textproduct: Philadelphia/Mt Holly

SYNOPSIS

Low pressure will remain across southeastern Canada through the end of the week. Cold Canadian high pressure will shift from the Plains eastward toward the east coast by Saturday. High pressure will shift offshore Saturday night, then another low pressure system will impact the region on Sunday. A cold front will pass offshore late Sunday with colder high pressure returning briefly on Monday. A coastal low pressure system looks to impact the region on Tuesday followed by high pressure returning for mid to late next week.

NEAR TERM /THROUGH TONIGHT/

Strong low pressure continues across Quebec, but it'll move off to the east tonight. Meanwhile, high pressure across the Plains states will quickly push towards the Ohio Valley by tonight. A notable pressure gradient between these two systems will maintain moderate gusty winds over the area today. While fair weather is expected across the region, we can't rule out some snow showers for the southern Poconos area. We'll continue the the chance pops for that area. The RAP model earlier this evening was indicating perhaps more significant snows for MPO, but this will be dependent on a solid connection with the upstream lake effect, Confidence on this is not the best attm.

Temperatures will remain below normal with highs in the low 40s most spots and mid/upper 30s for the southern Poconos area. Wind chills will largely be in the low/mid 30s today. West to Northwest winds 20 to 25 mph with gusts 30 to 40 mph at times. Lows tonight will be in the 20s with wind chills in the teens.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/

The period Saturday through Sunday night will feature a continuation of below normal temperatures, along with some light precipitation developing on Sunday.

Subsidence and ridging aloft will continue into Saturday. The next trough will begin to approach Saturday night, crossing the area late Sunday and then pushing offshore Sunday night. At the surface, high pressure will pass into the vicinity of our area then offshore on Saturday into Saturday night. Low pressure will pass north across the Great Lakes Saturday night and early Sunday, resulting in a southerly pressure gradient and warm advection locally on Sunday. This system's cold front will push offshore Sunday night with cold high pressure beginning to push in overnight.

The holiday weekend will start off with continued cold and dry conditions. Temperatures will remain on the order of 5-10 degrees below normal, which will translate to highs mainly in the low to mid 40s and lows in the mid 20s to near 30 degrees. It won't feel quite as cold on Saturday due to lessening winds, despite air temperatures being similar to Friday. We still expect a northwest breeze with winds near 10-15 mph, especially earlier in the day. Increasing cloud cover Saturday night will prevent temperatures from radiating too much.

Another mostly rainy system is forecast to impact the region on Sunday into Sunday evening. This will be another mostly rainy system as low pressure tracks northeastward from the Midwest into the Great Lakes region, putting the area on the system's warm side. The system will bring mainly some light rainfall to the area, and it is not anticipated to be a significant rain event. Our forecast is around 0.10-0.25" of precip across the board, but there is still some uncertainty on exact amounts and where the heaviest amounts occur. But in any event, we do not expect any flooding concerns. Also, it should be noted that there could be a brief period of a little light snow or a rain/snow mix at the onset early Sunday over our NW zones, especially near and north of the I-78 corridor. Any accumulation will be limited to a slushy coating to maybe a half inch or so before a change to rain occurs.

Temperatures will rebound some thanks to the brief warm advection regime, but this will be the advection of a modified arctic airmass, so not a particularly warm one. Highs will be mainly in the mid 40s northwest of I-95 (upper 30s in the Poconos) and in the low to mid 50s near the coast. South to southwest winds will increase to around 10-20 mph in the warm sector by Sunday afternoon, with gusts up to 30 mph possible. Winds will shift WNW following FROPA Sunday night, with temperatures falling to around 30 degrees by dawn Monday.

LONG TERM /MONDAY THROUGH THURSDAY/

Cold high pressure will support continuing below normal temperatures into the middle of next week. Coastal low pressure will bring another chance of widespread precipitation, including potential for measurable snowfall for eastern PA and northern NJ. Drying out and remaining relatively cold for Wednesday and Thursday.

Another trough will impact the region by late Tuesday following brief ridging and subsidence on Monday. At the surface, high pressure in place on Monday will begin to retreat Monday night, then a coastal low pressure system will impact the region on Tuesday. There remains significant uncertainly with regard to the strength, track, and timing of this system, which will ultimately dictate impacts to our region.

Another cold and breezy post frontal day on Monday with highs in the low to mid 40s. Lows in the mid 20s to near 30 degrees again Monday night.

As previously mentioned, there is a large amount of uncertainty regarding details for the coastal low pressure system on Tuesday. In terms of these details, high pressure looks to be departing as it retreats east and northeastward through the Canadian Maritimes Monday night into Tuesday. This will accelerate as cyclogenesis occurs and low pressure tracks northeastward across the Mid Atlantic and up the coast while strengthening. There are differences though in the models regarding the exact speed, strength, and track of the system. Some models track the low closer to the coast (a warmer and rainier setup), while others are more offshore (a colder and snowier setup). Synoptically speaking, a rapidly retreating high off to the east and northeast out to sea is generally not a favorable setup for a big snowstorm near and south/east of the I-95 corridor, and this is what most guidance suggests despite track differences with the low. The reason being that this type of pattern favors easterly low level winds, and thus a significant marine (warm) influence south of the I-78 corridor. However, the antecedent airmass will be cold for this time of year, so this may support at least some snow at the onset, especially away from the coast.

PoPs remain around 50-70% area wide for Tuesday. Mainly rain appears to be favored near the coast, with more potential for a period of snow or mixed/rain snow near the I-95 corridor at onset (a change to rain most likely occuring here as well). The greater potential for impacts from any snowfall accumulations will be northwest of the I- 95 corridor, and especially near and north of the I-78 corridor. This is our best analysis of the setup at this time, but it's worth stressing again the overall uncertainty in these specific details remains high so forecast confidence in them is still relatively low.

Guidance supports a dry and cold Wednesday through Thursday period.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

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

Today...VFR expected. A few CIGS 040-050 possible for KRDG/KABE, possibly KTTN for the late morning into the early afternoon. Gusty winds continue with gusts 25 to 30 kts possible for the morning and afternoon. High confid.

Tonight...VFR expected. Mostly clear skies. Gusty winds 20 to 25 kts early then diminishing towards dawn. High confid.

Outlook...

Saturday...VFR. No significant weather.

Sunday...Restrictions possible in low clouds and light rain. Gusty SSW winds and LLWS possible.

Monday...VFR. Gusty NW winds possible.

Tuesday...Restrictions likely as coastal low brings rain/snow and potential for strong winds. Mainly rain favored at MIV and ACY with some snow possible for the I-95 corridor before a change to rain. Best chances for impactful snow at RDG and ABE.

MARINE

The Gale Warning for the waters will go up early this morning and continue into the evening. An extension in time a few hours was added. Gusts 35 to 40 kts expected with the latest cold air push down from the Northwest today. Rough seas.

Outlook...

Saturday through Saturday night...No marine hazards expected. Some gusts near 25 kts possible early in the morning. Fair weather.

Sunday...Advisory conditions possible. Southerly winds increasing to near 20-25 kts and seas building 3-5 feet. Winds shifting northwest overnight. Periods of light rain likely.

Monday...No marine hazards expected. Fair weather.

Tuesday...Winds and seas building as a coastal low moves up the coast. At least Small Craft Advisory conditions likely with the potential for gales. Visibility reduction possible in rain and fog.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Warning until 2 AM EST Saturday for ANZ430-431-450>455.