Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 220251
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
851 PM MDT Tue Mar 21 2017

.UPDATE...
Issued at 837 PM MDT Tue Mar 21 2017

The showers have ended across the CWA. Cloudiness is on the
decreases as well. The wind field across the plains has become all
southeasterly at this time. Will clean up the pops, sky cover,
weather and temperatures according to actual conditions.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 400 PM MDT Tue Mar 21 2017

The shortwave trough helping much needed showers move across the
northern part of the state will continue pushing east tonight.
More showers formed to the north than further south near the
Palmer Divide, which is what more of the hires model runs had
been advertising. The Denver Cyclone formed further south and
east, not allowing the wetter airmass into the urban corridor for
that better chance for showers. Hi res models still cannot get
ahold of the cyclone`s position. Most activity should therefore
remain further north along the states border. Most thunderstorm
activity staying to the north of the state as well, will keep a
slight chance along the northern border early this evening, but
will take out any mention after sunset with loss of suns heating.
Showers will likely continue into the evening as the shortwave
passes overhead. A deepening surface low along the urban corridor
and high surface pressure over the Great Plains will keep moderate
southerly winds across most of the plains tonight. Moisture in the
southeasterly flow over the plains will keep low clouds over the
northeastern corner of the state.

Southwesterly flow aloft will increase Wednesday for a slightly
warmer and drier day. Winds will be increasing through the day,
but no fire weather criteria should be met. A few isolated showers
may move into the northern mountains by late afternoon.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 400 PM MDT Tue Mar 21 2017

An upper level low off the coast of CA by 00z Thursday will move
onshore to bring rain and snow to the extended. The incoming
trough will increase upper level SW flow over the state. At the
surface Wednesday night into Thursday a deepening lee side low on
the plains will increase the dry SW flow over portions of eastern
plains. This will aid in decreasing RH levels over areas such as
Elbert and Lincoln counties with highs increasing back into the
70s. With the gusty SW winds up to 35 mph Fire weather concerns
will be heightened. Elsewhere on the plains convection will be
possible slightly further north with build up along the dryline
created by the dry and warm SW flow combining with a cold frontal
push from the north by late afternoon Thursday. The timing of the
more moist air with max heating of the day could allow for some
severe weather to develop by late afternoon. Upper air soundings
show CAPE values over the Akron area hovering around 700 J/kg with
deep shear values up to 80 kts. This would support strong
thunderstorm development and possibly severe winds and hail along
and north of a line from Sterling to Akron. Conditions may be
capped until later in the afternoon and the onset of better
dynamics provided by the left exit region of a 80 to 90 kt jet.
Dewpoints will be higher over Kansas but could still see values
in the 40s over far eastern plains. Over the mountains moisture
will increase ahead of the incoming trough and bring initially
rain with a rain and snow mix at higher elevations and passes that
will change over by late Thursday evening and continue through
Friday. Temperatures for Thursday will continue to be warm
initially with highs in the lower 70s across the plains. Cooler
temperatures will be further north near Cheyenne and will drop
through the late afternoon as the cold frontal boundary pushed
south.

By 00z Friday the upper trough will be over the Great Basin before
closing off and transition eastward. Models have slightly
different trends as the low progresses across the CO and NM
border. The GFS and Canadian keep the track further south before a
sharp turn to the SE by 18z Friday. The EC has it further North
before the sharp turn SE late Friday. The key for this storm will
be the cold air intrusion onto the plains. Current model wet bulb
levels keep it hovering between 6000 and 7500 ft. Further North
near the Wyoming border levels could drop down to 5500 but
otherwise expect mostly rain on the plains Friday. Winds will also
be a factor for Friday with the strong northerly flow and deep
surface low to the south. Wind gusts up to 40 mph on the plains
will be possible by Friday afternoon and will continue into the
overnight hours. Amounts will vary with snow in the mountains from
8 up to 18 inches with higher amounts along the eastern slopes of
the higher terrain. On the plains QPF amounts could be upwards of
1.5 inches by early Saturday over the Eastern plains.
Temperatures for Friday will be cooler with highs in the upper 40s
and lower 50s. Overnight lows will drop below freezing into
Saturday.

The system will exit quickly by Saturday with ridging moving in
under increased subsidence. Conditions will be dry with any
lingering moisture in the mountains bringing a slight chance of
orographic flurries. Temperatures will rebound SAturday with highs
in the 60s. By 00z Sunday the next upper level disturbance will be
over the Great Basin with increasing moisture over the region.
This will bring another shot of snow to the mountains with rain on
the plains. This unsettled pattern will continue through Tuesday
with lingering snow in the mountains and rain possible again by
monday night into Tuesday. Temperatures will be in the 50s for
the rest of the forecast period.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 837 PM MDT Tue Mar 21 2017

Southeasterly winds are in place at DIA. Models do eventually
show normal drainage flow by 06Z. There will be no ceiling
issues.

&&

.FIRE WEATHER...
Issued at 400 PM MDT Tue Mar 21 2017

It will be warmer and drier Wednesday, however the only area of
possible concern will be the southern foothills 216 and possibly
over the Palmer Divide 221 and 240, where southwesterly winds may
be strong enough but humidities will be lowest. Worst expected
conditions shouldn`t hit criteria however, with winds only gusting
to 20 mph at the most.

Fire weather concerns will be heightened for Thursday afternoon
with strong SW flow over portions of Elbert and Lincoln counties.
RH levels will drop to 10-15% with winds sustained 15 to 20 and
gusts up to 35 mph between 18 and 21z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...RJK
SHORT TERM...Kriederman
LONG TERM...Bowen
AVIATION...RJK
FIRE WEATHER...Kriederman/Bowen


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