textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes from prior forecast.

KEY MESSAGES

1. Much colder temperatures are anticipated through Monday behind an arctic front.

2. Several waves of low pressure will impact the area starting Monday night with wintry precipitation possible during the Tuesday morning commute.

3. A significant warm-up is expected late next week.

DISCUSSION

KEY MESSAGE 1...Much colder temperatures are anticipated through Monday behind an arctic front.

After the passage of an arctic front through the region this morning, high pressure centered over the Upper Midwest will continue to shift eastward through tonight and into Monday.

Cold air advection is occurring in the wake of the arctic front, and temperatures are expected to hold fairly steady through the remainder of today despite increasing sunshine. Tonight, skies are expected to become clear across the entire area, and winds are expected to continue to relax. The cold airmass in place, combined with clear skies and relatively light winds, will allow for rapid cooling. Overnight lows are expected to be in the low to mid teens generally along and north of I-78, the upper teens to lower 20s across the remainder of southeastern PA and southern NJ, and mid 20s across Delmarva.

On Monday, high clouds should begin to increase by mid-morning, and increase further throughout the day. With the high pressure centered just north of the area, a cold day is anticipated. Afternoon highs may remain below freezing across the southern Poconos and into adjacent areas of far northern NJ, and only rise into the mid 30s for the remainder of the area.

A weak wave of low pressure will pass to the south of the region Monday afternoon. While the strong high pressure in place, there will be a tendency for the precipitation to be suppressed south. However, some light snow can't be ruled out during the afternoon hours across portions of Delmarva.

KEY MESSAGE 2...Several waves of low pressure will impact the area starting Monday night with wintry precipitation possible during the Tuesday morning commute.

Arctic high pressure will be over the Gulf of Maine Monday night, but will still have an impact on the area with sub- freezing temperatures Monday night into Tuesday morning. A warm front will lift north through the region both behind the offshore high and low pressure moving through the Midwest. Precipitation develops after midnight Monday night, initially as some snow, but then as mid-level warm air lifts north and overrides cold air at the surface, snow should mix with and change to freezing rain from south to north during the early Tuesday morning hours. Snowfall will generally be less than an inch, and a light ice accretion is possible as well, mainly from I-95 north and west. Wintry precipitation will change to plain rain throughout by Tuesday afternoon, though the wintry mix may hold a bit longer in the southern Poconos. Rain then continues through Tuesday night as low pressure passes north of the area.

KEY MESSAGE 3...A significant warm-up is expected late next week.

A spring-like warmup will develop over the area starting on Wednesday and continuing through at least Saturday. For some areas, highs will be some 15 to 20 degrees above normal, especially starting on Thursday.

Bermuda high pressure sets up off the Southeast and Mid-Atlantic coasts for the middle to the end of the week. While several impulses will pass through the region, bringing rain from time to time, strong warm air advection will be in place. Highs on Wednesday will generally be in the mid to upper 50s for southeast Pennsylvania and New Jersey, and in the low to mid 60s across Delmarva. Then it really gets warm.

Latest NBM continues to indicate widespread highs in the 60s for Thursday, with the exception of the Poconos and NW NJ. Thereafter, a weak cold front knocks temperatures down by some 5 to 10 degrees on Friday, then the warmth returns for Saturday. NBM has trended even warmer for Saturday, with highs near 70 in Philly and points south and west, with 60s elsewhere except the immediate coast, where the chilly water will almost certainly generate a strong sea breeze. Sunday still looks pretty mild, though clouds and rain may knock back temps a little. Overall, next weekend will be a near polar opposite of last weekend.

AVIATION /20Z SUNDAY THROUGH FRIDAY/

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

Rest of today...VFR. North wind around 10 kt with occasional gusts up to 20 kt. High confidence.

Tonight...VFR. North wind 5-10 kt. High confidence.

Monday...VFR. North wind around 5 kt initially, becoming northeast after 12-15Z. High confidence.

Outlook...

Monday night...Primarily VFR. Sub-VFR conditions could develop late in light SN.

Tuesday through Tuesday night...Sub-VFR conditions expected in RA/SN/FZRA Tuesday morning, then RA Tuesday afternoon into Tuesday night.

IFR conditions may linger much of Wednesday with low clouds. Conditions should improved Thursday, but may again see reductions due to low clouds Friday.

MARINE

No marine headlines are in effect through Monday.

North wind 10-15 kt with gusts to around 20 kt are expected through this evening. Tonight, winds are expected to become more northeasterly. On Monday, winds will slowly become east- northeasterly and decrease into the afternoon to around 10 kt. Seas are generally expected to be 3-4 feet through Monday.

Outlook...

Monday night through Tuesday...Sub-SCA conditions expected with winds below 25 kt and seas below 5 feet.

Tuesday night through Wednesday...SCA conditions possible. South-southwesterly winds 10-15 kt and gusts 20-25 kt with seas 3-5 feet. Conditions are likely to improve through the day on Wednesday.

Wednesday night...Sub-SCA conditions expected with winds below 25 kt and seas below 5 feet.

Thursday...SCA conditions possible with southwesterly winds increasing to 10-15 kt and gusts 20-25 kt. Seas 3-5 feet.

Friday...SCA conditions possible due to elevated seas of 4-6 feet. Wind gusts mainly 20 kts or less.

PHI WATCHES/WARNINGS/ADVISORIES

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