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Jan 19-20: Hoosier is not allowed to start this thread


mimillman
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We should start a movement on the sub forums to discourage posting of the Tropical Tidbits 10:1 snow/sleet maps. While there are flaws and some minor differences site to site with all the algorithm driven snow maps, at least the other sites are relatively similar in binning in QPF as snow. I prefer Pivotal Weather's maps overall, but COD maps are decent too.

A few tips:
- Algorithm snow maps are not the model producing that much snow - it's the specific algorithm ratio that converts snow QPF into snow accumulation. One of the few explicit model snow outputs is snow depth and then positive snow depth change utilizes the snow depth to give an idea on explicit accumulations.

There is a total snowfall output available on Pivotal Weather (for RAP and HRRR) that uses a model parameterized snow ratio and is an explicit model snowfall output. The NCEP HRRR site has explicit model output snowfall as well.

- Kuchera ratio is best used in below climo (wet/dense low ratio snow) to climo normal snow ratio scenarios, but is deeply flawed in very cold air masses. The ratio doesn't have an upper limit in extreme cold.

- 10:1 ratio is not bad as a first guess in climo normal snow ratio scenarios and even colder air masses because outside of banding or absent strong omega perfectly aligned with a deep DGZ, the Kuchera ratios will often be overdone. 10:1 can give a rough idea and then adjust up where you think mesoscale banding will set up.

- Positive snow depth change is a useful metric in low ratio to climo average ratios but will probably be a bit underdone in general.

- Tropical Tidbits is much more liberal in QPF to snow so the footprint of snow accumulations in marginal to mixed p-type scenarios will almost always be overdone. It's probably okay when p-type isn't an issue.

Sent from my SM-G998U using Tapatalk

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TT is very annoying.  Would never use it in mixed precip scenarios.  I've seen times when people have posted a TT map showing like 18" of snow in central Mississippi or something crazy like that.  Without even digging in, you can pretty well assume that it's not all snow.

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Expected Snowfall - Official NWS Forecast

MKX put out their graphics for this storm. 4-6" would be a nice hit here, although I really don't like being so close to the gradient like that. This would basically be undoing the last few weeks of warmth when it comes to our totals and send us right back to being above average which would be really nice as well. 

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18 minutes ago, Brian D said:

2-3" of mostly lake effect for me. Refresh the snowpack a little after the the rainy weather we just had. Then the colder weather, but still above average will turn the snowpack into ice.

We have a 55gal drum half full of water sitting on top of the snowpack this morning. I can’t believe it’s holding, must be a glacier. 

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New zone area forecast for me has upped my total to 4-6" for this storm. Probably not quite enough for a WSW but on the upper end of a WWA. I'm a bit surprised to see that total get bumped up. Not sure what MPX is seeing in their models but from everything I've seen I look to be pretty solidly in the 3-4" range. If these updated totals are accurate then we should see another row or two of counties on the north side get added to the WWA and a row of counties get converted to a WSW on the south side of the Twin Cities.

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11 minutes ago, OrdIowPitMsp said:

Probably the 18z NAM

59FE239E-8F59-4C40-B531-C60BF8C20EFD.jpeg

Yeah but the Nest seems an odd one to pick to make an official forecast from, especially when none of the other models (CAMs or otherwise) support WSW criteria snow for most of the metro. Idk maybe I'm missing something but I've been following weather for a long time and I don't see what they see in the models. 4-5" looks like a pretty solid bet.

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I feel like RC mentioned this exact scenario with the double barrel low. Brutal 
Yep, that was the death knell. If we got a more classic synoptic evolution where the 850 mb low was associated with the eastern surface low, parts of northern IL would've been in the game. The fact that even with the unfavorable 850 mb low placement, we're getting some mixed ptypes this evening shows it wasn't too far off from a wet snow event in parts of the CWA.


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