Updraft: March 31, 2011 Archive

Light rain/snow today; Bigger storm Sunday/Monday!

Posted at 9:17 AM on March 31, 2011 by Paul Huttner
Filed under: Winter storms, Winter/spring 2011

Two distinct weathermakers are on the map and taking aim at Minnesota.

The first one is already here, with a mixed bag of generally light rain and snow showers. A weak low pressure system is squeezing out lighter precip amounts today/tonight.

Low pressure "trof" moving east today. (Click all images to enlarge)

It looks like precip totals will be around or under .25" by Friday in most areas.

Morning Twin Cities radar loop shows spotty rian snow mix.

-Current Twin Cities radar loop here.

With temperatures hovering around or above freezing from the ground to around 5,000 feet above ground today, expect a rain snow mix that could trend toward all snow tonight. With temps above freezing at ground level, it will be difficult for any snow that does fall to accumulate much more than a slushy coating.

NAM snowfall: Slushy coating north?

Friday & Saturday: Sun returns

Look for the sun to make a return by Friday afternoon in most areas. Saturday looks downright nice, with plenty of sun and highs pushing 50 Saturday afternoon.

Potent storm Sunday & Monday:

The next "big" weathermaker moves into the Upper Midwest Sunday.

A strong hybrid late winter-early spring low pressure system will track eastward out of the Rockies toward the Upper Midwest Sunday. It appears a band of precip will push north into SW Minnesota Sunday morning, and overrun the state Sunday.

GFS places surface low in Kansas and pushes heavy precip into Minnesota Sunday.

As I sift through model data this morning to try and see what's credible, It looks to this forecaster right now like enough mild air will push north that the system will produce mostly rain from the metro south Sunday. Rain could be moderate to heavy at times...and there are indications that rainfall totals could exceed .50" to 1+" in some areas of southern Minnesota Sunday.

Over an inch of liquid precip (some as snow) Sunday & Monday?

It appears cold enough for a transition to mostly snow just north of the metro and toward Fargo, Brainerd & Duluth Sunday. The snow could be heavy in central & northern Minnesota. At this time the heavy snow axis seems to be focused on and north of a Fargo-Brainerd-Duluth line.

The GFS is cranking out some impressive (downright scary?) early snowfall numbers for Brainerd (20.2") & Duluth (19.6").

GFS: Some big numbers for Brainerd!

As the system moves by and cold air is drawn south Monday, it appears rain will change to snow statewide, including the greater Twin Cities metro. The snow could be heavy, and wind driven Monday.

Changeable forecast?

The Sunday-Monday system looks good (or bad) on paper at this point. I'd say there is a better than 50% chance we're going to get a potent storm. But keep in mind that the error margin 4 to5 days out for Midwest surface lows can often exceed the width of the heavy snow band.

Translation? A shift of 50 to 100 miles in the track of the surface low track or thermal profile of the storm can change rain to snow...and push the potential heavy snow band north or south in a hurry.

**There is some model data suggesting that the metro could fall within the heavy snow band Sunday & Monday. At this time, it is just too early to say with any credibility exactly where the heavy snow will fall, and who will get mostly rain Sunday.**

The storm system is well out over the north Pacific today, and will not enter the USA upper air (weather baloon) grid until Saturday. When it moves over the USA, the denser observation newtork may get a better handle on track & thermal profile.

Bottom line: There is the potential for a major hybrid winter/spring storm Sunday & Monday in the eastern Dakotas, Minnesota & Wisconsin. Plan accordingly.

Stay tuned for changes and updates as we get new model runs in the next few days.

PH

Weekend storm trends rainy? Floods, gravity waves, ISS

Posted at 6:18 PM on March 31, 2011 by Paul Huttner (1 Comments)
Filed under: Crow River, Flooding, Gravity waves, Minnesota River, Mississippi River, Red River, Snow, Winter storms, Winter/spring 2011

The latest model runs are trending toward a "mostly rainy" scenario for the metro with our incoming Sunday storm.

In the meantime, there's a mix of weather ahead...including a nice day Saturday!

Metro & greater Minnesota forecast:

Overnight & early Friday: Mix of rain showers and maybe a few wet snowflakes early Friday. Low near 33.

Friday PM: Trending sunnier & milder. High near 43. Light west wind.

Saturday: Best day of the weekend! Mostly sunny & milder. High near 50.

Sunday: Rain likely, possible heavy at times. Could start as wet snow, changing to all rain metro. Heavy wet snow possible Brainerd & Duluth. High near 47 metro, upper 30s north.

Monday: Windy. Rain changes to snow. Significant snow totals possible, especially north. Temps upper 30s & lower 40s.

Sunday rain?

The latest model trends support the notion of mostly rain Sunday from the Twin Cities south. There is some indication that it may be cold enough at the onset of precip early Sunday to be all snow...and maybe produce an inch or two before enough mild air surges north ahead of the low to change precip to all rain.

GFS brings precip Sunday.

Both the GFS & Euro models have shifted milder air north, supporting a mostly rain solution for Sunday. The latest GFS run is even hinting that mild air could remain in place much of Monday, keeping precip mostly rain from the metro south until late in the event Monday night.

Big rain totals?

The GFS is hinting at ran totals over .50" and maybe 1" or higher. Keep in mind the GFS has (wildly) over forecast rain/snow totals in the past few storms.

NAM painting heavy rainfall totals Sunday.

Heavy snow north?

Early indications are the rain snow line could set up close to Brainerd or Duluth. This could mean some heavy snow in these areas if it stays all snow. There is the potential for an early April snowstorm up north. There is also the chance mild air could shift even further north.

Bottom line? It's still too early to make any high probability predictions for potential snowfall totals at this point. You'll see some scary (and probably overblown) numbers thrown out...but early spring storms have a way of changing at the last minute.

As we say in the weather biz...stay tuned.

Rivers falling for now:

Most area rivers continue to fall late this week and into the weekend. In some areas river levels will drop 2 to 3 feet from crests earlier this week. This is good news, since it will give rivers some "breathing room" before the next wave of rain can potentially raise river levels again next week.

The "Renegade" at Valleyfair in Shakopee soaks in floodwaters.

You can get all the latest AHPS river info here, but some creative folks at MPR have also put together an excellent "flood aggregator" blog called "Floods '11" here. Check out the blog for some of the latest news related flood items & photos.

Anatomy of a "gravity wave"

We're learning more about mysterious "gravity waves" which are sometimes observed with severe weather outbreaks. These powerful, rolling atmospheric waves seem to supercharge thunderstorm clusters. Details from the UW Madison CIMSS Satellite Blog:

Mid-tropospheric gravity waves upwind of intense convection:

"McIDAS images of 4-km resolution GOES-13 6.5 µm water vapor channel data (above; click image to play animation) showed a well-defined warm/dry "arc" feature (denoted by the brighter yellow color enhancement) just upwind of a large Mesoscale Convective System (MCS) that was moving eastward along the northern Gulf of Mexico and the adjacent Gulf Coast states on 30 March 2011. The MCS eventually produced a number of reports of damaging winds, large hail, and tornadoes across northern Florida. Also note that a subtle signature of what appeared to be gravity waves could be seen within portions of this warm/dry arc feature (especially in the southern portion, over the Gulf of Mexico).

AWIPS images of 1-km resolution MODIS 6.7 µm water vapor channel data (below) offered a more detailed view of the packet of gravity waves that was associated with the southern portion of the dry arc feature. This warm/dry arc seen on the water vapor imagery could have been a signature of a region of strong compensating subsidence along the rear edge of the intense deep convection.

A number of pilot reports of moderate turbulence were co-located within this warm/dry arc feature seen on the water vapor imagery... There was also a report of severe turbulence along the northern portion of the arc feature as it moved over far southern Alabama at 17:35 UTC. This supports the idea that the warm/dry arc was likely a signature of strong subsidence in the wake of the MCS.

All of the above satellite evidence suggests that the gravity waves seen on the water vapor imagery were not surface-based, but were located at a higher altitude within the middle troposphere."

ISS sightings ahead:

Skies may be cloudy Friday morning, but Saturday should provide a good opportunity to see the brightly illuminated International Space Station (ISS).

ISS sightings for Minneapolis.

You can enter your zip code to get precise sighting times here.

Mysteries of thundersnow?

I don't know if we'll see or hear any "thundersnow" with the system over the weekend, but NASA has some interesting info on a "lucky" encounter with thundersnow here.

TWC's Jim Cantore's "thundersnow moment."

"Walt Petersen and Kevin Knupp have traveled far and wide to study winter storms. They never dreamed that the most extraordinary one they'd see - featuring freakish thundersnow, a 50-mile long lightning bolt, and almost a dozen gravity waves -- would erupt in their own back yards. The storm hit Huntsville, Alabama, on the evening of January 9th.

"This incredible storm rolled right over the National Space Science and Technology Center where we work," says Knupp. "What luck!"

Snowstorms usually slip in silently, with soft snowflakes drifting noiselessly to Earth. Yet this Alabama snowstorm swept in with the fanfare of lightning and the growl of thunder.

Eyewitness Steve Coulter described the night's events: "It was as if a wizard was hurling lightning behind a huge white curtain. The flashes, muted inside thick, low hanging clouds, glowed purplish blue, like light through a prism. And then the thunder rumbled deep and low. This was one of the most beautiful things I've ever experienced.'"

PH

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