Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
650 PM EST Sat Dec 21 2013
a strong cold front, stretched from the eastern Great Lakes, the
Ohio Valley and to the lower Mississippi Valley and Texas, will
progress slowly to the east. Low pressure is forecast to develop
along the front in Virginia late Sunday night and move to the
northeast, passing over our region Monday morning. The low should
pull the cold front through our area Monday afternoon. High pressure
is then anticipated to follow for Tuesday through Thursday. A cold
front from the northwest is forecast to arrive Thursday night with
another area of high pressure expected for Friday and Saturday.
Near term /until 6 am Sunday morning/...
a rather robust closed low across the Southern Plains this evening
will lift northeastward. This is resulting in a building ridge
across much of the east allowing very warm air to surge northward.
Our entire region pretty much resides within the warm sector,
however lingering snowcover and clouds have kept temperatures across
the northwest zones cooler compared to areas further south. A sharp
frontal boundary is draped from upstate New York to the Ohio and
Tennessee valley's then to southern Texas. There is ample moisture
riding up along this boundary, which will slowly edge eastward. The
greatest chance for some showers remains across the far northwest
zones, and therefore the pop gradient was tightened up some.
A robust low-level jet on the order of around 50 knots at 925 mb is
forecast to overspread the area during the course of the night. This
will help to maintain the warm air advection and also increase the moisture
advection. While the main lift is forecast to remain to our west,
some quick moving showers could occur as the low-level jet arrives
especially across the western zones. The increasing low-level
moisture will also add to the potential for low clouds and fog. The
guidance is robust at this occurring, however given the
strengthening wind field that is forecast to arrive and also keeping
some wind going at the surface, we have less confidence on how the
low clouds/fog potential plays out. For areas that still have
snowcover hanging on is where there is a better chance of fog formation
and it becoming locally dense, as the low-level inversion is
stronger due to the chilled lowest levels by the snow. However, the
increasing wind field may be able to overpower this. Overall, we
will maintain a fog mention for just about the entire area as we go
through the night.
The hourly grids were updated starting with the latest observation and then
the lamp/lav guidance was used to assist. This helped to capture the
quicker cooling so far across mainly portions of the northwestern
Short term /6 am Sunday morning through 6 PM Sunday/...
some fog and also low clouds are anticipated to be around for much
of the day. This could have an impact on temperatures and also the
vertical mixing. Given the forecast soundings though, we increased the
winds especially from about Interstate 95 on south and east where a
warmer boundary layer looks to assist in better mixing.
Otherwise, we are in the warm sector with low pressure moving northeastward toward
southeastern Canada and the cold front remaining to our west. It will be quite
cloudy through the day, however. Nevertheless, with increasing southwesterly
flow, it is expected to get very warm and record breaking temperatures are
anticipated. 800 mb winds are forecast to be above 60 kts Erly before
decreasing to around 40 kts. H9 will remain around 50 kts all day.
This wind will bring in the unseasonably warm air. Probability of precipitation will
increase Thursday the day, but should remain low until middle to late afternoon
outside of northern and western areas. By the end of the pd, expect the best
Long term /Sunday night through Saturday/...
the main weather event in the long term period is monday's cold
frontal passage and the moderate to heavy rain associated with the
feature. The bulk of the moderate to heavy rainfall should remain
to our northwest on Sunday. The models vary a bit with the
expected totals for Sunday night and Monday in our region.
Precipitable water values are forecast to be fairly high for late
December, mainly in the one and a half to one and three quarters
For the 24 hour period from 700 PM Sunday through 700 PM Monday,
the 1200 UTC operational NAM brings one to two inches of rain to
our region with the greatest amounts along the Interstate 95
corridor. The 1200 UTC operational GFS produces one to three
inches on our coastal plain with a quarter inch to an inch in
eastern Pennsylvania and northern New Jersey. The 1200 UTC
operational European model (ecmwf) indicates a pattern similar to the GFS with
amounts of one to two inches on our coastal plain and totals
similar to the GFS farther inland. We will favor the consensus
solution which brings the heaviest of the rain to the coastal
We should be able to handle the expected rainfall amounts based
on the latest flood guidance. However, some ponding of water on
roadways and flooding in areas of poor drainage is likely in the
heavier showers, especially with leaves and other debris blocking
Sunday night will remain quite mild, with lows mostly in the 50s.
Monday's maximum temperatures should be mainly in the lower and
middle 60s on the coastal plain and in the 50s to the northwest.
Developing low pressure along the eastward drifting cold front is
expected to be located over eastern Virginia around daybreak on
Monday. The low should move to the northeast reaching southern New
England or its adjacent waters early on Monday afternoon. As the
low continues to move away from our region, it will pull the cold
front through our forecast area with temperatures anticipated to
start falling on Monday afternoon.
The front is expected to move farther off the coast on Monday
night with strong cold advection in its wake. The last of the
frontal showers are forecast to pass off the coast on Monday
evening. However, scattered snow showers in the brisk west to
northwest flow may affect mainly our northwestern counties on
Monday night into Tuesday.
Cold high pressure is anticipated to influence our region from
Tuesday into Thursday with below normal temperatures on Tuesday
and Wednesday and near normal temperatures on Thursday.
A middle level trough is forecast to drop over the Great Lakes on
Wednesday night before progressing eastward. A cold front
associated with the trough should pass through our region on
Thursday night. It is expected to have limited moisture so we will
carry only a slight chance of snow showers. Another area of high
pressure is anticipated to follow for Friday and Saturday with
near normal temperatures.
Aviation /00z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Tonight...VFR, then ceilings lower to MVFR/IFR during the overnight.
As the low-level moisture increases, some fog is expected to
develop. However, the wind fields are forecast to increase quite a
bit with a low-level jet near 2,000 feet increasing to around 50
knots overnight. This could help keep the fog development at Bay at
least some, and therefore our confidence is on the low side. A
better chance of fog is around the kabe area where areas of
snowcover remains. Given the forecast low-level jet, low-level wind
shear is included however the timing was adjusted some. South-southwest
surface winds generally 10 knots or less.
Sunday...southwesterly flow will be maintained with an increase
anticipated at the surface as additional warming occurs. The
stronger winds should be from about the kphl metropolitan on south and east
where better vertical mixing can be obtained. Overall winds in the
10-15 knot range with gusts to about 25 knots. Low-level wind shear
is included for awhile in the morning before the stronger winds
start to shift to our east. Low clouds and some fog should be
around, however there is lower confidence on the improvements. Given
the forecast wind field, the ceilings may rise at least some from
what we are currently indicating. Some showers should arrive from
west to east through the day, especially in the afternoon.
Sunday night and Monday...moderate to heavy rain showers at times
with MVFR and IFR conditions likely.
Monday night through Thursday...mainly VFR.
the Small Craft Advisory flag has been extended through the end of the pd, due to
increasing southwesterly flow. This will in turn keep the seas elevated and
keep seas around 25 kts or possibly higher.
Sunday night...a Small Craft Advisory is in effect for our ocean
waters, mainly for wave heights at or above 5 feet.
Monday through Tuesday night...Small Craft Advisory conditions
Wednesday through Thursday...no marine headlines are anticipated.
record high temperatures for Sunday, 12/22...
Kacy...65 set in 1998. Por back to 1874.
Kphl...64 set in 1998. Por back to 1872.
Kilg...64 set in 1998 and 1984. Por back to 1894.
Kabe...61 set in 1998. Por back to 1922.
Kttn...64 set in 1998. Por back to 1865.
Kged...68 set in 1949. Por back to 1949.
Krdg...61 set in 1998 and 1949. Por back to 1869.
Kmpo...58 set in 1990. Por back to 1901.
Por = period of record.
For December as a whole we've taken a look at the all time record
highest temperature for the month. Based on expectations...the
following locations may equal or exceed their all time December
Kphl...73 set on 12/4 and 7/1998.
Kilg...75 set on 12/4/1998.
The short period of record kged is 77, set on 12/1/1991.
The Delaware December all time record high is 77.
The monthly records for all our County Warning Area long term climate stations are
in the 70s and in most cases featured the period of 12/4-7 1998. The
mpo all time December record is 66.
Marine...Small Craft Advisory until 6 am EST Monday for anz450>455.