Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 261804

Area Forecast Discussion
National Weather Service Mount Holly NJ
204 PM EDT Sun Mar 26 2017

Canadian high pressure is our primary weather influence today.
Low pressure from the Mississippi Valley into the Great Lakes
on Monday will draw a warm front northward through most of our
region. The low will move into southern New England Tuesday
night pulling the frontal system off the coast. Canadian high
pressure will edge into our area Wednesday and Thursday.
Thereafter, low pressure in the Ohio Valley on Friday should
exit seaward from the mid Altantic coast next Saturday.


930 am update: No changes to the forecast this morning. Onshore
flow to the north of a backdoor cold front is inundating the
region this morning with low clouds and occasional drizzle.
Mount Pocono remains below freezing, so a light glaze may occur
on trees, but no societal impacts have been observed or reported to
this point. Conditions will change little through the day, with
temperatures unable to rise in the low clouds and maritime
origins of the low-level flow. Expect little to no measurable
precipitation through the daytime hours as the midlevels should
remain relatively dry.

Previous discussion...

High pressure across Quebec/Maine will move offshore today while
weak low pressure slowly moves to near Chicago by evening. A
steady onshore flow will continue across our area thru the day.
This will promote an abundance of low clouds and fog along with
some light rain and drizzle at times. Pops will be greatest
across the northern areas where we have hi chc pops and the pops
taper off s/e to slgt chc across srn DE. Unlike Saturday,
temperatures will be below normal, with highs only in the 40s in
most areas, and a few low 50s over Delmarva.


The overall pattern will not change much tonight with high
pressure north/east and weak low pressure moving closer across
the Great Lakes. The onshore flow will continue and the chances
for more measurable rains will increase tonight. The best
chances will again be across the southern Poconos, Lehigh valley
and north NJ where we will have categorical pops. The pops
decrease back to likely over the Del Valley and cntrl NJ and the
chc pops over south NJ and srn DE. Patchy fog and drizzle will
occur between the bouts of rain. Overall qpf will not be that
great, a few hundredths across the south and up to 1/4 inch up


500 MB: A southern stream weakening short short wave crosses our
area Monday followed by a strengthening northern stream short wave
Tuesday, that closes off, east of New England Wednesday. The next
southern stream short wave probably passes to our south at the
end of the week. Westerly flow should follow for the weekend before
a trough tries to form in the Mississippi Valley early next week.

Temperatures: Calendar day averages Tuesday 10 to 15 degrees above
normal, near 5 above normal Wednesday, nearly normal Thursday
through Saturday.

Forecast basis:  50 50 blended 00z/26 GFS/NAM MOS Monday-Tuesday,
then 00z/26 MEXMOS Tuesday night and thereafter WPC guidance

The dailies...

Monday...Despite winds turning south or southeast,  the question
becomes how much warming can occur with a lack of mixing and
considerable cloud cover.  Showers possible with the short wave
passage and waa, especially early in the day. Dense fog may
form along the warm front and along the water where the
dewpoints exceed the SSTs in the 40s.

Tuesday...Dense fog potential early in the day. Now that we`ve had
almost a day of southerly flow, it may be easier to warm to the
guidance values. There should be a batch of showers and isolated
TSTMs associated with a developing negative tilt northern
stream short wave that will shove all the moisture out to sea at
night with a wind shift to westerly. (EC and to an extent the
GGEM are 6-12 hrs slower but have sided with the previous fcst
for continuity as well as the 00z/26 GEFS which emphasizes low
pressure tracking ewd from northern PA to near POU by 23z/27.

Wednesday...Partly sunny and nice. Northwest wind gusty 20 to
30 mph.

Thursday...Fair. Northwest gusty 15 mph.

Friday...Mostly cloudy with a chance of precipitation,  mostly rain
if it occurs. Lots of uncertainty on track of the event with a
wide ranging set of model solutions , inclusive of a little wet
snow potential near and n of I80. LOW confidence and have
followed WPC guidance. GEFS confluence of the nrn and srn stream
is across northern PA.

Saturday...clearing after any pcpn ends in the morning. Below
average confidence on pcpn occurrence.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

For the 18Z TAFs...General MVFR conditions will continue through
early this evening, likely deteriorating to IFR or possibly LIFR
during the overnight hours. Moderate confidence that light rain
will move in between 03Z and 06Z at KRDG/KABE and by 09Z at
KTTN/KPNE/KPHL/KILG. There may be slow improvement to MVFR after
sunrise, but scattered showers may continue through the morning
hours. Less confidence of precip at KACY/KMIV. Winds generally
east 10-15 kts through early evening with a trend toward S or
SSW late tonight through the morning hours tomorrow.


Monday thru Monday night...Periods of MVFR/IFR in low clouds
and fog, with showers especially to start the day. VFR cigs may
still develop Monday afternoon from around I-95 and points
southeast. South to southwest wind.  Confidence: average

Tuesday...IFR/LIFR st/fog possible in the morning but would probably
become VFR CIGS in the afternoon, with a period of MVFR/IFR
conds possible in shower. During the afternoon-evening, there
is 800J MLCAPE modeled, some instability and a neg tilt short
wave so a tstm is possible. Confidence: average

Wednesday...VFR. Northwest gusty 25 kt.  Confidence: average

Thursday...VFR. Northwest gusty 15 kt. Confidence: average


We will keep the SCA flags as they are on the waters and just
raise the next segment with the 330 am issuance, instead of
waiting until 6 a.m. The onshore flow will continue today and a
gradual building of seas will continue. Scattered showers and
patchy fog expected.


Monday thru Wednesday...Seas may remain elevated Monday into
Tuesday, and the SCA may need to extended into this period.
Quite a bit of uncertainty with regards to winds and seas on
Wednesday, which may be near SCA thresholds. Confidence: average

Thursday...Sub-SCA. Confidence: above average


Onshore flow is expected through Monday morning, with easterly
wind gusts up to 25 MPH at times today. Astronomical tides are
also increasing, coincident with the New Moon this Monday, March
27. The ESTOFS remains most aggressive of the guidance suite,
with near minor flooding for the sunrise Monday high tide along
the DE and NJ oceanfront, and it has has outperformed the other
guidance recently. Both the SIT multi model review and GFS ETSS
are more conservative. ESTOFS trends for positive departures
(surge) appear to be lessening. The wind will also be trending
more parallel (southerly) to the shore by sunrise Monday, so any
minor tidal inundation flood risk remains a low confidence forecast
with no action at this time.


March as a whole for PHL, is still on track to average one half
to 1 degree below normal, despite the warmth of ydy through


MARINE...Small Craft Advisory until 8 AM EDT Monday for ANZ450>453.


Near Term...CMS/O`Hara
Short Term...O`Hara
Long Term...Drag
Tides/Coastal Flooding...Drag
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