Area Forecast Discussion

KEY MESSAGES

- Cooling trend starts today!

- Scattered showers possible throughout the day before strong to severe storms this evening and overnight. All hazards are possible, so be prepared to act!

- Strong to severe storms may return Sunday afternoon and evening, with all hazards being possible again.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 100 PM MDT Sat Sep 19 2026

Upper low over Idaho this morning will move into Wyoming tonight. Lead shortwave will eject from the base of the low and across northern Colorado this afternoon and move through the area tonight. Thunderstorms have already developed in the Front Range southwest of Denver, and storms will continue to develop across northeast Colorado this afternoon. The shortwave is enhancing deep layer shear which is 30-40 kts. Instability is fairly limited for the initial storms, but as they move eastward it will increase to 1000-1500 j/kg through about 02z before decreasing after sunset. Initial discrete cells in Colorado will likely be supercells capable of large hail of golf ball size or larger, damaging wind gust in excess of 60 mph, and brief tornadoes. CAMs show the storms quickly merging into a line as they approach the Kansas border area, with a bowing signature indicating damaging wind gusts will be possible as it moves through the area this evening. Recent warm temperatures and lack of widespread rainfall has primed the soils for a risk of blowing dust and dust storms, as occurred yesterday with an isolated storm. The blowing dust may be more widespread as the line moves through tonight. The main line looks to move through the area by 06z, but additional storms will develop overnight, mainly south of Interstate 70. These will be driven by a southerly low level jet and likely elevated, posing a minimal threat for small hail as MUCAPE will be less than 500 j/kg at that time. Low clouds and patchy fog will also develop overnight.

The fog should burn off relatively early Sunday morning, but models show the low clouds persisting well into the afternoon due to light upslope surface winds. This will impact not only temperatures, but instability and therefore convective chances Sunday afternoon and evening. Best chances for some clearing will be in eastern Colorado, particularly near the Palmer Divide and possibly the Cheyenne Ridge, where CAMs show discrete cells developing around 21z. Deep layer shear will be favorable for supercells due to a 500 mb speed max moving through the base of the upper low now in the Nebraska panhandle, resulting in 0-6 km shear of 40-50 kts in eastern Colorado. East to southeasterly storm motions would take them into far northeast Colorado, with an accompanying risk for large hail, damaging winds, blowing dust and dust storms, and tornadoes. It is less certain how far east they will be maintained because of the influence of the low clouds and decreasing instability, but shear will be more than adequate through the early evening, and there is some risk for a supercell in the Colorado and Kansas border area through about 03z before dissipating. The low level jet appears to be active once again late in the evening and overnight, with scattered elevated convection generally south of Interstate 70 and MUCAPE 500-1000 j/kg. Given the saturated air mass and light winds, would expect the low clouds and patchy fog to return Sunday night into Monday morning.

For Monday, a zonal flow will develop over the top of a ridge centered over Texas. At the surface, upslope flow continues. However, CAMs show only isolated convection developing, probably due to lack of forcing. Also, instability is forecast to be weak at less than 200 j/kg. As a result, precipitation chances will be slim to none and severe weather is not anticipated.

On Tuesday, the upper ridge over Texas will amplify into the Central Plains. The axis will be just east of the area, resulting in southwest flow over the High Plains. This has been a familiar pattern through much of September. Scattered storms will develop in southeast Colorado and then move northeast into the area Tuesday night, but weakening and dissipating as they do so with loss of daytime heating. The probability of severe weather will be low and limited to gusty winds.

Temperatures through the period will be below normal with highs generally in the upper 60s to lower 70s and lows mainly in the 50s.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Issued at 226 PM MDT Sat Sep 19 2026

Beginning Wednesday, a weak ridge should begin to develop over the central plains, slowly propagating to the east through Saturday. Ensemble guidance is in general agreement on the ridge axis positioning to the east of our county warning area (CWA) which should give us upper level flow from the southwest as we head into next weekend. Higher confidence exists at the moment of this ridge weakening through Saturday, bringing zonal westerly flow aloft to the region during the weekend. A weak upper-level jet streak should be in place Wednesday, ushering in breezy conditions to the area. Confidence is medium that this feature will move out of the area by Thursday. At the surface, weak surface low pressure is forecasted to influence the area through Friday. Simultaneously, a frontal boundary moves through the area Wednesday which should give us boosted chances for showers and thunderstorms. Chances for precipitation the rest of the week will be dependent on shortwave passages through the ridging system.

With respect to Probability of Precipitation (PoPs), forecast guidance displays 25-40% Wednesday during frontal passage. Eastern portions of the CWA may see up to 50% PoPs overnight into Thursday morning as the front moves off to the east. Heading towards the weekend, 15-30% PoPs for Thursday as well as 25-45% Friday are highlighted by guidance. 15-30% is the current probability range Saturday as the overall pattern becomes zonal. Instability and bulk shear are forecasted to be low during this long-term period, making any chance for precipitation limited to showers and thunderstorms.

High temperatures are expected to be near the seasonal average for this time of the year for the Tri-State area heading into the weekend. Highs in the upper 70/low 80s are anticipated for the entire four-day forecast period. Surface winds should start off breezy on Wednesday at around 15-25 mph in the eastern and central parts of our CWA and 25-30 mph in eastern Colorado, gusting up to 40 mph. Winds should die down to a general 5-10 mph Thursday accompanied by gusts up to 15 mph. Finally winds likely bounce back a bit to 10-20 mph Friday and Saturday with gusting up to 25 mph.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1110 AM MDT Sat Sep 19 2026

Low clouds will continue to erode early this afternoon, with a return to VFR at both KGLD and KMCK by 20z. This evening, a line of thunderstorms is expected to move out of Colorado and across the area, accompanied by strong wind gusts of 40-50 kts and potentially reduced visibility in blowing dust. After the storms pass, low clouds and patchy fog will develop overnight and persist through Sunday morning. IFR and occasional VLIFR conditions can be expected.

GLD WATCHES / WARNINGS / ADVISORIES

KS...None. CO...None. NE...None.