Lower Merion, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

492
FXUS61 KPHI 191342
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
942 AM EDT Thu Jun 19 2025

.SYNOPSIS...
Bermuda high pressure remains offshore today. A cold front
passes through the region tonight, bringing relatively cooler
and drier air to the region for Friday. High pressure should
then generally dominate through the weekend and into early next
week with a building ridge aloft over the East Coast.

&&

.NEAR TERM /THROUGH TONIGHT/...
940 AM...No changes to the forecast at this time as latest
analysis continues to support previous forecast thinking. Latest
analysis shows low pressure over southern Ontario with a warm
front extending east across upstate NY into New England. This
places our area squarely in the warm sector. The cold front
extends S/W from the low into portions of NW Ohio and Indiana.
The sky is mainly clear and it should be mostly sunny through
midday. This will allow temps to soar into the upper 80s and low
90s, and with dew points in the low to mid 70s, heat indices
will spike up towards 100. As its still early in the season,
heat advisory remains in effect for the urban corridor where
early season criteria is lower.

By early-mid afternoon, clouds will begin to build as the front
approaches with the shortwave aloft. CAPE values look to reach
or exceed 2000 J/kg again, but shear and forcing is a bit
stronger today. Thus, SPC has most of the region in an enhanced
risk of severe weather. In fact the area of enhanced risk was
expanded east to include the coast with SPC`s morning update.
The main risk remains damaging winds, but large hail is also
possible, and the tornado risk is not zero either. Overall it
should be a more active day for severe weather than yesterday
was. With high PW`s, there could be localized flooding as well,
though storms should be moving along...main risks here would be
any unlucky training and very heavy downpours in the urban core.

Storms likely dwindle and push offshore by mid-evening. Cold
front probably doesn`t reach the region until later tonight, so
for a while it will be very warm and humid, but toward dawn the
cooler, drier air will finally push across the region. Lows
will return to the 60s, but not until after the frontal passage
very late tonight.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As the prominent shortwave axis shifts offshore on Friday, the
region will stay within northwesterly flow aloft as upper-level
ridging begins to take shape over southern and central portions
of the US.

At the surface, low pressure will continue to shift eastward
across far northern portions of New England and into New
Brunswick before entering the North Atlantic by Friday night.
This will keep winds across the area northwesterly. While ample
sunshine will still allow temperatures to warm into the mid 80s
(outside of a few upper 70s in the Poconos), the drier post
frontal airmass should feel much more comfortable than today.
With light winds and clear skies, Friday night should also be
fairly comfortable. Lows look to be in the low- mid 60s, though
they may remain in the upper 60s to near 70 across the Delmarva
and in the urban corridor.

Upper-level ridging will continue to build across the
southeastern US and into portions of the Ohio Valley on
Saturday. Under mostly sunny skies, afternoon highs will likely
warm into the upper 80s to near 90 outside of the Poconos and in
coastal regions. Thankfully, the airmass in place won`t be
particularly moist, keeping heat index values at bay.

Model guidance has been fairly consistent the past couple of
days that a shortwave will at least glance the area Saturday
night on the periphery of the ridge. This could provide a slight
chance for a few showers and storms to the northern half of the
area. No severe weather is expected with this disturbance.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
The reprieve from the dangerous heat will begin to come to an
end on Sunday. Upper- level ridging will be firmly established
across the Mid- Atlantic beginning on Sunday and continuing
through the first part of next week. At the surface, high
pressure will remain in control. The airmass in place will
become increasingly moist, with dewpoints likely rising into the
low 70s on Sunday and remaining that way through mid-week.

With the high pressure in place, increasing moisture, and ample
sunshine each day, it will likely be quite hot. Monday and
Tuesday look to be the hottest days, with temperatures likely to
exceed 90 areawide. Many inland locations outside of the
Poconos could potentially reach the upper 90s or near 100. Heat
indices could exceed 100 for a large portion of the area.

There are some subtle indications that ridging could begin to
break down slightly Wednesday and especially beyond. This could
provide some hope for slightly cooler temperatures and, perhaps,
some rain chances.

&&

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

Today...VFR through the rest of this morning. SHRA/TSRA will
develop from west to east after 18Z which may result in brief
sub-VFR conds. Stronger TSRA may result in wind gusts over 50
kt, should one pass directly over a given terminal. The
strongest activity may be after 21Z. SW winds 10 to 15 kt with
20 to 25 kt gusts in the afternoon. Moderate confidence.

Tonight...SHRA/TSRA end by 04Z. VFR with clearing skies. SW
winds around 5-10 kt becoming NW late. High confidence.

Outlook...

Friday through Monday...VFR.

&&

.MARINE...
No marine headlines are currently in effect through tonight.
South- southwest winds around 10-15 kt this morning will
increase to around 15-20 kt with gusts up to 22-24 kt possible
this afternoon into tonight. Seas of 3-4 feet, possibly up to 5
feet. Due to marginal conditions, have held off on a SCA for the
Atlantic coastal waters at this time, however, a SCA may become
warranted if further confidence is reached.

Otherwise, another round of showers and thunderstorms is
expected to occur this afternoon and evening. These storms may
warrant special marine warnings.

Outlook...

Friday through Monday...Sub-SCA conditions are anticipated with
winds below 25 kt and seas below 5 ft.

Rip Currents...

For today, winds and swell remain oriented south-
southwesterly. However, winds increase to 15-20 mph with seas
increasing to around 4 feet. As a result, breaking waves in the
surf zone of 2-3 feet look to occur across all beaches.
Therefore, a MODERATE risk for the development of rip currents
is forecast for NJ beaches today while for the Delaware beaches
we have a LOW risk.

For Friday, the winds shift to offshore and the wave heights
diminish however it looks like there will be some longer period
swell groups. For this reason, we will continue with a MODERATE
risk for the development of dangerous rip currents for the NJ
beaches with a LOW risk for the Delaware Beaches.

For specific beach forecasts, visit weather.gov/beach/phi

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 8 PM EDT this evening for PAZ070-071.
     Heat Advisory until 8 PM EDT this evening for PAZ102-104-106.
NJ...Heat Advisory until 8 PM EDT this evening for NJZ017>019.
     Heat Advisory until 8 PM EDT this evening for NJZ015.
DE...Heat Advisory until 8 PM EDT this evening for DEZ001.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Cooper/Deal/RCM
NEAR TERM...Fitzsimmons/RCM
SHORT TERM...Cooper
LONG TERM...Cooper
AVIATION...Cooper/RCM
MARINE...Cooper/RCM