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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 311959
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
359 PM EDT Tue Mar 31 2020

.SYNOPSIS...
A low pressure system crossing off the Carolina coast tonight is
expected to meander off the eastern seaboard through the rest of
the week. However, high pressure from the west is anticipated to
build slowly across our region through Saturday, keeping our region
mostly dry through this period. A weak cold front is expected to
cross the region Sunday into Monday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
A potent and progressive mid-level wave is making its way across the
southeastern US. The main vorticity lobe associated with this wave
will pass just to the south of the forecast area overnight. At the
surface, a strengthening area of low pressure will move up the
Carolina coast this evening and rapidly intensify (perhaps as low as
980 mb) as it continues offshore overnight. As the low draws a bit
farther north and east, the pressure gradient will increase
particularly across southern Delmarva and southern New Jersey. Winds
will shift from easterly to northeasterly and increase along the
coast to 15-25 mph with gusts of 35-40 mph.

The main axis of precipitation associated with this system is
forecast to remain mostly to our south, however the shield of
stratiform precip (in the form of rain) may nudge just across our
southern-most areas of Delmarva, mainly across Talbot, Caroline, and
Sussex Counties, where I`ve introduced some low end likely PoPs
overnight. Otherwise, the area will remain mostly dry and overcast
overnight. Expect low temperatures in the upper 30s to around 40
degrees.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
An upper trough axis will pivot across the area on Wednesday as a
strong surface low continues pushing offshore from the North
Carolina coast. Weak high pressure will begin to build toward the
end of the day. As heights begin to increase toward the latter half
of the day with the system departing, clouds should begin to break
up throughout the day. The HRRR indicates some showers across the
area during the afternoon, but this seems to be an outlier even
among other CAMs, so I`ve left the forecast dry. It`ll be a breezy
start to the day along and south of the I-95 corridor with higher
winds and gusts along coastal areas (see Near Term discussion).
Winds will subside later in the day as the surface low moves farther
away from the East Coast. Expect high temperatures mainly in the
lower 50s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Overview: No significant concerns in the long term until we get to
early next week, when another cold front approaches our region.

Details:

Thursday through Saturday...A mid level ridge is expected to build
from the southern Mississippi Valley to the Great Lakes region
starting mid week. The air mass should build slowly eastward with
the axis of the ridge passing off the coast on Saturday. The surface
low that will be crossing off the Carolina coast tonight is expected
to lift north and meander just off the eastern seaboard through the
week, even retrograding Thursday into Friday. The proximity of this
low will keep a relatively tight pressure gradient over our region
Thursday and Friday, and consequently breezy conditions are expected
to continue.

Sunday and Monday...The weak cold front is still expected to
approach and cross our region late this weekend. In the mid and
upper levels, there is a weak short wave trough which will be
crossing at the same time. With relatively weak support, it doesn`t
look like a significant precipitation event. The only change from
yesterday is it looks like the guidance is trending later with the
arrival of the front, now expected to cross our region Sunday night,
which seems like a reasonable trend given how stagnant the overall
pattern will be through the week.

Tuesday...A mid level ridge may try to build in behind the cold
front, but there is a lot of uncertainty given the lack of any well
defined features early  next week. Thus, have stayed close to the
previous forecast.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Tonight...Initially MVFR ceilings will lift to around 3kft after
00Z. Expecting mainly lower end VFR ceilings after this time, but
some patch MVFR may linger for a few hours. Initially easterly winds
will increase from 5-10 kts and shift northeasterly to around 10-15
kts after 06Z. Gusts of 20-25 kts possible mainly PHL and south
toward the coast. Moderate confidence.

Wednesday... VFR. Winds initially northeasterly will gradually shift
northerly then northwesterly between 18-21Z. High confidence.

Outlook...

Wednesday night through Thursday night...Mostly VFR conditions
expected. Northwest wind 10 to 20 kt with gusts near 25 kt
during the day Thursday. Moderate confidence.

Friday...Mostly VFR conditions expected, although there is a chance
for MVFR ceilings to develop. Northwest wind 5 to 15 knots,
becoming northeast. Moderate confidence.

Saturday...Mostly VFR conditions expected with light and variable
winds. Moderate confidence.

Sunday...Starting with VFR conditions, though ceilings could lower
to MVFR through the day. Southerly and southwesterly winds of 5 to
10 kt. Moderate confidence.

&&

.MARINE...
Conditions will quickly deteriorate later this evening into the
overnight with Small Craft Advisory criteria expected area wide
overnight along with winds increasing with gusts of 35-40 kts for
the southern-most ocean zones. Expect seas of 6-9 feet or higher
across the southern ocean zones as well. Have upgraded the SCA to a
Gale Warning for the impacted areas. Winds and seas are forecast to
peak around daybreak Wednesday then slowly diminish throughout the
day.

Outlook...

Wednesday night through Thursday night...SCA conditions are
expected. On Thursday, there may be a brief period of gale force
gusts on the Delaware and southern New Jersey coastal waters, but
confidence in this is low at this time.

Friday through Sunday...SCA conditions are expected, primarily on
the coastal waters due to elevated seas.

&&

.TIDES/COASTAL FLOODING...
The strengthening East to Northeast flow across the waters this
evening and overnight will create favorable conditions for the
enhancement of the tides the next few cycles. We have updated the
TWL forecasts early this afternoon to catch the latest guidance and
show these updated trends. It appears the the present tide cycle up
Delaware Bay may affect Reedy Point with that site reaching the `low-
end` range minor flooding. The overnight cycle (after midnight)
could affect more (DE and srn NJ) coastal and Delaware Bay sites
with action stage to possibly low end minor flooding. At this point,
an advisory doesn`t appear warranted, but we will continue to
monitor overnight in case anything changes.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ450>452.
     Gale Warning until 6 PM EDT Wednesday for ANZ453>455.
     Small Craft Advisory until noon EDT Wednesday for ANZ430-431.

&&

$$
Synopsis...Johnson
Near Term...Staarmann
Short Term...Staarmann
Long Term...Johnson
Aviation...Johnson/Staarmann
Marine...Johnson/Staarmann
Tides/Coastal Flooding...O`Hara