Area forecast discussion
National Weather Service Mount Holly New Jersey
1149 am EDT Wednesday may 22 2013
Synopsis...
high pressure will remain anchored off the southeastern United
States coast through Thursday. Low pressure will approach from the
west, tracking to our north, and will then drag a cold front through
our region late Thursday into Friday. High pressure will then build
into the region for the Holiday weekend and last into early next
week.
&&
Near term /until 6 PM this evening/...
some convection rapidly developed late this morning across
northeastern Pennsylvania. These seem to have initiated near the
warm front with perhaps some help from differential heating and
lift up and over the front. There is plenty of instability with
even some increase in shear as one crosses the warm front,
therefore perhaps some hail with them. The convective coverage
however looks low with more organization to our north. Some
adjustments in probability of precipitation were made, but overall no major changes.
Otherwise, a rather soupy airmass across the region. The 12z
Sterling, Virginia radiosonde observation showed a pronounced low-level inversion
which has helped to maintain the wealth of stratus. The stratus is
now lifting some and eroding from the west, and this should
continue toward the east through the afternoon. How quickly this
occurs will have an affect on our high temperatures, however the
12z radiosonde observation shows once we break out into the sunshine temperatures
will be rather toasty.
We then look to the convective potential especially this
afternoon. The model guidance overall seems to be keying in on our
northwest zones where these areas will be closer to the better
large scale forcing as a frontal boundary and surface low are
draped across the Great Lakes. A front sitting very close to our
northeast zones should lift northward through the afternoon. We are
not anticipating this to back southwestward. There is plenty of
instability to be in place today owing to the higher dew points.
However, the lack of focused forcing may keep the convective
coverage on the low side. After the initial convection near midday in
northeast Pennsylvania, the entity to watch is an incoming short
wave later this afternoon that could team up with a Lee side
trough, initiating convection to our west. The eastern and
southern zones may not have any convection through the day, unless
something is able to form with some low-level convergence near the
southeastern New Jersey coast.
The stronger westerly flow aloft is farther north and mostly from
the Great Lakes region and across New York state. Some of the high
resolution models indicate convection developing this afternoon
across central Pennsylvania then tracking northeastward. This
initiation could be enhanced some by the terrain and a Lee side
trough as a short wave approaches, and if this convection arrives it
could contain locally strong winds and hail mostly across our far
northwestern zones later this afternoon. The precipitable water values are a
little over an inch today, therefore any storm that is able to
develop will be capable of producing locally heavy rain. Our
confidence in the convective coverage and strength is on the
lower side, however a mention is in the hazardous weather outlook
for mainly the northwestern zones.
The hourly grids were adjusted with some of the lamp/lav guidance to
assist. Little in the way of changes were made at this time to the high
temperatures away from the immediate coast.
&&
Short term /6 PM this evening through 6 am Thursday/...
a couple of rounds of showers/thunderstorms look possible overnight
Wednesday into Thursday morning. The first round looks to be early
in the evening associated with short wave/vorticity maximum moving through
late in the day and into early evening. We may then get a break for
a portion of the overnight, followed by another possible chance of
precipitation closer to sunrise Thursday. This would be associated
with a second short wave/vorticity maximum moving through.
With dewpoints remaining elevated across the area, overnight lows
will remain high. Generally temperatures are expected to only drop
into the middle-upper 60s.
&&
Long term /Thursday through Tuesday/...
with high pressure sitting to our southeast, we will continue to
see a south to southwesterly flow which will continue to advect
warm and moist air to our area. This will keep our temperatures at
or above normal for Thursday.
A low pressure system will approach from the west on Thursday, with
the center passing off just to our north. The attached cold front is
forecast to move through our area Thursday into Friday, most likely
later in the day Thursday into early Friday. The latest model
guidance continues to slow down the frontal passage and also starts
to develop a middle level feature along the middle-Atlantic coast. With
precipitable water values around 1.5 inches, any slowing of the
frontal passage may end up contributing to flooding as heavy rain
will be possible. This will need to be monitored, especially for the
areas with lower ffg values, mainly across central and northern New
Jersey.
Showers and thunderstorms may develop ahead of the front on Thursday
as surface heating and some weak instability will be in place. While
the severe threat does not look to be all that great at this time,
there is a chance that some storms may become strong and Storm Prediction Center has
highlighted our area in their day 2 outlook with a see text.
The front pushes through and offshore on Friday morning. Some
lingering showers may continue through Friday morning but overall
the areas should dry out by Friday afternoon. Cooler air will be
pushed into the region on a northwest flow and temperatures will
fall below normal for Friday. Highs will generally be in the upper
60s to lower 70s.
Canadian high pressure will build into the region behind the front,
bringing in some cooler and drier air for the Holiday weekend and
into early next week. The models hint at a shortwave moving through
the middle levels on Saturday and another one on Sunday. The airmass
looks to be too dry for anything to make it to the surface and we
have kept the Holiday weekend and early next week dry. Temperatures
will remain below normal through the early part of the week with
highs in the upper 60s to lower 70s across the region. Temperatures
will gradually start to warm toward the midweek time frame.
&&
Aviation /16z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Rest of today...ceilings continue to improve to MVFR, then to VFR
during the afternoon. The reduced local visibilities due to
haze/fog are expected to improve by middle afternoon. There is the
chance of a few showers/thunderstorms this afternoon, with the
greatest potential to be near kabe and krdg. A mention was not
included due to a low potential at this time. Light southwest
winds increasing to 10-15 knots, with perhaps a little gustiness
at times during the afternoon if enough mixing can occur.
Tonight...VFR, then IFR/MVFR ceilings and visibilities are forecast
to develop late. There could be a shower or thunderstorm especially
in the evening north and west of kphl, then another chance toward
daybreak. Southwest winds generally under 10 knots.
Outlook...
Thursday and Thursday night...mainly VFR. MVFR, possibly IFR,
conditions possible in any showers and thunderstorms or heavy rain.
Friday...mainly VFR with a chance of showers mainly in the morning.
Northwest winds 10 to 15 knots.
Saturday and Sunday...VFR. Northwest winds 15 to 20 knots.
&&
Marine...
mainly a south-southwest flow will remain across the waters today
and tonight. The gradient may tighten some late today into
tonight, and winds may gust close to 25 knots. Wavewatch has been
running a little high, but even if we knock a foot off of the
seas, 5 foot seas could start late today into this evening.
Therefore a Small Craft Advisory has been issued starting late
this afternoon and continuing into at least tonight.
Outlook...
high pressure anchored off the southeastern United States coast will
continue to bring a to southwest flow through Thursday on the area
waters. Small craft conditions are expected to continue on Thursday.
The cold front will cross the area waters late Thursday into Friday.
The pressure gradient will tighten as the front departs to the east
and high pressure starts to build down from Canada. This may cause
winds to gust up around 25 knots, especially on Saturday. Seas will
likely remain at or above 5 feet into the early part of the weekend.
Both winds and seas are expected to subside by late Saturday and
then remain below advisory criteria through the rest of the Holiday
weekend.
&&
Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...Small Craft Advisory from 5 PM this afternoon to 6 PM EDT
Thursday for anz450>455.
&&
$$
Synopsis...gorse/meola
near term...gorse
short term...Robertson
long term...meola
aviation...gorse/meola
marine...Robertson/meola
