155
FXUS65 KBOU 060848
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
248 AM MDT Sun Jul 6 2025

.KEY MESSAGES...

- Scattered afternoon/evening thunderstorms today and Monday.

- Some strong to severe storms are possible with large hail and
  damaging wind gusts today and Monday, mainly across the eastern
  plains, but a few are possible across the urban corridor.

- Hot temperatures expected Wednesday with the upper 90s expected
  across the plains. It is possible the hot temperatures extend
  into Thursday.

&&

.UPDATE...
Issued at 248 AM MDT Sun Jul 6 2025

Huge model differences regarding moisture and instability
continue with the 06Z model runs. The 06Z NAM shows a stronger
northeast surge this morning with dew points in the lower 50s this
afternoon as far west as the base of the foothills. MLCAPE values
reach 1000- 2000 J/kg if we keep low 50s dew points into the
afternoon. The 06Z RAP and HRRR show drier mixing down (likely too
much mixing of the drier air) and dew points in the lower 20s
across the Denver area. CAPE values in this drier airmass only
reach 200-400 J/kg. Zooming out, a large area of thunderstorms
have persisted much of night across southwest South Dakota. Radar
is showing a strong outflow boundary diving south and southwest
into Wyoming and Nebraska. At its current pace this outflow
boundary would reach northeast Colorado around sunrise and advance
south through the area this morning. The NAM looks like the best
model at this time capturing this stronger northerly surge.
Northeasterly winds this afternoon increase the shear as well,
likely leading to at least a few severe storms today. SPC`s Day
One Convective Outlooks has Slight Risk for severe storms as far
west as I-25 with Marginal Risk into the Front Range mountains.
This seems very reasonable with the northerly outflow marching
towards the area, which will increase low level moisture and
instability. Large hail, possibly slightly bigger than golf balls
and damaging winds will be the main severe threats.

A similar scenario is expected for Monday with another chance for
severe thunderstorms. A shortwave trough tracks across the
northern plains Monday, which is expected to increase the number
of storms, especially over the northeast corner of Colorado and
northward into Nebraska.

&&

.DISCUSSION /Through Saturday/...
Issued at 222 PM MDT Sat Jul 5 2025

Scattered storms have formed across our CWA this afternoon and
have been sub-severe so far. Instability is modest with surface-
based CAPE values around 1,000 j/kg. Deep layer shear is rather
low with values generally around 25 knots. The main concern with
storms that form this afternoon and evening will be strong wind
gusts due to steep lapse rates and large dew point depressions in
the boundary layer. However, DCAPE values are around 1,400 j/kg
which suggests most downdrafts will be capable of gusts up to 50
mph and not necessarily severe gusts of 60 mph. We have
collaborated with SPC and we are in agreement that no Severe
Thunderstorm Watch will be needed at the time of this writing. If
a more organized MCS were to form, then a watch may be needed.

On Sunday, there is a decent chance that an outflow boundary from
overnight convection in Nebraska will keep easterly winds over
northeast Colorado for much of the morning and afternoon. This
would advect much better dew points into our area which would
lead to higher instability. In addition, the low level easterly
winds would increase deep layer shear. All factors seem to be
pointing towards Sunday having a much better severe weather threat
than Saturday with large hail and damaging wind gusts expected out
of strong storms over the I-25 corridor and eastern plains.

On Monday, conditions will be very similar to Sunday. Healthy dew
points should stay in our area across northeast Colorado. If that
is the case, another day of strong to severe storms with large
hail and damaging wind gusts will occur.

We break the pattern of daily strong to severe storms on Tuesday
as ridging strengthens aloft with more capped conditions. We will
then begin talking about heat on Wednesday as a 597dm 500 mb high
will form over our forecast area. With strong subsidence and
little cloud cover, temperatures will have the chance to get to
the upper 90s and around 100 degrees across the plains. GFS MOS
has 101 for Denver and the ECMWF ensembles have roughly half the
members at 100 or above. If these warmer solutions appear more and
more likely in the coming days, a Heat Advisory may be needed.

There is a good deal of uncertainty with Thursday`s forecast as a
trough will be quickly approaching from the west. If the trough is
quicker to move through, cooler temperatures near seasonal normals
can be expected with scattered storms. However, if the trough is
slow to move through, another very hot day with temperatures near
100 degrees across the plains is possible.

&&

.AVIATION /06Z TAFS through 06Z Monday/...
Issued at 1149 PM MDT Sat Jul 5 2025

Southerly winds will continue into Sunday morning, and then become
light and variable towards 18Z as they transition to the northeast
for Sunday afternoon (after 18Z Sunday). Another round of afternoon
thunderstorms are expected with the best time frame 21-24Z Sunday.
Will handle the thunderstorm threat with a PROB30, but a tempo may
be appropriate if confidence in storms increases. Easterly winds
are expected after 00Z Monday as storms become more organized east
of Denver.

&&

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

&&

$$

UPDATE...Meier
DISCUSSION...Danielson
AVIATION...Meier