406
FXUS65 KBOU 141747
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1147 AM MDT Tue May 14 2024

.KEY MESSAGES...

- Scattered afternoon and evening showers/thunderstorms today,
  most numerous along/south of I-70 where a few could be strong
  and produce hefty outflow winds.

- Front brings cooler and wetter weather on Wednesday. Light snow
  for elevations mainly above 10,000 feet.

- Warmer and generally drier starting Thursday, with lesser but at
  least isolated daily afternoon showers/thunderstorm coverage,
  highest for the mountains.

&&

.UPDATE...
Issued at 933 AM MDT Tue May 14 2024

Water vapor satellite imagery showing 2 well defined waves
spinning off to the north and northwest. The first one is over
eastern Wyoming with what appears to be a mid level front trailing
back into north central Colorado. This mid level front will
continue to travel east-southeast, and trigger storms this
afternoon. Models seem on track with the best storm development
lining up with peak heat along I-70. To the north of it, west-
northwest downslope flow is expected to limit convection, so plan
on dropping PoPs into the slight range for this afternoon. Main
threat with the thunderstorms will be gusty outflow winds. A
couple wind gusts could just reach severe threshold, 60 mph.

The second wave spinning over Idaho will track southeast through
this evening. A surface cold front associated with this system is
expected to bring a second round of showers and storms mid to late
evening. Winds shift to the northeast behind the front, ending
the the downslope flow. Expect to see better shower/storm coverage
to the north of Denver with this second round of activity this
evening.

&&

.SHORT TERM /Through tonight/...
Issued at 218 AM MDT Tue May 14 2024

A few light high-based showers are dotted across the high country
and eastern plains at this hour embedded within the westerly
synoptic flow in advance of the approaching shortwave trough.
These spotty showers may continue through the early morning hours,
mainly for the northern tier of our forecast area where QG lift
will be most pronounced.

Despite a fair amount of mid and high-level clouds at times today,
we should still see sufficient clearing and enough compressional
warming from near-surface downslope flow to push temperatures into
the mid 70`s for the urban corridor and locally upper 70`s in the
plains. Meanwhile, cold air advection will increase aloft,
contributing to notably steeper low-level lapse rates by this
afternoon, in excess of 9-10 C/Km in the surface to 3km layer per
most CAM forecast soundings. Under a well-mixed environment,
conditions will be favorable for the development of scattered to
numerous elevated showers and thunderstorms, particularly after
~2-3PM MT. There`s relatively good consensus as far as the bulk of
today`s convective activity being focused across the southern
half of our forecast area, roughly aligning with and south of
I-70, where MLCAPE should be maximized (with values ranging from
300-700 J/Kg).

With the aforementioned lapse rates as well as healthy DCAPE
surpassing 800-1,000 J/Kg, storms will be capable of producing
strong outflow winds, which in a few cases may approach 60 mph and
thus marginally severe levels. This threat will be primarily
confined to Douglas, Elbert, and Lincoln Counties, although
locally gusty outflow winds will be possible for almost all areas.
Models don`t appear to be handling the outflow wind potential all
that well, so have made some upward manual adjustments to our
wind gust forecasts to try and at least capture the median state.
The stronger storms are also likely to carry hail, albeit
generally on the smaller side in the majority of cases. Activity
will dwindle considerably by mid-evening, although isolated
showers and a few thunderstorms may linger, particularly in the
northeast plains. For the mountains, any snow today will generally
be confined to the highest elevations, above ~11,000 ft.

Tonight, temperatures will hold mostly steady, with a healthy
amount of cloud cover that will increase closer to sunrise as the
surface cold front approaches from Wyoming.

&&

.LONG TERM /Wednesday through Monday/...
Issued at 218 AM MDT Tue May 14 2024

A shortwave trough aloft will move across our forecast area on
Wednesday providing forcing. At the surface, there will be a cold
front that moves across the Colorado plains tonight through early
Wednesday morning. The post-frontal airmass will be cool and
moist. Highs will be in the 60s across the plains with a decent
amount of cloud cover throughout the day. The moisture and forcing
will combine with weak instability to create scattered to
numerous showers and thunderstorms mainly in the afternoon and
evening. The weak northeasterly flow in the low levels will
provide slight upslope flow that will make storms more frequent
over the Palmer Divide and southern foothills than anywhere else.
The instability, with mixed-layer CAPE around 500 j/kg, will not
be enough for severe storms to form. However, the storms could
produce small hail, gusty winds, and brief heavy rain.

There will be NVA over Colorado on Thursday as the aforementioned
trough departs the area. This will lead to drier conditions as highs
increase slightly due to more sunshine. There will be enough
lingering moisture along with slight instability across the higher
terrain that a couple of stray showers and storms could form.
However, most of our forecast area will remain dry.

An upper level ridge will move over Colorado Friday and Saturday.
This will provide subsident flow and much warmer mid level
temperatures. Highs will warm to the 80s across the plains each day
with only a few stray showers mainly over the higher terrain. The
only minor weather concern is elevated fire weather conditions
across the plains with relative humidity dropping to the teens with
breezy conditions.

Some models show a cold front moving across Colorado Saturday night
which would lead to slightly cooler conditions on Sunday. A broad
trough will move across the western US during next work week. There
will be southwesterly flow aloft which may keep temperatures
above normal. There will be small shortwave troughs within this
southwesterly flow that could bring storms to our forecast area.
This pattern could be conducive for severe weather and the
climatology of late May begins to strongly favor severe weather.

&&

.AVIATION /18Z TAFS through 18Z Wednesday/...
Issued at 1147 AM MDT Tue May 14 2024

West-northwest winds will continue to spread east off the
foothills, bring gusts to 25 knots and drier air. Satellite
showing some cumulus clouds forming, indicating we are starting to
reach our convective temperature. The question...is there enough
moisture for showers and storms? Model trends are leaning towards
no in the DEN area and likely in the APA area. May be able to
remove the VCTS from the DEN TAF in the next couple hours if the
drying trend pans out. Still may see a gusty outflow the
convection to the south of DEN.

Cold front will bring northeast to north winds mid evening, around
03Z. Will see an improved chance for showers with a slight chance
(20%) for a thunderstorm behind the cold front. The airmass
moistens up and low clouds are expected to form 09-12Z with
ceilings of 2000-4000 feet. The clouds slowly rise Wednesday
morning and afternoon, but expect ceilings to stay below 6000
feet. Scattered showers and thunderstorms are expected to form
after 20Z Wednesday.

&&

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

&&

$$

UPDATE...Meier
SHORT TERM...Rodriguez
LONG TERM...Danielson
AVIATION...Meier