Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Albany New York
1255 PM EST Wednesday Dec 11 2013
a brisk westerly flow will bring significant lake effect
snowfall to portions of the southern Adirondacks through tonight. An
Arctic cold front crossing the region will bring snow showers later
today and tonight...and followed by even colder air for Thursday
into Friday...along with some snow showers and flurries. Additional
lake effect snowfall will occur Thursday into Friday as well.
Near term /until 6 PM this evening/...
as of noon...all headlines remain in effect. After a brief hiatus
the lake band in ramping up again...producing up to 2 or more inches
per hour working into northern Herkimer County and possibly those
rates into Hamilton County.
A separate much weak lake effect snow band was working down the
Mohawk Valley into the capital district. We added isolated coverage
for snow showers right into the region...and even the Berkshires. A
few of the higher spots in the Taconics could get a coating with
Kept high temperatures as they were...although with plenty of clouds
in the capital district...temperatures rose as the wind was now
working of the helderbergs adding a bit of compression.
A lake effect snow warning remains in effect for northern Herkimer
and Hamilton counties through 6am EST Thursday. In addition...a lake
effect Snow Advisory remains in effect for northern Warren
County...specifically the portion bordering Hamilton County across
the higher terrain...through midnight tonight.
By this afternoon...although the low level wind flow within the
mixed layer will come across the long axis of Lake Ontario...there
will be somewhat limited upstream lake contribution...with some from
Huron...but little of Georgian Bay and Superior due to a persistent
backed southwest flow. So...although occasionally heavy snow showers
will occur across northern Herkimer Colorado...the inland extent of the
snowband may still be somewhat limited. However...as the top of the
mixed layer rises due to cooling aloft and increasing synoptic lift
with the approach of a shortwave from the west this
afternoon...there is a better potential for the band to intensify
and extend further inland...especially from late afternoon into early
tonight...before the mixed layer flow veers with the passage of an
Arctic cold front. So...still expect 5-10 inches across northern
Herkimer Colorado today and 3-6 inches across Hamilton Colorado...the bulk of
this may occur this afternoon and evening. Also...most of the
heavier snow showers in northern Warren Colorado are also expected this
afternoon/evening...with 1-3 inches expected through early evening.
It will be quite brisk today...with west to southwest winds
occasionally gusting into the 30-35 miles per hour range. Maximum temperatures will
reach 25-30 in most valleys...with teens to middle 20s across higher
Short term /6 PM this evening through Friday night/...
tonight...the lake effect snowband/S should be ongoing this
evening...before shifting southward with a veering low level flow
with and behind the cold front. Model soundings indicate the
potential for windex snow squalls and/or a penetration of lake
effect snowbands well inland for a period this evening through
midnight. Surface-700 mb lapse rates reach 7.5-8.0 c/km for areas near
and north of Interstate 90...with surface-3km convective available potential energy reaching 20-40
j/kg. Relative humidity values at or greater than 70 percent within the maximum
dendritic growth zone also appear probable for these areas.
So...have indicated high chance probability of precipitation for most of these areas...with
some likelies for higher elevations of western New England.
Although snowfall accums are expected to generally remain from a
coating to an inch...localized higher amts could occur should any
snow showers/squalls persist outside of the Main Lake effect
bands. Some snow showers or squalls could even reach portions of
the middle Hudson Valley and northwest CT around or after midnight. Within
the Main Lake effect bands...an additional 4-8 inches seems
probable this evening across the warning area before the bands
shift southward...and an additional 3-5 inches across the
advisory area. Temperatures should fall into the single digits and teens
by daybreak in most areas...with some subzero readings likely
across portions of the southern Adirondacks.
Thursday-Thursday night...although the Main Lake effect potential
should shift south and west of the region Thursday morning...the bands
may shift back north in the afternoon and at night as the low
level flow backs. Low level instability still looks rather
impressive across most of the region Thursday as the middle level
cold pool moves across...so at least scattered snow showers...and
perhaps a few embedded heavier squalls could occur...especially from
Albany and points north and west...with additional minor accums possible.
As for the lake effect potential...moderate additional accums could
occur across portions of the western Mohawk Valley and
Adirondacks...so New Lake effect snow advisories may be needed. It
will be quite cold...with maximum temperatures only reaching the single
digits and teens for higher elevations...and generally lower to
middle 20s across valley areas. Thursday nt/Friday am mins should fall into
the single digits and lower teens.
Friday-Friday nt...an Arctic frontal boundary is expected to approach
from the north during Friday...before stalling across southern
portions of the region late Friday or Friday nt. Low level
convergence...combined with increased middle level frontogenetical
forcing should lead to at least some snow showers or periods of
very light snow near and in the wake of the boundary Friday...and
north of the stalled boundary Friday nt. Also for Friday nt...a rather
impressive coupled upper level jet structure develops...possibly
enhancing synoptic lift and allowing for some bands of light snow
to develop Friday nt across central portions of the region. This will
need to be watched for possible minor accums. As for lake effect
snow...some may be ongoing across the western Adirondacks Friday am.
However...a lowering inversion levels...and veering winds with the
frontal passage should squelch lake effect by late Friday. Temperatures Friday
should reach the teens and lower 20s across higher
elevations...and middle to upper 20s for lower elevations...before
falling into the teens and single digits for northern and central
areas...and teens to lower 20s for southern areas Friday nt/Sat am.
Should northern areas clear out Friday nt...even colder
mins...perhaps well below zero...could occur.
Long term /Saturday through Tuesday/...
potentially significant winter storm impact this weekend...
The main ingredients for this potential winter event this weekend
were situated off the coast of Baja California California and energy coming
ashore across British Columbia. These systems are forecast to
somewhat phase either across the Ohio River valley or across the
middle Atlantic region this weekend. Global models are in rather
good agreement with this scenario but do differ /as expected/ on the
specifics. The European model (ecmwf) is the strongest with the surface ridge
extending just north of the Great Lakes region and into New England
on Saturday /1040mb/ as opposed to the GFS/ggem which keeps a
frontal system quasi-stationary across the i90 corridor. This makes
a difference with respect to keeping our weather initially dry on
Saturday or snowy. Per collaboration from wpc...we will lean closer
to the snow solution as our upper pattern remains somewhat stagnant
with a broad west-southwest to east-northeast flow which should keep
the front in the vicinity.
Meanwhile...these aforementioned systems begin their approaches
later in the day Saturday into Saturday night. Snow should evolve
from south to north through this time frame as the thermal profiles
and corresponding thickness schemes support snow for the entire
County warning forecast area. Quantitative precipitation forecast amounts vary from these global models with ensemble
members suggesting a little higher than operational runs. This is
due to a bit higher Standard deviations of the v-component of the
lower level winds for advecting higher moisture profiles into the
Eventually...some this warm air may result in a wintry mixture
Sunday morning. Ensemble mean points toward the middle Hudson Valley
and northwest Connecticut with the higher probabilities of the
wintry mixture. Elsewhere...snow is expected to continue in the
morning as main surface low develops over the middle Atlantic and
tracks east of Cape Cod Sunday afternoon. Deformation and perhaps
Mohawk Valley convergence could provide additional accumulating
snowfall. A diminishing trend is expected through the afternoon
hours as the main storm center and upper support track further
northeast of the region.
As a fresh snow cover is expected...and a surface high building into
the region early next week...we will undercut guidance numbers as
Monday night temperatures could be the coldest of the season with
many areas at or below zero degrees /not including the wind chill
index which could be much lower/.
Overall...temperatures through the period will average below normal
with at to above normal precipitation.
Aviation /18z Wednesday through Monday/...
even though isolated to scattered snow showers/squalls could produce IFR
conditions this evening as a secondary Arctic front moves through...
the probability of IFR conditions at any of the taf sites low so
have not included any IFR conditions in the kalb/kgfl/kpou/kpsf taf
sites for this taf period. Have forecast vcsh through about 08z/09z
with mainly VFR ceilings. The exception is MVFR ceilings are forecast at
kpsf after 00z. After 09z the cloud cover will become mainly scattered at
the taf sites for a time...then become broken again after around 15z.
Surface winds will be westerly at 10 to 15 kts with gusts of 20 to
25 kts into this evening...then decrease to mainly 10 kts or less
this evening and continue that way through early Thursday.
Thursday afternoon and night: low operational impact. Slight chance
Friday: moderate operational impact.Breezy chance of shsn.
Friday night: moderate operational impact. Chance of shsn.
Saturday: moderate operational impact. Likely snow.
Saturday night: high operational impact. Definite snow.
Sunday: high operational impact. Definite snow.
no Hydro related concerns are expected this week. The precipitation
that occurs will be in the form of snow...except a wintry mix is
possible over the weekend for southern areas.
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.
New York...Lake effect Snow Advisory until midnight EST tonight for
Lake effect snow warning until 6 am EST Thursday for nyz032-