textproduct: State College

WHAT HAS CHANGED

* Expanded fog coverage this morning * Marginal risk of severe weather issued for Sunday

KEY MESSAGES

1) Valley fog this morning gives way to abundant sunshine 2) Comfortable and dry end to an active month of July 3) Rain most likely Sunday with increased risk of flooding downpours and isolated strong wind gusts

DISCUSSION

KEY MESSAGE 1: Valley fog this morning gives way to abundant sunshine

High pressure centered over the Ohio Valley is delivering calm winds and clear skies in the presence of sufficiently moist dewpoints to produce widespread valley fog this morning. Nighttime microphysics imagery depicts a classic radiational cooling/dendritic fog pattern in the valleys of northern PA where air-water temperature differences are plenty wide to support dense fog. We expect fog to continue to expand/spread southward through daybreak with impacts possible along/west of I-99 and along/north of I-80. Once the sun comes up, fog should mix out relatively quickly giving way to a gorgeous day.

KEY MESSAGE 2: Comfortable and dry end to an active month of July

High pressure remains in control today and tonight under mostly sunny skies and a seasonably warm day. With a retreating upper trough overhead, cool temps aloft will support some fair weather cumulus development this afternoon. Highs will range from the upper 70s at the highest elevations in northern and western PA to the upper 80s in the valleys of southeast PA. High clouds will begin to increase late tonight as a broad area of low pressure approaches from the Mississippi Valley, but no rain is expected until later Saturday.

July goes out like a lamb after a record-setting month. Our office issued 12 Tornado Warnings in July, which is the most since 1996 when we issued 25. 95 Severe Thunderstorm Warnings is the 3rd most in any July on record, behind 1996 (96) and 2021 (122). Year-to-date, 226 Severe Thunderstorm Warnings is the most on record, passing 2019 (221), and 24 Tornado Warnings is 4th most behind 1998 (55), 2011 (37), and 1996 (30). 250 total Severe Thunderstorm Warnings + Tornado Warnings is the most on record year-to-date, passing 2019 (241).

KEY MESSAGE 3: Rain most likely Sunday with increased risk of flooding downpours and isolated strong wind gusts

An axis of anomalous PW ~1.5" along and ahead of an approaching cold front combined with favorable upper dynamics should support active convection reaching CPA as early as late Saturday night with max POPs centered on the 24hr Sunday window. With some potential for training in the moist low level SW flow parallel to the front and increased vulnerability given recent very heavy rainfall, WPC introduced a level 2/4 excessive rain outlook (ERO) that covers northwest PA (mainly northwest of I-99/I-80). Exact timing and placement of max QPF remains a bit unclear as there are still some model differences regarding the evolution of the upper trough, but model guidance is starting to converge on swaths of up to 2-4" of rain across western PA.

Although flooding will likely be the primary threat, sufficient destabilization could result in an isolated risk of damaging straight-line winds as well. Curved wind profiles could also support an isolated tornado threat in the presence of relatively strong shear. The degree of clearing/destabilization will be the primary predictor of any potential severe weather threat. Morning clouds/showers lend low confidence in much of a threat and a Marginal Risk (level 1 out of 5) reflects that uncertainty/low ceiling.

AVIATION /07Z FRIDAY THROUGH TUESDAY/

Calm winds and clear skies have combined to generate widespread valley fog across mainly northern PA this morning. Conditions at KBFD have improved, but cannot rule out additional restrictions there as well as at AOO, IPT, and UNV through daybreak.

Once the sun comes up, fog will lift/mix out and give way to a seasonably warm and dry day. It will be ideal for flying with only light winds and perhaps a few fair weather cumulus clouds. High clouds stream in overnight, but VFR conditions prevail.

Outlook...

Sat...Mainly VFR early with increasing chances of SHRA/TSRA later in the evening hours. Restrictions possible.

Sun...More widespread SHRA with PM TSRA possible, increased chances of restrictions in heavier SHRA/TSRA.

Mon...AM SHRA with PM TSRA possible. Restrictions possible, especially SE where chances for SHRA/TSRA are higher.

Tue...Upper-lvl low over the Ohio Valley may bring SHRA/TSRA with possible restrictions to the Commonwealth, though lower confidence in SHRA/TSRA compared to previous days.

CLIMATE

Here are a few key callouts to wrap up the month of July:

6th wettest at Altoona 2nd wettest at Bradford 10th wettest at State College

6th most # of days with maxT >=100F at Harrisburg (3) T3rd most# of days with maxT >=100F at Williamsport (2)

CTP WATCHES/WARNINGS/ADVISORIES

None.