Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
925 PM EST Wednesday Dec 17 2014
low pressure will depart to our northeast through Thursday. High
pressure then will move to our north on Friday. Weak low
pressure will develop in the Gulf of Mexico on Saturday that will
move northeast on Sunday to virgina beach. A second low pressure
system will then form and head up the East Coast Monday into
Tuesday. Another cold frontal boundary with associated low pressure
systems moves from the Ohio Valley Tuesday night into our region on
Near term /until 6 am Thursday morning/...
we didnt make too many changes to the overnight as the forecast
remains close latest hrrr and rap continue to bypass measurable in
our County Warning Area. So we just kept a chance of sprinkles or flurries for the
overnight far north near the path of the strongest DPVA. Not much
moisture at all above 850mb seems to be the limiting factor.
Temperatures were falling ever so slightly slower, so only slight
upward tweaks were made.
Short term /6 am Thursday morning through 6 PM Thursday/...
Thursday...we are in service backup and Sterling will be writing
the forecasts starting at about 8 am.
It will be a bit cooler (still above normal)...about 8-9f per modeled
925mb about 5c cooler...with gusty northwest winds to 25 miles per hour.
Considerable cloudiness Poconos with maybe a few flurries? Otherwise
a mostly sunny start is expected becoming partly sunny or mostly
cloudy for a time midday then clearing late in the day.
Long term /Thursday night through Wednesday/...
Thursday night through saturday: low pressure with an associated
cold front will be located well offshore over Atlantic Canada on Thursday.
This will allow for continued north to northwest flow into the
region through Friday. By Saturday we await the approach of a low
pressure system from the south with increasing clouds and a more
northeasterly flow. This low pressure has trended weaker and
weaker with each set of model runs. Many of the 12z models only
bring very light quantitative precipitation forecast if that and are faster. Will keep probability of precipitation in the
chance category highest across the south. Forecast temperatures
reflect closer to the European model (ecmwf) and the European model (ecmwf) MOS in these periods,
did edge cooler Friday night with clear skies.
Saturday night and sunday: the much anticipated low pressure system
will pass to our southeast Saturday night into Sunday. Considerable
differences from where the models and there respective ensembles were
a few days ago, particularly with the European model (ecmwf). The European model (ecmwf) has
trended about 20 mb weaker with the low pressure center toward the
drier GFS and CMC models. Strong agreement from it's ensemble mean
and the 06z gefs exist as well. Also, more features associated with
this system will be better sampled by the upper air network,
adding more initial data. Bottom line is that confidence continues
to increase little by little on each forecast package for a rather
light event focused on Saturday evening.
Sunday night through tuesday: as the previous storm departs we
should have a dry window Sunday night. Some of the middle-level energy
destined for the previous storm will stay over the southeast and
spawn another low pressure system which heads up the coast focused
on Monday night for our region. This is a new wrinkle in the model
guidance today and will not go much above chance pop till more
consistency is shown. The Poconos and northwest New Jersey have a chance to
see mixed precipitation. However, a substantial warm layer looks to
be in place which could lead to mixed precipitation quickly changing
to rain. For now general rain/snow to rain for the Poconos and all
rain elsewhere. With the rain possible not much spread in the
modeled two meter temperatures and MOS guidance, did not stray from
these on temperatures.
Tuesday night through Christmas eve: a strong cold frontal boundary will
move into the Ohio Valley into the deep south on Tuesday developing a
low pressure system to our west by Tuesday night which deepens as
the trough likely becomes negatively tilted. Easterly winds will
gradually strengthen and switch to southeasterly by Wednesday
morning. Warm air advection ahead of the low is likely to pick up as well with a
strong low level jet. Went above wpc guidance on the winds. Also, think the
winds due to deepening low pressure may be higher than currently
forecasted. This forecast does not commit to a time period of
much higher winds since we're still seven days out. With temperatures
well above freezing, rain is expected. This deepening low pressure
could promote heavy rainfall, coastal flooding and a few rumbles
of thunder depending on the exact evolution of the low pressure
system. The forecast for this time period will continue to be
adjusted as new data becomes available while likely not snow, rain
and wind may still create travel problems in this period. Wpc
guidance on temperatures captures the potential short warm-up
In terms of track all of the models and respective ensembles show a
spread going up either side of the Appalachians with the low being the
strongest over the lakes on Wednesday.
With the forecast in mind it doesn't take much to go slightly
forward in time. With any light snow melting from the weekend and warm
conditions on Christmas evening the prospects for a white Christmas are
not that good at this time.
Aviation /02z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
A VFR 00z taf issued.
For this evening and overnight...some VFR ceilings are likely from
kphl terminal area northward until an upper air disturbance clears
the area. We are not expecting precipitation to reach or impact terminals,
although there might be some MVFR condition at Pocono airports due
to snow. Farther to the south, no ceilings are predicted, very few
clouds at all.
West to northwest winds will average 10 to 15 knots. While we are
carrying gusts in the tafs, they should not continuously occur.
It will be pretty windy between 2k and 4k (winds greater than 30
kts) and we believe that will be enough to trigger gusts reaching
around 20 kts from time to time overnight.
On Thursday. A VFR ceiling is predicted to reform from kabe-krdg
northward. Elsewhere a scattered deck of flat stratocumulus clouds
around 4500 feet should occur. Sustained west to northwest winds
should increase to near 15 kts with peak gusts of around 25 kts.
Winds should decrease second half of Thursday afternoon and we
dropped the gustiness and reduced cloud coverage at the start of
Thursday night through saturday: VFR with increasing clouds
Saturday night and sunday: some restrictions to MVFR in light snow
showers and light rain/snow shower mix for phl,ilg, miv and Acy.
Sunday night: VFR.
Small Craft Advisory posted. Small Craft Advisory verification occurring most of the coast. Winds
should subside somewhat this evening then may pulse up during the
night with isolated gusts 30-33 knots possible by morning. Winds on
Thursday should be strongest during the morning then may subside a
bit during middle and late afternoon.
The Small Craft Advisory on Delaware Bay has been extended. Strong winds are forecast
above the boundary layer which should become more easily mixed
downward as the night progresses peaking Thursday morning.
Buoy 44009 full service restoration probably delayed until February
wind gusts close to 25 knots in spots Thursday night and Friday with
northwest flow. Not enough confidence to extend Small Craft Advisory at this time. Otherwise,
conditions will be below Small Craft Advisory criteria through Monday. Weak low
pressure passing to our south should not lead to seas higher than
four feet on the ocean. Southerly winds Monday. Winds shifting to
north or northeast Saturday into the weekend.
Marine...Small Craft Advisory until 5 PM EST Thursday for anz450>455.
Small Craft Advisory until noon EST Thursday for anz430-431.