Monday, November 14, 2011

The Convergence Zone that Keeps on Giving

Monday, November 14, 2011
6:12 P.M.

Weather Radar from the NWS at 9:06 A.M. PST

The Puget Sound area commonly gets strong convergence zones in the winter, but I have never seen one as persistent as the one that happened today. This convergence zone brought tons of snow to the central slopes of the Cascades, and eastbound Snoqualmie Pass was even closed at one point. Meanwhile, places like Crystal Mountain, outside of the convergence zone, received very little snow today.

Look at some of these tables for the weather today as recorded at Crystal Mountain and Alpental, near Snoqualmie Pass.  Snow levels were below pass level all day today, so to estimate the amount of snow recorded, I took the water equivalent and multiplied it by 10, since one inch of rain is approximately equal to one inch of snow most of the time.

11-14-2011
Northwest Weather and Avalanche Center
Crystal Mountain Ski Area, Washington

Total snow may read bushes

 MM/DD  Hour  Temp  Temp    RH    RH  Wind  Wind  Wind  Wind  Hour Total 24 Hr Total
         PST     F     F     %     %   Min   Avg   Max   Dir Prec. Prec.  Snow  Snow
             6830' 4570' 6830' 4570' 6830' 6830' 6830' 6830' 4570' 4570' 4570' 4570'
------------------------------------------------------------------------------------
 11 13  1900    24    30    99    98     6    15    39   248     0     0     5    14
 11 13  2000    25    30   100    99     8    21    40   285     0     0     5    14
 11 13  2100    25    30    99    99     6    17    33   173     0     0     6    14
 11 13  2200    24    30    99    99     7    18    42   294     0     0     6    13
 11 13  2300    25    31    99    99     7    19    44   306     0     0     6    14
 11 14     0    23    31    99    99    11    23    46   319   .01   .01     6    13
 11 14   100    22    30    99    97     8    22    42   346     0   .01     6    14
 11 14   200    23    31    99    89    11    29    49   318     0   .01     6    13
 11 14   300    23    31    99    88    11    30    54   339     0   .01     6    13
 11 14   400    22    30    99    95    11    26    54   316     0   .01     6    13
 11 14   500    23    30    99    96     9    22    37   265   .01   .02     6    14
 11 14   600    22    30    99    96     9    23    49   298   .02   .04     6    14
 11 14   700    22    30    99    96    15    30    50   292   .01   .05     6    14
 11 14   800    22    30    99    95    11    29    54   140   .02   .07     6    14
 11 14   900    22    30    99    93    13    29    52   315     0   .07     6    14
 11 14  1000    23    31    99    88    13    28    46   249   .01   .08     6    14
 11 14  1100    23    30    99    90    16    31    44   258   .01   .09     6    15
 11 14  1200    21    29    98    86    16    30    47   266     0   .09     6    14
 11 14  1300    21    30    98    82    12    29    54   263     0   .09     6    14
 11 14  1400    20    29    98    85    10    27    52    47   .01    .1     6    14
                20          98           2    19    39   296


    

                                                                       Total
                                                                       Prec.
                                                                       4570'
    ------------------------------------------------------------------------
                                                                          .1 

.1 inches of precipitation is not that impressive. The winds, on the other hand, are pretty strong! Mission Ridge, on the eastern side of the Cascades, had a wind gust to 96 miles per hour yesterday. Cliff Mass did a fabulous blog post on these strong winds, and you can find this post here.

Snoqualmie Pass, in the convergence zone, received much more snow. The gauge at the pass was malfunctioning, so I used the gauge from Alpental, which is a ski resort adjacent to the pass.


11-14-2011
Northwest Weather and Avalanche Center
Alpental Ski Area, Washington

Wind gages unheated and may rime
24 hr snow gage not yet iunstalled
Total snow may read bushes

 MM/DD  Hour  Temp  Temp  Temp    RH    RH  Wind  Wind  Wind  Hour Total 24 Hr Total
         PST     F     F     F     %     %   Avg   Max  Dir. Prec. Prec.  Snow  Snow
             5470' 4350' 3100' 3100' 5470' 5520' 5520' 5520' 3100' 3100' 3100' 3100'
------------------------------------------------------------------------------------
 11 13  1900    27    31    34    98    98     0     0   288   .03   .03     2    19
 11 13  2000    27    31    34    99    99     0     0   287   .02   .05     2    20
 11 13  2100    27    31    34    99    99     0     0   287   .04   .09     2    20
 11 13  2200    27    31    35    97    98     0     0   287     0   .09     2    18
 11 13  2300    27    31    33    99    99     0     0   287   .06   .15     2    19
 11 14     0    27    30    34    98    99     0     0   287   .01   .16     2    19
 11 14   100    27    31    34    98    99     0     0   287   .01   .17     2    19
 11 14   200    27    30    33    98    99     0     0   287   .04   .21     2    20
 11 14   300    26    30    33   100    99     0     0   287   .08   .29     2    20
 11 14   400    26    30    34    96    99     0     0   287   .02   .31     2    20
 11 14   500    26    29    33    99    99     0     0   287   .07   .38     3    20
 11 14   600    25    29    33    99    99     0     0   287   .06   .44     3    19
 11 14   700    26    29    32   100    98     0     0   285    .1   .54     3    17
 11 14   800    25    29    32   100    99     0     0   283   .15   .69     0    14
 11 14   900    24    28    32    99    97     0     0   285   .15   .84     1    19
 11 14  1000    22    26    30    99    98     0     0   287    .1   .94     2    19
 11 14  1100    22    26    30    99    97     0     0   290   .07  1.01     3    20
 11 14  1200    22    26    32    99    98     0     0   287   .05  1.06     4    19
 11 14  1300    22    26    31    98    97     0     0   287   .02  1.08     4   -25
 11 14  1400    22    26    31    98    97     0     0   287   .03  1.11     5    21


    

                                                                       Total
                                                                       Prec.
                                                                       3100'
    ------------------------------------------------------------------------
                                                                        1.11

1.11 inches of precipitation! That is astonishing, even for a strong convergence zone. The temperatures for the most part were slightly above, at, or slightly below 32 degrees, so I have a feeling the snow here would be wetter and have more of a 1:8 inch ratio of water to snow. Even though the temperatures were above freezing for a while, it was likely still snowing at the pass, as snow will often continue to fall 1,000 feet below the freezing level, especially when the atmosphere is unstable and the temperature varies rapidly with height, as it has over the past day.

The main convergence zone action occurred from around 6 A.M. this morning to 2 P.M. Believe it or not, a convergence zone is still going on and is located slightly south of Snoqualmie Pass. Take a look at the radar loop from 6 A.M. to 2 P.M. today, and notice the persistent convergence zone action over Snoqualmie Pass.

video

The Summit at Snoqualmie, which is typically one of the last places to open for the ski season due to its low elevation, may end up being one of the first areas to open because of this convergence zone dump. In addition, we will likely see plenty more convergence zones in the following week as we will be under a moist, cool northwesterly flow that is conductive to these zones. The snow at Snoqualmie will continue to pile up.

Many people have asked me about snow in the lowlands this coming weekend, and although the mountains will get heavy snow down to low elevations, I doubt we will see snow to the surface. We will not see enough arctic air in our area to see snow in the lowlands. This could change though, and if it does, I'll let you know!

Back to homework. Thanks for reading!
Charlie

4 comments:

  1. i masturbated while reading this

    ReplyDelete
  2. lol... this is a very professional weather blog anonymous!

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  3. Yo Charlie! Your blog posts are quite enjoyable to read. Keep up the good work! But yeah, this next wed and beyond looks a little interesting. First off the gradient looks pretty impressive with the cold front that passes. Looks to be at least wind advisory level with the new GFS pass. Strong storm indeed. What will be even more interesting is how much cold air that low that drops from the golf of AK afterwards. Latest run of the GFS was pretty cold. But the NAM was pretty warm. I bet we see pretty cold temps with possible snow/rain showers. But prob not a big snow event of any means.

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  4. Thank you Joey! I agree, there will not be a big snow event in the lowlands. I really wish the uw website could run a wrf or mm5 euro... that would be awesome!

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