Text Products for AFD Issued by BOU

Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
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FXUS65 KBOU 240535
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1135 PM MDT Tue Apr 23 2024

.KEY MESSAGES...

- Scattered showers and a few storms diminishing as they move east
  this evening.

- Stormier weather pattern in the works, starting late Thursday
  and peaking next weekend, with accumulating moderate snowfall
  in the mountains.

- Stronger storms possible northeast plains Thursday
  afternoon/evening.

&&

.UPDATE...
Issued at 743 PM MDT Tue Apr 23 2024

Radar shows widely scattered showers continuing across the
forecast area this evening. The strongest convection (as of the
time of this update) was over Boulder with light to moderate rain...
though even this hasn`t produced lightning in a while.

Showers should gradually decrease in coverage through the rest of
the evening and early overnight hours tonight. Most guidance keeps
a few showers around through at least 06z tonight but minimal
impacts are anticipated.

Have made some minor adjustments to the grids, but the previous
forecast was largely in good shape. Attempted to make some minor
PoP adjustments to better reflect current observations, but it`s
been difficult to differentiate between areas of virga and light
rain. Have kept broad slight chance/chance PoPs across most of the
plains for the next few hours.

&&

.SHORT TERM /Through Wednesday/...
Issued at 259 PM MDT Tue Apr 23 2024

Not much change to the forecast at this hour. Weak convection from
a little QG lift and diurnal heating over the mountains is
progressing eastward. There`s about 500 J/kg CAPE in the
mountains, enough for a few lightning strikes, but this should
decrease in an elevated mixed layer as it moves east across the
plains while the surface air should remain capped. We backed off
the PoPs for the eastern portion of the plains a bit more with
doubts about how much will be left when it gets there.

Skies gradually clear overnight, though there may still be some
clouds on the northern and eastern borders early Wednesday
morning. We`ll have warmer and drier air aloft, and should see
less convection. Still probably some cumulus and some light
showers over the northern mountains. There`s a small chance (10%)
of generating a storm or two on a Denver cyclone boundary in the
late afternoon, but we probably won`t quite be warm/moist enough.
Convergence may force some brief updrafts that don`t sustain
themselves. Current forecast and guidance temperatures look good.

&&

.LONG TERM /Wednesday night through Tuesday/...
Issued at 259 PM MDT Tue Apr 23 2024

A series of mid-level systems will bring multiple rounds of
precipitation throughout northeastern Colorado starting Thursday
through this weekend. As high pressure pushes eastward Wednesday
night, winds aloft shift southwest. A shortwave trough enters
western Colorado and mid-level moisture deepens from the
mountains to the plains Thursday morning. 700mb temperatures
remain warm ranging from 3-7 C/km which should lead to the warmest
day this week. Surface temperatures Thursday afternoon for the
mountains and valleys reach 49-60F while temperatures in the
plains and urban corridor increase near 70-80F. As the trough
enters our region, daytime heating and mid-level QG ascent should
allow for a few showers to develop in the foothills and northeast
plains early Thursday afternoon. MLCAPE values increase amongst
all guidance between 800-900 J/kg with pockets of higher values in
the northeastern corner. Additional, favorable SFC-3km wind shear
of 30-40kts and mid-level lapse rates between 7-8 C/km could lead
to an environment for scattered to numerous thunderstorms to
develop across the plains along with the potential for a few
embedded severe storms producing small hail. As DCAPE values
approach 1000 J/kg, expect storms to produce wind gusts up to
45-60 mph. These conditions persist through late Thursday evening
before exiting into Nebraska/Kansas. The highest threat of severe
storms exist mainly for the areas along and above I-76 through
Thursday night.

Our unsettled pattern continues Friday and there is a consensus
amongst guidance indicating wind aloft shift northwesterly. This
will allow additional moisture and surface winds to increase
across the mountains and plains. Scattered showers and storms are
possible Friday afternoon but with the lack of instability,
expecting these storms to be less robust leading to quick heavy
rainfall and lightning. This weekend as an additional shortwave
trough arrives from the western US coast. In terms of the severe
threat, atmospheric conditions of weak low level shear and MLCAPE
between 100-300 J/kg may lead to scattered to numerous showers
versus thunderstorms both Saturday and Sunday. In terms of
Saturday, precipitable water values increase over GFS and ECMWF
ensembles with the highest values mainly near the northeastern
corner reaching 0.50- 0.80 inches. Although conditions may change
leading up to Saturday, the atmosphere seems fitting for a heavy
rainfall threat throughout the plains. Across the other side of
the Divide, increasing QPF fields will likely lead to periods of
light to moderate snowfall for the mountains starting early
Saturday morning for areas above 8.5k ft. This may lead to winter
weather headlines depending on snow levels and uptick in QPF
values this weekend.

&&

.AVIATION /06Z TAFS through 06Z Thursday/...
Issued at 1135 PM MDT Tue Apr 23 2024

VFR through the TAF period with generally SCT-BKN mid-level
clouds. Showers were exiting the area and winds were now settling
back to the normal overnight flows. There`s still a small chance
of variable winds for the next few hours, but overall
south/southwest winds should prevail through 15Z for KDEN and
KAPA, with northwest/west at KBJC. After that, there is a tendency
for southwest winds at KDEN and KAPA, but can`t rule out a period
of variable winds again. In fact, some guidance keeps it variable
through the entire day, while pressure patterns and daytime
heating would suggest more of a southeasterly flow. Therefore,
we`ll keep that SE wind in the TAF for consistency...but winds and
persistence will be something to watch.

A couple of high-based showers are possible again after 21Z
Wednesday, but coverage at this point looks sparse enough that
VCSH wasn`t included. If anything does develop in the area, VRB
wind gusts to 30 kts possible given the dry sub-cloud layer and
DCAPE near 1000 J/kg.

&&

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

&&

$$

UPDATE...Hiris
SHORT TERM...Gimmestad
LONG TERM...AD
AVIATION...Barjenbruch
National Weather Service Regional Headquarters
