994
FXUS65 KBOU 190714
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
114 AM MDT Sat Sep 19 2026

.KEY MESSAGES...

- Isolated to scattered showers/t-storms return this afternoon to
  the mountains and urban corridor. These will become numerous
  over the plains, where some will be strong to severe through
  this evening, producing locally heavy rain and hail.

- Trending drier Sunday into Monday, although scattered afternoon
  storms may continue Sunday, particularly along and south of
  I-70.

- Cooler temperatures expected Sunday into Monday, before warmer
  temperatures return. Next week will bring a few additional
  opportunities for precipitation, mostly for our mountains, with
  lesser heavy rain potential.

&&

.DISCUSSION /Through Friday/...
Issued at 1243 AM MDT Sat Sep 19 2026

Ongoing showers over the eastern plains early this morning will
steadily dissipate as we near sunrise, while moisture will
continue feeding into the high country this morning where showers
will linger. Despite modestly cooler conditions today (highs will
remain below 80F over the plains), we`ll hold onto moderately
unstably conditions and ample moisture. The latest forecast
soundings indicate bulk shear of 35-50 kts across the majority of
the plains this afternoon, which would support another round of
numerous thunderstorms, some of which will be strong to severe.
Thus far, there isn`t much indication of low stratus this morning,
so don`t foresee convective temperatures not being reached.
Instability will be exceedingly marginal though for areas roughly
along and west of I-25, so the potential for stronger storms and
heavier rainfall will be considerably tapered outside of our rural
plains. Hail and heavy downpours will be the primary threats from
today`s stronger convection.

The bulk of the stronger thunderstorms will move out of the plains
by late evening. However, with the upper-level trough traversing
overhead, we`ll retain potential for overnight showers and weak
thunderstorms. Increased PoPs notably for our northern areas in
particular. Will additionally need to monitor potential for patchy
fog Sunday morning across portions of the lower elevations,
especially the South Platte River Valley.

Sunday stands to be our coolest day of the week with the passage
of the shortwave. If we`re able to clear out morning cloud cover
more efficiently, the environment would support renewed scattered
showers/t-storms in the afternoon and evening. It`s a big if, with
the convective potential being notably lower for the northern half
of our forecast area, and best for the Palmer Divide and areas
downstream into Lincoln County where it would be easiest to erode
any low-level capping. Depending on how quickly the low ejects to
our east, isolated to scattered late-day showers and thunderstorms
could linger into Monday, but any coverage should be notably
reduced relative to previous days.

Starting Tuesday, warmer conditions will return as a southwest
flow pattern takes hold aloft. An embedded shortwave late Tuesday
into Wednesday favors an increase in precipitation potential
namely for our mountains, with lesser coverage/more uncertainty
for the lower elevations. Regardless, moisture profiles won`t be
as robust as those currently being observed, so accumulations
should be on the lighter side if we see any.

&&

.AVIATION /06Z TAFS through 06Z Sunday/...
Issued at 1120 PM MDT Fri Sep 18 2026

Northerly flow remains in place across the Denver metro as of this
writing, but latest guidance is trending towards a shift to
westerly and eventually SW drainage winds within the next 3 hours
or so. Satellite imagery does not show any low stratus development
just yet, although patchy formation certainly can`t yet be ruled
out through the next couple of hours. Nonetheless, the threat of
any CIGS below 1,000 ft AGL at the terminals early this morning,
especially persistent ones, is trending favorably and confidence
is no longer high enough to justify any TEMPO groups, even if the
threat is indeed non-zero.

Looking ahead at the daytime period, expect a transition to
prevailing NE flow by 18-19Z after light and VRB morning winds.
Confidence is higher than previous days in afternoon convective
potential for KDEN and KAPA, however the potential for stronger
TSRA and associated vis restrictions appeared somewhat bullish in
preceding forecasts for areas west of I-25 in particular (i.e.
KBJC), so the latest forecast reflects this spatial disparity in
confidence and/or coverage with a PROB30 for the latter. Even
KAPA and KDEN will likely be on the western fringe of the
stronger TSRA potential. Timeframe of impacts remains the same,
generally 21-01Z for the metro before convection pushes into the
plains, leaving impacts primarily confined to the NE and SE KDEN
gates.

Lastly, still monitoring low stratus/fog potential for Saturday
night. Similar to this morning, the latest guidance is less
enthused with the northerly flow potential, at least in the
evening. Have thus opted to refrain or push back stratus
indications in the TAFs with the expectation that fog potential
would be more favored during the early morning hours, more in line
with local climatology. All of this is admittedly low confidence.

&&

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

&&

$$

DISCUSSION...BRQ
AVIATION...BRQ

NWS BOU Office Area Forecast Discussion