Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
407 am EST Sat Dec 27 2014
a high pressure system centered over the Carolinas will drift slowly
out to sea today. A cold front will cross the area on Sunday, then
stall to our south as a low pressure system rides along it Monday
and Monday night. A strong Canadian high pressure system will reach
the northern plains by Tuesday and is then expected to gradually
build south and then east reaching Kansas on Wednesday and the
Carolinas on Friday.
Near term /until 6 PM this evening/...
another fair weather day expected across our forecast area as high
pressure continues over the area. Skies will be partly to mostly
sunny and temperatures will once again be fairly mild for late
December. Readings will top out in the low/middle 50s for most areas.
Winds will be rather light from the west or SW.
Short term /6 PM this evening through 6 am Sunday/...
the high slides east into the Atlantic tonight and this allows the
next system to approach from the west. Low pressure will advance
across southern Canada and cause a cold front to push in from the
west. Increasing clouds are expected overnight and there is a chance
for some showers across the western/northwestern areas after midnight. Smaller
slight chance probability of precipitation are in the grids for northern Delaware...the del valley
into central New Jersey. Lows tonight will be in the upper 30s and low 40s
across the area.
Long term /Sunday through Friday/...
a lower confidence long term forecast continues for the wave on the
cold front as we kicked the problematical ptype can from Sunday
night to Monday night. Other than the operation ECMWF, the modeling
consensus is coming closer to our County Warning Area being affected by a wave of
low pressure forming on the cold front. This front will come through our
area on Sunday. There are still multiple issues of strength,
timing and thermal fields. A faster progressing system like the
UKMET has is warmer and Rainier, slower progressing system like
the can ggem has it snowier. The WRF-nmmb is both slower and
warmer which looks like its usual model bias of placing lows too
deep in the cold air. Add to the mix the op European model (ecmwf) still has no
second system at all.
The ensembling clustering puts the op GFS in the middle of the
Road. About a quarter of the members are wetter farther to the
northwest while a quarter of the members are similar to the European model (ecmwf)
solution. Conversely most of the 20 can ggem ensemble members are
more muted than the op or control, only about one or two are more
bullish. The "noise' in the European model (ecmwf) ensemble mean is still northwest
of the op. But not as much as the 12z run was.
Part of the issue remains the possibility of convection in the
northwest Gulf. Also while the low is heading toward a confluent
flow, not sure the system will get as suppressed as the op European model (ecmwf).
For this forecast package we are closest to the pgfs which has a
slightly slower and less robust solution than the op GFS. We have
gained another day to get a better handle, which we hope
subsequent sounding runs will do.
The sounding initialization in the southwest looked good. The trough
itself looks baggier, but the initial energy surge is heading to the
Great Lakes. Its the short waves along the California coast that
will initiate the secondary low. Thermally the GFS looked better
at both 850mb and 925mb. Another reason Monday night we were not
as warm as the WRF-nmmb.
Better modeling consensus on Sunday and Sunday night. The initial
surge of moisture is exiting faster and less of a ptype issue is
expected on Sunday night. In fact northwest of the fall line/i95
corridor it looks like a race for which will happen first, precipitation end
or a change to snow just before ending. Where precipitation should linger
deeper into the night, thermal fields support just rain south.
Backing up to Sunday day, there is decent model consensus of a short
wave moving through the southern half of our County Warning Area during the
afternoon and we upped probability of precipitation to likely south. Likely probability of precipitation were
carried into the evening south as the precipitation takes more of an anafront
look to it.
A precipitation break is expected on Monday, our break timing is
centered around the middle of the day. There might be some
sunshine north, less confident about seeing the sun south. Once
the break ensues, drier air will start working its way southward.
This will make it easier for the northern part of the precipitation to
transition to snow after boundary layer temperatures fall.
For now we are centering the best chance for precipitation associated with
the front to occur on Monday night. There are many moving parts to
this forecast, but suffice that the possibility for accumulating
snow which was northwest on Sunday night has shifted to around the
Delaware valley corridor on Monday night. Basically a tightening
fgen band coupled with a jet streak aloft is the trigger for precipitation in
our area. Isentropic lift is not there and neither is a trowal.
The predicted moisture transport at 290k is about a fourth of what
is heading our way on Sunday which may stand as a good precipitation forecast proxy.
Some of the more aggressive models bring a couple of inches of
snow to our region. We shifted our severe weather potential statement mention to the Delaware
valley and if there was to be an impact would be with the Tuesday
We linger a chance of mainly snow southeast on Tuesday morning, more
so for timing inconsistencies and not that it would be that a
protracted a precipitation event. Regardless of the ptype outcome into Tuesday
morning, the rest of the week will feature colder weather. The
vorticity maximum on Wednesday looks more channelized than was predicted
yesterday, so a cold, but dry end of the long term was continued.
Aviation /09z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
High pressure across the area this morning will move east later
today. A low pressure system and front will affect the area Sunday.
In between these systems we will find another good flying weather
day with VFR expected today and tonight. There will be some high
clouds across the area today and some middle level cloudiness will
arrive overnight. No precipitation is expected in the taf period. Winds will
be light today and tonight...favoring a SW direction much of the
Sunday and Sunday night...MVFR, possibly IFR, conditions possible
at times as a cold front moves through the region with showers.
Monday and Monday night...low confidence. A second wave of
precipitation could bring MVFR to IFR conditions back into the
region. Most likely to occur at southern airports and terminals.
Some precipitation could fall as snow.
Tuesday...VFR north, becoming VFR south.
Tuesday night and Wednesday...VFR.
another good day to be on the waters as high pressure remain in
control of the weather. The high slides to the east tonight. Dry
weather with increasing clouds expected today and tonight. Winds
will be mostly southwesterly 5 to 10 knots today and 10 to 15 knots
tonight. A few gusts closer to 20 knots possible tonight. Seas
today around 2 feet on the ocean and 1 to 2 across del Bay.
Sunday morning...a slightly stronger southwest flow preceding a cold
front will bring wind gusts closer to Small Craft Advisory criteria
on the ocean.
Sunday afternoon and night...sub Small Craft Advisory conditions
Monday through Tuesday...there is a chance for seas to reach Small
Craft Advisory criteria Monday night and Tuesday. Sub Small Craft
Advisory winds are still predicted. Lower confidence as a wave of
low pressure will form south of the area waters on the previously
mentioned front. Its possible that wind related Small Craft
Advisory conditions might also occur if this low intensifies
faster than we are currently forecasting.
Tuesday night through Wednesday...sub Small Craft Advisory