UPDATE
Issued at 804 PM MDT Thu Sep 12 2024

Wind gusts across most of the forecast area have decreased in the past couple of hours, in response to diminished mixing since sunset. The exception is across the far eastern plains where the low-level jet is still producing some gusts to 30-40 mph.
Thankfully, humidity values on that side of the dryline are already near 30-40%. With that in mind, the Red Flag Warning was allowed to expire at 8pm.

No significant updates to the forecast grids were needed this evening as they were largely in good shape. Did make some modest adjustments to the wind grids as a boundary/weak cyclone is moving across the northern metro. Also added a bit more detail to the smoke forecast through the night to better time the arrival of smoke into our forecast area. Tomorrow still looks smoky/hazy across the region.

SHORT TERM /Through Friday/
Issued at 308 PM MDT Thu Sep 12 2024

Warm, dry, and windy conditions continue this afternoon with a dry airmass in place across the region. Multiple hot spot notifications have been detected via satellite at the time of this writing, with a few wildfires confirmed across the region. Therefore, the Red Flag Warning will be allowed to continue through 8PM tonight as winds continue to gust to near 30 mph, and are expected to do so until around sunset this evening. Mountain wave enhancement has lead to mountain wave cloud development along the Front Range that have helped keep temps below 90 along the urban corridor thus far. This could limit some areas from reaching the 90s as previously forecast.

A cold front is expected to pass through the forecast area late tonight associated with a passing low to the north. Mountain cold spots in Jackson and Grand Counties are forecast to drop into the 20s, with 40s and 50s expected for the foothills and plains.
Behind the front, smoke concentrations from fires to our west are expected to increase causing hazy skies, and linger into the afternoon hours Friday. High temperatures are expected to cool to near normal behind the front as well. The plains should expect to see low to mid 80s, with 60s and 70s expected for the foothills and higher elevations.

LONG TERM /Friday night through Thursday/
Issued at 308 PM MDT Thu Sep 12 2024

Mainly dry weather will prevail Friday night through this weekend, but an isolated storm here and there still possible. One opportunity will be Friday night over the far northeast plains, but almost all models show sufficient capping and mid level drying to prevent any development in the overnight hours as low level moisture returns. However, by Saturday as low level moisture continues to increase across the plains, there is a small threat of one or two strong storms. Again, this will hinge on whether we can break the cap. There will be a narrow interface of weak CIN/moderate MLCAPE (1000 J/kg) where a stronger storm could develop, so we'll have some low PoPs over the northeast plains to account for that potential. Otherwise the main feature will be warmer temperatures for the rest of the forecast area, with readings a good 5 to 8 degrees above normal. We don't see much change for Sunday, with riding aloft but still some moderate MLCAPE over the northeast plains. Mid level moisture should accumulate slightly under the ridge, which would give a little better chance of high based showers/isolated storms over the mountains but not much more than gusty winds and light rain.

The pattern starts to change early next week, as by Monday a deep upper level trough/close low moves toward Nevada. This will lead to strengthening south/southwest flow across the forecast area and a continuation of warm temperatures. This will lead to higher fire danger once again. At the same time, weak moisture advection aloft continues to we'll have some low PoPs to account for that. There is reasonable agreement now between the NAEFS/ECENS that a piece of the trough gets ejected out over the Northern Rockies toward Tuesday, which should bring more wind but a little better chance of showers and storms. The precise details of this will be hard to time this far out, however.

For midweek, a trough hangs out in the Western U.S., which means eventually we should see additional cooling, and temperatures possibly heading toward below normal levels toward next weekend - outside of our deterministic forecast period.

AVIATION /00Z TAFS through 00Z Saturday/
Issued at 541 PM MDT Thu Sep 12 2024

Challenging wind forecast this evening for DEN. TDEN and KFTG radar data show a weak/compact cyclone northeast of EIK, which has generally been drifting to the north and east. A pronounced boundary/wind shift is draped to the south/southwest, and should arrive by DEN between 0030-0130Z. Quite a bit of uncertainty in how that changes wind direction this evening, but the general thought is that south or southwesterly winds will prevail, with a brief period where the winds turn a little more to the west.

Beyond that, a weak cold front is expected to arrive overnight, reaching DEN/BJC around or just after 06z. This front may wash out as it reaches the terminals, with light drainage flow potentially returning towards Friday AM. Winds become more predictable during the day Friday with a steady east flow likely.

The other concern in the TAF period is smoke, with recent smoke forecasts showing increased concentrations of near surface and elevated smoke across the Front Range overnight tonight, which then persists through the day Friday. Forecast concentrations may not be enough to reduce surface visibility significantly, but could have impacts to slant range visibility during the daylight hours.

FIRE WEATHER
Issued at 308 PM MDT Thu Sep 12 2024

Above normal temperatures mixed with enhanced south to southwest winds have lead to critical fire weather conditions developing across the plains, foothills, and mountain valleys this afternoon. Winds have been gusting to 30 kts and relative humidities have dropped to the single digits to mid teens. These conditions are expected to remain in place through the afternoon, diminishing near sunset.

Cooler temperatures are expected on Friday, however, a dry airmass will still be in place across the region. While critical fire weather conditions are not expected, elevated fire weather conditions may develop for a few hours in the afternoon. The area of main concern will be Jackson County where the strongest winds are expected. These winds may gust to 25kts for an hour or two in the afternoon hours.

The next round of critical fire weather conditions may develop by Monday, as southwest winds increase in a warm and dry airmass ahead of the next weather disturbance. The critical conditions could continue into Tuesday, depending on the speed of the next disturbance and cold front. This will eventually bring somewhat cooler weather and a bump in humidity.

BOU WATCHES/WARNINGS/ADVISORIES
None.