480
FXUS65 KBOU 090130
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
730 PM MDT Wed May 8 2024

.KEY MESSAGES...

- Continued light snowfall in the mountains with some blowing snow
  over the higher passes

- Cool and unsettled weather Thursday through Friday, with
  accumulating snow in the Front Range mountains, higher
  foothills, and Park County

- Gradual warming this weekend into early next week, but still
  somewhat unsettled with scattered showers and storms most days

&&

.UPDATE...
Issued at 730 PM MDT Wed May 8 2024

Water vapor satellite imagery showing a low spinning over the
Great Basin and a second low tracking southwest across the Black
Hills. These two come together over the Great Basin Thursday.
Radar shows a good amount of showers over Wyoming. Models indicate
most of this activity stays north of Colorado, though wouldn`t be
surprise to see a few over far northern Colorado as well. Airmass
over the area is still dry with a temperature/dew point of
20-30F, so it will take a while to moisten up. This will happen
behind a cold front that pushes south through the area Thursday
morning. Northeast low level flow behind the front will produce
low clouds and areas of rain. Best chance for rain/snow and
heaviest rain/snow will be over the upslope favored areas, mainly
west of I-25 and also over the Palmer Divide. This will be a
chilly system with the snow level falling to 6000-7000 feet. For
the update, delayed the increase in PoPs until Thursday morning,
after 12Z. Also removed/decreased the mention of thunder across
the Front Range where stratus is expected to stabilize the airmass
on Thursday.

&&

.SHORT TERM /Through Thursday/...
Issued at 245 PM MDT Wed May 8 2024

The latest radar scans currently show rain showers over the Northern
Rockies of Montana and Wyoming this afternoon associated with an
elongated upper level low. This low will shift southwestward into
Colorado and Utah overnight funneling moisture into the forecast
area.

For this afternoon and tonight, SPC mesoscale analysis shows mid
level lapse rates have increased enough this afternoon creating
enough instability to bring a slight chance of thunderstorms to
areas mainly west of I-25 while rain showers are possible across the
plains. Precipitation will develop along the northern state border
and spread south as a cold front passes from north to south later on
tonight bringing a chance for snow showers to develop in the
mountains and foothills. Temperatures will be a few degrees below
normal across the plains and foothills, and 10 to 15 degrees below
the norm for the higher elevations.

By tomorrow morning, snow levels will drop to between 6000`-7000`as
the elongated low splits into two and upslope flow develops across
the Front Range mountains. Max temperatures will be well below
normal as widespread 50s will be seen across the plains, 40s for
the foothills, and 30s and 40s for the mountains. See the long
term forecast below for specifics on snow amounts.

&&

.LONG TERM /Thursday night through Wednesday/...
Issued at 143 PM MDT Wed May 8 2024

The models have trended wetter with the elongating trough dropping
across our area, and the impacts of this could last through
Thursday night and even into early Friday morning. There is
persistent QG lift through this period, but the bulk of it will
stay to our south. That said, there is more of an upslope
component now advertised to last through Thursday night as the
elongated trough redevelops into a slightly deeper closed low in
the Great Basin. Thus, with all those ingredients we increased
PoPs and QPF/Snow forecasts for locations in/near the Front Range
through tomorrow night. Regarding snow levels, we think most of
the accumulating snow should stay above 7,000 feet per latest
forecast soundings, but we did have to nudge snow levels down
down to account for the upslope component and potential enhanced
precipitation rates and latent heat of melting. Thus, we would
not be surprised to see some accumulation down to ~6,500 feet
should the more significant precipitation/upslope develop. We
could certainly need Advisories for the Park/Summit County areas,
and possibly into portions of the foothills in updates to follow.
Current potential shows upward of 6-12" possible for Park County
and east facing slopes above 7,000 feet.

By later Friday and Friday night, we`ll turn to neutral forcing
or weak subsidence. Precipitation coverage will be on the
decrease, although there is still some weak upslope and potential
for shower redevelopment with sufficient daytime heating. There`s
not a lot of heating, however, with high temperatures likely
struggling to reach 60, and most likely holding in the 50s closer
to the foothills.

For the weekend, there seems to be more ensemble agreement that
weak troughiness will remain over the forecast area. This will
lead to only gradual warming, but a continuation of scattered
showers and a few thunderstorms each day. Instability is limited,
so there is little if any threat of severe.

We finally expect a return to above normal temperatures by early
next week. That`s when we begin to transition to more of a zonal
flow with downslope aiding the warmup. It is springtime, however,
so we`ll continue to see a chance of showers and storms most days.
The severe storm threat will remain limited due to a lack of
instability. It`s not impossible, however, that we start to see a
little stronger convection toward Tuesday or Wednesday if we can
build enough low level moisture.

&&

.AVIATION /00Z TAFS through 00Z Thursday/...
Issued at 545 PM MDT Wed May 8 2024

VFR to prevail through the rest of the evening and into the
overnight hours. West to northwest winds to decrease after sunset
(02Z). Wind direction becomes tricky to forecast and likely
becomes variable.

Cold front pushes through the Denver area around 12Z bringing
northeast winds and low clouds (1500-2500 feet) with it. Models
still showing a somewhat large window (12-15Z) when the front
could push through. Expect ceilings to slowly rise after 18Z, but
remain under 6000 feet through Thursday. After 00Z Friday ceilings
will slowly lower. Lowest clouds/visibility and best chance for
rain showers are expected to be at BJC due to the northeast
upslope flow.

&&

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

&&

$$

UPDATE...Meier
SHORT TERM...Bonner
LONG TERM...Barjenbruch
AVIATION...Meier