922
FXUS65 KBOU 091547
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
947 AM MDT Thu May 9 2024

.KEY MESSAGES...

- Snow will increase over the higher terrain through this afternoon
  and continue tonight into Friday. The heaviest snow is expected
  along and south of I-70 including South Park and above 7500 ft
  in the southern Foothills.

- Cool and unsettled weather will be in place across the rest of
  the area into Friday with the best chance of showers along the
  I-25 Corridor and Palmer Divide.

- Gradual warming this weekend into early next week along with
  scattered late day showers and thunderstorms.

&&

.UPDATE...
Issued at 947 AM MDT Thu May 9 2024

The forecast is in pretty good shape with scattered showers
developing this morning. So far, they have been strangely focused
in the northern foothills extending through Fort Collins toward
Greeley, while mostly dry conditions had persisted south of that
including Boulder & Denver, where showers had not yet developed
behind this morning`s frontal surge. We do expect that to change
with shallow instability, as noted by the developing stratocumulus
field that was actually a bit bumpy on top. There have been some
peeks of sunshine to aid destabilization in the weak upslope flow,
so scattered showers should develop farther south in/near the
foothills and then push back into the Front Range this afternoon
in the deepening but relatively weak upslope environment. There is
another lobe of instability and moisture rotating southwest from
the Black Hills area, and some of these showers/isolated storms
could work onto the northeast plains this afternoon. Overall, the
forecast is on track with only minor changes to PoPs to reflect
the latest trends.

Mountain and foothill locations above ~7,000 feet should be mostly
snow. The Winter Weather Advisory starting in those areas
along/south of I-70 late this afternoon, and especially tonight
and Friday morning when more impacts are expected, is looking
good.

&&

.SHORT TERM /Through tonight/...
Issued at 316 AM MDT Thu May 9 2024

The upper level low that was over the central US will split into
two parts as one piece of energy reforms into a weaker closed low
over ern UT and wrn CO. This feature will then slowly retrograde
into ern NV and wrn UT by late tonight. At the sfc, a cool front
will move across the plains this morning with upslope flow
developing thru the day and continuing tonight.

Overall, there is only weak QG ascent across the area thru tonight
but moisture depth and lapse rates will be favorable in and near
the higher terrain. In addition, persistent upslope flow should
allow for precip enhancement east of the Divide and across
portions of South Park. At this time, heaviest qpf should be
mainly along and south of I-70. Mosquito Range in Park county
probably will end up with the heaviest snow which may reach
warning criteria. However the majority of zn 34 will stay in the
advisory range along with South Park. Across the srn Foothills
amounts may reach advisory criteria as well above 7500 feet.

Across the plains, precip chances will be considerably less as best
chc of showers will be along and west of I-25 and across the Palmer
Divide.  Highs across the nern CO will mainly be in the 50s.

&&

.LONG TERM /Friday through Wednesday/...
Issued at 350 AM MDT Thu May 9 2024

Models are still showing an upper closed low over the southern Great
Basin at 12Z Friday morning along with weak upper troughing stretched
west to east across the forecast area.  These features move little
on Friday and Friday evening. By Saturday afternoon, the upper low
is over the Four Corners and right over the CWA by 12Z Sunday.  This
is a bit slower than yesterday`s 00Z model runs indicated.  There
is neutral to weak QG upward vertical velocity over the CWA Friday
through Saturday night.  The low level pressure and wind fields have
weak upslope over the plains on Friday into the evening,  Normal
diurnal wind patterns kick in after that and continue through
Saturday night.

For moisture, cross sections show it to be fairly deep early on
Friday, with some decrease over the plains in the afternoon. It
dries out quite a bit Friday night, even in the mountains late.  On
Saturday into Saturday night, moisture is pretty good again for much
of the CWA. CAPE values are a bit better on Saturday, with even
some out on the plains with better heating expected. So for pops,
"likely"s for the mountains and 10-40%s over the plains, with the
highest pops next to the foothills. Will keep some "isolated"
thunderstorms going as well. Pops look a bit higher on Saturday
with the better heating. Will go with 30-70%s for the entire CWA
during the afternoon and evening, then 10-30%s overnight. Again,
with keep some mention of thunder going, with better chances in
the alpine areas. Snow will be relegated to the mountains and
higher foothills on Friday, and mainly just for the mountains on
warmer Saturday.

Looking at temperatures, Friday`s highs will be below seasonal
normals but 2-3 C warmer than today`s highs. By Saturday, highs will
climb 2-5 C and be right at seasonal normals with mid 60s F to lower
70s F on the plains and 30s to 40s F in the mountains.

For the later days, Sunday through Wednesday, models have the upper
closed low moving east and out of the CWA Sunday and Sunday
evening. There is some short wave upper ridging for Monday. By
Tuesday and Wednesday, some of the models indicate weak upper
troughing and northwesterly flow aloft while others show more
zonal flow. There does seem to be enough moisture and heating
available for late day convection all four days, although
significant precipitation is not expected. Temperatures will be at
or a bit above seasonal normals all four days.

&&

.AVIATION /12Z TAFS through 12Z Friday/...
Issued at 513 AM MDT Thu May 9 2024

Cold front should reach DIA around 13z with light SE winds
becoming NNE. Should see IFR ceilings develop behind front
with a few light rain showers possible. IFR ceilings should
become MVFR by 19z with NE winds thru the aftn.

For tonight, MVFR ceilings will continue with NE winds.
By 07z ceilings may drop back to IFR with a slight chance
of showers overnight.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 PM this afternoon to noon MDT
Friday for COZ034-036-037.

&&

$$

UPDATE...Barjenbruch
SHORT TERM...RPK
LONG TERM....RJK
AVIATION...RPK