Saturday “slop storm” still on track; Mixed bag of rain/ ice/sleet & snow?

37F afternoon high at MSP Tursday

+7 degrees temps vs. average so far for December 2012

12.3" season snowfall so far at MSP Airport

-2.5" vs. average so far

8" current snow depth at MSP Airport

"Slop Storm" still on the way for Minnesota Saturday

"Mixed phase" precip with this system

Freezing rain, rain, sleet & wet snow all possible

"Temperature Critical" Precip type depends on temp variations as little as 1 degree F Saturday

ALL OF THE SOLUTIONS STILL SUGGEST GOOD WARMING IN

THE BOTTOM 5K FT OR SO OF THE PROFILE AHEAD OF THE SYSTEM...

MAKING PCPN-TYPE ISSUES THE MAIN FORECAST CHALLENGE. THERE ARE

DIFFERENCES IN THE DEGREE TO WHICH THE MODELS WARM THINGS ALOFT...

AND EQUALLY IF NOT MORE IMPORTANT DIFFERENCES IN HOW THEY HANDLE

NEAR SURFACE TEMPERATURES

-Twin Cities NWS late Thursday forecast discussion regarding Saturay's incoming system

Staying the course:

Thursday's model runs did little to change the thinking on Saturday's approaching messy weather system.

The basic elements remain the same. A Colorado low with temps near freezing brings a mixed bag of wet sloppy precip north. Ice, rain, sleet, snow? All of the above are likely Saturday in Minnesota. The only area to escape the mess will be northwest Minnesota where little or no precip will fall.

Watching the next system:

All weather eyes are pointed southwest in the next 48 hours as our next weathermaker approaches.

Image: Twin Cities NWS

What would normally be a classic "Colorado Low" with heavy snow will track from near Omaha to Des Moines to La Crosse Saturday. Climatologically speaking, this track is ideal for heavy snow in the Twin Cities and southern Minnesota. It's mid-December, and we should be talking about a system that's all snow...but not this time.

All the ingredients for a major winter storm are in place, except one. A decent pool of Arctic air behind the system.

The lack of cold air in place means mixed precip types, and increased difficulty in pinpointing snowfall totals with the system. Looking for a clear cut system with all snowfall and a 10:1 snow:liquid ratio with an "easy" snow forecast? Not this time folks.

So you want to be a meteorologist, huh?

Here's what we know...and what we don't know about Saturday's approaching weather system at this hour.

What the models agree on:

1) Storm Track: A moderately strong surface low pressure system will track along an Omaha-Des Moines-La Crosse-Green Bay line Saturday. This is a favored track for precip in southern Minnesota. Confidence near 100%

Image: NOAA HPC

2) Precipitation: We're going to get precipitation Saturday.

Confidence near 100%

3) Timing: A mixed bag of freezing rain & sleet should begin in southern Minnesota overnight Friday night, and reach the metro by about 6am Saturday, and last through about 9pm Saturday evening. Overall we're looking at about 12-15 hours of precip. Confidence 90%

NAM model shows a solid precip sheild moving into Minnesota at 6am Saturday morning.

Image: College of DuPage

4) Precip totals: There is less agreement on precip totals with this system for the Twin Cities metro and much of southern Minnesota.

Image: Iowa State University

Here is the latest model precip output.

NAM .80"

GFS .43"

Euro .55"

Confidence 75%

What we don't know: (yet)

1) Precipitation type:

The thermal profile (temp layout) of the lower mile of the atmosphere will be critical with this system.

Temps in the lowest 5,000 feet look to hover near freezing, with a layer of above freezing air between the surface and 5kft. That should bring the initial waves of precip in as rain. With temps (just) below freezing at ground level early Saturday AM that could turn much of southern Minnesota and the metro into a skating rink early Saturday morning.

Image: NOAA NAM depiction of possible rain-snow line at noon Saturday

Sleet and even just plain old rain is possible as temps warm to just above freezing at ground level as Saturday morning progresses.

Precip type confidence 50%

2) Changeover time to snow & snowfall totals:

One thing that's pretty clear is that the precip should changeover to all snow at some point Saturday. When it does so will determine how much snow any one location gets Saturday.

The latest NAM runs (06Z and 12Z today) strongly suggest an earlier change to a heavy wet snow Saturday AM...probably by 9am for the metro and most of southern Minnesota.

If that early changeover happens, we are looking at several inches of heavy wet snow Saturday, with some pretty decent snowfall rates.

The GFS is not bullish at all about rushing the change to snow...and paints a scenario with mostly mixed precip and very little snowfall.

Image: Iowa State University

The Euro has leaned colder for most of the system, but gave ground to warming and the notion of mixed precip types in the late overnight run.

Image: Norwegian Met Institute

Changeover time/snowfall totals confidence 30%

To my eye at this point, the NAM appears to be a reasonable looking solution, which means my weather spidey senses are leaning a little more toward the early changeover/heavier snow scenario at this point.

In any scenario it looks like the heaviet snow band (up to 6"?) could set up from eastern South Dakota through Brainerd to the North Shore where cold air may not be an issue.

Image: NAM snowfall via wxcaster.com

Stay tuned.

IPCC too conservative on climate change predictions?

Some have criticised IPCC reports for "alarmist" predicitons about future climate warming and effects. Now it appears the IPCC projections were too conservative.

Heres' a great summary of "then and now" from Climate Central and The Daily Climate:

Temperature

IPCC models use the emission scenarios discussed above to estimate average global temperature increases by the year 2100.

Projection: The IPCC's 2007 assessment projected a worst-case temperature rise of 4.3° to 11.5°F, with a high probability of 7.2°F.

Reality: We are currently on track for a rise of between 6.3° and 13.3°F, with a high probability of an increase of 9.4°F by 2100, according to the Massachusetts Institute of Technology. Other modelers are getting similar results, including a study published earlier this month by the Global Carbon Project consortium confirming the likelihood of a 9°F rise.

Why the miss? IPCC emission scenarios underestimated global CO2 emission rates, which means temperature rates were underestimated too. And it could get worse: IPCC projections haven't included likely feedbacks such as large-scale melting of Arctic permafrost and subsequent release of large quantities of CO2 and methane, a greenhouse gas 20 times more potent, albeit shorter lived, in the atmosphere than carbon dioxide

.

Projection: The IPCC has always confidently projected that the Arctic sea ice pack was safe at least until 2050 or well beyond 2100.

Reality: Summer sea ice is thinning faster than every climate projection, and today

scientists predict a largely ice-free Arctic Ocean in years, not decades. Last summer, Arctic sea ice extent plummeted to 1.32 million square miles, the lowest level ever recorded - 50 percent below the long-term 1979 to 2000 average.

Why the miss? For scientists, it is increasingly clear that the models are under-predicting the rate of sea ice retreat because they are missing key real-world interactions.

"Sea ice modelers have speculated that the 2007 minimum was an aberration... a matter of random variability, noise in the system, that sea ice would recover.... That no longer looks tenable," says Penn State scientist and IPCC contributor Michael Mann. "It is a stunning reminder that uncertainty doesn't always act in our favor."

PH