Weekend Storm Fizzles; Monday Night Storm Strengthens

For the meteorologically impatient, like my friend John Urban, my 6pm Monday to Noon Tuesday snowfall forecast is divided into two predictions:

Madison airport: 3.8 inches (up slightly from the 3.4 I projected Friday)
Platteville: 5.6 inches 

I'm including Platteville here because it appears to be in the heaviest band of snow for this Monday night Alberta Clipper.

A quick look back at the weekend storm: we fell far short of the precipitation projection (I had 3.1 inches; the Madison total that will be released later today will probably be between 1.0 and 1.5).  I'm pleased that other elements of my forecast -- the two rounds of precipitation, the temperatures, the wind -- were spot on.

On Thursday, I mentioned 4 components of a winter storm that I watch for:

Storm Track: very favorable
Storm Intensity: moderately favorable
Surface Temperature: very favorable
Speed of Track: somewhat favorable

"Storm Intensity" ended up being the downfall of last night's forecast.  The low didn't deepen nearly as much as projected (pressure is 29.80 as of this moment), which means it didn't have the strength to produce significant snow on the back (northwest) side of it.  Thus is the peril of winter forecasting for southern Wisconsin.

On Friday, I predicted a second storm for Monday night, and that storm still appears likely.  The National Weather Service has issued a Winter Storm Watch for far southwestern Wisconsin (Iowa, Lafayette, Green and Rock Counties).  The Watch runs 6pm Monday to Noon Tuesday.

The bulk of the snow will fall in the overnight hours Monday into Tuesday.  A few maps:

The MeteoEarth projection, just after midnight Monday night (click to enlarge)

NOAA probability of 4"+ of snow in the 24-hour period ending Noon Tuesday.

NWS precipitation model for 3am Tuesday.

In the last 24 hours, models have ticked the center of the storm further south and west, which is why I place Platteville roughly in the heaviest snow band.

As I mentioned Friday, the weather story behind this storm will be temperatures.  An arctic blast means that after sunset tonight, our temperatures will range from -15 to +10 through Thursday.  Tuesday and Wednesday will feel especially cold because of wind, as wind chills dip to -25 to -40.

Because of the Monday night snow and Tuesday morning wind/cold, don't be surprised if schools either delay or close on Tuesday.  The morning commute on Tuesday won't be fun, as wind whips the new snow.

Temperatures will be close to normal again by Sunday, with only slight chances of snow during the day Thursday and late Saturday.

I'll update the Monday night snow total if conditions change.

Weekend Forecast (Plus Bonus Monday/Tuesday Preview)

Since I didn't already have enough weather models to geek out on...

I'm using a new forecasting and imaging tool that I think you're going to like.  It's called MeteoEarth, and it allows me to show you time-stamped snapshots of what our weather might look like at any given point in time.  But before we get to the pretty new pictures, here's a quick glance at the next 4 days:

Saturday:  Wintry mix early, then a break in precipitation, then evening and overnight snow.

Sunday:  Gusty winds, cold, snow showers ending, blowing snow throughout the day, some clearing at night.

Monday:  Very cold with snow developing late evening and overnight.

Tuesday:  Snow ending by Noon, continued cold.

So that's two separate storm systems -- one coming from the southwest Saturday into Sunday, and another coming from Canada on Monday night.

I have to say this first about the weekend storm: it strikes me as nearly irresponsible that the National Weather service office out of Sullivan, WI has not issued any weather advisories for the southeastern half of the state.  They still might, but with the mix of precipitation in the forecast and the real potential for travel hazards, they should have done it by now.  Just sayin.'

OK, let's get to the detail...

The weekend storm is setting up just as I described it yesterday, with two exceptions:  1) precipitation Saturday into Sunday will fall in two rounds, not one, and; 2)  the first round of precipitation may include sleet and/or freezing rain.

That first round starts tomorrow morning as the low brings warm and moist air up from the south.  That warm air aloft will override the cooler air at the surface, causing rain to form in the upper atmosphere.  But with temperatures still below freezing at the surface, that precipitation will fall as either sleet or freezing rain.  Expect this first round of precipitation to essentially last from 6:00am to Noon Saturday.  This snapshot from MeteoEarth shows the leading edge of precipitation coming from the south before sunrise tomorrow morning.  (Remember you can click on any image to enlarge.  Also note future time stamps in the upper right of the MeteoEarth images).

After that first batch of precipitation goes through, we'll get into a brief dry zone.  Skies will remain cloudy and temperatures will fluctuate within only 2 degrees of freezing -- about 30-34 degrees.  As the low passes to our east late tomorrow evening, snow will wrap in behind it, giving us a 6-9 hour period of light to moderate snowfall Saturday night into Sunday morning.

Here's the overnight image for early Sunday morning:

My snowfall prediction, 6pm Saturday to Noon Sunday:  3.1 inches.  Totals will be higher to the northeast (Fox Valley area) and lower to the west/northwest (La Crosse area).

So far, I'm only seeing one projection that thinks there could be a heavier band of snow in southern Wisconsin.

That orange band over southern Wisconsin is showing an 80% probability of 4 inches or more by Noon Sunday.  The same model suggests a 40% probability of 6 inches or more in that same period.  As I mentioned yesterday, these types of storms often contain narrow bands of heavier snow, but they're nearly impossible to pinpoint geographically.  So, I'm generally discounting the model above.

Behind that system comes the first of 3 shots of cold air that we'll experience in the next 5-7 days.  This image from MeteoEarth shows strong north winds on Sunday, as indicated by the closeness of the isobars (or equal lines of barometric pressure):

That cold air gets reinforced again Monday, then again Tuesday night.  Look for highs only in the single digits Monday and Tuesday, and perhaps barely reaching zero on Wednesday.

In between those arctic blasts will come a second snowstorm on Monday night.  This "Alberta Clipper" will produce a prolonged period of light snow from about midnight Monday to Noon Tuesday.  Other forecasters have snow starting earlier in the late afternoon or evening Monday, but I can't find a single computer model to support that.

Here's what overnight Monday looks like, according to MeteoEarth.

My snowfall prediction, midnight Monday to Noon Tuesday: 3.4 inches.  This time, look for slightly higher totals toward La Crosse, and slightly lower totals toward Green Bay.

Long-range models look dry (but bitterly cold) for the rest of next week, with the next potential snowstorm late next weekend.  I'll watch that for those of you planning on going to Lambeau next Sunday for the Packers playoff game.

As always, if and when things change, I'll let you know!

Yup, It's Going to Snow

Happy New Year from Rippeology!

Here's hoping you had a chance to enjoy to the 24th warmest and 4th driest December on record in Madison.  Both temperature and precipitation trends are about to turn in the opposite direction.

Southern Wisconsin will see its first winter storm of the new year this weekend, and a pretty strong cold blast will follow in its wake.  Here's how I'm sizing up the 4 most important factors in winter storm development, specifically for our area:

Storm Track: very favorable
Storm Intensity: moderately favorable
Surface Temperature: very favorable
Speed of Track: somewhat favorable

So, the two things that prevent this storm from being a real whopper are A) intensity, or barometric pressure of the low; and B) the speed with which the storm will come and go.

Nonetheless, a low pressure system is taking shape right now in west Texas.  It's a somewhat disorganized storm at the moment, and will take another 36-48 hours to really wind up.  When it does, it'll head northeast toward Chicago.  If you need a refresher on Texas Panhandle Hooks, see this post from mid-December.

Based on current path, I think this means 3-5" of snow for southern Wisconsin, starting around 6pm Saturday and finishing up around Noon Sunday.  As is always the case with panhandle hooks, narrow bands of heavier snow can pad the totals in localized areas.

Here's the probability map of 4" or more of snow, ending Sunday afternoon.

So, far southern Wisconsin is in that 50/50 area of 4" or more.  If you're in far southeastern Wisconsin, you may actually see some mixed precipitation at the storm's outset, but locations near Lake Michigan may also get some lake effect snow as the low pulls northeast into Canada and winds switch to the northeast.

This model shows the anticipated position of the low over northern Illinois overnight Saturday.  Models have been gradually ticking the low farther west over the last few days.

This model supports that track, meaning that for the most part, there's far less disagreement about storm track than most storms we've seen this year.

It's possible that the National Weather Service out of Sullivan may issue a Winter Storm Watch for our area.  If they're going to do that, it would likely be issued with this afternoon's 3:35pm forecast, or tomorrow morning's 3:35am forecast.  Issuing the watch is a strong indicator of computer model consistency, and therefore, forecast confidence.

So there you have it.  On a side note, I'll be tracking my own forecast accuracy throughout 2015.  For winter storms, I'll post a specific snow amount (to a tenth of an inch) 24 hours before the storm starts.  My goal is to be within 1.5 inches on these projections (based on official Madison airport totals).  You'll see running accuracy results in the right sidebar of the blog throughout the year. 

Also for 2015: more video forecasts from Rippeology!

Watch for the final snow prediction here and on Facebook, to be posted Friday afternoon.

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.