textproduct: State College

WHAT HAS CHANGED

* Severe threat this aftn/evening bumped up to slight risk for the NW mountains. * Added more precip to the morning hours in the NW. * Refined timing on cold frontal precip

KEY MESSAGES

1) Numerous showers and thunderstorms will affect Central PA today and tonight. Some may be severe, especially in the northwestern third of CTP CWA.

2) Cold front moves through later tonight and early Easter Sunday. Much colder next week but warming up again by week's end. Light snow likely across the northern tier Monday/night.

DISCUSSION

KEY MESSAGE 1: Numerous showers and thunderstorms will affect Central PA today and tonight. Some may be severe, especially in the northwestern third of CTP CWA.

Warm front laying across Central PA this morning will be lifting to the north and east. Current cold side of things has temps in the L50s, and the warm side nearer to 60F. Some patchy dense fog is around Leb and Lanc counties at 5 AM. May have to post a quick DFA if things get murky over a wider area.

The warm front is a focal point for showers and thunderstorms. A trough aloft will pass overhead this morning and enhance the lift and expand/advect the rain in from western PA. As the showers lift away, breaks in the clouds should allow for diurnal convection. The first places to see deep convection form today will likely be the hill tops of the south-central mountains. Maxes in the L80s in the S will be close to record maxes (see below). The dewpoints will also be rising as the wind becomes more-southerly through the day. The storms in the south-central mountains will be displaced from the best shear, but likely have some of the best instability/CAPE for the day. These expand and move northward through all of the central mountains. That should get them into some of the better shear, but also put them into the colder/more stable air. If one is on top of the warm front, it could have some enhanced low level shear and have more potential to make a strong updraft and perhaps a risk for a tornado. Heavy rain is also possible, and may lead to minor flooding in spots where more than one downpour occurs.

A second round of storms is expected to flare up in the NW where a strong cold front will be moving in during the late evening hours. Some storms in the warm sector/ahead of the cold front could have supercellular characteristics, but the main threat will be wind damage. The front will be the main focus for severe weather in the evening and early nighttime. Storms reach Warren Co just after 00Z and Coudersport/Clearfield by midnight. The showers/storms along the front continue eastward at a slow clip, and may not get to Harrisburg until 12Z. But, they'll only spend 2-3 hrs there before leaving the CWA around noon on Easter.

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KEY MESSAGE 2: Cold front moves through later tonight and early Easter Sunday. Much colder next week but warming up again by week's end. Light snow likely across the northern tier Monday/night.

The air behind the cold front is going to make temps fall throughout the day over all but the Lower Susq. Temps probably peak in the Lower Susq in the morning and fall after the rain starts and then continue falling through the day. Mid aftn temps will be in the L40s NW and ~60F in the SE. Sfc low will pass way to our N, but the cente of the cold dome will slide to our S. Still, 8H temps drop to -8C along the NY border, and -4C in the S. Maxes on Monday will have some bust potential. Blended guidance mean maxes of 40F N and U50s S seems ripe for a bust with such cold temps aloft. Wild cards include: we may not mix to 8H that day, the April sunshine will try to do it's best, and downsloping in the Lower Susq.

A Clipper-like system dives across the Upper Great Lakes and into NY/PA later Mon/MOn night. After that, the flow favors lake-effect showers. The temps will be cold enough across the nrn tier of counties to allow it to be mostly snow anytime by the middle of the day. Some accums of <=1" should occur on the hills of the north, but that will be along a 48-hr stretch. Some snow may mix into the mostly-rain showers in the central mtns and Laurels Mon night. Dry and cold Tues with low RHs (m20s-30s), and a little warm up on Wed will result in even lower RHs (20s).

AVIATION /08Z SATURDAY THROUGH WEDNESDAY/

Overnight, the highest confidence for flight restrictions is across the Northern Tier (KBFD), where IFR to potentially LIFR ceilings are likely (60-70% chance) on the cool side of a weak frontal boundary which has passed through. For KIPT and our Allegheny Front sites (KAOO/KUNV), flight restrictions are less certain due to the impact of transient cloud cover. At 05Z, KIPT briefly dipped down to 1SM with clear skies overhead, followed by a rebound to VFR as a BKN035 cloud deck moved overhead. The HRRR and 3km NAM suggest that the weak frontal boundary will cross KIPT between 07-08Z, with visibilities improving to VFR thereafter due to boundary layer mixing and continued cloud cover. Across the Lower Susquehanna Valley (KMDT/KLNS), lighter cloud cover, calm winds, and mild/moist air may lead to low stratus and fog development through 12Z, with the LAMP showing moderate to high (40-70%) probabilities for IFR/LIFR, particularly at KLNS.

By 18Z Saturday, VFR is expected areawide, especially across our southern terminals (KJST/KAOO/KMDT/KLNS), with a low (20-30%) chance for MVFR to linger through 18Z across our northern terminals (KBFD/KUNV/KIPT). Scattered showers and thunderstorms are expected to develop across central PA between 18Z-00Z, with the HREF depicting an axis of confluence across KAOO/KUNV/KIPT, which may serve as a focal point for development within an environment of SBCAPE around 1000 J/kg. For this reason, PROB30s for -TSRA were introduced at these terminals.

Between 00Z-06Z Sunday, flight restrictions are possible as low-level moisture transport increases ahead of an approaching cold front, with ceilings down to MVFR being the most probable at this time. Moreover, a backdoor cold front may push into the Lower Susquehanna Valley (KMDT/KLNS) after 00Z, potentially extending as far west as KUNV by 03Z, which could reinforce MVFR flight restrictions at these terminals.

Outlook...

Sun...Restrictions possible with showers and thunderstorms ahead of and along 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.

Wed...VFR.

CLIMATE

Here are the warmest high and low temperatures recorded for April 4th at area climate sites:

SITE LOW HIGH Harrisburg 60/1974 | 82/1999 Williamsport 62/1981 | 84/1921 Altoona 61/1974 | 80/1950 Bradford 50/1981 | 72/1981 State College 57/1999 | 81/1910

CTP WATCHES/WARNINGS/ADVISORIES

None.