textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes at this time.

KEY MESSAGES

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

2. A couple opportunities for light snow to occur across the region this week. The first coming Tuesday night and the second coming on Friday. Removed wording suggesting any snowfall greater than one inch for Tuesday night.

DISCUSSION

KEY MESSAGE 1...Below normal temperatures will continue this week with many areas remaining below freezing. Dangerously cold wind chills return for the weekend.

High pressure situated off the coast of the Southeast U.S. Tuesday, with return flow allowing for slightly milder (relatively speaking) temperatures. Regardless, temperatures will remain below normal for the entire week ahead. Highs on Tuesday for the Delaware Valley, including Philadelphia, southern New Jersey, and Delmarva will top off in the mid to upper 30s with perhaps a few highs near 40 in southern Delaware. North of that area, for the southern Poconos, northern New Jersey, and the Lehigh Valley, highs will mostly be in the upper 20s to low 30s with some spots touching the freezing mark depending on the amount of sunshine. Temperatures for the rest of the week will then remain mostly below freezing where highs will generally be in the low 20s to low 30s. Another Arctic front arrives by Friday night and highs over the weekend look to be in the teens and 20s once again.

In terms of low temperatures, despite highs mostly in the 30s or so this week, lows will be in the single digits and teens with the exception of Tuesday night. By the weekend, lows will range from the single digits to as low as 5 below zero. Wind chills will once again return to dangerously cold levels over the weekend, where another round of cold weather headlines may be warranted towards the end of the week.

KEY MESSAGE 2...Two opportunities for light snow to occur across the region this week. The first is Tuesday night and the second for Friday.

Surface high pressure remains over the Southeast coast Tuesday before moving out into the western Atlantic Tuesday night. A broad upper trough digs down into the Southern Plains and into the Gulf Coast states while a closed mid-level low tracks across Ontario and Quebec. Associated strong shortwave energy passes across the Northeast as a weak surface low originating from the Midwest approaches the Middle-Atlantic late Tuesday. These features then pass through the area overnight on Tuesday into Wednesday morning. This system is quite weak in nature and moisture starved, but with strong shortwave energy and sufficient cold air in place, anticipate an area of light snow to overspread the area overnight. In terms of snowfall amounts, expecting a coating to an inch of snow in most places, especially south of I-78. For areas north of I-78, perhaps some flurries but no accumulations expected. Overall, minimal impacts are expected with snow ending by Wednesday morning.

The next chance for snow arrives on Friday and possibly into Friday evening. A strong clipper system moves by to the north and an associated Arctic front will cross the region. It's too early for any specifics on this system, but a period of light snow and/or snow squalls are probable.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas...

Tonight...VFR, with clouds increasing and lowering some overnight. West-northwest winds 5-10 knots, becoming light and variable. Moderate confidence.

Tuesday...VFR ceilings. Light and variable winds becoming west- northwest 5-10 knots during the morning, then becoming west to southwest. Moderate confidence.

Outlook...

Tuesday night...Prevailing VFR with sub-VFR conditions and light snow possible.

Wednesday through Friday...A chance of light snow on Friday, otherwise, no significant weather expected.

Friday night through Saturday...VFR. Gusty winds.

MARINE

A Small Craft Advisory is in effect through 1 AM for all ocean zones mostly for lingering elevated seas of around 5 feet. No marine headlines on Delaware Bay.

Sub-SCA conditions expected for Tuesday.

Regarding the river ice threat...Ice cover exists 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 cause restrictions in the 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 in the offing through the weekend. Rainfall, producing river rises, can also break up ice. But again, that's not in the forecast either this 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 week, temperatures at night will support expansion.

Outlook...

Tuesday through Friday... No marine headlines expected as winds mainly remain below 20 kt with seas around 2-3 feet. Periods of light snow possible on Tuesday night and Friday, otherwise fair weather.

Friday night through Saturday... Gales probable. Cold. Freezing spray expected.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 1 AM EST Tuesday for ANZ450>455.