textproduct: Philadelphia/Mt Holly

SYNOPSIS

High pressure builds overhead tonight, then moving offshore on Tuesday. Low pressure passes through the region Wednesday, followed by several strong cold fronts. Arctic high pressure builds into the region for the end of the week and next weekend.

NEAR TERM /THROUGH TUESDAY/

The region will be embedded within relatively weak flow aloft through tonight between enhanced flow associated with a closed upper- low over Quebec and a shortwave axis passing to the south. On Tuesday, another shortwave associated with the upper-low will pass just to the north of our area ahead of a more significant trough approaching from the northwest. At the surface, high pressure will continue to settle into the region through tonight as an area of low pressure tracks eastward off the coast of the Carolinas. High pressure will begin to depart to the east on Tuesday.

The far northern edge of the precipitation shield associated with the area of low pressure to the south of the region has tried to make its way into parts of the Maryland eastern shore and southern Delaware today, but dry air has kept most of this from reaching the ground. With that said, some flurries or very light snow will remain possible into the early evening hours across the aforementioned areas before chances diminish. No accumulation is expected.

Breezy north-northeasterly winds will quickly diminish as we head into the evening and overnight hours. Clouds will clear from northwest to southeast tonight, with the entire region expected to be mostly clear by dawn. The mostly clear skies and light winds will allow for effective radiational cooling, so a very cold night is in store. Temperatures are expected to bottom out in the single digits across the Poconos and into far northwestern NJ, and perhaps into the Lehigh Valley. Mid-upper teens are expected for the remainder of eastern PA and most of NJ. Where clouds clear the latest across southern DE and far southern NJ, temperatures could remain in the mid 20s.

Tuesday will feature increasing mid and high clouds from west to east, particularly in the mid to late afternoon hours. High temperatures look to be in the upper 20s to near 30 northwest of the fall line, mid 30s in the vicinity of I-95, and near 40 for the Delmarva and into southeastern NJ. Some CAMs feature snow showers across our far northern zones associated with the shortwave passing to our north during the afternoon and evening hours. Even though this cannot be entirely ruled out, forecast soundings indicate quite a bit of dry air below the DGZ which should make it hard for anything to reach the ground. This leads to confidence in occurrence being too low to include mentionable PoPs at this time.

SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/

A clipper system will dive into the Great Lakes and Ohio Valley Tuesday night and will pass through northern New York and northern New England late Wednesday, departing Wednesday night. A cold front will follow through behind the departing low Wednesday night, and then cold air advection will be underway.

Temperatures return closer to normal on Wednesday with highs generally in the low to mid 40s, and possibly near 50 in Delmarva. Precipitation develops across most of the area, with snow across the southern Poconos and northwestern New Jersey, a wintry mix just northwest of the I-95 corridor into the Lehigh Valley and northern New Jersey, and rain across the heart of the I-95 corridor into central and southern New Jersey and Delmarva. The rain/snow line will gradually lift north throughout the day Wednesday, with precipitation changing to plain rain as far north as the Lehigh Valley, and snow may mix with rain in the southern Poconos and northern New Jersey. During the transition period, particularly during the morning hours, snow may mix with sleet and freezing rain. In terms of overall snowfall accumulation, can expect generally 1 to 3 inches in the higher elevations of the southern Poconos and northwestern New Jersey, and less than an inch for areas southeast of there. For areas that receive any ice accumulation, currently a light glaze of less than a tenth of an inch is forecast.

Rain and snow tapers off late in the day Wednesday. Dry Wednesday night with lows mainly in the mid and upper 20s across northern areas and in the low to mid 30s elsewhere.

LONG TERM /THURSDAY THROUGH MONDAY/

Several reinforcing cold fronts will pass through the region through the end of the week, with an Arctic airmass building overhead this weekend.

Thursday looks to be mostly dry, though some flurries may be possible with the passage of a strong cold front. Highs return to below normal levels, generally in the upper 30s to low 40s. Lows Thursday night drop into the 20s across much of the area, and in the teens in the southern Poconos.

Temperatures will drop by a few degrees on Friday, generally topping off in the upper 30s to around 40.

A clipper-like system may pass through the region Friday night into Saturday morning. Models are not in good agreement in terms of the timing and placement of this system, and latest runs are trending a bit drier. Will use NBM guidance for this time with PoPs generally 35 to 45 percent, and mostly snow. An Arctic airmass then builds into the region for the weekend. Gusty winds may develop on Saturday afternoon.

Highs on Saturday and Sunday will struggle to reach the freezing mark for most of the area, though should be in the mid 30s or so in southern Delmarva and along the Jersey Shore. Highs will be a few degrees cooler on Sunday compared to Saturday. Lows Saturday night will be in the teens and low 20s.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

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

Tonight...VFR. SCT/BKN high clouds will decrease through the overnight hours. A north wind around 5-10 kt becomes more LGT/VRB around 05Z, though a more north-northeast direction will still be favored. High confidence.

Tuesday...VFR. A few high clouds to start with increasing mid- level clouds by the late afternoon. Light wind in the morning becomes more out of the south-southwest at 5-10 kt around 17Z. High confidence.

Outlook...

Tuesday night...VFR. NSW.

Wednesday through Wednesday night...Sub-VFR in RA and/or SN, though SN is most likely at KRDG/KABE. Conds lift to VFR Wednesday night.

Thursday through Thursday night...VFR. Gusty west winds possible on Thursday.

Friday through Saturday...Sub-VFR conds possible with RA and/or SN, most likely Friday night. Gusty westerly winds possible on Saturday.

MARINE

The Small Craft Advisory for the Delaware Bay was allowed to expire as winds continue to decrease. A Small Craft Advisory remains in effect for all coastal waters. It is set to expire at 8 PM for the coastal waters from Sandy Hook to Manasquan NJ, 1 AM Tuesday from Manasquan to Little Egg Inlet NJ, and 6 AM Tuesday for the remaining coastal waters.

Northeast wind initially 20-25 kt with gusts to 30 kt for the coastal waters will gradually diminish through this evening and into tonight. By daybreak Tuesday, winds are expected to be northeast at 15-20 kt. Winds will become southeasterly at 15-20 kt by Tuesday afternoon.

Seas 4-6 feet will diminish to 2-4 feet around daybreak Tuesday, and remain in that range through the day.

Outlook...

Tuesday night...SCA conditions develop. Winds increase to 15 to 20 kt with gusts up to 25 kt.

Wednesday through Wednesday night...Strong SCA conds likely, with gale force winds possible. S to SW winds 20 to 30 kt. Gusts up to 35 kt possible. Winds turn W Wednesday night, generally at 20 to 25 kt with gusts up to 30 kt.

Thursday through Thursday night...SCA conds Thursday subside to sub-SCA criteria Thursday night. W winds 15 to 20 kt with 25 to 30 kt gusts, diminishing to 10 to 15 kt with gusts to 20 kt.

Friday through Friday night...SCA conds possible. W winds 15 to 20 kt.

Saturday...Strong SCA conditions likely with gale force winds possible. Westerly winds 20-30 kts with gusts up to 35 kts possible.

CLIMATE

Very cold temperatures are expected tonight into Tuesday morning. At this point, do not anticipate any climate site to break its daily record low, however it is certainly possible that a few come within a few degrees of doing so. Below are the record lows for December 9.

SITERECORD/YEAR Allentown (ABE) 7/2002 AC Airport (ACY) 6/1968 AC Marina (55N) 5/1876 Philadelphia (PHL) 6/1876 Wilmington (ILG) 13/1960 Reading (RDG) 0/1989 Trenton (TTN) 12/2002 Mount Pocono (MPO) -1/1902 Georgetown (GED) 10/1976

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 8 PM EST this evening for ANZ450. Small Craft Advisory until 1 AM EST Tuesday for ANZ451. Small Craft Advisory until 6 AM EST Tuesday for ANZ452>455.