Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
609 PM EDT Monday Sep 22 2014
high pressure will build over the middle-Atlantic region tonight and
Tuesday, then intensify over New England on Wednesday. By Thursday,
low pressure will develop to our south bringing a chance for rain
to areas mainly south of Philadelphia. Weaker but persistent high
pressure should maintain mostly fair weather for Friday through
Near term /until 6 am Tuesday morning/...
high pressure over the Ohio Valley late this afternoon will build
eastward overnight. The daytime clouds will decrease across the
area...leaving mostly clear skies after sunset. Winds will decrease
as well...and should settle to around 5 kts overnight. Lows will
be cool...with some low 40s north/west and middle/upper 40s in most
other areas. Looks too dry for any widespread fog...a bit of
patchy fog possible however.
Highs today (calendar day) were generally around 3 degrees below
normal ranging from normal at kacy to 6 below norml at kmpo.
Short term /6 am Tuesday morning through 6 PM Tuesday/...
high pressure will settle over the area Tuesday. Another fair
weather day is expected with pleasant temperatures and a
comfortable air mass. Highs will be similar to today...with
readings in the 60s north/west...ranging to the low 70s over New Jersey
and the Delaware-Maryland-Virginia. Winds will be gentle...mostly nearly at 5 to 10
miles per hour.
Long term /Tuesday night through Monday/...
the extended period starts out fairly quiet on Tuesday night and
Wednesday...but then things get somewhat more interesting starting
Wednesday night and continuing through Thursday. An upper low is
forecast to develop over the Carolinas tonight from the southern end of
the eastern U.S. Trough now moving through. This upper low will be cut
off from the main band of westerlies across northern US and southern can and
its predictability seems to be below average. Although not a
strong feature...the models disagree on its future behavior and
also associated surface features.
High pressure now building from the Midwest into the middle-Atlantic
region is forecast to be reinforced over New England by Wednesday...
and then low pressure associated with the upper system begins to develop
along the southeastern Seaboard...somewhat east or west depending on the
model. Either way the result is increasing pressure gradient and on-
shore winds over the middle Atlantic region. There may not be much
forcing for upward vertical velocity...or the maximum forcing stays offshore...but clouds
and moisture are expected to spread northward through Delaware-Maryland-Virginia into New Jersey
starting Wednesday or Wednesday night and continuing through Thursday.
Have increased probability of precipitation somewhat for Thursday although still in the chance
ranged due to uncertainty. Most likely area for precipitation is
generally S/east of phl. Precipitation amounts should remain on the light
side. The main threats with this system would likely be winds and
waves along the New Jersey/Delaware coast and also over the marine areas.
Aviation /21z Monday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...remaining patches of SC near 5000 feet will clear this
evening just leaving scattered cirrus at or above 25000 feet. Northwest wind g 15-18 knots
now will become light northerly during the night.
Wednesday...VFR scattered clouds at or above 5000 feet which means some patchy
cirrus but also some afternoon scattered near 5000 feet. Light north wind
becoming S-southeast over kphl area south and eastward during the
Tuesday night and Wednesday...VFR conditions expected.
Thursday...cloudy skies but still mostly VFR conditions expected.
There is some chance for MVFR conds to develop...especially for
Acy/miv and areas S/east of phl. Somewhat gusty east to NE winds are also
possible from vicinity phl and southeastward.
Friday and Saturday...VFR conditions expected with generally light
Small Craft Advisory cancelled. Winds gusts and seas will probably be below the
Small Craft Advisory criteria through Tuesday. Fair weather is expected through
Tuesday. Winds will turn northerly by Tuesday morning.
Wednesday and Thursday...winds and seas will likely increase to
Small Craft Advisory criteria on Wednesday and continue through Thursday and possibly into
Friday. There is above average uncertainty about this situation
but winds and seas are likely to be higher for waters east of
Delaware vs eastern New Jersey. Note the wavewatch model is forecasting seas 8 to 10
feet on Thursday...but it is driven by the GFS which has stronger
surface winds compared to the NAM and European model (ecmwf).
Saturday...wind/waves should remain below Small Craft Advisory criteria.
have just cancelled the high risk for the formation of dangerous
rip currents and all products are updated. Swells have decreased
1.5 feet since midday and thereby the risk as well.
However...looking ahead potential fairly big surf looms for Thursday
(bigger than todays) as a near gale onshore flow should develop
and seas/surf build. A moderate or high risk for the formation of
dangerous rip currents will likely redevelop.
near term...drag/O'Hara 609