Scientific Forecaster Discussion
fxus61 kphi 120914
Area forecast discussion
National Weather Service Mount Holly New Jersey
414 am EST Thu Dec 12 2019
high pressure will build into the region today, moving offshore
tonight. A low pressure system will move through the southeastern
states and into the mid-Atlantic Friday into Saturday. The low will
quickly move off to the northeast allowing high pressure to briefly
build into the region for the start of the new week. Another low
pressure system will approach the region Monday into Tuesday.
Near term /until 6 PM this evening/...
its been a quiet evening with little in the way of cloud cover.
Surface dewpoints are sitting in the teens and temps will
continue to fall through the rest of the overnight hours. Modest
height rises and strong cold air advection have kept US from
reaching the coldest potential lows had we been able to
decouple. Even so, its certainly a chilly evening a few degrees
below our normal upper 20s for mid December. Highs today will
slowly warm through the morning and based on mixing we should
see temps in the mid to upper 30s across the region which
generally on the colder side of MOS guidance except for the
urban corridor where MOS guidance increases temps into the low
40s. Under strong cold air advection and building heights I just
dont think we'll get into the low 40s. The hourly lamp guidance
only gets to 37 which feels like a more accurate forecast.
Through the day today the winds should veer around from the
northeast to the southeast and as is the habit for these type
onshore flows, we'll start to see a marine layer develop. The
clouds wont arrive until the overnight hours but we should start
to feel some increased humidity especially along the coast.
Short term /6 PM this evening through 6 am Friday/...
high pressure should crest early in day Thursday and will begin
to push offshore this evening. Once the high pushes offshore the
aforementioned marine layer will start to push onshore in the
form of some low level stratus. Almost out of a force of habit
i've increased cloud cover to overcast by midnight which should
dampen how quickly temps fall this evening. The idea is that we
should only fall into the upper 20s to low 30s in the urban
corridor. The high res guidance is continuing to converge on the
idea that some light precip will start to lift into the region
as well so i've included mention of some very light rain across
Delmarva and parts of southern New Jersey heading into early
Friday morning. As the day shift mentioned yesterday, there
should be abundant dry air initially so while there may be
visible precipitation, the dry air at the surface may be just
enough to cause the rain not to reach the ground until later in
Long term /Friday through Wednesday/...
the high moves into the Canadian Maritimes Friday leaving our area
in east to southeast return flow. With the easterly flow setting up,
some moisture will work its way into the region Friday morning. Just
how fast the moisture arrives is still questionable and it may hold
off long enough for temps to warm. However, there continues to be
guidance showing the moisture making it in while temps are still
below freezing so have mentioned some freezing rain during the
morning, which would be mainly confined to the southern Poconos
portions of the Lehigh Valley, and the elevations of northern New
Jersey. With uncertainty related to the onset of any precipitation,
confidence is too low to raise any kind of winter weather advisories
so will hold off on that for now. Temperatures should rise through
the morning with the forecast area expected to rise above freezing
by early afternoon.
Meanwhile, a low pressure system will track up the southeast coast
and up into the mid-Atlantic late Friday into Saturday. The low will
intensify as it pushes northward and will bring rain to the region.
The ground is pretty sodden from the rain earlier in the week and
with pwats climbing around 1.0-1.3" on Saturday, we should see some
decent rains again and it may be heavy at times. While right now it
doesn't look like we will see enough rain to cause any big flooding
concerns (generally 1.0-1.5" across the region), there may be some
localized issues, especially in areas where there is poor drainage
and/or where the leaves may be clogging the storm drains.
A considerable amount of warm air will move up through the region
with temps expected to warm Friday night. 850mb temps of around 10c
are warm for this time of year and expect we see temps rise into the
40s and 50s on Friday with temps expected to be slightly warmer on
The low deepens as it tracks to the north and into New England by
late Saturday, continuing to push towards Newfoundland by early
Sunday. The precipitation clears out early on Sunday, giving way to
dry conditions. The pressure gradient will tighten up and Sunday
looks to be a pretty windy day with gusts potentially around 25 to
30 mph across the region.
Another low pressure system will develop to our southwest and move
towards our region on Monday. The low looks to start bringing some
precipitation to the region as early as later Monday and continuing
into Tuesday before exiting off to the east. There are some phasing
and timing issues between the various models which impact the amount
of warm air vs colder air moving through with the precipitation,
which would impact the precipitation type. For now will keep things
simple and go with rain/snow until more details can come into focus
over the coming days. For Wednesday, an upper trough will swing
through the region as surface high pressure starts to build in from
the west. Temperatures look to turn colder for midweek.
Aviation /09z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Rest of tonight...VFR at all terminals with light northwesterly
flow and mostly clear skies.
Thursday... VFR with light winds less than 7 knots become
northeasterly as high pressure moves offshore. Late in the
afternoon the high pressure system will be far enough east to
allow for a return of southerly flow at krdg/ kabe.
Thursday night...generally VFR ceilings with the potential for
MVFR ceilings as a marine stratus layer pushes onshore
overnight. Winds remain light and variable under 7 knots
Friday..MVFR conditions expected early and then MVFR or lower
conditions will develop across the terminals as rain moves into the
region. Light easterly winds. Moderate confidence
Friday night through Saturday...MVFR/IFR or lower conditions
expected in rain with the rain being heavy at times. East winds
around 8 to 12 knots veering to the south Saturday morning and then
to the southwest Saturday afternoon. Gusts up to 20 knots
are possible. Moderate confidence
Sunday...mainly VFR conditions expected. West winds around 10 to 15
knots with gusts up to 25 knots possible. Moderate confidence.
Monday...mainly VFR conditions expected. Rain/snow may move into the
terminals by late morning/early afternoon. West to northwest winds
less than 10 knots. Low confidence.
Small Craft Advisory conditions should dissipate shortly after sunrise this
morning as high pressure crests over the region. Winds will
relax through the day today gradually veer through the day
ultimately becoming more easterly-southeasterly by Friday
morning. Seas will generally be 2-4 ft through the period.
Friday...increasing winds and building seas expected, especially
later in the day, but expected to remain below Small Craft Advisory
conditions through the daytime hours. East winds around 10 to 15
knots with gusts around 20 knots and seas generally around 2 to 4
Friday night through Saturday...east winds will continue to increase
Friday evening into Saturday. Seas will build to 5 feet by Saturday
morning, and continue to build to 5 to 7 feet through the day. A
Small Craft Advisory will likely be needed.
Saturday night through Sunday... west winds around 15 to 25 knots
with gale force gusts possible on Sunday. Seas around 5 to 7 feet
will gradually subside to near 5 feet by later Sunday.
Monday...seas are expected to fall below 5 feet by early Monday
morning and will drop to around 1 to 3 feet through the day. Some 25
knot gusts may occur early Monday but expect winds to be out of the
northwest around 10 to 15 knots through the day.
Marine...Small Craft Advisory until 6 am EST early this morning for