Steamboat

000
FXUS65 KGJT 312311
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
511 PM MDT Sat Oct 31 2026

.KEY MESSAGES...

- Flooding/flash flooding concerns increase Sunday into Monday,
  especially for areas that have saturated soils from last
  week's rain. A Flood Watch remains in effect.

- Forecast river responses have increased, with a number of 
  gages in southwest Colorado expected to climb into at least 
  minor flood stage. River Flood Warnings are now in effect 
  along the La Plata River, and the San Juan River near Pagosa 
  Springs.

- Winter weather highlights have been issued for the San Juans
  and central Colorado mountains for accumulating snow Sunday
  morning through Monday evening.

&&

.DISCUSSION...
Issued at 1226 PM MDT Sat Oct 31 2026

QUIET SATURDAY:

Today will see eastern Utah and western Colorado under something of 
a dry slot, sandwiched between yesterday's shortwave and the 
approaching longer wave trough. Dry is a bit of a misnomer, though, 
as PWATs remain around 150% of normal today, resulting in widespread 
cloud cover and a few stray orographic showers through the 
afternoon. The upper level southwesterly jet noses in after 6PM this 
evening, bringing an increasing chance of showers and a few 
thunderstorms to areas around the Four Corners. Any activity at this 
time is expected to be isolated to widely scattered, and trick or 
treating for much of the Western Slope will be in the dry. 


LOWER ELEVATION RAIN, MOUNTAIN SNOW, AND FLOODING POTENTIAL:

Precipitation begins to fill in from southwest to northeast after 
midnight tonight, becoming widespread by daybreak Sunday. All this 
precipitation is being fueled by a robust AR that is taking a very 
favorable trajectory up through southern California and setting its 
sights on the Four Corners region. PWAT anomalies in both the 
Ensemble ECMWF and Ensemble GFS are on the order of 250-350% of 
normal for this time of year. This equates to between 0.75 inches 
and 1.00 inches of precipitable water. For comparison, normal for 
this time of year is 0.30-0.40 inches of precipitable water. This is 
an exceptionally juicy airmass, and as is often the case with 
airmasses of tropical origin like these, it will also be a warm one. 
Snow levels are expected to hover between 10k and 12k feet through 
all of Sunday and into Sunday evening, before finally beginning to 
lower to 7000-9000 feet late Sunday night into Monday. What this 
means, ultimately, is that a majority of locations will see this 
precipitation fall as rain, with snow relegated to areas above 10k 
feet. The San Juans are looking at 1-3 inches of QPE over a 24-36 
hour period, with locally higher amounts up to 4 inches possible. 
Elsewhere, lower elevation valleys could see 0.50-1.00 inches, with 
higher terrain in the 1-2 inch range during the same period. With 
already very saturated soils, periods of heavy rain could result in 
flash flooding and debris flow issues, especially for sensitive 
areas. Additionally, rivers are expected respond to all of this 
liquid precipitation, with some of the same areas hit hard last week 
looking at another round of river flooding. A Flood Watch is in 
effect for all of southeast Utah and southwest Colorado, with 
several targeted River Flood Warnings in effect across the same 
area. 

While snow is confined mainly to areas above 10k feet, amounts are 
nothing to sneeze at. For the San Juans, snow totals by Monday 
evening are on the order of 12-18 inches, with locally higher 
amounts up to 2 feet possible. For the central Divide mountains, the 
Grand Mesa, and the Flat Tops, amounts are less, in the 5-10 inch 
range, with locally higher amounts around 1 foot possible. As a 
result, a Winter Storm Warning is in effect for the San Juans, with 
Winter Weather Advisories in effect for the central Divide 
mountains, Grand Mesa, and Flat Tops. As snow levels lower late 
Sunday night into Monday morning, some of this snow will reach pass 
level. Be prepared for sloppy conditions during the Monday morning 
commute along US-550, US-50, and along I-70 over Vail Pass. 

NEXT WEEK:

Behind this system, conditions dry out for a few days as high 
amplitude ridging moves overhead. We'll see a slight warm up through 
the mid-week period, although highs remain 5-10 degrees below 
normal for early November. Looking further out, a quick moving 
clipper system has the potential to bring some light showers to the 
region mid-to-late next week, although model agreement is poor.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 508 PM MDT Sat Oct 31 2026

A few showers and storms will continue this evening though
coverage will remain isolated at best. There will no effect for
TAF sties. This will change from around 09z onwards as showers
and storms increase from the southwest. BY 15Z, widespread
precipitation is expected with drops in both cigs and vis due to
lower ceilings and rainfall. MVFR/IFR conditions will be common
through the day tomorrow with ILS breakpoints being met as well.

&&

.HYDROLOGY...
Issued at 1226 PM MDT Sat Oct 31 2026

Deeper moisture develops this evening into early Sunday. This is 
expected to produce widespread rainfall with stronger rain rates 
across southeast Utah and southwest Colorado Sunday and Monday, 
mostly below 10,000 feet. A growing concern lies in the potential 
for runoff around steep terrain in the region. This could produce 
rock, mud, and debris flows onto roadways, as well as flash flood-
prone burn scars, washes, slot canyons, and arroyos. Current 
guidance supports 1 to 3 inches of rainfall for far southeast Utah 
and portions of southwest Colorado, with locally higher amounts 
close to 4 inches possible. As a result, a Flood Watch has been 
issued for 5 AM Sunday through 11 AM Monday. Latest forecast 
guidance has a number of rivers in southwest Colorado climbing above 
minor flood stage, with the gage at Pagosa Springs now expected to 
hit Moderate to Major flood stage. As a result, targeted River Flood 
Warnings along the La Plata and San Juan rivers are in effect. 

Outdoor enthusiasts, motorists, and residents of areas recently 
impacted by flooding are encouraged to remain tuned into the 
forecast in the coming days.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory from noon Sunday to 6 PM MDT Monday 
     for COZ009-010-012-013.
     Winter Storm Warning from 6 AM Sunday to noon MDT Monday for 
     COZ018-019.
     Flood Watch from late tonight through Monday morning for 
     COZ019-021>023.
UT...Flood Watch from late tonight through Monday morning for 
     UTZ022-028-029.

&&

$$

DISCUSSION...BGB
AVIATION...TGJT
HYDROLOGY...TGJT