Monday, May 18, 2020

Hair Dryer Weather

Former KSL meteorologist Mark Eubank used to call it the HATU wind (Utah spelled backwards).  I lean toward the Great Basin Sirocco, a nod to the hot and sometimes dusty wind that blows to southern Europe from north Africa.  In any event, it's been a hot, dry, and sometimes dusty 24 hours, with strong flow expected to continue today and possibly extend into Tuesday. 

The setup for this is a slow moving and digging upper-level trough off the Pacific coast.  In the southwesterly flow ahead of that  upper-level trough, a southwest to northeast oriented surface trough has developed downstream of the Sierra, resulting in strong southerly flow across much of western and northern Utah, as illustrated at 1800 MDT yesterday afternoon (0000 UTC 18 May) below. 

The pattern is quite typical for springtime when southwesterly flow interacts with the Sierra Nevada.  There is typically flow splitting around the high Sierra, confluent flow downstream of the high Sierra, and a stark contrast in airmass across Nevada. 

Peak gusts at selected locations at bench or valley levels include 64 mph and 61 mph near Point of the Mountain, 51 mph along I-80 near the Salt Flats, 50+ gusts at multiple sites at Dugway Proving Ground, 47 mph along the Baccus Highway at SR-111, and 46 mph at Olympus Cove.  The two gusts near Point of the Mountain are new sites reporting to MesoWest and the gust to sustained wind speed ratio was fairly high, so I'm putting an asterisk on those until I have a chance to see if they are legit. 

At the University of Utah, wind speeds and gusts ramped up yesterday morning with frequent gusts in excess of 25 mph and occasionally greater than 30 mph from about noon to 2000 MDT.  After a brief lull therafter, the flow increased again and was fairly strong for most of the night.   The peak gust of 41 mph occurred at 1854 MDT and again at 0054 MDT. 

Source: MesoWest
Forecasts from the NAM below show continued strong southerly flow at 1800 MDT this afternoon (0000 UTC 19 May), a dry surface front pushing into northern Utah at 0300 MDT tonight (0900 UTC 19 May) but retreating back to the north by 1200 MDT tomorrow (1800 UTC 19 May) leaving us again in strong southerly flow, and then the dry surface front finally approaching Salt Lake City at 2100 MDT tomorrow (0300 UTC 20 May).  Precipitation during this period remains primarily over Nevada, although there are some pop up showers and thunderstorms over the mountains. 

Thus, it looks like we will see the Great Basin Sirocco continue at times into tomorrow south of the Salt Lake Valley.  North of the Salt Lake Valley, especially northwest, there could be a frontal passage Monday night or early Tuesday with a bit of a drop in temperature and weakening of the flow.  Sometimes those fronts in scenarios like this push down to the Salt Lake Valley, but I'd say the odds of that happening Monday night or early Tuesday are less than 50/50.

If you are hoping for rain, you'll have to hope for something to pop up tomorrow (low chances in the valley) or wait until Wednesday when the upper-level trough moves over.  The GFS is wet, the NAM dry.  Our downscaled SREF shows anything from very little precipitation to about 0.75 inches.  I'm hoping for something.  My gardens are parched. 

Public Service Announcement: Rattlesnakes in Neffs Canyon

My son encountered four mature rattlesnakes in different spots along the Neffs Canyon trail yesterday.   Be on the lookout and watch your dogs if you are hiking in the canyon. 

I also spotted my first snake of the year yesterday, although this one was what I think is a more benign gopher snake. 

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