-- Discussion containing changed information from previous version are highlighted. --
734
FXUS61 KALY 272029
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
429 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 /UNTIL 6 AM TUESDAY MORNING/...
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 even approaching 2" 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.

Breaks of sun earlier this morning within the moist environment
produced increased surface-based instability with the SPC
mesoscale analysis showing 500 - 1000J/kg of SB CAPE. 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. Given the
impressive shear, some weak bowing segments have developed
within the incoming thunderstorms but overall weak sfc forcing
and limited instability has reduce the severe threat so far.

A pre-frontal trough continues to march eastward through the
Mohawk Valley this afternoon and has led to an area of showers
and thunderstorms as it taps into the weakly unstable, very
moist and highly sheared environment. Heavy rainfall rates have
occurred within these storms producing a quick 0.25 to 0.75"
within an hour with some NYS mesonet sites showing hourly rates
up to 1 - 1.25". Latest CAMs suggest shower and thunderstorm
activity will spread eastward into the western New England by
21-22 UTC. Behind this initial batch of rain and thunderstorms,
a dry break will ensue and some additional isolated to scattered
thunderstorms may develop through early this evening but given
that our environment will be worked over, instability will be
even more limited thus reducing our severe potential.

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.

&&

.SHORT TERM /6 AM TUESDAY MORNING 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 push through the region with scattered diurnally driven
showers developing thanks to the incoming sharp wind shift
boundary and cool pool moving in aloft (500hPa isotherms range -18C
to -19C). 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. Areas south of I-90 could see a few
thunderstorms develop as mid-level lapse rates ahead of the
boundary steepen to 6.5 - 7C/km which looks to induce sufficient
instability before the boundary arrives in the afternoon.
Otherwise, 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. Overall lower dew points will likely
limit instability that can develop so severe weather is not
expected.

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 MONDAY/...
Temperatures remain cool through Thursday as northerly winds
behind the trough axis/secondary cold front boundary advect in a
cool and very dry air mass. The cold front from Wednesday looks
to stall somewhere in the mid-Atlantic and as a potent
shortwave from the Ohio Valley amplifies and digs eastward,
additional showers look to develop along the boundary. Current
trends keep the boundary far enough south that additional
showers that develop in response to the incoming shortwave also
remain to our south. However, given uncertainty we continue to
show low-end chance POPs but the forecast may trend drier if
the boundary stays to our south. Otherwise, northerly winds
Thursday turn a bit breezy in the wake of the boundary. Daytime
highs likely struggle to rise out of the 60s with low 70s in the
valley. Clearing skies overnight will promote radiational
cooling and given the very low dew points, we can expect an even
cooler night with lows in the 40s throughout the region. Some
upper 30s cannot be ruled out in the highest peaks of the
southern Greens and southern Adirondacks.

Upper level ridging and strong subsidence/sfc high pressure builds
back into the Northeast Friday through the first weekend of
June giving us a stretch of very pleasant, dry and increasingly
warm weather. Temperatures in the mid to upper 70s Friday and
Saturday trend back to the upper 70s and low 80s by Sunday.
Overnight lows Friday night remains quite cool thanks to
favorable radiational cooling yielding another night with
widespread 40s. Nighttime lows trend milder through the weekend
thanks to the incoming ridging and westerly return flow
developing. Dew points will remain low through the weekend so
humidity levels will remain low/comfortable for those who have
any outdoor activities planned.

&&

.AVIATION /21Z 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...TSRA.
Wednesday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Thursday: Moderate Operational Impact. Chance of SHRA.
Thursday Night: Low Operational Impact. NO SIG WX.
Friday: No 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...Speciale
SHORT TERM...Speciale
LONG TERM...Speciale
AVIATION...Gant