013
FXUS65 KBOU 170815
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
215 AM MDT Sat Aug 17 2024

.KEY MESSAGES...

- Heat peaks today. A few evening showers in the high country, and
  locally breezy late.

- Precipitation chances increase by Sunday, with isolated or
  scattered storms expected through next week.

- There will be a limited or greater threat of flash flooding over
  the burn areas Sunday through the middle of next week.

&&

.SHORT TERM /Through Tonight/...
Issued at 143 AM MDT Sat Aug 17 2024

Dry and subsident flow will prevail beneath an upper-level ridge
centered just east of the Front Range today, with ample stability
in place, particularly across the lower elevations. There,
abundant sunshine will persist through most of the afternoon, and
temperatures will peak in the mid to upper 90`s, potentially
scraping daily record high temperatures.

The warming will be more subdued for the higher elevations. A weak
shortwave and vorticity maximum will impinge on the western
periphery of the ridge, as it swings northeastward across the NW
corner of the state. This should provide for an increase in cloud
cover during the afternoon, and make for a more subtle (1-3
degree) increase in temperatures. PW values will climb modestly to
between 0.70-0.90" by this evening as this wave comes through,
and should be sufficient to generate some orographically-enhanced
showers or even a few weak thunderstorms in the mountains.
Instability will be lacking, and so too will the moisture despite
the relative increase. Thus, only light rain amounts are expected.
This activity will likely try and roll off the higher terrain and
into the foothills and adjacent urban corridor mid/late evening,
but will encounter much drier air. As a result, the main impact,
if any, for areas east of the mountains would come from potential
outflows, with localized gusts 30-40 mph possible during the
evening and overnight period. The downslope wind regime will
sustain quite mild nocturnal temperatures Saturday night, with
lows well into the 60`s across the board for the plains and I-25
corridor.

&&

.LONG TERM /Sunday through Friday/...
Issued at 143 AM MDT Sat Aug 17 2024

A warm and reasonably active pattern will continue through the
extended period.

An upper level ridge is forecast to be over the TX/OK panhandle
by Sunday, and this ridge will dominate the forecast pattern under
a quasi-Omega Blocking setup. A plume of monsoonal moisture is
expected to advect north/northeastward on this side of the ridge
axis, leading to multiple days of precipitation chances (though
not particularly widespread and/or heavy). While the ridge will
drift west and meander back east during the week, there isn`t
going to be significant day to day changes across the forecast
area over the next several days.

Sunday should mark the arrival of this moisture plume, with PWAT
normalized anomalies approaching 1-2 sigma across the region
(~0.9-1.1" across the metro). However, most guidance shows at
least some weak capping across the metro and plains Sunday
afternoon and evening. Without a discernible forcing mechanism,
the majority of showers/storms should initiate across the higher
elevations and struggle as they slowly move eastward. A few storms
may also develop across the far eastern plains where richer
boundary-layer moisture resides. The main concern for the day
would be burn area flash flooding, along with a conditional/low-
end severe threat closer to the eastern border.

Guidance favors Monday as the most active day across the metro,
with better agreement with regards to the amount of near-surface
moisture... resulting in stronger instability across the region.
Precipitable water values remain above normal for this time of
year, and we should see widely scattered storms across the region.
Heavy rainfall would be the main concern as 700-500mb specific
humidity increases to around 6g/kg, while mean flow across the
region remains light. Again the main concern would be burn area
flash flooding.

As we get later into the week, the airmass gradually begins to
dry out. There will still be widely scattered showers and storms
each afternoon, especially across the higher elevations. A wetter
day or two may be mixed into the forecast at some point, but there
isn`t a clear signal for any specific day.

The other story of the week will be our continued above normal
temperatures, which is unsurprising given the proximity to the
upper ridge. Nearly all of the 00z guidance tonight has 90F or
warmer temperatures for DEN continuing over the next 7-10 days, if
not longer (GFS). The one exception may be Monday, where
convective coverage may hold temperatures in the upper 80s.
Although record heat doesn`t appear likely at this point, a 90F
streak of 10 days or longer this late into the summer (beginning
August 15th or later) has only occurred a handful of times... and
would be a change of pace from the below normal to normal
temperatures we saw over the last week or so.

&&

.AVIATION /06Z TAFS through 06Z Sunday/...
Issued at 1129 PM MDT Fri Aug 16 2024

VFR conditions will prevail for all terminals through the TAF
period. Expect healthy southerly drainage winds early Saturday
morning, shifting more southwesterly towards sunrise, followed by
lighter and more variable directions through midday. At BJC,
winds may shift northwest to west over the next few hours. A
period of east then southeast winds are expected late afternoon
and early evening Saturday. Later in the evening, guidance still
favors development of scattered high-based showers over the higher
terrain, potentially drifting into portions of the urban corridor
late evening. Main impact would be enhanced westerly outflow
winds, with higher confidence west of I-25 (i.e. KBJC). Will keep
TEMPO groups for now to reflect this possibility.

&&

.HYDROLOGY...
Issued at 143 AM MDT Sat Aug 17 2024

Dry conditions will prevail for most areas Saturday, although a
late-day intrusion of moisture into the high country may provide
for scattered showers and possibly a weak thunderstorm or two in
the evening. Given a general lack of instability and only modest
moisture amounts, there`s very little concern for any heavy
rainfall from this activity.

A limited threat of burn area flash flooding is forecast from
Sunday through most of next week. Increasing moisture on the
northwestern edge of an upper level ridge will lead to isolated to
scattered thunderstorms each afternoon. Storm motions should be
slow given a lack of strong flow aloft. One or two days over the
next week may have a greater threat, but it`s difficult to say
which day(s) that will be.

&&

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

&&

$$

SHORT TERM...Rodriguez
LONG TERM...Hiris
AVIATION...Rodriguez
HYDROLOGY...Rodriguez/Hiris