997
FXUS61 KPHI 200609
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
209 AM EDT Mon May 20 2024

.SYNOPSIS...
High pressure across the Northeast builds across the Mid-
Atlantic through Tuesday before moving offshore on Wednesday. A
cold front approaches and swings through the area on Thursday
into Thursday night. High pressure returns for Friday with
another low pressure system approaching by next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure continues sitting to our northeast, but the axis
remains just to the northwest of most of the region. Thus, we
continue to have an overall easterly flow, which is providing a
fresh push of marine layer clouds into the region. There can be
some patchy fog in spots, but not expecting widespread dense
and no fog advisories are anticipated. This push is weaker than
yesterday as the flow is even lighter while high pressure ridge
axis slowly settles to our southeast over time, so think morning
clouds should be more efficiently burned off today. The result
should be a mostly sunny afternoon overall. A few models are
suggesting that the ample May insolation combined with
relatively moist atmosphere may spark a few light showers, most
likely in the Poconos, so have put a few sprinkles in the
forecast up there. Highs should be near to slightly warmer than
yesterday, mostly 70s, cooler along the coast.

Tonight, with the high axis pushing further to our southeast,
winds should become more southerly. However, they remain light,
and some more late night low clouds and fog are possible. Lows
mostly in the 50s.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
Overall, little changes were made to the short term period as
the mid to upper level ridge essentially lies overhead through
Tuesday night before beginning to breakdown and shift offshore
on Wednesday. Down at the surface, broad high pressure over New
England will expand southwest while becoming elongated into the
southern Appalachian region. The high will sink south of the
region on Tuesday and eventually settle offshore the Mid-
Atlantic coast by Tuesday night into Wednesday. This will yield
dry conditions throughout the period.

It is possible a round of fog may develop on Tuesday night, but
confidence in this is less than Monday night so have left the
mention out of this out of the forecast for now.

In terms of temperatures, it is looking like we will return
close to normal with respect to low temps both nights with lows
generally in the 50s to around 60 degrees. For high
temperatures, it is likely that much of the area will range
about 5-10 degrees above normal on Tuesday and as much as 10-15
degrees above normal on Wednesday. Meaning high temps will top
out 80s both days as southerly flow ushers warmer air north. The
exception will be for our coastal locales where a sea breeze
circulation looks to develop each day. Given how cold the water
temperatures are, there is potential for the sea breeze to
develop early enough in the day, that the sea breeze reaches far
enough inland that highs for most, if not all, of the coastal
plain could be slightly lower than what is forecast.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Summary: The main focus through the long term period is a cold
front that is expected to cross through the region on Thursday
bringing the chance for thunderstorms. High pressure looks to
return on Friday with another disturbance approaching over
Memorial Day Weekend.

Details:

Wednesday night...While run-to-run consistency remains poor,
indications are for a pre-frontal trough to approach our
northwestern areas on Wednesday night. This will result in a
slight chance of some thunderstorms across the Poconos and
Lehigh Valley for Wednesday night. PoPs are only around 20% so
while the probability of occurrence is low, it cannot be ruled
out. Elsewhere, dry conditions will continue other than an
increase in clouds.

Thursday...Deterministic global guidance between the
GFS/ECMWF/CMC now all lie in close relation to one another with
respect to the timing of the cold front. Based on current
depiction, still thinking that this will be a late
afternoon/early evening type of event with the cold front
pushing offshore on Thursday night. While the location of the
upper trough looks to remain over the Great Lakes, there should
be enough surface instability aided by sufficient diurnal
heating with temps rising into the 80s. This is supported quite
well by both analog-based and machine learning probabilities.
Considering this notion, it warrants some monitoring of severe
thunderstorm potential Thursday afternoon into Thursday evening.

Friday through Sunday...The forecast for Friday and much of
Memorial Day Weekend is highly variable and depends on how
quickly the upper flow pattern evolves. The GFS remains the most
aggressive with the upper level pattern with an upper ridge
building overhead on Friday before another shortwave trough
passes by on Saturday into Sunday. Meanwhile, the ECMWF/CMC are
much slower with the progression of upper level features,
keeping the upper ridge in place through Sunday and shortwave
trough delayed until early next week. Due to such drastic timing
differences, continued to use a blend of global guidance which
keeps a slight chance of showers (~20%) through the holiday
weekend. However, the weekend certainly does not look to be a
washout by any means, and there will likely be a period of dry
weather...just exactly when that will be is yet to be seen.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Through today...Variable conditions early this morning with
intervals of IFR cigs and vsby, possibly LIFR at times, with
cigs possibly down below 500 ft and vsby down below 1/2 mile not
out of the question. Best odds of these are the outer terminals,
with reduced chances at KPHL. Conditions should improve to VFR
across the board by 14UTC. Winds light northeasterly becoming
southeasterly. Moderate confidence.

Tonight...VFR to start but IFR cigs/vsby possible late as low
clouds/fog may redevelop. Winds light southerly. Low
confidence.

Outlook...

Tuesday through Wednesday...Mostly VFR expected. Some
visibility restrictions are possible on Tuesday night due to
mist/fog.

Wednesday night through Thursday night...Sub-VFR conditions
probable especially on Thursday and Thursday night. A slight
chance of a thunderstorm on Wednesday night with scattered
thunderstorms on Thursday into Thursday night.

Friday...VFR. No significant weather expected.

&&

.MARINE...
Sub Small Craft Advisory conditions over the waters through
tonight. Expect seas generally around 3 to 4 feet with gusts up
to 20 kts.

Outlook...

Monday night through Friday...No marine headlines are expected.
Fair weather expected through Wednesday night with a chance for
thunderstorms on Thursday into Thursday night. Fair weather is
expected to return on Friday.

Rip Currents...

A prolonged period of NE to E winds at 10 to 15 mph during the
day and 5 to 10 mph at night will continue through today. Along
with 3 to 4 ft seas, this will result in a MODERATE risk for
the development of dangerous and life threatening rip currents
today at New Jersey and Delaware beaches. The rip current risk
may be low for most of the day for southern New Jersey beaches.

By Tuesday, the winds will be veering to more of a southerly
direction at 10 to 15 mph which will reduce the onshore
component at most beaches. However we`ll also be heading closer
to the Full Moon on the 23rd so for this reason expect that most
of our beaches will continue to see a MODERATE risk for the
development of dangerous rip currents.

&&

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

&&

$$

SYNOPSIS...DeSilva/RCM
NEAR TERM...RCM
SHORT TERM...DeSilva
LONG TERM...DeSilva
AVIATION...DeSilva/RCM
MARINE...DeSilva/RCM