448
FXUS65 KBOU 180623
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1223 AM MDT Mon May 18 2026

.KEY MESSAGES...

- Rain and mountain/foothill snow increases overnight through
  Monday with much colder temperatures arriving.

- Accumulating snow for the mountains, and >70% chance of
  accumulation in the foothills. Only a few wet snowflakes
  possibly mixed in for the I-25 Corridor.

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

- Delay in the warming and drying trend for the week ahead, but
  still warmer and drier by Friday - next weekend.

&&

.DISCUSSION /Through Sunday/...
Issued at 1222 AM MDT Mon May 18 2026

An upper level trough over the Great Basin will move across the area
on Mon with favorable mid level ascent thru the aftn hours.  At the
sfc, upslope flow will be in place which will combine with the
upper level trough to produce widespread precip across the area.
Snow will occur in the mtns and higher foothills with several
inches of accumulation. Have upgraded areas north of I-70 in the
mtns to a warning as east facing slopes could see from 12 to 18
inches in some areas. Elsewhere will keep amounts in the advisory
range. In the foothills, some of the higher areas may see 4 to 8
inches above 8000 ft with lessor amounts below 8000 ft.

By Mon night precip should gradually decrease over the area during
the evening hours.  Overnight lows late Mon night into early Tue
morning may drop down to freezing or slighty below across portions
of the plains.

For Tue,  a disturbance will move across the area late in the aftn
thru Tue night.  As this feature moves across, there will be another
round of precip over the higher terrain and across portions of the
plains.  Highs on Tue will remain cool as readings stay in the 50`s
across the plains.

Looking ahead to Wed, an unsettled pattern will continue as decent
lapse rates will combine with lingering moisture to produce a good
chc of showers and thunderstorms over the higher terrain and
portions of the plains.  Most of the activity will occur in the late
aftn and early evening hours.  Highs will remain blo normal as
readings only reach the upper 50`s to mid 60`s across the plains.

By Thu into Fri, latest data shows another upper level trough moving
southeast towards the area.  Not sure about the timing of this
system, however, as it moves across should see another good chance
of showers and thunderstorms.  Temperatures both days will be in the
mid 60`s to lower 70`s across the plains.

For next weekend, will see a return to a drier and warmer pattern
based on latest data.

&&

.AVIATION /06Z TAFS through 06Z Tuesday/...
Issued at 1145 PM MDT Sun May 17 2026

Isolated to scattered showers will hang around the terminals for
much of the overnight period. KBJC will have the highest chance of
seeing additional showers overnight, but KAPA and KDEN could also
see periodic light rain. Shower coverage will start to increase
in the early morning, with widespread showers and storms likely
impacting all TAF sites by 16Z to 17Z. Rain is then expected to
continue for multiple hours before eventually moving off to the
east around 21Z to 23Z. Isolated to scattered showers will still
linger around the area for a few more hours before rain chances
come to an end in the late evening. Ceilings are currently MVFR
to IFR across the area, with CIGs continuing to drop overnight.
By Monday morning, all TAF sites will likely have CIGs below
1000ft, with a low to medium chance (30 to 40%) that KAPA and KBJC
drop to LIFR. Low clouds will continue throughout the day Monday into
Tuesday morning.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 PM MDT this evening for COZ031-
034.

Winter Storm Warning until 9 PM MDT this evening for COZ033.

Freeze Watch from late tonight through Tuesday morning for
COZ038>051.

&&

$$

DISCUSSION...RPK
AVIATION...AP

NWS BOU Office Area Forecast Discussion