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Meteorologists Ponder Sunday Severe Weather Threat

Posted at 6:35 PM, Nov 16, 2013
and last updated 2013-11-16 21:12:37-05

GRAND RAPIDS, Mich. — Meteorologists from the National Weather Service in Grand Rapids as well as FOX 17 (including other TV stations) were in attendance on Saturday for their annual media seminar. The purpose of these semi-annual meetings is to open up the lines of communications between broadcast meteorologists and NWS meteorologists on how we can better serve the public collectively. Before our meeting got started, all of us discussed the very real possibility of strong to severe storms across West Michigan on Sunday.

While a slight risk of severe weather in November is unusual, the moderate threat posed by the Storm Prediction Center in Norman, Oklahoma this far north…this late in the season is quite rare. A very powerful, developing, and still deepening (or strengthening) low pressure system will move in to and through the Great Lakes on Sunday/Monday. Strong southerly winds will deliver moisture from the Gulf of Mexico and briefly sharply warmer temperatures in the mid/upper 60s. That means showers and thunderstorms on Sunday with windy conditions and perhaps strong to severe weather as well.

One of the things meteorologists examine for severe weather is an index called CAPE…or convective available potential energy. We build more energy in the atmosphere to help storms fire when the sun can make an appearance. That said, our wind field is so strong on Sunday from this system that building additional energy (or CAPE) almost doesn’t matter. Wind shear, or winds coming in from different directions and at different speeds can induce a turning motion or rotation in the atmosphere. That can produce brief tornado spin-ups on one hand, and strong straight line damaging winds on the other hand.

Our concern on Sunday is two-fold. First, tornadoes can sometimes occur along a warm front with the turning of winds along/just ahead of the front. This would be during the mid/late morning. The second concern is during the afternoon as the actual cold front comes through the area. We have the potential of a line of strong/severe storms (known as linear convection or squall line) to develop. While brief tornadic spin-ups are possible along the cold front, the bigger threat will be strong, damaging straight line winds embedded within this line (if it develops) of at least 60 to 70 mph. What meteorologists refer to as discrete supercells can/may form along/ahead of this linear convection/squall line. These supercells are rotating thunderstorms with an updraft, can spawn tornadoes, and tend to occur separate from one another and are not part of the line of storms that can/may form. We already know winds that strong are associated with this system above the surface, so it certainly is possible that we mix these upper level winds down to the surface to produce damage on the ground. Click here to see the actual threat/severe weather outlook from the Storm Prediction Center. Again, I normally wouldn’t get too concerned about a slight risk, but most of our FOX 17 viewing area is actually in a moderate risk…so we have a better than average chance at seeing strong/severe storms, especially from Grand Rapids to the south/east. The time of concern is primarily mid/late morning (with the warm front), and through afternoon/early evening with the cold front.

I wouldn’t be surprised to also see a wind advisory posted for our area by Sunday night in to Monday morning as the core of the strongest surface winds come through behind the area of low pressure. Sustained winds of 25 to 35 mph are likely with gusts of 40 to 50 mph. That means scattered power outages are possible, especially if we see some brief, heavy rainfall where tree roots can be loosened and wind takes them down.

Lets also not forget Lake Michigan! Gale warnings are already in effect on the big lake as wave heights are expected to run well over 12 feet Sunday night in to Monday. If you decide to venture out, please stay off the piers and jetties to get your photographs! We won’t see the winds decrease until later in the day on Monday. Make sure to email damage photos, lake photos, and any reports to weather@fox17online.com. Thanks in advance.

Behind this system on Monday look for windy conditions, falling temperatures throughout the day (the warmest temps will occur at midnight in the upper 40s), and rain showers mixing with and changing to some light snow showers.  For you real weather geeks, take a look at what this system looks like on our forecast model on Monday morning here.  Note the map of the United States, the thin, gray lines packed tightly together depicting the strong winds, and the very strong “L” or low pressure system located to our northeast in Canada…the center of circulation of the storm! The purple and blue represent accumulated precipitation, most of which the heaviest will have departed from Michigan by Monday morning.

Stay safe and get the complete forecast, temperatures, satellite, and radar by going to www.fox17online.com/weather.