Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 222122

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

.SHORT TERM...(This evening through Friday)
Issued at 220 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

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 220 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 Plains.

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 18Z TAFS through 18Z Friday afternoon)
Issued at 220 PM MDT Thu Mar 22 2018

VFR conditions through Friday afternoon. Light winds with a
predominantly south component through the period.


Issued at 220 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 252 and 253, with areas to the north
more marginal.


Winter Weather Advisory from 9 PM this evening to 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...Sullivan/Schlatter is the U.S. government's official web portal to all federal, state and local government web resources and services.