Area Forecast Discussion
Issued by NWS Albany, NY

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000
FXUS61 KALY 300151
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
951 PM EDT Sat Apr 29 2017

.SYNOPSIS...
High pressure builds in from southeastern Canada overnight into
Sunday with cooler conditions. A warm front will slowly lift
northward late Sunday into Monday with an increasing threat of
showers and isolated thunderstorms. A cold front will bring
widespread showers and a chance of thunderstorms late Monday
afternoon into Tuesday morning.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of 950 PM EDT, a secondary cold front was settling southward
from northern New England. Winds become somewhat gusty near and
behind the boundary. Otherwise, patchy mid level clouds extend
from the eastern Catskills into the mid Hudson Valley, southern
Berkshires and NW CT, and continue to erode from NW to SE.

We expect the clearing trend of the mid level clouds to continue
overnight from NW to SE, although clouds may linger a bit
longer closer to the I-84 corridor.

As the secondary cold front moves south, there could be a brief
surge of gusty north to northeast winds behind the front across
portions of the upper Hudson River Valley/Lake George region,
where some gusts of 25-30 mph could occur around and especially
after midnight, as the flow funnels south from the Champlain
Valley region.

Expect temperatures toward daybreak to drop into the lower/mid
40s for most areas, except across the southern Adirondacks and
higher elevations of southern VT, where some mid/upper 30s or
slightly colder temperatures could occur.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Very tricky forecast through Monday as the front builds back
north through the period but there are inconsistencies in
guidance as to the the timing of the passage and the northward
extent of the front as it returns as a warm front. The boundary
layer thermal gradient tightens and sets up from NW to SE across
our forecast area Sunday with cooler, cloudier weather to the
east and potentially fewer clouds and a little warmer in
western and southern areas.

Of course, the surface boundary will likely be a bit farther
west and south of the boundary layer thermal gradient but the
boundary layer winds are expected to be west to west southwest,
which if strong enough, would be downslope and would result in
some counteracting of the southeast surface flow and cooling and
drying proximate to the slow eastward departure of the low
level ridging.

The boundary layer flow does look to be weak enough that any
moisture advection and isentropic lift along the boundary layer
thermal gradient should be too weak to support more than just a
few isolated showers through the day Sunday. Still, most of not
all areas should see a mostly cloudy to cloudy sky with
temperatures not having much a chance to warm above the 50s to
lower 60s with the warmest temperatures in southern and western
areas.

By Monday as the stronger more organized upper dynamics approach
and low level jet energy strengthens proximate to the northward
retreating boundary layer thermal gradient, coverage of showers
should increase along and north of wherever the warm front is
by Monday morning. There is a decent consensus from sources of
guidance that the surface boundary and the boundary layer
thermal gradient push well north through the day Monday and
boundary layer temperatures warm considerably in the warm sector
over our region.

Still, there are mixed signals as to how much convective debris
is over our region Monday morning and afternoon that could limit
the warming during the day. The boundary layer flow is southwest
and strengthens considerably. So, downslope process should be
present, suggesting temperatures Monday could be warmer than the
warmest temperatures guidance as long as there are no
convective remnants or debris around Monday. With those sources
of uncertainty, siding with warmer guidance, well into the 70s,
but some areas could get into the 80s if there is less cloud
cover. Some scattered showers and thunderstorms are possible in
western areas later Monday afternoon if a prefrontal trough can
develop as the forcing along the cold front looks to be delayed
until Monday night.

The timing of the cold front Monday night into Tuesday morning
is also in question. However, there is a high confidence in a
band of showers and thunderstorms with locally heavy rain Monday
night into early Tuesday morning. We will have to also keep an
eye on any severe weather potential.

Once the front exits, cold advection occurs and the upper
dynamics will be slow to cross through the Great Lakes. Guidance
suggests some fairly persistent clouds and scattered to isolated
showers Tuesday with the low level flow off the Great lakes
interacting with the upper dynamics. Highs Tuesday in the 60s to
near 70 but 50s in the southern Adirondacks.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
General upper level troughiness and below normal temperatures are
expected to dominate much of the long term period, although there is
increasing uncertainty for Thu-Sat regarding any potential
developing cut off low affecting the region.

For Tuesday night-Wednesday, although the main upper level low which
will translate northeast across the upper midwest/western Great
Lakes region should lift into east central Canada, some trailing
upper level impulses and cyclonic flow should keep occasional
clouds, and perhaps a few isolated/scattered showers across the
region, with greatest coverage expected across the western
Adirondacks, in closer proximity to the main upper level
troughiness. Some graupel/wet snow could occur mainly at night
across higher elevations of the Adirondacks. Tuesday night lows
should mainly be in the 40s for lower elevations, with some
mid/upper 30s possible across higher elevations. Wednesday highs
should be mainly in the 50s/lower 60s in valleys, with 40s/lower 50s
across higher terrain.

Some shortwave ridging may translate across the region Wednesday
night into early Thursday, before southern stream moisture/energy
approaches from the southwest. So, generally fair through Thursday
morning. It could be quite chilly Wednesday night if enough clearing
occurs, and could lead to some frost potential in areas where the
growing season begins.

Increasing chances for rain for Thursday afternoon and continuing at
least through Friday. 12Z/29 global deterministic GFS and ECMWF have
suddenly trended toward a splitting of upper level energy for late
next week, and instead of phasing leading to a large upper level
closed low forming somewhere over the Ohio Valley/northern
Appalachians, now favor the energy diving farther south and west,
separating from northern stream energy. The end result would be a
shorter period of rain for late next week, with possible improvement
for next weekend. For now, since this is a rather rapid change from
the previous 00Z/29 cycle, will keep unsettled conditions lingering
into Saturday, although with lower PoPs for next Saturday.

Below normal temperatures should continue Thursday through Saturday,
with daytime highs mainly in the 50s, and overnight lows in the 40s,
although some 30s could occur across higher elevations. If steady
rain occurs during the daytime Friday, it is possible that some
high temperatures barely exceed 50.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
One cold front has moves south and east of the TAF sites as of
early evening, with a weaker secondary cold front expected to
settle southward overnight. Other than occasional mid level
clouds, this second front should only be accompanied by a wind
shift from west/northwest into the north to northeast.

Otherwise, VFR conditions are expected to prevail at least
through Sunday afternoon, with mainly mid level clouds. Some
lower clouds could develop toward Sunday evening, esp at KGFL,
but due to low confidence, have kept out mention at this time.

Also, isolated showers may develop late Sunday afternoon, with
the best chance at KGFL, but again, due to limited areal
coverage, did not mention at this time.

West/northwest winds at 5-10 KT with some gusts of 20-25 KT
this evening will decrease through midnight, then shift into
the north to northeast at 5-10 KT. A brief period of stronger
wind gusts could occur at KGFL between roughly 04Z-08Z/Sun. On
Sunday, northeast to east winds of 5-10 KT are expected, with a
few gusts of 15-20 KT possible.

Outlook...

Sunday Night: Low Operational Impact. Isolated SHRA.
Monday: Moderate Operational Impact. Breezy Isolated SHRA...TSRA.
Monday Night: High Operational Impact. Breezy Likely SHRA...TSRA.
Tuesday: Moderate Operational Impact. Slight Chance of SHRA.
Tuesday Night: Low Operational Impact. Isolated SHRA.
Wednesday: Moderate Operational Impact. Breezy Scattered SHRA.
Wednesday Night: Low Operational Impact. Isolated SHRA.
Thursday: Moderate Operational Impact. Chance of RA.

&&

.FIRE WEATHER...
High pressure builds in from southeastern Canada tonight into
Sunday with cooler conditions. A warm front will slowly lift
northward late Sunday into Monday with an increasing threat of
showers and isolated thunderstorms. A cold front will bring
widespread showers and a chance of thunderstorms late Monday
afternoon into Tuesday morning.

RH values will recover 65 to 75 percent tonight with north to
northeast winds of 5 to 10 mph. Expect the RH values to lower to
50 to 70 percent with isolated light showers on Sunday as the
winds will shift to east to the southeast at 5 to 10 mph. RH
values recover to 80 to 100 percent Sunday night and fall only
slightly to 65 to 80 percent Monday with scattered showers and
thunderstorms late Monday afternoon. Winds will become south
Monday at around 15 mph.

&&

.HYDROLOGY...
A warm front will build north through Sunday night. Rainfall
amounts will be fairly light once again, with a few hundredths
to a tenth of an inch or so.

A strong cold front will cross through the region late Monday
afternoon into Monday night. This front may allow for some
locally higher rainfall totals due to more widespread showers
and a chance of thunderstorms due to a more humid air mass. No
problems are anticipated on the main stem rivers (as shown in
the MMEFS). Rainfall amounts will range from a quarter to three
quarters of an inch with some locally higher amounts in
thunderstorms. Ponding of water on roadways or low lying areas
and poor drainage within urban areas will be possible.

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...SND/KL/NAS
SHORT TERM...NAS
LONG TERM...KL
AVIATION...KL/NAS
FIRE WEATHER...NAS
HYDROLOGY...NAS


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