GOLDEN VALLEY, Minn. — There are some surprises that are always welcome... say, a great gift at Christmas, or an old friend dropping in at your place unannounced.
Others are not quite as welcome, like the powerful storm that hammered the Twin Cities Friday morning with a deluge of rain, powerful winds, lightning and thunder.
Based on forecast models our weather team here at KARE 11 on Thursday night predicted a couple of showers popping up around sunrise. Those who were shaken out of bed by booming thunder, or had to navigate blinding downpours on the drive to work would almost certainly tell you the morning forecast was, shall we say, a bit off.
So why the discrepancy? Blame it on an unexpectedly speedy low-level jet. No, we're not talking about a plane here, we're talking about a fast-moving ribbon of air low in the atmosphere (only a few thousand feet above ground level) that transports moisture and warmer temperatures from the Gulf northward. KARE 11 meteorologist Ben Dery defines a low-level jet as "a rapid source of heat and moisture that initiates and fuels thunderstorms."
Dery went on to call this morning's low-level jet "overachieving"
Those storms came fast and furious, dropping buckets of rain on locations like St. Michael where measurements indicate 3.2 inches of rain fell by approximately 8 a.m. In the Chanhassen area, rain totals were just under 2 inches.
"While it (the low-level jet) was not the only reason we saw storms last night, it certainly was a contributing factor," Dery explained.
Sunrise meteorologist John Zeigler says low-level jets develop at night and are frequently missed by forecast models. He says the one that blew in Friday morning quickly increased from 40 to 50 miles per hour, strengthening the storms that erupted.
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