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Area Forecast Discussion (AFD)

Issued by Denver/Boulder, CO (BOU)

FXUS65 KBOU 230239

Area Forecast Discussion
National Weather Service Denver/Boulder CO
839 PM MDT Mon Oct 22 2018

Issued at 838 PM MDT Mon Oct 22 2018

Forecast looks on track with the weak diurnal convection 
dissipating this evening. Meanwhile, the next batch of showers and
even a few thunderstorms continued to spread northeast out ahead 
of the Great Basin trough and through southwestern Colorado. 
These will continue to push northeast with the leftovers reaching 
our mountains after midnight. The heavier showers will dissipate 
however, as the majority of this moisture and precipitation will 
be wrung out over the Central and Southwest Mountains of Colorado.
A few of the higher peaks in Summit/Park County should still be 
able to pick up an inch or two through Tuesday morning, while a 
few snowflakes are expected down to about 9000 feet later 
tonight. We expect a few more breaks in the clouds tomorrow behind
this wave, but ahead of the additional convective development 
Tuesday afternoon. There is a couple hundred J/kg of CAPE over the
higher terrain so can't rule out an isolated thunderstorm over 
the mountains in the afternoon. There should be enough clouds 
around to prevent much fog formation, just a chance of that over 
the Palmer Divide/Cheyenne Ridge area later tonight with southeast
flow into those ridges. 


.SHORT TERM...(This evening through Tuesday)
Issued at 314 PM MDT Mon Oct 22 2018

Isolated to scattered showers are expected to continue over the 
mountains through early evening. Airmass has become unstable with 
surface based CAPEs of up to 400 J/kg. Showers should decrease 
early to mid evening as the airmass stabilizes. A strong short 
wave trough over northern Arizona and Utah lifts northeast tonight
and may bring additional showers late tonight and early Tuesday 
morning. Best lift looks to stay west of the area, but should be 
enough lift to produce more showers. Precipitation amounts are 
expected to be light. The snow level will remain high, 9,500 to 
10,000 feet MSL. Southeast winds will transport moisture into 
eastern Colorado late tonight and Tuesday. Expect low clouds to 
form by sunrise Tuesday morning across parts of eastern Colorado. 
They may hang on for a good part of the day and result in cooler 
temperatures. For the Urban Corridor, low clouds should stay east 
of the area, so temperatures are expected to be a little warmer 
with upper 50s to lower 60s expected Tuesday afternoon. 

.LONG TERM...(Tuesday night through Monday)
Issued at 314 PM MDT Mon Oct 22 2018

A weak upper level trough will move across the area Tue night 
through Wed. Quite a bit of moisture is associated with this 
feature along with some weak mid lvl qg ascent. This will bring a 
good chc of precip to the higher terrain along and south of I-70 
Tue night and across the plains on Wed. Snow amounts in the mtns 
should stay below advisory criteria. Highs on Wed will be in the 
mid 50s to lower 60s across nern CO.

For Wed night the upper level trough will move east of the area as 
drier air spread across.  Thus precip will end over the plains Wed 
evening.  On Thu northwest flow aloft will be over the area with 
some mid and high level moisture embedded in the flow.  The ECMWF 
has a weak disturbance moving across Thu night which may lead to a 
slight chc of showers in the mtns.  As for highs, readings will be 
in the 60's over nern CO.

On Fri northwest flow aloft will remain across the area with dry 
conditions expected thru the aftn hours.  Highs will remain abv 
normal with readings in the 65 to 70 degree range.  For Fri night a 
a pacific front will move across the plains in association with an 
upper level jet.  The ECMWF generates some light precip across the 
plains in association with the upper level jet while the GFS has no 
precip.  Will mention a slight chc of precip over the plains for Fri 

On Sat NW flow aloft will continue with limited moisture 
embedded in the flow so will not mention any precip.  As for highs, 
850-700 mb temps are similar to Fri so I'm not sure why blended 
solution is giving me lower temps which makes little sense.  Thus 
highs may end up just as warm as Fri. 

For Sun mainly dry NW flow aloft will remain with no precip 
expected. Both the ECMWF and GFS have a cold front moving across 
the plains which would bring cooler temps as readings drop back to
seasonal levels. 


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 838 PM MDT Mon Oct 22 2018

VFR conditions are expected to prevail through Tuesday with BKN
mid to high level clouds. There is low level moisture advection on
the plains tonight, but the majority of the low cloud/fog threat 
should stay mostly over the Cheyenne Ridge and on the southern 
side of the Palmer Divide given the south/southeast low level 
flow. We don't think there is enough low level moisture advection 
to produce much fog threat at KDEN, especially considering the 
lack of boundary layer cooling due to the mid/high level clouds. 
There will be a better chance for low clouds late Tuesday night 
and Wednesday. 

With regard to winds, a Denver Cyclone is in place resulting in
NW winds at KBJC, and a more southeasterly component at KDEN and
KAPA. Latest radar shows the cyclone weakening, but flow remains
favorable for the cyclone to remain in place overnight. By Tuesday
afternoon, we expect south/southeast winds to increase at KDEN and
KAPA with gusts to 20-25 knots after 18Z.