Tomer’s Take: A dip in the jet, trough of low pressure, and small surge of Monsoon moisture remains in my forecast for the West between 9/1-9/5. I say 9/5 now because there might be one additional small area of low pressure riding the coattails. This pattern delivers cooler mountain temps and rain/snow/thunderstorms. Snow accumulation appears possible across parts of higher elevation WY and MT. Overall, areas impacted 9/1-9/5 include PNW, Northern CAN, CO, UT, WY, ID, AZ, MT.
Current Setup
Water vapor satellite shows the shifting storm track in the PNW. This delivers a dip in the jet, trough of low pressure, and taps into a small surge of Monsoon moisture between 9/1-9/5. Red/orange = drier air aloft.
Active Jet
Below is the forecast jet stream valid 9/2. Notice the jet coddling an area of low pressure over CA/West Coast.
Trough
Below is forecast mid-atmosphere pressure anomalies valid 9/4. Notice the primary storm system over the Intermountain West, but also notice the second smaller area of low pressure riding its coattails. This may keep things active through 9/5.
Precipitation
Below is forecast precipitation valid 9/4. Green/blue = rain/snow/thunderstorms.
Specifics
Chicago Basin, CO
9/1: AM dry, PM 30% rain/thundestorms.
9/2: AM dry, PM 30% rain/thunderstorms.
9/3: AM dry, PM 40% rain/snow/thunderstorms.
9/4: AM 20% rain/snow, PM 30% rain/snow.
9/5: AM dry, PM 20% rain/snow/thunderstorms.
Kings Peak, UT
9/1: AM 10% rain/thunderstorms, PM 60% rain/snow/thunderstorms.
9/2: AM 20% rain/snow, PM 90% rain/snow.
9/3: AM dry, PM 100% rain/snow.
9/4: AM 60% rain/snow, PM 50% rain/snow.
9/5: AM 80% rain/snow, PM 20% rain/snow.
Grand Teton, WY
9/1: AM 60% rain/snow, PM 30% rain/snow.
9/2: AM dry, PM 20% rain/snow.
9/3: AM 40% snow, PM 90% snow.
9/4: AM 90% snow, PM 30% snow.
9/5: AM 70% snow, PM 40% snow.
Granite Peak, MT
9/1: AM 40% rain/snow, PM 30% rain/snow.
9/2: AM dry, PM 10% snow.
9/3: AM 20% rain/snow, PM 90% snow.
9/4: AM 80% snow, PM 80% snow.
9/5: AM 10% snow, PM 40% snow.