Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
900 PM EDT Sat Mar 28 2015
a high pressure system over the Great Lakes will sink southeast
and reach the southeast coast Sunday. A cold front will move through
the region on Monday. On its heals will be a fast moving low
pressure system which should sweep through the area Tuesday. High
pressure will build into the region for Wednesday. Another cold
front is expected late in the week.
Near term /until 6 am Sunday morning/...
snow showers and flurries are continuing to dissipate across the
southern portions of the area as instability begins to wane and
the vorticity impulse to the west is beginning to slide into our
southern areas this evening. There could still be a few isolated
showers/flurries across southeastern Pennsylvania, southern New
Jersey, and the Delaware-Maryland-Virginia for a couple of more hours, so we'll keep
slight chance probability of precipitation in for a little while longer. All showers
should fully dissipate after midnight as the vorticity impulse
slides to our east overnight.
The gusty winds will be around most of the night and with a
secondary surge of colder air in the low-levels we could see gusts
increase slightly stronger than they were during the day. None-the-
less the pressure gradient will be tight enough to keep US well
mixed so not expecting much in the way of radiational cooling as
the clouds dissipate. Went with a straight blend of the met/mavmos
Short term /6 am Sunday morning through 6 PM Sunday/...
high pressure moves in aloft and at the surface to provide a rather
tranquil day with dry conditions. Skies will remain mostly sunny
with the massive amount of subsidence taking place but this will
also limit The Heights to which we can mix. The airmass aloft starts
to moderate later in the day and as the winds back towards the west-
southwest we should see temperatures several degrees warmer than on
Saturday. We edged closer to the warmer mavmos for highs tomorrow
though it is quite possible that with any downsloping addition we
could tack on another degree...expecting middle to upper-40s.
Long term /Sunday night through Saturday/...
with a split flow pattern...very limited model agreement...and a
series of frontal passages over the next week, this definitely has
all the hallmarks of a transition season pattern.
Sunday night Monday...the first low to talk about in the long
term should pass well to our North, Crossing over the Great Lakes
and into northern New England. However, the associated cold front
should sweep through our region during the day on Monday.
Isentropic lift looks to be enough for light precipitation,
primarily in the form of rain given the timing of the front.
However, if the front comes through early enough, some snow is
possible in the higher terrain west of the fall line.
Tuesday and Tuesday night...fast moving clipper system is expected
through this time. Any window of opportunity for precipitation
with this system will be brief. However, model disagreement on
track and timing of this low leads to considerable uncertainty
with precipitation type. The European model (ecmwf) and CMC have a track much
further south than the GFS, keeping most of the area in the cold
sector through this entire period. However, even in the cold
sector, precipitation should be mostly rain during the day. The
big question will be if the system is slightly slower, with the
further south track, how much snow will be possible. For now, have
kept mostly rain mentioned in the forecast as it appears to be a
fast moving system. The exception to this is the Poconos and northwest
New Jersey where if precipitation can linger into the late evening hours, snow
will be possible.
Wednesday and Thursday...high should first build in over the
region then track east off the coast through this time, bringing
what appears at this point to be the best chances for beautiful
Spring days, with highs generally in the 50s and 60s.
Thursday night through Saturday...here is where the model
differences are really noticeable. We'll be watching two surface
lows through this time. One will be lifting into Quebec Thursday
night into Friday, while the over will be developing over the
southern High Plains during that same period before lifting NE
toward our region on Saturday. If you believe the GFS, the first
low will pull a strong cold front across our region late Thursday.
Like the previous shift though, kept the forecast closer to the
European model (ecmwf) as that far north of a track doesn/T really favor a strong
frontal passage for US. The second low however, tracking very
close to US, appears to be our best chance for precipitation
(possibly even thunderstorms - though instability appears to be
very elevated at this time), and its cold front should bring
temperatures back down into the 40s and 50s to start the weekend.
Aviation /01z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy, and surrounding areas.
This evening - tonight...VFR. Ceilings around 5,000-8000 feet will
scatter out overnight as clouds lift and dissipate. Northwest
winds around 15 knots with gusts into the low-20 kts range.
Sunday...VFR. By middle- Sunday morning the gusts begin to wane and
winds slacken under clear skies. Winds back towards the west-
Sunday night into Monday...MVFR ceilings and visibilities possible
in rain showers and shsn primarily Sunday night into Monday morning,
otherwise VFR expected. Cold front on Monday will bring an abrupt
shift of gusty northwesterly winds.
Tuesday...MVFR ceilings and visibilities with -ra possible through
the day and overnight.
Wednesday and Thursday...mostly VFR conditions...rain showers moving in
tonight...we continue with the Small Craft Advisory through middle-Sunday as
winds and seas are expected to remain elevated. Gusts upwards of 25
knots are still expected across the waters, and with a secondary
surge of colder air tonight, we could gusts climb upwards of 30
Sunday...sub-sca expected by Sunday afternoon as high pressure
settles in overhead. We lose the gusts rather quickly and with the
offshore winds the seas should quickly drop as well. Winds begin to
veer towards the west-southwest by Sunday afternoon.
Sunday night...another round of Small Craft Advisory conditions, and possibly gale
conditions, is possible in the increasing SW flow preceding the
next cold front.
Monday and Monday night...the cold front should sweep through
Monday, bringing an abrupt shift of westerly and northwesterly
winds. Gusts near or above 25 knots will be possible through the
evening hours. Seas will be slow to subside.
Tuesday through Wednesday...winds are expected to stay below Small Craft Advisory
criteria through this period. However, if the passing low pressure
system is stronger than forecast, winds above 25 knots are possible
primarily Tuesday night. Seas near or above 5 feet are possible on
the coastal waters through this time, but there is still
Thursday...increasing southerly and southwesterly flow will result
in another round of Small Craft Advisory conditions on Thursday.
Marine...Small Craft Advisory until noon EDT Sunday for anz430-431-