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2/12 Winter Storm


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Some hindsight involved here, but I think the average of the ensemble 10:1 mean, probability and percentile stuff told a pretty consistent story. From the NWS perspective, I haven't been directly involved in the forecast process this time, but the inter-office collab and collab with WPC aspect is way more challenging than many realize. Internally, we felt that the QPF and ratios were too aggressive but there's only so much we can do when trying to form a consistent picture across large regions.

To me this looked like a advisory to perhaps low end warning event, particularly on the non-GFS/GEFS data. It's easy to get caught up in the Kuchera ratio output when assessing the snowfall forecast, that method is too simplistic though. 10:1 gets bashed, and it should in marginal temp situations and more clear cut high ratio setups, but I think it's a good first guess plenty of the time for synoptic systems.

Use the 10:1 and then adjust up where you're confident better banding is going to set up, through using model diagnostics like f-gen and cross sections, and utilizing the Cobb output.

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3 minutes ago, RCNYILWX said:

Some hindsight involved here, but I think the average of the ensemble 10:1 mean, probability and percentile stuff told a pretty consistent story. From the NWS perspective, I haven't been directly involved in the forecast process this time, but the inter-office collab and collab with WPC aspect is way more challenging than many realize. Internally, we felt that the QPF and ratios were too aggressive but there's only so much we can do when trying to form a consistent picture across large regions.

To me this looked like a advisory to perhaps low end warning event, particularly on the non-GFS/GEFS data. It's easy to get caught up in the Kuchera ratio output when assessing the snowfall forecast, that method is too simplistic though. 10:1 gets bashed, and it should in marginal temp situations and more clear cut high ratio setups, but I think it's a good first guess plenty of the time for synoptic systems.

Use the 10:1 and then adjust up where you're confident better banding is going to set up, through using model diagnostics like f-gen and cross sections, and utilizing the Cobb output.

Sent from my Pixel 9 Pro using Tapatalk
 

Thanks!!

I honestly only use the 10:1 ratio when looking at the models.  I only see the Kuchera when someone posts here (stopped looking at those a long time ago).  My thought is anything above the 10:1 model look is bonus snow!! 

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snippet from Milw

Initially, dry Arctic air lingering at the surface will prevent
snowfall from reaching the ground. However, by mid-morning
Wednesday, expect boundary layer to saturate and steady snowfall
to begin. Rates in the initial band will likely be in the
0.25-0.50 inch per hour range as it will primarily be driven by
WAA in the 700-500 mb layer. That being said, high ratio
snowfall is possible as the WAA actually nudges more of the
column into the dendritic growth zone. The highest rates develop
during the afternoon as low pressure begins to lift northward,
WAA in the mid-levels is enhanced, and convergence off Lake
Michigan begins to shift inland with a higher fetch. Rates up to
1 inch per hour are possible during this time frame, especially
in the Milwaukee to Kenosha corridor
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There are some noise level changes with the development of the defo on the 12z euro that if they continue to trend in the right direction can have a decent impact on LOT CWA. All in all I’d say positive signs from the 12z suite and we might start getting back an inch or two in next couple runs. 

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Just now, mimillman said:

There are some noise level changes with the development of the defo on the 12z euro that if they continue to trend in the right direction can have a decent impact on LOT CWA. All in all I’d say positive signs from the 12z suite and we might start getting back an inch or two in next couple runs. 

 

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LOT going with WWA

####

.UPDATE...
Issued at 1131 AM CST Tue Feb 11 2025

Quick update on tomorrow`s snow...

After getting a look at 12z guidance, the trend of the sfc low
being slower to deepen, thus farther east of the area continues.
The result is lower QPF versus yesterday morning`s (and prior)
guidance, so amounts that had looked to be borderline high end
advisory/low end warning, are now looking more solidly advisory.
As far as impacts go, snow, possibly heavy at times, is
expected during the day tomorrow, likely causing significant
travel issues. Ultimately, there really isn`t much difference
between a 3-6" snow vs a 4-8" snow, so the key messages for the
event remain largely unchanged. Still looks like southeastern
CWA could see lower snowfall totals, but snow could mix
with/change to some freezing rain or freezing drizzle Wed
evening. So will be upgrading the winter storm watch to a winter
weather advisory for our entire CWA.
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3 minutes ago, DocATL said:


Toss.

But seriously why are we so bad at predicting the weather?

Models definitely seem to struggle more these days. This is probably worse downfall in a system I seen in a long time. 

1 minute ago, Stebo said:

HRRR is a bit too dry for what the simulated reflectivity looks like plus it is notoriously dry with synoptic snows.

Simulated reflectivity did look like it should have produced more snow than it did

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