NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Jun 19, 8:39 PM EST, 2 hours 6 minutes earlier.
Area forecast discussion, Jun 19, 8:39 PM EST, 2 hours 6 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
939 PM EDT Wed Jun 19 2019
.SYNOPSIS...
A stalled front will remain across our area through tonight, then
begin to lift north during Thursday as an area of low pressure moves
toward the area. This low tracks just to our north late Thursday
afternoon and Thursday evening, with its cold front crossing our
region Thursday night. A secondary front arrives early Friday
morning, then high pressure arrives for Saturday night before
shifting offshore Sunday. A warm front lifts across the area Sunday
night into Monday. High pressure builds to our south through the
middle of next week, while a surface trough develops across the East
Coast.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A stationary front has been enhanced by convection this evening, and
an analysis earlier this evening showed stronger convergence
occurring from Berks to Philadelphia counties in PA then across
Camden/Gloucester and Burlington counties in NJ. The convection was
backbuilding for a time and produced a swath of 2 to 3.5 inches of
rain and resulted in flash flooding, however it is settling
south and east now across a less urbanized area. Some additional
showers and perhaps a thunderstorm will be around through the
overnight within a moisture laden environment. Given the
potential for some additional locally heavy rain, we will hold
onto the Flash Flood Watch for now.
Warm rain processes and a more low-topped nature of the convection
is limiting the lightning, however some updrafts have pulsed up some
to result in a stronger core aloft for a time and therefore more
lightning. Overall, the thunder coverage looks more isolated. As of
930 PM, a stronger storm is entering far western Berks County.
For the 930 PM update, adjusted the PoPs based on trends thus far
and expectations through the overnight. Much of the guidance
indicates an uptick in showers and perhaps isolated thunder later
this evening into the wee hours of Thursday morning mostly along and
west of the I-95 corridor. This may be tied to the convection now in
the Washington DC to Baltimore corridor. Temperatures are somewhat
of a challenge due to the stalled front and effects of low clouds
and downpours, however these were adjusted using the current
observations then the LAMP guidance was blended in. Some low
temperatures needed to be adjusted down a little based on trends
this evening. Some low clouds along parts of the New Jersey coast
and the northern zones are expected to spread across much of the
area through the overnight within this moisture rich airmass and
light low-level flow. Some fog will be around however most of the
moisture should be in the form of stratus.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
For the 630 PM update, made some adjustments to the PoPs with
the increase delayed some eastward. Also added in a mention of
heavy rain and gusty winds for the afternoon given the potential
for strong to severe thunderstorms.
Another day, more convection. Seems to be the theme of the week
around the Mid-Atlantic but thankfully this looks to be the
last day of unsettled weather as we head towards the end of the
week.
A low pressure system will track through the Ohio Valley and
into the mid-Atlantic along the stalled boundary. Good surface
heating is expected to take place on Thursday and will help with
convective initiation as the majority of the forecast area
looks to remain in the warm sector. SPC has placed the majority
of our forecast area into a slight risk for severe weather.
There is decent shear (improved in the lower levels than is
present Wednesday) and CAPE >1000 J/kg present and convection
should have no problem developing ahead of the approaching cold
front, although there may be more forward storm motion present
than there is Wednesday. Damaging winds looks to be the main
threat at this time but there is some indication we could see
supercells develop in which case we can't rule out the
possibility of rotating cells. May need to watch the track of
the weak surface low as the surface winds back back to the
southeast ahead of it resulting in enhanced low- level shear.
With PWATs remaining around 2 inches, we will continue to have a
heavy rain threat and though the coverage may not be as
widespread, several areas have had a fair amount of rain this
week. Another Flash Flood Watch may be needed for the day
Thursday, although given storm motions should be faster and some
uncertainty where the heaviest rain will fall we held off for
now.
Temperatures will rise into the 80s through much of the area
and even into the lower 90s across southern Delaware and nearby
areas of eastern Maryland. The limiting factor, especially
across our northern areas, will be the cloud cover as the day
starts off with fog/low clouds across the region and just how
fast they clear will play a role in just how fast temperatures
can rise through the day.
&&
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
An area of low pressure will continue to move to our north and
strengthen as it does so. This will drag a cold front across the
area during the evening and overnight hours Thursday, with a
secondary front or surface trough moving across the area Friday
morning. This will keep enhanced precipitation chances through
Thursday night and Friday morning as several short
wave/vorticity impulses will move across the area and combine
with some enhance moisture. There remains instability Thursday
night and Friday morning, so thunderstorms will remain in the
forecast, and with PW values around 1.5 inches, heavy rainfall
could continue to be a threat.
The fronts will continue to push to our south during the day
Friday, and showers will come to an end by midday. However, the
pressure gradient will tighten with low pressure to our
northeast and high pressure to our northwest. This will likely
lead to be quite gusty during the day Friday, possibly reaching
20-30 mph.
High pressure remains to our west for Friday night into
Saturday, briefly building over the area Saturday night. This
will keep dry conditions across the area through Friday night
and Saturday. Winds will likely gust again Saturday, but not as
gusty as Friday, generally 15-20 mph.
The high then shifts offshore Sunday, before a warm front
begins to approach Sunday night. Most of the day Sunday is
expected to be dry, however, this could begin to change by late
Sunday into Sunday night as some moisture and a couple of short
waves move across the area and may lead to a chance of showers
and thunderstorms.
High pressure builds into the Northeast Monday as the upper
level trough lifts out of the region into the Canadian
Maritimes. A surface low will move just north of the Great
Lakes, drawing a warm front northward across the mid-Atlantic
during the day. Thus, warmer highs than Sunday can be expected.
Precipitation looks rather limited at this point with the front,
but kept a chance for showers and thunderstorms in the grids
for now. A return to a more humid airmass will occur, though, as
PWATs jump back to near 2 inches across the region.
The surface low continues to deepen as it moves into central
Ontario and eastern Quebec Monday night into Tuesday. As it does
so, a cold front will be pulled out of the Ohio Valley toward
the mid-Atlantic. At this point, model consensus appears to
shunt the precipitation north of the area. Best chances for
showers and thunderstorms looks to be across the northwestern
portions of the CWA at this time. There will be some
instability, so there is the potential for thunderstorms, but
timing will help determine any potential severe risk. If the
front is slower to arrive, coming Tuesday afternoon, the threat
may be greater. Regardless, it looks to be a warm a humid day
with highs in the upper 80s to near 90.
Highs will be a little cooler Wednesday behind the front, with
most places topping out in the mid 80s. Some discrepancy remains
as to how quickly the trough exits the Northeast, thus,
continued a slight chance for showers through the day Wednesday.
&&
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Tonight...Some showers and isolated thunderstorms. Any thunderstorms
should end prior to about midnight. Much of this should be near ILG
to PHL to the north. Ceilings varying from VFR to MVFR and IFR with
even localized LIFR occurring. Overall, the ceilings are anticipated
to all settle into the IFR to LIFR range overnight. Visibility
restrictions with local downpours, and also some fog. Winds
northeast or southeast around 5 knots, to locally light and
variable. Low confidence on the timing of widespread IFR or lower
ceilings.
Thursday...IFR ceilings improve to MVFR during the morning, then to
VFR especially from the PHL metro south and east by early afternoon.
Some showers possible early especially from ILG, PHL, PNE, TTN north
and west, then more widespread showers and some thunderstorms from
west to east during the afternoon. Times of IFR/LIFR especially
visibilities with the downpours. Variable winds, becoming south to
southwest near 10 knots. Locally higher wind gusts possible with
stronger afternoon thunderstorms.
OUTLOOK...
Thursday night... VFR possible early, lowering to MVFR
overnight. Especially with any showers and thunderstorms.
Friday...MVFR conditions possible early, before improving to
VFR during the day. Chance of showers early. Winds shift to
northwest with gusts 20-25 knots.
Friday night-Saturday night...VFR conditions expected. Northwest
winds may gust 15-20 knots during the day Saturday.
Sunday-Sunday night...MVFR conditions expected. Chance of
showers Sunday night. West to southwest winds may gust around 15
knots during the day Sunday.
Monday...VFR with southwest winds 5 to 10 knots. Gusts to 15
knots possible, especially along the shore.
&&
.MARINE...
Sub-Small Craft Advisory conditions are expected to continue
through Thursday. Winds out of the south to southeast around 10
to 15 knots tonight, becoming southwest on Thursday. Seas around
1 to 3 feet.
Higher winds and waves in showers and thunderstorms.
Outlook...
Thursday night-Friday night...Small Craft Advisory conditions
possible with guts 25-30 knots possible. Gale force winds
possible during the day Friday.
Saturday-Sunday night...Conditions expected to drop below
advisory levels by Saturday and remain below advisory levels
through Sunday night.
Monday...sub SCA conditions expected with southwesterly winds
10 to 15 knots and seas 1 to 3 feet.
Rip Currents...
A low risk for the development of dangerous rip currents continues
through Thursday, with winds becoming more southerly and waves in
the surf zone about 3 feet.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flash Flood Watch until 6 AM EDT Thursday for PAZ054-055-
060>062-070-071-101>106.
NJ...Flash Flood Watch until 6 AM EDT Thursday for NJZ001-007>010-
012>019.
DE...Flash Flood Watch until 6 AM EDT Thursday for DEZ001.
MD...None.
MARINE...Small Craft Advisory from 8 PM Thursday to 6 PM EDT Friday for
ANZ430-431-451>455.
Small Craft Advisory from 8 AM to 6 PM EDT Friday for ANZ450.
&&
Synopsis...Gorse/Robertson
Near Term...Gorse
Short Term...Gorse/Meola
Long Term...Davis/Robertson
Aviation...Davis/Gorse/Robertson/Meola
Marine...Davis/Robertson/Meola