Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
400 PM EST Friday Feb 12 2016
an Arctic front will cross the area tonight. High pressure will
build across the area later this weekend and then move east
Sunday night. Low pressure will deepen across the lower Mississippi
Valley Monday and then move along the Appalachians Tuesday and then
north into Canada Wednesday. More high pressure will build in for
the end of next week.
Near term /until 6 am Saturday morning/...
flurries possible Poconos and extreme south edge of our area late
this day as per radar and observation.
Tonight...shallow moist advection on S-SW flow prior to the cold front passage.
Snow showers or flurries appear probable for a few hours near
midnight as per a blend of models and wpc. Hrrr and hrrx look
acceptable as a timing guide. SW wind may gust 15 miles per hour early
tonight. Then a wind shift to northwest and gusty 20-30 miles per hour by
dawn Saturday....possible isolated gusts 40-45 miles per hour at sunrise per
arriving strong cold air advection and pressure rises.
Short term /6 am Saturday morning through 6 PM Saturday/...
Wind Chill Advisory and Wind Advisory posted in addition to prior wind
chill warning. Special Weather Statement from ydy no longer needed.
Deepening boundary layer momentum Transfer is featured associated
with the oncoming Arctic airmass invasion. Large low level lapse
rates and btv snow squall parameter indicating a possibility of
flurries or squalls but will the surface tt/dew point spread exceed 25f and
make those squalls just virga? Seems like best chance for a squall
would be the morning and in the region S of the PA Turnpike.
Am thinking of gusts 50 miles per hour in the Poconos and also scattered 50
miles per hour gusts developing in the krdg-kphl-kilg kacy and north side of
Delaware Bay slot for the afternoon. Wind Advisory issued. Not sure how many
noticed but the NAM and op European model (ecmwf) have been a little conservative
on wind. Just looks like too deep a mixed layer to avoid connecting
a few eddies of 50 knots gusts down from 6000 to 7000 feet aloft. The
inversion sinks to near 850 mb late in the day Saturday.
Strongest winds aside from the initial burst near 11-12z, may be
late afternoon and evening. For now wanted to limit advisory only to the
day and if its gusting 40 knots at 3 PM Saturday, then suspect it can
gust 40-45 knots through 10 PM. Confidence on verification is
average. This could be overdone but have seen repeatedly the pocs
wind match the overwater wind near 44065, and northwest flow strongest
gusts near a ridge-phl line. Also added Maryland East Shore along the still
warm ches Bay and Delaware along the Bay from Wilmington to Lewes
where I think some hefty gusts could add to the chill.
Otherwise widespread gusts 40 miles per hour Saturday with partly to mostly
sunny skies .. tending to clear late day.
Winds were derived from the GFS, the temperatures from the NAM MOS blended
with the 2m temperatures of the 12z GFS/NAM. Hrrx indicated near 0 at kmpo
at 17z Saturday...without a wind chill. Cant see it more than 17f
at phl at 18z Sat...maybe even a degree or 2 colder?.
Long term /Saturday night through Friday/...
The Heart of the Arctic air mass will be across the area Saturday
night and into Sunday. Dangerously cold temperatures and wind chill
readings will be across the entire forecast area. No precipitation
is expected. Winds will diminish through the day Sunday. Low
temperatures Sat night around -10 across the far north and closer to
5 degrees across the metropolitan philly areas and over the Delaware-Maryland-Virginia. High
temperatures Sunday in the teens most areas...but single digits over the
southern Poconos. Wind chill readings -20 to -32 far north and -5 to -10
over the Delaware-Maryland-Virginia.
The next storm system will deepen across the south Monday and move
up the inland East Coast Tuesday/Wednesday. The track of the system
that seems to be coming into better agreement amongst the op models
favor a low track across the central/western part of our area. This
will allow a decent flow of warmer air to overspread the region. The
precipitation will begin across the area Monday as snow...but will
change to rain later Monday night and remain mostly rain Tuesday. The
quantitative precipitation forecast could be up to 2 inches of rain in many areas. There is also
some chance for an accumulating snow Monday across (most likely)
eastern/northestern PA before the change to rain. Earliest predictions for snow
accums would be around 1-3 inches at this point. The details will be
tuned up as the weekend progresses.
The storm moves up into Canada Wednesday and will be followed by high
pressure and drier cooler air for the middle of next week.
Aviation /21z Friday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
This evening...VFR conditions will continue with light south to
southwest winds across the terminals.
Tonight through early Saturday morning...a cold front will approach
the region from the west. An area of snow showers looks to develop
in advance of the frontal passage and snow showers are expected to
reach all terminals. Visibilities and ceilings are expected to drop
to MVFR conditions as the snow showers move through. Once the
showers clear the region, between 05-09z from west to east, a return
to VFR conditions is anticipated. Snow showers may dissipate before
fully reaching kacy and kmiv but latest guidance leads US to include
the snow showers for late tonight/early Saturday.
Saturday...the biggest issue affecting aviation travel on Saturday
will be the winds. Behind the aforementioned cold front, the winds
will quickly turn to the west then northwest and become very gusty.
Sustained winds will be around 15-20 knots by 12-15z and increase
into the afternoon. Wind gusts from 25 knots early will increase to
near 40 knots by the afternoon.
Saturday night and Sunday...VFR conditions expected. Northwest
winds 10 to 25 knots with gusts 30-35 knots early, diminishing
some overnight into Sunday. Gusts still 20-25 knots overnight into
Monday-Monday night...degrading conditions with MVFR/IFR likely
through the day Monday into Monday night. Snow possibly
beginning Monday for many areas, possibly mixing with rain at
times for some areas.
Tuesday-Tuesday night...widespread MVFR/IFR conditions. Windy.
Wednesday...improving conditions. Windy.
lull in the wind and seas will end shortly after midnight.
Gales and freezing spray warnings-advisories posted. The heaviest
freezing spray will be midnight to 7 am along the shore where SSTs
now down to about 35-36f and used 35 for the zy threshold.
Isolated 50 knots gusts possible Saturday in funneled northwest wind down Delaware
Saturday-Saturday night...Gale Warning continues with strong
northwest flow across the area. Freezing spray advisory remains in
effect as very cold air and strong winds will lead to at least
moderate freezing spray.
Sunday-Sunday night...Gale Warning and freezing spray advisory
continue into Sunday morning. However, winds will diminish through
the day and Sunday night as high pressure builds into the area.
Monday night-Wednesday...Small Craft Advisory conditions
likely...gales possible as strong low pressure moves up the East
before everyone heads into the weekend, I wanted to bring next
week's storm into light and mention that there is a potential for
flooding across the hsa. There's still a lot that needs to unfold,
but the 5-day wpc quantitative precipitation forecast of 1.50 to 2.50 inches of liquid combined with
another 0.25 to 0.50 inch of swe on the ground would very likely
cause nuisance low-lying flooding and possibly some minor to
moderate river flooding (rivers associated with our forecast
points). This assumes most, if not all, the precipitation falls as
The uncertainty this afternoon is large. Yesterday at this time, the
precipitation was heaviest Tuesday and Tuesday night. Now it's late
Monday night into Tuesday. Besides timing, track is quite different
between the GFS and Euro with the Euro being further west and more
liquidy. Track will play a role in temperatures and not only affect what
type of precipitation falls, but also affect what remaining swe
melts. There's about 0.25 to 0.50 scattered across the area. I can
say we are in a better spot than on the 3rd and 4th when there was
in excess of 2.00 of swe along the I-78 corridor. As an fyi, one of
the main reasons we didn't see the flooding, that models suggested,
on the 3rd and 4th was because all the swe did not rapidly come out
of the snowpack. Snowmelt can be a tough nut to crack.
While the lack of swe is looking better across the hsa, not all the
rivers have receded back to where they were prior to the 3rd. So
rivers will start higher and the cold this weekend will surely get
the ground hard for a very efficient runoff.
So the take away heading into the weekend is to understand that if
the Monday into Tuesday (or Tuesday into wednesday) event is all
liquid across the area, low-lying, poor drainage flooding is likely
and minor to moderate river flooding is possible. If the
precipitation starts off as snow or ice, the flooding threat
decreases. If all snow falls, we're potentially just kicking the can
down the Road for future flooding. Time will tell.
near record cold is still expected for portions of our area Sunday
morning, despite the MOS guidance...and by far the coldest air of
the season so far.
Best chance for record equaling or exceeding for Valentines day:
kabe, kttn, kphl and kmpo.
Record low Max's can only occur for this event on Sunday the 14th,
if then. Those have been added recently below.
Site 2015-16 coldest so far record low Feb. 14th ----rer low maximum
Abe 8 -1 in 1979 14-1979
Acy 10 -6 in 1979 13-1979
Phl 12 +2 in 1979 14-1979
Ilg 12 -4 in 1979 13-1979
Ridge 10 -4 in 1983
Ttn 9 0 in 1916
Ged 13 -7 in 1979
Mpo -1 -12 in 1970
PA...Wind Chill Advisory from 6 PM Saturday to 9 am EST Sunday for
Wind Advisory from 6 am to 6 PM EST Saturday for paz054-055-
Wind chill warning from 6 am Saturday to 1 PM EST Sunday for
New Jersey...Wind Chill Advisory from 6 PM Saturday to 9 am EST Sunday for
Wind Advisory from 6 am to 6 PM EST Saturday for njz001-014-
Wind chill warning from 6 am Saturday to 1 PM EST Sunday for
Delaware...Wind Chill Advisory from 6 PM Saturday to 9 am EST Sunday for
Wind Advisory from 6 am to 6 PM EST Saturday for dez001>004.
Maryland...Wind Chill Advisory from 6 PM Saturday to 9 am EST Sunday for
Wind Advisory from 6 am to 6 PM EST Saturday for mdz008-012-
Marine...heavy freezing spray warning from midnight Saturday night to 9
am EST Sunday for anz450>453.
Gale Warning from 4 am Saturday to 10 am EST Sunday for anz430-
Freezing spray advisory from 4 am Saturday to 10 am EST Sunday
near term...drag 4p
short term...drag 4p