Tuesday, July 26, 2011

Weather.com Nails Last Weekend's Extended Forecast Temps; KSTP Best of Local Forecasters

If you're like most people, you like to start thinking about your next summer weekend just about the time the current weekend winds down (at least that's how we like to think!). That's the approach we took on Sunday, July 16. That evening, we gathered the temperature forecasts for the ensuing weekend (July 23-24) and plotted them on our handy Excel spreadsheet as follows (note: KARE11 does not formally forecast beyond five days, but Sven Sundgaard suggested that "90s were quite possible for the weekend"):

We thought that this forecast had a fair amount of challenge because there was a major heat wave that was about to hit high gear early in the week for a somewhat uncertain duration. The following table summarizes the forecast error for each of the weather oulets (we arbitrarily used 92 as the predicted temperature for Saturday and Sunday for KARE).

Amazingly, Weather.com (The Weather Channel) was exactly right for both days' forecasts. Based on our analysis, the rank order of all outlets was:

#1: Weather.com
#2: KSTP
#3: Intellicast
#4/#5: NWS/WCCO
#6: Fox
#7: Accuweather
#8: Star Tribune
#9: KARE

There's not all that much to take from this. It is, after all, just a one-weekend extended forecast sample. Were we do to this for every weekend over the course of a longer time -- months to a year -- the results would be a lot more meaningful. Also, and just as importantly, we didn't record the forecast as it related to sky conditions/storms, etc.

Sunday, July 24, 2011

A Case of Nowcasting Gone Terribly Wrong

We've been meaning to post a small philosophical essay about the pros and cons of nowcasting, the practice of giving short-term updates on weather activity that's generally not considered forecasting. While that post will have to wait for another day, today's weather forecaster analysis wouldn't be complete without reviewing today's "nowcast" tweets of @JonathanYuhas. We're not trying to pick on Jonathan, but it sure seemed like everything he said turned out to be completely wrong. The following chronicles a night of forecasting-challenging weather juxtaposed with Jonathan's nowcasting tweets.

We begin tracking Jonathan's tweets about 4:45 p.m. as the Twins game was moving into the later innings.

While the quantification of a possible "25-minute rain" seemed overly precise, particularly since there was no guarantee the rain would even arrive, it was a nice little heads up, both for fans watching on TV and fans attending the game.

About 15 minutes later, Jonathan issued his next tweet, delaying the possible arrival time of a 25-minute rain to 5:30.

As 5:30 approached, Jonathan determined that the rain was breaking up, and called off the possibility of rain for Target Field. Notably, he stated that the storms WILL fire up over the next 7 hours (not "might" fire up):

Next, Jonathan decided it would no longer be a stormy night, mentioning the possibility of only light showers.

By approximately 8:45, Jonathan minimized the threat of rain even further, calling for the possibility of sprinkles at worst for the U2 concert-goers. He pronounced that the cooler airmass over the Twin Cities precluded the possibility of any severe storms.

But just as Jonathan seemed to kiss any chance of significant rain goodbye, things started to change. Shortly after that, the radar began to blossom. Light green echoes turned to dark green, and then quickly to yellow, orange and red.

Jonathan took note of the changing radar and alerted concert-goers about the possibility that some rain and thunder could "graze" the U2 concert.

At about this time, 1" hail estimates were coming in from Brooklyn Park. The line of storms began to sag southeast and back-build to the west. At 9:49 p.m. the National Weather Service issued this special statement noting significant storm activity for the University of Minnesota, site of the U2 concert:
Shortly thereafter, reports of torrential rain and cloud-to-ground lightning were reported at the University of Minnesota's TCF Bank Stadium. At 10:19 p.m, here was the Weather Underground radar depiction:

Unfazed by his missteps that seemed to occur with every tweet, Jonathan, the consummate professional, plowed forward, giving his followers one last concert update:

A final tweet, five minutes before 11 p.m., pronounced the storm still sitting over the U of M:

In fairness, other forecasters noted some of the same general trends, but their tweets weren't quite so precise or quite so wrong. We do think Jonathan deserves credit for actively tweeting in the first place, as it reflects his passion for what he does (and an understanding of the emerging importance of social media in weather communication).

Still, tonight's events raise a few questions: Is nowcasting, particularly in a convective summer environment, really such a good thing? And is too much credence given to every turn of the radar, sometimes at the expense of seeing the big picture of possibilities?

Friday, July 22, 2011

Severe Saturday?

Twin Cities forecasters are talking about the possibility of severe storms on Saturday, which means Twins fans and U2 fans can't rest easy. Weigh in with your thoughts here.

Tuesday, July 19, 2011

How Legitimate Are All These Heat Index Readings?

How Reliable Are Weather Stations?
With higher and higher heat index reports coming in from parts of the state (mostly western MN) like competing bids at a Sotheby auction, we wondered how reliable such readings might be. We asked a National Weather Service meteorologist for an opinion on the legitimacy of such readings and how often the NWS might review or approve weather stations beyond the larger ones such as the Minneapolis/St. Paul airport. Here's what he had to say:
The first-order stations with ASOS (Automated Surface Observing System) instruments (such as the MSP airport) are rigorously monitored and maintained by NWS technicians. They undergo at least routine maintenance, and when errors are detected non-routine maintenance is performed. As for all the other stations out there -- FAA, AWOS (Automated Weather Observing System), MNDOT system, etc. -- I am not aware of the maintenance they undergo, but based on my experience I believe it is less rigorous than the NWS maintained stations.

If a record high dew point is observed in the state (which may have happened I believe) there will be a much closer look done, likely by the state climate office consulting with the local NWS office and possibly some other folks at national climate centers.

Why Isn't Wind Factored Into the Heat Index Calculation?
If you're like us (which is to say weather enthusiasts with very little scientific knowledge), you might wonder why wind conditions don't factor into the heat index. At some level, it would seem that wind -- even a warm, humid wind -- would slow the effect of heat on the body. Of course a scientific explanation trumps a misinformed hunch. Thanks to Nick Benson (@Ottergoose on Twitter), we received a well-reasoned explanation:
The heat index doesn't take wind into effect because heat loss at high temperatures comes from perspiration, not convection. Only air cooler than you can actually cool you down; sweating only works if the air has capacity to absorb your perspiration. Think of air as a mop; if it's saturated, the floor will stay damp no matter how quickly you scrub it. Likewise, saturated air blowing over you will have a minimal impact on absorbing perspiration (cooling).
And so ends a Simply Science version of TMF.

Will Wednesday Provide the Century Icing to the Heat Wave Cake?

Tuesday's 119 heat index
OK, "icing" may not be the right word, but you get the drift. Will Wednesday delivery the coup de grĂ¢ce for this record-setting heat wave? The majority of local forecasters are predicting that Wednesday will indeed be the hottest of the current heat wave. (The national forecasters, not so much.) As of late afternoon on Tuesday, here's how the weathercasters saw Wednesday:

WCCO: 100
KSTP: 100
FOX: 97
KARE: 100
NWS: 97
Weather Channel: 96
Accuweather: 96
Intellicast: 95
Star Tribune: 99

Monday, July 18, 2011

Widely Predicted Heat Wave Finally Arrives in Earnest. Eighties or 90s Next Weekend?

Heat wave update as of 4 p.m.
Until today, the heat wave that was so universally predicted for so many days didn't pack the punch we were led to believe. Today, the forecasts came true. For the first time in many days, the forecast high temperature and heat indexes were reached, and even exceeded. By late afternoon, the heat index of 112 in Minneapolis was the highest of any major city in the U.S. Take a bow, y'all.

Here's a summary of how the heat wave is "performing" against forecasts made on Friday night.

Here's a summary of the over (under) prediction of the heat wave to date for the period since Friday night. At this juncture (and assuming the 98-degree high for Monday holds), KARE has the best forecast record for the period measured; Fox, the worst.

80s or 90s for Next Weekend?
Finally, in another test of the extended outlook forecasting ability of the weather mavens in our midst, here's next weekend's forecast temperatures as of last night's (Sunday night) evening forecasts. (Note: KARE does not provide specific forecasts beyond day 5. The "90s" information was provided anecdotally.)

Saturday, July 16, 2011

"Massive Heat Wave" Off to Tepid Start

The 90 Run Has Yet to Begin
A funny thing happened on the way to that streak of 90s ... it hasn't yet begun. Despite universal forecasts of temperatures above 90 today, the temperature reached "only" 87. The highest heat index for the Twin Cities today was a not-off-the-charts 97. It seems questionable at best as to whether an excessive heat warning was really necessary.

The 80-81 degree dew point predicted by the Star Tribune weather columnist also never materialized. While the dew point did reach a tropical 77, it did not approach the record to near-record high dew point predicted in several recent Star Tribune blog posts.

A Forecasting Slump?
Perhaps you've noticed, but the weather gurus haven't been at the top of their game the last three days. The original prediction for heavy rain (to be measured in inches) was for Wednesday night into Thursday. Yet, Thursday saw only .13 inches of rain. The Friday forecast generally (and yes, we're generalizing about the forecasts) called for the chance of a few spotty storms and a high in the upper 80s. However, Friday saw the first bout of torrential rain (more than two inches) and a high of only 77. And as of Friday night, most forecasters called for only a small chance of rain overnight on Friday. In fact, more torrential rain fell in the early a.m. hours of Saturday. It all serves as another reminder that forecasting, particularly amid the chance of convective storms, is a tough task.

Weather.com Seems a Little Nuts
Weather.com is displaying an odd range of forecast temperatures for Sunday. It forecasts 96 for Minnetonka, 101 for St. Paul and 104 for Minneapolis, including the zip code for the Mpls/St. Paul airport. The official weather.com forecast is: Intervals of clouds and sunshine. Record high temperatures expected. Heat index near 120F. High 104F. Winds S at 10 to 20 mph.

Recapping the Original 7-Day Heat Wave Forecast
Here's an updated comparison of heat wave predictions made on Friday night to the actual temperatures reached so far. Note that all predictions for the first two days of the period have been well above actual.

Friday, July 15, 2011

File Under: Things That Don't Seem Logical

Here is a depiction of the latest heat watches and warnings. The red-shaded areas represent Excessive Heat Warnings; the lighter-colored shading represents Excessive Heat Watches. It makes some sense that the always-cooking urban core could be under a warning when surrounding areas are under watches. But what makes less sense to us is why there would be a warning for two counties (one in Minnesota, one in Wisconsin) that are midway between the Twin Cities in Duluth. Is the heat really expected to arrive in such an unusual arc pattern? Or is the thinking that the two counties didn't receive much rain today and thus will heat up faster? Hmm.... Professional meteorologists, what can you tell us?

Read It and Weep - Your Universal Heat Wave Forecast

Interestingly enough, the greatest amount of variability in the 7-day forecast is for today. Blue outline marks forecasts that (sort of) stand out as being cooler than others; red outline marks forecasts that stand out for heat. If you're not desiring a heat wave, you should be rooting for the Intellicast forecast, which "only" forecasts five consecutive days in the 90s.

The following information is based on forecasts collected this Friday morning.

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Wednesday, July 13, 2011

National Forecasters Outperforming Locals for This Week

Last Friday night, temperature trends varied by forecast outlet in a rather interesting way. Virtually all national forecasters (weather.com, accuweather and intellicast) saw the current week as being cooler than the local prognosticators. The national weather providers envisioned several days in the 70s, whereas the hometown studs maintained temps in the 80s throughout. Given the rather odd dichotomy in temps, we captured the forecast for later review. Our thinking -- our guess, really -- was that the locals would be better at forecasting local weather than the nationals. However, as this week has played out, and given the forecast for Thursday, that's not been the case. If you had your money on Weather.com, you were a winner.

Tuesday, July 12, 2011

Summer in the City: All Forecasters Predict Major Heat Wave

Start getting ready to hear the heat wave classics on the radio ... according to virtually all weather forecasters in the Twin Cities, a major heat wave is expected to arrive by the end of the week. For Sunday, no forecaster is going lower than 95. At this point, KSTP is most bullish on a persistent heat wave, forecasting a high of 98 next Tuesday. As of Tuesday evening, here's how both the local and national weather outlets saw the steamy forecast (Strib forecast is as of Tuesday morning):

Update: As of Wednesday night, here's how forecasters saw the upcoming heat wave (Saturday through Wednesday). Note that KSTP, as it often seems to be, forecasts the highest temperatures, with an average heat wave temperature of 97.4 for the five-day period.

Sunday, July 10, 2011

Future Scan vs. Reality: How Did It Stack Up for KARE11 Sunday Night?

Future scan, or "future radar" as some weather outlets call it, has increased in popularity over the last several years. Yet we've always wondered how future radar verifies. A tweet from KARE11's Sven Sundgaard detailed the future radar for 11:39 (the tweet was issued at 10:40 so the "future" in this case was about one hour). Here is how the future scan appeared (click here for actual depiction):

Here is TMF's screen capture of KARE11 radar's actual scan at 11:40:

Finally, for good measure, here's a radar scan from Wunderground.com at about the same time:

In our opinion, while the future scan reasonably communicated the essence of the storm movement -- and therefore did provide a service, the future scan did not account for the heavier showers that persisted on the north side of the Twin Cities. A big deal? Probably not in this case. But we think that given the inherent unpredictability of summer storms, it can be risky business to provide an image that suggests an all-knowing future.

How would you assess the effectiveness of KARE11's future radar and the concept of future radar in general? Leave your comments below.

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Saturday, July 9, 2011

Fox9 Weather App Amiss With Fox9 Website

Fox9 has made a big deal promoting its newly released weather application for mobile phones. While the app has a few nice features (good radar, alerts and ability to mark favorite locations), there is a discrepancy between the application and the weather television presentation.

What seemed most curious is that the forecast temperatures and sky conditions don't match between the app and what's posted on the website (not to mention that both forecasts were a day light in being updated). For example, on Friday evening at 11:45 p.m., here's what displayed on the app and website:

From Fox9 Weather App

From Fox9 website
Note that for Tuesday through Thursday the variance in high temperatures is considerable, with an eight degree difference on Thursday. There are also differences where the weather app icons show rain while the website icons show sun. It's hard for us to take a station's weather app seriously when there is such a difference.

Our guess is that the source for the app's weather forecast is not made by the on-air mets. The app appears to be produced by the WSI Corporation, which produces weather forecasts of its own through places like Intellicast.com. Fox needs to square this issue before it can expect its mobile phone viewers to take the new app seriously.

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Monday, July 4, 2011

A Baseball Geek, A Weather Geek

OK, a little aside that weather geeks might get a kick out of ...

A recent article in Sports Illustrated analyzed a pitch called the cut fastball. Included in the article were funky "heat" graphs that depicted the difficulty hitters are having in hitting the increasingly popular and nasty pitch.

Per the graphic above, any weather geek would quickly conclude that the graphs looked nearly identical to radar images reflecting nasty thunderstorms and hook echoes, right? So what's a baseball fan/weather geek to do? How about write an article to Sports Illustrated? The graphic below reflects that the popular sports magazine does indeed have a sense of humor. (Note the letter that begins at the top of the second column.)

Source: Sports Illustrated, July 4-11, 2011