In Casper this morning, the weather is warm, still and sunny. There were a few mid-level cumulus clouds, but they have mixed out.
The National Weather Service (NWS) in Riverton forecasts a sunny and windy day today, with a high temperature of 91 F and southwest winds of 16-25 mph. This evening will be partly cloudy, with a low temperature of 53 F and 19-24 mph southwest winds, shifting to west-northwest winds of 5-10 mph. The NWS has issued a Hazardous Weather Outlook and a Red Flag Warning, based on the high winds, low humidity and risk for fires. The Storm Prediction Center (SPC) has issued a Critical Fire Weather risk, as shown below.
The visible satellite imagery shows a few clouds moving in from the northwest along the cold front.
The enhanced infrared satellite imagery shows that these clouds are not very thick thus far this morning.
The water vapor satellite imagery shows dry upper air followed by the moisture that make up the heavy cloud cover. The middle of the state has dry upper air.
The 12Z upper air sounding from Riverton shows a dry sounding, minus a humid layer near 500 mb. This layer is nearly saturated. Overall, there was only 0.43 inches of precipitable water and no Convective Available Potential Energy (CAPE) present in the column. There was a strong thermal inversion near the surface and the 0-3 km average lapse rate was 6.3 C/km.
The deep-layer shear was 60 kts (mostly speed changes), and the low-level shear was 29 kts (mostly directional changes).
The surface observations (from the SPC Mesoscale Analysis Map) show the winds shifting from the southwest to the north as the cold front passes through the area. Otherwise, skies are clear over most of the state and the temperatures are climbing. The radar overlay shows a few drops of rain in the northwestern part of the state.
The surface pressure map shows a low pressure associated with the trough over southern Idaho. Currently, there are no strong pressure gradients over the state.
However, the RAP shows that, over the next six hours, the low will deform and a sharp pressure gradient will develop across the western third of the state.
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows that the trough broke free of the Pacific Northwest coastline and will have moved over the Northern Rocky Mountains by 0Z. This will put most of Wyoming underneath the exiting side of a jetstreak that is moving around the trough.
At the 500 mb level, the NAM shows some vorticity, but it is not advecting over the state by 0Z, so it has been excluded from this post.
The 700 mb NAM chart shows rapidly rising air in the northeastern part of the state this afternoon. This will be ahead of the cold front, and will add to the fire danger due to the increased risk of lightning strikes
The 850 mb NAM chart shows the cold front as Cold Air Advection (CAA) moving into the state from the northwest. Notice the winds blowing across the thermal gradient from cold to warm.
Overall, I expect a hot dry day today, though a few dry thunderstorms may work their way through, particularly near the cold front. The fire risk today is the largest concern.
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC