Deconstructing Goliath; Bonus January Outlook

One of the benefits of being a hobby/amateur forecaster is that I really have no "skin" in the game.  While I really do want to give you good insight and accurate forecasts, my career doesn't depend on doing so.  So, unlike the pros, I'm happy to admit when I made a miscalculation in the spirit of learning and doing better next time.

While I realize I'm grading my own homework here, I thought it might be fun to deconstruct yesterday's storm against my own forecast.

What I Got Wrong:

1. The biggest thing I got wrong was the high temperature, and that impacted other parts of the forecast.  I predicted a high of 33, thinking that the warm air wrapping around the low would drive up the temperature as the system approached in the late afternoon.  Instead, I recorded a high of 28 in New Glarus -- also the official high at the Madison airport.
2. Because of the colder temperatures, we saw more snow accumulation than I expected.  I predicted 2-4".  Madison's official snowfall was 5.9", and here in New Glarus, I measured 4.5".  Still within the meteorological margin of error, I suppose, but I was low nonetheless.

Here's what the early snow totals look like around the region (click to enlarge).

What I Got Right:

1. First and foremost, I was ahead of this storm by 6 days.  While it's risky to start talking about a December 28th storm on December 22nd (as I did on Facebook), I felt that with the holidays and folks traveling, the reward outweighed the risk.
2. I got the "pre-slopitation" right.  Here in New Glarus (and nearly all other locations I was tracking), we had sleet, freezing rain and snow.  In fact, the sleet was steady for almost a 5-hour period between 2pm and 7pm, when precipitation changed back to snow.
3. The wind forecast was also correct.  The highest speed I recorded was 34 MPH, but other reports were as high as 60 MPH (which I accurately predicted would occur in the far southeast corner of the state).  
4. I mostly got the timing right.  I said the storm would start mid-morning.  Here in New Glarus, it started at 8am.
5. Finally, and this might actually be the most important thing, I said in a Saturday Facebook post that driving would be a really bad idea on Monday.  Safety is important to me in winter forecasts.  As you probably heard, emergency services responded to hundreds of crashes, rollovers and slide-offs in southern Wisconsin alone.

With that, let's look ahead to what January may have in store.

All models are currently showing a southern jet stream through at least the third week of the month.  This allows colder Canadian air to infiltrate the Midwest, setting us up for seasonably cold temperatures.  I don't see any polar vortices on the horizon; in fact, there's a chance we could get through January without even seeing subzero temperatures.  I don't know if that's ever happened before in January, but I'm looking into it with the State Climatology Office.  I'll keep you posted.

At the same time, major storm systems for the first couple weeks of January seem like they'll be relegated to both the east and west coasts (a trademark of El Nino winters), with very little action here in the Midwest.  The GFS model is showing a weaker disturbance next Thursday, January 7th, so I'll keep on eye on that.  Otherwise, there's not much out there.  Of course, that can change.

Finally, I want to say "thanks" to those of you who are genuinely interested in Rippeology.  Obviously, I enjoy it, but it is a bit of work.  Since Saturday, the blog has had over 250 visitors, which is pretty cool.  I appreciate your interest!

As always, let me know if I can answer any questions for you, either here or on Facebook.

~Scott

The Ice Man Cometh

In my November 13th winter preview post, I predicted, among other things, "more ice events" than usual this winter.  That should start to materialize tomorrow in Southern Wisconsin.

In fact, with temperatures hovering between 29 and 35, depending on your location, we could see the full gamut of winter pre-slopitation Monday and Monday night, including freezing rain, rain, sleet and snow.  Oh, and a shit-ton of wind.

Officially, the National Weather Service has posted a Winter Storm Watch for all 72 Wisconsin counties.  But the nature of the storm will be very different from north to south.

Here's the scoop:

The same intense low pressure creating extreme blizzard conditions right now in parts of New Mexico and Texas will push northeastward toward central Illinois overnight tonight.  Normally, this kind of "panhandle hook" track (explained here) would put much of Wisconsin in a heavy snow area.  But with El Nino's influence, this low will be so strong that it will wrap warmer air all the way over to the northwest side of the low.  With that warm air aloft, precipitation then starts as rain, and ends up falling to the surface either as sleet or ice, depending on the surface temperature.

Here's how the National Weather Service sees the map shaping up for 6am Monday (and remember, you can click on any image to enlarge):

That orange color represents freezing rain.  You'll see the low positioned in extreme southwestern Missouri.  What happens after that depends completely on where the low goes from there.  A track toward Rockford or Chicago keeps us in relatively "warm" space, meaning that rain and sleet are more likely.  A track toward Detroit puts us in a colder position, meaning more snow and freezing rain.

The GFS weather model, which forecasters rely on to predict the position of pressure systems, seems to split the difference between those tracks -- maybe just east of Chicago, but just west of Detroit.  These two images show the 12-hour advance of the low...

 

In all winter storms, pinpointing the track of the low is the key to accurate forecasting.  But in this storm, low track is even more important, because temperatures will hover right around the freezing mark.  That means that two areas only 10 or 20 miles apart, with only a 1-2 degree temperature difference, could see completely different types of precipitation at the same time.  

In fact, the only thing really certain about this storm is wind.  As the low gets closer during the day tomorrow, look for east/northeast winds to gust as high as 35-45 MPH.  This wind forecast shows lower Lake Michigan taking the brunt of the strongest winds:

Wind and ice, as all Wisconsinites know, is a terrible combination if you want to drive somewhere.  And an extra word of caution about that driving thing -- you may step out of your house and office, and driving conditions will seem fine.  But 5 miles down the road could be a completely different story.  If you are on Twitter, and you absolutely have to drive Monday or Monday night, keep your Twitter feed on Madison Traffic, 511 Wisconsin and Ready Wisconsin for timely updates on weather, traffic and crashes. 

If ice accumulates to more than a tenth of an inch -- which is likely in parts of South-Central and Southwestern Wisconsin, power outages and downed trees are also a distinct possibility.  So today is the day to get prepared for that eventuality.  Ice of a quarter inch or more is considered an extreme ice storm, and that can't be ruled out in some locations.

Mateo Earth models show New Glarus right in the sleet/ice (yellow) band for a lengthy period of time.  Here's 1:00pm Monday and 1:00am Tuesday:

Okay, I'm sure that's a lot more than you wanted to know about freezing rain.  What about the snow?

We can be pretty sure that snow amounts will be lowest in the far Southeastern part of the state, and highest in the Northwest.  Some locations won't see any snow at all.  In the New Glarus and Madison areas, I think we see 2-4 inches as the low passes to the east on Monday night.  That's not much, unless there's a layer of ice and sleet underneath it.  

So here's my official New Glarus forecast, subject to change as I watch the low progress today:

Monday:  Sleet and freezing rain starting mid-morning, changing to all rain for a brief time in the early afternoon, and changing back to sleet and freezing rain around sunset.  Total sleet and ice accumulation about 0.15 inches.  High 33.  Strong east wind of 15-25 MPH becoming northeast late in the day, with gusts up to 40 MPH.

Monday night:  Sleet turning to snow in the evening, accumulating 2-4 inches before diminishing late.  Winds remaining strong and gusty from the northeast, creating blowing and drifting snow.  Low 29.  

If you're traveling to the north or northwest Monday or Tuesday, look for snow totals as high as 8-14 inches toward the Eau Claire area.  

FYI, there is another chance of light snow on Wednesday, as a weaker system approaches from the west.  Late this week, we'll see our coldest temperatures of the season, with highs only getting into the teens in most places.

I'll take your questions both here and on Facebook!  And remember, you heard about this storm on Rippeology before anyone else was talking about it.  First post was last Tuesday morning on Facebook.  Just sayin'.