UWFPS 2017 daily cold-air pool forecast valid Saturday 01/28/2017 8:00 MST (8:00 am local time)

Summary: A major cold-air pool episode is underway. Minimal stratus and low clouds have formed at the onset of the episode, and will likely not affect flight operations tonight. Pollution concentrations are expected to increase daily through Wednesday. Increasing mid-level clouds, southerly winds at the top of the shallow cold-air pool, and top-down erosion of cold-air pool is expected Thursday, with a storm system and mix-out possible Friday.

Current weather synopsis and short-term forecast for Saturday 28 January:

The temperature inversion has lowered and strengthened overnight, and this trend is expected to continue into Monday.

 

SLC sounding at 5 am. Note the descending capping layer at 800 hPa.

The feared widespread low clouds and fog that plague other basins within the western US have not materialized thus far for the Utah basins, with drier air filtering into the area helping to prevent the development of widespread stratus and fog. However, as of 8 am, low clouds were expanding over the Western Desert and northern Great Salt Lake area (yellow colors):

 

Satellite low cloud/fog product 7 am 1/28/2017. Low clouds are in yellow.

Given the low model forecast skill with fog, persistence is generally the best forecast in the 24-hr range. Thus, a 60% chance of mostly clear conditions is expected through the flight tonight although the expansion of the clouds noted over west desert will need to be watched.

Visibility/ceiling/clouds: Mostly sunny and cold highs in the 20s, lows in the 5-10 F range. Mostly sunny and hazy conditions are expected through the period at this time. There is a 30% chance of low stratus deck or dense fog forming in the evening after sunset and will need to be monitored.

Winds: light and variable.

Sunday 29 January:

The cold-air pool will continue to strengthen Sunday. Partly cloudy. Cold, highs in the 20s, lows in the 5-10 F range. 30-50% of dense fog at Salt Lake Airport and Logan Airports in the morning, 30% chance of fog and stratus cloud deck forming in all basins and will need to be monitored.

Visibility/ceiling/clouds: 30% chance of stratus and fog. Ceilings less than 1000 feet and visibility less than 1/2 mile possible if low clouds and fog occur. Winds: light and variable.

Monday 30 January – Wednesday 1 February :

Pollution levels should ramp up notably each day Monday-Wednesday with the combination of a descending strong, low-level capping inversion and increased emission rates as the work week starts. The cold-air pool will continue to strengthen Monday and remain strong Tuesday. Partly cloudy. Cold, highs around 30, lows in the 10-15 F range.

Visibility/ceiling/clouds: 40% chance of stratus and fog during this period, although confidence is low. Ceilings less than 1000 feet and visibility less than 1/2 mile possible if low clouds and fog occur. Winds: light and variable.

Thursday 2 February – Friday 3 February

Complex decay period of the cold-air pool. Details are uncertain at this time. Southerly winds are expected to erode the top of the cold-air pool on Thursday, making for a shallower polluted layer that could be harder to sample with the aircraft. The southerly winds may also ‘clean-out’ the Utah and southern Salt Lake Valley before other areas on Thursday. A storm system with rain/snow mix at this time is also possible Friday. The combination of the increasing southerly winds and storm system result in complete mix-out of the cold-air pool on Friday in current numerical model prediction. Stay tuned as we get closer and model skill improves.