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 FRIDAY/

Strong surface low over central Quebec with closed upper low over southwestern Quebec will continue to dominate our weather thru Friday. While the wind has been present so far today, the gradient is actually a bit relaxed compared to areas further west and northwest, so we haven't seen the worst of it...yet. The gradient being more westerly has also kept most flurries and snow showers from the lakes away from our region... so far. However, they haven't kept the clouds away, which are more due to an upper level jet streak than the low-level moisture lurking to our west.

Tonight, the surface and upper lows try to edge further north and east as a trough rotates around the upper low, all the while with high pressure slowly building eastward from the northern Plains. End result is not much change, with continued breezy conditions with some clouds, but a bit less wind than during daylight hours today, and still no real risk of lake- effect snow showers or flurries. Lows end up below freezing for most of the region, generally 20s to near 30. Wind chills will dip into the teens in much of the area, low 20s warmer spots.

Continued eastward shift of the surface and upper level lows on Friday, coincident with the passing upper level trough rotating around the closed low, will result in some changes. As high pressure continues to build eastward, the pressure gradient will actually tighten up, and loss of the upper level shortwave means we should end up sunnier on Friday than today, resulting in better insolation and thus, vertical mixing. Overall this will mean a windier day Friday than what we've had today, with gusts up to 40 mph likely. Still think we fall short of Wind Advisory levels, but just barely. The other change will be the wind direction, which will become more northwesterly as opposed to westerly. This will help shift some lake effect flurries and snow showers further south, and there's a decent chance some of them make it into the Poconos and NW NJ on Friday afternoon. We've kept chance POPS with a slight accumulation across these regions. Despite a bit more sun for much of the area (outside the Poconos/NW NJ), highs look likely to drop slightly thanks to enhanced cold advection, with most areas low 40s, 30s Poconos/NW NJ.

SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/

For Friday night through Saturday, the winds ease as high pressure moves eastward building in right over the area during the day Saturday. Expect lows generally in the 20s for Friday night with highs Saturday mainly in the low 40s under mainly sunny skies and NW winds generally around 5 to 10 mph. This means that despite similar temperatures to Friday, the wind chills will not be as low.

For Saturday night, it becomes mainly cloudy as high pressure moves eastward offshore and the next system approaches. This will be another mostly rainy system anticipated to impact the region mainly during the day Sunday 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. Indications are for around .10 to .25 inches of precip but there is still some uncertainty on exact amounts and where the heaviest amounts occur. But in any event, we do not expect any hydro concerns. Also, it should be noted that there could be a brief period of a little snow or a rain/snow mix at the onset early Sunday over our NW zones...mainly over the Poconos but potentially as far south as portions of the Leigh Valley into NW NJ. 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 warm advection regime, with highs mainly in the low to mid 40s northwest of I-95 (upper 30s in the Poconos) and in the low to mid 50s near the coast. Finally, south to southwest winds could become a bit gusty by Sunday afternoon.

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

The long range pattern will remain on the chilly and active side as a mean long wave trough continues to dominate over central and eastern Canada extending at times into the midwest and northeastern states. Following Sunday's system, forecast guidance is indicating a more significant system will impact the area Tuesday into Tuesday night as low pressure tracks from near the Gulf coast north and eastward up the coast while deepening. While forecast guidance is coming into fairly good consensus that it will be turning stormier Tuesday due to this low, there remains a lot of uncertainty regarding the details.

Getting into the details, for Sunday night, low pressure will pass by to our north as it advances northeastward through eastern Canada. This will drag a cold front through the area Sunday evening from NW to SE with rain tapering off as this occurs. Cooler temperatures will follow with lows by Monday morning generally in the 20s to low 30s.

For Monday, an expansive area of high pressure will build in over the northeast extending southward into the mid Atlantic states bringing chilly but dry conditions. Generally expect highs in the low to mid 40s (30s over the southern Poconos). The day should begin mainly sunny with some high clouds starting to move in by late day ahead of the next system.

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 Accra as low pressure tracks northeastward up the coast while strengthening. There are differences though in the models regarding the exact speed, strength, and track of the system with some models tracking the low near the coast (a warmer and rainier setup) while others are more offshore (a colder and snowier setup). That said, a retreating high off to the east and northeast out to sea is generally not the best setup to get a big snowstorm near and south/east of the I-95 corridor and this is what most guidance shows despite track differences with the low. 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. The bottom line: POPs have been increased to 60-70% 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 with a change to rain most likely occuring here as well. The greater potential for impacts from any snowfall accumulations will be N/W of the I-95 corridor and especially near and north of the I-78 corridor. This is our best thinking 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. The system should be out of the area by Wednesday with most guidance supporting a dry and chilly Wednesday and Thursday.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

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

Tonight...VFR, with few mid and high clouds. West winds 10 to 15 kts with occasional gusts 20 to 25 kts. High confidence.

Friday...VFR, though KABE and KTTN may occasionally see ceilings around 5000 ft AGL. Strong westerly winds with prevailing gusts 30 to 35 kts by afternoon. High confidence.

Outlook...

Friday night through 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 storm 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

Small Craft Advisory conditions will continue on the waters thru tonight before ramping up to low-end gales on Friday. Direction will remain generally westerly. Gust thru tonight 25-30 kts, increasing to around 35 kts on Friday. Seas 3-5 feet building to 4-6 feet. Fair weather otherwise.

Outlook...

Friday night...Advisory conditions. WNW winds 20-30 kts gradually diminishing overnight. Seas generally 3-6 feet.

Saturday through Saturday night...Still some gusts to 25 knots possible through around mid morning Saturday but otherwise sub SCA conditions with 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 ramping up as coastal low moves up the coast. At least Small Craft Advisory conditions likely with the potential for gales.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EST Friday for ANZ430-431- 450>455. Gale Warning from 6 AM to 10 PM EST Friday for ANZ430-431- 450>455.