to the north.

AVIATION /12Z MONDAY THROUGH FRIDAY/

VFR conditions expected to prevail through the majority of the 13/12Z TAF period. Some fair wx VFR cumulus will likely develop with diurnal heating by late morning particularly over western and northern PA. A stray, slow moving shower/t-storm is possible during the afternoon and evening over northern Pennsylvania, but latest probs/confidence in sigwx or flight cat impact in the vicinity of KBFD is below 30% (so did not include PROB30 group).

Outlook...

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

Fri-Sun...Chance of showers and t-storms.

CLIMATE

Daily record high max temperatures July 14-16 _____________________________________________ SITE|7/14|7/15|7/16| --------------------------------------------- MDT | 101/1954| 99/2024 | 104/1988 | --------------------------------------------- IPT| 102/1936| 103/1995| 103/1988| --------------------------------------------- AOO| 95/1954| 98/1995| 100/1988| --------------------------------------------- BFD| 89/1979| 88/2013| 97/1988| --------------------------------------------- STCP1| 93/1988| 97/1887| 102/1988| ---------------------------------------------

CTP WATCHES/WARNINGS/ADVISORIES

Heat Advisory from 11 AM to 8 PM EDT Tuesday for PAZ004>006- 010>012-018-019-027-028-037-041-042-045-046-049>053-056>059.