334 
FXUS65 KBOU 270522
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1122 PM MDT Sat Sep 26 2026

.KEY MESSAGES...

- Drier and warm Sunday, with highs reaching into the 80s across 
  the plains.

- Low chances (<30%) for light mountain snow above 12,000ft 
  Monday through Wednesday.

- Potential for heavy rain Wednesday and Thursday, but confidence
  in amounts and locations remains low.

&&

.DISCUSSION /Through Saturday/...
Issued at 1110 PM MDT Sat Sep 26 2026

A potent upper level trough will move onto the West Coast on
Sunday, nudging the upper ridging over our area east. As the 
ridge starts to slide east, southwesterly flow will bring 
increased moisture at mid and upper levels from the Pacific. The 
higher moisture in the mountains and some weak upslope from 
southeasterly surface winds could produce some isolated to 
scattered showers in the higher terrain and areas generally north 
of I-76 tomorrow afternoon. While most of this activity is 
expected to remain on the weaker side, we could see an isolated 
storm or two. MLCAPE will be weak, but looking at lapse rates and
DCAPEs, any storm that can get going could have the potential for
some gusty winds (maybe around 40kts). The showers and potential storms
are forecast to move northeast into the late evening, but no 
impacts are expected.

The upper trough is forecast to dive into southern California on 
Monday, progressing into Arizona on Tuesday. As the trough moves 
east/southeast, moisture will continue to flow into the area, 
increasing PWs to around 200% of normal. A few weak disturbances 
will likely move through the southwest flow at mid levels, 
providing weak lift for showers and storms Monday and Tuesday. 
Widespread coverage is not anticipated with this activity, with 
the best chances for precip over the mountains. While coverage 
will be minimal, we will want to keep an eye on the localized 
heavy rain potential both days due to the anomalous moisture. A 
cold front is still poised to move through the forecast are late 
Monday into early Tuesday. Overall impacts from the front will be 
pretty limited, other than slightly cooler temperatures for 
Tuesday and Wednesday. Snow chances for the mountains continue to 
decrease as each new model run comes in. While there will likely 
be a few rounds of flurries and a dusting at the highest 
elevations, temperatures just look too warm to support decent snow
totals (snow levels are generally 12,000+ft for Monday through 
Wednesday and SLRs are below 5). 

Models now have better agreement that the strong upper low will 
eventually move into southeast Colorado by Thursday. The main 
difference between models now is where they develop the surface
low, impacting where the heaviest rain band forms. If the surface
low ends up a bit closer to our area, we could see some wrap 
around moisture, bringing heavy rain potential for Wednesday and 
Thursday. However, if the surface low ends up too far south and 
east, our area will end up on the drier side of things. The exact 
location of the axis of heavier precip will be very difficult to 
forecast, and very impactful. Models are hinting at some pretty 
substantial rain amounts with this system, but right now, the 
majority of ensemble members keep the highest rain totals to the 
south and east of our forecast area. The best chance for heavier 
rain totals for our area will be in Lincoln County. All this being
said, even if we don't end up with the widespread heavy rainfall,
moisture will be high enough that localized flash flooding will 
be a concern for any storms that pop up.

This system and the better rain chances will start to push off to
the east on Friday. The speed at which that system exits and the 
next moves in is still up in the air. The GFS wants to bring in 
the next shortwave and frontal system almost immediately over the 
weekend, however the Euro wants to delay the second system and 
hold onto the first for a bit longer. Either way, the weather with
the highest potential impacts over the next week will be that 
Wednesday through Thursday time period.

&&

.AVIATION /00Z TAFS through 00Z Monday/...
Issued at 525 PM MDT Sat Sep 26 2026

Winds will become south by 02z and then turn more SSW by 05z.
HRRR shows a few weak high based showers between 02z and 04z but
no gusty winds expected so have not mentioned for this evening.

On Sun, winds will become SE by 18z and then increase thru the
aftn with gusts up to 25 mph by 21z. Have mentioned a prob30
for higher based showers beginning at 22z for APA and BJC and 23z
at DIA. Brief gusty outflow winds up to 30 mph will be possible 
thru 03z. 

&&

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

&&

$$

DISCUSSION...AP
AVIATION...RPK