Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 290731 CCA
Area Forecast Discussion...CORRECTED
National Weather Service Mount Holly NJ
331 AM EDT SUN MAY 29 2016
High pressure will continue to push further off the Middle Atlantic
coast tonight. Tropical Storm Bonnie will move along the
southeastern United States coast over the next several days.
Moisture from this system will move northward and into our area
today and Monday. High pressure will build towards the region
Tuesday, remaining to our north through Thursday. A cold front
will move through the area over the weekend.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1230 AM ESTF: little change to the overnight forecast grids.
Temps and dewpoints are following the guidance from 24 hours
ago...tending to run cooler than 24 hours ago as a wedge of very
dry aloft slides nwd over our fcst area. fair skies with a light
south wind. Patchy dense fog possible along and N of I-80 where
ydy afternoons heavy rains have left a moist near sfc layer.
Today...Still very warm but with lower dewpoints into midday, not
quite as uncomfortable...however, high dewpoints will be returning
from south to north during the mid and late afternoon hours with
morning southwest winds of 5 to 15 mph turning more southerly.
It will be a mostly sunny morning with increasing cirrus during
the afternoon. Then a wall of water starts advancing nwd through
the delmarva late afternoon with showers, some heavy and possibly
a thunderstorm. More details on timing will be attempted in the
330 am AFD.
Max temps...again well above normal...10-15F...ranging from the
mid to upper 80s Delmarva...PHL 88, to around 90-91F along and
north of I-78 (Lehigh Valley ewd through WRI-MMU). NAM BL temps
have been increasing on recent cycles.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
Deep layer moisture, PWAT up to 2 inches, in part from Tropical
Storm Bonnie is forecast to move across the area with widespread
showers and isolated T-storms. General lift is aided as
represented by an upper level 250MB jet...rrq of the 90kt core
over southern Ontario. A sfc boundary will focus the heaviest
rain, usually found in the lift region just in the light northerly
flow along a forming sfc wind shift. A 30 kt 700mb speed max may
initially focus heaviest rain near Chesapeake Bay-E Pa Sunday
evening, it appears the 850 southerly inflow will shift the axis
of excessive rain potential somewhere just to the east of I95 by
Monday morning. Potential exists for a couple of narrow swat5hs of
1-3" rains by 12z Monday...more details possible at 330 am but
more likely delayed til the Sunday afternoon-evening assessments.
Mild nighttime mins...well above normal.
Light southerly wind with a wshift to north near a developing sfc
convergence zone around or just east of I-95 late at night.
Will probably post daily record rainfalls as believed appropriate
in the CLI section by 5 am Sunday.
.LONG TERM /MONDAY THROUGH SATURDAY/...
Moisture from Tropical Storm Bonnie will push northward and we will
continue to see showers and some thunderstorms on Monday. PWATS
remain high, around 2 inches in some areas, so expect some of the
showers to be fairly heavy, especially during Monday morning.
Memorial Day continues to look like a washout across the region. The
pops will start to drop from northwest to southeast but it looks
like we will continue to see some showers continuing into Monday
evening. Rain will linger longest over our southeastern areas,
likely ending by late Monday night.
With heavy rain possible, we will need to monitor the flash flooding
potential. As mentioned before, the PWATS are 1.5 to just over 2
inches across the region. Some heavy showers and thunderstorms could
drop one to two inches of rain with locally higher amounts possible.
We will continue to mention the flash flood threat in the HWO.
The guidance shows some pretty decent differences in how the
remnants of Bonnie are handled. The GFS is a bit dryer and keeps the
low to the south of the area and eventually dissipates it near the
Carolina coast. The ECMWF keeps the low spinning over the Carolina
coast with a gradual push to the northeast, moving it up the Mid-
Atlantic coast through the week. The ECMWF solution would keep us in
a cloudier set up and a wetter pattern with the chance for the
remnant moisture to make its way into the region for Tuesday through
Friday, with the best chances across our south and east zones.
With the uncertainty of where and when Bonnie will track
north/northeast, we have upped the cloud cover through the week and
introduced some slight chance/low chance pops. Again, the best
chances will remain across southern New Jersey and the Delmarva.
A low pressure system will arrive from the west and drag a cold
front through the region over the weekend.
.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Through 12z...Generally VFR. small chc MVFR vsby toward 10z
KRDG/KABE. Light south wind.
Today after 12z...VFR with a south-southwest wind gusty to 15 kt
midday. Then MVFR or IFR conds in showers/iso tstms spread north
through the Delmarva into southern NJ and the Philadelphia during
the afternoon. Please see the TAFS for more timing details.
Tonight...MVFR to IFR conditions in low clouds, fog, and heavy
showers/isolated tstms. Sustained winds mostly under 10 kt with a
convergence zone of south wind along the coast while a light north
wind should develop near I-95 late at night.
Monday...MVFR to IFR conditions in rain, fog, and thunderstorms
affect the terminals. Conditions may drop below IFR at times due to
heavy rain. Light winds early will become south to southwest
around 10 knots or less. Higher gusts possible in showers and
Tuesday through Thursday...Mainly VFR conditions expected. Westerly
winds on Tuesday will become more easterly on Wednesday and
Thursday. Winds will generally be around 10 knots or less with gusts
up to 15 knots.
No marine headlines are anticipated through tonight although fog
may become a marine hazard toward dawn Monday on the atlantic
Monday...Sub-SCA conditions are expected on the area waters. Fog is
possible in the early morning and again overnight. Waves may start
to build in response to Tropical Storm Bonnie but we expect them to
remain below 5 feet at this time. However, confidence is not high
that we will see much affect until Bonnie moves north of the
Tuesday through Thursday...Sub-SCA conditions are expected on the
There is potential for heavy rain and localized flooding from tonight
through Monday. This is due to an influx of tropical moisture from
Tropical Storm Bonnie. PWATs are forecast to be near 2 inches,
well above normal, especially for late May. Depending on how the
heavier showers and t-storms set up, some locations could receive
2 inches or more of rainfall. This may result in localized
flooding. The potential for heavy rain was added to the forecast.
Once our overnight assessment is completed, we`ll post around 5 AM,
any daily record rainfall considered for exceeding. This will also
impact monthly totals, probably pushing some of our locations into
a top ten wettest month of May.
You probably saw the near records yesterday at KMPO (-1), KABE
(-1), KRDG (-2). Daytime max temp guidance continues to be
significantly under forecast across PA/NJ for the past 3 days,
especially by Super and National blends. We are better off in
these sunny non- marine influenced summerlike regimes using the
latest op guidance as a starting point and modifying this upward
by adding 4F to the 18z ECMWF 2m temps. The GFS 2m temp fcsts have
also been biased low, think in part to too much low lvl moisture.
Also a note about heat waves: here in the northeast USA, we tend
to stay close to the AMS glossary of Meteorology definition of a
heat wave and as follows: In 1900, A.T Burrows more rigidly defined
a `hot wave` as a spell of three or more days on each of which the
maximum shade temperature reaches or exceeds 90F.