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000
FXUS61 KPHI 081716
AFDPHI
Area Forecast Discussion
National Weather Service Mount Holly NJ
1216 PM EST Sun Dec 8 2019
.SYNOPSIS...
High pressure will shift off to the east today. A warm front will
move through the region Monday as an area of low pressure tracks
through the Great Lakes. A cold front associated with that low will
then approach and move through the area on Tuesday and into Tuesday
night. A wave of low pressure tracking along the front will likely
affect the mid-Atlantic Tuesday night into Wednesday. Strong high
pressure will build in Thursday and into Friday. Unsettled weather
may return by next weekend.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
12:30 AM Update...Adjusted temperatures and dew points to match
current observations, then warmed them slightly this afternoon.
Increased cloud cover a tad this afternoon given the cirrus on
their way from the Midwest. Rain is still on par to move in
overnight. Tomorrow will be a far cry from today's seasonable
weather.
Previous Forecast...High pressure builds offshore of the east
coast through today, which will set up a return flow across the
area. Dry weather remains across the area as there is little
moisture across the area as evident of PW values less than 0.50
inches. Clouds will increase through the day, especially later
this afternoon as a short wave moves into the area from the
west. As wind shift to a southerly direction today, a few gusts
around 15-20 mph will be possible.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
The evening will start out dry across the area with increasing cloud
cover. However, as the low levels become saturated, and more
moisture lifts across the area ahead of a warm front approaching
from the south, areas of precipitation may develop for many areas.
Initially, some patchy light rain or drizzle may develop as the low
levels become saturated as the low level inversion become more
pronounced. As the deeper saturation develops north of the
approaching warm front and short wave, the drizzle will likely
become a steadier light rain for many areas. The overnight hours
will not be a super soaker, but that will likely change for Monday.
If the precipitation begins early enough across portions of
northeast Pennsylvania and northern New Jersey, some sleet may mix in
for a brief period, before changing to all rain.
&&
.LONG TERM /MONDAY THROUGH SUNDAY/...
Overview...
An active week of weather is ahead, as multiple disturbances will be
impacting the region with several periods of precipitation. The most
prominent synoptic feature for the first half of the week will be a
Great Lakes low passing to our west Monday and into Tuesday, leading
to a major warm-up but also a prolonged unsettled stretch. By late
Tuesday night and into Wednesday, we will be watching what happens
behind the cold frontal passage associated with the Great Lakes low.
A wave of low pressure behind the front could bring some snow to the
area during that time. Strong high pressure and cold air look to
build in towards the end of the work week. By next weekend, most
indications are that active weather will return, though uncertainty
is high during that period.
Dailies...
Monday-Monday night... As low pressure moves across the Great Lakes,
a warm frontal passage will bring a period of rain to the region,
especially during the afternoon, evening, and early overnight. In
addition, an area of moisture offshore looks to get entrained in the
strong low level southerly flow behind the warm front. This could
further enhance rainfall especially in coastal areas. Mainly light
to moderate rain is expected but could see a couple downpours. Rain
should taper off later Monday night especially to the south, with an
unseasonably warm overnight expected. Also some wind concerns Monday
as guidance indicates 60 kt or more of wind possible at 850mb.
However, as usual in cold season southerly flow, the low levels look
pretty stable and much of that wind will fail to mix down. So right
now expecting surface gusts to stay mostly under 30mph but there is
some room for those numbers to go up if thermodynamic profiles start
to look a little more favorable.
Tuesday... We'll still be under the broad sphere of influence of the
same weather system from the prior day on Tuesday, with a cold front
approaching from the west. I have a suspicion Tuesday may actually
turn out to be a decent day at least over its first half, as we
briefly get deeper into the warm sector. Reduced PoPs dramatically
for the morning hours, still at chance levels but even that may be
too high especially to the east. As the front gets closer and a
vorticity impulse tracks up along it, another steadier period of
rain or showers is likely by later in the day. Very warm Tuesday as
well ; many areas will break into the 60s, and some guidance
suggests parts of Delmarva could exceed 70, though did not go that
far yet. Between Monday and Tuesday, total rainfall should range
from 1 to 2 inches. Not expecting this to cause any noteworthy hydro
issues based on current hydrologic conditions, maybe just isolated
nuisance or poor drainage flooding during any periods of heavier
rain.
Tuesday night-Wednesday night... Uncertainty increases here. The
approaching cold front slows down as it crosses the region, and
guidance indicates multiple additional impulses will ride up along
the front Tuesday night and early Wednesday. This should lead to
steady precip continuing through Wednesday morning, and with colder
air seeping in there will be ptype concerns this period. Guidance
indicates a change to snow from west to east Tuesday night into
Wednesday, with varying degrees of overlap between colder air and
QPF. Am always skeptical of setups like this, as it is a game of
"thread the needle" to actually get accumulating snow in the coastal
plain, which is where it looks like QPF will be most focused this
period. We've seen two similar setups this season with negligible
snowfall. While this one does look a little more impressive, I'd
need to see signals a little stronger in the guidance before I'd be
on board for more than a nuisance snow event. Surface temps will
likely stay above freezing even after the change over, with snow
ratios likely to be well below 10:1 in most areas. So while early
indications are that some light snow accumulations are possible, not
holding expectations too high. There was somewhat of a trend with
this cycle to shift the trailing impulses and associated precip a
little further west. If the westward trend continues, there may be a
better shot of accumulating snow in the interior since those areas
will be colder. Everything should pull away Wednesday afternoon and
evening with dry weather returning and a cold night with continued
CAA. Another reinforcing cold front may move through during the
night Wednesday, but it looks to be a dry frontal passage save for
maybe a snow shower or squall in the Poconos.
Thursday-Friday... Dry weather, but also quite cold as strong high
pressure builds in. Thursday looks especially cold, with highs
likely struggling to crack the freezing mark in most areas just two
days removed from being in the 60s. Lows Thursday night may be
colder than currently forecast as it will probably be a good night
for radiational cooling. Some moderation occurs by Friday but still
below average. Probably still dry as well, assuming the GFS is too
fast with bringing in the next system from the south, with the high
remaining nearby.
Next weekend... A lot of uncertainty, mainly to do with timing
differences in the guidance on an area of low pressure coming up
from the south. Given active weather earlier in the week didn't dive
too deep here and kept the forecast for this period close to
consensus and the previous forecast. Best guess at this point would
be that Saturday is an unsettled day with potentially some clearing
by Sunday. Early indications are for mainly rain with the system
next weekend, but we will fine tune as it gets closer.
&&
.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Today...VFR conditions will continue through today with mostly high
level cirrus clouds through most of the day. Clouds will increase
through the day however. Light and variable winds early increase out
of the southeast, then south through today as high pressure builds
offshore of the east coast. Speeds will be mostly 5-10 knots, with
occasional gusts around 15-20 knots. High confidence.
Tonight...Clouds continue to increase in coverage and lower with
their heights through the evening and overnight. MVFR conditions are
expected to develop by 05z-06z and lower through the overnight into
early morning hours Monday. Light rain or drizzle may also develop
by 05z-06z, before becoming a steadier rain by daybreak Monday.
South to southeast winds around 5 knots during the evening will
become light and variable for most places overnight. Moderate
confidence.
Outlook...
Monday-Monday night... MVFR or IFR conditions likely in periods of
rain. Steady southwest winds likely, with gusts to 30 kt possible at
times. LLWS is likely as well. Moderate confidence.
Tuesday... Could be a period of VFR conditions Tuesday morning, but
a return to MVFR or IFR is likely later in the day as more rain
moves in. West-southwest winds of 10 to 20 kt. Moderate confidence.
Tuesday night-Wednesday... IFR likely Tuesday night into Wednesday
morning with rain changing to snow. By later Wednesday, conditions
may trend towards MVFR or VFR. Winds becoming west-northwesterly for
most of this period with speeds around 10 kt. Moderate confidence.
Wednesday night-Thursday... VFR. Light northwest winds becoming
northerly on Thursday. Moderate confidence.
&&
.MARINE...
Today-tonight...Conditions on the waters are expected to remain
below advisory levels through most of the day as high pressure
shifts offshore. However, a brief period of Small Craft Advisory
levels winds are expected for the Atlantic coastal waters from Great
Egg Inlet northward later this afternoon into this evening. Winds
will diminish back below advisory levels overnight.
Outlook...
Monday-Tuesday night... Marine headlines are likely for the early
part of the week. Mainly SCA conditions expected from Monday through
Tuesday night. Considered a Gale Watch for Monday and Monday night;
while current forecast keeps conditions below gale force, cannot
rule out a period of southerly gales on Monday. Winds turning
southwesterly Monday night and Tuesday then northwesterly on Tuesday
night with gusts mainly 25 to 30 kt, but decreasing on Tuesday
night. Seas 5 to 9 ft.
Wednesday... Conditions are expected to fall to sub-SCA levels with
lighter northwest winds and 3 to 4 ft seas.
Wednesday night-Thursday... Current forecast calls for marginal SCA
level conditions with north-northeasterly winds gusting to around 25
kt. Building seas later in the week will likely yield additional
marine headlines.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 5 PM this afternoon to 1 AM EST
Monday for ANZ450>452.
&&
$$
Synopsis...O'Brien
Near Term...Davis/Robertson
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