Snow, and lots of it, looking likely late this week!

Models have been in fairly good agreement for several days but confidence continues to increase as we move closer to the event as the global models are less likely to back track from here on out. After a few more warm, dry days, the weather will change dramatically to a very cold, snowy pattern. Timing still looks like the initial front will move through Thursday night and snow levels will drop Friday to all valley floors. Good orographics and decent moisture behind the front will allow for snow to continue in the mountains and on and off in the valleys for much of Friday night and Saturday. Lake effect snow is also a very good bet with cold, moist air traveling over the relatively warm GSL–this is very hard to forecast so we’ll have to wait until we get closer before we make any exact lake effect forecasts, but be aware that the possibility exists for it.

Later we’ll have a full update where we’ll take a first look at potential snowfall totals. Hint: they have potential to be significant for all elevations.

Looking like we may see a couple more systems trying to dive into the area next week as well. The ski areas should open on time at least!

CPC showing 50% chance of above normal precip for Nov 9th-13th.

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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Rain looking likely Thursday-Friday

       A LOW IS PROGGED TO TRACK ALONG THE CALIFORNIA COAST THROUGH 
  TOMORROW BEFORE QUICKLY MOVING EASTWARD BEGINNING 
  THURSDAY...MAKING ITS WAY ACROSS SOUTHERN UTAH ON FRIDAY. MOISTURE 
  WILL BE ON THE INCREASE OVER SOUTHWEST UTAH TOMORROW...ALLOWING 
  FOR A FEW SHOWERS OVER THE TERRAIN. INCREASED MOISTURE ALONG WITH 
  INCREASED INSTABILITY AHEAD OF THE LOW WILL ALLOW FOR BETTER 
  COVERAGE OF CONVECTION OVER SOUTHERN UTAH ON THURSDAY. INCREASED 
  CLOUDS WILL ALSO RESULT IN A DECREASING TEMPERATURE TREND FOR THE 
  SOUTH BY THURSDAY. MEANWHILE...MAXES IN THE NORTH WILL BE AS HIGH 
  AS 10F ABOVE CLIMO AWAY FROM THE CLOUDS AND CONVECTION. 
   
       THE SYSTEM IS EXPECTED TO PUSH ACROSS SOUTHERN UTAH 
  FRIDAY...ALLOWING PRECIPITATION TO BECOME MORE WIDESPREAD AND 
  SPREAD INTO NORTHERN UTAH BY FRIDAY AFTERNOON. ABUNDANT CLOUD 
  COVER AND COOLER 700 MB TEMPS SHOULD BRING TEMPS BACK AROUND CLIMO 
  OVER THE NORTH...AND UP TO 10F BELOW THOSE VALUES OVER SOUTHERN 
  UTAH. PRECIPITATION WILL MOSTLY FALL AS RAIN...WITH SNOW POSSIBLE 
  AT HIGH PEAKS ABOVE ABOUT 9000 FEET. THE LAST FEW MODEL RUNS HAVE 
  SHOWN VERY GOOD RUN-TO-RUN CONSISTENCY...AND GLOBAL MODELS ARE 
  SHOWING BETTER THAN USUAL AGREEMENT...SO FORECASTER CONFIDENCE IS 
  HIGHER THAN USUAL.  
   
  MODELS INDICATE THE STORM SYSTEM WILL QUICKLY EXIT THE AREA ON 
  SATURDAY...ALLOWING FOR A DRIER NORTHWESTERLY FLOW TO DEVELOP. 
  COMPUTER MODELS INDICATE A RIDGE WILL GENERALLY DOMINATE THE WEATHER 
  PATTERN THROUGH EARLY NEXT WEEK...THOUGH A TROUGH MOVING OVER THE 
  RIDGE WILL WEAKEN IT AND GRAZE NORTHERN UTAH DURING THE DAY MONDAY 
  BEFORE HIGH PRESSURE BUILDS BACK BEGINNING AT DAY 7.  
   

 

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Possible pattern change

 

Cool temperatures continue this weekend with quiet, sunny weather.  As the California low mentioned in our previous discussion slowly drifts into the desert Southwest over the beginning of the upcoming week, we’ll see an increase in moisture from the south starting on Wednesday in Northern Utah.  With the bulk of the moisture from this system arriving on Thursday and Friday.  While not a particularly cool system, it is likely that we’ll see snow high in the mountains.  At this time, we are not expecting anything significant, and any snow that does fall will be of the wet variety–good base building snow.

Beyond that, signs are pointing to an unsettled and cool pattern continuing.  GFS (computer model) in particular has been very consistent for the last 5 or 6 runs with a trough entering the area from the northwest during the weekend with another stronger trough on its heels for early in the week of October 15.  This is the type of pattern that, if it verifies, could go a long way to building a base for the Wasatch. Good news!  So anyway, while this pattern is still very much developing in the models, it is looking increasingly likely that at the very least, Autumn is here to stay.  

Keep praying for snow!

October Outlook

 

Short term:
The first part of the advertised cool down began yesterday with high temperature about 5-10 degrees lower than they were on Tuesday.  Today is another near average day before temps will dip below average tomorrow through the weekend along the Wasatch Front with the arrival of a reinforcing shot of cold air that will push slightly farther west than yesterday’s.  We, however, will see nothing in the way of precipitation, as all of that action is well to our east.  A few more clouds tomorrow and light breezes is all that will accompany the cooler temperatures.  Night time temps tomorrow night through the weekend will dip below freezing in mountain valleys and some of the colder low valleys as well. Time to cover up or harvest the plants.
Next week, the closed cut-off low pressure system that has been sitting off the California coast will gradually move inland.  Over Southern California, Southern Utah, and Arizona.  Not too much dynamics or moisture associated with this system but it will bring us a slight chance of showers–with the best chance for precip mostly to our south.  The timing on this looks to be about Wednesday of next week.  Southerly flow that develops ahead of the low may warm us up back to near average by Tuesday



Long term:
Everything beyond the next 7 days is very vague at this point but there is nothing to suggest that the blocking high pressure ridge parked off the coast of British Columbia will be going anywhere anytime soon.  So our best chances for snow will remain with cut-off low pressure systems or weak, cool systems that periodically drop down the east side of the ridge.  El Nino, which for a couple weeks, was looking a little stronger in the models, now looks weaker again.  The CPC has now given only 55% chance of development.  I was never as sold on it’s development as they were so I’m not too surprised.  I also believe that an ENSO neutral year or a very weak El Nino is better for Northern Utah’s chances at seeing average or above precipitation.  La Nina has a tendency to favor the Northwest, El Nino – the southwest, but an ENSO neutral year often aims the jet stream more at the mid-latitudes (including the Wasatch).  Teleconnections begin to play a significant role in our weather this time of year, but as of now, most of those are in neutral states and forecasted to stay that way for at least the next ten days or so.  We’ll keep an eye on those as well as the MJO over the next few weeks to see if they show signs of livening up, whether good or bad.
For the month of October, it’s looking mostly dry until at least mid-month.  After that, the CFSv2 suggest near average precipitation through the end of the month. So overall, I think we’ll be below normal precip-wise and near normal temperature-wise for the month barring some drastic change in the pattern.  Not too much excitement as of yet, but remember, things can change in a hurry once the Pacific steps on the gas.


 As far as seasonal outlook, not much reason to change my original snow forecast for the season of about normal.  If a weak El Nino does indeed develop, the southern parts of Utah may be more likely to jump above average with the North slightly below.  But I’m guessing that El Nino will be mostly a non-factor for us this winter so most areas of Utah will have equal chances of seeing above/below average snowfall.  Sounds a bit like a cop-out to say just an average year, but the best we can do is call it as we see it, and right now there isn’t anything out there to suggest otherwise.  Besides, I think after last winter, we’d all be quite happy with an average snow year, right?

Fall is on the Way!

Well above average temperatures have been the main story for the last few days.  That is expected to change on Wednesday and beyond as a cold system will drop out of Canada into the interior sections of the United States.  Most of the energy will stay to our east and we’ll see little more than clouds, but temperatures will take a serious dive, dropping 10-15 degrees over Northern Utah.  After the front moves through, the intermountain west well be under a long-wave trough that will allow disturbances to periodically move through the area.  These are likely not to be precip producers, but will rather bring with them a few clouds and reinforcing shots of cooler temperatures through next weekend.  So enjoy the warmth for the next couple days before Autumn makes it’s return on Wednesday.  At this time, there is nothing in the future that screams, “snow”, but this time of year models have a difficult time dealing with global pattern changes as we transition seasons, and sometimes storms can pop up when we don’t expect them.  Until then, enjoy the beautiful Fall weather.