Monday, November 27, 2017

So Much Weather, So Little Time

Looking west from the University of Utah Campus at about 7:15 AM this morning
It was a Mordor-like sunrise over the Salt Lake Valley this morning (e.g., above), simultaneously spectacular and apocalyptic.  With the overnight southerly flow, there is a decent plume of dust over the western valley (evident below the fire-lit clouds above), but clear skies to the east. 

The weather over the past 24 hours has been quite remarkable if you know where to look.  While it was quite mild across much of northern Utah during the holiday weekend, a thin lens of cold air remained over the relatively cold waters of the Great Salt Lake.  Our Hat Island observing site, for example, hasn't eclipsed 55ºF over the past five days. 

Source: MesoWest
Yesterday, that airmass made its presence known by penetrating into the northern Salt Lake Valley.  At 4 PM (2300 UTC), a sharp lake-breeze front extended across the central part of the valley with southerly flow to the south and northwesterly flow to the north.  Temperatures dropped from 70ºF in the Sandy "banana belt" to near 50 (or lower) near the Great Salt Lake.  Almost climatology! 

Source: MesoWest
The sounding from the Salt Lake City airport at about that time showed the shallow nature of the cold lens, with a surface temperature of just under 10ºC (49ºF), but temperatures of almost 17ºC at 827 mb (about 5600 feet). 

Source: SPC
Forecasters predicting a record high for the Salt Lake Airport were likely flummoxed! 

Fortunately, the south winds saved the "day", blowing the lake breeze north and causing temperatures to rise rapidly around 8 PM. 

Source: MesoWest
The transition from cold, damp lake-modified air to warmer, drier air was remarkably abrupt, and led to a high temperature for the calendar day of 69ºF.  That is the 2nd latest 69ºF temperature recorded at the airport on record (December 1st is the latest), and it happened in the dark.  In addition, a temperature of 68ºF was recorded after midnight, which sets a record high for today.   This is not your grandparents (or even parents) climate that we are living in.

Moving on to the weather this morning, we are still in the warm southerlies with some wind-borne dust over the western Salt Lake Valley.  However, cooler air remains over the Great Salt Lake with northwesterly flow developing over northwest Utah. 

The HRRR brings the surface front into the northern Salt Lake Valley at 1900 UTC (1 PM MST) this afternoon.  It will be a dry frontal passage, with the precipitation trailing the surface front. 

We will be "storm chasing" with the DOW, which we plan to deploy just south of Stansbury Island to examine the front penetrating into the Tooele Valley and across the Great Salt Lake.  Although a dry frontal passage, we're hoping there is enough dust in the air to be able to examine some fine-scale aspects of the frontal passage.  We'll then work on whatever precipitation comes through, focusing on the frontal-band interaction with the Stansbury and Oquirrh Mountains.

For skiers, this looks like a pretty pathetic event.  The models have the band fall apart as it moves in.  Snowshowers are possible, but it won't add up to much, as we discussed over the weekend.   Sad!

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