Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
908 PM EDT Monday Sep 15 2014
high pressure will shift offshore tonight. A fast moving area of
low-pressure will move through the region early Tuesday. High
pressure will slide in from the west during middle week. Another cold
frontal passage probably occurs late Thursday. Canadian high
pressure follows to New England Friday and lingers into next
weekend. A cold front from the west may reach the eastern Seaboard
Near term /until 6 am Tuesday morning/...
we have not made too many big changes to the previous forecast. A
quick moving short wave and surface front will move across the area
overnight. Increasing clouds are overspreading the area...and scattered
showers are continuing across northwest PA at this time. More showers will move
across mostly the northern third of the County Warning Area overnight. We have adjusted
probability of precipitation slightly down in most areas. Temperatures from before looked okay
and were not changed much. Light S/SW winds will switch to wrly by
Short term /6 am Tuesday morning through 6 PM Tuesday/...
the cold front will be progressing trough the area and offshore
during the morning hours Tuesday. Any remaining showers across our
eastern half of the area will pull away during the morning as the
short wave quickly lifts to the northeast. This will lead to a dry
forecast for the afternoon with partly-mostly cloudy skies.
Daytime highs are a blend of mixed European model (ecmwf) 925 mb temps, mav/met MOS,
and mosguide which keeps everyone pretty close to normal.
Long term /Tuesday night through Monday/...
500 mb: trough in eastern North America flattens and warms next
weekend in advance of a strong short wave moving southeastward into the
upper Midwest and Great Lakes next Sunday and Monday.
Temperatures: several degrees below normal Wednesday-friday; nearly
normal Saturday and possibly several degrees above normal next Sunday
Forecast basis: unless otherwise noted the long term period of this
forecast is generally based on a 50 50 blend of the 12z/15 NAM/GFS
MOS for the period Tuesday night - Wednesday night...the 12z/15
GFS MOS Thursday...then thereafter (friday onward) the 1522z/15
wpc gridded guidance which at times is blended 50 50 with the 12z/15
mexmos. All this was eventually checked against the 12z/15 European model (ecmwf) to
see if we're in the ballpark with European model (ecmwf) cyclically persistent 18z
2 meter temperatures. Precipitation probability guidance is checked
against the 09z/15 sref 3hrly probability of precipitation for .01 through 00z Friday and
thereafter the 12z/15 gefs 6hr probability of precipitation for 0.05
The dailies below...
Essentially dry Tuesday night through Sunday with maybe the best
chance of showers next Monday. Overall this looks like an extended
period of decent late Summer/early Fall weather for our area.
Tuesday night-Wednesday...fair and cool as weak high pressure
arrives. Light wind.
Wednesday night - Thursday...partly cloudy. Light wind becoming
north late Thursday.
Friday...there may be more cloudiness than currently forecast with
a combination of gusty onshore flow and the cool pool associated
with the high pressure system. Northeast flow gusty at times 15
to 20 miles per hour. Maybe some sprinkles?
Next weekend...partly cloudy. Still an easterly flow Saturday probably
turning light southerly Sunday.
Next monday: a cold frontal passage or approach with possible showers.
Fall begins at night.
Aviation /01z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas
We expect VFR conditions to remain across the area through the taf
period, although clouds will thicken and lower through the night
into Tuesday morning as a cold front approaches and moves through
the area. There remains a chance for showers to accompany the front,
especially for our northern tafs, so tempo shower groups remain in
the tafs at this time, centered around the daybreak hours.
Variable winds this evening will become more south to
southwesterly overnight, generally less than 5 knots. Once the
front passes through tomorrow morning, winds will switch to a
northwest direction, picking up to around 10 knots.
Tuesday night - Saturday...VFR with intermittent patchy ceilings at or above
3500 feet at times. Light wind may become gusty northerly 15 knots late
Thursday especially along the coast...then gusty northeast 20 knots
Friday and wind turning easterly Saturday with gusts to 15 knots.
sub-advisory conditions will remain across the waters as high
pressure moves offshore tonight. A cold front will move across the
waters Tuesday morning, which will allow winds to gust up to 20
knots, but remain below advisory levels.
Tuesday night...light wind and seas at or below 3 feet. No marine headlines.
Wednesday and Thursday...Small Craft Advisory may be needed for portions of the
Atlantic waters either for hazardous seas Wednesday into Thursday
or possibly increasing northerly wind late Thursday...subsequent
to the next cold front passage.
Confidence on any Small Craft Advisory for Wednesday is well below average despite
the GFS ww3 guidance. Suspicion is that this guidance will be 1-2
feet too high for Wednesday...and prefer a closer fit to the lower
hurricane ww guidance. Edouard's northward track well to the east of
70w is the reasoning for hesitating on buying into the GFS ww3
guidance. Recent history with cristobals high swell bias for our
portion of the middle Atlantic coast lingers in the memory bank.
Friday-Saturday...stronger onshore northeast flow is expected to
develop and Small Craft Advisory level wind gusts and/or seas should be realized,
most likely for the central to southern Atlantic coastal waters
and lower Delaware Bay. Winds gusts around 25 knots and seas of 5
to 7 feet are possible.
Wednesday and thursday: there may be an enhanced risk for the formation
of dangerous rip currents...especially along the New Jersey coast...in response
to the arrival of 12 to 15 second period swells from Edouard. Edouards
northward passage far to the east of 70w probably will mean the GFS ww
swell guidance is too high and so have favored the lesser hurricane
model guidance (osbh07). At this time the confidence for moderate
risk potential for Wednesday/Thursday is considered below average and we'll
need a 3 foot east-southeast swell of 13 to 15 seconds to raise that risk