textproduct: Philadelphia/Mt Holly

SYNOPSIS

High pressure over the Northeast slides offshore this evening. A warm front extending out from low pressure moving into the Great Lakes will lift north through the region overnight, followed by a strong cold front Monday afternoon. High pressure briefly returns on Wednesday, then several weak cold fronts will pass through the region into the end of the week.

NEAR TERM /THROUGH MONDAY NIGHT/

940 PM update... Seeing as we're starting to get dense fog across parts of the region, decided to issue a dense fog advisory for areas along and NW of I-95. Fog hasn't quite become widespread yet but since temps are also near freezing, the risk of spotty ice is also a factor, at least on anything untreated.

630 PM update... Spotty radar echoes with reports of light rain and temps near freezing have been reported south of the winter weather advisory this evening. However, expect any icing to be patchy and light, and with most roads likely heavily treated from the event a couple nights ago, have no plans to expand the advisory further south. Did include a chance of freezing rain further south, however, given obs. That all having been said, latest indications suggest this initial burst of precip will be the majority of it for the night, with a long lull likely with little if any precip falling until we get closer to morning.

One thing added to the forecast was areas of fog. Warm advection over cold ground seems likely to result in areas of fog, potentially quite dense, and guidance is now hinting at it strongly as well. Will hold off on any advisories until we start to see some more observations of it at lower elevations, but it definitely is a distinct possiblity that we'll need Dense Fog Advisories before the night is through.

Otherwise, made some tweaks to boost winds and change the rain on Monday to showers, while slowing the warming a bit overnight. That's it for now.

3 PM discussion... Northwesterly flow aloft will continue to overspread the region through today, gradually weakening with rising heights as a ridge axis initially centered over portions of the Ohio Valley shifts eastward into our area. Tonight, rapid height falls and enhanced southwesterly flow aloft will begin to overspread the region ahead of a strong upper-trough approaching the region. At the surface, high pressure initially centered over the Mid- Atlantic will gradually shift east through the day as low pressure initially over the Midwest shifts east into the Great Lakes. A warm front will lift through the region overnight tonight.

High clouds will continue to overspread the region into this morning, with low clouds working in from west to east this afternoon. The combination of background ascent from the approaching trough and additional lift from the approaching warm front will lead to light precipitation overspreading the northern half or so of the area beginning during the mid to late afternoon hours. Precipitation chances will be greatest along and north of I-78 (60-80%), and decrease as you go south from there. There will only be a 20-40% chance of a few showers for the Philly metro and south. Temperatures look to top out in the mid 30s to near 40 northwest of I-95, and the low-mid 40s southeast, with southern portions of the Delmarva and far southern NJ potentially approaching or breaching 50.

As light precipitation overspreads the area, temperatures this evening into the first part of the night look to be near or below freezing across northern areas. Forecast soundings indicate this below freezing surface layer will be quite shallow, with a significant warm nose aloft. Therefore, precipitation type looks to be either freezing rain or rain depending on surface temperatures. Confidence is high that portions of the Lehigh Valley northward into the Poconos and adjacent areas of northern NJ will experience a period of freezing rain during the evening and into the early overnight hours. Outside of these areas, temperatures should be above freezing for the duration of any precipitation, so rain is expected. Overall precipitation amounts look light, but for areas that see freezing rain, hazardous travel conditions are expected.

In terms of ice amounts, confidence has increased enough in a glaze of ice for Lehigh and Northampton Counties in PA and Warren and Morris Counties in NJ to expand the areal coverage of the Winter Weather Advisory to include them. For Carbon and Monroe Counties in PA, amounts have trended up slightly, and we now anticipate many locations to see a tenth to perhaps two tenths of an inch of ice accretion. The primary forecast challenge with this event is that temperatures will bottom out early in the evening and begin to rise from there as warm air advection begins with the approaching warm front. The areal extent of below freezing surface temperatures during the evening and overnight hours remains somewhat in question. A brief period of light freezing rain is not entirely out of the question for areas south of the current advisory, but if this were to occur it would likely be quite brief with marginal and rising temperatures.

As the warm front lifts through the area during the overnight hours, temperatures will rise areawide. Temperatures are likely to rise above freezing areawide during the pre-dawn hours. Any remaining light freezing rain will change to plain rain during this time. There will likely be a brief period where the majority of the region is precipitation-free prior to daybreak Monday.

SHORT TERM /TUESDAY THROUGH WEDNESDAY/

Deep low pressure moving down the St. Lawrence Valley Tuesday morning will continue to influence our weather by keeping a strong west to northwest flow at the sfc and aloft across the northern Middle Atlantic region. We will continue with the below normal temps Tue with upper 20s to mid 30s most areas. Readings bump up a bit Wed ahead of a reinforcing cold front which arrives during the long term. Wind chills Tue will be winterlike with teens and single digits for the Lehigh Valley and areas N/W. WC readings in the 20s for metro Philadelphia and Delmarva regions. Winds will gust 20 to 30 mph much of the day. The winds will relax somewhat Wed bringing wind chills back closer to the cold ambient temps.

Not much precipitation in the short term. It;s possible that snow showers will be across the southern Poconos and north NJ Wed as upstream winds shift and bring lake-effect showers from NY state into our region. We'll accept the NBM slight chance pops for Wed attm.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

The below normal temperatures from the end of this year will carry over into 2026 with upper ridging out West and troughing for the East coast. The pattern will remain into next weekend when upper heights begin to subtly rise for our region. Solid winter pattern into the New Year.

Temperature will remain some 10 degrees below normal Thu/Fri with highs on the low/mid 30s most spots and 20s for the southern Poconos and north NJ. We'll moderate a little next weekend with most areas S/E will get maxs in the upper 30s and low 40s for Delaware. Lows will be in the 20s with teens far N/W.

Precipitation will likely remain rather scarce thru the period with most of the systems moving thru the upper flow being rather weak and fast moving. A cold front and minor low pressure system may bring snow showers late Wed and into Thursday for our entire fcst area. Better chances for snow will be with some spill-over lake effect Wed night/Thu for the Poconos. Friday looks dry across the region. The models are dissimilar with regards to next weekend's weather we'll hold with the NBM pops for the region Saturday which features chance pops for Delmarva and south NJ and slight chc pops elsewhere.

AVIATION /02Z MONDAY THROUGH FRIDAY/

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

Tonight...IFR cigs developing all terminals, with IFR vsby possible especially northern terminals. KABE in particularly could go VLIFR vsby and cigs late tonight. South wind 5-10 kt. LLWS of up to 50 kts expected at all terminals starting around 02-03Z. Moderate confidence.

Monday...IFR cigs all terminals to start, with IFR vsby particularly northern terminals, VLIFR possible esp KABE. Showers also move into the region after 12Z. LLWS will also continue. After around 17Z, we trend towards VFR with clouds scattering out and ceilings lifting. Rain showers also move out. A SW wind 10 to 15 kt with 20 to 25 kt gusts in the morning, turning W in the afternoon and increasing to 15 to 20 kt with gusts upwards of 35 to 40 kt. Moderate confidence

Outlook...

Monday night... VFR. Gusty West winds 25 to 35 kts. Tue/Tue night... VFR. Gusty West winds 20 to 30 kts.

Wed/Wed night... VFR most areas. Snow showers and lower conditions possible for the southern Poconos and North NJ with snow showers. Thu/Thu night... VFR. A few snow showers possible.

Friday... VFR expected.

MARINE

A southwesterly wind through this evening at around 10-15 knots and seas 2-4 feet. For tonight, winds will again increase to 20-25 kt, with gusts upwards of 30 kt. Seas will increase to 4-6 feet tonight. A Small Craft Advisory has been issued and will be in effect starting at 1 AM for all Atlantic Coastal waters as well as the Delaware Bay.

During the morning hours, gale force winds develop on all marine zones with a Gale Warning in effect starting at 6 AM. A South- southwesterly wind in the morning at 20-25 kt and gusts to 35 kt. Winds increase to 25-30 kt with gusts of 40 kt for the afternoon. Seas are 5-7 feet.

Outlook...

Gale flags will come down Tuesday and winds slowly subside. Long term SCA conditions expected after that into the end of the week with the potential for gusts around 25-30 kts and 5 ft seas possible. Fair most of the time except for a few snow showers Thursday and Thursday night.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Wind Advisory from 10 AM Monday to 1 PM EST Tuesday for PAZ054- 055-060>062-070-071-101>106. Winter Weather Advisory until 2 AM EST Monday for PAZ061-062. Dense Fog Advisory until 10 AM EST Monday for PAZ054-055- 060>062-070-101>106. Winter Weather Advisory until 4 AM EST Monday for PAZ054-055. NJ...Wind Advisory from 10 AM Monday to 1 PM EST Tuesday for NJZ001- 007>010-012>027. Winter Weather Advisory until 2 AM EST Monday for NJZ001- 007>010. Dense Fog Advisory until 10 AM EST Monday for NJZ001-007>010- 012-015. DE...Wind Advisory from 10 AM Monday to 1 PM EST Tuesday for DEZ001>004. MD...Wind Advisory from 10 AM Monday to 1 PM EST Tuesday for MDZ012- 015-019-020. MARINE...Small Craft Advisory from 1 AM to 6 AM EST Monday for ANZ430- 431-450>455. Gale Warning from 6 AM Monday to 6 PM EST Tuesday for ANZ430- 431-450>455.