Area Forecast Discussion
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FXUS61 KPHI 071451
Area Forecast Discussion
National Weather Service Mount Holly NJ
951 AM EST Wed Dec 7 2016
Low pressure off the mid Atlantic coast will move out to sea today
while another area of low pressure drifts through southeast Canada.
This low will continue to slowly drift eastward through the end of
the week and move offshore of the Canadian maritimes by Friday and
Saturday. With high pressure to our west, a strong west to
northwest flow will remain through the end of the week. High
pressure briefly affects the area Saturday night. An area of low
pressure is forecast to move north of the area Sunday into Sunday
night, bringing a cold front across the area.
.NEAR TERM /THROUGH TONIGHT/...
930 AM ESTF: Cleaned up the drying process a little and slowed down
the temp rise this morning but back on the previous fcst this afternoon.
Measurable drizzle for parts of NJ will end from west to east by
midday. Eastward moving trough near 950 mb will probably help dissipate
the westward inverted trough from the mid Atlc coastal low. The result:
Low clouds and drizzle gradually dissipate to cigs near and above
3000 ft. Some clearing along and south of I-78 should occur this
High temperatures will generally be in the 45-50F range with cooler
spots in the higher elevations of NE PA and NW NJ (mid 30s to lower
40s) and warmer spots in S DE and E MD (low 50s).
Tonight...An incredible 1054 mb surface high over the northern
Rockies is forecast to build southward into the Great Plains
tonight. An extension from this high will ridge eastward toward
the Mid- Atlantic region tonight. Meanwhile, an area of low
pressure will move across James Bay and into northern Quebec
tonight. This system`s cold front advances southeastward into the
Great Lakes region.
The pressure gradient is modest but it may still be strong enough to
produce a light W-NW across most of the area. However, the sheltered
valleys will likely see the boundary layer decouple and temperatures
dropping rather fast after sunset. Accordingly, we`ll likely see a
decent spread in temperatures tonight depending on location. High
clouds associated with a strong upper-level jet streak are expected
to move into the region from SW to NE overnight, but the impact on
radiational cooling is questionable. A blend of the MAV/MET was used
to make the min temperature forecast, but also used some of the
mesoscale model guidance (RGEM, NCEP WRF ARW/NMM) to highlight the
.SHORT TERM /THURSDAY/...
Considerable mid and high cloudiness during the morning becoming
mostly sunny and breezy during the afternoon with westerly winds
gusts expected to increase to 25 mph.
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
On Thursday, an area of low pressure will slowly be moving across
eastern Canada, before reaching the Canadian maritimes Friday into
Saturday, while high pressure remains across the central part of
the country. This will keep a steady west to northwest flow across
the area. A broad trough aloft will remain across the east coast,
with an elongated vorticity impulse moving across the area
Thursday and a weaker impulse moving across the area Friday. There
is not a lot of moisture across the area Thursday as it`s forecast
to remain northwest of the area, but the strength of the vort max
and the surface winds may help carry some flurries/sprinkles
across the area during the day. On Friday, the short wave is
weaker, but there is more enhanced low level moisture and steep
low-mid level lapse rates during the day, so there could be even
more widespread showers or flurries/sprinkles across the area.
Especially across our northwestern areas. By Saturday, another
short wave/vorticity impulse is forecast to move across the area
as the northwest flow begins to weaken as the low lifts farther
away and high pressure begins to approach from the west. There
will continue to be steep low-mid level lapse rates during the
daytime combined with some enhanced moisture, especially across
the northern areas. Therefore there will continue to be a chance
for some isolated showers/flurries across the northern half of the
area. High pressure briefly affects the area Saturday night,
providing dry conditions. Thursday through Saturday will be a cold
and windy period, with Friday being the windiest, and Saturday
being the coolest of the 3 day period.
On Sunday night, an area of low pressure is forecast to move
north of the area, pulling a cold front across the region. Another
low pressure is forecast to develop along the boundary, although
the GFS and ECMWF differ on where they develop the low. The GFS
develops this secondary low north of the area, while the ECMWF
develops it to our south. Sunday night looks like the most likely
period for precipitation, but it could linger into Monday if the
low does develop around or south of the area as the ECMWF
indicates, so we`ll keep a chance of precipitation into Monday.
Temperatures will be cold enough for portions of the area to
experience wintry precipitation. The exact timing and placement of
wintry precipitation is still to be determined, but as usual, the
most likely areas for snow would be the northern half of the area.
Dry conditions are currently expected for Monday night into
Tuesday as high pressure is forecast to briefly build to our south
and nose its way into our area. The GFS and ECMWF are showing the
potential for a coastal low to develop on the old frontal boundary
to our south by next Wednesday, which could bring some
precipitation to the southern half of the area. With cold
temperatures, it`s possible that a period of snow could develop
for the southern portions of the area.
.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Rest of today...IFR conditions in drizzle/fog many of the TAF sites
at 1445z will improve from southwest to northeast late this morning,
first to mvfr cigs and eventually to VFR cigs this afternoon. Wind
generally northwest with gusts under 15 kt.
Tonight...VFR. W-NW winds will be light (under 10 kt).
Thursday...VFR multi layered cigs aoa 10000 ft during the morning
becoming VFR clear by late in the day. Westerly wind with gusts
20-28 kt during the afternoon.
Thursday night-Saturday...MVFR CIGS may be possible each morning
before lifting to VFR during the day. Scattered showers or
flurries/sprinkles are possible during the daytime of each day
which may temporarily lower conditions. Gusty west to northwest
winds 15- 25 knots, strongest winds Thursday and Friday.
Sunday...VFR early, lowering to MVFR then IFR by the afternoon and
overnight. Rain or snow possible late in the day and overnight.
SCA converted to SCA seas with a caveat for isolated 25 kt gusts
this morning near the entrance to DE BAY. Seas are still running
well above predicted in response to last evenings gale and the
fcst adjustments were made. Pls see MWW or the CWF.
Seas subside this evening.
Thursday...anticipating the need for a westerly flow cold air
advection small craft advisory for many of the waters Thursday
Thursday night-Saturday...Small Craft Advisory levels winds expected
through the periods with west to northwest winds gusting 25-30 knots.
Saturday night-Sunday...Winds expected to drop below Small Craft
Advisory levels, but pick up again late Sunday.
MARINE...Small Craft Advisory for hazardous seas until 10 PM EST this
evening for ANZ452>455.
Small Craft Advisory for hazardous seas until 6 PM EST this
evening for ANZ450-451.
Near Term...Drag 950A
Short Term...Drag 950A