Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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186
FXUS65 KBOU 230320
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
920 PM MDT Sat Apr 22 2017

.UPDATE...
Issued at 904 PM MDT Sat Apr 22 2017

Not much in the way of changes overnight, just some minor
adjustments but that is it for tngt.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 307 PM MDT Sat Apr 22 2017

Isolated convective showers had developed near the Front Range
and crest of the Palmer Divide, but these will be dissipating as
the airmass stabilizes with the loss of daytime heating. Then
expect mostly clear skies and a cool night across the forecast
area. Patchy frost is possible across the plains with light winds
through most of the night. However, southerly breezes will
increase late in the night across the Palmer Divide to Denver and
Akron corridor with an increasing pressure gradient. This will be
the onset of warm advection.

On Sunday, temperatures will warm considerably with strong warm
advection aloft under a short wave ridge and increasing
southwesterly flow aloft. 700 mb temperatures and downslope
suggest temperatures pushing well into the 70s on the plains,
with 50s and 60s mountains. Breezy conditions will develop through
the afternoon with increased mixing, although locations around
Boulder county will be last to see the winds increase with Denver
cyclonic convergence zone likely to develop.

.LONG TERM...(Sunday night through Saturday)
Issued at 307 PM MDT Sat Apr 22 2017

Cooler unsettled weather pattern returns early next week...with a
chance for precipitation through much of the period.

Sunday night the upper ridge shifts eastward over the Central Plains
States as a broad upper trough develops over the western United
States. Models are showing this upper trough dominating the Rocky
Mountain Region through next Saturday...with a series of upper level
shortwaves moving across Colorado.

GFS and NAM cross sections show a mountain wave developing on the
lee side of the Rockies Sunday night...with a 50 to 60KT component
along wind mainly above 700mb. As a result...the mountains and
foothills should see some gusty winds. A less then impressive wind
gradient and mountain stable layer along with increased speed
shear aloft should keep winds below criteria levels. In
addition...there should be enough mid level moisture combined with
orographics to produce scattered showers in the mountains Sunday
night and Monday.

Snow should increase across the high country Monday night as upward
QG forcing and increased moisture associated with a 90kt jet moves
over northern Colorado. Models are hinting at a front moving across
the plains Tuesday morning. The GFS and NAM show downsloping flow
across the Front Range Urban Corridor behind the front which would
limit precipitation chances. However...a slight change in wind
direction to a more northerly direction...with the jet overhead
could lead to a better chance for precipitation. Therefore...the
scattered pops loaded by Forecast Builder look reasonable.

Thursday through Saturday...models diverge quite a bit as well as
poor run to run consistency. Latest GFS an ECMWF models have flipped
flopped with the GFS now showing a closed 500 MB low tracking from
northern Utah over the Four Corners Region into northern New Mexico.
The ECMWF has trended further north and east with the low and has it
forming over eastern Colorado Saturday morning. The GEM is more
progressive and only shows an open trough moving across the state.
Impossible to iron out the details at this time. However...one thing
I am pretty sure of that it will be much cooler during this period
with some precipitation expected.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 904 PM MDT Sat Apr 22 2017

VFR conditions through Sunday. Normal transition to south/southwest
winds by 06Z, and increase to 10-15 knots at KDEN and KAPA through
15Z Sunday. Then winds should turn more southeasterly 18Z-21Z. At
KBJC, lighter and variable winds are expected through most of
Sunday.

&&

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

$$

UPDATE...Cooper
SHORT TERM...Barjenbruch
LONG TERM...Kalina
AVIATION...Cooper



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