Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 160814
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
314 AM EST Fri Feb 16 2018

.SYNOPSIS...
A cold front will move slowly southeast through our area today.
High pressure builds into the mid Atlantic states tonight and
then offshore on Saturday. Low pressure develop just off the
mid Atlantic coast Saturday night and speed away by Sunday
morning. High pressure briefly builds across the area again
Sunday, then offshore Sunday night. A strong warm front will
slowly edge north of the mid Atlantic states early next week,
followed by a cold front late Wednesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A 180 kt 250 MB jet core over NYS at 18z today combined with
height falls at 500 MB (vorticity maxima) passing through n PA
appear to be primary driver for continued periodic showers
today.

Periods of showery rains, heaviest this morning, will end from
northwest to southeast late this afternoon. Turning colder with
light winds becoming northwest and eventually gusty 20-30 mph
near sunset. Storm totals for this event will probably exceed 1
inch in parts of southeast PA. There will be some dense fog
patches in parts of i95 corridor northwestward this morning.
There is a small chance of pcpn ending as ice pellets vcnty
KMPO mid aftn.

Forecast basis was use of multimodels for qpf and near 100%
pops with special consideration of the hrrrx. Temps were a
multimodel but again relying closely on a blend of the 00z/16
GFS/NAM MOS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
Tonight...any leftover rain ends by 8 PM extreme se DE, otherwise
becoming clear and much colder! Gusty northwest winds 15-25 mph
during the evening becoming northerly and diminish after
midnight.

This part of the forecast was a 50 50 blend of the 00z/16
GFS/NAM MOS blended with the colder EC 2m temps.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
this section updates around 4am.

High pressure builds across the area Friday night, before moving
offshore Saturday. This will bring a period of dry conditions
overnight Friday into early Saturday.

The main concern in the long term period is the coastal storm that
will be affecting the area late Saturday into Saturday night. High
pressure retreats to our northeast through the day Saturday, while
an area of low pressure develops across the deep south. The low will
track across the southeastern states during the afternoon, then move
offshore by the evening. It will then strengthen as it moves up the
coast just offshore. The low itself will remain just to our south,
but there is plenty of moisture and lift forecast to move across our
area within the southwest flow aloft as a short wave/vorticity
impulse approaches the area during the evening and overnight.

While the confidence on the low bringing precipitation to the
area is high at this point, there is still some uncertainty on
how much precipitation occurs and how warm the atmosphere gets,
in turn affecting snowfall amounts. The NAM and ECMWF are
slightly north with the low compared to the GFS and Canadian. If
this northward shift were to take shape, the transition zone
would shift farther north than what we have. At this time, we
think that areas north of the I-95 corridor should stay all
snow and could see anywhere from 3-5 inches of snow. Areas
along the I-95/I-295 corridor will be the transition zone and
see 1-3 inches of snow, with sleet and rain mixing in at times
during the evening, before changing back to snow overnight.
The remainder of the area across the coast and southern areas
should see less than an inch as they are the likely areas to
change over to all rain, or a mix of rain and sleet/snow during
the evening hours, before possibly changing back to snow. For
areas along and south of the I-95 corridor, there could also be
a mix of sleet or freezing rain at times during the overnight.
This system is expected to be fairly quick moving, so this would
also limit snowfall amounts as well. For the areas across the
south where the precipitation remains rain, southern New Jersey
and southern Delaware/Maryland, it is possible for some areas of
moderate to heavy rainfall to occur. This could cause some
urban and poor drainage/low lying area type flooding.

Once the low moves to our northeast Sunday morning, the
precipitation will come to an end. High pressure is expected for
Sunday, before building offshore Sunday night. This will bring
another period of dry weather to the area Sunday through Sunday
night.

On Monday, the high pushes farther out to sea, while a warm front is
forecast to lift into the area. As this happens, a couple of short
wave/vorticity impulses are expected to move across the area as
well, which could help produce some light precipitation Monday and
Monday night. Temperatures are expected to be above freezing, except
at the beginning of Monday morning, so precipitation should be all
rain unless it begins early enough Monday.

Tuesday into Tuesday night will likely be dry unless a few isolated
showers develop if any short wave vorticity impulses move across the
area. Wednesday into Wednesday night are the periods more likely to
see rain as a cold front moves across the area. Thursday should dry
out across the area as the front continues to push to our south.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

This morning...Generally MVFR or IFR conds in st/fog/showers
with patchy LIFR in dense fog patches. Light wind trending
northwest.

This afternoon...Generally MVFR or VFR conds in bands of
showers, ending late in the day from nw to se. Northwest wind
increases considerably toward 22z when gusts should become
widespread 15-25 kt.

Tonight...VFR. Gusty northwest winds 15-25kt early become northerly
toward 09z/17 and max gusts diminish to 15 kt or less.


OUTLOOK...

this section updates around 4am.

Saturday...VFR through much of the day. Increasing clouds late.
Rain or snow possible across the south late, with conditions
possibly lowering during the afternoon. Moderate confidence.

Saturday night...Lowering to MVFR/IFR with rain or snow
possible. High confidence on precipitation and lower conditions
occuring, low confidence on specific precipitation types.

Sunday-Sunday night...VFR. Moderate to high confidence.

Monday...VFR early, lowering to MVFR or IFR during the day with
rain possible. Winds may gust around 15 to 20 knots. Moderate
confidence.

Monday night...MVFR/IFR conditions continue, with rain possible
in the evening, and fog/drizzle possible overnight. Moderate
confidence.

Tuesday...Conditions improving to VFR. Southwest winds may gust
around 20-25 knots. Moderate confidence.

&&

.MARINE...
SCA continues as previously advertised. Its mostly for seas
this morning and then northwest wind gusts 25-30 kt late this
afternoon and much of tonight. Thereafter, winds trend north
and gusts diminish to 20 kt toward sunrise Saturday. Fog may be
a marine hazard this morning.

OUTLOOK...

this section updates around 4am.

Friday night...Small Craft Advisory conditions with gusty winds
overnight.

Saturday-Saturday night...Conditions lower below advisory
levels, although winds may gust around 20 knots at times.

Sunday-Monday...Sub Small Craft Advisory conditions expected.

Monday night-Tuesday...Sub Small Craft Advisory conditions
expected, although winds may gust around 20 knots.

&&

.CLIMATE...
Around 4 AM we will add some records that we think may be
approached early next week.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until midnight EST tonight for ANZ450>455.
     Small Craft Advisory until 10 PM EST this evening for ANZ430-
     431.

&&

$$
Synopsis...Drag/Franck/Robertson
Near Term...Drag  315A
Short Term...Drag
Long Term...Robertson
Aviation...Drag/Robertson
Marine...Drag/Robertson
Climate...



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