641
FXUS65 KBOU 152003
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
203 PM MDT Fri May 15 2026

.KEY MESSAGES...

- Growing risk of severe storms over the northeast plains
  Saturday.

- Shower and storm coverage will gradually increase this weekend
  through Monday. Still some uncertainty as to where and how much.

- Much colder temperatures by Monday, with some possibility
  (40-50% chance) of snow all the way down into the I-25
  Corridor.

- Accumulating snow (>70% chance of 4-10+ inches) for the
  mountains, and >60% chance of accumulation in the foothills.
  Less than 20% chance of anything more than a half inch for the
  I-25 Corridor.

- One last spring freeze possible on some of the plains Monday
  night.

- Gradually drier with a warming trend through the end of the
  week.


&&

.DISCUSSION /Through Friday/...
Issued at 202 PM MDT Fri May 15 2026

Summerlike warmth and dryness will be replaced by active spring
weather with a severe storm threat Saturday and potentially into
Sunday, before more winterlike weather arrives Monday.

In the short term, isolated high based showers and thunderstorms
are already developing over the Palmer Divide as we reach
convective temperatures. Given DCAPE near 1100 J/kg, we expect the
main threat outside of lightning to be gusty winds to around 40
mph. Those isolated showers and high based storms may continue
this evening and overnight, especially with a little moisture
advection noted from the southeast.

That moisture advection will set us up for a greater risk of a few
severe storms Saturday. While the moisture advection is marginal,
surface dewpoints increasing into the lower to mid 40s over the
eastern plains combined with daytime heating should drive MLCAPE
into the 600-1300 J/kg range for afternoon. Bulk shear increases
significantly to 40-50 kts, with decently curved hodographs more
than sufficient for supercell formation. The highest MLCAPE would
be east of a Fort Morgan to Akron line, where the greatest risk of
strong storms would be found and thus a Slight Risk over most of
the plains. The most recent Storm Prediction Center increased the
risk to Enhanced over the far northeast plains where storms may
organize further and updraft helicity values increase. Storm
Relative Helicity values are not terribly strong, with 0-1 km
values mostly under 100 m2/s2 and 0-3km in the 100-200 m2/s2
range. However, those could be locally enhanced along/just ahead
of a dryline expected to develop off the Palmer Divide and a warm
front extending from there into west central Kansas. Therefore,
while large hail to 2" in diameter and damaging winds to 60+ mph
will be the main threats, one or two brief tornadoes will also be
possible.

On Sunday, we`re still keeping an eye on another day of severe
storm potential, but signs are growing (more model agreement) that
the cold front will be pushing south through most of our forecast
area and taking the majority of the instability and severe
weather threat with it. As discussed yesterday, however, a sharper
trough digging into the Great Basin could hold the front up
slightly or allow it to stall near the Palmer Divide into east
central Colorado, so we`ll continue to monitor this threat.

The main concern then shifts to Sunday night and Monday with
high potential for accumulating snow in the mountains, and even a
few snowflakes down into the lower elevations including the I-25
Corridor by Monday. Overall, ensembles have trended colder due to
more agreement that the trough moving across the forecast area
will be in more more organized piece. Thus, about 50% of ensembles
are hinting at some snow mixing in for the I-25 Corridor. It`s
important to note this does not appear to be like last week`s tree
breaking storm, as temperatures will be several degrees warmer
making it hard to accumulate any snow - even if it does mix with
or turn completely over. The majority of the precipitation will
also fall during the day. For the mountains, several inches if not
close to a foot of snow can be expected, while foothill areas
could see anywhere from a trace to 10". Those heavier amounts
would be favored toward the north, including the higher foothills
above 7,500 feet in Larimer County.

The heaviest total liquid equivalent precipitation from this
storm system is still expected along and north of I-70 and I-76 on
the plains. Ensembles have bumped up things a little, with the
25th-75th percentiles now at 0.50-1.25 inches for the Denver metro,
with a floor (10th percentile) near 0.25" and a mean of 0.80-1.0
inch. From those means, add on another 0.3 to 0.5 inch for
locations near the Wyoming border and take away about 0.5 inch for
points farther south along the Palmer Divide.

The weather pattern settles down for much of next week. As this
first trough exits and cold air lingers, some frost/freezing
temperatures can be expected down onto the plains late Monday
night into Tuesday morning. That, of course, depends on how much
clearing and drying we see. Weak troughiness should then keep a
few showers and weak storms in the forecast Tuesday and Wednesday,
with temperatures gradually moderating. We`ll be warming back to
normal or above normal levels by the end of next week as a more
zonal flow aloft develops.

&&

.AVIATION /18Z TAFS through 18Z Saturday/...
Issued at 1128 AM MDT Fri May 15 2026

VFR conditions will prevail for all terminals through the TAF
period. Winds are likely to oscillate between N and ENE through
mid-afternoon, when a shift to SE flow is anticipated. A period of
higher gusts is still favored for KDEN in particular this
afternoon, beginning near 22Z. Expect a return to drainage winds
this evening, although these will become increasingly light and
variable overnight, thereby raising the uncertainty in the
prevailing direction.

For Saturday, winds will be dominated by a Denver cyclone setup,
favoring southerly flow for KAPA, light northerly for KBJC, and a
more uncertain mix of NE to SE flow for KDEN. Nonetheless,
scattered -TSRA look to develop early to mid afternoon, mainly
east of I-25, bringing potential for robust outflow winds.

&&

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

&&

$$

DISCUSSION...20
AVIATION...BRQ

NWS BOU Office Area Forecast Discussion