Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
525 am EDT Monday Apr 27 2015
a large blustery low pressure system over the western North Atlantic
will move slowly out to sea later Tuesday. Then wet low pressure
over the southeastern United States Wednesday will intensify as it
plods northward along the middle Atlantic coast later Thursday and then
seaward just southeast of Nantucket Friday night. High pressure is
expected to build south of our region by Sunday.
Near term /until 6 PM this evening/...
an upper trough across New England and upstate New York early this morning
will move southward across our region this afternoon. The feature
will bring mostly cloudy skies across much of the region today.
There is a slight chance for a shower this afternoon...but we will keep
probability of precipitation only around 20 percent...since the airmass remains rather dry.
Temperatures today will remain a little below normal with highs only
topping out in the 50s far north and low 60s elsewhere. Winds will
be northwest at 5 to 10 miles per hour this morning...then increase to 10 to 15
miles per hour with gusts around 20 miles per hour this afternoon.
Short term /6 PM this evening through 6 am Tuesday/...
the upper trough will be across the southern parts of the County Warning Area and it
will continue to pivot away from the area. Any scattered showers from the
late afternoon will diminish during the evening with the 20 pop
carrying in the evening. Clouds will continue to circulate across
the area...with a trend toward fewer clouds by daybreak Tuesday. Lows
tonight will be in the upper 30s to low 40s north and low/middle 40s
elsewhere. Winds will be moderate...from the northwest 10 to 15 miles per hour.
Long term /Tuesday through Sunday/...
**wind swept soaking rains may be on the way here Thursday-
500 mb: below normal heights dominate our area through Saturday
morning then a warming ridge develops here Sunday.
The large closed low in the western Atlantic south of Nova Scotia
Tuesday weakens eastward during middle week. Meanwhile a strong southern
USA short wave on Wednesday has a good chance of being scooped
northward by a south central Canada short wave diving southward
along 83 degrees west longitude. The two should phase into a new
robust closed low along or east of the middle Atlantic coast Friday.
Temperatures: calendar day averages around 3 degrees below normal
Tuesday then near or somewhat below normal Wednesday - Saturday,
with a definite warming trend to follow next Sunday!
Hazards this 6 day period: fire weather is a possible consideration
prior to Thursday. Thursday-Friday is uncertain but minor Hydro
and wind issues may develop?
Forecast basis: unless otherwise noted, a 50 50 blend 00z/27
GFS/NAM MOS guidance Tuesday-Wednesday, 00z/27 mex MOS Wednesday
night and Thursday, then the 0541z/27 wpc gridded elements of
maximum/min temp, 12 hour pop, 6 hour dewpoint-sky-wind from Thursday
through next Saturday.
Tuesday...mostly sunny morning, considerable cloudiness afternoon.
A gusty north-northwest wind to 20-25 miles per hour. Clear at night. Confidence: above
Wednesday...sunny (cirrus arrives late day?) Light northwest-west wind but
chilling afternoon sea breezes coasts confidence: above average
Thursday...mostly cloudy. East wind, possibly gusty 20-30 miles per hour by
late in the day. Periods of rain likely, possibly pockets of heavy.
Small chance of a gusty thunderstorm southern Delaware late Thursday night where
00z/27 GFS models tt 55+, swi -2 and 40-50 knots 850 inflow.
Temperature guidance was undercut by 4 degrees Thursday and Thursday
The gefs is becoming ever more robust with this system while the
Euro remains just offshore. Unless the gefs starts backing down,
think we need to be thinking of a decent storm. Still early.
00z/27 gefs has a 20-30 percent 48 hour probability of 2" in parts of our area
and widespread 48 hour 1 inch amts. 850-925 mb east-northeast inflow is about
3 or 4 South Dakota deviations above normal. If the phase occurs - this
should be quite a precipitation producer. 00z naefs has significant quantitative precipitation forecast as
well, amounts exceeding 1/2 inch, especially S New Jersey southeast PA southward.
Confidence: below average due to coastal storm track uncertainty.
Friday...morning rain then considerable cloudiness and blustery
north-northwest winds 25-35 miles per hour. Right now our gridded wind forecast
looks far too low. Guidance temperatures lowered several degrees.
Overall confidence: below average due to uncertain proximity of
the coastal storm.
Surge will need to exceed 2 feet before its a minor coastal flood
problem,. Right now guidance is 1 to 2 above normal at the time
of the evening high tides Thu/Fri.
Saturday...partly to mostly sunny. Northwest wind gusts 15-20 miles per hour.
Confidence: below average due to uncertain proximity of the departing
Sunday...partly to mostly sunny. Milder. Light wind. Confidence:
Outlook: a substantial ridge from the west is forecast to build over
the eastern states for the first full week of may.
Aviation /09z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
We are continuing the VFR tafs for all sites today and tonight. An
upper trough and a few embedded vorticity maximums will cross the region
today moving basically north to S. A shield of clouds across northern PA will
progress southward early today and will bring broken middle level
cloudiness early today. Later today...daytime cumulus/SC and more ac will
affect the region. There is a very small possibility for a
shower...but none were inserted in the tafs with low confid in
timing/location. Winds will be mostly northwest at 5 to 10 knots
early...then pickup in speeds with some around 20 knots this
afternoon. Scattered-broken cloudiness tonight with moderate northwest winds
Tuesday...VFR with predominance broken clouds at or above 5000 feet midday-
afternoon. North-northwest wind gusty to 20-25 knots diminishes to light at
night. Confidence: above average.
Wednesday...VFR clear with cirrus arriving late in the day. West-northwest
wind gusts at or below 15 knots during the day and light at night.
Confidence: above average.
Thursday and Thursday night...VFR ceilings occasional MVFR or IFR conds in
rain. Chance of a thunderstorm Delaware Thursday night? East to northeast wind
may gust 20-30 knots late Thursday. Probable impact on operations at kphl.
Detail confidence: below average due to uncertain proximity of
the coastal storm.
Friday...blustery. Morning rain? Otherwise mainly VFR ceilings clearing
at night. North-northwest wind gusts 25-35kt. Detail confidence: below average.
winds and seas will remain below Small Craft Advisory conditions today. An upper
trough will move across the area...then some cooler air and surface
gustiness will bring low-end Small Craft Advisory gusts to the waters tonight. The
ongoing 00z/Tuesday start time still looks good at this point...so no
changes will be made. Mostly fair weather today with only a slight chance
or a shower this afternoon and early this evening.
Tuesday morning...a Small Craft Advisory is in effect for a northwest
to north wind gusting to 25 or 30 knots. Confidence: above average.
Tuesday afternoon through Thursday morning...no marine headlines
are anticipated. Confidence: above average.
Thursday afternoon through Friday...a Small Craft Advisory for
sure for NE wind gusts of 25 to 30 knots backing to north or northwest Friday
and for waves on our ocean waters well in excess of 5 feet.
There is increasing potential for gale force 35 to 45 knots gusts
late Thursday or Friday morning but track confidence is below
average. Confidence on a headline marine event is well above
north-northwest wind gusts of 20 to possibly 25 miles per hour are expected
Tuesday as relative humidity values drop around 30 percent in much
of our region Tuesday afternoon. Further daytime evaluation and
possible partner discussions may eventually require a Special Weather
Statement highlighting marginal more rapid rate of spread conditions
Relative humidity Wednesday afternoon about the same or possibly slightly lower
but wind gusts are less than 18 miles per hour.
Marine...Small Craft Advisory from 8 PM this evening to noon EDT
Tuesday for anz430-431-450>455.
long term...drag 523