textproduct: State College

WHAT HAS CHANGED

Minor changes changes to the cloud cover forecast for the rest of the day.

KEY MESSAGES

1) A few showers over the region overnight.

2) Turning more humid and unsettled early next week with the highest probability for showers and thunderstorms Monday afternoon and evening and again on Tuesday and Tuesday night.

DISCUSSION

KEY MESSAGE 1: A few showers over the region overnight.

Broad, low-level streamline convergence with its N/S axis near the RT 219 corridor in Western PA has resulted in some showers since earlier this afternoon. Not real warm to the west this evening, but western areas have dewpoints into the lower 60s. compared across most of the Susquehanna Vly. Also while winds are rather weak, directional shear is there on the 00Z soundings this evening.

Surface convergence becomes more focused over the eastern half of the forecast area for tomorrow. Slightly higher dew points will allow for instability to be a little higher than it is today, possibly approaching 1000 J/kg in a few locations. Though upper level forcing looks to be weak, we would expect to see at least a few showers and thunderstorms develop during the afternoon. This location of the fcst activity is different than what was noted the other day. Location could shift more as we near Sunday aft.

KEY MESSAGE 2: Turning more humid and unsettled early next week with the highest probability for showers and thunderstorms Monday afternoon and evening and again on Tuesday and Tuesday night.

Main chance for widespread showers and storms will be Tuesday into Wednesday. Fcst dewpoints not all that high for late July, and there has been a slight downward trend with fcst dewpoins over the last few days.

Main things supporting showers and storms is a deepening low, and a large scale pattern that supports directional shear to be present into next week. Models today do show a pattern change out toward day 10, a change from recent model runs the last few days. Thus will have to seen if this trend holds.

Earlier discussion below.

Minor modifications for this period that will be highlighted by a warm front moving across western PA Monday afternoon/evening, followed by a rather potent/digging mid/upper level shortwave, that will support a sub-995 mb sfc low over the Lower Glakes and Western NY Tuesday afternoon and evening. Latest model runs have trended several hours or so slower compared to runs 24 hours ago.

The timing of the favorable lift associated with the thermally indirect, left front quad of the 80+ KT jet max moving across the Ohio Valley, WVA and southern PA Tuesday afternoon and evening will help to enhance a low level lee trough and convection along it. Scattered strong to severe TSRA are likely Tue afternoon and evening over at least the eastern half of the CWA with a second line of TSRA likely along the cold front across NW PA Tuesday afternoon.

AVIATION /01Z SUNDAY THROUGH THURSDAY/

For the 00Z TAF period, flight restrictions will be possible due to overnight fog (mainly across the Allegheny Front/Plateau for KBFD/KJST/KAOO, with localized fog with lower coverage possible around KMDT/KLNS downwind of the Chesapeake) and due to scattered showers/thunderstorms tomorrow afternoon (primarily along and downstream of a north-south oriented sfc trough situated near KUNV/KMDT/KLNS/KIPT tomorrow afternoon).

Spotty showers have developed along the sfc trough which will slowly continue eastward through tomorrow, with localized flight restrictions possible (20-30% chance) but not prevailing. Increasing moisture via light southerly flow will promote overnight fog development across the Allegheny Front/Plateau (mainly KBFD/KJST/KAOO), with lower confidence in fog development at KUNV/KIPT. A secondary moisture axis around KMDT/KLNS, where southerly flow may bring enhanced moisture from the Chesapeake Bay, may result in localized overnight fog in this area as well, with lower confidence in visibility restrictions at the terminals.

Overnight fog will mix out during the morning hours on Sunday, with prevailing VFR expected regionwide outside of any afternoon/evening showers/storms. Garden-variety, isolated instability showers are possible across the area, though shower/storm activity will mainly be focused around the north- south sfc trough over central PA, around KUNV/KMDT/KLNS/KIPT. Visibility restrictions from heavy rain would be the primary impact, though gusty winds primarily around 15-20 kts with variable wind direction may occur as well.

Outlook...

Mon...Restrictions likely in afternoon -SHRA/-TSRA. Patchy overnight fog possible.

Tue...Restrictions likely with scattered -SHRA/-TSRA.

Wed-Thu...Restrictions possible as -SHRA/-TSRA becomes less numerous. Patchy overnight fog possible.

CLIMATE

Cooler than average temperatures across the region led to multiple record low temperatures being broken for July 23rd and July 24th across central Pennsylvania.

On July 23rd:

* Altoona set a record low temperature of 47 degrees, breaking the previous record of 50 degrees set back in 1981.

* Bradford tied a record low temperature of 38 degrees which was previously set in 1981.

* Johnstown tied a record low temperature of 49 degrees which was previously set in 1983.

On July 24th:

* Altoona set a record low temperature of 47 degrees, breaking the previous record of 50 degrees set back in 1957.

* Bradford set a record low temperature of 41 degrees, breaking the previous record of 44 degrees set back in 1993.

CTP WATCHES/WARNINGS/ADVISORIES

None.