textproduct: State College

WHAT HAS CHANGED

* Certainty in a non-diurnal temp trend on Sunday is high. * Slowed the heating/mixing in the E/NE zones by a few hours today as cold air damming does not usually give up easily. * Added mentions of gusty winds/small hail to the thunderstorms on Sat.

KEY MESSAGES

1) The cold air dam breaks today. Weak forcing touches off a few rounds of showers and thunderstorms.

2) Temperatures near record levels on Saturday, mainly in the south, ahead of a strong cold front which will pass through on Easter morning.

3) Colder next week but warming up again by week's end.

DISCUSSION

KEY MESSAGE 1: The cold air dam breaks today. Weak forcing touches off a few rounds of showers and thunderstorms.

Deep easterly flow continues to keep the eastern half of the area in the cold wedge. Temps haven't moved much overnight in the eastern and central zones. They will likely struggle to rise as fast as guidance has them doing thanks to the pesky cloud cover. The clouds will take many hours to burn away in the Poconos and northeastern mountains. But, the mixing will help temps get very warm in the afternoon, especially in the west and south. Showers over the NW this morning will creep a little to the east, but dwindle as they do so. Thanks, stability. There will be a slight nudge from some additional, but shearing, forcing. That is currently generating storms over IL/IN. That will be the kicker to help the well-mixed atmosphere this afternoon and early evening to reach it's full but limited potential. The weak forcing will be timed right with peak heating. The topography gives a helping hand to convective initiation, and warm temps and almost-60F dewpoints supply fuel. Mixed-layer CAPEs get in the 500-1000 J/kg range over the west. But, the deep-layer shear will be decreasing at the same time. So some storms could get tall, and generate some gusty winds. This is most possible in the Laurels where it all come together. Still, it's only worth a MRGL risk of severe storms today. --------------------------------------

KEY MESSAGE 2: Temperatures near record levels on Saturday, mainly in the south, ahead of a strong cold front which will pass through on Easter morning.

A weak trough/front over the area tonight will move northward and allow much warmer air in for Saturday. If we set record maxes, they would more likely occur Sat than Fri. Maxes in the 70s N and 80-85F S. Clouds in the morning will mix away before popping up in another life in the afternoon heating. Shear of 30KTs or so in the north and 20 in the south, but CAPE progged in the S will beat that up north. Overall, the numbers only yield a(nother) SPC MRGL risk day, but it covers all of Central PA for Day2 (Sat).

The warm air will linger into the nighttime. But, by Sunday morning, a strong cold front will be crossing the CWA from NW- SE. The precip along the front will still have some instability, so we left mentions of thunder in there. Temps on Easter Sunday will be headed downward, losing 6-8F through the whole day. Not a terrible rate, especially when it starts out very mild (in the SE half). The band of rain/showers along the front should be off to the SE of the CWA in the afternoon. Hold onto your bonnets, as there will be some gusts into the 20s as the cold air moves in. Lows Sunday night U20s N, U30s S.

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KEY MESSAGE 3: Colder next week but warming up again by week's end.

From a precipitation perspective, scattered rain and/or snow showers are possible Monday and Tuesday. A trough crossing the Great Lakes will slide across PA during the Monday-Tuesday time frame and should generate some SHSN. Temps will only be favorable for an accumulation during the overnight periods. Tuesday will be the coldest day with maxes not out of the 30s in the nrn tier counties and only near 50F in the far S. Wednesday morning will be the coldest under high pressure with mins below freezing everywhere. This will occur about 3 days before the climatological average date of the last freeze, so we'll be right on track. Thursday morning could be that cold, too, but that depends on just how fast the high slides to the east. For now, we'll hang with the NBM/WPC guidance mins then (30s). The outlook trends warmer for the end of work week with some showers in the north.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Flight categories will improve west to east between 12-18Z Friday as cold air damming erodes, with high confidence (>80%) of VFR prevailing across most of our airfields after 18Z. Confidence of VFR is more moderate (50-60%) at KBFD, where convective activity and higher moisture could limit cloud ceiling heights to MVFR.

Scattered convection is expected to develop across north-central and western PA after 18Z, driven by peak diurnal heating and increasing instability. Showers with a few thunderstorms are possible, especially near KBFD where SBCAPE of 500-1000 J/kg and steeper 0-3km lapse rates will be in place, though scattered thunderstorms will also be possible at KIPT and KUNV later in the day as convection advances eastward. Given the scattered, loosely organized nature of this convection, PROB30s have been used at these sites to signal at the thunderstorm potential, though timing and coverage will be determined with later TAF packages.

From 00Z Saturday to the end of the TAF package, flight categories are moderately likely (50% confidence) to deteriorate to at least MVFR across our airfields as wind diminishes overnight with the mild, moist air mass in place. The highest confidence in flight restrictions is across the Northern Tier (KBFD), with IFR likely (60-70%) by 06Z. Moreover, lighter cloud cover across the Lower Susquehanna Valley (KMDT, KLNS) could contribute to low stratus and fog development, with the LAMP showing a low to moderate (30-40%) chance for at least IFR visibilities between 09Z and 12Z.

Outlook...

Sat...Restrictions possible in the morning due to light winds and low-level moisture, with VFR in the afternoon outside of scattered showers and thunderstorms..

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

Mon...Breezy and cooler with MVFR N/W and VFR elsewhere, with scattered rain/snow showers possible.

Tue...Mainly VFR with a few rain/show showers.

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

Dense Fog Advisory until 11 AM EDT this morning for PAZ058.