textproduct: Grand Junction

KEY MESSAGES

- Periods of moderate to occasionally heavy rain will impact southern Colorado through Friday with drier conditions across the north and far West.

- Warmer and drier conditions arrive for the weekend with another push of moisture arriving by early next week.

DISCUSSION

Issued at 1026 PM MDT Wed Sep 23 2026

A shortwave trough is getting pinched by high pressure ridge trying to build back over the west, forming a Rex Block with a low over the Baja. This is introducing some drier air in from the northwest and across eastern Utah, resulting in clearing skies across the northwest portions of the CWA and shunting the deeper moisture plume further east. This moisture is currently being squeezed between the shortwave trough to our west and high pressure to our east, with showers currently concentrated across southwest Colorado and up the central divide and areas east of the divide. These showers are fairly shallow with low tops but still producing light to moderate stratiform rainfall underneath across our southern mountains and valleys. Over the last 36 hours, precipitation totals across these areas range from 0.5 to 1.5 inches, with the higher amounts concentrated the southern and eastern San Juans as well as San Juan River Basin and eastern portions of the Animas River Basin. This is providing a good soaking rain, which this area has been getting plenty of over the past couple weeks. Little instability and lack of forcing isn't quite resulting in the heavier rates or convection needed to cause flash flooding and the rivers have seen a little response, but nothing concerning at the moment. Winds have also been on the lighter side due to the cloud cover and more stratiform nature. However, as anticipated, thunderstorm activity this afternoon was confined to the periphery of this cloud shield along the areas that received more sunshine. Overnight tonight, there is still some indications of a weak circulation moving up the divide from the south which could result in continued stratiform rainfall. However, this moisture gets shunted further to the east by Thursday with a Rex Block forming to our west and the high pressure on top of the Rex Block introducing drier air across the west, keeping this moisture to our east. Storms will fire Thursday afternoon across the high terrain along this periphery, so there is a chance that we see some heavier rates with thunderstorm activity. However, the instability and forcing is lacking so do not expect storms to last very long and be more of the pop and drop variety while the southern divide might see continued stratiform rainfall. QPF numbers have come down even further with the latest model runs, probably due to the eastward shift in the better moisture, less instability and lack of forcing. Decided to keep the Flood Watch going through Thursday night given the amount of rainfall received thus far across southwest San Juans and southern valleys, in case any area rivers see some rises in response and any convection could lead to heavier rates on already saturated soils.

By Friday, the deepest moisture gets shunted eastward as the Rex Block breaks up and the low over the Baja weakens and lifts across the Desert Southwest and Four Corners as an open shortwave Friday afternoon. More sunshine Friday morning will result in more instability to fire scattered showers and storms. The focus does seem to be across southwest Colorado where abundant rainfall has already fallen. This shortwave moves east by Friday evening, with drier air behind it and a high pressure ridge building in for the weekend. So we will see another break in the active weather this weekend.

Looking ahead to early next week, the models are struggling with whether or not we will see remnants of Hurricane Polo get pulled into the region. While the weather does get more active with some moisture returning and scattered showers and storms, the latest model runs of the GFS and ECMWF are also bringing in a rather progressive low pressure trough into the Great Basin and across our region around the same time frame that Hurricane Polo moves inland across the Baja. So, some tropical moisture may get pulled northward but the deeper trough may keep the deeper moisture south of the Four Corners as another high pressure ridge tries to build across the west. GFS is trending drier while the EC is trending wetter. There's a lot that can change about the forecast between now and early next week, but this is a situation to keep an eye on over the coming days. Regardless of whether the moisture is tapped from Hurricane Polo, or just from more typical subtropical Pacific sources, the return of showers and cloud cover will see temperatures drop below normal once more.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 543 AM MDT Thu Sep 24 2026

Midlevel ceilings are being reported at some TAF sites this morning and they will lift some after sunrise before another round of showers and storms form this afternoon. The far north and west will see scattered skies today. Remaining TAF sites will see chances for showers and storms, especially mountain sites. Isolated precip will continue for much of western Colorado overnight. VFR conditions are expected to remain in place though occasional, brief MVFR is possible under and near any convection.

GJT WATCHES/WARNINGS/ADVISORIES

CO...None. UT...None.