670
FXUS65 KBOU 260915
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
315 AM MDT Wed Jun 26 2024

.KEY MESSAGES...

- Scattered to numerous thunderstorms today.

- Some storms will be strong to severe with heavy rain, large
  hail, and strong winds.

- Scattered-numerous thunderstorms return Thursday, some strong to
  possible severe, especially in the plains.

- Turning drier into the weekend, with some moderation in
  temperatures Saturday.

- Potential for significant heat will rise again next week.

&&

.SHORT TERM /Through tonight/...
Issued at 243 AM MDT Wed Jun 26 2024

Upper level high that`s been centered over the Central and Southern
Rockies will slowly sink south today. At the surface, a weak cold
front drops south across eastern Colorado this morning. Temperatures
today drop to near normal with highs in the upper 80s to lower 90s
across northeast Colorado. We see a good increase in moisture today.
Water vapor satellite imagery showing a plume of moisture across the
Four Corners region. This moisture will rotate northeast around the
upper level high today. Also, low level moisture will increase
behind the cold front this morning with dew points in the 50s to
lower 60s across the Front Range and plains. This will result in
precipitable water values of 125-150% of normal east of the
mountains and over the higher terrain precipitable water values near
200% of normal. Heavy rain will be possible with the stronger storms.
Mid level winds of 20-30 knots will help to keep storms moving along.

There are small differences on the amount and placement of
instability and shear today. Models generally agree we will see
MLCAPE of 1000-1500 J/kg over a good part of northeast Colorado. The
main difference is how far west the better instability will be. As
far as shear goes, where southeast surface winds reach 15-20 knots,
bulk shear (0-6km) reaches 30-40 knots. This is enough instability
and shear for severe storms. Hi-Resolution models show scattered
storms forming over the higher terrain this afternoon. The storms
then progress eastward across the Front Range. Once this convection
reaches the plains (east of the metro area), it is expected to
increase in intensity and coverage with a broken line tracking across
the plains. Main threats will be hail up to golf ball size and
strong damaging winds.

&&

.LONG TERM /Thursday through Tuesday/...
Issued at 243 AM MDT Wed Jun 26 2024

Of the extended forecast period, Thursday certainly carries the
higher potential for severe weather, together with more expansive
coverage of late day convection. Ample moisture will remain in
place, only negligibly lower than today`s values, with precipitable
water peaking between 1.10-1.40" over the urban corridor and plains,
the bulk of this above 600mb. The weakening 500mb ridge will
continue to flatten, but a 700mb shortwave becomes more noticeable
in advance of broader troughing to our northwest. Sustained warm
temperatures into the lower 90`s for much of our lowlands will make
for drier near-surface conditions, but with dewpoints in the 50`s
along the urban corridor and 60`s in the eastern plains, and
steepening lapse rates as cold air advection increases aloft, we`ll
have sufficient instability to support scattered to numerous
afternoon showers and thunderstorms.
Rainfall will likely be more efficient in the high country relative
to today given richer low-level moisture, becoming less productive
due east of the Front Range, especially along the I-25 corridor
where precipitation should be more limited. As far as timing is
concerned, a strengthening upper-level jet will help provide for
some enhanced dynamic support in the evening, with a few
showers/storms likely lingering in the eastern plains and high
country.

The trough axis traverses overhead on Friday with robust westerly
flow prevailing aloft, resulting in a marginal moderation of
temperatures and breezier conditions across our higher elevations.
Subsident flow will keep drier conditions in place below 600mb, and
help reduce thunderstorm coverage and intensity east of the
mountains. Nonetheless, a chance of afternoon storms (35-60%) will
persist.

A cold front Friday evening/night will usher in milder
temperatures for Saturday, with highs descending into the low to mid
80`s for the lower elevations - most likely the coolest day of the
forecast period. More stable conditions will also develop as a
ridging pattern begins gaining prominence, with notably lower
precipitation chances region-wide. ML CAPE will be much more
marginal, outside of perhaps the southernmost row of our plains
counties and Palmer Divide where chances for afternoon/evening
convection will be highest.

Warming and drying then accelerates into Sunday under the
expanding ridge, quickly returning us to the 90`s for highs and
keeping precipitation chances quite low outside of the mountains.
Come Monday, there are some signs of troughing over the northern
plains with enhanced west-northwest flow along its leading edge,
which carries potential for some fire weather concerns depending
on just how dry we stay. Regardless, expect the heat to linger and
precipitation chances to remain on the low side. Depending on the
timing and amplitude of the trough, we could see a slight reprieve
in temperatures for Tuesday, but moisture still appears rather
lacking and any cooling is likely to be short-lived, with hotter
temperatures favored to take hold for the mid to late portions of
the week.

&&

.AVIATION /06Z TAFS through 06Z Thursday/...
Issued at 1138 PM MDT Tue Jun 25 2024

There are still some weak outflow boundaries around, which are
keeping winds from settling a drainage direction. Expect southerly
winds to set up 06-07Z or sooner at APA and DEN. These southerly
winds will be short lived. There is a boundary tracking
southwestward that just entered far northeast Colorado. This will
bring a wind shift to the north/northeast overnight, in the 09-10Z
time frame. The airmass behind this boundary is much more moist.
Low clouds are expected to form over parts of the northeast
plains. There`s roughly and 30-40 percent chance the Denver area
sees low clouds. For the TAF will keep the FEW010, for the chance
at seeing low clouds Wednesday morning, after 12Z.

With better moisture in place, showers and thunderstorms will be
more common Wednesday afternoon. Will keep the tempo for
thunderstorms in the TAF beginning Wednesday 21Z at DEN and APA,
20Z at BJC. There stronger storms will be capable of producing
heavy rain, hail, and outflow winds.

&&

.HYDROLOGY...
Issued at 243 AM MDT Wed Jun 26 2024

With an increase in moisture, thunderstorms will be capable of
producing heavy rainfall today. Mid level is expected to be strong
enough to push storms along. However, where storms train or remain
anchored, flash flooding will be possible. Also, flood prone areas,
such as burn scars could see flooding if heavy rain is slow to leave
the area. Conditions will be similar Thursday with ample moisture
remaining in place. Precipitation efficiency could even be
slightly higher in the mountains given a more favorable low-level
moisture profile, although storm motion should still be decent
enough to keep most storms moving fast enough to limit the scope
of flash flooding concerns. Expect the pattern to turn notably
drier heading into the weekend.

&&

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

&&

$$

SHORT TERM...Meier
LONG TERM...Rodriguez
AVIATION...Meier
HYDROLOGY...Meier