Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1004 am EST Friday Nov 27 2015
high pressure located across the Middle-Atlantic States today will
move offshore tonight. A cold front will move through the region
on Saturday. This front will remain south of the region early next
week while high pressure passes by to our north. The boundary will
come back northward as a warm front midweek before a cold front
moves through later in the week.
Near term /until 6 PM this evening/...
the dense fog which covered much of the area earlier this morning
seems to have been rather shallow and is rapidly dissipating as of
mid-morning. It doesnt look like there will be much in the way of
lingering low clouds from the fog...however there is some fairly
dense cirrus spilling over the upper ridge. Still it seems there
should be enough sun...together with downward mixing from warmer
air aloft...to push afternoon temperatures into the middle or even upper
60s most areas.
Previous discussion below...
surface high pressure was centered over the northwestern Atlantic Ocean
early this morning but the ridge axis extends southwestward all the way
into the Middle-Atlantic States. Ideal radiational cooling conditions
underneath the ridge last night has resulted in the development of
fog across the coastal plain. The fog has become dense in some
spots in central and southern New Jersey as well as northern Delaware. Knowing that
many of the ASOS/AWOS sites that are reporting dense fog are sited
in fields and a lack of evidence of dense fog on the numerous
traffic cameras, it appears that the dense fog is mainly limited
to rural and forested areas. This may lessen the extent of the
adverse impacts, but it still warrants a dense fog advisory. The
advisory is in effect through 9 am.
Warm air advection and southerly return flow will continue overhead today as we remain
along the western side of the ridge. The models continue to exhibit
significant differences in temperatures today. For example, met stat
guidance for maximum temperatures is 5-10f lower than the mav today. The
differences seem to be tied to how quickly they mix out the
stratus. The GFS/ECMWF/Gem/WRF nmm show the low clouds eroding
across most areas quickly by middle to late morning, allowing US to
warm up to near record levels this afternoon with highs in the
middle 60s (perhaps 70f in southern de). Meanwhile, the NAM/hrrr/WRF arw
keep the low clouds over the area for most of the day, which is
always a concern this time of year due to the low sun angle. The
cloudier scenario would cut down on highs by 5-10f. For eastern PA
and western MD, where fog or stratus this morning has not materialized,
sided with the warmer mav guidance as less moisture trapped
underneath the inversion should allow any morning low clouds to
mix out quickly. Farther east where the fog and low clouds have
been established, took a 60/40 blend of the mav/met.
Short term /6 PM this evening through 6 am Saturday/...
the ridge axis will finally shift to our south this evening as a
cold front approaches from the northwest. The front is expected to
move into the area overnight.
There isn't a great deal of synoptic lift expected to accompany
the front as our area will be located in the right-exit region of
an upper-level jet streak. Additionally, the thermal advection
pattern in the low- and middle-levels is neutral ahead of the front
and the frontogenetical forcing lags behind the surface trough.
Therefore, probability of precipitation were kept low and low chances for showers late
tonight were confined to the higher elevations of NE PA and northwest New Jersey.
Expect fog to develop again tonight and likely in the same areas
as last night...southern New Jersey and the Delaware-Maryland-Virginia.
Long term /Saturday through Thursday/...
saturday: a cold frontal boundary will slowly move southward into
the region. This will result in quite the temperature spread
across the region with highs south of phl near 60 and in the 40's
across the Poconos and northern New Jersey. Both the 00z GFS and European model (ecmwf)
have similar timing with the front getting into northern New Jersey and
the Poconos in the morning and reaching the Philadelphia metropolitan
later in the day. The 00z NAM looks to be a bit slower, typical
bias at this range for the NAM. Ahead of the front, temperatures
will rise throughout the day. However, areas that see the frontal
passage will actually see falling temperatures in the afternoon.
Enough moisture will likely be lifted by the front to produce some
light rain showers with quantitative precipitation forecast under 1/10th of an inch. Deeper
moisture should stay across the Southern Plains and Ohio Valley,
in fact 00z European model (ecmwf) is almost totally dry. This also keeps the
forecast from going bullish on probability of precipitation at this time. A non- diurnal
temperature trend was used close to met/mav guidance. Current
forecast has highs a couple of degrees warmer across the Delaware-Maryland-Virginia
with less cloud cover and lower shower chances.
Saturday night through Sunday night: the front will slowly move
southward through the region. The mean model timing on the frontal
passage would result in some lingering light showers from
Philadelphia to the south on Sunday. Temperatures will be cooler
with northerly winds ushering in a cooler airmass. Low
temperatures Sunday night with clear skies have a chance to
radiate down fairly rapidly. However, one limitation is possibly the
wind. For now have added some localized radiational cooling by a
couple of degrees with lows across The Pine Barrens and in the
Lehigh Valley to Delaware River in central New Jersey.
Monday through tuesday: the front will be south enough through Monday
night to where we should be precipitation free with high pressure
to the north as well, though the 00z European model (ecmwf) is starting to speed up
closer to the GFS. However, by Tuesday this front will likely
come back northward as a warm front with some scattered showers.
Did nudge high temperatures warmer than ensemble guidance by
Tuesday with a more pronounced southerly and southeasterly wind
direction. Low temperatures Tuesday morning may be close to
freezing, right now forecasted just Above. All rain is in the
forecast at this time but we may have to watch for some freezing drizzle
or freezing rain around sunrise Tuesday in the Poconos/Sussex New Jersey
if temperatures were to trend cooler at the onset.
Tuesday night and wednesday: our region will be firmly in the warm
sector ahead of the next cold front and low pressure system. A more
expansive moisture stream from the Gulf of Mexico and Atlantic
will be in play with southeast winds. This also corresponds to the
highest probability of precipitation in the entire seven day period. Temperatures should
be quite a bit warmer (well int0 50s). Continued to nudge warmer
than ensemble guidance Tuesday night then a little cooler
Wednesday with slightly faster timing of the cold front. Frontal
timing may determine if another day with a non-diurnal temperature
Wednesday night through Thursday night: high pressure builds back
into the region with northwesterly winds brining in a more
Aviation /15z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg,kmiv, kacy and surrounding areas.
As of 1500z conds at most terminals have improved to VFR. All
should be VFR in another hour or two. The earlier possibility of
lingering stratus this morning seems to have dissappeared also.
Current calm or light/variable winds will become SW 5 to 10 knots this
Previous discussion below...
potential for fog and low clouds to redevelop tonight from I-95
Light southerly winds under 5 knots this morning will become southwesterly 5-10 knots this
afternoon and westerly late tonight.
Saturday and Saturday night: mainly VFR with lower MVFR
restrictions in scattered showers. West winds at or under 10
knots gradually shifting to the north.
Sunday through Monday night: VFR. Northerly winds shifting to
southeast late Monday, generally under 10 knots with gusts up to
20 knots (highest kacy).
Tuesday: MVFR or lower restrictions in scattered showers.
Southeast winds at or under 10 knots.
Small Craft Advisory for hazardous seas remains in effect for the
Atlantic coastal waters for today and tonight. Seas have already
reached 5 feet at 44009. Expect 5 feet seas to expand northward off
the New Jersey coast through the morning.
Winds will be light...generally at or below 10 knots.
Small Craft Advisory extended till 23z Saturday. Winds are expected to be below
Small Craft Advisory criteria throughout most the outlook period. However some
northeasterly gusts around 25 knots are possible. Seas are likely
to be at or above five feet through Saturday night with a frontal
boundary moving through the region. On Sunday, seas lower below
five feet and stay below five feet till sometime on Tuesday till
the next low pressure system approaches the region. A brief
interval of five foot seas is also possible late Sunday night.
the following locations may experience near record warmth today,
November 27, presuming the low clouds this morning dissipate and
enough sunshine develops from midday/early afternoon Onward.
Differences in the guidance this morning concerning how long the
low clouds hang on today bring question to how close we will
actually get to these record highs.
We are currently forecasting record highs for Abe and ridge but it
will be close at Acy if the stratus erodes early enough.
Record highs for today(november 27)
kabe 62 -1988 and 1959
krdg 65- 2011
kacy 69- 1981
Marine...Small Craft Advisory for hazardous seas until 6 PM EST
Saturday for anz450>453.
Small Craft Advisory for hazardous seas until 6 PM EST
Saturday for anz454-455.