146
FXUS65 KBOU 031129
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
529 AM MDT Wed Jul 3 2024

.KEY MESSAGES...

- Strong to severe thunderstorms will be possible across the
  plains this afternoon/evening.

- Elevated fire weather conditions across the high country and
  urban corridor this afternoon

- Gorgeous weather conditions are expected on the Fourth of July
  with only a slight chance of an evening shower or storm.

- Somewhat cool and mainly dry conditions will persist Friday
  through early next week.

&&

.SHORT TERM /Through tonight/...
Issued at 303 AM MDT Wed Jul 3 2024

Another day, another complicated convective forecast across
northeast Colorado.

Weak elevated convection has persisted through most of the
overnight hours tonight across Lincoln county into the
southeastern portion of the state. SPC Mesoanalysis still shows
roughly 500-1000 J/kg of MUCAPE across the plains, in part due to
continued low-level moisture advection back into the state.
Surface obs this morning show upper 50s dew points east of the
urban corridor, which is a bit more moisture than most near-term
guidance had predicted. Weak showers and a couple of storms will
remain possible through the early morning hours as this convection
gradually lifts to the north and east.

The synoptic scale players are largely set for today, as a broad
upper trough axis and accompanying jet streak move across the
region this afternoon through tonight. This should provide some
weak broad scale ascent, but neither of these features are
particularly strong. What`s left are the mesoscale details. A
surface dryline is expected to setup across the plains, with dry
northwesterly flow on the dry side (more on this later), with
moist southerly flow east of the boundary. Models generally have
this boundary stalling near a Kimball NE - Fort Morgan - Deer
Trail line.

Areas east of the dryline should be in a broadly favorable
environment for severe weather. With surface dew points in the
upper 50s to low 60s, MLCAPE should increase to 1000-1500 J/kg. As
mid-level flow increases ahead of the approaching shortwave, deep
layer shear should also generally reach 35-45kt. With generally
straight-line hodographs, this setup would favor splitting
supercells with primarily a large hail/damaging wind threat. While
a tornado or two can`t be ruled out, any tornado threat would be
driven by subtle/mesoscale boundary interactions. Models also hint
at some weak capping across the warm/moist sector this afternoon,
which would likely limit overall convective coverage. This is
(somewhat) well-modeled by the 00z HREF members, with paintball
plots showing at least a couple of supercells, but little
agreement in the exact location.

Further west... warm, dry and breezy will be the story of the day.
Guidance shows a deep, well-mixed boundary layer across the high
country and the I-25 corridor, with relative humidity values
falling to around 15%. BUFKIT momentum transfer plots suggest
mixing down from ~500mb (if not higher), which should lead to a
few gusts around 30-35kt, especially across the higher elevations.
Did think for a bit about a Red Flag Warning, but don`t have the
confidence that we`ll reach the areal/time thresholds for an RFW.
With Independence Day just around the corner, please be mindful
that there is still some fire danger on any dry/breezy days. Be
aware of any local fire restrictions this week!

A fairly strong cold front (for July standards) is expected to
push into the region overnight tonight... but more on that below.

&&

.LONG TERM /Thursday through Tuesday/...
Issued at 133 AM MDT Wed Jul 3 2024

The Fourth of July will have very pleasant weather conditions.
This is due to a cold front that will move through our forecast
area Wednesday night and, as a result, Thursday will start off on
the cooler side with lows in the low to mid 50s across the
plains. As a shortwave trough moves east of the area, there will
be mostly sunny skies for much of the day with subsident flow.
The latest high resolution model runs are showing that there will
be just enough instability due to steep lapse rates that a couple
showers and perhaps a thunderstorm or two could develop in the
evening hours. The models focus on northern Weld and Larimer
Counties as the primary location for these showers and storms but
there is a slight chance that they form anywhere on the plains.

South Park will be the focus for the worst fire weather conditions
on Thursday. Relative humidity will decrease to as low as 10
percent with gusts around 30 mph possible. Fire weather highlights
may be needed for fire zone 214. Across the plains, the cool
temperatures will limit fire weather conditions as minimum relative
humidity will be above 22 percent.

The upper level pattern will become stagnant for the rest of the
long term period. There will be a strong ridge aloft over
California which will create a heat wave out west. There will be
troughing over the Midwest during this period which will put
Colorado under northwesterly flow aloft between these features.
Our forecast area will see a period of generally cool and dry
weather from Friday through Tuesday. There are two primary
exceptions, however. The first is on Saturday as temperatures
will reach the 90s across the plains and fire weather conditions
may near critical limits as relative humidity drops to the teens
with gusts near 25 mph. The other exception is Sunday when a more
substantial shortwave trough will move across Colorado. There
will be a cold front at the surface that brings in cool and moist
air which may lead to good coverage of afternoon showers and
thunderstorms.

At some point next week, the aforementioned ridge aloft over
California will move eastward over Colorado. When this happens,
Colorado will experience a heat wave. Over the past couple of
days, models seem to hold off this ridge moving over Colorado
until later in the week.

&&

.AVIATION /12Z TAFS through 12Z Thursday/...
Issued at 523 AM MDT Wed Jul 3 2024

VFR through the TAF period with no ceiling or visibility concerns
today.

Main challenge in the forecast is the winds. Expecting gusty
west-northwesterly flow to develop by late morning or early
afternoon at DEN/BJC, with an uncertain wind forecast at APA. Any
outflow from storms to the east would also complicate things this
afternoon/evening but chances of that look quite low.

Winds will weaken this evening but likely won`t manage to
transition to drainage flow before a strong cold front shifts
winds to the north. Guidance has pretty robust gusts behind the
frontal push and have bumped up the timing and strength of winds
in this period. There are still some occasional hints of low
stratus developing closer to 12z Thursday but will stick with some
FEW020-030 for now.

&&

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

&&

$$

SHORT TERM...Hiris
LONG TERM...Danielson
AVIATION...Hiris