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000 
FXUS61 KPHI 261405
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1005 AM EDT Wed Apr 26 2017

.SYNOPSIS...
The coastal low that has affected the East Coast the past 
several days will begin pulling away from the region today, but 
will be slow to exit. A cold front will move across the area 
Thursday night, with a second Saturday night. A warm front is 
expected to lift across the area Sunday night, followed by 
another cold front on Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
930 AM ESTF: cloudy with areas of drizzle and isolated showers
spinning west and southward through the forecast area into this
afternoon due to the close proximity of the vertically stacked 
low pressure system off the mid Atlantic coast. 

No changes to the 330 am fcst temps/dews.  

From the 330 AM fcst discussion for temps today. 

Model guidance continues to show considerable spread regarding 
temperatures today. MOS guidance from the MAV (highs in the 70s)
is 5-10F warmer than the MET (highs in the 60s) due to 
differences in how much sunshine develops this afternoon. There 
does not appear to be a notable mechanism to mix out the marine 
stratus today with a strong low-level inversion remaining in 
place, light N-NEly winds and no notable source of dry/cold air 
advection. Accordingly, forecast weighted more toward the cooler
and cloudier NAM-based guidance though not quite as extreme. If
breaks in the clouds were to develop this afternoon, forecast 
temperatures would need to be adjusted upward by several degrees
(which would be more likely to occur farther inland toward the 
eastern shore of MD and our far western zones in eastern PA).

Tonight...The coastal low will continue to weaken tonight as it
moves out to sea, passing south of Long Island/southern New 
England. Marine moisture will remain trapped underneath the 
subsidence inversion. Any stratus that mixes out this afternoon 
should redevelop quickly after dark tonight. At least patchy fog
is anticipated late this evening and overnight, but the extent 
of the fog should be limited by the presence of stratus 
beforehand. It should be noted that some of the guidance shows 
dense fog forming late tonight but we have not quite bit on that
due to the previously mentioned reasons. Cloud cover should 
curb how much cooling takes place tonight. Forecast lows are in 
the 50s. Nearly calm wind.

&&

.SHORT TERM /THURSDAY/...
On Thursday, our area will be under the influence of return 
flow ahead of an approaching cold front. Brighter... but still a
lot clouds. warmer. Wind becomes southeast to south.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
It is possible that an isolated shower may develop across 
northeast Pennsylvania and northern New Jersey as a weak short 
wave/vorticity impulse approaches the area. However, the best 
chances for rain are expected to be during the overnight hours 
as the front moves across the area and a stronger short 
wave/vorticity impulse moves across the area. Although much of 
the guidance dissipates the more widespread showers as they 
approach, they do keep some scattered showers across our area.

The front moves offshore Friday morning and any showers will 
dissipate and/or move offshore through the morning as well. The 
remainder of Friday will remain dry as weak high pressure 
briefly affects the area. 

By Friday night, another frontal boundary is forecast to begin 
approaching the area from the north as it crosses Pennsylvania 
and New York. The front will cross through the area during the 
day Saturday, then stall to our south Saturday night into 
Sunday. There is some slight timing differences in the model 
guidance on when the front moves through. But as a couple of 
short wave/vorticity impulses move across the area Friday night 
through Saturday night, there will be a chance for 
isolated/scattered showers.

The front will stall to our south during the day Sunday, which 
should allow Sunday to be dry. Being the front is a back- door 
front coming from the north, it will bring cooler conditions on 
Sunday. But the front will not stay to our south very long as it
is expected to lift back northward as a warm front Sunday 
night/Monday morning. While there is a chance of showers Sunday 
night into Monday morning, the more likely time period for any 
precipitation would be later Monday into Monday night as a cold 
front approaches from the west. Being we should enter into the 
warm sector during the day, we should warm quite nicely, and in 
turn some instability should build ahead of the front. Therefore
there will be a chance of thunderstorms Monday afternoon and 
Monday night.

The front will move offshore by Tuesday morning, but a 
secondary surface trough may move across the area during the day
Tuesday. With a short wave/vorticity moving across the area 
during the day, there could be some isolated showers across 
northeastern Pennsylvania and northern New Jersey.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY and surrounding areas.

Rest of today...IFR cigs and in some cases IFR/LIFR conds in
drizzle fog isolated showers...all should improve this afternoon
to generally MVFR cigs...except maybe IFR continues along the 
coast in st/fog. Light northeast wind.

Tonight...IFR conditions in st/fog should redevelop in nearly
calm wind though it may take until near 06z for IFR to redevelop
at the inland sites, dependent on how warm it gets there late 
this afternoon.

Thursday...Ifr or MVFR conds in st/fog to start the day, probably
improves to VFR sct-bkn clouds aoa 3500 feet during the 
afternoon. Wind becoming southeast to south. 


OUTLOOK... 

Thursday night...Generally VFR. A chance of showers overnight 
which could temporarily reduce conditions to MVFR.

Friday...VFR conditions expected.

Friday night...VFR early. Patchy fog and low CIGS may develop 
overnight.

Saturday...Becoming VFR during the morning, then a chance of 
showers during the afternoon. Conditions may temporarily be 
reduced with any showers.

Saturday night-Sunday...Low clouds and fog may develop 
overnight Saturday and continue into Sunday leading to reduced 
conditions. There will also be a chance of showers.

&&

.MARINE...
The Small Craft Advisory hazardous seas continues through
Thursday as does the MWW for areas of dense fog this morning. 
Waves are currently around 7-9 ft and will gradually subside to 
4-7 ft late this afternoon and tonight.

OUTLOOK... 

Thursday night...Small Craft Advisory for hazardous seas 
through Thursday night.

Friday...Winds expected to remain below advisory levels, but 
seas may remain elevated to advisory levels.

Friday night-Sunday...Winds are expected to remain below 
advisory levels. Seas may approach 5 feet at times, but mostly 
remain around 4 feet.

&&

.TIDES/COASTAL FLOODING...
We will continue to monitor the high tide this evening since it
will be the higher one that occurs with a new moon. If the water
does not drain away from the coast fast enough, we could see 
some localized minor flooding at that time. ETSS and a few of 
the higher NYHOPS ensemble members predict levels reaching minor
threshold (but below local advisory criteria) at Lewes, Cape 
May and Reedy Point while the majority of the remaining guidance
(including ESTOFS) keeps it short of minor.

&&

.CLIMATE...
Presuming our forecast temps these last 5 days of April are
accurate, we are assured of a top 3 warmest April on record in 
much of our forecast area. Sunday is the critical day for 
determining record or not. 


April projected within the top April avg temps, the normal for
April and the period of record (POR). 

PHL normal 54.0 POR 1874

59.4 1994
59.2 2017? 
58.5 1921 
58.4 2010 
57.9 1941

ABE normal 49.9 POR 1922

56.6 projecting record
56.4 1941
54.7 1994

ACY normal 51.7 POR 1874

57.2 projecting record
56.3 2010
56.1 2011

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until noon EDT today for ANZ431-450>455.
     Small Craft Advisory for hazardous seas until 6 AM EDT Friday 
     for ANZ450>455.

&&

$$
Synopsis...Robertson
Near Term...Drag/Klein
Short Term...Drag/Klein
Long Term...Robertson/Miketta

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