Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/27/22

AREA FORECAST DISCUSSION

National Weather Service Eureka CA

 351 PM PST Mon Dec 26 2022

.SYNOPSIS...A potent storm will bring heavy rain and strong south
winds to Northwest California tonight. Showers, isolated thunderstorms
and high surf will follow on Tuesday. Additional periods of rain
and high mountain snow will continue through Saturday.

&&

.DISCUSSION...A powerful and wet storm has been bearing down on
Northwest California this afternoon. A strong frontal boundary
will move across the area tonight, generating strong winds and
heavy rainfall rates. A 60-80 kt 925mb southerly pre-frontal
coastal barrier jet will develop this evening in response to a
developing surface cyclone, and when combined with a tight surface
pressure gradient, will favor south winds gusting from 50-60 mph
over the coastal plain and gusts from 60 to 75 mph across the
ridges of Del Norte and Humboldt Counties. Winds will shift to the
southwest early Tuesday morning after the front progresses southward
and some gusts to 50 mph will remain possible.

IVT`s or moisture flux will peak in excess of 1000 kg/m/s for a
short duration tonight. The extreme moisture flux will support
torrential rainfall rates of 0.50 to 1.00in/hr along/ahead of the
cold front this evening into early Tuesday morning. Low flows on
the rivers, low reservoir levels and the short duration (6 to 8
hours) of IVT`s over 750kg/m/s will limit the threat for major
flooding. We maintained the flood watch for urban/small streams
for much of the forecast area tonight into early Tuesday due to
the anomalously high IVT`s. The frequency of occurrence of IVT`s
over 1000kg/m/s for this time of year is about 1 day in every 10
years with respect to the CFSR-climatology. Latest NAEFS IVT`s
return intervals are outside the CFSR-climatology. IVT`s this
high have never occurred before for this time of year and are
extremely rare. For that reason, the flood watch is warranted due
to the potential for rapid rises on small rivers, streams and
creaks and flooding of low-lying areas with poor drainage. Also,
a flash flood watch for debris flows on burn scars, particularly
the River Complex for the Coffee Creek basin has been issued.
The Coffee Creek area is most vulnerable to debris flow. For the
more recent burn scars of 2022, particularly the Six Rivers
Lightning Complex, rain rates will need to be monitored closely
for possible debris flow. The HRRR and blended/calibrated
guidance continues to indicate rates below thresholds of 1.4in/hr.

Snow levels will remain quite high through the duration of the
heavy rain. Latest HREF guidance indicates increasing potential
for convection and lightning late tonight. The potential for
brief-locally heavy downpours will continue into the day on
Tuesday due to the 500mb cooling and steepening mid level lapse
rates. Snow levels will fall to 3500-4500 feet and some small hail
will possible by Tuesday night, but will probably melt before
hitting the ground. Some light snow is expected for the higher
elevations of Trinity county Tue night into Wed, with low travel
impacts expected for Scott Mountain Summit on HWY 3.

Ensemble based 500 mb cluster analysis shows Northwest California
remaining exposed to a long fetch of westerlies spanning across
much of the North Pacific during the next 10 days. That pattern
signals a prolonged period of mostly wet weather and potentially
an increased threat for flooding into the first week of the new
year. This our wettest time of year and we need the rain and
mountain snow to mitigate our prolonged drought.

&&

.AVIATION...Another winter weather system and associated front will
continue to bring impactful weather hazards to the region today.
Therefore conditions will further deteriorate as the front nears
the coast. Southerly winds continued to accelerate through the
day, with substantial LLWS probable at the coastal terminals
today...and continuing at ACV through the TAF period. The
strongest winds, along with heavy rain, are expected ahead of the
frontal passage late tonight, then winds shift SW and weaken early
Tuesday morning after the front passes overhead. Areas of inland
valley fog should lift (particularly at UKI) by late afternoon.
Rain will spread across the all airports/airfields in the
afternoon. Prefrontal deteriorating conditions includes: light to
moderate rain, MVFR to LIFR CIG/VIS, LLWS and notably strong
southerly winds. Post frontal conditions at Coastal sites will
include a threat of thunderstorms. /TA

&&

.MARINE...Hazardous marine conditions will developed across the
waters this evening into Tuesday as a storm system moves through,
bringing widespread gale winds. Storm force gust up to 60 kts will
be likely North of Cape Mendocino. The strongest winds are expected
around midnight ahead of the front, then a brief period of high-end
gale force southwesterly gusts is possible as the front sweeps
overhead early Tuesday morning. Winds are expected to weaken
significantly and veer to SW behind the front, dropping to the mid 20
kts range for all zones by dawn on Tuesday. This front will be
followed by another solid W swell, with heights likely reaching 20
to 25 ft at 15 seconds across all zones. Conditions then look to
settle down a bit later this week, although advisory-level seas and
southerlies likely continue for the foreseeable future, with the
next pulse expected Wednesday night and Thursday.

&&

.HYDROLOGY...A strong to extreme atmospheric river (moisture
flux or IVT`s over 1000kg/m/s) will result in heavy rain across
all of Northwest California this evening through early Tuesday
morning. Rainfall rates from 0.50in/hr to 1.00in/hr are forecast
tonight resulting in an increase threat for debris flow on burn
scars, particularly the River Complex burn scar in Northern
Trinity county. The Coffee Creek drainage basin will be particularly
vulnerable and flash flood watch has been issued for tonight.
Hourly rates approach 1.00in/hr for the August complex burn scar
from 2020 and the Six Rivers Lightning Complex burn scar from
Summer of 2022, but are under thresholds of 1.20in/hr and
1.40in/hr, respectively.

Otherwise, minor flooding of small creeks, streams, and urban
areas will be possible due to heavy rainfall. Main stem rivers
will rise rapidly by early Tuesday morning, however flood stages
are improbable (less than a 10% chance) at this time due to the
pre-existing low flows and the short duration of the heaviest
rain rates, 6 to 8 hrs. All in all, 24 hour rainfall totals are
forecast to range from 2 to 4 inches across valleys and the
coastal plain, while 3 to 6 inches are expected for the mountains,
particularly west and southwest facing terrain.

Additional rainfall is forecast for the remainder of the week
with the highest threat for hydrological concerns arriving late
in the week and into Saturday. Ensemble mean peak IVT`s are under
500kg/m/s. Duration of IVT`s over 250kg/m/s range from 30-40
hours. Some ensemble members indicate higher IVT`s with similar
durations which could yield a moderate to strong AR and higher
rain rates. Right now it is looking like a weak AR.

&&

.BEACH HAZARDS...A high surf advisory is in effect from Tuesday
morning through late Tuesday night. A large westerly mid period
swell near 25 feet will aid in breaking waves ranging from 22 to
26 feet along area beaches. The large breaking waves along the
coast will lead to increased wave run-up on beaches with waves
topping and washing over large rocks and jetties. These large
waves can be erratic and unpredictable, and will be capable of
sweeping people into the frigid and turbulent ocean water. In
addition, mariners traversing the bar are urged to exercise
extreme caution or stay in port until the threat subsides.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     High Wind Warning from 7 PM this evening to 4 AM PST
     Tuesday for CAZ101-102-104>106.

     High Surf Advisory from 6 AM to 11 PM PST Tuesday for
     CAZ101-103-104-109.

     Wind Advisory from 7 PM this evening to 6 AM PST Tuesday
     for CAZ103.

     Wind Advisory from 10 PM this evening to 4 AM PST Tuesday
     for CAZ107>115.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 4 PM PST this afternoon for
     PZZ450-455-475.

     Gale Warning from 4 PM this afternoon to 3 AM PST Tuesday
     for PZZ450-455-475.

     Storm Warning until 3 AM PST Tuesday for PZZ470.

&&

$$

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 Greenville-Spartanburg SC

 1044 PM EST Mon Dec 26 2022

.SYNOPSIS...
A weak low pressure system could bring brief snow showers to the
western and southern parts of the forecast area this evening into
tonight. Then, surface high pressure will build in and keep dry
conditions and a warming trend through much of the week. A low
pressure system approaches from the west on Friday, increasing
the rain chances through New Year`s weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 1031 PM EST Monday: Extensive mid-level cloudiness has spread
across the region ahead of an approaching clipper-type short wave
approaching from the west. The radar mosaic has been gradually
filling in with very light streams of echoes indicative of light
precip aloft, but the lowest cut from the KGSP radar suggests that
little is reaching the ground at this time because of sublimation
in the very dry boundary layer. Better reflectivity was noted over
N central GA and on the east side of metro Atlanta. Recent HRRR
runs still fail to drop much light snow east of the mtns, but if
anywhere stands a chance it would be the Lakelands/Lower Piedmont
late tonight. Meanwhile, some light returns were gradually shrinking
over northeast TN, but light snow was doubtless falling along the
TN border still. Expect a few reports of flurries elsewhere thru
the early morning hours. We will continue to let the fcst ride
for better or for worse. Either way, no significant snow accum
is expected.

Otherwise, expect most of the forecast period to be dry outside
of the little bit of excitement for later this evening. Overnight
lows will be 5-10 degrees below normal for most locations. Any
precipitation will shut down by daybreak Tuesday as the axis of the
shortwave slips east of the CFWA and DNVA filters in. Surface high
will extend across the East Coast during the day Tuesday following
the exiting shortwave. Expect decreasing clouds during the morning
and mostly sunny skies by the afternoon. Temperatures will start a
"warming" trend that will continue through the rest of the week,
but most locations will still remain 5-10 degrees below normal
for highs on Tuesday.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 200 PM EST Monday: The short term looks pretty quiet, with a
nice warming trend continuing thru the middle of the week. Temps
starting out a few deg below normal Tuesday night, then warming
to a few deg above normal for Thursday`s highs. This will be
thanks to an upper ridge building across the Southeast within
an amplifying upper pattern across the CONUS, setting up along
the Eastern Seaboard by Thursday. At the sfc, high pressure will
become anchoring along the East Coast, with a persistent SLY/SWLY
low-level flow atop the forecast area advecting in warmer temps. Dry
conditions are expected thru the period.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 215 PM EST Monday: A deep trough axis will eject east of the
Rockies on Friday, with strong southerly flow developing well ahead
of this feature across the central and eastern U.S. The warm-up
will continue in earnest as the surface high over the southeast
moves off the Atlantic seaboard. Temperatures Friday will rise to
5 to 10 degrees above normal in most areas, with upper 50s to near
60 maxes feeling downright balmy after the recent weather.

The 12z model runs are in decent agreement on the upper trough
slowly tracking east across the Great Plains Saturday, bringing
an embedded shortwave trough thru the Southeast that takes on a
negative tilt and lifts northeast of the area Sunday. A low pressure
system is expected to develop in response, and activate a warm
front across the Deep South. Increasing moisture over the front
will allow PoPs to ramp up late Friday thru early Saturday. Temps
will remain about 15 deg above normal Friday night due to the cloud
cover and strong WAA, and several deg above normal Saturday. So
no wintry p-types are expected with showers that break out ahead
of the front. The low pressure occludes over the Ohio Valley and
brings a cold front thru the area on Saturday. The front should
bring a fairly solid band of rain showers across the area. Will
cap PoPs at likely for now, given slight timing differences in the
guidance. There will be some in-situ CAD that may keep sfc-based
CAPE to our south. But some elevated CAPE may result in at least
isolated rumbles of thunder Saturday aftn-eve. The GFS and ECMWF
bring a dry slot into the area Sunday, while the Canadian keeps
things unsettled. The Canadian seems to be an outlier. Either way,
Sunday looks like a warm day, with mid 60s possible across the
Piedmont behind the "cold front." The upper ridge rebounds quickly
across the eastern U.S., and another deep trough digs into the
Rockies by Monday. This could bring another front toward the area
and returning rain chances late Monday.

&&

.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: VFR through the period at all
terminals. Cloudiness associated with a passing clipper-type wave is
expected to remain mostly above 050 thru late tonight. A mid-level
ceiling may persist thru the early morning, but should scatter out
by late morning Tuesday. If there is a forecast problem it will
be the coverage and chances of light snow thru the early morning
hours. Recent guidance has backed off with the precip coverage,
so until we see a better indication of snow reaching the ground,
most terminals get a VCSH for passing light snow. The exception
is KCLT where the TEMPO was kept from the previous forecast for
continuity purposes for the time being, because the worst-case
scenario depicted remains reasonable. The wave should pass well
before daybreak Tuesday. From mid-morning onward, expect only a
few patches of cirrus and a light/variable wind.

Outlook: Drier VFR weather is expected to last into early
Friday before rain chances return for all terminals late Friday
into the weekend as a low pressure system approaches out of the
west. Temperatures will be on a gradual warming trend throughout
the week.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...ARK
NEAR TERM...CAC/PM
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...PM



Area Forecast Discussion

National Weather Service Northern Indiana

 617 PM EST Mon Dec 26 2022

.SYNOPSIS...
Issued at 337 PM EST Mon Dec 26 2022

Cloudy skies will persist through tonight with pockets of light
snow and freezing drizzle winding down this evening. Fog may
develop later tonight into Tuesday morning across portions of the
area. A trend towards much warmer temperatures will continue
through the upcoming week.

&&

.SHORT TERM...(This Evening through Tuesday)
Issued at 337 PM EST Mon Dec 26 2022

Clipper system, nicely depicted on water vapor with the center over
far west central IL, will continue to drift SE out of the area this
evening. Although this feature will pass well SW of the area, large
scale, weak low level lift was expanding across the area with some
pockets of light snow (mainly very light) and even some patchy
freezing drizzle as the DGZ continues to flirt with the better lift
residing just below it. Not expecting much in the way of impacts
at this point but will monitor into the early evening hours when
the low level lift hopefully diminishes.

Next, and potentially much more problematic issue will be risk for
freezing fog, possible dense later tonight into Tuesday morning.
Hi res models to some extent or another all show a very shallow
but strengthening near sfc inversion with plenty of lingering
moisture from the departing clipper and slightly ripening
snowpack. The challenge will be how far south the drying works in
behind the clipper and if, despite no break in the stratus, can
freezing fog develop and potentially become dense. After
coordination with surrounding offices, have added a mention of
patchy freezing fog to mainly SE sections to start things off. LAV
and HRRR all sock in these areas with 1/4 mile or less vsby which
would cause some travel issues and warrant headlines. Will defer
any further expansion of the fog and headlines to the evening
shift.

Last, but not least, a vort lobe extends from the clipper north
and then east across southern Lk MI with radar returns over the
past hour or 2 trying to enhance some. Models continue to show
some weak omega lingering in the vicinity of the trough through
much of the night, but a fair amount of drying will be underway in
the low level as a NW low level flow sets up. The greatest lift
will exist into this evening before slowly weakening. Delta Ts
will be sufficient in the mid to upper teens with inversion
heights in the 4-5Kft range. However DGZ will be above the main
omega, which should limit flake size and overall threat. Will
maintain slgt chc or may low end chc that was inherited, but not
expecting much (1/2 inch to maybe inch) through 12Z Tue.

Drier air should finally begin to move in during the day Tuesday,
but the low sun angle and strength of the inversion may delay the
clearing in the SE areas much of the day. Continued with clearing
taking place, but may need to slow even further. Tuesday will be the
last day for most, if not all areas, to be below freezing.

&&

.LONG TERM...(Tuesday Night through Monday)
Issued at 337 PM EST Mon Dec 26 2022

Pattern shift will continue going from one extreme to the other as
closed upper low moving into the NW US opens with the energy
dropping southeast, carving out yet another longwave trough
across the western US. Increasing SW flow will setup up with highs
climbing above freezing Wednesday. Snow pack across most of the
area of generally 1 to 3 inches, with locations closer to Lk MI
seeing upwards of a foot more more in spots. The lesser snowpack
should quickly release and melt off Wednesday for most areas
(maybe even start Tuesday afternoon where sunshine is realized),
but deeper pack will take a bit more time.

The Gulf of Mexico will be wide open for business as the trough
begins to move towards the Great lakes for the second half of the
forecast, bringing in abundant low level moisture which will not
only help get rid of even the deeper snow pack, but also bring
increasing chances for rain Thursday night into Saturday as well
as some fog and the main push commences. The fog will likely start
as early as Thursday and could become dense in some areas, but for
the time being has been left out of the forecast.

In terms of precip, likely to categorical pops have been
maintained. With dewpoints expected to climb well into the 40s
(maybe even some 50s in far SE areas) should see the potential for
a decent amount of rainfall. Hopefully by the time it arrives the
ground is sufficiently thawed (was frozen around 2.5" thick here
this morning) to allow the ground to start absorbing it. Rivers
should be able to handle it in most areas. The area to be
monitored will be where the greater snowpack exists with roughly
one half to 1 inch of water trapped and set to release. At this
point the heaviest rain may remain southeast of this area but a
lot of factors to monitor in later forecasts.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
Issued at 603 PM EST Mon Dec 26 2022

FZDZ and -SN continue to exit eastern Indiana. Dry conditions are
expected for the remainder of the TAF period. Lake effect clouds
are likely to roll over KSBN within the next couple hours
according the satellite data and derived GOES flight rules. This
stratus is rather broken, however, so flight categories may
bounce around. Drier air moves into the low-levels and LL wind
becomes westerly such that confidence is high that VFR conditions
will prevail prior to 12z.

The KFWA TAF is low confidence with regard to the previously (18z
discussion) mentioned FZFG chance. My pattern recognition leans
toward this not being a slam-dunk FZFG case, especially in the
absence of a surface stationary front. Forecast soundings are
split with regard to low- level saturation. Upstream dew points
are in the single-digits with no hints of FG quite yet.
Additionally, while stratus is slowly exiting, high clouds are
rushing in from WI which may negate the FZFG chance as well.
Overall, I cannot completely discount the FZFG chance, but I do
have doubts. Therefore, this portion of the TAF is unchanged.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...Fisher
SHORT TERM...Fisher
LONG TERM...Fisher
AVIATION...Brown


Visit us at www.weather.gov/iwx

Follow us on Facebook...Twitter...and YouTube at:
www.facebook.com/NWSNorthernIndiana
www.twitter.com/nwsiwx
www.youtube.com/NWSNorthernIndiana



Area Forecast Discussion

National Weather Service Marquette MI

 735 PM EST Mon Dec 26 2022

.SHORT TERM...(This evening through Tuesday Night)
Issued at 306 PM EST MON DEC 26 2022

Water vapor imagery and RAP analyses show mid-level ridging along
the western US and troughing over the east half of CONUS. In the
resulting nw flow across the central U.S., a well-defined shortwave
is tracking well to our southwest, into western IL this afternoon.
Closer to home, under low-level NW flow and 850mb temps of
-15 to -18C, lake effect snow continues to stream off of Lake
Superior. Inversion heights remain modest at around 4 to 6kft, but
with the DGZ generally occurring at around 2 to 4kft. So, this is
helping to keep in some fairly high snow ratios and lighter, fluffy
snowflakes. We continue to see a brief burst of heavier snowfall
rates at times with some higher-reflectivity echoes on radar. This
type of setup is also favorable for flurries and snow showers to
extend well inland from the lake, possibly crossing hwy 28 into the
central UP at times.

The rest of the afternoon, winds start to back more to the west.
This will cause lingering lake effect to become more isolated to the
Keweenaw and eastern Superior shorelines. With some deepening of the
moisture profile from the NW UP into eastern Upper MI, LES may get a
little boost in intensity tonight. While lower inversions will be a
negative, the DGZ dominating the convective layer will support 1-2
inches, possibly isolated 3 inches, of fluffy snow accumulation into
the eastern forecast area where longer fetch will support deeper
convection than over the west. The Keweenaw may end up with an inch
to locally 2in by the time lake effect snow shifts north of the area
early Tuesday.

The weather turns somewhat active for Tuesday with a clipper moving
through and bringing in a quick burst of precipitation into the
afternoon. Persistent southwesterly flow will lead to robust warm
air advection aloft through Tuesday, with a fairly prominent warm
nose developing in soundings by the afternoon as 850mb winds
increase to 40 to 50kts and the shortwave drops southeast through
the area. While much of the current deterministic and ensemble
guidance allows for some QPF across most of the UP, there is a
general consensus now for a swath of higher QPF across the Keweenaw
and the eastern half of UP and fairly light amounts elsewhere. A
local maximum across the southeastern UP may be owing to some
localized enhancement from Lake Michigan amid southwest flow.

With that warm nose extending well into the area according to latest
model soundings, precipitation should pretty quickly change over to
a wintry mix with snow and sleet - though some icing is not totally
out of the question in the southern UP, where the re-freezing layer
may become rather shallow. It should be noted that surface
temperatures are only expected to peak in the teens to lower 20s
area-wide. Snow and sleet totals will be highest across the Keweenaw
and eastern UP, with a potential for some spots to flirt with the 2
to 4in range by the time precipitation starts to move out late
Tuesday night. However, there is still a bit of uncertainty with
totals, as a more northerly track could result in much of the area
missing out on any precipitation at all.

In addition to a potential quick round of wet snow or snow/sleet,
winds will also be turning gusty on Tuesday with quick pressure
falls and the low level jet nosing in. Gusts to 20 to 25mph are
possible across much of the area by Tuesday afternoon, through the
first half of Tuesday night. Higher gusts around and even in excess
of 30mph are possible closer to the water, especially the Lake
Michigan shoreline. This marriage of wet, heavy snowfall and gusty
winds will be something to keep an eye on, as fallen tree limbs and
power outages may become a concern.

.LONG TERM...(Wednesday through Monday) Issued at 148 PM EST MON
DEC 26 2022

Starting off 12z Wednesday, upper level pattern begins to amplify
across CONUS as broad troughing exits out of the Rockies and pushes
ridging over the eastern half eastward. As this progression occurs
into the weekend, Upper Michigan will find itself on the western
flank of the ridge in southwesterly flow as the trough approaches.
Within this pattern, a system is expected to lift northeastward into
the northern Plains/Upper Great Lakes Thursday night. Overall, with
the airmass aloft supporting above normal temperatures during this
period, the forecast period includes a mix of ptype possibilities.

Mid-upper level ridge axis shifts through the forecast area
Wednesday as a warm front is draped across the forecast area.
Guidance suggests a mixed bag of options for where the boundary is
expected to be, but confidence is high that eventually Upper
Michigan will find itself south of the boundary in the warm sector
and under the influence of increasing increasing moisture. Model
soundings suggest that periods of light mixed precip, drizzle, and
fog will be possible until at least Friday, when a low`s cold front
swings through the region. Model spread in the track of the low
still exists, but there is increasing confidence that the low will
track to our west, resulting in highs and dewpoints climbing above
freezing. As the cold front swings through, deeper moisture and
frontal forcings may support a mix of ptypes.

Beyond this, the pattern continues to be muddy, but its now looking
possible that the New Year`s Eve Holiday may be dry. The next system
of note on the horizon looks to lift northeastward through central
CONUS early next week. Similarly to the late week low, the airmass
with this system continues to suggest mixed precip type could be on
the table.
&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 734 PM EST MON DEC 26 2022

VFR conditions have returned to all TAF sites this evening with a
shift in wind to the WSW.  However, the good conditions will be
short-lived as another system enters the area tomorrow.  Conditions
will quickly deteriorate back to MVFR and even some IFR by the
afternoon.  In addition, southwest winds will become strong with
sustained speeds in the 12 to 15 kt range, gusting to 27 kts.  LLWS
will be a threat at KIWD from mid morning tomorrow through tomorrow
afternoon.

&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 148 PM EST MON DEC 26 2022

Northwest flow today has resulted in winds across Lake Superior of
around 25-35 kts, with a decreasing trend observed in observations
through the morning. For the remainder of the afternoon and overnight
tonight, expecting similar conditions, expect winds shift to
westerly in the east and southwesterly in the west ahead of another
system moving through the region. Winds look to remain around 25kts
through the day Tuesday midday. By Tuesday afternoon and into the
evening, pressure falls and a LLJ moving overhead will support winds
increasing to around 30kts in the east. Some gales of ~35kts could
mix in during this period, but confidence is low. After this system
exits east, a couple weak systems could move through the region, but
guidance suggests winds of 20kts or less could persist over the lake
through the end of the week.

Patches of moderate freezing spray are possible across the lake
tonight with more widespread moderate freezing spray diminishing on
Tuesday.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...LC
LONG TERM...JTP
AVIATION...TDUD
MARINE...JTP



Area Forecast Discussion

National Weather Service Pocatello ID

 739 PM MST Mon Dec 26 2022

.UPDATE...Dense fog has developed on ITD observation sites and at
the KRXE and KIDA ASOS sites. Since it appears widespread, and
with only warm advection expected tonight, do not see any mixing
of faster air to the surface and so only expect the fog to worsen.

A Dense Fog Advisory has been issued to highlight the hazard.

Messick

&&

.PREV DISCUSSION... /issued 211 PM MST Mon Dec 26 2022/

SHORT TERM...Tonight through Tuesday night.
Atmospheric river event set for southeast Idaho tonight through
Tuesday night with heavy precipitation and warm temperatures
expected. Right now it appears heaviest snow will be above 6,500
feet with rain at lower elevations. Wind gusts of 40 to 50 mph
also expected at the highest elevations where 8 to 20 inches of
snow are expected at pass level. Winter storm warnings have been
issued in the central mountains and Sawtooth region overnight
tonight through Tuesday and for the eastern mountains Tuesday
morning through Tuesday night. Rain is expected for the Magic
Valley and Snake River Plain and even the lowest mountain region
valleys with the system. At elevations where snow does fall
extensive blowing snow is expected with very hazardous driving
conditions. Highs Tuesday are expected to be in the low to mid 40s
along the interstate corridor in the Snake Plain with 30s in the
mountains. It is expected to drop below freezing again Tuesday
night behind the cold frontal passage.
GK

LONG TERM...Wednesday through Monday.
Afternoon highs will drop for Wednesday behind the cold front with
most of the Magic Valley and Snake Plain in the low to mid 30s and
the Upper Snake Plain and Eastern Highlands a couple degrees cooler,
in the upper 20s to low 30s. Highs drop a couple of degrees more by
Thursday afternoon with more low 20s to low 30s before we gain those
couple of degrees back by Friday and Saturday. Cooler air begins to
work its way in on Sunday and Monday with highs mostly in the 20s
with some low 30s as you head west through the Magic Valley.
Wednesday will still be a bit breezy throughout the Snake Plain with
gusts in the 20-30kts range.

Now to precip chances in the extended forecast. As the trough shifts
eastward on Wednesday, snow will still be falling in the Bear River
Range and upper elevations of the Eastern Highlands before beginning
to taper off in the second half of the day. Light snow is possible
on Thursday as we remain in northwest flow. The next bigger push of
moisture moves in on Friday as another shortwave passes through and
returns us to more westerly flow. Models want Friday`s precip to be
all snow, but with highs for some of us above freezing, we could see
a mix at times. For now, the NBM 4.1 is showing a 20-50 percent
chance of at least 2 inches of snow by Saturday morning for those of
us at the lower elevations. Yet another trough moving through on
Saturday brings the potential for some moisture along the Idaho/Utah
state line, but the bulk of that looks to stay just a bit farther
south. It will bear watching as it could bring some moisture to more
of our CWA according to the GFS as the trough shifts northeastward.
The ECMWF would rather dig it farther south and east, allowing brief
ridging to build in over us on Monday.
AMM

Aviation...18Z Monday to 18Z Tuesday.
Conditions throughout the better part of Monday look to stay
generally VFR at all sites with borderline MVFR CIGs at times at
DIJ. For now, we`re actually getting to see some sunshine and fog
has lifted north of Idaho Falls, though looks like it settles back
in around 03-04Z tonight, approaching minimums. Moisture will move
in from west to east overnight though and winds will pick up on
Tuesday. With the winds, LLWS looked marginal overnight into early
Tuesday, so have kept it out of TAFs for now, but it will be worth
watching. At SUN, precip looks to stay all snow, arriving around 10Z
and drops VIS and CIGs to IFR. At BYI and PIH, mostly rain which
arrives around the 12-13Z time frame Tuesday morning. Conditions
drop to MVFR, but IFR looks more likely at PIH closer to 18Z.
Outside of fog issues at IDA, more moisture arrives around 14Z, but
with temps right at or just below freezing, the NAM and HRRR both
agree we could see brief FZDZ or rain/snow mix before switching over
to all rain. For DIJ, have kept it all SN once moisture arrives
around 14Z with VIS and CIGs dropping quickly once it begins. The
wind is already beginning to increase at BYI, but look for more
widespread gusts generally 25-35kts at BYI, PIH, and DIJ after 13Z
with IDA following suit shortly after. Wind doesn`t really pick up
at SUN until closer to 20Z Tuesday. AMM

HYDROLOGY...Temperatures will gradually warm up through mid-
week, with lower elevations pushing into the low/mid 40s and
generally no colder than low/mid 30s elsewhere. Overnight lows
tonight will remain right at or below freezing, with the
exception of portions of the eastern Magic Valley and lower Snake
Plain which could remain in the mid 30s. Overnight lows Tuesday
into Wednesday will be cooler, with mostly everywhere reaching at
or below freezing. Rain and mixed precipitation will be likely as
snow levels rise, increasing the potential for minor flooding and
ponding concerns.

AIR QUALITY...An Air Quality Advisory is in effect for Franklin
County due to stagnant air and degraded air quality. Members of
sensitive groups may experience health effects and are encouraged
to limit their exposure. Air quality is expected to improve
Tuesday, once the next system arrives and the atmosphere becomes
mixed.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon MST Tuesday for IDZ052-053-065-068.

Winter Storm Warning from 5 AM Tuesday to 5 AM MST Wednesday for
IDZ058-060-062>064-066.

Winter Storm Warning from 11 PM this evening to 11 PM MST
Tuesday for IDZ071>075.

&&

$$