textproduct: State College

WHAT HAS CHANGED

* Decreased snowfall totals slightly in the lower elevations of south-central PA as well as in the Lower Susquehanna Valley.

KEY MESSAGES

1) Moderate to heavy snow continues today and tonight as low pressure develops off of the east coast.

2) Multiple chances for rain and snow throughout the coming week.

DISCUSSION

KEY MESSAGE 1: Moderate to heavy snow continues today and tonight as low pressure develops off of the east coast.

Accumulating snow so far today has largely been confined to the northern and western mountains, while a shallow warm layer near the surface for areas farther to the southeast has resulted in precipitation falling mainly in the form of rain. We still expect a quick changeover to snow across the Lower Susquehanna Valley later this afternoon as an area of low pressure rapidly deepens off the coast and pulls colder air into the region from the northeast.

Three areas of higher snowfall totals are expected across the region, with relative minimums in between. The first is in the Laurel Highlands where northwest flow on the back side of the coastal low will support a prolonged period of upslope snow into early Tuesday morning. Total snowfall amounts of 8 to 12 inches are expected along the ridges of Cambria and Somerset Counties.

The second maximum will be found from the Franklin and Adams Counties northward through eastern Centre and Clinton Counties. This is associated with an inverted trough that is developing and will slowly pivot across the region through the afternoon and evening. The enhanced low-level convergence associated with this feature has allowed for a couple of quasi-stationary snow bands to develop this afternoon which should slowly translate eastward through the rest of the day. Surface temperatures near or slightly above freezing in part of the area have limited accumulations to grassy surfaces, but we anticipate that this will change as we get closer to sunset.

Most guidance continues to support a third maximum across far eastern portions of the forecast area as the coastal low deepens and mesoscale bands of heavy snow develop. Most of these bands likely remain to our east, but much of the high resolution guidance continues to support some of the heavier snow making it into far eastern Lancaster, Lebanon, and Schuylkill Counties.

Wind gusts increase to 30 to 40 mph overnight, leading to blowing and drifting snow. This will make travel difficult, particularly in the Laurel Highlands and in the southeast. Snow tapers off Monday morning for most of Central PA as the coastal low moves off to the northeast, but upslope and lake enhanced snow showers will continue across the northern and western mountains.

KEY MESSAGE 2: Multiple chances for rain and snow throughout the coming week.

A clipper system tracking to our north Tuesday night and Wednesday will bring light to moderate snow to parts of the region. An initial wave of snow is likely as warm advection overspreads the area with additional snow showers and potentially a few snow squalls possible along the cold front as it moves through during the afternoon.

Most model guidance shows a stronger low pressure system moving through the region Thursday night and Friday, but details remain uncertain. A mix of rain and snow would be favored for much of Central PA.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

A mixture of snow and rain is currently ongoing across most of Pennsylvania, with some areas holding onto warmer temperatures at the surface across the SE that is preventing the transition to snow at the lowest levels. The transition from rain to snow at MDT and LNS should occur within the next few hours. Widespread visibility and ceiling restrictions will continue to deteriorate into this afternoon and evening. Expect all airfields to be at IFR around 00Z and through Monday morning.

The bulk of restrictions will be based on visibility based on recent GLAMP/NBM model guidance; however, will highlight that low ceilings (between 500-1000ft AGL) are also expected across much of central Pennsylvania as the low pressure area along the coast intensifies with the approach of an amplifying, increasingly neg tilt trough digging SE across the Glakes today/tonight.

Winds will remain light throughout the first half of this current TAF package; however, a steady increase in wind/gusts from the NNE to NNW will occur tonight into Monday leading to frequent blowing and drifting of the snow and reduced vsbys. A mention of blowing snow has been included at all sites in southern PA.

Outlook...

Mon...Widespread IFR restrictions in snow. Gusty winds late Monday.

Tue...MVFR-IFR restrictions possible in snow showers at BFD/JST, largely VFR elsewhere.

Wed-Thu...Scattered rain and snow showers, restrictions possible.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 1 PM EST Monday for PAZ005-006- 010-011-037-041-046-051>053. Winter Storm Warning until 1 PM EST Monday for PAZ012-017>019- 025>028-034>036-042-045-049-050-056>059-063>066. Winter Storm Warning until 1 AM EST Tuesday for PAZ024-033.