Major Pattern Change This Week

A developing storm system over the eastern Pacific will drop into the Great Basin later today into Thursday. This system will bring widespread shower activity across Western Wyoming, especially across the southwest. Much cooler air will be present as this system advances, and will cause snow levels to decrease rapidly, especially over the southwestern mountains. Mountain snowfall will be common by Thursday night with valley snowfall possible across southern and western Wyoming by early Friday morning.

Current model imagery depicts a large ridge across the American Midwest with a cold trough across the north Pacific and along the west coast. The white lines represent the 500 MB heights across the region (showing the overall flow in the atmosphere at roughly 15K ft above ground level). Where the lines are closer together, the flow is faster and the change in height is more dynamic. Lowering heights indicate the presence of a low pressure system and usually more inclement weather.

The colored image shows the 700 MB (roughly 10K ft above ground level) temperatrues. 700 MB Temperatures are often referenced by meterologists because thet 700 MB level is just high enough off of the surface to mitigate surface radiational influences, thereby making it a good estimate of airmass temperature. As expected, the cold temperatures in blue and purple coincide with the trough, the moderate to warm airmass is co-located with the ridge.

Click on the image for a full resolution version.

This storm system is expected to track across Southern Wyoming Thursday night into Friday morning with showers and colder temperature spreading north and east, to impact the majority of central and western Wyoming. Snow levels across central Wyoming may briefly decrease to below 6,000 feet by Thursday night or early Friday across
Southern Fremont and Natrona Counties. Another disturbance Friday night may bring another round of lowering
snow levels in Natrona County down to around 6000 feet.

By late Friday night, this storm may produce significant mountain snowfall with the potential for a rain and snow mix turning to snow across the lower elevations.

Here is the current model solution for Friday's pattern. The ridge has shifted well to the east of the area and the nice warm temperatures have retreated south. The cold trough that is currently in the Pacific has shifted east by Friday, it now resides in the intermountain west, bringing cold temperatures and possibly snow.

Click on the image to see the full resolution version.

Look below for an animation of the current model solution from Tuesday through Saturday.

Hunters and others with outdoor interests should be prepared for this dramatic change to cold, unsettled, and even snowy conditions. Keep abreast of the latest forecasts by listening to NOAA weather radio or check us out on the web or on facebook. We will also discuss the latest information we have on this system through the latest Special Weather Statements and in the Hazardous Weather Outlook product.

 Further detail regarding specific temperatures and snow amounts will be revealed later in the week as the system approaches. The models have not quite come into agreement as to where the most snow will fall and where the coldest temperatures will settle. Until then, keep an eye on our homepage for the latest forecast, and check out the forecaster discussion for the latest information on how the models are performing and why the forecast is evolving this way.

Animated Model Solution. The loop begins with Wednesday morning and ends with Saturday evening. The image is of the 700 MB temperatures, and the white lines represent the 500 MB heights.

The timestamp in the images is located at the bottom right hand corner in Zulu (or UTC) Time. For reference:

00Z = 6PM MDT          (so 00Z Friday = 6PM Thursday)

06Z = Midnight MDT   (06Z Friday = Midnight Friday)

12Z = 6AM MDT           (12Z Friday = 6AM Friday)

18Z = Noon MDT         (18Z Friday = Noon Friday)










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