Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 241347
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
947 AM EDT TUE MAY 24 2016

.SYNOPSIS...
Low pressure offshore of Long Island this morning will track
northeastward during today. High pressure will then build to our
south tonight through Wednesday before shifting offshore. A frontal
boundary is forecast to be draped mainly from the Great Lakes to New
England Thursday through Monday as some weak low pressure systems
track along it. This front may settle southward into at least
northern Pennsylvania and northern New Jersey at times late this
week and during the holiday weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The back edge of the precip shield over northern NJ is slowly
eroding as the upper level low continues to lift away from the
region. However, have kept the mention of isolated showers and
thunderstorms across the region this afternoon. Though there will
be little in the way of synoptic scale lift by this afternoon,
morning sounding from IAD indicates will will have a deep mixed
layer with steep lapse rates, so even orographic lift could be
enough to get isolated storms to develop. One other thing to watch
however, will be the dry air advection over the western portions
of our region which could further hinder convective initiation.

Temperatures today will be near normal across the wrn/srn areas
where more sunshine is expected. The abundant cloud cover n/e may
hold temps just below normal today. Overall highs low 70s north/east
and upper 70s south/west. Winds will be mostly n or nw this morning
and then w or sw this afternoon. Winds speeds mostly 5 to 10 mph.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
High pressure will begin to build across the area tonight. Except
for a few sct showers n/e during the early evening...it should be a
dry fcst. Clouds will thin out across the area as drier air moves
in. Low temperatures tonight will drop into the low 50s across the
north and bottom out in the mid/upper 50s over the Delmarva and Sn
NJ. A little patchy fog is possible away from the urban areas.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Summary...A pattern change leads to a stretch of very warm to hot
conditions through much of the holiday weekend, with some increase
in the humidity especially starting on Friday. A frontal boundary
nearby Thursday through Monday though may help trigger some
showers and thunderstorms mainly each afternoon and evening.

The synoptic setup is comprised of the pesky closed low that will
weaken as it shifts farther away from our area Wednesday. This
allows ridging to arrive in the east for the second half of the
week, and this ridge which becomes centered offshore looks to remain
over or near our area right through Monday. There will be several
pieces of energy deflected around this ridge with a sharp trough
possibly occurring in the vicinity of the Canadian Maritimes. This
setup should result in a frontal zone becoming draped from about the
Great Lakes to New England. This front looks to meander north and
south from Thursday through Monday, with it potentially getting into
at least our northern areas at times. Some energy along this front
combined with plenty of heating to the south of it may result in
mainly some diurnally driven convection Thursday through the holiday
weekend. Overall though, a washout is not anticipated. We used a
model blend approach for Wednesday through Thursday night, then
blended in the 00z WPC Guidance with continuity thereafter. Some
adjustments were then made based on additional collaboration with
our neighboring offices.

For Wednesday and Thursday...The pattern finally makes a transition
to much warmer air as the slow moving closed low weakens as it
shifts into the Canadian Maritimes Wednesday. This allows a ridge to
the west to slide eastward, with surface high pressure sliding to
our south Wednesday and then anchored just off the southern Mid
Atlantic coast Thursday. This results in considerable height rises
through this time frame along with a more southerly flow regime.
This will boost the warm advection and the model guidance increases
the 925 mb temperatures to +20C Wednesday and between +20C and +25C
Thursday. This combined with west to southwest flow will drive the
temperatures well into the 80s for much of the area both days. The
exceptions will be the higher terrain and especially the coastal
areas where the surface flow may back more southerly and allow some
cooler ocean influence. We bumped up the temperatures some
especially away from the coast.

As the ridge axis is still to our west Wednesday, energy sliding
across northern New England will drag a cool front southeastward.
Given the presence of the incoming ridge, this front should stay to
our north although it may get rather close to our northern areas
late Wednesday and Thursday. There may be some convection with it
Wednesday which may brush our very far northern zones in the
afternoon. For now though we left the forecast dry. Low pressure
tracking into the Great Lakes Thursday should provide enough of a
downstream push to move the front back north. A few showers and
thunderstorms may develop Thursday afternoon across our western
zones due to terrain circulations and the presence of a lee-side
trough, however much of the convection should reside well to our
west.

For Friday through Monday...The ridge axis may build right across
our area through much of this time frame. This will result in very
warm to hot conditions along with a more noticeable increase in the
surface dew points. Some mainly diurnally driven convection cannot
be ruled out each afternoon and early evening Friday and Saturday.
At least some guidance brings low pressure off the Atlantic into the
Carolinas Sunday as the ridge aloft remains. Depending on the
organization of this feature and if it exits may push some
additional moisture our way into Monday. In addition, the ridge may
amplify enough as a deep trough passes near the Canadian Maritimes
Sunday and Monday to push a frontal boundary down through our area.
If this were to occur, then Monday would be much cooler and
potentially be prone to more showers/thunder. There is much less
certainty with the details regarding this, therefore we followed
close to the WPC Guidance which brings the front into our
northeastern areas Monday.

&&

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

Mostly VFR conditions are expected through 06Z. Isolated showers
and thunderstorms are possible this afternoon (generally between
16 and 22Z). However, have not included this in most of the TAFS
as the limited coverage means that there is low confidence that
any one TAF site will be affected. Winds will be shifting from
northwesterly and westerly to southwesterly by late this afternoon
or evening.

After 06Z...some light fog may develop for KRDG, KABE, and
Coastal Plains TAF sites, reducing visibility to MVFR. Otherwise,
VFR conditions should continue through the remainder of the TAF
period.

Outlook...
Wednesday...VFR. West to southwest winds up to 10 knots.

Thursday through Saturday...VFR overall, however brief times of
MVFR/IFR conditions are possible each afternoon and evening due to a
few showers and thunderstorms.

&&

.MARINE...
A few seas near 5 ft early this morning...but a trend towards
lessening winds and seas today. No SCA flag will be needed for today
or tonight. Winds will be mostly n or nw today and then w or sw
tonight. Scattered showers and perhaps a tstm is expected for the
waters. Winds and seas will be locally higher in any tstm.

Outlook...
Wednesday through Saturday...A ridge aloft over the area combined
with high pressure at the surface to our south and east will allow
for mainly a southerly flow regime across our area. The flow looks
like enough and therefore the conditions are expected to be below
Small Craft Advisory criteria.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Gorse
Near Term...Johnson/O`Hara
Short Term...O`Hara
Long Term...Gorse
Aviation...Gorse/Johnson/O`Hara
Marine...Gorse/O`Hara


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