Scientific Forecaster Discussion
fxus61 kphi 261727
Area forecast discussion
National Weather Service Mount Holly New Jersey
1227 PM EST sun Feb 26 2017
high pressure builds south of the region today and moves
offshore by Monday afternoon. Low pressure approaching from the
west will lift a warm front through the region on Tuesday. The
aforementioned low will track from the Great Lakes region into
eastern Canada. The associated cold front will move through the
East Coast by Thursday morning. An upper trough builds into the
northeast for the end of the week.
Near term /until 6 PM this evening/...
1230 PM update: cold air advection is beginning to wane across
the area at this time, and the snow showers upstream in
central/northern PA are beginning to retreat away from the
southern Poconos. Additionally, stratocumulus deck is beginning
to erode on the south and east side, allowing for sunnier skies
in Delmarva and southern New Jersey. Inherited forecast was modified
somewhat to account for sky cover/temperature trends, but these
changes were minor at most.
930 am update: only change to the forecast was to add some
flurries to the southern Poconos and portions of Sussex County,
NJ, as some northwest flow light snow showers occasionally make
a push into these areas. Otherwise, forecast is in good shape.
For the 630 am update, increased the sky cover for much of the
area faster at least for awhile this morning given a wealth of
stratocumulus advecting southeastward. The hourly temperature,
dew point and wind grids were tweaked based on the latest obs.
A much colder day today as we get back to reality following a
stretch of very warm temperatures (away from the immediate
A strong upper-level trough will continue to lift out of New
England this morning with cold air advection in its wake. This
cold air advection pattern will weaken especially this afternoon
as the flow begins to back toward the west. A trailing strong
short wave will become more channelized vorticity, therefore
this combined with cold air advection mostly this morning
results in any lingering isolated snow showers/flurries across
the northern areas ending this morning.
Surface high pressure will be sliding to our south later today,
however its northern extent reaches into our area allowing for
the pressure gradient to relax with time. Until this occurs,
efficient mixing will occur especially after sunrise and
therefore a breezy day is anticipated with gusts to around 30
mph. The winds are expected to drop off as we go through the
afternoon due to incoming high pressure and waning cold air
advection. Given the cold pool aloft for awhile, stratocumulus
enhanced by the eastern Great Lakes will get pulled
southeastward allowing for more cloudiness across much of our
area through about early afternoon. These clouds should tend to
thin/dissipate as gradual warming starts aloft this afternoon
and some increasing subsidence occurs.
High temperatures were mostly a MOS/continuity blend. A much
colder day especially with the added wind, however temperatures
will be much closer to where they should be for this time of the
Short term /6 PM this evening through 6 am Monday/...
high pressure centered to our south will gradually start to
shift offshore through the overnight. As this occurs, the flow
will continue to back more from the west and southwest. Some
warm air advection aloft combined with low pressure tracking
north of the Great Lakes should promote some high level clouds
overnight. The winds are expected to quickly become light or
even locally calm, setting the stage for a colder night. Low
temperatures were mostly a MOS blend.
Long term /Monday through Saturday/...
unsettled weather on tap for most of the new week.
High pressure centered just off the mid-Atlantic coast Monday
morning will continue to drift offshore during the day. Upper
trough over the northeast moves offshore as well, and upper flow
flattens out. Return flow sets up during the day, and
temperatures warm back up to above normal levels with highs in
the mid 40s in the Poconos, and in the mid and upper 50s for the
rest of the County Warning Area.
From there, low pressure organizes and develops over the
central U.S. On Tuesday. A warm front develops ahead of this
low, and lifts north through the mid-Atlantic and northeast
during the day. Some light rain will develop with the passage of
the warm front, but think the bulk of the rain will hold off
until the late afternoon and evening when weak low pressure
passes north of the region.
Stronger low pressure over the Midwest then lifts into the
Great Lakes on Wednesday, and then tracks towards northern New York
state, and then into eastern Canada Wednesday night. There are
some differences between the GFS and the European model (ecmwf) in terms of the
timing and placement of the low, and a cold front tracks across
the region behind the departing low by Thursday morning. With
deep SW flow and warm air advection on Wednesday, temps soar back into the 50s
and 60s, and possibly around 70 across the Delmarva. With
several shortwaves passing through the region ahead of the
upstream low, this may touch off some showers across the region,
but low confidence on timing and placement of any showers. Will
follow guidance and carry likely pops for Wednesday afternoon
and Wednesday night with the approach and passage of the cold
front. Will carry isolated thunderstorms as well. GFS indicating
Cold front will be through the region by Thursday morning, and
deep upper trough builds into the northeast. Several strong
shortwaves will pass through the region Thursday afternoon and
Friday, and this will keep at least chance pops in the forecast
during this time.
Temps should be warm enough for rain on Thursday, and then cold
enough for snow Thursday night through Friday morning.
Strong cold air advection will be underway. Max temps will fall into the 40s
and 50s on Thursday, which is still above normal, and then back
to normal on Friday with highs in the 30s across the Poconos and
in the low to mid 40s elsewhere.
Canadian high pressure builds into the region by Saturday. Cold
and dry conditions on tap with highs a few degrees below
normal, in the 20s in the Poconos and in the upper 30s/low 40s
Aviation /17z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
For the 18z tafs...stratocumulus deck is beginning to erode in
southern New Jersey and Delmarva, but scattered-broken clouds around 5000 feet
are expected for most of the afternoon west of the Delaware
River. Northwest winds should continue to gust 20-30 kts
through about 21z then diminish quickly 21z-00z. Skies will
rapidly clear after dark, but clouds will increase after 09z
with cigs of 8-15 kft expected after 12z. Southwest winds will
develop tomorrow, but should generally remain below 10 kts.
Monday night through Tuesday night...scattered showers with
MVFR conditions. S-SW winds 5-10 knots. Low confidence forecast.
Wednesday through Wednesday night...better chance for showers
and isolated thunderstorms. SW winds 10-15 knots. IFR and lower
conditions. Low confidence forecast.
Thursday...scattered showers. Winds become west-northwest 10-20 knots with
20-30 knots gusts. Low confidence forecast.
1230 PM update: no changes to the forecast or current Small
Craft Advisory were made at this time.
Cold air advection occurring (into this afternoon) is allowing
the boundary layer to cool early this morning. This is creating
an improved vertical mixing environment, with gusts up to 30
knots. A Small Craft Advisory is in effect through the day,
except through early this evening for the northern two Atlantic
coastal waters zones. The winds are expected to diminish from
south to north this afternoon and especially this evening as the
pressure gradient relaxes and the cold air advection wanes.
Seas have lowered some given the gusty offshore flow.
Monday through Monday night...sub-sca conditions on the waters.
Tuesday through Wednesday night...Small Craft Advisory conditions. S-SW winds
15-20 knots with 25-30 knots gusts. Visibility restrictions in rain/fog,
especially Wednesday and Wednesday night. Isolated thunderstorms
possible Wednesday afternoon/evening. Locally dense fog
possible Wednesday night.
Thursday...wind become west-northwest 15-20 knots with 25-30 knots gusts.
Marine...Small Craft Advisory until 6 PM EST this evening for anz430-
Small Craft Advisory until 9 PM EST this evening for anz450-