textproduct: State College

WHAT HAS CHANGED

Dense Fog Advisory issued for a portion of the west-central Alleghenies early this morning; rainfall totals trended a bit lower for Monday

KEY MESSAGES

1) Hazardous driving conditions due to reduced visibility in dense fog across the west-central Alleghenies early this morning

2) Locally heavy rainfall and strong to marginally severe thunderstorm wind gusts remain possible over south central PA Monday afternoon/evening

DISCUSSION

KEY MESSAGE 1: Hazardous driving conditions due to reduced visibility in dense fog across the west-central Alleghenies early this morning

Combination of IR satellite and ASOS+RWIS observations prompted the issuance of a dense fog advisory (DFA) for a portion of the west-central Alleghenies early this morning. With astronomical summer officially underway (as of 424AM EDT) and the shortest night of the year nearly over, expect dense fog to dissipate by 8AM.

-------------------------------------------------------------------

KEY MESSAGE 2: Locally heavy rainfall and strong to marginally severe thunderstorm wind gusts remain possible over south central PA Monday afternoon/evening

Excessive rainfall concerns remain focused over south central PA on Monday PM where best overlap of high pwats and instability will exist per HREF/REFS. This area also remains in a level 2 of 4 ERO from WPC. A limiting factor is the ongoing dryness and D1/D2 drought conditions over the LSV. This setup most likely favors urban areas with the best chance to experience flash flooding. Rain rates of 1-2 in/hr could lead to localized 2+ inch amounts over a short duration - and in the right location would result in at least some runoff issues. QPF has trended lower on the margin, so there is still some uncertainty in play with decreasing instability with northern extent. In terms of severe storm potential, the best combination of shear and CAPE is located just south of the MD line where SPC has placed a level 2/SLGT risk. The exact location of the warm sector will be a key factor and ultimately modulate overall severe storm risk.

AVIATION /07Z SUNDAY THROUGH THURSDAY/

VFR conditions will prevail for the vast amount of time through this 06Z TAF cycle, though some impacts from areas of valley fog are possible at a few airfields through about 12-13Z. Included VCFG for several hours at KBFD, KAOO, KUNV and KIPT with prevailing vsbys likely only dipping to around 6SM.

or the daylight hours today (and in contrast to Saturday) we will reside under the descending right exit region of an upper level jet into the early/mid afternoon hours with slight height rises ahead of a flat Ohio Valley ridge.

As the jet segment shifts to the ENE this afternoon and a few- svrl hundred j/kg of MU CAPE develops after 18Z, the thermally direct branch of the jet (and its rising portion associated with the right entrance region) will lead to some isolated -SHRA across mainly the Ncent Mtns of PA. Any low-topped convection will dissipate early this evening followed by a gradually thickening deck of mid and high clouds later tonight into Monday.

Periods of steady light to moderate rain will follow for Monday as much of the CWA stays in the cool stratiform precip regime with sfc low pressure moving out of the Ohio Valley and tracking across Central PA and possibly the Poconos.

The SE half of the state should see some instability as fleeting breaks of sunshine develop Monday afternoon. This could result in a small tornado threat as any strong TSRA that form (will move east/NE over a quasi strnry frontal boundary that will extend east from the aforementioned low - across the Scent Mtns and Southern Poconos or Lehigh Valley) could ingest the favorable shear and tilt/stretch it vertically creating some low-topped supercells.

Areas of low ceilings and to a lesser degree areas of low visby will impact all central PA airfields to some extent Monday through Monday evening.

Outlook...

Sun...Showers and thunderstorms after Midnight over the Central and Western portions of the state.

Mon...Restrictions likely with a few periods of rain/or showers and thunderstorms.

Tue...Lower chances of showers, mainly VFR.

Wed...Mainly VFR, watching for precipitation chances though in the evening/overnight.

Thu...Restrictions possible in another round of daytime showers.

CTP WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 8 AM EDT this morning for PAZ004>006- 010>012-017>019-024>027-045.