Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/29/20
Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
533 PM CST Mon Dec 28 2020
.AVIATION...
MVFR cigs will continue to spread from south to north across the
TAF sites this evening. Rain and freezing rain is expected to
develop across the area mainly after midnight. Conditions will
likely be down in the IFR/LIFR range overnight into early
afternoon. Conditions will slowly improve from west to east during
the afternoon on Tuesday.
&&
.PREV DISCUSSION... /Issued 306 PM CST Mon Dec 28 2020/
SHORT TERM...Tonight through Tuesday Night...
Isentropic lift will increase overnight as low level southerly
flow increases over the top of modified shallow cool airmass in
place in advance of a strong approaching trough. With very low
condensation pressure deficits developing, anticipate this will
lead to lowering CIGs and eventually development of widespread
drizzle and/or light rain late this evening and esp after
midnight. Nearly all models including most CAMs at this point, now
show the southern half or so of the area remaining just above
freezing tonight, but quite a bit of guidance (not all, but
including the NBM) does still show temps of 29 to 32 across the
northern Panhandles and a plenty deep layer of sub-freezing air to
lead to frozen precip concerns. While we can`t completely rule
out a mix bag of precip early (esp with some seeder-feeder
potential from current high clouds), the warm nose builds
substantially and quickly overnight and freezing rain and freezing
drizzle should become dominant weather types in the north.
Marginal temps make ice accumulation forecasts difficult, but we
continue to show up to around 1/10" ice in the far north. The
morning commute will be the main concern as temps should climb
above freezing around mid-morning was very strong WAA erodes the
cold air. We have issues a winter weather advisory from 6Z to 16Z
in the northern two rows plus Hartley.
Dynamics from the upper level trough and 100 kt+ jet streak on the
east side will take over in the afternoon as weak SFC low and
assoc trough move east across the area to maintain shra and
possibly even TSTM potential along and east the the trough across
the ERN Panhandles. This is where heavier precip amounts are
expected, although better moisture is shunted east into OK by
around 21Z per H7 theta-e. In addition to the SFC trough that
helps dry out this some from west to east, the low will also user
decent cold front trough the region Tue night. Models have mostly
been backing off POPs for Tue night except for possibly the SE,
but the 18Z HRRR has actually gone the other direction and is back
to showing snow develop (or rain to changing to snow) along the
H7 trough which does appear to have decent convergence along it.
In fact the 18z HRRR produced 2-4" snow along this feature across
a diagonal roughly Potter Co to Lipscomb/Beaver COs with the
localized higher amounts near the good old Canadian River Upslope
added areas near Highway 60 NE of AMA. This will have to be
watched, but for now stuck close to the NBM POPs that are only
20-30 percent in this region with higher values SE.
Gittinger
LONG TERM...
By early Wednesday morning, there should be some lingering PoPs in
the east and southeast, as some snow will likely be lingering.
However, any wrap around precipitation will be short lived as the
main system moves east. The position of the upper low will then
determine if we get anything else this week. The ECMWF keeps the
upper low in Central Oklahoma, which would be just close enough
for some additional wrap around precipitation in the eastern Texas
Panhandle. However, the GFS is slightly further east, which means
a near miss for the eastern Texas Panhandle on Friday. Given the
Euro`s track record for this system in particular, have leaned on
its solution for the forecast, which keeps low PoPs on Friday and
early Saturday in the east.
The end of the year/beginning of the year forecast is looking
pretty good, although it might be a bit cold. Overnight lows
Thursday into Friday will be slightly below normal, but not much.
Lows will likely be in the teens to near 20. Normal lows for the
1st is 23. Afternoon highs for both Thursday and Friday will be in
the lower 40s, which is about 5 degrees below normal. Once the upper low finally moves to the northeast, there should be
a brief warmup, with highs getting back to near 60 degrees for the
first week of 2021.
Next short wave trough will then approach the area by the middle
part of next week. Medium range models and their ensembles are in
decent agreement in the timing and location of this next feature,
but still a bit soon to determine with any confidence on what that
system will bring.
Fox
&&
.AMA Watches/Warnings/Advisories...
TX...Winter Weather Advisory from midnight tonight to 11 AM CST
Tuesday for the following zones: Dallam...Hansford...
Hartley...Lipscomb...Ochiltree...Sherman.
OK...Winter Weather Advisory from midnight tonight to 11 AM CST
Tuesday for the following zones: Beaver...Cimarron...Texas.
&&
$$
15/29
Area Forecast Discussion
National Weather Service La Crosse WI
952 PM CST Mon Dec 28 2020
.UPDATE...
Issued at 945 PM CST Mon Dec 28 2020
A large area of surface high pressure extending over MN/IA and an
an arctic front was still pushing through the area. Temperatures
were in the teens to lower 20s, but in the single digits or colder
behind the front. We are seeing a few flurries with the MVFR
ceilings at Medford and earlier at KRST. These clouds have
decreased over MN with some dense fog developing in southwest MN.
There is a hint on the RAP/HRRR that patchy fog will develop with
the dense fog remaining to the west of KRST. Some patchy dense fog
may develop in northeast IA though.
The forecast for the storm Tuesday afternoon into Wednesday
appears on track. The forecast soundings are initially quite dry,
however between 11am and 2pm really moisten up at KRST and from
1pm and 4pm. The 0 deg 850mb line from near KTOP into central MO
works north toward the southern part of the forecast area by 00Z
tomorrow. Some freezing rain potential and should be greater
closer to the warmer air across our southern county warning area.
The NAM supports a small northern shift of higher amounts and the
00Z HRRR has a small increase in amounts, but still within our
current forecast range. The models continue to have the heavier
snow where our current winter storm warning is. Will want to
watch this warm air and just north of it for high snowfall rates
of 1 to 2 inches per hour. EMC HREF 18z/00Z have a similar
footprint with the heavy snow/isentropic lift/frontogenetic band
from Iowa into southern WI/northern IL, so this is good to see the
run to run consistency. The data is still coming in...but
headlines are looking good for now.
&&
.SHORT TERM...(This afternoon through Tuesday)
Issued at 307 PM CST Mon Dec 28 2020
Clouds continue to stream southeast today per GOES satellite
imagery with a sharp wind shift along an arctic front making its
way through MN. At 17Z the front was located along a DLH-ABR line
with colder air behind...mainly the single digits above zero.
There were also some flurries along the front in the observations.
Some pockets of light snow were also falling across northwest WI
and have added some scattered snow showers in the forecast this
afternoon north of highway 29 in WI.
The arctic front moves through in the early evening with some
flurries and clouds. While there are breaks across the
Dakotas...no confident these will completely clear the area
tonight. Might be kind of messy.
A slightly earlier timing has now focused a bit more concern on
the evening commute and pushed the Winter Storm Watch over to a
Warning for northeast IA and southwest WI. The strong moisture
surge arrives and almost immediately begins nearly 1" per hour
snow rates south of I-90. By 6 pm 2-3.5" inches will have fallen
in MN/IA according to our latest forecast.
.LONG TERM...(Tuesday night through Monday)
Issued at 307 PM CST Mon Dec 28 2020
Many of the winter storm signals remain unchanged for Tuesday
afternoon through Wednesday morning. Among the ensembles, there
remains a decent amount of spread to give a seasoned forecaster
like myself more grey hair. The lower values for the storm appear
to be from a more transient solution, shifting the moisture surge
off to the east more rapidly. However, the deterministic runs do
favor a SW-NE band of frontogenesis that remains in place after
the big push northward of warm and moist advection. This is when
the southern snow amounts climb higher. The 28.12Z HREF and WPC
Superensemble members suggest amounts in the Warning have ~ 50%
potential for 8+". The highest HREF snowfall band is 10-12" across
Clayton and Grant counties. With the speed of the system, it is
still a bit unnerving to go high with snow amounts...but do have
8-9" totals in the far south.
With the broad isentropic lift over the region /290K surface in
the RAP/ widespread accumulating snow will be found by Tuesday
night. The highest impact period looks to be from onset through
about 10 pm Tuesday evening south of Interstate 90. The 28.12Z
SPC HREF indicates 70-80% probabilities of 1"/hr snowfall rates
in that area...which was one reason the Watch was converted to a
Warning. This will be a challenge for plows to keep up with.
Lower snow amounts (a miss) are certainly possible with the
forecast, but the WPC Superensemble of 60 members places a 90%
chance for at least 2" in the north to 5" in the south. This is
rooted in the strong and broad isentropic lift across the region
with this system. So, confidence is high that *everyone* will see
2" of snow. There are also still chances for a wintry mix /sleet/
moving into far southwest WI, although the probabilities are low.
Friday...
Signals continue in the model ensemble data and deterministic
runs for accumulating snow on Friday. At this time it appears WI
is the main snow target with amounts of 1-3 inches as a common
mean in the ensembles. This cyclone will have major Gulf of Mexico
moisture as it heads due north from said Gulf. It appears most of
the impact will be south and east of the area...but this storm
definitely bears watching.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 559 PM CST Mon Dec 28 2020
A brief period of MVFR clouds and flurries is possible early this
evening, with VFR conditions then expected later tonight into
Tuesday morning. A winter storm Tuesday afternoon into the overnight
is expected to bring MVFR and IFR conditions to the TAF sites.
A weak cold front will bring a short period of low VFR/MVFR clouds
and northwest winds early this evening, with a few flurries noted in
upstream observations. Behind this, skies should clear out under
brief high pressure later tonight, with winds gradually turning more
southerly to southeasterly by morning. Will have to watch out for
some patchy fog development with light winds and clear skies,
though confidence in this occurring is low. Clouds will increase
Tuesday morning ahead of a low pressure system approaching from
the west, with snow and MVFR to IFR visibility and ceilings
expected to work into the TAF sites by mid to late afternoon.
Winds could gust to near 20 kts at times in the tight gradient
ahead of the low pressure system Tuesday afternoon.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Warning from noon Tuesday to noon CST Wednesday for
WIZ053>055-061.
Winter Weather Advisory from 6 PM Tuesday to noon CST Wednesday
for WIZ017-029-034-042>044.
Winter Weather Advisory from noon Tuesday to noon CST Wednesday
for WIZ032-033-041.
MN...Winter Weather Advisory from noon Tuesday to noon CST Wednesday
for MNZ079-086>088-094>096.
IA...Winter Storm Warning from noon Tuesday to noon CST Wednesday for
IAZ009>011-018-019-029-030.
Winter Weather Advisory from noon Tuesday to noon CST Wednesday
for IAZ008.
&&
$$
UPDATE...Zapotocny/Lee
SHORT TERM...Baumgardt
LONG TERM...Baumgardt
AVIATION...Lee
Area Forecast Discussion
National Weather Service Binghamton NY
1046 PM EST Mon Dec 28 2020
.SYNOPSIS...
Lake effect snow develops tonight and continues through Tuesday
before dry weather returns later in the day. Dry weather
continues Wednesday before the next shot of rain and snow
Thursday and Friday.
&&
.NEAR TERM /THROUGH TUESDAY NIGHT/...
1030 PM Update...
Lake effect snow bands are developing off lake Ontario as
expected and a weaker band off of lake Erie is extending across
the Southern tier. The Erie band is expected to drift south,
become disconnected from the Lake and dissipate across the far
northern tier of PA by late evening. Meanwhile the band off
Lake Ontario is now becoming better organized on an almost due
westerly flow. CAMs are now in good agreement that this band
will drift south through the NY Thruway corridor (Syracuse to
near Utica) between now and 1AM...then its southward progress
should halt...remaining nearly stationary along the NY Thruway
corridor through at least daybreak. It will be in this time
period that advisory level snow amounts are expected. If the
band becomes well organized, snowfall rates of 1-2 inches per
hour will be possible in and around the Syracuse metro for a
period of time. HRRR Bufkit profiles for SYR show a very
favorable setup for high snow to liquid ratios, with an omega
bullseye in the snow growth layer.....and equilibrium levels
just above 10 k ft agl. Will need to watch this closely, as
there is potential to eclipse the 7" warning criteria quickly if
the band can remain in place long enough.
Then, the lake effect snow band should drift south again into
the hills south of Syracuse, and across Cayuga, Cortland &
Chenango counties by mid morning. The snow band breaks up into
showers and flurries by afternoon.
730 PM Update...
Snow showers are beginning to break out across CNY at this time
as an upper level trough and associated shortwave approach from
the west. Cold air advection is continuing, with 850mb temps
down to around around -8C...but forecast to fall to around -14C
by morning. The overall flow remains 250-260 off of Lake Ontario
and Erie currently; but as this shortwave passes by to the east
the flow is expected to quickly veer around to 290-300 degrees
overnight. Another vort max/shortwave could temporarily shift
the bands back north on a 270-280 flow for a few hours after
midnight...but then it veers back between 300-320 Tuesday
morning as 850mb temps fall to around -15C. West winds will be
breezy at 8-15 mph, with gusts 20-25 mph overnight...increasing
to 10-20 mph with gusts up to 30 mph on Tuesday. This could
cause some localized blowing snow (where lake effect
accumulation occurs). Otherwise, the near term forecast remains
on track and only minor adjustments where made to PoPs, QPF and
Snow amounts with this update. Winter weather advisory remains
in effect for the lake effect snow across Onondaga, Madison and
N. Oneida counties into Tuesday.
330 PM Update...
Low clouds linger across the area, with temperatures having bee
able to peak a little higher than expected, in the mid 40s for
our valley locations. However, the cold front moving through the
rest of the evening will allow temperatures to quickly fall
back through the 30s.
Meanwhile, another shortwave is forecast to ripple through the
area. This will touch off additional chances for some snow
showers across most of central NY this evening into the early
part of the night. Steepening lapse rates courtesy of cooling
air aloft will contribute to a chance for some of these
convective snow showers to take on more squall- like activity,
with periods of higher snow rates and gusty winds. As this will
be well after the evening commute, we are not expecting to need
to issue any additional headlines. Snow totals associated with
this next round of convective snow showers should generally be
less than an inch area-wide, but higher totals in excess of an
inch would be more likely in northern Oneida county, where
westerly flow will lead to some lake enhancement. Higher totals
nearing an inch would also be possible where higher snowfall
rates in any squalls can occur.
However, once this passes through, the primary concern from
midnight onward will be a lake effect snow as temperatures
falling back to as low as -12 to -15 C under west/northwest
flow. Simulated reflectivity shows a band developing across
central Oneida county, then this drops southward and into the
Thruway/Syracuse/Utica area by 3am. This eventually reaches the
hills south of Syracuse by the late morning, but then dissipates
into the afternoon as northwesterly flow starts to veer more
northerly and slackens slightly.
As for totals: additional snow totals up to 2 to 3 inches are
now expected in northern Oneida county as the band may set up
slightly to the south, but higher amounts are not out of the
question where any more persistent snow showers can develop
earlier in the night. Conditions will be most favorable during
a period from 4 am to about 10 am where snowfall rates will be
1-2 inches per hour as the band drops more southward towards the
Thruway. However, if this band checks up and/or slows down
significantly, snow totals could be a bit higher. Expected
totals for southern Oneida, Madison and Onondaga Counties is 2
to 5 inches, especially across a corridor from Baldwinsville to
Cazenovia. Some locally higher amounts are possible Heading
into the late morning, drier air working in will help to cut
down on the presence of ice crystals and lessen our snowfall
rates as the band moves more southward.
The 850mb ridge axis will move in late Tuesday afternoon and
veer the winds more to the north and also usher in some
suppression and a drier air mass. This will allow the snow to
come to taper off after 2 pm and come to an end completely
before sunset. Temperatures will be on the cool side Tuesday
with highs only into the mid and upper 20s. Gusty northwest
winds will make it feel like the teens at times.
Temperatures fall back into the teens Tuesday night as
decreasing winds and partially clearing skies allow for better
radiational cooling, but higher clouds will be working in and
lowering from the west by the early hours of Tuesday. This may
keep lows slightly higher across our western zones compared to
the east.
&&
.SHORT TERM /WEDNESDAY/...
Next storm system is again complex and will come through in two
pieces as per GFS and NAM. First an upper level low and trough is
projected to track just north of the Great Lakes on Wednesday. This
feature is tied to a low-level cyclone which was almost vertically
stacked which reaches south of James Bay Canada by 00z
Thursday. Models shows strong warm advection on a southwest low-
level flow pattern during the day Wednesday across NY and PA.
GFS shows decent isentropic lift between the 290 K and 300 K
surfaces, but the local pressure tendency term is showing some
descent canceling some of the lifting. Additionally and
probably more importantly, moisture will be lacking originally.
So despite strong warm air advection we don`t expect much
precipitation just increasing cloud cover Wednesday. The surface
layer and lower-levels start off dry so not expecting any
freezing precipitation to start. So we are going to hold back or
limit POPs for Wednesday before 00z Thursday.
For Wednesday night, 12z NAM and 12z GFS shows a low-level
frontal boundary sliding south with colder air pushing into NY
and far northern PA by 12z Thursday. This colder air continues
to work south and east on Thursday in a confluent flow pattern
from the departing northern upper level trough across southeast
Canada and the next system which is in the southern branch over
Texas at 12z Thursday. Moisture from this system is feeding
northeast into this confluent zone. Given the temperature
gradient over NY and PA and the confluence there will be some
frontogenetical forcing and moisture so we will have POPs.
Looks like mainly rain as the boundary layer takes longer to
cool down vs aloft. QPF amounts are pretty light so not
expecting much accumulations of snow.
Then for Thursday, transition from light rain showers to snow
showers occurs over central NY and northeast PA as the front gets
farther south of our area. Weak low-level ridging builds in later in
the day before the southern branch system begins to develop and
track north. So we will have POPs for rain and snow with minimal
accumulations at this point. The NAM does have 1 to 3" of snow
across the Twin Tiers and across northern Oneida co. The 12z
Euro, 12z GFS, 12z CMC all have 1-3" over Oneida Co and less
than 1" farther south. Am inclined to have 1-3" northern Oneida
co and less than 1" elsewhere for starters.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Next major storm system arrives from the southern branch New Year`s
Eve at night and New Year`s Day as per GFS and Euro. The CMC keeps
the southern branch wave suppressed and no precipitation reaches
northeast PA or central NY through 00z Saturday. The Euro/GFS have a
vertically stacked / barotropic low reaching far northern Illinois
at the same time. Both the 12z Euro and 12z GFS have the QPF
just south of northeast PA and central NY at 12z Friday. So we
will hold off/limit precipitation before 12z Friday. Then for
Friday strong lifting from warm advection and from strong upper
level PV advection will combine significant lifting in the
presence of strong moisture transport from a 50-60 knot low-
level jet. Initially dewpoints and temperatures show that the
boundary layer will be cold enough for a mix of sleet and
freezing rain before a change-over to rain by Friday afternoon
or early evening. Timing will no doubt be hard to pin point
this far in advance but we will mention so rain and freezing
rain Friday. Then with strong thermal advection any mixed
precipitation turns to rain which will last until overnight
Friday to Saturday before tapering to rain and snow showers.
Departed from NBM here since the colder CMC and other ensembles
makes for unmeteorological outcomes. Using NBM you get mixed
snow with sleet/freezing rain despite 850 mb temperatures way
above freezing on Euro/GFS. So we used a blend of the Euro/GFS
temperatures for the time period 18z Thursday to 12z Saturday.
In this way we have freezing rain changing to rain everywhere
given the dewpoints on the euro/gfs which exceed 35F across all
of CWA by Friday evening.
The colder air arrives behind this upper level low which makes it
way across the Great Lakes to Quebec by 18z Saturday. Colder air
will follow enough to change rain to snow showers across central NY
and northeast PA by 00z Sunday.
Saturday night looks like lake effect snow showers in north central
NY but ridging rapidly building in at 850 mb will cut off lake
effect snow showers by midday Sunday. Then both the Euro and GFS
both advertise a coastal low well southeast of our area as to have
no influence on our area Sunday to Monday except north winds. 850 mb
temperatures are projected to be mild on the Euro Sunday and Monday
running around 3C. The GFS is a bit chillier being around -3 to -5C.
So we will use NBM for the temperatures.
Basically we will start with NBM for the extended but make
adjustments for precip-type to keep it simple and make sure
temperatures are aligned with precipitation type.
As for flood potential, GFS/Euro operational models all
indicate around 1" to 1.5" inches in an axis from northeast PA
to the Catskills and another 1" to 1.5" inches over Oneida
County. Both indicate a local minimum of QPF around the Finger
Lakes into the twin tiers. with .5 to .75". The ensemble means
from the Euro/GFS and CMC all are similar. Temperatures and
dewpoints peak in the low to mid 40s which should keep
significant melting of what is left of our snow water equivalent
at bay. So we are not expecting many flood problems at this
early stage. But stay tuned here as well.
&&
.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
Mainly VFR to MVFR conditions are expected this evening,
although brief lower restrictions are possible in scattered snow
showers. A lake effect snow band then sets up east of Lake
Ontario after 06Z, which will likely bring IFR-or-worse
conditions to KSYR and KRME. Brief visbys of 1/2SM or less will
be possible in the most persistent portion of this band.
Otherwise, while mainly MVFR restrictions continue through most
of Tuesday morning, gradual improvement to VFR is expected
during the afternoon.
Winds will be mainly westerly tonight, shifting to more
northwesterly during the day on Tuesday. Winds become gusty
Tuesday afternoon before diminishing by the evening.
Outlook...
Tuesday night...Mainly VFR.
Wednesday...VFR expected.
Thursday and Friday...Restrictions possible in rain showers;
freezing rain possible Friday morning.
Saturday...restrictions possible in rain and snow showers,
mainly across KSYR and KRME.
&&
.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...Winter Weather Advisory until 4 PM EST Tuesday for NYZ018-036-
037.
Winter Weather Advisory until 11 AM EST Tuesday for NYZ009.
&&
$$
SYNOPSIS...HLC
NEAR TERM...HLC/MJM
SHORT TERM...DJN
LONG TERM...DJN
AVIATION...BJG
Area Forecast Discussion
National Weather Service Dodge City KS
453 PM CST Mon Dec 28 2020
...Updated Aviation...
.SHORT TERM...(This afternoon through Tuesday night)
Issued at 1200 PM CST Mon Dec 28 2020
Radar indicated a band of light snow/flurries from Ness to Rush
counties at midday, moving northeast. Light snow or flurries will
continue across the northern counties/I-70 corridor this
afternoon and evening, with small accumulations possible. Impacts
from this snow are expected to remain limited, but 12z NAM does
accumulate about one inch of snow in this region into this
evening.
Closed 546 dm cyclone over central California at midday will
weaken into an open, positively-tilted longwave trough across the
Rockies by 6 am Tuesday. Ahead of this approaching trough, a
strong warm air advection synoptic regime will unfold tonight and
Tuesday, with low stratus and widespread precipitation expected.
Made no substantial changes to the inherited winter weather
advisory with the newest model guidance. Widespread rain will
develop from West Texas to western Oklahoma after midnight
tonight, and rapidly expand northward into SW Kansas late tonight
through sunrise Tuesday. Increased pops to 100% across the central
and eastern zones for several hours early Tuesday morning, with
widespread warm conveyor belt precipitation production. So it
comes down to the thermal profile and surface temperatures to
determine phase changes. Overnight, initial bands of precipitation
will take the form of light snow, but quickly transition to sleet
and then freezing rain as the warm nose aloft deepens. We continue
to feel confident that surface temperatures will hold in the 28-32
degree range for several hours during the first half of Tuesday
morning, and this is the expected ice accumulation window.
Light to moderate freezing rain is expected to yield ice
accumulations of 0.1-0.2 inch, with localized amounts to 0.25 inch
possible where surface temperatures can remain below 32 the
longest in the face of strong warm advection (most likely NE
zones). Do not feel ice storm warning criteria (1/4 inch) will be
achieved, but will monitor the NE zones closely. Ice
accumulations will dwindle rapidly NW of a Liberal- Jetmore line.
These amounts do not sound like much, but remember it takes very
little freezing rain to make sidewalks and bridges very dangerous.
Allow extra time for travel Tuesday morning.
Warm front will make steady NE progress through midday, with
temperatures climbing above freezing, and cloud ceilings gradually
improving, from west to east. Warm conveyor precipitation shield
is expected to be along/east of US 283 by noon per the latest
HRRR, and all precipitation is expected to be rain Tuesday
afternoon. Western counties will warm well into the 40s Tuesday
afternoon, with the NE zones remaining in the 30s where rain will
be last to exit. SE winds of 10-20 mph tonight and Tuesday morning
will trend southerly midday Tuesday as the warm sector arrives.
Rain will continue well into Tuesday evening across Barber county
and vicinity as the warm conveyor belt slowly migrates east.
Elsewhere, cold/dry advection is expected Tuesday night as the
primary trough axis arrives with an attendant cold front. An
abrupt shift to NWly winds is expected Tuesday evening, and
followed the stronger MAV guidance for this. Also hung on to some
pops Tuesday night, with HRRR showing scattered showers
progressing west to east with the trough and cold core aloft.
Whatever precipitation we get Tuesday evening will change back to
snow, but it should be light with an open/positive tilt trough and
dry advection. Temperatures sunrise Wednesday well down into the
20s.
.LONG TERM...(Wednesday through Monday)
Issued at 133 PM CST Mon Dec 28 2020
The base of the positively tilted longwave trough over Arizona at
6 pm Tuesday will dig well down into Mexico Wednesday and
Wednesday night, closing off another mid level cyclone south of
Big Bend National Park by Thursday morning. Much more sunshine is
expected Wednesday as this occurs, as a dry subsident airmass
overspreads SW KS. Light north winds with temperatures not far
from seasonal normals, in the upper 30s and lower 40s Wednesday
afternoon.
Thursday, 12z ECMWF ejects the Mexican cyclone into Texas and
strengthens it further to 546 dm. New Year`s Eve will remain dry
with plenty of sun, with dry air and any clouds favoring the SE
zones nearest the Texas storm system. Thursday afternoon
temperatures will moderate a little farther into the 40s.
We will need to monitor this "Texas hooker" system closely
Thursday night/early Friday (during the New Year`s holiday).
NBM only introduced minimal pops for snow across the SE zones
during this time, but deterministic 12z ECMWF tracks the cyclone
close enough to impact areas east of US 283 with accumulating
snow. 12z ECMWF places a 542 dm closed low in NE Oklahoma at
6 am Friday, with deformation shield of rain/snow impacting much
of central/eastern Kansas. Further increases in pops are likely
for the eastern zones during the New Year`s holiday.
Quiet dry weather is expected over the upcoming weekend, with
moderating afternoon temperatures.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 447 PM CST Mon Dec 28 2020
Through 01Z scattered snow showers and IFR conditions will be the
case around HYS and then slightly higher ceilings and improved
visibility will occur through 08Z. After 06Z cloud ceilings should
start to fall for all TAF sites as a storm system enters into the
Colorado and New Mexico Rockies. Expect IFR to LIFR flight
categories from 11Z-21Z for all airport sites as moisture moves
through western Kansas. Initial precipitation will develop after
09Z and start out as either snow or sleet. Warmer air aloft will
change the precipitation to freezing rain from 11Z-18Z. Icing
potential could get as high as 0.10-0.20 inch for DDC and HYS with
lesser amounts for GCK and LBL. After 18Z we should see a slow
transition to rain. All the precipitation should start to depart
from west to east after 21Z.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 29 41 25 39 / 70 100 30 0
GCK 27 43 21 39 / 60 70 20 0
EHA 30 48 25 41 / 40 50 20 0
LBL 26 44 23 41 / 50 80 20 0
HYS 28 38 22 37 / 80 80 30 0
P28 30 45 29 41 / 80 100 70 10
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 AM to noon CST Tuesday for
KSZ064>066-076>081-085>090.
Winter Weather Advisory from 3 AM to 3 PM CST Tuesday for KSZ030-
031-045-046.
&&
$$
SHORT TERM...Turner
LONG TERM...Turner
AVIATION...Tatro
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
536 PM CST Mon Dec 28 2020
...AVIATION UPDATE...
.DISCUSSION...(This evening through Monday)
Issued at 321 PM CST Mon Dec 28 2020
Focus for this forecast is centered around the long expected winter
system pulling through the Central Plains tonight into Tuesday
evening.
As expected, a band of light snow/flurries has developed to the
southwest with some isentropic lift/warm air advection and will
eventually work its way north to give us some light snowfall by
tonight.
Our main problems our mounting more toward our southeast
CWA. Not to say won`t see a decent amount of snow in the 3-5 inch
range along and north of I-80 where we had been putting most of
our focus. But, the southeast is where the heaviest QPF band seems
to be setting up as models are trending toward a convergence on
this solution. The 18Z run of the HRRR has backed off of the ice a
bit, so that is good news. The total ice amounts may technically
show close to a quarter inch in our far south, but in reality, we
would possibly get ice in the morning, melt with some rain in the
afternoon, and finish with a bit more light icing in the evening
before ending. We are looking closer to a tenth inch of ice for
max accumulation on surfaces.
Models did seem to be nudging this band heavier qpf band farther
northwest on 12Z runs than what we had introduced to our forecast
this morning for Tuesday QPF. But 18Z runs indicate a possible
nudge to the southeast again. So for now, I am thinking areas
from maybe near York County, stretching down across Nuckolls, and
into Osborne County in Kansas would be the extent of the highest
qpf. There is clearly going to be a warm layer aloft present that
appears to be warm enough to support some sleet or freezing rain.
This is a very tricky forecast as this hinges heavily on a few
things, including QPF, warm air aloft, temperature at the surface,
and how far northwest the heavier QPF stretches. There will be a
few hours during the daytime on Tuesday when our precipitation
rate may be quite heavy as a nice slug of moisture works northeast
into our CWA. On the northwest edge of this precip band, we may
have a strip of particularly heavy snow toward 4-6 inches or snow
if it comes down hard enough. Tough call on where exactly this
band would set up if it does. Snow ratios may not be high enough
to support this too. Down toward Mitchell County, the surface
looks like we can clearly warm up enough above freezing that parts
of our far southern CWA could warm up to all rain and would tamp
down on ice accumulation concerns way down there, as mentioned
earlier.
Farther north toward the tri-cities and points northward. Forecast
soundings seem a bit cool with the warm layer to allow much more
to occur than sleet other than snow. I couldn`t rule out a little
freezing rain, but this looks like less of an issue for points
farther north. However as we start winding down, forecast
soundings indicate the possibility of some freezing drizzle to put
a light glaze on fallen snow. If this occurs, this may be a time
period of particularly hazardous driving. It does not take much
precip to create problems. Just another thing to consider with
this event.
Overall, this event has an earlier ending time than what had been
forecast before, and I can see this being cancelled sometime
during the evening if we don`t wind up getting light freezing
drizzle occurring through Tuesday evening.
Looking cool a few days post winter system, but nothing extreme,
with a warm-up early next week. Upper low comes out of Mexico by
late Thursday/Friday for parts of the central Plains, but it
appears we remain too far west/north to be affected very much by
this, but we do have some slight POPs in are southeast Thursday
night/Friday just in case some light precip makes its way into our
area.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Wednesday)
Issued at 532 PM CST Mon Dec 28 2020
A winter storm is on our doorstep currently and will be working
its way through the area overnight tonight and through tomorrow.
Cigs are expected to drop to MVFR along the leading edge and then
down to IFR with the incoming snow bands. Snowfall is likely to
reduce visibility at times to less than 1 mi. As temperatures warm
tomorrow afternoon snow is expected to transition to a freezing
rain mix until the system moves off to the east later in the
evening hours. Winds could also become gusty during the morning
hours tomorrow.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from midnight tonight to midnight CST
Tuesday night for NEZ040-041-047>049-062>064-075>077-
085>087.
Winter Weather Advisory until midnight CST Tuesday night for
NEZ039-046-060-061-072>074-082>084.
KS...Winter Weather Advisory from midnight tonight to midnight CST
Tuesday night for KSZ006-007-018-019.
Winter Weather Advisory until midnight CST Tuesday night for
KSZ005-017.
&&
$$
DISCUSSION...Heinlein
AVIATION...Shawkey
Area Forecast Discussion
National Weather Service Lincoln IL
813 PM CST Mon Dec 28 2020
.SYNOPSIS...
Issued at 330 PM CST Mon Dec 28 2020
A chilly night is in store across central Illinois as low
temperatures bottom out in the upper teens and lower 20s. An
approaching storm system will spread wintry precipitation across
locations along and west of the I-55 corridor by Tuesday afternoon.
A minor accumulation of ice and snow is likely...especially
northwest of the Illinois River.
&&
.UPDATE...
Issued at 805 PM CST Mon Dec 28 2020
Main changes this evening are to slow clearing of clouds and to
drop temperatures several degrees NW of the Illinois River Valley.
Temperatures quickly fell into the teens upon clearing in
northwest portions of the CWA and lowered overnight lows into the
lower teens for this area. Elsewhere, cloud cover is holding on
longer than expected but does continue to slowly erode from the
north and west.
&&
.SHORT TERM...(This evening through Tuesday)
ISSUED AT 330 PM CST Mon Dec 28 2020
Low clouds continue to plague central Illinois this afternoon with
21z/3pm satellite imagery showing overcast conditions across the
entire KILX CWA. The clouds are beginning to dissipate/thin across
the Illinois River Valley and this process will accelerate over
the next couple of hours. Based on current satellite trends and
HRRR forecast, will hold on to mostly cloudy skies along/east of
I-57 through early evening...followed by a period of mostly clear
skies across the board through early Tuesday morning. All models
are showing an increase in mid/high clouds from the southwest
overnight, resulting in a return to overcast conditions across the
Illinois River Valley by dawn. Low temperatures will drop into the
upper teens and lower 20s.
A deepening upper trough over the southwest CONUS will be the main
weather-maker in the short term as surface low pressure develops
in the lee of the Rockies on Tuesday then tracks into the Great
Lakes by Wednesday morning. An initial surge of WAA precip will
develop well in advance of the low by Tuesday afternoon. The
atmosphere will initially be quite dry, so top-down moistening may
be slower than some CAMs suggest. Even still, enough solutions
suggest precip will develop across the W/NW CWA to warrant PoPs
along/northwest of a Champaign to Taylorville line during the
afternoon. Will hit PoPs hardest along/northwest of the Illinois
River where likely to categorical PoPs are in order. Based on
NAM/GFS forecast soundings, the precip will begin as light snow.
As the low approaches from the west, boundary layer flow will
gradually veer to a more southerly direction...allowing
temperatures to climb Tuesday night. Thermal profiles suggest
mixed phase precip for a few hours during the evening, with the
greatest amounts focused in the Illinois River Valley. With
projected ice accumulations of up to one tenth of an inch and
snowfall of 1 to 2 inches, have issued a Winter Weather Advisory
for locations along and northwest of a Canton to Minonk line.
Further southeast across the remainder of the area, precip will be
much lighter and will temporarily come to an end during the
evening. Surface temps will continue to climb overnight, allowing
the precip to change to rain everywhere shortly after midnight.
.LONG TERM...(Tuesday night through Monday)
ISSUED AT 330 PM CST Mon Dec 28 2020
A rainy Wednesday is on tap across central Illinois. As low
pressure tracks into the Great Lakes and pulls a cold front
through the area, the rain will diminish from northwest to
southeast during the evening. In fact, most models agree that a
period of dry weather will develop across nearly the entire CWA
Wednesday night into Thursday morning.
After that, attention will turn to a developing surface low along
the trailing end of the cold front across the lower Mississippi
River Valley. 12z Dec 28 models are now in much better agreement
with this process, with model consensus showing the low pivoting
northward into central Illinois by Thursday night. Given a
cold/dry boundary layer and E/NE flow, think freezing rain or a
mix of freezing rain and snow will develop as the precip spreads
back northward. The exact track of the low and the resulting wind
direction/surface temps will determine how much icing will
occur...however, the potential exists for icy/hazardous travel
Thursday night into Friday morning before temps warm sufficiently
to change the precip to rain. Once this system departs, a return
to cool/dry weather is expected next weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 511 PM CST Mon Dec 28 2020
MVFR conditions persist this evening but continue to slowly erode
from the northwest and should clear out at the terminals
overnight. NW winds this evening will become light and veer to a
SE direction Monday morning, then increase through the day as low
pressure approaches. Lower ceilings and wintry precip will
overspread portions of the Illinois River Valley with snow
initially changing over sleet and freezing rain. Best chance for
precip is at PIA then BMI, but there are lesser chances at
SPI/DEC/CMI so have no introduced anything more than a VCSH to
those locations at this time.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from noon Tuesday to 4 AM CST Wednesday
for ILZ027>031-036-037.
&&
$$
UPDATE...Deubelbeiss
SYNOPSIS...Barnes
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Deubelbeiss
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
635 PM CST Mon Dec 28 2020
.SHORT TERM...(This evening through Tuesday night)
Issued at 245 PM CST Mon Dec 28 2020
Primary concern is obviously the system moving through Tuesday and
Tuesday night, which still looks to bring widespread light to
moderate snow to much of the area. Until then, things will be fairly
benign. An upper trough is currently moving through the region, and
has a weak surface reflection evident via the subtle wind shift
currently moving south through the area (along with some flurries and
snow showers). A couple area of low clouds will continue to push
south/east through this evening, with mostly clear skies for a good
part of the night before we see mid/high clouds work in ahead of
Tuesday`s system. Model guidance is actually in very good agreement
with the system now, with the preponderance of solutions bringing a
period of warm advection induced precipitation through the area
tomorrow afternoon and evening. The heaviest activity looks like it
will cover a three to four hour window from the late afternoon into
mid-evening (a bit earlier west of I-35 and a bit later to the east).
Consensus QPF from the guidance (including the HRRR and other CAMs
which are now starting to include the system in their time window) is
from around 0.2 to 0.35 inches. Forecast soundings are not
particularly impressive with either the depth of the dendritic growth
lower or the strength of Omega, so it looks to be more of a steady
mostly light snow with visibilities of around three quarters of a
mile (with mainly smaller flakes). Given these conditions, don`t
expect snow to liquid ratios to differ too much from climatology, and
could actually be a bit less than climatology. Considering these
factors, forecast amounts are slightly less than previous values, but
still sufficient (generally AOA 3") to continue an advisory across
the area (and even expand it northward to cover the remainder of the
forecast area).
.LONG TERM...(Wednesday through Monday)
Issued at 245 PM CST Mon Dec 28 2020
The tail end of the Tuesday system may bring some lingering snow
into early Wednesday morning, but generally Wednesday looks dry.
Cloud cover will be a bit slower to move out, lingering into the
overnight hours before clearing some for Thursday. Temperatures will
be cool to start the long term period with highs in the upper teens
and low 20s and lows in the single digits.
Looking ahead, the dry conditions stick around and temperatures
slowly warm as we approach the end of the week with ridging
building in. The only area that may see a slight chance of snow
showers Friday is extreme southeastern Minnesota as a low skirts
our area to the southeast. In any case, there do not appear to be any
strong signals for measurable snow through the forecast period.
However, there is agreement that temperatures will continue to warm
through the weekend, with ridging and southwesterly flow intensifying
for the late part of the forecast period. Highs look to approach
freezing or just above by Sunday and Monday, which is nearly 10
degrees above normal for early January.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 627 PM CST Mon Dec 28 2020
Some low stratus lingers in western WI, otherwise skies will be
generally clear overnight through daybreak. As a potent storm system
lifts out of the Deep South tomorrow, a swath of snow will move in
from the southwest midday and persist through Tuesday evening,
diminishing going through the early morning hours Wednesday.
Confidence is high on having snow amounts in the 3-5" range for much
of central-southern MN into western WI, including at all TAF sites.
MVFR conditions are likely at the onset of snowfall, with conditions
dropping to IFR for about a 4-hour period shortly after the onset of
snowfall. IFR conditions will most likely be due to visibility
although ceilings under 1000ft may also develop. Onset of snow will
be in the 18z-21z range then continuing through the end of this TAF
period. Breezy southeast winds will increase to 10-15kt with gusts to
around 20kt in the afternoon. While well short of blizzard
conditions, the impacts to visibility will be evident.
KMSP...Snowfall onset still looks to be about 21z but could vary an
hour or so either way. Timing will be problematic as this is right at
the start of the evening push, and peak intensity may well come
during the push between 21z and 01z. Snowfall will continue through
the evening hours with visibility in IFR range and ceilings below
1700ft. Not expecting frequent rates of 1 in/hr but isolated bursts
of snowfall producing as such cannot be ruled out. Snowfall total for
the duration of this event is expected to be 3-4".
/OUTLOOK FOR KMSP/
Wed...MVFR possible early. Wind NW 10-20 kt.
Thu...VFR. Wind SE 10-20 kt.
Fri...VFR. Wind variable around 5 kt.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Winter Weather Advisory from 9 AM Tuesday to 6 AM CST Wednesday for
Anoka-Carver-Dakota-Freeborn-Goodhue-Hennepin-Le Sueur-Ramsey-
Rice-Scott-Sherburne-Steele-Waseca-Washington-Wright.
Winter Weather Advisory from 9 AM Tuesday to 3 AM CST Wednesday for
Benton-Blue Earth-Brown-Chippewa-Douglas-Faribault-Kandiyohi-
Lac Qui Parle-Martin-McLeod-Meeker-Morrison-Nicollet-Pope-
Redwood-Renville-Sibley-Stearns-Stevens-Swift-Todd-Watonwan-
Yellow Medicine.
Winter Weather Advisory from noon Tuesday to 6 AM CST Wednesday for
Chisago-Isanti-Kanabec-Mille Lacs.
WI...Winter Weather Advisory from noon Tuesday to 6 AM CST Wednesday for
Barron-Chippewa-Dunn-Eau Claire-Pepin-Pierce-Polk-Rusk-St.
Croix.
&&
$$
SHORT TERM...
LONG TERM...Dye
AVIATION...JPC
Area Forecast Discussion
National Weather Service Omaha/Valley NE
833 PM CST Mon Dec 28 2020
.UPDATE...
Issued at 833 PM CST Mon Dec 28 2020
Forecast overall remains in good shape, but made some minor
tweaks to the grids on timing of the arrival of the snow through
6am.
Looking at 00z models just starting to come in, feel OK with the
area of the winter storm warning and the potential for 6 inches of
snow for southwest IA and a few counties in southeast NE, but also
the potential for a mix of freezing rain/sleet. However, the 00Z
Nam is now focusing a heavy band of snow perhaps one tier of
counties northward, which would put this moreso toward I80.
Conceptually, this is likely an area that could see heavy
snowfall, just north of where the snow/freezing rain line could be
setting up. This is also supported by the 00z HRRR model, but not
necessarily other Hires models such as the RAP, the 3km Nam, or
the Hires ARW/NMM. Very challenging forecast as an expansion of
the winter storm warning may be needed into the Omaha metro area
if the 00Z Nam/HRRR are correct. Will continue to look over data.
&&
.DISCUSSION...
Issued at 347 PM CST Mon Dec 28 2020
.Impact Summary:
A winter storm will affect the region beginning tonight and
continuing into Tuesday night. Accumulating snow and ice will result
in minor to moderate travel impacts.
.Tonight through Tuesday night:
The forecast remains largely on track with the overall idea that the
split-stream system deepens through the evening over the Northern
Great Plains, making it to the area tonight. The trends in model
output have decreased overall model QPF output across much of
eastern Nebraska and southwestern Iowa, but regardless a slug
moisture is expected to be accompanied by strong warm air
advection and a strong low-level jet. Certain features of note
this forecast period is a rather deep nearly-isothermal layer that
for much of the area sits right around or just above freezing.
850 mb temperatures reach above freezing generally southeast of
I-80 and indicates a region where increased melting to occur aloft
and increased freezing rain at the surface where surface
temperatures are at or below 32 degrees. Just north of the
transition zone between the better snow and increasing ice is an
area where heavier snowfall could occur as better dendrite
maintenance and aggregation can happen. With the current model
suite, the are of heavier snowfall looks like it could be from
Nebraska City/Plattsmouth extending northeastward into central
Iowa. This zone is still in flux, but is expected to occur just
north of the snow/freezing rain transition area.
Snow is expected to begin overspreading the around midnight tonight,
beginning as snow and reach the Omaha area around 6 am. Surface
temperatures are expected to begin warming through the morning, with
freezing rain beginning to reach into southern Nebraska after 9 am.
Beginning just after noon, a period of peak snowfall and general
precipitation intensity is expected to occur and will be where a
good chunk of snowfall and ice accumulation occur. Mid-to-late
afternoon will begin the intrusion of dry mid-level air into
northeastern Nebraska and will cause the back end of the snow to
begin mixing in freezing drizzle, and could deposit a glaze over
the fresh snow. Snow/freezing rain and drizzle are expected to
exit the area during the overnight to early morning hours.
The general snowfall forecast of total amounts of 2" to 4" over
southeast NE and 3" to 6" elsewhere across the area continues to
look on track, with a glaze of ice expected over much of the area on
the backside of the snowfall. In far southeast Nebraska, high
moisture output is expected to make increase ice accumulation with
amounts reaching just over 0.25" just southeast of Falls City. As
mentioned before, an area of higher snowfall is possible just north
of the snow to ice transition and could push snow amounts slightly
higher than 6".
.Wednesday and Thursday:
Winds out of the northwest are expected to increase and usher in
cold temperatures with highs in the 20`s expected.
.Friday through Monday:
Mid-level troughing is expected to pass through the area and an
northeastward-ejecting surface cyclone looks to clip southeastern
Nebraska and southwest Iowa, bring chances for light snow back to
those areas. Following the departure of that system early Saturday,
dry weather and a warming trend looks to take us into next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 523 PM CST Mon Dec 28 2020
VFR conditions with light southeast winds at TAF issuance.
Conditions deteriorate as snow moves in by 07-09z. Clouds becoming
MVFR and eventually IFR by 11-15z. Snow could change to freezing
rain/drizzle at KOFK by 20z, and at KLNK by 23z toward the end of
the TAF period. Snow changes to freezing drizzle at KOMA just
beyond the end of the TAF period. Totals snow accumulations at
KOFK/KLNK 3-5" and 3-6" at KOMA.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from 6 AM Tuesday to 6 AM CST Wednesday
for NEZ015-034-045-052-053-090>093.
Winter Storm Warning from 6 AM Tuesday to 6 AM CST Wednesday for
NEZ067-068.
Winter Weather Advisory from midnight tonight to 6 AM CST
Wednesday for NEZ011-012-016>018-030>033-042>044-050-051-
065-066-078-088-089.
IA...Winter Weather Advisory from 6 AM Tuesday to 6 AM CST Wednesday
for IAZ043-055-056-069.
Winter Storm Warning from 6 AM Tuesday to 6 AM CST Wednesday for
IAZ079-080-090-091.
&&
$$
UPDATE...DeWald
DISCUSSION...Petersen
AVIATION...DeWald
Area Forecast Discussion
National Weather Service Pueblo CO
545 PM MST Mon Dec 28 2020
.UPDATE...
Issued at 539 PM MST Mon Dec 28 2020
Updated the precipitation chances across the region for this
evening based on the latest radar and high-res model trends. Warm
air advection lifting north across southern Colorado has led to
banded snowfall over the Eastern Mountains, out into the I-25
corridor. This will continue through the next several hours.
Mozley
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 310 PM MST Mon Dec 28 2020
Currently...
Snow continues to fall across the area, currently centered over the
Sangre de Cristo and Wet Mountains and spilling east into the
plains. Snowfall is also currently west of our area making its way
towards the eastern San Juans.
Today and Tomorrow...
As the upper-level low moves onshore today, southwesterly flow aloft
will be continuing to advect moisture into the area, giving us some
good snowfall. Consistent with the last few days, the peaks of the
San Juans and Sangres will be seeing most of the action, with 15 to
almost 20 inches expected near both areas. The surrounding terrain
will also be seeing a good 4 to 8 inches, as will higher portions of
Lake County.
Current additional concerns for the forecast begin with El Paso
County this evening into tomorrow morning. Ahead of this incoming
system the eastern half of our area is experiencing some good
southerly flow and potent warm air advection at the mid-levels,
supporting a thickening of the cloud deck and additional snowfall.
An extra 3-5 inches is possible near Colorado Springs, and have
issued an advisory as the snow could come down during evening rush
hour. Overnight and into tomorrow morning, the mid and high levels
dry out a decent bit, mostly stopping chances of additional
snowfall. However, warm air and moisture will still inhabit the
lower levels, and there could be enough lift present to generate a
little freezing precipitation in the early morning hours. While
confidence in this isn`t 100 percent, there is a possibility this
could impact the morning commutes in El Paso County.
The second forecast concern is for the far southeast plains, namely
eastern Las Animas and most of Baca Counties. Moisture advection
from the south along with cool surface temperatures suggest a strong
possibility of freezing drizzle impacting that region overnight and
into tomorrow morning. Most model guidance showed negligible amounts
of ice accumulation, merely a short glazing, but a few runs,
including the NAM, NAM Nest and some runs of the HRRR were
indicating measurable ice accumulation by around 8 AM tomorrow, so
went with an advisory on that as well.
Precipitation over the plains is expected to wane by midday tomorrow
as downslope flow increases, while snowfall is expected to persist
west of I-25 through tomorrow afternoon as the trough axis dips far
to the south.
.LONG TERM...(Tuesday night through Monday)
Issued at 411 PM MST Mon Dec 28 2020
The low pressure system that is currently propagating in over the
region from the southwest US will be the main factor driving the
current conditions throughout the region with mostly cloudy to
overcast skies, reduce visibilities at times in light to moderate
snow showers, and breezy conditions for the next 36 hours. There
will be gusty winds expected across the plains and on the higher
mountains peaks, as well as in and along the mountain passes and
canyons. Bands of snow have set up ahead of the frontal boundary
and will continue to provide a feed of moisture over the Sangre De
Cristo/Wet Mountains and over the plains, with a higher
concentration of snowfall primarily west of the I-25 corridor.
Highest accumulations of snowfall will be over the Eastern San
Juan Mountains, especially the western-facing slopes with over 2
feet possible. There is a possibility of freezing drizzle for Las
Animas County and Baca County early Tuesday morning. The upper-
level trough will move in over the area tomorrow evening with only
a few more snow showers possible. This should begin to taper off
by late tomorrow evening and into early Wednesday morning with
only some lingering snow showers over the eastern mountains, with
clearing conditions and warmer temperatures expected by later in
the day. Lows will be the coldest for Tuesday night with low upper
teens in the plains, single digits for the mountains, and coldest
in the mountain valleys and San Luis Valley from -5 to 5. West-
southwesterly winds will also diminish by Wednesday morning to
become light and variable.
There will be a temporary break along with some weak ridging on
Thursday and then by later in the evening on Thursday the next
trough will begin to approach and allow for a slight chance for more
precipitation, mainly to the north and over higher elevations along
the westward facing slopes. Winds will also be a factor with the
onset of this trough propagating through as the pressure gradient
tightens.
After the system moves through later in the week, a ridge will set
back in for the weekend and continue to build into early next week,
allowing for a return of clearer skies and warmer conditions over
the entire region.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 310 PM MST Mon Dec 28 2020
As an area of low pressure over the southwestern US continues to
propagate towards the region, expect CIGs and VIS to be impacted for
all stations, primarily later this evening and into early tomorrow
morning. Expect IFR criteria to be prevalent with CIGs slightly
lowering later in the day, as well as on and off -SHSN. There will
be a break later tomorrow morning with VFR conditions returning as
early as 16Z for ALS and 15Z for both COS and PUB. Expect IFR
conditions to be possible again later in the day tomorrow as the U/L
low moves in over the area.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST Tuesday for COZ058>060-
066.
Winter Weather Advisory until 11 AM MST Tuesday for COZ061>063-
074-076>082.
Winter Weather Advisory from 11 PM this evening to 8 AM MST
Tuesday for COZ094-099.
Winter Storm Warning until 5 PM MST Tuesday for COZ067-068-072-
073-075.
Winter Weather Advisory until 8 AM MST Tuesday for COZ084-085.
&&
$$
UPDATE...MOZLEY
SHORT TERM...GARBEROGLIO
LONG TERM...STEWARD
AVIATION...STEWARD
Area Forecast Discussion
National Weather Service Topeka KS
529 PM CST Mon Dec 28 2020
...AVIATION UPDATE...
.DISCUSSION...
Issued at 418 PM CST Mon Dec 28 2020
Currently, the forecast area is under a low amplitude mid level
ridge that is being suppressed with a broad trough over the Great
Lakes region. A deep western trough works eastward which will
provide for a very active Tuesday weather wise.
The forecast appears on track with some uncertainty leading to how
much of any given type of precipitation will occur tomorrow morning
into the early afternoon. The trend with short term and longer term
model solutions appear to hinge on the strength and overall movement
north of the warm nose - as well as the depth resulting in the
poleward push. Cooler overnight lows with a slight northeast breeze
appears to start the morning Tuesday off a bit cooler overall. This
leads to a lower overall wet bulb surface temp. The end result is
that the expectation will be that light snow beginning before
sunrise will begin to gradually transition to a wintry mix including
freezing rain. With a slower warm nose, melting precip in the warm
layer will likely provide for a longer duration of freezing
rainfall. This along with slightly higher wind as the system
intensifies will help keep a more efficient situation in place for
ice accumulation to take place. Have increased overall ice amounts
with some areas being closer to the two tenths of an inch range.
This also results in overall lower snowfall amounts with around 3
inches remaining along the KS/NE border. Trends overnight will be
very important but there is potential that even slightly higher
amounts of ice could result with a more slowly building warm nose.
The GFS continues to be more aggressive with warmer air overall.
But, again, a colder low level wedge of air in place longer also
supports the idea of more ice potential. Thinking the transition to
rain will be by mid to late afternoon but may struggle to reach the
border. Higher amounts of rain appear to be likely and could act to
reduce ice into later morning hours with strong isentropic ascent and
negative EPV working over the area providing for some upright
instability to support banding precipition. The cold air pushing
into the area overnight into Wednesday morning will supporting
another mixed precipitation period but overall amounts should be
low, so have not extended the advisory for this period.
New Year`s Eve into the day on Friday is trending toward the active
side as well weather wise - this time heavy snow could be in cards.
As a deepening upper low lifts into the area with the long wave
trough slow to move through, a TROWAL feature develops and extends
west into the area. Still no amounts to officially mention as we
will take the tomorrows system one at time first. Do expect that
amounts for Friday morning could be somewhat impressive.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday)
Issued at 529 PM CST Mon Dec 28 2020
Confidence is good in wintry precip overspreading the area Tuesday
morning. Main challenge is timing when warm air advection will
raise sfc temps above freezing. Have used the RAP forecast
soundings along with the gridded forecast to try and time these
transitions. Otherwise increasing low level moisture advection
will promote lowering CIGS with LIFR conditions likely by mid day
Tuesday.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 AM to 3 PM CST Tuesday for
KSZ021>024-026-034-039-040.
Winter Weather Advisory from 6 AM Tuesday to midnight CST
Tuesday night for KSZ008>012-020.
Winter Weather Advisory from 6 AM to 1 PM CST Tuesday for
KSZ035>038-054>056-058-059.
&&
$$
DISCUSSION...Drake
AVIATION...Wolters