Scientific Forecaster Discussion
fxus61 kphi 140543
Area forecast discussion
National Weather Service Mount Holly New Jersey
1243 am EST Thu Dec 14 2017
a fast moving low pressure system will move across the area tonight
and then offshore Thursday. A ridge of high pressure will build over
the area later Thursday through Friday. A low pressure system will
move up along the coast Friday night. More high pressure will affect
the area much of this weekend. Another few disturbances will be
across the area beginning later Sunday and lasting into early next
Near term /until 6 am this morning/...
mesoscale update: vigorous but fast-moving snow band moved
through the southern half of the County Warning Area during the past 3 hours.
Snow reports indicate generally 0.5-1.5 inch totals with the
band, mostly in about 1-2 hours. Pronounced dry slot has moved
into the area generally along/south of I-76/I-295 corridor, and
hi-res models show little precip occurring the rest of the night
in this area. Meanwhile, precip to the north looks lighter but
longer-lasting. For now, will keep current advisory as is given
the signal for at least light precip to the north for the next
few hours, but the snow looks mostly done philly southward.
Expect slick roads tomorrow morning, but I suspect there will be
little additional snow. If current trends continue, portions of
the advisory will need to be cancelled early.
Grids update: dew points were way too low (which makes sense
given the very sudden snowfall and shallow dry layer), so needed
to adjust these upward considerably overnight. Spatial
distribution of temperatures is largely based on presence of
snow or not, so frequent updates to temps will be required
through the night. For now, teens in the Poconos and twenties
Short term /6 am this morning through 6 PM today/...
snow tapers off fairly quickly after sunrise Thursday morning, but
not before dropping up to 1/2" of additional snowfall across
northern zones. Behind strengthening and departing low, west to
northwest winds will increase to 15-20 mph with gusts up to 25 mph
starting in the late morning hours. The pressure gradient relaxes
during the afternoon.
Temperatures moderate a bit Thursday afternoon compared to highs
today, but will still be below normal.
Long term /tonight through Wednesday/...
weak high pressure will be across the middle Atlantic region
Thursday night and Friday. It will bring mostly fair and continued
cool weather to the area. Temperatures will remain some 5 to 10
degrees below normal. A quick moving low pressure system will move
just off the New Jersey/Delaware coastal areas Friday night. This could bring some
light precipitation (most likely snow) to parts of southeast New Jersey Friday
evening. Overall, confid in this is low however with the system
looking disorganized and the trends are to minimize any qpf over the
area. We'll just keep the slgt chc pops for now, with this low and
an upper trough crossing the area.
Much of the upcoming weekend will be fair, with high pressure
building over the area. Sunny weather is expected most of Saturday
and much of Sunday before clouds increase later Sunday. Temperatures
will still be a little below normal Saturday before moderating back
to normal levels Sunday. A few showers are possible Sunday afternoon
in a warm advection pattern, but again confid in this is rather
low attm, so we'll just have slgt chc or small chc pops only
for this time.
A better chc for rains (a some higher elevations snows) will develop
Sunday night and last into Monday as a upper trough begin to affect
the area. We'll have chc pops for Sunday night and slgt chc pops for Monday.
We'll carry the low pops into Tuesday as well, with the different
models having varying solutions for this period. Most of the precip
will be rain with the temperatures Monday and Tuesday having
moderated back to above normal by then. A few snow showers
across the southern Poconos are possible however.
Aviation /06z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...IFR in snow but generally VFR or MVFR (cigs) in the
absence of snow for the rest of the night. Best chances of snow
are north of phl, with most snow probably done at phl, ilg, miv,
and Acy. Some light snow/flurries should be present for the next
couple of hours, so kept some mention here, but improved
cigs/vsbys considerably from previous tafs. Winds
light/variable, though may see some stronger south/southeast
winds at times. Medium confidence.
Thursday...potential for residual MVFR cigs between 12z and 15z,
but rapid improvement to VFR is expected. Gusty west or
northwest winds will commence 15z to 22z for most of the area
(speeds 5 to 15 kts with gusts 15 to 25 kts). High confidence.
Thu night thru Fri...VFR.
Fri evening thru Sat morning...mostly VFR. Few showers psbl.
Sat afternoon thru Sunday...mostly VFR.
Sunday night thru Monday...mostly VFR. Slgt chc showers.
Small Craft Advisory conditions expected for the rest of tonight
as winds have decreased. There may be a brief lull in Small Craft Advisory
conditions on Delaware Bay.
Small Craft Advisory conditions will prevail through Thursday. Gusts may increase
close to gale force again as we head into Thursday.
Snow will develop late tonight and into Thursday morning, mainly on
the New Jersey coastal ocean waters, and this will result in visibility
Thu night...Small Craft Advisory conditions early, diminishing. Fair,
Fri thru Fri evening...sub-sca. Chc rain/snow.
Fri night thru Sat...Small Craft Advisory with low end gale psbl. Chc rain/snow.
Sat night thru Sunday...mostly sub-sca. Mostly fair.
PA...Winter Weather Advisory until 10 am EST this morning for
New Jersey...Winter Weather Advisory until 10 am EST this morning for
Marine...Small Craft Advisory until 6 PM EST this evening for anz430-