337
FXUS65 KBOU 192106
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
306 PM MDT Sun May 19 2024

.KEY MESSAGES...

- A couple severe storms will move across the northeast plains
  late this afternoon. Isolated to scattered showers/storms
  elsewhere with gusty outflow winds.

- Another round of strong to severe storms expected Monday
  afternoon and evening across most of the eastern plains.

- Cooler, wetter pattern late Monday into Tuesday as a couple weak
  systems track across the region

- Warming/drying trend for the second half of next week

&&

.SHORT TERM /Through Monday/...
Issued at 300 PM MDT Sun May 19 2024

Scattered storms, a couple severe with one already having a
landspout, were moving east across the plains. Surface analysis
shows a ribbon of 1500-2000 J/kg MLCAPE extending across areas
east of a Sterling to Akron line where dewpoints were in the mid
50s. There was some CIN noted farther east, but that is eroding
and therefore the existing storms should continue to strengthen or
become more numerous as the dryline works eastward. There could
even be a lone severe storm in Lincoln County where MLCAPE is
holding close to 1000 J/kg, and the dryline progression has been
slower than expected.

Most of the storms will diminish or move east of the area by 6 pm.
That occurs as weak subsidence is noted in the QG fields, and
indeed, the convection around Denver and points west and southwest
over the mountains is quite shallow. Thus, mostly dry conditions
are expected after dark. A cold front then arrives overnight with
a push of north/northeast winds back into the Front Range. This
should set the stage for a more active weather day on Monday.

Low level moisture increases back toward the Front Range on Monday,
and this should allow MLCAPE to increase to near 1000 J/kg. It
will be a little cooler, and the amount of stratus (if any) could
play into destabilization. There is also considerable uncertainty
with regard to the frontal location and where it could stall out -
adding to the necessary lift required for convective initiation.
Forecaster experience would say it aligns closer to where the NAM
suggests, stretching out across the Palmer Divide/South metro
eastward onto the adjacent plains. Hodograph curvature is
impressive along this boundary, with potential surface-1km
helicity near 100-150 m2/s2 and surface-3km over 350 m2/s2!
But....that`s just one model and others are not nearly as strong
and updraft helicity is limited per some of the HREF members.
Instability could also be limited to less than 1000 j/kg. We
coordinated with SPC on the Day 2 outlook, bringing the Slight
Risk area into northeast Colorado and Marginal back to the I-25
Corridor. Depending on how the instability and shear profiles
appear, further adjustments may occur. Stay tuned for the latest
updates. Large hail, damaging winds, and tornadoes would be
possible should the higher end instability/shear profiles develop.

&&

.LONG TERM /Monday night through Sunday/...
Issued at 300 PM MDT Sun May 19 2024

The threat of severe weather will carry into Monday evening and
night as storms push east into the plains. Large hail, wind gusts up
to 60 mph, a possible tornado, and brief heavy rainfall could
occur until 11 PM MDT. Late Monday night, overcast skies and a
lack of instability will likely lead to stratiform rain across
the region. The threat of flooding should remain low due to
rainfall intensity becoming lighter and soil moisture values are
slightly drier in the eastern plains. QPF fields display 0.50-1.50
inches total Tuesday along the foothills and plains. With
rainfall continuing into early Wednesday morning, expect overcast
skies and lower temperatures Tuesday afternoon and night. West of
the Divide, light snow will occur for areas above 8k ft. Snowfall
totals between 2-5 inches are possible with the highest totals
mainly along the Park Range through Wednesday morning.

As this system exits, lingering moisture and weak MLCAPE values
between up to 100 J/kg may lead to an isolated storm or two mainly
near the WY/NE/CO border. Short-lived ridge pattern enters
northeast Colorado starting Thursday evening which could limit
severe weather. An isolated shower or two could occur along the
foothills and plains but the likelihood of severe remains low. A
front develops late Thursday which will slightly cool afternoon
temperatures Friday through the weekend. Near normal temperatures
are likely for northeast Colorado. It is possible an additional
shortwave could bring additional moisture to the region each
afternoon Friday through this weekend leading slight chance of
showers and storms

&&

.AVIATION /18Z TAFS through 18Z Monday/...
Issued at 1036 AM MDT Sun May 19 2024

Main concern is gusty outflow winds from high based showers or
virga this afternoon.

ACARS soundings show the inversion weakening and we`re starting to
mix a little better now. While we could go variable winds for an
hour or two initially, overall a west to northwest wind should
prevail through 00Z. We are already starting to see cumulus
develop in/near the mountains, and thermal/moisture profiles would
suggest strong and gusty outflow wind potential to ~40 knots
possible with any high based convective activity. Coverage is
expected to be great enough per upstream satellite imagery to
warrant VRB gusty winds with a VCSH from around 19Z to ~00Z. The
threat of any thunder is less than 10%.

Winds should settle down toward 00Z but could still be variable
between northerly and east or southeast. A cold front then arrives
toward 09Z-11Z with a northeasterly push of winds. That will also
usher in higher low level moisture with potential for stratus. At
this point, the upslope appears pretty shallow and weak, so we`ll
just go with SCT clouds around 3000 ft AGL for the Denver area TAF
sites 12Z-16Z. There`s about a 30% chance it goes BKN for MVFR
ceilings.

&&

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

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...AD
AVIATION...Barjenbruch