Edition 47: Building A Better Forecast
One of the biggest concerns of life concerns the weather. It affects us in practically every part of our life. Rain, snow, sleet, and hail are more than just part of the United States mail delivery service motto; they are all things that could change our outdoor keg-fest into a basement beer-brawl.
One thing for certain, there is no shortage of people who forecast the weather. Amateurs and professionals alike, methods differ greatly.
Gus Wickstrom claims to be able to do a long-term forecast for your area by reading your pig�s spleen! Meteorologists at a television station usually garner a large chunk of newscast time. You�ve undoubtedly seen the promotional commercials pumping up the features of their �EXCLUSIVE LIVE CHEETAH DOPPLO-3000 WITH 3-D STREEEEEET LEVEL TRACKING RADAAAAAAAR!!!� Television stations in the same market will even openly compete in a �Weather War.� A �Weather War� is essentially a battle for you, the viewer, and where you turn when �SEVERE WEATHER STRIKES!!!�
What a lot of people don�t know is that almost every piece of television weather technology is essentially bells and whistles. When severe weather conditions are forecast, these bells and whistles are combined with a healthy dose of doom and gloom that forces people to become slaves to a technology that most do not understand even in the slightest. What television stations fail to understand is while they show you a lot of information, the common viewer cannot even begin to comprehend what is going on and even worse, if they are in danger or not. Some of the responsibility lies in the lap of the television Meteorologist but one could equally blame the poor display of complex weather products. Despite the cause, the common viewer is inconvenienced and could even be in danger.
I�ve been directly involved in weather computers now for almost 12 years. The one thing that bothers me the most is how imperfect the science is. Because of this, Meteorologists constantly hear about the forecasts they blow. There is always a healthy amount of examples to choose from and the public never forgets ANYTHING! Meteorologists never hear about the big storms they nailed a week ahead of time, and there are a select few. It has to be the only job where you can be 50% accurate, but no one remembers the 50% of the time where you were right.
So, instead of relying on the hit-and-miss system on television, let�s take a look at how to make ourselves better forecasters!
First, let�s take a look at some common weather terms that you�ve likely heard in the past:
WATCH: A watch means that conditions are favorable for a severe event to happen. There are many types of Watches that can be issued. For example: Winter Storm, Thunderstorm, Tornado, Flood or Flash Flood are a few. �Watch Boxes� are issued nationally and then sent to your local National Weather Service (NWS) office where they are broken down into counties and summarily issued to the public. A Watch means that the public should remain aware of the weather situation and take precautionary steps if conditions worsen.
WARNING: A warning means that a severe weather event is happening or will happen in the very near future. Some types of Warnings that can be issued are Winter Storm, Thunderstorm, Tornado, Flash Flood, Flood, Heavy Snow, Blizzard, or High Wind. A Warning is issued when danger is imminent and action should be taken immediately, if necessary.
ADVISORY: Just like it sounds� �Be advised! Something is happening!� I think this is one of the most entertaining items issued by the NWS. We�re likely to already know what the NWS is telling us by simply opening a window. This information seems to be aimed at those traveling into or through the area. Some Advisories you may hear of are Wind, Winter Weather, Snow, Wind Chill, or Fog. If the weather worsens, you�re likely to see the Advisory bumped up to a Warning.
There are certain criteria that a weather event has to meet in order to have a Watch or Warning issued. The most common weather event criteria can be found here:
http://www.erh.noaa.gov/box/warningcriteria.shtml (While these are listed on a Boston website, these common criteria are accepted nation-wide)
DOPPLER RADAR: Doppler is a type of radar which is used for a lot of things, not just for weather. While I could write a literal term paper on the Doppler Effect, I�ll stop this short by saying that a Doppler radar reads the skies by sending out a frequency. How much that frequency changes when it returns (if it does) can tell the radar a lot of information about the item it reflected off of. The more wattage (power) a radar has, the more sensitive it will be and the farther it will see (Depending on the settings at the radar�) Read more about Doppler here:
http://whatis.techtarget.com/definition/0,,sid9_gci211991,00.htmlBAROMETRIC PRESSURE: The Barometric Pressure is a measurement of pressure from the atmosphere upon the earth (It�s always there!) Pressure can be expressed in millibars or the more common �inches of mercury,� when referring to a barometer. The �inches� measurement comes from the old days when people actually had to measure the amount of mercury in a long tube to tell what the short-term weather may be. An average millibar measurement is around 1000 whereas a common �inches� measurement falls around 30.00. A low-pressure indication usually indicates bad weather. A high-pressure measurement usually indicates good weather. The movement of storm systems (remember hearing �high� and �low� pressure during a weathercast?) affects the Barometric Pressure.
DEW POINT: The Dew Point is the temperature where the air would become saturated with water and condense, forming fog. The dew point can never be higher than the real air temperature. If it is the same as the air temperature, fog is formed. This is a fairly important measurement because it lets us know how much moisture is in the air. This moisture could be available for storms. Higher Dew Point levels give storms more to work with increasing their precipitation levels and intensity.
JETSTREAM: The Jet Stream is a concentration of relatively strong winds always present in the atmosphere. The Jet Stream changes height and position constantly. It moves from West to East in the Northern Hemisphere of the earth; however changes in the Jet pattern may cause it to temporarily go south, north, or even (rarely) to the west. The Jet Stream pushes storms along and is largely responsible for the path they take. Storm systems that break away from the Jet Stream can often stall out over a particular area for long periods of time.
COMPUTER MODELS: (a.k.a. �Models,� or �Weather Models�) Computer Models predict the weather. There are many to choose from. The government sponsors some of them. There are a few colleges that have them as well. Models are fed with a lot of old weather data, and based on current conditions will try to predict what will happen in the future. Each Model has a name. Frequently used Model names are the E.T.A & the A.V.N. Meteorologists read the charts produced by these Models and hopefully it helps the meteorologist predict what may happen. Models run several times a day. These �runs� are timed off of �Zulu� time (GMT) and each map they produce is categorized by the time which it is produced. For example, a model may run at 0Z, 6Z, 12Z, 18Z, 21Z in a single day.
The Computer Forecasting Model is the root of weather forecasting inaccuracy.
First of all, no computer weather model is perfect. Each hardly ever agrees with the other. Even when they do, the weather still may not abide. Once the weather computers produce the models, the results are transferred all over the United States to Meteorologists everywhere. The Meteorologist reads the model and attempts to predict which model they think is the closest (judging by how it has performed over the last few runs) and then attempts to figure out which aspect of the model is wrong. They make their adjustments and from that and build a forecast.
When it comes to television Meteorology, the problem deepens. TV Weathermen will read the models themselves, read what the Meteorologists at the NWS think will happen and then take that information and twist it even farther! By the time the viewer sees it, a television Meteorologist�s forecast could be third-generation information! Is there anything we can do about this?
Yes. We can cut out the middle-man.
The first thing you need to do is find your local National Weather Service webpage. Go to
http://www.google.com and type in �NWS <your city>�. You should get a return for �National Weather Service Forecasting Office� or something to that effect in the first few links. If that doesn�t produce the result I explained, try substituting a large town nearby. Once at the homepage, you will likely find a map of your local area. You can click on your town to find out your local forecast. There is a lot of information available. The bright side is you no longer have to wait until the news comes on. It�s all there. The current conditions, live radar, forecasts, discussions, explanations, everything!
Let�s take a look at some of the more important products you will find on your town�s NWS page. Underneath the �Detailed 7-day Forecast� header, you will find several links to many products. Some of them are as follows:
�Hazardous Weather Outlook� � This product will give you a look at the upcoming severe weather potential, and will explain what that threat may be, if it exists.
�Short Term Forecast� � This product will give you a look at the forecast for the next few hours.
You may also find detailed explanations of any Advisories, Watches or Warnings that may be posted for your area.
One great thing about using the National Weather Service webpage is that when you see that snow may be coming, you can look at discussions posted by the Meteorologists to see how strong the threat may be. Some items can be very complex, but with a discerning eye, you can pick out the information you need. Take a look on the lower-right hand portion of your NWS webpage where it says something to the effect of �Additional Forecasts & Information.� There are several items listed here, but the one we are concerned with is the �Forecast Discussion.� This is something your local Meteorologist looks at when coming up with his forecast. Let�s take a look how to read it! First of all, the seven day forecast for Davenport is fairly clear. However, my NWS webpage is calling for sleet and snow Saturday. Let�s say I had something going on then and I needed to know how bad it could possibly get� Here�s the Davenport Area Forecast Discussion.
FXUS63 KDVN 252135
AFDDVN
(These are codes used by computer systems to identify the product)
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
325 PM CST TUE JAN 25 2005
(This product is usually issued twice a day, once in the early morning, and once in the afternoon. It can be issued more if a long-term severe weather situation is imminent; however, the NWS usually uses other products such as the Hazardous Weather Outlook in such cases.)
.SYNOPSIS...
INCREDIBLE WARMING HAS SPREAD OVER THE UPPER MIDWEST TODAY...WITH SNOW COVER LOOSING ABOUT 3 INCHES SO FAR TODAY IN MANY LOCATIONS. THIS LEAVES LITTLE OR NO SNOWCOVER SOUTH OF THE QUAD CITIES...AND LESS THAN 6 INCHES ACROSS THE NORTH. TEMPERATURES OVER THE SNOW ARE IN THE UPPER 30S TO MID 40S...AND THE AROUND 50 TO MID 50S WHERE THE GROUND IS BARE. WOW! A FAST MOVING STORM SYSTEM OVER THE GREAT LAKES IS DRIVING A COLD FRONT SOUTH THROUGH NORTH DAKOTA THIS AFTERNOON...WITH TEMPS ABOVE FREEZING UNTIL WELL NORTH OF THE FRONT.
(An overall look at the current local weather and mitigating factors causing such.)
.SHORT TERM...(TONIGHT AND TOMORROW)
AFTER MOSTLY CLEAR EARLY EVENING...THE COLD FRONT WILL SWEEP FROM NORTH TO SOUTH FROM 1 AM TO 5 AM. UNTIL THE FRONT MOVES THROUGH A GRADUAL INCREASE IN CLOUDS ALONG WITH TEMPS OF 35 TO 40 CAN BE EXPECTED. AFTER THE FROPA...
(Aaah! An abbreviation. You will commonly find these in a Discussion. It�s not usually important to know what the abbreviation stands for other than to figure out what it means in context of the sentence. In this case, FROPA is referring to the time which the front comes through, which was mentioned in the previous sentence.)
TEMPS WILL CRASH INTO THE 20S...AND STRATUS CLOUDS WILL INCREASE. COLD ADVECTION WILL INCREASE OVER THE AREA TOMORROW...WITH 850MB TEMPS DOWN TO THE -8 TO -12C BY AFTERNOON. THIS WILL LEAD TO A EARLY DAY HIGH IN THE MID 20S NORTH
TO MID 30S SOUTH...WITH FALLING AFTERNOON TEMPS IN THE 20S. THIS IS GENERALLY A 4 DEGREE RISE FROM MORNING LOWS...WITH A GRADUAL FALL AFTER 1 PM. CLOUDS WILL DECREASE SOME DURING THE AFTERNOON AS SUBSIDENCE INCREASES. ...ERVIN...
(He�s telling us here that there is going to be a 8 to 12 degree drop in the 850 Millibar temps, which means temps will be dropping in the upper atmosphere. We�re getting a great look at what exactly is expected to happen in the short term.)
.LONG TERM...(WEDNESDAY NIGHT THROUGH NEXT TUESDAY)
PAST 60-90 DAY 500 MB HEIGHT ANOMALIES CONSISTENT WITH MODERATE EL NINO WITH LARGE POSITIVE ANOMALIES ACROSS THE NORTHERN CONUS AND PERSISTENT NEGATIVE ANOMALY CENTERS NORTH/WEST OF THE HAWAIIAN ISLANDS...
(A lot of weatherese here. We can comprehend El Nino, and we likely know what that means for our own local area. That�s the important part here. Anomalies are irregularities in the mentioned areas. Things that occur thousands of miles away have a big effect on local long-term forecasts.)
OVER THE DESERT SOUTHWEST (CA/NV) AND BETWEEN 40 AND 70W IN THE ATLANTIC...WHICH IS CONSISTENT WITH STRONG SOUTHERN JET. LATEST ONI (OCEANIC NINO INDEX)AT 0.9 PUTS EL NINO AT MODERATE STRENGTH. PATTERN THROUGH THE PERIOD REMAINS
CONSISTENT WITH MODERATE EL NINO WITH STRONG ACTIVE SOUTHERN BRANCH OF JET. THIS WILL TRANSLATE INTO TEMPS NEAR/ABOVE NORMAL WITH PCPN BELOW NORMAL THROUGH THE END OF THE JAN. CANADIAN HIGH WILL DOMINATE THE WX ON THURS WITH COOLER TEMPS. THE HIGH WILL SLOWLY SHIFT EAST...BUT CWA WILL REMAIN UNDER IT/S INFLUENCE THROUGH THE END OF THE WEEK.
MODELS SHOW A PIECE OF ENERGY LIFTING OUT OF THE SOUTHWEST TROUGH...BUT DPROG/DT OF GFS SHOWS IT TRENDING SOUTH...WHICH IS TO BE EXPECTED WITH ACTIVE SOUTHERN JET. DEEPER MOISTURE INTO THE SOUTHERN PLAINS AND LOWER MISS VALLEY...WHERE
HEAVY RAIN THREAT WILL EXIST.
(Now the good stuff we�ve been looking for!)
OUR AREA LOOKS TO BE SANDWICHED IN BETWEEN WITH NORTHERN STREAM SYSTEM SKIRTING THROUGH THE UPPER MIDWEST AND
GREAT LAKES LATE FRI/SAT. WILL ALSO BE DEALING WITH DRY LLVL E FETCH THUS...NOT OPTIMISTIC ON SEEING MUCH PCPN...BUT WITH BROAD WARM ADVECTION HAVE KEPT SILENT 20 POPS FRI NIGHT AND CHC POPS SAT FOR LIGHT MIX OF SLEET/SNOW. COULD END UP BEING MORE LIKE FLURRIES/DRIZZLE/FREEZING DRIZZLE IF LIFT ENDS UP BEING WEAKER. REGARDLESS...ANY PCPN WILL BE EXTREMELY LIGHT.
(�Pops� means precipitation. 20 means 20% chance. They aren�t even mentioning that in the public forecast but now we know about it! Also, he mentions a chance of light precipitation, which means my �plans� might not be in danger as of right now. The sleet and drizzle that is showing up on the 7-day forecast is not nearly a threat as it appears!)
POTENTIAL FOR ANOTHER PIECE OF ENERGY EJECTING FROM THE WESTERN TROUGH LATE IN THE WEEKEND AND HAVE CHC POPS TO COVER THIS. WOULD NOT BE SURPRISED TO SEE A FURTHER SOUTH TREND IN MODELS WITH THIS SYSTEM.
(It appears there�s another chance for a storm late this weekend. We�ll have to watch the forecast and wait to be sure, but now we know about this chance before anyone else!)
BEYOND...LOCAL STUDY WITH H5 HEIGHT ANOMALIES SUGGEST POTENTIAL FOR MODERATE TO STRONG STORM SYSTEM IMPACTING CENTRAL/SOUTHERN U.S. IN THE FEB 3-6TH TIMEFRAME WITH RAIN/SNOW AND HEAVY TO POSSIBLY VERY HEAVY QPF AMOUNTS.
ECMWF LOOKS MUCH MORE REASONABLE ON IT/S UPPER PATTERN AND IS CONSISTENT WITH LOCALLY STUDY AS NEGATIVE HEIGHT ANOMALY CENTER IN CA/NV SHOWS ENERGY WANTING TO POOL THERE. THUS...SUGGESTIVE OF KEEPING SOUTHWEST TROUGH...WHICH
IS WHAT THE LATEST ECMWF SHOWS...AND FOR THIS REASON HAVE DISCARDED MUCH MORE PROGRESSIVE GFS. EXPECT TROUGH TO EVENTUALLY BE KICKED OUT AS BARRAGE OF PACIFIC ENERGY IN ZONAL FLOW BREAKS DOWN WEST COAST RIDGE. THE LONGER IT TAKES TO FOR THE TROUGH TO EJECT THE MORE MOISTURE WILL BE AVAILABLE. WILL BE KEEPING CLOSE WATCH ON THIS IN THE COMING DAYS...AS IT/S LOOKING QUITE INTERESTING FOR THE 3RD-6TH OF FEB. ...MCCLURE...
(This is the long-term look at the local forecast. While there appears to be a lot of weatherese here, we can read it while simply touching on the �English� portions of the text. We can see that this meteorologist is eyeing a possible storm to occur from Feb. 3rd to the 6th. No one else has any idea about this possibility yet other than you and the other meteorologists around the area.)
Just by doing a little research you can cut out a lot of the extra stuff shoved down your throat every night on the local news. There are a few rules to remember however when predicting the weather.
Reading the Radar: When severe weather is happening in your area, your local radar can be a life saver. Know where your town is on the radar and observe the precipitation. Nine times out of ten you can tell when and how long the precipitation will fall. Take a look at the loop. Is the precipitation moving towards your area? See how fast it moves. Use the time stamp on the top of the radar page to tell when the precipitation will hit your town and how long it is going to last. Is the precipitation increasing or decreasing in intensity? Add that information to your radar prediction as well.
Forecasting Storms: Forecasting is a difficult job. But, by knowing a few simple truths, you can increase your chances of being right.
1. Temperatures are usually fairly easy to forecast give or take a few degrees, even in the long term.
2. Storm occurrence predictions are getting easier. Where the problem lies is in knowing how intense the storm will be. It is especially hard to tell when you are speaking of winter storms and thunderstorms. With winter storms, a simple 20-mile variation in the track of the storm in any direction can mean the difference between getting 15� of snow and a dusting. With thunderstorms, even if all the elements are in place to have huge tornado-producing super-cells, sometimes it just don�t happen. So, while knowing that a storm is coming is a nice comfort, the intensity will likely be a puzzle until the precipitation starts falling. Don�t believe much you hear about snow or rainfall amounts until the storm is starting. Once it gets going, take a look at the NWS webpage and stay abreast of the situation.
3. The weather forecast is a constantly evolving animal. Keeping your knowledge current is the most important weapon. Forecasts change at least twice a day. Sometimes those changes can be very drastic. By checking the NWS page frequently, you will rarely be surprised.
One additional note: in times of severe weather, your television meteorologist can be your friend. Televisions stations have the ability to broadcast watches and warnings very quickly. They may also have information regarding evacuations and imminent flooding that may help save your life. Despite all of this, the first time I hear a watch or a warning on TV, the first place I stop is the NWS webpage to see what is happening myself without having to listen to the promotional hype of a television station. I get the information I need NOW. I don�t have to wait for the guy to talk about my town. THAT could save MY life.
Well, I hope this makes everyone a better understanding of the weather forecast. It�s a great tool to have in your arsenal. If you get good enough, your friends will start relying on you instead of the television weather people. If you look at the materials I suggested, chances are you�ll be more right than they are.
If you have any questions, please feel free to post them here and I�ll get back to you.
