Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 201741
Area Forecast Discussion
National Weather Service Mount Holly NJ
141 PM EDT MON JUN 20 2016
High pressure will continue to influence our weather today.
A surface trough approaching from the northwest will arrive late
tonight, followed by a cold frontal passage Tuesday night. High
pressure briefly regains control Wednesday. Low pressure is
anticipated to move quickly from the Ohio River Valley on Thursday
to the waters off the Middle Atlantic coast on Thursday night. High
pressure will follow eastward to the Middle Atlantic Coast later
Friday through the coming weekend.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Comparing current conditions to yesterday and model solutions for
this afternoon, we see winds will back to the southwest once the
heating gets going. Speeds will be similar to yesterday...mainly
in the 5 to 10 mph range except along the coast we`ll they`ll gust
to 15 mph maybe 20 mph at times. We see H8 temps rising a degree
or two by 00/21 versus where they topped out yesterday. Dewpoints
are starting off higher than yesterday, so while they certainly
aren`t oppressive, there will be a bit more humidity in the air
today even after we begin to mix a bit later this morning and
With the above in mind, the forecast is on track with temperatures
at the same levels compared to yesterday or up a degree or two.
There are no POPS in the forecast until tonight.
Happy first day of summer! Summer will officially begin at 634 pm
today and the weather will definitely reflect more summer-like
High pressure remains in control of the weather across our region
once again today. The airmass remains dry and with mostly sunny
skies through much of the day, we will see temperatures rise well
into the 80s to lower 90s across the region. Areas along the coast
will remain cooler with highs only reaching into the low to mid 80s.
Without much moisture around, the humidity levels will remain low
and as a result the heat index values will be at or below the actual
The high starts to sink to the south through this afternoon as
a weak cold front pushes down from the northwest.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
Low pressure will cross well to the north of our area. The low has a
weak cold front that will drop down into our area tonight. Clouds
will start to fill in from north to south as the front approaches.
As the front moves through, there is just enough moisture available
for some showers to move through late tonight into Tuesday morning.
In addition, marginal instability may allow for some thunderstorms
to accompany the front. The front, as previously noted, is weak in
nature and as it reaches our area, it is expected to weaken further
and we do not anticipate that the showers or thunderstorms will be
all that strong.
It seems the cooler air remains to the northwest of our area
until the front fully cross through the region, so temperatures
overnight will remain warm, in the 60s to near 70.
.LONG TERM /TUESDAY THROUGH SUNDAY/...
**Dry pattern across our area this month looks to continue through
at least Wednesday**
500MB: A short wave trough moving southeast through the Great
Lakes Tuesday and into the northeast USA is followed by another
next Thursday. Considerable ridging develops next weekend.
Temperatures: the month as a whole through the 20th has averaged
within 2 degrees of normal. Calendar day averages will still be
about 5 degrees above normal Tuesday, then cool to near or a bit
below normal Wednesday-Friday before probably warming a bit above
normal next weekend.
Forecast basis: Unless otherwise noted, a 50 50 blend of the 00z/20
GFS/NAM MOS guidance Tuesday-Wednesday, thereafter the 00z/20 GFS
MEX MOS for Wednesday night-Thursday and WPC Guidance Thursday night-
Increased diurnals are occuring because of dry surface soils, resulting
in cooler nights and warmer days than might be expected with greater
soil moisture. The dry topsoils are related to the more than 50 percent
deficit of normal rainfall this month and also the considerable wind
related drying episodes of June 8th and 12th.
Probable 3 day modest heat wave looks to occur with day3 (Tuesday)
a bit uncertain but probable for portions of the I-95 corridor.
Tuesday...Partly to mostly sunny, very warm to hot and more humid.
A remnant surface trough associated with the predawn convection is
anticipated to settle across the southern part of our region on
Tuesday. Showers and thunderstorms are expected to re-fire along
the boundary during the afternoon in advance of a mid level short
wave and surface cold front approaching from the northwest.
Therefore, severe thunderstorm potential Delmarva, especially
vicinity and south of KESN-KGED where modeled MLCAPE is between
1500-2000J, along with TT in the mid 50s, plenty of instability
and 0-6KM bulk shear over 40 kt. PWAT 1.75 inches over the Delmarva
but fast moving storms prevent anything more than brief poor drainage
street flooding. Max temps 90-93F east of I-95 to the coasts
(westerly wind component) and probably to PHL as well. Westerly
winds gust 15-20 mph in e PA and N 1/2 NJ during the afternoon
while more humid southwest winds gust 15-20 mph Delmarva and s NJ
during the afternoon (I95 sewd), prior to lines of strong
thunderstorm development there. Confidence: Above average.
Tuesday night...Whatever convection develops in our region on
Tuesday afternoon should work its way off the coast on Tuesday night
along with the mid level short wave trough and the surface cold
front. Dewpoints lower late at night. May be a little patchy fog
which is not now in the forecast. Confidence: above average.
Wednesday...Mostly Sunny and seasonable. West winds gust 20-25 mph
during the afternoon. PWAT down to .8 inches. Nice day! Confidence:
well above average.
Thursday...Warm air advection showers and thunderstorms ahead of
and near low pressure approaching from the west. SVR storms possible
near the warm front along with 1-3 inches of rain, presumably Delmarva
where the most extensive showers and thunderstorms should occur.
Thinking the GFS and ECMWF are too far north. Modeled MLCAPE from
the 00z/20 GFS is 1000-1500J along and somewhere to the south of
I78 (warm front). Plenty of 0-6KM bulk shear (over 40 kt),
instability and TT probably near 50-52. PWAT back up to 1.75"
Delmarva. Variable winds...probably easterly most of the area but
may briefly shift south or southwest southern part of the forecast
area south of the temporarily northward oscillating warm front.
High temperatures Thursday are highly uncertain and dependent on
most persistent showers and thickest cloud cover. Blended the 00z/20
MEX temps with our previous fcst from Sunday afternoon and then
shaved a few degrees near PHL where I think showers will be more
persistent as compared to near I80 in NNJ. We also note the GGEM
is relatively dry Thursday. So confidence on details is average or
below with least confidence in max temps.
Thursday night...Convection ends from west to east. patchy fog
may develop in the leftover moist airmass but that is not in the
fcst at this time.
Friday...Improving weather with clearing. Seasonably cool.
Northeast wind. Confidence. Above average.
This coming weekend...Daytime temps should begin warming above
normal and probably rainfree. Looks like a nice weekend.
Confidence: above average
.AVIATION /18Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Today...VFR conditions expected. Light and variable winds this
morning will become south southwest by this afternoon, around 10
knots or less across the terminals. A seabreeze is expected to
develop once again today in the light flow. However, there is some
uncertainty as to whether it will be as efficient as Sunday`s
seabreeze and move well inland. For now, the seabreeze is reflected
in KACY`s TAF only.
Tonight...A cold front will start to move into the region late
tonight. Some showers, possibly a thunderstorm, are expected to
accompany the front as it moves through from west to east.
Increasing cloud cover through the evening/overnight. Southwest
winds will become more westerly overnight but are expected to
remain 10 knot or less.
Confidence in the outlooked days below is well above average with
only the timing and extent of thunderstorms Tuesday and Thursday
a bit less certain.
Tuesday...Mainly VFR. A chance of showers and thunderstorms which
could briefly lower conditions to MVFR or IFR during the afternoon
or evening, mainly vicinity KMIV-KILG-KACY (primarily just south and
east of KPHL). Severe thunderstorm potential (strong westerly wind
gusts near 50kt and large hail) is relatively high for southern DE
Gradient (not thunderstorm influenced) west winds gust 15-20 kt
during the afternoon over E PA and N 1/2 NJ, but somewhere near or
just southeast of KPHL, afternoon winds will be southwest gusting
to 15-20 kt, especially KMIV.
Late Tuesday night through Wednesday night...mainly VFR. Westerly
winds Wednesday will gust to 20-25 kt.
Thursday...Vfr cigs lower to MVFR or IFR conditions in probable
showers with tstms possible, especially KPHL area southward. Some
severe tstm potential appears to exist for the Delmarva.
Friday...Mainly VFR. northeast wind.
Fairly quiet conditions are expected to continue across the area
waters. Seas of 2 to 3 feet across the ocean front, 1 to 2 feet on
the Delaware Bay. Winds will generally be out of the south around 10
knots, with some gusts near 20 knots this afternoon. No headlines
are anticipated through tonight.
Based on observations along the shore of a 3 to 4 foot ground
swell, and the full moon being tonight, we have upgraded the rip
current risk to moderate today.
Monday night through Thursday...No marine headlines are anticipated.
Thursday night and Friday...Wave heights on our ocean waters may
build near 5 feet in a southeast to northeast flow and an SCA may be
needed at that time. Fog might also be a problem.
At this time we have less concern about the formation of dangerous
rip currents Tuesday, in part because the wind will have less of an
onshore component. It will be a low enhanced risk day. Low risk does
not mean NO risk. A hot day with water temperatures above normal
makes it easier to swim. For safety, please do not swim along jetties
and piers where rip currents tend to recur. Preferably, swim within
eyesight of our lifeguards.