Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/21/25
Area Forecast Discussion
National Weather Service Denver/Boulder CO
519 PM MST Thu Feb 20 2025
.KEY MESSAGES...
- Moderate to briefly heavy snow will fall across the I-70
corridor mountains, South Park, southern foothills, Denver
metro, and portions of the Palmer Divide this evening through
Friday morning. This will create hazardous travel conditions and
will impact this evening`s commute and especially Friday
morning`s commute.
- Warming trend on the plains into the weekend and early next week.
&&
.SHORT TERM /Through Friday/...
Issued at 232 PM MST Thu Feb 20 2025
Water vapor imagery shows a beautiful cutoff trough over Utah with
multiple vertices rotating around it. This trough is slowly
moving eastward towards our CWA. The QG omega fields show strong
QG ascent ahead of this trough which is now entering the northern
mountains of Colorado. In addition, the SPC mesoanalysis shows mid
level lapse rates of 8.5 C/km which indicates healthy
instability. The combination of instability and QG ascent is
already creating snow showers in the central mountains and
southern foothills. Radar shows some of these snow showers have up
to 37 dbz so moderate to briefly heavy snowfall rates will occur
in these showers. Model guidance is beginning to come into better
agreement that, as the trough moves eastward, snow will become
more widespread and intense across the central mountains, southern
foothills, and South Park. The model guidance has increased QPF
over these areas with 0.4-0.7" mainly focused over the I-70
mountain corridor. With such good lapse rates and forcing, snow
ratios should be around 17-18:1 despite the small dendritic growth
zone. That results in amounts roughly between 4-12" across the
I-70 mountain corridor and southern foothills. A Winter Weather
Advisory was issued for the I-70 mountains and South Park to cover
the hazardous travel impacts this snow will create. There is some
concern about a few of the high resolution models showing even
higher snow amounts. The HRRR has been consistent in showing over
1" of QPF in Clear Creek County. That could create up to 20" of
snow in the worst case scenario. There was consideration for
issuing a Winter Storm Warning for zones 34 (I-70 mountains) and
36 (southern foothills) but no upgrades were made at this time due
to the continued uncertainty. If snow rates and accumulation are
high for the next 3-4 hours, the next shift may choose to upgrade
to a warning.
Across the Denver metro and Palmer Divide, models have generally
stayed with their slight southern shift from last night. There is
less instability over the lower elevations and without much wind
at all, there will be limited upslope flow. The best instability
and upslope flow will stay close to the foothills so the towns of
Golden and Highlands Ranch will likely see the highest amounts.
Snow amounts will likely be closer to 6-7" inches there. On the
northeast side of the Denver metro, the instability and upslope
will be very minimal. So much of the snow is expected to stay
south. Amounts in northeast Denver may be closer to 1-3". The
areas in-between like Boulder, downtown Denver, and Aurora, still
have considerable uncertainty with this event. A slight northward
shift with the forcing and low, may put these areas closer to
5-7". However, a southern jog of the low may result in amounts
closer to 2-3". The highlights were left unchanged for the Denver
metro and Palmer Divide. Most of the snow may arrive at the back
end of the evening commute tonight so the hope is that roads will
be ok for the evening commute. The commute tomorrow morning will
be worse as roads will be snow-covered and slick.
The trough will move out of our forecast area shortly after
sunrise tomorrow morning. The QG ascent will quickly turn to
descent so snow will decrease in coverage and intensity quickly
throughout the morning. Warm air advection in the low levels along
with clearing skies will allow temperatures to moderate by the
afternoon. Fort Collins, Greeley, and other nearby areas will
likely reach the 40s.
&&
.LONG TERM /Friday night through Thursday/...
Issued at 232 PM MST Thu Feb 20 2025
Any lingering snow showers across the higher terrain should
quickly come to an end Friday as the shortwave departs and drier
air works back into the region. Saturday should be warmer and
drier across the region as weak ridging begins to build across the
southwestern CONUS. Warming mid-level temperatures should lead to
highs returning to the mid 40s to mid 50s - though this will
likely be somewhat dependent on snow cover across the plains.
The warming trend will continue across the lower elevations from
Sunday through early next week, with flat ridging over the region.
A weak shortwave moving across the state will bring a chance of
some light snow to the mountains Sunday into Monday, but there`s
little moisture embedded in the west-northwesterly flow. There
could be some gusty winds and blowing snow across the higher
mountains as well, but winds don`t look close to meeting wind
criteria. Across the plains, the increased downslope component
will allow temperatures to warm into the low to mid 60s, with good
support for this warmth across the deterministic/ensemble suite.
The pattern will turn a little more active by mid-week, as a
stronger shortwave tracks across the northern Rockies into the
central Great Plains. Guidance suggests that this will be a fairly
dry trough, with a chance for orographic snow in the mountains but
little or nothing across the plains. A cold front associated with
this shortwave should drop temperatures back into the 50s for the
lower elevations. Any cooldown looks to be short-lived, as
guidance generally redevelops the ridge across the western U.S. as
we approach the end of next week.
&&
.AVIATION /00Z TAFS through 00Z Saturday/...
Issued at 448 PM MST Thu Feb 20 2025
Models have continued to keep the heaviest snowfall towards the
southern Denver metro and foothills for tonight into tomorrow. We
are expecting 1 to 3" to accumulate for KDEN, with higher
accumulations for KBJC and KAPA, 3 to 6" and 5 to 7" respectively.
Ceilings have started to lower late this afternoon at KBJC and
KAPA, with KDEN expected to follow suite shortly. Dewpoint
depressions indicate we still have a little ways to go to moisten
up the lower levels, but snow showers are still on track to begin
in the next hour or two. We are expecting visibilities to drop as
low as 1/2SM during the period of heaviest snowfall at KAPA and
KBJC between 4Z to 8Z, while KDEN looks to keep slightly higher
vis (1SM or higher) as it will be on the northern side of the
heaviest snow. During the period of heaviest snow, there may be a
brief period of VLIFR conditions, with the highest chances of this
occurring being for KAPA.
The heaviest snow is expected overnight, with lighter snowfall
expected through the early morning. Conditions will improve from
north to south, and we expect a return to VFR conditions by 15Z -
17Z for KDEN/KBJC, with MVFR holding on slightly longer for KAPA.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 8 AM MST Friday for COZ034-036-037-
039>041.
&&
$$
SHORT TERM...Danielson
LONG TERM...Hiris
AVIATION...Bonner
Area Forecast Discussion...CORRECTED
National Weather Service Goodland KS
651 PM MST Thu Feb 20 2025
.KEY MESSAGES...
- Wind chills will fall to around 15 below zero tonight.
- Another chance of light snow (20%-30%) arrives tonight,
continuing through the day Friday. Could have narrow corridors
of more than an inch under the bands of snow.
- Watching a potential for a snow band to develop in the morning
across the area. The exact location of the snow band still
remains in question however along with amounts. The snow band
wherever it sets up will be very localized probably around 30
miles wide and 30-40 miles in length.
- Much warmer temperatures return Saturday through Tuesday with
the warmest day being Monday when high temperatures will be in
the mid 60s to around 70.
&&
.UPDATE...
Issued at 634 PM MST Thu Feb 20 2025
Continuing to see the signal for a snow band Friday morning
across portions of the CWA. The RAP and NAM all show 12-20
microbars of lift within the dendritic growth layer along with
some slightly negative EPV* in that layer as well. Theta E lapse
rates are however a little high and low and mid level lapse
rates are a little weak as well. All of this said, yes it may
have some convective elements to it but how long will they last
as the surface low that is causing the snow will be progressive
in nature. Confidence is increasing in the snow band occurring
but the big question continues to be exactly where as guidance
continues to jump around with it. At this time ECMWF members
favor it developing along the Highway 27 corridor and back into
eastern Colorado; whereas Hi-RES guidance which typically
handles mesoscale features a little better has some hints of it
as far east as Highway 83. At this time am favoring the ECMWF
ensemble members for the location. The next question will be
amounts. 1-2 inch per hour amounts are possible with this band
but as mentioned above how long will it last in one spot. If the
low is a little slower then some 3+ inch amounts may be
possible. With the amounts and exact location still in question
will forego an advisory at this time. Remain aware however,
wherever this band does set up at will impact the morning
commute.
&&
.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 124 PM MST Thu Feb 20 2025
Latest upper air analysis shows a closed low over the Great Basin.
Ahead of it cloud cover was moving southeast over the forecast
area. At the surface breezy south winds were helping warm
temperatures from what we had yesterday.
Tonight cloud cover will persist over the forecast area.
Meanwhile the closed low will continue to move east, moving
toward the forecast area. Ahead of it corridors of lift will
form. Within the layer the lift will occur in the environment
is neutral to slightly unstable, allowing the environment to
more efficiently use the lift. The big question is not if, but
where will these narrow bands set up. The current forecast is
reflective of the general model consensus. However this may not
be the case. The best time for snow to form will be during the
overnight hours into the early morning. Snow will end from west
to east overnight through Friday morning.
Given the stability of the environment, there could be windows of an
inch an hour snowfall rates, yielding a narrow corridor of an
inch or so of snow.
Overnight the wind chills will fall to around 15 below zero. The
coldest wind chills will be over the eastern part of the forecast
area. Cloud cover will help keep the temperatures warmer than
otherwise. Most of the forecast area will be near or below -15 for
a wind chill. For simplicity have placed the entire forecast area
in a cold weather advisory, even though some counties may approach
but not meet the criteria.
Friday the wind chills will improve mid morning. Meanwhile the snow
will slide east through the morning, exiting the forecast area
around noon.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 124 PM MST Thu Feb 20 2025
Saturday through Thursday will be dry. Temperatures will rebound to
potentially record values Monday as a short wave ridge builds
in.
Mid week an upper level short wave trough will move across the
Northern Plains. As it does so the base of the trough will move
over the forecast area. Winds rounding the base of the trough will
be windy. Latest model probability shows 30% or less for sustained
winds greater than 30 MPH. Probability for wind gusts of 50 MPH or
higher is 20% or less. The pattern does look favorable for strong
winds to occur, so the probabilities may increase as this day nears.
During the latter half of the week temperatures will be closer to
normal due to a cold front passage behind the upper level short wave
trough. Forecast continues to look dry for the frontal passage.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 354 PM MST Thu Feb 20 2025
Latest guidance suggests that MVFR cloud cover is forecast to
persist at KGLD through around 05Z with occasional flurries.
Any blowing snow that was ongoing at this time looks to end as
the sunsets as well so will maintain a P6SM for now. Also am
watching for light snow to move again towards sunrise. There is
also the potential for a snow band to form and impact the KGLD
terminal. Guidance is all over the place currently with the
location of it so will go with a PROB30 to introduce this
potential for now. As for KMCK; VFR conditions are currently
forecast to prevail and not seeing any threat for snow at this
time.
&&
.CLIMATE...
Issued at 300 AM MST Thu Feb 20 2025
Record daily low temperatures:
Feb 20 Feb 21
Goodland..........-1F (1953) -5F (1953)
Hill City.........-4F (1918) -8F (1978)
McCook............-8F (1918) -7F (1911)
Burlington........-8F (2018) -8F (2018)
Record daily low maximum temperatures:
Goodland...........16F (1918) 19F (1971)
Hill City..........14F (1918) 18F (1968)
McCook..............9F (1918) 20F (2013)
Burlington.........16F (2018) 16F (1913)
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Cold Weather Advisory from 11 PM MST /midnight CST/ this
evening to 8 AM MST /9 AM CST/ Friday for KSZ001>004-
013>016-027>029-041-042.
CO...Cold Weather Advisory from 11 PM this evening to 8 AM MST
Friday for COZ090>092.
NE...Cold Weather Advisory from 11 PM MST /midnight CST/ this
evening to 8 AM MST /9 AM CST/ Friday for NEZ079>081.
&&
$$
UPDATE...Trigg
SHORT TERM...JTL
LONG TERM...JTL
AVIATION...Trigg
CLIMATE...99