Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/24/24

Area Forecast Discussion

National Weather Service Des Moines IA

 527 PM CST Fri Feb 23 2024

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Colder tonight with diminishing wind and clearing skies.

- Warming through the weekend with All-Time February records
  highs possible on Monday at some locations.

- Strong storm system arrives on Tuesday and may bring winter
  weather to the region by late Tuesday/Tuesday night.

&&

.DISCUSSION...
Issued at 238 PM CST Fri Feb 23 2024

The first wave of cold advection moved through Iowa last night and
was followed by some weak warm advection. The primary cold front is
moving into northern Iowa early this afternoon, though temperatures
are still warming a few degrees due to differential cold advection
and mixing before beginning to slowly drop upstream in southern
Minnesota. That cold front will continue to drop through the
remainder of the area this afternoon and early evening and it will
keep the breezy to gusty northwest winds in place. Still monitoring
the potential for some very light precipitation following the
boundary passage across northern Iowa. The better moisture remain
off to the east/northeast in central/southern Wisconsin. There have
been reports of flurries/very light snow reported in the Twin Cities
area. Several deterministic models including the NAM and RAP are
really saturating the low levels with some low level instability
suggesting rain/snow shower potential. That said there depth of
vertical extent is limited even with the over saturating. Therefore,
have kept a mostly dry forecast until something more definitive
suggests otherwise.

High pressure will quickly settle into Iowa overnight and will drop
winds off quickly. If sky conditions clear as expected, there will
be a period with radiational cooling and the likely possibility some
areas fall well below NBM guidance. Dew points will drop into the
single digits over parts of northern Iowa later tonight where the
NBM is suggesting lows in the upper teens. Have dropped lows several
degrees but may need to drop them further this evening if trends
persist.

The high pressure system will move off to the east on Saturday with
warm advection quickly returning to Iowa. Highs on Saturday will be
in the 40s and 50s with the coolest values east and warmest west.
The warming will continue into Sunday with highs in 50s and 60s. By
Monday a strong system will begin to drop southeast into the Pacific
Northwest and move the thermal ridge east over Iowa. Very dry air
should be over Iowa on Monday with the Gulf moisture stream off to
the southeast through the Ohio Valley and any upper level Pacific
moisture still off to the west, though there could be some passing
high level clouds. Currently forecasting highs in the upper 60s to
mid 70s. This will make a run at the all-time February high
temperatures, in particular at Mason City (66/1981) and Waterloo
(71/1921). Des Moines (78/1930) and Ottumwa (79/2017) will have some
work to do to reach their all-time February records. The daily
records for Monday are all well within reach.

Fire weather will also be a concern on Monday. The warm temperatures
and low dew points will result in relative humidity values dropping
into the 20s and may areas. This combined with gusty south winds and
dry fuels will lead to conditions for high fire growth potential. In
addition, these types of days the public tends to get out and due
early "spring" clean up burning and these types of fires can quickly
get out of control. Should the forecast conditions persist or become
more favorable, then Fire Weather headlines may be needed.

The big transition will be arriving sometime on Tuesday as that
upper level system to the west moves swiftly towards the Midwest and
will bring a strong cold front with it. Therefore, timing of the
system will play a big role in highs on Tuesday. Parts of southeast
Iowa may be well into the 70s with northwest Iowa much colder.
Currently highs on Tuesday for the forecast area is in the 40s near
Estherville to near 70s southeast near Bloomfield and Ottumwa. The
contrast will likely be much sharper wherever this boundary is
on Tuesday. While there is some convective instability over
southeast Iowa on Tuesday so there could be a few storms nearby
but the primary dynamics are still to the southeast of the area.
Several solutions still suggesting a deformation area of
accumulating snow in the region following the boundary. There
remains fairly widespread differences in the temporal and
spatial aspects with this system but this may arrive as early as
Tuesday afternoon or into the overnight.

The push of cold air looks short lived once again with warm
advection already returning by Thursday. The potential limiting
factor of the degree of warming for the end of the forecast period
will be any lingering snow cover and cloud cover.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 516 PM CST Fri Feb 23 2024

Overall, VFR conditions expected to prevail through the TAF
period. There is a chance for a small window of MVFR ceilings
in/around KMCW, signaled in hi-res guidance and looking
upstream. With majority of non-VFR ceilings expected to slide
just to the north and east of KMCW, have left VFR. Otherwise,
breezy/gusty N/NW winds will ease overnight as the parent low
pressure system slides away eastward and switch southerly
through the morning hours.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Donavon
AVIATION...Curtis



Area Forecast Discussion

National Weather Service Indianapolis IN

 950 PM EST Fri Feb 23 2024

.Key Messages...

- Snow late tonight and early Saturday with light accumulations over
the northeast half of central Indiana
- Chilly Saturday then turning much warmer Sunday into early next
week
- Potential for severe storms and heavy rainfall Tuesday and
Tuesday Night

&&

.Mesoscale Update...
Issued at 949 PM EST Fri Feb 23 2024

The lowest levels are now beginning to saturate with light rain
noted at LAF, but temperatures remain above 40 degrees across
central Indiana with the surface front just to the northwest of the
forecast area. Surface temperatures behind the front are still
running warm with several sites around 35 with above freezing
dewpoints. Drier surface air is present across northeast Indiana
which will be more favorable for wet bulbing as precipitation
expands further to the southeast. Details on adjustments to the
forecast can be viewed in the Forecast Update section and earlier
thoughts on the mesoscale are below...

Issued at 750 PM EST Fri Feb 23 2024

Latest radar imagery is beginning to show some higher areas of
reflectivity across north central Indiana but as shown by latest
model soundings there remains a fair amount of dry air near the
surface. This leading to none of the precipitation to reach the
ground according to area METARs.  Surface dewpoints are still
running in the low 30s with many observation sites above 32 which
doesn`t bode well for efficient snow accumulation.  This is backed
up by the latest HRRR snow accumulation forecasts showing 1-2 inches
of accumulation but a positive snow depth change closer to a half
inch.

Observations upstream also hint that the system may end up
underperforming a bit with the higher accumulations further into
Ohio where the later onset will allow for the lower dewpoints to
work in, but don`t want to make any major changes to the forecast
yet with signals of pretty robust lift right along the northern
border which may allow for higher snow rates to overcome the
marginal thermodynamic profile.  Model road temp forecasts are also
generally showing above freezing road conditions which will limit
impacts to just the periods with higher snowfall rates.

Will continue to monitor over the next couple of hours on
observational trends and will make adjustments to the forecast as
needed.

&&

.Forecast Update...
Issued at 949 PM EST Fri Feb 23 2024

As mentioned earlier in the latest mesoscale update, conditions
continue to look less favorable for snow accumulations across much
of central Indiana with surface dewpoints still in the 33-37 degree
range and temperatures in the low 40s. This combined with a subtle
shift in model trends keeping the better lift between 850mb and
700mb northeast of the forecast area warrants a northeastern shift
in the higher snow amounts with little to no snow accumulations now
looking likely south of a line from Kokomo through Muncie.  Any
accumulations to the south would then be limited to grassy and
elevated surfaces with road surface temperatures staying above
freezing through 5AM and little chance for banding robust enough to
overcome the warmer surfaces.

Some accumulations across areas along and to the north of the
aforementioned line still look reasonable as the colder air works
into the area and dewpoints drop into the upper 20s towards the end
of the better forcing. Impacts though will be limited outside of the
heaviest bands of snow due to the warmer ground temperatures and
marginal thermodynamics. Based on latest trends, current thoughts on
the best chance for snow accumulations will be from 08Z to 11Z with
rain changing over to snow after 06Z. Adjusted snow amounts to
show a tighter gradient between areas that may see an inch to
those likely to see no accumulations.

Outside of the precipitation, wind gusts will gradually creep up
during the night with colder air arriving faster aloft and allowing
a 30kt LLJ  at around 1500ft to mix down. These wind gusts will
gradually relax towards daybreak.

&&

.Short Term...(This Evening through Saturday)
Issued at 255 PM EST Fri Feb 23 2024

Nice late winter afternoon in progress as the region is enjoying
abundant sunshine and seasonably mild temps. The steady northwest
winds providing a subtly brisk feel to the air but hard to complain
about temperatures in the low and mid 50s over a large part of the
forecast area as of 19Z.

The primary focus for the short term is on the growing confidence in
a brief but potentially impactful period of snow late tonight and
early Saturday especially over the northeast half of the forecast
area. Model guidance continuing to uptick moisture and qpf which in
turn is having an impact on light snow accumulations over northeast
counties. The snow will then be followed by a cold day Saturday
before we flip back to warmer conditions on Sunday.

Through early Saturday Morning

Scattered cu field has developed as we near peak heating this
afternoon but otherwise a pleasant afternoon continues. Focus has
already shifted northwest to a developing area of low pressure with
a cold front dropping through the western Great Lakes. The arrival
of mid and high level clouds associated with the feature will expand
into the northern forecast area by late afternoon then spread south
and east this evening as the surface wave drops into the northern
part of the state.

The cold front will sweep across the region into the early overnight
with increasing levels of moisture through the mid levels may be
enough to generate scattered light rain showers along it. Saturation
through the boundary layer however will lag and likely limit
coverage of any showers for much of the evening. The gradual
moistening of the boundary layer via evaporative cooling will pull
surface temps down closer to freezing into the overnight aided by an
influx of cold advection as the front passes through. May begin to
see snow mix in and become the predominant precip type by midnight
across far northern counties.

The primary timeframe for the snow impacts however will come between
06 to 14Z as a trailing surface trough on the back side of the
surface wave moving through becomes the focal point for increased
lift and convergence in tandem with strong mid level forcing and
deeper moisture that now appears will saturate through the dendritic
growth zone for a couple hours predawn Saturday with rain
transitioning to snow. While the potential for snowflakes to fly
will be present over most of the forecast area...there is increasing
confidence that the main impacts will be confined to a Lafayette-
Indy Metro-Greensburg and points northeast for any sort of minor
accumulations with the highest impacts focused over far northeast
portions of central Indiana.

Besides the forcing from the surface trough...there are hints of a
TROWAL pivoting back into the northeast half of the forecast area as
colder air rushes in with a brief signal for stronger mid level
deformation and perhaps a brief surge of frontogenesis that may aid
in a brief bump in snowfall rates. This supports an axis of higher
snowfall that may potentially exceed 2 inches by the time precip
wraps Saturday morning across Randolph and northern Delaware
Counties...dropping back to around a half inch or so along the I-65
corridor from Lafayette to Indy and I-74 from Indy to Greensburg.
While the bulk of the accumulation should focus on elevated and
grassy surfaces...surface and road temps are likely to slide back to
the upper 20s and lower 30s just prior to daybreak Saturday. Any
brief enhancement in snowfall rates will enable some accums on
roadways which may lead to minor travel issues. Will introduce an
SPS for the northeast half of the forecast area to highlight the
snow along with graphics.

Saturday

Flurries may linger over eastern counties for a couple hours
Saturday morning but the trend will be for snow to end with low
clouds lingering through midday to early afternoon. Brisk wind gusts
late tonight and Saturday morning will fall back with the arrival of
high pressure in the afternoon. Deep subsidence will aid in breaking
up the clouds and make for a sunny but chilly second half of the
day.

Temps...lows will fall into the 20s by daybreak Saturday...with low
20s likely as a starting point over northern counties. Recovery
Saturday will be limited with temperatures largely holding in the
30s. As mentioned above though...this will be a 1 day cold shot with
much warmer air returning on Sunday.

&&

.Long Term...(Saturday Night through Friday)
Issued at 255 PM EST Fri Feb 23 2024

Saturday night through Monday...

Generally quiet weather conditions are expected early in the period
with quasi-zonal aloft. At the surface, high pressure will likely be
settled over the region before shifting east towards the end of the
weekend. Guidance shows a deep upper trough pushing into the Pacific
Northwest during which will set the stage for a more active weather
pattern heading into Tuesday and Tuesday night. Temperatures will be
near seasonal Saturday night thanks to cold air advection earlier in
the day and efficient radiational cooling during the evening.
Temperatures will then quickly warm into next week as
south/southwesterly flow increases. The surface pressure gradient
between the departing high pressure and a surface low moving across
Canada/Northern Great Lakes will tighten on Sunday promoting breezy
conditions. Widespread highs in the 60s are expected by the start of
the work week due to increasing S/SW flow. Monday`s record high at
Indianapolis is 68F, the current forecast max is 64. Tuesday`s
record high minimum is 51F, the current forecast low for the 24-hour
day at Indianapolis is 54F.

Monday night Through Wednesday...

Confidence continues to increase in a late winter storm system
impacting the area. The aforementioned deep trough across the
Pacific northwest will shift east towards the Midwest Tuesday. An
initial subtle wave ahead of this trough is expected to move through
late Monday with the potential for scattered showers and
thunderstorms. This feature should quickly move out Tuesday morning.
A strong surface low associated with the deeper trough further west
is then expected to deepen while tracking from the central Plains
into the Great Lakes Region. A large broad warm sector ahead of this
system with strong warm air advection and increasing large scale
ascent will support the potential for storms during the day Tuesday.
One caveat is that some guidance show a EML advecting  in from the
southwest during the day which would limit precipitation chances.
More widespread showers and thunderstorms are expected during the
evening and overnight hours as a cold front moves through.
Increasing deep-layer shear combined with at least modest
destabilization ahead of the front supports the potential for severe
thunderstorms. However, models are still not in great agreement
which leads to uncertainty in exact details. Heavy rain will also be
possible with anomalous moisture return and the potential for
multiple rounds of thunderstorms.

The surface low will likely move out of the area by Wednesday
morning. NBM tries to keep POPs in the forecast late Wednesday into
Thursday, but with a drier airmass moving in behind the departing
system precipitation is unlikely

&&

.Aviation...(00Z TAF Issuance)
Issued at 607 PM EST Fri Feb 23 2024

Impacts:

-MVFR to briefly IFR vsbys at IND and LAF 04Z to 09Z.
-MVFR cigs from 03Z to 12Z.
-Northwesterly wind gusts up to 25kts 04Z to 10Z.

Discussion:

Periods of light to moderate snow are expected tonight at LAF and
IND with generally MVFR cigs/vsbys but brief periods of IFR are
possible.  No snow is expected at HUF and BMG but cigs should drop
to MVFR.  In addition to the snow, northwesterly wind gusts to 25kts
are expected from 04Z to 10Z with winds closer to 10kts afterwards.
Skies will then gradually clear after daybreak with VFR conditions
through the rest of the TAF period.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Mesoscale...White
Update...White
Short Term...Ryan
Long Term...Melo
Aviation...White



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 837 PM CST Fri Feb 23 2024

.KEY MESSAGES...

- Windy and sharply colder overnight.

- Accumulating snow ending late evening/early overnight. Amounts
  from less than an inch southwest cwa, to 1-2 inches along and
  north of about a Rockford to Valparaiso line.

- Near-record warmth early next week.

- An active weather pattern is expected early to mid-week next
  week with periods of precipitation and potentially
  thunderstorms.

- Severe weather appears probable somewhere in the region on
  Tuesday. However, uncertainty still remains as to whether
  this threat will materialize in northern Illinois and
  northwest Indiana.

&&

.UPDATE...
Issued at 837 PM CST Fri Feb 23 2024

Had made some earlier changes to the going forecast to capture
the faster temperature drop and changeover to snow for areas
north of about the I-80 corridor. Have also bumped snow amounts
a bit generally along/north of I-90 for this evening where
webcams show probably 1" plus on the ground from solid moderate
snow. Still looking at around an inch for areas roughly east of
a Rockford to Chicago line, though with some 1-2" totals
expected across the northern Chicago metro. Webcams and road
reports have indicated mainly wet to slightly slushy conditions
through early evening, though with temperatures continuing to
fall through the 20s across far northern IL, may indeed see
untreated roads becoming icy and hazardous tonight. Will issue
another SPS shortly to address that concern.

Surface analysis at 8 pm shows the sharp cold back-door cold
front was along our southern cwa border. Temperatures have
fallen a good 20-25 degrees in many areas since early afternoon
north of I-80. Within the sharp temperature drop, precipitation
developing behind the front (driven by strong low-level
frontogenesis and increasing larger scale ascent ahead of robust
mid-level short wave digging into the region) went fairly
quickly from a rain or rain/snow mix to light-moderate snow.
Regional radars indicate the highest reflectivities now from the
city/southern Lake Michigan into northwest IN. This should
continue to trend southeast over the next few hours as the vort
tracks overhead and the column dries out significantly (per
RAP/HRRR forecast soundings). Thus should see snowfall
diminishing and eventually ending from northwest to southeast
across northern IL through late evening/midnight, and in
northwest IN by 1-2 AM. As indicated above. Starting to see some
radar evidence of weak lake-effect bands along the western
shore near Manitowoc WI, but as day shift indicated the
thermodynamic profiles look fairly unimpressive due to low lake-
induced inversion heights which only briefly tag 6000` after
midnight per RAP soundings. As indicated above, did boost
snowfall over Lake (IL) and Cook counties to the 1-2" range
based on this evenings amounts and little extra with the light-
lake effect.

While much of the accumulation has been on grassy surfaces, and
snow will be coming to an end in a few hours in most areas,
roads may become more slick overnight as moisture/slush freezes
as temps fall into the teens and lower 20s. Will issue another
Special Weather Statement shortly to highlight these concerns.

Ratzer

&&

.DISCUSSION...
Issued at 300 PM CST Fri Feb 23 2024

Through Saturday night:

A potent backdoor lake enhanced cold front is already quickly
shifting onshore across far northeastern IL. In advance of the
front temperatures are generally in the lower 50s. However,
directly in its wake, gusty (up to 30 mph) north-northeast winds
are developing and quickly driving a colder airmass (featuring
lower 30 temperatures) southward into the area. These same trends
can be expected for the remainder of the area into early this
evening as the front continues to shift southward across the area.

A potent mid-level impulse (currently noted in water vapor
imagery shifting southeastward across southeastern MN) will
dive southward across the western Great Lakes this evening
following the passage of our back door cold front. Forced ascent
associated with this approaching feature is expected to
continue to result in an uptick in precipitation development
across southern WI and northern-northeastern IL over the next
couple hours. While conditions may briefly be warm enough for a
short (<1 hour) period of rain, we expect the precipitation type
to quickly transition to snow.

Once snow becomes the primary precipitation type, it appears that
the snow may fall at a decent clip (half inch + per hour) for
an hour or two this evening as the decent but transient forced
ascent interacts with a corridor of steepening mid-level (700-
500 mb) lapse rates, which look to approach 7C per km. The peak
intensity looks to be roughly in the 6 to 9 pm timeframe across
much of northeastern IL, and in the 8 to 11 pm timeframe across
northwestern IN. This transient nature of the good forcing will
result in total snow amounts remaining in the inch to possibly
inch and half range through the evening. While most of this will
be confined to grassy and elevated surfaces due to the warm
ground, some slick travel conditions may develop through the
evening as air temperatures drop into the 20s and ground
temperatures approach freezing. We will continue to highlight
the possible impacts to travel tonight with an SPS and in our
weather stories.

Expect the snow to gradually abate for most areas from northwest
to southeast later this evening into the overnight. The only
exception will be some lingering lake effect snow showers across
parts of far northeastern IL in and near Chicago overnight. While
some minor isolated additional accumulations could result across
parts of Cook and Lake counties in IL with this activity overnight,
the overall thermodynamic set up across Lake Michigan tonight
does not look overly impressive to support significant additional
snow amounts. The main negating factor will be lake induced
equilibrium heights, which will be capped by a stout subsidence
inversion based around 5,500 ft. This is thus likely to limit the
quality and magnitude of any lake effect snow band that develops,
especially considering that lower-level moisture quality will
become poor later tonight. Any lingering lake effect snow showers
overnight will end by, or shortly after, daybreak Saturday
morning.

A chilly day is expected on Saturday, but fortunately wind chills
will not be an issue as the winds ease during the day as a
surface ridge axis builds overhead. Expect high temperatures to
hold in the upper 30s under mainly sunny skies. Winds will turn
southwesterly into Saturday evening following the eastward
departure of the surface ridge axis. This will promote a return to
warmer conditions for the second half of the weekend.

KJB


Sunday through Thursday:

Breezy return flow along the western periphery of a departing
surface high will help advect milder and above normal temperatures
back into the area on Sunday, with high temperatures likely to top
out in the 50s across most of our forecast area. A southward-sagging
cold front may then briefly turn winds northerly Sunday night and
cease the warm air advection pipeline temporarily. However, with
surface high pressure residing off the southeast Atlantic Coast and
a region of surface low pressure developing over the northern Plains
in response to a northern stream trough amplifying over the
northwestern CONUS, the front should quickly be turned back
northward, and breezy southerly low-level flow will become
re-established once again by mid-day Monday. With open thermal and
moisture trajectories extending from the Gulf of Mexico all the
way up into western Ontario, anomalously warm and moist air will
be advected into the Midwest/Great Lakes with ease, setting the
stage for 60+, and potentially even 70, degree temperatures to
return to the area on Monday and especially Tuesday.

Anomalous warmth this time of year often comes with consequences in
the form of severe weather, and the overall weather pattern does
appear quite favorable for severe weather occurring somewhere (and
potentially across a large area) between the central/southern Plains
and the Appalachian Mountains during the Monday night to Wednesday
time frame. The key player in this potential early-mid week severe
weather event will be the aforementioned amplifying western CONUS
northern stream trough, which is slated to track into the country`s
mid-section on Tuesday and interact with an energetic southern
stream jet. The extent to which this northern stream trough phases
with another disturbance embedded within the southern stream (and
when) will largely dictate how far north the severe weather threat
will get, the degree to which certain failure modes could play a
role in mitigating the severe weather threat in an otherwise
favorable parameter space, and the overall magnitude of the severe
weather as well.

Generally speaking, if a relatively clean phasing could occur
sooner, then the conjoining trough/jet stream would likely start to
acquire a negative tilt as it approaches our longitude and help
spawn a stronger low pressure system that would track into the Great
Lakes, likely putting most or all of our forecast area in the
crosshairs of the associated severe weather threat on Tuesday. On
the other hand, if little to no phasing were to occur, or if the
phasing occurred later, then the expectation would be for the flow
pattern to remain more split with the northern stream trough
retaining a positive or neutral tilt as it tracks across our
longitude. In a scenario like this, the severe weather threat for
our forecast area would likely be more subdued/questionable for
multiple reasons, and could potentially end up remaining south and
east of us altogether, especially if a more progressive variant of
this general scenario verifies.

While there is still a fairly large spread within the broader suite
of ensemble and deterministic guidance on how things will evolve
next week, over the past couple of days, support has generally
increased amongst ensemble members for a more progressive pattern
with less phasing (i.e. the second scenario). That being said, there
is still some support for the other general scenario, and with model
solutions still bouncing around from run-to-run, it`s still too
early to say with much confidence that either scenario will or won`t
happen. For now, the Storm Prediction Center has maintained a 15%
contour in their Day 5 Severe Weather Outlook, albeit a hair farther
to the southeast, but we want to emphasize that a lot can still
change in 4-5 days with these dynamic weather systems, so continue
to check back for forecast updates.

Lastly, there is currently about a 20-30% chance for snow to occur
on Wednesday on the back side of the system as another brief
shot of cold air filters into the region in its wake. Like the
severe weather threat, whether this comes to fruition will be
heavily dependent on the mid-week system`s exact evolution, but
at this time, it appears more likely than not that the system`s
snow will either remain to our north or end up being light
enough in our forecast area to not produce any notable
accumulations.

Ogorek

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 554 PM CST Fri Feb 23 2024

Forecast concerns include...

Period of snow this evening.
Strong/gusty northeast winds this evening.

Snow will spread across all of the terminals early this evening
with visibilities dropping as low as 3/4sm. A brief mix with
rain is possible for another hour but the prevailing precip type
is expected to be snow. The snow will taper off to flurries
from mid to late evening with a chance of lake effect snow
showers overnight. Confidence is low for this potential and
maintained current snow shower mention for ORD/MDW but changes
are possible with later forecasts.

Cigs are expected remain low mvfr this evening, though some
brief ifr cigs are possible with any heavier periods of snow.
Outside of any possible lake effect snow showers overnight, cigs
will likely lift to vfr but only medium confidence for cigs
overnight. Eventually the lower cigs will scatter out Saturday
morning with a period of skc possible then high/mid clouds will
move back across the region Saturday afternoon and evening.

Northwest winds will gust as high as 30kt this evening though
prevailing gusts may stay in the mid 20kt range. Speeds and
gusts will slowly diminish from the late evening through the
early morning hours, as directions turn northerly. A ridge of
high pressure will move across the region early Saturday
afternoon, allowing winds to quickly shift from north/northwest
to south/southwest in just a few hours. Wind speeds will then
increase by early evening into the 10-12kt range with some
higher gusts possible during the mid/late evening. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until noon CST Saturday for the IL and IN
     nearshore waters.

&&

$$

Visit us at weather.gov/chicago



Area Forecast Discussion

National Weather Service Marquette MI

 606 PM EST Fri Feb 23 2024

.KEY MESSAGES...

- Light lake effect snow showers continue mainly across the NW wind
  snow belts in the eastern UP tonight.
- Much colder temperatures are expected tonight with many places
  falling below zero across the western UP.
- More well above normal temperatures expected early next week.
- A more active and colder period is likely for the middle of
  next week (Tue night-Thu) with a stronger low pressure system
  lifting northeast through the Upper Great Lakes.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 212 PM EST Fri Feb 23 2024

The Great Lakes remain under broad midlevel troughing this
afternoon, with RAP and water vapor imagery indicating one last
embedded impulse dropping through MN and NW WI at this time.
Otherwise, rather dry air is apparent on satellite. Bands of shallow
lake clouds are showing up quite well on satellite this afternoon,
but reflectivity is increasingly less impressive - likely owing to
that dry airmass and falling inversion heights working against lake-
induced instability. Will not rule out additional light
accumulations well below an inch across Marquette and Alger counties
this afternoon, otherwise just some stray flurries are expected.

The trough axis shifts eastward overnight with ridging expected into
Saturday. With flow turning more cyclonic, expect lingering LES to
shift over to the NW snowbelts of the eastern UP. Soundings do
moisten up through the DGZ, and that wind regime does put the
eastern UP into a nice long fetch off of Superior, so we could stand
a better chance at picking up on some measurable snow overnight.
This would be mainly across Alger and northern Luce counties, with
ensemble probability of at least some QPF at around 100% and a
chance (around 40%) for QPF up to a tenth of an inch. That could
leave some isolated spots with upwards of an inch of snow by the
morning, with totals around a quarter to half inch more likely.

Otherwise, with clearing skies cross most of the area, light winds,
and our Arctic airmass in place, expect temperatures to plummet
overnight. Across the eastern UP, where lake clouds linger,
overnight lows should generally be in the single digits above 0F.
The western UP should see many spots falling below zero, and wind
chills in the chilliest spots may fall below -10F by Saturday
morning.

&&

.LONG TERM /SATURDAY THROUGH FRIDAY/...
Issued at 444 PM EST Fri Feb 23 2024

Models and ensembles indicate a fairly progressive pattern across
North America this weekend through much of next week with a series
of shortwave troughs/ridges moving across the Upper Great Lakes. The
trough and associated colder air mass over the Upper Great Lakes
today will push east on Saturday as shortwave ridging and warmer,
drier conditions replace it from the west. A weak trough and
associated cold front moves through Sat night/Sunday. Better
isentropic lift associated with the shortwave will support some
light pcpn mainly north and east of the fcst area. CAA behind the
associated front is probably not cold enough to support anything
more than flurries across the Keweenaw and far east. Another ridge
and WAA regime moves over the area Monday into Tuesday with much
above normal temps expected and increasing probability among
ensemble data (especially the EPS) of max temps both days reaching
50F or higher at some locations over west half or western 2/3
portions of the U.P. The next best chance of pcpn, shot of cold air
and perhaps more significant snowfall looks to be late Tuesday into
Wednesday as models/ensembles indicate a stronger wave moving
through the Upper Great Lakes. The snow and cold won`t last long
,however, as broad ridging and another WAA regime spreads over the
area late next week, beginning Thu into the weekend.

Over this weekend, the mid-upper level trough lifts into eastern
Canada and the eastern U.S. as ridging expands across the Upper
Great Lakes. In this transitioning flow, another fairly vigorous
shortwave will track ese from Saskatchewan/Manitoba Sat to northern
Ontario late Sat night/Sun. Strong waa in response to this wave
pushes into the area Sat aftn/night and may support a period of -sn
into the eastern fcst area late Sat night or Sun morning (only 20pct
chc for now), but better chc of pcpn will certainly pass by to the n
and ne, closer to track of shortwave and deeper into the retreating
cold air where saturation for pcpn production is more likely. As
this wave continues eastward, another push of caa occurs Sun, but
probably not quite cold enough to generate any LES except for maybe
some flurries into the Keweenaw and eastern fcst area.

On Mon, deepening mid-level trough over western N America will
quickly back flow to the sw into the Great Lakes, leading to
unseasonable warmth spreading out of the Plains to the Great Lakes
Mon/Tue and breezy/windy conditions on Mon. Strong waa/isentropic
ascent lifting into the area late Sun night/Mon morning suggests
some potential of a light wintry mix (less than 20pct maybe over the
tip of the Keweenaw), but again, the better chc of pcpn will be n
and ne of the area, deeper into the retreating cold air. Ensembles,
particularly the EPS, show increasing probability (60-90 pct) of max
temps exceeding 50F Mon into Tue over west half or western 2/3rds
portions of the U.P.

As for pcpn Tue-Thu, models/ensembles still seem to coming into
better agreement on an unphased stronger system moving through the
Upper Great Lakes late Tue into early Wed time frame which will
bring our next best chance of pcpn and perhaps some more significant
snowfall Tue night into early Wed. Models indicate southern stream
energy originating off of CA most likely won`t phase with the
shortwave in the amplifying northern stream. These lead waves would
support some shra across Upper MI as they lift thru the Upper
Mississippi Valley/Great Lakes on Tue. The main shortwave of
interest will be the southern wave which take on a negative tilt and
swings into our area late Tue into Wed, leading to an
deepening/organizing sfc low along cold front that tracks across
northern Lower Mi/Straits area Tue night/Wed. It`s looking like the
low and the now model consensus favored track across northern Lower
MI/Straits of Mackinac could support perhaps some more significant
snow/lake enhanced snow Tue night/Wed into portions of Upper Mi so
model/ensemble trends with this system will warrant close monitoring
in the coming days. It looks like LES will begin to taper off late
Wed and probably end sometime Thu as winds back more northwesterly
in response to a sfc ridge building into the area.

The midweek shot of colder air and snow won`t last long as
models/ensembles support broad ridging and another WAA regime moving
across the area late week into next weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 605 PM EST Fri Feb 23 2024

The MVFR conditions across the TAF sites become VFR again over KIWD
and KCMX this evening, with KSAW hanging onto the MVFR cloud cover
until late tonight. The VFR conditions remain to the end of the
period, with the winds increasing from the SW during the day
Saturday.

&&

.MARINE...
Issued at 444 PM EST Fri Feb 23 2024

Winds are expected to diminish mostly blo 20 kts tonight as a high
pres ridge builds across the area. Southwest winds increase quickly
on Saturday on the backside of the departing sfc ridge as another
low pres descends se into northern Ontario late in the day.
Southwest winds reaching 25-30kt late Sat morning into the
afternoon. Local probabilistic guidance indicates an increasing
probability (60 pct or greater) of brief low-end gales at times Sat
into Sat evening, but given the short duration expected decided to
just mention gale force gusts to 35 knots at this time. Winds will
shift w to nw on Sun and diminish just a little. After winds briefly
fall off to under 20kt later Sun night, they will quickly increase
to southerly gales 35-40kt on Mon, mainly over the east half of the
lake. After winds diminish blo gales over the east half later Mon
evening, there will be a period of winds blo 20 kt late Mon night
into Tue morning before north winds ramp up to 35-40 kt gales Tue
night into Wed behind a strong low and cold frontal passage moving
across the Upper Great Lakes.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Small Craft Advisory until 6 AM EST Saturday for LSZ248>251.

Lake Michigan...
  Small Craft Advisory until 10 PM EST this evening for LMZ221-
     248-250.

  Gale Watch from Saturday evening through Sunday morning for
     LMZ248-250.

&&

$$

SHORT TERM...LC
LONG TERM...Voss
AVIATION...TAP
MARINE...Voss