Old Man Winter is knocking on the door . . .

            Everything is starting to look a little clearer through at least Wednesday of the upcoming week.  The Wasatch and adjacent Wasatch Front will see its first real winter pattern this week with one large Low sending in reinforcing impulses every 24 hours starting today.Click here for latest western satellite.     Today’s impulse will do little more than bring in some clouds, winds, and slightly cooler temps.  Tomorrow’s will be a little stronger with a slight chance for showers.  The first real threat for accumulating snowfall will start on Monday in the mountains with rain showers in the valleys below 6,000 ft.  At this time it looks like rain and snow will increase in intensity on Monday into Monday night before clearing out Tuesday morning a bit before a reinforcing wave of energy picks things up a bit on Tuesday evening through Wednesday.  This latter impulse could be strong and cold enough to bring snow levels down to SLC valley floors, or at the very least, to the bench locations.

 Also of note is that the GSL temp is very warm which might bring us a lake effect storm! Here is the latest info for the lake:

WRF-NMM LAKE TEMPERATURE CALCULATION
LAST UPDATE: 05:45 UTC 10/20/2012
WEEKLY AVERAGED AVHRR-DERIVED TEMPERATURES       
7-DAY MEAN ENDING 10/15/2012
NORTH ARM
16.28 C
SOUTH ARM
15.77 C

CLIMATOLOGICAL LAKE TEMPERATURE                 
13.5 C
LAKE TEMPERATURE USED IN WRF
14.7 C

TLAKE EDITED IN WRF-NMM AT: 05:45:06 UTC 10/20/2012

As you can see the Avg water temp this time of year is 13.5 c (56.3 F) but with the HOT summer we had it is sitting at a mean of 16.0 (60.8). if we drop to -1c (30.1 F) we will be cold enough for lake enhanced or lake effect squalls, but there is a few more ingredients needed to make this happen as described below.

 

 Lake-effect and lake-enhanced snow is more complicated than just cold air within northwest flow moving over the warmer Great Salt Lake. The necessary ingredients include sufficient over-lake temperature differential (i.e. greater than 17C from the surface to 10,000 ft MSL or 700 mb), sufficient distance of air flowing across the lake (northwest or north flow provides this across the longer portion of the Great Salt Lake ), minimal change of wind speed or direction in the boundary layer, deeply unstable boundary layer (top layer above 600 mb level preferred for sufficient convective growth), adequate steering flow to develop banding, and over-water surface convergence which is often driven by a land breeze circulation under radiational cooling at night (air flowing toward the warmer water from the colder surrounding land). The lake bands can be further enhanced when they are sufficiently deep and extend well inland resulting in upslope flow of the moist air along the west slope of the Wasatch Range. For a given event the ingredients for lake-effect and lake-enhanced precipitation varies with respect to the potential for generating snow. This will determine if a lake band or lake enhanced area of precipitation will develop and how long and intense the snowfall will be.

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