Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
936 PM EDT Friday Mar 27 2015
low pressure and a associated cold front will continue moving
offshore overnight. 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/...
considerable clouds overnight with possibly some flurries drifting
southeast of the PA Appalachians after midnight. Noticed the 18z
runs of the GFS/NAM and 12z ec, sort of had a spike in deeper relative humidity
near 12z Saturday. The NAM/rap/hrrr spot some flurries southeastward to
krdg overnight. Not sure how extensive this might become.
Pressure gradient is weak over our area as of 01z/28, between the
developing offshore low east of Virginia and what I think is a
pretty cold air mass beneath the southeastward moving and sharpening trough
aloft over the Great Lakes/S Ontario and western nys, poised to
make its move down over our area Saturday when the pressure
gradient increases. For now, we increase the gusts a bit toward
morning, especially the Poconos in developing stronger cold air advection.
Short term /6 am Saturday morning through 6 PM Saturday/...
high pressure will continue to build in from the west on Saturday...
but the cold 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 and eastward. Some of the greatest instability appears to
be moving from central PA midday to the Delaware-Maryland-Virginia Saturday evening.
Its matched with a surface trough. 700mb temperatures are modeled to near -24c
along the Mason Dixon line north of kbwi at 00z/29.
Gusty northwest winds will increase to 25-30 miles per hour during the afternoon adding
to an otherwise nippy day with daytime temperatures at least 10 degrees
below normal! Our currently forecast temperatures may be a degree or two on the
warm side, especially if its MO cloudy
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 /01z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy, and surrounding areas.
Rest of tonight...VFR ceilings at or above 4000 feet. North-northwest wind gusts at or below 15
knots may increase slightly after 09z. Confidence: above average.
Saturday: VFR ceilings at or above 4000 feet. Northwest wind gusts increase to 25-30
knots by or during the afternoon. Scattered showers of snow or rain/snow are
possible on Saturday which could temporarily lower ceilings/visibilities to
MVFR...but not for long. Confidence on the overall scenario is above
average though confidence on on MVFR ceilings/visibilities in showers is below
Saturday night and sunday: VFR. Northwest wind gusts 20-25 knots Saturday
night and early Sunday then diminishing Sunday afternoon.
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.
northwest wind gusts tonight which are under 15 knots at 9 PM EDT will
increase toward dawn. Have slightly delayed the start of the Small Craft Advisory
on Delaware Bay and it may not really start there until about 6 am.
Meanwhile seas off the coasts are generally aob4ft except near 5
feet at 44009.
Saturday...a widespread Small Craft Advisory develops, especially during the
afternoon with northwest wind gusts increasing to near 30 knots by days
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.
March monthly average temperatures departures should be close to the values
seen on the cf6's through the 26th. For phl thats about 4 degrees
below normal. Not a top 20 coldest month of March.
Marine...Small Craft Advisory until 6 am EDT Sunday for anz450>455.
Small Craft Advisory from 2 am Saturday to 6 am EDT Sunday for
near term...drag 935
short term...amc/drag 935