331
FXUS65 KBOU 182345
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
545 PM MDT Mon May 18 2026

.KEY MESSAGES...

- Rain and mountain/foothill snow will gradually decrease through
  this evening. A few wet snowflakes may still mix in for the
  I-25 Corridor.

- Near freezing temperatures and frost/freeze highlights for most
  of the plains, but some uncertainty as to how cold with more
  lingering cloud cover.

- Still unsettled Tuesday through Thursday with scattered to
  numerous showers and a few storms, most numerous in/near the
  Front Range.

- Warming and drying trend for the weekend.

&&

.DISCUSSION /Through Monday/...
Issued at 123 PM MDT Mon May 18 2026

Satellite shows the upper level trough ejecting east/northeast
across the forecast area this afternoon, with an enhanced band of
precipitation and even a couple thunderstorms moving east across
the forecast area. The precipitation will weaken as it moves onto
the eastern plains as the upper level trough continues to shear
and weaken, and upper level support is replaced by weak
subsidence. After the trough passage, we still have some
weak upslope to work with so we`ll delay the dissipation of
showers in/near the Front Range overnight. In fact, a few light
showers could linger well past midnight, with the last of them
dissipating in/near the southern foothills toward daybreak
Tuesday. All existing Winter Storm Warnings and Advisories will
remain in tact through 9 pm, but any travel impacts should be
waning as precipitation rates decrease. Still can`t rule out a few
snowflakes mixing in with the snow down toward the I-25 Urban
Corridor during heaviest convective showers this afternoon and
then this evening as temperatures aloft cool slightly.

With regard to the potential freeze across the plains tonight. The
latest trends are for more clouds and higher low level moisture,
making it more difficult for temperatures to drop. We think most
of the Denver/Boulder metro area will stay just above freezing due
to mostly cloudy skies persisting through the night, while the
plains north and east of Denver could see areas of frost with
partial clearing but still some light northerly winds. The Palmer
Divide should still end up colder so went with a Freeze Warning
there, but even then only the higher elevations above 6500 feet
would be most prone to sub freezing temperatures.

On Tuesday, the airmass will be more stable but there`s still
enough moisture and shallow instability for late day
shower/isolated storm development in/near the higher terrain. That
shower development and coverage will also be supported by weak QG
forcing. Temperatures will remain well below normal, with highs
only in the 50s over most of the plains.

Wednesday should see an uptick in convective shower/storm coverage
in the afternoon as lapse rates aloft become moist adiabatic, and
we continue to see weak forcing as the mean upper level trough
axis holds off to our west. Temperatures will only moderate a few
degrees, and still be 10-15 degrees below normal.

The trend for Thursday has been toward more active and stronger
convective development. The main reason behind this is a stronger
and deeper upper level trough dropping southeast across the
Rockies. That will support steeper lapse rates, and combined with
moderate low level moisture means increasing instability. MLCAPE
from various more reliable progs indicate 500-1000 J/kg across
most of the plains and I-25 Corridor, so there will be potential
for a couple severe storms.

As long as this trough passes by Thursday night (and the slower
passage has continued in the latest ensemble means), Friday
should finally trend drier. Temperatures will then start a warming
trend for this weekend with more zonal flow advertised in the
ensembles, so eventually we should return to near or above normal
temperatures.

&&

.AVIATION /00Z TAFS through 00Z Wednesday/...
Issued at 541 PM MDT Mon May 18 2026

Model soundings and cross sections keep ceilings at DIA in the
BKN-OVC008-020 range through 12Z Tuesday morning. Will keep a
TEMPO group in for -SHRA through 03Z/04Z this evening. Some models
indicate the potential for -SHRA through around 10Z or so. It
doesn`t look as though any fog will develop at DIA overnight or
Tuesday morning. Visibilities should stay P6SM overnight and on
Tuesday.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 PM MDT this evening for COZ030-
031-034-035.

Frost Advisory from midnight tonight to 8 AM MDT Tuesday for
COZ038-042>051.

Freeze Warning from midnight tonight to 8 AM MDT Tuesday for
COZ041.

&&

$$

DISCUSSION...20
AVIATION...66

NWS BOU Office Area Forecast Discussion