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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 082108
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
408 PM EST Mon Mar 8 2021

.SYNOPSIS...
High pressure will remain centered west and south of the region
through tonight. A weak surface low moving across Quebec will drag a
weak cold front through most of the region on Tuesday. Strong high
pressure then dominates the weather Wednesday and Thursday with a
continued warming trend. Low pressure moving out of the Midwest and
through the Great Lakes will send a cold front through the region
Friday into Saturday. High pressure then builds back in for next
weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
Skies are mostly clear this afternoon as a large center of high
pressure remains to our south. As expected, temperatures are still
on the cool side, though a little warmer than recent days, as
troughing and associated colder air from over the weekend moves
offshore. It`s also been very dry today with dew points in the teens
and even some high single digits. We`ll see cool and dry weather
through the evening.

Quiet weather continues into tonight. A shortwave trough and
associated weak surface wave will be passing to our north even as
larger scale height rises and ridge building occur across the East.
Model guidance has steadily moved the track of this shortwave
southward over the past couple of days. This disturbance could lead
to some increase in cloud cover later tonight especially up north,
but no precipitation is expected. Given the very dry air and winds
turning light, temperatures could fall quickly this evening, and may
be close to their lows by midnight. But from there, they should
level off or even rise a bit in many areas as a light southwest wind
develops and patchy clouds potentially move in. Forecast lows are
mainly in the lower 30s, but could shift a few degrees in either
direction depending on how winds and cloud cover behave.

Trends from tonight factor into Tuesday`s forecast as well. It now
looks as though a weak cold front associated with the system to our
north will move far enough south to push through at least most of
our region during the day, shifting our winds from southwest back to
northwest. This does not result in too many changes to the sensible
weather forecast. Lift with the front is weak, and the air mass is
dry, so there is no concern for rainfall. Skies may be more partly
to mostly cloudy with the frontal passage in the morning before
turning mostly sunny by afternoon. Even regarding temperatures, the
air behind the front is still warmer than that of recent days as
longwave ridging shifts eastward and strengthens. So Tuesday still
looks much warmer than recent days with highs getting into the upper
50s and low 60s, a bit cooler up north. Overall, should be a nice
day.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
High pressure and deep subsidence will lead to a nice day
Wednesday across the region as warm air advection continues
aloft. A relatively cold ocean and on shore flow will likely
cool the immediate inland areas a bit but low 60s seems like a
pretty sure bet elsewhere. Wednesday evening should be quiet
but we`ll see the on shore flow start to become more southerly
which starts the big churn of warm air at the surface. Heading
into Thursday, we`ll see a surge in warmer temps. With 925mb
temps in warming to 12 to 14C aloft we`ll see surface temps
warming well into the upper 60s to near 70. With partly cloudy
skies we likely wont fully reach the low to mid 70s that those
925mb could support. Looking a sounding profiles, there should
be quite a bit of dry air that mixes to the surface and so we`ve
significantly lower afternoon dew points relative to guidance.

Clouds will continue to thicken through the evening with warm
air advection still firmly in place and we`ll likely stay in the
50s overnight Thursday night. With relatively low records for
3/11 there a chance we`ll break the record for max temp at PHL
and the record high minimum as well.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
The end of the week should start to become more active as a
phased closed low tracks through Quebec. This will sweep a
surface cold front extending all the way from New England to
Kansas east across the eastern CONUS. This should bring some
rain showers through the region Friday into Saturday. Guidance
continues to slow the front down and so we`ll likely enjoy
another warm day Friday before the front starts to fully impact
the region.

The front still looks like it will slow way down or even stall
as it crosses our region. So while precip seems likely, its
going to be quite a challenge as to where the front actually is.
Consequently, the temperatures on Saturday remain uncertain.
Similar to the previous shift I continued the forecast with
highs near normal but I trended the shift slightly below normal
as I tend to think the front should south. That sets up another
extended period of below normal temps under northwest cold air
advection for the rest of the weekend and heading into next week.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Through this evening... VFR. West-northwest wind gradually shifting
to west-southwest at 5 to 10 kt. High confidence.

Tonight... VFR. Model guidance is showing an unusually large spread
in cloud cover forecast tonight, with the potential for most of the
terminals to see anywhere from FEW to BKN cloud layers through most
of the night. The best potential for more cloud cover appears to be
in northern areas. It does appear that even if cloud cover is more
extensive than forecast, any CIGs should still remain at VFR levels
in the range of 5000 to 9000 ft. Winds southwest at around 5 kt,
though may be light and variable at times especially early. There is
also some LLWS potential especially near RDG and ABE where westerly
winds around 2000 ft will increase to near 35 kt. Have left out a
mention of LLWS from any of the TAFs for now due to it being
marginal in strength, but this will continue to be monitored.
Moderate to high confidence.

Tuesday... VFR. West-southwest winds in the morning shifting to
northwest through the day with speeds around 10 kt. High
confidence.

Outlook...
Tuesday Night: VFR. Light northerly flow. High Confidence.

Wednesday: VFR. Southwesterly winds of 5 to 15 kt and occasional
gusts. Medium Confidence.

Wednesday Night: VFR with ceilings increasing.  Light southwesterly
flow overnight. Medium Confidence.

Thursday: VFR. Southwesterly wind 10 to 15 kt with gusts to 20 kt.
High confidence.

Thursday Night: VFR. Southwesterly wind 5 to 15 kt. High confidence.

Friday: Mainly VFR to start, with MVFR becoming possible as showers
move through region late. Southwesterly winds initially becoming
westerly behind a front. Low confidence in timing.

Friday Night: Generally VFR with MVFR possible as showers move
through region. Westerly winds will become northwesterly overnight.

Saturday: VFR. Northwesterly winds 10 to 15 kt.


&&

.MARINE...
Through tonight... Fair weather. Westerly winds will become
southwest this evening at 5 to 10 kt. Southwest winds then increase
to around 15 kt through the night. Gusts to 20 kt or slightly higher
are possible by late tonight, but conditions are expected to remain
below SCA criteria. Seas 1 to 2 ft.

Tuesday... Sub-SCA conditions and fair weather continue. Southwest
wind 10 to 15 kt becoming more west or west-northwest in the
afternoon and evening. Gusts to 20 kt or slightly higher are
possible mainly in the morning. Seas 2 to 3 ft, waters could be a
bit choppy with a period of around 4 seconds.

Outlook...
Tuesday Night: Sub-SCA. Winds less than 15 kts. Seas less
than 2 feet. NO SIG WX.
Wednesday: Sub-SCA. Wind gusts to 15 kt. Seas less than 2 feet.
NO SIG WX.
Wednesday Night: Mainly Below SCA Conditions expected. Wind gusts to
20 kt. Wave heights up to 3 feet. NO SIG WX.
Thursday: SCA Conditions possible. Wind gusts to 20 kt. Wave heights
up to 5 feet on short period swells.
Thursday Night: SCA Conditions expected. Wind gusts to 20 kt. Wave
heights up to 6 feet on short period swells.
Friday: SCA Conditions possible. Wind gusts to 20 kt. Wave heights
up to 4 feet. Slight chance SHRA.
Friday Night: Sub-SCA. Wind gusts to 15 kt. Wave heights up to 4
feet. Slight chance SHRA.
Saturday: Sub-SCA. Wind gusts to 15 kt. Wave heights up to 3 feet.
Slight chance SHRA.

&&

.FIRE WEATHER...
A prolonged dry period will remain in place over the region, so
there will be continued monitoring for fire weather potential this
week. Winds appear low enough to preclude any fire weather concerns
through at least Wednesday. Tuesday and Wednesday will be warmer
than normal with minimum relative humidity values of mainly 35% to
45%. By Thursday, a combination of even warmer temperatures,
breezier conditions, and RH levels near to below 40% may lead to an
increase in fire weather concerns.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...O`Brien
Near Term...O`Brien
Short Term...Deal
Long Term...Deal
Aviation...Deal/O`Brien
Marine...Deal/O`Brien
Fire Weather...WFO PHI