Thornton, Colorado 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

768
FXUS65 KBOU 151016
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
416 AM MDT Wed Oct 15 2025

.KEY MESSAGES...

- Areas of dense fog from Weld County to the northeast corner this
  morning.

- Becoming windy this afternoon. Thunderstorm coverage is expected
  to be low, but any storms could produce near severe wind gusts.

- Showers increase tonight into Thursday morning. Light snow for
  the mountains above 8 or 9 thousand feet.

- Cooling overnight low temperatures to start bringing frost to
  portions of the plains overnight Thursday, with freezing
  temperatures expected by Saturday night/Sunday morning east of
  the urban corridor.

&&

.UPDATE...
Issued at 416 AM MDT Wed Oct 15 2025

Dense fog has formed across our northern tier of counties. South
winds are starting to increase across the plains and are trying to
push the fog northward. However, the combination of nocturnal
cooling and a weak Denver cyclone-type eddy have caused fog to
redevelop north of highway 34 and push south a bit in Weld County.
With the south winds increasing over the next couple of hours, we
don`t think this will progress much further southward, and should
erode from the south and dissipate shortly after sunrise.

Short term models have been jumping around on the convective
potential for this afternoon. Some of the late runs yesterday kept
better moisture closer to the mountains and were more active. The
trend is back towards drier solutions now. We should at least have
a drying trend over and near the mountains, and with a shallow
moisture layer the coverage over our plains this afternoon will
probably be pretty limited too. There`s still a threat of strong wind
gusts since the ambient flow will be around 30 knots by this
afternoon so it won`t take a lot to generate near severe gusts.

There should be a better chance of weak showers this evening ahead
of the trough axis, and it still looks like the mountains should
get some showers overnight though amounts should generally be
light.

UPDATE Issued at 816 PM MDT Tue Oct 14 2025

Satellite and some FAA webcams show fog has quickly developed
across the northeast corner of the state over the last hour or
two. There are at least a couple pockets of dense fog out there
(KHEQ for example), but that is expected to shift northwestward
during the early overnight hours, before attempting to curl around
into the northern Denver metro/I-25 corridor close to sunrise
Wednesday morning. The HRRR gets the edge of the fog all the way
to Boulder and just north of KDEN, with fairly good consistency
over the last several cycles. Main update this evening was to add
fog into the grids... and while I did contemplate a Dense Fog
Advisory, I didn`t feel confident enough that any specific zone
would see dense enough fog for a long enough time overnight. Will
pass these concerns along to the night shift instead.

&&

.DISCUSSION /Through Tuesday/...
Issued at 125 PM MDT Tue Oct 14 2025

Satellite imagery shows drier air has moved into the forecast area
as the remnants of Tropical Storm Raymond have pushed to the
northeast. Also visible on satellite is an upper level low currently
spinning over western California. Ensembles are in wide agreement
that this low will move across the Great Basin through the day
tomorrow before ejecting to the northeast across the northern
Rockies Thursday. Additionally, it looks like a piece of energy
associated with this system will break apart and move across
Arizona and New Mexico. This will put our forecast area right
between the two areas of maximized lift, keeping the strongest
forcings to the north and south.

Before discussing the above impacts, let`s first talk about the
rest of today. The drier air has allowed for skies to see
significant clearing through the late morning. Surface heating
and downsloping southerly winds off the Palmer Divide have allowed
for temperatures to climb to the mid to upper 70s, generally for
areas along and south of I-76. Clouds are expected to continue to
clear through the afternoon and we should see a few degrees more
of warming before the quickly diminishing sun angle forces them to
a halt. Aside from the pesky DCVZ in place over the Denver TAF
sites making for a difficult wind forecast, the rest of today
should be quiet across the forecast area. Overnight low
temperatures will be a touch warmer than last night`s across the
plains, slightly cooler for the mountain valleys, with 40s and 50s
expected for the former, 20s and 30s for the latter.

As the low starts to move eastward, we will see increasing
southwesterly flow aloft as a near 70 kt 500mb jet moves over the
forecast area by Wednesday afternoon. Mid level moisture will
increase through the day as ridging to the east helps pull
tropical moisture into Colorado. At the surface, lee troughing
will aid in gusty winds developing across the eastern plains,
where gusts between 35-45 mph will be possible for the afternoon
and evening. With dewpoints expected to be in the 50s and
afternoon temps climbing into the upper 70s to low 80s across the
plains, we expect instability to increase through the day. While
southerly winds typically make for drying conditions north of the
Palmer Divide, some of the hi-res guidance continues to hold onto
a line of storms moving from west to east across the plains
through the afternoon. While the NBM has trended PoPs slightly
upwards for tomorrow, have increased them slightly more to get a
mention of at least a slight chance for thunderstorms across the
plains for the afternoon and evening to account for the persistent
trend of convection potential guidance has held onto through even
the latest run. With the increasing flow aloft, 0-6 km bulk shear
will range from 35-55kts which would certainly bring the
potential for a few stronger to severe storms developing. The main
threat will be for gusty winds and hail. Due to the southerly
winds bringing upslope flow to the Cheyenne Ridge, this area would
have the greatest potential for the stronger storms, and as such,
the SPC has included Weld, Logan, and Morgan Counties in a
Marginal Risk for severe wind and hail potential.

QG ascent will reach its max Wednesday evening into Thursday as
the upper level low ejects across the Rockies to our north and a
cold front slides south across Colorado. This will bring some
light snow to the mountains, where the highest concentrations are
expected for the northern mountains, where 1-4 inches are expected
to accumulate through Thursday, and the Park Range is once again
the favored range. Where temperatures are warmer at the lower
elevations, expect scattered showers and storms throughout the
day, with the greatest coverage expected for the northern portions
of the plains.

Behind the cold front, Thursday`s afternoon high temperatures
will cool between 10-20 degrees below Wednesday`s 70s and 80s.
Overnight, there will be patchy frost potential for much of Weld
County where lows are forecast to be around 34 degrees. Along the
Palmer Divide, temps will be slighter cooler bringing potential
for areas of frost/freeze, as temps are currently forecast to
range between 32-35F. Expect to see some more frost advisories
across portions of the plains through the forecast period as we
approach the end of the growing season and freezing temperatures
greet us by the beginning of next week. If you haven`t winterized
your sprinkler system, consider doing so soon!

Quieter conditions are expected by Friday, with near normal
temperatures on tap into Saturday. Warmer and drier conditions are
expected by Sunday as ridging rebuilds over the western CONUS.
With the warmer and drier conditions will come some elevated fire
weather concerns for portions of the plains on Sunday and Monday,
with relative humidities dropping into the mid teens and winds
picking up with some lee troughing ahead of our next potential
weather system. A lot can change as we are still a ways out, but
snow enthusiasts rejoice! There is potential for our first shot
at lower elevation snowfall by the beginning of next week. Stay
tuned as we get closer!

&&

.AVIATION /12Z TAFS through 12Z Thursday/...
Issued at 416 AM MDT Wed Oct 15 2025

VFR conditions are expected through tonight. There is a slight
chance (20%) of IFR/LIFR conditions at KDEN and KBJC for a few
hours between 12z and 15z. Most likely the fog in the valleys
north of Denver will not make it south into these airports, but
it`s possible there will be light north winds advecting the fog
towards the city before it burns off. The worst case scenario
would be 1 or 2 hours of 1/4 mile visibility/800-1600 foot RVRs.

After that, south winds should increase, with gusts of 25 to 35
knots in the afternoon at KDEN/KAPA. There`s a slight chance (20%)
of thunderstorms producing stronger wind gusts, up to 50 knots
(10% chance) with the main threat of that 22z-02z. Winds will
likely still be out of the south with any thunderstorm activity.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM MDT this morning for COZ038-042-
043-048.

&&

$$

UPDATE...Gimmestad
DISCUSSION...999
AVIATION...Gimmestad