Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 171001

Area Forecast Discussion
National Weather Service Denver/Boulder CO
401 AM MDT Sat Mar 17 2018

.SHORT TERM...(Today and tonight)
Issued at 400 AM MDT Sat Mar 17 2018

SW flow aloft will be over the area through tonight as an upper
level trough is over the wrn US.  Cross-sections show some mid
and higher level moisture embedded in the flow, however, lower
levels will remain dry. At this time will only mention low pops
over zn 31 late tonight with dry conditions elsewhere. Meanwhile
with sfc low pres developing along the front range will see gusty
southerly winds by early aftn across the plains. As far as highs,
readings will be in the upper 50s to mid 60s across nern CO except
over the far nern corner where highs may only reach the lower

.LONG TERM...(Sunday through Friday)
Issued at 400 AM MDT Sat Mar 17 2018

...Snow expected for much of the forecast area by Sunday

Satellite analysis shows one significant shortwave associated with
the western U.S. trough lifting northward into Idaho early this
morning, while the next piece of energy was just beginning to
organize off the central California coast. This wave will move
inland today and be our weather maker starting Sunday afternoon
and Sunday evening.

Sunday will start off rather mild with warm and relatively dry southwest
flow aloft across the forecast area. We should see a fair amount
of sunshine with such southerly flow ahead of the deepening
trough. Moderate to strong surface pressure falls will occur ahead
of this system with daytime heating and increasing Q-G lift. At
this time, expect the main surface low pressure system to
organize over southeast Colorado Sunday afternoon, and then push
into southwest Kansas or the OK/TX panhandle region by Monday
evening. This is where the forecast gets tricky.

There are still a few model runs including the EC and Canadian
which take the low and mid level circulation center a bit farther
south than the GFS and NAM. That farther south solution would
keep the deeper and stronger upslope flow away from the Front
Range, with a more northerly component expected. However, even the
farther north GFS and NAM have a short-lived upslope event, and
also keep the developing TROWAL (trough of warm air aloft) farther
east across the plains. At this time, it looks like the bulk of
the precipitation across the mountains will be convectively
induced, starting Saturday afternoon and continuing into the
evening. As a result, most of the snowfall amounts are expected
to be in the advisory criteria, unless the location and intensity
of the upper low are off (and we`ll need to monitor this today as
the main upper disturbance moves onshore). Then, we could still be
looking at more significant precipitation across the Front Range
Mountains and foothills. At this time, we have pretty good
confidence for a moderate snow event of 4-10 inches across the
Front Range mountains and foothills, with locally higher amounts
possible due to convective bursts tomorrow afternoon/early
evening. We could even see some thundersnow with a couple hundred
joules of CAPE and synoptic lift in play during peak daytime
heating. Will continue to adjust these amounts as necessary.

On the plains, the tricky forecast is in play here as well given
marginal temperature profile, convective nature, and position of
eventual TROWAL. We do think the convective character and heavier
precipitation rates will lend itself to a quicker changeover to
snow Sunday evening, and a difference of an hour or two could lend
itself to big changes in the total accumulation forecast. At this
time, the most likely scenario is for rain to change over to snow
by mid evening along the I-25 Corridor, and across the eastern
plains after midnight. If that occurs, then we`d be looking at
1-3" of snow (outside of the strong downslope areas like Greeley),
and up to 4-8" over the Palmer Divide. If the changeover occurs
just an hour or two earlier, then we could easily add on a couple
more inches in Denver. The Palmer Divide is where the most concern
is now for solid Winter Weather Advisory numbers, if not higher.
For now confidence is still not high enough in any of our
forecast area for a Winter Storm Watch, and will let the later
shifts to see how the upper low track and confidence in any given
scenario plays out.

Snow will taper off and end from west to east across the plains
later Sunday night into Monday morning. Behind that, look for
scattered lighter snow showers to linger - mostly in the
mountains. Winds will become quite gusty across the plains in the
wake of the deepening surface low, with gusts of 35-45 mph Sunday
night through Monday. This may produce some blowing/drifting in
areas that see colder temperatures and more snow (Palmer Divide).

Beyond that, upper level ridging and warming temperatures will
take hold for Tuesday and Wednesday. Then the next system which
has some subtropical characteristics to it will bring a return of
some wet but mainly light snow in warm/neutral temp advection
Thursday into Friday. Plains should stay mostly dry through this


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 400 AM MDT Sat Mar 17 2018

A Denver cyclone will develop by early aftn to the southwest of DIA
with a convergence zone across the metro area. South winds early
this morning may become light west or southwest by 15z and then
transition to more northeast by midday. By 21z southerly winds may
move across the airport as boundary lifts north. If cyclone
becomes well defined could see a few hours of sustained winds in
the 15 to 20 mph range with higher gusts. By early evening Denver
cyclone may move to the east/northeast of DIA with a northwest
wind shift for a few hours. By midnight winds will transition back
to drainage.


Issued at 400 AM MDT Sat Mar 17 2018

Fire danger will become elevated over the Palmer Divide and across
Lincoln county this afternoon as humidity levels drop down to 15%.
South winds of 15 to 20 mph will develop with a few gusts up to 25
mph at times.

Fire danger will be elevated again on Sunday across Elbert and
Lincoln counties where southerly winds gusting to 25 mph and RH
will drop under 15%.




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