696
FXUS65 KBOU 210620
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1220 AM MDT Sun Jun 21 2026

.KEY MESSAGES...

- Critical fire weather conditions are expected for the mountains
  and high valleys today.

- Strong to severe storms possible across the eastern plains
  today and Sunday. For today, very large hail, damaging wind
  gusts, and a couple of tornados possible across the far
  northeast plains.

- Scattered coverage of showers and storms on Monday and most of
  next week across the plains.

- Elevated fire weather conditions possible for the mountains and
  high valleys most of next week.

&&

.DISCUSSION /Through Saturday/...
Issued at 1259 PM MDT Sat Jun 20 2026

Visible satellite imagery shows mid level clouds over the
northern and central mountains of Colorado indicating mid level
instability. Some weak showers have develop mainly over the
foothills with some briefly making it onto the plains before
dissipating. While a couple of these showers could grow strong
enough to create some lightning, they will stay below severe
limits across all of the foothills and I-25 corridor.

There are two other significant features to note in the
observations and satellite data. One is a DCVZ that has setup over
the far southeast side of the Denver metro. Winds remain from the
northwest to northeast to the north of this boundary with dew
points staying in the low 50s. To the south of this boundary,
southwest winds have developed with much warmer temperatures and
dew points in the 30s. This is the boundary that will create the
initial strong to severe storms today. Storms will begin in Elbert
and Arapahoe Counties and as they encounter much greater
instability in Lincoln and Washington Counties, they will grow
strong to severe. Large hail and strong winds will be the primary
threat from these storms although a tornado cannot be ruled out.

The other feature worth noting is a warm front-like feature that
is an east-west oriented boundary over the border of
Washington/Logan Counties and Phillips/Yuma Counties. Low clouds
have persisted for the entire morning to the north of this
boundary keeping temperatures in the low 70s to upper 60s and dew
points in the low 60s. To the south of this boundary, temperatures
are in the upper 80s to low 90s with dew points in the 50s. The
parameter space near and just north of this boundary is
exceptional for Colorado standards. Mixed-layer CAPE is forecast
to be around 2,500-3,000 j/kg. Deep layer shear will be above 50
knots to the north of this boundary and may approach 60 knots.
Plus, the boundary has greatly increased the low level helicity
with effective helicity values forecast to be 300-400 m2/s2. Any
storm that forms in this area will be capable of very large hail
up to baseball size, damaging wind gusts up to 70 mph, and a
supercell tornado. The Storm Prediction Center has highlighted
this area in an enhanced risk of severe weather for good reason. A
convective watch will be needed later this afternoon for this
area. The one factor that may limit the chance of severe weather
in this area is a lack of a lifting mechanism during the
afternoon. There is a somewhat significant cap on soundings and
convective initiation this afternoon is uncertain. Storms may not
form until later this evening when storms that initiate north of
Cheyenne, WY reach that area. If storm initiation doesn`t occur
until this evening, the main risk would be very large hail.

A shortwave trough will move through our forecast area tonight
and there will be slight subsident flow tomorrow morning. West
winds will mix down in the morning hours which will clear any fog
or low clouds that develop across the eastern plains tonight. A
dryline will setup roughly from Sterling to Limon which may
initiate storms. Mixed-layer CAPE values around 1,500 j/kg will
support the formation of a couple of strong to severe storms to
the east of the dryline. The main threats would be large hail and
damaging wind gusts. Otherwise, temperatures will be slightly
above normal in the Denver metro with a limited chance of rain.

Low level winds will have an easterly component Monday through
Thursday of this upcoming week. This will keep healthy moisture in
place over the eastern plains of Colorado. The moisture and
upslope flow will generate daily afternoon/evening showers and
thunderstorms. This will also keep temperatures below normal most
days. There may be a severe threat from some of these storms but
any details about this threat is unknown at this time.

&&

.AVIATION /06Z TAFS through 06Z Monday/...
Issued at 1208 AM MDT Sun Jun 21 2026

Low stratus clouds with bases 008-020 are present across much of
the Denver metro area with SCT-BKN coverage. The duration of these
is rather uncertain and hinges on the consistency and strength of
any drainage flow that develops. Winds currently are retaining a
NE and N component but speeds are weakening and a gradual
counter-clockwise rotation to SW drainage flow is expected between
08-11Z. Forecast is for low clouds to largely dissipate past 12Z,
with 14Z being the latest possible return to VFR conditions.

This afternoon, winds should be out of the NW to N and gusty with
some gusts up to 25 kts looking likely for most of the afternoon.
There is a very low chance of showers/thunderstorms tomorrow
afternoon, but are currently expected to stay south and east of
the terminals.

&&

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

&&

$$

DISCUSSION...Danielson
AVIATION...BRQ

NWS BOU Office Area Forecast Discussion