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FXUS61 KPHI 081716

Area Forecast Discussion
National Weather Service Mount Holly NJ
1216 PM EST Sun Dec 8 2019

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.


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
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.


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.



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.


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 

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.


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


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.


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.


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.


MARINE...Small Craft Advisory from 5 PM this afternoon to 1 AM EST 
     Monday for ANZ450>452.


Near Term...Davis/Robertson

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