textproduct: State College

WHAT HAS CHANGED

* Added more details for the severe thunderstorm potential this afternoon and evening, with a mesoscale update. * Increasing confidence in heavy rainfall signal across portions of central Pennsylvania, with highest uncertainty in the exact placement of this heavy rainfall.

KEY MESSAGES

1) Hot and humid conditions for Independence Day will bring another round of strong-to-severe thunderstorms with an increased risk for damaging winds.

2) Chances of showers and storms become more widespread on Sunday and Monday, bringing both severe and flooding concerns for the end of the weekend and into the first of next week.

DISCUSSION

KEY MESSAGE 1: Hot and humid conditions for Independence Day will bring another round of strong-to-severe thunderstorms with an increased risk for damaging winds. A Severe Thunderstorm Watch is in effect for portions of western Pennsylvania.

Current heat index values in the upper 80s to lower 100s across central Pennsylvania are currently being observed as of 1PM, which jives well with out current heat products (see NPWCTP) in effect through 8PM this evening. In short, very few changes to the temperature/dewpoint forecasts with the main changes in near-term dewpoints with the NBM pushing two to three degree to warm and pushing heat index values higher than could be expected across portions of northwestern Pennsylvania. At this time, products look good to be dropped this evening with no heat products expected to be issued for tomorrow. It will still be warm and humid; however, with heat index values still reaching into the mid-to-upper 90s across the Lower Susquehanna Valley, so still good to continue precautions for heat-realted illnesses given the duration of this heat wave.

In terms of severe threat, today's set-up looks fairly similar to yesterday's in the fact that we are looking at an ample amount of instability and not the most favorable shear profiles across central Pennsylvania. We'll likely see some initial cells starting to pop-up over the next couple of hours both across northwestern Pennsylvania and southwestern Pennsylvania. These cells could initially struggle and have more of a pulse thunderstorm nature at first given the lack of favorable bulk shear; however, generally expectations are for some stronger- to-severe thunderstorms to begin to form and sustain themselves into the late afternoon and evening hours. Recent SPC Mesoanalysis outlines extremely favorable DCAPE values, in the 1200-1400 J/kg range across portions of southern Pennsylvania as of 17Z/1PM EDT. This indicates that while coverage of storms remains uncertain moving into the afternoon hours, damaging wind potential within storms will be extremely plausible given favorable DCAPE values and higher LCLs that would promote downburst potential. For thunderstorm development across northwestern Pennsylvania, DCAPE values are not as impressive, but still soar fairly well into the 900-1000 J/kg range which will still be sufficient for some downburst potential, especially with *slightly* more shear up that way. MCD#1492 from SPC generally mirrors those thoughts. This threat will gradually shift towards eastern Pennsylvania later this evening, where similar sentiments with regards to if there is a thunderstorm, damaging winds are plausible continue.

Storms today will likely bring some locally heavier downpours with storm motion likely between 25-40 knots, thus while we cannot rule out some localized flash flooding, this would be limited to areas that receive multiple rounds of stronger thunderstorms. Ample low-level moisture overnight will bring some potential for locally dense fog across the ridges of central Pennsylvania with could make travel tonight into Sunday morning hazardous for those driving to/from locations with Independence Day activities.

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KEY MESSAGE 2: Chances of showers and storms become more widespread on Sunday and Monday, bringing both severe and flooding concerns for the end of the weekend and into the first of next week.

Recent HREF ensemble guidance and hi-res model guidance indicate some precipitation around the area late Sunday morning into the early afternoon hours before a general increase across the board on shower/thunderstorm coverage. The air mass across central Pennsylvania will be fairly moist, with HREF guidance indicating PWATs approaching in the 1.50-1.75" range across N/W PA with some locations in SE PA approaching 1.75-2.00" PWATs by the afternoon and evening hours. For reference to climatology if this solution pans out, this would be in the 90th to 95th percentile for PWATs for the beginning of July. Recent NBM QPF forecast brings 1.50-2.00" of rainfall into portions of SE PA on Sunday, with heaviest rain expected in the afternoon and evening hours with some heavier rain considering overnight into Monday morning. This heavy rain signal is matched in recent HREF ensemble guidance, with 24 hour LPMMs outlining some spot amounts between 3-4" for this same timeframe. This signal for heavy rain will bring some flooding concerns to the more urbanized corridors of SE PA, which is matched in the Slight Risk for Excessive Rainfall from WPC. The main thing that would preclude flooding concerns would be the fact that this area is in Severe (D2) Drought based on the most recent Drought Monitor; however, heavy rain will still very well cause instances of flash flooding. This heavy rain signal will be in place on Monday; however, slightly less rainfall forecast on Monday and will have to see what rainfall this evening though Sunday brings to the region before reading too much into this threat. There also will be some severe threat stationed across southern Pennsylvania, mainly south of the I-80 corridor with damaging winds being the main concern given ample instability in place.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Back to aviation after brief break from earlier aviation duties.

Main change was to adjust fcst to current obs and radar. Severe storms in the MDT area and just a few minutes away from LNS.

Earlier information below.

For the 18Z TAF package, main change is to slow down the start time of showers and storms. This based on a similar pattern to what we had yesterday. Also lower dewpoints and more of a NW wind so far today. Yesterday storms fired up across the north during the early to mid afternoon hours, and stayed northeast of MDT and LNS.

Another set of storms moved eastward into central PA toward UNV by late evening.

The airmass so far today has dewpoints lower than the last few days. Maybe not a huge factor for humans, but storms are happy with the more humid airmass, thus a slight change in moisture can lead to large changes in the outcome.

The other change was to add more detail later tonight into Sunday, where some fog and lower CIGS possible, mainly in spots like BFD and IPT and in areas that get some rain.

Lower CIGS Sunday could occur and linger behind the front if widespread showers form early enough, before heating takes hold. Poor conditions could occur from time to time right into Tue, before some improvement by mid week.

Outlook...

Mon-Tue...Restrictions possible in A.M. fog and P.M. T-storms. Wed-Thu...Improving conditions expected.

CLIMATE

Williamsport tied their record max 7/3/26 (100F in 1966).

Record maxes for the next few days:

Station/Date...07/04...07/05 MDT.............104.....102 IPT.............100.....100 AOO............. 97......94 JST.............100.....101 BFD..............91......91

CTP WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM EDT this evening for PAZ019-025>028- 034-045-046-049>053-058. Extreme Heat Warning until 8 PM EDT this evening for PAZ035- 036-056-057-059-063>066.