Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/22/24
Area Forecast Discussion
National Weather Service La Crosse WI
600 PM CST Sat Dec 21 2024
.KEY MESSAGES...
- Potential for light snow and/or freezing drizzle late Sunday night
into Monday morning. Amounts look to be minimal, but the morning
commute may be affected if freezing drizzle does occur.
- Warming trend for Tuesday onward, but details become unclear
late next week.
&&
.DISCUSSION...
Issued at 327 PM CST Sat Dec 21 2024
Potential for light snow and/or freezing drizzle late Sunday night
into Monday morning
Sunday night into Monday morning, upper wave, currently off the
Pacific Northwest coast, will advance over the CWA. Warm, moist
advection ahead of this feature should saturate the low levels
and warm temperatures to near - but likely below - freezing. As
the upper wave approaches, dry air intrusion around 700mb may
dry out the DGZ while, nearer to the surface, some isentropic
lift on the 280/285K surfaces looks to continue, as suggested by
the 21.12z GFS. The end result for many locations may be
freezing drizzle if the mid-level dry air leaves enough of that
near surface layer saturated for droplets to form. The freezing
drizzle potential will primarily reside in southwest of I-94
while areas to the northeast look to feature deeper saturation
and snow for much of the event. Finally, locations in SW WI may
end up a bit too warm for freezing temperatures to hang on at
the surface due to the effects of aforementioned advection.
There are a lot of remaining uncertainties with this system,
mainly centering around where the dry air intrudes and how deep
said intrusion will be, so have endeavored to keep PoPs less
than 50 percent outside of north central WI, where confidence in
at least some snow is better (60-70%) and spread mentions of
both snow and freezing drizzle across much of the area. Due to
timing, the morning commute may be impacted, so hopefully
details will become clearer over the next day.
Warming trend ahead
Predictability across guidance becomes relatively low through the
rest of the forecast, with poor agreement on timing and placement of
several upper waves, particularly by late next week. However,
general trend is for higher heights aloft which favors a slow return
to highs in the 30s. May even see some temperatures in the 40s
Friday and next Saturday, but NBM interquartile ranges at that time
begin to approach 10 degrees, reflecting the low confidence in the
exact details of the pattern by that portion of the week.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 553 PM CST Sat Dec 21 2024
Surface high pressure located over the region is forecast to
shift eastward overnight and Sunday ahead of a shortwave trough.
The flow aloft is from the northwest, however the low level flow
strengthens from the southwest. An area of mid-clouds has been
overspreading the region and these will continue to push
eastward overnight. Meanwhile, an area of MVFR stratus extends
from central MN into central Iowa. The RAP/HRRR both bring
MVFR/patchy IFR conditions eastward toward KRST and the RAP
spreads then eastward across much of southeast MN and WI
overnight. Confidence was not high enough to include at KLSE,
but did include the MVFR ceilings at KRST through Sunday
morning. Light southeast winds increase 10 to 15kts overnight
into Sunday with some gusts 20 to 30kts Sunday afternoon.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
DISCUSSION...Ferguson
AVIATION...Zapotocny
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
554 PM CST Sat Dec 21 2024
.KEY MESSAGES...
- A light wintry mix likely Sunday night into Monday with snow
accumulations generally less than an inch. However, an inch of
snow is possible in west-central WI.
- A warming trend will occur this week with highs in the lower
to mid 30s by Christmas. Upper 30s to near 40s highs possible
by late next week.
&&
.DISCUSSION...
Issued at 207 PM CST Sat Dec 21 2024
Fittingly on the winter solstice, what little sunlight there is
available was lessened by mostly cloudy skies today.
Temperatures remained cold as highs only rose into the mid teens
to lower 20s this afternoon. They will not fall much tonight,
though, as WAA occurs ahead of an approaching mid-level trough.
Mostly cloudy skies will remain but we will warm in response
Sunday with highs in the mid 20s in central MN to lower 30s in
southern MN. The shortwave will encroach upon western MN Sunday
night, at which time, most models try to develop precip over the
southern half of MN. This precip advances east, ahead of the
trough, into WI Monday morning before exiting our CWA by around
noon. Examining GFS and NAM forecast soundings shows that at
minimum we could see freezing drizzle, as the thermal profile is
saturated from the surface to about 800 hPa within subfreezing
temperatures. Farther above, an additional layer of saturation
is evident with in the DGZ layer such that snowflakes to periods
of full snow are possible. However, between these 2 layers is a
layer of dry air such that it could limit how many snowflakes
make it to the surface. This issue currently seems most
prevalent over MN whereas over WI the profile becomes more
vertically saturated. Thus, our WI counties have a greater
chance at seeing possibly up to an inch of snow while areas west
could only see a few flakes to a dusting. But, being this will
occur Monday morning and at least some freezing drizzle seems
possible, it will have a good chance at making a potentially
hazardous commute. Keep your guard up when traveling to start
this week of Christmas.
After Monday morning, we will dry out for a few days with
temperatures gradually rising throughout the week. By Wednesday,
forecast highs are in the lower to mid 30s and should climb to the
mid 30s to near 40 by Friday. Despite these temperatures, with
multiple inches of snow on the ground across most of our area, a
majority of our CWA should see a white Christmas. Our next chance of
precipitation looks to be towards the end of the week as long-range
models show an upper level trough moving northeast through the
central CONUS. Big differences exist though between model suites in
that it causes NBM to smear 20-30% PoPs Friday through Saturday.
Currently, the precipitation type looks to mostly be rain as
temperatures should be largely above freezing (during both the day
and night). These are just very early observations of the forecast
and uncertainty will decrease with time as we approach later next
week. In support, Climate Prediction Center does forecast us for
likely above normal temperatures and above normal precipitation the
end of December into early January.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 541 PM CST Sat Dec 21 2024
Tricky forecast tonight with plenty of model spread with just
how widespread IFR/MVFR stratus coming out of Iowa becomes. With
that stratus already up to MKT, decided to get more aggressive
with it than the going TAFs had, with support from the
HRRR/RAP/NAM for fairly expansive stratus overnight, with it
lifting off to the northeast through the morning on Sunday.
Helping establish those low cigs will be southeast winds, which
will remain fairly steady in the 10-15 kt range this period.
KMSP...With stratus slowly expanding out of Iowa, decided to
follow the LAV and HRRR with MVFR stratus developing overnight.
We could see IFR cigs in the morning, but for now, started with
just bringing MVFR cigs in. It looks likely that whatever
stratus we get overnight will lift out between 14z and 18z, with
VFR conditions remaining until late Sunday night.
/OUTLOOK FOR KMSP/
MON...MVFR cigs likely. Wind NW 5-10 kts.
TUE...MVFR cigs likely. Wind S 5 kts.
WED...MVFR cigs likely. Wind SE 5-10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
DISCUSSION...CTG
AVIATION...MPG
Area Forecast Discussion
National Weather Service Marquette MI
706 PM EST Sat Dec 21 2024
.KEY MESSAGES...
- A southerly wind lake effect snowband will impact eastern
Upper MI on Sunday, bringing up to 4 inches of snowfall in a
narrow band near Manistique.
- A clipper system moving through the Great Lakes is anticipated
to bring widespread light snowfall to the UP. Some lake
enhancement over the far east may locally boost totals up to
3-4 inches, resulting in minor travel impacts Sunday through
Monday.
- Drier and warmer conditions expected behind the early week
system for Christmas Eve and Christmas Day.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 103 PM EST Sat Dec 21 2024
GOES Water Vapor and RAP analysis positions Upper Michigan within
northwest flow aloft between mid-upper level troughing to our east
and broad ridging to our west. At the surface, high pressure ridging
stretching from northern Ontario south across Lake Superior and
Upper Michigan toward the Middle Mississippi River Valley has kept
winds light and mostly northerly across the area. With 850mb temps
analyzed between -18 and -15C and Lake Superior near +4-6C (per
SPC mesoanalysis and GLERL respectively), in addition to the mixed
layer extending to near 5k feet through the DGZ, the environment has
supported high snow ratio lake effect snow showers pressing south
into Upper Michigan. KMQT and CASMR radars limit activity mainly to
Marquette County and points eastward, but webcams have shown some
light off and on shower activity in the western counties. The
strongest bands have been focused along the lakeshore of Marquette
County down to near Gwinn where weak convergence has supported
periodic radar reflectivities between 30 and 35 dbz. These higher
signatures have been mainly located southeast of the radar in a
narrow corridor approximately from Harvey south to Little
Lake/Gwinn between Sands/KSAW/Gwinn and Skandia/Carlshend. I suspect
these locations could have observed a couple inches of snow this
morning, particularly where terrain has supported additional lift,
and the most restrictive visibilities.
Through the remainder of the afternoon, high pressure will slowly
migrate through the region, enabling flow to become southerly.
Guidance appears to have delayed this wind shift a little, so snow
showers may continue in the northern wind snow belts into the early
evening hours. At that point, southerly flow will help lift shower
activity over Lake Superior for the overnight period. If the showers
are a little slower to diminish, additional snow of an inch is
generally expected with localized snow amounts near 3 inches not
being ruled out. Will need to monitor CAM, radar, and satellite
trends though after publishing this to determine if another Special
Weather Statement is needed for Marquette County.
After activity ends, the overnight period should be mostly dry with
lows falling into the single digits. Isolated spots in the interior
west may dip close or just below zero. Just prior to 12z, southerly
flow will help to support lake effect snow off of Lake Michigan/Bay
of Green Bay by morning. Recent CAMS are supporting a wider range of
where showers may be experienced. At this point, light snow showers
streaming north may end up as far west as Escanaba before sunrise.
If this does occur, the thought is for these to migrate east into
Schoolcraft/Mackinac counties. Any snow experienced prior to sunrise
would likely amount to an inch or two of fluffy snow.
&&
.LONG TERM /SUNDAY THROUGH SATURDAY/...
Issued at 358 PM EST Sat Dec 21 2024
The UP extended forecast starts off with northwest flow aloft as a
trough over New England departs east and shortwaves ride southeast
toward the Great Lakes. That said, a sfc low over the SD/NE state
line and high pressure shifting east to New England results in low
level southerly flow. What is more unusual is that under this
persistent south flow, 850mb temps over Lake MI will start around
-9C to -12C then warm to between -4C to -6C for Sunday night. With
much of northern Lake MI sfc temps around 7C, delta-Ts will range
from 11C to as high as 19C...sufficient for LES. Placement of the
dominant snow band looks to impact Delta and Schoolcraft Counties
earlier, then expanding northeast to Luce County as well. Some of
the CAMs are yielding some trace/lighter snow amounts as far west as
Escanaba earlier in the day, so there some wiggle room yet in
placement of best LES. Model soundings show initial moisture
inhabiting a few kft of the DGZ, resulting in a SLR around mid to
upper teens:1. As the day progresses, warming raises the DGZ height
and diminishes the moisture within the DGZ. As a result, SLRs lower
to around 10:1 for Sunday night into Monday. In addition, a weak
shortwave and WAA rippling over northern WI may result in some
flurries in the central UP Sunday afternoon and evening ahead of the
sfc low.
System snow begins to ramp up Sunday night with an approaching sfc
low from the west. The better dynamic support looks to mainly remain
south of the UP over WI/Lower MI, but some widespread light snow is
expected up to 2" across the UP (highest south central and east).
Additional lake enhancement off Lake MI is likely with this system,
yielding up to 3-4" of snow over areas in Schoolcraft and Luce
Counties. Between the LES and system snow, some Winter Weather
Advisories may be needed for the east. Opted to hold off for now
given the LES band is still shifting around and sfc low track also
has some spread in track. Some trailing lake enhanced snow off Lake
Superior for the north half of Upper MI is possible (15-30%) Monday
afternoon and evening, but accumulations will be low (<1") with a
less than ideal thermodynamic profile.
Dry weather returns by Tuesday as high pressure descends over the
Great Lakes. A pattern of mainly mid level ridging returning the
eastern CONUS brings warmer than normal temps back to the region.
How long the dry period lasts early next week will depend on when
the next shortwave moves through. Guidance spreads quickly with
shortwave timing and track as well as later systems in the week, but
there is a consensus on a low pressure system tracking northeast
through the Upper Great Lakes late next week/early next weekend.
With highs warming well into the 30s to possibly low 40s with lows
lifting to near freezing by then, the primary p-type moving forward
will be rain. This alongside dew points lifting to near freezing
late next week will result in melting some of the snowpack in the
coming days. That said, much of the UP should still have some snow
on the ground for Christmas. A return of colder air looks to hold
off until the new year.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 705 PM EST Sat Dec 21 2024
Sfc high pres ridge extending n to s across central Upper MI will
continue shifting e this evening. On the backside of the high, lake
effect stratocu (MVFR cigs) has already cleared out to VFR at IWD.
CMX will clear out to VFR at the start of this fcst period or within
the first hour. Both CMX and IWD will then remain VFR thru the end
of this fcst period. At SAW, MVFR cigs should clear out by 02z, but
with low-level winds becoming southerly instead of sw to w, the
clear out to VFR may end up being delayed for an hour two longer.
Thereafter, expect VFR to prevail at SAW thru end of the fcst
period. Tightening pres gradient on Sun due to appraoching low pres
trof will result in gusty southerly wind to around 20kt at all
terminals by aftn.
&&
.MARINE...
Issued at 358 PM EST Sat Dec 21 2024
Southerly winds increase this afternoon through tonight as high
pressure shifts toward the Lower Great Lakes and a low pressure
system approaches from the west. South winds of 20-30 kts are
expected on Sunday with the increased pressure gradient across the
lake. Strongest winds are expected over the east half of the lake
where there is a 15% or less chance for gales to 35+ kts. These
winds build waves up to 5-8 over the northeast, mainly north of the
international border Sunday and Sunday night. Winds weaken to 15-25
kts Sunday night as they gradually veer southwest, but quickly
become northwest behind a frontal boundary early on Monday. Winds
mainly hold 20 kts or less Monday onward as the low departs from the
Great Lakes and high pressure returns, but turn southerly for the
back half of next week.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...JTP
LONG TERM...Jablonski
AVIATION...Rolfson
MARINE...Jablonski