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.

39 comments:

  1. 90 with a 82 degree DP here in 55350 this afternoon.

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  2. We get to experience what the guys in Alabama deal with all summer. Ridge of high pressure over head with random pop up storms that can cause you to look like an idiot.

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  3. It was 91 with an 82 degree dewpoint in the 55355 saturday.

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  4. Since the ridge is south of us, there is also high bust potential for SOME people because storms have a habit of popping up around the edge of the ridge (ring of fire) causing heavy downpours that could mean a high of 89 instead of 96.

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  5. 78 DP in 55432 already at 9am

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  6. 82 with a DP of 79 in Red Wing @ 8:50am

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  7. State record for heat index is 125. Could make a run at it.

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  8. That's a record I have NO DESIRE to hit.

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  9. CAPE might hit 10,000 over northern/central MN later today. Thankfully its just about the only severe parameter thats positive (for severe weather) today.

    Wouldn't be surprised to see some 2"/hr rains under these storms that do get going though.

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  10. Well, looks like parts of the state might have a bigger issue with severe weather then planned.

    MESOSCALE DISCUSSION 1639
    NWS STORM PREDICTION CENTER NORMAN OK
    1024 AM CDT SUN JUL 17 2011

    AREAS AFFECTED...PARTS OF ERN ND...NW MN

    CONCERNING...OUTLOOK UPGRADE

    VALID 171524Z - 171630Z

    GIVEN THE PRESENCE OF STRONG TO EXTREME POTENTIAL INSTABILITY... AND
    MODEST TO STRONG DEEP LAYER VERTICAL SHEAR...PROBABILITIES FOR THE
    EVOLUTION OF AN ORGANIZED SEVERE MESOSCALE CONVECTIVE SYSTEM APPEAR
    TO BE INCREASING...EITHER FROM ONGOING ACTIVITY OR NEW DEVELOPMENT
    LATER THIS AFTERNOON. THIS WILL BE REFLECTED IN A CATEGORICAL
    UPGRADE TO A MODERATE RISK FOR SEVERE STORMS ACROSS PARTS OF EASTERN
    NORTH DAKOTA AND NORTHWEST MINNESOTA IN THE 1630Z OUTLOOK UPDATE.

    ..KERR.. 07/17/2011

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  11. @CW will be interesting how close that gets to the metro, I wonder if it will include the area that was shown for the hatched hail risk.

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  12. @NovakWeather on TwitterJuly 17, 2011 at 11:14 AM

    It will be nearly impossible to reach 100 degrees actual air temp. unless we get some drier air into the region. That potential will exist mid-week. Until then, the BUST potential remains high in the temp. department as clouds, storms & moisture content wreak havoc with some bold predictions.

    I'm very concerned about severe weather potential for later this afternoon and into the evening. Atmosphere is like an explosive right now. Just needs something to light the fuse.

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  13. currently at Blaine airport 88/81 heat index is 106

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  14. @NovakWeather Concern for severe weather in MSP as well or just north and east?

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  15. Storms building/popping out west,looks like high temps won't be realized today with those moving east,man is it gross out,weather channel is live at target field today talking about our heat and comparing it to the last time they were here when we were approaching -30 below wind chills,I would take that weather then this any day

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  16. from the SPC in Norman OK

    IF THE
    SCENARIO EVOLVES AS EXPECTED INTO THE AFTERNOON...THE MDT RISK AREA
    MAY NEED TO BE EXPANDED FARTHER SE INTO MORE OF MN...AND POSSIBLY
    EVEN NW WI FOR LATE THIS AFTERNOON/EVENING.

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  17. Currently in Waconia: 89/105 with a dew point of 79. The temperature has gone up 2-3 degrees per hour. Could still reach the low 90s. The storms seem to be fizzling a little as they hit the hottest air.

    Yes, the high temperature predictions appear to be off due to the amount of clouds around, but the heat index is what matters and it's right where they said it would be. A few degrees "cooler" temperatures will NOT reduce the severity of this heat wave.

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  18. Staggering... take a look at this. If you are familliar with this, you will be amazed...

    http://www.spc.noaa.gov/exper/mesoanalysis/new/viewsector.php?sector=13#

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  19. sorry... forgot explanation... (fron SPC in Norman, OK)

    A multiple ingredient, composite index that includes effective bulk wind difference (EBWD), effective storm-relative helicity (ESRH), 100-mb mean parcel CAPE (mlCAPE), 100-mb mean parcel CIN (mlCIN), and 100-mb mean parcel LCL height (mlLCL).

    The index is formulated as follows:

    STP = (mlCAPE/1500 J kg-1) * ((2000-mlLCL)/1500 m) * (ESRH/150 m2 s-2) * (EBWD/20 m s-1) * ((200+mlCIN)/150 J kg-1)

    When the mlLCL is less than 1000 m AGL, the mlLCL term is set to one, and when the mlCIN is greater than -50 J kg-1, the mlCIN term is set to one. The EBWD term is capped at a value of 1.5, and set to zero when EBWD is less than 12.5 m s-1. Lastly, when the effective inflow base is above the ground, the entire index is set to zero. A majority of significant tornadoes (F2 or greater damage) have been associated with STP values greater than 1 within an hour of tornado occurrence, while most non-tornadic supercells have been associated with values less than 1 in a large sample of RUC analysis proximity soundings.


    Additional information can be found here. (Please open this link in another browser window.)

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  20. wow look at this, if convection does get going copious rain are possible

    http://www.spc.noaa.gov/exper/mesoanalysis/s13/pwtr/pwtr_sf.gif?1310941651306

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  21. Hello I have a question for the pros on this site, I just looked at the meso analysis page from the SPC , I see 26-29°C at the 850mb level. Is that to warm for convection to get going?

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  22. easy up people looks like "garden variety" storms,nothing we havent seen before or produce an f2 or greater tornado,relax!

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  23. current DP in golden valley is 81,highest I have ever been in,down right disgusting,oh how I wish it was 50 degrees air temp right now.

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  24. This weather is crazy! Forecasters can't even settle on a forecast for tonight. One minute they're saying partly cloudy, the next minute they're saying torrential rains, and then back again. The same can be said about tomorrow. Sunny and scortching hot or stormy and miserably humid or both? The weather's been unpredictable since our first snowfall in November. So, do I wear shorts tomorrow? Jeans? Bring an umbrella? Sunglasses? Oy!

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  25. @AB I think part of the problem is that forecasters are hyper sensitive to every appearance of a storm ramping up or winding down and make their forecasts accordingly. There's an underlying perception that they can be far more precise than they are ... and in a liquid (no pun intended) situation such as this, they just can't be.

    As for tomorrow, make sure you have an ice scraper handy in your car. :-)

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  26. @Bill ...the ice scraper never leaves the car!!!

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  27. nice storm bearing down I-94,within metro I would say in 2hrs or less

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  28. @big daddy: radar trends look like this cell may go just southwest of the metro loop

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  29. yeah anonymous they do seem like they will move southwest of metro,well I guess I'll crank that AC at least it wont be a noisy night

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  30. Bill,was watching the national news this morning(GMA)when the weather segment came on they showed Minneapolis heat index at 124,seriously is there any truth to that,have the local mets gone that high?

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  31. To Anonymous at 8:15 yesterday...

    Be careful what you say...

    http://www.spc.noaa.gov/climo/reports/yesterday.html

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  32. "they showed Minneapolis heat index at 124,seriously is there any truth to that,have the local mets gone that high?" .......@big daddy, it is possible. Mid 90s with relative humidity at 75% would get it near 120; however, while our dew points have been 75-80, the relative humidity has been hovering between 60-70% most of the time. The real test will be Tue/Wed. With temps nearing 100 degrees, you only need 50-60% humidity for a heat index above 120.

    Here's NOAA's heat index chart: http://www.weather.gov/om/heat/index.shtml

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  33. Madison, MN looks like it may win the prize again today. Currently they're at 95 with humidity and dew point both at 84. Heat index: 115.

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  34. 93 with a dewpoint of 81 here in Red Wing right now...yesturday we hit 118 thought for sure we were the hottest heat index in state but i was suprised. wouldn't be shocked if we got up to 116 or 117 today

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  35. Anyone wonder if the Madison weather set up is kosher?

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  36. It might be a little off, but Marshall is reporting similar numbers. That area is usually the hottest and most humid part of the state and this year it has extremely wet crops and farmland to moisten the air. Currently Madison's dew point is back up to 86 with humidity at 84% and a heat index of 121 while Marshall is currently reporting 82/71/116.

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  37. Just posted new heat wave thread...

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  38. Thank you for this blog, I'm actually interested in following weather updates.
    I enjoy the heat wave by the way, I love when it's hot outside.

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