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RIddle me this. What do you get when warm moist air over-runs cold dense arctic air? Warm advection snow! That is the set-up that will lead to our winter storm Friday afternoon and night.The arctic high with its frigid temps is directly over us Thursday. By Friday it advances into the Ohio Valley and the return flow on its backside sends a slug of mild juicy air up and over the chill before it can retreat. Bingo! You have yourself a mess,

Here's the surface parameters showing the south winds surging into the Midwest at noon Friday, about the time precipitation breaks out.

Here's the 850mb jet (5,000 feet just above the surface). A max of 85 mph is pushing from Iowa into Minnesota.

That rapidly transports moisture into the central U.S. Precipitable water vapor is over an inch into central Missouri.

That leads to available water vapor that is more than 300 percent above normal just to the south.

The key to how much snow we get is tied to the 850 temperatures. As long as they are at or below 0 degrees C. (32 F) we are in snow. At 9:00 pm Friday evening the GFS has the 0 (freezing line) extends from Marshalltown to Iowa City and on to Muscatine. Everything north of there should be falling as snow. South of that line you get a mix and eventually a transition to all rain.

The position of the freezing line is the wild card in this forecast. How far north it gets determines who gets all snow. How soon it passes a location determines how much of the moisture that would have been snow is lost to a mix of freezing rain, sleet, or even rain. If the timing is off a couple hours, that can be the difference between gaining or losing 2" of snow. Also, if the line ends up further south or north than projected that can seriously alter amounts as well. How the 850 line evolves is going to be the critical component of how much snow ultimately falls, especially in the southern half of my area...say HWY 30 south.

One thing that is different in this warm air advection event from the one of last weekend is that this time we will have cold air and cold ground temperatures in place at the onset of the storm. That was not the case last time and it led to high levels of ice and rain. In this situation, at least 60 percent of the precipitation should be snow in my southern counties (I-80 south) and more like 80-100 percent HWY 30 north. Cold is gold when it comes to snow.

Here are the most recent snowfall forecasts. This is just raw data and not a hard final call. You can see the differences that exist between the models.I should also point out these are 10:1 ratios. For a time ratios will be greater than that implying higher totals but I prefer to stay conservative at this point. I still like a general range of 3-5". Maybe a few spots in the far south with only 2" and the far north with up to 6".

The GFS 10:1

The EURO 10:1

Back to the issue of higher snow ratios. Just to give you an idea of what they look like. Here is what the EURO snowfall comes out like using the Kuchera method which accounts for ratios that at times are more than 10:1. In Cedar Rapids the total goes from 4.7" to 5.8".

The 12k NAM at 10:1

The GEM (Canadian)

The SHREF guidance, a model blend.

The GFS shows this for sleet and ice accumulations. Very hard parameters to predict.

No matter what, snow or snow changing to sleet and freezing rain is going to make for a mess and some tough travel. As it stands now snow should kick in around noon and last much of the night in some form be it liquid or frozen.

Winds will also be pretty frisky...up to 30 mph and that won't make things any easier.

When the snow and mix comes to an end, winds will get even stronger as another surge of arctic air plows southeast. Blowing snow could be an issue in the areas up north that don't get a crust from sleet or freezing rain. Temperatures early Saturday morning should begin near or a bit above freezing and then a flash freeze sets in as readings drop as much as 25 degrees during the day. By Sunday morning lows will be 5 to 10 below with wind chills 25-30 below zero.

Depending on where you are, winter storm watches currently in place will be upgraded to warnings or advisories at some point by the NWS Thursday. (If that hasn't already happened). No problems today though. Just a nice fresh January day with highs not getting out of the single digits and teens north of I-80.

Winter is waking up, Question is for how long? Much more to come on this storm. Roll weather...TS

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You want to know the essential online sites to use for models, radar, and the basic weather tools? DONE! You want to understand the structure of models and the role they play? DONE! You want to be able to construct forecasts from the ground up? DONE!

WEATHER SCHOOL will be presented in a seminar-type format where you'll have the ability to ask questions and dig deep. You’ll get the scoop on data acquisition, model analysis, severe weather, and actual forecasting from the big dog himself, T. Swails. With 43 years of experience and an uncanny ability to break the science down, you’ll open the door to forecasting like never before.

Along with the head master T. Swails himself, meteorologists Rebecca Kopelman and Nick Stewart of KGAN TV will be there to lend their knowledge and experience to the discussion. It will be fun, informative, and factual! This is the day for you to see, feel, and experience what it’s like to be in the hot seat of a meteorologist.

The seminar will be held January 25th and will last from noon until 5:00pm. We have limited seating and the cost is $99 dollars per person. A catered lunch will be provided. Again..not a lot of seats so reservations with a pre-payment are required. Sorry, no refunds. If there’s enough interest, a second session will be added in early February. To register or get additional information send an email to

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Purpose: To help weather enthusiasts understand the basics of forecasting and apply the knowledge and techniques learned to construct personal forecasts.


The essential on-line sites for models, observations, satellite and radar images, and general weather data.

Session 2: ANALYSIS:

Determining your objective goals. Short term, intermediate, or long-term. Understanding the process of analysis and its relationship to forecasting.

Model options and choices. What to use and when!

The GFS, EURO, NAM 3k, NAM 12K, Canadian, HRRR, MJO, ensembles, teleconnections, etc.

Locating, learning, and knowing what’s essential to make a reliable forecast.

The art and science of model interpretation: Using and understanding model output. Its called guidance for a reason!

Learn how to analyze key parameters such as:

Surface and upper air data

Vorticity and energy

Precipitation output

Wind and pressure


A simulation of the basic process using model output.

BREAK: A 25-30 minute recess to enjoy a catered lunch…


Thunderstorms, tornadoes, derechoes, and squall lines.

Soundings. What are they and why should I care?

Instability (CAPE) vs (CIN) Critical interaction involving moisture, heating, and forcing.

Uncovering the ingredients of a severe weather set-up.

TVS signatures. What to look for on radar.

Role of SPC vs NWS, and your local TV station regarding the warning process.

Simulated model driven forecast of a severe weather event/tornado outbreak


The key ingredients required for significant winter storm:

How to forecast the rain snow line.

How to forecast snow totals from QPF

Determining totals from snow ratios.

What to look for at the surface and at upper levels (500 and 850mb)

Model bias and determining the storm track

Simulated model driven forecast of a significant Midwest winter storm


An open period for attendees to ask questions regarding relevant topics or issues discussed during the day.


Some final words of inspiration from the events headliners

Once again, to reserve a spot or ask questions send an email to See you when the bell rings! Roll weather...T. Swails

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