Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 290206
Area Forecast Discussion
National Weather Service Mount Holly NJ
906 PM EST Mon Nov 28 2016
High pressure will continue to lose its influence over our
weather tonight. Strong low pressure is forecast to pass across
the Great Lakes during the mid week period. The low should pull a
couple of warm fronts through our region on Tuesday and Wednesday
before a strong cold front arrives from the west on Wednesday
night. A secondary low is expected to develop over southern New
England on Wednesday night before moving across Nova Scotia on
Thursday. High pressure is anticipated to follow for Friday into
the weekend. Low pressure or a cold front may affect our weather
on Sunday night and Monday.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
-- Changed Discussion --As of mid-evening, a light southeast surface flow continues over
the forecast area, although a few locations have calm conditions
which have allowed temperatures to fall to near the forecast
mins. A high-level overcast now covers most of the area and these
clouds should thicken and lower with time tonight and prevent too
much additonal cooling. Meanwhile the nearest rain is back over
central Ohio, but the latest model guidance has rain spreading
west to east across eastern PA, NJ and northern Delmarva between
about 500 and 900 am. Temperatures are expected to be well above
freezing everywhere by the time rain begins.
Previous discussion below:
Surface observations across the forecast area this afternoon
indicate a light southerly return flow has developed in response
to high pressure moving off the Mid-Atlantic coast. The high will
shift farther offshore tonight as a storm system over the central
CONUS expands its reach farther downstream. While the low pressure
center will remain nearly stationary tonight over the Northern
Plains, a warm front will become better defined farther east
across the Mid- Atlantic region. This warm front is expected to
lift northward and into the area early Tuesday morning.
Expect tranquil weather through this evening with a shortwave
ridge aloft taking place along the eastern seaboard. High clouds
ahead of the approaching storm system will continue to overspread
the region from southwest to northeast this evening. Clouds should
be thin enough, especially across northeastern PA and northern NJ,
to not have much of an impact on radiational cooling this evening.
Therefore, temperatures will likely fall sharply after sunset,
especially in the sheltered valleys (where winds in the boundary
layer are most likely to decouple). Min temperature across most of
the area may occur earlier in the night than usual (within a few
hours of midnight) as clouds thicken, strengthening winds help mix
the nocturnal boundary-layer, and WAA increases.
NWP models are in reasonably good agreement regarding the arrival
time of the precipitation late tonight. Expect the rain to reach
our western zones in PA by around 3 AM. Rain may hold off until
around daybreak east of the Delaware Valley.
-- End Changed Discussion --
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
The aforementioned warm front will lift northward through the
region on Tuesday. A 50-60 kt southerly low-level jet on the
eastern flank of the storm system will draw warm, moisture air
from the Gulf of Mexico northward and up the eastern seaboard.
This will produce a good overrunning setup across the warm front
Rain will continue to expand eastward across the area during the
morning. The rain looks to be widespread for much of the day,
resulting in a washout tomorrow. Models continue to differ
slightly on where the best lift and axis of heaviest rain falls
tomorrow, with one camp of guidance targeting our far western
zones (RDG-MPO- FWN) while the eastern solutions depict the I-95
corridor. The small difference seems to be tied to where the warm
front gets hung up. Rainfall amounts within this heavier band look
to be 1-2 inches on Tuesday.
High temperatures in the warm sector south of the warm front may
reach the mid 60s while temperatures north of the boundary will
only be in the 50s. Southerly winds in the warm sector are
expected to become breezy. Wind speeds near 20 mph with gust to 30
mph are forecast for the afternoon in the coastal plain of NJ and
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
A deep mid level low is forecast to be located over Minnesota and
vicinity on Tuesday night. The feature is expected to pass across
the Great Lakes on Wednesday and Wednesday night before reaching
southern Quebec and Atlantic Canada late in the week. A mid level
ridge should begin building over the eastern states during the
weekend. The model guidance begins to diverge significantly for
the early part of next week.
The initial shot of rain should be working its way off the coast
on Tuesday evening. Some clearing may follow. We are anticipating
areas of fog on Tuesday night due to the clearing and light wind
along with abundant lingering low level moisture. A second warm
front approaching from the south and southwest will aid in the
process, as well.
Warm advection aloft along with a connection to the Gulf of
Mexico will result in the development of additional rain in our
region on Wednesday. As a cold front begins to approach from the
west late in the day, additional lift should result in increasing
rainfall rates. A moderate to heavy rainfall is anticipated into
Wednesday evening along with a chance of thunder. Additional
rainfall totals of 0.75 to 1.25 inches are possible across parts
of eastern Pennsylvania and northern New Jersey with lesser
amounts on the coastal plain. Locally higher amounts are possible
in the upslope regions.
The cold front is expected to pass though our region around
midnight on Wednesday night. Temperatures will be about 15 degrees
above normal from Tuesday night into Wednesday evening ahead of
Dry air and a return to near normal temperatures should follow
for the late week period into the weekend. A west northwest flow
may bring some cold advection stratocumulus at times, especially
to our northwestern counties.
We have mentioned a chance of precipitation for Sunday night and
Monday. However, the spread in the guidance makes this a low
confidence forecast. The GFS is suggesting a cold frontal passage
while the ECMWF is indicating that a strong area of low pressure
will influence our weather at that time.
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
VFR through 06Z. High clouds will continue to expand
northeastward across the region with CIGs gradually lowering to
mid-levels. Sly winds around 5kt this evening may back slightly
out of the SE tonight.
Rain moves in to RDG-ABE between 08-10Z, the I-95 terminals
between 10-12Z and ACY between 12-14Z. CIGs will quickly lower to
MVFR after the rain begins. Expect periods of MVFR and IFR
conditions in rain for much of the day.
LLWS was added to the TAFs for Tuesday morning, when forecast
profiles show southerly winds associated with a low-level jet
increase to 50 kt while SE winds at the surface are 10 kt or less.
Surface winds will increase after a warm front passes thru from
south to north later in the morning and LLWS concerns will lower.
Southerly winds at the surface will increase to 15-20 kt with
gusts 25-30 kt across most of the area during the afternoon.
Tuesday night...Low ceilings and fog are expected to develop
along with IFR conditions.
Wednesday...IFR conditions with low ceilings and fog should
improve to MVFR and possibly VFR during the day. However, rain is
expected to build into the region and it will become moderate to
heavy at times with the potential for IFR conditions returning.
Wednesday night...MVFR and IFR conditions in moderate to heavy
rain during the evening with a chance of thunder. A strong cold
front should arrive around midnight followed by clearing and
improvement to VFR. Low level wind shear is possible in the
evening due the the expectation of a 45 to 50 knot low level
southwesterly jet at that time.
Thursday through Saturday...mainly VFR.
-- End Changed Discussion --
Sly winds and seas will gradually increase tonight but remain
below SCA levels.
SCA in effect for the waters Tuesday. A 50 kt low-level jet will
move overhead Tuesday. Sly winds are forecast to strengthen to
20-30 kt during the afternoon. Poor lapse rates owing to warm air
atop the cooler waters do not favor stronger winds mixing down to
the surface. Held off on upgrading to a GLW in this setup but
there is still a possibility of a isolated gale-force gusts late
in the day. Seas will build to 5-8 ft by the afternoon.
Tuesday night and Wednesday...A Small Craft Advisory is in effect
for our ocean waters for wave heights of 5 to 7 feet. Also, wind
gusts of 25 to 30 knots are possible on Tuesday evening and again
on Wednesday afternoon.
Wednesday night...Wind gusts of 25 to 30 knots are possible
initially from the southwest then from the west following the
passage of a cold front after midnight. There could be a brief
surge of gale force gusts on either side of the frontal passage.
Thursday through Saturday...West to northwest wind gusts of 25 to
30 knots are possible through the period.
QPF guidance was in decent agreement regarding the placement of
the axis of heaviest rainfall from this midweek event setting up
somewhere in the CWA (generally eastern Pennsylvania and northern
New Jersey) although there are some differences in QPF amounts.
Storm total rainfall will most likely average 1-2 inches but
isolated higher amounts of 3+ inches are certainly possible if the
heaviest rain from both waves falls over the same area.
Conversely, some areas on the coastal plain may receive less than
an inch of rain.
We are not expecting main stem flooding or even smaller basin
flooding since these rainfall amounts will be spread out over a 48
hour period and the antecedent conditions are dry. Poor drainage
flooding is always a possibility if the localized 3+ inch rainfall
amounts materialize but impacts from this type of flooding are
MARINE...Small Craft Advisory from 6 AM Tuesday to 6 PM EST Wednesday
Small Craft Advisory from 6 AM to 6 PM EST Tuesday for ANZ430-