Denver - Boulder, Colorado

• Areas of fog again late tonight through Sunday morning across portions of northeast and eastern Colorado.
• Mild and mostly dry today.
• Unsettled weather returns late Sunday and Monday.Mountain snow is likely (>70% chance) above 8500ft during thistime. High uncertainty remains for the foothills and plains.

Once again will be dealing with areas of dense later tonight thru Sat morning over portions of the plains and I-25 Corridor. Timing of its development, closer to nrn areas of the I-25 Corridor and over Weld county, is still a bit uncertain. However, believe it will begin developing around 09z and then spread south into the Denver Metro by 11z or so. Fog will likely last thru 16z and then gradually lift in most areas.

Meanwhile, for the rest of Sat, a disturbance embedded in SW flow aloft will move across the higher terrain by midday. This feature will bring a chc of showers to portions of the higher terrain as it moves across. Over the plains, expect mainly dry conditions with highs in the mid 50`s to lower 60`s.

Looking ahead to Sun, the ECMWF and GFS have an elongated upper level trough moving into the nrn Rockies and Great Basin by late Sun aftn. Ahead of this feature, rather stg SSW flow aloft will be over the area with an influx of subtropical moisture. For most of the day, the best chc of precip will stay to the west but by late aftn should see an increasing chc of showers over the higher terrain. Across the plains, sfc low pres will extend from ern WY into ern CO with gusty southerly winds by aftn.

For Sun night into Mon, the elongated upper level trough will move eastward with a couple pieces of energy associated with it. One piece of energy will move into the Dakota`s while the 2nd piece of energy tracks across srn CO/nrn NM. As the main upper level trough and associated QG ascent moves across will see rain and snow over the higher terrain Sun night into Mon. Over nern CO, a cold front will move across Mon morning with gusty NNW winds behind it. QG fields still show favorable mid level ascent across the plains thru the aftn so will keep in a good chc of showers over the plains. However, the downslope NNW winds may reduce precip chances closer to the I-25 Corridor.

By Mon night, the main upper level trough will move east of the area with drier air moving in behind the system. Will continue to see a good chc of showers Mon evening mainly over the east central plains. However, by late Mon evening should see precip gradually end.

On Tue, an upper level ridge will begin to build into the area with dry conditions and near seasonal temperatures. Looking ahead to the middle part of next week, there is considerable uncertainty as to whether another system will affect the area or not. The latest GFS tracks this system across the nrn Rockies while the ECMWF has it moving across Colorado.

Light northerly winds, high clouds, and poor mixing have made it difficult for the fog to dissipate. The higher clouds are movingoff and visibilities are finally improving. We expect haze to persist through the day due to limited mixing with restricted visibilities below 6SM through 20Z to 21Z. Light north to northeast winds continue today and then turn southerly tonight. If southerly winds persist through tonight and Sunday morning, fog should not form. However, a Denver cyclone is expected to form and a wind shift to the northwest will be possible for DEN. If this occurs, fog will very likely roll in. Added tempo for fog to the TAF for Sunday morning. A shortwave trough lifts across the area late Sunday morning, helping to break up the fog and possibly bring light rain showers. By 18Z Sunday the shortwave is expected to be northeast of the area with gusty south winds prevailing.

None.