309
FXUS65 KBOU 040159
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
759 PM MDT Wed Jul 3 2024

.KEY MESSAGES...

- Gusty winds behind a cold front for a few hours late this
  evening

- Quiet Fourth of July forecast with mostly sunny skies and cooler
  temperatures

- Potential for critical weather conditions for southern Park
  County Thursday afternoon

- Somewhat cool and mainly dry conditions will persist Friday
  through early next week.

- Best chance for showers and storms in the extended will be
  Sunday.

&&

.UPDATE...
Issued at 753 PM MDT Wed Jul 3 2024

Severe storms have ended early this evening. A cold front is
moving quickly southward and is near the CO-WY border at 02Z.
This front will continue southward with a brief period of gusts
from 40-50 mph as it moves across the plains. Doesn`t appear
convection will develop with or behind its passage except possibly
over the far northeast corner.

&&

.SHORT TERM /Through Thursday/...
Issued at 339 PM MDT Wed Jul 3 2024

Active afternoon with thunderstorms continuing to initiate along
the dryline positioned across the eastern plains. So far, this was
predicted decently by the high resolution CAMs runs today. A lot
of the action has been on the northerly segment of storms across
the northeast corner with a couple severe storms. Radar shows
storms firing on the southerly portion of the boundary now. SPC
mesoanalysis shows a favorable severe environment in Elbert,
northern Lincoln, and Washington counties as well. Large hail,
damaging winds will be the main threat with these storms as they
move eastward across the plains this afternoon/early evening.

Storms exit the far east plains by mid evening. The next feature
to impact the region will a fairly strong cold front the drops
southward in the 10 pm to 12 am timeframe overnight. Model
guidance expresses the potential for gusty northerly winds,
especially at the initial onset of the front. Generally could
see onset gusts as high as 35-45 mph, but some spots closer to
the northern border could see higher for a short period of time.

Thursday, Colorado sits in a post-frontal airmass with
northwesterly flow aloft. This will make for cooler temperatures
for the Fourth of July holiday. Highs in the upper 70s to low 80s
across the lower elevations, 60s for the foothills, and 50s/60s
for the mountains. With subsident flow, it will be dry and stable
for most areas tomorrow. The mountains and northern Larimer
county develop marginal instability in the afternoon supporting
the low chance for an isolated shower in the afternoon. The east
plains and the high country will be breezy in the afternoon with
gusts mainly 20-25 mph. The high mountain valleys will be dry and
breezy in the afternoon, leading to at least areas of elevated
conditions in the afternoon. More in the Fire Discussion.

&&

.LONG TERM /Thursday night through Wednesday/...
Issued at 128 PM MDT Wed Jul 3 2024

A slight chance for showers and perhaps a thunderstorm will
continue into the evening of the 4th of July. SBCAPE not
impressive, up to 200J/kg and the same goes for moisture, with
precipitable water values only 75 percent of normal. Any shower or
storm that forms during the evening is expected to be weak and
short lived. Models continue to favor northern Larimer/Weld
Counties and the Palmer Divide for these showers/storms, though
the latest model trends have been for fewer showers/storms.

Upper level high will remain west of the Central Rockies and over
California/Nevada through at least early next week. Flow aloft
across Colorado will be northwesterly. Temperatures under this
pattern are expected to be near to below normal. Shower and
thunderstorm chances will depend on the location and timing of the
weak waves embedded in the northwest flow, but overall rainfall
chances will be on the low side through at least Saturday.

Friday`s forecast continues to look cool with highs in the lower
to mid 80s. The airmass will be stable across northern Colorado.
May be unstable enough for a few weak showers and storms along and
south of the Palmer Divide. There are some differences on the
strength and location of a short wave Friday night and early
Saturday. The ECMWF is stronger and farther west with this wave
and brings a round showers and thunderstorms with it to far
northeast Colorado late Friday night and early Saturday morning.
In addition to the convection, a cold front brings another shot of
cooler air for Saturday. Meanwhile the GFS and NAM are weaker
with this trough, keeping it too far northeast of Colorado for
showers and storms. Temperatures are also 5-10 degrees warmer
under GFS/NAM scenario. Will start to trend the forecast towards
the cooler scenario, with recent extended guidance generally being
too warm. Another wave is expected for Sunday, which will
reinforce the cooler air, and bring a better chance for showers
and storms.

For early to mid next week, cooler temperatures continue through
at least Tuesday under northwest flow aloft. When/if the upper
level high begins to move over the Central Rockies expect
temperatures to climb into the 90s. Not sure when this will occur.
Over the past week, models have been way too progressive shifting
this ridge eastward and the latest trends have been to continue
to slow the eastward progression of the ridge.

&&

.AVIATION /00Z TAFS through 00Z Thursday/...
Issued at 541 PM MDT Wed Jul 3 2024

Gusty NW winds should diminish before 01z.  A cold front
will move across around 05z with gusty north winds up to
35 mph.  These winds will subside by 08z.  There is low
confidence in whether stratus will develop in the 08z-11z
time period so have left a sct group in for now.  On Thu,
light and variable winds in the morning will become east
by 18z.

&&

.FIRE WEATHER...
Issued at 339 PM MDT Wed Jul 3 2024

It will be breezy across the high country Thursday afternoon with
gusts up to 30 mph. Relative humidity values drop into the 12-20
percent range. This may lead to elevated to spotty critical fire
weather conditions at times. Southern Park County in particular
displays higher probabilities of more consistently meeting Red
Flag criteria in the afternoon. Went with a Fire Weather Watch for
southern Park County from noon to 6 PM for now. Didn`t go straight
to a Warning due to lower confidence in how widespread the 25 mph+
gusts will be. It is possible it ends up being spottier in
coverage.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch Thursday afternoon for COZ214.

&&

$$

UPDATE...RPK
SHORT TERM...Mensch
LONG TERM...Meier
AVIATION...RPK
FIRE WEATHER...Mensch