Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
539 am EDT Wednesday may 6 2015
a cold front will slowly move through our region today as high
pressure settles into the area from the north and east on Thursday
through the weekend. Another slow moving cold front will approach
our area early next week...and move through the region by middle week.
Near term /until 6 PM this evening/...
fog has developed along and south of the front. This should be
short lived as after sunrise, wind speeds should increase.
Therefore, updated the weather grids through middle morning to add
mention of patchy fog along and south of a reading to philly to
Atlantic City line.
Previous near term discussion...front is already becoming
diffuse, and with frontolysis expected through the day, that trend
should only continue. That combined with synoptic scale subsidence
associated with the middle and upper level ridge building closer
means precipitation chances through the day are modest at best. At this
point, think the best chances for rain will be in the northern
portions of the County Warning Area this morning as the band of very light showers
over north PA now clips our region, and then another chance exists
from middle day through the afternoon hours along the front (which
could be over Delaware-Maryland-Virginia and far S New Jersey by that time) thanks to some
Short term /6 PM this evening through 6 am Thursday/...
ridge continues to build closer, and with the loss of diurnal
instability, any lingering showers should quickly dissipate.
Previous model runs had shown a weak short wave moving over the
region tonight. However, latest model runs show it much less defined
and really not much of a factor for our region.
Long term /Thursday through Tuesday/...
middle-level pattern features a rexy looking block through the first
half of the longterm period, with split flow being the main player.
Closed low over the southeast coast will begin to lift/open up over
the weekend and the split flow breaks down by early next week.
Confluent flow with multiple waves of energy will affect the region
for the remainder of the longterm...Monday Onward.
Thursday and Friday...have gone dry both days with the offshore
ridge's axis across the region and the lack of a defined lifting
mechanism. Light south-southeast flow will keep low-level moisture
streaming into the region, though not a significant increase but
dewpoints climb into the middle to upper-50s. Temperatures will remain
above normal with Friday being the warmer of the two days...low-80s.
Saturday - Sunday...even with a decent surface and middle-level ridging
around the region, the slow northward advancement of the coastal/sub-
tropical low off the Carolina coast gives some pause for concern
with possible showers spreading northward into our southern zones
both days. Have introduced some slight to low-end chance probability of precipitation this
weekend. Light upslope flow across our western zones may allow for
an enhancement/convergence along the ridges for better chances of
showers/convection on Saturday. The flow veers towards the southwest
on Sunday with another increase in moisture and temperatures. Once
again have pegged our western zones, with the differential heating
and moisture pooling along the ridges for chances of convection.
Have also introduced some patchy fog/stratus along the eastern zones
each morning with the light onshore flow and damp marine layer.
Temperatures each day expected to be in the low-80s.
Monday and Tuesday...as a cool front approaches...there will be
greater moisture, lift, and instability available. Given a slow
frontal passage with ample Gulf/subtropical moisture, and favorable
jet dynamics...heavy rainfall is possible during this time frame.
Aviation /10z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe,
krdg, kilg, kmiv, kacy and surrounding areas.
Generally VFR conditions are expected through the taf period with
the following two exceptions. First, localized fog is possible
through 15z along and south of a krdg to kphl to kacy line.
Reduced visibilities to MVFR and briefly IFR are possible.
Second, there remains a small chance for showers at all the
terminals through the day. If any showers move over a terminal,
brief MVFR conditions are possible.
Thursday - Friday...VFR. Light south-southeast winds expected.
Saturday - Sunday...mostly VFR. Some early morning fog/stratus
possible around our eastern most terminals. Southeast flow giving
way to southwest winds on Sunday. Possible afternoon showers/thunder
each afternoon...better chances across the western terminals.
winds and seas should remain below Small Craft Advisory criteria today and tonight.
Winds should gradually shift to be out of the northeast through the
day, but wind gusts will remain less than 20 knots.
Thursday - Sunday...generally a sub-Small Craft Advisory forecast with seas
increasing a bit under a persistent southeasterly flow through