Albany Office Forecast Discussion

000
FXUS61 KALY 211311
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
911 AM EDT Thu Mar 21 2019

.SYNOPSIS...
The start of Spring will be unsettled, as a developing coastal
low pressure system brings widespread rain and snow today
through Saturday morning night. This system is expected to track
northeast along the mid Atlantic and southern New England coast
today through tonight, and eventually into Maine on Friday. A
moderate to heavy snowfall is expected for elevations mainly
above 1000 feet. It will turn cold and blustery for Friday night
and Saturday, with any rain changing to snow even across lower
elevations where minor accumulations are possible.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 910 AM EDT...12Z sounding reveals wet bulb zero heights
were around 1300` and NY Mesonet Web Cams and regional radar
mosaic shows precipitation advancing northward across the
Catskills and mid-Hudson Valley. The higher terrain of the
Catskills it was snowing (Claryville sitting at 1421` per NY
Mesonet Web Cam) with rain being reported at KPOU. So we will
make adjustments to the grids just a bit to match up
observations and recent trends. As the day progresses, so does
the warm advection and the transition to mainly rain southern
areas. Further north into the Dacks and southern Greens, wet-
bulb processes will likely allow the onset of rain/snow mixture
before transitioning to mostly rain as we continue with the warm
advection regime per RAP/HRRR hourly model forecasts.

Prev Disc...Low pressure has developed along the SE coast of
N. Carolina early this morning, with falling pressure noted to
the north of the cyclone center. This low will track inland
through N. Carolina and eastern Virginia, to eventually over the
Delmarva this evening. The cyclone is forecast to deepen, as
separate upper level disturbances currently over the Midwest and
Tennessee Valley regions consolidate into a negatively tilted
upper level trough over the Ohio Valley and central
Appalachians. Ahead of this system, isentropic lift on the
285-290K surfaces will allow for precipitation to develop from
south to north this morning. Onset delayed by a few hours
compared to prior forecasts, which is also consistent with
trends from the latest hi-res guidance HRRR and NAMNest. Thermal
profiles indicate precip will likely be rain for much of the
area, although some wet snow could mix in across the higher
elevations mainly above 2000 ft. Precip will overspread areas
south of Albany through the morning hours, then shift north and
west during the afternoon.

After this first area of precip associated with the isentropic
lift moves through, there will likely be a break in the
precipitation from around Albany south and east during the late
afternoon. However, the next surge of moisture associated with
the deepening cyclone will be arriving by early evening for
areas south of Albany. Again, mainly rain will occur except
across the highest mountains. Highs today will be seasonable,
but the clouds and rain will make it feel rather damp and cool.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
Winter Storm Watch expanded to include Schoharie County and all
of the southern Adirondacks. Winter Storm Watch remains in
effect for the western Mohawk Valley, western Adirondacks and
southern Green Mountains. Timing of the watch now starts at 2 AM
Friday and has been extended to Noon Saturday...

Model guidance has come into better agreement regarding the
track of the coastal storm as it is forecast to track from near
the Delmarva this evening, to just south of NYC late tonight.
The upper level trough is expected to become negatively tilted
as additional short wave energy feeds into the trough. The
result will be a Nor`Easter, which have not been common thus far
during the winter season. Strong upward motion will lead to
widespread precipitation enveloping the region from south to
north this evening.

Tonight is when the precip type forecast become tricky. We are
anticipating thermal profiles to cool for areas west of the
Hudson Valley, as precip intensity increases. So rain will
change to wet snow for this area, and also across the southern
Greens overnight. The heaviest axis of QPF is expected to be
displaced well north/west of the surface cyclone including
locations west of the Hudson Valley, in the area of max
850-700mb F-Gen. The uncertainty lies in how quickly the
changeover to snow will occur. There are discrepancies among the
guidance with the NAM coldest, while the GFS appears too warm
in the near-surface layer. So we will mention rain/snow mix
changing to snow overnight except in the Hudson Valley from
around the Capital District southward where it will be too warm
for snow through the night. Most areas above 1000 ft should see
a changeover to snow by late tonight. The heaviest snow should
line up across the western Mohawk Valley, southern Adirondacks
and into the Schoharie Valley, where the Winter Storm Watch has
been expanded. Portions of western Greene/Ulster counties may
receive heavy wet snow as well, but we did not have enough
confidence to include this area in the watch yet. Due to the
uncertainty in timing of the change to snow, we have also pushed
back the start time of the watch to 2 AM.

By early Friday morning, the axis of heavier QPF will start to
shift eastward into the Hudson Valley. This is when it will be
possible for a brief period of wet snow to fall even in the
Capital District if precipitation rates are intense enough. We
have included mention of rain/snow mix with up to a half inch of
snow mainly on grassy surfaces locally. As the precipitation
intensity weakens somewhat by Friday afternoon and diurnal
effects occur, snow will likely change back to rain in valley
locations and even a rain/snow mix up to around 1500 ft
elevation. Accumulating snow will continue though, across the
western/southern Adirondacks and southern Green Mountains
through the day on Friday, although snow may be more
intermittent across the southern Greens until Friday evening.

Friday night is when the event will transition to more of an
upslope/terrain driven snowfall with abundant wrap-around
moisture, as the upper level low center shifts east of the
region and the flow becomes northwest. The northwest winds will
increase substantially as the surface cyclone lifts NE into
Maine and deepens to somewhere around 980mb creating a strong
pressure gradient. Mixing heights will not be very tall, but
wind speeds of 45-50 kt at the top of the mixed layer could
result in Advisory level wind gusts of > 45 mph across much of
the area. Will continue to mention this potential in the HWO.
Snowfall will really start to pile up across favored NW flow
upslope areas in the western Adirondacks and southern Greens.
Snow-liquid ratios should also start to increase as colder air
takes hold. There could even be some minor accumulations in the
Hudson Valley from Glens Falls/Saratoga region southward through
the Capital District, as an area of deformation potentially
develops. We have mention 1-2 inches of accumulation, with
potential for Advisory level snowfall in the higher terrain
areas outside the Watch above 1000 ft, such as the northern
Taconics and Berkshires.

Upslope snow and strong gusty northwest winds will continue
into Saturday morning in the cyclonic flow regime. However, the
storm system is expected to finally pull away by Saturday
afternoon. So snow should end even in the mountains by around
Noon. It will remain cold and blustery through the afternoon.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The extended forecast will feature a dry ending to the weekend,
and then a strong arctic cold front will move through on Monday
with below normal temperatures expected into the mid week.

Saturday Night into Sunday... Low pressure moves into the
Canadian Maritimes with high pressure building in from the Ohio
Valley into the mid Atlantic States Saturday night into Sunday
morning. The sfc pressure gradient will weaken and the winds
will diminish Saturday night. Lows will be on the chilly side
with mid teens to around 20F over the higher terrain, and lower
to mid 20s across much of the valleys. The close of the weekend
will feature temps rising to normal to above normal readings, as
mid and upper level heights rise aloft with the sfc ridge
building in from the south. The subsidence from the anticyclone
will yield mostly sunny conditions with highs in the upper 30s
to mid/upper 40s over the higher terrain, and upper 40s to upper
50s in the lower elevations.

Sunday night into Monday...The mid and upper level flow becomes
zonal, as an upper level trough continues to dig equatorward
from south-central Canada. A cold front front will begin to dip
south/southeast towards upstate NY and New England Sunday night
with some clouds increasing. The consensus from the latest
GFS/ECMWF/CMC and many of the Ensembles is to bring a slight to
low chance of snow showers into the southern Adirondacks/western
Mohawk Valley Sunday night, and then expand the PoPs southward
during the day into the high chance category. The arctic cold
front shows characteristics like an ana-cold front with most of
the pcpn in its wake and behind the wind shift. Some scattered
rain to snow showers are possible, as H850 temps will fall from
from +2C to -4C across the region from south to north at 12Z/MON
to -3C to -15C by 00Z/TUE. The better chance of snow showers
looks to be north and west of the Capital Region at this time.
After lows in the 20s to mid 30s, expect high temps from the
mid/upper 40s to lower 50s from the Capital District south and
east, and upper 20s to lower 40s north and west.

Monday night into Tuesday...Strong cold advection continues in
the wake of the arctic boundary Monday night, as H850 temps
plummet to 2 to 3 STD DEVs colder than normal based on the
latest 00Z GEFS for Mon night and TUE. The actual H850 temps
will be in the -16C to -20C range. Expect cold and brisk
conditions with lows in the teens to mid 20s with some single
numbers over the southern Dacks. The below normal temps continue
on Tuesday, as a cyclonic flow of chilly early spring air
persists with the upper level trough over the northeast CONUS.
Temps on Tuesday will run about 10 degrees or more below normal.


Tuesday night into Wednesday...Cold and dry weather continues
with high pressure ridging in over NY and New England. H850
temps will still run below normal by 1 to 2 STD DEVs based on
the latest GEFS and NAEFS. Lows Tue night will be in the single
digits and teens over most of the region and highs on WED will
generally be in the lower to mid 40s in the Hudson River Valley
and portions of NW CT, but expect 30s outside the Hudson River
Valley with some upper 20s over the southern Dacks, and southern
Greens.

&&

.AVIATION /13Z THURSDAY THROUGH MONDAY/...
A low pressure system will form over the Mid Atlantic States
this morning with the clouds further thickening and lowering
with moisture streaming northward into the TAF sites in the late
morning and into the afternoon with mainly light rain. The
precipitation will increase in coverage and intensity tonight,
as the coastal wave get closer to Long Island and southwest New
England.

VFR conditions are expected with the clouds gradually
thickening and lowering with the best chance of MVFR cigs/vsbys
shortly before 15Z/THU at KPOU with light rain moving in. The
trend continues for the -RA to move north/northwest between 17Z-
21Z/THU with the potential of MVFR cigs/vsbys in the -RA at
KALB/KGFL. We were less certain at KPSF and used a PROB30 group
between 23Z/THU and 03Z/FRI due to the east/southeast
downsloping winds which may hold conditions at VFR there. The
rain will expand in coverage between 00Z-04Z/FRI with
widespread MVFR conditions impacting the eastern NY and western
New England terminals. Widespread IFR conditions of vsbys/cigs
are possible between 04Z-08Z/FRI at all the TAF sites. The IFR
conditions will last until the end of the TAF cycle, and snow
may mix with rain at KGFL beginning at 08Z/FRI.

The winds will generally be south to southeast at 5-10 kts
during the late morning into the afternoon with some gusts in
the 15-20 kt range at KALB. The winds will begin to back to the
east to northeast at less than 10 knots tonight, as the wave
approaches from the south. The winds will vary from the north to
east at less than 10 kts after midnight.

Low-level wind shear may increase below 2 kft AGL at KPSF after
06Z/FRI.

Outlook...

Friday Night: High Operational Impact. Very Windy Likely RA...SN.
Saturday: High Operational Impact. Very Windy Chance of SHSN.
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: No Operational Impact. NO SIG WX.
Sunday Night: No Operational Impact. NO SIG WX.
Monday: Moderate Operational Impact. Chance of SHRA...SHSN.
Monday Night: Low Operational Impact. Slight Chance of SHSN.
Tuesday: No Operational Impact. NO SIG WX.

&&

.FIRE WEATHER...
A developing coastal low pressure system will bring widespread
rain and snow today through Saturday morning night. A moderate
to heavy snowfall is expected for elevations mainly above 1000
feet. It will turn cold and blustery for Friday night and
Saturday, with any rain changing to snow even across lower
elevations where minor accumulations are possible. Liquid
equivalent precipitation amounts will range from around an inch
across the southeast portion of the area, to 1.5 inches north
and west of the Capital District.

&&

.HYDROLOGY...
No widespread hydrology problems are anticipated through the
next 7 days.

Widespread precipitation will occur across the area starting
today and lasting into Saturday morning. QPF amounts 1 to 1.5
inches are expected, with the greatest amounts for areas north
and west of the Capital District. Mainly rain is expected in the
valleys with some light snow accumulation, while across the
higher terrain above 1000 feet a moderate to heavy wet snow is
expected. Where there is existing snowpack, temperatures are not
expected to get warm enough to produce much snowmelt. Some
within bank rises on rivers are expected. The latest MMEFS
guidance continues to not have any points reaching flood stage.
Any runoff which does occur will slow and/or end at night with
temperatures dropping below freezing through the weekend.

&&

.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Winter Storm Watch from late tonight through Saturday morning
     for NYZ032-033-038-042-047-082.
MA...None.
VT...Winter Storm Watch from late tonight through Saturday morning
     for VTZ013-014.

&&

$$
SYNOPSIS...JPV
NEAR TERM...BGM/JPV
SHORT TERM...JPV
LONG TERM...Wasula
AVIATION...Wasula
FIRE WEATHER...JPV
HYDROLOGY...IAA/JPV

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NWS ALY Office Area Forecast Discussion