Midwest Snowfall is About Ratios and Temperatures

We are once again faced with the 10:1 snowfall ratio model snowfall verses the reality of what will be on the ground. Using the Kuchera snow ratio map for 6z (1am CT Thur) about the time the heaviest snows are falling, notice that the ratios are about 8:1 on average meaning for every inch of rain you get 8 inches of snow. The standard is typically is 10:1 and in the coldest storms can be 20:1.


Wild Weather from Snow to High Winds

to Severe Storms to Flooding Rains


In addition to the snow ratios, you have to take into account surface temperatures which will be around freezing. All this means that the amount of snow that actually falls verses what is on the ground can be quite different. So when using the model 10:1 snowfall and saying that is how much will fall is actually in accurate.

 

Below are examples of the GFS and NAM model showing the 10:1 ratio snow maps verses the snow that will actually be on the ground. That’s why I think it’s a 1-8 inch snow event for the Midwest leaning more toward the lower side then the higher side.

 

 

 

 

 

 

 

 

Wild Weather from Snow to High Winds to Severe Storms to Flooding Rains

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Denver to Madison Snowstorm(s), Two Events as Winter Starts Early!

A two shot snow event will occur this week letting us know that winter is on the way. Denver was hit this morning with snow and now a bigger snowstorm is coming to Denver to Madison, Wi, perhaps even the Upper Peninsula of Michigan.

While Denver is going to have 4-8 inches of snow with over a foot in the mountains, snow coming into the Plains and Midwest will be 1-8 inches depending on location.


Dam-Breaking High Wind Event with Possible

Weak Tornadoes NYC to Richmond!


The 10:1 ratio computer models are showing over a foot of snow but given the time of the year, we are probably looking as less, that’s why I am showing the Kuchera snow amounts which take into account snow ratios.

The first storm is comes out tonight with light snows across the Midwest and Plains. The second comes out of the Rockies Wednesday and heads in the Great Lakes Thursday night. Models still differ some on amounts, but going with the low ratios of 8:1 we are probably looking at 1-8 inches of snow. Despite all that, travel be poor in Denver, probably slushy and slippery into the Plains and Midwest.

 


Snowfall Accumulation (Kuchera Method)

Notes: This product shows solely the total amount of snowfall using a solid-to-liquid-equivalent ratio derived from the Kuchera Method. Where Tmax represents the maximum temperature in the lowest 500mb in Kelvin, the Kuchera Method uses one of the following two formulas to approximate snowfall ratio based on the value of Tmax being greater or less than 271.16K (~28°F or ~-2°C).


The snowfall amount is then calculated by multiplying ratio by the forecast QPF. The amount displayed is cumulative, starting at the beginning of the model run and accumulating throughout the entire forecast period.


 

Below are the computer model snows. I like the NAM amounts thinking that GFS is too high on amounts.

 



Links
  1. Computer Models
  2. Hazard Maps
  3. Snow Maps

Dam-Breaking High Wind Event with Possible Weak Tornadoes NYC to Richmond!

model1A strong cold will blast over the Appalachians Thursday night and into the Mid-Atlantic early Friday producing wind gusts 40-70 mph and perhaps even a few weak tornadoes. This is what I term a “Dam-Breaking High Wind Event” where cold air builds up west of he Appalachians and eventually breaks over the east slopes of the Appalachians, accelerating down the slopes producing high wind gusts. Low-top thunderstorms will be associated with the leading edge of the high winds that will only enhance wind gusts.


Rockies to Midwest Snowstorms, Severe Weather May Include Tornadoes!


GFSMA_925_spd_090Winds at 925 mb which is just above the surface show winds over 50 kts so if that wind is tapped and brought to the surface you can get gusts over 40 mph. There is also enough rotation that weak tornadoes may occur within the thunderstorms as well.

 

 

Areas from New York City to Richmond and 100 miles west of I-95 will be impacted by the winds. Expect tree damage, power outages and perhaps damage to homes.

 

sim1

Sounding from Virginia.

model3