Thornton, Colorado 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

579
FXUS65 KBOU 211126
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
426 AM MST Thu Nov 21 2024

.KEY MESSAGES...

- Dry, with well above normal temperatures through Saturday.

- Elevated fire weather conditions likely on Saturday across the
  foothills and adjacent plains due to very dry and breezy
  conditions.

- A system will bring snow to the mountains and a mix of rain and
  snow to the plains late Sunday into Monday morning. Light snow
  accumulations are expected in the mountains and none across the
  plains.

- Another system will bring moderate snow to the mountains on Wednesday
  and Thanksgiving. The plains could also see a round of snow
  during this period and travel could be impacted.

&&

.SHORT TERM /Through Tonight/...
Issued at 225 AM MST Thu Nov 21 2024

We`ll continue the warming trend today, with further warm
advection under the upper level ridge spreading across the Central
Rockies. 700 mb temperatures rise another 4C, and there`s enough
downslope component just off the deck to warm temperatures another
6-10F from those observed yesterday. We won`t fully break
inversions, however, with initially cold air and light
east/southeast winds in the boundary layer. That said, we should
still be pushing 60F in the Denver metro area for highs, while the
snowpacked areas farther east including Limon only make it into
the lower to mid 40s. There will still be some wind over the
higher elevations due to modest westerly flow under the flat
ridge, but much less than yesterday. All other locations (i.e.
below 9,500 feet) will see relatively light winds. Regarding
cloud cover, we`ll likely see another relatively narrow wave cloud
develop today with advection of upper level moisture. However, we
don`t think this would be enough to impact high temperatures that
much. Overall, a really nice late November day shaping up after a
chilly start.

Lows tonight will moderate a few more degrees as the airmass warms
slightly. Low lying areas will once again see the coldest
temperatures, while weak downslope areas in/near the foothills
will reside in the thermal belt - where lows may not dip below
40F in a couple spots.

&&

.LONG TERM /Friday through Wednesday/...
Issued at 225 AM MST Thu Nov 21 2024

A strong ridge aloft will be over Colorado on Friday which will
lead to pleasant weather conditions. There will be light winds,
mostly sunny skies, and well above normal high temperatures.

A jet streak will move into the Intermountain West on Saturday and
Colorado will be under the right exit region leading to strong
subsident flow. Ensemble guidance has a low spread for
temperatures and those temperatures are well above normal. Highs
will be in the upper 60s and a few spots will be in the low 70s
across the I-25 corridor and plains. The ECMWF MOS mean has a high
of 69 F in Denver and there is a solution that predicts DIA to
reach the daily record high of 73 F. The mild and dry conditions
will bring fire weather into the picture. Relative humidity will
drop to as low as 10 percent across the southern foothills and
adjacent plains. With such low humidity, the wind forecast will
be in focus for the potential for Red Flag conditions. With the
jet streak nearing the area, breezy conditions may develop in the
afternoon across the foothills and adjacent plans with gusts
between 25-30 mph. This will lead to areas of elevated fire
weather conditions and the potential for near critical fire
weather conditions.

A shortwave trough will pass mainly to the north of Colorado on
Sunday and Sunday night. This will bring Pacific moisture that
will lead to light snowfall in the mountains late Sunday through
Monday morning. Some moderate travel impacts can be expected from
this snow with Monday morning seeing the worst conditions. Across
the plains, a cold front will move through Sunday night and weak
frontogenesis in the low to mid levels along with warm air
advection will allow for the possibility of banded precipitation.
This precipitation will likely fall as a mix of rain and snow. It
does not appear snow with this wave would be heavy enough to
produce any accumulation over the I-25 corridor and plains.

Continued west-southwesterly will keep a stream of Pacific
moisture coming into Colorado on Tuesday. Some light snow will
fall in the mountains along the western slopes with limited
impacts.

Ensemble data is starting to latch onto a stronger system moving
through Colorado on Wednesday and into Thanksgiving. This system
has the potential to bring moderate to heavy snow to the mountains
given that this system will likely have west-northwesterly flow
which is more favorable orographic flow for our CWA. There is
still plenty of uncertainty with this system but there is
potential for the I-25 corridor and plains to receive accumulating
snow. Over half of the ECWMF ensembles showed measurable snow in
Denver although almost all of the runs had accumulation on the
lighter side. This system will need to be watched closely as many
people will be traveling for the holidays. Due to the uncertainty,
not many details can be discussed but the chance seems high that
people traveling in the mountains will see impacts.

&&

.AVIATION /12Z TAFS through 12Z Friday/...
Issued at 426 AM MST Thu Nov 21 2024

VFR will persist through the TAF period, along with light winds
under 10 kts. Light drainage winds from the south/southwest
should turn a little more east/southeast by 18Z through a
combination of weak diurnal flow and drainage off the snow field
to the southeast of KDEN. By 00Z-01 expect normal south/southwest
winds to reestablish themselves.

&&

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

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Danielson
AVIATION...Barjenbruch