218
FXUS65 KBOU 150558
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1158 PM MDT Sat Sep 14 2024

.KEY MESSAGES...

- Dry today and tonight with temperatures above seasonal normals.

- Scattered showers and isolated thunderstorms Sunday afternoon
  and evening with gusty outflow winds and only light to briefly
  moderate rainfall. A stronger storm possible far northeast
  plains.

- Fire weather conditions get elevated to locally critical again
  next week with the worst fire weather conditions being on
  Tuesday and Thursday.

- Cooler temperatures and the potential for precipitation expected
  for the latter half of next week.

&&

.UPDATE...
Issued at 805 PM MDT Sat Sep 14 2024

Radar and satellite paint a quiet picture across the forecast area
this evening. One lone supercell in the Nebraska panhandle this
afternoon did briefly contemplate a motion towards the CO border,
but quickly decided to simply dissipate instead. In the meantime,
temperatures have decreased back to a value that I find tolerable,
and overnight lows should be near to a little above normal.

Didn`t have to make any significant adjustments to the forecast
grids overnight, as the previous forecast was in good shape. One
remaining question is if any fog does form across the far
northeast corner towards tomorrow morning. Some deterministic hi-
res guidance does develop some fog, but BUFKIT profiles at STK/AKO
would favor mist or perhaps patchy low stratus for a few hours
before it quickly burns off.

&&

.SHORT TERM /Through Sunday/...
Issued at 135 PM MDT Sat Sep 14 2024

Temperatures have made it into the mid and upper 80s across the
urban corridor this afternoon. With a few more hours of surface
heating to go, these should climb a few more degrees. Mostly clear
skies are expected overnight tonight that will allow temperatures to
cool into the low 50s across the plains, 40s for the foothills and
Palmer Divide, and 30s for the mountains. Conditions are expected to
remain dry, however, one area to note is the far northeastern plains
where dewpoints remain in the 60s. The SPC meso analysis currently
shows 1500-2000 J/kg of MLCAPE in this area. Forecast soundings keep
this capped through the evening, but if the cap were to break, we
could end up with a slight chance for thunderstorms developing. Have
kept a slight chance in the grids to account for this.

For Sunday morning, low dewpoint depressions and light winds are
expected across the far eastern plains before sunrise, which could
initiate fog formation. The hi-res Grand Ensemble indicates a 30-50%
chance that visibility will drop to less than .5 miles for a few
hours in the morning from Weld County east across the state. Added
areas of patchy fog to account for this.

Ensembles show an uptick in mid-level moisture tomorrow afternoon,
mainly for the high terrain with the GFS/ECMWF indicating PW
anomalies of 115-155% of normal. Inverted V forecast soundings
translate to afternoon high-based showers initiating across the high
country. Guidance show potential for outflow winds to gust to 50 mph
in areas where showers/storms develop. Marginal instability is
expected across the majority of the CWA, with the exception of the
northeastern plains. However, forecast soundings continue to portray
a capped environment, but if the cap were to break, we could see
some stronger storms develop, especially for this time of year.
Above normal temperatures are expected to continue, climbing a
degree or two warmer than today.

&&

.LONG TERM /Sunday night through Saturday/...
Issued at 135 PM MDT Sat Sep 14 2024

Southwesterly flow aloft will be over Colorado on Monday with
diffluence in the upper level jet streak. A shortwave trough will
begin moving toward Colorado throughout the day with a slight
increase in QG ascent. At the surface, moderate southerly winds
will develop across the plains with lee cyclogenesis developing
over Montana. Soundings show the low levels will be rather dry so
only isolated showers and storms will form mainly over the higher
terrain. Gusty winds will be possible out of these storms due to
large DCAPE values. Otherwise, there will be warm temperatures
with a high around 90 in Denver. That is well above the normal
high of 80 but not within reach of the record high of 95.

The axis of the shortwave trough will move through our forecast
area by late Tuesday. There will be moderate QG ascent due to PVA
and this forcing may create a line or two of showers and storms.
Some model solutions like the Canadian are rather wet with most
ensembles showing some rain falling across the majority of the
area. However, the ECMWF is drier and with southwesterly flow at
the surface, the drier solution seems more likely at this moment.
PoPs were kept on the low side as a result. The strong southwest
winds may gust up to 40 mph across the plains. With the warm,
windy, and dry conditions, there may be some areas that approach
critical fire weather conditions.

There will be subsident flow on the backside of a departing trough
on Wednesday will result in dry weather. Cooler temperatures
aloft will transition to the surface with highs being about 5 F
cooler than Tuesday. Highs will still be above normal.

Another shortwave trough will be quick on the heels of the first
one. It will arrive in Colorado on Thursday and into Friday and
will provide QG ascent. There are many different solutions within
the ensembles for the evolution of this trough. Some have a
quicker-moving trough that is more positively tilted. In that
scenario, there may be a brief chance of rain across our forecast
area but light amounts would be expected. There are also plenty of
solutions with a slower, more negatively tilted trough. This would
be a much wetter scenario and some of these solutions have over an
inch of rain in Denver. It is still too early to have an idea of
which solution is more likely but climatology seems to favor the
drier solution.

&&

.AVIATION /06Z TAFS through 06Z Monday/...
Issued at 1140 PM MDT Sat Sep 14 2024

Winds at DIA still have a bit of easterly component to the
southerly flow. Models eventually show true DIA drainage winds
around 09Z. The speeds are also lighter than the current speeds.
Consensus of a number of models yield keeping the "VCSH" and
TEMPO outflow winds gusting up to 40 knots going this afternoon
with no thunderstorms at this time. There will not be any ceiling
issues.


&&

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

&&

$$

UPDATE.......Hiris
SHORT TERM...Bonner
LONG TERM....Danielson
AVIATION.....RJK