Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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520
FXUS65 KBOU 221702
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1102 AM MDT Wed Mar 22 2017

.UPDATE...
Issued at 1040 AM MDT Wed Mar 22 2017

Todays`s forecast looks on track for high temperatures. Made some
minor adjustments to the winds as the Denver Cyclone has set up as
expected and will keep the winds from I-25 and west on the light
side. Conditions look favorable for red flag warning criteria
Thursday afternoon, and the fire weather dicussion will handle
that below and we are watching a major change in the weather
pattern starting Thursday evening. Biggest challenge will be
whether snow levels drop below 6000 feet elevation as the models
continue to differ on this detail, leading to uncertainty in the
precipitation type for the Denver metro area. Stay tuned.

&&

.SHORT TERM...(Today and tonight)
Issued at 446 AM MDT Wed Mar 22 2017

Cooler air with southeast winds across the plains today. There
are some low clouds along the eastern border, but the air is drier
further west. Expect these clouds to dissipate during the day, but
it will help keep temperatures cooler near the border.

Meanwhile the mountains are in a warmer and drier southwest flow
ahead of the approaching system. There may be some minimal
convection this afternoon, but the main story will be increasing
wind, especially overnight. South to southwest direction is not
favorable for our normally windy areas but will hit some spots
that don`t usually blow too hard, especially southwest of Denver.

The Denver area will be in between these two regimes. The
combination of the plains winds and inversion will maintain a
Denver cyclone with some kind of lighter northerly wind prevailing
across the city much of the day. HRRR insists on gradually washing
out the cyclone and bringing some warm/dry west winds off the
foothills late in the day. This looks overdone. Upgraded NAM is
actually capturing the circulation fairly well, so its wind fields
were used heavily this morning.

Some moisture increase overnight may bring light showers to the
mountains, but this should be limited and the snow level will
remain high, between 9 and 10 thousand feet.

.LONG TERM...(Thursday through Tuesday)
Issued at 446 AM MDT Wed Mar 22 2017

On Thursday, one more warm day ahead of our incoming storm system.
Gusty southerly winds, coupled with low relative humidities and
dry fuels will elevate the fire danger along the Palmer Divide
region in the afternoon, reference the discussion below. Next
trough over the Great Basin region 12z Thursday, will be near the
Four Corners region by 00z Fri, and intensifies over sern CO by
12z Friday. All the mdls are in fairly good agreement regarding
its location by 12z Friday. Mid level qg ascent increases rapidly
over east central CO Thu aftn, Weak to moderate qg ascent over
northeast CO Thursday aftn, with enough instability to warrant a
slgt chc of tstms. Rain and snow showers will develop in the
mountains during the day, but the intensity of the pcpn will pick
up significantly Thursday evening, with strong qg ascent over
eastern CO as the upper low closes up over sern CO. Increasing
northeasterly upslope with the ams saturating THU night. Should
see heavy snowfall develop in the Front Range Mountains and
foothills especially from Jefferson County southward overnight.
Heaviest snowfall will be 03z to 15z Friday, then the low and mid
level flow transition to northerly through the day Friday. Snow
level still a big question mark for the Urban Corridor, but the
mdls have been trending a little colder, nudging the snow level a
little lower. No highlight yet since its the fourth period, but
will likely need to hoist a Winter Storm Watch later today for the
Front Range Mountains, Foothills and possibly the Monument Ridge
above 6 kft or ZN 41. Very strong northerly winds gusting to 50
mph on Friday will likely produce blowing and drifting snow over
the Palmer Divide as well. Mdls still showing rain or a mix of
rain/snow for most of the the urban corridor but could see some
accumulating snowfall above 5500 feet near the foothills of
Jefferson/Douglas Counties. Gradient from rain to snow will likely
be pretty tight. Further north, if the low and mid level flow
transitions to northerly too fast, than downslope off the Cheyenne
Ridge could be stg enough to keep mainly rainfall north of
Boulder. Storm will transition to the plains of CO on Friday as
the system makes its way into scentral KS/northern OK by 00Z
Saturday, with diminishing pcpn fm west to east Friday night.
Trend for drier and warmer on Saturday still on track. The next
system is progged to move across CO midday Sunday so another chc
of snow mountains with rain across northeast plains Sunday
aftn/evng. Drier Sunday night into Monday, with another chc of
pcpn for the region by Wednesday of next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1040 AM MDT Wed Mar 22 2017

VFR conditions through Thursday afternoon with just scattered mid
and high clouds. Winds will be tricky today at APA and DEN under
the influence of lee troughing and a Denver Cyclone. The HRRR and
NAM have both picked up on the formation and evolution of the
cyclone this afternoon, keeping APA and DEN in a N or NNE flow at
less than 10 kts. Will keep that in place in those TAFs until 06Z
when southerly drainage kicks in. BJC should go from WNW this
evening to WSW drainage winds after 10Z.

&&

.FIRE WEATHER...
Issued at 1040 AM MDT Wed Mar 22 2017

We`ve already issued one spot forecast for a wildfire in southwest
Jefferson County. Conditions today will continue to be very dry
but winds should remain below red flag warning criteria across the
CWA today. We upgraded the watch to a red flag warning for
Thursday afternoon and included fire weather zones 239 and 216.
Very dry air and an increase in winds are expected across the
southern half of our area along and east of the foothills. Winds
will be marginal in parts of 239, especially the northern half of
239, and in 216, but given the dry fuels and very dry conditions,
coupled with much above average temperatures, an RFW is warranted.
Elsewhere across the warned area winds will be out of the
southwest 15-25 mph with higher gusts possible, leading to rapid
fire growth. Thursday evening and overnight into Friday should
bring relief in the form of precipitation and much cooler
temperatures.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 6 PM MDT Thursday for COZ216-
239>241-245>247-249.

&&

$$

UPDATE...Schlatter
SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Schlatter
FIRE WEATHER...Schlatter



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