Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/02/24
Area Forecast Discussion
National Weather Service Cleveland OH
1021 PM EST Sun Dec 1 2024
.SYNOPSIS...
A surface trough will continue to impact the area through
Tuesday before a brief ridge builds across the Ohio River Valley
into Tuesday night into Wednesday. Another low pressure system
will impact the Great Lakes region Wednesday afternoon through
Thursday before high pressure returns Friday.
&&
.NEAR TERM /THROUGH MONDAY NIGHT/...
9:30 PM Update...
The lake-effect band is getting slighly better organized over
far NE Cuyahoga, northern and central Geauga, and southern Lake
Counties, although it is still fighting shear causing the snow
to fan out. This is bringing snow into southern Ashtabula and
northern Trumbull Counties, so expanded higher PoPs into those
areas. Still expect the convergence to increase with a
strengthening band later tonight over the east suburbs of
Cleveland, and some Lake Huron moisture is starting to reach
into eastern Erie County, PA as the flow veers behind a trough,
so snow amounts look reasonable overnight. The snowfall rates
will not be as impressive due to the shear and fetch starting to
shortern, but several more inches overnight will slow the clean
up process. The good news is that the heaviest snow for
lakeshore areas of Ashtabula and Erie Counties may be done as
the flow continues to veer more WNW to NW, with the heavier
amounts now becoming focused in inland upslope areas.
6:30 PM Update...
The forecast remains on track this evening with no changes
needed, at least not yet. The main lake-effect band that hit
much of Lake County very hard today has weakened and become
much less organized the past few hours. This appears to be from
both shear and subsidence behind a shortwave that crossed the
region this afternoon. Snowfall has lightened significantly as a
result, although the band has become more fanned out and is now
affecting eastern Cuyahoga, northern Geauga, central and
southern Ashtabula, and Trumbull Counties, in addition to Lake
County. This will bring additional light to moderate snow the
next few hours.
The latest RAP BUFKIT forecast soundings suggest that moisture,
lift, and instability will deep again later this evening through
tonight, with equilibrium levels progged to increase to 12-15
thousand feet again with strong Omega through a saturated DGZ.
This combined with the persistent south shore convergence thanks
to lake aggregate thermal troughing should allow the band to
become better organized tonight. It may not become as heavy as
it was this morning due to continued shear, but snowfall rates
should increase to 1 inch per hour tonight. In terms of band
location, still favor a position north of the HREF members which
continue to turn the low-level flow NW and break the band up
tonight. The strong thermal convergence near the shore should
keep the low-level flow more westerly and cause a dominant band
to remain in tact over NE Cuyahoga, southern and western Lake,
and northern Geauga Counties tonight into at least Monday
morning. The band may wobble a bit and affect adjacent areas,
but this should be the main location. With all of this in mind,
current snowfall forecasts look good, with an additional 10-20
inches over these aforementioned areas through Tuesday morning.
Farther to the east, additional lake-effect bands are trying to
organize into Ashtabula, Erie, and northern Crawford Counties.
This should continue through Monday morning before the flow
turns more NW and allows a Lake Huron band to connect into NW
PA. Until then, lighter snows are expected in NW PA given the
shorter fetch tonight through Monday morning, but still could
add up to 8-12 inches where the squalls persist. The highest
totals may finally fall inland of the lake tonight in upslope
favored areas as opposed to on the already buried lakeshore
communities.
Original Discussion...
The overall forecast has not changed much from the previous
update. The only change made with this main forecast update is
extending the Lake Effect Snow Warning for Erie County PA
through Tuesday afternoon or until 00z Wednesday evening. The
eastern Great Lakes region remains in a large cyclonic flow and
on the backside of a large deep upper level trough which the
axis center was located over southeastern Quebec this
afternoon.
The main weather story and impacts will come from lake effect
snow impacting the primary and some of the secondary Snowbelt
areas over the next 36 hours. There has been a main lake effect
snow band that has slowly drifted southward from far NEOH down
closer to the Cleveland metro area. As of 315 pm EST, the main
snow band is hitting Lake County into northern Geauga very hard.
This band has now drifted into northern and northeastern
Cuyahoga County and this trend will continue through the evening
and overnight. There is high confidence amongst the high-res
forecast guidance that is main band will position itself from
west to east across northern Cuyahoga, Lake, and Geauga Counties
for much of the night into Monday. There is hints of a weaker
secondary Lake Effect snow band trying to form offshore of
Ashtabula and Erie PA this afternoon which may become better
organized tonight into Monday.
The overall message is additional heavy snowfall is expected in
the Snowbelt area already hardest it and northern and eastern
Cuyahoga County will be seeing heavy snowfall tonight through
Monday night. There is a shortwave trough moving through right
now that is helping to change the low level flow to more west-
northwesterly. This subtle chance in the low level flow will
help keep the Lake Effect snow machine going through Monday
night with areas from the Cleveland area to Erie PA seeing heavy
snowfall. The current Lake Effect Snow Warnings are remain on
track with the forecast snowfall amounts. Be sure to see the
latest WSW text product and the detail information in the Lake
Effect Snow Warning for specific snowfall amounts and
expectations.
Elsewhere outside the snowbelt region, the weather will be
relatively quiet but cold. There will be variable cloudiness
this afternoon through Monday night. There may be some passing
snow flurries or very light snow showers from time to time but
no significant accumulations or impacts are expected. High temps
during the day will be in the upper 20s to low 30s. Overnight
temps will be in the upper teens to low 20s.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Active weather will persist for the short term period as lake effect
snow lingers across the snowbelt on Tuesday, followed by another
strong system Wednesday night. Only headline updates with this
package were to extend the Lake Effect Snow Warning for Erie County
through 7 PM Tuesday.
A ridge will begin to build east across the Midwest on Tuesday,
though stubborn lake aggregate troughing underneath a cold air mass
and primarily northwest flow aloft will result in continued lake
effect snow across the snowbelt. The most persistent and heaviest
snow will likely be found across Erie County, PA, aided by an
upstream Lake Huron moisture connection and thus have extended the
current Lake Effect Warning through 7 PM Tuesday. Residual lake
effect snow should eventually lift north out over Lake Erie Tuesday
night as the ridge axis becomes centered overhead, shifting flow
towards the southwest.
By Wednesday, a strengthening upper-level trough will swing
southeast across the Great Lakes, extending a strong cold front
through the region and ushering in a potentially even colder air
mass. Will need to monitor the low-level wind field Wednesday
afternoon and evening with southwest 925 mb winds around 35 to 40
knots, lower confidence in that wind field translating to surface
gusts exist due to the initial warm air advection. Widespread
precipitation will arrive across the area Wednesday night into early
Thursday morning with this system with the primary precipitation
type being snow, although some rain may mix in, especially earlier
in the evening.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
Active weather and below average temperatures will continue for
the long term period. Strong winds, lake effect snow, and
single-digit wind chills all appear possible.
The aforementioned cold front will be sweeping southeast through the
area Thursday morning, ushering in another cold air mass, with 850
mb temperatures briefly dipping to around -15 degrees C Thursday
afternoon. Stronger northwest flow will accompany this cold air
mass, so anticipate that both the primary and secondary snowbelts
will have accumulating snow potential. Mixing heights are expected
to rise near 850 mb in the wake of the cold front on Thursday which
could result in wind gusts of 35 to 40 mph across the region. At
this time, confidence is low (10 to 30%) for wind gusts greater than
45 mph, but we`ll continue to monitor trends.
Lake effect snow will likely persist through Friday, though will
begin to lift and/or subside by Friday night as another weak ridge
axis becomes centered across the OH Valley. Models are showing the
potential for another clipper-like system to traverse southeast
through the Great Lakes on Saturday, though initial signs suggest it
won`t be as strong as the mid-week system.
&&
.AVIATION /00Z Monday THROUGH Friday/...
Tricky, low confidence TAF forecast continues, especially at
KYNG and KERI which will be most frequently impacted by lake-
effect snow squalls. First off, KTOL, KFDY, KMFD, and KCAK
should largely remain dry and VFR, with some MVFR possible
Monday. There will be some passing flurries and snow showers at
any time during the TAF period at these terminals, but overall
low impacts are expected. For KERI, lake-effect snow showers and
heavier squalls will continue to be very frequent. This will
maintain nearly constant MVFR to IFR conditions. Some periods of
LIFR are possible in heavy snow, but the wind direction is
gradually turning more NW through the period, so this will make
timing heavier snow squalls very uncertain since there will be
multiple, weaker bands as opposed to the single heavy band of
the past few days. KCLE and KYNG will be brushed by the lake-
effect snows at times. KYNG is likely to be affected more
frequently with near constant light snow and MVFR to low end
VFR, but there will be heavier squalls passing through, so tried
to time these windows in PROB30 groups where visibility could
drop to 1 mile or less. KCLE is the toughest. Most of the
impactful snow should stay north of the terminal, but there will
be frequent light snow, and used PROB30 groups there too for
trying to time windows of heavier squalls that could drop
visibilities to 1 mile or less.
Generally W to WSW winds of 5-10 knots are expected through the
period, except 10-20 knots at KERI tonight.
Outlook...Non-VFR likely in lake-effect snow bands through
Tuesday. The heaviest and most-persistent lake-effect snow in
our region is expected to impact the primary snowbelt in far
Northeast Ohio and Northwest Pennsylvania.
&&
.MARINE...
Rough marine conditions are expected to persist through the week for
much of Lake Erie. Flow will primarily remain west to northwest, 15
to 25 knots, through Tuesday, before becoming southwest, 25 to 30
knots, on Wednesday. Confidence is increasing for Gale conditions
behind a strong cold Wednesday night through Thursday as winds shift
back towards the northwest, 30 to 35 knots. Elevated northwest flow
will persist on Friday, 15 to 25 knots, with additional Small Craft
headlines needed following any potential Gales.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...Lake Effect Snow Warning until 7 AM EST Tuesday for OHZ011>014-
089.
PA...Lake Effect Snow Warning until 7 AM EST Tuesday for PAZ003.
Lake Effect Snow Warning until 7 PM EST Tuesday for PAZ001-002.
MARINE...Small Craft Advisory until 7 AM EST Wednesday for LEZ145>149.
&&
$$
SYNOPSIS...Griffin
NEAR TERM...Garuckas/Griffin
SHORT TERM...Kahn
LONG TERM...Kahn
AVIATION...Garuckas
MARINE...Kahn
Area Forecast Discussion
National Weather Service Des Moines IA
538 PM CST Sun Dec 1 2024
...Updated for the 00z Aviation Discussion...
.KEY MESSAGES...
- Light snow arrives late this afternoon into tonight with minor travel
impacts possible for return Thanksgiving travelers and/or
Monday morning commute. Snow chances are above 70% over areas
west of I-35 in the state.
- Tonight`s snow accumulations mainly under an inch, but there`s
a 20% chance of a narrow corridor of 1 inch or slightly more
from northwest into perhaps south central Iowa.
- Monday through Friday features below normal temperatures except on
Wednesday with near normal conditions for early December.
- Increasing winds during the day Wednesday with gusts over 40
mph possible.
&&
.DISCUSSION...
Issued at 253 PM CST Sun Dec 1 2024
Early afternoon satellite imagery over the CONUS shows little
in the way of significant change from this time yesterday. A
broad trough remains over the eastern half of the US with Iowa
residing beneath northwesterly flow with a developing Rex block
off the West Coast. RAP analysis shows a 100 knot jet streak off
to the west of Iowa with a strong shortwave trough moving into
North Dakota that will bring light snow into Iowa. Ahead of this
shortwave, there is an expansive shield of clouds over the
Dakotas with more scattered and broken clouds from Nebraska down
into northwestern Missouri. Radar returns over the Dakotas are
generating enough snow for visibility and surface station
observation. Closer to Iowa, radar echoes over southwest Iowa
and southeastern Nebraska with collocated recent mPING reports
are either very light snow or more likely flurries given no
recent surface observations or observations on Iowa DOT
streaming webcams. The arrival of the clouds and light snow has
slowed down a bit so have adjusted near term forecast for this
delay, but eventually the upstream clouds will spill into the
state through tonight. With the the strong thermodynamic and
modest kinematic forcing associated with the shortwave trough,
light snow will develop. Forecast soundings show this as
saturation in the mid- levels working its way down with much of
this saturation residing just below to within the dendritic
growth zone (DGZ). The lift is weak to modest and is expected to
produce snowfall rates under a quarter of an inch per hour with
snow totals generally under an inch. However, there does remain
a less than 20% chance of 1 inch or slightly more in a narrow
corridor (30ish miles wide) from somewhere in northwest Iowa to
near if not just west of Des Moines into perhaps south central
Iowa per deterministic and latest 12z HREF guidance. This chance
may increase if the depth of saturation within the DGZ is
deeper than currently shown in the forecast soundings such as
the RAP, NAM, and GFS. While all of this snow will fall within
or less than 6 hours at any given location, slick spots on
untreated roadways may be encountered by any return Thanksgiving
travelers and/or for those heading out the door Monday morning
for work or school. Flurries may linger for a brief bit on the
backside as clouds persist longer than the snowfall into the
daylight hours of Monday morning, but have not advertised that
beyond this mention.
The week ahead will feature below normal temperatures with the
exception of Wednesday. Surface high pressure will drop over Iowa
Monday into Monday night. With high pressure overhead Monday night
and with a clearing sky and fresh snow even an inch or less, we
could see temperatures outperform and drop lower than current
forecast, which does have some single digits above zero over western
and northern Iowa. The high pressure will move off to the southeast
on Tuesday with our surface flow becoming more southwesterly. This
will allow temperatures to rise Tuesday and Wednesday with highs
peaking in the middle 30s to low 40s on Wednesday. However, a
surface cold front will already be sliding through Iowa Wednesday
and with gusty winds developing behind the front, it won`t feel like
the middle 30s or low 40s with wind chills ranging from the upper
teens to low 30s. Forecast soundings show deep boundary layer mixing
within the cold air advection, subsidence regime and gusts over 40
mph could occur, particularly over northern Iowa late morning into
the afternoon. A stronger shortwave trough associated with this cold
front will drop into the western Great Lakes with much of its
precipitation looking to remain northeast of the state. As Iowa
falls back into the northwesterly flow late in the week, other
shortwaves may pass near the state, but moisture availability
remains in question. At this point, the end of the week looks to
have below normal temperatures with no obvious large scale
precipitation chances.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 538 PM CST Sun Dec 1 2024
Light snow will move through the area overnight, mainly between
about 04Z and 12Z, bringing with it periods of reduced
visibility and low ceilings. Most probable categories will be
periodic IFR visibility and MVFR ceilings, but it is possible
ceilings could fall to IFR at times. Expect rapid improvement
after sunrise Monday morning as the system moves away.
Amendments may be necessary overnight into the morning hours
based on short-term observational and radar trends.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
DISCUSSION...Ansorge
AVIATION...Lee
Area Forecast Discussion
National Weather Service North Platte NE
522 PM CST Sun Dec 1 2024
.KEY MESSAGES...
- Coldest day for the next 7 days will be felt on Monday with
high temperatures falling into the below normal range in the
20s and 30s.
- Above normal temperatures in the 40s and 50s and dry
conditions return Tuesday into the weekend. The exception will
be Thursday when a dry cold front will knock temperatures back
into the mid-20s to low-40s.
&&
.SYNOPSIS...
Issued at 119 PM CST Sun Dec 1 2024
Recent GOES-16 WV imagery and RAP 500-mb analysis showed a broad
positively-tilted trough extending across New England into the
Great Lakes and Midwest. Further to the west of this feature, a shortwave
trough was sliding southeast across Manitoba. Upper-level
ridging extended northwest from the Desert Southwest to Yukon.
An upper-level low over the Southwest of Alaska was
retrograding into the Bering Sea. Northwesterly flow aloft
prevails across the northern Rockies and northern Plains. At the
surface, a stationary boundary was draped along Highway 61 into
southwest Nebraska. Persistent cloud cover over portions of
north central Nebraska has resulted in quite the range of
temperatures across the area for the first day of meteorological
winter. At 1 PM CT, temperatures ranged from 25 degrees at
O`Neill to 52 degrees at North Platte and Imperial.
&&
.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 119 PM CST Sun Dec 1 2024
Surface high pressure will build south out of Canada into the
northern Plains bringing a reinforcing shot of cold air with it
for the short term period. Temperatures will fall into the
single digits across northern Nebraska to the teens further
south. With 3 to 5mb/3 hour pressure rises and cold air
advection (CAA) increasing over the local area, winds will
become breezy out of the north/northwest overnight. Gusts of 15
to 20 mph combined with the previously mentioned temperatures
will result in brisk below and above zero single digit wind
chills for Monday morning. As the surface high pressure ridge
and northerly surface flow continues into Monday, daytime
temperatures will struggle to get out of the teens across north
central Nebraska to the mid-30s across southwest Nebraska. The
high pressure ridge will begin to shift south and east of the
local area Monday night allowing overnight temperatures to not
be as cold as compared to tonight, generally in the 10 to 20
degree range.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 119 PM CST Sun Dec 1 2024
A quiet and dry weather pattern will set up across the region
through the long term period with fluctuating temperatures.
Fortunately, a deepening surface trough across central Canada
will shunt the cold surface ridge into the southeast US. With
southwesterly return flow, temperatures will rebound back into
the 40s and 50s for Tuesday and Wednesday. An upper-level
shortwave will drop out of Nunavut with the surface trough
deepening as it tracks into the Great Lakes. This will force a
dry cold front to track through western and north central
Nebraska late Wednesday. As cold surface high pressure builds in
behind the frontal passage, temperatures will once again fall
back into the below normal range in the 20s and 30s for areas
east of Highway 83 to seasonal values in the 40s for areas west
of Highway 83. The NBM continues to highlight a return to above
normal temperatures for the latter end of the week into the
weekend. However, another clipper system appears to be on the
table during this period and may result in colder temperatures
to be felt vs what is advertised by the NBM. Despite this
possibility, this will be quite the mild start to December
across western and north central Nebraska.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 521 PM CST Sun Dec 1 2024
A back door cold front, will push stratus cloud cover into
northeastern and eastern Nebraska overnight. The lower ceilings
should remain east of the KVTN and KLBF terminals. For the KLBF
terminal, skies will remain mostly clear this evening with a few
to scattered high clouds around 20000 FT AGL developing
overnight. For the KVTN terminal, skies will be mainly cloudy
with ceilings around 10000 FT AGL. There is a minute threat for
lower ceilings overnight tonight, however, there is not enough
forecast confidence to introduce any MVFR ceilings attm.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Viken
SHORT TERM...Viken
LONG TERM...Viken
AVIATION...Buttler
Area Forecast Discussion
National Weather Service Marquette MI
944 PM EST Sun Dec 1 2024
.KEY MESSAGES...
- The long duration moderate to occasional heavy lake effect
snow event continues into Monday. Winter weather advisories
remain in effect through Monday.
- Another clipper system moving through the area Wednesday will
bring widespread system snow late Tuesday into Wednesday with
another uptick in lake effect snow behind it Wednesday
through Thursday for the northwest to north Lake Superior snow
belts.
- Blustery northwest winds, gusting up to 30-40 mph are possible
late in the day Wednesday through Thursday morning. During
this period, wind chills drop to near 0 over the east and
single digits below 0 in the west.
- Temperatures remain mainly below normal through at least next
weekend.
&&
.UPDATE...
Issued at 944 PM EST Sun Dec 1 2024
The forecast remains largely on track this morning. Lake effect snow
showers continue mainly in the NW wind snow belts in the north-
central and eastern UP, as well as in the Keweenaw. With surface
observations as well as MRMS estimates of up to 0.10-0.20 of liquid
precipitation over the past several hours in the eastern UP, would
not be surprised by some spots having picked up a few inches of snow
over the course of the evening. Will keep in similar amounts the rest
of the night where any steadier banding is indicated.
PoPs have been pulled back somewhat in the far western UP as winds
with a more westerly component have limited snowfall thus far.
However, as winds veer more northerly once again through the second
half of the night, expect snow to re-develop in the west and to
begin to shift more westward across the eastern and north-central
UP. This could bring accumulating snow to the Marquette area by the
morning commute. The Winter Weather headlines remain unchanged.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 401 PM EST Sun Dec 1 2024
Radar loop from late last night into early this afternoon shows a
gradual westward progression of the dominant LES band over the east
half of the U.P. This westward progression has been caused by a
combination of the wind flow veering more northerly this morning and
NE land breezes off Ontario and eastern Upper Mi. The increased low-
level convergence from the land breezes combined with
preconditioning off Lake Nipigon has resulted in a strong LES band
(max reflectivity of 40 dBZ) into central Alger and Schoolcraft
counties early this afternoon. This band is still probably
producing locally heavy 1-2"/hr snowfall rates from Munising to
Shingleton to Seney and McMillan while reducing vsby to near
zero in snow and blowing snow. Satellite and radar imagery shows
much of the rest of the U.P. under a mix of clouds and sun with
isolated to scattered light LES.
CAMs show dominant LES band to the east slowly pushing west through
time late tonight into Monday due to a gradual veering of winds to
the north through this time. Latest HRRR seems to have the best
handle on the position and movement of this band so have followed
it`s guidance for timing of headlines tonight. Will allow the
warning to expire over Alger, Luce and northern Schoolcraft by 00Z,
but will replace the warning with an advisory from 00-18Z Monday for
Alger and northern Schoolcraft as the dominant LES band lingers over
central Alger and northern Schoolcraft through at least the evening
hours tonight due to strengthening low-level convergence aided
by strengthening land breezes off Ontario. Late tonight into
Monday morning, CAMs generally show the LES band weakening a bit
as it begins to move west into Delta and Marquette counties so
have a winter weather advisory posted for these counties
starting at 06Z and continuing through 00Z Tue. Will continue
the advisory for Gogebic County through 00Z Tue as a wind shift
to a more favorable northerly wind late tonight into Monday
should bring in moderate LES accumulation.
&&
.LONG TERM /MONDAY THROUGH SUNDAY/...
Issued at 400 PM EST Sun Dec 1 2024
The weather pattern through the next week will consist primarily of
stubborn ridging over much of western North America with a number of
shortwaves rotating around broad troughing over much of eastern
North America. The most prominent of these shortwaves sweeps across
the region Wednesday afternoon through Thursday morning, with a
resulting surface feature bringing synoptic snowfall before a
reestablishment of cool northwesterly flow aloft for late in the
week. While intra-ensemble spread increases late in the week through
the weekend, ensemble mean guidance suggests another shortwave
passage early in the weekend and then again to kick off the
following week. In the meanwhile, lake surface-850mb temperature
deltas remain 50+% likely to support lake effect snowfall in between
synoptic systems throughout the entire forecast period, with surface
winds staying within the range of NNW to SW throughout the week and
next weekend, giving winter a snowy start for those mainly in the NW
wind snow belts.
While northerly lake effect snow will still be ongoing to begin the
work week, the chances of snowfall rates over an inch/hr will fall
to around 10-20% in Marquette, Alger, and Delta counties as a nearly
uniform northerly boundary layer flow means that no synoptic support
(or suppression) is present to provide convergence for the
snowbands. Still, HREF PMM shows some pockets of 0.1-0.25 inches of
6-hourly QPF, which in concert with 15-17 to 1 snow ratios will lead
to some UP spots reaching 2-6 inches of snow during the day
tomorrow, locally higher if the Lake Nipigon connection can enhance
conditions near the Marquette/Alger county line. Throughout the
overnight Monday through overnight Tuesday, winds will gradually
back from NW to SW in response to weakening 1030s high pressure
sliding south of the Great Lakes. This backing and general
anticyclonic surface flow will cut into the coverage and intensity
of the lake effect snow and reorient the bands into more traditional
westerly bands. By the afternoon Tuesday, this will limit the only
areas getting more than an inch of snow per 6 hours to be Keweenaw
County and the Luce County shores east of Deer Park.
By Wednesday morning, a strengthening clipper low will arrive over
the northern shores of Lake Superior at around the upper 990s mb.
This will bring a quick shot of synoptic snowfall, with an LREF mean
of between a tenth and a third of an inch of QPF, SLRs around 15:1,
leading to expected snowfall totals around an inch and a half to 5
inches of snow depending on the exact track of the low and available
moisture. Along with the snow, gusty winds to 30-35 mph widespread
are expected with a few gusts to 45 mph possible (up to 50%) over
the Keweenaw Peninsula. This in conjunction with a steady stream of
cool air from the continental polar airmass will lead to wind chills
in the negatives by Thursday morning. Another bout of NW band LES is
sure to follow for at least some period following the passage of the
cold front as 850mb temperatures already supportive of LES plummet
into the -15 to -19 C range. How long this LES lasts along with the
orientation of the bands is challenging to predict as ensembles
begin to fan out in their solutions on the trailing high pressure,
with the 12Z GEFS showing high pressure centers from KY to northwest
Ontario by Friday 06Z. A close pass by the high pressure could
suppress LES a significant amount, so it will be worth watching how
the ensembles converge following the clipper low. Any break in the
precipitation will likely be short lived as another clipper low
seems favored early in the weekend, though run-to-run, the ensembles
have been a bit inconsistent in tracking this clipper. The pattern
is likely to wash, rinse, and repeat in the following days, with 850
mb temperatures 90+% likely to support LES in some capacity over the
weekend and the 500mb plots show yet another clipper trough to kick
off next work week, though by that timeframe, the ensembles are
widely spread in the details of said solution.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 619 PM EST Sun Dec 1 2024
Ongoing lake effect snow event continues to result in flight
restrictions for all TAF sites. MVFR ceilings persist at all
terminals. However, as flow turns slightly more northerly than WNW
tonight, expect snow bands to move back over the terminals tonight
with visiblity dropping to IFR by 12Z at all sites. MVFR/IFR persists
at least through Monday afternoon, then snow begins to taper into
the evening while MVFR ceilings linger. Expect winds out of the WNW
this evening to turn more to the NW or NNW late tonight, gusting up
to 20 knots at times.
&&
.MARINE...
Issued at 400 PM EST Sun Dec 1 2024
Ongoing NW to NNW winds gusting to 20-25 kt in the west and 25-30 kt
in the east will veer to be out of the N and NNE tonight and Monday.
As a high pressure slides to the south of the Great Lakes, winds
become NW again, weakening to around 20 kt overnight Monday into
Tuesday and below 20 kt Tuesday morning. SW winds begin to ramp up
Tuesday evening ahead of a clipper low passing along the northern
shores of Lake Superior, with SW wind gusts approaching 30 kt
overnight into Wednesday. As winds become NW behind the cold front,
winds ramp up quickly to high-end gales to 45 kt with up to 50%
chances of wind gusts exceeding 50 kt Wednesday night into Thursday,
though wind gusts quickly fall below gales Thursday afternoon and
remain mainly around 20-25 kt throughout the remainder of the
forecast, though chances for gales increase to around 20-30% over
the weekend with another potential clipper low. Waves over Lake
Superior will be mainly 4-8 ft until falling below 4 ft Tuesday
afternoon. Waves then increase to 4-8 ft through Wednesday
afternoon, then the gusty winds behind the front force waves to 10-
15 ft by Thursday morning, locally up to 20 ft north of Grand Island
and Pictured Rocks National Lakeshores. Waves then fall to 5 ft or
less by Friday afternoon.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Weather Advisory from 1 AM to 7 PM EST Monday for
MIZ005-013.
Winter Weather Advisory until 1 PM EST Monday for MIZ006.
Winter Weather Advisory until 6 PM CST Monday for MIZ009.
Winter Weather Advisory until 1 AM EST Monday for MIZ014.
Winter Weather Advisory until 7 AM EST Monday for MIZ085.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
UPDATE...LC
SHORT TERM...Voss
LONG TERM...GS
AVIATION...LC
MARINE...GS
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
457 PM PST Sun Dec 1 2024
Updated short term discussion, aviation discussion and PQR
WATCHES/WARNINGS/ADVISORIES.
.SYNOPSIS...High pressure over the region will produce dry
weather through at least the middle of the coming week, with areas
of inland clouds and fog and sunshine elsewhere. Rain chances
increase late in the work week into next weekend with snow levels
remaining above the passes in the Cascades.
&&
.UPDATE...Webcam, satellite and surface weather observations from
4-445 pm Sunday depicted areas of dense fog expanding over the
central and southern Willamette Valley from the Woodburn area to
Eugene, including portions of the I-5 corridor. Suspect dense fog
will continue expanding over the central/southern valley this evening
into tonight as the boundary layer continues to cool and the low
stratus deck lowers to the ground, trapped under a strong surface
temperature inversion. The latest iteration of the HRRR and NAM Nest
back this up well, showing fairly widespread dense fog continuing
through at least 10-11 am Monday before lifting off the surface and
lingering as a low stratus deck through the afternoon hours.
Therefore, have issued a Dense Fog Advisory for the central/southern
valley through 11 am Monday. Allow extra time for your Monday morning
commute if your area is under a Dense Fog Advisory.
The northern Willamette Valley and Portland/Vancouver metro remain
clear with breezy east winds over the eastern metro and western
Columbia River Gorge. Areas with east winds will not see any fog
development tonight, however areas without wind will have chances for
fog and/or frost. -TK
&&
.DISCUSSION...Water vapor satellite imagery reveals a shortwave ridge
over the Pacific Northwest. Models and their ensembles are in good
agreement that this pattern will more or less persist through at
least Wednesday. The end result will be mild temperatures for the
coast and higher terrain and periods of fog and low clouds for the
inland valleys with below average temperatures for areas remaining
socked in. The areas most prone to fog and low clouds persisting for
most, if not all, of the day will be the central Columbia River
Gorge, the southern half of the Willamette Valley and the lower
Columbia/Cowlitz River Valley in southwest Washington. With colder
air developing in place in the Columbia Basin, east winds near the
mouth of the Columbia River Gorge will persist through at least
midweek. Air stagnation advisories for areas away from the east
winds look on track.
While the global ensembles are in good agreement that shortwave
ridging will continue across the western US and 500mb heights
anomalies will remain positive through the weekend, there remains
some uncertainty in how much the ridge will flatten and shift
eastward. The end result is that precipitation chances will be on
the increase beginning late Wednesday night and Thursday and will
climb further over the weekend. There remains quite a bit of
uncertainty when, and for that matter, if the first front will bring
rain to the region Wednesday night into Friday. Global ensemble
agreement in another round of wet weather impacting the region is
higher on Saturday. Given the above average 500 mb height fields and
a couple fronts sagging southward towards the region during this
time, there remains high confidence that snow levels will remain
above the passes in the Cascades if precipitation materializes. In
addition, valley temperatures should moderate as southerly to
southwesterly flow increases across the area, particularly for areas
away from the Columbia River Gorge. For example, the NBM suggests
there is a 10% chance for the Portland Airport to hit 60F on Friday
and 25-35% chance for Salem and Eugene. These temperatures are at or
near daily records for the date.
&&
.AVIATION...High pressure over the region with an inversion at
the surface. Satellite imagery and surface observations show LIFR
fog and stratus below 1000 feet elevation across the central and
southern Willamette Valley, and low MVFR stratus in the central
Columbia River Gorge. Offshore flow will maintain VFR conditions
at KTTD and along the coast though the next 24 hours. Satellite
imagery and observations show terminals within the Willamette
Valley beginning to fill back in with dense fog, while others are
clearing. Clear skies and light winds will allow temperatures to
drop below freezing again overnight, and radiational cooling
produces another round of dense fog and freezing fog after 06z
Monday. Again, expect much of the east Portland metro to remain
VFR as east winds persist with gusts up to 30 kt at KTTD.
PDX AND APPROACHES...VFR under mostly clear skies through 06Z.
Breezy offshore winds will keep conditions unsaturated before
transitioning after 09Z Mon. Once winds ease, another round of
dense fog is possible by 09z Monday. High resolution models are
struggling to represent this probability, likely due to winds
remaining elevated. If the fog does form though, there is a 10-15%
chance of it being freezing fog. Frost is also possible if winds
ease, but remain between 3-6 kt.
-Muessle
&&
.MARINE...High pressure over the northeast Pacific will maintain
relatively benign conditions through at least the middle of next
week. Seas around 6 to 8 ft today as a dominant westerly swell
with a period of 16 to 18 seconds moves through the coastal
waters. Have issued a Small Craft Advisory for the Columbia River
Bar later this afternoon during the period of a strong ebb. This
long period swell will also result in a moderate sneaker wave
threat along the coast today. Seas subside to around 4 to 6 feet
early in the week. Late Wednesday into Thursday, high pressure
weakens and allows a weak front to push across the waters, with a
40-60% chance of small craft conditions developing and southerly
winds gusting up to 25 kt. Another frontal system will likely
follow late in the week. /DH
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 4 AM PST Thursday for ORZ104-105-
108-109-113>118-123>125.
Dense Fog Advisory until 11 AM PST Thursday for ORZ114-115.
Dense Fog Advisory until 11 AM PST Thursday for ORZ116>118.
WA...Air Stagnation Advisory until 4 AM PST Thursday for WAZ202-
204>206-208.
PZ...Small Craft Advisory until 6 PM PST this evening for PZZ210.
&&
$$
www.weather.gov/portland
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