Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service Mount Holly New Jersey
345 am EDT Sat Aug 23 2014
high pressure will slowly build south out of Canada towards our
region through the weekend. The high will be entrenched over our
region through at least middle week before it weakens. A cold front
could push through the region late in the week.
Near term /until 6 PM this evening/...
there has been a persistent area of showers associated with a weak
vorticity impulse that have remained nearly stationary just to our
west through the overnight hours. Without much flow aloft, they have
not moved much. However, as the weak impulse continues to side
eastward though the early morning hours, these showers will begin
drifting eastward and should begin dissipating.
However, there will remain a chance for scattered showers through
the day as a stronger short wave/vorticity impulse moves across the
area. Vertical moisture is expected to dry later in the day as the
impulse approaches as high pressure continues to push farther south
into the area. However, there should be enough to interact with the
short wave to produce some shower activity. With precipitable water values near 1.5
inches, there remains the potential for some heavy rain with any
shower development. There is really no instability expected today,
so we do not have thunderstorms in the forecast, although it would
not be surprising to see an couple of isolated lightning strikes.
For highs, used a blend of mav/met MOS, mosguide, and mixed 925 mb
Short term /6 PM this evening through 6 PM Sunday/...
the short wave/vorticity maximum will be moving through our southern areas
this evening, while high pressure continues to build in from the
north. Meanwhile, precipitable water values will be dropping off quite sharply as
drier air moves in. There may be a few isolated showers early in the
evening, but whatever is out there should dissipate and/or move
southward through the evening, and the remainder of the night should
be rain free.
For overnight lows used a blend of mav/met MOS and mosguide.
Long term /Sunday night through Friday/...
not many changes through middle week from the previous forecast.
Still expecting an extended period of dry weather as the surface
high builds over our region, and in the upper levels, a short wave
ridge propagates southeast over our region Monday into Tuesday.
With the cooler air settling in on Sunday, should start with below
normal temperatures, but have a steady warming trend through middle
week, especially as low level southwesterly flow develops
Thursday through Saturday remains the period of most interest over
the next week, but also with the greatest uncertainty. There are
three features that will be watched over the next few days that
could have big impacts with our weather in the late week periods.
First...the topical system which could develop over the next few
days. While nearly all of the long range models have this system
staying well off shore, and thus not directly impacting US, it
could help to weaken the surface high over the middle Atlantic
earlier than previously forecast, resulting in an indirect impact.
Second, the surface cold front, which long range models either
keep pushing back the arrival in our region, or keep it north of
US all together. At this point, it still seems likely that the
front will push through our region, but probably not until Friday
as the third feature, a broad upper level trough, slides east over
the Great Lakes region. All that said, our next good chance for
rain will come when the front arrives, along with temperatures
well below normal. However, given the uncertainty in the timing
and track of the front, have kept probability of precipitation through the late week
period in the 20s and 30s.
Aviation /07z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Taf sites remain VFR at the start of the period, however, we still
expect ceilings to drop to MVFR by daybreak as low level moisture
increases. It is possible for IFR ceilings to develop, mainly for
Abe/rdg/ttn, although the other sites may drop into the low end of
MVFR. Once these lower ceilings develop, we expect them to remain
through the middle-late morning hours, before an improvement to VFR for
the afternoon. Additional showers are possible later in the day, but
confidence in occurrence and timing is not high, so we left them out
of the afternoon forecast; except Abe/ridge this morning where
showers are more imminent. If any showers do occur, they could briefly
VFR conditions are expected for the overnight hours as drier air
filters in as high pressure builds in from the north.
Winds will be mostly out of the east to northeast 5-10 knots or less
through the period.
Sunday through Wednesday...VFR conditions expected.
Small Craft Advisory remains in effect for the ocean, and has been
expanded to include the entire New Jersey Atlantic coast. Seas are
expected to build later today and continue into tonight as the east
to northeasterly flow increases. Winds may gust around 20-25 knots
as well later today into tonight.
Sunday...seas and winds are expected to subside below Small Craft
Advisory early in the day.
Monday through Wednesday...winds and seas will likely stay below
Small Craft Advisory conditions.
a moderate risk of rip currents remains today into tonight as seas
are expected to build in the persistent easterly flow. The moderate
risk may continue into Sunday.
Marine...Small Craft Advisory from noon today to 8 am EDT Sunday for