It's Complicated

If you want to skip the set-up and get straight to the 7-day forecast, scroll down.  But don't tell me you did that.

Yup, complicated.

So complicated, in fact, that some forecasts for south-central Wisconsin are warning of the possibility of "several inches" of snow on Christmas Eve day (Channel 3), some are calling for mostly rain and just a bit of snow (Channel 27 among them), and some are being completely non-committal or taking the very unhelpful "maybe" approach to forecasting (like the National Weather Service and The Weather Channel).

NWS goes so far as to whip out the dreaded "significant uncertainty" crap...

Notice how the NWS completely skips over Wednesday in the graphic above, opting to show the easier-to-predict Tuesday and Thursday instead.  Cowards.

The one thing we all agree on is the exact thing that makes it so complicated: low pressure will approach southern Wisconsin from the west on Tuesday, and sometime Tuesday night or early Wednesday, it will combine with another low to the east, strengthen significantly, and then essentially stop in its tracks to our northeast.

Two factors create the "significant uncertainty":

1. The exact track of the first low.  If it moves directly over southern Wisconsin, as the image above and some other forecasts seem to suggest, we'd experience southerly winds on Tuesday and all precipitation would fall as rain.  If it tracks to our south, over northern Illinois, the low would wrap cold air into southern Wisconsin and Tuesday precipitation would fall as snow.

2. Where the intense "combined" low decides to slow down.  If it slows just east of upper Michigan, it drives bands of strong winds and moderate snow behind it, counter-clockwise, from the north, during the day on Wednesday.  If it moves farther to the east, we still get strong winds but less snow.

So there's one thing we can be confident about: wind.  Lots of wind from the north and northwest on Wednesday.  Add some snow into the mix, and travel will be a bitch.

Rippeology sees it thusly:

A strong southerly flow (which will actually start setting up late today) will prevent the first low from dipping too far south, which puts the low over southern Wisconsin on Tuesday.  That means rain Monday night and Tuesday.  Then I see the lows combining near Lake Huron on Tuesday night, slowing, and kicking back the wind and moderate snow on Wednesday.  Winds remain strong on Thursday, until another low approaches from the southwest on Friday to accelerate the storm to the northeast.

We'll get to that Friday low in the 7-day forecast below.

Of the 6 weather models I studied this morning, this one best represents what I expect on Wednesday:

Where I depart from this surface forecast, however, is that I think the combined low is strong enough to kick snow back further to west than what is indicated here.

This NOAA model shows heavier bands of precipitation on the back side of the low:

I tend to favor that line of thinking.  If you'd like to see the full animated loop of the above, taking us from now until Wednesday morning, click here.

I'm putting a lot of focus on Christmas Eve because of travel implications, but it's not the only area of concern in the next 7-10 days.  As we come out of the mild spell that I predicted back on December 2nd and head into a significantly more active weather pattern, there are multiple weather events that could impact southern Wisconsin between now and the new year.  One is that low pressure system I mentioned above for Friday the 26th; another storm could impact us on Monday the 29th.

Here's the 7-day Rippeology forecast for the New Glarus/Madison area:

Today: Mostly cloudy, light winds, high of 33.

Tonight: Cloudy with areas of fog developing.  South winds will squeeze a little moisture out of the upper atmosphere, resulting in some light freezing drizzle later tonight.  Low 26.

Sunday and Sunday night: Still cloudy, with drizzle (daytime) and freezing drizzle (nighttime) continuing.  A few flurries may mix in.  Winds start to increase from the south and southeast.  High Sunday of 37; low Sunday night of 30.

Monday and Monday night: Yup, more clouds. Rain (mostly light) develops late in the day as that first low approaches from the west, and continues through the night.  Breezy.  High Monday of 37; low Monday night of 32.

Tuesday and Tuesday night: Rain decreases for a time during the day as the low passes over southern Wisconsin.  Winds continue to increase from the south, then switch to the northeast at night.  Rain changes to snow late Tuesday night, with up to an inch by morning.  High Tuesday of 38; low Tuesday night of 30.

Christmas Eve: Very windy with snow.  Accumulations of 2-4 inches.  High temperature of 32 early in the day; temperatures fall to the mid 20s by late afternoon.  Snow tapers Wednesday night but strong winds continue, creating some blowing and drifting, especially on east/west roads.  Low Wednesday night of 22.

Christmas Day: Still breezy, with some peaks of sun as the combined low starts to push well into eastern Canada.  High of 29; low Christmas night of 20.

Friday: Winds switch to the south as another system approaches from the southwest.  Becoming cloudy with snow developing late.  I'll update accumulation predictions as we get closer.  High of 31.

Looking farther ahead: another snowstorm is possible early the week after Christmas, followed by colder temperatures.  New Year's Eve could be pretty chilly!

Questions?  Feel free to leave a comment.  As always, when something changes, I'll update it here on the blog.  After all, it's complicated.  And there is significant uncertainty.  :)

Dreaming of a White Christmas?

We might fall just a couple of degrees short of today's 50-degree prediction that I made earlier in the week, since the dense fog isn't really conducive to temperature fluctuation.  Still, I think we'll hit 47 or 48 today, and again tomorrow.  The fog isn't going anywhere anytime soon.

So the mild weather may have you wondering about the chances for a White Christmas in southern Wisconsin.  With 11 days to go, here are the three snow chances I see between now and Christmas Day:

1.  Tuesday afternoon (12/16):  low pressure moving out of the southern plains will bring light rain Monday and Monday night.  As the low moves into southeast Wisconsin Tuesday morning, there is a chance for some snow showers to wrap in behind the system.  Chances are much better in northwest Wisconsin, as it'll take awhile for temperatures to fall after 4 straight days of mild weather.  Rippeology's chance of 1" or more on Tuesday: 30%.

2.  Saturday (12/20):  A couple of days ago, weather models were indicating a potentially strong storm for southern Wisconsin, but as of this morning, those same models are taking that storm on a more southerly track, as pictured here:

Surface forecast for Saturday afternoon (12/20)

This forecast could change again in the next 6 days, but I don't think it will.  Multiple high pressure systems to our north will likely block the southern storm from tracking much farther north than this model predicts now.  Rippeology's chance of 1" or more on Saturday: 30%.

3.  Christmas Eve (12/24):  A system coming out of western Canada (an "Alberta Clipper," for fellow weather geeks) could bring some snow late Tuesday (12/23) into Christmas Eve day.  Generally, these systems bring light, dry snow.  Since many of you (and me) will be traveling on Christmas Eve day, I'll keep a close eye on this.  Again, much can change in 10 days.  Rippeology's chance of 1" or more on Christmas Eve day: 40%.

As for the temperature outlook, there are no indications of major cold outbreaks in the next couple of weeks.  We'll stay at or slightly above normal (which is upper 20s) throughout the next 10 days at least, with only slight variations in either direction.  Nighttime lows will mostly seasonal as well.

I'll update the chances of a White Christmas as forecasts change in the next few days.  In the meantime, feel free to read about the historical chances of a White Christmas over at climate.gov.

A Little Ice, Then A Warm-Up

How does 50-degree weather sound for the middle of December?

We could get there -- potentially for 3 straight days next Friday, Saturday and Sunday -- but we'll have to get through a slow Monday morning commute first.

A weak cold front from the west will go through Wisconsin tonight, bringing a mixed bag of precipitation as temperatures fall just below freezing.  Sleet, snow and light freezing rain are all possible, starting around midnight tonight and going through the morning hours.  A few more flurries behind the system will make Monday feel wintry.

If you get up and see snow on the ground tomorrow morning, test your driveway to see if there's a layer of ice underneath.  Just use a broom to sweep away an area of snow (away from the house) to see if ice lurks beneath.  If you're on Twitter, follow @MadisonTraffic to see what's going on on the roads.

After Monday, the warm-up begins.  Temps will slowly increase throughout the week.  Currently, it looks like sun and a southerly breeze will allow highs to reach into the 50s all weekend, before a new front brings rain late Sunday.  Last December, highs were 24, 23 and 20 for the second weekend of the month.

Boring, Boring, Boring!

I'm guessing 9 out of 10 of you (if there ARE 10 of you reading Rippeology) will be elated with the paragraphs that follow.  The other 10% are probably serious weather geeks like myself.

When I started this blog, I had visions of frequent snowstorms, complex weather patterns to challenge me, polar vortices, canceled school days, watches and warnings.  Stuff I could really sink my meteorological teeth into.

Sure, November was the 12th coldest on record in Madison.  And yes, there were a few threats of snow that turned out to be false alarms.  But if you were reading, you would have known they were false alarms.

December is setting up to be the boringest weather month ever -- little temperature fluctuation, mostly mild, and little precipitation.  ZERO. FUN. AT. ALL.

Here's why...

Wisconsin is currently nestled between two winter jet streams.  The jet to the north is keeping all of the cold air well up into Canada.  The jet to the south is keeping all the moisture from reaching the Midwest.  And both are far enough away from us to take winter storms in a different direction.

Here's a great example of what that pattern looks like in the upper atmosphere.  This forecast jet stream is for this Saturday.  Because we're stuck between these two jets, our winds will come predominantly from the west for the foreseeable future -- sometimes switching to the northwest (but without major cold outbreaks), and sometimes switching to the southwest (but without any moisture to speak of).

How long will it last?  Right now, I'd say 2-3 weeks.  Our average high temperature ranges 29-35 during that period, and westerly winds will allow temperatures to surpass those averages for the most part. 

So for the next 14 days (at a minimum), expect above average temps and below average precipitation.  Like I said, boring.

But if anything should change, you'll hear it here first.

Oh, and for those of you who were kind enough to try adding my name to this Weatherist poll, I am humbled by your confidence.  In case you're curious, Doogs got my vote.