De Kalb
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the De Kalb clear sky chart from 2005-11-06 to 2024-11-05.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	12% 9% 3 8% 5% 4 5% 4 6% 7% 37%	101377
	Night	13% 10% 3 8% 5% 4 4 4 5% 6% 38%	97752
Transparency	Day	44% 5% 12% 23% 14% 2	104942
	Night	44% 5% 11% 23% 15% 2	102328
Seeing	Day	16% 10% 28% 26% 15% 6%	15831
	Night	17% 9% 31% 30% 12% 1	25662

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 12% 8% 14% 6% 4 6% 3 3 6% 26%	2527
	11th to 20th	Day	11% 12% 5% 17% 6% 4 5% 6% 10% 5% 19%	2530
	21st to end	Day	17% 19% 9% 12% 5% 4 3 3 5% 6% 19%	2919
February	1st to 10th	Day	13% 15% 4 9% 7% 6% 5% 3 6% 6% 26%	1710
	11th to 20th	Day	13% 11% 4 8% 6% 5% 4 4 5% 6% 35%	1847
	21st to end	Day	14% 12% 5% 11% 4 5% 3 4 5% 6% 30%	1570
March	1st to 10th	Day	14% 13% 3 8% 4 4 4 3 4 6% 37%	3120
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 8% 39%	3302
	21st to end	Day	19% 13% 5% 13% 6% 5% 6% 3 5% 5% 20%	4160
April	1st to 10th	Day	17% 13% 4 8% 6% 5% 3 4 5% 7% 30%	2280
	11th to 20th	Day	16% 10% 2 7% 5% 5% 5% 4 6% 7% 34%	2254
	21st to end	Day	19% 9% 3 8% 5% 5% 5% 4 4 6% 33%	2349
May	1st to 10th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	4082
	11th to 20th	Day	15% 6% 2 6% 3 4 5% 4 5% 7% 43%	4387
	21st to end	Day	11% 7% 2 6% 5% 5% 5% 4 6% 10% 41%	4824
June	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 7% 8% 46%	2660
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	2660
	21st to end	Day	10% 7% 2 7% 5% 5% 6% 5% 7% 8% 38%	2660
July	1st to 10th	Day	10% 8% 3 7% 5% 6% 6% 5% 8% 9% 33%	4440
	11th to 20th	Day	6% 4 2 5% 4 4 4 5% 7% 9% 49%	4440
	21st to end	Day	8% 6% 3 8% 5% 5% 6% 4 6% 8% 40%	4813
August	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	4342
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 44%	3729
	21st to end	Day	8% 6% 2 6% 5% 4 4 4 6% 9% 48%	4180
September	1st to 10th	Day	11% 4 2 6% 4 4 5% 4 5% 7% 48%	2280
	11th to 20th	Day	12% 4 2 4 3 3 4 4 5% 8% 53%	2187
	21st to end	Day	10% 6% 2 7% 5% 4 4 3 6% 8% 45%	2090
October	1st to 10th	Day	12% 7% 3 5% 3 4 4 4 5% 7% 47%	1995
	11th to 20th	Day	16% 9% 3 7% 4 4 4 3 5% 6% 37%	1900
	21st to end	Day	20% 9% 3 6% 4 4 4 3 4 6% 37%	1900
November	1st to 10th	Day	11% 10% 3 6% 4 4 4 3 5% 6% 45%	1708
	11th to 20th	Day	15% 13% 4 9% 5% 4 4 4 5% 8% 32%	1710
	21st to end	Day	17% 12% 4 9% 5% 4 3 3 4 5% 35%	1601
December	1st to 10th	Day	14% 14% 4 10% 5% 4 5% 3 4 6% 32%	1520
	11th to 20th	Day	12% 13% 5% 10% 5% 5% 4 4 5% 7% 28%	1918
	21st to end	Day	19% 22% 9% 13% 6% 4 4 2 3 3 15%	2783
January	1st to 10th	Night	13% 13% 5% 14% 6% 4 4 3 4 4 30%	4428
	11th to 20th	Night	14% 17% 6% 14% 6% 3 3 5% 8% 4 20%	4440
	21st to end	Night	18% 18% 8% 11% 5% 4 4 3 4 5% 21%	4746
February	1st to 10th	Night	14% 14% 4 8% 5% 5% 4 3 5% 5% 33%	2470
	11th to 20th	Night	13% 11% 3 7% 5% 4 4 3 5% 7% 39%	2218
	21st to end	Night	15% 14% 4 7% 4 4 3 2 5% 5% 35%	1884
March	1st to 10th	Night	18% 10% 3 5% 3 4 3 3 4 5% 41%	3733
	11th to 20th	Night	10% 6% 3 6% 4 3 5% 4 5% 6% 48%	3686
	21st to end	Night	22% 11% 5% 10% 5% 4 4 3 4 5% 26%	3471
April	1st to 10th	Night	16% 10% 3 7% 4 4 4 4 4 5% 40%	1900
	11th to 20th	Night	19% 9% 3 5% 4 4 4 3 4 6% 40%	1875
	21st to end	Night	16% 9% 2 7% 5% 4 5% 3 5% 6% 38%	1829
May	1st to 10th	Night	14% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	2813
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 7% 11% 39%	2515
	21st to end	Night	9% 7% 2 7% 4 4 4 5% 6% 7% 45%	2743
June	1st to 10th	Night	9% 5% 2 6% 4 3 4 4 7% 8% 48%	1520
	11th to 20th	Night	8% 5% 2 6% 4 5% 4 5% 6% 9% 48%	1520
	21st to end	Night	8% 5% 3 6% 6% 4 6% 5% 6% 7% 44%	1520
July	1st to 10th	Night	12% 7% 2 7% 5% 5% 6% 4 6% 8% 38%	2530
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 3 6% 9% 53%	2530
	21st to end	Night	5% 5% 2 7% 6% 5% 5% 4 8% 9% 43%	2750
August	1st to 10th	Night	5% 5% 2 6% 4 5% 4 5% 7% 8% 51%	2592
	11th to 20th	Night	7% 6% 2 6% 4 4 5% 4 5% 8% 49%	3100
	21st to end	Night	8% 4 2 4 3 3 4 4 6% 10% 51%	3476
September	1st to 10th	Night	9% 6% 2 4 3 3 3 3 4 6% 56%	1900
	11th to 20th	Night	9% 4 1 5% 3 4 3 3 5% 8% 54%	1973
	21st to end	Night	10% 5% 2 5% 5% 4 4 4 5% 8% 47%	2090
October	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 5% 5% 52%	2183
	11th to 20th	Night	16% 8% 2 5% 4 3 4 2 4 5% 46%	2280
	21st to end	Night	19% 10% 3 6% 4 4 4 3 5% 7% 37%	2697
November	1st to 10th	Night	12% 8% 2 5% 3 3 3 3 5% 6% 49%	2470
	11th to 20th	Night	15% 9% 3 9% 5% 4 4 3 5% 7% 37%	2470
	21st to end	Night	16% 11% 3 7% 4 3 4 3 5% 6% 37%	2577
December	1st to 10th	Night	15% 11% 3 9% 6% 4 4 3 5% 7% 32%	2660
	11th to 20th	Night	15% 12% 4 9% 5% 5% 4 3 5% 6% 32%	3279
	21st to end	Night	21% 18% 7% 10% 6% 4 4 4 5% 5% 16%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	61% 4 12% 17% 7%	2528
	11th to 20th	Day	60% 4 13% 13% 10%	2530
	21st to end	Day	67% 4 10% 13% 6%	2919
February	1st to 10th	Day	56% 4 12% 16% 9% 2	1710
	11th to 20th	Day	48% 4 11% 24% 10% 2	1857
	21st to end	Day	54% 6% 11% 20% 9% 2	1570
March	1st to 10th	Day	49% 5% 12% 22% 11% 2	3120
	11th to 20th	Day	40% 6% 13% 30% 11% 1	3302
	21st to end	Day	65% 5% 13% 13% 3 1	4160
April	1st to 10th	Day	54% 5% 10% 22% 9%	2280
	11th to 20th	Day	48% 6% 10% 23% 11% 2	2254
	21st to end	Day	52% 5% 12% 17% 13% 1	2349
May	1st to 10th	Day	45% 6% 11% 24% 13%	4120
	11th to 20th	Day	40% 6% 11% 28% 15%	4391
	21st to end	Day	36% 6% 13% 22% 17% 5%	4837
June	1st to 10th	Day	34% 6% 14% 27% 17% 2	2660
	11th to 20th	Day	34% 5% 12% 25% 21% 3	2660
	21st to end	Day	41% 7% 13% 24% 13% 3	2660
July	1st to 10th	Day	45% 6% 13% 23% 11% 2	4371
	11th to 20th	Day	28% 6% 17% 30% 17% 1	4365
	21st to end	Day	40% 6% 15% 17% 19% 3	4662
August	1st to 10th	Day	35% 6% 17% 29% 12% 1	4327
	11th to 20th	Day	33% 5% 12% 34% 15% 1	3765
	21st to end	Day	33% 5% 12% 31% 17% 2	4179
September	1st to 10th	Day	35% 5% 12% 25% 18% 4	2280
	11th to 20th	Day	30% 5% 12% 29% 22% 3	2187
	21st to end	Day	37% 4 10% 28% 19% 2	2090
October	1st to 10th	Day	25% 4 7% 31% 32% 1	3320
	11th to 20th	Day	32% 3 11% 26% 26% 2	3140
	21st to end	Day	43% 3 10% 27% 14% 3	3112
November	1st to 10th	Day	40% 4 13% 25% 16% 2	1708
	11th to 20th	Day	51% 4 13% 22% 10% 1	1710
	21st to end	Day	53% 4 12% 23% 8%	1601
December	1st to 10th	Day	54% 4 13% 20% 8% 1	1520
	11th to 20th	Day	54% 3 14% 18% 8% 2	1915
	21st to end	Day	76% 3 7% 9% 4	2783
January	1st to 10th	Night	56% 4 11% 19% 9% 1	4428
	11th to 20th	Night	64% 4 10% 13% 9%	4440
	21st to end	Night	66% 3 10% 14% 6% 1	4746
February	1st to 10th	Night	53% 4 11% 18% 13% 2	2470
	11th to 20th	Night	46% 4 11% 24% 14% 1	2219
	21st to end	Night	50% 4 11% 19% 11% 4	1884
March	1st to 10th	Night	46% 3 13% 23% 11% 4	3733
	11th to 20th	Night	36% 5% 11% 28% 18% 2	3686
	21st to end	Night	60% 3 11% 18% 7% 1	3471
April	1st to 10th	Night	45% 4 12% 23% 14% 2	1900
	11th to 20th	Night	45% 3 8% 22% 17% 4	1875
	21st to end	Night	46% 5% 11% 24% 10% 3	1829
May	1st to 10th	Night	45% 5% 13% 21% 13% 3	2840
	11th to 20th	Night	37% 7% 18% 26% 11% 1	2516
	21st to end	Night	34% 7% 12% 21% 21% 4	2751
June	1st to 10th	Night	33% 5% 13% 26% 19% 3	1520
	11th to 20th	Night	32% 6% 12% 25% 23% 3	1520
	21st to end	Night	38% 7% 14% 22% 17% 3	1520
July	1st to 10th	Night	43% 5% 15% 19% 14% 3	2490
	11th to 20th	Night	27% 6% 14% 32% 20% 1	2482
	21st to end	Night	34% 8% 15% 18% 21% 4	2662
August	1st to 10th	Night	28% 6% 15% 30% 18% 1	2583
	11th to 20th	Night	31% 6% 14% 31% 18% 1	3130
	21st to end	Night	28% 5% 13% 33% 17% 3	3476
September	1st to 10th	Night	29% 5% 11% 27% 24% 3	1900
	11th to 20th	Night	28% 5% 9% 34% 23% 2	1973
	21st to end	Night	34% 4 12% 30% 17% 2	2090
October	1st to 10th	Night	22% 3 7% 36% 29% 2	3638
	11th to 20th	Night	34% 3 7% 25% 29% 3	3779
	21st to end	Night	42% 3 8% 26% 18% 3	4435
November	1st to 10th	Night	37% 5% 9% 27% 19% 3	2470
	11th to 20th	Night	47% 3 12% 23% 13% 2	2470
	21st to end	Night	48% 4 12% 24% 12%	2577
December	1st to 10th	Night	53% 3 11% 23% 9% 1	2660
	11th to 20th	Night	53% 4 12% 20% 10% 1	3281
	21st to end	Night	68% 6% 10% 12% 4	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	21% 11% 33% 26% 9% 1	270
	11th to 20th	Day	19% 14% 42% 19% 5% 1	270
	21st to end	Day	24% 12% 33% 25% 6% 1	297
February	1st to 10th	Day	17% 17% 38% 20% 6% 1	270
	11th to 20th	Day	21% 16% 34% 24% 4	270
	21st to end	Day	22% 20% 38% 18% 3	225
March	1st to 10th	Day	21% 18% 37% 21% 4	270
	11th to 20th	Day	22% 17% 37% 15% 9% 1	270
	21st to end	Day	28% 13% 31% 20% 7% 2	501
April	1st to 10th	Day	24% 11% 36% 23% 5%	460
	11th to 20th	Day	20% 18% 31% 20% 10% 3	452
	21st to end	Day	22% 13% 30% 23% 9% 2	460
May	1st to 10th	Day	21% 11% 30% 27% 9% 2	463
	11th to 20th	Day	20% 11% 26% 26% 13% 3	663
	21st to end	Day	16% 10% 26% 24% 17% 8%	734
June	1st to 10th	Day	10% 6% 30% 30% 18% 6%	680
	11th to 20th	Day	10% 7% 29% 31% 18% 5%	680
	21st to end	Day	13% 9% 28% 30% 15% 5%	680
July	1st to 10th	Day	10% 4 18% 30% 22% 17%	671
	11th to 20th	Day	10% 3 22% 31% 22% 11%	668
	21st to end	Day	7% 3 21% 35% 27% 8%	739
August	1st to 10th	Day	9% 2 19% 32% 26% 12%	666
	11th to 20th	Day	10% 6% 17% 27% 23% 17%	479
	21st to end	Day	7% 4 16% 31% 30% 11%	539
September	1st to 10th	Day	13% 4 20% 30% 26% 7%	490
	11th to 20th	Day	11% 3 17% 29% 28% 12%	490
	21st to end	Day	13% 11% 26% 25% 19% 6%	490
October	1st to 10th	Day	14% 6% 28% 27% 19% 6%	395
	11th to 20th	Day	20% 17% 31% 23% 8%	300
	21st to end	Day	31% 12% 30% 20% 5% 1	330
November	1st to 10th	Day	15% 13% 35% 22% 11% 4	282
	11th to 20th	Day	22% 17% 34% 19% 6% 2	270
	21st to end	Day	24% 10% 34% 26% 6%	270
December	1st to 10th	Day	19% 14% 38% 21% 7% 1	270
	11th to 20th	Day	17% 12% 39% 23% 9%	270
	21st to end	Day	25% 18% 40% 15% 2	297
January	1st to 10th	Night	19% 13% 39% 24% 5%	950
	11th to 20th	Night	20% 13% 38% 23% 5% 1	950
	21st to end	Night	21% 11% 34% 30% 4	1045
February	1st to 10th	Night	21% 12% 39% 23% 5%	950
	11th to 20th	Night	20% 13% 35% 27% 5%	743
	21st to end	Night	23% 13% 40% 20% 4	628
March	1st to 10th	Night	21% 11% 38% 24% 6%	760
	11th to 20th	Night	15% 11% 37% 28% 7% 1	698
	21st to end	Night	23% 12% 34% 25% 6% 1	627
April	1st to 10th	Night	20% 14% 36% 25% 5%	570
	11th to 20th	Night	23% 12% 33% 25% 7%	563
	21st to end	Night	19% 9% 35% 29% 7%	570
May	1st to 10th	Night	16% 11% 34% 31% 8% 1	570
	11th to 20th	Night	18% 7% 33% 30% 12%	561
	21st to end	Night	14% 4 29% 34% 19%	617
June	1st to 10th	Night	9% 4 27% 43% 16%	570
	11th to 20th	Night	9% 3 30% 45% 12% 1	570
	21st to end	Night	10% 4 27% 38% 19% 1	570
July	1st to 10th	Night	9% 2 15% 41% 30% 4	555
	11th to 20th	Night	9% 2 21% 37% 26% 4	552
	21st to end	Night	5% 1 16% 49% 26% 2	624
August	1st to 10th	Night	5% 1 15% 44% 30% 5%	567
	11th to 20th	Night	7% 2 14% 41% 30% 5%	564
	21st to end	Night	10% 1 18% 39% 30% 2	627
September	1st to 10th	Night	11% 4 20% 34% 27% 4	570
	11th to 20th	Night	10% 4 19% 35% 28% 4	643
	21st to end	Night	13% 7% 24% 35% 18% 3	760
October	1st to 10th	Night	14% 6% 28% 34% 17% 2	760
	11th to 20th	Night	21% 11% 30% 26% 11%	760
	21st to end	Night	24% 11% 33% 23% 8%	836
November	1st to 10th	Night	16% 10% 39% 23% 11% 1	760
	11th to 20th	Night	19% 16% 34% 24% 7%	760
	21st to end	Night	21% 11% 37% 25% 6%	867
December	1st to 10th	Night	21% 13% 38% 23% 6%	950
	11th to 20th	Night	22% 11% 34% 27% 5% 1	950
	21st to end	Night	27% 14% 34% 22% 3	1045

Page generated at 2024-11-03 01:11:24. Version ac07

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