401
FXUS65 KBOU 080014
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
614 PM MDT Tue May 7 2024

.KEY MESSAGES...

- Freeze warning for the Palmer Divide...and a Frost Advisory
  most of the plains and I-25 corridor early Wednesday morning


- Continued snowfall with blustery conditions across the high
  terrain through midnight.

- Cool and unsettled pattern Wednesday through Friday.

- Warming Saturday through Tuesday with more normal late day
  shower and storm chances

&&

.UPDATE...
Issued at 614 PM MDT Tue May 7 2024

Main changes to this evening`s forecast were to the highlights.
First, the RFW for southern Lincoln was cancelled because RH had
increased 25-30% under thick cloud cover, adn wind gusts were in
the 20-25 mph range. Area radar and CDOT webcams show poor travel
conditions in several areas through the mountains. Both sides of
the tunnels, Tenmile Canyon, and the east approach to Vail pass on
I-70, US40 on both sides of Berthoud and across Rabbit Ears, and
Cameron pass have snow covered roads for long stretches at those
higher elevations. The loss of solar heating to melt the roads
will also come into play in the next hour, resulting in
development of icy spots and increasing the chances of snow
accumulating on the road surfaces. In addition, CAMs continue to
show pockets of convective snow showers with another 1-3" possible
through midnight. Because of all of these factors, we extended
the Winter Weather Advisory through midnight for the mountains
abovfe 9,000 ft. Conditions should impove overnight with weak
lapse rates above ridge top and minimal snow expected. Maybe just
the Park Range gets an inch or two through early Wednesday.

Finally, we opted to issue a frost advisory for much of the plains
and I-25 urban corridor where low temperatures tonight are
expected to drop between 31-36 degrees. It will be too dry to
actually form frost in most if not all of the advisory area, but
very sensitive plans are prone to damage from the cold when it
drops below 35 even in the absence of frost. Most plants should do
okay tonight, but it would be a good idea to take protective
action for those highly sensitive plants, like tomatoes, peppers, peonies,
and related common plants across northeastern Colorado if you
already have them planted outside.

The rest of tonights forecast looks on track and minimal updates
were made to the gridded forecast elements.


&&

.SHORT TERM /Through Wednesday/...
Issued at 1201 PM MDT Tue May 7 2024
Remainder of Today and Tonight...Still windy and quite frankly we`re
over it! Elongated trough axis and perpendicular jet streak
careening into the Continental Divide continues to create pockets of
heavier snow combining with stronger winds will drop visibilities to
a mile or less. As mentioned earlier, lapse rates are still very
steep so we`re looking at convective snow showers, so impacts will
vary greatly within a small amount of real estate. The Winter
Weather Advisory continues through 6 PM MDT for the high country.

Across the foothills and plains, winds, virga, virga driven winds,
maybe a hundredth or two of rain (right along the foothills),
otherwise no big sensible weather concerns...did we mention wind!?

We continue the Red Flag Warning across southern Lincoln County as
numerous gusts 30-40 MPH are expected the remainder of the afternoon
with relative humidity values hovering right around 15% at this time.

Overnight we really don`t lose the winds, though we remove a
majority of the stronger gusts outside of the high terrain. While
the skies do clear and the airmass is rather dry, we should cool
enough to get close to the freezing mark in a lot of places early
Wednesday morning. The highest confidence we have in a harder freeze
is across the Palmer Divide where we expect shelter temperatures to
drop into the upper-20s. DESI viewer shows nearly a 100% chance of
being below freezing in this area...chances drop off quickly outside
of the Palmer to around 30% of being below freezing. The warmer
overnight temperatures and the addition of the winds is the main
reason why we canceled the Freeze Watch tonight.

Wednesday...Much the same, though a tad less wind...finally! 700mb
low pulls further to the east-southeast so winds should back more
towards the northwest throughout the day. Lapse rates aren`t as
steep as today but a little bit of heating during the afternoon we
could see some pop-up showers, 20% chance, across the northern
plains counties.

&&

.LONG TERM /Wednesday night through Tuesday/...
Issued at 200 PM MDT Tue May 7 2024

A more tranquil (and less windy!!) pattern will dominate our
weather through early next week. There will still be a few showers
or isolated thunderstorms around in typical spring fashion, but no
big storms are in the works.

For Wednesday night into Thursday, the elongating upper level
trough will sink slowly southward into Colorado and the Great
Basin. Moisture will increase, leading to scattered but mostly
light showers. It`s quite a chilly system with 700 mb temperatures
near -6C along the Front Range by early Thursday morning, perhaps
leading to a little rain/snow mix all the way down to Denver`s
elevation, if we see precipitation Thursday morning. Then daytime
heating would lift any snow levels closer to 7000 feet by the
afternoon hours. That said, any accumulation in the higher
elevations will still be light given weak dynamics and
orographics. We may be hard pressed to push far into the 50s for
highs considering the additional moisture and cooler airmass
overhead.

For Thursday night, most showers are expected to come to an end as
the best lift settles into the Great Basin, leaving a weak col
but somewhat drier air over our forecast area. If it clears out
sufficiently we could be looking at frost/freeze conditions again.
For Friday, enough instability would still exist though to keep a
few convective afternoon and evening showers in the forecast,
mainly over the higher terrain. Some drying should allow for more
solar insolation, pushing highs into the 60s.

For Saturday through Monday, there is still uncertainty and no
clear solutions for the forecast in this period. Ensembles are
coming into a little better agreement, but it all depends on how
far north the low kicks to the east, and the timing of said
feature. For now, there`s not much confidence in any one
particular solution, as there`s a relatively even split between
lifting the upper low back up across Colorado at some point next
weekend, or keeping it sufficiently to our south for mostly dry
weather and warmer temperatures. There`s still no clear solution
at this point, so we`ll go with the consensus model blends showing
the warmer temperatures but also a chance of showers/isolated
storms most days. This pattern would not favor any threats of
significant weather or strong thunderstorms.

&&

.AVIATION /00Z TAFS through 00Z Wednesday/...
Issued at 614 PM MDT Tue May 7 2024

VFR conditions through Wednesday. Any showers that temporarily
lowered CIGs to close to MVFR have evaporated and no further
shower activity is expected at the terminals. That of course
leaves the wind. There is still some uncertainty about when the
strong west winds will weaken this evening. Confidence in
increasing that after 01Z, west wind gusts over 20 kts are
unlikely, though may occur at BJC through 02Z. The other useful
devleopment is that winds are more WNW than W this evening. After
01 or 02Z, winds should be 15 kts or less at the terminals, and
mostly out of the west. Winds should back to SW at around 10 kts
after 08-09Z.

On Wedneday, winds will be much weaker than the previous 2 days,
and should also be more out of the WNW and even north, both of which
are good news for DEN. For now, winds should increase by 15Z, but
gusts should remain under 25 kts (other than BJC), and weak
anitcycloning of the NW flow may actually result in north winds
around 10 kts at DEN and APA by 20Z. BJC will probably stay out of
280 or 290 and may gust 25-30 kts through the middle of the
afternoon before the pressure gradient relaxes across Colorado,
reducing winds for everyone.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight MDT tonight for COZ031-
033-034.

Frost Advisory from midnight tonight to 8 AM MDT Wednesday for
COZ038>040-042>047-049.

Freeze Warning from midnight tonight to 8 AM MDT Wednesday for
COZ041.

&&

$$

UPDATE...Schlatter
SHORT TERM...Heavener
LONG TERM...Barjenbruch
AVIATION...Schlatter