Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 301037
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
637 AM EDT Fri Jul 30 2021

.SYNOPSIS...
A cold front will move across the region early this morning.
Behind the front, a cooler and drier air mass will build in with
gusty northwest winds developing. A few more showers possible
mainly through early afternoon, with drying trend later today.
Dry conditions with below normal temperatures in store for
tonight through Saturday, as high pressure tracks eastward
across the Ohio Valley and Mid Atlantic regions. The next chance
of showers and thunderstorms arrives late Saturday night into
Sunday, as a low pressure system approaches from the Great
Lakes.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
.UPDATE...Line of low-topped convection ahead of the cold front
is still holding together as it pushes southeast across the
central part of the area. Raised POPs for the Capital District,
Schoharie Valley, southern Greens and northern Taconics to
account for this activity this morning. Embedded convective
elements occurring with brief downpours. Radar and observations
indicated around a quarter to third of an inch of rain.

.PREVIOUS [0545]...Quick update to raise POPs across the far
southern Adirondacks, Mohawk Valley, Lake George and Saratoga
region early this morning. Fairly solid line of showers with
embedded downpours holding together as it pushes south/east.
Line being forced by a cold front, which is now moving across
the Adirondacks. SPC Mesoanalysis indicating a pocket of MLCAPE
around 100-500 J/kg, which has resulted in convective elements
are even isolated thunder. Thus far rainfall rates have been
around or less than a half inch per hour so no additional hydro
concerns at this time, but will continue to monitor trends.

.PREVIOUS [0341]...Well defined short wave trough evident in
GOES East water vapor imagery, moving southeast across
northern/eastern NY. Low level convergence along associated cold
front resulting in a cluster of showers with embedded
thunderstorms moving into the Adirondacks. Most of the activity
is expected to primarily move through the western Adirondacks to
the Lake George region, which is just north of where a
significant swath of heavy rain occurred earlier (far southern
Adirondacks, Saratoga/Washington Counties and southern VT). Will
have to watch if convection moves across these areas, since any
additional heavy rainfall could result in renewed flooding.

As the cold front and upper level short wave progress southeast
across the region this morning, scattered showers and isolated
thunderstorms will persist. Instability parameters indicate
limited SBCAPE around 200-500 J/Kg, decreasing from west to east
as drier air moves in. So will maintain slight chance of
thunder into the early morning hours until the instability
wanes. Not expecting any additional hydro issues unless an area
of persistent showers or storms with downpours moves over areas
that received heavy rainfall Thursday.

It will become noticeably breezy by this afternoon as winds
shift to the northwest. Gusts of 25 to 30 mph will be common,
with occasional gusts up to 35 mph in some spots as the pressure
gradient increasing in a cold advection regime. Humidity levels
will lower considerably during the afternoon, as dewpoints drop
into the 40s and 50s from early day values in the 50s and 60s.
High temperatures will be well below normal (10-15 degrees),
with 850 mb temp anomalies dropping to between -2 to -3 STDEV
late in the day across the entire area. Valley areas will see
temps in the lower to mid 70s, but much cooler 60s in the higher
terrain. The NW wind will make it feel more like early fall
than late July. Clouds will tend to hang on longest over the
mountains, but N-S valleys should see appreciable sunshine by
this afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
Dry and cool conditions in store for tonight, with a continued
northwest flow regime. High pressure will be centered to out
south/west across Ohio/PA, so there should be at least a slight
persistent breeze in most areas. This should prevent
temperatures from really plummeting. Still, it will be quite
chilly for late July with lows expected to be mainly in the mid
40s to lower 50s with some lower 40s in parts of the Adirondacks
and southern Green Mountains.

On Saturday, high pressure will be centered just to our south
across PA/NJ although there will be a weaker pressure gradient
in place in eastern NY and western New England so there will be
less wind compared to Friday. A cool/dry air mass will remain in
place with 850 mb temp anomalies of -1 to -3 STDEV across the
area. So highs will continue to be much cooler than normal with
lower/mid 70s in valley and 60s in the mountains.

Saturday night will start out dry, but clouds will start to
increase as yet another upper level short wave trough starts to
approach from the upper Great Lakes. Will start to mention
chance POPs for areas north/west of Albany prior to daybreak
Sunday as large scale forcing starts to increase ahead of the
trough. Low temps will still be cool, but slightly milder than
the previous night due to increasing cloud cover.

Another period of active weather will begin on Sunday, as the
aforementioned short wave trough tracks into the lower Great
Lakes and goes from a positive to neutral tilt. Strong forcing
expected form this vigorous trough, which will result in
widespread showers developing during the afternoon. There could
also be some instability present depending on timing of the
trough, as both the GFS and NAM are indicating a corridor of
SBCAPE of 500-1200 J/Kg across the Mohawk Valley and
Adirondacks. So will mention chance of thunderstorms. With 0-6
km shear increasing to around 30-40 kt some stronger storms will
be possible. However, main threat with any convection will be
locally heavy rainfall and potential for flash flooding based on
wet antecedent conditions. Most sources of guidance indicating
the greatest QPF across the northern half of the area. WPC has
introduced a Slight Risk of excessive rainfall in this area,
which seems reasonable given the most soils (despite modest
PWATs). Will continue to monitor trends.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Our persistent northwest flow regime continues as a rather
strong trough axis is forecast to swing across the eastern Great
Lakes Sunday with its associated surface reflection tracking
across the St Lawrence Valley. Best upper dynamics is expected
across the northern 2/3rds of the CWA as we will place likely
PoPs in the forecast/grids Sunday evening with a gradual
decrease expected overnight. Some breaks in the overcast are
expected along with patchy fog as low temperatures should be
into the 50s.

As we begin the first week of August, a rather confluent flow
is expected across the northeast corridor. This should allow for
upstream high pressure to ridge into the region for a tranquil
start to the work week with slightly below average temperatures.

Tuesday into Wednesday, latest global model runs suggest the
confluent flow begins to weaken as an evolving cut-off upper low
over the Ohio Valley begins to take shape. Deeper sub-tropical
moisture begins to advect northward along the Atlantic seaboard
late Tuesday and into Wednesday. With the increase in moisture
and gradual thermal profiles moderating, expectations are for
more August-like weather with warmer and more humid conditions.
The threat for isolated convection may develop south of Albany
later Wednesday. Valley temperatures moderate back toward 80F,
along with dewpoints climbing back through the 50s and into the
60s.

Wednesday night into Thursday, increasing signals for a period
of rainfall to develop. If the ECMWF is correct, a prolonger
period of moderate to some heavy rainfall is possible. The GFS
is a bit further east with the GGEM and ICON the furthest
displaced east and southeast of the region with the moisture
stream. However, they all agree with increasing cloud coverage
as we will continue with that forecast along with chances of
showers and some thunderstorms.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Strong short wave continues to track across eastern New York
accompanied by a line of showers and some embedded
thunderstorms. We will place TEMPO groups for KGFL-KALB-KPSF
with MVFR flight conditions for a couple hours this morning.
Some lower ceilings may linger with upslope conditions into the
Berkshires but even here conditions should improve through the
afternoon. For KPOU, expectations are for this line to weaken
before it arrives so we will leave the mention of VCSH in the
forecast at this time.

Winds will likely be on the increase today with gusts above
20kts expected from the west northwest direction.

VFR conditions late this afternoon into most of the late
evening hours as winds become light and variable. Could see some
patchy fog late tonight.

Outlook...

Friday Night: No Operational Impact. NO SIG WX.
Saturday: No Operational Impact. NO SIG WX.
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: High Operational Impact. Likely SHRA...TSRA.
Sunday Night: High Operational Impact. Likely SHRA...TSRA.
Monday: Low Operational Impact. Slight Chance of SHRA.
Monday Night: No Operational Impact. NO SIG WX.
Tuesday: Low Operational Impact. NO SIG WX.

&&

.FIRE WEATHER...
A cold front will move across the region early this morning.
Behind the front, a cooler and drier air mass will build in with
gusty northwest winds developing. A few more showers possible
mainly through early afternoon, with drying trend later today.
Dry conditions with below normal temperatures in store for
tonight through Saturday, as high pressure tracks eastward
across the Ohio Valley and Mid Atlantic regions. The next chance
of showers and thunderstorms arrives late Saturday night into
Sunday, as a low pressure system approaches from the Great
Lakes.

Minimum relative humidity values today will be around 50 to 65
percent, increasing to between 80 and 95 percent tonight.
Minimum RH values on Saturday will be around 40 to 50 percent.

Winds today will northwest increasing to 10 to 20 mph with
gusts up to 30 mph. Winds tonight through Saturday will be
northwest around 5 to 15 mph.

&&

.HYDROLOGY...
While the threat for widespread rainfall has ended, additional
showers and few thunderstorms will remain possible through the
early morning hours as a cold front crosses the area. Heavy rain
of 2-4 inches occurred in a swath between the far southern
Adirondacks, Saratoga/Washington Counties and southern VT which
resulted in flash flooding and even some river flooding. Flood
Warnings for the Mettawee at Granville, the Saxtons and Williams
River in southern VT have been cancelled as levels continue to
fall.

Dry weather returns by this afternoon, with breezy and cooler
conditions. It should remain dry through Saturday, with
increasing chances for showers and some thunderstorms late
Saturday night into Sunday as a strong disturbance moves across
the region. Additional rainfall will likely occur in parts of
the area, which could result in some hydro issues. Stay tuned
for further updates.

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...JPV
NEAR TERM...JPV
SHORT TERM...JPV
LONG TERM...BGM
AVIATION...BGM
FIRE WEATHER...JPV
HYDROLOGY...JPV


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