279
FXUS65 KBOU 210541
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1041 PM MST Wed Nov 20 2024

.KEY MESSAGES...

- Dry, with well above normal temperatures through Saturday.

- Pattern changes on Sunday with a long duration light snow event
  for the mountains. The mountain snow looks to be heaviest on
  Monday, with a chance for the plains to see precipitation on
  Monday as well.

&&

.UPDATE...
Issued at 816 PM MST Wed Nov 20 2024

Once again, we`re getting pretty good cooling in the areas without
much wind. There`s still a little wind overnight to hold up
temperatures in some areas, and they may be nearly steady in the
foothills, but the colder areas should still drop quite a bit. We
nudged tonight`s lows down a little in most areas, more so in
snow covered areas from Elbert County west to Park county that are
already near the forecast lows. Also added some more wind to the
mountain ridges and higher east slopes. We`re still gusting to 50
mph above timberline in the Front Range, and there`s not much
change to the flow aloft or stability tonight, and only a gradual
decrease after that.

&&

.SHORT TERM /Through Thursday/...
Issued at 239 PM MST Wed Nov 20 2024

An upper level ridge will continue to build and shift eastward
tonight into tomorrow, with the ridge axis firmly centered over
Colorado by tomorrow afternoon. This will mark the start of a
warm/dry period across the region that will persist into the
weekend.

Tonight should be pretty quiet. Low temperatures won`t be as cold
as last night`s, but with large-scale subsidence and clear skies,
it won`t be too difficult for low to drop into the teens across
the plains, with single digits likely in the cold spots of
North/Middle Park. A light downslope component will keep overnight
temperatures mild for most of the Foothills and I-25 corridor.

Tomorrow will be very quiet, with just a little cloud cover
possible. High temperatures should peak in the mid to upper 50s
for the urban corridor, aided by a weak downslope component to the
mid-level flow.

&&

.LONG TERM /Thursday night through Wednesday/...
Issued at 239 PM MST Wed Nov 20 2024

An upper level ridge pattern prevails over northeast Colorado
through Saturday. Model cross sections indicate weak relative
humidities values at 11-20% between 500-700mb with a few pockets
of 30-45% for the higher mountains Friday. Given the lack of
moisture, majority of areas will experience a few high clouds but
mostly sunny skies. There good agreement across models for above
normal temperatures across our region Friday. NBM temperatures are
reasonable with slight adjustments to decrease a few areas that
still have snow on the ground otherwise, Friday`s highs for the
mountains and valleys increase to 37-49F. Friday afternoon, the
urban corridor and plains will be a few degrees warmer than
Thursday reaching the mid 50s to low 60s. Saturday`s 700mb
temperatures are even warmer than Friday increasing to 7-9C. This
will likely lead to surface temperatures almost 6-12 degrees above
normal for our entire forecast area. Although this won`t break
records for Denver, there is certainty potential for a few areas
along the urban corridor to tie daily high records.

Our upper level pattern shifts Saturday night as a shortwave
trough approaches from the northwest. 700mb frontogenesis
increases Saturday night through Sunday morning along the
foothills and plains. With cloud cover increasing and much colder
air behind the front potentially arriving Sunday afternoon, high
temperatures will be several degrees cooler. Models do not display
much upper forcing which makes sense given the shortwave trough
becoming more of an "open wave". It is possible areas above 9
thousand feet could receive light snow as early as Sunday
afternoon. With the lack of model agreement on QPF and cold air
timing, large amounts of uncertainty linger in total snowfall
amounts mainly for the foothills and lower elevations. Parts of
the Park and Gore Ranges should receive periods of light to
moderate snow due to orographics. The ECMWF displays higher total
QPF values for the lower elevations versus the GFS thus decided to
at least keep rain snow showers possible with a slight chance
(30-40%) for the parts of the foothills and urban corridor Sunday
evening. Additionally, the next round of precipitation Monday
through Wednesday will greatly depend on how much Pacific moisture
wraps along a deepening trough. Without much agreement beyond
Monday, keeping NBM chances of rain snow mix showers due to
potential for additional series of "open waves" which will likely
result in little to no snowfall on grassy surfaces for the lower
elevations along the I-25 corridor.

&&

.AVIATION /06Z TAFS through 06Z Friday/...
Issued at 1039 PM MST Wed Nov 20 2024

VFR will persist through the TAF period, along with light winds
under 10 kts. Light drainage winds from the south/southwest
tonight should turn a little more east/southeast by 18Z Thursday
through a combination of weak diurnal flow and drainage off the
snow field to the southeast of KDEN. By 00Z-01Z Friday, expect
normal south/southwest winds to reestablish themselves. KBJC has
just a slight (20%) chance of seeing gusty west winds til about
14Z due to weakening mountain wave.

&&

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

&&

$$

UPDATE...Gimmestad
SHORT TERM...Hiris
LONG TERM...AD
AVIATION...Barjenbruch

NWS BOU Office Area Forecast Discussion