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.