From the Lee Side

The Ice Boom across Lake Erie: Not Much Action This Winter

By: 24hourprof, 6:34 PM GMT on March 21, 2017

Each December (typically), an ice boom is deployed across 1.7 miles (8800 feet) of extreme eastern Lake Erie near the mouth of the Niagara River. The purpose of this boom is to prevent large chunks of ice from flowing down the river, where they might block water inflow to hydroelectric plants, cause ice jams and flooding, and damage private property.

A section of the ice boom. Courtesy of the Army Corp of Engineers.

On March 6, the New York Power Authority and Ontario Power Generation began work to remove the protective ice boom. It’s not the earliest that the ice boom has been removed, but it speaks volumes about the lack of ice on the Great Lakes this winter. To further put March 6 into broader context, consider that the average opening date for the eastern end of Lake Erie is April 3. In case you’re wondering, February 28 (in 2012) is the earliest opening date, and May 3 (in 1971) is the latest.

Deploying the ice boom.

The governing body overseeing the ice boom is the International Joint Commission’s Niagara Board of Control. By agreement, the ice boom can be deployed as early as December 16 or when the water temperature at the Buffalo water intake (30 feet below the Lake surface) reach 39 degrees Fahrenheit (39 degrees Fahrenheit is the “magical” temperature at which water reaches its maximum density, a characteristic of water necessary to understand how ice forms on Lake Erie).

Also by agreement, eastern Lake Erie must be open by April 1, although local ice conditions can sometimes delay the removal of the ice boom (if ice still covers at least 250 square miles of eastern Lake Erie or if removing the boom would cause problems downstream in the Niagara River. Ice conditions are closely monitored by the Army Corp of Engineers (check out this video showing how the Corp of Engineers use helicopters to monitor Lake Erie ice).

The boom consists of 22 “spans.” As you can glean from the photograph at the top of my blog, each span consists of a number of steel pontoons and is anchored to the bottom of the Lake by steel cables 2.5 inches in diameter (every 400 feet).

To no one’s surprise, the coverage of ice on Lake Erie has declined by 50% from 1973-2010. The ice coverage of the Great Lakes, taken as a whole, has declined 71% during the same period (see graph below). Check out this animation showing the ice coverage on the Great Lakes since 1973.

The decline in ice coverage over the Great Lakes between 1973 and 2010. Courtesy of Glisa.

I found this revealing animation of the historical record of ice on the Great Lakes, courtesy of the Great Lakes Environmental Research Laboratory.

I decided to write this blog after reading Jeff Master’s terrific blog on the dramatic warmth of February.

Thanks for reading.


Ice Climatology

It's the Same Old Song

By: 24hourprof, 3:35 PM GMT on March 16, 2017

Just a short blog about a few of my takeaways from the winter storm in the Northeast this week...I had no doubt that precipitation type would be an issue in some of the major cities, and I thought forecasters were aware of the difficulties with regard to predicting snowfall.

However, all the forecasts I saw were deterministic rather than probabilistic. And many forecasts were framed in the context of the European and GFS models (essentially, choosing the model of the day). I'm certain many forecasters looked at the ensembles, but I didn't see anybody frame the forecast in probabilities (probability of snowfall exceeding six or twelve inches, for example, or even probabilities of precipitation type). Instead, it was the same old song...although some forecasters talked about uncertainty, they refused to issue probabilistic forecasts and universally defaulted to deterministic maps of snowfall.

It was pretty clear early on that some major metropolitan areas might not receive all snow. And probabilities, especially early on, conveyed this uncertainty. Check out the forecast for probabilities of snowfall greater than 12 inches from WPC's super ensemble issued 00 UTC on Monday (Sunday evening) and ending 00 UTC Wednesday (Tuesday evening). And yet, the some media still ran with huge snowfalls in Philadelphia and New York City. In fairness, probabilities increased toward the onset of the storm, but there was still enough uncertainty for some forecasters to be a bit more cautious. That's what happens when media starts publishing hyperbolic numbers two to three days in advance of the storm. Yes, a swing for the fences, hoping that the pitcher throws a fast ball right down the middle of home plate. When are we going to learn that the atmosphere is a knuckle-ball pitcher?

A loop of successive SREF forecasts (36-, 30-, 24-, 18-, 12-, and 6-hour forecasts) for the probabilities of snow, all valid at 21 UTC on March 14, 2017. Courtesy of SPC.

Yes, I know. The public wants deterministic forecasts. Why do we, as a profession, always acquiesce to this demand? Like I always say...maybe this isn't too difficult to understand in light of this country never adopting the metric system.

Nothing ever seems to change these days, including some of the bad science used to convey the meteorology of the storm. For example, I saw water-vapor imagery being used to generally quantify the moisture feeding into the storm's circulation. For the millionth time, water vapor imagery cannot routinely detect moisture in the lower troposphere (below 700 mb), where most water vapor resides. If that's the message you want to convey, you should not use water vapor imagery; you should use charts of precipitable water (PWAT).

The loop of GFS model analyses of 500-mb heights (in meters) and 500-mb absolute vorticity (color-filled) from 00 UTC on March 14 to 12 UTC on March 15. Only vorticity values greater than or equal to 16 x 10-5 sec-1 are shown in order to emphasize vorticity maxima. Courtesy of Penn State..

After the storm, I read media blogs / discussions that claimed that the prominent northern and southern 500-mb short-wave troughs actually phased during the storm. In my opinion, such phasing did not occur, Check out (above) the loop of GFS model analyses of 500-mb heights and 500-mb absolute vorticity from 00 UTC on March 14 to 12 UTC on March 15. Note that I only present contours of absolute vorticity (color-filled) of 16 x 10-5 sec-1 or greater in order to emphasize the vorticity maxima.

I don't see any phasing...just a Fujiwhara near the end of the loop. Why am I raising such a fuss? Well, the lack of phasing probably resulted in the storm jogging a bit more westward, allowing warmer air to gain more ground inland and to knock snow totals down in places. Yes, you gotta know your science.

All in all, however, I believe forecasters had a pretty good handle on this storm. Their deterministic tenor of their message, however, likely gave some people the wrong impression about the lingering uncertainty of the storm.

As for some of the media's explanations after the storm (phasing, use of water-vapor imagery, etc.), I can only shake my head.

It's the same old song.

Many thanks to Jon Nese and Steve Seman of Penn State's Department of Meteorology for their helpful input.


Forecasting Snowstorms

Miller-B Type Winter Storm System

By: 24hourprof, 8:13 PM GMT on March 12, 2017

To my dismay, I read a short-range discussion about the imminent winter storm along the Atlantic Seaboard tomorrow night and Tuesday. I quote: "A low pressure system crossing the Midwest states is expected to phase (sic) with another low off the southeast U.S. coast." I don't know about you, but the word, phase," in this context suggests two low-pressure systems merging along the East Coast. It's just not true.

For the record, I usually reserve "phasing" to describe the merging of two 500-mb short-wave troughs. The idea that low-pressure systems "phase" is a new one on me.

The 36-hour forecast from this morning's GFS 12 UTC run of 500-mb heights (in meters) and large values of 500-mb absolute vorticity (color-filled) greater than 20 x 10-5 sec-1. Valid at 00 UTC Tuesday (Monday evening at 8 P.M. EDT). Courtesy of Penn State.

Given that 500-mb data are obligatory in any analysis and forecast, let's start there.
The 36-hour forecast from this morning's 12 UTC run of the GFS (above, valid at 00 UTC Tuesday, which is Monday evening at 8 P.M. EDT) showed a compact but feisty 500-mb short-wave trough over Mississippi and Alabama. The solid contours are 500-mb heights (in meters) and values of 500-mb absolute vorticity greater than 20 x 10-5 sec-1 are color-filled.

In time, this 500-mb short-wave trough is predicted to move eastward to the Atlantic Seaboard, and then become negatively tilted as it moves northward along the coast (see animation of the 27-hour to 60-hour 500-mb forecasts below (every three hours). The forecasts are valid from 15 UTC Monday to 00Z Wednesday (11 A.M. EDT Monday to 8 P.M. EDT Tuesday).

An animation of the 27-hour to 60-hour GFS forecasts (every three hours) of 500-mb heights and 500-mb absolute vorticity, Valid from 15 UTC Monday to 00 UTC Wednesday (11 A.M. EDT Monday to 8 P.M. EDT Tuesday). Courtesy of Penn State.

At the surface, the GFS 36-hour forecast, valid at 00Z on Tuesday, shows two centers of low just west of the southern Appalachians and an incipient low off the Southeast Coast (below).

The 36-hour forecast of MSL isobars from this morning's 12 UTC run (valid at 00 UTC Tuesday, which 8 P.M. EDT Monday evening). Courtesy of Penn State.

Those two lows have as much chance of "phasing" than I do of winning the Tour de France. For starters, it would be curtains for a surface low to cross the Appalachians to the "Lee side" (Get it? :-). Indeed, a low-pressure system crossing the Appalachians would have to lift cold, very stable air associated with cold-air damming. In effect, cold air damming puts the brakes on low-pressure systems attempting to cross the Appalachians. Instead, the low tends to migrate northward along the western foothills of the Appalachians, where easterly winds downslope and create some slightly negative pressure tendencies (an inverted trough). But the writing is already on the wall...with the short-wave trough heading toward the East Coast, the low west of the Appalachians will eventually dissipate.

An animation of the 27-hour to 60-hour GFS forecasts (every three hours) of MSL isobars, Valid from 15 UTC Monday to 00 UTC Wednesday (11 A.M. EDT Monday to 8 P.M. EDT Tuesday). Courtesy of Penn State.

Meanwhile, the 500-mb short-wave trough will move toward the Southeast Coast (revisit the 500-mb animation), where the temperature contrasts between land and sea provide fertile grounds for cyclogenesis. Indeed, divergence ahead of the advancing 500-mb short-wave (and over the low-level baroclinic zone) will pave the way for cyclogenesis and, eventually, a nor'easter. For proof, check out the rapid development of the coastal low on this animation of 27-hour to 60-hour GFS forecasts from the 12 UTC run this morning (above).

In this way, the low west of the Appalachians is sometimes said to "transfer its energy to the coast." Any way you slice it, the imminent winter storm in the Northeast Monday night and Tuesday will initially consist of two dissipating low west of the Appalachians and one rapidly developing low along the Southeast Coast.

Such a scenario is described as a Miller-B type storm system. There is nothing resembling a "phasing" of low-pressure systems as the short-range discussion I read early this morning pontificated. Just more sloppy language and science in the age of fast-food meteorology.

The 54-hour GFS forecast for 850-mb isotachs (in knots) and 850-mb streamlines, valid ay 18 UTC on Tuesday. Courtesy of Penn State.

Looks like there is a potential for really heavy snow across interior New England and parts of the northern Middle Atlantic States as a low-level jet stream rapidly imports moisture from the Atlantic. Check out (above) the 54-hour forecast for 850-mb isotachs (in knots) and 850-mb streamlines (valid at 18 UTC on Tuesday, which is 2 P.M. EDT Tuesday). Hmmm...greater than 60 knots at 850 that's a low-level jet stream!!

Look out Loretta!


Imminent Winter Storm

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

From the Lee Side

About 24hourprof

Retired senior lecturer in the Department of Meteorology at Penn State, where he was lead faculty for PSU's online certificate in forecasting.