Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 201043
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
343 AM MST Mon Feb 20 2017

.SHORT TERM...(Today and tonight)
Issued at 343 AM MST Mon Feb 20 2017

The short wave trough responsible for light rain showers across the
Plains and a welcome snow to the ski country Sunday night into early
this morning continues to shift east into the Central Plains.
Moisture and instability has decreased quite a bit as the trough
axis pulls away from Colorado.  The last of the light sprinkles will
exit NE Colorado in the next hour or so. Expect the snow to end
in the mountains by about 9 AM.

Today Colorado will be on the backside of the trough with dry NW
flow aloft. A flat ridge with synoptic scale subsidence will
result in parly to mostly sunny skies and continued well above
normal temperatures across much of the CWA. 700 mb temperatures
are similar to Sunday`s and there is neutral temperature advection
occuring throughout the day today and overnight into Tuesday.
Thus, expect high temps across the Plains in the low to mid
60s.Winds across the Plains will also be strong out of the
northwest (20-25 mph with gusts to 30 mph) this afternoon given a
tight pressure gradient between the surface high iacross W.
Colorado and low across the Northern Plains of the U.S. Mountains
will be in the 40s, though North Park and the snow cover there
should keep temps in the 30s. Above 9000 feet temps should also
stay in the 30s. Overnight lows Tuesday morning will be above
normal with mid 30s across the Plains, though in and near the
foothills lows will remain in the mid and upper 40s with downslope
winds blowing all night and increasing after 3 AM or so.

In addition to keeping min temperatures Tuesday morning up in and
near the foothills, the intensity of the winds will lead to elevated
Fire Weather conditions from the foothills east to the Plains.
Please see Fire Weather Discussion below for details. Models are
indicating favorable conditions for a mountain wave to set up early
Tueasday morning with a strong potential temperature trough
downstream of the Continental Divide, and flow at ridge tops out
of the West at 40-50 kts. Models differ on the stability of the
layer at and above 650 mb however. Still think that gusts 50-60
mph are possible from the ridge tops down to favored locations
near the foothills.

.LONG TERM...(Tuesday through Sunday)
Issued at 343 AM MST Mon Feb 20 2017

Wly flow aloft will increase across the area on Tue with stg
downslope flow in the lower levels.  Will see gusty winds across the
higher terrain spreading across the plains during the day.  Hi-Res
WRF shows some potential for high winds thru 15z Tue in and nr the
Foothills with some gusts near warning criteria.  Gusts across the
plains will range from 30 to 40 mph with the higher speeds nr the WY
border.  With downslope warming aftn highs will rise into the 70s
over nern CO with record high of 71 at Denver likely being broken.
In the mtns there will be some moisture affecting the far nwrn mtns
in zn 31 so will keep in some low pops.

For Tue night into Wed the flow aloft will become more wsw with
gusty winds continuing across the higher terrain.  Cross-sections
continue to show some moisture affecting the mtns mainly mainly
north of I-70.  With upper level jet over the area could see some
enhancement of pcpn especially in zn 31 with favorable wsw flow so
will mention likely pops with sct pops in zn 33.  Over nern CO a sfc
low will dvlp over sern CO on Wed as a wk fntl bndry move across the
plains by aftn.  Thus aftn highs will not be as wrm with readings
in THE 60s across most of nern CO except for lower to mid 70s
over srn Lincoln county. Winds will remain gusty over the plains
esp nr the WY border and over the Palmer Divide.

By Thu an upper level trough will move across the area with a decent
shot of mid lvl QG ascent along with favorable lapse rates.  Thus
this will bring a good chance of snow to the mtns.  At lower
elevations a sfc low will be over sern CO/swrn KS as a cold fnt
moves across nern CO.  The last few days the ECMWF and GFS have had
varying solutions as to how much moisture there will be over nern
CO. With the fnt moving across early in the day with upslope flow
developing, hard to believe there won`t be some pcpn across nern
CO especially in the aftn into the evening hours, as mid lvl
ascent affects the area. As for highs readings will likely occur
before noon and then fall thru the aftn.

For Thu night into early Fri both the ECMWF and GFS show a possible
disturbance moving across in wnw flow which will bring more snow to
the mtns. Across nern CO there could be a chc of light snow as
well especially if the wetter ECMWF verifies. By Fri aftn into Fri
night the ECMWF shows drier air spreading across in wly flow
while the GFS shows an increase in moisture. With an upper level
jet being over the area if there is enough moisture around could
see some banded pcpn based on the GFS solution so this will be
something to watch the next few days. As for highs on Fri readings
will stay in the 30s over nern CO.

On Sat the flow aloft will stay mainly wly with sme moisture embdded
in the flow so will keep a chc of snow in the mtns. Across nern CO
it looks dry with highs in the 35 to 40 degree range. For Sat
night into Sun an upper level trough is fcst to move across the
area which will bring more snow to the mtns. Across nern CO there
could be a chc of snow as well Sat night into early Sun with
temps remaining blo normal.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 343 AM MST Mon Feb 20 2017

VFR conditions through Tuesday 18Z at all three
terminals. Only mid and high level clouds are anticipated. Strong
west winds are possible at BJC this morning with a weak mountain
wave possibly setting up. Weak SW drainage winds expected at APA
and DEN through mid morning. Once sufficient vertical mixing kicks
in, winds will be NW at 8-12 kts this afternoon at DEN and APA.
BJC again could be west with speeds exceeding 15-20 kts with a
mountain wave. Tuesday morning looks like a much more significant
mountain wave event for east of the Rockies. Winds at BJC are
likely to be quite strong out of the west after 09Z, while APA
and DEN should have typical drainage winds kicking in after 03Z.

&&

.FIRE WEATHER...
Issued at 343 AM MST Mon Feb 20 2017

Elevated fire weather conditions will occur this
afternoon across the eastern plains roughly east of a line from
Cheyenne WY southeast to Lincoln County, CO.  Opted not to issue a
RFW for this area as conditions are marginal for 4-5 hours between
11 AM to 4 PM. Nevertheless, conditions are favorable for rapid
brush fire growth given NW winds 20-25 mph with higher gusts and
relative humidity values in the teens. In the lower foothills
where the snow pack has melted and across the adjacent plains west
of I-25, west winds will be gusty this morning and afternoon. Low
relative humidity values, warm temperatures, dry/dormant fuels,
and gusty winds will also result in an elevated fire danger in
those areas.

Fire danger will increase across the foothills and adjacent plains
on Tuesday due to gusty winds...low humidity and well above normal
temperatures so a Fire Weather Watch has been issued for the
afternoon and early evening hours.

Fire danger will remain elevated for Wednesday although winds may
not be as strong across the plains but will remain gusty in the
foothills.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Tuesday afternoon through Tuesday
evening for COZ215-216-238>251.

&&

$$

SHORT TERM...Schlatter
LONG TERM...RPK
AVIATION...Schlatter
FIRE WEATHER...RPK



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