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000
FXUS61 KPHI 091435
AFDPHI
Area Forecast Discussion
National Weather Service Mount Holly NJ
935 AM EST Mon Dec 9 2019
.SYNOPSIS...
A warm front lifts north through the Northeast today as low
pressure moves through the Great Lakes. The low passes north of
the area on Tuesday, and a cold front passes through the region
Tuesday night. The front then becomes nearly stationary along
the coast. Low pressure will develop on that front and will
affect the area Tuesday night and Wednesday. Strong high
pressure builds in from the west on Thursday and moves offshore
on Friday. Low pressure affects the Northeast next weekend,
followed by high pressure for the start of the following week.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
930 AM Update: The first round of rain is exiting the area at
this hour. The next round is forecast to move through starting
around 11 AM from west to east. The warm front is making its way
inland as well and will continue to do so over the next few
hours. I updated the temp/dewpoint forecast to better reflect
its progression inland through the rest of the day.
Previous discussion...
A coastal front is located along the Mid Atlantic coast from
New Jersey southward to the Carolinas. This front will remain in
place across the Mid Atlantic coast through today, before
beginning to wash out later this afternoon as an area of low
pressure lifts to our north along this boundary. Meanwhile,
several short wave/vorticity impulses will move across the area
as well today. Another short wave/vorticity impulse will be
moving across the area this afternoon. This impulse will bring
additional enhanced lift, creating more widespread rainfall
across the area. PW values will increase to 1.00-1.25 inches,
which could help lead to some periods of moderate to heavy
rainfall. Daytime rainfall amounts will be mostly 0.50-1.00
inches, with some locally heavier amounts possible, which could
lead to some ponding on roadways and poor drainage type
flooding.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
The coastal front will be out of the area by this evening,
however, additional short waves/vorticity impulses are expected
overnight. The first will occur during the first half of the
night. This impulse will have more moisture associated with it,
so higher chances of rainfall are expected for the first half of
the night. By the second half of the night, the next short wave
is not expected to have as much moisture associated with it, so
there will be decreasing rainfall chances overnight. There will
remain PW values of 1.00-1.25 inches, so some pockets of
moderate to heavy rainfall will be possible this evening.
Rainfall amounts this evening into the overnight will be mostly
0.25-0.50 inches or less.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
The start of the day Tuesday will find the region in the warm
sector ahead of the approaching cold front. Temperatures will be
well above normal, with highs in the 50s to low 60s. As the
front approaches, rain develops in the afternoon, and continues
into Tuesday night as the cold front works its way through the
region. Rain should mix with and change to snow in the southern
Poconos and northern New Jersey late Tuesday night through
Wednesday, and then rain and/or snow will gradually taper off
during the day Wednesday for southeast Pennsylvania, the rest of
New Jersey, and Delmarva. CAA will be underway on Wednesday,
and highs will be some 20-25 degrees colder than Tuesday,
topping off in the 30s to low 40s. Best chances for accumulating
snow will be in the southern Poconos and northern New Jersey,
but lighter amounts are possible in southeast Pennsylvania and
the rest of New Jersey. Will have to see how the arrival of the
cold air lines up with the timing of the precip.
Strong 1040 mb high pressure over the Northern Plains then
builds through the Great Lakes and into the Ohio Valley
Wednesday night, and will be over the region on Thursday. A
bitterly cold airmass overspreads the region with lows Wednesday
night in the teens and 20s, and highs on Thursday in the 20s in
the southern Poconos, and in the low to mid 30s elsewhere.
That high moves into the Gulf of Maine and towards the Canadian
Maritimes on Friday, and east to southeast flow develops behind
the departing high. Temperatures warm back up to near and
slightly above normal levels on Friday.
Meanwhile, low pressure will develop over the southeast U.S.
and will begin to lift north. A warm front will develop out
ahead of that low and will lift towards the Mid-Atlantic and
Northeast during the day Friday. Although Friday starts out dry,
some light precip may develop late in the day. It should be
warm enough for mostly rain, but there may be some frozen precip
up north.
GFS and ECMWF are dry, but the CMC brings precip north Friday
afternoon. Think slight chance/low chance PoPs will cover this
for now.
Rain likely Friday night and Saturday as low pressure lifts
north along the coast. Do have to watch for potential for
freezing rain Friday night in the southern Poconos, as it may
take some time for the lowest levels of the atmosphere to warm
above normal. By Saturday, expecting rain throughout. Should be
warm with highs in the 50s.
There is some uncertainty in the forecast from there.
Conditions should dry out on Sunday, but some weak upper
shortwaves could keep unsettled weather in the forecast into the
start of the following week.
&&
.AVIATION /15Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Today...IFR conditions will continue through the rest of the
day, with some areas lowering to LIFR. A couple of periods of
rainfall will be possible across the TAF sites. The first is
currently on its way out this morning, then a temporary break
is expected late this morning into the early afternoon before
more rainfall moves in for the remainder of the afternoon. IFR
conditions will remain regardless of the rainfall. LLWS will
also be a concern today across the TAF sites developing late
this morning into the afternoon.
Variable winds will be in place across much of the area through
the morning hours, before settling into a south to southeast
direction by this afternoon. Winds will increase to 5-10 knots
once the southerly wind begins.
--High confidence in IFR conditions and rainfall.
Tonight...IFR conditions will continue through the evening
hours and into the first half of the night as rainfall continues
to move northward across the area. However, as the rain moves
to our north, conditions may lift to MVFR for a time later in
the night.
Winds will increase out of the south to southwest this evening
and overnight, and may begin gusting 15-20 knots for some areas.
Where areas are not gusting, low-level wind shear may continue
into this evening.
--Moderate confidence in conditions improving overnight.
Outlook...
Tuesday and Tuesday night...Brief VFR conditions Tuesday
morning, otherwise MVFR/IFR Tuesday afternoon and night.
Southwest winds abruptly shifting to the northwest Tuesday
afternoon 10 to 15 kt with some gusts to 20 kt especially
Tuesday afternoon. Moderate confidence.
Wednesday...Widespread MVFR/IFR in rain, possibly changing to
snow at KRDG/KABE before ending. Conditions should gradually
improve to VFR in the afternoon. West winds near 10 kt.
Wednesday night-Thursday... VFR. Light northwest winds becoming
northerly on Thursday. High Confidence.
Thursday night-Friday... Generally VFR. Light northeasterly
winds Thursday night veering more easterly (around 5kts) on
Friday. Conditions may begin to lower Friday afternoon.
&&
.MARINE...
Today-tonight...A Small Craft Advisory continues for the
Atlantic coastal waters for today and tonight as winds will
increase to 20-25 knots, with gusts of 30 knots. Winds above the
surface increase even more, 40-45 knots at a few hundred feet,
however, there should be enough of an inversion to prevent these
winds from mixing down to the surface. If they do end up
increasing, we may end up having to issue a short fused Gale
Warning.
OUTLOOK...
Tuesday and Tuesday night...SCA extended through Tuesday for the
ocean waters, and SCA conditions may continue through Tuesday
night. SW winds will shift to the NW in the afternoon, and
gusts up to 30 kt possible. Tuesday night, winds and seas should
gradually diminish below SCA criteria.
Wednesday...Conditions should stay below SCA criteria, though
some westerly gusts to 25 kt are possible.
Thursday... Sub SCA conditions expected with northerly-
northeasterly winds gusting 15-20kts.
Friday...Seas potentially increasing above SCA criteria Friday
PM but uncertainty is high. Winds becoming easterly and gusting
15-20 kts by Friday afternoon.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EST Tuesday for ANZ450>455.
Small Craft Advisory from 7 PM this evening to 6 AM EST
Tuesday for ANZ430-431.
&&
$$
Synopsis...MPS
Near Term...Robertson/Staarmann
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