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fxus61 kphi 280503 
afdphi

Area forecast discussion
National Weather Service Mount Holly New Jersey
103 am EDT Tue Mar 28 2017

Synopsis...
a warm front from central New Jersey through the Delmarva will
drift south today as low pressure in the Ohio Valley heads east,
exiting seaward from the mid Atlantic coast this evening. High
pressure will build down from Canada for Wednesday and Thursday.
Low pressure in the lower Mississippi Valley Thursday night
will move through our area on Friday and Saturday. Weak high
pressure returns for late Sunday and Monday.

&&

Near term /through today/...
1230 am estf: has new 5050 blended 00z/28 GFS/NAM MOS guidance
for temps/dews/winds through 12z Wednesday. This blend is cooler
than prior guidance, in part due to NE flow, showery rains, and
cloudy skies. The fog and shower fcst was not changed for the
1230 am update as it seems to be working quite well, showers
sprouting up and moving NE from NE PA and New Jersey...some are briefly
moderate to heavy. Isolated thunder is possible early this
morning.

It is possible that the dense fog advisory may need to be
expanded westward in the 330 am fcst, but confidence on how
widespread it will be, is low, at this time.

Today...in addition to the info in the 1230am estf...yesterdays
fcst discussion for today still works. Am not as confident in
thunder this afternoon as I was ydy, in part due to cooler new
flow with mlc suppressed swd a bit.

Here is that discussion: surface low in the Ohio Valley at 12z
moves east along or just south of the Mason-Dixon line into
Maryland/Virginia by 00z Wednesday as the shortwave trough
begins a curve toward the southeast on the outer fringe of a
subtropical ridge in the Gulf of Mexico. Degree of cooling in
the midlevels combined with strong ascent downstream of the vort
Max will promote the development of storms in much of the mid-
Atlantic on Tuesday. Most model guidance suggests two rounds may
occur. The first would occur early in the day as elevated
convection along the nose of enhanced low-level isentropic
ascent. After a brief lull in the late morning and early
afternoon, more convection is expected to develop along/east of
the low and southward- extending cold front, aided by
substantial cooling in the midlevels and large-scale ascent via
differential cyclonic vorticity advection. Vertical shear looks
relatively weak, and MUCAPE values will generally remain at or
below 1000 j/kg (mlc aob 600j and mostly delmarva), especially
if early- day convection eradicates preexisting instability.
Prospects for severe convection look limited at best, but
scattered storms are still a good bet as The Rounds of
precipitation move through the region, particularly in the
afternoon. Best chances appear to be along and south of the
Mason-Dixon line given the track of the low and the associated
lifting mechanisms. However, overall uncertainty remains given
the multiple rounds of precipitation that may occur. Therefore,
a general broadbrush of chance to likely pops was placed in the
grids for now.

There is better potential for locally heavy rainfall given the
decent pwats of ~1.25", multiple rounds of precipitation
expected, and potential for localized training storms,
especially if storms can align along the baroclinic zone. Though
widespread flooding is unlikely, think isolated instances of
nuisance short-term flooding is a possibility. This will
continue to be monitored in later forecasts.

Temperature forecast remains a concern with the placement of the
eastward-extending warm front again a complicating factor. Errors
in these values are likely given timing of the rain cooling
factor and where skies may thin to allow a little sun.

&&

Short term /tonight/...
any remaining showers end from west to east with a slightly
faster modeled end to the rain than 24 hours ago.

There could be some patchy fog, especially early at night in
the still moist boundary layer with a light north wind
increasing a bit late at night and trending northwest.

Forecast basis was a 50 50 blend of the 00z/28 GFS/NAM MOS.

&&

Long term /Wednesday through Monday/...

Canadian high pressure will start to push southward into our area on
Wednesday and persist across the region through Thursday. While the
system itself isn't particularly strong, it should allow for US to
dry out as a decent northwest flow is across the area on Wednesday.
Winds will lighten up for Thursday with cooler air settling over the
mid-Atlantic. Highs will be slightly above normal on Wednesday and
much closer to normal on Thursday.

The next system starts to advance towards our area on Thursday. Low
pressure will develop to our west and then move into the Tennessee
Valley by late Thursday. As the low continues to move towards our
area, we will start to see cloud cover increase and showers will
once again start to move into the area. Expect some light rain to
develop in the vicinity of the approaching warm front

The center of the low will cross just to the south of the region on
Saturday, by around mid morning. The rain will end from west to east
and we should see a little bit of clearing occur. However, there is
not much of a flow behind this system and it may end up remaining
pretty cloudy, especially for areas inland.

Weak high pressure will again be around the region for Sunday
and Monday. Models indicate that a shortwave may move through later
on Sunday, which may trigger a few light showers. Confidence is low
at this time.

&&

Aviation /06z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Through 12z...VFR or MVFR vsby gradually deteriorating to IFR
conds in St/fog by 12z with scattered showers. Light wind,
mostly east or northeast at the taf locations.

After 12z Tue...IFR variable MVFR conds in St/fog scattered
showers and a generally light east to northeast wind.

Tonight...MVFR/IFR conditions possible in showers and fog...
becoming VFR late. Light north winds will become north to
northwest overnight around 10 knots.

Outlook...

Wednesday...VFR conditions expected. Winds will be north around
10 to 15 knots, some gusts up to 25 knots possible.

Thursday...VFR conditions expected. Light north winds... becoming
east late afternoon.

Friday...IFR or MVFR conds in periods of rain. East to southeast
winds around 10 to 15 knots.

Saturday...MVFR/IFR conditions early in rain... becoming VFR late.
North to northeast winds around 10 knots or less.

&&

Marine...
dense fog advisory has been issued for the New Jersey coastal
waters north of little egg. Areas south may also develop fog
overnight, but it is less certain at this time. This will be
monitored closely this evening. Winds/seas will be under
advisory criteria through Tuesday night. Scattered showers/isolated
thunderstorms through today, with showers ending this evening.

Outlook...

Tuesday night...southerly winds will become west then northwest
overnight. Speeds around 10 to 15 knots. Seas 2 to 4 feet.

Wednesday...northerly winds around 10 to 20 knots with gusts around
25 knots late. Seas increasing to around 5 feet . A Small Craft Advisory will likely
be needed as conditions near criteria by Wednesday evening.

Thursday...decreasing seas through the day. North winds becoming
easterly late in the day, mainly around 10 to 15 knots.

Friday...east to southeast winds around 10 to 20 knots with gusts up
to 30 knots possible. Seas will build through the afternoon,
exceeding 5 feet by Friday evening. A Small Craft Advisory looks likely.

Saturday...Small Craft Advisory conditions continue. Northerly winds around 10 to 15
knots. Seas will remain above 5 feet through Saturday, starting to
subside a bit late.

&&

Equipment...
knel appears to be reading 10f too warm the past several days.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...dense fog advisory until 10 am EDT this morning for njz013-014-
020-026.
Delaware...none.
Maryland...none.
Marine...dense fog advisory until 10 am EDT this morning for anz450-451.

&&

$$
Synopsis...meola/drag 103
near term...drag/Robertson 103
short term...drag 103

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