Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/25/22
Area Forecast Discussion
National Weather Service Boston/Norton MA
1058 PM EST Sat Dec 24 2022
Periods of ocean effect snow showers will continue to impact
parts of the Cape and especially the Islands into Christmas
morning before coming to an end. Across the rest of the region,
dry but very cold weather continues through Christmas. High
pressure will bring dry weather next week with a gradual warming
trend, then rain showers are possible for New Year`s weekend as
low pressure approaches from the Ohio Valley.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
No major changes to the ongoing forecast this evening. Did
update precipitation chances and timing heavily using the latest
HRRR and 00Z 3-km NAM, which represented the ocean-effect snow
band very well. Expecting this band to move slightly north
overnight, before making one last push southward towards
daybreak. Will need to keep an eye on accumulations, but this
band should be spending most of its time over the coastal
waters. Should that not be the case, then possibly looking at
several more inches of snow on the Vineyard and Block Island.
Minor tweaks to temperatures to reflect latest observations.
755 PM Update...
We have cancelled the Winter Weather Advisory for Cape Cod.
As of early this evening, westerly winds have shifted the band
of ocean effect snow south of Cape Cod, leaving mainly clear
skies. Mesoscale models show winds returning to more of a WSW
to SW direction late tonight, and we are expecting the band to
shift northward again overnight. The northward extent looks to
be right along the south coast of Cape Cod well after midnight.
We have reduced PoPs to zero for the next few hours and up to
50-60 percent for the extreme south coast of Cape Cod late
tonight. Additional amounts, if any, are expected to be light
and below Advisory levels.
Otherwise, snow continued on Martha`s Vineyard and Nantucket
this evening. Clear skies across the rest of southern New
England. No change to winds or temperatures from previous
* Two Main Ocean Effect Snow Bands to watch into Sunday AM for
the Islands as well as parts of the Cape Cod and immediate
* Dry & Very Cold Elsewhere with lows of 5 to 15 above
An extremely rare and significant Long Island Sound effect snow
band that impacted Marthas Vineyard this morning has shifted
north into the Falmouth to Hyannis region this afternoon,
although in a weakened form perhaps form diurnal heating. There
are some discrepancies in the high resolution model
guidance...but the tendency appears for this band to
eventually shift further south again tonight into Sun am and
impact Marthas Vineyard again for a time. It sill may oscillate
north and south at times...just very mesoscale in nature and
will have to be monitored closely. There are lighter snow
showers outside this band in more of a spray gun formation.
Based on climo...we may see the Long Island sound effect snow
band strengthen/consolidate a bit with the loss of diurnal
heating with less lighter snow showers around it. Also...some of
the guidance indicates a second band may develop near Nantucket
tonight into Sunday morning.
Most of the time our ocean effect snow events are dealing with
northerly flow with a shallow inversion layer and often a
limited fetch. This results in very minor snow accumulations in
most cases. In this situation...rare arctic air invaded the
region on a 240/250 degree wind. The soundings indicate a rather
deep mixed layer up to the inversion at 4-5 thousand feet with
uniform WSW winds. Large temp differentials from the top of the
mixed layer to the SST were on the order of 22C/23C. This was
resulting in impressive instability with ocean induced Capes of
500+ J/KG and Normalized Capes in excess 0.25.
We expect total snow accumulations in the 5 to 10 inch range for
Marthas Vineyard through Sunday morning where there will be
considerable blowing and drifting snow at times. 1 to 5 inches
across parts of the Upper Cape...mainly in the FMH to HYA
areas with little if any accumulations north of Wellfleet into
Ptown. An inch or two of snow is also possible across portions of
the very immediate south coast...but many of these locations may
just have flurries. Snowfall amounts will vary considerably over
short distance given mesoscale nature of the bands. Winter Storm
Warnings continue for Marthas Vineyard with Advisories for Cape
Cod...mainly for accumulations in the FMH to HYA corridor with
little if any north of Wellfleet to Ptown. Winter Weather Advisories
are also in effect for Block Island and Nantucket.
Otherwise...across the rest of the region mostly clear skies with
just a bit of mid-high level cloudiness tonight. The cold advection
aloft has stopped and in fact 850T warm a few degrees overnight. And
given the boundary layer does not decouple...low temps probably only
drop 4 to 8 degrees from their current readings. Most locations
should see overnight lows in the 5 to 15 degree range. Southwest
winds will be enough to result in wind chills of 0 to 10 below zero.
Parts of the Berks may see wind chills flirt with 15 below
zero...but felt it was too marginal for any Wind Chill
Headlines at this point.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
* Ocean Effect Snow Dissipate on Christmas for the Cape/Islands
* Plenty of sun on Xmas elsewhere with highs recovering to 25-30
Ocean effect snow showers may linger into Christmas morning across
the Islands and perhaps parts of the Cape...but should be winding
down as the day wears along. Would expect the bulk of the
snow shower activity to pretty much be over by afternoon given 850
mb flow turning more westerly across Long Island sound coupled with
warming temps aloft reducing the instability.
Otherwise...across the rest of the plenty of sunshine and still
breezy with strong low pressure in eastern Canada. It will
still be cold...but 850T moderating to between -14C and -16C should
allow highs to recover close to 10 degrees from today. Most
locations should see Christmas high temps between 25 and
30 with lower to middle 20s in the highest terrain. Still breezy
with gusts of 20 to 30 mph and around 35 mph at times across the
Mostly clear and cold weather continues Sunday night as the low
pressure system in eastern Canada continues to weaken and lift
further north and away from the region. Low temps will mainly be in
.LONG TERM /MONDAY THROUGH SATURDAY/...
4 PM update...
* Dry next week with a gradual warming trend.
* Mild with rain showers possible over New Year`s weekend.
Significant pattern change will get underway next week as closed
low that`s bringing our current Arctic blast exits Quebec around
Tuesday and is replaced by a building ridge along the eastern
seaboard from midweek into Saturday. The result is dry weather
through Saturday morning, with and a slow, gradual warming
trend. Max temperatures rise about 3 to 5 degrees each day,
such that we`re into the lower 50s by Friday. The only fly in
the ointment is a weak short wave that passes to our north
Monday night. Clouds will increase late Monday afternoon and
there is a chance of flurries or light snow showers in northwest
MA Monday night.
There are some indications that there could be a dry backdoor
wind shift to the northeast over northeast MA on Friday,
but the only impact would be slightly lower temperatures there.
The upper ridge moves off the coast Saturday while at the
surface, low pressure will be moving eastward through the lower
Great Lakes and Ohio Valley on Saturday, bringing continued mild
weather, but an increased chance of rain showers for New Year`s
Eve and on New Year`s Day.
.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight and Sunday...High Confidence.
VFR, except for ocean-effect snow showers at times on KBID,
KMVY, and KACK into Sunday morning, which will result in IFR to
even localized LIFR conditions. KFMH and KHYA could have some
light snow showers return late tonight and early Sunday morning,
but it is not guaranteed. These ocean-effect snow showers should
begin to dissipate Sunday afternoon as upper flow turns more
westerly and large SST differences dissipate. WSW wind gusts of
15 to 25 knots, except 25 to 35 knots across the Cape and
Sunday night...High Confidence.
VFR with SW winds diminishing to between 5 and 15 knots.
KBOS Terminal...High confidence.
KBDL Terminal...High confidence.
Outlook /Monday through Thursday/...
Monday: VFR. Breezy.
Monday Night through Thursday: VFR.
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
755 PM update...
Tonight through Sunday night...High Confidence.
Very cold WSW flow will continue to result in excellent mixing
and persistent gusts between 25 and 35 knots. The tendency will
be for these gusts to edge towards the lower side of these
numbers, especially later Sun and Sun night. We will gradually
convert Gales to Small Crafts Sunday into Sunday night.
Outlook /Monday through Thursday/...
Monday: Winds less than 25 kt. Seas up to 5 ft.
Monday Night: Winds less than 25 kt. Areas of seas approaching
Tuesday through Tuesday Night: Winds less than 25 kt. Seas
locally approaching 5 ft.
Wednesday through Wednesday Night: Winds less than 25 kt.
Thursday: Winds less than 25 kt. Areas of seas approaching
MA...Winter Storm Warning until 1 PM EST Sunday for MAZ023.
Winter Weather Advisory until 1 PM EST Sunday for MAZ024.
RI...Winter Weather Advisory until 1 PM EST Sunday for RIZ008.
MARINE...Small Craft Advisory until 1 AM EST Monday for ANZ230-236.
Gale Warning until 11 PM EST this evening for ANZ231-234.
Small Craft Advisory until 1 AM EST Monday for ANZ231.
Gale Warning until 5 PM EST Sunday for ANZ232-233-235-256.
Small Craft Advisory until 4 AM EST Monday for ANZ234.
Gale Warning until 1 PM EST Sunday for ANZ237-250.
Small Craft Advisory until 4 AM EST Monday for ANZ251.
Gale Warning until 8 PM EST Sunday for ANZ254-255.
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
344 PM PST Sat Dec 24 2022
.SYNOPSIS...Mild temperature with occasional periods of light rain
will occur through Monday morning. A significant rain storm will
then impact the region Monday afternoon through Tuesday with heavy
rainfall rates, strong south winds and high surf. After Tuesday,
additional periods of rain and high mountain snow will continue
for the remainder of the week into next weekend.
.DISCUSSION...Low level southwesterly moisture flux associated
with a shortwave trough passing into the Pacific NW has generated
brief heavy rain across Del Norte county today. Some embedded
convection and lightning was noted offshore with this plume of
anomalously high PWATS. Another influx of moisture will arrive
this evening with the highest rain rates expected across Del Norte
county. About an inch of rain is forecast in 12 hours from 10 AM
to 10 PM. The rain will begin to diminish overnight with residual
light showers possibly lasting through the day in Del Norte county
on Sunday. Elsewhere, rain will be generally much lighter with no
more than a tenth north of Cape Mendocino. Mendocino and Lake
counties and much of Trinity county will remain dry with areas of
valley fog tonight through Sunday morning under the influence of a
broad upper level ridge.
The main and most impactful rain storm this season will start to
bear down on the area starting Monday afternoon. Heavy rain with a
strong (bordering on extreme) atmospheric river is forecast to
impact the entire area Monday night through Tuesday with 24 hour
rain amounts of 2 to 6 inches. Highest amounts will occur in the
mountains and southwest-west facing slopes. The highest rain
rates of 0.50in/hr or more will most likely occur late in the
evening Monday and into early Tuesday morning as integrated water
vapor transport values (IVT`s) or moisture flux increases to 750kg/m/s
or more. West-WRF ensemble indicates IVT`s potentially spiking to
1000kg/m/s or more for a short duration, about one standard
deviation higher than the ensemble mean. The mitigating factors
for major flooding are pre-existing dry conditions for many of
the watersheds (low flows on all rivers) and the short duration of
IVT`s over 750kg/m/s. NAEFS and ENS mean IVT return intervals are
1 day every 10 years. There will still be a potential for some
minor flooding of streams, creeks and low-lying areas with poor
drainage. Main stem rivers will experience rapid rises, however
due to the mitigating factors mentioned above, flood stages appear
unlikely. For the Russian river at Hopland, the chance of
exceedance is no more than 17% and for the Navarro river at
Navarro it is no more than 14%. North Coast stages could approach
or reach monitor levels, about a 19% chance for the Mad river at
Arcata and a 26% chance for the Eel river at Fernbridge. Flood
stage is not completely impossible, but there is only 10% chance
or less on both rivers. Smaller rivers will also need to be
watched, in particular the Garcia river on the Mendocino coast.
If it goes over 10 feet, flooding will be possible on highway 1.
Also, there will be a potential for urban and small stream
flooding and an outside chance for debris flow on burn scars if
deep convection or thunderstorms develop and rain rates reach or
exceed 0.80-1.40in/hr. The HRRR should shed more light on hourly
rates once within range of the convective allowing mesoscale
models. We have hoisted a flood watch for portions of the
forecast, mostly for southern Humboldt, southern Trinity and much
of Mendocino county where the highest rain rates are expected to
Precipitation rates will start to wane as the plume of high IVT`s
head southeastward later on Tuesday. Locally heavy showers will
still be possible due to weak instability and steepening lapse
rates. Models remain consistent with another weak or moderate
atmospheric river (AR) arriving toward the end of the week into
early next weekend. This AR probably will not produce as much rain
or long duration heavy rain rates. It will need to watched as
there are some ensemble members that suggest a possible wetter
outcome and higher IVT`s.
Strong southerly winds with a barrier coastal jet in advance of a
powerful front will impact the area Monday night into early
Tuesday. Initially, when the 925mb winds are the strongest Monday
evening (60-80kt) offshore, the atmosphere appears too stable for
deep mixing and downward momentum transport. Thus, only the
ridges will probably have gusts to 50-70 mph. After the moisture
plume heads southward, stability will decrease and the potential
for gusts to 45-55 mph will increase for the coastal plains. Even
portions of Mendocino and Lake counties could see advisory level
gusts up to 50 mph over the ridges and exposed coastal headlands.
An advisory for wind will be forthcoming with blended guidance
and all deterministic models indicating gusts from 45 to 55 mph.
High wind warning level winds to 70-80 mph is not as probable for
coastal low lands, however some of the exposed ridges will be
close as instability and mixing increases toward early Tuesday
morning after the IVT maximum progresses southward.
Mid to late in the week and over the weekend...ensemble based 500
mb cluster guidance shows a generally zonal upper flow regime
positioned across the North Pacific through the next 10 days. The
orientation of that flow regime will place NWRN CA within a
favorable pattern for multiple rounds of widespread rainfall, the
cumulative effects possibly leading to hydrological impacts in the
form of increased flood potential.
.AVIATION...Isolated showers are moving northeastward across
the northern portion of the region this afternoon. Mainly MVFR
conditions dropping to IFR visibility with the heaviest rain are
expected through this evening for the coastal terminals. There is
also a potential of slight chance of thunderstorm in the vicinity of
KCEC during evening with increasing instability. Thereafter,
ceilings and visibilities drop once again late this evening and
tonight, with another round of valley fog formation expected. Winds
will gradually diminish, although some occasional gusts remain
possible at KCEC through this evening. In addition, low level wind
shear around 2000 ft is expected to persist through 24/03Z.
.MARINE...Shower activity moving northeastward across the northern
waters will continue through tonight. Doppler radar detected some
lightning strikes early this afternoon. Isolated thunderstorms
and occasional gusty winds up to 30 kts remains possible during
the evening. Advisory level winds are expected through tonight
with the southerly winds diminishing to moderate breezes.
Otherwise, this will be followed by another W swell filling in
tonight, bringing seas above 10 ft by Sunday afternoon. Small
Craft Advisories remain in place as a result. Winds are expected
to increase once again Sunday afternoon as the next frontal system
approaches Sunday night. Fresh to strong breezes will develop
across the outer waters, with the strongest north of Cape
Mendocino. Isolated gale force gusts up to 35 kts will be possible
over the northern outer waters. Locally gusty winds up to 30 kts
is expected near PT St George and Cape Mendocino beginning Sunday
night. This front will likely be followed by another reinforcing W
swell reaching into the mid teens, possibly pushing combined seas
into the high teens by Monday.
A strongest frontal system is forecast to arrive Monday night and
Tuesday, with widespread southerly gale sustained winds forecasted
and storm force gusts across the outer waters and nearing downwind
of Cape Mendocino. This front will be followed by another solid W
swell, with heights likely pushing into the mid 20`s at 15 seconds
across all zones. Conditions then look to settle down a bit late
next week, although southerlies likely continue for the foreseeable
.HYDROLOGY...Heavy rain with a strong atmospheric river (bordering
on extreme) is forecast to impact the entire area Monday evening
through Tuesday morning. Rainfall totals during that time are
forecast to range from 3 to 6 inches...with rainfall rates
expected to be 0.50 inch per hour or more. The duration of this
rainfall event will be relatively short, probably no more than 6-8
hours. However, main stem rivers will experience rapid rises
Monday night into Tuesday. The probability of exceeding monitor
stage is forecast to be 15-25%, with a roughly 10% chance of
flood stage being achieved. The potential for urban and small
stream flooding will also increase during this period of heavy
rain, and there is also a non-zero chance of debris flows
occurring across area burn scars.
.BEACH HAZARDS/COASTAL FLOODING...King tides will continue to
yield minor flooding across portions of Humboldt Bay during the
late morning hours through Sunday. As usual, King Salmon and
Fields Landing will be the most probable locations for minor
flooding. Otherwise, a large westerly swell will impact the coast
of Northwest California Tuesday through Wednesday. Breaking waves
from 25 to 30 feet will be possible, and will create very
hazardous conditions along area beaches, jetties, and rock
Coastal Flood Advisory until 2 PM PST this afternoon for
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory from noon Sunday to 3 PM PST Monday
Small Craft Advisory from 3 PM Sunday to 3 PM PST Monday
Small Craft Advisory until noon PST Monday for PZZ470.
Small Craft Advisory until 9 PM PST this evening for PZZ475.
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Area Forecast Discussion
National Weather Service Goodland KS
900 PM MST Sat Dec 24 2022
Issued at 735 PM MST Sat Dec 24 2022
At 0230z, a warm front extended from Wray, Colorado to Goodland
and Russell Springs, Kansas per satellite imagery showing
scattered clouds around 6-8k ft and light south to southwest winds
behind the front and northeast to southeast winds ahead of it.
Temperatures behind the warm front are in the 20s and 30s with
single digits to the upper teens ahead of it.
For the remainder of the night am expecting the warm front to move
very little, perhaps a county or so further east but not much
more. This will result in nearly steady or slowly rising
temperatures in the 20s behind the front to readings ranging from
zero to the teens ahead of it. Ultimately, low temperatures are
expected to range from zero to five above zero from Trenton to
Hill City east, lower to perhaps middle 20s across Cheyenne and
Kit Carson counties in Colorado.
Will be watching for patchy low clouds and fog to possibly develop
just east of Kansas Highway 27 in the next few hours, moving east
toward a McCook to Oakley line by 12z Sunday if the RAP and HRRR
models are correct. The 00z NAM model has this setup about a row
of counties further west.
.SHORT TERM...(This evening through Wednesday Morning)
Issued at 210 PM MST Sat Dec 24 2022
A developing ridge over the western CONUS is resulting is
northwesterly flow over the plains. Upper level moisture is
advecting in scattered to broken cloud cover over the area. WAA from
Colorado is trying to push its way into western Kansas, currently
lying roughly along Highway 27. Locations along and to the west of
the WAA have risen above freezing ranging from 32 degrees in
Goodland to 45 degrees in Burlington. If any breaks in the cloud
cover the temperature may warm a few more degrees. To the east of
Highway 27 the cool dry air mass continues to hang on with
temperatures ranging from the upper teens to the upper 20s with the
coldest temperatures east. As we head into tonight clouds continue
to increase with the moisture advection which may lead to some
low stratus into Christmas morning. The NAM has consistently been
showing some freezing drizzle potential associated with the
stratus across western portions of the area; I have low confidence
in this occurring as the NAM is the outlier but opted to put in
low pops (~5%) to address it especially with it being Christmas
morning. Christmas morning will see temperatures near zero over
the east to the mid teens over the west; so be sure to bundle up
if traveling in the morning.
Partly cloudy skies are expected Christmas Day along with westerly
downsloping winds which will help warm the entire area up. High
temperatures in the upper 40s to mid 50s are expected, which is not
to shabby for Christmas Day. The focus then turns to a fast moving
clipper system down the east side of the ridge starting Sunday
evening and lasting overnight with a quick shot of colder air.
Precipitation chances have pushed a bit further west for this
package with mainly light rain expected. Eastern portions of the
area may see a brief transition to freezing rain after midnight
Sunday as the main push of cold air moves in, due to low
confidence in that scenario occurring will leave out of the
forecast. Further west light snow may mix in with the rain as
overnight temperatures cool below freezing. Currently, not
expecting much if any ice accumulations over the east. However if
the cool air does move in a bit quicker and more to the west than
some slick roads may be of concern Monday morning.
Monday, effects of the clipper system are still being felt with
as temperatures will feel more like late December. Eastern
portions of the area will struggle to make it to the freezing mark
with warmer temperatures in the low 40s to the west. If the
cooler air does set up a bit further west (similar to what the
ECMWF suggests) then areas to the Colorado state line may struggle
to get above freezing. This chill will be short lived, as early
as mid afternoon Monday WAA will again push off of the Rockies
thanks in part to downsloping with winds becoming westerly. This
will help keep lows fairly comfortable for this time of the year
in the mid to upper 20s over the west and upper teens over the
Strong WAA with southwesterly winds is in store Tuesday as lee
troughing develops over the area. Winds may become breezy during
the afternoon depending on how far east the pressure gradient sets
up. High temperatures will be well above average in the mid 50s
to mid 60s; after this past weeks cold snap this may feel
downright warm. Despite the warm temperatures it currently doesn`t
appear that record highs will be in jeopardy. Lows Wednesday
morning will be around the freezing mark area wide.
.LONG TERM...(Wednesday through Saturday)
Issued at 142 PM MST Sat Dec 24 2022
Trough axis over the western CONUS will deepen as it approaches
the Rockies Wednesday and Thursday before ejecting into the
central plains Friday and Saturday. GFS and ECMWF not in very good
agreement at this time with track or timing of the system, with
GFS further north with more precipitation compared to a more
southerly, drier track from the ECMWF. End result will be
occasional low confidence pops for light precipitation during the
long term period. Temperatures will be such that the precipitation
could be in the form of rain (mainly during the day) or a wintry
mix of rain, snow or freezing rain at night. Temperatures will be
much above normal to start the period on Wednesday, then cool to
near or slightly above normal for Thursday-Saturday.
.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 900 PM MST Sat Dec 24 2022
KGLD...VFR conditions are expected through the period. A southwest
wind up to 10kts at taf issuance will continue through 17z. From
18z-22z, west winds gusting to around 20kts veer to the northwest
with similar gusts as a cold front moves through. After 23z,
northwest winds up to 11kts are expected. There is a slight chance
for light precipitation in the 01z-03z timeframe.
KMCK...VFR conditions are expected through the period. A light and
variable wind at taf issuance will establish a southwesterly
component at speeds around 7kts from 16z-19z. From 20z-22z, west
to northwest winds gusting to 22kts or so are expected as a cold
front moves through. After 23z, northwest winds around 11-12kts
are expected. There is a slight chance for light precipitation in
the 22z-01z timeframe.
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
548 PM CST Sat Dec 24 2022
Issued at 232 PM CST Sat Dec 24 2022
The Great Lakes reside on the western side of broad upper-level
cyclonic flow across eastern North America anchored by a powerhouse
966mb low pressure system centered in west-central Quebec. With a
1035mb high pressure system across the central US, there is a nearly
70 mb pressure gradient across the Great Lakes! It is thus no
surprise winds continue to gust 35-40 mph this afternoon which
continues to lead to pockets of blowing snow particularly in open
and rural areas. Thanks to the position of the surface low, the
predominant wind direction has become west to even west
southwesterly over the past few hours, confining lake effect snow
showers to LaPorte and Berrien counties and points northward. Mostly
sunny skies are treating our area, which is no doubt making it feel
nicer than the sub-zero wind chills that continue at this hour.
Tonight, the sprawling storm system in Canada is expected to
continue lifting further away from our area. Even as winds ease this
evening, mostly clear skies allowing temperatures to fall toward
0F will support a continuation of nippy wind chills down to
around - 20F. For this reason, we will hoist a Wind Chill Advisory
for all but central Cook county where the urban heat island
should hold values closer to -15F (criteria is -20F). Meanwhile, a
wiggle in the departing upper-level cyclonic flow will allow for
winds to modestly veer northwesterly bring a return of lake
effect snow showers in far northeastern Porter county. For now,
will let the Winter Storm Warning go though a few spots (really
within a mile or two into the northeastern part of the county) may
still see low visibility from time to time tonight.
Compared to the past few days, Sunday looks wonderful with mostly
sunny skies and temperatures in the lower teens. West winds of 10-15
mph will continue to support sub-zero wind chills, so still cover up
from head to toe to be safe.
Issued at 216 PM CST Sat Dec 24 2022
Monday through Saturday...
The long term forecast begins with a chance for some snow Christmas
evening and night. Through the day on Sunday, an Alberta clipper
will quickly take shape and drop through the northern Plains and
eventually on into the western Midwest. Despite the rather compact
size of the system and the low amplitude of the associated trough,
some impressive forcing is anticipated to set up around the base of
the trough, especially in the low levels. However, it appears that
the better forcing will miss the area to the west and to the south.
Additionally, the strong positive tilt of the trough will result in
a quasi-isothermal profile through from the surface through roughly
700mb. Whereas prior model runs were suggesting this isothermal
layer would sit near -9 or -10C, the profile has been on a cooling
trend, especially in the RAP and HRRR which have since pulled the
layer down into the DGZ with temps near -11 and -12C resulting in a
DGZ potentially 10,000-12,000 ft deep. Despite a nearly saturated,
deep DGZ, the lack of forcing aloft will keep the snow production
and resultant snowfall rates somewhat humble. Snow totals are
looking like around an inch across much of the area with locally
higher totals possible in the western and southwestern CWA and
lesser totals likely across northwest IN. Mid-evening Sunday through
the earlier part of Monday morning appears to be the most likely
timeframe for snow.
Monday and Tuesday will see highs in the lower and middle 20s before
a robust low level jet moves over the Midwest on Wednesday and reels
in a much warmer airmass from the southwest with the aid of the SW
return flow from the backside of the prominent Bermuda high. Lower
40s are looking likely on Wednesday followed by 50s potentially on
Thursday as the efficient WAA continues. As a trough digs in the
western US Wednesday into Thursday, a surface Low is expected to
spin up in the Plains and push into the upper Midwest. As it does,
the system`s cold front looks to slowly drag across the area and
provide us with some rain showers through much of Thursday and
Friday. As the trough continues to dig, guidance shows a second low
pressure center forming along the front dropping widespread showers
along its warm front as it pushes through the CWA on Saturday. With
the center of each system missing the area just to the west, the WAA
will continue through the end of the week likely keeping the upper
40s/lower 50s hanging on into the weekend.
For the 00Z TAFs...
Aviation forecast concerns:
* Gusty westerly winds persist through tonight
* Low chance for brief MVFR cigs - more likely remain VFR
* Chance for snow late Sunday evening/night
Winds remain gusty out of the west early this evening to around
30kt. This will very gradually ease with time overnight and into
tomorrow with gusts still in the low 20kt range through the daytime
hours. There is a signal for low clouds (1500-2000ft range) to
develop overnight into Sunday morning, though a similar signal
existed for today and it remained cloud free across the area, so
think the more likely scenario is that we remain VFR.
Toward the end of the 30-hr TAFs light snow may begin moving
through the region with a quick moving weather system late Sunday
evening and overnight. Have left this out of the TAF for now and
will be addressed with later updates as confidence increases.
IL...Wind Chill Advisory...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
Saturday to 10 AM Sunday.
IN...Wind Chill Advisory...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
Saturday to 10 AM Sunday.
LM...Gale Warning...nearshore waters until 10 PM Saturday.
Heavy Freezing Spray Warning...nearshore waters until 10 PM
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Area Forecast Discussion
National Weather Service Marquette MI
640 PM EST Sat Dec 24 2022
.SHORT TERM...(This evening through Sunday)
Issued at 222 PM EST SAT DEC 24 2022
Water vapor imagery and RAP analysis show a deep mid-level low
centered just south of James Bay this afternoon. A shortwave
rotating around the low is pushing south through Ontario. A tight
pres gradient remains btwn the 965 mb sfc low near James Bay and a
1042mb sfc high nw of Lake Winnipeg and with core of the strongest
low-level winds shifting south across the area today, there has been
an uptick of sustained winds and gusts. 50 to 55 kt gusts have
occurred today over the Keweenaw and between Harvey and Munising
resulting in gusts near 65 mph. Elsewhere, gusts btwn 35 to 50mph
today have been more common. With model soundings showing a steady
state of the deep moisture profile, wind direction thru the low to
mid-levels, and the DGZ which is well positioned in the lake induced
convective layer, expect little change in intensity of the snowfall
streaming off of Lake Superior into early evening and little change
in the areas being impacted. Strong low-level wind fields will
continue to push lake enhanced snow much farther inland than is
typical. Addiitional snow accumulations into the evening should be
in the 3-8 inch range w and n and less than 1 inch s central. With
the strong winds, considerable blowing and drifting snow will
continue, most severe across the Keweenaw and then eastward across n
central Upper MI closer to Lake Superior. Where plowing is
infrequent, some roads will become impassable from the drifting.
Power outages will remain a concern as well.
As far headlines go, I have extended the Blizzard Warnings through
06Z across the Keweenaw and for Marquette County eastward through
Luce counties. Also extended the Winter Storm Warnings through 06Z
for Delta, Baraga and southern Houghton due to lingering moderate to
heavy LES and blowing snow. In the western counties of Gogebic,
Ontonagon and Iron where warnings are set to expire at 00Z and I
have issued a Winter Weather Advisory to extend from 00Z through 12Z
Expect conditions to slowly improve from west to east overnight as
winds slowly die down and drier air works in. There could be
lingering vsby issues into the eastern counties through the night as
LES and blowing snow could linger there. It`s possible headlines may
need to be extended through 12z for the eastern counties.
.LONG TERM...(Sunday through Saturday)
Issued at 155 PM EST SAT DEC 24 2022
Mother Nature`s Christmas present to da Yoop will be a much quieter
and less impactful period of weather across the Upper Peninsula as
the main low of interest for today lifts north near James Bay and
high pressure settles into the middle-Mississippi River Valley. As
the surface high presses southeast toward the Gulf Coast, mid-upper
level ridging building in should begin the downward trend of snow
showers during the day Christmas in the west. Guidance suggests a
northward lifting of showers, so places like Ironwood should start
to see a break from the showers but areas along the Spine into the
Keweenaw could continue to see shower activity. Increasing dry air
and subsidence is expected to start squashing inversion heights
though, so accumulations appear to be light. In the east, expecting
continued snow showers through the day in the northwest wind snow
belts. Much like the west, increasing dry air aloft should work
against the showers, but additional accumulations may still add up
to 2-4 inches. While the stronger winds are expected to begin
lightening tonight, lakeshore areas could still see gusts near 40
mph at times Christmas morning, but decreasing gradient winds should
support improving conditions through the day. Interior areas removed
from the lakes could see wind speeds of 20-30 mph Sunday morning.
Areas prone to drifting snow will likely continue to see additional
drifts Sunday morning, but as the winds weaken during the day
Sunday, expecting conditions to improve.
A shortwave drops southeast through the Northern Plains Sunday
night. While precip tied directly to this is expected to avoid us,
winds may take on a more northerly direction in the west, so shower
activity may end up pressing south toward Ironwood/Porkies again.
However, if it does, accumulations would be light. Elsewhere Sunday
night, expecting light scattered to numerous snow showers in the
eastern northwest wind lake effect snow belts. Overnight lows should
dip to near zero in the interior west half and single digits above
zero to near 10F in the east half and near the lakeshores. As the
shortwave continues its track away from the forecast area, another
shortwave rotating through the broad mid-upper level trough to our
north is expected to swing through Lake Superior and Upper Michigan
Monday evening. This may support a couple hours of more moderate
snow showers in the east before winds shift to the west and
Another shortwave tracks east through the northern Plains on
Tuesday, positioning Upper Michigan in southwest flow and a WAA
regime. While the warmer airmass moving in isn`t impressive,
isentropic forcing ahead of the shortwave may support another round
of snow. Right now the better forcing is focused over Lake Superior
and Ontario, so any snow from this system would be limited to the
north half. From here, the deterministic guidance suite gets muddy
with the timing and position of key features ejecting eastward
through the Plains. Regardless though, a warming trend is expected
going into the later half of the week and into the weekend.
Depending on the track of any shortwaves and degree of warming, its
possible there could be some mixed precip during this period.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 640 PM EST SAT DEC 24 2022
Strong winds and snow showers continue to impact all three TAF
sites, with LIFR conditions continuing. KCMX, as expected, has seen
the most impressive winds today, and this trend will continue for
this forecast as expect gusts there to remain around 50 knots early
in the forecast, and then gradually diminish to around 30 knots by
daybreak. KSAW will see wind gusts of around 30 knots overnight,
with KIWD a little lower, but both will have diminishing winds
overnight and during the day with winds falling and the major winter
storm winds down. And with winds relaxing and the snows gradually
ending, conditions will improve from LIFR this evening to MVFR late
tonight and early Christmas Day.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 155 PM EST SAT DEC 24 2022
Continued storm force winds and large waves are expected this
evening. While the winds begin lightening overnight from west to
east, gales are likely to persist through Sunday morning across the
east half of the Lake. In the west half overnight, conditions may
fall below gales by sunrise. Winds near 30kts are likely to persist
through late Sunday night in the north/east, but a majority of Lake
Superior looks to be below 25kts Sunday night through Tuesday. Winds
during this period should be primarily out of the northwest, but
Monday night they are likely to shift to westerly in the east and
southwesterly in west before becoming southwesterly or southerly
lake-wide Tuesday ahead of the next system.
There are some timing differences in the guidance suite for the
Tuesday/Tuesday night system, but overall, the expectation is for
winds to increase to around 30kts or near low-end gales ahead of the
With the strong winds through Sunday combined with the cold airmass
overhead, areas of heavy freezing spray will be likely. But as winds
weaken Sunday, moderate ice accumulation potential is more likely.
Blizzard Warning until 7 AM EST Sunday for MIZ001-003-006-007-
Lakeshore Flood Warning until 10 PM EST this evening for MIZ001.
Blizzard Warning until 7 PM EST this evening for MIZ002-009.
Lakeshore Flood Advisory until 10 PM EST this evening for MIZ002-
Winter Weather Advisory until 7 AM EST Sunday for MIZ002-009-010.
Winter Storm Warning until 1 AM EST Sunday for MIZ004-013-084.
Blizzard Warning until 1 AM EST Sunday for MIZ005-014.
Lakeshore Flood Warning until 7 AM EST Sunday for MIZ006-007.
Winter Storm Warning until 7 PM EST this evening for MIZ010.
Winter Weather Advisory until 7 PM EST this evening for MIZ011-
Storm Warning until 1 AM EST Sunday for LSZ162-240>251-263>267.
Heavy Freezing Spray Warning until noon EST Sunday for LSZ162-
Gale Warning from 1 AM to 7 AM EST Sunday for LSZ162-240>242-263.
Gale Warning from 1 AM to 1 PM EST Sunday for LSZ243>248-264-265.
Gale Warning from 1 AM to 4 PM EST Sunday for LSZ249>251-266-267.
Gale Warning until 5 AM EST Sunday for LMZ221-248-250.
Heavy Freezing Spray Warning until 7 PM EST this evening for
Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
928 PM EST Sat Dec 24 2022
Issued at 910 PM EST Sat Dec 24 2022
Overall, no significant changes for the evening update. Just some
minor tweaks here and there. Skies are mostly clear late this
evening, save some clouds lingering in mainly the mountains from
Unicoi county northward into the eastern parts of Washington
county Virginia. Satellite trends over the last couple of hours
have shown a marked decrease in cloud cover in those same regions
so expect that to continue and the entire CWA be cloud free by
midnight or shortly thereafter. Strong surface high pressure was
anchored over the plains this evening, with low pressure over
eastern Canada. Locally, there`s still an 8-10mb pressure
gradient in place from northern AL/MS through southern West
Virginia this evening, which is keeping winds elevated through
the valley. This likely won`t go away overnight, which means that
low temps may be a bit warmer than forecast (they were already
running a degree or so on the high side vs the previous forecast).
The last few runs of the HRRR seem to have caught on to this trend
so I bumped lows up a notch. This was only a minor adjustment
however, and still expect to see teens and single digits in many
locations in the valley, with even colder conditions at elevation.
Otherwise, no real adjustments were necessary, and the Wind Chill
Advisory still seems to be in good shape as well.
(This evening through Sunday)
Issued at 314 PM EST Sat Dec 24 2022
1. Dangerous cold wind chills continue across the higher elevations
through Christmas morning.
2. Temperatures will remain below freezing throughout the forecast
Clouds are eroding this afternoon as a shortwave lifts off to the
northeast. A few flurries may linger across extreme northeast TN and
into southwest VA through early evening but clouds will eventually
break up across these areas as well and flurries will end. The wind
chill warning expired earlier today as temperatures continue to
slowly rise and winds further decrease. However, a wind chill
advisory remains in effect across the east TN mountains and
portions of southwest VA through Christmas morning.
Though winds are decreasing, we still keep light winds through
the night which will again keep temps from plummeting. Overnight
lows will be a few degrees warmer than last night, generally
ranging from the single digits to just above single digits.
Christmas day should be sunny and warmer as the Arctic airmass
continues to moderate across the region. Look for high temps in the
mid to upper 20s, with some areas getting into the low 30s. Though
highs are still well below normal, plenty of sun and the warmer
temps will make it feel much nicer than what we`ve seen the past few
(Sunday night through next Saturday)
Issued at 314 PM EST Sat Dec 24 2022
1. A warming trend is expected this week but we will not get back to
normal temps until Wednesday.
2. Increasing precip chances are expected Friday and Saturday but
with above normal temps expected precip type will be rain.
In the upper levels, a potent short wave will move through the
region Monday and Monday night. Some snow flurries will be possible
mainly in the mountains. The best chance for a light snow shower
will be in the northern Cumberland Plateau counties and Lee and Wise
counties in Virginia. Little to no accumulation is expected with a
dry air mass in place. A warming trend is expected early this week
but normal temps will not return until Wednesday.
A ridge will build into the region midweek and the warming
continues. Late this week the warming trend will continue with highs
around 60 on Friday which is about 10 degrees above normal. The next
system will arrive this weekend with POPs starting to increase
Friday afternoon. With above normal temps expected precip type will
be all rain. Wind direction may be favorable for downslope wind
enhancement next weekend as a strong system approaches but it is too
far out to see specifics.
Issued at 614 PM EST Sat Dec 24 2022
Satellite imagery shows the back edge of MVFR CIGS pushing
through KTRI at the moment so expect them to be clear (or at least
FEW-SCT027) when the 00z observation comes in. Will go ahead with
VFR categories at all sites for the entire 00z TAF period. Winds
should stay at 10 kt or lower at all sites, execpt maybe at KTYS
for a couple more hours.
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 14 33 17 37 / 0 0 0 0
Knoxville McGhee Tyson Airport, TN 12 30 15 35 / 0 0 0 10
Oak Ridge, TN 12 31 13 33 / 0 0 0 10
Tri Cities Airport, TN 8 27 11 33 / 0 0 0 10
NC...Wind Chill Advisory until 10 AM EST Sunday for Cherokee-Clay.
TN...Wind Chill Advisory until 10 AM EST Sunday for Blount Smoky
Mountains-Cocke Smoky Mountains-Johnson-Northwest Carter-
Sevier Smoky Mountains-Southeast Carter-Southeast Greene-
VA...Wind Chill Advisory until 10 AM EST Sunday for Russell-