Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/22/21
Area Forecast Discussion
National Weather Service La Crosse WI
530 PM CST Tue Dec 21 2021
.SHORT TERM...(This evening through Wednesday)
Issued at 250 PM CST Tue Dec 21 2021
GOES water vapor imagery showing a dynamic but fast moving
shortwave trough in WI with good subsidence over much of NW WI at
1945Z. This is corresponding with a well depicted 500-300mb
QVector convergence/divergence dipole signal in the latest RAP
analysis and forecast. Surface low pressure has reformed and
intensified over the MI U.P. associated with this strong forcing
and the shortwave trough becoming negatively tilted. Surface
pressure tendencies show a great dipole now of -7mb/+4mb 3 hr MSLP
change over eastern WI and western MN, respectively. This
gradient overhead, along with cold advection and steepening lapse
rates, will cause gusty winds to 30-35 mph for some hours into the
evening. Snowfall should be winding down across northcentral WI
over the next hours with very little additional accumulations.
Overall, stability increases overnight with diminishing wind
gusts.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 250 PM CST Tue Dec 21 2021
Key Messages
-Periodic snow/rain threats clutter the forecast into next week.
-Near seasonal temperatures overall, with a brief warmup into the
40s on Friday.
Winds decrease late tonight into early Wednesday morning as the
pressure gradient relaxes ahead of transient surface ridge. The
weather for Wednesday should be quiet with the region situated
between the polar and subtropical jets, with periods of sun and high
clouds streaming over the Rockies. By Wednesday night, a subtle
impulse crests the subtropical jet and slides through the Upper
Midwest Thursday morning. Moderate WAA/mid-level isentropic ascent
ahead of the H500-300 trough axis should lead to a band of light
snow, mainly over Wisconsin. However, there remains a modest spread
with the QPF axis between the CPM/longer range CAM solutions and
have kept PoP forecast broader that what the eventual snow band
footprint will probably shape up to be. Given the transient nature
of the forcing and lack of any deep moisture, impacts should be
fairly minimal.
The precipitation forecast for the end the week and into early next
week remains on the lower confidence side, both in terms of the
precipitation potential and impacts. The breakdown of the Polar
Vortex will result in a quasi-stationary upper low over western
Canada, sling-shotting PV lobes across the region in rapid
succession within a west to southwest flow pattern. The first of
these ripples passes through on Friday, followed by a second
negatively-tiled trough for Saturday and then the third in the
caravan Sunday night into Monday. Temperatures on Friday look to
warm into the 40s as warm air streams north of the initial wave,
but this will be fleeting as Canadian air surges southward in its
wake. The weekend systems may have more potential for impacts with
the EPS clusters latching more onto the latter wave, but the
temporal consistency of these solutions remains on the low side.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 530 PM CST Tue Dec 21 2021
The MVFR cloud shield will clear KRST and KLSE by around 22.00Z.
However, patchy SCT/BKN MVFR/low VFR ceilings remain possible
through the evening with NW winds gusting to 20-25 kts. Winds will
diminish overnight and any lingering low clouds will erode with
the approach of high pressure. Otherwise, expect VFR conditions
with some increase in mid/high clouds later tonight into
Wednesday morning. Light winds early Wednesday will increase from
the south, with some gusts in the 20-25 kt range by afternoon.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...Baumgardt
LONG TERM...Skow
AVIATION...JM
Area Forecast Discussion
National Weather Service Cleveland OH
936 PM EST Tue Dec 21 2021
.SYNOPSIS...
A low pressure system moving through the central Great Lakes
tonight will drag a strong cold front across the region. High
pressure returns Wednesday afternoon before the next area of low
pressure pulls a warm front into the region late Thursday into
Friday.
&&
.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
Cold front is making rapid progress east and is now entering the
northwest corner of Ohio at this time along with the associated
cloud cover. Latest guidance still suggesting temperatures will
fall through the night after frontal passage and bottom out
around 12Z in the morning. There will be a brief slight rise
during the morning and then level off through the afternoon as
colder air pushes deeper into the local area. Went ahead and
lowered temperatures a degree or two to maintain nearly steady
temperatures through the day tomorrow. Otherwise, no other major
changes with this update.
Original Discussion...
A cold shot is on tap late tonight into Wednesday as a mid/upper
shortwave trough, currently analyzed over the upper Great Lakes,
progresses through the central Great Lakes and Ontario Province
tonight dragging a strong cold front across Lake Erie and NE
Ohio/NW PA. The front is progged to cross in the 07 to 12Z
timeframe bringing a seasonably cold blast of air as a fairly
deep longwave trough drops 850 mb temps to -12 to -14C by mid
morning Wednesday. This strong cold air advection across the
roughly 42F lake will lead to a lake to 850 mb delta t of 15 to
20C late tonight through Wednesday morning. This is conditional
instability with lake induced CAPE values greater than 300 J/Kg.
An initial west to southwest fetch (250-260 deg) ahead of the
front will quickly veer to northwest as the front crosses
between 08 and 12Z. Low-level convergence will be maximized in
this timeframe immediately ahead of the front, so a west-east
band of lake-effect snow, aided by mid-level Omega ahead of the
front, will blast quickly onshore from north to south. HREF CAMS
suggest this band starting around Erie, PA around 07Z then
pushing through Ashtabula, Lake, Geauga, and Cuyahoga Counties,
as well as portions of Lorain County, in the 09-12Z timeframe.
This will bring a burst of snow to most of these areas,
including part of the morning commute. The limiting factors with
this event are the following. 1) Inversion levels only rise to
around 7000 feet with equilibrium levels only slightly better,
and these levels are confined to a short 07 to 12Z window before
lowering through the morning. 2) Moisture and Omega within the
optimal -12 to -18C DGZ is lacking the entire time with only
45-55% RH at best detected off NAM and RAP BUFKIT soundings.
3)The quick veering of boundary layer winds to NW will move the
band quickly through. This all points to a minor event with most
areas in the Ohio snowbelt from Lorain County east seeing 0.5
to 1 inch of snow or less. Erie County PA will see 1 to 2 inches
due to the band persisting a bit longer before shifting. The
biggest impact will be the early morning commute timing.
Surface high pressure will build across the Ohio Valley through
the day Wednesday, so the NW flow will become more anticyclonic
through the afternoon with increasing shear. This will also
scour out the moisture quickly as well as rapidly lower the
inversion. Light lake-effect snow showers and flurries will
persist across inland NE Ohio and NW PA into mid afternoon, but
do not expect more than a dusting of additional snow anywhere
before completely ending Wednesday evening. Think that the flow
will stay NW enough that any lingering band off of Lake Huron
will be funneled into western New York, so even dried out NW PA
in the evening. Highs Wednesday will be much colder with low
30`s expected. Radiational cooling as the high centers over the
Ohio Valley Wednesday night will drop lows into the low 20`s as
skies clear.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
A relatively weak shortwave trough will move east across the Great
Lakes region Thursday through Thursday night. Isentropic lift and
moisture content will be sufficient for a little, scattered
precipitation field moving across north-central Ohio to northwest
Pennsylvania Thursday afternoon through Thursday evening.
Precipitation type will primarily support a rain/snow mix though
will likely be all snow for inland northwest Pennsylvania. Snow
accumulations at this point look to be a half inch or less.
Southerly winds develop on Friday, causing advection of warm
temperatures into the area. This will allow highs to reach to the
upper 40s to low 50s (except northwest Pennsylvania where highs will
remain in the low to mid 40s). A shortwave trough and associated
surface low will move across the area, allowing for rain showers to
impact the area Friday evening through Friday night.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
Aforementioned shortwave trough/low combo will be quickly followed
by another system on Saturday, allowing for another area of rain
showers to impact the region all day Saturday and perhaps into
Saturday night. Cold air advection behind this system will allow for
a transition to rain/snow and maybe all snow late Saturday night.
Significant uncertainty remains in the forecast for Sunday onward as
model guidance show significant differences. For now, will go with
an ensemble mean of chance precipitation each day and slightly above
normal temperatures until models can converge onto a general
synoptic pattern.
&&
.AVIATION /00Z Wednesday THROUGH Sunday/...
A cold front will move east across the area overnight and winds
behind and just ahead of the front will begin to increase.
Expecting MVFR clouds to move into the area with the cold front
but is expected to remain dry over much of the area. Some lake
effect rain/snow showers then all snow showers are expected
across northeast Ohio and northwest Pennsylvania later tonight
into tomorrow. MVFR visibilities will be possible at Erie
through much of the day in the snow shower activity. Winds will
be gradually diminishing tomorrow.
Outlook...Non-VFR possible Thursday as an upper level
disturbance moves southeast across the area. A better chance for
non-VFR is expected for late Friday afternoon in response to a
warm front lifting northeast across the area. This will continue
through Saturday. Another chance for non-VFR expected Sunday
afternoon.
&&
.MARINE...
Low pressure moves east across the Great Lakes region tonight, with
southwest winds rapidly increasing to 20-30 knots this evening into
tonight. A cold front associated with the low will move east across
Lake Erie tonight, allowing for winds to shift to out of the
northwest tonight. Northwest winds will hold around 20-30 knot
behind the frontal passage through the morning hours before
diminishing through Wednesday afternoon/evening. A Small Craft
Advisory will be in effect for this reason, starting this evening
and gradually expiring from west to east Wednesday evening through
Wednesday night. High pressure ridge moves east across the lake
Wednesday night with southwest winds developing on Lake Erie once
again Thursday onward somewhere between 10-20 knots, though there is
low confidence in the wind speed forecast due to model variability
Thursday onward. Winds generally stay out of the south and west
through at least Saturday.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...Small Craft Advisory until 1 AM EST Thursday for LEZ147>149.
Small Craft Advisory until 4 PM EST Wednesday for LEZ142>144.
Small Craft Advisory until 10 PM EST Wednesday for LEZ145-146.
&&
$$
SYNOPSIS...Garuckas
NEAR TERM...Garuckas/Lombardy
SHORT TERM...Saunders
LONG TERM...Saunders
AVIATION...Lombardy
MARINE...Saunders
Area Forecast Discussion
National Weather Service Gray ME
1034 PM EST Tue Dec 21 2021
.SYNOPSIS...
A warm front will lift north across the region tonight into
Wednesday bringing a period of wintry weather as it does so.
High pressure will quickly return Thursday but gusty west
northwest winds will bring in colder temperatures. A weak
clipper type low will pass south of the region Friday night and
Saturday morning which would provide some light snow or rain.
&&
.NEAR TERM /TONIGHT/...
1030PM UPDATE...
Still seeing sustained cooling across the center of the forecast
area in between the two areas of cloud cover. Lowered forecast
temperatures a bit more in this region, although eventually the
clouds will spill in from the south and halt the cooling. Also
delayed onset of precipitation a bit. Otherwise no significant
changes in forecast thinking.
730PM UPDATE...
Much of our area is currently sitting between two areas of
higher clouds, allowing some decent cooling conditions
especially across the center of the forecast area this evening.
This will set a colder stage for the onset of precipitation by
early morning. Made some adjustments to temperature and
precipitation forecast, with the primary adjustment being to
simplify the weather types by removing the drizzle. Some
freezing drizzle is possible by early morning, but the practical
impact of this will be the same as freezing rain so preferred to
stick to one type of freezing precipitation for the event.
ORIGINAL DISCUSSION....
Thru the bulk of the overnight the weather is expected to be
quiet. Clouds will gradually increase from the S and W. Temps
will fall initially but then begin to level off as WAA begins. I
expect the interior to stay cold while we begin to warm
slightly near the coast and in the CT River Valley. Precip
largely holds off until closer to 4 AM.
&&
.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
730PM UPDATE...
Made some minor adjustment to the forecast for this period
primarily to simplify weather types and remove mention of
drizzle or freezing drizzle. Overall thinking for icing
locations and total snow and ice amounts has not changed much.
ORIGINAL DISCUSSION...
***Icy Conditions Likely Wednesday***
Very complex forecast on tap for Wednesday. The major difficulty
is ptype across most of the area.
The situation overview is that a coastal storm is forecast to
develop and pass largely on the outer edge of the Gulf of ME.
Ahead of the storm precip will focus within an inverted trof
before transitioning mostly to precip shield forced on the NW
side of the low. The storm will pull away later Wed followed by
a period of gusty WNW winds and upslope snow showers.
With the initial precip tonight in the inverted trof ptypes look
to be mainly drizzle. Low levels are saturated but snow growth
zones will not be. Ptype will be determined by surface
temps...freezing drizzle where they remain below freezing. I
expect that to be most of the area so I have freezing drizzle in
the forecast prior to about 7 AM.
Once deeper moisture moves in and a larger shield of precip
develops the ptype forecasts get more complicated. Some guidance
like the NAM are quiet warm in the boundary layer. HRRR and HREF
along with global guidance is colder and hangs on to damming
longer. I have opted for warmer guidance aloft but colder at the
surface. This results in a forecast for a band of freezing rain
from SWrn NH thru the Capital Region of ME. The best chances of
freezing rain will accumulation approaching a half inch flat
ice/0.2 inches radial will be interior Wrn ME. I have also
brought some above freezing temps into the coast with a change
over to rain...but that is lower confidence given the tendency
for cold air to hang tough. Winter weather advisories were
already in place for these areas and some ice is still expected
before any warm up...so no change in headlines other than to
expand one zone into Cheshire County NH.
To the NW of the freezing rain...especially across the White
Mtns and Wrn ME mtns the amount of snow will be tricky too.
Forecast soundings are very close to isothermal around 32
degrees. So it could be heavy, wet snow...or it could be lighter
snow with poor snow growth depending on how deep the moisture
gets. The best combination of forcing and moisture will be
approaching Moosehead Lake in our forecast area. Here several
inches are likely...with amounts pushing 6 inches possible near
the lake. I have issued a winter weather advisory for snow for
central Somerset County.
Precip quickly moves out Wed evening. CAA begins and clears out
much of the forecast area with gusty WNW winds. In the mtns
upslope snow showers are expected to continue into Thu morning.
An additional couple inches of snow is possible in the favored
west facing slopes.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Models advertising some changes coming to the 500 MB pattern
across the N Hemisphere, with downstream blocking breaking down
starting this weekend, and more zonal flow setting up next
week, which may eventually lead to omega blocking stretched
across NOAM. This pattern will pull some very cold air out of
Alaska, but lock it up in trough over the western Canadian
provinces, which should lead to normal to above normal temps by
next week over New England.
Thu and Fri should be mainly dry and maybe a few degrees below
normal, as sfc high is anchored over Quebec, and noses
equatorward into New England. There is a weak wave that passes
to our S, which could produce a few SHSN Thu night, but POPs are
low. Highs Thu will range from near 20 in the mtns to around 30
in the S, despite a fair amount of sun. Some mid to high clouds
roll through Thu night, especially in the S, which will prevent
lows there from dropping too much but lows range from around 5
above in the mtns to around 20 in the S. Friday will see a fair
amount of cirrus, but still worth a partly sunny call, with
highs a couple degrees warmer than Thu.
The next chc of precip come late Friday night into Saturday. The
Euro has trended this system to a moisture starved clipper,
which would produce little if any snow, while the GFS is a
little more robust and would bring some accumulating snow to
southern and wrn zones late Friday night into Sat morning. It`s
possible that precip changes to rain briefly in S NH and on the
ME coast, assuming we get much at all. Highs range from the
upper 20s N to the mid 30s S, with some clearing possible by
afternoon.
Sun and Mon look dry and seasonable cool, as sfc high becomes
established just to our west, with warmer temps on Tuesday and the
next chc of precip, on Wed.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Short Term...VFR conditions expected thru very early Wed. Then
onshore flow and increasing moisture will bring in a MVFR CIG to
all terminal except HIE and maybe LEB. This CIG will lower to
IFR or lower within a few hours of onset. In addition periods of
FZDZ are expected in the morning before steadier precip moves
in. I expect a band of FZRA during the day...but this may occur
inland from most TAF sites. This puts the greatest chances of
FZRA at AUG...but I do think most sites see it for a time before
any change over to RA or SN. IFR or lower conditions sweep out
of the area during the afternoon Wed. This will be followed by a
return to VFR and gusty WNW winds. Upslope SHSN around HIE will
keep MVFR or lower conditions going thru Thu morning.
Long Term...Mainly VFR Thu-Fri, with possible MVFR and slight
chc IFR late Fri night into Sat morning at least. VFR Sat night
into Sun.
&&
.MARINE...
Short Term...Onshore flow will increase tonight into early Wed
and may gust to 25 kt at times N of Cape Elizabeth. I have
issued a SCA in Penobscot Bay for these gusty winds. Coastal
storm will pass out to sea and cold front will cross the waters
Wed night. Wind may gust above gale force for a time overnight.
I have issued a SCA for Casco Bay and gale watch for the outer
waters for this time period.
Long Term...SCA likely to needed in NW flow Thu into Thu night,
but winds seas subside on Friday.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory from 1 AM to 4 PM EST Wednesday for
MEZ012-018>020-023-024-033.
Winter Weather Advisory from 1 AM to 7 PM EST Wednesday for
MEZ013-014-021-022-025>028.
Winter Weather Advisory from 7 AM to 7 PM EST Wednesday for
MEZ009.
NH...Winter Weather Advisory from 1 AM to 4 PM EST Wednesday for
NHZ006-008>015.
MARINE...Small Craft Advisory from 7 PM Wednesday to 4 PM EST Thursday
for ANZ153.
Gale Watch from Wednesday evening through Thursday morning for
ANZ150-152-154.
Small Craft Advisory from 4 AM Wednesday to 4 PM EST Thursday
for ANZ151.
&&
$$
NEAR/SHORT TERM UPDATE...Kimble
NEAR/SHORT TERM...Legro
LONG TERM...Cempa
Area Forecast Discussion
National Weather Service Jackson MS
914 PM CST Tue Dec 21 2021
.UPDATE...
Updated for evening discussion.
&&
.DISCUSSION...
Clear skies prevail across the ArkLaMis this evening and this will
continue through the night. There could be some patchy areas of
fog early on Wednesday, but currently dense fog is not expected.
Lows tonight will range from the low to mid 30s tonight./15/
Prior discussion below:
Tonight through tomorrow (Wednesday):
Tonight: As split synoptic flow becomes more phased overnight, cold
core low will help sfc low/frontal system move across FL Peninsula &
off the Atlantic seaboard, while N stream energy/front moves through
the Great Lakes. At the sfc, dry front will drag down through the
NE/Mid-Atlantic, Carolinas & across the SE. This will only reinforce
CAA, with mean NW flow. 1023mb sfc high will move across the Ozarks,
keeping dry air & subsidence locked in through the overnight hours.
Clouds will clear, but some lingering low-level moisture & some
crossover temp will be possible, even with low-level drying. Due to
that, leaned towards the RAP & put some patchy fog potential into
the overnight hours. For now, lows will fall into the lower 30s &
some spots could reach near the freezing mark, but dense fog or
freezing fog potential looks unlikely at the moment. Confidence in
dense fog is low so did not introduce into the HWO.
Wednesday: Mean trough/jet energy will dig into the Pacific NW &
Intermountain W Wed, keeping persistent NW dry flow. Low-level
thermo ridge will build through, keeping N-NE winds, & nice warm,
dry & mostly sunny aftn. With thermo profiles warming some 5-6 deg.
C in low levels at 850mb & 925mb, highs will moderate near to
slightly above normal in mid-upper 50s N to low 60s S. /DC/
Wednesday night through Tuesday...
The forecast period begins with a deep high pressure ridge building
from the west and impacting the southeastern region with warmer and
drier conditions. Low level northerly flow looks to keep conditions
dry throughout the end of the week and through the holiday weekend
despite a weak frontal boundary that looks to lift just north of the
central MS region. By Friday afternoon, the Euro and GFS are
trending dry as opposed to the latest Canadian run, which has
showers in the northeastern portion of the CWA. With weak lapse
rates and a very stable environment, this forecast period will opt
out of any chances for showers in the NE, but we will continue to
monitor any changes for the Christmas Eve forecast.
On Friday and Saturday, the llvl pressure gradient is something to
keep an eye on as there is change in pressure favorable for stronger
winds, particularly in the N/NW portion of the CWA. As of now,
nothing has been noted in the HWO, but will be revisited in future
forecast cycles. The main focus over the next couple of days will be
unseasonably high and possibly record breaking high temperatures.
The average temperatures for the end of December roughly range in
the mid to upper 50s. High temperatures will range in the mid to
upper 70s Friday through the beginning of next week, making for a
warm and dry Christmas Eve and Christmas.
The next chance of rain looks to be on Tuesday where a potential
high pressure system off the coast of Florida may drive in southerly
moisture to the region. Otherwise, we look to remain mostly dry and
above average through the beginning of next week. /AJ/
&&
.AVIATION...
00Z TAF discussion:
All TAF sites are VFR this afternoon and this will continue
through much of the night. Patchy fog may bring some MVFR
conditions to sites early on Wednesday. The winds will be light
and variable through much of the period./15/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 34 60 35 65 / 0 0 0 0
Meridian 34 60 32 62 / 0 0 0 0
Vicksburg 33 60 36 67 / 0 0 0 0
Hattiesburg 35 63 34 65 / 0 0 0 0
Natchez 34 62 37 66 / 0 0 0 0
Greenville 35 55 35 63 / 0 0 0 0
Greenwood 33 58 35 64 / 0 0 0 0
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.
&&
$$
15
Area Forecast Discussion
National Weather Service Marquette MI
657 PM EST Tue Dec 21 2021
.SHORT TERM...(This evening through Wednesday)
Issued at 319 PM EST TUE DEC 21 2021
Ongoing snow across the UP continues this afternoon, with
visibilities around a mile or less pretty much everywhere. Snowflakes
are a bit smaller than anticipated, explains the reduced vis without
increase in accums, especially considering the depth of the DGZ and
amount of lift throughout the DGZ column. There are some stronger
winds aloft as the trough lifts through Wisconsin towards northern
Lake Michigan though...so am assuming these stronger winds have some
to do with the smaller flake size and lower SLRs than anticipated.
The drier air ahead of the system as well lead to some loss in snow
amounts and snowfall size for the first hour or two. The 12 to 18Z
ob at the office was only an 11:1 snow with an inch in IMT and at
the office in the same timeframe.
Heading into tonight, CAMS are still hinting at possible convergent
lake-enhanced band across the eastern UP along Lake Michigan. There
are signs of this on KMQT reflectivity as well. While we may be just
short of the warning criteria, still think we will see 1+ in per
hour for the next 2-3 hours along US 2. RAP and HRRR have continued
these chances for the past several hourly updates, although the
amounts have slowly trended downward. While there will be some snow
ongoing still across the far eastern portions of the winter wx
headlines, don`t plan on extending at this time. Light LES will
develop and continue through the night in the NW wind LES belts.
Inversion heights are deeper tonight than last night, but DGZ
saturation depth is on the smaller end. Couple that with some gusty
conditions and we will probably see only modest snowfall amounts
with some better reductions in vsbys and some blsn. Expect 1 to 3
inches across the west, with some potential for higher amounts up to
4-5 inches in isolated locations as some higher-res guidance shows
potential convergent enhancement along M26 near Ont/Houghton county
line. Across the east, 2 to 4 inches is expected, but some CAMs show
a convergent signature traversing across the eastern UP near western
Alger, which could bring isolated higher totals.
By tomorrow, heights begin to rise as sfc ridging skirts by to the
south. Winds will back more to the SW as LES begins to shift off
shore. There could be some ongoing enhancement across Luce County
and to the east, but snowfall will be mostly over with for the day
until another sfc trough approaches on Wednesday night. Temps a
850mb will still be near -16C, so temps shouldn`t climb too high,
peaking somewhere near 20F into the low 20s.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 405 PM EST TUE DEC 21 2021
Last 24hrs of medium range model runs have maintained an overall
consistent depiction of the large scale flow for the next 10 days,
but some rather significant changes have occurred with
amplitude/timing of waves. Flow across N America for the next week
and half will be driven by an anomalously strong ridge over the N
Pacific and Aleutians, extending to the Bering Sea at times. This
will force a downstream western N America trof, which in turn will
tend to force ridging farther downstream over eastern N America.
However, a -AO and -NAO are also present. The AO is forecast to
remain in the negative phase, increasingly negative over the next 7
days. The NAO is forecast to trend briefly to neutral in about a
week, but otherwise, it should remain in the negative phase. The
negative phase of both should work to temper eastern ridging and the
warmth downstream into the Great Lakes that would be expected to
result from the mean western N America trof. End result of this
pattern will be a series of shortwaves ejecting from the western
trof with associated sfc low presures tracking across the Great
Lakes region. Amplitude of western troffing/eastern ridging at the
time of the passage of each wave will determine how much warm air
surges northward with each. Waves will affect the Upper Great Lakes
Thu, Christmas Eve, possibly late Christmas Day, and early next
week. The wave Thu will be a minor snow producer, the wave for
Christmas Eve will likely feature light mixed pcpn, including rain
for at least some of Upper MI, the wave late on Christmas Day may
bring some -sn, and the wave early next week will be another snow
producer. Right now, none of these events are expected to produce
significant pcpn. However, the wave early next week could be a more
important feature to monitor. As for temps, temps will show some
fluctuation due to the series of shortwaves moving across the Great
Lakes region. However, overall thru early next week, expect temps on
the majority of days to be above normal as the bulk of the coldest
air will become held up over western Canada underneath the mean
western trof.
Beginning Wed night, shortwave tracking across northern Ontario on
Wed will send a weakening associated cold front s over Lake
Superior. Shallow caa/wind shift blo 850mb will probably support
some light LES into nw Upper MI along the convergence zone. Front
may not make it onshore into the eastern fcst area before
dissipating on Thu.
On Thu, a couple of weak shortwaves will track e to the western
Great Lakes. Modest waa/isentropic ascent regime should support some
areas of -sn across the fcst area, perhaps beginning w prior to 12z.
Could be a little lake enhancement off Lake MI, but rising temps
will become marginal for enhancement.
Fcst for Fri thru the weekend has become more uncertain due to
timing/amplitude changes of waves ejecting from developing mean
western trof. Changes over the last 24hrs of model runs are fairly
significant. The more well agreed upon scenario from the models
24hrs ago was for a more consolidated shortwave trof to swing
negative tilt into the Great Lakes by Fri evening. Models now show a
more disorganized series of waves exiting e and ne from the
developing western trof. For now, there is still a signal for a
light mixed pcpn event, (ra/sn possibly fzra) for Christmas Eve day.
Trend has definitely been lighter with this pcpn. New change is for
another wave to potentially bring some -sn into the area Sat night
into early Sun. If you have travel plans Fri thru the weekend, be
aware that there may be some light pcpn at times that could make for
slippery road conditions.
Another shortwave is still on track to eject ne to the Upper Great
Lakes early next week. Last 2 deterministic ECMWF runs have trended
stronger with this wave, and today`s 12z run would bring a decent
snowfall to Upper MI Sun night/Mon morning as would the 12z CMC.
However, there is very little support among CMC/GFS ensembles for
such a system right now. Nonetheless, it will be something to
monitor in the coming days. Not much colder air will follow, so it`s
likely that very little or no LES will follow this wave later Mon
into Tue. Given the frequent ejection of shortwaves from the western
trof, there will probably be another approaching later Tue into Wed.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 648 PM EST TUE DEC 21 2021
Low pressure deepening over eastern Lake Superior this evening
will produce gusty northwest winds in its wake tonight. Cigs will
be MVFR to VFR through the period with the more prolonged MVFR
cigs at KCMX in longer duration onshore flow. Vsby could be IFR
this evening at KCMX and KIWD in -SHSN and BLSN but otherwise
expect vsby to improve to VFR late tonight. Generally VFR vsby is
expected at KSAW through the period.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 319 PM EST TUE DEC 21 2021
A low pressure system will deepen overhead tonight as a sfc trough
moves over the Upper Great Lakes. This will bring a quick ramp up to
the winds tonight, with a brief period of NW gales of 35 to 40 knots
across the central and eastern portions of Superior. As a sfc ridge
moves overhead by tomorrow morning, winds will diminish quickly to
around 20 knots...remaining there until around Friday morning.
Southerly winds will increase up to 30 knots across the east on
Friday afternoon. A trough of low pressure will remain over the lake
Friday into Saturday evening, before a cold front moves over the
lake Christmas evening, which will bring NW winds of 20 to 30 knots.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Storm Warning until 8 PM EST this evening for MIZ007-014-
085.
Winter Weather Advisory until 1 AM EST /midnight CST/ Wednesday
for MIZ001>003-009.
Winter Weather Advisory until 8 PM EST this evening for MIZ006-
013.
Lake Superior...
Gale Warning until 6 AM EST Wednesday for LSZ249>251-266-267.
Gale Warning until 2 AM EST Wednesday for LSZ248-265.
Lake Michigan...
None.
&&
$$
SHORT TERM...JAW
LONG TERM...Rolfson
AVIATION...Voss
MARINE...JAW
Area Forecast Discussion
National Weather Service Shreveport LA
942 PM CST Tue Dec 21 2021
.UPDATE...
Sfc ridge axis is directly ovhd this evening and as a result,
winds have become light to near calm across just about the entire
Four State Region. With the absence of any appreciable cloud
cover, should see good radiational cooling conditions overnight as
a result. Fcst overnight low temps are in the ballpark and did not
make any adjustments to temperatures. Did add more widespread
patchy dense fog overnight given the above conditions but its too
soon to know if a Dense Fog Advisory will be required for any of
our locations overnight. Will allow the next shift make this call
if it becomes necessary.
Updated forecast has been sent...13.
&&
.PREV DISCUSSION... /issued 421 PM CST Tue Dec 21 2021/
AVIATION...
VFR conditions will prevail through much of the evening but the
HRRR and the NBM are indicating that dense fog and vertical
visibilities will once again return to areas of our airspace by
late this evening and through the overnight hours. Have hinted at
this possibility overnight across all terminal locations, maybe a
little harder than the above mentioned models but will take
another look with the 06z package.
Should see VFR conditions returning areawide beyond 15-16z
timeframe on Wednesday with only high thin cirrus increasing by
late in the TAF period.
Look for light to near calm winds overnight becoming light east
and/or southeasterly by Wed Aftn with speeds generally under
10kts.
13
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 35 61 44 71 / 0 0 0 0
MLU 35 58 37 67 / 0 0 0 0
DEQ 33 58 38 67 / 0 0 0 0
TXK 34 57 44 69 / 0 0 0 0
ELD 33 56 37 66 / 0 0 0 0
TYR 38 64 49 72 / 0 0 0 0
GGG 35 63 46 72 / 0 0 0 0
LFK 37 66 48 73 / 0 0 0 0
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&
$$
13/13