Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/23/24
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1044 PM EST Fri Nov 22 2024
.SYNOPSIS...
Low pressure developing off the New England coast will keep
unsettled conditions across the area through Saturday, with
rain and mountain snow showers overnight, gradually tapering off
on Saturday. It will become windy Saturday, with breezy
conditions continuing Sunday along with a mix of sun and clouds.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Winter Weather Advisory cancelled for Schoharie County...
Winter Storm Warning remains in effect for western Greene and
western Ulster counties until 1 AM Saturday for elevations
mainly above 1500 feet.
.UPDATE...As of 1040 EST, earlier band of heavy wet snow across
the higher terrain of the eastern Catskills has weakened.
However, another band of mostly rain is backing westward into
southern VT. In this area, slightly warmer air aloft is present,
with H925 temps/wet bulbs around +1 to +2C. With higher freezing
levels, mainly rain is expected for elevations below 1500 feet.
However, near and above 1500 feet, some snow will be possible
with additional accumulations overnight 1-3 inches expected.
Elsewhere, expect rain showers across southern VT to continue
pivoting west and south, affecting the Lake George/Saratoga
region around or shortly after midnight, eventually shifting
south and west into the Capital Region between midnight and 3
AM. Some additional snow could occur for elevations above 1500
feet in the Helderbergs/northeast Catskills and also portions of
the Berkshires, where accumulations of an inch or two could
occur.
Otherwise, with this update, mainly adjusting PoPs according to
latest radar trends, along with temps/dewpoints to latest obs.
[PREVIOUS 423 PM]...Our chilly and damp Friday continues as our
mature/occluded surface low meanders over the eastern Catskills
and gradually fills in/weakens. Now that the cold conveyor belt
has wrapped into the east side of the surface low, steady bands
of precipitation have developed up the Hudson River valley into
the southern Adirondacks. Despite marginal sfc temperatures in
valley areas, rain has transitioned to wet snow as precipitation
becomes steadier thanks to wet-bulbing processes. However,
accumulations are unlikely in valley areas given temperatures in
the mid-30s. Wet snow will accumulate in the elevations at and
above 1000 feet especially in the northern/eastern Catskills
through this evening with an additional 1 to 3 inches expected.
Additional power outages for these higher terrain areas are
possible given the wet snow weighing down on tree branches.
These higher elevations areas will drop into the upper 20s to
around freezing tonight so any wet and untreated surface tonight
can become slippery. Valley areas drop a few degrees into the
low to mid-30s but continued breezy winds should help mitigate
refreeze. Even still, patchy refreeze is not completely ruled
out where temperatures reach freezing.
Based on latest NYS mesonet obs and ground truth data, highest
snowfall totals have occurred in the eastern Catskills for
elevators around and above 1500 feet where reports range from 6
to 14 inches. Even western Albany County in elevations above
1000 feet have received 2 to 5 inches of wet snow with wet snow
showers evident on the NYS mesonet cameras. Use caution with
snow removal as the heavy, wet nature of the snow will make it
more difficult to shovel and clear.
Rain and higher elevation wet snow shower wind down this evening
before Midnight as the sfc low continues to weaken. However, a secondary
sfc low will rapidly develop off the New England Coast tonight as
a potent shortwave rotating around the parent cyclone becomes
negatively tilted and induces sfc cyclogenesis. There is good
agreement that an inverted/norlun trough develops on the west
side of the coastal low providing a focus for enhanced mid-
level FGEN resulting in a band of precipitation that extends
off the coastal low well inland. High res guidance suggests that
band including the HRRR reaches into southern VT around 03 - 06
UTC and continues through 12 UTC. While temperatures in valley
areas will likely be marginal enough to support plain rain, the
southern Greens, on the other hand, will be cool enough to
support wet snow accumulations, especially as diabatic cooling
processes cool the column down even further. Overall QPF amounts
look to range 0.10 - 0.30" and with marginal SLRs around 7-9:1,
total wet snow accumulations look to range 1 to 3 inches with
the highest amounts along the spine of the southern Greens. Some
light accumulations under 1 inch look to also accumulate in northern
Berkshire County mainly above 1500 ft.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
Heading into Saturday, our secondary coastal low will continue
to rapidly deepen as it tracks into the Gulf of Maine and towards
Nova Scotia. In fact, expected pressure falls suggest it may
even become a "bomb cyclone" as it deepens to around 975 hPa by
Saturday afternoon. The pressure gradient over the Northeast
tightens as this occurs resulting in strong gusty north to
northwest winds. In fact, cold air advection on the backside of
the low will help deepen boundary layer mixing and promote
efficient momentum transfer of strong winds down to the sfc.
Probabilistic guidance shows greater than 30 - 60% chance for
wind gusts to exceed 30mph through much of the day tomorrow
mainly for areas down the Mohawk Valley into the Capital
District and Taconics as well as the eastern/northern Catskills
and nearly all of western New England. Areas that still have
heavy wet snow weighing on tree branches may see renewed power
outages as the winds become gusty tomorrow. Otherwise, as
northerly winds shift to the northwest, wrap around moisture
supports upslope showers in the Taconics and southern Greens.
Froude numbers remaining below 1 through the day indicate
blocked flow with upslope showers remaining on the west side of
the Taconics and southern Greens. Marginal temperatures in the
mid to upper 30s warming into the low-40s will support initial
rain and leftover wet snow showers in the southern Greens
transitioning to mainly plain rain p-type.
As we lose daytime, winds shift to become more west-northwest
and will support enhanced cold air advection and as well as an
increased fetch off Lake Ontario. With Lake Ontario waters still
around 10-11C, the incoming air mass over the lake will surpass
the 13C difference criteria and likely will generate lake
effect showers that extend into the Mohawk Valley and northern
Catskills Saturday night. However, temperatures in the boundary
layer remain too marginal to support much in the way of snow,
especially in valley areas. In fact, a lack of moisture in the
mid-levels suggests cloud temperatures may be too mild to even
support ice nuclei. With sfc temperatures also only dropping
into the mid-30s, expecting mainly rain showers from lake effect
Saturday night. Otherwise, gusty northwest winds Saturday
evening gradually weakens overnight but winds remains breezy.
Lake effect rain showers diminishes Sunday morning but west to
northwest winds remain breezy with gusts up to 20-30kts. As
surface high pressure from the mid-Atlantic builds northward,
inversion heights fall and the lake effect response should end
leaving drying conditions for the afternoon. With some partial
breaks of sun, temperatures will turn a bit milder in the mid to
upper 40s. Partial clearing into Sunday night will allow
temperatures to cool into the upper 20s to around 30.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
After weeks of relatively tranquil weather, we are finally beginning
to settle into a more active pattern. In fact, Monday will likely be
the driest day of the extended forecast period with upper-level
ridging and surface high pressure building into the region in the
wake of upper-low that brought many areas their first measurable
precipitation in quite some time. High temperatures Monday will
reach the 40s and 50s with isolated pockets of upper 30s across
higher terrain before lows fall widely into the 30s Monday
night.
While at least the first half of the overnight period Monday looks
to remain dry, by early Tuesday morning, rain looks to begin to
spread into the region from southwest to northeast along and ahead
of a warm front associated with a parent surface low approaching
from the southeast Great Lakes. Within the warm sector of this next
system, much of eastern New York and western New England will see
rain as the predominant precipitation type, though some wet
snowflakes could mix in at higher elevations. High temperatures
Tuesday will be similar, though a few degrees warmer than Monday,
again primarily in the 40s and 50s. Rain continues Tuesday night
though gradually reduces in spatial spread as the surface low pulls
off to the north and east. By Wednesday morning, much of the
existing showers will be confined to the Southwest Adirondacks and
western Mohawk Valley as the result of lake effect influences driven
by the rotation of shortwave pulses through the southern periphery
of a closed low that will begin to take shape in southeast Canada.
With low temperatures Tuesday night falling into the mid/upper 20s
to low 30s, snow is likely to become the primary precipitation type
with these additional showers, though accumulations look light at
this time. With our region locked into cyclonic flow throughout the
day Wednesday, additional scattered showers will be possible before
the upper low overhead begins to pull away. High temperatures
Wednesday will primarily reach the mid/upper 30s across higher
elevations with low to upper 40s in valley areas, though pockets of
low 30s will be realized above 2000 ft. Therefore, showers that
persist through the day Wednesday could also produce some wet
snowflakes.
The remainder of the extended forecast period is rather uncertain as
significant differences exist within run-to-run guidance pertaining
to a potential storm system that could impact the region beginning
Thanksgiving Day and lasting through the end of the week. We will
continue to monitor this storm as lead time decreases, but at this
time there is not enough consistency to form a confident consensus
on what impacts, if any, will be had across the region.
&&
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Cigs have briefly lifted to VFR with the exception of KPOU, and
these Cigs should persist for another 2-3 hours before dropping
back to MVFR after 06Z/Sat as low level moisture begins wrapping
back westward into the region. Shower coverage will also
increase once again later tonight as showers across southern New
England expand westward. A period of IFR Cigs is possible at
KPSF toward 12Z/Sat which could linger through ~14Z/Sat due to
a developing upslope northwest wind flow. MVFR Cigs should
linger at most TAF sites through midday Saturday, gradually
lifting to VFR during the afternoon. Isolated sprinkles will
remain possible Saturday, with best chance at KPSF.
Light/variable winds will become north to northwest by later
this evening at 5-10 KT, then increase and become west to
northwest at 10-20 KT with gusts up to 25-30 KT for Saturday
afternoon.
Outlook...
Saturday Night: Moderate Operational Impact. Windy With Gusts To 30 kts. Chance of SHRA.
Sunday: Moderate Operational Impact. Windy With Gusts To 31 kts. NO SIG WX.
Sunday Night: No Operational Impact. NO SIG WX.
Monday: No Operational Impact. NO SIG WX.
Monday Night: High Operational Impact. Likely SHRA.
Tuesday: High Operational Impact. Breezy. Likely SHRA.
Tuesday Night: Low Operational Impact. Breezy. Slight Chance of SHRA.
Wednesday: Low Operational Impact. Breezy. NO SIG WX.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Winter Storm Warning until 1 AM EST Saturday for NYZ058-063.
MA...None.
VT...None.
&&
$$
SYNOPSIS...Speciale
NEAR TERM...KL/Speciale
SHORT TERM...Main
LONG TERM...Gant
AVIATION...KL
Area Forecast Discussion
National Weather Service La Crosse WI
505 PM CST Fri Nov 22 2024
.KEY MESSAGES...
- Clouds likely holding through Saturday morning
- Rain/snow chances (20-50%) return Sunday night into Monday
with minor wet snow accumulation possible in Taylor and
northern Clark counties
- Turning much colder in the coming week, especially around
Thanksgiving; not much active weather locally to impact
holiday travel
&&
.DISCUSSION...
Issued at 204 PM CST Fri Nov 22 2024
Clouds likely holding through Saturday morning:
North to northwest flow persists over the region behind a deep
departing cyclone east of the Great Lakes and an upper ridge over
the Plains. Shallow moisture and weak low level flow has led to a
persistent widespread low stratus shield over the region, though the
clearing line is not far off in south-central Minnesota and
central Iowa. The cloud cover is expected to hold in place
tonight, based on a plan view of RAP 950mb RH and also RAP/HRRR
forecast soundings. In fact, partial clearing looks unlikely to
arrive until closer to midday Saturday when the 850mb ridge axis
finally arrives. Thus, with more cloud cover tonight than
originally expected, have nudged tonight`s minimum temperatures
up by generally a couple degrees.
While the weekend still looks to trend dry overall, there are some
signals suggesting weak warm air advection and fgen forcing could
try to interact with a bit of incoming mid-level moisture. Forecast
soundings are rather dry through roughly 950mb to 700mb, so this may
be more of a virga setup, or perhaps a few sprinkles at most. Will
maintain a dry Saturday forecast for now, but something we`ll be
monitoring.
Rain/snow chances return Sunday night into Monday:
Sunday night into Monday brings our next main chance of
precipitation as the upper ridge exits. A digging upper trough in
the lee of the Rockies will encounter a favorable plume of moisture
extending northward from the Gulf. It looks likely that there will
be an open shortwave that advances overhead on Monday, along with a
closed low riding Minnesota`s northern border. Some solutions try to
phase these two features as they approach the Great Lakes, while
others keep them separate. Regardless, precip chances are
increasing, ranging from 50% in Taylor and Clark counties to 20% in
our far southern/western counties. GEFS members are a little more
aggressive with a southwestward trail of light QPF extending back
into central Iowa Monday between 6am and noon, whereas ENS and GEPS
ensembles cut off precip chances more along our southern border.
Depending on temperatures (which should climb above freezing for
much of the area), much of the precip may fall in the form of rain
before mixing with or changing to all snow. Any accumulating snow
potential, though minor, looks to be mainly favored across north
central Wisconsin where we currently have 0.5 to 1.5" across Taylor
and northern Clark counties.
Holiday travel and Thanksgiving outlook:
The rest of the coming week doesn`t look to be quite as unsettled as
it had been looking earlier. A couple weak shortwaves with limited
moisture could clip northern areas Thanksgiving Day into Friday, but
otherwise the more robust storm system looks to pass just south of
the Ohio Valley with impacts likely to stay south of our area.
The bigger story for next week will be an intrusion of colder air,
with a glancing blow Monday and Tuesday before we get deeper in the
cold 850mb blob around Thanksgiving. By Friday, ensemble guidance
keeps highs below 30 degrees area wide with lows heading into the
weekend in the teens to single digits.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 505 PM CST Fri Nov 22 2024
CIGS: persistent low stratus expected to hang around into Sat with
RAP/HRRR bufkit soundings scattering the low deck out west of the
Mississippi river between 12-18z, and west of there 18-00z. Expect a
break with vfr scattered conditions for a few hours but a VFR mid
deck of clouds slated to return with warm air advection/upper level
shortwave Sat evening, and could drop into MVFR/IFR by 18z Sun.
WX/vsby: southeast MN developed mostly MVFR fog late night/early
this morning and short term guidance favors that again tonight.
Latest HREF places a 60% for sub 4sm at KRST...and will continue to
lean forecast this way. Lesser probs for IFR (35%) but will monitor
and adjust if these look like they will be realized. Expect
improvement by 12z Sat.
Next chance for light pcpn (likely rain) will come later Sunday
afternoon into the night, with continued chances into Monday.
Amounts and impacts look relatively minor at this time.
WINDS: northwest to west tonight with some variability/decrease in
speeds as high pressure builds in Sat. Expect a swing to the
southeast for Sat night.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
DISCUSSION...Kurz
AVIATION.....Rieck
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
247 PM PST Fri Nov 22 2024
.SYNOPSIS...A strong atmospheric river has finally began to move out
of the area. Isolated showers and coastal thunderstorms are possible
this evening through Saturday morning. Another weaker system is
possible Sunday into Monday, bringing more rain and gusty wind.
&&
.DISCUSSION...The strong atmospheric river affecting us for the last
few days has finally started to make it`s way out of our area. Some
rain is still being seen in interior Humboldt county and southern
Lake county, but the worst is officially over. Colder air aloft will
continue to spread across the West Coast this afternoon and evening.
As result, instability will increase to around 100-300 J/kg of CAPE.
Instability could allow for low-topped thunderstorms (15 to 40%
chance) over the waters and right along shore. Another round of
periods of moderate to locally heavy rainfall are anticipated. HRRR
model indicates max hourly rain rates around 0.15 to 0.30 inches.
Additional rainfall amounts from this system are forecast to range
from 0.75 to 2.0 inches from today through late Saturday afternoon.
The highest amounts are expected across the southwest windward
facing terrain with total rainfall up to 3 inches.
Snow levels in NE Trinity are expected to lower between 5000 to 4000
feet this evening into Saturday morning. 3-5 inches will be possible
above 4000 feet and could impact travel on Highway 3 at Scott
Mountain Pass late this afternoon through Saturday afternoon. More
significant snowfall is expected for the Trinty Alps. A Winter Storm
Advisory is now in effect from 4 PM this afternoon to 4 PM Saturday
for elevations above 4000 feet in portions of NE Trinity County.
A brief break will be possible over the weekend, before another
series of fronts impacts the area Sunday through Tuesday. These
fronts will be progressive and have less moisture. 6-hourly rainfall
and snowfall rates and storm total rain and snow amounts are
forecast to be much less than our current storm with less potential
for major impacts. Storm total precipitation is highest over the
King Range and Del Norte County, with 2-4 additional inches possible
there. Elsewhere, 1-2 inches are possible. Gusty winds are also
possible with this system; NBM has a 40-80% chance of southerly
gusts greater than 40 mph along the coast of Humboldt and Del Norte,
with higher probabilities along ridges and coastal headlands of
Humboldt and Del Norte. Snow levels start around 4000 ft Sunday,
and are forecast to gradually rise to about 5000 ft through the
day Sunday into Monday. A Winter Storm Watch has been issued
starting Sunday morning for elevations above 4000 ft in NE Trinity
County, which includes Scott Mountain Pass on Highway 3.
Upper ridging is forecast to restore more peaceful and dry weather
mid to late next week, though after multiple days of rain, valleys
will no doubt fog up during the night and morning hours. JB/ZVS
&&
.AVIATION...Flying conditions have improved to mostly VFR with
occasional MVFR ceilings and vsbys in showers. Satellite and radar
data indicated showers and isolated thunderstorms over the coastal
waters. This activity will spread toward the coastal terminals this
evening and overnight. Brief IFR in locally heavy showers and gusty
winds and moderate turbulence may impact coastal terminals overnight
into Saturday. Ukiah will also have occasion rain and MVFR
conditions overnight. Some fog and low clouds may also form in the
valley after multiple days of rain, but the atmosphere will probably
remain too well mixed for that. DB
&&
.MARINE...Showers and isolated thunderstorm will spread into the
waters tonight through Saturday night. Brief wind gusts to 30 kt
will be possible with stronger showers and isolated thunderstorms as
cold and unstable air spread over the waters. Seas remained elevated
today due primarily to a combination of a short period SW wave group
and a short period NW wave group. These wave groups will continue to
combine through Saturday and keep seas elevated around 10 ft into
Saturday. Southerly and southeasterly winds will increase Saturday
night into Sunday as another surface low and frontal boundary
approaches the outer waters. Brief gale gusts are possible (50%
chance) - mostly around Cape Mendocino and over the northern outer
waters in advance of the occlusion. Greater uncertainty arises early
next week as additional frontal systems or troughs pin-wheel around
a nearly stationary surface low that will weeble-wobble around over
the NE Pacific into early next week. DB
&&
.HYDROLOGY...The rise on most of the main stem rivers has slowed or
started to slowly recede this afternoon. Flooding impacts from
main stem rivers will continue into tonight and tomorrow. The Eel
River at Fernbridge is forecast to fall below flood stage (20 ft)
by 8 AM Saturday. The Navarro River near Navarro and the Russian
River at Hopland is forecast to fall below flood stage (23 ft and
15 ft, respectively) is forecast to fall below flood stage (23 ft)
by 8 PM tonight. Rain showers tonight into tomorrow are expected
to be intermittent, and are not expected to make any impacts to
main stem rivers. Although, a heavy shower could bring localized
small stream impacts given soils are completely saturated. More
rain Sunday through Tuesday could cause the rivers to rise, but
main stem river flood impacts are not currently expected. JB
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
Winter Weather Advisory until 4 PM PST Saturday for CAZ107.
Winter Storm Watch from Sunday morning through late Monday
night for CAZ107.
Flood Watch until 10 PM PST this evening for CAZ114-115.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 9 AM PST Saturday for PZZ450-455-
470-475.
&&
$$
Visit us at https://www.weather.gov/eureka
Follow us on Facebook and Twitter at:
https://www.facebook.com/NWSEureka
https://www.twitter.com/NWSEureka
For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png
Area Forecast Discussion
National Weather Service North Platte NE
525 PM CST Fri Nov 22 2024
.KEY MESSAGES...
- Mild and dry conditions on Saturday ahead of a cold front
moving in Sunday bringing much cooler temperatures, breezy
winds, and a threat for light snow across portions of
northwest Nebraska.
- Benign weather Monday and Tuesday before an even colder
airmass settles into the central US by the middle to end of
next week with a threat for wintry precipitation, potentially
impacting Thanksgiving holiday travel. Though uncertainties
remain in regards to snow accumulations, greater confidence
exists in seeing the most significant cold air outbreak of the
season thus far heading into the start of December.
&&
.SYNOPSIS...
Issued at 235 PM CST Fri Nov 22 2024
Recent GOES-16 WV imagery and RAP 500-mb analysis showed three
strong low pressure systems. The first system was centered over the
mid-Atlantic with a trough extending south into the
northeastern portion of the Gulf of Mexico. Further to the west,
the third system continues to spin, just off the coast of
Washington State with a trough extending southwest into the
eastern Pacific. The third upper-level low was noted across
northern Manitoba. An upper-level ridge expands across the
Intermountain West into the Plains. At the surface, high
pressure extended along the Plains. A warm front extended south
from an area of low pressure centered over southwest South
Dakota. Outside of some high clouds, mostly clear skies prevail
across western and north central Nebraska with temperatures at
2 PM CT ranging from 51 degrees at O`Neill to 65 degrees at
Ogallala.
&&
.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 235 PM CST Fri Nov 22 2024
Tonight`s lows falling into the 20s will moderate back into the 40s
and 50s on Saturday as broad warm air advection (WAA) continues. The
upper-level ridge axis will slide east into the northern Plains
through the day on Saturday. An upper-level shortwave will eject
from the main system centered off the coast of the Pacific Northwest
into the northern Rockies late Saturday. As this shortwave moves
eastward into the northern Plains, a cold front will be forced
southward, moving through the area late Saturday night into Sunday
morning. Northwest/north winds will strengthen behind the front with
3 to 4mb/3 hour pressure rises and robust cold air advection (CAA)
increased across western and north central Nebraska. Widespread
gusts in excess of 20 mph will be common during the day on Sunday
with the strongest gusts of 30 to 35 mph expected across northern
Nebraska. This frontal passage will bring the first of a series of
cold air intrusions expected through next week with temperatures
falling into the below normal range for Monday and beyond. As for
Sunday`s highs, a range of temperatures will set up across the area,
ranging from the upper-30s across northern Nebraska to the mid-50s
across southwest Nebraska. Divergence will increase under the left
exit region of a 250-mb jet streak moving through western Nebraska
Sunday night, downstream of the upper-level trough. This area of
divergence will be parallel to a band of moderate mid-level (700 to
500 mb) frontogenetical forcing that develops as well. Increased
moisture and mid-level forcing will present a threat for light
snow/flurries across northwest Nebraska Sunday night. Little to no
accumulation is expected as current NBM Probabilities of 24 Hour
Snowfall > 1" remains at 20% or less for northwest Nebraska. At this
time, any winter weather impacts appear low, though this will lead
to much colder temperatures as we head into Monday.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 235 PM CST Fri Nov 22 2024
Benign weather will mark the start of the long term period on Monday
and Tuesday as the flow aloft becomes zonal and surface high
pressure builds southward out of Canada. CAA will continue across
the region with temperatures falling into the 30s to low-40s on
Monday. Temperatures moderate back into the 40s as the upper-level
ridge flattens over the northern Plains on Tuesday. Though near-
normal for most locations, chilly overnight lows in the teens will
be felt Monday night and Tuesday night.
Attention then turns to the next system ejecting out of the
Rockies mid-week, potentially impacting Thanksgiving holiday
travel. The deterministic ECMWF, GFS, and Canadian continue to
have run-to-run differences that have significant implications
on potential impacts for Thanksgiving holiday travel across our
area. When comparing the deterministic GFS vs ECMWF, the GFS is
dry while the ECMWF highlights light snow/flurries across
western and north central Nebraska. Despite this, the GFS
Ensemble does show some ensemble members hinting at the
potential for snow across the area. Although uncertainties
remain, with such cold air in place, the threat for
accumulating snow is non-zero across the area. Thanksgiving
travelers should continue to stay up to date on the latest
forecast and be prepared to make adjustments to your plans if
needed.
One thing appears more certain with this system is the northern
Plains seeing the most significant cold air outbreak of the
season thus far. Ensemble guidance shows a ridge developing
over Alaska and northern Pacific, favoring surface high pressure
to build southward into the central CONUS by late next weekend,
continuing into the 7 o 10 day range. Just how cold it will get
remains uncertain at this time, however, confidence continues
to increase in a period of sub-freezing and perhaps well-below
freezing temperatures to be felt across the region as we head
into the first part of December.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 524 PM CST Fri Nov 22 2024
Over the next 24 hours VFR conditions will prevail. Winds will
remain light and mostly variable with wind speeds generally
around 5 kts or less.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Viken
SHORT TERM...Viken
LONG TERM...Viken
AVIATION...Gomez
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
840 PM CST Fri Nov 22 2024
.KEY MESSAGES...
- Mostly cloudy skies will prevail tonight and tomorrow with
relatively muted temperature swings (lows in the mid 30s,
highs in the mid 40s).
- There is a chance of rain on Monday, with some threat for rain
and snow Wednesday into Thanksgiving Day particularly for
areas south of Interstate 80.
- Temperatures will turn much colder later next week and
beyond.
&&
.UPDATE...
Issued at 840 PM CST Fri Nov 22 2024
Nighttime microphysics satellite imagery shows an extensive
swath of stratus clouds blanketing the region, who`s back edge
is over in central Iowa. Some lowering of cloud decks are
possible through the overnight. However, with persistent and
relatively breezy northwest winds within the cloud layer,
mechanical mixing looks like it will reduce the chances for
stratus to build down into a fog layer into tomorrow morning.
The pockets of patchy drizzle that has lingered through the
evening, particularly on the southeastern tip of Lake Michigan,
is slowly diminishing. Parts of Lake and Porter county in
Indiana may still get random spits into early Saturday morning,
but nothing of any real note. As the upper level ridge keeps
northwesterly flow over the area into Saturday morning, models
are suggesting that increased moisture in the mid levels could
move down with an associated wave during Saturday morning. The
RAP was notably aggressive suggesting a short window of light
rain or even drizzle, but most recent runs have backed off.
Maybe there were be some isolated pockets of drizzle tomorrow
morning, but the probability was too low to add it in the grids
for now. Otherwise, the rest of the forecast mentioned below
remains on track.
DK
&&
.DISCUSSION...
Issued at 209 PM CST Fri Nov 22 2024
Through Saturday night:
Regional satellite imagery depicts a scene quintessential of
the cool season with pervasive cloud cover from the Great lakes
to Northwest within broad upper-level cyclonic flow.
As the back edge of the upper-level cyclonic shear axis of the upper-
level trough shifts eastward and away from our area tonight, neutral
to modestly positive upper-level height tendencies and associated
mid-level subsidence should encourage the base of the low-level
inversion to gradually lower. Accordingly, the blanket of stratus
draped across our area won`t be going anywhere anytime soon.
Interestingly, the HRRR/RAP have been persistent in depicting
"splotchy" QPF typical of drizzle during the overnight hours.
Considering BUFKIT soundings depict only filaments of
discernible lift and/or wind shear within the marginally-deep
stratus layer, will keep any mention of drizzle out of the
forecast. Cold air advection facilitated by (albeit weakening)
northwesterly winds should make up for an otherwise muted
diurnal drop in temperatures, with lows expected to drop into
the mid 30s.
Tomorrow, a surface high pressure system will traverse across the
Ozarks allowing for low-level steering flow across the Lower Great
Lakes to turn west southwesterly. Accordingly, the back edge of the
stratus should gradually lift northeastward across our area
throughout the day in spite of the continued lowering (via mid-level
subsidence) and eventual strengthening (via low-level WAA) of the
inversion. Even as (if?) low-level stratus clears, mid-level clouds
will be in the neighborhood as a low-amplitude upper-level shortwave
propagates southeastward across the Upper Mississippi River
Valley. For these reasons, will hold onto mostly cloudy skies
all day tomorrow and advertise limited diurnal warming with
highs in the mid 40s. Of course, if clouds manage to clear
(particularly during the afternoon), temperatures may verify
above our forecast.
Tomorrow night, upper-level clouds will spill over the Great Lakes
as a series of upper-level shortwaves propagate across the
northern Plains. Overnight lows should fall into the mid 30s.
Borchardt
Sunday through Friday:
Warm advection and a seasonably mild starting point will yield
above normal temperatures on Sunday. The main uncertainty in
Sunday`s forecast is the effect of cloud cover on how mild
temperatures get. Thick overcast this time of year is a common
recipe for under-performing temps, so confidence is a bit lower
than usual in forecast highs (officially 48-55F range, warmest
southwest). Regardless, it will be a fairly nice day for this
time of year for outdoor work and holiday shopping.
In a stark change from recent cool seasons, the shortened
Thanksgiving week and into the beginning of December will mark a
transition to a decidedly wintry pattern. Pronounced high
latitude riding over the northeast Pacific near Alaska will
allow for plenty of cold air to surge southward from our source
region (Canada and the northern Plains) later week and beyond.
The first cold front in the pattern change will be accompanied
by a wave of weak low pressure developing in the frontal trough
Sunday night into Monday. Spotty light rain or sprinkles/showers
are conceivable for parts of the area late Sunday night into
Monday morning. Then on Monday afternoon, a period of wind-
whipped (primarily light) rain is looking more favorable as a
northern stream short-wave trough digs in behind the departing
weak surface low. PoPs up into the 30-40%+ range for most of the
area appear reasonable for now. At this time, the cold air
advection looks to lag enough to preclude a changeover from rain
to snow before the precip ends Monday evening. High temperatures
will tumble from above normal levels on Monday to only mid to
upper 30s on Tuesday, following lows in the 20s to around 30F
early Tuesday morning.
For the all important busy Thanksgiving travel period, there are
a few features of interest. Most notably, a fairly moisture
laden southern stream wave is likely to emerge from the
southern Rockies. Strongly confluent flow over northeastern
North America caused by a deep PV lobe near James Bay may
initially have some suppressive influence on our southern stream
wave of interest. Meanwhile, a strong northern stream short-wave
is forecast to approach into Thanksgiving, packing mid-winter
type cold building in for the start of December.
The above described pieces could plausibly yield a higher impact
weather event for our area, though the general tendency over
the past few model cycles is higher precip. chances to be
favored generally farther for our southern CWA and points south.
If the southern stream and northern stream waves don`t end up
constructively interfering with each other to bring a stronger
surface low farther north and west, the northern stream trough
could bring a chance of light snow Thanksgiving night into early
Friday, associated with an Arctic frontal boundary. Stay tuned
for updates regarding the Wednesday-Thursday forecast!
Friday looks to be windy and cold (highs only in the upper
20s-lower 30s!) for the busy holiday shopping day. The lake
effect machine will undoubtedly get going in this pattern,
though likely primarily east of our CWA on Friday due to west-
northwest flow.
Castro
&&
.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 531 PM CST Fri Nov 22 2024
Key messages:
- MVFR cigs tonight and into Saturday. Some potential for
stratus to build down to IFR, particularly at RFD late tonight
and Saturday morning.
- Small chance for drizzle tonight--too low for a mention in the
TAFs.
- Low confidence in the return of VFR conditions late Saturday
afternoon and evening.
Expansive low stratus blankets the region and extends back into
central Iowa and northeast Missouri at this time. MVFR cigs will
remain locked in place tonight and through much of the day on
Saturday. Have added a mention of IFR cigs at RFD where the
potential for some stratus build down is greatest.
Pockets of drizzle will be possible tonight, mainly across parts
of northwest Indiana in the vicinity of onshore flow off the
lake, as well as west and south of c90 where low-level
moisture is expected to remain the deepest. As a result,
chances for -DZ at the TAF sites remains a bit too low for a
mention at this time, but will continue to monitor trends.
Winds will turn westerly and eventually southwesterly on
Saturday. As this occurs, the back edge of the stratus deck
should inch towards the region. Most guidance suggests VFR
conditions will return by Saturday afternoon. However, given the
expansiveness of the low cloud shield, have maintained MVFR
conditions through 00z Sunday, although will note this is a low
confidence from group.
Carlaw
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 4 AM CST Saturday for Winthrop
Harbor IL to Gary IN.
Small Craft Advisory until 10 AM CST Saturday for Gary to
Burns Harbor IN-Burns Harbor to Michigan City IN.
&&
$$
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