NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Feb 18, 4:35 AM EST, 1 hour 10 minutes earlier.
Area forecast discussion, Feb 18, 4:35 AM EST, 1 hour 10 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
435 AM EST Fri Feb 18 2022
.SYNOPSIS...
A strong cold front will cross the zones approach the area
overnight and pass through our region early Friday morning. A
clipper system will pass over of the region on Saturday, then
high pressure returns to close out the weekend. Another area of
low pressure looks to affect the region Tuesday, possibly
followed by another on Wednesday.
&&
.NEAR TERM /THROUGH TODAY/...
The strong cold front is roaring into the region this morning,
running, as these systems often do, a little ahead of schedule.
Winds overnight have generally behaved and if anything have run
lighter than forecast overall in the southerly flow, not surprising
due to a low level inversion being present. They have started to
pick up more recently however, and will remain strong from the south-
southwest ahead of the front. Rainfall has also not been much of a
factor with everything pretty much going according to forecast in
that department and no hydro concerns.
The most pressing forecast item is growing concern for a period of
enhanced winds along and just behind the cold front over the next 4
to 6 hours. We'll see a couple of things transpire in the coming
hours. First, along and just ahead of the front, one or two lines or
broken lines of low topped convection will move through. There
remains a low risk for a rumble of thunder with that activity,
though that would be highly isolated at best. But the showers will
likely contain gusty winds. From there, winds will shift around to
west-northwest. A strong pressure rise couplet will pass through the
area behind the front, in the neighborhood of 8 to 10 mb in 3 hours.
As winds shift, the low level inversion will also rapidly break as
we mix out. There is strong agreement in the hi res guidance for a 1
to 3 hour period of higher winds from about 5AM to 8AM this morning
due to the pressure rises and rapid steepening of the low level
lapse rates. Gusts of 45 to 55 mph, and locally a little higher, are
likely. Did contemplate an upgrade to a High Wind Warning, but the
expected values are still marginal versus criteria, and we are at a
time of year where wind impacts tend to be mitigated due to bare
trees. And duration of the higher gusts will be limited. Still, a
few instances of tree damage and power outages can be expected. As
the pressure rises subside, winds should steadily diminish towards
mid to late morning.
Once all this commotion passes, we should transition to more
tranquil conditions for most of the day. Rapid clearing is expected
behind the front with dry weather expected once it moves through.
Northwest winds will remain on the breezy side into mid-afternoon,
but not nearly as strong as early this morning, and they will
subside further by late this afternoon. Temperatures will be diving
behind the front, from the unseasonable 50s and 60s presently down
into the 40s. That transition will happen this morning, and
temperatures should pretty much then flatline for the afternoon.
Winds will drop off further tonight, likely going near calm. With
mainly clear skies in the wake of the cold front, it will be a cold
night. Lows in the upper 10s to low 20s are anticipated.
&&
.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
An impressive deepening mid-level wave will be heading southeast
across the Great Lakes region Saturday morning with a rapidly
tightening pressure gradient. Ahead of the mid-level wave, the
region will rapidly become warm sectored with forecast soundings
still indicating impressive mixing of the PBL. The latest
forecast soundings from the GFS show mixing to around 800 MB
forecast, while the NAM continues to show mixing to around 700
MB. The general feeling is that the mixing will initially be to
around 850/800 MB out ahead of the wave. As this mixing starts
to occur Saturday morning, almost immediately as the sun rises,
gust of 30 to 35 MPH are forecast. This strong mixing, will also
promote a rapid rise in surface temperatures Saturday. Lows
Saturday morning will be in the lower 20s, and by 10 AM
temperatures into the 40s appears likely.
By Saturday afternoon, the mid-level wave will be moving
overhead with a 180 m height fall/ rise couplet forecast. The
latest run of the GFS also continues to forecast an impressive
tropopause fold moving overhead, with the 1.5 PV surface down to
around 600 MB Saturday afternoon. As the fold and surface cold
front sweep through the region, mixing will rapidly increase to
around 750 MB with surface winds increasing in speed. Gusts of
45 to 55 MPH appear possible during this time frame. These gusts
are further supported by ~6 MB pressure falls behind the front.
Winds will then slowly start to relax Saturday evening, but
gusts will likely continue though as lapse rates remain steep.
As the cold front moves through the region, there will be a
chance of precipitation. The highest chance of precipitation
currently exists near and north of I-78. This will likely come
in the form of all snow, but some rain could mix in closer to
the urban corridor. The steep low level lapse rates with
transient saturation in the DGZ will promote the potential for
some snow squalls. Towards the urban corridor and south high
temperatures will likely be in the mid 40s. These highs well
above freezing will make any precipitation (that does transition
to snow) difficult to stick to the pavement. North of I-78
temperatures will likely remain in the 30s, where there could be
impacts from a quick burst of snow (followed by temperatures
rapidly falling). This potential will need to be monitored
closely.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
The overall synoptic pattern in the long term will generally be
governed by a long wave trough axis centered over the western
United States and a sub-tropical ridge centered over the
southeastern Gulf of Mexico. Most of the period will feature
above normal temperatures with dry conditions giving way to
chances of precipitation Tuesday into Wednesday. Towards the
end of the extended period, below normal heights will slowly
head east, as ridging across the Gulf of Mexico becomes
surpressed.
Surface high pressure will be centered across central VA Sunday
morning as the core of the ageostrophic convergence moves
overhead. The latest set of probabilistic guidance is slightly
slower with the progression of the surface high pressure, and
therefore keeps the core of the coldest 850 MB temperatures
overhead a bit longer. This means temperatures will be solidly
below normal Sunday, with guidance now showing upper 30s for
high temperatures. Dry conditions expected with clear skies.
On Sunday night, a potent upper level wave will be diving
southeast out of British Columbia helping to reinforce the long
wave trough axis back west. As this occurs, heights will rise
across the east coast of the United States, allowing high
temperatures to surge well into the 50s. Monday looks to be the
nicest day of the week, with dry conditions and sunny skies in
the forecast.
By Monday night, the upper level low that was off the coast of
California will get shredded by the approaching deepening wave
to the north. Fragments of the leftover closed low will eject
northeast around the top of the sub-tropical ridge. This will
lead to increasing clouds late Monday night with precipitation
moving into the region Tuesday morning. Precipitation will then
continue through the day Tuesday as multiple rounds of PV cross
the area. The main wave axis will be located over the Ohio River
Valley Tuesday afternoon with surface low pressure heading
northeast across the St Lawrence River Valley. One thing of note
here are the forecast rainfall totals. Latest run of the NBM
continues to advertise 1 to 2" of rainfall from a Tuesday
through Wednesday period. These type of totals could produce
some issues across the region depending on how quickly and where
it falls. A cold front will then cross the region Wednesday
evening, ushering in cooler and drier weather.
&&
.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Through 14z... A frontal system continues to bring rain showers to
the region. Mainly VFR conditions have prevailed so far. It still
looks like MVFR should become more prevalent for the rest of
tonight, but any IFR looks limited at the most, and some terminals
may stay entirely VFR. Gusty south-southwest flow continues ahead of
the front and will persist through about 10z. Beyond then, a wind
shift to west-northwest is expected with the frontal passage. Winds
will likely increase even more for a time just behind the front,
with gusts around 40 kt and locally a little higher for a couple of
hours. Rapid clearing should also take place behind the front with
any areas of sub-VFR quickly becoming VFR once the front passes.
High confidence in overall trends, moderate confidence in timing and
flight category details.
Rest of today... VFR. Northwest winds around 15 kt with gusts 25 to
30 kt, but steadily diminishing by mid to late afternoon. High
confidence.
Tonight... VFR. Light west-northwest flow lingering initially, but
winds turning light and variable or calm by 06z. High
confidence.
Outlook...
Saturday through Saturday night...A fractured VFR cloud deck can
be expected through the day with cigs remaining VFR. Southwest
winds in the morning will veer around from the west as a surface
cold front approaches the terminals. Winds will quickly begin to
gust Saturday morning to around 25 kts and then increase in
speed to near 40 kts by Saturday afternoon. The strongest wind
gusts will likely occur between 19z Saturday through 03z Sunday.
Winds will slowly begin to relax after 03Z, but transient gusts
will remain at times. There will also be a chance of rain or
snow with the frontal passage.
Sunday through Sunday night...VFR. Southwest to south winds 5
to 10 kt. Occasional gusts to 20 kt possible in the afternoon.
Winds 5 kts or less at night. High confidence.
Monday...VFR. Southwest to south winds 5 to 10 kt. High
confidence.
Monday night through Tuesday...MVFR ceilings developing along
with light to moderate rain. Winds becoming south to southeast 5
kts or less after 00Z Tuesday then increasing to around 10 kts
after 12Z. Moderate confidence.
&&
.MARINE...
Through today... A Gale Warning remains in effect through 1PM. A
wind shift from southwest to northwest is expected this morning due
to a frontal passage. This will be accompanied by a line of gusty
showers and possibly an isolated thunderstorm. The strongest winds
will likely occur during and just behind the frontal passage once
the wind direction shifts. A brief and isolated storm force gust is
possible, but overall, it should remain more of a gale force event.
By early afternoon, winds should start to gradually subside. For the
remainder of the day, SCA conditions will continue as northwest
winds continue to gust 25 to 30 kt. Seas mostly 8 to 12 ft but
beginning to decrease during the afternoon.
Tonight... On the Atlantic coastal waters, SCA conditions will
continue for at least the first half of the night with seas still
running 4 to 6 ft. However, conditions should drop below SCA levels
later in the night. On Delaware Bay, conditions should quickly drop
below SCA levels after sunset with decreasing northwesterly
flow.
Outlook...
Saturday through Saturday night...Southwest winds will begin to
rapidly increase in speed Saturday morning as the next cold
front approaches the area from the west. Northwesterly winds
will increase to around 25 to 35 kt by the late afternoon and
evening. Most gusts currently look to be in the 40 to 45 kt
range for Saturday, or just shy of storm force. A Gale Warning
will be required for this period with the potential for a few
storm force gusts. Seas 4 to 7 feet. Conditions remain above SCA
criteria through Saturday night as winds and seas gradually
diminish.
Sunday through Monday...Sub-SCA conditions as high pressure
builds over the waters. Southerly winds 10-15 kts and seas 2-4
feet.
Tuesday...Surface high pressure will move well offshore with
southerly winds increasing in speed as an area of low pressure
approaches. Sustained winds of 15 to 20 kts with gusts up to 25
kts possible. Seas increasing to near 5 feet. An SCA might be
needed. Periods of rain.
&&
.FIRE WEATHER...
Strong west to northwest winds will develop on Saturday,
especially into the afternoon and evening as a strong clipper
system passes across the region. Winds speed of 20-25 mph are
expected with gusts of 45-55 mph possible. Meanwhile, relative
humidity values will drop to around 30%, possibly lower across
the coastal plain of southern new Jersey and Delmarva, into the
afternoon. This period is expected to reach meteorological Red
Flag Warning criteria, but given the expected wetting rainfall
tonight (roughly 36 hours prior) and recent melting snowpack,
soil moistures will likely preclude any significant fire weather
concerns. In any case, we will continue to monitor this
potential and contact any fire weather partners as necessary.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Wind Advisory until 10 AM EST this morning for PAZ054-055-
060>062-070-071-101>106.
NJ...Wind Advisory until 10 AM EST this morning for NJZ001-007>010-
012>027.
DE...Wind Advisory until 10 AM EST this morning for DEZ001>004.
MD...Wind Advisory until 10 AM EST this morning for MDZ012-015-019-
020.
MARINE...Gale Watch from Saturday afternoon through late Saturday night
for ANZ430-431-450>455.
Gale Warning until 1 PM EST this afternoon for ANZ430-431-
450>455.
&&
Synopsis...Haines/Staarmann
Near Term...O'Brien
Short Term...Haines/Staarmann
Long Term...Haines/Staarmann
Aviation...Haines/Iovino/O'Brien/Staarmann
Marine...Haines/O'Brien/Staarmann
Fire Weather...WFO PHI