685
FXUS65 KBOU 152109
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
309 PM MDT Sat Jun 15 2024

.KEY MESSAGES...

- Warmer, drier, and breezy on Sunday with Heat Advisories across
  the southeast Denver metro.

- Critical fire weather conditions on Sunday, likely continuing on Monday.

- Snowmelt producing minor impacts from high streams. Gradually
  diminishing flows next week.

- Cooler for Tuesday and Wednesday

&&

.SHORT TERM /Through Sunday/...
Issued at 228 PM MDT Sat Jun 15 2024

Gusty showers will linger into the early evening hours today. One
of these high-based showers produced a microburst almost directly
over KAPA earlier in the afternoon with a gust to 44kt... and
while that`s likely on the higher end of the gust potential, it
wouldn`t be surprising to a few additional gusts of 40-50 mph.
Showers will quickly diminish near sunset.

Tomorrow`s forecast is surprisingly challenging. Southwesterly
flow aloft will gradually strengthen through the day, advecting a
hotter/drier airmass into the region. Model cross sections show
very little moisture through the column, and skies should be
mostly sunny through the day. Meanwhile, temperatures should also
increase to about 18-20C, which is roughly 2-4C warmer than today.

This would all be pretty straightforward, if not for a push of
cooler/more moist airmass associated with a weak front/outflow
from a storm system tracking across the northern Rockies/Great
Plains this evening. Guidance is in good agreement that this
shallow boundary will reach the northeastern edge of our forecast
area by Sunday morning, but models remain largely inconsistent on
how that boundary moves during the afternoon hours. This is
further complicated by the potential for a lee surface
trough/Denver cyclone to form during the day as well.

On the hotter/drier side of this boundary, high temperatures
should reach the mid to upper 90s. Experimental Heat Risk values
are borderline for issuing advisories, but given the lack of
cloud cover and the (relatively) early season... have opted for a
Heat Advisory for Denver and southeast into the Palmer Divide and
Lincoln county. There will also be an increased fire danger on the
dry side of this boundary and across the high country (see the
Fire section below).

&&

.LONG TERM /Sunday night through Saturday/...
Issued at 228 PM MDT Sat Jun 15 2024

The extended forecast period will begin with a persistent
southwesterly flow aloft as upper level troughing develops over
the western CONUS. After another 90+ degree day across the plains
on Monday, things will cool down for Tuesday and Wednesday with a
cold frontal passage before the heat ramps back up for the end of
the week.

Monday is forecast to be warm and dry ahead of the aforementioned
cold front. Forecast soundings indicate a dry boundary layer with
DALR and a lacking moisture profile. With only 13% of ensemble
members showing a roughly 15% chance of precipitation, will keep
isolated PoPs in the forecast for locations over the eastern
portion of the CWA. With relative humidities and wind gusts
crossing into critical fire weather criteria, highlights will
likely be needed Monday afternoon. See the fire weather
discussion below for more details.

Southwesterly flow aloft will continue Tuesday and Wednesday,
however, the passing cold front will help usher in some moisture and
cooler air from the north. Max temps will drop to a few degrees
below normal, and roughly 10-15 degrees cooler than what was felt
on Monday. A few showers and isolated storms are possible in the
afternoon over the mountains and the Palmer Divide, but from a
deterministic standpoint, agreement with regards to moisture and
precipitation is lacking past this point. Ensembles show a 30%
chance of overnight storms and showers across the plains on
Tuesday night, east of DIA, with thunderstorms more likely over
the farthest east locations.

Southerly surface flow looks probable to provide ample moisture
support from the Gulf to allow for afternoon storms to develop for
the remainder of the week. Surface dewpoints look to steadily
increase beginning Wednesday, and may reach the upper 50s to mid
60s across portions of the plains by Friday. Temperatures will
climb back up into the 80s and 90s beginning Thursday, and
ensembles show mean CAPE values climbing to 1000+ J/kg both
Thursday and Friday across portions of the plains, mainly east of
DIA.

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1122 AM MDT Sat Jun 15 2024

VFR through the TAF period. Still a slight chance of a high based
shower or two this afternoon. Main impacts would be from
variable/gusty outflow winds with little precipitation expected.
Winds should remain light through the afternoon hours outside any
outflow. Drainage flow is expected to prevail overnight.

Low confidence in the wind forecast tomorrow as a weak frontal
push, a Denver cyclone, or a well mixed southwest flow are all
possible by midday Sunday. For now have opted to keep a fairly
light northeast in at DEN.

&&

.FIRE WEATHER...
Issued at 228 PM MDT Sat Jun 15 2024

A much drier airmass is expected to advect into the high country
and portions of the Palmer Divide/plains tomorrow. HREF ensemble
mean relative humidity falls to 10-15% across the high valleys and
across the Palmer Divide/plains south of I-70 by the early
afternoon. Winds are marginal but would likely support a window of
near Red Flag criteria gusts for several hours on Sunday
afternoon. However, a shallow cold front is also expected to sink
south into the plains Sunday with substantially more surface
moisture north of the boundary. Some uncertainty with the position
of that boundary and about overall fuel conditions, but enough
confidence to go ahead with a Red Flag Warning where confidence is
a little higher.

Multiple days of 90+ degree temperatures and fuels at critical
status will lead to widespread elevated and critical fire weather
conditions across the forecast area on Monday afternoon. Critical
fire weather conditions are likely for Zones 212-216 and Zones
238-247 and Zone 249. Highlights will be issued in the coming
shifts.

&&

.HYDROLOGY...
Issued at 228 PM MDT Sat Jun 15 2024

Elevated flows continue in the mountain streams, with Flood
Advisories remaining in effect for the streams above Granby and
Grand Lake. Remain alert of the dangers of water that is running
high and cold. Flows are expected to gradually decrease next week
as the peak snowmelt is passing by.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 6 PM MDT Sunday for COZ213-214-241-
245>247.

Heat Advisory from noon to 7 PM MDT Sunday for COZ040-041-
045>047.

&&

$$

SHORT TERM...Hiris
LONG TERM...Bonner
AVIATION...Hiris
FIRE WEATHER...Bonner/Hiris
HYDROLOGY...Hiris