NWS Denver/Boulder, CO wrote its last area forecast discussion before the first event at Feb 14, 10:31 PM MST, 1 hour 29 minutes earlier.
Area forecast discussion, Feb 14, 10:31 PM MST, 1 hour 29 minutes before
Area Forecast Discussion
National Weather Service Denver/Boulder CO
1031 PM MST Tue Feb 14 2023
.UPDATE...
Issued at 807 PM MST Tue Feb 14 2023
Well, things are getting under way as anticipated this evening,
with showers increasingly filling in on radar across the
foothills, Palmer Divide, and western Denver metro. We are still
rather dry at the surface, particularly in the lower elevations,
so not all of it is reaching the ground, however a few spots have
already picked up a dusting on the SW side of town and in the
foothills. Road conditions will begin to deteriorate in the
foothills very soon, whilst the urban corridor will take a few
more hours. Once the low levels moisten up and road temperatures
come down, one or two hours before midnight, we'll see rapidly
worsening conditions on the roads.
The current suite of headlines looks appropriate at this time.
Denver still looks to be straddling that fine line separating
heavier snowfall due south and west, and lighter amounts due
north. One change was made this evening to incorporate most of
Park County into the Winter Storm Warning. Prevailing flow becomes
more southeasterly overnight across South Park, which is a highly
favorable wind direction for enhanced orographics and snowfall in
this area. Suspect most communities may end up with 8-12", with
lesser amounts in the sparsely populated lower elevations of the
valley, thus warranting the upgrade.
&&
.SHORT TERM...(This evening through Wednesday)
Issued at 300 PM MST Tue Feb 14 2023
Water vapor imagery shows a shortwave trough over eastern Kansas
that is quickly moving northeastward. Meanwhile, a broad trough
with multiple small shortwaves within it has moved over the Desert
Southwest. The main shortwave of the broader trough is currently
over the Las Vegas area with strong QG ascent ahead of it creating
precipitation over southern Utah and western Colorado.
Currently, at the surface, there are strong northwesterly winds
across much of the northeast plains of Colorado. Some of these
gusts have exceeded 50 mph but as the shortwave over Kansas gets
further away, these winds will decrease. This evening, strong lee
cyclogenesis will develop over southeast Colorado and will turn
winds northeasterly across our forecast area. In fact, there are
already signs of this occurring as winds on the Palmer Divide are
increasing out of the northeast. These northeast winds, along
with southwest winds in South Park, are starting to create
frontogenesis in the southern foothills. A few light snow showers
are showing up on radar and webcams although it doesn't appear
much, if any, snow is reaching the surface. Over the next few
hours, this convergence/frontogenesis will only strengthen and it
will create strong upward forcing. There appears to be enough low
level moisture to allow precipitation to form and this
precipitation will be able to tap into the steep lapse rates that
may be close to 9 C/km. This will lead to heavy snow in the
southern foothills mainly south of Highway 285 and along the
Palmer Divide. Snowfall rates could be close to 2 inches per hour
at times this evening and travel will be very hazardous. It is
this area that should see the highest storm total snowfall amounts
as over a foot could occur. There was consideration for upgrading
the higher elevations of Park County to a Winter Storm Warning
but the focus for higher amounts should stay closer to the base of
the foothills due to better upslope flow there.
Once the upper level trough moves closer to our forecast area
later this evening, it will provide QG ascent and the coverage of
snow will increase as a result. Snow will spread across the rest
of the foothills and most of the I-25 corridor as well as into
east-central Colorado. Recent model trends have been keeping this
trough slightly more neutrally tilted compared to the positively
tilted nature models showed the past couple of days. Models have
also slowed down the progression of the trough which allows for
more of an easterly component of the low level winds to develop.
Both of these factors have lead to an increase in snow totals by
an inch or two. The trough will be in no hurry to move past our
forecast area tomorrow and the light to moderate snow will
persist through the majority of the day. It is not until midnight
Wednesday night that this system should be totally out of our
area.
New storm total snow amounts have been bumped up to 6-12" in the
southern foothills, Palmer Divide, and mountains of Park County.
The southern foothills could even see a couple snow totals nearing
18 inches. That area is where the worst impacts will occur with
very hazardous travel and plenty of road closures possible. The
east-central plains, including Byers, Limon, and Last Chance,
will see amounts between 5-9 inches. Considering winds will be
highest in that area with gusts up to 50 mph possible, blowing
snow will be an issue there. The fear is that I-70 east of Denver
and Highway 36 in Arapahoe and Washington Counties will be shut
down. Therefore, highlights were upgraded to Winter Storm Warnings
to draw more attention to significant impacts. As for the Denver
metro, amounts will range from 4-8" with the higher amounts closer
to the foothills and lower amounts towards the northeast suburbs
of Denver. There was a lot of consideration given to upgrading to
a warning in the Denver metro. However, a Winter Weather Advisory
was kept due to the uncertainty with exact snow amounts there. The
gradient in snow amounts will be quite large in the Denver metro
and if the storm tracks farther south or snow ratios are lower
than the ~16:1 that are expected, amounts could end up being at
the low end of the range. However, if the slower, more northerly
track with higher snow ratios verifies, the amounts may be closer
to 8 inches. The evening shift was briefed to watch the trends
closely for a possible upgrade to a warning for the Denver metro.
Elsewhere, the snow amounts in southern Weld and Morgan Counties
(which should be in the 2-5 inch range) should be enough to create
impacts to travel so a Winter Weather Advisory was issued for
those zones. With winds being more easterly than the previously
expected northeaster winds, the northern foothills should get hit
with heavier amounts. The foothills of Boulder County could get
up to 8 inches of snow while the foothills of larimer County will
see lighter amounts in the 2-4 inch range. With those high totals
in Boulder County, a Winter Weather Advisory had to be issued for
the entire zone despite the lower impacts farther north.
Otherwise, it will be chilly tomorrow with highs in the teens
across the plains and in the single digits in the mountains. Winds
may be just strong enough for wind chills to get close to 0F.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 229 PM MST Tue Feb 14 2023
Wednesday night, the large storm system will move into the Central
Plains States with scattered light snow showers continuing across
the high country and the plains south of I-76 during the evening
hours. The fresh snow cover combined with gusty north-northwesterly
winds to 40 mph could create areas of blowing snow across the plains
east of Denver through midnight with windchill readings as low as
-15F.
On Thursday, upper level high pressure will build over the
Intermountain West with continued troughiness over the Central
Plains States. Colorado will be in-between these two systems under
the influence of a drier northerly flow aloft. This pattern will
result in dry weather and continued below normal temperatures across
the CWA. Dry and much warmer conditions are expected on Friday as
the upper level ridge of high pressure moves over the Rocky Mountain
Region.
Over the weekend, the upper ridge flattens with a stronger zonal
flow setting up over Colorado. This pattern should bring continued
dry and mild conditions to areas east of the mountains due to a
downsloping flow. The mountains should also remain dry through
Sunday morning due to the presence of a somewhat dry airmass at
mid levels.
The chance of snow should increase across the high country by Sunday
afternoon as increasing mid level moisture and lift associated with
an upper level shortwave moves across the region. In addition, the
deterministic GFS and ECMWF runs suggest the potential for some
brief snow bands Sunday night into Monday morning due to the passage
of a cold front and possibly some CSI associated with a strong upper
jet over Southeastern Colorado. However, most of the other
deterministic and ensemble members keep the upper jet too far to our
south to produce any precipitation across our plains.
Early next week, Colorado will be under the influence of a moist
west-northwesterly flow aloft with a series of upper level
shortwaves moving across the CWA. As a result, the mountains should
see periods of light to moderate snow through this period with
cooler unsettled weather on the plains.
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1026 PM MST Tue Feb 14 2023
Light to moderate snow will continue spreading north and northeast
across terminals through 08z. The snow will continue through the
night and much of the day on Wednesday before diminishing by
evening. Expect mainly IFR conditions through much of the period
with the snow. Surface winds will remain north and northeast at
10-20kt. Snow accumulations on runway surfaces will be 4-6" at
KDEN and 5 to 8" at BJC/APA.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight MST Wednesday night for
COZ034.
Winter Weather Advisory until midnight MST Wednesday night for
COZ035-039-040-043-044.
Winter Storm Warning until midnight MST Wednesday night for
COZ036-037-041.
Winter Storm Warning until midnight MST Wednesday night for
COZ045>047-049.
&&
UPDATE...Rodriguez
SHORT TERM...Danielson
LONG TERM...jk
AVIATION...Entrekin