textproduct: State College

WHAT HAS CHANGED

Continued to lower temperatures from NBM model guidance for this morning based on radiational cooling across the entire forecast area. Increasing precipitation mentions Tuesday and into Thursday morning given low-level warm-air advection, mentions mainly limited to slight chance outside of the northern tier. Wind/gusts increased Tuesday-Thursday given relatively tight surface pressure gradient.

KEY MESSAGES

1) Bitter cold continues this morning before a warming trend emerges into the middle of the week.

2) Increasing chances of rain/snow showers on Tuesday, with the chance for post-frontal snow showers west of the Alleghenies Tuesday night through Wednesday.

3) Initial signals for potential accumulating snowfall across much of central Pennsylvania this weekend, impacts not certain at this time.

DISCUSSION

KEY MESSAGE 1: Bitter cold continues this morning before a warming trend emerges into the middle of the week.

Current temperatures have trended below NBM guidance so have continued using the NBM10pct/MAV model guidance approach in the near-term under ideal radiational cooling conditions across much of central Pennsylvania. A light breeze has continued across portions of the Laurel Highlands and eastern Pennsylvania, which has allowed for less surface cooling; however, this has allowed for wind chills to hover near/below 0F across much of the area this morning. A couple more hours of cooling likely knocks a couple more degrees down ahead of sunrise, so current forecast remains mostly on track with no changes to the Cold Weather Advisory, set to expire at 9AM EST.

All model guidance points towards a moderating trend for the beginning of the week, with temperatures trending closer to seasonal averages for the second week of February. Influence of high pressure over the region likely allows for fairly decent surface heating today; however, snow cover currently on the ground could limit MaxTs reaching their full potential. Recent HREF model guidance and RAP model guidance outline fair agreement with respect to a layer of mid-to-high level clouds limiting radiational cooling, which will assist in keeping MinTs tonight much more tolerable than this morning.

KEY MESSAGE 2: Increasing chances of rain/snow showers on Tuesday, with the chance for post-frontal snow showers west of the Alleghenies Tuesday night through Wednesday.

An approaching shortwave passing through the region will lead a slight increase in precipitation mentions across northwestern and northern portions of central Pennsylvania late Tuesday evening and into Wednesday afternoon. Cold air advection with decent saturation in the lower levels of northern Pennsylvania will lead to a slight uptick in precipitation mentions, highest across the northern tier of Pennsylvania where *slightly* more moisture will be available. Use of slightly in the previous sentence is due to there being not a lot of available moisture despite the ample lift in place; however, a slight uptick in low-level moisture across the northern tier does promote mentions (SChc) of at least some precipitation in this timeframe.

In terms of precipitation types, model guidance continues to outline a 850mb warm nose that could result in a brief period of mixed precipitation before lower temperatures into Tuesday night allows for snow to prevail as the predominant precipitation type as the cold front passed through the region. Main concern with precipitation would be colder temperatures filtering into the region once again behind a cold frontal passage, which could allow for any moisture on roadways to freeze and lead to slick conditions. Gusty winds are also expected with cold frontal passage as a fairly tight pressure gradient, leading to an increase in winds/gusts from NBM model guidance this cycle.

Some potential for lake effect snow showers will be possible Wednesday afternoon and into the evening hours, despite much of Lake Erie having an extensive amount of ice cover. Why lake effect when Lake Erie is covered in ice? The aforementioned low- level saturation and cold air advection would be the main driver with respect to continuing lake effect snow showers despite a frozen Lake Erie. Ice cover will allow for lower snowfall totals; however, with many locations receiving less than one inch of accumulation Wednesday afternoon-evening.

KEY MESSAGE 3: Initial signals for potential accumulating snowfall across much of central Pennsylvania this weekend, impacts not certain at this time.

Recent ENS/GEPS ensemble guidance has increased on the potential for measurable snowfall across all of central Pennsylvania with regards to an upcoming weekend system. Deterministic ECMWF guidance has outlined a low pressure stationed over the central Plains racing northeastward late Saturday night into early Sunday morning which would be the main driver with respect to precipitation. Recent GFS model guidance initially showed some agreement with EC model guidance; however, tracks a weaker area of low pressure further south with limited precipitation mentions with an area of high pressure over the region blocking any precipitation mentions for the area. Another complicating factor with respect to the weekend system will be temperatures, where rain could potentially be a more dominant precipitation type and could limit snowfall potential that ENS ensemble guidance is keying in on at this time. Still a lot of uncertainty with respect to this system, but still something to continue to monitor over the coming days.

AVIATION /12Z MONDAY THROUGH FRIDAY/

High pressure over the region will allow for VFR conditions under mainly clear skies this morning. Mid and high clouds increase from the west during the afternoon ahead of an area of low pressure that will track to our north on Tuesday. Moisture will be very limited with this system, but a few snow showers are possible across northwest PA in the early morning as a warm front moves through. Ceilings gradually lower through the night, but should remain VFR through 12Z Tuesday for all TAF sites.

Outlook...

Tue...Scattered rain/snow showers.

Wed-Thu...Small chance for some very light mixed precipitation, mainly across the north. Trace amts.

Fri...Small chance for some very light snow across the south.

CLIMATE

A record low temperature has preliminarily been set at Bradford Regional Airport this morning (02/09) where as of 5AM EST, the lowest temperature overnight in five-minute observations has reached -12F. This would break the old record of 1F set back in 1963.

A record low temperature has preliminarily been set at Altoona Blair County Airport this morning (02/09) where as of 5AM EST, the lowest temperature overnight in five-minute observations has reached 0F. This would break the old record of 1F set back in 1979.

The preliminary climate reports for these sites will be sent out at 5PM this evening.

CTP WATCHES/WARNINGS/ADVISORIES

Cold Weather Advisory until 9 AM EST this morning for PAZ004>006-010>012-017>019-024-025-033-034-037-041-042-045-046- 049>053-057>059-065-066.