Updraft: November 29, 2012 Archive

"Pineapple Express" kicks in: Epic California storm drives Minnesota thaw

Posted at 7:10 AM on November 29, 2012 by Paul Huttner (2 Comments)

Major Pacific storm series invading West Coast

6" to 12"+ of rain expected in northern California in the next few days

100" of snowfall possible above 8,500 feet in the Sierra & Cascades next 7 days?

Record floods, mudslide & avalanche danger increasing

Storm's effects reach to Minnesota & Canada

4 day thaw ahead for Minnesota Friday through Monday

+20 degrees vs. average - near record warmth by Monday

Heavy snow 12" to 18" possible by Tuesday near Lake Winnipeg?

-It never rains in California
But girl don't they warn ya
It pours, man it pours

ALBERT HAMMOND
"It Never Rains In Southern California"

A 2006 heavy rain event drives the Stillaguamish River at Granite Falls, to 9 feet above flood stage
Image: Walter Siegmund

Epic "Mega Storm" slams California

This may be your lead on national newscasts by this weekend.

The opening salvo of the 2012-'13 winter storm season is slamming the West Coast today with torrential rain, fierce wind and prolific mountain snow.

Image: WxUnderground

The system will likely deliver some incredible, flood spawning rainfall totals up to 1 foot in some areas in the next 5 days.

Source: NOAA/HPC

In the mountains, heavy snow will fall above 8,500 feet. Since this is a relatively warm early season system, snow levels will remain relatively high. Winter Storm Warnings are flying for the High Sierra.

It's the first wave in a series of low pressure systems that will ram the West Coast through early next week. The storms are being fueled by the infamous "Pineapple Express" - a plume of tropical moisture that injects copious rainfall enhancing moisture into storms that strike the western USA.

Wide open "fire hose"

NOAA's "Integrated Water Vapor Loop" forecast into early next week shows the effects of the snake-like moisture plume as it sprays the West Coast with a series of blasts....like and out of control, wide open fire hose.

Each of "Atmospheric River" events will dump several inches of rain in the valleys, and several feet of snow above 8,500 feet. NOAA elbaorates.

Heavy Precipitation Event Developing in Northern California

Heavy precipitation (Fig. 1) is predicted for Northern California over the next 5 days [for official National Weather Service (NWS) weather forecasts, visit: http://www.wrh.noaa.gov/, and for river forecasts, visit: http://www.cnrfc.noaa.gov/]. As with most extreme precipitation events in the region, this one is associated with a strong atmospheric river (AR).

Just a few of these "Atmospheric River" events produce 30% to 50% of California's average annual precipitation.

The lyrics in the Albert Hammond classic song nailed the meteorology.

Storm will affect Minnesota & southern Canada this weekend:

I wish I could say this system will dump heavy, desperately needed rainfall on Minnesota this weekend. The northerly track will preclude that possibility.

What it will do is pump unseasonably mild air north into the Upper Midwest. I could see 70 in Kansas with this system this weekend, and upper 50s in Minnesota by Monday...a good 20 degrees above average for early December.

Image: NOAA

Cooler weather will follow by Tuesday, but mild temps in the 40s will liekly return by next Wednesday & Thursday.

Image: ECMWF output for Minneapolis from Norwegian Met Institute

On the colder side of the storm, heavy snow will fall in southern Canada either side of Lake Winnipeg. The storm may dump as much as 12" to 18" by Tuesday.

Image: NOAA GFS 120 hour snowfall output via wxcaster.com

The heavy snow cover just north of Minnesota may have implications as we move into early December. Winter storm tracks are notorious for setting up just south of the southern edge of heavy snow cover. I am watching what seems to be a trend toward increasing Minnesota's chances for significant snow...possibly in the December 10th to 13th time frame.

NOAA's GFS model keeps hinting at show chances after December 10th
Image: NOAA via College of DuPage

It's early...but the big storm coming through to the north may be paving the way for future snow in Minnesota.

Stay tuned!

PH

(2 Comments)

Fog & freezing drizzle early Friday; Mega thaw weekend approaches; Snowy rumors next week?

Posted at 6:07 PM on November 29, 2012 by Paul Huttner

40F high at MSP Airport Thursday at 3:12pm

Fog & freezing drizzle possible early Friday AM

40s this weekend as milder air surges north

50s likely on Monday - peak of early "December Thaw"

California storm sending waves of rain and snow ashore through this weekend

Pineapple Express feeding tropical moisture into West Coast storms

A Big Maybe but at least one model hinting at snow chances for Minnesota late next week

Too early to be credible about snow chances next Thursday night/Friday...but worth watching

Icy start Friday?

Things could get a little icy in spots Friday AM in the metro and much of Minnesota.

Low level moisture is pushing north, and fog and some freezing drizzle and a few snowflakes are quite possible. Precip will be light in this mixed weather grab bag Friday morning...but it doesn't take much to ice up a few roads and sidewalks. Be careful driving...and walking early Friday morning.

Poised for the big thaw:

40 felt nice Thursday. It's amazing how good 40 in Minnesota feels after a chilly sub freezing run.

This weekend will feel more like late October or early April at times as milder air pushes north. High will push well into the 40s this weekend from the metro south. It won't shock me to see an eager bank thermometer or two flashing 50F in the metro this weekend.

Source: Iowa State University

By Monday 50s will be widespread in southern Minnesota, and 60F is possible south of the metro.

Image: NOAA

The best chances for rain come Saturday and again Monday...but overall rainfall totals look to be less than .25".

After the thaw the GFS hints we turn colder again next Tuesday as highs fall back into the 30s, but the Euro holds mild air in place with a week long thaw.

Image: Norwegian Met Institute

Either way the brief December chill won't last...warmer air appears ready to ease north again by next Wednesday & Thursday.

Image: Caltech

California storm a boon for snow lovers!

I've been hammering the massive California storm in my posts this week. Here's another angle from my MPR colleague Dr. Mark Seeley in a preview of this week's Weather Talk on how snow lovers will appreciate the massive snow dump. I added the italics.

Topic: A snow lover's forecast

The National Weather Service in Medford, OR issued the following forecast for Mt Shasta in California this weekend. For snow lovers it must have brought all smiles, but look at the wind speeds!

-Friday Snow showers. The snow could be heavy at times. Temperature falling to around 15 by 4pm. Wind chill values as low as -13. Windy, with a south southwest wind 80 to 85 mph decreasing to 70 to 75 mph in the afternoon. Winds could gust as high as 115 mph. Chance of precipitation is 100%. New snow accumulation of 23 to 29 inches possible.

-Friday Night Snow. The snow could be heavy at times. Low around 14.
Wind chill values as low as -13. Windy, with a south southwest wind
70 to 80 mph, with gusts as high as 115 mph. Chance of precipitation is 100%. New snow accumulation of 21 to 27 inches possible.

-Saturday Snow. The snow could be heavy at times. High near 19.
Windy, with a southwest wind 75 to 80 mph, with gusts as high as 115 mph. Chance of precipitation is 100%. New snow accumulation of 22 to
28 inches possible.

-Saturday Night Snow. The snow could be heavy at times. Low around 17. Windy. Chance of precipitation is 100%. New snow accumulation of
29 to 35 inches possible.

-Sunday Snow. The snow could be heavy at times. High near 18. Windy.
Chance of precipitation is 100%. New snow accumulation of 11 to 17 inches possible.

-Sunday Night Snow showers likely. Cloudy, with a low around 9. Windy.

Somehow putting out a forecast of a 12"+ "megastorm" for Minnesota in winter suddenly feels... inadequate.

Rumors of snow late next week?

Call it "A big maybe" at this point.

GFS runs Thursday hinted at some "phasing" of upper air and surface systems near Minnesota late next week. If that happens...and it's a big if a week out...there could be a chance of some significant snow next Thursday night or Friday on Minnesota.

Source: NOAA GFS via College of DuPage

It could also be just a passing forecast model fantasy...especially from the notoriously dicey GFS Model.

Still, the overall pattern suggests something may be in the cards. It's (always) too early for apocalyptic headlines a week out, but this one may be worth watching.

Image: Caltech

Forecasting snow: Tougher than hurricanes

People often ask me "What's the toughest thing to forecast Paul?"

My quick answer is always "snow storms."

Snow systems are highly complex animals. Storms tracks, moisture, temperature profiles and upper air energy all have to come together to get heavy snow. If just one element is missing, or if a storm track moves just 50 miles...or enough warm air works north to raise temperatures 2 degrees...it can be the difference between an inch of rain and a foot of snow.

These big beautiful beasts of winter are challenging to forecast. Forecasting hurricane tracks 3 days out actually proves more accurate than forecasting snowfall totals 3 days ahead.

That's why here at the Weather Lab we use the "24 hour rule."

Before a storm, I'll let you know about potential timing and the relative size of the storm. If there is a potential for significant snow...or heavy snow I'll say that if I think it's credible a few days in advance. That gives you, our customers, good longer range planning capability for a possible event.

As we approach 24 hours before the snow flies, I'll issue an more specific "inches" forecast. Why 24 hours? 24 hours is about where overall forecast accuracy..the "state of the science" that is meteorology...and having adequate time to plan ahead for a storm are "optimized."

You may hear forecasters throwing around multiple "inches forecasts" days in advance. 6" to 12" becomes 3" to 6" becomes 1" to 3" and back again. It gets to the point where that approach has little value...except to entertain and confuse.

The "meteorological reality" is that snowfall forecasting accuracy dramatically increases about 24 hours before the event. Even then, forecasting snow is one of the toughest forecasts we make as meteorologist.

It's also one of the most entertaining things I've ever done in my life. Instant gratification or widespread public ridicule is only a few hours away!

PH