Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210946

Area Forecast Discussion
National Weather Service Denver/Boulder CO
346 AM MDT Mon May 21 2018

.SHORT TERM...(Today and tonight)
Issued at 346 AM MDT Mon May 21 2018

Residual low level moisture combined with radiational cooling is
producing areas of low clouds and fog over northeast Colorado. The
low clouds and fog will be shallow and should be short lived once
the sun rises this morning. Temperatures will warm into the mid
70s to lower 80s this afternoon under partly cloudy skies.

A weak wave embedded in the southwest flow aloft is expected to
trigger isolated to scattered showers and thunderstorms this
afternoon and evening over the mountains. At the surface, a low is
forecasted to form just north of the Palmer Divide and then shift
east this evening. Convergence along this may also help produce
few showers and thunderstorms. Best chance to see convection will
be south of I-70. ML CAPE is expected to be 500 J/kg or less over
the mountains and south of I-70, so convection should be on the
weak side. Better instability will be over far northeast Colorado,
but storm development is expected to be capped.

.LONG TERM...(Tuesday through Sunday)
Issued at 346 AM MDT Mon May 21 2018

An upper level low over srn California will lift north northeast
into the Great Basin on Tue.  This feature will then continue to
move north northeast into the nrn Rockies on Wed and weaken. Overall
this leaves nrn CO in southwest flow aloft both days.

Cross-sections show an increase in moisture over the higher terrain
on Tue as a disturbance embedded in the flow moves across
northwest CO Tue evening. Thus should see a better chc of
aftn/evening showers and tstms over the higher terrain. Across
nern CO, sfc low pres will be in place with a pseudo dryline over
the plains. Capes will be decent over the far nern plains in the
aftn/evening so there could be a better chc of stronger storms in
this area. Elsewhere over the plains only expect isold/widely sct
storms. Highs on Tue will be in the lower to mid 80s over nern CO.

On Wed, drier air will spread across the higher terrain in
southwest flow aloft, thus expect tstm coverage will be in the
isold-wdly sct range. Across nern CO, sfc low pres will be located
nr the Denver area with a weak boundary/dryline across the
plains. Once again there will be decent cape along and north of
the boundary, so this would probably be a focus area for a few
stronger storms in the late aftn/early evening hours. Highs on Wed
will remain in the lower to mid 80s across nern CO.

For Thu and Fri the flow aloft will become more westerly with cross-
sections showing limited moisture over the higher terrain so will
keep pops on the low side.  Across the plains, weak sfc low pres
will remain near the Denver area with a boundary/dryline still
located across the plains.  Thus will keep in a slight chc of tstms
for the late aftn/early evening hours.  Highs will continue to be in
the 80s over nern CO both days.

On Sat an upper level ridge will begin to build into the area which
will keep temps 10 to 15 degrees above normal. Cross-sections
show limited moisture so tstm chances will be on the low side.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 346 AM MDT Mon May 21 2018

Airmass remains moist in the lower levels. There are areas of
haze and fog in the Denver area and north to Fort Collins. Patchy
low clouds and fog will remain possible through 15Z. Will have
some reduced visibility in the TAFs for this. Can`t rule out
visibility falling to a quarter mile. The fog will be shallow and
should burn off quickly where it forms, around 15z.

Isolated showers and thunderstorms are expected to form this
afternoon mainly from Denver south. The showers and storms are
expected to be weak and the biggest impact may be a wind shift. The
main time frame for the showers and thunderstorms is expected to be
22Z to 02Z.




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