textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No major changes to the forecast through this evening. Winter Weather Advisories remain in effect.Another period of snow will affect the area this afternoon before winding down this evening from west to east. This second will be more focused on areas near and S/E of the urban corridor as opposed to this morning's snow which was heaviest farther north and west. Near the coast, expect rain changing to snow late this afternoon into early this evening before ending.

For the cold snap, no major changes to the forecast. Monday Night and Tuesday Night will be the coldest stretch. Wind chills will be more severe on Monday Night, even with lower air temperatures anticipated on Tuesday Night.

KEY MESSAGES

1. A coastal low will slide by offshore through this afternoon into this evening. An additional coating up to 2 inches of snow can generally be expected across the area for the remainder of the event for the afternoon and evening before the snow ends by late this evening.

2. A prolonged period of below normal temperatures are expected this upcoming week, with single digit and below zero wind chills possible both Monday Night and Tuesday Night.

Discussion...

Key Message 1...A coastal low will slide by offshore through this afternoon into this evening. An additional coating up to 2 inches of snow can generally be expected across the area for the remainder of the event for the afternoon and evening before the snow ends by late this evening.

A complicated forecast continues to unfold across the area this afternoon. Following an initial round of precipitation this morning, the precipitation is starting to fill back in again after a brief lull. As of 1 PM, surface low pressure was centered off the coast of North Carolina and Virginia. This low will move north and east well off our coast through this evening while deepening. So far, precipitation has fallen as rain near the coast with some snow mixed with rain at times near the I-95 corridor and mainly snow N/W of here where up to a couple inches of snow have fallen. As this second round continues to pick up this afternoon, colder air will be drawn into the system as the low pushes offshore and winds continue to back to more of a N/NW direction as opposed to NE. This will result in the rain/snow line gradually collapsing S/E to the coast through the late afternoon into this evening. For areas near and N/W of the I-95 corridor this should be a mainly snow event from here on out. And as the best upper level dynamics associated with the low move into the area late this afternoon into early this evening, snowfall rates of a half to potentially as much as three quarters of inch per hour will be possible at times where near and S/E of the I-95 corridor where the steadiest/heaviest precipitation will be. Farther north and west through Berks County into the Lehigh Valley and NW NJ, the snow will be lighter since these areas will be near the N/W fringe of the system.

By around 7 PM this evening, all areas still seeing precipitation should be all snow. However the back edge of the system will be moving through from west to east bringing an end to the snow. As far as additional accumulation for the remainder of the event, generally expect a half inch to as much as 1-2 inches near and S/E of the I-95 corridor with the lowest of these amounts near the coast since it will take longer to change to snow. Our north/west zones will likely just see a coating up to an inch or so.

Key Message 2...A prolonged period of below normal temperatures are expected this upcoming week, with single digit and below zero wind chills possible both Monday Night and Tuesday Night.

A deep trough sets up over the eastern US tonight, ushering in an arctic airmass. The stretch of below normal temperatures commences tonight, with lows in the mid to upper teens for most. The height of the cold airmass will be over our area on Monday Night through Tuesday Night, where 850 mb temperatures will be around -15 to -20 C, resulting in low temperatures at the surface into the teens and single digits. Combined with breezy winds expected Monday night, this will result in wind chills between -10 and -15 in the southern Poconos, near or below zero over the Lehigh Valley, and in the single digits over the rest of the area. We almost certainly need some cold weather headlines, especially in the southern Poconos, but cannot rule them out for the rest of the region.

With the arctic airmass directly overhead on Tuesday, highs won't climb out of the 20s. With a steady westerly breeze, wind chills will be in the single digits and the low teens. Areas in the southern Poconos likely won't get above 0 for wind chills even during the daytime.

High pressure will center itself overhead Tuesday night, allowing winds to diminish and skies to become mostly clear. We could see decent radiational cooling as a result, potentially leading to more widespread overnight lows in the single digits than the previous night. While temperatures may be colder, the calmer winds will make the wind chills less severe, though still in the single digits for most and below zero in the southern Poconos. These values will not warrant any cold weather headlines, but it will be bitterly cold nonetheless.

We briefly break the cold snap on Wednesday into Thursday as temperatures get back toward more seasonable levels. However another arctic front moving through late week will bring a return to colder conditions by next Friday into Saturday. Highs will return to the 20s to low 30s for most areas with lows in with lows mainly in the teens to around 20. The weather pattern could get more active again for next weekend but confidence is low on this. A lot of the latest model guidance now is more suppressive with the storm track which could result in it staying mainly dry but continuing quite cold.

AVIATION /00Z MONDAY THROUGH FRIDAY/

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

Tonight... Conditions will improve over the next several hours from SW to NE across the terminals. Precipitation will end as mostly snow with a little rain at KPHL thru 02Z. VSBYs improve followed shortly thereafter by CIGs with VFR expected to return most areas by 04Z/05Z. Winds increase from the NW 10 to 15 kts with gusts around 20 kts. Winds will diminish late after switching to W/WSW. Medium confid overall.

Monday... VFR expected. Mostly high and some mid level clouds at times. West to Southwest winds increasing to 10 to 15 kts with gusts to 25 kts possible after the late morning. Medium/high confid.

Outlook...

Monday Night and Tuesday...VFR. West/southwest wind gusts 15-20 kt.

Tuesday Night through Wednesday Night...VFR. No significant weather expected.

Thursday through Thursday night...Mainly VFR. Chance (15-30%) for a rain or snow shower.

MARINE

NW winds increase into this evening with a Small Craft Advisory now in effect beginning at 6 PM for our southern ocean zones as well as the Delaware Bay. This includes coastal waters as far north as off the coast of Cape May County in NJ. There will likely be a brief lull in winds early Monday before winds ramp back up again Monday afternoon but for all waters.

Outlook...

Monday night though Tuesday...SCA conditions expected as wind gusts of 25- 30 kt expected.

Tuesday night through Wednesday...Generally sub SCA conditions expected

Wednesday night through Thursday...Another period of SCA conditions possible.

Friday...The conditions should be sub SCA levels.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Winter Weather Advisory until 8 PM EST this evening for PAZ060>062-070-071-101>106. NJ...Winter Weather Advisory until 8 PM EST this evening for NJZ001- 007>010-012-013-015>019. DE...Winter Weather Advisory until 8 PM EST this evening for DEZ001. MD...None. MARINE...Small Craft Advisory until 6 PM EST Tuesday for ANZ430-431- 453>455. Small Craft Advisory from 9 AM Monday to 6 PM EST Tuesday for ANZ450>452.