-- Discussion containing changed information from previous version are highlighted. --
843
FXUS61 KALY 271755
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
155 PM EDT Mon May 27 2024

.SYNOPSIS...
Muggy and breezy conditions continue for this Memorial
Day holiday with showers and thunderstorms increasing in coverage
through the afternoon into this evening. Storms will be capable of
producing heavy downpours and gusty winds. A few scattered showers
and storms and breezy winds return tomorrow into Wednesday before
the main cold front swings through the region resulting in cooler
and much less humid conditions for the remainder of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1050 AM EDT...A strengthening low pressure system reaching
~997hPa in the Great Lakes today will advance into Ontario and
Quebec this afternoon and tonight. A tight pressure gradient
ahead of it has led to strong southerly low and mid-level winds
and will maintain a strong moisture fetch up the East Coast.
Thus, dew points remain in the 60s today making it feel quite
muggy with PWATs exceeding 1.5", even approaching 2" later this
afternoon. Gusty southerly winds still expected this afternoon
with sustained winds 10 - 20kts and gusts up to 30-35kts,
especially in north - south oriented valleys.

We will have a dry break through early this afternoon with even
breaks of sun showing up on the GOES16 visible satellite
imagery. Breaks of sun within the moist environment will support
increased surface-based instability with CAMs such as the HREF suggesting
up to 1000J/kg developing. However, skies will overall mostly
cloudy with just some breaks of partial sun so instability will
be limited. The strong kinematics in place thanks to the
overall synoptic set- up has led to 0-6km shear values ranging
40-45kts (also seen on the ALY 12 UTC sounding) which will be
more than sufficient to support organized convection. As
mentioned in the previous AFD, most of the shear is within the
lower 0-1km layer too.

A pre-frontal trough continues to march eastward through western
NY late this morning and has led to increased coverage of
showers and thunderstorms ahead of it as seen on GOES16
satellite imagery and radar mosaic. Increasing height falls,
forcing for ascent and cooler air aloft (including steepening
mid-level lapse rates) will spread eastward through the
afternoon. Latest CAMs suggest shower and thunderstorm activity
will reach our western zones including the western Mohawk
Valley, western Adirondacks, and eastern Catskill by 18 - 20
UTC (2 - 4pm) before spreading eastward into the Capital
District, mid-Hudson Valley, and Upper Hudson Valley by 20 - 22
UTC (4 - 6pm). Since we have a few hours of dry time and breaks
of sun ahead of the strong upper level forcing and sfc pre-
frontal trough, the environment should become favorable to
support thunderstorms and while overall instability is not very
impressive, in the presence of the strong shear in the low and
mid-levels, the environment will likely be favorable to support
some organized thunderstorms, especially west of the Hudson
River where there should be more insolation and thus more
instability. This explains why the slight risk (level 2 of 5)
from the Storm Prediction Center remains in the western Mohawk
Valley, eastern/northern Catskills and western Adirondacks with
just a marginal up to the Hudson River. Should more instability
develop further east, the severe weather potential could expand
eastward.

Gusty winds is the primary hazard from any severe thunderstorm
but given the high PWATs, high freezing levels >10kft, and
forecast soundings showing most of the instability within the
warm cloud layer, the environment will also support efficient
warm rain processes and thus heavy downpours/high rainfall rates.
With 40-45kt winds within the LCL-EL layer and these wind
oriented close to the orientation of the pre-frontal trough,
some convection may repeatedly impact an area so we will have to
monitor for some isolated instances of flooding. CAMs including
the HREF probabilities continue to point to the eastern
Catskills for the heaviest rainfall amounts where southerly
winds abutting the terrain could favor high rainfall rates (HREF
3-hr probabilities for >1" of rain are around 75% late this
afternoon into this evening). Latest WPC rainfall amounts so
1.50 - 2" possible in this region but given dry antecedent
conditions, we are not expecting widespread flooding but some
localized flash flooding cannot be ruled out. This support the
WPC Excessive Rainfall Outlook and the slight risk in the
eastern Catskills. Luckily, the strong winds aloft should keep
the overall convection moving and progressive.

Thunderstorm activity including potential for heavy
downpours/high rainfall rates continues into this evening but
with instability diminishing, storms should end by 03 - 06 UTC.
The main cold front and cooler air mass lags well to our west
so still expecting muggy/humid conditions tonight. Clouds should
partially clear after Midnight as drier air moves in aloft but
forecast soundings suggest low-level moisture lingers beneath
the subsidence inversion so only expecting partial clearing
through sunrise. Between the lingering clouds and muggy air
mass, temperatures will stay mild tonight with lows only
dropping into the low to mid 60s in the valley with low to mid
50s in the hill towns and higher terrain.

Previous discussion...Model soundings shows PWATs
will surge above 1.50" and ensemble guidance suggest PWATs will
reach 1 to 3 STD above normal for this time of year. Although
showers and thunderstorms look progressive, some heavy downpours
are expected and there could be some isolated poor
drainage/urban flood issues around. A rogue flash flood can`t be
ruled out if heavy rainfall repeats over any one location,
although this looks like a low-end threat due to rapid movement
of precip and likelihood that the heaviest batch will be within
one main band ahead of the pre- frontal trough late today. WPC
suggests the greatest risk for this will be across the
Catskills, as this is where they have a Slight Risk for
Excessive Rainfall.

In addition, there is a threat with this activity for some
gusty winds. While instability will be limited (00z SPC HREF
shows MUCAPE values under 1000 J/kg), there is a lot of shear in
place. 0-6 km bulk shear values will be around 40 kts, with a
lot of this in the 0-1 km layer (about 30 kts or so). It won`t
take a tall storm to bring down some gusty winds, so downed tree
limbs are possible within any heavier convective element. SPC
has a marginal to slight risk for severe weather across western
areas for late today.

Showers and t-storm will still be ongoing this evening and will
linger into the first part of the overnight, as the storm`s
cold front slowly makes progress from west to east across the
area. CAMs show most of the activity should be done by midnight
to 2 AM or so and the threat for the heaviest showers/thunder is
likely early, as the loss of heating should help keep storms
from staying strong. Otherwise, mostly cloudy skies will
gradually become partly to mostly clear towards daybreak
Tuesday, with temps falling into the mid 50s to mid 60s and
dewpoints starting to fall.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Early stratus clouds from the overnight erodes away tomorrow
morning giving us a period of morning sunshine. With the main
parent low positioned in Quebec, the attendant parent trough
and sfc cold front will be tracking through western/central NY
through the morning with a warm air mass still place across
eastern NY and western New England. Guidance suggests 850hPa
isotherms will be able to reach +9C to +11C which combined with
morning insolation and deepening boundary layer mixing should
support afternoon temperatures reaching into well into the 70s
with even low 80s in the mid-Hudson Valley and parts of NW CT.
The sfc pressure gradient ahead of our approaching boundary
remains tight thanks to our 990hPa low positioned in southern
Canada so southwest to westerly winds should become breezy
through the afternoon with gusts reaching up to 25-30kts. Dew
points remain elevated as well in the upper 50s so morning sun
and the slightly humid air mass should contribute to generating
some weak instability in the afternoon (500 - 1000J/kg). Once
the main front and trough axis arrives from west to east,
expecting scattered showers and thunderstorms to develop and
spread eastward. Not expecting severe weather thanks to the
limited instability with thunderstorm activity diminishing after
sunset with the loss of daytime heating.

The upper level trough axis lingering overhead through Tuesday
night will support upslope driven showers and clouds along the
west facing slopes of the Taconics, southern Greens, northern
Catskills and western Adirondacks. Clearing skies in the valley
along with the incoming cooler and drier air mass behind the
front will support overnight lows dropping into the 50s with
even upper 40s in the higher terrain of the southern Greens and
southern Adirondacks.

Moist, cyclonic flow continues into Wednesday as upper level
troughing remains overhead. Westerly winds become northerly
through the afternoon as the trough axis and secondary cold air
front pushes through the region with a few isolated to widely
scattered diurnally driven showers still possible thanks to the
cool pool moving in aloft (500hPa isotherms ranging -18C to
-19C). Cannot completely rule out a thunderstorm given the cool
pool aloft mainly south of I-90. The better shower coverage
looks displaced to our south in PA/NJ where a more potent
shortwave tracks through at the base of parent trough.
Temperatures trend cooler relative to the past few days with
daytime highs only reaching into the low to mid 70s and much
lower dew points in the low 50s to even 40s making it feel much
more comfortable.

Clearing skies ensue Wednesday night with temperatures turning
even cooler in comparison to the previous few nights. Overnight
lows drop into the low to mid 40s in the higher terrain and hill
towns with low 50s in the valley thanks to radiational cooling
effects.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
An upper-level trough swinging across the region midweek will exit
eastward on Thursday, with rain showers diminishing from west to
east through the day as drier air arrives in its wake. Heights aloft
begin to rise late Thursday into Friday as high-amplitude upper
ridging builds over the region, bringing a return to dry weather
with clearing skies into the weekend.

Temperatures through the period trend upward each day, with
afternoon highs increasing from upper 50s in high terrain to low 70s
along the Hudson Valley on Thursday to upper 60s near 80 across the
region on Sunday. Overnight lows similarly trend warmer, from
widespread 40s on Thursday night to upper 40s to upper 50s on Sunday
night.

On the far side of the weekend, numerical guidance begins to show
substantial differences in the evolution of the upper ridge, leaving
some potential for rain shower chances late Sunday, although
confidence is low at this lead time.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
Through 18Z Tuesday...MVFR to VFR ceilings across the region
this afternoon as bands of rain and thunderstorms approach from
the west with the nearing of an upper-level disturbance and
surface low pressure system. Rain is only just now beginning to
grace the western edge of our forecast area, so terminals are
not expected to be impacted for the next hour or two other than
a stray shower out ahead of the main band.

Once the main band arrives in the next hour or two, rain should
start light before becoming moderate to heavy shortly after
onset. Embedded thunderstorms are also expected with KALB/KGFL
and KPOU more likely to be impacted. MVFR to IFR conditions are
expected from heavy rain and thunderstorms with already gusty
winds increasing out of the southeast. The most likely time for
thunderstorms to impact KALB/KGFL/KPOU looks to be between
21-24z so included TEMPO groups to account. KPSF could also
experience a thunderstorm, but maintained a period of heavy rain
without the addition of thunder due to lower confidence. Will
monitor and make amendments where necessary.

Rain will gradually taper off through this evening, reducing to
mere showers by 00-02z. Ceilings will then gradually improve,
but will likely maintain MVFR levels through much of the
overnight. There were some hints in the guidance that ceilings
could break closer to daybreak which could lead to fog
development, but with low confidence in this part of the
forecast due to differences in the models and the expectation
for light winds overnight, we left this out for the time being.

Winds throughout the 18z period will be gusty out of the
southeast to start. Sustained speeds will range from about 15-20
kt with gusts up to 30-40 kt. Gusts could become closer to 50 kt
should a stronger thunderstorm cross over the terminals. Speeds
will gradually decrease through the night, falling to 5-10 kt
and gradually shifting more to the west-southwest. Tomorrow,
speeds should pick up again but will be less than today. Expect
sustained speeds of 5-10 kt with gusts up to 15 kt.

Outlook...

Tuesday Night: No Operational Impact. NO SIG WX.
Wednesday: Moderate Operational Impact. Chance of SHRA.
Wednesday Night: Moderate Operational Impact. Chance of SHRA.
Thursday: Moderate Operational Impact. Slight Chance of SHRA.
Thursday Night: No Operational Impact. NO SIG WX.
Friday: Low Operational Impact. NO SIG WX.
Friday Night: No Operational Impact. NO SIG WX.
Saturday: No Operational Impact. NO SIG WX.
-- End Changed Discussion --

&&

.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.

&&

$$

SYNOPSIS...Frugis/Speciale
NEAR TERM...Frugis/Speciale
SHORT TERM...Frugis/Speciale
LONG TERM...Picard
AVIATION...Gant