Scientific Forecaster Discussion
fxus61 kphi 200829
Area forecast discussion
National Weather Service Mount Holly New Jersey
329 am EST Mon Nov 20 2017
high pressure over the southern Mississippi River valley will build
east, then move off the mid-Atlantic coast tonight. A cold front
will approach Tuesday night and pass through the area on Wednesday.
At the same time, low pressure over the southeast portion of the
country will approach the mid- Atlantic and move out to sea. High
pressure will build through the area by the end of the work week. A
cold front is expected to pass through on Saturday, with high
pressure gradually building east early next week.
Near term /until 6 PM this evening/...
impressive vort Max moving through the region at this time with deep
northwesterly flow very effectively streaming sufficient moisture
from the Great Lakes southeastward into northern portions of the County Warning Area
the past few hours. Several snow showers have developed in this
regime, with even some bursts of moderate snow and brief, gusty
winds with some of them given the favorably deep low-level
thermodynamic profiles and strong winds aloft. The snow showers are
now on the wane, mainly confined to northern New Jersey as of 2:30
am. Another streamer is moving into the southern Poconos, so a
couple more hours of occasional snow showers are expected. However,
as the lift diminishes thanks to the departing wave, should see snow
showers mainly confined to areas farther north/west of the County Warning Area by
daybreak. As such, I have no pops in the forecast after 8 am.
Surface high pressure should progress eastward to the Carolinas this
afternoon, with midlevel flow becoming somewhat more zonal upstream
of the vort Max. A fairly strong north-south pressure gradient will
exist today as a strong surface low meanders in the maritime
provinces. Thus, another breezy day should be expected, albeit far
less windy than yesterday.
Clouds have been stubborn to dissipate in the northern/western County Warning Area
as the low levels are dry enough (and mixing strong enough) to
maintain a scattered to broken deck around 4000-6000 feet. However,
as deep-layer descent increases today, there should be noticeably
clearer skies than yesterday. Temperatures will be below average as
cold air advection continues this morning before winding down later
today. Expect highs around 5 to 10 degrees below seasonal averages.
There is very good agreement among the statistical guidance, so used
a blend for Max temperatures.
Short term /6 PM this evening through 6 am Tuesday/...
the surface high will progress offshore to our south tonight, and
midlevel flow will become more southwesterly as a vort Max digs
southeastward into the upper Midwest by 12z Tuesday. Low-level warm-
air advection should be in full swing by the overnight hours, and
this will prevent much of a fall in temperatures, despite the
lighter winds and mostly clear skies expected.
Once again, statistical guidance is in good agreement regarding
temperatures, so a blend was used for lows. Generally expecting
readings around average. Temperatures may actually flatline
relatively early in the night as warm-air advection increases via
increasingly more favorable low-level trajectories.
Long term /Tuesday through Sunday/...
high pressure over the mid-Atlantic is expected to move off the mid-
Atlantic coast on Tuesday. Return flow sets up, and highs on Tuesday
will be about 3-5 degrees above normal, topping off in the 40s in
the Poconos, otherwise in the low to mid 50s north and west of I-95,
and near 60s in the Delmarva and southern New Jersey. S to SW winds increase
Tuesday afternoon to 15-20 mph with gusts up to 30 mph.
Low pressure is expected to develop over the Gulf Coast on Tuesday,
move off the southeast U.S. Coast Tuesday night, then approach the
mid-Atlantic coast before moving out to sea on Wednesday. A cold
front will pass through the region Wednesday afternoon. Based on
latest model guidance, will continue a swath of likely pops across
southern Delaware and southeast NJ, and chance pops for most areas south
and east of the fall line. Cooler temps will move into the Poconos
Wednesday afternoon, but stronger cold air advection will not get underway until
Chilly high pressure builds through the region Thanksgiving day
with temperatures 6-8 degrees below normal. Highs top off in
the mid and upper 30s in the Poconos, otherwise in the low to
High pressure reestablishes itself over the area Friday with
highs a few degrees warmer than Thursday.
Low pressure passing well north of the region will drag a cold
front through the region on Saturday, and then low pressure remains
over eastern Canada through next weekend even as surface high
pressure begins building in from the west. Unsettled weather
Aviation /09z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Today...VFR with west winds increasing to 10 to 15 kts with gusts to
25 kts. Confidence above average.
Tonight...VFR with west winds decreasing quickly after sunset and
likely becoming southwesterly with time. Speeds generally below 10
kts. Confidence above average.
Tuesday...VFR. SW winds 15-20 knots with gusts up to 25 knots Tuesday
Tuesday night and Wednesday...mainly VFR. Rain possible south
and east of I-95 Tuesday night through Wednesday morning with
MVFR or lower conditions. SW winds 5-10 knots become northwest Wednesday
afternoon and increase to 10-20 knots.
Wednesday night and Thursday...VFR. Northwest winds gradually
diminishing. A storm system is currently expected to remain
offshore. Forecast confidence: medium to high.
Friday...VFR. Northwest winds 5-10 knots.
Saturday...VFR early...then MVFR or lower conditions possible in
rain showers later in the day. SW winds 10-15 knots.
Gale Warning was dropped, as gusts above 34 kts have not been
observed in the past couple of hours. Trend with the winds will be
downward today, but Small Craft Advisory conditions will continue
through the morning for Delaware Bay and the Delaware coastal waters
and through much of the day off the New Jersey coast.
There will likely be a brief lull in winds off the New Jersey coast
late this afternoon and this evening before southwest winds pick up
again overnight. For this reason, kept the Small Craft Advisory
going through Monday night.
Tuesday and Tuesday night...brief lull in Small Craft Advisory conditions through
Tuesday morning. Otherwise, 25-30 knots wind gusts, primarily on the
ocean waters, may possibly over lower Delaware Bay Tuesday afternoon.
Wednesday...lull in Small Craft Advisory conditions possible Wednesday morning.
Otherwise, winds shift to the northwest and increase to 15-20 knots with
25-30 knots gusts.
Thursday through Saturday...sub-sca conditions expected.
Marine...Small Craft Advisory until 6 am EST Tuesday for anz450>453.
Small Craft Advisory until 1 PM EST this afternoon for anz430-