Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
927 PM EST Thursday Dec 12 2013
high pressure over the southeast states will gradually weaken and
shift east off the southeastern Seaboard through Friday. A cold
front from the northwest is expected to cross our region during
Friday, followed by a high pressure system across southern Canada
building into the northeast states late Friday into Saturday. Over
the weekend, low pressure developing over the lower Mississippi
Valley Saturday will track to off the middle Atlantic coast by early
Sunday. This system will strengthen as it quickly moves up toward
the Canadian Maritimes through the remainder of Sunday. For next
week, a quick moving clipper system will pass to our north Tuesday,
followed by high pressure influencing our region into middle week.
Near term /until 6 am Friday morning/...
looking at the 500mb soundings vs the NAM initialization and the
ec and GFS 6 to 12 hour forecasts, both players are stronger than
forecast or NAM initialized. The closed low in the southwestern
Continental U.S. Has stronger ridging east of it and the short wave entering
Washington state is also deeper. Would think the 00z model suite
should course correct toward a faster deepening/phasing solution.
With the next estf update we are going to try to time some of the
warm air advection mainly middle level cloudiness better. This will hold up temperatures
north the next couple of hours. Elsewhere winds above the surface
are forecast to increase toward morning and makes confidence once
again about min temperatures toward morning shakier than average. The
flow is not coming from the Great Lakes tonight, so we are
expecting our County Warning Area to stay dry.
High pressure will continue to build to our south overnight tonight,
keeping our area on the northeastern periphery of the high.
Thicknesses rise some tonight, but with diminishing winds and mostly
clear skies, good radiational cooling should take place. With low
dewpoints and the snowpack remaining in some areas, temperatures may
drop off rather quickly after sunset, before settling down
overnight. Overall, a cold dry night is expected with temperatures
falling into the teens in most areas, to single digits in the colder
Short term /6 am Friday morning through 6 PM Friday/...
a dry, cold start to the day Friday, before a weak frontal boundary
drops into the forecast area later in the day. The frontal passage
should be mostly dry, but it is possible that some showers could
occur across our northern zones as a weak short wave/vorticity
impulse slides northward across the area and interacts with the
front later in the day. Anywhere snow showers occur, a light
accumulation is possible.
Long term /Friday night through Thursday/...
more wintry precipitation is anticipated Saturday into early Sunday
as a quick moving storm system passes nearby.
Latest model guidance continues to indicate the potential for some
messy wintry weather into this weekend. Going into Friday night,
rather strong surface high pressure across southern Canada is
expected to build into the New England states. There appears to be
the potential then for a cold air damming set-up into the middle
Atlantic region going into Saturday. Model output from the GFS,
ECMWF, and others is in rather good agreement regarding the overall
timing and progression of low pressure from the lower Mississippi
Valley early Saturday to off the middle Atlantic coast by early Sunday.
There are differences, though, regarding thermal fields through the
atmosphere and precipitation amounts, which continue to make this a tricky
As organizing low pressure tracks northeastward from the lower
Mississippi Valley toward the middle Atlantic coast Saturday through
Saturday night, warmer air aloft will be pushing northward, while
strong high pressure over New England helps to keep cold air in
place at the surface into our region. With this set-up in mind, we
continue to forecast a period of mixed wintry precipitation from
southeast to northwest for Saturday through Saturday night,
especially north and west of the I-95 corridor. Forecast soundings
indicate that a quicker transition from snow to rain may occur for
areas south and east of Interstate 95, while a more gradual
transition from snow to sleet and possibly freezing rain takes place
for areas north and west as the stubborn low-level cold air lingers.
Through Saturday and Saturday night, the Poconos will hang onto snow
as the main precipitation type for a longer duration, and the Lehigh Valley
region and surrounding nearby areas of eastern PA into northern New Jersey
look to be more in the transition zone where mixed precipitation-types are
expected. By early Sunday, precipitation across the forecast area
should be ending rather quickly as the center of low pressure off
the coast tracks northeast and toward the Canadian Maritimes.
For early next week, a somewhat quieter stretch of weather looks to
be in store. High pressure to our south should briefly build into
our region for Monday into Monday night, before moving east and
offshore. Into Tuesday, a clipper type system is forecast to track
across the Great Lakes and southern Canada. While moisture appears
to be rather limited across our area and the better forcing with
this system looks to be to our north, isolated snow or rain showers
cannot be ruled out, especially for the northern half of our County Warning Area.
Following this system, more high pressure is expected to build
toward the middle Atlantic for Wednesday and Thursday.
Aviation /03z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
The 00z tafs are VFR throughout. Overnight some warm air
advection VFR middle level clouds may make it into the terminals.
Even if cigs, they should not reach down to stratocu levels. Winds
will be light from the west.
Friday morning, a VFR cirrus level ceiling with possible some
scattered stratocu/cumulus level clouds around 5k. Some of the stronger
winds above the surface should start mixing downward. We should have
sustained west to northwest winds around 10 knots with peak gusts
close to 20 kts.
End of the taf period, we will lose the gustiness, and a thicker
cirrus ceiling should start to arrive as a prelude to Saturday.
Friday night...mainly vfr; although, increasing and lowering clouds
late at night.
Saturday and Sunday...MVFR to IFR conditions developing during
Saturday as snow arrives. The snow will mix with and change to rain
from the south and east; although, some sleet and freezing rain
should occur at kabe and krdg. The precipitation looks to taper off
early Sunday morning. A return to VFR may occur as early as midday
Sunday. Northeast to east winds around 10 knots Saturday, shifting
to the northwest 10-20 knots Sunday as the storm moves away.
Confidence is high regarding precipitation occurring; however, it is
lower with the timing and precipitation types.
Monday and Tuesday...mainly VFR. An isolated snow/rain shower
possible Tuesday, especially kphl and north.
the Small Craft Advisory remains in effect although winds have
dropped off below advisory levels for now. The winds will increase
later this evening into the overnight hours and continue into
Friday. The advisory level winds are expected to continue into
Friday the Atlantic coastal waters, but could drop off across the
Delaware Bay by sunrise. We pushed the ending time on the southern
waters into Friday as soundings show winds could remain around 25
knot through the morning; otherwise, the ending times stay the same.
into Friday night...winds and seas are expected to below Small Craft Advisory levels.
Saturday and Sunday...a low pressure system is expected to near our
waters during Saturday and strengthen as it pulls away to the
northeast on Sunday. Wind gusts and seas are expected to reach Small Craft Advisory
levels Saturday night through Sunday.
Monday and Tuesday...weak high pressure will be near our area
waters, and sub-advisory conditions are expected.
Marine...Small Craft Advisory until 1 PM EST Friday for anz450>455.
Small Craft Advisory until 7 am EST Friday for anz430-431.