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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS65 KBOU 221153
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
553 AM MDT Mon Apr 22 2024

.KEY MESSAGES...

- Warmer on Monday with a slight chance of afternoon showers
  and isolated thunderstorms.

- Cooler Tuesday, but then above normal temperatures again for
  Wednesday and Thursday.

- Stormier weather pattern in the works, starting late Thursday
  and peaking next weekend.

&&

.SHORT TERM /Through tonight/...
Issued at 409 AM MDT Mon Apr 22 2024

Today, we will remain under WNW flow aloft. Flow will be enhanced
enough to support breezy conditions across the high country and
most of the plains toward the afternoon once winds mix down. Gusts
30-40 mph in the high country and up to 25 mph for the lower
elevations. A bump of several degrees in the 700mb temperatures
will support a sufficiently warmer day today with highs in the 70s
across the plains, 50s/60s for foothills, and 40s for the
mountains. The northeast corner will stay a couple degrees cooler
as a weak backdoor cold front moves across the plains in the
afternoon. If the front makes it far enough west, it may cool
highs a few degrees. Model cross sections show moisture embedded
in the flow moving in this afternoon and combined with lapse rates
8-9C/km and marginal CAPE, will support isolated showers or a
stray storm in the mountains. Marginal instability will develop
across the plains as well; however, model soundings are quite dry
toward the lower levels. If any showers do stray onto the plains,
this environment will be more supportive of virga and brief gusts
up to 30 mph near any showers rather than rain. Given the dry and
breezy conditions, elevated fire weather conditions are possible
over portions of the Palmer Divide and Lincoln County.

No impactful weather expected tonight. Another cold front moves in
after midnight. Lows in the 30s for the plains and 20s/30s for the
high country.

&&

.LONG TERM /Tuesday through Sunday/...
Issued at 330 AM MDT Mon Apr 22 2024

The forecast guidance in the long range remains largely unchanged,
with just minor fluctuations noted. We`ll stay mainly dry and
relatively mild most days (outside of Tuesday), but then the
pattern changes Thursday with more active and wet weather becoming
more likely for next weekend.

On Tuesday, a large and cool surface high will build across the
Northern High Plains. This will keep cooler and more stable
upslope flow in place across northeast Colorado. With that in
mind, we`ll nudge down our high temperature forecast a couple
more degrees. There is also some cloud cover to favor lowering
temperatures, in the form of both stratus Tuesday morning and
then thicker mid/high clouds and a few showers around for the
afternoon. The mountains will stay largely unchanged with mild
temperatures, but we will likely see an uptick in showers and even
a couple afternoon/evening thunderstorms as the airmass
destabilizes, and moistens under the influence of weak QG lift
and strengthening mid level frontogenesis. We`re uncertain about
the amount and depth of moisture in this pattern, but enough to
have the higher PoPs over the mountains and then northern border
area of the plains toward the evening and overnight hours as best
QG support and Fgen lifts that way.

For Wednesday, the models have continued the trend of slowing the
ridging and warmup. That said, ensembles are still pointing to
highs in the mid 70s over most of the plains as warm advection
kicks in. At this rate, Thursday could very well end up being the
warmest day of the week. For now, we`ll keep forecast high
temperatures in the lower elevations just under the 80 degree
mark. It could be warmer, but there is reasonable ensemble
agreement that the first ejecting shortwave will be getting close
enough to increase clouds and bring scattered showers and
thunderstorms late in the day.

We`re still seeing some flat ridging forecast for Friday, but
enough moisture could linger to keep a few showers and storms in
the forecast.

There is now more agreement in the ensembles that a deeper trough
will dig into the Desert Southwest late Friday into Saturday, and
then deepen as it moves east/northeast across the forecast area
sometime in the Saturday night to Sunday time frame. Of course
there`s still a fair amount of uncertainty with regard to track,
intensity, and timing. Nonetheless, when it does kick out this
storm will have potential to bring significant precipitation to
our forecast area. The top 20% of the combined 18Z and 00Z GEFS
runs are showing precipitation amounts in excess of 1.5 inches,
and approximately the top 10% are greater than 2.5 inches. With
regard to precipitation type, most of the ensemble members keep it
rain for the lower elevations, but snow for the higher foothills
and mountains. Finally, for the convective fans of the audience,
ensemble average CAPE increases to 600 J/kg over the eastern
plains in advance of this potentially negatively tilted trough.
Should some of the more unstable solutions verify, we could be
looking at our first severe storm(s) of the season. This one will
be an interesting storm system to keep our eyes on for the next
several days.

&&

.AVIATION /12Z TAFS through 12Z Tuesday/...
-- Changed Discussion --
Issued at 553 AM MDT Mon Apr 22 2024

VFR conditions are likely today and this evening. SSW/SW drainage
winds continue this morning at 10-15 kts at KDEN/KAPA. Winds
gradually transition SW this morning, eventually becoming more
westerly. In the 17-20z timeframe confidence is lower with regard
to wind direction. The wind direction will depend on if a backdoor
cold front moves far west enough to impact DEN. If it does, light
easterlies will cross the field. If it doesn`t, breezier WNW winds
(10-15 kts gusts 25 kts) that will continue for the remainder of
the afternoon. For now, included this easterly potential as a
TEMPO as a couple models are keen. APA and BJC will likely not be
impacted by this and will stay WNW/NE with gusts 20-25 kts. A
front moves through between 08-11z overnight with a switch to
northerly flow behind it. This will bring in mid-level ceilings
and potentially lower (low end VFR-MVFR).
-- End Changed Discussion --

&&

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

&&

$$

SHORT TERM...Mensch
LONG TERM...Barjenbruch
AVIATION...Mensch