Scientific Forecaster Discussion
fxus61 kphi 112101
Area forecast discussion
National Weather Service Mount Holly New Jersey
401 PM EST Wed Dec 11 2019
high pressure will build into the region from the Midwest through
the overnight, then move offshore by Thursday evening. By Friday,
another area of low pressure will track across the southeast and
into the mid-Atlantic, exiting the region by Saturday night. A brief
area of high pressure will move across the region before another
strong storm system moves up the coast from the southeasterly next
Near term /until 6 am Thursday morning/...
drier air is continuing to filter into the region this afternoon and
consequently expect that clouds will continue to thin out as we
head into the evening, with the diurnal stratocumulus, that formed
in The Breaks behind the primary cloud shield, also clearing out
after sunset. A weak low passing through Quebec this evening will
drive a weak cold front through the area this evening. Given a
notable lack of moisture this frontal passage should be dry over our
area with maybe a few mid-lvl clouds developing over the far northwest
closer to the mid-lvl trough axis.
Pressure rises behind the front combined with continued cold
advection aloft will keep west/northwest winds elevated through at least the
first half of the overnight period. Consequently leaned a bit on the
higher side of guidance for the overnight lows, although there is a
chance that winds lighten sufficiently around daybreak for some
locations to dip a bit lower than forecast. That being said, given
the cold airmass in place it will still likely be a cold night with
low to mid 20s over the most of the area, and some teens in the far
Short term /6 am Thursday morning through Thursday night/...
a very quiet day is expected on Thursday as 1040mb high pressure
moves in more or less overhead. Despite mostly sunny skies (apart
from occasional cirrus), the cold December airmass (925 temps around
-5 to -7c), should keep highs generally in the low to mid 30s (apart
from upper 20s in the Poconos and upper 30s to around 40 in
The high will move off to the northeast late Thursday afternoon and
the light near-sfc flow will veer a bit more easterly/southeasterly
in response. Meanwhile just above the surface will begin to acquire a
southerly component, and thus warm air advection aloft and moisture advection will
begin to ramp up Thursday night into Friday morning. Consequently
expect we will see some lower clouds begin to move in from S-north
Thursday night, which would mostly have the effect of tempering
overnight mins (with an atypical diurnal T curve as a result). Went
with this idea for the mint forecast which generally resulted in
lows in the mid to upper 20s (a bit warmer in Delmarva a bit colder
in the poconos). However in direct contrast to the situation
tonight, it is possible a few locations get a bit colder than
forecast early in the overnight period (good radiational cooling in
advance of the clouds moving in). Although the NAM and its
derivatives want to bring some patchy drizzle/freezing drizzle with
this moisture surge am not buying this given how dry the antecedent
low-lvl airmass will be initially, and the nam's general (high)
Long term /Friday through Wednesday/...
synoptic overview...high pressure will quickly shift off to the
north and east Friday as another strong surface low moves out of the
southeast and up the eastern Appalachians into the mid-Atlantic
driven by an amplifying shortwave trough. Given the negative tilt of
the trough, this low will quickly shoot northward into the northeast
by Sunday afternoon, with high pressure building into our region in
its wake. A secondary amplifying shortwave trough will eject from
The Rockies Monday, quickly developing a surface low across the
southeast. This low will build below a strengthening 250 mb jet and
move up the coast through Wednesday. In contrast to the previous
storm system, the mid and upper-level trough will remain positively
tilted, eventually stretching out as the surface low moves toward
the Canadian maritime provinces.
Friday...a mostly dry day in store, with rain moving
northeast into the region by afternoon and evening. Highs in the 40s
Saturday...an overall crummy day with periods of moderate to heavy
rain moving through the region. 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 may see some decent rains again and it could be heavy
at times. Added the mention of heavy rain into the forecast as it
looks clearer that heavy rain will occur within the forecast area.
While right now it doesn't look like we will see enough rain to
cause any big flooding concerns, 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. Highs in the low to upper
50s through the region.
Sunday...clearing conditions as the low moves northeast and out of
the area, with clearing skies by the afternoon. It will be breezy
though with wind gusts to 20 mph across much of the area and highs
will be in the 40s generally.
Monday through Wednesday...the next storm system will quickly shoot
into our region Monday. Details are still uncertain regarding this
system with model discrepancy between the global models regarding
the mid to upper level trough development in the pattern. If the
system this weekend brings heavy rain, as is indeed possible, we may
have additional flooding concerns. This will be something to monitor
in the coming days. Seasonable highs in the 30s and 40s.
Aviation /21z Wednesday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Late afternoon...VFR. Clouds across srn New Jersey will continue to
decrease. Winds will be mostly west or northwest around 10 kts. A few gusts
in the 15 to 20 kt. Range are possible.
Tonight... VFR. Mostly sky clear. Light northwest or north winds.
Thursday... VFR. Mostly sky clear. Light variable winds during the morning
then NE to east winds 5 to 10 kts during the afternoon.
Thursday night...although most sites should be initially VFR
some MVFR ceilings could move in from south to north after
midnight, although confidence is low in this occurring. Winds
will generally be under 5 kts and favor the easterly half of the
Friday...VFR in the morning will slowly give way to MVFR conditions
as rain moves northward into the region. Easterly wind near or below
5 knots. Medium confidence.
Saturday...MVFR to IFR as periods of rain move through the region.
Easterly winds turning southwesterly from 5 to 10 knots with gusts
up to 15 knots. Moderate confidence.
Sunday...VFR conditions return as a storm system lifts to our north.
Breezy with westerly winds from 10 to 15 knots and gusts to 25
knots. Low confidence.
Monday...generally VFR with west-northwesterly winds from 5 to 10
knots. Moderate confidence.
tonight into Thursday morning: after a lull in Small Craft Advisory conditions this
afternoon, a cold front will pass through the waters this evening
which should result in another period of gusty northwest winds. Gusts could
approach or exceed 30 kts over the northern ocean areas, while gusts
will generally be in the 20-25 kt range. Despite fairly marginal
gusts decided to add Delaware Bay to the Small Craft Advisory in effect until 11z
Thursday, since water temps are in the mid 40s allowing for
relatively efficient momentum Transfer with some of the stronger
Thursday and Thursday night: winds will relax through the day on
Thursday and gradually veer through the day ultimately becoming more
easterly-southeasterly by Friday morning. Seas will generally be 2-4
ft through the period.
Friday...elevated winds and seas, but conditions are expected to
remain below Small Craft Advisory criteria with easterly winds from
10 to 15 knots and gusts to 20 knots. Seas from 3 to 5 feet.
Saturday...winds may approach Small Craft Advisory criteria by the
afternoon with gusts nearing 25 knots out of the southwest. Seas
from 5 to 7 feet.
Sunday...gale force gusts possible out of the west from 30 to 35
knots through the afternoon. Seas ranging from 4 to 6 feet.
Monday...Small Craft Advisory conditions possible in the early morning with
northwesterly winds from 20 to 25 knots dropping below criteria into
the afternoon with northwesterly wind from 10 to 15 knots. Seas from
1 to 3 feet.
Marine...Small Craft Advisory until 6 am EST Thursday for anz430-431-