587
FXUS65 KBOU 150944
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
344 AM MDT Sun Jun 15 2025

.KEY MESSAGES...

- Increasing risk of a few severe storms late this afternoon and
  evening over northeast Colorado. Possible repeat Monday but less
  confidence. Only isolated high based showers or storms across
  the Foothills and I-25 corridor.

- Very warm today and Monday.

- Cooler Tuesday and Wednesday as a storm system moves through.
  Better chances for rainfall across the metro and plains Tuesday.

- Strong signal for near record breaking heat late next week into
  next weekend.

&&

.UPDATE...
Issued at 343 AM MDT Sun Jun 15 2025

Main update early this morning is for an increasing risk of a few
severe storms over northeast Colorado late this afternoon and
especially during the evening. MLCAPE will be at seasonal highs as
latest model projections show higher low level Tds advecting
northward across eastern Colorado. This seems reasonable given
latest surface observations, with a ribbon of near 70F dewpoints
lurking across southwest Kansas. While we won`t get 70F dewpoints
into our forecast area, that does set the table for a strong
theta-e ridge to build across the eastern plains this afternoon
and evening in south/southeast low level flow. As a result, MLCAPE
may reach an impressive range of 2000-3000 J/kg.

There are a couple bust scenarios. One being a stronger cap due
to slightly cooler temperatures in the higher Td air. The second
being some cirrus currently moving northeast from Utah and
northern Arizona. While shear is marginal to start under upper
level ridging, it does increase this evening as the ridge axis
shifts slightly eastward. SPC has upgraded most of the northeast
plains to Slight Risk, and this seems reasonable with even a
further expansion possible southward into Lincoln County. Large
hail and damaging winds would be more likely given the large
MLCAPE, but as we`ve seen the last couple days a landspout
possible as well along any boundary interaction.

The I-25 Corridor appears to be once again too far west and in a
drier high based, virga/sprinkle, isolated thunder, and
microburst regime. We have added some low PoPs to account for
that - similar to yesterday`s minimal activity.

&&

.DISCUSSION /Through Saturday/...
Issued at 217 PM MDT Sat Jun 14 2025

It`s warm out there. We`ve seen our first 90F readings at DEN (91F
so far) and Central Park (93F) this afternoon, and we may have
another degree or two of warming to go across portions of the
metro. Meanwhile, there`s been a gradual increase in CU across the
Foothills and western metro. Though there won`t be a ton of
coverage to the high-based showers this afternoon, there should be
at least a few gusty outflow boundaries from this activity as it
drifts eastward. Recent ACARS soundings show MLCAPE near 250-500
J/kg, with more than sufficient DCAPE (~1400 J/kg) for a few gusts
of 40-50 mph. The severe threat should remain north and east of
the Denver metro, with CAMS loosely favoring a cluster of storms
along the northern edge of our CWA (northern Weld county through
Sedgwick/Phillips counties) where there`s better instability/shear
overlap.

Tomorrow will feature more of the same - well above normal
temperatures across most of the forecast area, along with the
afternoon showers over the I-25 corridor and a marginal severe
threat across the far eastern plains. Highs should again reach the
90s with little issue, and could end up a degree or two warmer
than today.

Monday will more than likely be our 3rd day of >90F temperatures
across the metro and plains, though there`s perhaps a little more
uncertainty in the temperature forecast. The upper ridge is
expected to slowly flatten with a weak shortwave working into
Wyoming during the afternoon. Southwesterly flow aloft will
increase a little bit in response to a second shortwave deepening
to the west of the region, and we could downslope our way to some
mid 90s temperatures. There is more spread than usual in this
timeframe for Monday`s highs, with an equal number of ECMWF
ensemble members in the upper 80s vs. the upper 90s.

A cooling trend is likely on Tuesday as the aforementioned
stronger shortwave moves into the region. We should see some
increase in surface moisture as northeasterly flow strengthens
Monday night/Tuesday AM, leading to a broad axis of
instability/shear over most of the lower elevations. Depending on
the amount of cloud cover/daytime heating, this setup would
generally favor more coverage of strong/severe storms during the
afternoon hours along and east of I-25. SPC`s Day 4 outlook seems
appropriate at this time, with the greatest threat of severe
weather still east of the Denver metro.

As we move into the latter half of the week, there is remarkably
good agreement across the deterministic/ensemble suites that an
expansive upper level ridge will build across the south central
CONUS. The mid-level thermal ridge axis essentially sits right
over Colorado for a couple of days between Thursday and Saturday,
leading to easily the warmest weather of the year. 700mb
temperatures on both the GEFS and ECME approach 21-22C... which
translates to roughly a return interval > 1 day per 10 years (but
not quite outside their respective model climatology).
Temperatures in the mid to upper 90s are forecast in this period,
with Friday being the highest confidence day. It`s worth noting
that all but one ECMWF ensemble member has a high >100F at DEN on
Friday, with a handful of members approaching some all-time record
heat on both Friday and Saturday... though in previous years the
mid/long range surface temperature forecasts were frequently well
too warm. Either way, heat headlines look like they could be
needed as early as Thursday, assuming that the synoptic pattern
does not change substantially over the next couple of days.

&&

.AVIATION /06Z TAFS through 06Z Monday/...
Issued at 1146 PM MDT Sat Jun 14 2025

Outflow from storms to the east is again delaying the transition
to normal south/southwest drainage winds. That will still happen
overnight, eventually moving from east/southeast to south to
southwest 06Z-11Z. Then winds become light and variable by 16Z,
with light east/southeast winds by 18Z-20Z. Sunday is nearly a
rinse/repeat day like Saturday with isolated high based
convection. We expect strong surface heating and just enough
moisture collecting at the LCL for Prob30 gusty/VRB winds to ~30
kts 21Z-02Z. While south/southeast winds should prevail into the
evening, there`s still potential for another east/southeast
enhanced outflow from stronger storms that develop over the
eastern Colorado plains. That would be most likely to arrive
03Z-05Z Monday so we`ll have a more easterly component in the TAFs
then, before returning to more south/southwest again through 12Z
Monday.

&&

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

&&

$$

UPDATE...Barjenbruch
DISCUSSION...Hiris
AVIATION...Barjenbruch