Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
938 am EST Monday Dec 22 2014
weak low pressure is forecast to develop off the North Carolina
coast today. The low is expected to move northward and then
dissipate off the New Jersey coast on Tuesday. Another area of low
pressure is anticipated to develop over the northwestern Gulf of
Mexico Tuesday and strengthen as it lifts northward and across the
eastern Great Lakes Wednesday night. The low is expected to pull a
warm front through our region Wednesday, followed by a cold front
early Thursday. High pressure builds into our area for Thursday and
Friday. Another cold front is then expected to arrive over the
Near term /until 6 PM this evening/...
an upper-level trough continues to amplify across the central part
of the nation. Meanwhile, a ridge is shifting off the East Coast.
High pressure at the surface however remains wedged down into the
middle Atlantic from New England, although this is forecast to
gradually weaken and shift eastward through today. Low pressure is
developing off the Carolina coast.
The relentless inversion is present today with cloudiness across a
good portion of the County Warning Area. Interestingly enough just like yesterday,
an area of clearing developed west to east across the central
portion of the area. The moisture will be on the increase and at
first this is in the lower levels as sampled by nearby 12z radiosonde observations.
The 12z Upton radiosonde observation shows more of a southeasterly low-level flow,
while the Sterling one indicates the winds veering more south or
southwest. Therefore a portion of our area is left in between and
this may be helping with just enough low-level subsidence and drying
to create the less cloud-filled area. The depth of the moisture will
increase some through the day from south to north, and a
southeasterly flow below the inversion has allowed just enough lift
to produce some snow grains across portions of northwestern New
Jersey this morning. This is generally occurring below the radar
beams and is rather light.
Otherwise, some rain will overspread the southern areas through the
day and lift northward with time. The temperatures at the surface
are cold this morning especially where there has been less cloud
cover, however these are increasing now. The dew points while on the
low side are also showing signs of increasing some especially across
the south. Therefore, freezing precipitation is not anticipated
across the south. There is a chance that some light snow and/or
sleet may mix with any rain at the onset of the precipitation as the
soundings show a dry layer for a time with the potential for some
Some tweaks were made to the hourly grids based on the latest
observations, and also some adjustments were made to the probability of precipitation
showing a little slower increase across the south. The sky cover was
adjusted based on satellite data and the less cloud-filled area was
attempted to be captured better.
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 /15z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Today...MVFR ceilings north and west of kphl may lift north some
/scatter out/, however any VFR should lower especially this
afternoon. Some rain is anticipated later today from south to north,
with areas mainly from kphl on south and east having the best
chance. Some MVFR visibilities should occur at times, mainly during
the rain. Light/variable to calm winds becoming northeast or
east-northeast around 5 knots.
Tonight...MVFR ceilings are anticipated to lower to IFR/LIFR with
light rain or drizzle. Northeast winds generally around 5 knots.
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.