Scientific Forecaster Discussion
fxus61 kphi 201939
Area forecast discussion
National Weather Service Mount Holly New Jersey
339 PM EDT sun Oct 20 2019
a low pressure area will track offshore tonight. High pressure will
build in Monday and crest over the area Tuesday morning before
weakening. A cold front attached to low pressure in Canada will
cross the area later Tuesday and Tuesday night. Another high will
affect the weather for Wednesday and into Friday. Late during the
week, another disturbance will move towards the area.
Near term /until 6 am Monday morning/...
rain is expected to wind down through the evening as the remnant low
moves further off shore. Dew point depressions are already quite
low, and although we will see a wind shift to northerly overnight,
significant dry air advection is not expected until late tonight at
the earliest. This, combined with the wet ground and clearing skies
could lead to patchy fog development. The one factor working against
fog development is wind speeds, which will still be quite breezy
along the coast until very late tonight. Given all the factors in
favor of fog, I don't think it will be enough to completely preclude
fog development, though it may limit the fog from becoming dense
Because of the low dew point depressions, we are not expecting
temperatures to drop off too much overnight from Sunday afternoon.
Lows tonight are expected to be in the 40s and lower 50s across the
Short term /6 am Monday morning through 6 PM Monday/...
Monday will be a brief respite from the active weather pattern as a
surface high propagates directly over the region leading to
tranquil and dry weather for the region. Once the fog dissipates in
the morning, we should have mostly sunny conditions through the day.
Thus, despite northerly low level flow, temperatures are expected to
recover into the 60s for most locations, with highs near normal.
Long term /Monday night through Sunday/...
an upper air pattern featuring faster flow and more energy develops
across the Continental U.S. With a large broad trough moving into the plains
and then weakening as it slides east. A ridge tries to develop
across the East Coast late week before another trough deepens across
the Great Lakes.
Temperatures...during the week, temperatures will not vary from
normal readings by very much. Normals for the Delaware valley this
time of year feature highs in the mid 60s with lows in the upper
40s. Across the north/west areas, normals are 6 to 8 degrees cooler than
the Delaware valley normals. Friday will probably be the warmest day
with highs 2 or 3 degrees above normal. The overnight period
Wednesday will be cool with mid/upper 30s across the north and
low/mid 40s elsewhere. More frost across the north/west areas is possible
Precipitation...there are two periods during the long range which
will have the greatest chances for rain. First, a slow moving cold
front will cross the middle Atlantic later Tuesday and into Tuesday
night. This should bring some light rains across most areas during
the period. A weak low may form along the front across Delmarva. If
so, this could delay the ending time somewhat. Either way Wednesday
will be nice after perhaps some morning clouds.
Another system may arrive at the end of the work week and persist
into Saturday. The 12z runs of the ec and GFS differ quite a bit
with the details of the system. Nonetheless, it's possible that
this could bring another opportunity for some rains across the
area. The GFS shows that the low could tap into some Gulf of
Mexico moisture, so the potential for a soaker exits during the
first part of next weekend. Chc pops in the fcst at this point.
Aviation /20z Sunday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...we will start with MVFR and even localized IFR conditions
this evening. We could then see a brief improvement to VFR late in
the evening (between 02 and 06z), before fog develops, mostly after
06z, resulting in widespread MVFR and localized IFR conditions once
again. Northeasterly winds of 5 to 15 kt are expected to diminish
below 10 kt and back to northerly after 06z. Low confidence in the
period of VFR and the timing of any flight category changes,
moderate confidence otherwise.
Monday...patchy fog could linger through 15z, but once it
dissipates, VFR conditions are expected through the day. Northerly
winds will veer to easterly through the day, but wind speeds should
be less than 10 kt.
Monday night...VFR. Increasing clouds late.
Tue/Tue night...lower ceilings and visibilities with occasional showers.
Wed thru Fri...mostly VFR.
the remnant low of Nestor moves into the Carolina coast this
afternoon, and then out to sea tonight.
Small Craft Advisory conditions have already developed on much of
the waters. Gales force gusts are expected to develop soon on the
Delaware coastal waters and the southern New Jersey coastal waters by this
evening. We have seen a few gale gusts already in the vicinity of
Lewes and Cape Henlopen. Therefore, the Gale Warning was expanded to
include the lower Delaware Bay.
Small Craft Advisory and gales are expected to continue for most, if not all of
tonight, though winds are expected to gradually diminish overnight.
By Monday morning, winds and waves should be below Small Craft Advisory criteria on
the Delaware Bay. On the Atlantic coastal waters, Small Craft Advisory conditions,
primarily for elevated seas, will continue through the day on Monday.
Mon night...sub-sca. Fair.
Tue night into Wed morning...Small Craft Advisory possible. Showers Tue night.
Wed afternoon thru Thu...sub-sca. Fair.
Fri...winds and seas building. Showers possible late.
Marine...Small Craft Advisory until 6 PM EDT this evening for anz452-
Gale Warning until 6 am EDT Monday for anz452-453.
Small Craft Advisory until 6 PM EDT Monday for anz450-451.
Gale Warning until 6 am EDT Monday for anz454-455.
Small Craft Advisory until 6 am EDT Monday for anz430.
Gale Warning until 2 am EDT Monday for anz431.