SPC Outlooks Explained

posted in: Michigan Weather Forecast | 57

I dusted off my Skywarn ‘Go’ bag yesterday which includes all the instruments I use should severe weather move into the area.  I would generally go south and west of of the Otsego/Plainwell area or head northwest on M-89 towards Allegan where there is flat land and fields where the visibility is unobstructed by trees and buildings.  I have a handheld scanner to keep track of weather, EMS, Ham and police reports, a lightning detector which can track lightning strength and movement, an anemometer to record wind speed, a high definition video camera and off course my cell phone which has Radarscope to track storm locations and to report to the NWS.  I won’t go out after dark or, if I do it won’t be far from home base, just far enough to get out of the valley I live in.  Bittersweet is a good location if the gates are open and I can get up the hill.

We haven’t had much in the way of severe weather the past couple years, just a few thunderstorms with heavy rain and a bit of small hail.

I will be at the Skywarn session in Shelbyville with my brother on Saturday.  Over the past month I have been talking to a lot of people at various area businesses in the Otsego/Plainwell area which have shown a lot of interest in attending.


Here are the latest SPC graphics for today and an explanation of what the colors mean.

Storm Outlook
Tornado Outlook

Wind Outlook
Hail Outlook

 

Overview: Convective outlooks for days 1, 2, and 3 consist of categorical and probabilistic graphics that depict severe and general thunderstorm threats across the continental United States, along with a text narrative.

 

Graphical categorical risk: Using numbers, words, and colors, the categorical graphic depicts general thunderstorm areas (TSTM-light green) and up to five risk types (1-MRGL-dark green, 2-SLGT-yellow, 3-ENH-orange, 4-MDT-red, and 5-HIGH-magenta) based on the coverage and intensity of organized severe weather such as supercells, squall lines, and multicell thunderstorm complexes. Pulse type thunderstorms, consisting primarily of solitary brief severe updrafts (often found in weakly sheared environments), are not considered organized.

 

The TSTM area encloses where a 10% or higher probability of thunderstorms is forecast during the valid period. A 1-MRGL-dark green risk area includes severe storms of either limited organization and longevity, or very low coverage and marginal intensity. A 2-SLGT-yellow risk area implies organized severe thunderstorms are expected, but usually in low coverage with varying levels of intensity. A 3-ENH-orange risk area depicts a greater concentration of organized severe thunderstorms with varying levels of intensity. A 4-MDT-red risk indicates potential for widespread severe weather with several tornadoes and/or numerous severe thunderstorms, some of which may be intense. A 5-HIGH-magenta risk area suggests a severe weather outbreak is expected from either numerous intense and long-track tornadoes, or a long-lived derecho system with hurricane-force wind gusts producing widespread damage.

 

Graphical probabilistic risk: The probability of severe weather drives the outlook categories, with the tables below showing the conversion for each threshold. On day 1, the outlook contains individual severe probabilities for tornadoes, wind, and hail. With greater uncertainty about severe-storm type into the future, the outlooks on day 2 and 3 only forecast the combined probability of all three types of severe weather. For all outlooks, the probability values represent the chance of severe weather occurring within 25 miles of any point, which is about the size of a major metropolitan area.

 

As an example, if you have a 15% probability for tornadoes, this means you have a 15% chance of a tornado occurring within 25 miles of your location. This may seem like a low number, but a tornado is very uncommon at any one location. Normally, your chances of getting hit by a tornado or other severe weather are small, purely based on statistical average. Let’s say you have a 1% statistical (climatology) history of tornadoes within 25 miles on this day, which still is large. Having a 15% probability means 15 times the normal odds of a tornado nearby, meaning it should be taken seriously. The probabilities for severe thunderstorm wind and hail also have the same meaning as they do for tornadoes, but typically will be higher numbers than for tornadoes, since they are much more common.

 

Sometimes, a black hatched area will be overlaid with the severe probabilities. Black hatching means a 10% or higher probability for significant severe events within 25 miles of any point. “Significant” is defined as: tornadoes rated EF2 or greater, thunderstorm wind gusts of hurricane force (74 mph) or higher, or hail 2 inches or larger in diameter.

 

The outlooks on day 2 and 3 combine all forms (tornado, wind, and hail) into a single black hatched area for a 10% or higher significant-severe risk. In addition, for tropical cyclones (hurricanes, tropical storms and depressions), the outlooks on day 2 and 3 allow a 5% total severe probability to be a SLGT risk because they are specifically tornado-driven.



The U.S. map has been colorful the past couple days with a wide range of hazards.  There are multiple reports in eastern Colorado of wind speeds of over 80mph with snow up to 13 inches.  Kansas has also reported wind gusts over 80mph.  Storm reports can be found here.

We have flood watches for most of northern lower Michigan through tomorrow evening.  We will remain in an unsettle pattern until Monday when we will finally have a calm pattern setting up for a good portion of next week.

The threat for strong/severe storms this afternoon/evening looks lower than previously thought with areas south/east of Lower Michigan most at risk.  You can find the latest area forecast discussion here.

Below is the NAM forecast for today:


 

386 total views, 1 views today

57
Leave a Reply

avatar
29 Comment threads
28 Thread replies
0 Followers
 
Most reacted comment
Hottest comment thread
12 Comment authors
Rocky (Rockford)Gun Lake DebJeff(Portland)MichaelVBarry in Zeeland Recent comment authors
newest oldest
INDY
INDY

I was out chasing a little this afternoon these storms really pick up steam heading east we had a wonderful set up this early this evening not to often a sunny dry slot fires good storms if only Lk Michigan would of been a lot warmer storms would of been rocking hard in GR…Have a good night INDY!

Sandy (Hudsonville)
Sandy (Hudsonville)

Some nice thunderstorms rolled thru here this afternoon. Little thunder & lightning. Heavy downpour a couple of times. Quiet now. I was just outside & temp feels cooler. This afternoon when the sun was out it was beautiful.

Barry in Zeeland
Barry in Zeeland

Not the best, but I grabbed a pic with my iPad at work of the rainbow. Of course it looked 100 times better than the pic shows.

http://tinypic.com/usermedia.php?uo=jJm7XUcEEIwYgXpzLbvNjIh4l5k2TGxc#.XIrcn7IpChA

Sandy (Hudsonville)
Sandy (Hudsonville)

Nice!! Thanks for sharing.

Mark (East Lansing)
Mark (East Lansing)

Tornado warning for the cell that passed over us a half hour ago. It was ominous looking when it was over us.

Mookie
Mookie

First tornado of 2019 for Michigan

Mark (East Lansing)
Mark (East Lansing)

I always chuckle when watches are issued after warnings.

Barry in Zeeland
Barry in Zeeland

Yeah I’ve always wondere about that. They predict it’s coming, know it’s coming, but don’t put a watch out until after its hit. But they’ll throw up a snow advisory 2 days ahead of time for 1.3 inches of snow.

Mark (East Lansing)
Mark (East Lansing)

NWS even mentioned us in the warning. Nowhere near severe level here. Very little wind and no hail.

Rocky (Rockford)
Rocky (Rockford)

Bring it! This should help set up my ski trip up to snow country very nicely! I love it!

comment image

Rocky (Rockford)
Rocky (Rockford)

Did gr even hit 60 degrees today! What a joke!

Barry in Zeeland
Barry in Zeeland

I’m not in GR, but here it hit 61. Is there a prize?

Mark (East Lansing)
Mark (East Lansing)

62° here. What do I win??

Slim

A nice pat on the back.
Slim

Barry in Zeeland
Barry in Zeeland

That 100mph storm looks almost unreal on the radar loop. When comparing it to all the other storms, it just rockets away from them like it’s in a drag race.

Mark (East Lansing)
Mark (East Lansing)

Just got home. Sun has been shining for the past 45 minutes. Car thermometer read 62°

Slim

The official high at Lansing was 62 at GRR it was 58 here at my house I reached 60
Slim

Barry in Zeeland
Barry in Zeeland

Ton of rain, some lightning, but little wind here. Suns out now with a brilliant rainbow to the NE! Actually a faint double rainbow!

Mookie
Mookie

Per radio just now: a storm in Michigan is moving at 100mph. The fastest ever recorded in the state! I think it’s a storm on the east side. Wow

Mark (East Lansing)
Mark (East Lansing)

STRONG THUNDERSTORM WILL AFFECT SOUTHERN LAPEER…NORTHERN
OAKLAND AND SOUTHEASTERN GENESEE COUNTIES…

At 513 PM EDT, a strong thunderstorm was located over Clarkston, or 9
miles northwest of Pontiac, moving northeast at 100 mph.

That’s incredible!

Gun Lake Deb
Gun Lake Deb

Just WOW! Of course that also means that should it decide to drop a funnel, there’s going to be no warning it…..

Mookie
Mookie

Apparently, we can’t post CPC anymore here – but it’s looking WARM!

Jeff(Portland)
Jeff(Portland)

Yup, looking at more spring like temps next week.. The snow piles are all but gone here ..

Slim

bring your truck over still a good amount of snow piles here yet. More like ice piles
Slim

Mookie
Mookie

Max GR temp so far today is 58 degrees.

Slim

It has just touched 60 here at my house
Slim

Barry in Zeeland
Barry in Zeeland

Getting really dark to the SW. Radar loop shows pretty good thunderstorms heading directly at us.

Slim

There are some heavier showers in southern Lake Michigan that had some lightning with it. That line is heading NE so will be in SW Michigan shortly the current temperature here at my house is 57 with some breaks in the clouds. The last reading at GRR was 56 with light rain.
Slim

INDY
INDY

52* degrees now out at thee YARDofBRICKS NE GR with light rain and clouds I’m thinking out Severe weather and mid 60’s today like the NWS forcast is out the window still low 50’s feel wonderful..INDY!!

Slim

55° here at my house so it might not reach 60 today. BTY the last reading at GRR was 57 and that was you guess for the March maximum. We shall see
Slim

INDY
INDY

Give me the trophy lol…This maybe the warmest March day …INDY!

Slim

Here are the maximum March temperature guesses from last week Rocky 49.4, Indy 57, Mark 59, MV 62, Mookie 62, Andy 65, Sandy 69, SS 70, Barry 71, Sarah 72 and my guess is 64. The latest reading at GRR was 54.
Slim

Sandy (Hudsonville)
Sandy (Hudsonville)

Don’t forget my guess of 69. We are going to get close to some of these today.

Slim

Sorry Sandy I will add your guess of 69. Rocky is already out and at this time Indy is right on it as the current temperature at GRR is now 57
Slim

Mookie
Mookie

Rocky way off already. Not surprised LOL

Slim

Here at my house I received 0.36″ of rain yesterday. And while there is a lot of bare ground here there is still a lot of snow in the woods and in the shady areas and of course the snow piles will be with us for some time yet. With some sun the current temperature here is 55° Will have to see just how “warm” it gets today.
Slim

*SS*
*SS*

We went sledding yesterday…. snow was very icy & slushy in spots, but we were out enjoying the last day *fingers crossed*!!!

Mr. Negative
Mr. Negative

“No snow on the ground”???…hard to imagine for Ada…maybe April 🙁 A line of severe storms?…we all know better. Try to enjoy the temporary thaw, as more snow is on the way.

Slim

There is a chance that the big parking lot snow piles will last until April
Slim

Mark (East Lansing)
Mark (East Lansing)

Great info!

I hope we hear some thunder today.🌩

Mookie
Mookie

As suspected, GR is now reporting zero snow on the ground. Yesterday, was +10 degrees above average, and this morning felt very springy.

Mark (East Lansing)
Mark (East Lansing)

I think it’s safe to say we’ve turned the corner.

Slim

I agree
Slim

Slim

While there may no a reported “zero” snow on the ground at the airport and much of the city of Grand Rapids, here in my nick of the woods there is still a lot of snow on the ground in the woods and in shady areas. So here in this part of Kent County the report would be a trace.
Slim