textproduct: State College

WHAT HAS CHANGED

* Severe thunderstorm watch #83 has been cancelled

KEY MESSAGES

1) Big temperature swings and periods of rain/thunderstorms continue through Easter weekend into the first full week of April

DISCUSSION

KEY MESSAGE 1: Big temperature swings and periods of rain/thunderstorms continue through Easter weekend into the first full week of April

At the surface, a quasi-stationary front will be located from southern Indiana east-northeastward into southern Pennsylvania by the afternoon. Surface dewpoints in the upper 50s and lower 60s F to the south of the front will contribute to weak instability. Increasing low-level convergence near the front and warming surface temperatures into the 70s should trigger scattered thunderstorms. 0-6 km shear in the 25 to 35 knot range and steep low-level lapse rates will support isolated strong to severe storms with potential for damaging wind gusts focused within west-east corridor to the south of I-80 to MD line. Periods of rain/showers continue tonight into Thursday morning.

The first big temperature swing is expected Thursday with max temps +/- 20 degrees in the NW and SE corners of the CWA. CAD pattern behind east/southeast low level flow will drive cool/moist air (highs 50-60F) into the eastern half of the forecast area while downslope along and west to the Allegheny Front sends temps into the 70-80F range in western PA. Big temp swing #2: A major surge of warmth for early April returns to CPA into Easter weekend with max temps fcst to approach and potentially break daily records Friday and Saturday, April 3-4 (see climate section). A more intermittent, limited coverage rainfall pattern is likely Friday into early Saturday.

Big temp swing #3 arrives Easter Sunday into Monday as a strong cold front shifts eastward across the Appalachians to the Atlantic coast. Rain and thunderstorms should accompany the cold front across CPA on Sunday followed by noticeably cooler air. A severe storm threat may develop depending on the degree of pre-frontal destablization. Low temps Sunday night (Monday morning) will be -15 to -20 degrees cooler than Saturday night (Sunday morning).

The cooldown lasts into early next week (first full week of April) with max temps fcst below the historical average Monday and Tuesday.

AVIATION /07Z WEDNESDAY THROUGH SUNDAY/

As of 1245 AM just adjusted the TAFS for current conditions and expected conditions.

Thinking is much of the current activity will weaken and spotty showers will linger across the central and southern sections of central PA but less likely across the north prior to 00Z Thu.

CIGS likely to lower at time goes on, as temperatures hold steady or cool.

For later on after 00Z Thursday, some models hint at another band of showers setting up across the northwest part of PA into the southern tier of NY. Will look this over and adjust more for the 12Z TAF package.

Earlier discussion below.

Ceilings and visibilities will lower from north to south through 00z Thursday as the cold front slowly moves southward across the region, with the front reaching the Northern Tier around 08z Wednesday, then to the Lower Susquehanna Valley by 00z Thursday. Highest confidence in MVFR for the TAF period is at KJST due to upslope westerly winds and orographic lift, and at KBFD where cool/moist air will be further entrenched behind the cold front. LAMP guidance also highlights IFR being possible at KBFD after 09z (50% chance), particularly between 11z and 14z where probabilities rise to 60-70% for IFR, corresponding to the diurnal minimum. On the other hand, KMDT and KLNS are expected to remain in the warm sector for much of tomorrow, staying VFR through much of the period. With that said, the LAMP suggests an increasing chance (30-40%) for MVFR at these southern sites by 22z Wednesday when the cold front may pass through. Winds will shift from west-southwest to north as the front passes over air sites in the region, with sustained winds generally between 10-15 kts.

In terms of precipitation tomorrow, scattered showers are expected to continue across the Commonwealth, with the focus for renewed convection over the Lower Susquehanna Valley (KMDT/KLNS) primarily after 18z. The HREF shows SBCAPE values of 500-1000 J/kg within that area, which would be sufficient for thunderstorms, though coverage and timing uncertainties preclude further details in the TAF.

Outlook...

Thu-Sat...Numerous SHRA with restrictions possible, especially on the cool side of a frontal boundary that oscillates across central PA during this timeframe.

Sun...Restrictions possible with showers and thunderstorms ahead of a strong cold front.

CLIMATE

Daily record max temperatures for April 3rd and 4th:

SITE APRIL 3 APRIL 4 Harrisburg 86/1963 | 82/1999 Williamsport 83/1963 | 84/1921 Altoona 81/1963 | 80/1950 Bradford 80/2010 | 72/1981 State College 79/1963 | 81/1910

CTP WATCHES/WARNINGS/ADVISORIES

None.