textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Snowfall potential tonight has decreased with best chance for snow shifting south.

Confidence increasing in another period of dangerous cold coming this weekend in the wake of a strong arctic cold front. This front will bring a brief period of snow and gusty winds behind it, which will result in very cold wind chills likely below zero.

KEY MESSAGES

1. Light snow expected tonight, mainly for Delmarva and far South Jersey with minimal accumulations expected.

2. Below normal temperatures will continue this week with many areas remaining below freezing. Dangerously cold wind chills return for the weekend.

3. An arctic cold front will bring a shot of snow (and potential snow squalls) on Friday Night, with strong winds expected in the wake of the front on Saturday

DISCUSSION

KEY MESSAGE 1...Light snow expected tonight, mainly for Delmarva and far South Jersey with minimal accumulations expected.

An upper trough and weak surface low pressure will move by to the south of our region tonight. Since the system has limited moisture available to it, we continue to have (only) high chance/low likely pops for some light snow for Delmarva later tonight. It still appears that at most, around a half inch could occur. Flurries are possible further north into south NJ The overnight lows will be in the low/mid 20s across Delmarva so some slippery conditions on untreated roads. Overall, minimal impacts expected.

KEY MESSAGE 2...Below normal temperatures will continue this week with many areas remaining below freezing. Dangerously cold wind chills return for the weekend.

While not as cold as the previous week, temperatures both Thursday and Friday will still be 5 to 10 degrees below normal, with highs in the upper 20s/low 30s and lows in the single digits or low teens. The saving grace will be light winds, resulting in wind chills not being much lower (if at all) than the ambient air temperature. Overall though, it will be cold, though not nearly as bitter compared to the last several days and cold weather headlines will not be needed until the arctic front comes through.

Another Arctic front arrives by Friday night, ushering in another arctic airmass and shot of dangerous cold. This will result in highs for the weekend in the mid to upper teens and low twenties. Temperatures in the Poconos may not even escape the single digits. The most severe impacts this weekend though will be felt at night as lows will range from the single digits to as low as 5 below zero. Gusty winds in the wake of the front will result in dangerously cold wind chills, especially on Saturday Night. Another round of cold weather headlines may be warranted as early as Friday Night, but looking more and more likely needing headlines Saturday Night and Sunday Night.

Temperatures start to moderate early next week, however below normal temperatures are expected through the middle of next week.

KEY MESSAGE 3...An arctic cold front will bring a shot of snow (and potential snow squalls) on Friday Night, with strong winds expected in the wake of the front on Saturday

A clipper system will slide by to the north on Friday Night, dragging a cold front through our area. This front looks to pack a bit of a punch as it moves through. Medium range guidance continues to show a shot of snow as it moves through. Global deterministic guidance is not the best at depicting snow squalls, however from a pattern recognition standpoint, it would be not be a surprise for some snow squalls to develop as the arctic front moves through. Better confidence for the snow-squall potential will come once we get in range of the CAMs, but a quick inch or two of snowfall is certainly possible on Friday evening/Friday Night along with the usual impacts from snow squalls (gusty winds, reduced visibility, brief heavy snow).

Once the front clears the area on Friday Night/Saturday Morning, winds will increase sharply, with the strongest winds coming Saturday. Gusts over 50 MPH certainly are on the table and Wind Advisories may be needed. Winds taper off Saturday Night into Sunday, though a steady breeze will result in dangerous wind chills (more on that in Key Message 2).

Wednesday

VFR expected. Mainly clear skies thru the day. Winds will be mainly North to Northwest at 5 to 10 knots much of the day. High confid.

Outlook...

Wednesday Night through Thursday Night...VFR. No significant weather.

Friday through Friday Night...Restrictions possible with a chance of snow (40-50%) on Friday evening. Winds increase Friday Night with gusts up to 30 kt possible late.

Saturday...VFR. Wind gusts up to 40 kt possible out of the northwest

Saturday Night through Sunday...VFR. Northwest wind gusts 15 to 25 kt.

MARINE

Sub-SCA conditions tonight and Wednesday. Light snow is possible across the Delaware Bay and the Delaware coastal waters and perhaps into the southern NJ coastal waters too. Fair on Wednesday.

Regarding the river ice threat...Ice has formed across area bay waters and inland estuaries. This includes, but is not limited to the Delaware estuary. On rivers, the ice has grown in thickness enough to start causing restrictions in flow. An example of this can be seen at the Trenton River gauge. Per satellite imagery, the Delaware River is pretty much ice covered from just south of Trenton upstream to about Washington Crossing.

The most common ways river ice can break up is either through a thermal or mechanical means. We would like to see temperatures rise into the 40s for a few days, but that's not expected this week into the weekend. Rainfall, producing river rises, can also break up ice. But again, that's not in the forecast either this coming week.

As a result, we expect the ice we're seeing to expand before it contracts. Even though there may be a pause in the growth during the daylight hours this coming week, temperatures at night will support expansion.

Outlook...

Wednesday Night through Friday...No marine headlines expected.

Friday Night through Saturday Night...Gale conditions expected with a chance (25-40%) of storm force wind gusts in the wake of a strong cold front. Freezing spray expected across all waters.

Sunday...SCA conditions expected, lingering gale conditions possible (30-40%).

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.