Purgatory

000
FXUS65 KGJT 221129
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
529 AM MDT Thu Oct 22 2026

.KEY MESSAGES...

- Widespread rain continues through early Friday.

- Strong to severe thunderstorms will be possible favoring
  southeastern Utah and far Western Colorado generally from I-70
  south through tonight.
 
- The potential for flooding increases today and Friday, 
  especially for portions of southeast Utah and southwest 
  Colorado. 

- Rainfall amounts in the southern mountains range from 1-3
  inches with higher amounts of 2-4" or more possible in the 
  San Juans and southern foothills.

&&

.DISCUSSION...
Issued at 1038 PM MDT Wed Oct 21 2026

A deep trough off the West Coast and High pressure to the southeast 
near Big Bend is keeping the Desert Southwest under a strong south 
to southwesterly flow aloft advecting deep subtropical moisture 
north through Arizona into eastern Utah and Western Colorado. Models 
are in good agreement with satellite imagery showing the low just 
turning the corner in the base of the trough off the SoCal Coast 
before ejecting to the northeast into the Great Basin Thursday 
evening and continuing into Montana Friday evening taking most of 
the moisture with it. Meanwhile, another shortwave system descending 
into the trough Friday cuts off over SoCal Friday night to eject 
farther east over the region Saturday night into Sunday to keep 
unsettled weather in the forecast through the weekend. Models stay 
in fairly good agreement through the weekend, but are diverging on 
the timing and track of the second system by Sunday with some 
solutions tracking it to the west over northern Utah. The models do 
generally agree on setting up a dry zonal flow across the region 
next week that could extend into the next weekend, but that a long 
way out and confidence is lot on the extended period. 

Today we saw quieter showers with rain rates remaining on the low 
side only around a half inch per hour in the heavier showers. Even 
though we had strong vertical sheer and plenty moisture on hand, 
with all the heavy cloud cover and the warm air aloft, we just 
didn't have any CAPE to feed stronger storms. Both the 18Z and 00Z 
soundings showed a saturated atmosphere nearly up to 200mb for 
efficient rain making, but with zero CAPE there wasn't the strong 
convection. That being said, much of the southern half of the region 
still received an inch or more rain today saturating the soil with 
water and priming the area for flash flooding should heavier showers 
come overnight into tomorrow. 

These conditions look to change overnight into tomorrow as we come 
more under the influence of the trough to the west cooling the air 
aloft to provide some CAPE to support convection. Additionally, upper-
level dynamics increase as a 70-90 kt jet moves in over the region. 
The primary concern with convection will be strong winds over 60 mph 
possible as the winds aloft mix down. The atmosphere remains 
saturated through the day, making localized heavy rain in showers 
and thunderstorms much more likely leading to flash flooding, 
especially near recent fire scars and areas prone to flooding like 
slot canyons and steep terrain. Stay tuned to the forecast for 
updates as weather develops through the day. Drier air starts moving 
into the region late tomorrow which looks to scatter out the showers 
and thunderstorms, but also looks to increase the potential for 
stronger thunderstorms overnight into Friday. Most of the moisture 
is swept out of the region Friday limiting convective activity 
through the afternoon, but has the second low starts moving in from 
the west, showers and thunderstorms will pick up again Friday night 
into Saturday feeding on the residual moisture and continue through 
Saturday night and Sunday as the low tracks over the region. The 
storms move on off to the east as a zonal pattern sets up across the 
region Sunday night through mid next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 525 AM MDT Thu Oct 22 2026

Widespread rain and rainshowers continue today with some
thunderstorms possible from KMTJ southward this afternoon. Low
ceilings will be common as will visibilities under the stronger
cells. Conditions will fluctuate between VFR down to IFR through
the day with the worst conditions expected south of the I-70
corridor. ILS breakpoints will be met for most TAF sites thanks
to the same low ceilings and visibilities. Generally light winds
are expected though gusty outflows can be expected near any
showers or storms. Flight conditions will slowly improve after
12Z tomorrow, if not a bit before.

&&

.HYDROLOGY...
Issued at 257 PM MDT Wed Oct 21 2026

Hydrologic concerns remain elevated through Friday due to the 
influx of highly anomalous tropical moisture across the 4 
Corners area into the Central Rockies. Potential hazards 
include localized flash flooding from thunderstorms producing 
heavy rainfall rates and river flooding due to a prolonged 
period of widespread moderate to heavy rainfall. 

Southeast Utah and the lower valleys along the CO/NM border 
will be under the highest threat of strong to severe 
thunderstorms capable of producing flash flooding across desert 
floors and dry washes the through tomorrow evening. 

There is a moderate risk of excessive rainfall leading to
flooding across portions of the San Juans and adjacent southerly
valleys where precipitation totals of 2 to 4 inches will be
possible. The bulk of this precipitation will fall overnight
through early Friday morning. Higher precipitation totals over 
portions of the southern San Juans of 4 to 5 inches are 
definitely possible. An additional concern of rain on snow 
leading to additional runoff making it into the waterways. Snow 
levels are forecast above 12-13 kft throughout the day Thursday,
which will likely result in melting of some of the existing 
early-season snow pack. The combined runoff from rain and rain- 
on-snow will result in a rapid rise in many of our creeks, 
streams and rivers. Modeled responses suggest several rivers 
reaching bankfull or higher at river forecast points across 
southwest Colorado and southeast Utah. The highest confidence in
minor flooding and related impacts along the San Juan River, 
Piedra, Animas, La Plata Rivers and above Vallecito Reservoir. 
However, other creeks and tributaries within the Four Corners 
region remain susceptible. All river responses are heavily 
dependent on where the heaviest precipitation falls, so please 
continue to monitor the forecast as the week unfolds.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Flood Watch through Friday morning for COZ019-021>023.
UT...Flood Watch through Friday morning for UTZ022-027>029.

&&

$$

DISCUSSION...DB
AVIATION...TGJT
HYDROLOGY...ERW