409
FXUS65 KBOU 170514
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1114 PM MDT Sun Jun 16 2024

.KEY MESSAGES...

- Isolated showers and storms over the northeast plains this
  evening.

- Hot and dry across most of the area Monday, with critical fire
  weather conditions likely again.

- Cooler by Tuesday and Wednesday.

- Impacts from snowmelt across the high country will continue to
  diminish through the week.

&&

.UPDATE...
Issued at 712 PM MDT Sun Jun 16 2024

Updated the forecast to add a slight chance for showers and
thunderstorms over the plains, mainly north of I-70 and east of I-
25. A few showers and storms have been able to survive and actually
intensify moving off the higher terrain. The airmass is fairly
capped over the plains, so expect the showers and storms to remain
isolated. However if a storm gets enough forcing to overcome the
cap, it could become severe as MLCAPE is 1000-2000 J/kg over the
plains.

&&

.SHORT TERM /Through Monday/...
Issued at 232 PM MDT Sun Jun 16 2024

If you liked today`s forecast uncertainty, you`ll likely
appreciate tomorrow`s as well.

Little change in the overall synoptic pattern is expected in the
next 24 hours, as a broad ridge continues to build to our east
with a strong upper trough over the Pacific Northwest. The
mid/upper level flow should gradually strengthen by tomorrow as
the trough gradually approaches the region, but otherwise the
pattern is quite similar.

Despite the similar look aloft, there`s still quite a few parts
to the forecast that remain uncertain. The shallow cold front that
moved through earlier today continues to wreak havoc on my
forecast grids, and guidance hints at yet another subtle frontal
surge by tomorrow morning. This will have impacts on the
temperature forecast here but also where the higher fire danger is
across the lower elevations. At DEN, NAM MOS gives a high of
86 while the GFS/ECM MOS are in the mid 90s. It doesn`t take much
searching to find hotter solutions (HRRR/RAP) as well as ones that
keep the cooler/moist easterly flow in place across much of the
plains. The current forecast is a blend of a lot of different
things in an attempt to find the middle ground. If the
hotter/drier solutions verify one could justify the need for Heat
Advisories again tomorrow, but we`ll hold off until something
becomes more clear. There are also widespread fire weather
concerns tomorrow... see the Fire Wx section below for more
details.

&&

.LONG TERM /Monday night through Sunday/...
Issued at 232 PM MDT Sun Jun 16 2024

Southwesterly flow aloft is expected through the work week as a
troughing pattern persists over the western CONUS. The forecast area
will get a short reprieve from the current pattern of above
normal temperatures for Tuesday and Wednesday as a cold front is
expected to drape across the state beginning late Monday night.
Temperatures are forecast to drop below the freezing mark
overnight Monday for elevations above 10,000 feet. With dry lower
levels in place, precipitation is unlikely Monday night, with the
exception of portions of the northeastern CWA where guidance
indicates dewpoints may reach the 60s on the east side of a
dryline. Depending on how far east the dryline sets up could mean
sufficient moisture may be in place to allow for some isolated
thunderstorms to develop.

Tuesday`s high temperatures are expected to be more on par with the
norm as they will likely reach the 70s and low 80s across the plains
and foothills, 60s for the mountains. Lower level moisture will
begin to increase Tuesday afternoon as the surface flow
transitions to a more easterly component. This could allow for
some isolated showers and storms to develop over the higher
elevations. Confidence is low in this scenario as only ~20% of
ensemble members show CAPE values increasing to greater than 500
J/kg, mainly for the Palmer Divide and portions of the adjacent
plains into the overnight hours. Guidance indicates the increased
instability looks to remain just south and east of the CWA.

For Wednesday, 700 mb temperatures are likely to be a few degrees
cooler than Tuesday, which will assist in keeping another day of
high temps in the 70s and lower 80s across the lower elevations, and
60s for the mountains. East/southeasterly low level flow is
expected to bring increasing moisture support from the Gulf
throughout the day Wednesday. Skies are expected to remain cloudy
throughout the day that may prevent surface heating across the
plains and inhibit any convection from developing. With less cloud
coverage expected over the higher terrain, and mid level lapse
rates becoming unstable, there is a better chance for afternoon
storms to develop in these higher elevations. Overnight, a weak
shortwave embedded in the southwesterly flow aloft looks to pass
through the area that may initiate convection across portions of
the plains.

Thursday will bring a return to above normal temperatures and better
chances for afternoon storms as forecast soundings indicate MLCAPE
values exceeding 1300 J/kg across portions of the plains. A few weak
upper level disturbances embedded in the flow look to pass through
the area Thursday and Friday. After this, solutions diverge on when
the trough pattern will shift eastward and ridging will begin to
build over the western CONUS. There will likely be a chance for
afternoon storms through the weekend.

&&

.AVIATION /06Z TAFS through 06Z Tuesday/...
Issued at 1107 PM MDT Sun Jun 16 2024

Winds remain from the north and may stay in that general
direction overnight. Once concern overnight will be the
redevelopment of stratus around sunrise as an outflow
boundary/weak front moves back into the area. Stratus could linger
thru 16z before burning off. Next issue on Mon is where exactly
the boundary will be by aftn. NAM has been handling this boundary
much better than other models and keeps it around DIA much of the
aftn. Thus, depending on its location, winds could stay easterly
if it resides just to the south. On the other hand, if it lifts to
the north then gusty SSW winds will develop by mid aftn.

&&

.FIRE WEATHER...
Issued at 232 PM MDT Sun Jun 16 2024

Another challenging fire weather forecast through tomorrow
afternoon. Near critical to critical fire weather conditions have
been observed across most the current RFW zones this afternoon and
will likely continue for a few more hours this evening. The cool
front/moist boundary has setup from roughly Monument Hill to just
north of Limon and may drift north later this afternoon, but no
additional changes are planned for today`s RFW.

Humidity will struggle to recover overnight across the higher
elevations under a very dry airmass. Across the plains, another
weaker/subtle frontal surge should arrive overnight or early
Monday AM. How strong this boundary is and how far south it
progresses will likely determine the overall fire danger for most
of the plains tomorrow afternoon. There is considerable
uncertainty in the T/Wind/RH forecast tomorrow afternoon, with
high resolution models showing the moisture/wind gradient as far
south as the southern Denver metro/I-70 corridor and as far north
as the Wyoming border. Have gone with additional RFWs where
confidence is higher (south/west CWA) and a Fire Weather Watch for
Denver and the adjacent plains to the north/east.

&&

.HYDROLOGY...
Issued at 232 PM MDT Sun Jun 16 2024

Elevated flows continue in the mountain streams, but have
diminished over the past couple of days. While additional snowmelt
could briefly push a few sites back towards advisory level
stream flow, it appears that the peak of snow melt season has
already passed. Continue to remain alert of the dangers of water
that is running high and cold.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 AM to 9 PM MDT Monday for COZ213-214-
216-241-246-247.

Fire Weather Watch from 11 AM MDT Monday through Monday evening
for COZ239-240-243>245-249.

&&

$$

UPDATE...Meier
SHORT TERM...Hiris
LONG TERM...Bonner
AVIATION...RPK
FIRE WEATHER...Hiris
HYDROLOGY...Hiris