Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 230249

Area Forecast Discussion
National Weather Service Denver/Boulder CO
849 PM MDT Thu Mar 22 2018

Issued at 831 PM MDT Thu Mar 22 2018

No major adjustments planned for the grids at this time. Snow
showers developing around 10.5 kft at this time, with snow
reported at the Copper Mtn AWOS. A mix of rain and snow showers
will increase over western Colorado this evening, turning to snow
overnight as the snow levels continue to lower. Southwesterly flow
will favor zone 31 initially, with the best window for snowfall
between 06z and 18z Friday. As the trough axis passes over, then
mid level winds will be westerly Friday afternoon. Gusty west to
northwest winds expected following the passage of the cold front
Friday afternoon. Good sfc pressure gradient sets up 21z-01z
Friday, with gusty winds in the 30-40 mph range across the
northeast plains Friday afternoon and early evening.


.SHORT TERM...(This evening through Friday)
Issued at 335 PM MDT Thu Mar 22 2018

With an upper level ridge in place, clouds will continue to
increase through the day as moisture moves in from Utah.
Precipitation will fall over the northern mountains this evening,
above pass level snow is expected. Below 11,000 feet, the
precipitation will be first in the form of rain, due to warm
temperatures, and a few thunderstorms possible. Snow levels will
fall overnight as a short wave disturbance embedded in the
southwest flow moves over the mountains. The highest accumulations
are expected for the Gore and Park ranges, 4 to 8 inches through
Friday. Other mountain areas should see 2 to 6 inches.

Friday will be another warm day with temperatures around 70 across
the plains and 40-50 for the higher terrain. Due to the airmass
being slightly unstable with CAPE near 500 J/kg, the plains will
see isolated to scattered rain and possible thunderstorms in the
afternoon. The urban corridor will see less precipitation due to
downsloping winds as the system moves east.

.LONG TERM...(Friday night through Thursday)
Issued at 335 PM MDT Thu Mar 22 2018

Main story in the extended is the snow potential area-wide Monday
evening through Tuesday.

After a very warm day Friday, a surface low pulls east-southeast
into the southern Plains and forces a cool front across the plains
of Colorado. A ridge axis will build over the state after
midnight and the Plains will remain dry. However, some residual
moisture combined with reasonably steep lapse rates should
continue light orographic snow across the northern and Central
Mountains, including the I-70 corridor. Expect an additional
Trace-3 inches through sunrise Saturday. After that the ridge
takes over leading to mostly clear skies and continued warmth with
southerly flow from 700 mb to the surface. We are expecting highs
in the 60s to near 70 across the Plains and upper 40s to mid 50s
across the higher terrain and dry area-wide. Winds will be pretty
strong across most of the Plains and Palmer Divide, in the 20-30
mph range with higher gusts and with RH around 15% fire danger
will be elevated with a chance of critical across much of the

On Sunday southwest flow aloft increases, inducing a broad lee
trough east of the mountains. Winds should be weaker across much
of the Plains other than the east side of the Palmer Divide and
the far northeast Plains. Fire danger will be highest across
Elbert/Lincoln counties with continued very dry air. Weak low-
level moisture may sneak into the northeast corner of Colorado
reducing the fire weather concerns despite stronger winds. Highs
Sunday will again be well above normal area-wide, with highs
around 70 for the Plains and similar temps in the mountains
compared to Saturday.

It`s still a ways out but models are slowly coming into better
agreement on the strength and movement of the West Coast trough.
By Monday morning the trough digs into Utah. As has been the case
so far with this system, the GFS is strongest, the Canadian the
weakest, and the ECMWF in between but closer to the Canadian
model. The increasing flow aloft combined with synoptic forcing in
the curved flow should lead to a deepening surface low across
southeast Colorado/southwest Kansas. This low will drive a strong
cold front across the Plains, which will keep temperatures in
check on Monday. The high temperature is likely to occur around
noon as strong cold advection combined with thick stratus behind
the front dramatically reduce the power of the late March sun,
dropping temperatures into upper 30s to low 40s by sunset across
much of the Plains. With the trough pretty far southwest of our
area, synoptic lift is limited. Moisture and moderate lapse rates
aloft in the southwest flow should result in orographic snow in
the mountains through Tuesday night. A 120 kt jet looks to put
Colorado in the left exit region early Monday as well, leading to
an additional source of lift for mountain snowfall. At this time
rates and total amounts do not look to be impressive but they will
take anything they can get up there. Low-level moisture across
the Plains looks good behind the front, and combined with deep
easterly upslope flow precipitation should begin around midday on
Monday. The low deepens across SE Colorado through late Monday
night, resulting in a pretty good chunk of time for upslope
precipitation, with the best amounts along and west of I-25 and
along the Palmer Divide. Snow levels are likely to start right
around 6000 feet across the urban corridor, but even a little wet
bulbing should result in a fairly quick changeover to snow, if not
all snow to begin with. Further east, roughly east of a Fort
Morgan to Limon line, wet bulb temps remain warmer so any precip
that falls will likely start off as rain until midnight or so and
the low-level cold air advection increases across eastern
Colorado. It`s much too early to say now much snow could fall but
accumulating snow is certainly a possibility through Tuesday
morning. Tuesday will feel pretty raw, especially if there is any
snow cover, as continued cold advection holds temps in the 40s
across the Plains and 30s in the mountains.

The models continue to disagree a bit on the evolution of the
trough which will determine if snow will fall Monday and Tuesday
and what impact it may have on travel across our area. There looks
to be a massive blocking ridge that builds across the west coast
Tuesday and Wednesday, as well as a ridge over the SE U.S.,
leading to slow forward progress of the trough Monday through
Thursday. Unfortunately for those of us who really like
precipitation, downstream of the West Coast ridge the jet forces
the trough to dig south into New Mexico by Wednesday morning,
effectively shutting off precipitation across our area by early
Wednesday. The ECMWF has quick moving clipper system trough moving
southeast across our area late Wednesday into Thursday, while the
GFS has Colorado in the doldrums in between the cutoff to the
south and northwest flow across Montana. Thus slight chance PoPs
are in the forecast in the mountains but uncertainty is still
quite high from Tuesday on. Given a cut off well south of us and
the polar jet across the far northern Rockies, we are likely to be
cool area- wide and dry across the Plains with slightly below
normal temperatures through Thursday.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 831 PM MDT Thu Mar 22 2018

VFR conditions over the next 24 hrs. Boundary pushing through KDEN
at this time with west/northwest winds of 8-12kts, should
eventually transition to drainage after 05z. South/southwesterly
winds should persist through 18z Friday, then transition to
northwesterly following fropa. Could see some gusts in the 25-35
kt range develop at the terminals after 21z Friday afternoon.


Issued at 335 PM MDT Thu Mar 22 2018

Southern Lincoln County will be under a Red Flag Warning Friday
due to warm temperatures, gusty winds, and low relative humidity
values. Saturday afternoon looks like a potential repeat of
Friday, with winds 20-30 mph across the Palmer Divide and areas
east, combined with around 15% RH. Elevated to near critical
conditions may exist in zones 246 and 247, with areas to the north
more marginal.


Winter Weather Advisory until 6 PM MDT Friday for COZ031.

Red Flag Warning from 11 AM to 7 PM MDT Friday for COZ247.



SHORT TERM...Sullivan
LONG TERM...Schlatter
FIRE WEATHER...Schlatter is the U.S. government's official web portal to all federal, state and local government web resources and services.