NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Jul 12, 1:59 PM EST, 2 hours 27 minutes earlier.
Area forecast discussion, Jul 12, 1:59 PM EST, 2 hours 27 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
259 PM EDT Tue Jul 12 2022
.SYNOPSIS...
A cold front will push through the region this evening bringing
showers and thunderstorms. The front will stall to our south for the
remainder of the week keeping daily precipitation chances in the
forecast, largely for the southern portions of the forecast area as
high pressure noses in from the north. The high will move offshore
on Saturday and the front will drift north, continuing the daily
precipitation chances through the weekend.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
A severe thunderstorm watch has been issued for portions of E
Central PA through 7 PM this evening. The cold front continues to
progress through western PA. The pre-frontal trough is just west of
our region. In the mid and upper levels, a short wave trough
embedded in the larger broad trough is starting to propagate near
our region.
We continue to monitor the dry layer in the lower to mid levels that
was evident on many of the regional soundings this morning. See
evidence of moisture advection eating away at the dry layer in the
15Z OKX sounding, though there still remains a rather deep layer
that is far from saturated. Will be continuing to monitor this as
other mid day soundings come in.
As far as timing, expect the coverage of showers and storms along
the pre-frontal trough to increase in coverage over the next few
hours, with the main impacts for our region being from late
afternoon through the evening hours. Shear vectors appear to be
closer to parallel with the trough, so storms should organize into a
linear system as they get into our region.
Bulk shear values in excess of 40 kts and CAPE potentially
approaching or even exceeding 2000 J/kg should be enough to result
in some severe storms, with damaging winds being the highest
concern. Still can't completely rule out the large hail or tornado
threat, but given the expected storm mode, expecting the primary
hazard to be damaging winds. Storms should begin to weaken once they
reach and especially pass east of I-95/US 301, but some uncertainty
about just how quickly that can happen exists.
While there is a potential for heavy downpours, flood risk appears
limited given relatively fast storm motion potential and recent
dryness. That said, isolated flooding can never be ruled out with
strong thunderstorms.
Later tonight, main concern becomes potential for patchy fog,
primarily over the coastal plains, as precip should end and skies
start to clear overnight. The highest risk will be over the coastal
plains which will be the last to see the wind shift with the front.
As mentioned by the previous shift, the winds with and behind the
front aren't very strong, but even 5 to 10 mph with the shift to
northwesterly flow may be enough to limit fog development elsewhere.
Otherwise, since the advection behind the front will remain weak
overnight, temps should remain on the warm side, with 60s to low 70s
remaining common.
Much of the region should be dry during the day on Wednesday as the
main trough axis stays to our west and the low approaching from the
southwest will stay well away from our region. Though temperatures
will not be much cooler than today (with highs ranging from the
lower 80s to lower 90s.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
The period starts with the cold front turning stationary over
Delmarva or just to the south. And with the mid-level trough axis
remaining over the western Great Lakes and SW flow over the Mid-
Atlantic, the front doesn't go anywhere fast.
As a result of the slow moving front and it's proximity, while there
isn't a high chance of showers and thunderstorms across the forecast
area, it's not zero. Besides the front to the south, a couple
vorticity impulses, embedded in the mid-level flow, are also
forecast to move across the region. This all said, slight chance
PoPs dot the landscape through the entire period with the best focus
being across our southern zones.
There's not much gradient behind the front, so lighter winds are
expected throughout the period. There's also not much of an airmass
change.
Overnight lows will basically be in the upper 50s across the far
NW, around 70 across the I95 corridor, and in the 60s in between.
Afternoon highs will be near our climatological norms with highs
ranging from the upper 70s to upper 80s depending on location.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
Weakening high pressure moving further offshore Saturday will give
way to the possibility of pop up showers and thunderstorms
Saturday afternoon to Saturday night. Models indicate multiple
shortwaves could approach from the west in the following days
while moving eastward with time. These shortwaves bring a
pattern of unsettled weather along with them through the end of
period; widespread pop up showers and thunderstorms are to be
expected. Prevailing southwesterly flow should remain over the
region from the Sunday to Monday afternoon or Monday night
timeframe.
&&
.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Through this evening...Predominantly VFR. Strong to severe TSRA
likely to develop near KABE/KRDG near 21Z and then spread SE towards
KPHL/KTTN/KPNE/KILG around 00Z, then possibly reach KMIV/KACY closer
to 03Z. Moderate confidence on the overall pattern, but low
confidence on timing of thunderstorm impacts at each site.
Late Tonight...Predominantly VFR. Potential fog development
overnight. Highest risk for KMIV and KACY. Winds may become light
and variable for a time but should settle out of the northwest by
early Wednesday morning. Moderate confidence.
Wednesday...VFR conditions expected. Winds varying from SW to NW 5
to 10 kt. Moderate confidence.
Outlook...
Wednesday night and Thursday...Mainly VFR. Isolated showers
possible. Light and variable winds Wednesday night and west to
northwest winds 5-10 kts on Thursday. Moderate confidence.
Thursday night through Friday night...Mainly VFR. Isolated showers
possible. North to northeast winds 5-10 kts during the daylight
hours and light and variable winds overnight. Moderate confidence.
Saturday... Predominantly VFR. A few isolated showers possible in
the afternoon. Winds light and variable in the morning, becoming
southeast at 5-10 knots in the afternoon.
Sunday... Predominantly VFR. A chance of showers and thunderstorms
in the afternoon and evening. Winds south to southwest at 5-10
knots.
&&
.MARINE...
Seas on the Atlantic coastal waters are at or just below 5 feet
currently, and should continue to build into early evening. Thus,
will keep the Small Craft advisory going through midnight. Once seas
subside late tonight, winds and seas should stay below SCA criteria
through the day tomorrow.
Outlook...
Wednesday night and Thursday...Sub-SCA conditions expected. S to SW
winds 5 to 15 kts. Seas 2 to 3 ft.
Thursday night...Sub-SCA conditions expected. N to NE winds 5 to 15
kts. Seas 2 to 3 ft.
Friday and Friday night...Sub-SCA conditions expected. E to SE winds
5 to 15 kts. Seas 2 to 3 ft.
Saturday... A slight chance of showers in the afternoon. Easterly
winds 5-10 knots in the morning, becoming southeasterly in the
afternoon. Seas 2-3 feet.
Sunday... A chance of showers and thunderstorms. Southerly winds 5-
10 knots with gusts to 20 knots. Seas 2-4 feet.
Rip Currents...
Through this evening elevated wave heights within the surf zone are
expected to continue. While not especially conducive to rip currents
with an overall offshore Ekman transport, a medium-period swell from
the east-southeast of 2 to 4 feet and increased tidal departures
with the full moon on Wednesday will result in higher than typical
rip current threat in this regime. Thus, a MODERATE risk for the
formation of dangerous rip currents continues.
For Wednesday, winds will initially turn offshore, but then become
southerly in the afternoon. Thus, we are again forecasting a
MODERATE risk of rip currents for portions of the New Jersey
Shore, with LOW risk for the Delaware beaches.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ450>455.
&&
Synopsis...Brudy
Near Term...Johnson
Short Term...Kruzdlo
Long Term...Brudy/Wunderlin
Aviation...Brudy/Johnson/Kruzdlo/Wunderlin
Marine...Brudy/Johnson/Kruzdlo/Wunderlin