Tomer’s Take: We’re still waiting on the arrival the Seasonal Monsoon. It remains blocked by a high pressure dome and strong Subtropical Jet Stream. This jet is also generating strong wind on many high peaks across the West. Data suggest a possible Monsoon arrival after 7/20, but confidence is low. Normally, Monsoon Season runs July 1 – August 31. El Nino might also be a contributing factor.
Monsoon Blocked
A stronger than normal Subtropical Jet continues to be the headline across the West. It delivers frequent cold fronts to northern UT, ID, WY, MT, and NE CO along with severe weather, heavy rainfall, and strong wind on many high peaks. This jet stream effectively shuts the door on the Monsoon.
In addition, a large dome of high pressure remains entrenched with a significant pool of dry air.
Below is water vapor satellite imagery from 7/5. Red/orange colors = dry air.
Colorado
Northeast Colorado had it’s wettest June on record and 4th wettest May on record. Denver has received its entire yearly rainfall in just TWO MONTHS.
Look at the precip anomalies – notice the bullseye over Denver.
Below is total precipitation. Denver has received about 15 inches of rainfall in two months.
What is the Monsoon?
The North American Monsoon normally occurs July 1 – August 31 each year. Primary impacts are to AZ, NM, NV, UT, WY, and CO.
Atmospheric winds turn southerly and escort new moisture into these locations. This helps fuel more intense afternoon thunderstorms with hail, frequent lightning, flash flooding, and gusty wind.
It shortens weather windows in most places.
Below are lightning injuries and deaths in Colorado. The peak occurs during Monsoon Season in July.
Forecast Now – 7/19
Data suggest a drier than normal pattern (brown shaded areas) through 7/19. Above normal precipitation in NE CO, and parts of WY.
Monsoon After 7/20?
Data suggest a possible arrival after 7/20, but confidence is low. One contributing factor might be El Nino. Historical records show it can disrupt and weaken the Monsoon.
Below, the Climate Forecast System starts to paint a small amount of green across the Rockies on/after 7/19. The signal is weak.
