Upper Merion, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

038
FXUS61 KPHI 130544
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1244 AM EST Wed Nov 13 2024

.SYNOPSIS...
High pressure remains in control through Thursday. A weak low
will approach the region on Thursday night with a coastal low
developing to our south which will move out to sea on Friday.
High pressure returns for the weekend ahead of a cold front that
approaches the region early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Through the near term, short wave ridging will be the dominant
feature leading to dry and calm conditions. See the fire weather
section below about implications for fire spread. Otherwise, the
other big story of this period will be low temperatures tonight
which outside of the urban corridor and immediate coast could
be the lowest temperatures we have seen so far this fall. The
calm winds, dry air, and clear skies will lead to efficient
radiational cooling, especially in the pine barrens, river
valleys, and interior Delmarva.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
The Wednesday night and Thursday period will feature tranquil
and seasonably cool weather overall, as strong high pressure
slowly shifts east across southern Canada. Clouds will gradually
increase through this time as the next weather system
approaches from the Midwest. Lows on Wednesday night will mainly
be in the mid 20s to mid 30s with highs on Thursday in the 40s
and 50s.

Attention then turns to the Thursday night into Friday period
as a decaying trough and weakening surface low moves toward the
area. The surface low is forecast to track into the eastern
Great Lakes before translating its energy to a developing
secondary coastal low off the coast off the Carolinas. This low
will then move out to sea without posing much of a threat to the
Mid-Atlantic. So as this initial low approaches, rain showers
are expected to move into our area, especially south and west of
Philadelphia (where PoPs are up to 40- 60%). To the north and
east of Philadelphia, the strong high pressure over Canada
should cause a sharp moisture gradient, so these locations may
see a few isolated showers to nothing at all. In terms of QPF,
generally looking at 0.10-0.25" south and west of Philly, with
less than 0.10" north and east of Philly. Surprisingly, this
set-up does appear to be a cold air damming set-up, mainly in
the Pocono region, so wouldn`t be surprised if there is a short
period of frozen precip on Thursday night if any precip is to
make it into these areas. Lows will mainly be in the 30s/40s.

Any showers will then taper off from north to south early on
Friday with clearing skies by the afternoon as high pressure
builds back in from the west. Highs will remain a few degrees
below normal mainly in the upper 40s to mid 50s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Heading into next weekend, upper level ridging is forecast to
build as an expansive area of high pressure approaches from the
west. This will result in a dry weekend with temperatures
returning to above normal standards. It may be breezy at times
over the weekend however and with dry northwesterly flow, this
could spark an additional round for some fire weather
concerns...however its too far in advance to narrow down
specifics.

By early next week, a shortwave trough will approach the region
with a surface cold front. Current timing at this point appears
to be on Monday where a few rain showers may be possible with
the front. High pressure then returns for Tuesday as
temperatures still remain a few degrees above normal.

&&

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

Through today...VFR with only few high clouds building in late
today. Winds starting NNE, but becoming more NE. Wind speeds
should generally be at or below 10 kt.

Tonight...VFR with increasing high clouds. NE winds 5 kt or
less.

Outlook...

Thursday through Thursday night...Mainly VFR. Sub-VFR
conditions possible on Thursday night with a chance of rain
showers.

Friday through Saturday...VFR. No significant weather expected.

&&

.MARINE...
Small Craft Advisory remains in effect for the entire marine
area. Winds should continue to gradually diminish, but are
remaining elevated for longer than previously anticipated, so
extended the SCA on the Delware Bay through 6 AM.

Winds should be below 25 kt everywhere by mid day. Elevated seas
may linger on the Atlantic coastal waters through at least the
end of the day. However, will be watching trends closely. Some
guidance depicts elevated seas lingering through the night.

Outlook...

Thursday through Friday...Small Craft Advisory conditions on
the Atlantic Ocean coastal waters are possible mainly due to
seas hovering around 5 feet.

Friday night through Saturday...Small Craft Advisory conditions
likely due to winds around 25-30 kt and seas around 5 feet.

&&

.FIRE WEATHER...
For Wednesday, dry conditions are expected to continue. Winds
will generally be near 5-10 mph with a few gusts up to 15 mph,
much lower than the day before. A very dry airmass will be in
place however with minimum RH values will falling into the
20-30% range.

RH values do recover Thursday with a chance of showers in the
afternoon and evening. Best chance for rainfall will be south
and west of the Philadelphia Metro with minimal rainfall north
and east.

Looking farther ahead, RH values remain in the 30-40% range for
Friday and into the weekend along with some breezy conditions.

&&

.TIDES/COASTAL FLOODING...
Confidence has increased that a combination of persistent shore
parallel winds and increasing astronomical tides with a full
moon on Friday look to lead to coastal flooding for the back
half of the week. Widespread minor tidal flooding is expected
along the Atlantic Ocean coasts of New Jersey and Delaware and
the associated backbays as well as the central Delaware coast of
the Delaware Bay beginning with the Thursday morning high tide.
Additionally, potential remains for moderate coastal flooding
within this area. As a result, a Coastal Flood Watch has been
issued beginning early Thursday morning and continuing through
midday Friday.

Leading up to the more potentially impactful high tides, tides
will begin to pile as the shore parallel flow limits the amount
of water that can drain away from the coast at low tide. As a
result, minor tidal flooding is expected to occur beginning with
the early Wednesday morning high tide. A Coastal Flood Advisory
has been issued for Cape May, NJ and Sussex, DE counties
beginning at 4 AM Wednesday morning where minor tidal flooding
is expected to be most widespread. Spotty minor tidal flooding
is forecast with the early Wednesday morning high tide for the
remainder of the area within the Coastal Flood Watch.

By Thursday and into Friday, tidal piling into the lower Delaware
Bay looks to result in minor tidal flooding occuring further
north, along the shores of the upper Delaware Bay as well as the
tidal Delaware River.

Coastal flooding is not expected to occur along the Chesapeake
Bay in the Eastern Shore of Maryland.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Watch from late tonight through Friday morning
     for NJZ012>014-020-022>027.
     Coastal Flood Advisory from 4 AM to 10 AM EST this morning for
     NJZ023-024.
DE...Coastal Flood Watch from late tonight through Friday morning
     for DEZ002>004.
     Coastal Flood Advisory from 4 AM to 10 AM EST this morning for
     DEZ003-004.
MD...None.
MARINE...Small Craft Advisory until 6 AM EST early this morning for
     ANZ430-431.
     Small Craft Advisory until 1 PM EST this afternoon for ANZ450.
     Small Craft Advisory until 6 PM EST this evening for
     ANZ451>455.

&&

$$

SYNOPSIS...DeSilva/Hoeflich/RCM
NEAR TERM...Johnson
SHORT TERM...DeSilva
LONG TERM...DeSilva/Hoeflich
AVIATION...DeSilva/Johnson
MARINE...DeSilva/Johnson
FIRE WEATHER...
TIDES/COASTAL FLOODING...