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 2024-04-25.

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	13% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	83243
	Night	14% 9% 4 7% 5% 3 4 4 5% 6% 38%	85935
Transparency	Day	47% 5% 12% 22% 12% 2	82944
	Night	46% 4 12% 22% 13% 2	85755
Seeing	Day	16% 9% 28% 26% 15% 6%	14995
	Night	17% 9% 31% 30% 12% 1	25030

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% 11% 8% 13% 7% 3 5% 4 3 6% 26%	2527
	11th to 20th	Day	12% 11% 5% 15% 7% 3 5% 7% 10% 5% 19%	2530
	21st to end	Day	17% 18% 9% 11% 6% 3 4 4 5% 6% 19%	2919
February	1st to 10th	Day	13% 13% 5% 8% 8% 4 7% 5% 5% 7% 26%	1710
	11th to 20th	Day	13% 10% 4 7% 7% 4 5% 5% 5% 6% 36%	1847
	21st to end	Day	14% 12% 5% 10% 5% 3 4 4 5% 7% 30%	1570
March	1st to 10th	Day	14% 12% 4 8% 4 3 4 4 4 6% 37%	3120
	11th to 20th	Day	11% 6% 2 6% 6% 4 5% 5% 6% 8% 40%	3302
	21st to end	Day	20% 12% 5% 12% 7% 4 6% 5% 4 5% 20%	4160
April	1st to 10th	Day	17% 11% 5% 7% 7% 4 4 4 4 7% 30%	2280
	11th to 20th	Day	16% 9% 3 6% 6% 4 5% 5% 5% 7% 34%	2254
	21st to end	Day	19% 8% 3 7% 6% 4 5% 5% 4 6% 33%	2274
May	1st to 10th	Day	16% 9% 4 6% 6% 4 5% 5% 6% 7% 31%	2340
	11th to 20th	Day	19% 8% 3 6% 5% 4 5% 5% 5% 8% 34%	2467
	21st to end	Day	13% 7% 3 6% 6% 4 6% 5% 6% 9% 36%	2725
June	1st to 10th	Day	9% 4 2 5% 5% 3 5% 5% 6% 8% 46%	2520
	11th to 20th	Day	9% 5% 2 5% 5% 3 5% 5% 6% 9% 46%	2520
	21st to end	Day	10% 6% 3 6% 6% 4 6% 6% 7% 8% 38%	2520
July	1st to 10th	Day	7% 4 3 4 5% 3 5% 6% 7% 9% 47%	2520
	11th to 20th	Day	9% 4 2 4 4 3 5% 6% 6% 10% 46%	2520
	21st to end	Day	6% 5% 2 6% 5% 4 5% 6% 6% 9% 45%	2743
August	1st to 10th	Day	8% 5% 3 5% 6% 4 5% 5% 7% 10% 43%	2468
	11th to 20th	Day	9% 5% 2 5% 5% 3 6% 6% 7% 9% 44%	2125
	21st to end	Day	9% 4 2 4 6% 3 5% 5% 6% 9% 48%	2376
September	1st to 10th	Day	12% 4 3 5% 5% 4 4 5% 5% 7% 46%	2160
	11th to 20th	Day	13% 3 2 4 3 2 3 5% 5% 7% 53%	2072
	21st to end	Day	10% 6% 3 6% 6% 3 4 4 6% 8% 45%	1980
October	1st to 10th	Day	13% 6% 3 5% 4 3 4 5% 5% 7% 46%	1890
	11th to 20th	Day	18% 9% 3 6% 5% 3 4 4 5% 6% 35%	1800
	21st to end	Day	21% 8% 4 5% 5% 3 4 4 4 6% 37%	1800
November	1st to 10th	Day	11% 9% 3 6% 5% 3 4 4 5% 6% 45%	1672
	11th to 20th	Day	15% 12% 4 8% 6% 2 4 5% 5% 8% 32%	1710
	21st to end	Day	18% 10% 4 8% 6% 3 4 3 4 5% 35%	1601
December	1st to 10th	Day	14% 13% 5% 9% 6% 3 5% 4 4 6% 32%	1520
	11th to 20th	Day	12% 12% 5% 9% 7% 4 5% 5% 5% 7% 28%	1918
	21st to end	Day	19% 21% 10% 11% 7% 4 3 3 3 3 15%	2783
January	1st to 10th	Night	13% 12% 5% 13% 8% 3 4 4 4 4 31%	4428
	11th to 20th	Night	14% 17% 7% 12% 7% 3 3 6% 7% 4 20%	4440
	21st to end	Night	18% 17% 8% 10% 6% 3 4 4 4 5% 21%	4746
February	1st to 10th	Night	14% 13% 5% 7% 6% 4 4 4 4 5% 33%	2470
	11th to 20th	Night	14% 10% 3 7% 6% 3 4 4 5% 6% 39%	2218
	21st to end	Night	16% 13% 4 7% 5% 3 4 3 5% 6% 36%	1884
March	1st to 10th	Night	18% 10% 3 4 4 3 3 3 4 6% 41%	3733
	11th to 20th	Night	10% 6% 3 6% 5% 3 4 5% 5% 6% 48%	3686
	21st to end	Night	22% 11% 6% 9% 6% 3 5% 4 3 5% 26%	3471
April	1st to 10th	Night	17% 8% 4 6% 5% 3 4 5% 4 5% 40%	1900
	11th to 20th	Night	19% 8% 3 4 5% 3 4 4 4 6% 40%	1875
	21st to end	Night	16% 8% 3 6% 6% 3 5% 4 5% 7% 38%	1783
May	1st to 10th	Night	14% 7% 3 5% 5% 3 6% 5% 7% 8% 37%	1620
	11th to 20th	Night	16% 6% 2 5% 5% 2 5% 5% 5% 10% 39%	1425
	21st to end	Night	12% 6% 2 6% 6% 3 4 6% 7% 8% 41%	1551
June	1st to 10th	Night	9% 5% 2 5% 5% 2 4 5% 6% 8% 49%	1440
	11th to 20th	Night	9% 5% 2 5% 4 3 5% 5% 6% 9% 48%	1440
	21st to end	Night	8% 5% 3 5% 6% 3 6% 6% 6% 8% 44%	1440
July	1st to 10th	Night	6% 4 2 3 4 3 6% 5% 7% 11% 49%	1440
	11th to 20th	Night	6% 4 2 4 4 3 5% 5% 6% 10% 52%	1440
	21st to end	Night	5% 3 2 5% 5% 3 5% 5% 7% 9% 51%	1575
August	1st to 10th	Night	4 4 1 5% 5% 3 4 6% 7% 9% 51%	1466
	11th to 20th	Night	7% 5% 2 4 4 2 4 5% 5% 10% 52%	1776
	21st to end	Night	9% 4 1 3 4 2 4 4 6% 9% 53%	1980
September	1st to 10th	Night	10% 6% 3 4 4 2 3 4 4 6% 55%	1800
	11th to 20th	Night	10% 4 2 4 4 3 3 4 4 7% 54%	1869
	21st to end	Night	11% 5% 2 3 6% 3 4 4 5% 8% 48%	1980
October	1st to 10th	Night	12% 5% 2 5% 4 3 4 4 5% 6% 51%	2068
	11th to 20th	Night	17% 8% 2 5% 4 3 4 3 4 6% 45%	2160
	21st to end	Night	19% 10% 3 5% 5% 2 4 4 5% 6% 37%	2555
November	1st to 10th	Night	12% 8% 2 5% 4 2 3 3 4 6% 50%	2406
	11th to 20th	Night	15% 8% 4 7% 6% 3 4 4 5% 7% 37%	2470
	21st to end	Night	16% 10% 4 6% 5% 3 4 4 4 6% 37%	2577
December	1st to 10th	Night	16% 10% 4 8% 7% 3 4 4 5% 7% 32%	2660
	11th to 20th	Night	15% 12% 4 8% 6% 3 4 4 5% 6% 32%	3279
	21st to end	Night	21% 17% 7% 9% 7% 3 4 5% 5% 6% 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	51% 5% 12% 17% 13% 1	2274
May	1st to 10th	Day	51% 5% 13% 23% 7%	2340
	11th to 20th	Day	48% 6% 11% 23% 11%	2471
	21st to end	Day	44% 6% 14% 19% 15% 2	2725
June	1st to 10th	Day	34% 6% 14% 28% 17% 2	2520
	11th to 20th	Day	35% 5% 12% 25% 21% 3	2520
	21st to end	Day	41% 7% 14% 23% 13% 2	2520
July	1st to 10th	Day	32% 7% 15% 30% 14% 3	2451
	11th to 20th	Day	32% 6% 16% 28% 16% 2	2445
	21st to end	Day	33% 6% 17% 26% 15% 3	2591
August	1st to 10th	Day	34% 7% 17% 30% 11% 2	2453
	11th to 20th	Day	36% 6% 14% 27% 16% 1	2125
	21st to end	Day	31% 6% 12% 28% 20% 3	2376
September	1st to 10th	Day	37% 6% 12% 24% 17% 4	2160
	11th to 20th	Day	31% 5% 12% 29% 21% 3	2072
	21st to end	Day	37% 4 10% 28% 19% 2	1980
October	1st to 10th	Day	38% 6% 11% 26% 18% 1	1890
	11th to 20th	Day	49% 5% 11% 21% 13% 2	1800
	21st to end	Day	49% 4 12% 23% 10% 2	1800
November	1st to 10th	Day	40% 4 13% 25% 16% 2	1672
	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	1783
May	1st to 10th	Night	45% 5% 14% 25% 11%	1620
	11th to 20th	Night	42% 6% 14% 23% 14% 1	1426
	21st to end	Night	39% 7% 14% 21% 17% 2	1552
June	1st to 10th	Night	33% 5% 13% 26% 20% 3	1440
	11th to 20th	Night	33% 6% 13% 24% 23% 3	1440
	21st to end	Night	37% 7% 14% 23% 17% 3	1440
July	1st to 10th	Night	29% 6% 15% 28% 18% 4	1400
	11th to 20th	Night	28% 6% 14% 30% 20% 3	1392
	21st to end	Night	28% 6% 17% 26% 18% 6%	1487
August	1st to 10th	Night	27% 7% 17% 32% 14% 2	1457
	11th to 20th	Night	27% 6% 16% 29% 20% 1	1776
	21st to end	Night	27% 5% 12% 30% 21% 5%	1980
September	1st to 10th	Night	30% 5% 11% 27% 23% 3	1800
	11th to 20th	Night	29% 5% 9% 33% 22% 2	1869
	21st to end	Night	34% 4 12% 30% 17% 2	1980
October	1st to 10th	Night	34% 5% 10% 27% 22% 2	2068
	11th to 20th	Night	42% 3 9% 25% 19% 2	2160
	21st to end	Night	48% 4 10% 24% 13% 1	2555
November	1st to 10th	Night	36% 5% 9% 27% 19% 3	2406
	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% 12% 30% 24% 9% 2	437
May	1st to 10th	Day	22% 11% 30% 26% 9% 2	423
	11th to 20th	Day	22% 11% 26% 25% 13% 3	613
	21st to end	Day	16% 8% 26% 24% 18% 8%	679
June	1st to 10th	Day	9% 5% 29% 31% 19% 7%	630
	11th to 20th	Day	10% 6% 28% 31% 19% 5%	630
	21st to end	Day	12% 8% 27% 32% 15% 5%	630
July	1st to 10th	Day	9% 3 16% 30% 23% 18%	621
	11th to 20th	Day	11% 3 22% 32% 22% 11%	618
	21st to end	Day	6% 4 21% 36% 26% 7%	684
August	1st to 10th	Day	9% 2 18% 32% 27% 12%	617
	11th to 20th	Day	10% 6% 15% 27% 24% 19%	439
	21st to end	Day	7% 4 17% 32% 28% 12%	495
September	1st to 10th	Day	14% 4 20% 30% 25% 7%	450
	11th to 20th	Day	12% 4 17% 30% 25% 12%	450
	21st to end	Day	11% 11% 26% 26% 20% 6%	450
October	1st to 10th	Day	16% 5% 28% 27% 18% 5%	360
	11th to 20th	Day	22% 18% 31% 21% 7%	270
	21st to end	Day	33% 12% 29% 20% 5% 1	297
November	1st to 10th	Day	14% 13% 36% 23% 10% 4	270
	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% 34% 30% 8%	555
May	1st to 10th	Night	16% 11% 34% 31% 8% 1	540
	11th to 20th	Night	18% 7% 33% 29% 12%	531
	21st to end	Night	14% 4 28% 34% 20%	584
June	1st to 10th	Night	10% 4 26% 44% 17%	540
	11th to 20th	Night	10% 3 29% 45% 12% 1	540
	21st to end	Night	10% 4 26% 39% 20% 1	540
July	1st to 10th	Night	7% 2 14% 41% 31% 5%	525
	11th to 20th	Night	9% 2 21% 37% 27% 4	522
	21st to end	Night	6% 2 16% 49% 26% 2	591
August	1st to 10th	Night	5% 1 14% 45% 30% 5%	537
	11th to 20th	Night	7% 2 13% 41% 32% 5%	534
	21st to end	Night	10% 1 18% 38% 30% 2	594
September	1st to 10th	Night	11% 4 20% 34% 26% 4	540
	11th to 20th	Night	10% 4 19% 34% 28% 4	609
	21st to end	Night	13% 7% 24% 35% 18% 3	720
October	1st to 10th	Night	15% 5% 28% 33% 17% 2	720
	11th to 20th	Night	22% 12% 30% 26% 10%	720
	21st to end	Night	25% 11% 34% 22% 8%	792
November	1st to 10th	Night	16% 10% 39% 24% 11% 1	740
	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 2024-04-22 08:25:42. Version ac07

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