Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 181721
Area Forecast Discussion
National Weather Service Mount Holly NJ
1221 PM EST Sat Feb 18 2017
A warm front will lift north of our area through today. A weak cold
front is expected to settle through our area late tonight and early
Sunday as low pressure tracks well to our north. Another cold front
is forecast to push through the area early Monday, then high
pressure moves in later Monday into Tuesday before shifting offshore
Tuesday night. A weakening cold front moves across the area early
Wednesday, then another frontal boundary approaches Thursday and
stalls near the area through Friday.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --Surface low pressure at midday is located between the Great
Lakes and Hudson Bay, while an upper-level low is centered over
Arkansas. A warm front will continue to progress northeastward
across our area through the day, with warmer air low-level
overspreading the region. Speaking of warmer air, the 12z
Sterling, VA raob showed a very strong low-level inversion due
to radiational cooling last night and early this morning. At the
top of this inversion (near 1500 feet), the temperature was
measured at nearly +14C. As this inversion continues to erode
due to boundary layer heating, temperatures have jumped quite a
bit. The hourly temperature grids were adjusted to reflect this,
and high temperatures for several areas were increased some.
Just some high level clouds around, which will begin to increase
toward late afternoon ahead of two systems mentioned above.
The hourly temperature and dew point grids were adjusted based
on the latest obs. A more southerly wind component though along
the coast and up Delaware Bay will result in cooler temperatures
given the colder water temperatures.
-- End Changed Discussion --
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Winds should shift from southwesterly to westerly overnight,
resulting in weak downslope low level flow. That, combined with
the moisture advection, will limit radiational cooling. Lows are
forecast to be 15 to 25 degrees above normal, ranging from the
mid 30s to upper 40s.
A closed mid level low, currently over OK and AR is expected to
cross VA and Delmarva late tonight. However, it is expected to
fill and weaken today and tonight as it does so. Thus, we are
not expecting the same widespread convection currently on the
front side of this low. However, isolated rain showers will be
possible generally south of Philly as the low crosses Delmarva
.LONG TERM /SUNDAY THROUGH FRIDAY/...
On Sunday, the cold front that affects the area overnight
Saturday will push through the area. Any precipitation
associated with this boundary will end before daybreak, and a
dry forecast is expected Sunday through Sunday night. Sunday is
forecast to be a warm day, and several places could get within
a few degrees of record. However, no one is expected to break
any records at this time.
A back door front is forecast to push southward through the
area early on Monday before high pressure builds across the
area later Monday into Tuesday. Cooler conditions are expected
Monday and Tuesday as compared to Sunday, but will remain above
A warm front may pass across the area Tuesday into Tuesday
night as high pressure shifts offshore. Dry weather should
continue on into Tuesday.
A cold front is then expected to approach the area Tuesday night
and pass through during the day Wednesday. Precipitation may
start overnight Tuesday as a short wave/vorticity impulse slides
across the area. If precipitation starts early enough, there
could be a wintry mix across the far northern areas, mainly
along and north of I-80 corridor. Guidance indicates the
precipitation beginning to dissipate as it approaches the east
coast as the front moves through the area. So we`ll keep a
chance/slight chance for isolated showers across the area
Tuesday night into Wednesday.
Another front is forecast to approach the area Thursday, then
stall near the area through Friday. There is a chance that some
scattered showers could develop overnight Thursday into Friday
as a couple of short wave/vorticity impulses move across the
area. However, the best chance for precipitation looks like
Saturday as a stronger frontal boundary moves into the area.
.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
This Afternoon...VFR with just some high level clouds
increasing mainly later in the day. Southwesterly winds
increasing to around 10 knots.
Tonight...VFR with thickening clouds, however a ceiling should only
lower to 8000-10000 feet. Southwest winds less than 10 knots,
Sunday-Tuesday...Generally VFR expected. CIGS may approach MVFR
at times Sunday night into Monday morning. Gusty winds 15-20
knots during the day.
Tuesday night-Wednesday...Conditions lowering to MVFR or IFR
overnight into Wednesday morning with a chance of showers.
-- End Changed Discussion --
Winds and seas should stay below SCA criteria. Gusts above 20kt
are possible late this afternoon and this evening, but winds
are expected to remain below 25kt.
Sunday-Monday...Generally sub Small Craft Advisory conditions
expected, although winds may approach advisory levels across the
northern New Jersey coastal waters overnight Sunday into Monday
Monday night-Wednesday...Sub Small Craft Advisory conditions
expected although winds may gust up to 20 knots at times.