How about that slow-moving monsoon storm last night in Boulder….definitely our most intense rainfall since late last summer.  Between 7and 9 PM, 0.5 to 1.0″ of rain was recorded as torrential rain pounded the city. The radar image from 7:42 PM is below, with the storm that affected Boulder circled in pink.

Radar image from Wednesday night at 7:42 PM. Monsoon storms!

Yesterday had a lot of solid meteorology working together to produce the heavier rainfall. Today we will not see quite as favorable of conditions. Moisture has dropped and the frontal boundary has pushed well south and east.

After morning sun, expect partly cloudy skies in the afternoon and storms forming after 2PM, first across the higher elevations. We expect storm coverage to be isolated across the Metro area, with scattered activity in the Foothills (especially south and west of Denver). Highs will remain cool in the lower 80’s.

Unsettled conditions will remain through the upcoming weekend, with at least isolated chances of storms each day.

Fujiwhara Effect! 

While checking the health of our monsoon flow for this forecast, I noticed a rare phenomenon in the models that is expected to happen between two tropical systems off the western coast of Mexico in the coming days. It is known as the Fujiwhara Effect and it happens when two nearby low pressure systems (normally tropical cyclones) orbit each other and spiral closer together. You can see this happening in the animation below between Tropical Storm Irwin (left) and Hurricane Hilary (right). Here is some additional reading from Wikipedia on this rare effect if you are interested.

Animation showing a likely Fujiwara interaction between two tropical cyclones off the western coast of Mexico this weekend.

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Ben Castellani

Ben grew up in southwestern Pennsylvania and holds both a bachelor's and a master's degree in Meteorology, the latter being from CU Boulder. His hometown received nearly three feet of snow from the Storm of the Century back in March of 1993, sparking his initial interest in impactful weather. Ben currently works on remote sensing and data analysis software at L3Harris Technologies in Boulder.

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