514
FXUS65 KBOU 111742
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1142 AM MDT Sat May 11 2024

.KEY MESSAGES...

- There will be a 30-70% chance of showers and a few thunderstorms
  this afternoon and into the evening across our area. Snow
  levels should remain around 10,000 feet.

- Showers/thunderstorms are possible (>50%) for much of the day
  Sunday, with locally moderate rainfall. Thunderstorms could
  begin as early as 8 AM, but become fore favorable during the
  afternoon hours.

- Drier and milder Monday outside of a few mountain
  showers/storms.

- Turning more active again Tuesday onward with increasing
  thunderstorm potential.

&&

.UPDATE...
Issued at 1054 AM MDT Sat May 11 2024

The current forecast for today looks on track. Made minor updates
to PoP based on area radar data. We also bumped up the winds in
the east central plains from Elbert to Lincoln to Washington
Counties, where winds are already gusting 25-30 mph this morning.
We dropped max temps where there is already cloud cover and temps
are behind the forecast, especially since clouds will certainly
be increasing across the entire area throughout the day as the
trough approaches and convective cloud cover gets going in
earnest. Speaking of, the latest CAMs have convective
precipitation forming across the mountains of central Colorado,
moving northeast across our area after 2 PM. The best chance of
showers and thunderstorms look to be between 3 and 7 PM,
especially south of US-34. The best forcing and instability look
to be across the southern half of our area of responsibility,
though all of our area has at least a 30% chance of seeing
measurable precipitation. Existing PoP/QPF forecasts through this
evening are on the right track and were left alone.

&&

.SHORT TERM /Through tonight/...
Issued at 330 AM MDT Sat May 11 2024

Satellite pictures are showing and upper level circulation over
the northwestern corner of Arizona at this time. There is a batch
of lower and middle cloudiness over the southeastern quarter of
Colorado at this time moving northeastward. Observations and
radars are showing some light rain showers to our south also
moving northeastward. Temperatures across the plains and lower
foothills are in the mid 30s to lower 40s F at this time, with 20s
and 30s over the rest of the CWA.

The upper low is progged to move eastward into the Four Corners
later this afternoon around 00Z, then it progged to be over the
southern CWA by 12Z Sunday morning. There is weak synoptic scale
upward vertical velocity over the CWA today and tonight according
to the QG fields. Moderate southerly low level winds are expected
over the plains through the day, with weak normal drainage winds
tonight.

Models show moisture to increase today and tonight across the CWA
with precipitable water values getting into the 0.50 to 0.80 inch
range for the plains and foothills by 12Z Sunday morning. There is
some instability this afternoon with CAPE values in the 200-800 J/kg
range for much of the CWA. Will leave the "scattered" to "likely"
pops going this afternoon and evening for the forecast area along
with limited thunderstorms. The better heating and instability
warrants it. The QPF fields keep minor measurable precipitation in
overnight as well. With the warming expected, snow will be
relegated to the mountains above 9,500-10,000 feet today into this
evening, then come down a little overnight. For temperatures,
today`s high are 1-4 C warmer than Friday`s highs.

&&

.LONG TERM /Sunday through Friday/...
Issued at 139 AM MDT Sat May 11 2024

The extended forecast period kicks off with relatively active
weather, as the upper-level closed low pushes into the plains
passing directly over southeastern Colorado Sunday. As it does
so, healthy mid-level wrap around flow will provide for a notable
increase in column moisture, and forecast soundings are relatively
consistent in depicting PWAT values of 0.70-0.80" over the lower
elevations Sunday morning. With enough cold air present aloft
leading to marginally unstable conditions, the ingredients appear
aligned for the development of more expansive showers and even a
few thunderstorms during the morning hours. Guidance suggests the
southern mountains/foothills, Denver metro, and Palmer Divide
would be favored for the heavier and more persistent
precipitation, in line with a period of enhanced northeasterly
upslope flow. This is not well reflected in the NBM, which
continues to show the higher precipitation potential for the
afternoon period. While scattered afternoon showers/thunderstorms
certainly appear likely (50-70% chance for most), believe the
greater potential for healthier rainfall totals outside of the
plains will occur in the morning. Thus, made significant upward
adjustments to the PoPs to reflect this. It`s worth noting that
QPF ranges are still rather significant amongst ensemble members,
and it would not be entirely surprising for a few (localized)
spots to pick up 1" or more of rain on Sunday. Most locations
should see much less than that, however.

Upper ridging builds in on Monday with flow aloft returning to a
more typical northwesterly regime. Enough moisture aloft will
remain to support scattered afternoon convection primarily in the
high country, but subsident flow in the lee of the Front Range
will result in Monday having the lowest precipitation potential of
the next several days. Temperatures will also warm a few degrees.

The thermal ridge amplifies some for Tuesday under continued
subsident flow, leading to renewed warming and pushing high
temperatures well into the 70`s for the urban corridor, and
possibly even low 80`s for parts of the South Platte River Valley.
With warm surface conditions in place and colder air moving in
aloft ahead of a developing trough over the Intermountain West,
instability will be on the rise, resulting in increased afternoon
thunderstorm coverage. A few could be on the stronger side both
Tuesday and into Wednesday, especially in the eastern plains where
instability should be maximized. The trough and associated cold
front are slated to move through the region on Wednesday, bringing
cooler temperatures. Thursday looks to be on the drier side in
general as upper-level flow becomes more zonal behind the trough
and we begin to warm back up.

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1142 AM MDT Sat May 11 2024

Definitely a complicated aviation forecast from this afternoon all
the way through Sunday evening. Starting with today, winds should
increase out of the south at APA and DEN by mid afternoon. Showers
and thunderstorms are possible (>50%) after 21Z but especially
between 22 and 01Z this evening at all three terminals. They will
be moving southwest to northeast during the late afternoon and
evening hours. Lightning is a safe bet with the strongest showers,
and wind gusts to 25, maybe 30 kts could occur. We`ll need to
watch wind shifts with the showers and thunderstorms. Drainage
winds are expected after 05Z with SSW winds at APA and DEN, SW at
BJC.

MVFR CIGs are expected much of Sunday morning. We have low
confidence in the evolution of both the CIGs and
shower/thunderstorm potential on Sunday. Most models show a very
moist low to mid level of the atmosphere, which would support OVC
CIGs around 020-030 through at least midday. We have moderate
confidence in a band of showers forming late morning, probably
between 15-18Z, but the location of that band of showers is highly
uncertain. Have decided given the uncertainty, and the fact that
lightning is not expected with the band of morning showers, to
keep the MVFR CIGs in place and just handle the shower potential
with VCSH. Models are hinting at a second round of showers this
time with a low lightning potential later Sunday afternoon. This
seems like a low chance overall (30%), so have used a PROB30
group to handle that. Northeast winds 10-15 KT gusting to 25 kts
should be the norm in the absence of afternoon thunderstorms. VFR
could return by midday but without confidence either way, will
keep the lower CIGs in place in the TAF for the time being.

&&

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

&&

$$

UPDATE...Schlatter
SHORT TERM...RJK
LONG TERM....Rodriguez
AVIATION...Schlatter