Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 212206
Area Forecast Discussion
National Weather Service Mount Holly NJ
606 PM EDT SAT MAY 21 2016
Low pressure off the Virginia coast will lift northeast of our
region through the day Sunday. However, a second offshore low is
expected to develop by Monday, before lifting away from the region
on Tuesday. A ridge will build over our region mid week. By Friday,
the ridge is expected to shift east as another low begins to slide
over the Great Plains.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Surface low pressure will continue to move northeastward and
out to sea tonight. However, a upper low level pressure system to
our northwest will continue to be a focal mechanism for some
scattered light showers across the region tonight with a decrease
overnight in coverage. The more concentrated showers along the shore
will move offshore early this evening. With cloudy skies,
temperatures will be slow to fall tonight falling into the upper
40`s and low 50`s. Fairly good model agreement with the forecast for
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
The upper level low pressure system that will be to our northwest
will drop southward on Sunday. The 12z GFS/CMC/UKMET are a bit
further west than the 12Z ECMWF with this feature. With this
forecast package, we opted to go with a slightly more west track of
the low. This could potentially keep the highest coverage of showers
across Eastern Pennsylvania throughout the day. The areal coverage of
showers looks to be of a diurnal nature as low level lapse rates
steepen (instability mechanism) to increase the coverage by the
afternoon. Rainfall amounts are going to be light but a continued
low freezing level around 10,000 feet may result in a few showers
containing pea size hail in the afternoon hours. Coverage of
hail looks to low to place in forecast attm.
The track of the low will also effect the high temperatures. A
further east and cloudier ECMWF keeps highs down in the low and mid
60`s for most. On the other hand, A further west low track would
allow for breaks of sunshine and a chance at 70 degrees for Delaware
and New Jersey.
.LONG TERM /SUNDAY THROUGH SATURDAY/...
Monday through Tuesday...As the upper level short wave trough digs
and intensifies over the Mid Atlantic, a surface low will
subsequently develop off the coast of VA/NC. As a result, expect the
work week to begin with much of the same weather pattern we`re
seeing this weekend. Northeasterly flow will temper max temperatures
a bit, staying slightly below normal. However, thanks to air mass
modification, we should see a modest warming trend into Tuesday and
highs may be near normals. The moisture advection, thanks to
persistent onshore flow, and synoptic scale lift thanks to the upper
level low will result in continued rain chances. How quickly we dry
out will be dependent on how quickly the low lifts out of the
region. On this point, there are some slight differences between the
models with the GFS being a bit slower to clear everything out.
Would expect the bulk of the precipitation to be done by mid day
Tuesday as the flow turns more northwesterly, but a few showers
could linger into Tuesday evening.
Wednesday and Thursday...Upper level ridge shifts east, with the
ridge axis over our region by Thursday morning, bringing a lull in
rain chances and a very noticeable warming trend, with 80s expected
across much of the region both days.
Friday and Saturday...ridge shifts further east offshore through
this time, leaving our region on the periphery of the ridge. As
such, could see primarily afternoon and evening showers and
thunderstorms as shortwave troughs embedded in the upper level SW
flow slide over the region.
.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Tonight: Mainly VFR through early evening, some MVFR possible from
KPHL and southeast with the steadiest showers through early
evening. Ceilings will gradually lower by late evening likely
becoming IFR for the overnight hours. Some MVFR VSBY restrictions
will also occur throughout the night as well. Winds will be
easterly- northeasterly around 10 knots.
Sunday: Ceilings will start off IFR/MVFR in the pre-dawn hours and
gradually lift to VFR by the afternoon. Chance for some brief
scattered showers to impact TAF site, to low of a chance for TAF
inclusion attm. Northerly winds around 10 knots.
Monday and Tuesday...Occasional MVFR conditions possible with
showers and fog especially Monday night.
Wednesday and Thursday...VFR conditions likely. Small chance of MVFR
conditions with showers and thunderstorms Thursday afternoon and
-- Changed Discussion --SCA starting at 4 pm this afternoon. Easterly winds have increased
but are still only around 20 knots on the bay attm. A window still
looks present for some easterly wind gusts near 25 knots by
evening both on the ocean and in Delaware Bay. Seas will be slow to
rise and should get above five feet tonight on the ocean.
Sunday: Winds will be more northerly and lighter. However wave
heights will still run from five to eight feet. SCA in effect.
RIP CURRENTS...Moderate risk for rip currents today as well with
the onshore flow and increasing easterly winds. A cool, raw day to
be out at the beach. Rip current forecast will be updated this
evening for Sunday. At this time, despite a significantly lighter
onshore wind...the onshore swell have increased, leaving a residual
day-after storm effect, likely resulting in a moderate or greater
risk for the formation of dangerous rip currents. water
temperatures are near normal..upper 50s to around 60.
The Experimental one stop shop National Beach Forecast page may
begin posting on our web site, for our area, midday Sunday, or
more likely midday Monday. We hope you will like it. This is the
beginning of what we hope will be potentially more useful rip
current information coming in a year or two. You`ll click the
umbrella and from there its all self explanatory.
Sunday night into Monday...Seas are expected through this
period and could be at or above 5 feet as early as Monday morning
(especially on the southern coastal waters).
Monday night...SCA conditions are likely on the coastal waters,
primarily for seas above 5 feet, though gusts near or above 20 kt
Tuesday...seas should slowly subside, though SCA conditions may
linger through much of the day.
Tuesday night through Thursday...winds and seas should stay below
-- End Changed Discussion --
With the full moon today (Saturday), and on shore flow developing
later today and persisting through at least Sunday morning, tide
levels should be higher than normal on the Atlantic oceanfront and
the Delaware Bay. However, we expect water levels to fall short of
minor flooding thresholds at this point. The highest water levels
are expected with the high tide cycles on Sunday and Monday evening.
-- Changed Discussion --Well, many have bemoaned the fact that April and May, so far, have
been relatively cool, especially after our top 5 warmest March in
over 140 years of data gathering.
Well, we ran the numbers for the rest of the month, using today`s
max/min of 62/56, and the SFTPHI gridded max/min temp for PHL the
22nd-28th, and thereafter the FTPRHA max/min from the 12z/21 GFS
2m temps for the 29th-31st.
Our current 4 degree negative departure warms to only a degree
below normal (warms 3 degrees over the last 10 days). So it looks
as if summerlike warmth will develop here late this week and
potentially last through the Memorial Day weekend. 90 degree
warmth may be occurring in parts of our area and the cold feel to
the month of May will be replaced by the possibility of air
conditioners firing up.
By the way, while the month is top 5 coldest as of the 20th, it
should end up middle of the pack with no notable cold departure,
at least not more than a degree. If it does end up below normal
as now projected, it would be Philadelphia`s first month with
below normal average temperatures since March 2015.
-- End Changed Discussion --
MARINE...Small Craft Advisory until 6 PM EDT Monday for ANZ452>455.
Small Craft Advisory until 6 AM EDT Monday for ANZ450-451.
Small Craft Advisory until 10 PM EDT this evening for ANZ430-