Area Forecast Discussion
Issued by NWS Albany, NY

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000
FXUS61 KALY 230121
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
921 PM EDT Sun Apr 22 2018

.SYNOPSIS...
High pressure will bring dry weather and slowly moderating
temperatures through Tuesday. The next chance for widespread
rainfall arrives late Tuesday and continues into Thursday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 920 PM EDT, cloudless skies continue across the region,
and with winds decreasing to less than 5 KT for most areas,
temperatures are dropping off quite rapidly, with some temps
already dipping into the lower 30s across portions of the
western Adirondacks, with upper 30s/lower 40s across most other
high terrain areas, and mid 40s to near 50 in valley areas.

Our 00Z/23 KALY sounding reveals a PWAT of 0.14 inches. The
record min for this time/date (as depicted on the SPC Sounding
Climatology Page) is 0.10 inches, so we were quite close. This
very dry air mass in place, along with clear skies and winds
trending to calm will help temperatures to fall to the 20s to
lower 30s for most areas toward daybreak. Some mid/upper teens
will be possible across sheltered areas within the western
Adirondacks once again.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
High pressure builds east and light south winds will occur over
our region Monday and Tuesday, with steadier winds Tuesday. High
clouds will spread into our region Tuesday ahead of the next
system approaching from the west.

The strong April sun and slowly increasing boundary layer warm
advection will help temperatures to reach well into the 60s
Monday but near 70 southern areas and around 60 northern areas.
With the prospect of some clouds Tuesday afternoon limiting the
sun a little, highs in the mid to upper 60s with around 60 to
lower 60s northern areas.

Increasing warm and moisture advection, isentropic lift and
boundary layer low level jet convergence will support rain
spreading over our region late Tuesday afternoon and night,
continuing through Wednesday. Highs Wednesday in the mid to
upper 50s but around 50 northern areas.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
At the start of the extended period Wednesday night, the Northeast
will be contending with widespread showers thanks to warm air
advection ahead of an approaching weak shortwave and associated
surface low paralleling the mid-Atlantic coast. During this time, a
strong cut-off Alberta Clipper looks to eject from the Great Lakes
and steer our surface low into eastern New England. This interaction
is worth monitoring as that will determine where the triple point of
our surface low travels and thus areas of steadiest rainfall. While
there are slight difference among the latest 12z guidance, the
consensus is that the triple point remains mainly south and east of
the Capital District which would keep the low`s warm sector mainly
south and east of our CWA.

By 12z Thursday, the initial surface low quickly exits into northern
New England but the cut off Alberta Clipper remains vertically
stacked over western NY. While strong southwest flow ahead of the
cut off looks to bring a surge of dry air behind the exiting surface
low, we continued chance/slight chance POPs in the forecast for
Thursday as this cut off low and its wrap around 700mb moisture
progresses eastward into our CWA. Timing its arrival will be
important in determining the POPs as a slower solution could be mean
more daytime heating to work with (which the ECMWF shows) which
would increase the threat for isolated/scattered showers. A quicker
arrival, as shown in the GFS/CMC, would limit the amount of daytime
heating. Given these trends, kept chance POPs for the entire daytime
Thursday north/west of the Capital District but trended down to
slight chance after 18z south/east as this area could miss out on
the highest 700mb moisture.

It`s worth mentioning that most of the guidance hint at the
potential for a mid level cold pool with this cut off (most
pronounced on the ECMWF with a pocket of -2C to -3C isotherms
at 850mb over the Adirondacks) which could influence mid-level
lapse rates and boundary layer mixing potential. Despite the
uncertainty with POPs, kept high temperatures similar to
Wednesday only reaching the mid-upper 50s (below normal for late
April) due to cloud coverage and west-northwest flow.

The cut off exits Thursday night with high pressure briefing
building in for Friday. With a deepening longwave trough in the
Mississippi Valley leading to strong southwest flow from the Gulf of
Mexico surging into the Northeast, temperatures Friday should rise
to and could even exceed normal, reaching well into the 60s.

Uncertainty increase for the weekend as multiple shortwaves round
the base of the aforementioned longwave trough. There are
considerable model differences in the strength and timing of these
shortwaves with GFS and CMC showing a more pessimistic solution. One
thing we can note is that most of the guidance does suggest a return
to cooler than normal temperatures for the second half of the
weekend.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
High pressure and a dry air mass will remain in control through
Monday, with mainly clear skies continuing through the 24 hour
TAF period ending 00Z Tuesday.

Winds tonight will become light and variable and persist through
Monday morning, then trend into the south to southwest Monday
afternoon at 5-10 KT.

Outlook...

Monday Night: No Operational Impact. NO SIG WX.
Tuesday: High Operational Impact. NO SIG WX.
Tuesday Night: High Operational Impact. Likely RA.
Wednesday: High Operational Impact. Definite RA.
Wednesday Night: Moderate Operational Impact. Likely SHRA.
Thursday: Moderate Operational Impact. Chance of SHRA.
Thursday Night: Low Operational Impact. Slight Chance of SHRA.
Friday: No Operational Impact. NO SIG WX.

&&

.FIRE WEATHER...
High pressure will bring dry weather and slowly moderating
temperatures through Tuesday. The next chance for widespread
rainfall arrives late Tuesday and continues into Thursday.

Relative humidity values will drop to 15 to 30 percent Monday
afternoon and 25 to 40 percent Tuesday afternoon. RH values will
recover to 70 to 100 percent Monday night.

North to northwest winds around 15 mph will become variable at
less than 15 mph tonight. Winds become south at 15 mph or less
Monday and Monday night, increasing to 15 mph with gusts
possibly to 20 mph Tuesday afternoon.

&&

.HYDROLOGY...
Rivers and streams continue to slowly recede from heavier
rainfall earlier this week.

Dry weather is expected today through Tuesday with a moderating
trend in temperatures which will allow for some snowmelt in the
mountains. There will be some evaporation of the snow pack and
snow melt through Tuesday afternoon due to the the very dry
atmosphere and strong daytime April sunshine. So, not all the
snow melt will run off into area rivers through Tuesday
afternoon because of the evaporation. The next chance for
widespread precipitation mainly in the form of rain will arrive
late Tuesday and continue into Thursday.

For details on specific area rivers and lakes, including
observed and forecast river stages and lake elevations, please
visit the Advanced Hydrologic Prediction Service /AHPS/ graphs
on our website.

&&

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

&&

$$
SYNOPSIS...NAS
NEAR TERM...KL/NAS
SHORT TERM...NAS
LONG TERM...Speciale
AVIATION...KL/JPV
FIRE WEATHER...NAS
HYDROLOGY...NAS



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