National Weather Service Forecast Discussion

Thornton Weather Forecast   
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117
FXUS65 KBOU 170547
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1047 PM MST Mon Feb 16 2026

.KEY MESSAGES...

- Very windy with critical to extremely critical fire weather
  conditions Tuesday for all of the eastern Colorado plains.

- Additional fire weather concerns for elevated to critical fire
  weather conditions Wednesday and Thursday.

- Snow returns to the mountains after midnight tonight and into
  Tuesday. Snow and blowing snow will lead to travel impacts
  across most of the higher elevations beginning early Tuesday
  morning. Additional mountain snow possible through most of the
  week with continued travel impacts.

&&

.DISCUSSION /Through Monday/...
Issued at 119 PM MST Mon Feb 16 2026

The shear zone is set up just to the south/southeast of the Denver
metro this afternoon (you can see the cyclone pretty well looking
at TDEN velocity). Winds in the Denver area are weak from the
north, while winds in the counties just south of Denver county are
gusting from the south around 25 to 45 mph. Breezy winds will
continue in our south and southeastern counties into the evening
and potentially overnight. We`ll see a significant increase in
the winds across the Palmer Divide overnight, with the stronger
winds spreading across the area throughout the overnight and
morning period. 700mb winds around 40 to 60kts will move over the
area overnight Monday into Tuesday. The cold front is expected to
race through the area Tuesday morning, turning surface winds from
the southwest to the west. Soundings suggest that some of the
higher winds aloft should be able to mix down to the surface,
giving the plains occasional gusts around 50 to 65mph. The wind
gusts reaching High Wind Warning criteria everywhere in the
Warning, still isn`t a slam dunk, but our confidence is high
enough that portions of the area will see gusts around 60mph that
we converted the High Wind Watch to a Warning and added a few
counties. The High Wind Warning will go into effect at 10AM
tomorrow. However, there is some potential for winds along the
Wyoming border and in the Palmer to start gusting maybe an hour or
two earlier. Winds in the mountains will also be very strong,
with gusts around 50 to 70mph in the morning and afternoon. No
mountain wave enhancement is expected with these strong mountains
winds, due to the insane lapse rates and other factors discussed
below. These strong winds and continued dry conditions across the
plains will also lead to critical to extreme fire weather
concerns, which are discussed further in the fire weather section
of this AFD.

Outside of all the wind and fire weather concerns, we are on the
cusp of a very active winter weather pattern for our mountain zones,
with multiple storm systems and orographics expected to bring a
prolonged period of light to heavy snow starting early Tuesday
morning. The first wave, associated with a shortwave moving through
a deep trough off the West Coast of the CONUS is currently dropping
large amounts of precipitation over the Sierra Mountain Range. A
plume of Pacific Moisture embedded in the approaching southwesterly
flow is currently visible on water vapor imagery, and headed our
way. This is expected to bring the first wave of heavy snowfall into
Colorado late tonight, with winter impacts expected by early Tuesday
morning in our mountain zones. With the expected strong winds
(discussed above), blowing snow and reduced visibilities are
expected to bring hazardous to very dangerous driving conditions
across the mountains for Tuesday and Wednesday. The first push of
snow is expected to be fairly hefty as a cold front drops 700 mb
temps from around 3C to -7C between the 15-18Z time frame, leading
to a period of potent 700 to 500 mb frontogenesis as the front
moves through. As the front passes across the region, there will
be potential for snow squalls to develop that could bring brief
periods of intense snowfall rates. A few changes were made to
today`s forecast that include the mention of thunder in the grids,
and a slight increase to snowfall amounts over the highest
elevations of the Park Range and RMNP, based on the latest hi-res
guidance. With the amount of SBCAPE and steep lapse rates expected
to bring enough instability, we may end up with some thunder snow
tomorrow afternoon! The current winter headlines will be allowed
to continue, with a Winter Storm Warning in place for the Park
Range, where roughly 12-24 inches of new snowfall is expected from
Tuesday morning to Thursday morning. The Winter Weather Advisory
has been expanded to include both North and Middle Parks, where
strong winds are expected to create blowing snow and reduced
visibilities. Snowfall amounts will be a little greater in North
Park, where around 5 to 9 inches are forecast and 3 to 6 for
Middle Park. Areas elsewhere in the advisory should expect between
5 to 12 inches, with localized heavier amounts in the mountains
of RMNP, where between 16 to 18 inches will be possible at the
highest elevations. The heaviest snowfall rates are expected with
the initial first wave Tuesday morning, with continuous moderate
snowfall expected for the Park Range through the period, and
mostly light to moderate snowfall rates expected for the rest of
the mountains through the period, with a second shortwave still
expected to reinforce snowfall Wednesday afternoon and evening.
While light snowfall may persist after the winter highlights end,
things should be settling down by Thursday morning.

On Wednesday, a strong surface low is forecast to develop to our
north, keeping the pressure gradient tight and winds breezy. The
strongest winds in our area (other than in the higher mountains
elevations) will be primarily east of I-25 and south of I-76.
Wind gusts around 35 to 50 mph will be possible in the afternoon
in this area. Looking beyond the current winter highlights,
lingering moisture in the mountains should be enough to keep
orographic snowfall potential in place through Thursday. The
surface low will move off the the east late Wednesday into
Thursday, sending another cold front through the area and even
giving us a shot at light QPF making its way onto the northern
plains overnight. Behind the front we`ll see decent cooling aloft
and at the surface, with forecast highs dropping around 10 to 20F
from Wednesday to Thursday. With the cold front dropping
temperatures, we may finally see some snow somewhere outside of
the mountains (mainly along the Wyoming border if it`s gonna
happen), but still no real significant precipitation is expected
across our lower elevations through the forecast period.

Thursday we will be monitoring the potential for some mountain
wave enhancement of the winds. Models are showing winds out of
the west, a steep inversion around 550mb, very little or even
reverse shear above ridge top, and GQ subsidence over the area
(all of these are good for mountain wave development). Luckily,
models are only showing winds at ridge top around 50kts as of late
this morning. So, our level of concern isn`t too high right now
in terms of impacts from these winds. But we will have to keep a
close eye on model trends with the mountain top winds, because if
they start to trend upwards we could see some very strong winds
move down into the Foothills and adjacent plains. Beyond
Thursday, temperatures will remain near normal through the
weekend, with additional chances for some light precip across the
plains as another shortwave move through.

&&

.AVIATION /06Z TAFS through 06Z Wednesday/...
Issued at 1047 PM MST Mon Feb 16 2026

Southwest winds are already increasing at APA and DEN ahead of
the incoming system with gusts to 25 knots. Southwest winds are
expected to increase overnight and towards 12Z with gusts of 30-35
knots and possibly reaching 40 knots. A line of showers move off
the mountains and foothills Tuesday morning. It`s uncertain if
rain makes it as far east as DEN, but a blast of west winds is
expected with gusts reaching 40 to 50 knots. Timing of this looks
to be 15-16Z. Strong west winds are expected to persist through
Tuesday afternoon with gusts of 35 to 45 knots. Winds decrease
after sunset and turn southwesterly. VFR are expected to prevail
through tonight and Tuesday. However, a brief ceiling down to 6000
feet will be possible during the morning showers. Blowing dust
could restrict visibility at times, especially if winds gust close
to 50 knots.

&&

.FIRE WEATHER...
Issued at 119 PM MST Mon Feb 16 2026

Critical fire weather conditions are in place this afternoon for the
southeastern portion of our area. Winds are gusting around 25 to
45 mph and RHs are generally around 10% to 20%. RHs will start to
improve this afternoon between 4 and 5PM, with RHs going above
critical thresholds between 6 and 7PM. Winds aren`t really going
to die down overnight, rather they`ll stay elevated in the areas
that saw stronger winds today, with winds starting to increase
around midnight tonight (starting first in the mountains and
Palmer and then spreading across the plains by tomorrow morning).

Tomorrow still looks to be the most widespread RFW conditions of the
week. Winds will be well above RFW criteria for our whole forecast
area by mid morning. Winds will gradually decrease starting in the
late afternoon/early evening. There is a potential hiccup in the RH
forecast for tomorrow due to the potential for moisture and showers
to spill off the mountains into the foothills and plains. Some
models are showing light showers moving of the mountains into the
adjacent plains early Tuesday. It will likely be too dry at the
surface on the plains for any precipitation, but these areas
could see erratic winds with the virga and some increase in
moisture as the precip evaporates. In the afternoon, cooler
temperatures will follow the front, dropping temperatures from
west to east. The cooler temperatures and moisture spillover could
help keep RH values above that critical threshold for portions of
the foothills and adjacent plains (zones 215, 216, 238, 239, and
maybe 240) in the afternoon. Because of this we removed zones 215
and 216 from the Fire Weather Watch. The rest of the zones
mentioned were still converted to an RFW, due to the potential for
RH values to stay below critical thresholds in at least some
portion of the zone.

On Wednesday, elevated to near critical conditions are expected
for the far southeastern portion of our forecast area. Right now,
RHs are a bit on the marginal side, with minimum values around 14
to 20%. The winds in this area will be gusting around 30 to 45mph
in the afternoon. We considered a Fire Weather Watch for Lincoln
county, but decided to hold off for now. Fire weather conditions
should start to improve for the second half of the week, but
elevated to near critical conditons could hang around for portions
of the area for a few more days.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 2 AM Tuesday to 11 PM MST Wednesday
for COZ030-032>034.

Winter Storm Warning from 2 AM Tuesday to 5 AM MST Thursday for
COZ031.

High Wind Warning from 9 AM to 5 PM MST Tuesday for COZ038-
042>051.

Red Flag Warning from 10 AM to 7 PM MST Tuesday for COZ238>251.

&&

$$

DISCUSSION...9/AP
AVIATION...12
FIRE WEATHER...AP

NWS BOU Office Area Forecast Discussion