Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/22/21
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1009 PM EST Sun Feb 21 2021
Clouds will be on the increase tonight. A storm system
approaching from the central U.S. will bring another round of
accumulating snow to the area on Monday. Snow could mix with some
rain across the lower elevations south and east of Albany.
Temperatures early in the week will moderate to above normal levels
by midweek, before trending colder than normal again by the end of
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 1008 PM EST...As a strong 1034 hpa high pressure area
departs off the New Jersey shore, IR satellite imagery shows
increasing high level clouds starting to expand towards the
area. Sky cover will increase through the rest of the overnight
hours, with skies become mostly cloudy for the entire area by
the late night hours. 3km HRRR shows some light snow showers may
start to work into parts of the western Adirondacks towards
With the fairly clear skies and light winds this evening, temps
have crashed rather quickly. NYS Mesonet obs show some places
have dropped into the single digits and teens already, which
will likely be the lows for the night. Once clouds move in,
temperatures should hold steady and could even begin to increase
into Monday morning. By late in the overnight, a southerly wind
will begin to increase, especially for the north-south valleys,
with some gusts starting to exceed 20 mph.
.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
A Winter Weather Advisory has been issued for northern Herkimer,
Hamilton, and northern Fulton counties from 7 am EST Monday to 1 am
Key Takeaways regarding Monday`s winter weather event:
* Initial band of light snow between 4-7am (a quick coating to
less than one inch expected; best chance eastern Catskills and
areas north of I-90)
* Prime time for accumulating snow: Between Noon-4pm or so
* Snow could be heavy at times with snow rates exceeding 1"/hr
(especially higher elevations)
* Snow tapers to snow showers/flurries after 21z or so
* Snow showers/flurries end between 7pm-1am everywhere except
for maybe SW Adirondacks (Herkimer/Hamilton counties)
Projected snowfall amounts:
* 3-6 inches portions of SW Adirondacks extending into the
northern Mohawk Valley and northwest Saratoga County (locally
higher amounts of 6-8 inches across parts of Herkimer and Hamilton
* 2-4 inches across southern VT and eastern Catskills with locally
higher amounts of 4-6 inches
* 1-3 inches Berkshires into NW CT
* Dusting to 2 inches elsewhere (lowest amounts over Albany and the
* Liquid to snow ratios: 9:1-15:1 (highest north, lowest south)
* Snow will be wetter south, drier and fluffier north
* Snow could mix with rain along the Hudson Valley (especially south
and east of Albany)
The short-term period will feature active weather with not one, but
two chances at additional wintry precipitation.
We start off the short-term forecast period with a negatively
tilted, occluding surface low pressure system approaching from the
central Great Lakes region. Before daybreak on Monday (roughly
between 4-7am), a narrow band of light snow, associated with the
leading edge of mid-level isentropic lifting, will move over the
area. BUFKIT soundings depicts a moderate to deep column of dry air
in the lower levels of the atmosphere (particularly under 800 mb).
Because of this, snow will likely evaporate before reaching the
ground (virga). This is especially true for the valley areas. That
said, the best chance for snow to reach the ground with this initial
band will be across the eastern Catskills, SW Adirondacks, and
higher elevated areas north of I-90. Here, a coating to less than an
inch of snow is possible. This could create for some locally
hazardous driving conditions during the morning commute in these
As the storm system draws closer to the area, 850 mb low-level
jet winds will increase in speed to near 50 kts around 18z (1pm).
The increase in the warm conveyor belt winds will allow for an
increase in temperature and moisture advection. Surface
dewpoints around 18z (1pm) were sampled in the upper 20s to
lower 30s across the ALY area. During this time, profile
soundings indicate adequate moistening of the lower levels
(below 800 mb) around 17z (noon).
The main precipitation shield associated with more robust forcing
from this storm system will move over the area from west to east
beginning around 16-18z (11am-1pm). Because the lower levels of
the atmosphere will have become saturated, the 16z-18z (11am-
1pm) timeframe is when we can expect the onset for
Unlike the last storm system, this storm system will be warmer.
Temperatures are projected to climb into the lower to mid-30s on
Monday with mid-30s predominantly located over the Hudson Valley.
Because of this, we have to deal with the potential for various
precipitation types (p-types). At this time, trends continue to
point towards things remaining all snow across the higher elevations
and snow mixing with rain across the lower elevations/valleys (esp
south and east of Albany). Things could initially start off as snow
across the valleys. Diabatic cooling via wet-bulbing, however,
will not be enough to offset the warmth advected into the area.
Therefore, we expect an approximate 2-3 hour period of snow in
the valleys before transitioning over to a rain/snow mix.
The synoptic setup with this storm system supports orographic
effects with upsloping favoring higher snow totals across the higher
elevations and downsloping/shadowing favoring lower snow amounts
across the valley areas.
Large to meso-scale ageostrophic forcings, as well as mid-level
instability is quite impressive especially during the beginning
parts of this event. By 17z (noon) or around the onset time of
precipitation, the area will be placed in the left exit region of a
145-150+ KT 250 mb jet that will be passing over the mid-Atlantic
region. The best lift will be below the dendritic growth zone before
the onset of precipitation, but by the start of precipitation
adequate vertical ascent will have transitioned within/through the
dendritic growth zone between 560-700 mb with omega values
approaching or even slightly exceeding -2 Pa/s, according to some of
the hi-res guidances. According to some of the deterministic models,
three-hour isallobaric wind fields at the surface suggest 6-7mb
pressure falls around 18z (1pm) which supports sufficient
upward motion. Lastly, mid-level instability will be impressive
with H7-H5 lapse rates approaching/exceeding 7C/km. All of this
suggest that light to moderate snow could become heavy at times
with snow rates likely exceeding 1-1.5"/hr. Given these
impressive numbers, precipitation could show some convective
This is not expected to be a long-duration winter event, but
rather a quick hitter with good snow rates. Between 21z-00z
(4pm-7pm), snow is expected to taper down to snow
showers/flurries. Snow showers/flurries should be coming to an
end across most places except for the higher terrain areas
between 00z-06z (7pm Monday- 1am Tuesday). The bulk of the
accumulating snowfall will occur between 17z- 21z (noon-4pm) or
As far as snow amounts expect 3-6 inches over portions of SW
Adirondacks extending into the northern Mohawk Valley and northwest
Saratoga County (locally higher amounts of 6-8 inches across parts
of Herkimer and Hamilton counties), 2-4 inches across southern VT
and eastern Catskills with locally higher amounts of 4-6 inches, 1-3
inches Berkshires into NW CT, and a dusting to 2 inches elsewhere
(lowest amounts over Albany and the Capital District). Travel
conditions will be slippery with the evening commute being most
impacted. Use extra caution if you have to go out.
Light southerly winds will pick up in intensity between 14z-21z
(9am-4pm) becoming sustained at 10-20 mph and gusting 25-40
mph. Peak wind speeds will be between 15z-19z (10am-2pm) and
will be concentrated along the Hudson Valley.
We`ll get a very brief reprieve from any form of wintry
precipitation Monday evening/night into Tuesday before another storm
system tracking well to our north in Canada brings another round of
light snow or rain/snow to the region. Early signs suggest that this
will be another mountain snow valley rain/snow mix. Light snow
accumulations appear likely due to 1) the best forcing being well to
our north, 2) the snow associated with this system being pretty
moisture starved, and 3) this batch of light snow being a quick
hitter. Anywhere from a dusting to 3 inches of snow is plausible
with the highest amounts once again over the higher elevations
(upsloping) and lowest amounts along the Hudson Valley
(downsloping/shadowing potential as well as rain/snow mix p-type).
Temperatures will begin its trend higher early to mid-week. High
temperatures on Monday are expected to top out in the lower to mid
30s and on Tuesday into the mid 30s to near 40F degrees (cooler
higher elevations). Low temperatures Monday night into Tuesday
morning will be mostly in the mid to upper 20s.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
An exiting upper level disturbance may still allow for a few
lingering snow showers over the Adirondacks or southern Greens on
Tuesday evening, otherwise, it should be dry across most of the
area. Some breaks in the clouds are possible, especially for valley
areas, but temps will only be lowering into the mid 20s to low 30s
for lows on Tuesday night.
Although Wednesday will start off dry, the next storm system will be
approaching for later in the day and into Wed night. This will be a
fairly weak wave of low pressure that will be approaching from the
Ohio Valley/Great Lakes region and heading towards northern parts of
the area as it lifts towards the Northeast. Best chance of seeing
some light snow showers (mixed with or changed to rain at lower
elevations) will be across western and northern parts of the area
for late Wednesday into Wednesday evening and the first half of Wed
night. Any snowfall amounts look fairy light and limited to mainly
just the Adirondacks. Ahead of the approaching storm system, a
southerly flow should allow for milder temps. Highs on Wednesday
look to range from the mid 30s over the Adirondacks to the mid to
upper 40s in the Capital Region and Hudson Valley. Behind the storm,
temps look to fall into the 20s to near 30 for Wednesday night.
Fast west-southwest flow aloft look to set up over the region for
Thursday into Friday. This should keep mainly dry weather in place
with fairly seasonable temps. There could be a few lake effect snow
showers Thursday over CNY, but these should mainly be staying west
of the area based on the expected northwest flow at lower levels.
Valley areas should reach the mid to upper 30s for Thursday, but
only lower to mid 30s for Friday.
Another chance for some light rain or snow is expected over part of
the weekend depending on the exact track of a southern stream storm
system. At this point, the majority of models/ensemble members are
showing this to be on the light side, as the best moisture/dynamics
remain south of the region. However, this is subject to change. As
of right now, temps look to continue to be close to seasonal normals
for Saturday, with milder weather possible by Sunday.
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
VFR conditions are expected overnight. Clear skies and
light/calm winds this evening will gradually give way to
increase mid and high level clouds after midnight. Towards
daybreak, southerly winds will begin to increase, especially at
On Monday morning, clouds will continue to lower and thicken,
but it will remain VFR for most of the morning hours. Southerly
winds will increase to around 10 kts, with some higher gusts at
times. Towards midday, light snow will begin spreading from
west to east across the TAF sites, which should lower visibility
to IFR range of 1 to 3 SM quickly once snow begins. Ceilings
will generally be around 2-3 kft for all sites through the
afternoon hours. Snow will last for most of the afternoon, but
will be tapering off around 20z-22z, allowing for visibility to
improve back to VFR levels. During the afternoon/early evening
hours, southerly winds will be 10 to 20 kts for all sites. Some
gusts of 20 to 30 kts are possible, with the strongest gusts at
KALB. Some rain could mix in with the snow at KALB/KPOU,
especially for the late-day hours. Winds will diminish slightly
for Monday evening, but will still be somewhat gusty.
Monday Night: Moderate Operational Impact. Scattered SHSN.
Tuesday: Moderate Operational Impact. Breezy. Scattered SHRA...SHSN.
Tuesday Night: Low Operational Impact. Breezy. NO SIG WX.
Wednesday: Low Operational Impact. NO SIG WX.
Wednesday Night: Moderate Operational Impact. Chance of SHRA...SHSN.
Thursday: Low Operational Impact. Slight Chance of SHRA...SHSN.
No widespread hydrological issues are expected over the next several
Near seasonable temperatures are expected through early this
week. This will continue to support mainly frozen precipitation
types and allow ice to expand and thicken on area waterways.
A storm system for Monday will bring additional light to
moderate snow, possibly mixed with some valley rain on Monday.
Temperatures will moderate to slightly above normal levels into the
middle of next week, possibly allowing for some ripening/warming
of the snowpack.
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
NY...Winter Weather Advisory from 7 AM Monday to 1 AM EST Tuesday
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
706 PM CST Sun Feb 21 2021
706 PM CST
Overall, the evening is going as expected with wet/sloppy/slushy
snow (at times mixing with light rain) falling across parts of
northern Illinois and northwest Indiana. Temperatures across much of
the area have climbed above freezing for the first time since
February 4th (when interestingly enough the warmest temperatures
were also during the evening), and southeast to south winds have
been gusting in the 25 to 35 mph range. It`s a decidedly raw evening
At this point in time, we`re at about the midpoint of this system
with peak areal coverage of precipitation. Trends in RAP forecast
total positive energy (essentially the amount of "energy" available
to melt falling snowflakes) suggests we may see snow changing to
rain generally along and south of I-88 over the next few hours, with
all snow continuing near the Wisconsin state line. Thus, any
additional slushy accumulations will become increasingly confined to
locations north of I-88. Precipitation should taper from west to
east between 10 pm and 2 am, with all areas expected to be dry by 3
am. Breezy west to northwest winds will then return temperatures to
below freezing by daybreak. As such, Monday morning commuters should
keep an eye out for slick spots on untreated roadways (especially on
bridges and overpasses).
315 PM CST
Through Monday night...
Regional radar mosaic loops show the coverage of radar echoes
gradually blossoming across northern and central Illinois this
afternoon, serving as visual confirmation of the ongoing ascent and
saturation of the air in the region owing to isentropic upglide,
DPVA out ahead of the incoming shortwave, and upper divergence in
the left exit region of jet that`s overhead and extending out to the
southwest. Most the of reflectivity being sampled over the CWA was
not quite reaching the ground yet as of 2:30 PM CST, but recent
METARs from Rockford and Peru have indicated that precipitation
has started across our western counties and is imminent elsewhere as
the column continues to saturate and the surface low over central
Iowa continues to work its way off to the northeast.
Temperatures have warmed into the mid 30s in parts of the Chicago
metro this afternoon, marking our first time above freezing in
almost 17 days! With these temperatures likely remaining a few
degrees above freezing for a few more hours, wouldn`t be surprised
to see a brief period of at least a rain/snow mix if not outright
rain at the very onset of precipitation in the Chicago metro, but
given that below freezing wet-bulb temperatures will be present
across the metro through the late evening and with somewhat heavy
precipitation rates likely shortly after precipitation onset,
we`ll likely cool down closer to freezing pretty quickly and any
rain that falls at precipitation onset will change over to all
snow soon after.
Overall, the same general thoughts about snow rates and snow ratios
from previous forecasts apply for this current forecast iteration.
The potential for at least brief bursts of heavy snow still
remains generally north of I-80 due to 7-8 C/km lapse rates
through and just above the dendritic growth zone, with the most
favored area for this still being generally northwest of a Dixon
to Woodstock line. The favored timing for the heavier snow rates
is still shortly after the onset of precipitation through the
early evening. Snow ratios still look to range from about 7:1 to
12:1 with the lower ratios generally expected across our south and
the higher ratios more likely farther north. Regardless of the
exact ratios, this snow will be a wetter type of snow and not the
fluffy kind that we had consistently seen over the past few
There are a few minor changes regarding thoughts on final snow
totals for the area. While the higher totals (2-4") are still
favored to occur across northwestern and far north-central Illinois
where the steeper lapse rates could overlap with some mid-level
f-gen support and the lower totals (under 1") are still looking
likely for areas well south of I-80, there are still concerns with
the pesky dry slot currently to our west nosing a little farther
north than previously expected which could cause some locations to
underperform a bit in terms of final snowfall totals. Have nudged
down snow totals slightly along the I-80 corridor where model and
observational trends have increased confidence of the rain/snow
mix line creeping that far north by mid-evening and to account for
the potential for less precipitation occurring overall with the
dry slot issue. Potential for loss of cloud ice is also evidently
there with the 500 mb dry slot likely to chew up a good amount of
moisture through the DGZ, which would suggest that a changeover to
drizzle and/or snizzle is looking more possible by mid-evening.
Nevertheless, hazardous travel due to sharp visibility reductions
and slick roads (from both accumulating snow and any rain/drizzle
that manages to freeze on roadways with sub-freezing surface
temperatures) can still be expected late this afternoon and evening.
Snow will begin to taper off later this evening as the steeper lapse
rates move off to the east and the surface cyclone occludes to our
north and northeast. Any lingering light snow or drizzle will end
from west to east roughly between 10 PM and 2 AM CST. While the
precipitation will end, gusty west winds of up to 30 mph will
continue overnight into tomorrow afternoon.
Another shortwave trough will swing down through the Great Lakes on
Monday, but with the mid-levels deprived of any deep moisture and a
lack of favorable dynamics over the region, any precipitation from
this system should remain well to our north. Westerly to
southwesterly flow will allow us to warm up a tad from Sunday`s
highs, but cloud cover trapped under a stout 900 mb inversion will
likely keep highs from getting any higher than the mid-upper 30s.
105 PM CST
Tuesday through Sunday...
With high temperatures expected to consistently push north of the
freezing mark into the middle and end of the week, it`s certainly
going to feel quite a bit different than the last several weeks
here. Extended guidance continues to suggest, however, that we`ll
remain in a fairly active pattern, with numerous disturbances
slated to crest the eastern Pacific ridge and zip across the CONUS
into next week. The main question is just what side of the
baroclinic zone we`ll find ourselves.
Tuesday offers up a pretty significant high temperature bust
potential. The latest GFS, NAM, CMC, and UKMET continue to
suggest that a robust subsidence inversion will keep low-level
moisture and associated stratus locked in place, possibly even
through Wednesday. The ECMWF, on the other hand, insists that
we`ll readily chew through this via the combination of mechanical
mixing and insolation, and commensurately drives high temperatures
well in to the 40s across the region. The former guidance locks
stratus in place all day, which would hold temperatures closer to
the low to mid 30s. The path of least regret at this time is to
follow the offered blended guidance, which is close to what local
climatology would suggest with a deep snowpack in place. Either
way, it looks like some bonafide 50 degree temperatures may not be
too far to our south...
A fast-moving disturbance offers a glancing blow of ascent Tuesday
night into Wednesday. Low-levels look pretty parched, but this
system could intercept sufficient moisture as it passes our
longitude to start producing some precipitation. Could envision
needing some slight chance PoPs south and east of I-55/57 for
this, but for now, a dry forecast looks fine given the multi-model
consensus. Temperatures will be a bit cooler on Wednesday with
renewed northwesterly flow and cold advection.
There are indications that a more amplified positively tilted
trough shifts overhead Thursday behind the aforementioned short-
wave, with temperatures trending cooler during that time.
Currently expecting highs in the lower 30s, and lows Thursday
night in the upper single digits to mid teens. Beyond Thursday
guidance begins to diverge resulting in low confidence in any
specific features. Will maintain slight to low chance PoPs early
Saturday morning into Sunday, in line with the previous forecast
and offered blended guidance today. However, as it stands, it
appears the better chance for precipitation may lie just beyond
the extended period as the upper level pattern becomes more
amplified into early next week. Based on the latest forecast, some
degree of snow melt during the days with re-freezing at night
should help temper and flooding concerns.
For the 00Z TAFs...
The primary concerns for the Chicago airports are:
- Waves of moderate snow this evening, with period(s) of drizzle
in-between; snow may mix with true rain after 03Z before ending
- Slight chance of ice pellets mixed within any moderate/brief
heavy snow areas
- Gusty south-southeast winds becoming southwest after 03Z-04Z;
will likely be temporarily out of the due south prior to shift
- IFR ceilings moving in this evening and gradually lifting into
MVFR by Monday morning
- Gusty west winds overnight turning southwest again by midday
The first wave of snow looks to end at ORD and MDW by 0000Z-0015Z
with a more prevalent light snow/drizzle then onsetting and
persisting through 0100Z-0130Z. The chance for freezing drizzle
looks low at this time, as surface temperatures will actually be
inching upward on gusty southerly winds. A few gusts to 30 kt are
possible, including during the next batch of snow/snow showers,
which looks to arrive by not long after 01Z. With the combination
of moderate snowfall rates expected and the gusty winds, we
continue to note temporary 1/2SM visibility in the TAF.
Confidence in this is a smidge lower at MDW, and will watch
upstream trends to see how far south moderate/brief heavy snow is
being observed. Precipitation should taper late evening into early
overnight, and again a mix or even possibly a change to rain is
possible before ending.
IFR ceilings look to be prevalent much of this evening with higher
confidence than earlier. Cannot rule out ceilings as low as 500 ft
temporarily, especially at RFD, but even ORD may briefly see that
low. As the system cold front passes early overnight, winds will
turn westerly and gust to over 25 kt and ceilings should inch
upward to the lower MVFR category by daybreak Monday.
Confidence in low clouds scattering or clearing midday Monday is
medium to high, though specific time is still low. If clearing
fully occurs, some southwesterly gusts over 30 kt may be realized
during the afternoon.
LM...Small Craft Advisory...Winthrop Harbor to Northerly Is. until midnight Monday.
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