Text Products for AFD Issued by BOU

Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
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FXUS65 KBOU 240930
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
330 AM MDT Wed Apr 24 2024

.KEY MESSAGES...

- Slight Risk of severe thunderstorms Thursday, east of a line
  from Sterling to Akron, including large hail, damaging winds and
  isolated tornadoes. A marginal risk south and west of this
  area.

- Cool and unsettled Friday into the weekend, with accumulating
  moderate snowfall in the mountains, widespread rain showers over
  the plains

&&

.SHORT TERM /Through tonight/...
Issued at 330 AM MDT Wed Apr 24 2024

One fairly quiet weather day today before we get more active
Thursday through much of the weekend. Satellite and radar shows a
few showers lingering in these early morning hours over the far
northeast plains, while ridging is starting to take hold with
clearing skies building in from the southwest. The ridging and
warm advection will bring a bump in temperatures today, with much
above normal readings expected. Most of the plains and I-25
Corridor will reach the mid to upper 70s (slightly cooler far
east), while mountain areas will enjoy 50s and 60s.

There is slight drying aloft moving into the forecast area, but
temperatures are warming and models still show a bump in
instability this afternoon. Thus, despite the upper ridging we
still expect isolated showers and storms late this afternoon and
evening, favoring areas in the mountains and across the plains
closer to the Wyoming and Nebraska borders. We can`t totally rule
out isolated high based showers farther south along a surface
convergence zone, but that would be quite weak and only brief
sprinkles/very light rain.

For tonight, low level moisture advection begins in earnest across
the northeast plains as low level flow turns south/southeast. That
will draw in the current airmass in the Texas Panhandle with
dewpoints rising into the mid 40s overnight. Stratus and patchy
fog expected to develop, with higher ridges being more prone to
advection fog.

&&

.LONG TERM /Thursday through Tuesday/...
Issued at 330 AM MDT Wed Apr 24 2024

On Thursday, a couple severe thunderstorms will be possible over
the northeast plains. The first short wave trough will move across
CO around 00z Friday, with moderate mid and upper level QG ascent
ahead of the trough in the afternoon. At the surface, an west-
east oriented warm front will move off the Palmer Divide, with
southeast winds north of the front advecting low level moisture in
the plains. Fog and/or stratus will be an issue through Thursday
morning north fo the front. Model soundings indicate ML 100mb CAPE
around 1000-1200 j/kg in the afternoon, with 0-3km storm relative
helicities of 150-200 m2/s2. The combination of instability/shear
appears to be sufficient to warrant a slight risk of severe
thunderstorms, primarily east of a line from around Sterling to
Akron. Large hail, damaging wind as well as a tornado or two may
be possible. West and south of this line, the risk will be more on
the marginal side. Timing wise, it appears that the storms will
initiate along the warm front around 21z then move northeast
through 03z.

By 12z Friday, the upper low will be over southwest NE, with wrap
around moisture associated with northwesterly flow on the west
side of the exiting trough, impacting the plains through the day.
There will be enough moisture and instability around for snow
showers to in the mountains, and rain showers/isolated tstms over
the plains. The best coverage for showers would appear to be to
the north and east of Denver on Friday. By Friday night, a short
wave ridge will move across the forecast area which may allow for
a brief decrease in precipitation intensity overnight but not
necessarily coverage as the impact (subsidence) from the ridge
will be short lived.

On Saturday, the next trough will move out of the Great Basin and
into central CO by 00z Sunday, then exiting into southwest
NE/northwest KS by 12z Sunday.  Moderate mid/upper level QG ascent
will be over northeast CO through the day Saturday, then decrease
from west to east Saturday night. In this time, the models
generate anywhere from 6-14 inches of snow in the higher
mountains. The main window will be from 06z Saturday to 00z
Monday. If this trend continues, then either a Winter Storm Watch
or Advisory may be issued. Light snow accumulations can also be
expected over the Palmer Divide Saturday night into Sunday
morning. Across the northeast plains, the pops will start to
decrease Sunday afternoon into Sunday night. Total qpf generated
by the models will be around 2 inches, with the highest amounts in
the mountains, and across the northeast plains towards the WY and
NE.

By early next week, the trough will have exited to the east but
enough moisture will be available at least in the mountains for a
chance of residual showers on Monday, then dry and warmer weather
returns on Tuesday.

&&

.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.

&&

$$

SHORT TERM...DB
LONG TERM...Cooper
AVIATION...DB
National Weather Service Regional Headquarters
