Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
433 am EDT Tuesday Oct 6 2015
high pressure across the northern United States moves off the New
England coast Thursday night. A strengthening cold front and
developing low pressure moves through the middle and North Atlantic
states late Friday into Saturday. Thereafter, high pressure becomes
established across the southern United States next Sunday and
Near term /until 6 PM this evening/...
the atmospheric Road block continues to lessen today as the
persistent closed low to our south shifts eastward. At the surface,
weak high pressure will build into the area however this will lessen
the northeasterly flow even more. The day is anticipated to start
with sunshine /a chilly start for many/, although lingering
stratocumulus may hug some of the coastal areas early as the low-
level convergence area weakens and shifts farther southeast. Some
moisture though arriving from the west and southwest should result
in some middle to high level clouds into this evening. This moisture
can be seen on the water vapor imagery early this morning moving up
the Ohio and Tennessee valleys. In addition, the forecast soundings
do show enough moisture near 850 mb to result in shallow
cumulus/stratocumulus development through the afternoon. This should
be more noted across the west to northwest zones, therefore we
carried some more cloud cover there through the afternoon.
As we lose the onshore flow and the pressure gradient continues to
collapse farther offshore, the airmass will modify along with the
assistance from more sunshine. This is reflected in the afternoon
high temperatures, which is mostly a MOS/continuity blend.
Short term /6 PM this evening through 6 am Wednesday/...
a weak surface high will be in place as the flow aloft is more zonal
tonight. While our weather looks to be on the tranquil side, it
appears that moisture advection above the surface is maintained to
some extent. This may result in more cloudiness at times, which will
have an impact on the low temperatures. We did maintain areas of
cloudiness moving through in the westerly flow aloft as surface high
pressure is forecast to be on the weak side. There may be patchy fog
late, mainly in the rural areas and/or near bodies of water however
this may be affected on the amount of cloudiness through the night.
Overall, a quiet night is anticipated in the weather department.
As for the low temperatures, we used a MOS/continuity blend but then
lowered these a little mainly for the typically cooler locales
assuming any cloudiness is thin enough.
Long term /Wednesday through Monday/...
500 mb: a relatively benign westerly flow this week before short
waves amplify into eastern North America Friday and Saturday.
Temperatures: calender day averages above normal Wednesday through
Friday with potentially cooler than normal conditions this weekend
before a warmer than normal period begins again next Monday. The
warmest departures of nearly 10 degrees above normal should occur
tomorrow and possibly again Friday.
Forecast basis: unless otherwise noted, a 50 50 blend 00z/6 GFS/NAM
MOS guidance Wednesday - Thursday, 00z/6 GFS mex MOS Thursday night
and Friday, then the 0521z/06 wpc gridded elements of maximum/min temp,
12 hour pop, 6 hour dewpoint-sky-wind from Friday night Onward.
Did use the warmer of the available guidance Wednesday-Thursday,
raised the GFS mex guidance by 3 degrees Friday I-95 corridor
westward. Saturday's highs could be as forecast or 5 to 10
degrees colder if its raining much of the day. The wpc maximum temperature
guidance for Sunday- Monday was blended with the warmer 00z/GFS
and even Monday, raised that a couple of degrees. Probability of precipitation...a rain
event is likely sometime late Friday into Saturday and so chose
Friday night as the most likely time for widespread rainfall in
our region...timing uncertain but the probability of precipitation were raised to the likely
category to express more confidence in a showery event late this
Hazards: the severe weather potential statement for now has "the probability for widespread
hazardous weather is low". There could be patchy dense fog Thursday
morning, Friday morning and Sunday morning north of I-78. A touch
of frost is a small possibility in the most vulnerable locations
of northwest New Jersey and NE PA for Sunday morning...depending in part on the
pressure gradient and skycover.
Wednesday...partly cloudy and nice. Maximum temperatures 7 to 9 degrees above
normal. Northwest wind gust 15 miles per hour. Confidence: above average.
Wednesday night...fair. Patchy fog possible late in northwest New Jersey and NE
PA. Low temperatures may dip 3 degrees below the forecast in the
Countryside of northwest New Jersey and NE PA (42f). Already had slightly
lowered the 00z/6 guidance up there. Confidence: above average.
Thursday...mostly sunny and maybe 5 degrees cooler but still
slightly above normal. Light wind. Coastal sea breezes.
Confidence: above average.
Friday...showers expected ahead of the cold front passage. So far, less than one
inch rain was ensembled from the multiple 12z/5 guidance and available
00z/6 GFS/ec guidance. The past two runs of the operational European model (ecmwf)
are slower than the progressive GFS/UK/ggem as the ec separates a
short wave from the northern stream toward the southern Middle Atlantic States.
Therefore have reserved most of the rain for Friday night.
Thunder is maintained but only as a slight chance.
South to southwest wind may briefly gust 20-25 miles per hour in the afternoon.
High confidence on showers eventually wetting most of the area
with at least a quarter inch. Low confidence on wind.
Saturday...uncertainty on when the showers end but eventually
partial clearing. Northwest to north wind gusty 20 miles per hour. Confidence: average.
Sunday night...our forecast low temperatures may be 5 to 6 degrees too
warm north of I-80. Expecting radiation cooling there, patchy fog
and a small chance for a touch of frost. Could see it dropping to
around 33-35f parts of NE PA and far northwest New Jersey low lying areas.
Sunday...after any early morning patchy fog, increasing high
clouds. Light northwest to west wind. Confidence: average.
Monday...partly cloudy. SW wind gusty 15 miles per hour. Confidence: average.
Aviation /09z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy, and surrounding areas.
Today...VFR with some developing cloud bases between 4000-5000 feet.
The best chance for a ceiling is in the krdg and kabe areas by late
afternoon /some lingering for a time this morning near kacy/. Light
northerly or calm winds to start, becoming north-northwest at 5 to
10 knots. The winds should then diminish toward evening.
Tonight...VFR overall with a ceiling at times mainly at or above
5000 feet. Some local rural MVFR visibilities possible toward
daybreak due to ground fog. Winds light northwesterly or light and
Wednesday through Thursday night...predominately VFR conditions.
Northwest wind gust 15 knots Wednesday and then a light wind Thursday
with afternoon coastal seabreezes vicinity kacy. Confidence: above
Friday...VFR to start then MVFR conditions late day or night with
showers/isolated thunderstorms. SW wind probably gusts near 20 knots during
the day. Confidence for a rain event above average but confidence
on timing the start of the rain is below average.
Saturday...some MVFR ceilings possible in leftover showers early?
Otherwise becoming VFR with northwest-north wind gusting 20-30 knots.
as the persistent closed low to our south shifts eastward today, the
pressure gradient will continue to collapse offshore. This will
continue to result in a diminishing wind from north to south, which
is expected to occur this morning across the far southern waters to
convert the Small Craft Advisory over to a Small Craft Advisory for
hazardous seas. As a result, we continue to transition to elevated
seas as the hazard and the advisory for the coastal waters remains
in effect for today and tonight. Light winds and seas 1-3 feet will
occur on Delaware Bay.
Wednesday... Small Craft Advisory conditions for hazardous 5 foot
seas are forecast due to lingering effects from Joaquin and last
weekends very strong southeast Canada high pressure system, at
least for the morning. Confidence: average.
Wednesday night through Thursday night...sub Small Craft Advisory
conditions are outlooked. Confidence: above average
Friday and Friday night...winds and seas could briefly reach Small
Craft Advisory criteria in the southwest flow preceding the next
cold front. Confidence average.
Saturday...Small Craft Advisory conditions are expected for a time
in the Post- frontal or behind low pressure moving eastward from
New Jersey. North- northwest wind gusts 20-30 knots. 00z/6 gefs probabilistic
guidance has a 30-40 percent chance of sustained 25 knots winds in our New Jersey
waters for 12z Saturday. Overall confidence: average.
for the Atlantic coast and Delaware Bay, The Tides continue to be
above normal however with diminishing wind speeds and a shift to a
more north and then northwesterly wind direction through today,
coastal flooding chances will decrease. While there will still be
water backed up into the back bays, the relaxation in the winds and
the directional shift should help to drain them over the next couple
of tidal cycles. As a result, no advisories are anticipated.
For portions of the Eastern Shore of the Maryland Chesapeake Bay,
the departures increased last evening during low tide and this was
most likely in response to the weakened northeast winds that allowed
the water piled up on the western shore to slosh back toward the
Eastern Shore. This resulted in water levels getting to minor flood
criteria. The late morning to midday high tide looks to be close,
but may fall just short of advisory issuance. This evenings high
tide is higher and could come close again, however by then the
departures may be able to decrease some. As a result, we held off on
issuing another advisory however The Levels will be monitored.
Marine...Small Craft Advisory for hazardous seas until 2 PM EDT
Wednesday for anz450>455.
long term...drag 433a