Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
401 PM EDT Friday Mar 27 2015
low pressure and a associated cold front will continue moving
offshore tonight. High pressure will build eastward from the Ohio
Valley into the Middle-Atlantic States this weekend. A couple of cold
fronts and associated low pressure systems will move through early
next week. High pressure will then build back into the region
Wednesday into Thursday before another cold front moves through the
region by Friday.
Near term /until 6 am Saturday morning/...
a cold front has pushed well offshore and cooler air is advecting
across the area on north-northwest low-level winds. However an upper level trough
remains to the west/northwest across the Great Lakes and is moving only slowly
southeastward. The result is southwesterly flow aloft across the middle-Atlantic region
which is continuing to bring moisture and light rain across much of
Delaware-Maryland-Virginia and far southeastern New Jersey. The mosaic radar loop suggests that the
last batch of rain may be moving across central delmava as of middle
afternoon. For that area we have chance probability of precipitation for the remainder of
the afternoon decreasing to slight chance this evening and below
mentionable threshold overnight.
For tonight...expect middle/hi level clouds to remain over the area as
the upper level trough remains to the northwest. Clouds will limit cooling in
spite of continued low-level cold advection. In fact it looks like a
secondary surge of cold air will move in overnight with stronger north-northwest
winds developing. A blend of MOS guidance was used for the min temperatures
which should be roughly 10 degree f colder than this morning.&&
Short term /6 am Saturday morning through 6 PM Saturday/...
High pressure will continue to build in from the west on Saturday...but
the upper-level trough will also be moving across the area. Deep-layer
moisture will generally be decreasing and there does not seem to be
any organized upward vertical velocity. However...with cold air aloft any breaks in the
clouds and surface heating may result in some instability and possibly
some scattered snow/rain showers. Cold 850 mb temperatures would certainly
support snow...however warmer/drier air below could cause melting or
evaporation before snow reaches the ground...especially from phl southward
Long term /Saturday night through Friday/...
the majority of this forecast period will be dominated by quick
moving cold fronts in a northwest flow pattern with chances for
light precipitation. By late in the week, the potential for a warmer
pattern with more southerly flow exists.
Saturday night through sunday: fairly quiet overall with high
pressure moving south of the region. Setup is very favorable for
radiational cooling in The Pine Barrens and across parts of eastern
PA with clear skies and light winds. Chilly with lows in the 20's
across most of the region. Temperatures should rebound into the 40's
Sunday afternoon, with modeled two meter temperatures to cool.
Sunday night and monday: a cold front will move through the region
Monday morning. The parent low pressure system will be located over
southeast Canada with limited moisture transport north. Both of
these factors keep precipitation light and in the chance range at this time.
Low temperatures near freezing northwest warrant mixed p-type
chances at this time with no wintry accumulation. With more clouds, low
temperatures will stay in the 30's with light southerly flow. Even
with a wind direction change to west/northwest on Monday, 925 mb
temperatures don't fall much and the potential for some peaks of sun
exists in the afternoon. So will go with the warmer ecm and mex
guidance. Wind gusts around 20-25 miles per hour are possible Monday
afternoon with some mixing potential.
Monday night and tuesday: a return to light southerly flow ahead of
the next system. Model divergence in the track of these northwest
flow systems diving southeast of Canada starts to vary in this
period. Fairly tight spread in all guidance on the temperatures with
most locations getting into the 50's after a chilly start in the
Tuesday night and wednesday: the 12z GFS and 00z European model (ecmwf)/UKMET are
similar with the track of a low pressure system tracking it across
southern New England close to the wpc forecasts. The CMC looks to far
south with the track. This brings a chance of rain showers and light
qpf, highest chances across the north. Temperatures may rise late
Tuesday night south of the low track. Stayed close to ensemble
guidance in this period for most weather elements.
Wednesday night through friday: the potential exists for a stronger
ridge to develop off the East Coast near Bermuda. This would have
the effect of increasing southerly flow, pumping a milder airmass
into the region. Modeled 925 mb temperatures respond nicely to
this pattern change in this time period. Will take the forecast on
the warmer side of the guidance range in this timeframe. A
stronger cold front could lead to another shower chance by
Thursday afternoon with the 12z GFS the most aggressive. In terms
of any thunderstorms, shear will likely be abundant ahead of the
front with instability lacking but possibly enough for a few
rumbles of thunder. Still a considerable time to examine any
thunder threat with this cold front.
Aviation /19z Friday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy, and surrounding areas.
VFR conds are noted at all our taf sites as of 300 PM except for
Acy. Acy/miv should continue to see some tempo MVFR ceilings for the rest of
the afternoon...but overall conds there should be improving with VFR
by evening and continuing overnight. Drier/cooler air will be moving in on
north-northwest winds...especially after midnight with a secondary cold surge
and stronger north-northwest winds. The winds are expected to become gusty on
Saturday with some heating and better low-level mixing of momentum.
Some scattered showers are possible on Saturday which could
temporarily lower ceilings/visibilities to MVFR...but not for long.
Saturday night and sunday: VFR, winds under 10 knots.
Sunday night and monday: some lower MVFR ceilings and visibilities in
scattered rain showers. Southerly/southwesterly winds under 10
knots shifting to west/northwest on Monday and gusting to around
Monday night and tuesday: VFR, winds under 15 knots shifting from
northwest to southwest.
Tuesday night and wednesday: potential MVFR restrictions with
scattered showers with the highest chances at Abe and ttn. Wind
shift from south/southwest to northwest on Wednesday.
as of middle afternoon...winds and seas appear to be below Small Craft Advisory criteria
although seas at buoy 44009 are still near 5 feet. However...an Small Craft Advisory remains
in effect for coastal waters...and will go into effect at midnight
for del Bay...as a secondary surge of colder air overnight will
produce increasing northwest winds starting overnight and continuing
through Saturday. Northwest wind gusts to at least 25 knots are expected on
Saturday with seas building to around 5 feet well offshore. Small Craft Advisory conds
will likely continue into Sat night.
Saturday night: Small Craft Advisory conditions continue with northwesterly flow. Seas
around five feet with gusts around and just over 25 knots.
Sunday and Sunday night: sub Small Craft Advisory winds and seas Sunday which
increase Sunday night to Small Craft Advisory criteria by Monday morning with
Monday and Monday night: Small Craft Advisory seas and wind gusts shifting from west
to northwest and decreasing below Small Craft Advisory criteria by Monday night.
Tuesday through wednesday: sub Small Craft Advisory wind gusts and seas.
Marine...Small Craft Advisory until 6 am EDT Sunday for anz450>455.
Small Craft Advisory from midnight tonight to 6 am EDT Sunday