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FXUS61 KPHI 090825

Area Forecast Discussion
National Weather Service Mount Holly NJ
325 AM EST Mon Dec 9 2019

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.


Multiple rounds of rain are expected through today as several 
short wave/vorticity impulses will be lifting across the area 
today as a coastal front moves across the area as well.

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. The first is moving across the area this morning,
bringing with it enhanced lift which is leading to increasing 
drizzle and rain. This rain will spread northward through the 
morning hours, before a temporary break occurs for some area 
later this morning into the early afternoon. This break will be 
brief as another short wave/vorticity impulse will be moving 
across the area this afternoon. This second 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 


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. 


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.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY and surrounding areas.

Today...Those areas who have not lowered to IFR will do so 
through the rest of the early morning hours. Then 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 moving this morning,
then a temporary break will be possible 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.

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.

There will also be low-level wind shear for many areas today as
winds above the surface increase and surface winds remain 

--High confidence in IFR conditions and rainfall. Lower 
 confidence in how low conditions will drop.

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. 


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.


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 


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.


MARINE...Small Craft Advisory until 6 PM EST Tuesday for ANZ451>455.
     Small Craft Advisory from 9 AM this morning to 6 PM EST 
     Tuesday for ANZ450.
     Small Craft Advisory from 7 PM this evening to 6 AM EST 
     Tuesday for ANZ430-431.



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