FXUS61 KPHI 160904
Area Forecast Discussion
National Weather Service Mount Holly NJ
404 AM EST Sat Feb 16 2019
A low pressure will remain to the south of our area as it rides
along a boundary stalled well offshore. Another area of low pressure
will move across the region later Sunday into Monday followed by
high pressure building across to the north of the area Tuesday. A
complex low pressure system will move into the region Wednesday into
Thursday. Another area of high pressure will build across the Mid-
Atlantic on Friday.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A low will develop and propagated east along the front which arrived
in our region last evening (now well south of the region). The 00Z
runs of most of the operational models continued the trend further
south with the precipitation shield associated with this low.
Consequently, lowered PoPs even further. Still have a slight
chance/chance mention in southern Delaware and adjacent MD counties
as well as Cape May, but even there I am not confident will see any
precipitation. This is especially true considering the significant
dry air advection that has occurred behind the front. Dew points
quickly dropped from the mid 40s ahead of the front to the lower 20s
and teens behind the front.
Cold air advection hasn't been as significant as the dry air
advection overnight. None the less, with the ridge building south
through the day, and continued northerly/northwesterly flow, still
expect highs to be 15 to 20 degrees lower than Friday's highs.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Dry conditions, mostly clear skies, and relatively light winds will
mean efficient radiational cooling conditions across the region
overnight. Therefore, expect lows in the teens and 20s across the
region. Some high clouds may begin to advect in very early Sunday
morning, in advance of the next system, but will likely not have a
significant impact on morning temperatures.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
A low pressure system will cross through the Tennessee Valley on
Sunday and into the Mid-Atlantic Sunday night. While there are two
surface lows present on the models during the this time, the
southern low looks to be the more dominant of the two and the one
that looks to be the driver for our weather. The center of the low
remains just to the south of the forecast area. With colder air
residing to the north of the system and limited warm air aloft, we
are more likely to see mostly snow, especially to the north of west
of the I-95 corridor. However, the soundings are marginal in some
cases with some having more warm air aloft than others, mainly
through the I-95 corridor, and that leads to less confidence that we
see straight snow through this area. Kept the mention of a wintry
mix of snow/rain/sleet as it remains a possibility, but could be
limited to fairly narrow area. Snow amounts will largely be confined
to the I78 corridor and points north, with only up to an inch or two
expected. The low moves offshore and away from our area on Monday
and we should start to dry out through the day.
High pressure will then build down across the midwest and into the
eastern United States For Tuesday, which will give us a brief
respite between systems. The high will start to slide across to the
north of the region and is expected to remain dry so we keep any
mention of precip out during the day.
As we head into Tuesday night, the high shifts to the northeast of
the region, signaling a decent cold air damming setup. The flow
starts to turn more to the south and southeast allowing for warmer
and moister air to flow into the lower levels. While precipitation
may occur Tuesday night as warm air advection and lift increases, it
may be slowed down by the presence of the high to the north. Even
knowing that, it seems likely that some precip will work its way
into the area from the south and pops will gradually increase
through the overnight hours.
Wednesday and Thursday look like they could echo the mess of this
past weeks storm. A surface low will travel up from the Gulf coast
states and up into the Great Lakes with a secondary low developing
near the Mid-Atlantic coast. The initial low remains to the west of
the area as the cold air damming in place prevents it from making
much headway into our area. This leads way to the second low
developing near or just south of our area. With the cold air
remaining in place, we are primed for overrunning to occur as the
warmer air to the south tries to override the colder air trapped in
the lower levels. This complicates the forecast as it tends to lead
to multiple precipitation types, and in many instances can signal a
risk for accumulating ice and snow. While the details may not all be
worked out at this point for this system, it does appear that parts
of our area will have the potential for a sloppy mess and travel may
become hazardous and difficult.
The low moves quickly offshore Thursday night and allows for high
pressure to build in from the west for Friday. The high slides
across the region and offshore later in the day. Another system may
approach our area later Friday but the high appears to block it, in
a similar way to the midweek storm. However, with so much to
transpire before the end of the week, there is time for the models
to work out the kinks for the next system.
.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Today...VFR conditions are expected with only few to scattered
high clouds. Northwest to north wind 5 to 10 knots. High
Tonight...VFR conditions expected with light (generally 5 kt or
less) northerly wind. High confidence.
Sunday...Mainly VFR conditions expected. Light northerly winds
generally light and variable, becoming east to southeast. High
Sunday night...Snow and/or wintry mix will lower conditions to
MVFR/IFR. Winds will be generally light and variable. Moderate
Monday...MVFR conditions linger through Monday morning before
clearing out Monday afternoon. West to northwest winds around 10 to
15 knots. Moderate confidence.
Monday night through Tuesday...Mainly VFR conditions expected.
Northwest to north winds less than 10 knots. High confidence.
Tuesday night through Wednesday...VFR will become MVFR by Tuesday
night and then become MVFR/IFR as snow, rain, and a wintry mix move
through the terminals. Northeast to east winds around 10 knots or
less. Low confidence with respect to precipitation type.
Winds and seas are expected to remain below Small Craft Advisory
criteria today and tonight. Winds will be shifting to northwesterly
shortly and should remain northwesterly or northerly, but with
speeds well below SCA thresholds.
Sunday through Tuesday...Sub-Small Craft Advisory Conditions are
expected on the area waters.
Wednesday...Increasing east to northeast winds with gusts up to 25
knots possible. Seas will build from 2 to 4 feet during the day to
around 3 to 5 feet Wednesday night. A Small Craft Advisory will
likely be needed.
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