Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
348 am EST Monday Dec 22 2014
high pressure centered over eastern Canada early this morning
will continue to drift eastward and it will lose its influence
over our region gradually. Weak low pressure is forecast to
develop off the North Carolina coast today. The low is expected to
move northward and it should dissipate off the New Jersey coast on
Tuesday. Another area of low pressure is anticipated to develop
over the northwestern Gulf of Mexico on Tuesday and it is forecast
to strengthen as it lifts northward and across the eastern Great
Lakes on Wednesday night. The low is expected to pull a warm front
through our region on Wednesday, followed by a cold front early on
Thursday. High pressure is forecast to build into our area from
the southwest for Thursday and Friday. Another cold front from the
west is expected to arrive over the weekend.
Near term /until 6 PM this evening/...
high pressure remains across eastern Canada and extends southward
across the East Coast this morning, although it will begin to
retreat through the day and lose it's influence over the area.
This has allowed the stratocu cloud deck to remain across the area
and build southward. Where this cloud deck is temperatures have
remained warmest, and where skies were clear or only middle/high
level clouds temperatures have cooled off. As we go through the
morning and through midday, we expect the low cloud deck to begin
pulling northward as the high retreats and a short wave/vorticity maximum
lifts across the area. However, these clouds will be replaced by
additional clouds advecting into the area from the south ahead of
an approaching coastal low to our south. Low-middle level moisture
will increase ahead of the coastal low, and as several pieces of
vorticity move across the area in the southwest flow aloft, rain
chances will increase through the afternoon. The best
lift/moisture should begin moving into our southern areas during
the afternoon, although there could be some showers across our
southern areas as soon as late morning.
Where the precipitation falls during the day, it should be all
liquid rain as temperatures are expected to warm above freezing
where the precipitation chances are most likely. However, there is
still a chance that some snow and/or sleet may mix with any rain
at the onset of the precipitation, especially for areas north and
west of the Delaware valley.
Short term /6 PM this evening through 6 am Tuesday/...
the coastal low continues to lift northward this evening and
overnight toward our area. This will continue to allow low-middle
level moisture to spread across our area. Additional pieces of
vorticity will continue to move across the area within the
southwest flow aloft, leading to enhanced low-middle level lift. The
best lift/moisture will move from south to north overnight and
will likely affect all areas at some point during the evening and
overnight. Most areas will warm above freezing before the main
precipitation moves into those area. However, the northern three
counties (carbon/Monroe, Pennsylvania and Sussex, new jersey) will
likely take longer to scour out the cold air. Therefore we expect
a period of freezing rain to occur across these areas later this
evening and overnight. There could be some sleet and/or snow mix
in at the onset of the precipitation, but the main threat is
expected to be freezing rain. Therefore we have issued a Freezing
Rain Advisory for these areas for this evening and into the
overnight hours. All precipitation is expected to change over to
all rain by daybreak Tuesday, so the advisory will end at 4 am.
Long term /Tuesday through Sunday/...
the middle level pattern is expected to feature a low over Iowa with
a trough extending down to the Southern Plains on Tuesday morning.
Meanwhile, a ridge will be located over the western North
Atlantic. Our region is forecast to be under an increasingly moist
and relatively mild southwesterly flow for Tuesday and Wednesday.
The initial middle level low is anticipated to lift over central
Ontario on Tuesday night with another low developing over eastern
Oklahoma and vicinity at that time. The second middle level low
should reach southeastern Ontario late on Wednesday night and
Quebec on Thursday, when it should pull its trough axis over our
region. Our weather is expected to be rather unsettled through
that time, with periods of rain from Tuesday into Wednesday night,
tapering to rain showers on Thursday morning before ending.
Forecast temperature profiles for that period suggest all liquid
A light surface flow from the east to south quadrant is forecast
for Tuesday and Tuesday night. The wind is expected to settle into
the south on Wednesday as a warm front lifts through our region.
Temperatures are anticipated to become quite mild on Wednesday
with maximum readings in the 50s and 60s.
As our middle week weather system evolves, it will have ample
opportunity to tap into moisture from the Gulf of Mexico which it
will draw in our direction. A low level jet around 45 to 55 knots
is expected to develop over the coastal plain. The strongest of
the winds should have a difficult time mixing to the surface.
However, some gusts around 30 or 35 miles per hour seem possible. The system
is anticipated to pull a cold front through our region early on
Christmas morning signaling the beginning of the end of the rain
event as well as a return to near seasonable temperatures for the
balance of the week and into the weekend.
The models have been trending toward lower rainfall amounts for
the middle week event than they had been showing over previous days.
The general consensus suggests rainfall totals mainly in the 0.75
to 1.25 inch range for our region. We should be able to handle
those amounts based on antecedent conditions with not much more
than some localized flooding in areas of poor drainage.
The model guidance continues to differ on the handling of the middle
level short wave and the accompanying cold front for the coming
weekend. We will keep the mention of a slight chance of snow
showers and rain showers for the time being with the hope that the
models will come into better agreement during their subsequent
Aviation /09z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
MVFR ceilings remain across the northern half of the area as the
strato cumulus cloud deck remains across the area. This deck may
sag down across phl and ridge this morning. We expect this cloud
deck to retreat northward during the day, with a brief period of
VFR conditions possible. However, this will be temporary as
additional MVFR ceilings should return to the taf sites by the late
afternoon/evening hours as rainfall moves into the area. As we
move into the evening and overnight hours, we expect ceilings to lower
to IFR with light rain or drizzle continuing into the overnight
Winds are mostly light and variable/calm this morning, although
any wind direction is from the northwest-north. Winds will
increase to around 5 knots out of the northeast-east during the
day and continue into this evening and overnight.
Tuesday...conditions possibly lowering into the MVFR category
with a chance of light rain.
Tuesday night...MVFR and IFR conditions anticipated with rain
Wednesday and Wednesday night...MVFR and IFR conditions with rain
likely. The rain may be heavy at times.
Thursday...conditions improving to VFR with a gusty west wind.
Thursday night and Friday...mainly VFR.
conditions are expected to remain below Small Craft Advisory
levels today as high pressure to our north begins to retreat. As a
coastal low approaches the area this evening and overnight, winds
may begin to increase and could gust to around 20 knots. Seas
around 1-2 feet this morning will increase later today and
especially overnight as the coastal low approaches and seas may
begin to approach 4 feet.
Tuesday and Tuesday night...wave heights on our ocean waters may
build to 5 feet in a developing east to south flow.
Wednesday...southerly wind gusts in excess of 25 knots are
expected. Wave heights on our ocean waters may build to 6 to 9
Wednesday night...a south wind becoming west. Wind gusts in
excess of 25 knots are expected. Wave heights on our ocean waters
may be 6 to 9 feet.
Thursday...westerly wind gusts in excess of 25 knots are
expected. Localized gale force gusts are possible. Wave heights on
our ocean waters may be to 5 to 7 feet.
Thursday night...wind gusts and wave heights are forecast to fall
gradually below the Small Craft Advisory criteria.
Friday...no marine headlines are anticipated.
PA...Freezing Rain Advisory from 6 PM this evening to 4 am EST
Tuesday for paz054-055.
New Jersey...Freezing Rain Advisory from 6 PM this evening to 4 am EST
Tuesday for njz001.