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Area forecast discussion 
National Weather Service Mount Holly New Jersey
359 am EST sun Feb 1 2015

Synopsis...
high pressure will move offshore today. Tonight, low
pressure will move into the Ohio Valley and then will track into our
region on Monday. Another area of high pressure will move into the
region Tuesday. Low pressure will then track from the Ohio Valley
into New England on Wednesday. A cold frontal boundary then will
pass through the region Wednesday night and be followed by yet
another high pressure system for the end of the week.

&&

Near term /until 6 PM this evening/...
as the initial cold front approaches the region through the day,
precipitation may begin to nudge into the western and northwestern portions
of the region this afternoon. Temperatures will likely not rise too
much through the day as middle level clouds are already in place from
phl northward.

&&

Short term /6 PM this evening through 6 am Monday/...
though some precipitation may move in through the day today, the main
period of when our region will be affected by this system will be
starting this evening as the center of the surface low lifts from
southern Indiana into western PA by Monday morning. First a few
notes about the synoptic pattern. The main upper level trough
associated with this system is sliding east over the High Plains
now, the base of the trough earlier became a cutoff low over the
Baja California peninsula. Without a strong upper level jet on the back side of
the trough, and with the window of opportunity for any Lee side
cyclogenesis quickly closing as it moves further away from The
Rockies, this should be a rather progressive system. The GFS
however, shows the low intensifying and deepening over the next 24
hours, much more so than any of the other deterministic models. This
as a result, affects the timing of the warm front tonight, and thus
does affect timing of precipitation transitions. As with the previous
shift, am concerned that this is too fast in scouring out the cold
air in the boundary layer that is already in place. So with that in
mind, the forecast favors a slightly colder solution which shows the
precipitation as mostly snow (with the exception of central and southern
Delaware-Maryland-Virginia and far southeast New Jersey. Through 06z, should see a band of sleet and
freezing rain mix develop over the i95 corridor. This band of mixed
precipitation is expected to slowly move north after midnight as the warmer
air moves in from the south.

Snow and ice amounts did not change too much from the previous
forecast. Still looks like the highest snow amounts will be over the
Poconos and far northwest New Jersey which will likely see only a small window of
mixed precipitation early Monday morning. Have changed the Winter
Storm Watch to a warning, with the exception of western Chester
which is in a Winter Weather Advisory along with far northern
Delmarva, far southeast PA, and much of central and southern New Jersey.

&&

Long term /Monday through Saturday/...
Monday through Monday night:
* winter storm continues for at least the northern half of the region*

A frontal boundary will be stalled from west to east across the
region as low pressure rides along the boundary. Plenty of moisture
and upper level warm air will continue to be drawn north and rung
out along the frontal boundary. This may lead to
potentially moderate to heavy periods of precipitation Monday
morning. The rain/ wintry mix line will slowly move north from the
northern suburbs of Philadelphia toward the Lehigh Valley and
central New Jersey from 12-15z. A secondary low may form offshore as well
during the morning which could allow cold air to advect in at the
surface during the late morning and afternoon, non-diurnal
temperature trend. Mav and met both appear to warm Monday afternoon
but the European model (ecmwf) two meter temperatures look to cold. The cold air advection would
stop the northward advance of the changeover to rain by middle morning. A warm
nose may make all the way into the Poconos around sunrise Monday if
the 00z GFS sounding is to verify, so have added sleet into the
equation here. The precipitation type forecast is mainly derived
from the 00z NAM. The 00z GFS looked to have to intense of a low
pressure system which in turn allows for more warm air advection.
The European model (ecmwf) is still on the cooler end of the spectrum with the NAM in
between these solutions. The sref and wpc quantitative precipitation forecast forecast was used as
well with good model agreement on quantitative precipitation forecast in this period. This results
in additional snow and ice accumulations for northern parts of the
County Warning Area in this period. Also, soundings indicate the potential for some
30 miles per hour northwest wind gusts Monday evening as well.




Tuesday and wednesday: behind the system, a pretty potent blast of
cold comes into the region by Tuesday. 925 and 850 mb both will be
well below -10c coupled with strong northwesterly winds. This
quickly modifies by Wednesday as high pressure moves offshore
coupled with a return to southerly winds. Stayed close to the
ensemble guidance on temperatures both days. A shortwave and
associated weak low pressure will likely track northwest of our
region Wednesday and have included a chance for some light snow
in the Poconos and northwest New Jersey.

Wednesday night through Friday night: a cold frontal boundary will
approach the region Wednesday night and move through the area on Thursday.
Enough forcing looks to to be present for a band of light snow,
perhaps a rain/snow mix across the Delaware-Maryland-Virginia on and behind the cold
front. Maintained low chance probability of precipitation centered on Thursday. Depending on
the frontal timing a non-diurnal temperature trend could occur. Of
continued uncertainty is the potential for a low pressure in the
Gulf of Mexico to ride northeast along the front. The UKMET and CMC
have been persistent in this possibility for a few model cycles now.
The 00z European model (ecmwf) appears to have trended less progressive than in
previous runs as well. With that said, will continue slight to low
chance probability of precipitation for snow Thursday night. Temperatures remain close to a
consensus of the wpc ensemble guidance and that of the modeled two
meter temperatures in most parts of this period. The 00z GFS was stronger
with a cold blast on Friday, for now, did not incorporate the
temperatures from this run on Friday.



Saturday and Saturday night: moderating trend, clipper system by
Saturday night can not be ruled out. For now went dry.

&&

Aviation /09z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.

A middle layer cloud deck around 3000 to 3500 feet above ground level will continue to
propagate southeast over the region through 09z. For most locations,
still anticipate VFR conditions through 12z, with possible
exceptions of Abe and ridge. There may be a brief break in middle and
low level clouds between 12 and 18z, before low level clouds
(generally MVFR ceilings) build back in over the region.
Precipitation is expected to begin after 18z, slowly building in
from west to east. For the Delaware valley and points further
west, expect the precipitation to begin as -sn through 06z. At
miv and Acy, precipitation could begin as freezing rain or rain depending on
how quickly the precipitation moves in and how quickly the warm
front lifts north.

Outlook...
monday: MVFR and IFR ceilings in rain at most taf sites, snow or a
wintry mix for Abe and ridge. Taf sites south of Abe may end as a
rain/snow mix late Monday afternoon. Northwest wind gusts late
increasing to over 20 knots.

Monday night: improving conditions to VFR. Northwest wind gusts
20-30 knots.

Tuesday and wednesday: VFR. Increase in clouds Tuesday night.
Northwest winds shifting to southwest under 10 knots.

&&

Marine...
winds and seas will remain below Small Craft Advisory criteria for much of the day
today. Beginning tonight, winds will increase and could reach gusts
to 25kt after midnight.

Outlook...
Monday through tuesday: Small Craft Advisory seas through Tuesday morning. Northwest
winds increasing Monday with some gale gusts likely from 23z
Monday through 11z Tuesday. Gale watch in effect. Period of Small Craft Advisory northwest
wind gusts Tuesday morning following the northwest gale wind gusts.
Medium to high confidence in gale gusts.



Tuesday night through wednesday: sub Small Craft Advisory seas and winds.

&&

Phi watches/warnings/advisories...
PA...Winter Storm Warning from 7 PM this evening to 1 PM EST Monday
for paz054-055-060>062-103-105.
Winter Weather Advisory from 7 PM this evening to 4 am EST
Monday for paz070-071-101-102-104.
Winter Weather Advisory from 7 PM this evening to 7 am EST
Monday for paz106.
New Jersey...Winter Storm Warning from 7 PM this evening to 1 PM EST Monday
for njz001-007>010-012.
Winter Weather Advisory from 7 PM this evening to 4 am EST
Monday for njz016>022-025>027.
Winter Weather Advisory from 7 PM this evening to 7 am EST
Monday for njz013>015.
Delaware...Winter Weather Advisory from 7 PM this evening to 4 am EST
Monday for dez001.
Maryland...Winter Weather Advisory from 7 PM this evening to 4 am EST
Monday for mdz008-012.
Marine...gale watch from Monday evening through late Monday night for
anz430-431-450>455.
Small Craft Advisory until 4 am EST early this morning for
anz450-451.

&&

$$
Synopsis...Gaines
near term...Johnson
short term...Johnson
long term...Gaines
aviation...Gaines/Johnson
marine...Gaines/Johnson

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