Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1212 PM EST Monday Mar 2 2015
high pressure will build over our area tonight, then shift off the
middle Atlantic coast on Tuesday. A warm front is expected to lift
through our area on Tuesday evening. A cold front is anticipated to
arrive Wednesday afternoon, then the front should settle slowly to
the southeast Wednesday night and Thursday as low pressure rides
along it. Another Arctic high is forecast to build across our region
for Friday into Saturday. A warm front may begin to approach from
the southwest on Sunday.
Near term /until 6 PM this evening/...
high pressure moving into the Ohio Valley at midday will continue to
slide eastward through the afternoon. The combination of increasing
subsidence and drier air advecting in continues to erode the clouds.
This is being enhanced some by a downsloping flow. Prior to this
occurring though, enough instability and lift aided in the
development of several bands of snow showers across the north. Some
of this was briefly heavy across the Poconos. This activity
continues to diminish as is shifts off the northeastern New Jersey
coast. The visible satellite imagery shows the snow/ice cover very
well, but also shows less and less clouds. Therefore, lots of
sunshine looks to occur through the afternoon.
There will continue to be plenty of mixing as the boundary layer has
warmed and cold air advection occurs aloft. This will promote wind gusts up to 35
miles per hour across the area, although this should start to diminish late in
the afternoon. The downsloping flow and increasing sunshine has
helped boost the temperatures especially from the Interstate 95
corridor on south and eastward, and therefore the high temperatures
were increased some.
The hourly grids were adjusted based on the latest observations and
then blended in the lamp/lav guidance.
Short term /6 PM this evening through 6 am Tuesday/...
high pressure begins to move into the area this evening, before
centering itself across the area overnight. Skies will clear out
this evening, although some high level cloud cover may return
overnight. Wind gusts will have dropped off by the evening,
although a steady breeze will remain through the evening, before
becoming light and variable overnight. With mostly clear skies and
light winds, temperatures should be able to drop well below normal
Long term /Tuesday through Sunday/...
there is not much change regarding the forecast for Tuesday into
Precipitation is expected to overspread our region quickly from
the west on Tuesday afternoon. The forecast temperature profiles
suggest that the precipitation will begin as snow in most
locations with perhaps sleet at the start in our far southern
Strong warm advection is anticipated aloft from Tuesday afternoon
into Tuesday evening. Warming at the surface will lag a bit. There
should be a gradual transition from a wintry mix to rain from
south to north. However, trapped cold air in our far northern
counties could result in several hours of freezing rain there on
Tuesday night into early Wednesday morning. Our latest projections
for Tuesday into Tuesday night bring 1 to 3 inches of snow across
our northern counties and less than an inch to our central and
southern counties where accumulation may be cut down by the
presence of sleet. Freezing rain should cause a problem only
across our northern counties where up to a tenth of an inch of ice
may accumulate on top of the new snowfall.
It continues to appear as though the precipitation will change to
all rain for Wednesday. A bit of drying may begin to work its way
down from the northwest on Wednesday afternoon. It seems possible
that some locations, especially in the central and southern parts
of our forecast area may pick up a half inch to an inch of
rainfall during the period. The rain in combination with snowmelt
and the frozen ground, along with ice movement in area waterways
may result in a bit of minor flooding.
The models are coming together on the idea of a wave of low
pressure riding along the slow moving cold front. It should bring
US another round of precipitation for Wednesday night into
Thursday. As cold air filters down into our region from the north
and northwest, the precipitation type will likely transition to
snow. There is enough spread in the guidance solutions to make the
details a bit uncertain at this point. However, it is looking
increasingly possible that we will see accumulating snow in much
of our forecast area at that time.
High pressure from the west is anticipated to bring dry weather
and below normal temperatures for Thursday night into Saturday
The 0000 UTC GFS and the 0000 UTC European model (ecmwf) are both suggesting the
potential for precipitation to be nearing our region from the
southwest on Sunday due to a weak area of low pressure along with
a warm front.
Aviation /17z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
This afternoon...VFR. Northwest winds around 15 knots with gusts
up to 30 knots.
Tonight...VFR. Northwest winds quickly diminishing to 10 knots or
less in the evening, then locally becoming light and variable
Tuesday...VFR for much of the day with increasing clouds. The
conditions should lower to MVFR/IFR late in the afternoon from west
to east as snow and sleet overspreads the region. Light and variable
winds, becoming northeast then southeast at 5-8 knots. A southerly
low-level jet /2000 feet/ near 40 knots should arrive late in the
afternoon, therefore included low-level wind shear in the 30-hour
Tuesday night...MVFR and IFR conditions with a wintry mix of
precipitation changing to rain from south to north. The rain may
be moderate to heavy at times. Low level wind shear is possible
due to a southwesterly low level jet that is forecast to develop
Wednesday...MVFR and IFR conditions in rain. The rain may be
moderate to heavy at times, especially south of kphl.
Wednesday night...MVFR and IFR conditions in rain, mixing with
then changing to snow from north to south.
Thursday...MVFR and IFR conditions in morning snow. Conditions
improving gradually to VFR with a lessing chance of snow in the
Thursday night and Friday...mainly VFR.
Small Craft Advisory remains in effect on the waters into tonight as
winds will increase. An occasional gusty around 34/35 knots is
possible around midday, but we are not confident on gale force gusts
being frequent enough to need a warning at this time. As high
pressure builds into the area overnight, winds will diminish below
Tuesday...no marine headlines are anticipated.
Tuesday night and Wednesday...a Small Craft Advisory may be
necessary due to a gusty south to southwest wind.
Wednesday night through Thursday night...a Small Craft Advisory
may be needed to due to gusty northwest wind.
Friday...no marine headlines are anticipated.
the next round of precipitation is forecast to move into our area
on Tuesday afternoon and it will continue into Wednesday and
This midweek event appears to start as a wintry mix before
changing over to rain as temperatures rise well above freezing on
Wednesday. The quantitative precipitation forecast amounts for Tuesday into Wednesday favor the
0.25 to 0.75 inch range.
The combination of the brief warm-up on Wednesday, locally
moderate to heavy rainfall, melting snow, a frozen ground, and
above normal ice in creeks, streams, and rivers could lead to
increased runoff and possible flooding. Where the depth of the
snowpack is greatest (in NE PA and north nj), rapid snowmelt is not
expected since temperatures will not rise as sharply as in areas to the
Increased flow 0n area creeks, streams, and rivers could also
start to move ice, and in a worst case scenario, create
restrictions or jams.
Continue to monitor the forecast. Keep in mind that snowmelt and
warmth by themselves typically do not cause flooding. The amount
of rain that we receive will be the determining factor.
The rain is forecast to change back to snow on Wednesday night.
Marine...Small Craft Advisory until 2 am EST Tuesday for anz430-431-