444
FXUS65 KBOU 182347
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
547 PM MDT Tue Aug 18 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms this afternoon into tonight.
  A couple strong to severe storms possible across the eastern
  plains later this evening.

- Isolated storms again for Wednesday, though chances of stronger
  storms shift to the south.

- Warming and drying trend to end the week, before monsoon
  moisture attempts to return Sunday into early next week.

&&

.DISCUSSION /Through Tuesday/...
Issued at 1229 PM MDT Tue Aug 18 2026

A somewhat uncertain forecast for the rest of the day today.
While a weak surface boundary - I`m not sure it`s strong enough to
even be called a cold front - is working its way south towards
the Denver metro. Where virga and light rain has been falling in
North Park and south central Wyoming, temperatures are much
cooler. Understandably, short-term forecast models don`t seem to
have a great handle on both the initial wind shift we`re seeing
now, and with the eventual stronger push of cooler air later this
evening. In general, it seems the most likely scenario for the day
is two rounds of convection - with the first round developing
over the Front Range and generally remaining weak (given meager
surface moisture/MLCAPE), with chances of another round or two
along or behind the front later this evening. Initial
showers/storms this afternoon would be capable of producing gusty
winds as DCAPE increases to about 1200 J/kg. If the second round
of convection does develop, the environment would favor multicell
clusters or splitting supercells that would come with both a wind
and hail risk. SPC`s marginal risk with a CIG1 "hatch" for
hail/wind across most of our plains seems to be a good
representation of today`s conditional severe threat.

The flow aloft will turn a little more northwesterly on Wednesday
as the upper ridge tries to establish itself closer to the Four
Corners. Some moisture still lingers across the state, though
guidance keeps the majority of convection across the far southern
fringes of our CWA into south-central/southeastern Colorado during
the day. We should see at least isolated, weak convection across
most of the higher elevations, with precipitation chances dropping
off towards the north and east.

The rest of the week will be dominated by a large ridge off to
the south, leading to a return of above normal temperatures and
generally dry conditions. While temperatures will still be warm,
this round of heat looks much different than the previous spells
of heat earlier in the month. First, 700mb temperatures are
nowhere near as warm, with 700mb temperatures generally peaking
around 16-19C... meaning highs should reach the mid 90s. There`s
also still a decent amount of moisture trapped underneath this
ridge, with precipitable water values near or even slightly above
normal. We`ll likely at least see a few showers over the high
country each day, while the metro and plains stay dry.

The ridge is expected to weaken and slowly shift eastward by this
weekend into early next week, allowing monsoon moisture to drift
back into the forecast area. There`s some modest timing
differences in this period, but in general there`s a good signal
for rain across the region by Sunday. Guidance has generally been
a day or two too quick to break down ridges here over the summer,
so it`s possible the better rain chances will wait until early
next week.

&&

.AVIATION /00Z TAFS through 00Z Thursday/...
Issued at 533 PM MDT Tue Aug 18 2026

Scattered showers will develop this evening with a ~30% chance of
lightning before 03Z at all terminals. An outflow boundary/cold
front is currently moving through Cheyenne with gusty northerly
winds behind it. This front will move through KDEN around ~2-4z,
KBJC ~2-4z, and KAPA around ~3-5z with northerly winds gusting to
35 kts with a small chance for gusts up to 40 knots. An upper
level trough moving across the area late this evening will provide
enough forcing for showers and storms to form mainly between
03-06Z at all terminals. These will be capable of producing microburst
gusts up to ~30-35 kt.

After ~06z, model guidance indicates there could be some
lingering showers in the area to monitor but any impacts from
these showers would be minimal if they occur. Winds will be light
tonight and may not settle on drainage in the overnight hours. If
drainage winds don`t develop, variable or brief periods of
northeasterly winds may occur. There is also a ~10% chance of
fog/low clouds at KDEN and KBJC in the morning, ~10-14z timeframe.


Showers and a storm or two will likely form over the southern
foothills and Palmer Divide tomorrow afternoon. There is a chance
(30%) that a couple of these showers or storms drift towards KBJC
and KAPA. The primary impact will be gusty winds up to 30 knots
from these showers/storms. There is a lower chance (10%), that any
showers or storms impact KDEN with wind gusts being the primary
concern.

&&

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

&&

$$

DISCUSSION...Hiris
AVIATION...Danielson

NWS BOU Office Area Forecast Discussion