textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Small Craft Advisories for the Atlantic coastal waters were extended to 1 AM Tuesday.

KEY MESSAGES

1. Another frigid morning expected with wind chills below zero for most of the area.

2. Widespread minor coastal flooding expected for much of the Atlantic coasts of New Jersey and Delaware with the Monday morning high tide.

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

4. A couple opportunities for light snow to occur across the region this week. The first coming Tuesday night and the second coming on Friday.

DISCUSSION

KEY MESSAGE 1...Another frigid morning expected with wind chills below zero for most of the area.

Lows this morning will be between 5 and 15, combined with a steady breeze (or even outright gusty conditions in the Poconos) will result in wind chills below zero for most of the region. As a result, a Cold Weather Advisory remains in effect for central and most of southern NJ, northern Delmarva, and SE PA including Philadelphia, valid through 10 AM Monday morning.

North Jersey and the Lehigh Valley were left out as their criteria for cold weather headlines are lower than what is forecast. For areas in southeast NJ and lower Delmarva that were left out, wind chills should stay just above 0. Outside of SE NJ and lower Delmarva, wind chills region-wide will hover between 0 and 5 below zero. In the Poconos, wind chills as low as 15 below zero are expected.

Overall, this looks like it will be the last morning for the Cold Weather Advisory for at least a few days. Temperatures on Monday climb into the upper 20s/low 30s but unlikely any locations gets above freezing.

KEY MESSAGE 2...Widespread minor coastal flooding expected for much of the Atlantic coasts of New Jersey and Delaware with the Monday morning high tide.

Another round of widespread minor coastal flooding is expected to occur with the Monday morning high tide. Tidal levels remain higher across multiple observing sites due to higher astronomical tides with the full moon this evening, as well as continued swells from the offshore system. As a result, with the higher of the high tides, water levels will once again increase and result in widespread minor coastal flooding for coastal areas from Ocean County southward along the Atlantic coast of New Jersey, as well as the coasts of Sussex County, Delaware. A Coastal Flood Advisory has been issued for 7 AM - 1 PM Monday as a result. Spotty minor flooding may occur along the coasts of Monmouth and Middlesex County as well as the Delaware Bay and along all the aforementioned coasts with the high tide tonight. Impacts of tidal flooding will continue to be complicated by ice that is already developing along the back bays and could be pushed onshore during high tide, as well as flood waters potentially freezing on roadways.

The threat for coastal flooding will decrease following Monday morning's high tide as we move away from the full moon and the offshore coastal low continues to track further away. Tidal flooding is not expected along the coasts of the tidal Delaware River, or the Chesapeake Bay in the Eastern Shore of Maryland.

KEY MESSAGE 3...Below normal temperatures will continue this week with many areas remaining below freezing. Dangerously cold wind chills return for the weekend.

High pressure will be situated off the coast of the Southeast US on Tuesday, where return flow will allow for somewhat warmer (relatively speaking) temperatures. Regardless, temperatures this week 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 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 possibly touching the freezing mark depending on the amount of sunshine. Temperatures for the rest of the work 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 next 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 next weekend, lows will range from the single digits to as low as 5 below zero by next weekend. 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 4...A couple opportunities for light snow to occur across the region this week. The first coming Tuesday night and the second coming on Friday.

Surface high pressure remains over the Southeast coast on Tuesday before moving out into the western Atlantic by 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 Mid-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. Localized amounts over an inch possible, with the greatest chances across northern Delaware and southern New Jersey. 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 night as a strong clipper system ahead of an Arctic front passes through the region. Too early for any specifics on this system, but a period of light snow and/or snow squalls appear to be on the table.

AVIATION /07Z MONDAY THROUGH FRIDAY/

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

Early this morning (through 12Z)...VFR. Northwest winds 10-20 knots with gusts to 25 knots, then some diminishing overnight. Moderate confidence.

Monday...VFR. Northwest to west-northwest winds 10-15 knots, with some gusts to 20 knots. Moderate confidence.

Monday night...VFR. Winds becoming light and variable. High confidence.

Outlook...

Tuesday...VFR with increasing clouds in the afternoon. No significant weather expected.

Tuesday night...Prevailing VFR with sub-VFR conditions possible. Periods of light snow expected overnight.

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

MARINE

Small Craft Advisory goes through Noon Monday on Delaware Bay and through 1 AM Tuesday for the New Jersey and Delaware Atlantic coastal waters. Elevated seas will gradually subside through Monday given the offshore wind component. Light freezing spray possible through Monday afternoon.

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...

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, otherwise fair weather.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Cold Weather Advisory until 10 AM EST this morning for PAZ054- 055-070-071-101>106. NJ...Cold Weather Advisory until 10 AM EST this morning for NJZ009- 010-012>022-026-027. Coastal Flood Advisory from 7 AM this morning to 1 PM EST this afternoon for NJZ020-022>027. DE...Cold Weather Advisory until 10 AM EST this morning for DEZ001- 002. Coastal Flood Advisory from 7 AM this morning to 1 PM EST this afternoon for DEZ003-004. MD...Cold Weather Advisory until 10 AM EST this morning for MDZ012. MARINE...Small Craft Advisory until noon EST today for ANZ430-431. Small Craft Advisory until 1 AM EST Tuesday for ANZ450>455.