Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
402 am EDT Friday Jul 25 2014
high pressure will build across the Ohio Valley and middle-Atlantic
today and move offshore tonight. On the backside of the high pressure
system a warm front and associated low pressure system will move across
the Midwest on Saturday and into our region by Saturday night and
push north of the region on Sunday. A cold frontal boundary then
will sweep from west to east across the region on Monday. A high
pressure system will build in behind the cold front for the middle
half of next week.
Near term /until 6 PM this evening/...
high pressure will build into the region today and a dry and pleasant
day is in store, with dew points in the 40s and 50s, which is
spectacular for late July! Temperatures are generally expected in the middle 80s.
Short term /6 PM this evening through 6 am Saturday/...
the high will move to the east tonight and the wind will become more
S to southwesterly but still be light and dew points will creep up a bit, but
again dry weather is expected.
Long term /Saturday through Thursday/...
Saturday and Saturday night: a warm front approaches the region
from the Midwest and Ohio Valley then pushes northeast through the
region Saturday night. The result will be increase in southerly
moisture and moisture transport into the region. Middle-level and
surface temperatures look to respond in kind with the southerly
and southwest advection, 925 mb temperatures near 20c should yield
surface temperatures just under 90 for phl and in the 80's
elsewhere across the region. As mentioned in the previous forecast
the rapid rise of dewpoints appears suspect and is much slower
with the latest 00z mav and met guidance sets. The slower dewpoint
rise may limit the amount of destabilization that occurs during
the day as well. A few hundred j/kg of cin coupled with 700 mb temperatures
near 10c could allow for the formation of a weak cap across the
southern part of the region. The majority of the operational
models suggest the best chance of any shortwave/trigger for
convection to be across the northern half of the region Saturday
night, closer to the warm front. Will maintain chance probability of precipitation across
the north and slight across the south. Also of interest is the
potential for 30-50 kts of 0-6 km bulk shear as well. If storms
can form Saturday night there is a potential for organization and
a damaging wind threat if instability of the modeled 1000 j/kg or
so does materialize. Precipitable water values just under 2 inches suggest a heavy
rain threat with any storms as well. The current Storm Prediction Center outlook does
not feature a severe threat in this period likely due to the
limited coverage of the storms. As the main storm chance is late Saturday
modeled momentum Transfer suggests some gusts from 15-20 miles per hour are
possible in the afternoon on Saturday.
Sunday and Sunday night: continued west-southwest flow in the warm
sector. Good agreement among the GFS ensembles, 12z European model (ecmwf) ensemble
mean and the operational GFS and CMC runs that the highest chance
of storms will be Sunday night in association with the strongest vorticity
maximum and associated shortwave. On the other hand the new 00z European model (ecmwf)
run is slower and has the main show on Monday. Went high chance
probability of precipitation Sunday afternoon and low end likely probability of precipitation for Sunday night
more along the line of the CMC and GFS. For quantitative precipitation forecast stayed close to
the 21z sref. Similar to Saturday enough bulk shear may be present
to organize storms that do form. However the amount of
destabilization is in question with modeled cape values only
around 1000 j/kg and will be dependent on convection from the
night before, precipitable water values near 2 inches suggest a continued heavy
rain threat from storms. Temperatures may be rain cooled Sunday
but did not go in that direction at this time. Fair shot at 90 for phl
with slightly warmer modeled middle-level temperatures than Saturday.
The Storm Prediction Center features the region in a slight risk for severe
thunderstorms due to the potential for the storms to organize and
for wind/hail threats. The severe weather potential statement has been updated for this.
Monday and Monday night: the cold front moves through likely Monday
afternoon. However this should be to little to late in terms of
another round of showers and storms on the GFS and CMC. The new 00z
European model (ecmwf) is slower with the front leading to another round of showers
and thunder. For now continued with a more progressive idea
centering the chances in earlier periods but did raise probability of precipitation in this
period. Another gusty day as once modeled momentum Transfer shows
potential for some gusts of 15-20 miles per hour. Rain may keep temperatures
down but middle-level temperatures suggest another hot day.
Temperatures may try and spike ahead of the cold front as well. More
uncertainty with temperatures in this period as rain may keep
temperatures down but a temperature spike could occur ahead of the
Tuesday through thursday: another Canadian airmass comes down into the region
as the same general pattern from the wintertime continues with few
breaks. Cool northwesterly flow will be in place as most locations
struggle to 80 for highs on Tuesday and Wednesday. Even with this
abnormally cool airmass there is good agreement among the mex, wpc
and modeled two meter temperatures in this period. Went on the
cooler end of guidance close to wpc in most periods. Lapse rates may
steepen up Tuesday afternoon for the formation of some cumulus on
the backside of the trough across the north with the aid of
elevation. Otherwise each day looks mostly sunny. Dewpoint
depressions look to large for Wednesday and Thursday for much in the
way of afternoon cumulus.
Aviation /08z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
VFR conds expected through the taf pd, with high pressure in control. The
high will gradually move eastward through tonight and the wind will shift
from north or northwest Erly to west to SW by tonight. Wind speed should generally be
less than 10 knots. With the light wind, the guidance is hinting at a bit
of a seabreeze, mainly for kacy and possibly for kmiv during the late
Saturday and Saturday night: brief MVFR and IFR restrictions in scattered
thunderstorms. Highest chance for restrictions is on Saturday
afternoon and evening for rdg, Abe, ttn, and points north.
Sunday through Monday night: brief MVFR and IFR restrictions in
thunderstorms. Some southwest wind gusts around 15 knots possible
Monday afternoon outside of thunderstorms.
with high pressure over the region today and moving over the coastal waters
tonight, no marine headlines are anticipated through the near and
short term periods.
Saturday: seas and winds expected to stay under Small Craft Advisory criteria. A few
wind gusts around 20 knots possible Saturday afternoon.
Saturday night: seas approaching five feet at times. Winds below Small Craft Advisory
Sunday through tuesday: four feet seas decreasing late in the day.
However seas may approach four feet at other times in this period.
Winds below Small Craft Advisory criteria.