Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Mount Holly New Jersey
800 PM EDT Friday may 22 2015

high pressure across the Great Lakes will build eastward tonight
reaching our region tomorrow. This area of high pressure will slide
off the coast Sunday. A warm frontal boundary will then pass
northward through our region on Monday. A trough of low pressure
will move in behind the warm frontal passage for the middle and
later half of next week.


Near term /until 6 am Saturday morning/...
the last of the scattered showers from earlier heating are
crossing the far northern parts of New Jersey and will soon be history. Clouds
will continue to decrease overnight. A weak cold front will cross
the area overnight.

Temperatures will drop off overnight behind the cold front, with
everyone dropping close to 10 degrees below normal. There could even
be some patchy frost across the northern areas. Portions of the
Poconos have the best chance of being the coldest with more
widespread frost, so an advisory has been issued for Carbon/Monroe,
Pennsylvania. We did include patchy frost for Sussex County, New
Jersey, but are not sure it will be as widespread as the Poconos, so
we did not issue an advisory there.


Short term /6 am Saturday morning through 6 PM Saturday/...
other than the patchy morning frost up north,Saturday will be a
beautiful day as high pressure crests over the area and temperatures
will remain around close to 10 degrees below normal. Precipitable water values will
drop below 1/4 of an inch, and only cirrus clouds are expected
through the day.


Long term /Saturday night through Friday/...
this forecast is weighed more on the European model (ecmwf) operational runs today
and it's respective ensemble mean. This results in a drier and hot
period for most of next week. The GFS looks to have to much
convection. The main reason for this conclusion is the lack of a
focused triggering mechanism present. The first heat wave of the
season possible Tuesday-Thursday next week, maybe past thu?, Particularly phl
metropolitan area and SW.

Saturday night through Sunday night: high pressure will move off the
Carolina coastline. This will lead to a more dominant south to
southwest wind and a warm frontal boundary moving north into the
region Sunday night. Moisture will be on the increase with the
temperature trends on both highs and lows increasing. Still pleasant
overall with plenty of sunshine!

Monday: a warm frontal boundary will move through early in the day.
Some convection may attempt to fire up or move along the boundary
with the highest chances across northern parts of the County Warning Area. However,
the trend over the past few model cycles is for decreased chances of
shower or thunderstorm activity. Only went with slight chance for
the Lehigh Valley and Poconos in this period. Shear is going to be
very weak through all periods, so the main threats from any
thunderstorms will be from locally heavy downpours and frequent
lightning, high precipitable water values. Continued warming trend and southerly
flow after the warm frontal passage as well. Some wind gusts from 15-
20 miles per hour possible as well based on GFS sounding analysis Monday

Monday night through Tuesday night: region firmly in warm sector.
With continued southerly-southwesterly winds and warm air advection. Some gusts
close to 20 miles per hour are once again possible Tuesday afternoon. Surging
925 mb temperatures from 20-25c may contribute to the first widespread 90
degree day of the year by Tuesday. A broad trough to our northwest
may be enough of a trigger for a thunderstorm or two across the
Lehigh Valley north and west. Overall, trend in the next few
periods, like with many weather systems in recent weeks is to lower
probability of precipitation as we get closer to an event. Highest chances focused northwest of phl.

Wednesday through friday: well we continue to be on the backside of
the ridge with the a similar pattern to Mon-Tue. As stated earlier,
this forecast leans in the direction of the European model (ecmwf) and it's ensemble
mean. That limits the influence of the incoming trough allowing for
a hotter period with lower rain chances. 925 mb temperatures suggest
the hottest day to be Wednesday, in the low 90's with highs around
90 for Thursday and Friday. Muggy nights are likely as well with
lows in the upper 60's to 70 on average. By weeks end, the
influence of any trough may increase. This would lead to more in the
way of scattered clouds and popcorn thunderstorm chances.
Temperature forecasts are warmer than the ensemble guidance output
at this time for highs, particularly the GFS which looks to much
driven by questionable convection.


Aviation /00z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.

VFR conditions will persist through the period. Wind gusts should
slowly diminish around an after sunset. A cold front will move
through the area around/after sunset which may have a few gusts
right behind it, but winds will drop off overnight behind the
front as high pressure begins to move into the area.

VFR conditions and lighter winds will persist for Saturday. The
northwest winds should become more west and southwest through the


Saturday through Sunday night: VFR, southwest winds around 10 knots.

Monday through wednesday: VFR, with some lower restrictions
possible in any isolated to scattered storms. Best chance for
storms Abe and ridge Tuesday and Wednesday in the late afternoon
hours. South to southwest winds with some gusts from 15-20 knots
possible each afternoon.


Small Craft Advisory across the southern coastal waters has been
extended until match up with del Bay. Winds have
been slow to decrease this evening and the trend to lighter winds
will begin after sunset. We may cancel it at 10 PM if conditions
warrant. The Small Craft Advisory for the northern waters will continue overnight. A few
scattered showers north this evening...then fair weather overnight. Fair
weather Sat. Northwest winds becoming west late...speeds mostly 10 to 15

Outlook... seas and winds are expected to remain below Small Craft Advisory
criteria throughout the entire outlook period. However, isolated
to scattered thunderstorms are possible Monday through Wednesday
focused in the afternoon and evening. Winds will be out of the
south to southwest with some wind gusts around 20 knots. Highest
seas around four feet across the northern waters on Tuesday.


Rip currents...
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 may 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.


Phi watches/warnings/advisories...
PA...frost advisory from 3 am to 8 am EDT Saturday for paz054-055.
New Jersey...none.
Marine...Small Craft Advisory until 6 am EDT Saturday for anz450>453.
Small Craft Advisory until midnight EDT tonight for anz430-431-


near term...Robertson/po
short term...Robertson
long term...Gaines
fire weather...
rip currents...

National Weather Service Glossary of Abbreviations