Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 141116
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
516 AM MDT Sun Apr 14 2024

.KEY MESSAGES...

- Very warm and dry today, with fire weather concerns for parts of
  the plains.

- Elevated to critical fire weather conditions over the plains
  Monday afternoon.

- A windy weather system will bring snow showers to the mountains
  with rain showers likely on the plains late Monday into Tuesday.

- Cooler, windy and unsettled the rest of the week. Occasional
  snow showers in the mountains with a chance of mostly rain
  showers for the plains.

&&

.SHORT TERM /Through tonight/...
Issued at 405 AM MDT Sun Apr 14 2024

Clear skies abound early this morning over the region, and this will
generally remain the case much of the day as the thermal ridge
anchors overhead. There will be a few mid-level clouds around, but
certainly much less extensive compared to yesterday. Coupled with ~2
degrees C of warming aloft, this should firmly lead us to the
warmest day of the year so far for the majority of our forecast
area. The urban corridor will climb into the low 80`s, with mid 80`s
making an appearance across the eastern plains, and mountain
communities pushing well into the 60`s.

Once again, we`ll be dealing will a very well-mixed environment this
afternoon. Flow aloft will be a little stronger today as warm
southeasterly winds preceding the advancing trough over the
Intermountain West surge northward, and some of that will trickle
down to the surface. The breezier conditions look to develop in the
plains, mainly east of I-25 and south of I-76, where gusts may push
25-30 mph - enough for some fire weather concerns and associated Red
Flag Warnings. See Fire Weather discussion below for more on that.
The southeast flow is progged to strengthen later this evening and
tonight between 800-700 mb, and could provide for some strengthening
winds across the eastern plains before the lower levels decouple.
There are a few high-resolution runs (e.g. NAM 3km, WRF ARW) that
have been depicting gusts in exceed of 50-55 mph late evening in the
plains. These seem just a little overdone, but have nevertheless
bumped speeds up a touch above NBM to account for this.

With breezier conditions around tonight for our entire area,
overnight cooling will be tapered, and it`ll be notably mild for
this time of year, with low temperatures remaining above 40F for all
but the coldest plains locations, and some areas in northeast plains
and along the base of the foothills possibly not dropping much below
50F. Mountain valley inversions should keep high country lows a
little closer to seasonal normals.

&&

.LONG TERM /Monday through Saturday/...
Issued at 405 AM MDT Sun Apr 14 2024

Only subtle trends in the models this morning. Perhaps a slight
slowing still with the passing trough late Monday/early Tuesday.
There`s more of an elongation of the trough than a northward
shift, but this still keeps the best lift along the northern
border and really diminishes the threat of upslope low level
winds. It`s now looking like there will be a pronounced downslope
component the whole time for the eastern plains.

The slower motion means a longer warm, dry, windy period on the
plains before the cold front comes late in the afternoon. See
below for fire weather concerns. With the strengthening downslope
winds, we`ve backed off on PoPs a little and are focused more on
the middle of the night and early Tuesday morning hours as
anything before that will likely be over a lot of dry low level
air. Even with a fairly well organized deformation band moving
over Tuesday morning, it might be hard to get rain to the ground
with increasing northwest winds beneath. Guidance continues to
trend upward with wind speeds, and we could be near high wind
criteria much of the day Tuesday.

There may be a period of upslope into the Medicine Bow range and
the Larimer county foothills where NNE winds are uphill Monday
night, and there could still be significant snow above 7 or 8
thousand feet there. The operational GFS liked this area enough to
produce two inches of QPF, while other model runs have that focus
much are closer to an inch or a bit less. There could be a period
of decent snow in the Park and Rabbit Ears ranges as well as the
back edge deformation band develops Monday night. But northwest
winds becoming northerly isn`t the best for an orographic component,
and the snow will be driven as much by the larger scale dynamics.

Valleys and lower foothills will be warm enough for mostly rain,
though North Park might be cold enough for a few inches of snow as
the deformation band moves over Monday night.

For the rest of the week, there`s a continued gradual trend
towards a solution that doesn`t get as cold. It still looks like a
decent front late Wednesday, followed by weak QG lift from
overrunning of that boundary Wednesday night into Thursday. After
that things are more subtle, with uncertainty about that lift
continuing or reoccurring, and the strength of a possible
secondary surge of cool air behind that jet streak that could
bring a little more cooling and low level convergence on Friday.
The colder solutions get cold enough for a rain/snow mix on the
plains with any showers by Friday, but the presence of any lift or
instability and that much cooling all look doubtful. We made sure
we have a mix mentioned, and it wouldn`t surprise me if we`re too
warm or too stable for any snow at lower elevations.

&&

.AVIATION /12Z TAFS through 12Z Monday/...
Issued at 515 AM MDT Sun Apr 14 2024

VFR conditions will prevail for all terminals through the TAF
period, with some FEW-SCT high clouds at/above 150 Sunday
afternoon.

A well-mixed environment should produce enhanced southeasterly
winds most of the day with gusts at times exceeding 20 kts, mainly
for KDEN/KAPA. This robust southeasterly flow could hold together
longer than usual into the evening and early overnight period,
with some guidance even suggesting a little strengthening after
~2100 MT as pre-frontal southeast flow aloft continues to mix down
to the surface due to a late decoupling (i.e. inversion
development). Eventually, weaker drainage flow should return
Sunday night.

&&

.FIRE WEATHER...
Issued at 405 AM MDT Sun Apr 14 2024

A few hours of critical fire weather conditions look increasingly
likely this afternoon for portions of our plains and Palmer Divide,
with efficient vertical mixing making gusts in the 25-30 mph more
likely for areas south of I-76 and east of Denver. With the upper-
level ridge overhead, ample sun, and unseasonably warm temperatures,
all of the lower elevations will see very dry conditions return,
with minimum humidity of 8-14% across the region. Have opted to go
with a Red Flag Warning for those plains zones where the potential
for gusts exceeding 25 mph this afternoon appears highest.

A low pressure system will intensify in northeastern Colorado on
Monday. There will be warm, dry, and windy conditions south and
east of the low, mainly along and south of Interstate 76, with
critical fire weather conditions in that area. Further north and
west it will be windy, but humidities will be higher.

It will be windy Tuesday, especially on the plains, with cooler
temperatures. Some precipitation late Monday into Tuesday should
reduce the fire weather threat. Cooler weather is expected for the
rest of the week with occasional mountain snow and a chance of
showers on the plains. It will still be breezy at times, but not
as windy as the early part of the week.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 1 PM this afternoon to 8 PM MDT this
evening for COZ241-245>247-249.

Fire Weather Watch from Monday afternoon through Monday evening
for COZ241-244>251.

&&

$$

SHORT TERM...Rodriguez
LONG TERM...Gimmestad
AVIATION...Rodriguez
FIRE WEATHER...Rodriguez/Gimmestad


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