Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 221917

Area Forecast Discussion
National Weather Service Mount Holly NJ
317 PM EDT Thu Mar 22 2018

High pressure in Canada will very slowly build south into the
northeastern USA by Saturday. Low pressure over the southern
Plains on Saturday will move off the Carolinas Sunday morning.
Thereafter, it will become an intense and large storm meandering
over the western Atlantic early next week, held just far enough
offshore by the high pressure system to our north.



Storm over... and probably final PNS is posted. Map to post 330
PM and is our best presentation today for the reality that
occurred Tue aftn-Wed night. Dual nor`easter imo performed, on
a scale 1 to 5 scale, not quite what I expected which was a 5.0
for late March. It came in ~4 (winds down 5 kts from expected,
CFlooding was down 1 category from expected and snowfall
probably about 4" less than expected). STILL, this was a major
winter storm for our area.

On the map, you may want to take a close look in the rural
hinterland of Sussex County NJ where elevations vary from
roughly 400 ft to ~1800 ft. The elevated northwest corner was
spared...less than an inch. The se part of the county up to 10
inches. The gradient between Sussex and Newton NJ...about 7
inches in 12 miles (similar elevation),a 20 minute drive at
most. The gradient to elevated Highland Lakes, even greater.

Models had a sharp northern cut off...we just were never
sure where it would be. While this storm produced... it was
never completely organized as one mammoth storm that we
sometimes see spin up just south of LI.

A nice afternoon is in progress for cleaning up. Gusty northwest
winds to 25 mph with variable amts of cirrus. Visible imagery
shows the extent of the snowcover from ydys storm.

Tonight...Cirrus early then clear late. Temperatures tonight
are expected to be lower than what we saw this morning, with
lows tonight forecast to be generally in the 20s across the
region, or about 5 to 10 degrees below normal. As a result, any
water on the roads from snow melt during the day could freeze
leading to slippery conditions on area roads tonight into early
Friday morning.


Friday...A cold core mid level low (-18C at 700MB) and a 90M
12 hr 500mb HFC , digs quickly southeast over the region
through the mid and late aftn. This will result not only in
increasing low clouds, but also scattered rain and snow showers,
especially along and north of the I-78 corridor through the
afternoon. BTV snow squall parameters appear to be met so we`ll
be on the lookout. Most models are dry, and moisture could be
very limited with little chance for moisture advection before
this event. However, lower resolution models tend to underforecast
precip with these types of clipper systems, so we have
mentionable pops basically I78 north. Max temps 30s high terrain
northwest, 40s elsewhere or about 10 to 15 degrees below normal.

Northwest wind gusts 20 MPH.


Did not spend much time on the forecast beyond Friday to focus
on wrapping up the winter storm event. From the previous
discussion...Another strong vort max moves southward from
eastern Canada on Saturday as a separate vort max moves west-
to- east through the central U.S. and interacts with the digging
perturbation. Attendant surface low in the central plains
Saturday looks to be shunted southward somewhat as it tracks
into the Ohio/Tennessee Valleys. Just how far south is a
challenging question, with considerable disagreement among the
operational guidance. The GFS looks especially suspicious,
though, given its very progressive evolution of the northern-
stream vort max. The 12Z CMC/ECMWF are slower and (as a result)
have the track of the southern- stream system a little farther
north. This may give the Delmarva Peninsula a chance for some
precipitation Saturday night and Sunday. Additionally, there are
some indications that as the surface low intensifies off the
coast that wraparound (light) precipitation may affect the
eastern CWA on Sunday (aided by the passage of the main
northern-stream vort max). Cannot discount chances of rain
and/or snow for much (if any) of the area during this period, so
kept slight-chance PoPs in the grids. If the southward-
deflection of the southern-stream system occurs later than
anticipated, this may bring somewhat heavier precipitation into
the area (especially Delmarva). A low- confidence forecast
exists for this period, to be sure.

Strong ridging develops early next week as the strong cyclonic
vortex meanders eastward off the Atlantic coast. This should bring a
prolonged dry period to the area along with a warming trend. A
system may affect the region by mid to late week, but models have
large timing differences. Generally included slight-chance to low-
chance PoPs on Wednesday for now, but temperatures fortunately look
more seasonal by then.


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

Remainder of this afternoon...VFR cirrus. NW winds 10-15 kt
with gusts up to 30kt. High confidence.

Tonight...VFR with only high clouds (15000 AGL or higher) and
those clear after 09z. Northwesterly winds near or below 10 KT.
High confidence.

Friday...VFR to start. Potential for MVFR or low VFR CIGs and
rain/snow showers, especially vcnty of ABE-TTN during the
afternoon. Northwest winds 5 to 15 kts with potential for gusts
to 20 kts or so. High confidence.


Friday night and Saturday: VFR with northwest winds 5 to 15
kts, potentially lighter during the night. High confidence.

Saturday night and Sunday: Some potential for sub-VFR conditions
with light rain and/or snow. Winds north to northeast under 10 kts
Saturday night and 10 to 20 kts on Sunday. Very low confidence.


Today and tonight...nw winds gusty 20-30 kt this afternoon and
15-25 kt tonight. Atlantic seas will continue to slowly subside.
Seas continue to run above the NWPS forecast by 2 ft. So its
mainly an SCA this aftn all waters, then into tonight for the
Atlc waters.

Friday and Friday night: May see a lull in winds on Friday
morning, but they should increase again by afternoon evening to
advisory criteria.

Saturday and Saturday night: Sub-advisory winds/seas expected. A
slight chance of rain and/or snow late, especially near/south of
Delaware Bay.

Sunday: Advisory-level northeast winds expected, with some potential
for gales (though this is low confidence). Some potential for rain
and/or snow.


RTP water equivalent pcpn: MANY stations were set to missing as
the pcpn amounts were far too low as melted by the system.

What we KNOW.

PHL: today is the 18th consecutive day of below normal temps in
PHL. Looks like we could add 5 more to the string.

There were several record daily maximum snowfalls set yesterday,
March 21st. This occurred at Philadelphia, Wilmington and
Allentown (which smashed their daily record). Atlantic City just
missed the daily snowfall record.

Location        Record for 3/21     Actual Snowfall 3/21/18
--------        ---------------     -----------------------

PHL             4.7" (1932)          6.7"
ACY             5.9" (1889)          5.7"
ILG             5.4" (1964)          6.7"
ABE             4.3" (1964)         13.2"

ACY 1 day snowfall of 5.7" ranks as the 7th highest March,
single day total.

Philly did not place top 10 1 or two day.

Wilmington 6.7 was the 6th highest 1 day total in the historical
database and the two day 8.1 was tied for 7th highest.

Allentown 13.2 was the 4th largest single day total behind the
16.7 3/13/93
16.5 3/20/58
13.8 3/3/60

ABE Monthly 20.7 ranks #4 behind
1958 30.5
1993 21.6
1960 21.3

ACY monthly 9.2 ranks #5 behind
1969 17.6
2014 15.6
1960 13.4
1956 12.7

ILG monthly 20.3 ranks #2 behind
1958 20.3

PHL monthly 15.2 ranks #2 behind
1941 17.2

I tend to remember everything (at least vaguely) after 1950.

Yearly July 1-June 30 snow year ACY 33.7 ranks # 9 well behind
the record of 58.1 in 2010.

What is as yet unconfirmed and may not be for several days...

A new NJ state record for the month of March, may have been set
this morning. This is as yet unconfirmed so we`re not saying
RECORD, but near record works for me...something else may turn
up in the database that was overlooked. Jefferson Township 11.1
inches ydy (1.03 w.e) raised the monthly total to 44.3 inches.
So far the record, as we know it, is 43.0 in 1958 Canistear
Reservoir. UNOFFICIAL but as fyi... but impressive if you like


MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ450>455.
     Small Craft Advisory until 6 PM EDT this evening for ANZ430-


Near Term...Drag  317
Short Term...Drag 317
Long Term...CMS/Johnson
Aviation...CMS/Drag 317
Marine...CMS/Drag 317
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