Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1005 PM EST Monday Jan 26 2015
a rapidly intensifying low pressure system east of the Virginia
convective available potential energy will move northeast and pass near Cape Cod Massachusetts
during the middle of the day on Tuesday before weakening as it moves
toward the Canadian Maritimes on Wednesday. A high pressure system
from the west is expected to arrive over the region on Wednesday
night. A clipper type low pressure system is expected to follow with
its cold front moving through early Friday. Another high pressure
system is then anticipated for Saturday. Another low pressure system
should move through the eastern United States late Sunday or early
Near term /until 6 am Tuesday morning/...
major winter storm continues to strengthen this evening off the
East Coast. The trough aloft has become fully negatively tilted to our
south and west this evening. A short wave/vorticity maximum has
rounded the base and will lift to the northeast overnight. As this
happens, the surface low off the Delaware-Maryland-Virginia coast this evening will
rapidly intensify as it lifts to the northeast and south of Long
Heavy snow is now beginning to fill in from eastern Massachusetts,
southward across Long Island, and off the New Jersey coast, and is
continuing to show signs of pivoting and moving toward our area
over the next few hours. Additionally, snow has also been developing
and moving across much of our area over the last several hours as
well. Model guidance continues to show snowfall spreading across
the area from northeast to southwest through the night as strong
omegas within the dendritic growth zone are expected to begin
developing across the eastern half of the area between now and
midnight, and continue into the morning hours Tuesday.
We have not made any changes to the warnings and advisories from
earlier today as we have not gotten into the heaviest snow period
yet. However, the latest NAM has cut back on its snow totals and
is more in line with other guidance. So we have cut back totals
some across the area, but we will wait to make big changes until
we get more into The Heart of the storm and have all the 00z
guidance in to get a better handle on the potential snow amounts.
The highest amounts continue to be expected across northeast and
eastern New Jersey and decreasing south and west from there.
Short term /6 am Tuesday morning through 6 PM Tuesday/...
it looks like the surface low will reach its deepest point sometime
around 12z to 15z Tuesday morning somewhere south of Cape Cod or
eastern Long Island. Some wrap-around bands of heavy snow will
likely be continuing over northern New Jersey for a while in the morning but will
start to weaken and/or move northeastward by mid-day. A few more inches of
accumulation are expected in the morning but not much else in the
afternoon. Probability of precipitation on Tuesday go from categorical in the morning to none
or slight chance in the late afternoon...decreasing from SW to NE as the storm
pulls away. Gusty winds may cause blowing snow to continue even
though precipitation has ended.
Long term /Tuesday night through Monday/...
the GFS initialization looked slightly better than the WRF-nmmb. The
trough itself looked slightly broader, not as sharp, but already was
taking a slightly negative tilt. Thermally 850mb and 925mb it was a
mixture of GFS and WRF-nmmb.
Overall there has not been that much of a change in the long term
with a clipper type system for Thursday night and possibly a
stronger system late Sunday into Monday. It will be unseasonably
cold and most if not all of the precipitation will be in the form of snow.
For Tuesday night even looking at the slowest modeling solutions,
they barely have any measurable in our County Warning Area. The faster can
ggem/UKMET/GFS snow is long gone. We removed probability of precipitation except for far
northestern County Warning Area and possibly some lake effect snow showers making it into
the Poconos. Winds will be decreasing, but wind chill factors will
still fall into the single numbers and below zero northwestern
County Warning Area. Because of the fresh snow cover, we sided with the colder
datasets, closer to NAM MOS.
A quieter day on Wednesday with high pressure nosing closer to our
area. The predicted low level moisture does not look that impressive
and skies should be mostly sunny. Even so, we likely will not reach
the freezing mark in the bulk of our County Warning Area.
Wednesday night will be a very cold night. How cold will depend upon
how quickly cloudiness starts moving across from the next clipper
like system. Winds will be light regardless. We are colder than
all of the guidance datasets with min temperatures and in reality may
not be cold enough.
Decreasing sunshine as Thursday progresses. There is good modeling
consensus of middle level Omega and qvec convergence with this system
arriving by 00z. Given that the warm air advection phase likes to sneak in early,
we kept precipitation chances in for late in the day. Ptype should be
primarily snow. Some mixing based on forecast 925mb temperatures above zero
might occur far southeast.
The bulk of the clipper precipitation is expected to occur at night. Assuming
it does not arrive in time for the evening commute, its appearing to
be a borderline advisory criteria type event snow. Precipitation should
end by Friday morning with a windier day in wake of the system's
Colder weather for Friday night and Saturday as the next
Arctic/Canadian air mass moves eastward. We then repeat the process
later in the weekend as the high pressure system moves offshore and
another front approaches the region. Another low pressure system is
forecast to form on the front. This one could tap gulfmex moisture
and thus be a snowier system.
Aviation /01z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
**High impact event, especially tonight and Tuesday morning**
Tonight-early Tuesday...conditions vary from site to site this
evening as scattered areas of light snow continue to develop. As
the snow spreads across the area overnight, conditions will
continue to deteriorate through the night and IFR conditions will
become the norm at all sites. A period of moderate to at times
heavy snow is expected to continue to develop and spread across
the area through the night, and produce snowfall rates of one to
two inches per hour at times, especially through New Jersey and the
Delaware valley. IFR to LIFR ceilings and visibilities are expected as the
snow develops and moves across the area. Gusty north- northeast
winds will continue, with gusts to around 25-30 knots at times. Areas
of blowing snow are expected.
Rest of Tuesday...around midday and into the afternoon, improvement
to MVFR conditions are expected with some continued light snow
remaining across the region. Blowing and drifting snow will be
an issue, though, as winds back more toward the northwest with
continued gusts into the 25 to 30 knot range. Some late-day
improvement to VFR is expected, but timing is a little uncertain.
Tuesday night...VFR. Gusty northwest winds.
Wednesday and Wednesday night...primarily VFR.
Thursday into Friday morning...VFR to start Thursday then likely
becoming MVFR or IFR in snow with highest confidence northern
airports and terminals.
Friday afternoon and evening...VFR with gusty northwest winds.
Friday overnight into Saturday...primarily VFR.
storm and gale warnings have been left as is. Winds are forecast to
increase tonight into Tuesday as low pressure off the middle-Atlantic
coast deepens to around 975 mb by 1200z tomorrow morning. Winds are
expected to gust to near 50 knots north of Cape May and 40 to 45 knots
south. Seas will build to 10 to 12 feet or higher tonight with the NE
fetch. Winds and seas will gradually subside on Tuesday but conds
will remain quite rough. Also...visibility will be very poor at time
tonight and Tuesday morning in bands of heavy snow.
Tuesday night...we will be transcending from gales into Small Craft
Advisory conditions. Freezing spray.
Wednesday...Small Craft Advisory conditions are expected with
Wednesday night through Thursday night...no marine headlines are
anticipated. Some freezing spray possible Wednesday night.
Friday and Saturday...a Small Craft Advisory should eventually be needed Friday as a
northwest flow of cold air advection develops behind the departing
clipper low. We might come close to gale force gusts Friday night.
Winds should start decreasing below Small Craft Advisory levels on
no change for the coastal flooding highlights with this forecast.
Still relatively high confidence of the upper end of minor to the
lower end of moderate tidal flooding along the Atlantic coast with
tonight/S high tide cycle, so kept the coastal Flood Warning as is.
There is less confidence on the upper Delaware Bay and the tidal
Delaware. By the time of the high tide on the Upper Bay, winds
should have shifted to northwesterly, limiting tidal departures.
Minor flooding is possible, but at this time confidence is too low
to issue any coastal flood advisories for these locations.
record (vulnerable) daily snow fall for our long term climate
sites. Tuesday 1/27.
Acy 4.0 1946
phl 4.1 1941
ilg 2.9 2004
Abe 8.0 1897
PA...Winter Storm Warning until 6 PM EST Tuesday for paz070-071-
Winter Weather Advisory until 3 PM EST Tuesday for paz060-101-
Winter Storm Warning until 3 PM EST Tuesday for paz054-055-061-
New Jersey...Winter Storm Warning until 6 PM EST Tuesday for njz001-007>010-
Coastal Flood Warning until 7 am EST Tuesday for njz012>014-
Blizzard Warning until 6 PM EST Tuesday for njz012>014-020-026.
Delaware...coastal Flood Warning until 7 am EST Tuesday for dez002>004.
Winter Weather Advisory until 3 PM EST Tuesday for dez001>004.
Maryland...Winter Weather Advisory until 3 PM EST Tuesday for mdz008-012-
Marine...Storm Warning until 6 PM EST Tuesday for anz450>453.
Gale Warning until 6 PM EST Tuesday for anz430-431-454-455.