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?

HPC Puts On Their Skates

Taking a quick glance of data this morning concerning Sunday-Monday and the possibility of freezing rain.  Last night’s European computer model (ECMWF) continues to be bullish on the potential whereas NOAA’s global forecast model (GFS) is downplaying the icing side.

One thing the models are in agreement about, rain, heavy at times, will fall Saturday night through early Sunday morning.  A cold front will be slowly moving through Missouri, Illinois and Indiana at the time.  There will be shallow cold air behind the cold front while a few thousand feet up in the atmosphere winds out of the southwest will keep temperatures above freezing.  There are two big questions at this time:

1. How long will water be available?
2. Where will be the location of the cold front?

Most likely, just north of the front will see freezing rain.

The Hydrometeorological Prediction Center is getting in on some of the freezing rain chatter.  There latest Day 3 Freezing Rain Probability Forecast and Day 3 Freezing Rain Accumulation Forecast is out and includes parts of Arkansas, Missouri, Illinois and Indiana.  The images below look at the Saturday night through Sunday morning time frame.

24-Hour Probability of Freezing Rain Accumulation 0.01”+:

Click the image to see larger version.

24-Hour Probability of Freezing Rain Accumulation 0.25”+:

Click image to see larger version.

48-Hour Freezing Rain Accumulation – 95^th Percentile:

Click image to see larger version.

Notice how HPC keeps the freezing rain out of western Kentucky, southern Indiana and northeast Arkansas.  The European computer model has the freezing rain going further south in to those areas.

Will the models continue the way of the GFS, keeping the freezing rain away, or will they lean towards the Euro, hinting at an ice storm?  We’ll have to wait and see what the runs come in with over the coming days.

FREAK-OUT-METER:

• Southeast Missouri: 3
• Southern Illinois: 3
• Western Kentucky: 2
• Central Indiana: 2
• St. Louis metro: 3

Wet and Slick Weather Ahead

Quite a few weather “things” coming to the Midwest over the next five to six days and there are still a lot of question marks as to what will hit the ground.  One thing is for sure, there will be a significant and beneficial amount of rain falling at least through Sunday.  In some instances, upwards of 6” of rain could fall in parts of Missouri, Illinois and Kentucky.

Here is the Hydrometeorological Prediction Center’s precipitation forecast for the next five days.

Click image to see larger version.

If the computer models are correct, the numbers on the map (above) might be on the low side of reality.  Just through Friday, a four computer model average for rainfall is:

• Cape Girardeau:  0.96”
• Indianapolis: 0.89”
• Paducah: 1.32”
• St. Louis: 0.96”

Considering much of the area is still well below normal (precipitation), the rains will definitely be beneficial.

CLEAR SLICK STUFF

Now  the main reason for writing this post… What comes Sunday/Monday.

In the next 24-48 hours I think you are going to start to hear television meteorologists/weather-peeps starting to mention “freezing rain” (a.k.a. ice).  Freezing rain isn’t fun as it only takes a very small amount to make things slick.

The temperature profile of the atmosphere will be a HUGE factor in determining what type of winter weather will reach the ground.  It is the changing temperatures with height that makes winter forecasting the most difficult.

Instead of going in to detail how each type of winter precipitation is formed, check out the following links for tutorials from the University of Illinois on how the various winter weather types are formed.

• Snow
• Sleet
• Freezing Rain

Ok, now that you have a better understanding of how the different precipitation types form, let’s take a look at what some of the computer models are advertising for a few select locations.  (Note:  This is just an overview of what a few locations could see.  The data used is coming straight from computer models and is not the forecast.  It is also subject to change, and likely will.)

For the last couple of runs, computer models are hinting at cold shallow air to be in much of the Midwest.  The cold air is scheduled to arrive late Saturday night through Sunday depending on your location.  The models have temperatures slightly above freezing at 5,000 feet and  how thick that “warm” layer is will determine the type of precipitation hitting the ground.

This is a meteogram for St. Louis.  Each line is a representation of a different run of a computer model’s prediction of freezing rain accumulation.

Click image to see larger version.

The light blue line shows the amount of freezing rain accumulation from this morning’s run of NOAA’s global forecast model, the GFS.  Disregard the dark blue line (comes from the 6z GFS which I hold little faith in).

Not shown in the above meteogram is the European forecast agency’s computer model, the ECMWF.  The Euro is suggesting 0.59” of rain may fall while temperatures at the surface are below 32°F.  (Keep in mind that not all precipitation falling accumulates.  That is a reason for difference in numbers.)

Here are meteograms for a few other locations along with how much precipitation is projected to fall by the Euro.

Cape Girardeau, Mo:   Euro – 0.63”

Click image to see larger version.

Indianapolis, In:  Euro – 0.60”

Click image to see larger version.

As we get closer to Sunday the models should get better at predicting the minute details needed for determining precipitation type. 

Bottom Line… What I want you to take away from all of this is that there is a chance we could see freezing rain Sunday in to early Monday morning (timing varies by location).  It could also fall as all rain or sleet.  There are still considerable uncertainty as to what will fall.

I know many are skittish after the 2009 ice storm but as of today I do not think this will be anywhere near that storm.  As you will see below in my “Freak-Out-Meter”, I don’t think you should be freaking out nor should you be stocking up supplies to go weeks without power.  Instead, what I think you should do is keep an eye on the forecast over the next couple of days, maybe beat the lines and grab a can of deicer and a few batteries.  Worst case (for me anyway), this doesn’t pan out and you’ve got an extra can of deicer and batteries.

FREAK-OUT-METER:

• Southeast Missouri: 2
• Southern Illinois: 2
• Western Kentucky: 2
• Northeast Arkansas: 2
• St. Louis Metro: 3
• Central Indiana: 2

4:30pm Weather Update

The morning run of both NOAA’s global forecast model (GFS) and the European agency’s (ECMWF) is in.  Both continue to indicate an area of low pressure developing early next week in the mid-Mississippi Valley.

We start our journey with the ECMWF (the Euro).  Generally, this is my preferred computer model for forecasting, especially beyond 48 hours.  The Euro develops an area of low pressure  initially over Oklahoma and Texas Monday afternoon.  The low then moves east.  Below is look at the Euro’s projection of Mean Surface Level Pressure and precipitation at 6am CT Tuesday, December 18.

(Click the image to see a larger version.)

You can see the area of low pressure centered over NW Mississippi.  That is a perfect location for measurable snow in parts of southeast Missouri, western Kentucky and extreme southern Illinois.  The big thing to note, look at the lack of moisture.  The storm doesn’t draw up a lot of moisture.

I also want you to note the grey and blue area in SW Missouri.  This is likely generated by the upper-level low coming in on the NW side of the storm.  Upper-level lows can and often do produce snow.  Usually it isn’t the BIG amounts of snow you see in snow storms, but more of a drier/fluffier snow.

The next image is from 12pm CT Tuesday.

(Click the image to see a larger version.)

The upper-level low is located over SW Missouri/NW Arkansas.  Notice the moisture the model tries to develop on the NW side of the surface low over the “Heartland”.

Just a quick view of the model would suggest 1”-3” of snow in parts of southeast Missouri, extreme southern Illinois, western Kentucky and northwest Tennessee.

The GFS on the other hand is a little quicker with moving the storm through the Midwest.  It is also much drier.  Below is the GFS for 12pm CT Monday.

(Click the image to see a larger version.)

Note it has the area of low pressure over NW Alabama and SW Tennessee.  The location is good but look on the north/northwest side of the storm.  It is dry.  Also notice that we are talking about the storms location 24-36 hours earlier than the Euro.

Here is the GFS for 6pm CT Monday.

(Click the image to see a larger version.)

It is quickly moving east to the coast.  In fact, beyond 6pm CT Monday, it develops are large storm for the east coast.

At this point it is entirely too early to be talking about specific snowfall amounts.  Heck, at this point it is too early to know if this storm will develop for sure.  As I mentioned in my earlier post from today, I want to see the models continue to show the storm on Thursday and Friday’s runs before I get too excited.  I am keeping my “Freak-Out-Meter” at 0.5 out of 10.