Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
605 am EDT Friday may 22 2015
a cold front will cross our region later this afternoon, then high
pressure builds in Saturday before shifting offshore Saturday night
and Sunday. A warm front is forecast to lift north across our area
during Monday. A cold front is then anticipated to remain well to
our north and west Wednesday and Thursday as high pressure remains
anchored in the western Atlantic.
Near term /until 6 PM this evening/...
today...sunny this morning then partly sunny this afternoon as a band
of modest instability cloudiness ahead of a cold front passage passes southeastward
through the area with decent total totals but almost zero MLCAPE
(probably not enough moisture for anything other than a possible
high based sprinkle or .01 shower with gusty northwest winds to
35kt). We noted support for this in the 00z/22 NSSL WRF and Storm Prediction Center
WRF. The hrrr now has a group of showers running east-southeastward through east
central PA and central New Jersey in the 20-23z time frame.
Increasingly gusty west winds ahead of the cold front with 20 miles per hour
this morning and 28-38 miles per hour by middle afternoon. The wshift to north-northwest arrives
vicinity I-80 in the 6p time frame (which is really this evening-
Temperatures rebound after ydys 12 to 18 below normal maximum temperatures with this
aftns temperatures about 15-20 degrees warmer compared to Thursday afternoon
(near normal max's).
Forecast generated generally from a 5050 blend of 00z/22 NCEP MOS
Confidence: above average.
Short term /6 PM this evening through 6 am Saturday/...
clear and turning chilly as the cold front passage near I-80 (ne PA/nnj) in the
6p time frame slips down to vicinity kacy-kphl around 11p with a
period of gusty north-northwest winds of 20-25 miles per hour expected early
at night then decoupling-rapidly diminishing wind late as temperatures
Will continue a touch of scattered frost from Warren-Sussex counties in
northwest New Jersey into Monroe and Carbon counties of NE PA. Just not enough
coverage expected for a frost advisory. Also with full Greenup, probably
enough Leaf cover to prevent much damage. Still, cant be absolutely
sure and so patchy frost is in the forecast and possible Special Weather Statement material
later today for those located in such places as Walpack, Pequest,
the typically coldest low lying areas in the northwest fringe of our
A bit of high thin cirrus possible toward sunrise saturday?
Forecast generally from a 5050 blend of 00z/22 NCEP MOS guidance
Confidence: above average.
Long term /Saturday through Thursday/...
the synoptic setup is comprised of a closed low moving from northern
New England to the Canadian Maritimes Saturday. This is due to
energy starting to eject into the central and Southern Plains, which
will also build a ridge from Florida northwestward into the Midwest
Saturday into Monday. The ridge strengthens some as it shifts
eastward Monday and Tuesday, however it should then start to flatten
some on its northern side from about Tuesday Onward. The main
feature is a frontal boundary that slides across the northeast but
this then lifts back northward as a warm front Monday. It looks to
turn rather warm to even hot next week as the upper-level ridge is
in place despite it gradually shifting more offshore with time. We
used a model blend for Saturday through Monday, then the 00z wpc
guidance with continuity thereafter. Some tweaks were then made
following additional collaboration with our neighboring offices.
For Saturday...a chilly start /patchy frost up north/, otherwise
high pressure starts to shift offshore at night as ridging builds to
our west. The airmass will be cool, therefore highs should be in the
60s to about 70 degrees across the region. Due to high pressure in
place, less wind is expected compared to Friday.
For Sunday and Monday...a ridge to our west will gradually build
eastward. Some energy sliding southeastward across northern New
England will drop a frontal boundary into our area Sunday night.
This boundary generally looks to be on the weak side, however it
could be activated Monday as it lifts northward as a warm front. As
the ridge builds, our area is still within the northwesterly flow
aloft. The low-level flow is forecast to be southwesterly, and the
combination of warm air advection and some frontal lift aided by some short wave
energy along the front should produce some convection on Monday. It
appears that the bulk of the warm air advection/lift is aimed up the Ohio Valley
and across the Great Lakes. We will need to watch this though as
some convection could slip into our area from the west/northwest,
especially the northern half, during Monday before the ridge axis
reaches our County Warning Area. The amount of instability will be key as we
continue to recover from a rather dry airmass that is in place prior
to Monday. Overall, convection may produce at least locally heavy
downpours Monday. A much warmer airmass is expected to overspread
the area especially Monday as an expanding warm sector moves north,
and some increase in the dew points will also occur.
For Tuesday and Wednesday...we are expected to be in the warm sector
during this time frame as a short wave aloft and surface low tracks
to our north, which will flatten the ridge some. While the surface
cold front is currently forecast to stay well to our north and west,
some convection cannot be ruled out. This appears to be mainly
focused near a Lee side trough in the presence of a warm/hot and
increasingly humid airmass. Given the presence of the ridge and the
northwesterly flow aloft breaking down across our area, any
convection could be slow moving which would result in locally heavy
rain. As of now, the western zones have a higher chance of convection
given the forecast placement of the ridge and also a Lee side
trough. Some places are forecast to reach 90 degrees each afternoon.
The afternoon heat indices are forecast to be close to 95 degrees
especially Wednesday afternoon for the urbanized areas of the
Philadelphia metropolitan. It should be cooler along the coast due to a
For Thursday...it looks to be a repeat of the previous two days as
we remain in the warm sector, meanwhile a cold front slowly sags
southeastward across the Great Lakes. Some of the guidance is faster
with this front, however we went with the wpc timing. Once again a
warm to even hot day is anticipated, although it may be a little
cooler as the ridge weakens some. Since a southerly flow is
forecast, it should be cooler along the coast. Some mainly afternoon
and evening convection is possible especially inland, probably
focused along a Lee side trough.
Aviation /10z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Today...mostly VFR prior to 12z with a light west-northwest wind. Any remaining
MVFR fog southeast New Jersey soon dissipates. Then after 12z...VFR clear becoming
scattered-broken at or above 6000 feet this afternoon with the slight chance of a westerly 38kt
gusty sprinkle or light shower ahead of a cold front. Generally
gradient westerly gusts 20 knots this morning increase to 25-33 knots this
Tonight...VFR clear. Thin cirrus possible toward sunrise Saturday.
Wshift to 20-25kt gusty north-northwest this evening from north to south, first
near I-80 around 00z reaching kphl/kacy around 03-05z.
Confidence: above average.
Saturday...VFR. Northwest winds around 10 knots, becoming west-
southwest during the afternoon.
Sunday...VFR. Southwest winds 10 to 15 knots, then diminishing some
Monday and Tuesday...mainly VFR. Some showers and thunderstorms are
possible especially during Monday. Southwest winds mainly around
safe boating week concludes today. Our final public information
statement for this season posted at 408 am with the social media
Post around 8am. I did go ahead and add the new uscg safety app to
my smart phone, just in case it comes in handy via marine related
Small Craft Advisory vicinity 44009 early today with seas now responding.
Winds on Delaware Bay up a little more than anticipated and if
this continues may start the Small Craft Advisory back to where we had it, this
morning. Right now, no change.
Otherwise...Small Craft Advisory all other waters with the primary threat period of 2p-
midnight. Westerly wind gst 25-30 knots this afternoon ahead of a cold front
then just after of the cold frontal passage wind shift to north-northwest this
evening. Strongest wind near the shore where its warmer and better
Winds diminish toward sunrise Saturday.
Saturday and Sunday...northwest winds diminishing Saturday and then
becoming southwest toward evening. The southwesterly flow continues
Sunday and should increase some, however overall the conditions
should be below advisory criteria.
Monday and Tuesday...a southwesterly flow of 10-20 knots is
anticipated within a warm/hot airmass. This may result in the higher
winds closer to the coast. A few showers and thunderstorms are
possible especially Monday. Seas at or below 4 feet, although these
may near 5 feet Tuesday across the northern coastal waters.
wind gusts of 25 to 35 miles per hour are expected this afternoon and relative
humidity values should fall into the 20 to 30 percent range in
much of our region at that time. However, yesterdays rainfall is
forecast to keep fine fuel moisture from falling below critical
levels at those locations where the green-up is not complete, most
notably The Pine Barrens. As a result, we are not anticipating any
fire weather issues for Friday.
potential heat wave next week. This plus water temperatures continuing above
normal is not good for safety. Once it turns hot and beaches are
unguarded, swimmers may take chances at unguarded locations. Be smart
about any swimming early this season.
Rip current awareness week for Montana Holly is June 7-13 with psas
via public information statements, social media, National oceanic and atmospheric administration weather
radio and any media interviews desired (contact office).
For rip currents: despite anticipated projections of low or
moderate risk through the Memorial Day weekend, early season
fatalities occur when swimming at unguarded times/locations.
Weaker swimmers or swimming in areas where rip currents are
stronger (jetties) can quickly become life threatening. When
trained lifeguards are not nearby, timely Rescue is much less
likely. Lets get through the month of may with all swimmers safe!
Please broadcast this message: for ultimate safety, always swim
in the presence of life guards! Thank you!
**little doubt that a top 10 warmest will occur in large portions
of our forecast area**
The first 21 days of may in our forecast area were averaging
about 6 degrees above normal.
Running the numbers from this mornings 330am forecast through the
28th and the 00z/22 ftprha (gfs mos) for the last 3 days beyond
our weather forecast office responsibility (29-31) we find the following.
For Philadelphia...period of record (por) back to 1874.
Projecting a monthly average temperature of 69 to 70, at least 5
to 6 degrees above normal. Heading for second or third warmest on
record. Warmest was 70.8 in 1991. Then 69.2 2004.
For Allentown...period of record (por) back to 1922. Projecting
65.9 or about 6 degrees above normal which would be 4th-5th
warmest on record. 1991 was the warmest with 67.2, followed by
2012 66.1, then 1944 when may averaged 66.0 and finally the 2004
65.9 degree average. The next warmest was 65.3 in 1939.
The following was posted because its likely that we will
experience our first 90 in Philadelphia by the middle of next
week, and possibly a heat wave.
Normal first date of 90 or higher.
Philadelphia may 29
Allentown may 30
Wilmington June 4
Atlantic City June 11.
Marine...Small Craft Advisory from noon today to 6 am EDT Saturday for
Small Craft Advisory until 6 PM EDT this evening for anz454-
Small Craft Advisory from noon today to midnight EDT tonight
near term...drag 605