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Area forecast discussion
National Weather Service Denver/Boulder Colorado
830 PM MDT Sat Jul 21 2018

issued at 830 PM MDT Sat Jul 21 2018

Also, should have earlier stated there is some smoke in the air
this evening related to the flare-up of the Lake Christine fire
near Basalt. There is plenty of smoke aloft, some of which may
settle to the surface with developing inversions overnight.

Update issued at 750 PM MDT Sat Jul 21 2018

We had a couple severe storms over the eastern plains earlier this
evening but appears intensity is weakening. The weakening will
likely continue as storms push east into a more stable/higher
convective inhibition environment. There are some outflow boundary
interactions still occurring behind the main batch of
thunderstorms, but wouldn't expect more than a brief isolated
shower/storm through late evening. Otherwise we will see gradual
clearing as drier air over western Colorado moves across the
forecast area tonight. It will be another warm night with the warm
air dome over the forecast area.


Short term...(this evening through sunday)
issued at 317 PM MDT Sat Jul 21 2018

Short term models remain in good agreement showing convection
over the mountains and foothills this afternoon spreading eastward
along outflow boundaries through the late afternoon and evening.
Ml CAPES reach 500-1000 j/kg over most of the area, but up to 2000
j/kg over the northeastern plains where more moisture will
reside. Can't rule out a brief severe storm over the eastern
plains. Elsewhere, brief heavy rain and gusty winds look to be the
main threat from the storms.

Convection should end by mid to late evening across the area as
the airmass stabilizes. Due to cloud cover and high dew points,
expect a warm night with lows in the 60s for northeast Colorado.

For Sunday, a weak front from the north will push through mid to
late morning. As a result, highs will be slightly cooler. Airmass
stays about as moist as today with precipitable water values
around an inch to a little higher over northeast Colorado. Over
the higher terrain, precipitable water values will be around
three-quarters of an inch. Ml cape climbs 1000-2000 j/kg over the
eastern plains. There may be enough shear to produce a few severe
storms with damaging winds and large hail. Farther west across the
urban corridor and Front Range, heavy rainfall will be the
primary threat.

Long term...(sunday night through saturday)
issued at 317 PM MDT Sat Jul 21 2018

Medium range models continue to show a relatively moist week ahead
of US as the center of the upper ridge gradually migrates
westward, leaving northern Colorado under northwesterly flow
aloft. Today's satellite imagery shows there is a fair amount of
mid-level moisture and instability on the west side of the upper
ridge, rotating over Nevada and Utah. Over the next couple days,
this moisture will be migrating over Colorado. Ample mid-level
moisture is forecast to continue moving over the central rockies
through much of the upcoming week.

Monday afternoon and evening appear to be the first period with
the chance to produce heavy rainfall. At low levels, a cold front
will move into northern Colorado tomorrow night with north and
northeast winds continuing over northeast Colorado through Monday.
This upslope pattern will help to hold low level moisture in the
region while moisture aloft moves over from the west. Model
soundings indicate that precipitable water values should be over 1
inch, and possibly approaching 1.25 inches. Afternoon convection
will have the chance to be slow moving and becoming anchored to
higher terrain in the foothills. Will go with likely pops for now
and be keeping an eye out for heavy rain as additional model runs
come in.

The moist weather pattern is then expected to continue through
most of the week. MOS guidance is drier by Wednesday, but it is
possible that each day will be a repeat of the previous day as
moisture is re-cycled by the heating of each new day. The presence
of precipitation will also help to cool temperatures down on
successive days. It may be that the monsoon is ready to kick in
and stick around for a few days.


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 750 PM MDT Sat Jul 21 2018

Outflow boundaries are making for an interesting evening of
possible wind shifts, but these boundaries will slowly dissipate
through the rest of the evening with loss of convection. Winds
will go to normal south/southwest by 06z. On Sunday, a weak front
will cause winds to shift northerly after 16z. Another round of
scattered thunderstorms are expected to move across the Denver
area Sunday afternoon and evening, mostly with light rain and
gusty outflow winds to 35-40 knots again.


Bou watches/warnings/advisories...


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