Scientific Forecaster Discussion
fxus61 kphi 171204
Area forecast discussion
National Weather Service Mount Holly New Jersey
704 am EST Wed Jan 17 2018
low pressure will move into the Canadian Maritimes today. High
pressure will build across the Gulf Coast through the end of the
week, then offshore over the weekend. An area of low pressure
will move across eastern Canada over the weekend as a back door
cold front approaches from the north. Another area of low
pressure will move through the Great Lakes Monday night into
Tuesday, pulling a cold front across the area.
Near term /until 6 PM this evening/...
even though some light snow will linger for another hour or so
in Berks, Lehigh, upper Montgomery and outer Chester, we let the
advisory expire in those areas. There should be little or no
additional accumulation there. The remainder of the Winter
Weather Advisory and the Winter Storm Warning continues to look
A cold front passed through our region from west to east early
this morning. Meanwhile, low pressure was off the New Jersey
coast. The low will move northeastward and it should reach the
waters east of New England this afternoon.
Snow was falling in much of our region around 7:00 am. The snow
is expected to end gradually across our forecast area between
now and about 11:00 am. However, some light snow may linger a
little beyond 11:00 am, especially in northern New Jersey and in
areas near the coast.
The storm total snowfall amounts should range from up to an
inch in the Philadelphia metropolitan area and in parts of
southern New Jersey to around 6 inches in the elevated terrain
of the Poconos and northwestern New Jersey.
Temperatures are not expected to recover much today as cold air
builds into our region on a northwest wind. Wind speeds are
forecast to increase to 10 to 15 miles per hour with gusts around 20 miles per hour.
Short term /6 PM this evening through 6 am Thursday/...
the low is forecast to move across canada's maritime provinces
tonight as high pressure begins to nose into our region from the
west and southwest. We are anticipating a mostly clear sky
along with a northwest to west wind around 5 to 10 miles per hour.
Cold temperatures will return for tonight with lows mostly in
the teens. Single digit readings are possible in the Poconos and
in far northern New Jersey.
Long term /Thursday through Tuesday/...
main focus of the long term is the warmup late this week
through this weekend and a storm system moving through the
region early next week. Most of the focus today was on the first
36 hours of the forecast, so overall made few changes from the
Trough axis swings through the eastern Seaboard Wednesday
night, with a broad surface high building into the mid-Atlantic
and southeast for the rest of the week into the weekend. After a
small- scale perturbation moves through the northeast Thursday
night (which should be dry), midlevel zonal flow will be present
Friday through the weekend, allowing the surface high to slide
eastward and promoting southwesterly surface flow to develop
east of the Appalachians this weekend.
This pattern will result in a lengthy dry period and a distinct
warming trend after a chilly Thursday (when heights/thicknesses
will be lowest, owing to the proximity of the trough). Forecast
highs are in the 50s for philly this weekend, based on a
consensus blend of statistical guidance...though I leaned a
little on the higher side of consensus given the tendency for
MOS to be on the low side in warming patterns.
Operational models develop a strong surface cyclone in the
Central Plains this weekend (with downstream ridging further
contributing to warmth Sunday and Monday in our area) before
lifting it rapidly northeastward into the Great Lakes and
adjacent southeast Canada early next week. A strong cold front
will progress through the east Monday and Tuesday, with showery
precipitation developing near the front. Temperatures will
likely be warm enough for liquid in most locations for the
event, with the exception being the far northwest County Warning Area during the
precip's waning stages.
Regarding timing, models generally agree on Monday afternoon
through Monday night. Given such good agreement this far out,
boosted pops to high chance or likely during this time frame.
The greater uncertainty lies with the intensity of the
precipitation (given the southern origins of the system and the
warmth it advects downstream, there is some potential for decent
precipitation totals, especially if embedded convection can
develop), extent of cold air on the upstream side of the system
(i.E., Precipitation type issues as the system departs), and the
speed with which the precipitation moves out before the colder
air moves in.
As previously mentioned, did not change the details during this
time frame too much, but my initial thoughts were to go on the
warm side and on the quick side given typical model biases with
northeast- progressing inland surface lows originating from the
By midweek, temperatures will be slightly cooler, and
conditions should dry out.
Aviation /12z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Today...IFR and MVFR conditions this morning improving to VFR
for the afternoon. The snow is forecast to end from west to east
between about 1100z and 1500z in our region. We are expecting a
northwest wind around 10 to 12 knots gusting near 20 knots.
Tonight...VFR with a mostly clear sky and a northwest to west
wind at 5 to 10 knots.
Thursday through Sunday...VFR. West to southwest winds; winds
may gust 15-20 knots at time. High confidence.
a northwest wind is expected to increase to 15 to 20 knots
today with gusts of 25 to 30 knots. As a result, a Small Craft
Advisory is in effect for today and tonight.
Thursday...Small Craft Advisory extended through the day
Thursday as winds expected to gust to 25 knots.
Thursday night...conditions expected to drop below advisory
Friday-Sunday...conditions expected to remain below advisory
levels, but winds may periodically gust around 20 knots.
Sudlersville NWR conts off the air overnight. Ridge temp turned
off and our et staff hopefully can resolve tomorrow. Data went
bad in a gradual fashion beginning Ard 2325z. Ptw and Ged have
FAA comms issues.
PA...Winter Storm Warning until 11 am EST this morning for paz054-
Winter Weather Advisory until 11 am EST this morning for
Winter Weather Advisory until 9 am EST this morning for paz105.
New Jersey...Winter Weather Advisory until noon EST today for njz008>010.
Winter Storm Warning until 11 am EST this morning for njz001.
Winter Weather Advisory until 11 am EST this morning for
Marine...Small Craft Advisory until 6 PM EST Thursday for anz450>455.
Small Craft Advisory until 10 am EST Thursday for anz430-431.