Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/19/24
Area Forecast Discussion
National Weather Service Denver/Boulder CO
513 PM MST Wed Dec 18 2024
.KEY MESSAGES...
- Gusty winds expected tonight in the Front Range Mountains and
Foothills with gusts up to 80 mph.
- Isolated flurries/light snow possible for mountains Sunday into
Monday.
- Otherwise, dry and mild weather prevailing.
&&
.SHORT TERM /Through Thursday/...
Issued at 106 PM MST Wed Dec 18 2024
Northwest flow aloft will prevail tonight and Thursday. An upper
level trough passes north of the area tonight. Any precipitation
associated with it will stay well north of the area. The
subsidence and increasing mountain top flow will bring very windy
conditions to the Front Range Mountains and Foothills. HiRes
models in good agreement a mountain wave will develop tonight and
bring these very windy conditions down to the higher foothills.
HRRR has backed off a little on the strength of the winds, though
given the setup still expect locally strong winds to 80 mph. These
winds will subside Thursday morning as the mountain wave breaks
down.
The airmass over the state will be drier Thursday, leading to mostly
sunny skies. However, some high clouds, in the form of wave clouds
will be possible. This will help temperatures warm a little for
Thursday with highs in the 50s across northeast Colorado. A few
locations in the Denver area may top 60 degrees.
&&
.LONG TERM /Thursday night through Wednesday/...
Issued at 106 PM MST Wed Dec 18 2024
The pattern will not be particularly conducive for precipitation
through early next week. Dominant upper-level ridging will fill in
quickly through Saturday, keeping our region dry and mild, with
generally light winds outside of lingering breezy conditions for
higher terrain. Temperatures will peak Saturday and Sunday for the
high country and plains/urban corridor respectively, with
departures approximately 15 degrees above normal for this time of
year.
On Sunday, a weak wave embedded in westerly flow aloft will
traverse the northern US plains. It`s track will be too far north
to allow for any meaningful precipitation (~20% chance of high-
elevation flurries), but will result in increased cloud cover and
an uptick in winds. Behind this wave, winds aloft will see an
increasing northwesterly component, potentially advecting more
favorable moisture into our mountain region for higher chances
(50-60%) of light snow on Monday. Amounts would not support more
than minor impacts for the highest elevations, and still a sizable
portion of ensemble members (at least 1/3) do not buy into any
measurable precipitation at all.
Unless these features speed or slow, Tuesday is favored to remain
dry with high pressure rebuilding. The next opportunity for
precipitation (and first opportunity for the lower elevations)
wouldn`t come until Christmas, when ensemble mean solutions
suggest growing potential for influence from an upper-level low
ejecting southeastward from the PacNW. There`s minimal agreement
as far as how that evolves, and thus any impacts that may result,
if any.
&&
.AVIATION /00Z TAFS through 00Z Friday/...
Issued at 511 PM MST Wed Dec 18 2024
Models keep fairly weak south-southwesterly winds going all night
into Thursday morning. Speeds should remain light. There shouldn`t
be any ceiling issues overnight.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 6 AM MST Thursday for COZ033>036.
&&
$$
SHORT TERM...Meier
LONG TERM....Rodriguez
AVIATION.....RJK
Area Forecast Discussion
National Weather Service Burlington VT
925 PM EST Wed Dec 18 2024
.SYNOPSIS...
Snow and rain will result in elevationally dependent
accumulations through tonight. Slippery travel can be expected
this evening in areas of heavier snow; however, overall
accumulations will be only up to 4 inches, with perhaps a few
higher totals over 2000 feet in elevation. Following another
chance of snow showers on Friday, very cold conditions will
settle into the region, featuring below zero temperature
readings in many locations.
&&
.NEAR TERM /THROUGH FRIDAY/...
As of 922 PM EST Wednesday...Light precipitation is continuing
over most areas but there is a heavier mesoband across portions
of southern Vermont. That band will be where the heaviest snow
ends up and in it rates of an inch an hour are possible. The
band is expected to mostly stay in southern Vermont and it will
struggle to move north. Snow levels have been a little higher
than forecast. They are generally between 500-1000 FT but they
are lower in the St. lawrence Valley where almost everywhere is
seeing snow. They will lower slightly this evening but with a
lack of meaningful cold air advection and weak dynamics there
will not be able to be much cooling. However, there will be a
little more cold air advection aloft which should help bring
down snow levels a little. At this point, it looks unlikely that
the immediate Champlain Valley will see any accumulation. The
back end of the precipitation is about to reach the ST. lawrence
Valley and most of the steady snow will be done not long after
midnight.
Previous Forecast...A modestly strengthening low
pressure system and its associated front to our south will be
responsible for a short period of rain and snow for this
afternoon and evening. Total precipitation amounts look to
average a quarter to a half inch. While no Winter Weather
Advisories are issued due to most populated areas seeing under 4
inches of snowfall, localized higher amounts are possible in
higher elevations of south central Vermont, where mesoscale
banding is favored with periods of heavier precipitation.
The mid-level front that is displaced well to the north of the
low pressure system, and the lift and moisture tied to it, are
already producing banded structures that will create varying
precipitation rates across our region. Precipitation will taper
off from west to east as the surface low passes to our east
near Cape Cod around midnight. Two zones of widespread
precipitation are expected. The main one, occurring now, is tied
to a broad zone of 700 millibar frontogenesis lifting
northeastward into northern New York and the northern half of
Vermont. Snowfall rates will generally be 0.25" to 0.5"/hour,
consistent with light but steady precipitation rates and roughly
10:1 snow to liquid ratios. With temperatures at or slightly
above freezing and warm road temperatures from the surface
heating today, accumulations will be primarily on grassy
surfaces through the early evening. After dark, combination of
slight cooling of surfaces and areas of heavier precipitation
rates could lead to slippery conditions and a special weather
statement may be needed to highlight areas of difficult travel.
As the surface low intensifies this evening, we`ll be watching for
heavier precipitation rates tied to potential weak instability aloft
on the northern flank of stronger frontal forcing in southern
Vermont. There remain good signals for heavy snowfall rates in
excess of 1" per hour at times across portions of Rutland and
Windsor where modeling shows rounds of this favorable forcing in
a narrow axis. However, perhaps Orange and Caledonia counties
see this heavier snow as well through the evening, as mesoscale
bands often are displaced a bit north of where the best forcing
is modeled. This heavier snow is favored to blossom between 7
PM and 9 PM before departing to the east before midnight.
The forecast for wet snow at elevations above 1000 feet is
straightforward. Given relatively warm surface temperatures
near or above freezing along with snow growth temperatures being
largely 10 to 15 thousand feet above ground level, snow
character is favored to be wet and possibly heavy, especially in
higher elevations in south central Vermont. Crucially, because
of these mild surface temperatures and lack of cold air
advection due to southerly flow ahead of another surface trough
to our northwest, only when heavier snow falls will rain change
over to snow in the lower elevations. While the HRRR has proven
a little slow at changing rain to snow in the St. Lawrence
Valley, have leaned towards its depiction of precipitation type
shown in recent run, which has been consistent with itself and
observations today of milder boundary layer conditions in the
Champlain Valley. As such, most of the rain will remain liquid
in this region, with a rain/snow mix in the Winooski Valley and
other low elevations in Vermont, through most of the event. In
the St. Lawrence Valley, the low level air mass was just enough
colder that rain has already mixed with or changed to wet snow
with temperatures in the mid 30s, and these areas look on track
to see mainly snow this evening and accumulations of 1 to 2
inches. Much of Vermont above 1000 feet elevations should see 2
to 4 inches, with lower elevations generally a coating to an
inch, through tonight.
Overnight, the aforementioned trough to our northwest will sweep
eastward and allow winds to turn westerly and increase in speed
as pressures rise fairly quickly and colder air filters in. 850
millibar temperatures look to fall from -4 to -10 degrees
overnight while 700 millibar moisture remains elevated through
most of the night. With only modestly strong winds in the 20 to
25 MPH range in the high terrain, this pattern of blocked flow
supports upslope snow showers and flurries, with light
accumulations in the mountains and western slopes. The
breeziness will help reduce chances of any ice conditions
developing for the morning commute, as the mixing will both keep
temperatures near or above freezing in many areas, but also
help to dry out wet surfaces. During the day on Thursday, we
continue to advertise non-diurnal temperature trends with steady
cold air advection. Temperatures will generally be steady or
fall during the day. Aside from lingering morning snow
showers/flurries, it will be a dry day. A brief bit of clearing
is favored before the next system spreads some high clouds
tomorrow night from the west, with skies becoming overcast
overnight. No precipitation is anticipated through daybreak
Friday.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 354 PM EST Wednesday...The end to the work week will turn
rather cold and calm following a brief weak shortwave. A
clipper system will track out of the Great Lakes into the region
Friday afternoon encountering dry and cold air. Furthermore, a
developing coastal low off New Jersey will take most of the
available moisture with it Friday evening. While no impacts are
expected from the coastal low, remnant scattered snow showers
are forecasted Friday evening through Saturday afternoon. Models
indicate widespread light flurries and snow showers across the
region, with higher elevations seeing better precipitation
chances. Model trends show increasing probabilities of
precipitation in the Northeast Kingdom as compared to previous
runs. With moisture levels low, however, most places will only
see between a 0.25" and 1" of snow, with 1-2" possible in the
St. Lawrence Valley. Temperatures Friday be slightly below
average in the upper 20s across much of the region and teens
near the summits.
Behind the clipper, cold polar air 10-15 degrees below average will
filter into the area Saturday night as high pressure builds in for
the weekend. Below zero temperatures are expected across most of the
Adirondacks and parts of northeast Vermont. The Champlain Valley
will see temperatures in the single digits. Exactly how cold the
region gets will be partially dependent on how much snowfall the
region gets Friday and Saturday, as well as how much cloud cover is
present overnight. Areas with more snowfall will be cooler than
those without due to stronger radiative cooling.
&&
.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 354 PM EST Wednesday...High pressure will continue to
dominate Sunday and Monday with cold polar air remaining in
place during the overnights. Temperatures will struggle to reach
the mid-teens in the Champlain and St. Lawrence Valley, with
near zero highs in the higher elevations on Sunday. Overnight
temperatures in the Adirondacks will remain below zero with
single digits in the valleys. With the polar air in place over
the weekend, Lake Champlain may experience some steaming as the
lake will be considerably warmer than the air temperature. Some
flurries from the potential added cloud cover in the Champlain
Valley are possible Sunday night.
Many will be traveling for the Christmas holiday Monday and Tuesday,
and while no precipitation is expected Monday, temperatures will
remain on the cold side with highs in the upper-teens in the valleys
and single digits in the mountains Monday. Travel is expected to be
the best Sunday and Monday, as a pair of shortwaves move into the
area Tuesday morning. Models have come into better agreement with
less phasing between the waves, indicating two separate systems
Tuesday and then Wednesday. Precipitation chances increase Tuesday
morning into Tuesday night, and are expected to continue through
Christmas Day.
If you are hoping for a white Christmas, the ingredients are slowly
coming together for some frozen precipitation both Christmas Eve and
Christmas Day. While still uncertain on the exact timing and
intensity of the shortwaves, cool air looks to be in place at the
onset of the event. However, model uncertainty on the temperatures
during the event linger. The GFS indicates some warm advection with
a more positively tilted trough axis, whereas the European indicates
a more broad trough which would keep the cold air in place
throughout the event. How the shortwaves interact will ultimately
determine how much cold air is available and how much precipitation
the region receives. A faster phasing will increase the
precipitation chances, but increase the chance for a rain/snow
mix. However, less phasing, and a faster moving initial
shortwave, will keep the cold air locked in, but lessen the
chances of precipitation on Christmas.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Through 00Z Friday...Widespread rain and snow make for a
challenging 24 hour TAF period tonight. Flight conditions will
be a mix of anything from VFR to LIFR at times, largely changing
due to visibility changes in rain/snow, but there are also areas
of 700-900 foot cloud ceilings coming in and out of many sites.
BTV, PBG, MPV, and RUT are all rain at the moment, gradually
changing to rain/snow and then finally to snow by tomorrow
morning. Other sites are already reporting snow and should
remain so as temperatures fall tonight. Precipitation will
likely come to an end tomorrow, though SLK and EFK will have
the highest potential of snow showers lingering until at least
18Z with upslope flow. Winds southerly tonight will turn more
northwesterly tomorrow following the storm. Ceilings should
return to mostly VFR by the end of the 24 hour period.
Outlook...
Thursday Night: VFR. NO SIG WX.
Friday: Mainly VFR, with local MVFR possible. Chance SHSN.
Friday Night: Mainly MVFR, with areas VFR possible. Chance SHSN.
Saturday: Mainly MVFR, with areas VFR possible. Chance SHSN.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. NO SIG WX.
Sunday Night: VFR. NO SIG WX.
Monday: VFR. NO SIG WX.
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.
&&
$$
SYNOPSIS...Kutikoff
NEAR TERM...Kutikoff/Myskowski
SHORT TERM...Danzig
LONG TERM...Danzig
AVIATION...Storm
Area Forecast Discussion
National Weather Service Des Moines IA
611 PM CST Wed Dec 18 2024
...Updated for the 00z Aviation Discussion...
.KEY MESSAGES...
- Potential for light snow in northern Iowa Thursday. Highest
chances (50-60%) near the Minnesota border. Accumulations
generally an inch or less, but some travel impacts are still
possible.
- Strong northwest winds Thursday afternoon through Thursday
night. Highest gusts of 40+ mph most likely in western Iowa.
- Above normal temperatures next week including the Christmas
holiday period.
&&
.DISCUSSION...
Issued at 215 PM CST Wed Dec 18 2024
Quiet conditions at the moment as an area of surface high pressure
nudges into the state. A broken stratus deck has held temps in the
20s to low 30s, which is near average for this time of year. A
vigorous shortwave currently over the northern Rockies pushes into
the northern Plains tonight into Thursday. Winds become southerly
overnight in response to the approaching wave which will lead
to warmer temps for tomorrow, particularly central and south
where warm air advection will push highs into the mid 40s to
low 50s. Further north temps will be impacted by cloud cover and
precipitation as deep, phased synoptic forcing mechanisms
overspread the region. Models continue to paint a stripe of
snowfall across our far north/northeastern counties as dry air
on the southern periphery of the upper wave diminishes precip
potential. Hires models have trended a bit faster with snow
onset, possibly crossing the state border as early as 06-09z.
PoPs peak between 12-18z as the fast moving nature of this
system limits the precip window and should keep amounts on the
lighter side. Cobb output from the GFS and RAP at KMCW both
signal around 1" of accumulation with amounts quickly tapering
off to the south. Additional light precip is possible on the
backside of the system Thursday afternoon and evening. Model
soundings show a deep isothermal and nearly saturated layer just
outside the DGZ. Slightly cooler temps aloft would promote
efficient crystal growth and some flurries or light snow as far
south as I-80. Did not expand precip chances due to low
confidence in this scenario playing out, but this will need to
be monitored.
Another notable impact from this system are strong nw winds
Thursday afternoon into the overnight hours behind a cold front.
Phased isallobaric forcing and cold air advection is a
favorable setup for mixing down higher momentum air to the
surface. Still some model discrepancies on the higher end
potential for wind gusts, but most models advertise anywhere
from 35 to 45 knots at the top of the mixed layer. The strongest
gusts of 50+ mph are likely confined to portions of NE and SD,
but an advisory may be in play for portions or all of our area.
The wind gusts could also create areas of blowing snow in places
that receive accumulating snowfall earlier in the day.
The main theme from the weekend into next week is gradually warming
temperatures beneath a building ridge aloft. Confidence remains high
that the Christmas holiday will feature above normal temperatures
with highs into the upper 30s and 40s. A shortwave attempts to
breakdown the ridge axis a bit Sunday night into Monday. Moisture
return is lethargic, but models have begun to spit out spurious
light QPF as moisture and lift becomes better aligned over the
eastern half of the state. PoPs remain on the lower end (30% or
less) and temperatures near the surface may be warm enough to
support mostly liquid precip types. Forecast is a mix of
rain/snow for now. Widespread travel impacts are not anticipated
at this time, but something to file away for those with holiday
travel plans.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 542 PM CST Wed Dec 18 2024
MVFR stratus deck remains across much of central into eastern
Iowa including all 5 TAF sites. This stratus deck continues to
gradually erode on its western edge so improving conditions will
occur at KFOD and KDSM first before sites further east. However,
timing of improvement to VFR at sites like KMCW and KALO may be
short lived with additional cloud cover and light snow moving in
to northern Iowa. Guidance is starting to bring this snow in
sooner so main change is to add a Prob30 group on the front of
snow mentions at KMCW for this potential to see snow sooner. The
light snow may also impact KALO, but confidence is lower in
extent of impacts so kept with Prob30 groups. Visibility drops
still look to be around 1-2 miles in peak snow rates with
visibility also impacted by increasing winds and thus blowing
snow as winds out of the northwest increase Thursday morning
into afternoon, with gusts of up to around 25-35 knots, the
highest gusts in western Iowa. The snow does look like it may
occur in a couple different waves, so this second wave will
still need to be added to KMCW for the afternoon to early
evening hours. Ceilings also to become IFR (60-80% confidence)
for a time at KALO and KMCW during the daytime Thursday with
prevailing MVFR returning at most other sites. Adjustments in
timing are still likely and updates will be sent as needed.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Martin
AVIATION...KCM
Area Forecast Discussion
National Weather Service Green Bay WI
929 PM CST Wed Dec 18 2024
Updated aviation portion for 06Z TAF issuance
and new information added to update section
.UPDATE...
Issued at 911 PM CST Wed Dec 18 2024
Forecast appears to be on track, and no changes were made to the
winter weather headlines. Agree with the general trend of higher
amounts near the lakeshore due to lake enhancement, but not sure
if any accumulations to 12 inches will occur there. There is a
lot of shear through Thursday and early Thursday evening, then
winds steadily back from E to NNE through the rest of Thursday
night. Thus, not sure if any dominant bands will be be able to
form and set up in a given location.
&&
.KEY MESSAGES...
- A clipper type system will bring the first widespread
accumulating snow to the region from Thursday morning through
early Friday morning. There is a 40-70 percent chance of greater
than 6 inches of snow from central to northeast Wisconsin during
this time frame. These percentages are higher near Lake
Michigan where lake enhancement is expected. Lesser snowfall
will occur over north- central Wisconsin.
- Snow covered roads and difficult travel are expected from
Thursday morning through Friday morning. The Thursday evening
commute will be most impacted, and likely slow and hazardous.
Impacts to the Friday morning commute are also likely over
northeast Wisconsin, particularly near the Lakeshore.
- Another chance for area-wide snowfall is possible early next
week, which could impact travel ahead of the Christmas holiday.
&&
.DISCUSSION...
Issued at 212 PM CST Wed Dec 18 2024
Short Term...Tonight and Thursday
The latest RAP analysis and satellite/radar imagery show a 500mb
trough over the Great Lakes and northwesterly flow downstream of a
surface ridge which is positioned from Manitoba to Texas.
Widespread MVFR stratus prevails within a cold advection regime
across much of Wisconsin. Light flurries continue across most of
the region. The exception is over Vilas county where visibilities
have fallen to 2sm at times. Clearing is occurring upstream over
northern Minnesota which could push into the region later this
afternoon or evening. Looking upstream, an impressive shortwave is
moving across northern Washington/Idaho/northwest Montana and
poised to move into the region on Thursday. Forecast continues to
revolve around winter headlines and impacts with this system.
If clearing occurs, it will be short-lived tonight. That still may
be sufficient time for temps to plummet across north-central WI.
But then clouds rapidly spread in from the west from late evening
into the overnight. Any temps that fall quickly due to radiational
cooling will therefore rebound as clouds return.
Snow will begin to overspread the area on Thursday morning as
mid-level fgen/warm advection and QG forcing push into the region.
Snowfall rates could reach upwards of 3/4" per hour over central
Wisconsin between 9 am and 12 pm as the band of snow moves across
the area. 2 to 4 inches of snow could fall by midday over
Marathon/Wood/Portage county.
The snow will move into eastern WI in the afternoon. Convective
allowing models continue to indicate robust lake enhanced banding
taking place as the snow pushes into northeast WI. Several factors
are favorable for significant lake enhancement including delta T`s
15-18C and a 5000 ft isothermal layer in the dendritic growth
zone. Wind directions back slightly but change little (southeast)
during the 18z-03z Fri timeframe that favors locally heavy
banding in the lake enhancement. The HREF indicates snowfall rates
could approach 1"/hr in these snow bands in the late afternoon and
early evening hours. Attempted to manually add higher snowfall
totals where lake enhancement is expected to be greatest,
generally between I-43 and Sturgeon Bay on Thu afternoon, shifting
north across Door and Marinette counties on Thu evening. Guidance
then points towards the banding signatures returning south late
on Thu night as flow becomes northerly on the backside of the
cyclone.
Snowfall totals increased a bit across the board, and generally
range from 5 to 8 inches over central and east-central WI, 6 to 10
inches along the Lake and Bayshore, and 3 to 5 inches over north-
central WI. Think locally higher snowfall to 1 ft is possible
along the lakeshore where snow bands persist the most.
In terms of impacts, this will be a dry, powdery snowfall with
modest winds that will only lead to minor blowing/drifting along
the lakeshore. The Thu morning commute will likely be impacted as
snow first arrives over central WI and the I-39 corridor. By far,
the greatest impacts will occur with the Thu evening commute.
Snow covered roads may linger along the lakeshore on Friday
morning as well.
After coordinating with surrounding offices, have issued a Winter
Storm Warning for much of central to northeast WI and a Winter
Weather Advisory for north-central WI.
Long Term...Thursday Night Through Wednesday
Wintry precip early next week: There are some similarities
between the surface low due to impact the region on Thursday, and
the next system forecast to arrive on Monday. Both are relatively
dynamic and have similar tracks. However, the shortwave on Monday
looks more compact and thermal profiles also look warmer. In
addition, flow in the northern stream looks to be weaker so a more
northerly track is possible.
That said, robust dynamics would argue that this system could
lead to minor impacts on travel. Given the lack of cold air,
potential for a wintry mix seems plausible both ahead of the
system, and also behind the system (freezing drizzle).
Temperatures... After the low departs, below normal temperatures
are expected from Friday through Sunday. Highs in the teens and
20s and lows in the single digits above zero can be expected each
day. A warming trend then commences early next week with highs in
the 30s expected by Christmas.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 911 PM CST Wed Dec 18 2024
A mix of low-end VFR/MVFR stratus covered much of the region late
this evening, but large breaks had opened up from TKV-EZS-GRB.
Otherwise high/mid clouds were arriving in advance of the incoming
clipper system. Mainly VFR conditions are expected overnight.
Conditions will deteriorate rapidly from SW-NE Thursday morning
as a potent Alberta Clipper brings snow and IFR/LIFR conditions to
the region. Snowfall rates will increase to 1/2" to 1" per hour
over central WI between 14-16z/Thu, and 16z-18z/Thu in the Fox
Valley and Lakeshore areas. Some improvement in visibilities is
expected in NC/C WI late Thursday afternoon and evening, but poor
conditions will prevail in eastern WI. Snow amounts of 4 to 8
inches are likely by Friday morning, with higher amounts in the
lakeshore areas due to lake-effect. All airports in the forecast
area will likely require runway plowing operations.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 AM Thursday to 3 AM CST Friday
for WIZ005-010>012-018-019.
Winter Storm Warning from 9 AM Thursday to 6 AM CST Friday for
WIZ013-020-021-031-037>039-048-049-073-074.
Winter Storm Warning from noon Thursday to 9 AM CST Friday for
WIZ022-040-050.
Winter Storm Warning from 6 AM Thursday to 3 AM CST Friday for
WIZ030-035-036-045.
&&
$$
UPDATE.........Kieckbusch
DISCUSSION.....MPC/MPC
AVIATION.......Kieckbusch
Area Forecast Discussion
National Weather Service Grand Rapids MI
938 PM EST Wed Dec 18 2024
.KEY MESSAGES...
- Risk for Snow Related Impacts Thursday afternoon into Friday
- Very cold over the weekend
- Patchy Flurries/Sprinkles this evening
&&
.UPDATE...
Issued at 938 PM EST Wed Dec 18 2024
Scattered flurries continue this evening, and also had a brief
period of light freezing rain (sprinkles) earlier here at the
office. The droplets froze to the cars but not to the warmer
parking lot and sidewalks. The current areas of very light and
non-impactful precip are expected to end overnight as upper
shortwave trough departs and skinny sfc ridge and associated
subsidence arrive. No changes to the fcst beyond tonight at this
time.
&&
.DISCUSSION...
Issued at 147 PM EST Wed Dec 18 2024
- Risk for Snow Related Impacts Thursday afternoon into Friday
At this time, no winter weather headlines.
Models continue to show a decent mid level wave tracking down from
the Upper Plains through Northern Illinois and into Indiana later
Thursday into Friday. As this system tracks towards Michigan the
DGZ moistens up near and north of Interstate 96 Thursday morning,
however below that it is shown to be relatively dry. This should
act to delay any steadier snow until the afternoon and evening
when the low levels moisten up. The HRRR is showing the region
from near and north of Muskegon with an earlier onset of the snow
given some influence of Lake Michigan. However other high res
models keep this influence offshore for most of the event. As a
result some uncertainty with the timing and amounts for that
region as well. Along Interstate 94, the DGZ will be unsaturated
at times for this event and that could result in a variety of
precipitation types. The models do vary on the
saturated/unsaturated DGZ scenario and that will play a
significant role on how much this system ultimately impacts the
region. For now, we will keep it as mainly a snow event, but may
have to feature some windows for mixed precipitation, especially
closer to Interstate 94. Also, the surface temperatures will
likely be near freezing or possibly a degree or two higher in the
middle part of Thursday. Commonly this leads to melting on the
roads. If this is the case, impacts may hold off until the evening
commute when the surfaces start to cool off.
This system is already fairly organized over the Pacific NW and
the 500 mb trough does sharpen up as it tracks through later
Thursday night into Friday morning. Easterly flow Thursday night
could draw some moisture off of Lake Huron which may locally
enhance the snow for our northeast zones. FGEN was noted in the
700-600 mb level and parts of our area will be favored for the
trowal which should extend the snow. The flow turns north Friday
on the backside of the departing wave. Commonly low level
northerly flow draws down drier air which cuts off the
accumulating snow. Thus we will feature a sooner departure of the
snow for our northern zones as compared to areas near and south of
Interstate 96. . Based on all this we will generally feature a 2
to 5 inch snowfall which is in line with most ensemble guidance.
Any prolonged lake influence could quickly turn the amounts higher
and the region near and north of Muskegon will need to be
monitored closely.
- Very cold over the weekend
An arctic high pressure system will be tracking eastward through
southern Ontario during this time. Subsidence will act to limit
the cloud cover through most of the column here in Michigan.
However there will be some lake effect clouds around. With fresh
snow and light winds expected along with a cold start to Saturday
night, much of the region will likely fall into the single digits.
Any clearing could easily lead to some sub zero readings,
especially inland.
- Patchy Flurries/Sprinkles this evening
There will be a period of low level convergence as northwest flow
persists this afternoon and evening. The DGZ is shown to be mainly
dry. Thus any precipitation that falls is expected to remain very
light. Surface temperatures range from near 32 at Ludington to the
mid 30s around Battle Creek and Jackson. Given this scenario the
risk for freezing drizzle is not zero but with the temperature
expected to remain nearly steady through the evening, we will not
feature that in the forecast at this time.
-
&&
.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 617 PM EST Wed Dec 18 2024
Widespread MVFR cigs ongoing at this time as an upper trough moves
across the state. We may see cigs rise by mid evening as some
ridging moves in quickly ahead of tomorrow`s clipper.
Light snow will develop around noon at the lake shore and spread
east during the afternoon, but will probably miss the I-94
terminals, until closer to 01z Friday when the main area of light
snow will spread over the region.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 3 AM EST Thursday for LMZ844>849.
&&
$$
UPDATE...Meade
DISCUSSION...MJS
AVIATION...04
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
1011 PM EST Wed Dec 18 2024
.SYNOPSIS...
A strong cold front will move through late tonight with colder
and drier high pressure building in to the Southeast late this
week through early next week.
&&
.NEAR TERM /THROUGH THURSDAY/...
As of 1010 PM Wed...Cold front continues to push across the
Appalachians this hour. Across the coastal plain, pre-frontal
trough is providing surface lift needed for scattered shower and
thunderstorm activity, tapping into an unstable elevated layer
characterized by MLCAPEs north of 1000 J/kg per RAP analysis.
Shear and helicity have been just strong enough to support weak,
low-topped supercells especially along the I-95 corridor, but
the robust marine layer locked in place over eastern NC has
quickly eaten away at stronger cells. Convection threat will
persist for a few more hours, but once the pre-frontal trough
crosses and winds begin to veer northwesterly the thunder threat
will come to an end.
Dense fog continues to plague the Crystal Coast tonight as sea
fog advects off the Atlantic. Farther inland, pre-frontal
southerly winds are keeping fog at bay but a wide bank of low
stratus is overspreading much of the coastal plain and will
linger for much of the night.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH 6 PM THURSDAY/...
As of 3 PM Wed...Aforementioned cold front blasts through the
area from N to S and offshore of the Crystal Coast after 12Z.
Could be some wrap around showers but rain will be ending by mid
morning, with breezy, blustery, cool conditions expected with
mainly ovc skies. Temps will start out in the mid/upr 50s for
some areas, but fall through the low 50s throughout the
afternoon.
&&
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
As of 230 AM Wednesday..
KEY MESSAGES
- Scattered shower potential through Friday
- Much colder air arrives this weekend
- Trending milder over the holidays
A potent upper level shortwave is forecast to move through the
Carolinas on Friday, then offshore by Friday night. This wave will
be associated with a broad upper level trough that is forecast to
develop across the Eastern U.S. this weekend. Moving into the week
of Christmas, guidance is in good agreement with the upper trough
shifting east out into the Atlantic, with ridging or zonal flow then
developing across the Eastern U.S. The next shortwave to potentially
impact the Carolinas appears to be slated for around, or just after,
Christmas Day.
Friday:
A more potent shortwave is then forecast to move through the
Carolinas Friday and Friday night. Strong mid-level height falls
associated with this wave should help support cyclogenesis off the
Mid-Atlantic Coast. This will lead to a renewed surge of northerly
winds and CAA across ENC. Meanwhile, much colder temps aloft beneath
the shortwave will support steepening lapse rates over the region.
This combined with modest low-mid level moisture, and a diffluent
flow aloft, may lead to scattered showers Friday into Friday
evening. While temps aloft will be cold, low-level thicknesses are
forecast to be warm enough to support all liquid locally.
Saturday - Monday: ENC will be fully entrenched in a much colder
airmass this weekend into early next week. Notably cold low-level
thicknesses should lead to highs only topping out in the 30s and
40s. Meanwhile, the cold thicknesses plus light winds and clear
skies should allow for ideal radiational cooling conditions at
night, especially inland. This should set the stage for widespread
lows in the teens and 20s, with the coldest night expected to be
Sunday night. Barring more wind or clouds than forecast, inland lows
may reach the mid teens Sunday night, which puts temps close to the
new Cold Advisory criteria (ie. temp or wind chill < 15F). Advisory
or not, the key message is that this weekend will feature noticeably
colder conditions.
Tuesday - Wednesday (Christmas Eve/Christmas Day): Southerly return
flow developing beneath zonal flow aloft should support gradually
warming conditions as we move further into the holidays next week.
Based on this, highs are likely to warm back into the 50s, with low
60s possible by Christmas Day across southern sections of ENC.
Within the developing return flow, coastal troughing is likely to
develop offshore, and this may eventually support a chance of rain
showers by mid-week. This chance may then increase just beyond
Christmas Day as the next upper level wave moves through.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
SHORT TERM /through Thu/...
As of 725 PM Wed...LIFR conditions holding strong along the
Crystal Coast and vicinity where dense sea fog continues to
plague the region ahead of an approaching cold front over the
lee of the Appalachians. Further inland, more transient drops in
visibility are occurring but trend is for fog to become more
dominant as the evening progresses. Passing showers and an
occasional thunderstorm are likely ahead of the front,
especially across the coastal plain where elevated instability
is higher.
Pre-frontal trough will cross the region after midnight, likely
eroding the fog threat while holding onto IFR before the main
front makes its way across the region just before dawn on
Thursday. Still plenty of moisture behind the front and looking
at primarily MVFR especially along the coast. Farther inland
where drier air can work its way in, VFR is more likely in the
afternoon.
LONG TERM /Thursday night through Sunday/...
As of 2:30 AM Wednesday...
KEY MESSAGES
- Periods of sub VFR conditions possible Thursday and Friday
- Gusty north winds expected Thursday and Friday
Periods of gusty north winds are then expected to continue into
Saturday, followed by lighter winds over the second half of the
weekend. A couple of upper level systems may bring a chance of
SHRA and sub-VFR CIGs both Thursday and Friday. VFR conditions
then appear likely over the weekend.
&&
.MARINE...
SHORT TERM /through Thu/...
As of 3 PM Wed...Extended DFA for the southern waters through
early Thu, as warm/moist swrly breeze will cont to advect over
the cool waters. Have lifted the DFA for remainder of the
sounds/rivers/coastal waters, though may see periods of low
vsbys return once again this evening.
Seas will be 3-5 ft tonight, then strong cold front comes
through early Thu with winds 20-30 kt and quickly building seas.
LONG TERM /Wednesday night through Saturday/...
As of 2:30 AM Wednesday...
KEY MESSAGES
- Increased risk of impactful winds and seas through Saturday
Notable northerly winds of 20-30kt are expected across area waters
on Thursday in the wake of tonight`s cold front passage. Winds will
briefly lay down to 10-20kt Thursday night into Friday, then build
again to 20-30kt Friday night into Sunday as a potent upper level
system moves through the area, leading to the development of a
coastal low off the Mid-Atlantic coast. With both surges of
northerly winds, seas of 5-8 ft are expected across the coastal
waters north of Cape Lookout. South of Lookout, seas of 3-5 ft are
expected. Seas may not drop below 6 ft until early next week when
high pressure builds in with decreasing winds.
&&
.MHX WATCHES/WARNINGS/ADVISORIES...
NC...Dense Fog Advisory until 7 AM EST Thursday for NCZ195-196-199.
MARINE...Small Craft Advisory from 5 AM to 5 PM EST Thursday for AMZ131-
230-231.
Small Craft Advisory from 5 AM to 10 PM EST Thursday for
AMZ135.
Small Craft Advisory from 7 AM to noon EST Thursday for AMZ136-
137.
Small Craft Advisory from 5 AM Thursday to 1 AM EST Friday for
AMZ150.
Small Craft Advisory from 5 AM Thursday to 7 AM EST Monday for
AMZ152-154.
Small Craft Advisory from 7 AM Thursday to 6 AM EST Friday for
AMZ156-158.
Dense Fog Advisory until 7 AM EST Thursday for AMZ158.
&&
$$
SYNOPSIS...MHX
NEAR TERM...TL/MS
SHORT TERM...TL
LONG TERM...DAG/RM
AVIATION...RM/MS
MARINE...RM/TL
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
942 PM CST Wed Dec 18 2024
.KEY MESSAGES...
- Accumulating snow begins overnight & continues into Thursday
evening. Biggest impact is expected during AM commute.
- Snowfall totals of 4-7" are expected within the main band of
snow, with the best chances along and north of Interstate 94.
- Cooler temperatures heading into the weekend before a gradual
warm-up next week.
&&
.UPDATE...
Issued at 913 PM CST Wed Dec 18 2024
Latest trends in the hi-res guidance have increased forecast
confidence to support a few tweaks to the current Winter
Weather headlines.
First, Stevens/Pope/Kandiyohi/Meeker/McLeod counties have been
upgraded from a Winter Weather Advisory to a Winter Storm
Warning due to greater confidence of snow amounts in the 5 to 7
inch range. Localized areas with 6 inches + are likely.
Second, we have issued a Winter Weather Advisory for Lac Qui
Parle and Yellow Medicine counties with greater confidence of
accumulating snow & blowing snow Thursday afternoon/evening.
There will be sharp gradient across these counties with the
brunt of the impact occurring in the eastern portion along the
MN river. This portion will likely see 2 to 4 inches of new snow
& areas of blowing snow due to gusty northwest winds. Sporadic
gusts up to 40 mph will be possible Thursday PM.
There hasn`t been a significant change in forecast QPF or snow
amounts rather increased confidence on location. Our heaviest
snow is still on tap to occur through the Thursday morning
commute with several inches likely by lunch-time. One notable
trend is a longer duration of light snow Thursday afternoon &
evening. The 00z hi-res guidance depict light snow falling
through Thursday evening hours. This snow will be light & fluffy
thanks to the cold air advection pouring in behind our system
with SLR forecast to trend up towards 20:1 or greater in the
afternoon & evening hours. Forecast soundings depict better DGZ
depth through the evening with better forcing in the
deformation zone. This could lead to better odds of blowing
snow across portions of western and central Minnesota, helping
nudge the previously mentioned two counties into winter weather
advisories.
&&
.DISCUSSION...
Issued at 311 PM CST Wed Dec 18 2024
A Winter Storm Warning has been issued for portions of western &
central Minnesota into much of western Wisconsin where a band of
4-7" is expected. A Winter Weather Advisory was also issued for
areas south of the main band where there is less confidence for
totals greater than 6", but snowfall could still be impactful.
The main impacts from this storm look to be reduced visibilities
and quick accumulation right before or during the AM commute.
Strong winds (leading to blowing snow, especially across western
MN) and cooler air behind this system will keep travel
conditions impacted throughout the rest of Thursday.
Timing... Surface cyclogenesis will take place over Montana this
evening as the upper level shortwave progresses out of the
Rockies. Heavy snow will quickly fall over the Canada/NoDak
border becoming more moderate to light as it approaches western
MN. Most likely onset for western MN is 10pm-midnight,
midnight-2am for eastern MN, and 2-4am for west-central WI. As
the surface low tracks southeast, strong upper level lift,
surging CVA, and deep saturation will lead to snowfall rates
generally around 0.5"/hr at the heaviest. Periods of higher
rates (up to 1"/hr) are possible during the early morning with
sporadic potential for Fgen to enhance lift. If this were to
occur, it would be more off and on and largely a nowcasting
situation depending on where those bands set up and how long
they persist. The heaviest snow should only last 4 to 6 hours
given this is a fast moving pattern with the strong north
Pacific jet.
Totals... As the latest hi-res models continue to trend closer
to what we`ve been seeing with ensemble guidance, confidence has
increased in the location of the main swath of 4-7" (along and
north of I-94). It`s not always the case, but it is worth noting
that the longer range of the RAP can suffer at times,
especially in a fast moving pattern such as this. With the RAP
being a regional model, it depends on boundary conditions from
another model (in its case, the previous run of the GFS). The
HRRR can suffer a bit more, given its domain is even smaller and
is fed its boundary conditions from the previous run of the
RAP. Keeping all that in mind, it is fair to assume that this
southward trend of both these hi-res models are receiving
improved boundary conditions and doing a better job of handling
the evolution of the system now. Snowfall totals gradually fall
off south of I-94, with around 2-4" near the MN river valley and
closer to 1-2" across southern MN.
There are few things that may impact totals: 1) Snow to liquid
ratios will be key. We are expecting anywhere between 12:1 and
17:1, with areas further north getting more bang for their buck
(thanks to the cooler air). 2) strong winds could lower ratios,
but we are not expecting that to play as big of a role with the
heaviest snow falling ahead of the increase in winds. 3) some
compaction may occur, however given we are expecting light,
fluffier snow, that should not play a big role either. Hence all
of that together, the higher snowfall ratios are what gives
higher confidence in seeing this swatch of 4-7", with potential
for even some locally higher spots.
Friday and Beyond... A cool down will occur heading into the
weekend as a Canadian high pressure slides in behind the
modified Clipper. That should result in a period of clearer
skies and lighter winds Friday and part of Saturday. In
combination with a fresh snowpack from Thursday`s system, there
is a chance to over perform with lows. Bottom line, it will feel
cold and wintry to end the week. There will be a chance for
light snow in western MN overnight Friday as a system weakens
coming out of the Dakotas, but it should be low impact if any
snow does fall.
Ensembles continue to hint that the next shot of
precipitation could come overnight Sunday into Monday as a
surface low ejects out of the Rockies across the Upper
Mississippi River Valley. This will be a tricky forecast because
of how the low-level moisture will likely be lacking initially,
causing development to occur somewhere across MN into western
WI. Temperatures will also be a bit warmer, leading to p-type
uncertainties. All that said, if we are able to hold onto a few
inches of snow heading into next week... and potentially add a
couple more on top... there could be a decent chance of having a
white December 25th. A steady warm-up looks likely all next
week, with temperatures trending to the upper 30s and low 40s by
Friday.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 535 PM CST Wed Dec 18 2024
Brief lull in aviation concerns this evening, as the slow to
depart MVFR stratus deck finally exits into central Wisconsin
over the next few hours. Concerns then turn to the northwest, as
a broad shield of snow moving through the Dakotas is set to
turn southeast move across the region tonight through tomorrow
afternoon. General theme remains consistent in the TAFs, with
light snow starting after midnight for AXN/RWF and spreading
east overnight. Heavier snowfall rates will arrive in the first
few hours following precipitation onset, with visibility falling
to 1 SM or less during the heaviest period. TEMPOs have been
introduced to capture the period of heaviest snowfall rates at
each terminal, with 1/2SM visibility likely. IFR or lower
ceilings will accompany the heavier snowfall rates. Light snow
will continue into Thursday afternoon, prior to ending from west
to east. Storm total accumulations between 4-7" at AXN, STC,
MSP, RNH, & EAU. The latest forecast calls for 3-5" of total
accumulation at RWF & MKT.
Winds are forecast to increase out of the southeast tonight and
are expected to gust up to 20 knots or so by daybreak. Winds
will remain gusty as they turn out of the northwest Thursday
afternoon/evening.
KMSP...VFR this evening, prior to the arrival of light snow
around 08z. Snow rates will increase prior to daybreak, with the
heaviest snow expected between 12-16z. Have included a TEMPO for
1/2SM during this period. Periods of light snow will continue
through the afternoon, before the storm system moves southeast
of the terminal. Bulk of the 4-7" accumulation expected during
the morning, with another half inch to inch during the
afternoon. Southeast winds increase overnight and will flip out
northwest Thursday afternoon.
/OUTLOOK FOR KMSP/
FRI...VFR. Wind NW 5-10kts.
SAT...VFR. Wind E 5-10kts.
SUN...VFR. Wind SE 10-15kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Winter Storm Warning until midnight CST Thursday night for
Anoka-Benton-Carver-Chisago-Dakota-Douglas-Hennepin-
Isanti-Kanabec-Kandiyohi-McLeod-Meeker-Mille Lacs-
Morrison-Pope-Ramsey-Scott-Sherburne-Stearns-Stevens-Todd-
Washington-Wright.
Winter Weather Advisory until 3 AM CST Friday for Chippewa-
Goodhue-Lac Qui Parle-Le Sueur-Nicollet-Renville-Rice-
Sibley-Swift-Yellow Medicine.
WI...Winter Storm Warning from 3 AM Thursday to 3 AM CST Friday for
Barron-Chippewa-Dunn-Eau Claire-Pepin-Pierce-Polk-Rusk-
St. Croix.
&&
$$
UPDATE...Hewett
DISCUSSION...BED
AVIATION...Strus
Area Forecast Discussion
National Weather Service Marquette MI
1028 PM EST Wed Dec 18 2024
.KEY MESSAGES...
- Lake effect snow will taper off overnight. Before it does
though, another 1 to 2 inches of snow is expected in the
northwest wind snow belts of the eastern forecast area.
- A clipper system will bring widespread light to moderate snow
across the UP Thursday through Friday morning. Highest
snowfall totals will be in Menominee County where lake
enhancement could produce upwards of 6 to 8 inches.
- Another system could potentially bring a few inches of snow
on Monday with likely drier and warmer conditions behind the
system for Christmas Eve into Christmas Day
&&
.UPDATE...
Issued at 1027 PM EST Wed Dec 18 2024
Water vapor imagery and RAP analysis show a well-defined shortwave
over eastern MT. As this wave heads to the Upper Mississippi Valley
on Thu, it will spread snow into Upper MI. Trends from 18z and 00z
model guidance are notably slower in bringing the snow into the
area. Fcst updates this evening have been to refine the onset timing
of the snow, and this results in headline start times being pushed
back 3-6hrs. Menominee County still has the best shot at reaching 6
inches or so with lake enhancement off of Lake MI. Looks like there
may be a period of decent lake enhanced snow into
Baraga/Marquette/western Alger counties later Thu night/Fri morning
in association with sharp sfc trof passage. At the moment, models
indicate timing of this heavier snow will probably coincide with the
Fri morning commute in the Marquette area. Will be something for
future shifts to take a closer look at.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 152 PM EST Wed Dec 18 2024
Mid-upper level trough stretching from Hudson Bay southward to the
Gulf Coast has supported a colder airmass over the region. SPC
mesoanalysis suggests 850mb temps between -16 and -11C while Lake
Superior is running between +5 and 7C, per GLERL. This difference
has been more than sufficient for lake effect snow shower
development and KMQT radar has been able to observe these showers
pressing southeastward into Upper Michigan through the day. Where
radar coverage is lacking, webcams and surface obs suggest the
shower coverage is widespread downwind of Lake Superior and into
northern Wisconsin. Temperatures have been cooling slightly through
the day across the west half while the east has remained stable in
the mid to upper 20s.
Upstream high pressure, currently over the eastern Dakotas and
northern Minnesota, will lift northeast into Ontario this evening,
then continue pressing eastward overnight while a clipper exits the
northern Rockies and presses southeastward across the northern
Plains. This transition should result in lake effect tapering off
thanks to increasing dry air/subsidence and winds gradually shifting
to the southeast. The west half should see this change soon and
through the afternoon/evening and a mostly dry overnight period. The
east will be a little slower to see these effects and can expect
continued lake effect overnight. Another inch or so of snow can be
expected this afternoon through tonight in the west. In the east,
the longer duration of the showers could produce 1 to 3 inches in
the favored northwest wind snowbelts. With this in mind, opted to
cancel the inherited winter weather advisories in the west and
maintain the ones in the east, for the time being. These are
currently set to expire at 6z Thursday. Overnight lows should dip
into the single digits for most interior locations across the west
half. Elsewhere overnight temps should fall into the teens to near
+10F.
&&
.LONG TERM /THURSDAY THROUGH WEDNESDAY/...
Issued at 409 PM EST Wed Dec 18 2024
Active weather continues through the long term forecast starting off
with a clipper low diving southeast out of the northern Rockies
early Thursday through Friday morning. As the surface low pressure
nears Upper Michigan tomorrow morning, WAA/isentropic ascent will
force light to moderate snow across the UP. There is still some
uncertainty on the exact track of the low through the day, with
hi-res short range guidance continuing a more northern track
through south-central Wisconsin, while global guidance has been
consistent on a southern track along the WI/IL border, or
further south. The implications could mean an increase or
decrease in system snowfall totals with forcing being displaced
closer or further away from home. Regardless, Menominee county
will likely be the winner of who sees the most snow since both
tracks are favorable for lake enhancement via Lake Michigan.
North Lake Michigan water temps are still hovering in the 5-10C
range, resulting in a period of lake induced delta-Ts near
~12-14C late Thursday night. Snowfall rates during this
timeframe could reach near 0.25-0.5"/hour. As a result, have
opted to include Menominee county in a Winter Storm Warning
where 3-6 inches of snow is expected overnight and locally
higher amounts upwards of 6-8 are possible where lake
enhancement occurs. Nearby Lake Michigan adjacent counties Delta
and southern Schoolcraft could see a slight boost in snowfall
as well, though the highest confidence remains to the south in
Menominee county and into northeast Wisconsin.
As the surface low continues south and east across the Ohio River
Valley, hi-res guidance has been consistent in depicting a SW/NE
lake enhanced/effect band translating from northern Lake
Superior dropping into the Keweenaw and west early Friday
morning. This could provide a quick 1-2 inches of snow given
sufficient lake induced instability and convergence. This band
wobbles into the central UP through the afternoon, however,
should see a weakening trend as high pressure building in from
the northern Plains will work to lower inversion heights from
west to east through the day. The rest of the weekend should be
fairly quiet with cold north/northwest flow providing enough
support for light lake effect snow showers.
Expect a general warming trend for Christmas week as warm air from
more tropical areas of the Pacific moves over the Rockies and
downslopes into the Canadian and U.S. Plains. That being said, it
does look like we will hold on to cooler temperatures a little
longer early next week, enough to allow another warm advection
snowfall event to potentially occur on Monday as a wave moving over
the northern Rockies is forecast to track through the Northern
Plains into the Western Great Lakes. Models showing remarkably good
agreement on the track of this system five days out, and if model
consistency continues to hold over the next several model runs
forecast confidence will increase on the potential for a widespread
few inches of snow across the U.P. on Monday, increasing chances for
a white Christmas over much of the area.
After Monday`s system weakens and moves east, models indicate drier
and warmer conditions for Christmas Eve into Christmas Day as weak
ridging moves over the area and high temps possibly reach at or
above freezing both days. CPC`s extended outlook paints a bleak
picture for winter lovers in the northern CONUS with very high
probabilities for above normal temperatures to finish out the
rest of 2024.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 703 PM EST Wed Dec 18 2024
Sfc high pres ridge will pass across the area overnight thru early
Thu, bringing an end to lake effect shsn. An approaching disturbance
will then bring -sn into Upper MI during Thu. At IWD, MVFR cigs will
scatter out to VFR overnight with passage of sfc high pres ridge.
MVFR cigs will then return late Thu morning as -sn develops. Vis
should drop quickly to IFR and then remain IFR until near the end of
the fcst period. At CMX, expect MVFR cigs to prevail thru the night.
Flurries/-shsn will linger for much of the evening, but don`t
anticipate vis dropping out of VFR. If it does, vis will only
briefly fall to MVFR. Expect MVFR cigs at CMX to scatter out to VFR
Thu morning. MVFR cigs will return in the aftn with -sn developing
late aftn. At SAW, MVFR cigs will prevail thru the night with
flurries lingering for the next few hrs. Expect improvement to VFR
early Thu morning. Light snow will arrive at SAW mid to late aftn
with conditions falling to IFR.
&&
.MARINE...
Issued at 409 PM EST Wed Dec 18 2024
Gusty northwest winds 20-30 knots mostly over the eastern lake
diminish tonight and remain below 25 knots through Thursday morning.
A clipper low will pass to the southwest of Lake Superior Thursday
afternoon and continue towards the Ohio River Valley into Friday.
With its passage, southeast winds pick up to near 20 knots late
Thursday evening, then veer to the northeast early Friday morning
where gusts upwards of 20-30 knots will be possible across western
Lake Superior. As of right now, not expecting any gale force gusts,
however an isolated gust to 35 knots can`t be completely ruled out
Friday morning (<20% chance). Wave heights will build to 3-6 feet in
the west half, with the highest waves east of the Apostle Islands
Friday morning. As the surface low pressure continues pulling
further southeast and high pressure begins to build in from the High
Plains, winds will turn out of the north-northwest through Friday
evening, gusting upwards of 20-30 knots across the east and central
lake. Not expecting any gales with this slight wind shift but a
stray 35 knot gust is possible (<20% chance) north of Pictured Rocks
Nat`l Lakeshore overnight into early Saturday morning.
Winds and waves remain calm through Sunday. Low pressure moving
through the Upper Midwest could bring southerly gales early next
week, however, confidence at this time range remains low (<30%).
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Weather Advisory from 4 PM Thursday to 7 AM EST Friday
for MIZ001-003.
Winter Weather Advisory from 7 AM EST /6 AM CST/ Thursday to
10 AM EST /9 AM CST/ Friday for MIZ002-009.
Winter Weather Advisory until 1 AM EST Thursday for MIZ006-007-
085.
Winter Weather Advisory from 6 AM Thursday to 3 AM CST Friday
for MIZ010-011.
Winter Storm Warning from 9 AM Thursday to 6 AM CST Friday for
MIZ012.
Winter Weather Advisory from 10 AM Thursday to 7 AM EST Friday
for MIZ013-014.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
UPDATE...Rolfson
SHORT TERM...JTP
LONG TERM...BW
AVIATION...Rolfson
MARINE...BW
Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1018 PM EST Wed Dec 18 2024
...New UPDATE...
.UPDATE...
Issued at 959 PM EST Wed Dec 18 2024
No significant changes for the evening update. Mainly just made
some adjustments to the next 6hrs or so of PoPs to come in line
with current radar trends, as well as winds to account for current
gusty north winds. For the latter, trended heavily towards the
last two runs of the HRRR which seem to be handling the gusty
conditions well. Otherwise, that`s about it. Rain has pretty much
cleared the area to the east, although there`s likely still some
showery conditions in the mountains as the onset of upslope flow
is coincident with plenty of low level moisture. That should abate
within the next couple of hours though for dry conditions the
rest of the night.
&&
.SHORT TERM...
(This evening through Thursday)
Issued at 241 PM EST Wed Dec 18 2024
Key Messages:
1. Thunderstorms will continue to wind down this evening with
time, turning into showers. Trending drier after sunset into
tonight.
2. Cold front passage tonight will send drier air and cooler
temperatures for Thursday. Sunshine will return as well.
Discussion:
Left over thunderstorms from the initial line are about at our
eastern CWA border at this time. SPS or less level with isolated
lightning. Things will continue to trend downward as far as any
sort of wind threat or thunderstorm potential. Most of the showers
out there don`t have any thunder with them. Peak gusts only
recorded in the low to mid 30`s mph, especially at CHA, TYS, and
southwest VA. Looking at historical rainfall reported since this
morning, the heaviest of the rainfall fell west of the plateau
making it seem like the plateau rung out most of the moisture. As
much as over a half inch maxes with today`s event currently, but
of course that might not capture the heaviest shower/storm over an
area without reporting equipment.
Any threat for thunderstorms and gusty winds will soon end and
turn more showery behind the squall line that moved through
earlier this afternoon. Rainfall expected to end west to east.
Towards 00Z and after, chances for precipitation drop off with the
greatest chances lingering over the mountains. Patchy fog may be
possible tonight for anywhere that may clear out before sunrise.
Dry air and thus cooler temperatures, will follow the decreasing
precipitation chances tonight and into tomorrow. 50s dew points
today will drop to the 30s and 40s for Thursday. Low temperatures
may range in the 30s. With high pressure shifting east from
central Canada, clouds will dissipate into Thursday, providing dry
weather and highs ranging in the 40s to 50s after highs this
afternoon nearing 70 degrees.
&&
.LONG TERM...
(Thursday night through next Wednesday)
Issued at 241 PM EST Wed Dec 18 2024
Key Messages:
1. Turning colder for Thursday through the weekend.
2. Scattered rain and snow expected Friday afternoon and night.
Accumulating snowfall expected in the mountains with 1 to 3 inches
above 2500 feet.
3. Dry Sunday through Tuesday, with a gradual warming trend for
Monday and Tuesday.
4. Mild conditions and rain chances arrive by Christmas.
Discussion:
A quick moving shortwave trough and clipper low pressure system will
dive southeast across the Ohio Valley and Central Appalachians on
Friday with northwest flow behind the front. This will produce
orographic lift and continued precipitation across the higher
elevations of our forecast area Friday afternoon through Saturday
morning. Accumulating snow is expected across the mountains with a
mix of rain and snow across lower terrain with no impacts for valley
locations. Overall, 1 to 3 inches of snow will be possible across
the higher elevations of the mountains with locally higher amounts.
If this forecast trend continues, a Winter Weather Advisory will
likely be needed in subsequent forecast updates.
Flurries taper off on Saturday with clearing sky conditions. As
ridging builds in, upper-level heights rise to above normal levels
early next week with gradual warming conditions. Dry weather
continues through early next week.
Southerly flow and increasing moisture ahead of a low pressure
system to our west will result in gradually increasing rain chances
by the middle of next week. At this time, probabilities are
increasing for cloudy, and potentially wet, conditions on Christmas.
&&
.AVIATION...
(00Z TAFS)
Issued at 659 PM EST Wed Dec 18 2024
Flight categories will gradually come down to solid MVFR levels
over the next 1-3 hours as lingering SHRA move out and post-
frontal low clouds move in. These MVFR conditions should then last
through early afternoon before low clouds thin out enough to
return KCHA and possibly KTYS to VFR categories. KTRI likely
remains MVFR through the end of the period.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 70 39 54 35 / 80 40 0 0
Knoxville McGhee Tyson Airport, TN 68 39 50 35 / 90 60 0 0
Oak Ridge, TN 62 37 50 33 / 100 40 0 0
Tri Cities Airport, TN 57 37 48 35 / 90 70 0 10
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
SHORT TERM...CD
LONG TERM....JB
AVIATION...CD
Area Forecast Discussion
National Weather Service Pocatello ID
153 PM MST Wed Dec 18 2024
.SHORT TERM...Tonight and Thursday
Afternoon satellite imagery shows a weak shortwave moving well to
the north of the area across western Montana. This feature is
pushing some additional clouds through eastern Idaho but not much
in the way of appreciable precipitation. There remains a slight
chance we get a brief snow shower across the central mountains and
near the Montana Divide but for the most part, things will remain
dry. Hi-res CAMs aren`t too excited about the potential but the
forecast at least shows a brief period where some precipitation
could be realized. For the overnight, the only weather concern
will be for stratus/fog across parts of the upper Snake Plain,
upper Snake highlands and into the Arco Desert. There remains
abundant moisture in the lower levels in these areas and with high
pressure building over the region, there is at least some
potential. Forecast shows at least some patchy freezing fog
wording as such. High pressure ridge continues to build over the
region tomorrow keeping things dry and temperatures on the warmer
side of normal. McKaughan
.LONG TERM...FRIDAY THROUGH NEXT WEDNESDAY
No changes noted in the long-term as a ridge of high pressure
brings quiet weather through Saturday, followed by a transition
back to an active pattern with shortwave troughs bringing
elevation-dependent rain and snow chances Saturday night and
Sunday, then again Sunday night and Monday, then again Tuesday
night and Wednesday. These features continue to look relatively
short-duration with little wind and only modest rainfall/snowfall
amounts, perhaps supporting slick conditions at some mountain
passes with each wave. The Tuesday night/Wednesday system
continues to look the wettest, but with high temperatures topping
out in the upper 30s to lower 40s each day over this entire
period, chances for a white Christmas do not look great for most
lower-elevation population center...especially from the Snake
Plain south and west.
&&
.AVIATION...
VFR conditions have generally returned to the region and should
dominate the TAF period. Quite a bit of moisture remains in the low-
levels, so of course we need to talk about fog and low stratus
potential. On the one hand...impacts were a bit less than forecast
this morning, tonight and Thursday morning may be SLIGHTLY drier,
winds may remain a touch more elevated/breezier at least into early
tonight, and there isn`t strong support for fog/stratus in most of
our guidance. On the other hand, the HRRR and NBM still do feature
some development out over the Snake Plain perhaps getting close to
KPIH and KIDA, surface RH values will remain quite saturated, and
overall cloud cover at all levels should be less tonight, which
conceptually could support better radiational cooling and give fog a
better chance to coalesce. This all leads to a somewhat low-
confidence forecast for cigs/vsbys. Best potential appears to be at
KIDA, so for now have hinted at VCFG and SCT008 starting around
09z/2am. Future shifts will continue to evaluate this potential.
KPIH and KDIJ can`t completely be ruled out either, while confidence
is higher in no fog/stratus impacts for KBYI and KSUN.
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$