Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 200946

Area Forecast Discussion
National Weather Service Denver/Boulder CO
346 AM MDT Sun Aug 20 2017

.SHORT TERM...(Today and tonight)
Issued at 346 AM MDT Sun Aug 20 2017

Latest surface analysis shows a weak cold front pushing south
across the Northern High Plains. Front as of 330 AM has moved through
most of South Dakota and northeast Wyoming. Front will continue
to push this way through the morning, but only slight cooling of
2-5F is anticipated today. The airmass on the northeastern plains
will likely stabilize behind the front, as evidenced by the
forecast soundings showing a strong cap developing. However, storm
chances should increase along the Front Range as weak upslope
flow develops and airmass still destabilizes sufficiently. Most
storms will originate this afternoon over the higher terrain and
then shift slowly east/northeast across the I-25 Corridor by late
afternoon, and then the plains toward the evening as ongoing
convection should help weaken the cap. If the storms can tap into
the higher boundary layer moisture on the eastern plains, then a
stronger storm or two would be possible over the northeast corner
this evening where CAPE is advertised to increase to 1500-2000
J/kg. Otherwise storms closer to the Front Range will again
produce gusty outflow winds and only light rainfall.

We should see most convection end later this evening, but there
is some weak Q-G lift noted so will watch potential of anything
lasting past midnight. Finally, low level moisture and weak
upslope component late tonight may allow some stratus to develop
over portions of the plains.

.LONG TERM...(Monday through Saturday)
Issued at 346 AM MDT Sun Aug 20 2017

A shortwave will be pushing down from Montana down into the Great
Plains Monday. The 700mb trough will be slightly ahead of this
helping to produce weak upward QG motion from northeastern
Colorado into Nebraska. Current satellite shows clouds from the
expected increase of subtropical moisture moving up the southern
Rockies. Most models have varying levels of clouds over the area
Monday morning, with stability pushing in from the northwest late
morning to likely clear out some of the cloud cover. There is a
chance for patchy stratus over the far eastern plains due to
expected convection tonight over NE. Convection will again start
over the mountains around noon spreading east, dissipating
slightly over the Front Range corridor with better PoPs over the
eastern plains due to better moisture. A cold front will slide
south over the area Monday night to keep a chance of showers and
storms going through most of the night, mainly along and east of
the Divide.

Tuesday will be cooler, back to below seasonal norms in temperatures.
Expect an increase in storm coverage as southeasterly surface
flow increases by high surface pressure over the Great Plains, as
well as an increase in moisture and energy moving out of the
desert southwest. This trend will continue Wednesday with warmer

An upper low over the Great Basin Thursday will push east turning
flow aloft more southwesterly over the state, bringing up another
surge of moisture from the southern Rockies. Expect more
widespread storms Thursday. A fast moving shortwave over the
US/Canada border will increase flow across the state Friday while
the best moisture moves east. A cold front will likely push down
into the area next weekend.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 346 AM MDT Sun Aug 20 2017

Main concern for today will again be relatively high based
convection with gusty/variable outflow winds. Most storms should
develop over the Front Range mountains and foothills with
scattered coverage through the NW and SW approach gates starting
toward 19Z. A few of the storms are expected to eventually push
east onto the plains with a chance of gusty and variable outflow
winds up to 35 knots 22Z-02Z. For now, will have Prob30 in the
TAFS and upgrade to TEMPO later if confidence increases. Otherwise
VFR conditions will prevail. Only a slight chance that low level
stratus and IFR/MVFR ceilings would be able to work back to the
Front Range airports after 09Z tonight. Most of this should hold
on the eastern Colorado plains through Monday morning.




SHORT TERM...Barjenbruch
LONG TERM...Kriederman
AVIATION...Barjenbruch is the U.S. government's official web portal to all federal, state and local government web resources and services.