Weekend Storm: Snow Numbers

A significant winter storm is still in the cards for Missouri, Illinois, Kentucky, and Indiana.  If you have plans to travel, you should read this and then reconsider your plans.

Dry air is currently infiltrating the central United States following a passing cold front.  Dew points have dropped below zero, hinting at the arctic origins of the air.

It will take a small amount of time to saturate the atmospheric column, but it should not take long for precipitation to reach the ground as snow.

TIMING:

• Missouri: Snow will start to enter southeast Missouri from the southwest Saturday morning.
• Illinois: Snow will enter Illinois late Saturday morning/early afternoon.
• Kentucky: Snow will enter the extreme southwest corner of Kentucky Saturday mid-morning.
• Indiana: Snow will enter the southwest corner of the state Saturday afternoon.  It should enter central Indiana late Saturday afternoon.

HOW MUCH:

Computer models have been extremely consistent on how much water will be available in the atmosphere.  There is one computer model that has been consistent with lower water amounts - the GFS.

All that being said, there is copious amounts of water available and there will also be cold air in place.  Snow to Liquid ratios will be higher than normal due to the cold.  Normally, we look at 10 to 1.  For this storm, the ratio could range from 12 to 1 to as much as 18 to 1.

After looking over the Friday morning computer model runs (and the last several days worth of data) these are the numbers I think could fall as snow through Sunday night.

INDIANA 

• Bloomington: 8"-12"
• Columbus: 10"-14"
• Indianapolis: 7"-10"
• Shelbyville: 8"-11"

MISSOURI

• Cape Girardeau: 8"-11"
• St. Louis: 7"-11"

ILLINOIS

• Carbondale: 10"-15"

KENTUCKY

• Paducah: 7"-12"

These numbers could still fluctuate as more data comes in over the next 24 hours.  If there is any sleet mixed in, especially in western Kentucky and the Missouri bootheel, it could have significant impact to snowfall amounts.

The attached map may not exactly match what I have forecast above.  It is a display of a blend of computer model snowfall through 7am ET Monday.

Winter Storm Update

I have been monitoring data coming in from Wednesday night's and Thursday morning's computer model runs and it still looks like a winter storm will have a significant impact on the Ohio River Valley.

The upper-level energy for the storm is still located off the southwest coast of California.  It will be better once it is overland and models can get a better sampling of what is happening in atmosphere.  That being said, the NOAA Hurricane Hunters - the pilots and scientists that fly in to hurricanes to collect data - started to fly missions in to the storm over the Pacific earlier this week.  Another mission is scheduled for Thursday evening.  I can't emphasize enough how important is that they collect.  The data goes straight in to the computer models we use to forecast weather.

In Wednesday's update I talked about how much water there will be to work with over the region.  Wednesday night's computer model runs, and Thursday morning's, increased the projected water available.

A 34-computer model average suggests the following liquid equivalent 7am ET Saturday - 7am ET Monday along with the range in data.

INDIANA 

• Bloomington: 0.82" (0.58" - 1.02")
• Columbus: 0.86" (0.61" - 1.05")
• Indianapolis: 0.67" (0.47" - 0.86")
• Shelbyville: 0.76" (0.58" - 0.91"

MISSOURI

• Cape Girardeau: 1.01" (0.82" - 1.22")
• St. Louis: 0.63" (0.43" - 0.83")

ILLINOIS

• Carbondale: 0.91" (0.70 - 1.10"

KENTUCKY

• Paducah: 1.16 (0.88" - 1.55")

Needless to say, that is a LOT of water for a winter storm.  Especially when most locations - north of the Ohio River - will be mainly all snow.

Having enough cold air to create snow will not be a problem with this storm.  (There will be some, mainly along and south of the Ohio River, that may have a little bit of warm air in the atmospheric column which would create sleet, at times.)

Air will be cold enough for higher than normal snow to liquid ratios.  A good rule of thumb is for a 10 to 1 (10:1) ratio.  With the cold air expected to be in place, ratios could go from 12:1 to as much as 18:1.  

This is when the fun begins.  You - or your kids that know how to multiply - can start doing the math on how much snow that could potentially produce.  Multiply the water amount to the snow to liquid ratio.  Example:  0.86 x 14 = 12.0"

Areas that have sleet mixed in will drastically reduce the numbers.  Sometimes by as much as 40%+.

There is a little more massaging of the data that goes in to producing the snow forecast, but this can give you a rough idea.

If the models don't come in overnight/tomorrow suggesting much lower water amounts, this will likely be a "doozy" of a winter storm for many in Missouri, Illinois, Indiana, and Kentucky.  And that isn't talking about the BIG ice storm that will happen further south.

Let's see what Friday's information brings and that could warrant me issuing Freak-Out-Meters for several locations in Missouri, Illinois, Kentucky, and Indiana.  Stay tuned...

Weekend Winter Storm to have big impacts on Central United States

Chatter about a winter storm for the upcoming weekend is in full throat on the inter-webs.  I am just starting to dig in to the data and see what might be coming.

The good news... For most of the people that follow me on here - Missouri, Illinois, Indiana - the thermal profile of the atmosphere suggests this looks to be mainly a snow event, at the moment.  (This does not mean there could not be sleet involved for some.)  It looks to start in eastern Missouri pre-dawn Saturday and exit Indiana Sunday night.

Everyone wants to know how much.  Yes, people are throwing out numbers, but that is all it is at this moment.  Numbers.  To be honest, it is too early to talk specific snow amounts, snow no you will not see me giving snowfall amounts yet.  However, I will show you how much liquid precipitation computer models are suggesting for a few locales.

A 32-computer model average for 7am ET Saturday through 7 am ET Monday:

INDIANA

• Bloomington: 0.47"
• Columbus: 0.48"
• Indianapolis: 0.36"
• Shelbyville: 0.42"

MISSOURI

• Cape Girardeau: 0.79"
• St. Louis: 0.41"

ILLINOIS:

• Carbondale: 0.66"

Yes, at this distance it appears this storm has a hefty supply of water.

We can also look at ensemble computer models.  Instead of a single forecast run, an ensemble uses multiple model runs (often 20–50+).  Each run starts with slightly different initial conditions (temperature, pressure, wind, moisture).  The ensembles can give us a range of how things could happen.

Today, I want to show you how many members of five global ensemble models suggest there will be measurable snow on the ground Sunday evening.

Columbus, IN: 94% - 170 out of 180 members
Indianapolis, IN: 94% - 170 out of 180 members
St. Louis, MO: 94% - 170 out of 180 members

It does make me chuckle that out of 180 members, all three locations have identical numbers.

We know it will be cold, which will allow for some of the snow to be fluffed up, resulting in a higher snow to water ratio.

Winter Storm Watches have been hoisted from New Mexico to North Carolina.  As more data comes in, the forecast will be refined and the picture will become more clear.  As it becomes more clear, we will have a better idea for snow totals and impacts.  I suspect a Freak-Out-Meter will be issued before the weekend gets here.

BOTTOM LINE:  This will be a good weekend to stay indoors and watch the storm through the window.

What are you hoping for from the storm?