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Jan 14th-16th Potent Hybrid Clipper


Tom

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DMX likes Estherville to Des Moines for heaviest line--

Next up is a much more potent system which will bring widespread
snowfall to the state on Friday. An upper low dropping south out of
Alberta merges with another wave pushing through the Pacific NW,
eventually deepening as it drops south through the Plains states.
Deep lift is established within a zone of synoptic divergence aloft,
sandwiched between a jet streak crossing the Plains and another
traversing the Great Lakes. This divergence is sustained for an
extended period as the upper low pivots eastward, leading to a
lengthy window of snowfall for the state. Snowfall expands from
north to south Friday morning as isentropic ascent increases
within a zone of broad warm air advection. Moisture availability
is not usually high and stability parameters suggest low banding
potential, but snow piles up as deep lift is sustained for an
extended period lasting well into Friday night for most of the
area. This idea is supported by hourly Cobb output of recent
NAM/GFS runs which shows consistent ~0.5"/hr snowfall rates,
possibly peaking a bit higher at times between 21z-03z. Snow rates
wane as isentropic ascent diminishes Friday night. A deepening
DGZ and lingering support aloft should keep at least light
snowfall around into the early hours Saturday. Models may still be
a bit too quick to pull snow out of the forecast. A widespread
4-7"+ is in play for all of central Iowa, but models have focused
on a corridor from EST to DSM for the highest potential amounts.
More uncertainty resides over our far north and east counties
where drier air may eat into snowfall totals a bit. Ensemble
plumes reflect this uncertainty well with a larger QPF spread
amongst members.
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The two loudest sounds known to man: a gun that goes bang when it is supposed to go click and a gun that goes click when it is supposed to go bang.

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DSM raw data 18Z GFS

not happening fwiw- but still

FRI 18Z 14-JAN   0.1    -2.5    1017      97      97    0.10     553     539    
SAT 00Z 15-JAN  -0.6    -5.0    1017      98      97    0.46     548     535    
SAT 06Z 15-JAN  -6.6    -7.7    1023      94      97    0.29     546     528    
SAT 12Z 15-JAN  -9.4   -10.6    1029      93      94    0.14     545     523    
SAT 18Z 15-JAN -10.0   -11.5    1033      87      73    0.01     547     521    
SUN 00Z 16-JAN -15.5   -10.9    1033      97      28    0.00     549     525
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The two loudest sounds known to man: a gun that goes bang when it is supposed to go click and a gun that goes click when it is supposed to go bang.

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38 minutes ago, hlcater said:

I will never understand this board in particular's obsession with the ICON. Belongs with the brazilian and DGEX.

From a statistical view, the ICON (turquoise line, a.k.a. DWD) is more or less on par with the UKMET over the last few years, and not in a good way - indeed, for the month of November, the order of models from most- to least-accurate at the 120-hour timeframe was:

  1. ECMWF
  2. GFS
  3. CMC
  4. ICON
  5. UKMET
  6. JMA

On a side note, the GFS was more accurate than the ECMWF beyond hour 144.

monthly_ts_rmse_GZ500_NA_120.png

202111_eg_rmse_GZ500_NA.png

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FWIW, can't post the graphics but cluster analysis of the ECMWF ENS has 45% of members in line with what Grizz posted just above, 41% of members shifting the core of the snow about 20 miles west, and the last 13% having a further east trajectory not too dissimilar from the 18z GFS (with a sharper western cutoff however).

Not sure if it's useful, but there ya go

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1 hour ago, The Snowman said:

From a statistical view, the ICON (turquoise line, a.k.a. DWD) is more or less on par with the UKMET over the last few years, and not in a good way - indeed, for the month of November, the order of models from most- to least-accurate at the 120-hour timeframe was:

  1. ECMWF
  2. GFS
  3. CMC
  4. ICON
  5. UKMET
  6. JMA

On a side note, the GFS was more accurate than the ECMWF beyond hour 144.

monthly_ts_rmse_GZ500_NA_120.png

202111_eg_rmse_GZ500_NA.png

That's a patently false interpretation of the data. If you isolate 2021 then maybe so but the UKMET is generally a higher regarded model and prior years demonstrate why.

2021-22 Snowfall: (Hiawatha)

TOTAL: 10.2"

(12/28: 3.0") (12/29: 0.8") 

(1/1: 6.4")

 

 

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1 hour ago, hlcater said:

That's a patently false interpretation of the data. If you isolate 2021 then maybe so but the UKMET is generally a higher regarded model and prior years demonstrate why.

Oh I'm not here to advocate one side or the other, that's just my takeaway. The beauty of an open forum like this is that no one is forced to agree with another. 😉

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The 00z HRRR is still well northeast of most other models.  Like the RAP, it will certainly cave southwest tomorrow.  I sure wish it was right, but I wouldn't bet a dime on this outcome.

Edit:  Actually, I don't think I'd want the ridiculous HRRR run because it's all wet slop.

season snowfall: 34.8"

'22-23: 30.2"      '21-22: 27.1"      '20-21: 52.5"      '19-20: 36.2"      '18-19: 50.2"      '17-18: 39.5"

Average snowfall: ~30"

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