Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/03/24
Area Forecast Discussion
National Weather Service La Crosse WI
558 PM CST Mon Dec 2 2024
.KEY MESSAGES...
- Prepare for WIND and COLD Wed afternoon into Thu. Storm system
moving across southern Canada with bring strong/gusty northwest
winds (gusts 40+ mph possible Wed afternoon/night) along with a slug
of cold air (-5 to-15 wind chills likely Thu morning). Bulk of
related snow falls far to the north but snow showers possible Wed
afternoon.
&&
.UPDATE...
Issued at 455 PM CST Mon Dec 2 2024
Continuing to see flurries being reported in southeast
Minnesota. Taking a look at the model soundings, the HRRR
continues to show a shallow layer of low level moisture in the
dendritic growth zone. While this continues into the early
overnight, the lift in this layer (associated with a weak
shortwave trough over the eastern Dakotas) only last through
03.06z. Due to this, updated the forecast to include snow
flurries through midnight tonight.
&&
.DISCUSSION...
Issued at 200 PM CST Mon Dec 2 2024
Forecast focus sits squarely on a storm system set to impact the
region for Wednesday through Thursday. While the bulk of the
system`s pcpn looks to hold well north, related strong winds and
push of colder air will not. Battering northwest winds and wind
chills into the single digits/teens below zero are expected.
OVERVIEW: a shortwave trough from northwest Canada set to sink
southeast early this week, winding up/strengthening as drops over
southcentral Canada by 12z Wed (GFS progged 150+ kt 300 mb jet
streak playing a key role). The GEFS and EPS ensembles have good
agreement within/between themselves with taking the resulting sfc
low due east across southern Canada, moving in from just north of
Lake Superior at 18z Wed to the New England States by 18z Thu. The
trough lags southeast of the sfc low and doesn`t develop a negative
tilt until it shifts over the eastern great lakes.
GEFS and EPS track favors the bulk of the associated pcpn (snow)
north of the forecast area. However, strong/gusty winds will not
miss, with another slug of cold air funneling in post a secondary
cold front.
There will be wind and cold impacts to prepare for.
WINDS: winds will be on the increase from the south Tue afternoon as
sfc pressure gradient starts to tighten with the approaching,
deepening low. Winds will continue to strengthen moving into the
Wed, especially with the passage of the secondary cold front Wed
afternoon. Winds become unidirectional from the northwest upwards of
700-500 mb from 18-06z Thu. This, coupled with strong cold air
advection will aid in mix down of stronger winds a loft. Both the
05.12z Bufkit runs of the GFS and NAM push gusts into the lower 40
mphs at KRST (in the 18-06z time frame).
The slate of EPS members are the windiest of the bunch over the last
several runs, consistently suggesting 40+ mph will be realized (70-
100%). The GEFS is about 5 mph slower.
Trop fold could come into play, enhancing the wind potential. The
NAM/GFS/EC all bring the 1.5 PV sfc down to at least 750 mb 18z Wed
to 03z Thu, focused more across northern /eastern WI. The EC is more
bullish, inching tropospheric air closer to 800 mb.
With all that in mind, will increase wind/wind gusts for the Wed
afternoon/night time period above the model blend (NBM), leaning
more toward the 75% outcome.
TEMPERATURES: before the aforementioned cold moves in, a warm front
will lift northward across the region Tue, with the southerly fetch
returning air more seasonable for early December. Temps will be on
the rise Tue night with highs Wed forecast to bump above freezing
for most.
Cold air will be flowing in from the northwest already by mid to
late morning in the northwest as one, and then a secondary cold
front sweep through. Highs for most will likely be reached by noon,
with steady or falling temps for the afternoon. The EPS has been the
colder ensemble compared to the GEFS (by about 5 degrees) suggesting
single digit lows will occur (70-100%). The GEFS is a warm outlier
compared to the other models/ensembles and will continue to lean
into these colder solutions for the forecast.
With winds kicking up by Wed afternoon, along with the influx of
cold air, wind chills are going to "tank". Expect single digit to
teens wind chills for the evening commute Wed, and roughly -5 to -15
for your treks into work/school Thu morning. Not expecting
advisories, but certainly raw/cold conditions.
The cold doesn`t look to stick around long as the upper level
pattern looks to flatten, perhaps some shortwave ridging for the
weekend.
PCPN CHANCES: latest med/long range models hold much of the deeper
saturation/forcing to the north, and thus the bulk of their QPF from
northeast MN/northern WI northward. However, both associated cold
fronts have weak Fgen associated with them, and strong low level
cold air advection results in 8-9 C/km 1000:850 mb lapse rates.
NAM12/GFS Bufkit soundings also indicate the potential for (very)
weak instability. All this is very suggestive that convective snow
showers are possible Wed afternoon - and will cover with 20-30%
chances for now.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 558 PM CST Mon Dec 2 2024
A weak shortwave trough over the eastern Dakotas will bring MVFR
clouds to the area this evening. There will be even some
flurries in southeast Minnesota and northeast Iowa. During the
overnight, the 925 mb ridge axis will shift to the east. As this
occurs, the MVFR ceilings will exit the region.
North and northwest winds will be around 10 knots this evening
and then be light and variable overnight. Wind will then become
south and increase into the 10 to 15 knot range on Tuesday
morning.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
UPDATE...Boyne
DISCUSSION...Rieck
AVIATION...Boyne
Area Forecast Discussion
National Weather Service Grand Rapids MI
920 PM EST Mon Dec 2 2024
.KEY MESSAGES...
- Hazardous Lake Enhanced Snow Continuing Overnight
- Clipper Brings Snow Tuesday Night into Wednesday
- Arctic Air, Snow, and Wind Arrive Wednesday Night into Thursday
- Unsettled This Weekend but no Impactful Weather Expected Yet
&&
.UPDATE...
Issued at 920 PM EST Mon Dec 2 2024
Overall the previous forecast remains on track. Just made some
minor adjustments to the overall timing of the burst of snow that
is currently moving through Oceana and western Newaygo county. The
HRRR is handling the current area of snowfall well with snow
focusing in our counties currently in the warning late tonight
into Tuesday morning. An additional 8 inches of snow is possible
within the warning with the best chances in Allegan and Van Buren
Counties. Expect impacts to travel along the lakeshore. If you
need to head out, give yourself plenty of time, take it slow, and
make sure you have emergency supplies if you get stuck.
&&
.DISCUSSION...
Issued at 301 PM EST Mon Dec 2 2024
- Hazardous Lake Enhanced Snow Continuing Overnight
Radar currently shows South Haven beneath a mesolow induced LES
band with visibility down to a quarter mile and northwest winds
gusting to 20 mph, which is very different from the stagnant land
breeze regime we saw this morning. Travel impacts have been substantial
in this area with parts of I-94 still closed as I`m writing this.
Have extended the winter storm warning to 7 AM Tuesday. Farther
north towards Traverse City, we see an intense snow band dropping
southward. Favored HRRR and HREF guidance advertises this feature
to continue dropping southward near the lakeshore while curling
into a mesolow. Allegan and Van Buren counties could easily
accumulate an additional 4 to 6 inches after midnight tonight as
this quasi-mesolow interacts with the feature that currently is
affecting the South Haven region.
- Clipper Brings Snow Tuesday Night into Wednesday
No changes to previous thinking but will just add that desaturation
of the DGZ will curtail snowfall accumulations and introduce the
possibility of drizzle/freezing drizzle for some areas mainly
south of M-20. The window for any freezing drizzle will be limited
a bit by warming temperatures during the day but nonetheless
could impact some of the drier and more pristine inland roadways
early on.
- Arctic Air, Snow, and Wind Arrive Wednesday Night into Thursday
We are still looking at an impactful and headline-worthy event
beginning Wednesday night. Very gusty winds under strong cold
advection still looks likely. Lake effect snow should be able to
penetrate well inland thanks to an expansive plume of SBCAPE well
in excess of 100 J per kg overspreading much of southern Lower MI.
So, a very snow squallish character to precipitation can be
expected along with increasingly icy conditions. Visibility will
be very poor with both blowing snow and a large concentration of
smaller falling ice crystal associated with substantial fracturing
and sub-optimal microphysics.
- Unsettled This Weekend but no Impactful Weather Expected Yet
After what looks like a dry Friday with a cold start, a clipper is
expected to brush across Lower Michigan Saturday resulting in minor,
if any, accumulations. Unsettled weather continues into early next
week with continued chances for a wintry mix but with little to
no accumulations expected.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 636 PM EST Mon Dec 2 2024
Along the lakeshore, lake effect snow is expected to continue
overnight into Thursday. MKG may be on the edge of the lake effect
snow through most of the forecast, but the better potential will
be after 2Z as the snow that is currently north of Ludington
shifts south. If heavier bands of snow move over MKG IFR and LIFR
conditions will be possible. Otherwise farther inland little to no
snow is expected, but some lower ceilings of 500 to 1000 feet are
expected to develop along with some mist. These lower ceilings
will gradually improve during the late morning with lingering MVFR
conditions into the afternoon.
&&
.MARINE...
Issued at 301 PM EST Mon Dec 2 2024
Northwest to west winds will maintain 2 to 5 foot waves over Lake
Michigan through Tuesday. Areas of heavy lake-effect snow will
reduce visibility below a quarter mile through tonight.
Southwesterly gales to 35 knots are possible starting early
Wednesday morning, becoming northwesterly gales to 45 knots
Wednesday evening to Thursday morning. This will occur as a strong
low-pressure system passes through the Great Lakes region. Model
ensembles continue to indicate a 20 to 30 percent chance of gusts to
storm force, over 48 knots, Wednesday night to Thursday morning.
Freezing spray will also be possible starting Wednesday night as air
temperatures over the water plummet into the 20s.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 7 AM EST Tuesday for MIZ037-038-
043-050.
Winter Storm Warning until 7 AM EST Tuesday for MIZ056-064-071.
Winter Weather Advisory until 1 AM EST Tuesday for MIZ072.
MARINE...Small Craft Advisory until 1 AM EST Wednesday for LMZ844>849.
Gale Watch from late Tuesday night through Thursday afternoon
for LMZ844>849.
&&
$$
UPDATE...RAH
DISCUSSION...TJT
AVIATION...
MARINE...CAS
Area Forecast Discussion
National Weather Service Nashville TN
647 PM CST Mon Dec 2 2024
...New UPDATE...
.UPDATE...
Issued at 636 PM CST Mon Dec 2 2024
Snow flurries and light snow covers a large amount of the mid
state this evening. coverage across KY has decreased in the last
hour and we do see the back edge starting to work into southern KY
at this time. Latest short term models do show that the snow will
be ending from north to south in the next few hours. Trace amounts
of snowfall here and there has been the extent thus far. Our
Plateau area, particularly the northern Plateau, could see up to
or a little more than a half inch with this activity. Surface wind
component looks like it will be 330-340 degrees so not quite in
the 290-300 upslope sweet spot. Motorists should still exercise
caution and watch for some slick spots on some roadways as well as
bridges and overpasses, particularly across the Plateau area.
Otherwise, temperatures are now below freezing along and north of
I-40. The colder air should continue to infiltrate the area with
lows by morning ranging from the high teens Plateau, to the lower
20s elsewhere.
For the forecast, no adjustments at this time. However, I may need
to move the -sn weather grids back an hour or so. Will keep an
eye on the back edge of the snowfall as it heads our way. Will
then update if needed.
&&
.SHORT TERM...
(This afternoon through Tuesday Night)
Issued at 1239 PM CST Mon Dec 2 2024
Surface observations early this afternoon show it`s still quite
cold areawide with temperatures ranging from the mid 30s in our
northeast to around 40 in our southwest. Radar and satellite
imagery indicates clouds and snow falling aloft are beginning to
spread across the KY border into Middle Tennessee. Notably,
however, the low levels remain very dry across our forecast area
per the 12Z OHX sounding, with surface dewpoints down in the teens
and a PWAT of just 0.18 inches. Therefore it will take several
hours of precip falling aloft before low levels can saturate
enough for any snow to reach the ground, which the latest HRRR
estimates will be around 4-5 pm in our northwest, 5-7 pm in our
southwest/central/northeast, and 7-9pm in our southeast. Always
difficult to forecast snow amounts in these low end scenarios (or
any snow in the south tbh), but given the very cold and dry
atmosphere, snow ratios should be quite high and NBM forecasts
them to range from 12:1 in our southwest up to 19:1 in our
northeast. Given this, plus the expected couple hundredths of an
inch of QPF or less, a dusting to a few tenths of an inch of snow
seems possible across at least parts of the midstate. NBM, WPC,
and HRRR all generally agree with this, with splotches/bands of
light snow accum amidst areas with no accum, and highest amounts
(as usual) on the Plateau which could see around 1/2 inch. Since
this will be a light, dry snow, little if any impact to roads is
anticipated, although cannot rule out a slick spot or two where
accumulations are highest on the Plateau.
After today`s light snow, tonight through Tuesday night looks
quiet, cold and dry, with lows in the upper 10s and 20s and highs
only in the 30s to around 40.
&&
.LONG TERM...
(Wednesday through next Monday)
Issued at 1239 PM CST Mon Dec 2 2024
WAA will kick into gear on Wednesday ahead of another strong
Arctic cold front that will move across the area early Thursday.
Ahead of the front, temps will warm into the upper 40s to low 50s
on Wednesday afternoon with dewpoints rising into the 30s/40s.
This may be enough moisture return for some light rain prior to
fropa as the NBM suggests, but given the lack of QPF on the 12Z
GFS/ECMWF have undercut the NBM pops to just slight chance. The
coldest air so far this season will arrive, with lows expected to
fall down into the teens areawide on Friday morning. Highs will
at least rebound on Friday into the mid 30s to low 40s with ample
sunshine.
A pattern change begins over the weekend as our deep northwest
flow gets replaced by southwest winds out ahead of a cutoff low
located over northwest Mexico. Strengthening WAA and moisture
return from the Gulf could allow for some rain to spread into the
midstate as early as Saturday morning as shown by the GFS, but
more likely by Sunday into Monday once the deeper moisture
arrives as indicated by the ECMWF. QPF amounts currently looks to
be around one half inch areawide, but could be higher if the
global models are correct. Warmer temperatures are expected as
well over the weekend into early next week with lows in the
30s/40s and highs in the 40s/50s and possibly low 60s - which is
around 5-10 degrees above normal for early December.
&&
.AVIATION...
(00Z TAFS)
Issued at 509 PM CST Mon Dec 2 2024
Light snow showers are pushing through Middle TN this evening.
They will diminish from west to east from 01 to 04z. Locally lower
vis will be possible with the snow showers and may bring a period
of MVFR conditions. Some light accumulation will be possible
mainly for areas north of I-40. AS the snow moves out MVFR cigs
will build in overnight. Skies will start to clear after 13z with
VFR conditions returning. Northerly winds up to 12 knots this
evening falling below 5 knots overnight.
&&
.PRELIMINARY POINT TEMPS/POPS...
Nashville 23 38 25 52 / 30 0 0 10
Clarksville 20 36 24 49 / 20 0 0 10
Crossville 17 35 17 47 / 30 0 0 0
Columbia 21 39 21 52 / 20 0 0 10
Cookeville 19 35 20 48 / 30 0 0 0
Jamestown 18 34 19 47 / 30 0 0 0
Lawrenceburg 20 38 21 51 / 20 0 0 10
Murfreesboro 21 38 21 52 / 30 0 0 10
Waverly 20 38 24 49 / 20 0 0 10
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE.......21
SHORT TERM...Shamburger
LONG TERM....Shamburger
AVIATION.....Mueller