Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 231005
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
405 AM MDT Thu Mar 23 2017

.SHORT TERM...(Today and tonight)
Issued at 323 AM MDT Thu Mar 23 2017

For today, have trended the grids to a little warmer and drier
through 00z. Mdls slower to developing precipitation form the
Front Range Foothills eastward. The flow aloft will transition
from southwesterly to southerly today, with the strongest winds
aloft over the eastern plains. Reference the Fire Weather
discussion below as the Red Flag Warning has been expanded for
this afternoon. Upper low over Nevada at this time, and is progged
to move into the Four Corners region by 00z this evening. Dry
slot ahead of it so no qpf developed in any of the mdls until 00z
over the Urban Corridor and northeast plains. Transition from
abnormally dry conditions to cold and wet will occur this evening.

The mdls intensify a sfc low over southeastern CO from 03-06z this
evening with strong north/northwesterly winds developing across
the cwa from the Urban Corridor eastward across the northeast
plains. Weak mid level qg ascent over northeast CO through 18z
but increases significantly around 00z with developing
cyclogenesis over sern CO. moderate to heavy rainfall over the
northeast plains this evening as this system intensifies. The mdls
all consistent with the sfc and upper low over sern CO at 12z
with a nice fetch of moisture wrapping around the system. The
winds at the sfc and aloft generally north/northwesterly which
will shift the focus for the heaviest snowfall to the Southern
Front Range Foothills and Palmer Ridge late tonight. Snow will
develop in the mountains and foothills this evening, but the
heaviest snowfall is not expected until after 06z so have delayed
the Winter Storm Watch for Zones 36 and 34 until that time.
Confidence in heavy snow for Zone 33 not as high and harder to
justify so have changed the Winter Storm Watch there to a Winter
Weather Advisory. Strong winds with snow developing south and
southeast of Denver as the sfc low intensifies from 06z-12z
tonight. Have opted to go with a Blizzard Watch for zone 41 after
06z and added zones 45 and 46 to the Blizzard Watch after 09z.
Moderate to heavy snowfall expected to develop aoa 5500 feet, with
850-700 mb lyr winds of 50-60 kts by 12z which could impact
Interstate 70 east of Denver to west of Limon and Interstate 25
south of Denver toward Monument. Will keep zone 47 in the High
Wind Watch. Areas in the Denver area south of I70 could see some
light snow developing, but not much north of the interstate
expected.



.LONG TERM...(Friday through Wednesday)
Issued at 323 AM MDT Thu Mar 23 2017

A stg storm system will be over extreme sern Co at 12z Fri and then
will move east into cntrl KS by late aftn.  Stg mid lvl ascent will
be over nern CO in the morning but gradually shift eastward by
midday.  Meanwhile a stg low lvl gradient will be across all of nern
CO in the morning but will weaken by mid to late aftn as the storm
system moves eastward.

Low lvl flow is fcst to be mainly nly on Fri which generally should
keep heavier mainly along and east of I-25 and across the Palmer
Divide.  Buffer soundings show snow levels dropping blo 5500 ft by
12z so will see some accumulation on grassy areas.  Will see heavy
snow over the Palmer Divide which may extend out to the Limon area
as well.  Central and eastern areas of Denver metro could see some
heavier snow through mid morning however confidence isn`t high
enough to issue a watch

With 700 mb winds fcst to be in the 60-70 kt range stg winds with
blowing snow will be an issue thru midday so have decided to issue a
blizzard watch for zns 41 and 46. Srn portions of zn 45 could have
some issues as well so may include them too. Will also keep the high
wind watch going for zn 47 which will likely see high winds.

Across the rest of the plains will see a mix of rain and snow
through the aftn.  Winds will be gusty as well with speeds from 25
to 35 mph with gusts up to 50 mph.

In the mtns and srn foothills, if flow stays nly, amounts may end
mainly in the advisory range however will leave watch in place for
zns 34 and 36.

By Friday evening things will calm down as the storm system
continues to move eastward.  On Sat an upper level ridge will
briefly dvlp over the area before another upper level trough moves
across on Sun.  Sat should be dry with warmer temperatures.  On Sun
as the next system moves across will see a good chc of snow in the
mtns.  Over nern CO cross-sections show an increase in moisture
along with some weak upslope flow so will keep in a chc of showers
with cooler temperatures.

On Mon an upper level ridge will rebuild over the area ahead of
another storm system that will develop over the Great Basin.  There
will be some moisture in the mtns so will mention a chc of showers
over the higher terrain.  Over nern CO it will be dry with warmer
temperatures.

By Tue the ECMWF and GFS are in poor agreement.  The GFS digs the
Great Basin upper level low into cntrl AZ while the ECMWF has the
low nr the four corners.  Meanwhile on Wed he GFS has the low over
srn AZ while the ECMWF has it over srn CO.  With so much
disagreement between the two models will just mention a chc of pops
across the area until it becomes more clear how things will play
out.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 323 AM MDT Thu Mar 23 2017

VFR expected through 00z this evening with gusty south/southwest
winds through that time. Cig will lower dramatically late this
evening as the surface low associated with the storm system starts
to intensify over sern CO. Strong northerly winds will develop
after 03z with scattered rain showers through 06z, then a
rain/snow mix 06-09z with snow developing 09z-12z. ILS
restrictions with cigs 040-050 kft 03z-06z tngt, the MVFR cigs
until 09z, with IFR cigs/vsbys with the transition to
snow/blowing snow by 12z.

&&

.FIRE WEATHER...
Issued at 323 AM MDT Thu Mar 23 2017

Dry slot developing over the northeast plains today with very low
relative humidities and gusty south/southwest winds this afternoon
ahead of the nxt storm system. Have expanded the Red Flag Warning
to also include Fire WX Zones 242, 244, 248, 250 and 251. &&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 6 PM MDT this evening for
COZ216-239>242-244>251.

Winter Storm Watch from late tonight through Friday morning for
COZ034-036.

Winter Weather Advisory from midnight tonight to noon MDT Friday
for COZ033.

Blizzard Watch from late tonight through Friday morning for
COZ041.

Blizzard Watch from late tonight through Friday morning for
COZ045-046.

High Wind Watch from Friday morning through Friday afternoon for
COZ047.

&&

$$

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



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