830
FXUS65 KBOU 121951
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
151 PM MDT Sun May 12 2024

.KEY MESSAGES...

- Drier/warmer Monday, with scattered mountain showers/storms and
  more isolated coverage for lower elevations. Snow levels should
  be around 11,000 ft MSL

- Scattered showers and a few thunderstorms on Tuesday. Cooler and
  more widespread precipitation expected on Wednesday into early
  Thursday.

- Turning warmer and drier again late in the work week.

&&

.SHORT TERM /Through Monday/...
Issued at 150 PM MDT Sun May 12 2024

GOES-16 shows the trough responsible for the localized extremely
wet weather has finally moved east and is along the CO/KS border
in southeast Colorado. The deformation band of precipitation has
likewise shifted south and will exit our area this evening. Rain
showers should continue across the Palmer Divide and east of a
Sterling to Fort Morgan to Castle Rock line for several hours, as
well as snow above 8500 ft in Park County. Another inch or two of
snow is possible into this evening in Park County, but road
conditions have improved quite a bit other than around Wilkerson
Pass. The advisory will be allowed to expire at 3 PM.

Tonight things dry out and clear out, but temperatures don`t drop
too far given some warming aloft. Expect lows in the low to mid
40s across the plains, and around 30 degrees in the mountain
valleys. South Park should cool into the 20s with the impressive
snow cover from the last 18 hours.

On Monday, a 500 mb ridge begins to build into Colorado, and 700
mb temperatures increase from 0 degC to +6 degC, and combined with
mostly sunny skies through midday, temperatures will warm up
nicely. Expect mid 70s for highs across the plains and urban
corridor, and temps around 60 degrees for North and Middle Park.
South Park`s temperatures may lag behind on Monday due to the snow
cover, but still should get into the 50s. The low level warming
combined with residual moisture looks to result in 100-400 J/kg
CAPE, primarily for the mountains/valleys and foothills. Scattered
showers and isolated thunderstorms (20-50% for the high country)
will form over the mountains and drift southeast during the
afternoon, weakening as they encounter less instability and dry
low level air. The chances of those storms dropping measurable
precip east of I-25 are very slim (<20%). Expect gusty winds and
virga for the most part across and east of the I-25 corridor.

&&

.LONG TERM /Monday night through Sunday/...
Issued at 150 PM MDT Sun May 12 2024

Weak zonal flow should spread across the region by Tuesday with
plenty of mid-level moisture in place across the area. Despite
the increase in moisture, temperatures should be reach the mid 70s
across the plains, aided by weak downslope from the westerly
flow. Though CAPE values will be modest, there should be a good
enough combination of moisture and surface heating to allow for
widely scattered showers and storms, spreading east from the high
country into the plains during the afternoon hours. Main concern
would be gusty outflow winds and lightning, with organized severe
weather unlikely.

Warmer weather will be short lived, as a cold front drops into
the forecast area sometime Wednesday. Moisture and upslope flow
increase behind the front, which should result in widespread
stratiform rain. There is still some uncertainty about the timing
of the front and the moisture quality behind it, but ensemble
guidance has consistently dialed in on the Wednesday
afternoon/Wednesday night period. Across the high country, some of
this precipitation may fall as snow, with snow levels slowly
falling down to ~9000ft. Suppose we`ll need to watch this
potential as spring storms don`t always cooperate (as we`ve seen
today).

Cool/unsettled weather may linger into Thursday, but the general
trend will be towards a warmer and drier pattern as a ridge builds
off the West Coast. Guidance generally agrees on a return to
mid/upper 70s by Friday into next weekend. As we transition to
more of a summer-like pattern, widely scattered, fairly weak
afternoon showers/storms will likely be the theme across the high
country, with mostly quiet conditions for the plains.

&&

.AVIATION /18Z TAFS through 18Z Monday/...
Issued at 1149 AM MDT Sun May 12 2024

Rain showers and MVFR conditions should continue into the mid
afternoon hours before improvement occurs from the northwest,
though we do believe -TSRA are a strong possibility after 21Z at
DEN and APA. BJC should be the first to improve in terms of
rain/lightning and MVFR conditions. The band of stratiform rain
extending from NE Colorado across DEN and APA is resulting in
lower MVFR conditions but it shouldn`t get any worse than that,
even during periods of moderate rain. That band of rain should
move southeast of DEN and APA by 19Z or so. To the northwest of
that band of showers, enough instability is being generated for
widely scattered TSRA, including very small hail. That instability
axis should be positioned near DEN around 21Z, and APA around
22Z, which is why we have TEMPO groups in the TAFs. The best
instability is already east of BJC, so we have not included any
thunder in the TAF, but this is a very hard storm system to
forecast so we aren`t confident enough to say no TS period at BJC,
just to low to leave out of the TAF. Winds this afternoon and
evening should be east to northeast.

VFR conditions and light winds should occur after 01Z at all the
TAF sites, and VFR will continue all the way through Monday. Light
drainage winds are expected by midnight (<10 kts), then light NE
winds by midday on Monday.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 3 PM MDT this afternoon for COZ037.

&&

$$

SHORT TERM...Schlatter
LONG TERM...Hiris
AVIATION...Schlatter