Scientific Forecaster Discussion
fxus61 kphi 222145
Area forecast discussion
National Weather Service Mount Holly New Jersey
545 PM EDT Tue Oct 22 2019
a cold front passes through the region tonight. High pressure
returns for the midweek and dominates through most of Friday.
Another cold front passes through Friday night. Low pressure may
affect the area by late this weekend into the start of the new work
Near term /until 6 am Wednesday morning/...
it has been a cool and raw day across the area, with extensive low
cloud cover, patchy light fog, and areas of drizzle. Steady
southeasterly surface flow beneath low level warm advection has
created a favorable environment for the damp and gray weather. Now,
we await the arrival of the main frontal rain band, which has slowly
been making its way in from the west. No significant changes in
thinking as to how this will evolve. Timing has remained a little
slower than expected but all areas still look on track for a period
of rain over the next several hours.
Synoptically, a strong upper-level trough will continue to shift
eastward from the Great Lakes region with the associated occluded
surface low moving into Canada. The cold front will swing across our
area tonight. The front will be accompanied by mid and upper level
jet streaks. A low-level jet on the order of about 40 knots will
cross mostly our southern zones this evening in conjuction with a
weak surface low tracking along the front. These will enhance some
of the rain however the entire system looks fairly progressive and
therefore heavier rainfall duration should be limited. Given an axis
of nearly 2-inch precipitable water values ahead of the front, some heavier rain
cannot be ruled out with the highest rainfall amounts still expected
across mainly northeastern Pennsylvania and northern New Jersey,
though there is some potential for a secondary maximum in coastal
areas as a strengthening low level jet may help enhance rainfall as
the system starts to push offshore.
Continue to maintain no thunder in the forecast as today's weather
has obviously not allowed any instability to build, though there
could be a very small amount aloft. It should be noted that during
the evening and early overnight, especially across the southern
areas where the low-level jet is stronger, some heavier rain could
result in brief stronger wind gusts even without thunder, although
the soundings overall do not look all that favorable regarding the
Transfer of stronger winds down to the surface.
As the front moves offshore overnight, a wind shift to west and
northwest occurs allowing cold air advection to take over and also
some drying to work in. We are expecting clearing to take place
overnight from west to east as a result, and there could be a brief
period when the winds turn a bit gusty behind the cold front given
the rapid increase in cold air advection.
Short term /6 am Wednesday morning through 6 PM Wednesday/...
pleasant weather returns for Wednesday as high pressure starts to
build in from our southwest behind the cold front. Breezy conditions
are likely in the enhanced pressure gradient between the approaching
high and the departing low, but gusts should mainly stay in the 20
to 25 mph range. Westerly flow will advect much drier air into the
region with dew points falling through the day. We will have low
level cold air advection ongoing behind the front also. The air mass
behind the front is a good deal cooler than the one ahead of it, but
we already will be seeing height rises in the mid levels during the
day tomorrow. Along with full sunshine and dry air we should still
see temperatures climb into the low 60s in most places, with mid 60s
possible to the south. Overall, should be a nice day.
Long term /Wednesday night through Tuesday/...
Wednesday night through Friday...
High pressure dominates through most of this period resulting in
fair weather with light winds and seasonable temperatures. The one
thing that will have to be watched is that by late Friday an upper
disturbance looks to approach from the Great Lakes and this
will result in increasing clouds with a chance of some late day
showers across the north. This would be mainly for the southern
Poconos and northwest New Jersey.
Friday night through Tuesday...
There still remains a lot of uncertainty in the long range forecast
as forecast models continue to show differing solutions. The main
issue is regarding the handling of an upper level trough as it moves
southeast into the central part of the Continental U.S. Through the latter part of the
week. The GFS keeps this whole upper feature together as a more
progressive system while the European model (ecmwf) and the Gem fracture the trough
leaving behind a lagging southern stream upper level low over Texas
by Friday evening. How this plays out will impact our weekend
forecast and we continue to weight our forecast more towards the
European model (ecmwf)/Gem consensus. So this said, most likely scenario will be for
the northern stream wave to move through Friday night bringing with
it the chance of a few showers mainly over northern parts of the
forecast area before high pressure moves in and should dominate
through most of Saturday. However by late day Saturday as the
southern system begins to advance northeast, clouds may start to
increase. Beyond this time, chances for rain increase by Sunday as
low pressure looks to advance north and east towards the Great
Lakes. If the GFS solution were to pan out though, widespread rain
could arrive as early as the Friday night / Saturday time frame due
to the more progressive nature of the pattern and possibly linger
into Sunday. Please check back for updates as the weekend forecast
should come into better focus over the next day or two.
Uncertainty in the forecast continues into early next week as GFS
features dominant upper trough over central Canada into the northern
Continental U.S. And brings in the next system by late Monday while the European model (ecmwf)
features an upper level ridge over the southeast with the upper level
trough located farther west. This would keep the early part of next
week mainly dry with the next system arriving more towards the mid
to late week time frame. At this point, keep at least low chances
for rain in the forecast for next Monday and Tuesday but again, low
confidence this far out.
Aviation /22z Tuesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today... there has been some modest improvement in ceilings during
the afternoon, but most areas remain IFR with some low end MVFR. The
improvement will be short lived, and any areas that went MVFR this
afternoon should flip back to IFR as steady rain moves in. The worst
of the conditions in the phl area should be in the 22z to 02z time
frame, a couple hours sooner to the west and a couple hours later to
the east. Localized LIFR conditions are possible as the steady rain
moves through, but should stay mainly IFR. A fairly rapid
improvement to MVFR then VFR is likely once rain ends, generally on
either side of 04z, earliest to the west and latest to the east.
Winds will initially remain southeasterly at around 10 kt through
the evening. As the front moves through, winds will briefly turn
light and variable then shift abruptly to the west-northwest at
around 10 kt. Moderate to high confidence in overall trends and
flight categories, moderate confidence in the timing.
Wednesday... VFR. West-northwest wind at around 10 kt with gusts to
20 kt possible. High confidence.
Wednesday night through Thursday...VFR with mostly sky clear
conditions. Winds light and variable Wednesday night becoming SW
around 5-10 knots Thursday.
Friday through Friday night...VFR initially, then MVFR
possible, mainly at krdg/kabe in -shra. South winds less than 10
kt, becoming northwest Friday night.
Saturday...VFR if current forecast holds but low confidence as
there is little consistency among forecast model guidance. Northwest
winds less than 10 kt, but confidence is low on that as well.
Saturday night through Sunday...increasing chances for rain and
associated sub-VFR conditions. However continuing low forecast
A Small Craft Advisory is in effect for the Delaware Bay through
late tonight, and for all other waters outside the Delaware Bay
through Wednesday evening. For the Delaware Bay, southeasterly winds
may gust near 25 kt this evening, though this may be a stretch. Once
the cold front passes, there should then be a more solid period of
west-northwesterly gusts to near 25 kt late tonight and Wednesday
morning before winds start to drop off. Outside of the Bay, seas
will remain near 5 ft this evening and through tonight. Winds will
also increase late tonight as the cold front moves offshore. West-
northwesterly wind gusts of 25 to 30 kt are likely later tonight and
much of Wednesday, even as seas will be falling below Small Craft Advisory levels. So
the advisory will remain in effect for much of the day, though we
will trend towards sub-Small Craft Advisory conditions by evening.
Wednesday night through Friday night...winds and seas should
stay below Small Craft Advisory criteria.
Saturday...generally sub-Small Craft Advisory conditions, however gusts to 20 kt
are possible on the ocean waters by late day if low pressure
arrives sooner than currently expected.
Saturday night through Sunday...low pressure with increasing
winds and seas likely to affect the waters but confidence is low
on the details including wind direction as the track and timing
of the low remains uncertain. That said, increasing chances for
at least Small Craft Advisory conditions.
the persistent east to southeast flow has kept the water trapped
in the Chesapeake Bay, making each subsequent high tide higher
than previously forecast since Sunday evening. This is expected
to continue until a persistent westerly flow can push the water
out of the Chesapeake Bay, which will come later this evening
and overnight. Until then, the next high tide late this evening
into the early overnight hours is forecast to reach the advisory
minor level at Claiborne and Tolchester Beach. Therefore we
have issued a coastal flood advisory for Kent, Queen Anne's,
Talbot, and Caroline counties.
Maryland...coastal flood advisory from 2 am to 7 am EDT Wednesday for
Coastal flood advisory from 11 PM this evening to 4 am EDT
Wednesday for mdz015-019-020.
Marine...Small Craft Advisory until 7 PM EDT Wednesday for anz450>455.
Small Craft Advisory until 6 am EDT Wednesday for anz430-431.