Updraft: March 24, 2011 Archive

Watching the flood: Cold may help prevent higher crests

Posted at 9:42 AM on March 24, 2011 by Paul Huttner (2 Comments)
Filed under: Crow River, Flooding, Minnesota River, Mississippi River, St. Croix River, Winter/spring 2011

The cold weather we're feeling may have a benefit. Slightly lower flood forecasts and river levels.

Before I launch into the potentially slightly good news, let's be clear about one thing. This is going to be (and already is) a major flood for many river locations in Minnesota, Wisconsin & North Dakota.

We've already lost one brave life fighting the rising waters. Roads are already closed or washed out. Thousands of hard working public employees and river residents are working hard building dikes and levees to protect us all from the rising water.

That said, there are some rays of hope regarding the flood scenario late this week.

1) Snow, not rain:

The fact that the second half of out Tuesday-Wednesday storm was snow and not rain is good news. Instead of running directly into area rivers, Wednesday's snow is still white sitting on your lawn. This is good news since we didn't add any more runoff once the rain changed to snow.

2) Sub freezing air:

We may be tempted to bemoan yet another frigid Canadian high pressure center pouring south into Minnesota after this rigorous winter. But that cold air we're feeling has a benefit. The sub-freezing air means the snow is still frozen on the ground, and not running into already swollen rivers.

Mostly sub freezing next few days. (Click to enlarge)

The freeze will "lock up" most of the potential runoff the next few days. This will give rivers a chance to move water downstream, without adding copious amounts of "new" runoff that would further spike river levels.

3) Dry forecast through Monday?

Our friendly neighborhood Canadian high pressure center will provide another benefit with regard to the flood scenario. It looks like it may steer another storm system to our south this weekend, and keep us dry through Monday.

That should give us 5 days to dry out without adding additional moisture to the flood scenario.

Latest flood forecasts: Levels down 1 to 2 feet!

While most rivers are still forecast to reach major flood stage this weekend or next week, the trend is encouraging.

Today's flood forecasts from the NCRFC lower crests between 1 and 2 feet for many area rivers. (Keep in mind the river level "number" is within a greater forecast "range" of possibility.)

Here's the latest:

Crow @ Delano: Projected crest at 19.1' Saturday-Sunday.
(Down from 20.5' or 1.4' lower!)

Minnesota River @ Mankato: Projected crest 26' Saturday.
(Down from 27' or 1' lower)

Minnesota @ Henderson: Projected crest 737.7' Monday-Tuesday.
(Down from 738.5')

Minnesota @ Jordan: Projected crest 32' Monday-Tuesday.
(Down from 33')

Minnesota @ Savage & Shakopee:
(Also down about 1 foot below previous crest forecast)

Mississippi @ St. Paul: Projected rise to 20.4' next Wednesday.
(Down from 22.4' or 2.4' lower than previous projection!)

St. Croix @ Stillwater: Projected rise to 86.13' next Wednesday.
(Down from 87.8' or 1.6 feet)

Next snow Tuesday?

The GFS is hinting that a low pressure system may track this way by late Monday night or Tuesday of next week. That could be our next shot of snow, unless the system steers south. It's way early to say this system will hit us for sure...just a possibility at this point.

Tuesday snow chance?

Cold lingers next week?

It looks like we may end up colder than average through next week with highs mostly in the 30s and sub freezing nights.

Warmer next weekend?

There is still some indication temps may rebound nicely the weekend of April 2nd & 3rd. Highs in the 50s are possible, but we'll have to see if we get that warm as time evolves.

Potential rain (& snow?) week of April 4th & 5th?

Okay this is wayyy out on the proverbial weather limb. The GFS is hinting at the potential for significant rain possibly ending as snow during the April 4-5 time frame. Too early to make a call here (could be pure model fantasy at this point)...but the trend has been evident in more than one model run.

Double crest?

Add it all up, and you may have a "double crest" on many area rivers. One crest may occur this weekend or next week, and another could happen in the next 2-3 weeks.

This might not be a bad thing. It could keep overall river levels high for a longer period of time, but avoid a potentially higher flood crest in the process.

The downside of prolonged elevated river levels is that we're more vulnerable to a big storm that could dump heavy rain as the weeks go by.

Bottom line:

The cold is probably good news in the short run, but prolonged high river levels leave us vulnerable to flooding rains this spring.

Stay tuned!

PH

(2 Comments)

Breaking: Flood forecasts lowered again!

Posted at 7:39 PM on March 24, 2011 by Paul Huttner (4 Comments)
Filed under: Crow River, Flooding, Minnesota River, Mississippi River, St. Croix River, Winter/spring 2011

Here's some potentially good news in a sea of bad weather this week.

Most river level forecasts have been revised lower in the next week.

The latest updates from the hydrologists at the NCRFC in Chanhassen have lowered river level forecasts for some river locations as much as 3.5 feet from forecasts earlier this week.

The changes are largely due to the latest round of cold weather this week. The cold "locks up" moisture by freezing it in place on the landscape, instead of creating the runoff that would happen with above freezing temps.

You can see all the latest river data here, but here are a few select hydrographs for some key river points in southern Minnesota.

Keep in mind that specific forecast river crest "numbers" and timing are best estimates within a wider overall forecast range. Forecasts will likey be modified in the coming days as new data is fed into hydrologic models.

Mississippi @ St. Paul: Forecast rise to 18.9' next week.
(Down 3.5 feet from earlier forecast!)

Crow River @ Delano: Forecast crest at 18.8' Saturday night.
(Down 1.7 feet from earlier forecast) Forecast to fall below 17 feet again next week!

Minnesota River @ Mankato: Forecast crest at 25' Saturday.
(Down 2 feet from forecast earlier this week.)

Minnesota @ Henderson: Forecast crest at 737.4' Sunday.
(Down 1.1 feet from forecast earlier this week)

Minnesota @ Jordan: Forecast crest at 32' Monday & Tuesday.
(Down 1 foot from earlier forecast)

Minnesota @ Shakopee: Forecast crest 715.8' Tuesday & Wednesday.
(Down 1.2 feet from earlier forecasts)

Minnesota @ Savage: Forecast crest at 713.4 Thursday.
(Down from 0.6' from earlier forecasts)

St. Criox @ Stillwater: Forecast rise to 87.1' Thursday.
(Down 0.7' from earlier forecasts)

Let's hope these latest forecasts reflect an overall trend that keeps floodwaters a little more in check the next few days.

Next snow Tuesday?

I know, I know. I hate to even mention it. But after what looks like a few much needed dry days through the weekend, it looks like our next chance of snow could be on the horizon.

Remember models can and often do change dramatically 5 days out.

The GFS insists on brining another potentially potent low pressure system into the Upper Midwest by next Monday night and Tuesday. Take a deep breath and look at the meteogram below.

(Click to enlarge...if you dare)

Yep. That's 8+ inches of snow on the chart for the 12z morning run, but less from the 18z afternoon run. Remember, we don't issue snowfall forecasts 5 days in advance and there is some indication that system could steer south. Also the GFS has grossly overforecast snow totals for the last few events. And the European model seems to suggest the southward track which could leave Minnesota high and (thankfully) dry next week.

But be aware that there is at least the possibility of significant snow next Tuesday.

Hang in there; it still looks warmer by next weekend!

PH

(4 Comments)