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Saturday March 28, 2020

Assignment: Predict the 24 hr maximum temperature (deg F) for Des Moines, IA (KDSM)

Saturday provides another example of a location where uncertainty in the exact location of a frontal feature leads to big differences in temperature forecasts. The Saturday high temperature predictions for Des Moines, Iowa vary from 64 to 79 F, as a strong low pressure system passes by. Let's predict Tmax for Des Moines and see what happens.

Question: The NWS discussion mentions the possibility of a "dry slot" as an important part of the forecast. Here's a cloud cover prediction for late Saturday afternoon. So what do you think a dry slot is?

What Happened?

Saturday was an interesting day in Des Moines, as there was a dramatic dry slot, as you can see in this beautiful satellite image. Looking at the "Latest obs" link, at 3 pm, it was overcast with light rain and the temperature was only 57 F. Then the rain stopped and the cloud cover decreased for two hours, and the temperature increased to 68 or 69 F pretty quickly. So I assume that they were in the dry slot for a short time, but it was late in the afternoon and the temperature started decreasing again after the quick warming. If they had been in the dry slot earlier in the afternoon and if it had lasted longer, they probably would have been able to get the temperature well up into the 70's. So another tough forecast challenge.

Forecasts for Des Moines, IA (KDSM)
Forecaster Tmax, deg F (error) Comment Day Score
OBSERVED 69 Tmax FINAL (minor problem).
1. Abbygale15 69 (0) 3.3
1. Gus15 69 (0) 3.3
3. Jasper15 70 (1) 3.1
NAM-MOS-12-DAY01 70 (1) 3.1
3. Grace15 68 (-1) 3.1
3. ashleigh15 68 (-1) 3.1
6. Hannah15 67 (-2) 2.9
6. Dorothy15 71 (2) 2.9
6. Autumn15 67 (-2) 2.9
9. Keith15 72 (3) 2.7
9. Mathison15 66 (-3) 2.7
9. EmilyV15 66 (-3) 2.7
12. Sara15 65 (-4) 2.5
12. Josh15 73 (4) I think a dry slot is when in an area where a low pressure system is coming through their is an area or little slot on the side of the system where there is no rain or clouds. 2.5
12. Joscelyn15 65 (-4) 2.5
NAM-MOS-00-DAY01 65 (-4) 2.5
GFS-MOS-00-DAY00 74 (5) 2.3
GFS-MOS-12-DAY01 74 (5) 2.3
NAM-MOS-12-DAY02 64 (-5) 2.3
15. Shyann15 75 (6) 2.1
NAM-MOS-00-DAY00 62 (-7) 1.9
16. Anna15 76 (7) 1.9
GFS-MOS-06-DAY01 76 (7) 1.9
GFS-MOS-18-DAY01 77 (8) 1.7
GFS-MOS-12-DAY02 77 (8) 1.7
GFS-MOS-00-DAY01 78 (9) 1.5
17. Alex15 78.5 (9.5) 1.4
18. Miles15 59 (-10) ~(0-o)~ 1.3
GFS-MOS-18-DAY02 79 (10) 1.3
19. Hailey15 58 (-11) 1.1
19. EmilyS15 58 (-11) 1.1
21. Elizabeth15 57 (-12) 0.9
21. Lizzie15 81 (12) 0.9
CLIMATE 54.7 (-14.3) NCDC Climate Normals, 1981-2010 0.4
23. Gianni15 85 (16) 0.1
23. T-Dawg15 53 (-16) 0.1
PERSISTENCE 49 (-20) 0