Scientific Forecaster Discussion
fxus61 kphi 212035
Area forecast discussion
National Weather Service Mount Holly New Jersey
335 PM EST Thu Nov 21 2019
high pressure will move offshore overnight. Low pressure will pass
from the Great Lakes toward the Canadian Maritimes through late
Friday pushing a cold front across our region on Friday. Low
pressure will develop across the southern Appalachians and pass just
to the south of the forecast area and offshore late Saturday into
early Sunday. High pressure then returns into early next week then
another system may potentially impact the region by the middle of
Near term /until 6 am Friday morning/...
the ridge of high pressure across the area this afternoon will slide
offshore tonight. A continuation of fair weather is predicted for
the overnight. High clouds over the area will continue to thicken up
overnight and some lower clouds will be around by sunrise.
Temperatures will be milder than last night with lows expected to be
in the upper 30s/low 40s north/west and mid 40s across Metro Philadelphia
and much of Delmarva. Winds will be light from the S or SW
Short term /6 am Friday morning through Friday night/...
Friday...low pressure will be moving down the Saint Lawrence valley
Friday. An attached cold front will cross the area from northwest to southeast
during the afternoon. The models have been varying quite a bit
regarding how much organized precip will occur with the front. The
better chcs will be across Delmarva/ southeast PA and srn New Jersey. Slight chcs
will be across other areas. We haven't changed pops too much, with
mostly high chc, but some low likely pops will be across srn Delaware. The
previous cycles of the NAM were rather dry, but the 12z came in with
1/4 inch qpf in many areas. This may be overdone, so I have kept my
qpf fcst closer to 1/10th inch attm.
Like today, Friday will be mild, prior to frontal passage. Highs
will reach into the upper 50s or perhaps a few low 60s for Delmarva.
Highs across the north/west areas will be in the low to mid 50s. These
readings will be a little above normal for late November. Winds will
be south to southwest increasing to 10 to 15 mph late.
Friday night...the cold front continues east of the region while
high pressure builds in from the west. Clearing skies during the
evening which will continue overnight. Northwest winds with some
gusts to around 15-20 mph early then diminishing. Colder (than Thu
night) with lows in the mid/upper 20s north/west and near freezing across
the Delaware valley and Delmarva.
Long term /Saturday through Thursday/...
the main story early in this period will be the low pressure
system still progged to move through the area late Saturday into
Sunday. To start the period early Saturday, Ridge of high
pressure will be located along the East Coast with an area of
low pressure associated with the southern stream over Tennessee.
The day will get off to a mostly clear and chilly start however
through the course of the day the high will move off the coast
while low pressure approaches as it moves NE into the Ohio
Valley. This will lead to skies becoming mostly cloudy through
the afternoon with rain likely developing towards the late
afternoon / early evening time frame from SW to NE. Highs
Saturday generally range from around 40 over the southern
Poconos to the upper 40s over the Delmarva.
For Saturday night, aformentioned low moves NE into western PA
driven by strong but progressive southern stream upper level
wave. Forecast models also continue to indicate there will
likely be at least some phasing with a northern stream wave
dropping through the Great Lakes. Rain will become more
widespread through Saturday evening with the tricky part of the
forecast being precip types over northern zones. Temperatures
aloft will be above freezing with the strong warm air advection
however there looks to be a low level layer near or below
freezing over the north so we still think there will likely be
some freezing rain over the southern Poconos and possibly parts
of Sussex co, New Jersey. Best chances for this look to be elevations
above 1500 feet or so. Elsewhere, should be all rain.
By Sunday morning, rain will still be ongoing over most of the area
(with some freezing rain or light wintry mix still possible in
the far north) as a secondary low looks to take shape near the
New Jersey coast. This low will move NE towards New England through the
day as it deepens and will bring the precip to an end from west
to east as it moves away. Precip should wind down in the morning
over much of eastern PA and the Delmarva but possibly not until
into the afternoon over portions of northern New Jersey. While the
system will have a fair amount of moisture with it and good
dynamics, the progressive nature of it should limit total rain
amounts to around 0.75 to 1.00 inches so not expecting any
Hydro issues. Otherwise it will start to turn a bit breezy with
some sunny breaks possible by Sunday afternoon and temperatures
remaining on the cool side.
Heading into next week, the weather pattern looks to be overall not
too active for this region. High pressure moves in Monday and should
influence our weather right through Tuesday bringing dry weather
with sunshine for both day and temperatures returning to more
seasonable levels. A low pressure system passing north/west of the region
may then bring some showers by next Wednesday as its associated cold
front moves through.
Aviation /20z Thursday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight... VFR expected with an abundance high clouds. A few lower
clouds late. Light S or SW winds.
Friday... increasing clouds. A cold front crosses the taf sites
around the end of the period (18z), so showers with VFR ceilings was
added for the final few hours of the tafs at krdg,kabe,kpne,kttn.
For phl, added a MVFR group at 18z with 025 ceiling. Confid in the final
few hours of the tafs is limited. SW winds prior to frontal passage then northwest
behind it (afternoon).
Friday night...VFR. Decreasing clouds for the evening, then
mostly sky clear. Gusty northwest winds during the evening, then diminishing.
Saturday and Saturday night...VFR initially with MVFR
restrictions developing late in the day through the overnight.
Periods of IFR possible. Rain overspreading the region late in
the day and through the overnight hours. Winds 5 kts or less
initially west becoming variable. Low confidence.
Sunday...lingering sub-VFR restrictions likely in the morning.
Clearing skies throughout the day. Winds becoming northwest
around 10 kts with gusts 15-20 kts. Moderate confidence on
overall evolution; low confidence on timing of improving
Sunday night through Monday...VFR expected. Westerly winds
around 5-10 kts. Moderate confidence.
tonight...high pressure will move offshore tonight. An increasing SW
flow will develop behind the high with Small Craft Advisory gusts developing after
midnight. The previously issued Small Craft Advisory will remain. I didn't choose to
include the Delaware Bay in the Small Craft Advisory flag attm, although a few g 20-25 kts
are possible. Fair weather tonight.
Friday... the Small Craft Advisory flag will continue on the ocean as a cold front
arrives on the waters during the afternoon. Showers will accompany
the front. Winds will shift from SW to northwest after frontal passage.
Gusts in the Small Craft Advisory range will continue. Seas mostly 3 to 5 ft on the
Friday night...Small Craft Advisory gusts and seas continue with cold air pouring
across the waters. The Small Craft Advisory for Delaware Bay is still not certain, but
possible. I capped the gusts at 22 knts for now on lower Delaware Bay.
Fair weather expected. Cold.
Saturday...sub-sca conditions expected.
Saturday night...conditions nearing Small Craft Advisory criteria overnight along
with light to moderate rain.
Sunday...Small Craft Advisory conditions developing by the afternoon hours with
offshore winds gusting around 25 kts and waves 3-5 feet. Rain
ending during the morning.
Sunday night through Monday...lingering Small Craft Advisory conditions will
diminish by daybreak Monday, then sub-Small Craft Advisory conditions expected.
Marine...Small Craft Advisory from 2 am Friday to 6 am EST Saturday for