How does the NWS decide on the % for storms for each county? - BarrowCountyWeather.com - National Weather Service Local Storm Report - polala.com

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How does the NWS decide on the % for storms for each county?

How does the NWS decide on the % for storms for each county?
Published by: webmaster 2010-03-18

What is the web page where it says there a "xxx% chance of Severe Storms"? I don't recall having seen that one before.

90% chance for thunderstorms = 10% chance for NO thunderstorms.

10% > 0%

They don't do it by county. They create the forecasts by area by dragging and highlighting the areas that they want. It isn't even a 90% "chance" either, it means they are expecting an approx. 90% COVERAGE of thunderstorms or rain or whatever they are calling for. Even at that, nothing is given so being upset because you didn't get rain doesn't make sense. As others have said, I've never understood why people only rely on the NWS or SPC. Whenever I see "Well, the SPC says this, so I'll be chasing" or "Well, the SPC is negative on the new outlook so I think I will stay home" I cringe. Especially on a storm chasing forum, from a storm chaser's forecast. I understand not everyone is as gungho about forecasting as myself or others, but I get the feeling some people have no understanding of forecasting basics sometimes. That or today's storm chasers are just lazy and would rather have someone tell them where to go. Those are the people who get made at the SPC when they don't see a tornado on a high risk day. They all have access to the EXACT same models and current data that you do. Just because they are paid more to forecast doesn't mean they have fairies tell them what will happen, and that those fairies are wrong sometimes to make you mad. Go over the stuff for yourself and decide if YOU think you will get rain or not.

Thanks everyone I realy do need to learn more. First I made a forcast for thursday and assumed NE would not get anything based on early forecasts byt the SPC outlook and NWS. I screwed up. I never looked for myself to see what could happen I just assumed that was not the place to be. While only a few tornadoes reported I was not expcting any and made myself look bad in the forecasting forum. So yeah I do need to learn to forecast for myself instead of relying mostly on NWS/SPC and Stormtrack. I do have a basic understanding of forecasting and what to look for. I just dont know how to look for it. I will learn because I want to and need to know these things before I say something like that again.

As for % go thanks Alex for explaining that to me. It just seems like storms are always so intense over Des Moines and then I get the "leftovers". We get mabey one good severe storm to move through my county each year. Every slight risk so far this year for me has busted besides Thursday and I can only confirm a few hail stones made it to penny size. No branches snapped so winds were only in the 50 MPH range. It is sad and dissapointing.

To answer someone calling me a storm chaser no I am not. Let me be clear and honest with you all now. I have never chased before in my life. I plan to in a few years when I have a more stable job but at the moment I dont chase. I am far from a profesional chaser or someone who is very experiencced or knowledgeable. I knore more than the average person and have several books on weather but mostly for the basics or extreme weather. I got into Stormtrack through a crack. I sent in my info about me 3 times (Yes I did fill out the form and told the staff about myself) and only became a member when they were letting new people join for a short period of time. I joined because like all of you I LOVE the weather and cant get enough of it. When severe weather strikes I will be here reading the NOW threads. I do not make weather my life. I enjoy doing other things and try to balance weather into my life. I have been into weather my whole life. I would love to chase but I dont feel the urge to chase every slight risk. I am not like crazy over storm chasing but at the same time when severe weather is ongoing I cant take my eyes off the radar. I watch Twister a dozen times a year to lol So I feel I have a right to be here. Plus I donated to the Stormsof2006 DvD so I have contributed in my own way being a member. Let's just say I am still learning and have a long ways to go. Math is a horrible subject for me and I am a slow learner. Not the smartest guy on the block.

BarrowCountyWeather.com - National Weather Service Local Storm Report::
Barrow County Georgia Weather, Winder GA weather, Auburn GA weather, Carl GA weather, Braselton GA weather, Bethlem GA weather, Hoschton GA weather,
http://www.barrowcountyweather.com/wxnoaastormreport.phpHOME

I do know what to look for in a storm and where to be when I am on the storm thanks to being a member of this site. I know my first post in this topic was a rant. I felt like venting. I was mad the storms producing destructive 60-70 MPH winds crapped out and like always I got nothing more than rain. I get stressed out if I dont find some way to vent and letting my feelings out is the best way of doing this.

I do apreciate the links Nick Grillo and others have posted and will check them out because I want to. Nick that is asome that you pushed yourself to the limit and learned alot about weather in a year. Mabey I need to do that.

Thanks for all of the reply's. Your friend MatthewCarman.

What is the web page where it says there a "xxx% chance of Severe Storms"? I don't recall having seen that one before.

It is the local forecast page at the noaa site. I guess I should have checked there before asking here but I had a brain fart. I will check the NWS site but any links here would be apreciated.

Well, it's best to learn how to forecast yourself than depend on an NWS percentage... I'd have to suggest this link over any other:

http://www.theweatherprediction.com/habyhints/

I'd have to think being a member of ST for over a year that one would learn more about severe weather meteorology... Certainly am not intending to write this as a pun, I'm just saying... It is pretty easy to learn the basics of meteorology, just crack a book.

Take it from Nick... he went from knowing not much to being a met without a degree in under 12 months.

Seriously though, Nick is right. If you plan on storm chasing, you really need to forecast for yourself. NOAA is good for getting a general overview, but you really need to buckle down and pick your own targets or build your own forecast.

Jeff Haby's Hints is pretty much all you truely need to start out with... Just start learning about the basics about thermodynamics and kinematics, and then take it from there. You'll learn that if you ever want to begin chasing, you'll need to learn how to forecast yourself, and not rely on other's forecasts to pick your target, particularly graphics that depict synoptic-scale risk zones (i.e. convective outlooks issued by SPC).
This post is dead-on 100%.

Matt, it takes time. You're not going to learn it all in one day. Most of those who forecast, even amateurs, take years to get to where they are. And if you're chasing, every bit of both synoptic scale and mesoscale knowledge you have will be nothing short of essential. Take my experience on 6/7. With only having a year of experience under my belt, my teams' goal was to chase in IL, where the forests and hills are more managable than WI. Therefore, we had to decide where to chase. Looking at the Davenport 18z sounding, we decided to target from De Kalb on nwwrd because the cap was fairly strong farther south and likely wouldn't break until after dark. We got to De Kalb, gathered data, moved to Dixon, decided we were a bit too far south still, and moved to Freeport. From there, we were in PERFECT position to intercept two supercells that were crossing the river into Carroll and Jo Daviess Counties. We positioned on a bluff outside Cedarville and captured a great view of two supercells as they passed nearby. The first one produced a fairly well-defined wall cloud (by 6/7 standards), and we actually got right underneath the second one and observed a weak anticyclonic funnel at the edge of it. A very rewarding chase, considering how that day evolved with the higher-than-I-expected-which-shows-I-have-more-to-learn-about-boundary-layer-mixing LCLs helping to create cool and wet RFDs that severely hampered the tornado potential, that would have been impossible if not for a basic understanding of the atmosphere and its processes.

StormReady - Wikipedia, the free encyclopedia::
Kearney County, Nebraska, displays a StormReady sign. The National Weather Service (NWS) SKYWARN storm spotter program trains emergency The advisory board seeks to officially designate 20 communities each year The National Weather Service does not fund the program in forms other than review and recognition.
http://en.wikipedia.org/wiki/StormReadyHOME

Just start by browsing through the Haby Hints topics. For some, it's easy to learn the ropes. For others, it takes some time. It's well worth the effort. Trust me.

I agree with what Nick and Tony said, and to add to it some. Don't just study meteorology and forecasting. Get some foundational knowledge of math and physics. You don't have to get too involved with it, though. How much you need depends on what you already know, and how far you want to go.

In math, an understanding of basic algebra should be enough, especially an understanding of graphs and how to manipulate equations. Beyond that, you might want to learn some about statistics. Your original question actually deals with statistics because the percent chance of storms is found by statistical methods.

In physics, I'd recommend learning about motion and dynamics, gravity, electromagnetism, and thermodynamics. Check with your local community college to see if they offer a course in general physics or general physical science. That would also be a good place to check on math courses as well. Some community colleges even offer a Intro to Meteorolgy course.

Don't forget your local library. You can easily get a card and check out books and other materials about weather. I've heard that reading the printed page is easier on the eyes than reading a computer screen.

Remember the important thing is to keep learning. Isn't that one of the reasons to go storm chasing in the first place?

My thoughts on the SPC, and the new/learning forecaster....

As I'm sure a lot of you know, many folks chief interest in storm chasing is actually seeing the storm, and not much else. For many, it's a hobby, and in-depth forecasting isn't their interest. They'll take whatever they can get; they'll take the path of least resistence where finding a storm is concerned. (yes, of course more forecasting knowledge would help them to better achieve their chasing goals)

The folks at the SPC do represent some rather quality free information offered up to the public at large. And depending on your forecasting ability, they can certainly point out a thing or two you might not have been seeing. To this extent, I do believe they are a good enabler for the 'casual' chaser. (we're probably getting folks out there that might not have been out before such information was public)

At this point in my 'chasing career' I've only been attempting to forecast -- and chase, for that matter -- since spring 07, and I certainly find the SPC forecasts and discussions to be quite useful. While I certainly hope to keep learning and developing my forecasting skills -- though, this is just a hobby for me -- I'm still an opportunist and will take whatever I can get to get me closer to 'the storm.'

Mathew, a few words from a fellow newbie to the game:
1) Stop being intimidated. You've got to dive in. You're on a mission to understand something now. . . view it as exciting journy of discovery. (ok -- that was cheesy, but, point stands)
2) Don't become overwhelmed thinking of all the information you must learn. Learn one area, one subject at a time. It's not too hard. You don't need any advanced degree in anything to learn basic forecasting. Just focus on understanding one thing at a time. (For example, if you're trying to understand a forecast model such as the GFS, learn what the different symbols and measurements stand for. Just basic stuff. Honest to god, I didn't know what a wind-barb was until half a year ago... but it's not that hard to understand once you look it up, right?)
3) Ask "why?"... think "why?" You did that in this thread. Now do that in your quest in better understand and forecasting severe weather. When you see folks talking about this forecast, or that storm, or this weather-scenario, don't just mentally nod along, but rather, try to understand the significance of it. For example: you read a couple chasers throwing around the term "helicity" when speaking of a possible upcoming severe event -- go google it! Find out what it means. After doing so, you'll have gained another piece of knowledge. When I started reading this board I couldn't understand half of the crap folks were discussing. . . Not that I'm anything but a novice yet, but I've made some nice gains in this chasing season thanks to just a bit of reading and research. It's really not too hard -- give it a shot, it's quite rewarding.

I believe he is talking about this.

http://forecast.weather.gov/MapClick.php?site=DMX&map.x=197&map.y=174

It says for tonight:

90% chance of precipitation, with the possibility for severe storms

See, learning in-depth relies on the dedication of the chaser... If one never plans on actually chasing, and would rather post on weather forums for other reasons, the dedication of learning how to forecast accurately by one's self is usually pretty low, at least from my expierence of being in the "chase world" for the past 4-5 years. I've seen people on the forum that have been registered for 1-3 years now, and have still yet to chase or learn anything about meteorology.

In 2005, I planned on spending $3,000 chasing for 4-8 weeks (ended up taking two seperate long-term trips that accrued a total of about six weeks). I had been significantly underaged chasing in MI for the prior couple of years, and had to break out of here in a big way. In 2005, I had went from the knowing the absolute basics of severe weather meteorology to being enthused with learning advanced areas of meteorology within months. I had pushed myself to the fullest in order to accurately forecast, since it was my own hard-earned money that was being thrown on the table to chase with. If one doesn't have that ambition to successfully chase, then they likely won't bother learning anything about meteorology. They'd rather polute the TA with fluff that us chasers have to sift through with a 1-bar WiFi connection at some hotel we caught a connection with in the middle of Kansas. We know the SPC just issued a MDT risk for the area, and that GRLevelIII indicates 2.25" inch hail, and that a tornado warning was just issued... Learn something, and add something useful... :D

It's easy to learn... Just push yourself.

Here here.

Having to fund your own chasing really makes you need to understand what is going on so that you are throwing money down the drain. For instance, my team and I started chasing two years ago. We fund ourselves, and we really don't have the money to go out on the plains right now (plus, with drive a '91 Plymouth Acclaim that has given us good reason to be nervous taking it on long trips). However, we have taken it into IL on several occasions (great country when photogenic storms come about, which hasn't been much this year :rolleyes: ). Last year, we had little success aside from a fairly hair-raising experience on 9/22 between KAAA and KSPI. After understanding what we did wrong, learning how to correct it, and performing further study, I can say we have been much more successful in two chases this year than we were in six chases last year. Our greater understanding of what is going on has immensely helped us with choosing our locations and getting into position for the best shots we could get (and, trust me, we got about as good as anyone could have gotten in NW IL on 6/7 :rolleyes: ).

Matt, don't hate learning. Learn to love it. Learning opens doors to opprotunities you never knew existed. It's alright to be nervous. I'm a little nervous about the likely prospect of me going to OU in Fall '08 and being faced with all the math and physics. But I'm also incredibly enthused and excited because I know that I will learn the most I possibly can while I'm there. Be excited to learn. If you really want to chase and forecast, you'll learn how if you give it the time and effort.

There is a 90% chance of severe storms across central Iowa and a 90% chance for my county (Jasper). Does that mean I will get severe storms? I have seen a 100% chance of severe storms bust and every time the % is this high it busts more than verify.

How does the NWS decide if this county gets a 90% chance for severe storms or if that county gets a 10% chance etc? I see it bust more than verify when the % is this high for Iowa. I dont understand how this works.

The best severe weather days seem to be with low chances. May 7 of 2006 Eastern Iowa had around 17 tornadoes reported and the area had a 30% chance of storms, not severe just storms.

Well it has sort of been hashed out but I'll throw my 2 cents in here and hope I don't add to the confusion. When you see probabilities expressed as percentages on a local NWS forecast page those are merely the probabilities for measurable precipitation (defined as 1/100th of an inch of liquid) falling at that location for a specified period of time. Here is the exact definition I found by googling on weather.gov:

Is the likelihood, expressed as a percent, of a measurable precipitationevent (1/100th of an inch) at a grid point during the indicated valid period. On a local forecast page and in zone forecasts (ZFP) these are almost always for a 12-hour period (i.e. Monday Night). The difference is when you click on the map, you are receiving the forecast for a small gridbox in the forecast area. The old ZFP, which still plays over NOAA Weather Radio IIRC, is the forecast for an entire county.

So if you saw a forecast for tonight, and there was a 30% chance of rain, then that would mean the forecaster is expecting there is about a 30% probability that you will receive measurable precipitation at your house.

As far as severe weather wording goes...if severe weather verbiage is added to the forecast, the little graphics at the top of the local forecast page will indeed say severe t'storms or something similar. However, the actual text displayed below is key. It should say something like Thunderstorms likely...some may be severe. Chance of thunderstorms 60 percent. Thus, the probabilities merely indicate the percentage chance of measurable precipitation. The forecaster is indicating that this precipitation will likely arrive in the form of thunderstorms, some of which may be severe.

The bottom line is that when you look at a local NWS forecast and the PoPs, you are just being informed on what they think the chance of your driveway getting wet is (more or less).

If you want a realistic look at the chance of severe weather occurring at your location, you would want to look at an SPC convective outlook. They aren't going to give you a probability of a severe thunderstorm at your house, but the risk levels should give you some idea. You can also check your local NWS office's Hazardous Weather Outlook (HWO), which usually details the severe weather risk for your local area.

And, like the others said, best way to learn is to dive in, make mistakes and ask lots of questions. It may seem overwhelming at first but eventually you'll get the hang of it! That Haby Hints page is quite the gem for beginners and those still learning.

AJL

Thanks Nick I will check those links out.

To be honest I rely on the NWS and NOAA for all of my forecasts. I know I should use the models and graphs etc but that part is always confusing for me. I need things as simple as possible or I get a headache or just get confused.

Do you guys know any other good sites for forecasting or weather outlooks?

Jeff Haby's Hints is pretty much all you truely need to start out with... Just start learning about the basics about thermodynamics and kinematics, and then take it from there. You'll learn that if you ever want to begin chasing, you'll need to learn how to forecast yourself, and not rely on other's forecasts to pick your target, particularly graphics that depict synoptic-scale risk zones (i.e. convective outlooks issued by SPC).

"every time the % is this high it busts more than verify."

thats completely untrue and sounds like my grandma.

lets be logical. counties are big. you are not. its the likelyhood of whatever happening in any part of that county. they probably dont even divide it up by county. more than likely, they do it by area. its meteorology. its not an exact thing. it suprises me to hear a "storm chaser" say something like that.

I am sure they have this up for a whole area or divide it up for big areas but many times I have seen a % that high bust for a entire area. I am just trying to understand what is needed for a % that high or how the % system works etc. I want a better understanding of why they do this.

I know my thinking is wrong but I just get so annoyed when I have a 100% chance for a severe storm and dont see anything. (This has nothing to do with yesterdays 50-60% chance that verified)