Scientific Forecaster Discussion
fxus61 kphi 132231
Area forecast discussion
National Weather Service Mount Holly New Jersey
631 PM EDT sun Oct 13 2019
a weak area of low pressure will develop along a stalled front,
which is south and east of the area, then the low tracks
northeastward off the Delaware and New Jersey coasts later
tonight. High pressure then builds into the area Monday and
Tuesday. Low pressure and its associated fronts will approach
the area on Wednesday, while a secondary area of low pressure
develops offshore. Once this system moves away from our area,
high pressure will build in for Friday and Saturday.
Near term /until 6 am Monday morning/...
ongoing warm air advection across Delmarva into far southern
New Jersey is assisting in lift and resulting in some showers.
These showers should become more numerous this evening as a 250
mb jet streak arrives and helps induce a weak surface low. In
addition, jet streaks at 500 mb and 850 mb are forecast and this
is expected to focus much of the showers across southern New
Jersey southward. At least a few showers are anticipated to move
into the I-95 corridor, and radar trends are showing this
developing at this time. The farther north and west one GOES
across the forecast area, drier air and much less forcing should
preclude little to no shower activity. For the 630 PM update,
made some adjustments to the pops based on radar and short term
guidance trends. Tweaked the hourly temperature, dew point and
wind grids to match the current observations and also trends.
Otherwise, a weak area of low pressure will develop near the
mouth of the Chesapeake Bay this evening along a stalled front
located to our south and east. This low will lift northeastward
across southern Delmarva, then across southeastern New Jersey,
before it lifts to our northeast overnight. As this low moves
across the area, moisture will continue to increase, along with
some enhanced lift due to a couple of short waves moving across
the area within the southwest flow aloft. Most rainfall should
fall across southern New Jersey and central/southern Delaware
and Maryland, generally south of the I-95 corridor. Rainfall
totals should reach one-quarter to one-half inch across portions
of southern New Jersey and central/southern Delaware and
Maryland through the overnight.
As the low lifts to our northeast overnight, the rainfall will
come to an end between midnight and daybreak. As the low lifts
to the northeast and rainfall ends, patchy fog may begin to
develop overnight. Widespread dense fog is not expected at this
time, but visibilities could drop down to a mile or two in many
Short term /6 am Monday morning through 6 PM Monday/...
any low clouds and fog from the overnight and early morning
will lift and burn off through the morning hours. Then the
remainder of the day will end up pretty nice as skies begin to
clear out and temperatures warm up several degrees above normal.
A reinforcing cold front will swing across the area late in the
day, so drier and cooler air will begin to move in late in the
afternoon. Winds will also increase through the day, and may
begin to gust 15-20 mph by the afternoon our of the west to
Long term /Monday night through Sunday/...
summary... the long term period will be characterized by quiet
weather Tuesday, a period of widespread moderate-heavy rainfall
Wednesday, a wind day on Thursday, followed by quiet weather
Tuesday...the extended period will begin tranquil as surface
high pressure crests the area on Tuesday. Highs should be
seasonable with abundant sunshine.
Wednesday... the most active period of the long-term will be on
Wednesday as low pressure progress eastward across the Great
Lakes. At this point a secondary low looks to form over the southeast
US on Wednesday, with most guidance depicting this low rapidly
deepening as it moves northeastward. This seems reasonable given
that upper support will be quite favorable in its vicinity with
the left exit region of a near 150kt upper lvl jet approaching.
In terms of sensible weather expect widespread moderate rain
during the day on Wednesday, initially in the prefrontal warm
advection regime, and then just ahead of the cold front
Wednesday afternoon. Given the deepening low and associated h850
fgen more or less overhead Wednesday afternoon, went fairly
bullish with quantitative precipitation forecast. Although there is still some uncertainty (as
is common in these coastal low setups) would not be surprised to
see amounts over an inch in spots (particularly over northern
and eastern portions of the forecast area). Some isolated
thunder can't be ruled out but didn't have enough confidence to
include any mention at this time.
Wednesday night/Thursday... rainfall will taper off fairly
rapidly off from SW to NE Wednesday night as the low speeds off
to the northeast (deepening further as it does so), and drier
westerly flow filters in behind it. On Thursday the main story
will be the gusty westerly winds as a tight gradient will
develop between the departing low and high pressure over the
Mississippi Valley. Right now assuming efficient mixing
overland peak gusts look in the 30-35 kt range, but can't rule
out some locally higher gusts, particularly near the coast.
Additionally some fairly dense stratocu will be possible in the
cool Post-frontal northwesterly flow over the northwestern half
of the area, and can't even rule out a few light showers over
the Poconos as a backside shortwave slides down. Highs will
generally generally run in the mid 50s to low 60s.
Friday-Sunday... quiet/dry weather resumes as mid-lvl ridging
moves in, and surface high pressure progresses eastward. Highs
Friday should be similar to Thursday, before a warming trend
commences Saturday as the high slides to our east and southerly
flow develops. High temperatures could reach the lower 70s by
Aviation /00z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Tonight...VFR conditions start off all areas this afternoon, however
this will not last long as areas are expected to lower to MVFR later
this evening, then IFR overnight. MVFR conditions and rainfall are
expected to begin at miv/Acy by 00z-01z, the lower to IFR conditions
are expected by 03z with rainfall ending by 08z. For
ilg/phl/pne/ttn, MVFR conditions are expected between 02z-05z, with
IFR conditions developing by 04-07z. Winds will remain mostly east
to southeast this afternoon and early evening, before becoming light
and variable/calm overnight for most locations. -High
confidence this evening/moderate confidence overnight.
Monday...MVFR/IFR conditions will begin the day, before lifting to
VFR by late morning into the early afternoon. Winds begin the day
light and variable at all locations, before increasing out of the
west to northwest 5-10 knots. Some gusts around 15-20 knots are
possible during the afternoon. -Moderate confidence in the
morning, high confidence during the afternoon.
Monday night thru Tuesday night...VFR with increasing clouds
Tue night. Variable winds generally 5 kts or less. High
Wed/Wed night...sub-VFR conditions in steady rain expected,
conditions may improve Wednesday night as rain tapers off. Winds
initially from the south-southeast around 10 kts (possibly
higher and gusty towards acy) winds then veering sharply to the
west-northwest around 15 kts, behind a cold front Wednesday
night. Medium confidence
Thu...VFR conditions prevailing. West-northwest winds sustained
15-20 kts, gusting over 30 kts at times during the day. Medium
Fri... VFR with northwest winds around 10-15kts.
tonight...an area of low pressure will move across southern Delaware
and Maryland, then across southeastern New Jersey this evening and
overnight, before lifting to our northeast through daybreak. Winds
will become variable during this time period, before shifting to the
west to northwest behind the system. Winds are expected to increase
and gust around 20 knots, but likely remain below advisory levels.
Monday...conditions expected to remain below advisory levels through
the day, although winds could gust around 20 knots at times.
Monday night thru Tuesday night...sub Small Craft Advisory expected. Mostly fair
with light winds.
Wednesday...Small Craft Advisory conditions likely as seas build to 5-7 ft by
the late afternoon and southeast winds gust over 25kts. Rain expected.
Wednesday night/Thursday...gale conditions possible as westerly
gusts increase to near 35 kts. Seas decreasing below 5 ft by
Thursday evening. Rain diminishing by Wednesday night.
Friday...winds diminishing below Small Craft Advisory criteria on Friday although
northwest wind gusts 20-25kts will be possible, with seas around