textproduct: Philadelphia/Mt Holly

SYNOPSIS

A cold front moves through the region early this morning. High pressure then builds into the region later today before building 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 TONIGHT/

The cold front has now crossed through our area and has moved offshore. Behind the front, rather strong Arctic high pressure located over the Great Lakes will begin to build in, ultimately settling overhead tonight. Aloft, an impulse will be tracking across the Central Appalachians today, shifting off the coast of the Chesapeake tonight.

As the front passes through this morning, north-northeast winds will strengthen as cold air advection begins to pour into the region. Winds will not be overly strong, but conditions will be breezy at times with gusts up to 30-35 mph. These gusts should persist into the early afternoon, before diminishing as high pressure approaches. At the same time, a weak surface low associated with the aformentioned impulse will track off the coast of North Carolina. The impulse will enhance lift, resulting in precipitation developing across the Chesapeake region later this morning. With cold and dry high pressure situated to the north, this should suppress most precip to our south. However, the northern part of the precipitation shield could clip portions of the Eastern Shore of Maryland and southern Delaware resulting in a period of light snow this afternoon. Any accumulations would be negligible, possibly up to a tenth or two. High temps will range from the mid 20s to the mid 30s.

For tonight, the coldest night so far this season is expected as cold air advection continues. Surface high pressure will be located directly overhead yielding light winds. Skies will also gradually clear from west to east as the impulse aloft departs overnight. This should allow a pretty decent set-up for radiational cooling to occur. Opted to blend in some colder forecast guidance as a result, where low temperatures are expected to range from the single digits across the higher terrain and portions of the Lehigh Valley, with mainly teens expected elsewhere. Fortunately, wind chills will not be far removed from the actual air temperature due to light winds. These temperatures are anomalously cold for this time of year, so it is certainly possible for a few climate sites to come within a few degrees of their record values. For more details, refer to the Climate Section below.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/

Arctic high pressure will be centered over the Northeast on Tuesday morning before sliding offshore Tuesday afternoon. Continued cold, though maybe a few degrees warmer compared to today, with high temperatures some 10 to 15 degrees below normal, topping off in the low 30s north and west of the Fall Line, and in the mid to upper 30s across southern New Jersey and Delmarva. Return flow sets up Tuesday behind behind the departing high, and after temperatures fall into the upper 20s to low 30s in the evening, temperatures will hold steady or slowly rise into daybreak.

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, Lehigh Valley, and northern New Jersey, a wintry mix right along the I-95 corridor, and rain across southern New Jersey and Delmarva, generally south of the I-95 corridor. 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. In terms of overall snowfall accumulation, can expect generally 1 to 2 inches in the higher elevations of the southern Poconos and northern New Jersey, and less than an inch down to the Fall Line.

Rain and snow tapers off late Tuesday. Dry Tuesday night. Lows mainly in the mid and upper 20s across northern areas and in the low to mid 30s elsewhere Tuesday night.

LONG TERM /THURSDAY THROUGH SUNDAY/

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 40 to 50 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 /12Z MONDAY THROUGH FRIDAY/

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

Today...VFR. Increasing BKN/OVC mid-high clouds. North- northeast winds around 10-15 kt with gusts up to 20-25 kt, before diminishing to 5-10 kt by mid-late afternoon. High confidence.

Tonight...VFR. BKN mid-high clouds early, will give way to SKC after 06Z. North-northeast winds around 3 kt or less, becoming calm at times. High confidence.

Outlook...

Tuesday through 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...Sub-VFR conds possible late in RA and/or SN.

MARINE

Small Craft Advisories are in effect today for all Atlantic Coastal Waters and the Delaware Bay. Small Craft Advisories continue through tonight for the Atlantic Coastal Waters from Manasquan Inlet to Fenwick Island.

Following a frontal passage this morning, north-northeast winds around 10-15 kt will increase to around 15-25 kt with wind gusts up to 30 kt through this afternoon. Winds will diminish a bit tonight to around 10-20 kt. Seas around 4-6 feet. A period of light snow is possible today south of Cape May, otherwise, fair weather is expected outside of SCA conditions.

Outlook...

Tuesday through Tuesday night...SCA conds develop late Tuesday and Tuesday night. N winds Tuesday morning turn S in the afternoon. Tuesday night, 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...SCA conds possible. W winds 15 to 20 kt.

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 6 PM EST this evening for ANZ430- 431-450. Small Craft Advisory until 1 AM EST Tuesday for ANZ451. Small Craft Advisory until 6 AM EST Tuesday for ANZ452>455.