Area Forecast Discussion
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FXUS61 KPHI 072029
Area Forecast Discussion
National Weather Service Mount Holly NJ
329 PM EST Wed Dec 7 2016
Low pressure in southeastern Canada will move slowly eastward
through the end of the week. The strong cold front associated with
this low will cross the area on Thursday. Large high pressure will
then build in for the early part of the weekend. Then, another
area of low pressure will begin to bring precipitation possibly as
early as Sunday afternoon or Sunday night, with a cold front
crossing the region Monday night or early Tuesday.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Remainder of this afternoon...skies should generally brighten with
the lower clouds thinning out and clearing near sunset. Isolated
nw flow gusts 19 kt as observed.
Tonight...we will presume the subsidence inversion dissipates and
that so too, the low clouds continue their mid afternoon clearing
trend. However, a deck of mid or high clouds should arrive after
midnight from the west. light west to northwest wind. Fcst elements
are a 50 50 blend of the 12z/7 GFS/NAM MOS. Its possible that there
could be isolated frosty fog patches in the countryside in the light
boundary layer flow radiational cooling sitn (low confidence of
occurrence). Low temps above normal.
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Considerable mid and high cloudiness during the morning becoming mostly
sunny and breezy during the afternoon with westerly wind gusts expected
to increase to 25 mph. This cloud wind sequence in assn with the arrival
in the aftn of a ne-sw positive tilt 500 mb trough axis with 12 hr 100-140m
hfc overhead. max temps near normal.
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
A strong cold front will have crossed the area on Thu and high
pres will be building in behind in. Strong nwly flow will result
Fri into Sat, making it feel colder.
In the nwly flow, there cud be some snow shwrs mainly n on Fri,
but otherwise dry wx is expected thru Sun.
The aforementioned high pres will move off the coast durg Sun and
low pres will then begin to advance twd our region from the w.
There are mdl diffs with this sys. The GFS develops a low acrs IA
and moves it ewd acrs the Grtlks and into srn Canada. The wmfnt
assocd with this low will bring precip to the area beginning Sun
aftn, with the cdfnt Mon mrng.
The ECMWF develops a much stronger low over the srn plains, and
moves it newd int the OH Vly. By Mon AM. Due to the stronger low,
it is slower with its motion and the onset and ending time of
precip. The ECMWF doesn`t bring much precip before Sun night, with
the bulk of the precip on Mon before CFP late Mon.
The CMC soln is somewhere in the middle. So, while confidence is
lower than average on the actual timing, we do know that precip
will develop during the latter half of Sunday and continue for at
least the first portion of Monday.
Over northern and wrn areas, temps will be cold enough for at
least some wintry precip, some of that will be dependent on the
track of the low. The ECMWF is also a significantly warmer soln.
Most other areas will se all Or mostly rain, but the details on
this one will need to be ironed out as we get closer.
High pres returns for Tue. Temps look to be below nrml thru most,
if not all of the pd. They cud return to close to nrml around
Monday, before dropping again with the next CFP.
.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Remainder of this afternoon...mvfr cigs in the process of advecting
eastward to leave behind sct clouds aoa 3000 ft. Wind generally
northwest with gusts under 20 kt.
Tonight...VFR. W-NW winds will be light (under 10 kt).
Thursday...VFR multi layered cigs aoa 10000 ft during the morning-
midday with chance of an hour of cigs down to near 6000 ft during
midday with isolated sprinkles or flurries mainly higher terrain
of e PA. Then becoming VFR clear late in the day. Westerly wind
increasing, with gusts 22-28 kt during the afternoon as the caa
process develops more earnestly.
Thu night-Sat...Mainly VFR, but some local MVFR psble each mrng.
NW wind cud gust wo to 25 kts on Fri. Moderate to High confidence.
Sun and Mon...VFR early, lowering to MVFR then IFR by the
afternoon and overnight. RA and SN psbl Sun into Mon. Low to
Moderate confidence on the timing of precip.
SCA seas has been extended since easterly swells in the wake of
last nights short gale are slow to decrease. Guidance continues to
lower these swells/seas too fast. Pls see MWW or the CWF.
Eventually the seas should subside below the 5 ft sca criteria
Thursday...anticipating the need for a westerly flow cold air advection
small craft advisory for many of the waters Thursday afternoon.
Have begun the process with a DE Bay SCA.
Thu night-Sat...SCA conds expected in strong nwly flow. Wind could
gust to 25 to 20kts. There is a small chance of gales Thu night
into Fri behind the front.
Sat night-Sun...Sub-SCA conds are expected, but wind will increase
to just below SCA by later Sun.
MARINE...Small Craft Advisory for hazardous seas until 4 AM EST
Thursday for ANZ452>455.
Small Craft Advisory for hazardous seas until 11 PM EST this
evening for ANZ450-451.
Small Craft Advisory from noon Thursday to 7 AM EST Friday for