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 and 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.

NEAR TERM /THROUGH TONIGHT/

The deep low pressure area across southern Canada will continue to move slowly east today and tonight. Cold and drier air continues to sweep across the northern Middle Atlantic region this morning and this air is some 20 degrees cooler than yesterday. The gusty West winds 15 to 25 mph with gusts to 30 mph at times will make temps feel about 10 degrees cooler than the air temps with wind chills in the 30s thru the day. No precipitation is expected.

Tonight, skies will be mostly clear this evening then some low clouds will arrive for the W/NW areas as some upstream lake- effect clouds/snow showers make its presence known. Low temps tonight will be in the upper 20s to low 30s with wind chills mostly in the teens. West to Northwest winds 10 to 20 mph with gusts around 25 mph at times.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/

The period Friday through Saturday night will feature cold and windy, but mostly dry conditions.

The trough associated with the midweek system will be pushing out to sea on Friday, with substantial height rises and subsidence through Saturday. The next trough will begin to approach Saturday night. At the surface, we'll remain sandwiched between an expansive low pressure system across southeastern Canada and cold Canadian high pressure, keeping a stout westerly pressure gradient in place through early Saturday. These two features will shift east with time, and the high pressure will pass into the vicinity of our area then offshore on Saturday into Saturday night.

The main story through the first half of the holiday weekend will be the sustained cold and windy conditions. Temperatures will be 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. Daytime wind chills will only max out in the low to mid 30s on Friday, and will drop into the mid teens to near 20 degrees again Friday night and Saturday morning. As the gradient relaxes into the day Saturday, winds will become less of a factor, so it won't feel quite as cold despite air temperatures being similar to Friday.

Speaking of winds, it will be quite windy on Friday with westerly winds increasing to 20-25 mph with prevailing gusts near 35-40 mph. This will be the result of the surface pressure gradient strengthening along with another surge of cold advection. Low level wind fields (925-850 mb levels) respond by increasing to near 30-40 kts. While we cannot rule out a few gusts near 45 mph in spots (especially across our PA and NJ counties), it still appears we should stay below advisory criteria for this wind event. Synoptically, the pattern isn't supportive of an over performing event like we have experienced a couple times earlier this month. The winds will lessen into Friday night, but will remain gusty with gusts near 25-30 mph possible early in the night. Winds lessen even more into Saturday as the high pressure builds closer, but we should still see northwest winds near 10-15 mph, especially earlier in the day.

Some guidance still indicates that a lake effect snow band may extend far enough east to impact the southern Poconos and far northwest NJ on Friday. We have maintained 20-40% PoPs to highlight this threat for those areas. Some light measurable snowfall accumulations (generally less than 1") will be possible along the Pocono Plateau, where temperatures will be cold enough to support accumulations. If the snow band ends up being weaker, this could end up being mostly just flurries.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

Another mostly rainy system is anticipated to impact the region on Sunday into Sunday night, along with a brief rebound of temperatures closer to normal. Cold high pressure will bring a return of 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.

A pair of upper troughs and associated surface low pressure systems are anticipated to impact the region Sunday and Tuesday with brief ridging and subsidence in between on Monday. At the surface, low pressure will pass north across the Great Lakes 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 returning briefly on Monday. The high pressure will begin to retreat Monday night, then a coastal low pressure system looks to impact the region on Tuesday. There remains significant uncertainly with regard to the strength, track, and timing of this system, which will ultimately dictate any impacts to our region.

Sunday's system will bring some light rainfall to the area, and it is not anticipated to be a significant rainfall event. It is still outside of our QPF period, however initial indications are for rainfall amounts mostly around 0.1-0.25" or so. details regarding timing and placement of rainfall amounts still remain a little unclear at the moment. South to southwest winds could become a bit gusty during the daytime. Temperatures will rebound thanks to the warm advection regime, with highs in the mid 40s northwest of I-95 and in the low to mid 50s near the coast. Not as cold Sunday night with lows in the low to mid 30s.

Another cold and breezy post frontal day on Monday with highs in the low to mid 40s. Lows in the 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. PoPs are around 40-50% area wide. The greater potential for impacts from any snowfall accumulations will be from near the I-78 corridor and north, with rain more probable from the I-95 corridor and southeast to the coast. We are at the "keep an eye on it" stage of the forecast on this system for now. Most guidance supports a dry and chilly Wednesday.

AVIATION /12Z THURSDAY THROUGH MONDAY/

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

Today...VFR. High clouds then some mid clouds late morning and into the afternoon. Gusty West winds 15 to 20 kts with gusts up to 30 kts at times. High confid.

Tonight...VFR. Mostly just high clouds expected. West winds 10 to 15 kts with gusts 20 to 25 kts. High/medium confid.

Outlook...

Friday...VFR. Strong westerly winds with prevailing gusts 30 to 35 kts.

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.

MARINE

Strong low pressure remains well north of the waters across southern Canada. Meanwhile, high pressure remains across the Plains states. The low will eventually move east into the Atlantic this weekend. The high will ridge across our area Saturday. The strong pressure gradient between the two systems will keep fresh/strong winds across our waters. The SCA advisory will continue today and tonight. A few Gale gusts are possible before dawn today and again towards dawn Friday. Fair weather.

Outlook...

Friday...Gale force westerly wind gusts expected, with gusts up to 40 kts. Sustained winds 25-35 kts. The Gale Watch was upgraded to a Gale Warning for Friday through Friday evening for all coastal waters.

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

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.

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.