textproduct: State College

WHAT HAS CHANGED

* Added ridgetop fog tonight through Saturday * Minor adjustment to temperatures down a bit tonight and Saturday

KEY MESSAGES

1) Noticeably cooler into Memorial Day weekend with record challenging cold max temperatures on Saturday

2) Widespread soaking/beneficial rain dampers outdoor plans and activities to start Memorial Day weekend

3) A bit warmer for Sunday and Memorial Day

DISCUSSION

KEY MESSAGE 1: Noticeably cooler into Memorial Day weekend with record challenging cold max temperatures on Saturday

Model data shows the anomalous high pressure channeling southward down the east side of the Appalachians, setting up a classic cool wedge/cold air damming (CAD) pattern into Memorial Day weekend. We continue to reiterate a bearish outlook for daytime temps Sat-Sun with record challenging cold maxT fcst for Saturday (see climate section below).

850 mb show a highly anomalous V-component (wind from the SSE) at 18Z Sat with Standardized Anomalies of +3-4 St deviations over Central and NW PA, while winds around 925 mb highlight negative U anomalies of the same magnitude (from the ESE).

This will create an expansive llvl CAD regime with strong moisture advection aloft, leading to steady light to moderate rain/drizzle. The moderately gusty east/southeast wind will make it feel downright dreary/raw, unseasonably chilly and pretty miserable for this time of year - especially for outdoor activities Friday afternoon through Sunday morning.

The 2-3 day cool stretch will certainly be noticeable following an early taste of summer, but it won't have staying power with temperatures forecast to moderate and trend above normal into the middle of next week.

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KEY MESSAGE 2: Widespread soaking/beneficial rain dampers outdoor plans and activities to start Memorial Day weekend

Leading edge of the steady rain just south of the office, Tussey ridge most likely holding in checkmake for a bit longer.

Expect rain to spread northward through the evening into tonight. The rain will continue through the day on Saturday, with max QPF in the 12-18Z window per 6hr HREF PMM.

Expect widespread 1-2" rainfall totals which will be very beneficial for D1-D2 drought areas in the far southern tier into the LSV. Anomalous upslope east-southeasterly flow may result in locally higher rainfall amounts approaching 3 inches across portions of south-central PA. The precip pattern transitions from total washout with steady rain/drizzle Sat to more of a showery/low chance thunder regime for Sunday into Memorial Day.

KEY MESSAGE 3: A bit warmer for Sunday and Memorial Day

CAD wedge at low levels works out of the area on Sunday into Monday. While there will be a weak shortwave moving across the area, there is less support for widespread rain. More in the way of spotty showers, and temperatures being warmer.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

Rain has started across the southwestern airspace and will gradually continue to overspread the area. At onset, initial observations have trended towards low-end MVFR ceilings and expect this trend to continue throughout the evening. All model guidance points to further deterioration towards IFR/LIFR after 00Z Saturday. Recent 12Z HREF probabilities for IFR ceilings outline non-zero probabilities at all of central Pennsylvania's airfields, with highest chances (~80-90%) at BFD/JST/AOO with slightly lower chances (~30-40%) at UNV/IPT/MDT/LNS. Given this trend, have slowly introduced IFR ceilings at all airfields in the 18Z TAF package. The main uncertainty will be with respect to timing as model guidance has been particularly slow with precipitation onset, thus have made slight adjustment upwards in time in order to account for this model discrepancy.

Little improvement is forecast after sunrise tomorrow, with widespread LIFR-to-IFR conditions outlined by the bulk of model guidance. Recent HREF model guidance does indicate some potential for brief periods of MVFR; however, these timing window remain too short and too uncertain to warrant any mentions in this TAF cycle. In terms of winds, breezy winds are expected to pick up at all airfields overnight, with the most uncertainty in these winds increasing at UNV based on recent GLAMP model guidance. Given this, have increased wind gusts from previous forecast at all airfields, with gusts being included at MDT/LNS later on in the TAF package. Recent NAM/NBM model guidance does indicate potential for LLWS at BFD/JST/AOO after 09Z Saturday, thus have introduced these mentions in the TAF package with most uncertainty with respect to timing.

Outlook...

Sat...Widespread IFR/LIFR restrictions in steady rain

Sun...Minor improvement to MVFR/IFR restrictions as rain tapers off

Mon...IFR/MVFR early, then MVFR in light rain showers

Tue-Wed...Mainly VFR, some scattered SHRA could bring restrictions.

CLIMATE

Daily Record Low Maximum & Forecast Temperatures for May 23:

LOCATION RECORD (YEAR) FORECAST HIGH Harrisburg 54 (1982) 54 Williamsport 57 (1982) 53 Altoona 52 (2005) 51 Bradford 45 (1963) 49 State College 53 (1968) 51

CTP WATCHES/WARNINGS/ADVISORIES

None. A bit warmer for Sunday and Memorial Day