763 
FXUS65 KBOU 052333
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
533 PM MDT Sat Sep 5 2026

.KEY MESSAGES...

- Increasing risk of locally heavy rainfall this evening and
  overnight for the far northeast plains.

- A few strong thunderstorms possible this evening over the 
  northeast plains.

- Slight increase in afternoon shower and thunderstorm coverage is
  favored Sunday and Monday for most areas.

- Temperatures will remain very warm, with only slightly cooler
  conditions starting Tuesday.

&&

.UPDATE...
Issued at 525 PM MDT Sat Sep 5 2026

Given ongoing convection across Logan County as well as the 
latest CAMs, we have issued a Flood Watch through 3am Sunday for 
far Northeast Colorado (Logan, Phillips, and Sedgwick counties). A
Severe Thunderstorm Watch is also in effect for these locations 
through 9pm this evening. Storms are capable of producing gusty 
winds and large hail (up to about 2 inches in diameter), with a 
report of 1.75" hail in Sterling in the last 30 minutes. 

The bigger concern through this evening and overnight will be the
flooding threat. Dew points in Logan, Sedgwick, and Phillips 
counties are currently in the upper 50s to low 60s. Moisture is a
bit more impressive than originally modeled. As a result, the 
environment has been overperforming so far this afternoon with 
rainfall totals already as high as 1.30 inches in two hours in 
Logan County. Mean cloud layer winds are expected to slow this 
evening with multiple rounds of showers and thunderstorms 
possible- increasing the flooding risk. The majority of CAMs are 
now showing that isolated locations in the Flood Watch could 
receive 3 to 5 inches of rainfall this evening.

&&

.DISCUSSION /Through Saturday/...
Issued at 1153 AM MDT Sat Sep 5 2026

Midday cumulus development is more expansive today, suggestive of
the modest increase in mid-level moisture regionwide. Near surface
moisture however is much more variable, with dewpoint fields 
exhibiting a considerable zonal gradient between the I-25 
corridor (~40-45F) and our eastern plains (~58-63F). Given
limited forcing, meager instability and drier low-levels, areas
from the urban corridor westward will be limited to largely
isolated high-based shower activity late this afternoon and
evening, producing brief localized gusts of 25-35 mph. Over the
eastern plains, the warm and moist advection regime will hold
steady through tonight, leading to an increasingly buoyant
environment with MLCAPE values of 1,500-2,500 J/Kg present across
our northeasternmost counties by late afternoon. Thunderstorms
look to develop come this evening, with the bulk of the activity
favoring the late evening period coinciding with a moderate LLJ
setup over the plains. A few will be strong to perhaps marginally
severe, with an initial wind and hail threat that will 
nonetheless be tapered by the lack of shear, limiting overall 
storm organization. Given the clustering potential and abundant 
moisture (precipitable water values approach 1.5" this evening), 
locally heavy rain can be expected with any storms.

We'll gain a touch more moisture still on Sunday as moist
southerly flow continues and the trough to our west inches
slightly closer. The urban corridor also looks a little better
positioned to tap into higher surface dewpoints, supporting
modestly unstable conditions for the afternoon. Thus, anticipate
an increase in afternoon shower activity as well as potential for
actual convection. There will be minimal change as far as
temperatures are concerned though, with most of the lower
elevations breaking into the lower 90's once more.

A slight waning in the high pressure on Monday will allow for the
intrusion of stronger northwest flow at upper levels and thus some
actual forcing, which should support a slight uptick in coverage
of showers and thunderstorms, and likely the best precipitation
chances of the next few days. Unsurprisingly, temperatures will
continue to hold mostly steady.

At risk of sounding like a broken record, ensemble guidance still
indicates a flattening of the ridge starting Tuesday (though more
pronounced Wednesday), followed by a westward shift of the ridge 
axis over Colorado. Slightly cooler temperatures - albeit still 
above - should result from the initial flattening and transition
to zonal flow, but this trend appears increasingly transient in
nature, with ensemble guidance favoring a return to hotter weather
for the second half of the week. As previous discussions have
alluded to, confidence in precipitation potential remains lower,
although we still look to retain at least some moisture beneath
the ridge and thus a few opportunities for afternoon showers and
thunderstorms.

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1152 AM MDT Sat Sep 5 2026

Northeast winds will continue this afternoon and slowly turn
clockwise, becoming southeast this evening, after 00Z. The PROB30
for variable winds and showers was pushed back to begin at 02Z.
This lines up with recent model guidance which shows the best lift
occurring later. A wind shift or two will be possible from passing
by showers. For tomorrow, better instability and moisture will
lead to about a 30 percent chance for thunderstorms late Sunday
afternoon, after 22Z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 3 AM MDT Sunday for COZ048-050-051.

&&

$$

UPDATE...MV
DISCUSSION...BRQ
AVIATION...BM