textproduct: State College

WHAT HAS CHANGED

* Trending drier late week

KEY MESSAGES

1) Periods of rain today through Wednesday. Greatest areal coverage tonight.

2) Trending drier later in the week as a coastal storm develops offshore.

DISCUSSION

KEY MESSAGE 1: Periods of rain today through Wednesday. Greatest areal coverage tonight.

What remains of an MCV that dropped 3-5 inches of rain in OH/WV will move into the Laurel Highlands this morning and spread northward towards I-80 through the day. Given the lack of instability in central PA, rainfall rates will be on the light side, generally up to 0.25 inch/hr. We expect an uptick in areal coverage of the rainfall tonight as the pressure gradient between a subtle low pressure system moving into Ohio and a building high to our north results in increasing upslope SE flow at 850 mb. This will be coupled with isentropic ascent and some frontogenesis in the 800-600 mb layer. Even during max areal coverage, rain may struggle to get to the PA-NY border due to a sharp cutoff in moisture (PW values near 1.50" along I-80 vs 0.60" at the PA-NY border at midnight tonight). Periods of rain will continue through much of Tuesday before the dry air to our north surges southwestward late Tuesday night into Wednesday. Highs on Tuesday will be in the 50s to low 60s, perhaps the coolest afternoon since late May. Lingering showers on Wed will likely be confined to the Laurels. Highest forecast QPF in the Monday- Wednesday time frame is 1.00-1.50 inch in the Laurel Highlands, with locally higher amounts of 2.00 inches possible if some elevated instability moves into the region.

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KEY MESSAGE 2: Trending drier later in the week as a coastal storm develops offshore.

Northeast flow Wednesday into Thursday between 1038 mb high in Quebec and a developing coastal low will advect in dewpoints in the 40s and perhaps even the 30s at the sfc Wed-Thu, with even drier air in the 500-850 mb layer. This should bring an end to the rainfall for at least a couple of days. The next feature to monitor will be the coastal storm, which may meander off the New England and Mid Atlantic coast into the early part of next week with this blocking high to its north. Such blocky patterns are notoriously difficult to predict with respect to sfc features and precip potential/placement/timing. Depending on the size of the coastal storm and how much it retrogrades, rain will be possible in at least east central PA between Fri and early next week, but confidence is low. Higher confidence in wind gusts of 15-25 mph and below normal temps through the end of the week.

AVIATION /07Z MONDAY THROUGH FRIDAY/

N/NE'erly surface winds will guide drier/continental air southward across much of the Commonwealth through Monday morning, with dewpoints trending down into the 50s areawide. Although conditions will trend drier near the surface, lingering moisture aloft will blanket much of the area in mid/high clouds (VFR), with sub-VFR ceilings favored throughout the day along the Allegheny Ridge terrain (mainly MVFR for KJST/KAOO, and perhaps IFR at KJST). Moreover, periodic MVFR is possible through Monday morning at KMDT/KLNS downwind of the Atlantic Ocean.

Another round of rain will gradually overspread the southern 2/3rds of the Commonwealth throughout the day on Monday as a low pressure drifts across the Mid-Atlantic, with a stout 1030-1040 mb high pressure over southern Canada looking to keep the Northern Tier (KBFD) mainly dry. Surface winds will trend E/NE'erly at the surface Monday night and bring marine air back into much of our area, with mid-level (850 mb) SE'erly flow also helping to slowly bring moisture back north. This looks to favor a trend towards MVFR-IFR across all terminals Monday night as moisture rebounds.

Outlook...

Tue-Thu...Restrictions possible from -SHRA/BR and low ceilings, mainly S.

Fri...VFR favored as a developing coastal low looks to bring subsidence overhead, though -RA and lower cloud ceilings associated with this system may reach our eastern terminals.

CLIMATE

As of 5 PM, 1.05 inches of rain fell at AOO (Altoona) PA today. This broke the old record of 0.73 inches set in 1957.

CTP WATCHES/WARNINGS/ADVISORIES

None.