000 
fxus61 kphi 210235 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
935 PM EST Fri Jan 20 2017 


Synopsis... 
weak high pressure will build across our region through 
Saturday. A strong and complex area of low pressure will impact 
the mid- Atlantic from Sunday through Tuesday. Conditions 
briefly dry out for the mid- week period, and then unsettled 
weather returns to close out the work week. 


&& 


Near term /until 6 am Saturday morning/... 
we will remain between two weather systems overnight. A mid 
level short wave trough is forecast to continue lifting 
northeastward over the Great Lakes while another short wave 
moves eastward off the middle Atlantic coast. Low pressure at 
the surface is expected to weaken near Lake Huron while another 
weak low is anticipated to move from the waters off North 
Carolina eastward and out to sea. Weak ridging should impact our 
region with a light southeast to southwest surface flow. 


Abundant low level moisture is forecast to remain in 
northeastern Maryland, Delaware, New Jersey and eastern 
Pennsylvania tonight with drying expected aloft. The resulting 
subsidence should result in lowering clouds along with the 
development of patchy fog and drizzle. 


Temperatures are anticipated to remain nearly steady or they 
may rise a few degrees during the night due to the southerly 
flow and the cloud cover. 


&& 


Short term /6 am Saturday morning through 6 PM Saturday/... 
weak high pressure will build along the coast on Saturday and 
we should see mainly dry conditions across the region. 


The southerly flow will keep moisture up across the area and 
its possible some light drizzle may remain into early Saturday. 
Unfortunately, skies will remain pretty clouded over through the 
day. However, we will still see temperatures rebound a bit and 
rise into the upper 40s across the north to mid to upper 50s 
across much of the area as the warm southerly flow continues. 


&& 


Long term /Saturday night through Friday/... 
high pressure along the East Coast moves offshore Saturday 
night. During this time, closed 500 mb low will strengthen and 
develop over the Southern Plains and Gulf Coast. In addition, 
high pressure north of the Hudson Bay will begin to nose its way 
to the south and east. Dry conditions expected Saturday night, 
but clouds associated with the developing low will stream 
northward into the mid-Atlantic and northeast. 


The first wave of rain lifts to the north and east and into the 
mid- Atlantic by Sunday afternoon and Sunday night. 


There is still uncertainty with regards to the forecast from 
there. 12z NAM is the coldest solution, with the high over the 
Hudson Bay dropping farther to the south and east compared to 
the European model (ecmwf) and the GFS. This allows a shallow layer of below 
freezing temperatures to filter into far northwest zones, generally to 
the north and west of I-80, and results in a prolonged period of 
freezing rain. Since the GFS and European model (ecmwf) have a similar position 
with the high and have the surface low farther north than the 
NAM, will side with the warmer solution. That does not rule out 
at least a brief period of sub-freezing temperatures across 
parts of the Poconos, so will mention a chance of freezing rain 
on Monday. Latest trends lower the potential of freezing rain, 
but it cannot be ruled out at this time. 


Waves of rain slide along the coast Monday and Monday night as 
that low approaches from the south and west. A tight easterly 
gradient develops between the high to the north and the 
approaching low. Combined with a 65-75 knots llj, can expect strong 
easterly winds to develop on Monday, with winds potentially 
gusting to 50 miles per hour for much of New Jersey to the east of I-95, and gusts 
potentially reaching 60 miles per hour along the New Jersey coast. Wind advisories 
will likely be needed, and there is the possibility for high 
wind watches/warnings for sometime on Monday. 


With high pwats upwards of 1.5", can expect periods of moderate 
to locally heavy rainfall during this time. Please refer to the 
hydrology section of the afd for flooding information. 


Low pressure lifts through the region Monday night, and precip 
tapers off fairly quickly behind the departing low. Winds also 
diminish fairly quickly as the gradient relaxes. 


Few lingering showers possible on Tuesday as 500 mb 
trough/shortwaves pass through the northeast. 


Dry conditions expected on Wednesday as high pressure builds 
through the region. 


A deep upper trough then approaches for the late week period. 
Unsettled weather is possible through the end of the work week, 
but at this time, does not appear to be anything widespread and 
organized. A return to more seasonal temperatures is expected by 
Friday. 


&& 


Aviation /03z Saturday through Wednesday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, 
kilg, kmiv, kacy and surrounding areas. 


Abundant low level moisture will remain in our region for 
tonight and Saturday. 


We are anticipating lowering conditions for tonight with all 
eight of our taf sites dropping into the IFR range and perhaps 
the LIFR or vlifr category for a time. Areas of fog and drizzle 
are expected overnight into Saturday morning. 


We will maintain the low conditions into Saturday morning with 
some improvement possible for Saturday afternoon. We have kept 
the forecast somewhat pessimistic due to the presence of a 
temperature inversion aloft that should keep the low level 
moisture from lifting and mixing significant. The tafs indicate 
an improvement to MVFR for the afternoon. However, this remains 
a low confidence forecast. 


A light and variable wind tonight may settle into the southwest 
for Saturday around 5 knots. 


Outlook... 
Saturday night...VFR. High confidence. Nearly calm winds. 


Sunday...conditions deteriorating from S to north in the afternoon 
with IFR conditions in rain. Moderate confidence. East winds 
increasing to 10-15 knots. 


Sunday night through Monday night...IFR and lower conditions in 
rain. East winds 15-20 knots with 20-30 knots gusts at terminals north 
and west of I-95, and 20-30 knots with 30-50 knots south and east of 
I-95 likely on Monday. Conditions gradually improve Monday 
night. Moderate confidence. 


Tue...scattered showers with brief sub-VFR conditions. 


Wednesday...VFR. 


&& 


Marine... 
no hazards are anticipated on the waters through Saturday. Seas 
remain around 4 feet along the coast with a 10 to 12 second 
period. Seas are gradually subsiding and should drop to around 2 
to 3 feet overnight. East to southeast winds 5 to 10 knots or 
less will become more southerly on Saturday. 


Outlook... 
Saturday night through Sunday morning...no marine headlines 
anticipated during this time. Seas will genly be around 2 to 3 
ft with wind 10 kts or less. 


Sunday afternoon through Monday night...easterly flow increases 
to 15-20 knots with 25-30 knots gusts by Sunday afternoon. Sunday 
night, east winds increase to 20-30 knots with 35-45 knots gusts by 
Monday morning. For northern and central ocean waters, a storm 
watch was issued for Monday for the potential for 50-60 knots 
gusts. Meanwhile, a gale watch was issued for Monday for 
southern ocean waters and Delaware Bay for the 35-45 knots gusts. Periods 
of moderate to heavy rain expected during this time with low 
vsbys. Conditions should improve late Monday night. 


Tuesday...lingering Small Craft Advisory conditions possible. 


Wednesday...sub-sca conditions expected. 


&& 


Hydrology... 
before heading into the weekend, I wanted to address the 
potential Hydro impacts for the Sunday through Tuesday period. 
In short, we don't think there will be any river flooding unless 
basin-wide rainfall averages climb above three inches. The most 
sensitive responding rivers right now appear to be the 
Millstone and the Rancocas. 


The entire region has some positive things working in its 
favor...precipitation has been below normal the last 30 days, 
there's really no consequential snow cover to speak of, there's 
no ice on area waterways, streamflows are either running at or 
below normal as is soil moisture, and last but not least, the 
ground isn't frozen. We think all the above will help mitigate 
the flood threat. 


We feel the latest mmefs runs are running a bit hot. They show 
some impacts with about 2.50 inches of rainfall. But taking into 
account the above mentioned items and the fact that the rains 
will fall over a 24 to 36 period, we feel more rain will be 
needed for river flooding. Marfc in-house contingency runs agree 
with this. 


As of now, it appears poor drainage or nuisance flooding is 
more likely, not flash flooding or river flooding. But keep an 
eye in things if more than 3.00 inches of rain come to fruition 
and you reside in a flood prone river basin. 


&& 


Tides/coastal flooding... 
it continues to appear as though an onshore flow will develop 
on Sunday, then it should strengthen on Sunday night. The 
onshore flow is forecast to be strong on Monday morning and it 
may begin to weaken gradually from south to north along the 
coasts of Delaware and New Jersey on Monday afternoon and Monday 
evening as low pressure approaches from the southwest and the 
pressure gradient relaxes. 


We will continue to monitor the two high tide cycles on Monday. 
However, the astronomical tides are rather low at that time so 
we are anticipating mostly minor flooding. Any flooding may be 
enhanced by the wave action. Breaking waves are forecast to be 
in the 5 to 8 foot range. There is the potential for localized 
moderate flooding, especially from Long Beach island up to 
Raritan Bay, based on the latest guidance. 


The first high tide on Monday occurs in the early morning hours 
along the oceanfront and it would require a surge of about 2.0 
to 2.5 feet to reach the minor flooding threshold. The second 
high tide which occurs in the late afternoon along the 
oceanfront would require a surge of about 3.0 feet to reach the 
minor flooding threshold. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...gale watch from late Sunday night through Monday afternoon for 
anz430-431-452>455. 
Storm watch from late Sunday night through Monday afternoon 
for anz450-451. 


&& 


$$ 


Synopsis...mps 
near term...iovino 
short term...meola 



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