Grundy Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grundy Center clear sky chart from 2005-11-06 to 2024-10-24.

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% 8% 3 8% 5% 5% 5% 4 5% 7% 38%	101376
	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 41%	97498
Transparency	Day	45% 5% 13% 23% 13% 1	101173
	Night	44% 4 12% 24% 14% 2	97372
Seeing	Day	16% 9% 30% 27% 14% 4	15848
	Night	16% 8% 32% 31% 11% 1	25673

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	7% 12% 7% 23% 8% 7% 5% 3 4 5% 19%	2527
	11th to 20th	Day	8% 14% 4 11% 7% 8% 6% 4 8% 5% 24%	2698
	21st to end	Day	13% 15% 7% 18% 6% 5% 5% 3 4 6% 17%	3135
February	1st to 10th	Day	11% 11% 5% 11% 6% 5% 4 4 5% 8% 28%	1710
	11th to 20th	Day	12% 12% 4 7% 5% 4 6% 3 6% 7% 33%	1664
	21st to end	Day	13% 11% 3 10% 6% 4 4 3 6% 6% 34%	1532
March	1st to 10th	Day	15% 9% 3 8% 5% 3 3 3 4 5% 42%	3368
	11th to 20th	Day	11% 6% 3 7% 5% 4 5% 4 5% 8% 43%	3480
	21st to end	Day	21% 15% 7% 11% 5% 5% 4 3 4 5% 21%	3867
April	1st to 10th	Day	19% 12% 3 7% 4 4 4 4 5% 6% 32%	2280
	11th to 20th	Day	18% 8% 3 7% 6% 5% 5% 4 4 6% 34%	2254
	21st to end	Day	22% 8% 3 7% 4 4 4 4 4 6% 34%	2376
May	1st to 10th	Day	20% 8% 2 7% 4 4 5% 4 6% 8% 32%	4145
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 5% 7% 42%	4399
	21st to end	Day	14% 7% 3 6% 5% 4 4 4 6% 7% 41%	4824
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 5% 6% 8% 43%	2660
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 3 5% 9% 44%	2660
	21st to end	Day	11% 7% 2 7% 5% 6% 5% 5% 7% 8% 38%	2660
July	1st to 10th	Day	9% 7% 2 8% 6% 6% 6% 5% 7% 9% 35%	4440
	11th to 20th	Day	5% 4 2 5% 4 4 4 3 6% 8% 56%	4440
	21st to end	Day	6% 4 2 6% 6% 5% 6% 5% 8% 10% 42%	4595
August	1st to 10th	Day	9% 5% 2 6% 4 5% 6% 4 7% 9% 43%	4104
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 9% 39%	4041
	21st to end	Day	7% 5% 2 6% 4 4 4 3 6% 8% 49%	4215
September	1st to 10th	Day	11% 6% 2 6% 3 3 3 3 6% 7% 51%	2280
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 5% 7% 50%	2278
	21st to end	Day	11% 6% 3 5% 4 4 4 4 4 8% 48%	1981
October	1st to 10th	Day	13% 6% 2 7% 4 4 4 3 5% 6% 45%	1900
	11th to 20th	Day	16% 9% 2 6% 4 4 3 3 4 6% 43%	1900
	21st to end	Day	15% 10% 3 6% 4 4 4 3 4 6% 41%	2010
November	1st to 10th	Day	10% 7% 3 8% 3 5% 4 3 5% 8% 45%	1692
	11th to 20th	Day	12% 11% 4 10% 5% 3 4 3 6% 8% 34%	1520
	21st to end	Day	14% 12% 3 7% 4 4 4 3 4 7% 37%	1520
December	1st to 10th	Day	12% 13% 4 9% 6% 6% 5% 3 5% 7% 30%	1520
	11th to 20th	Day	12% 12% 4 11% 5% 4 6% 3 5% 6% 32%	1918
	21st to end	Day	21% 18% 7% 14% 5% 3 3 3 3 5% 18%	2783
January	1st to 10th	Night	9% 13% 5% 21% 7% 5% 4 3 4 5% 24%	4428
	11th to 20th	Night	10% 15% 5% 12% 6% 4 5% 4 8% 7% 23%	4271
	21st to end	Night	15% 15% 7% 14% 6% 4 4 3 4 5% 22%	4532
February	1st to 10th	Night	9% 13% 5% 12% 7% 4 4 4 4 7% 32%	2470
	11th to 20th	Night	12% 9% 4 7% 5% 4 4 4 5% 6% 40%	2403
	21st to end	Night	13% 10% 4 7% 6% 4 4 2 4 5% 39%	1922
March	1st to 10th	Night	13% 9% 4 6% 4 3 3 3 5% 5% 45%	3515
	11th to 20th	Night	11% 6% 2 6% 4 4 3 3 5% 8% 49%	3480
	21st to end	Night	24% 13% 4 11% 5% 4 4 3 4 4 24%	3764
April	1st to 10th	Night	14% 10% 2 8% 5% 4 3 3 5% 6% 41%	1900
	11th to 20th	Night	14% 10% 3 7% 5% 4 4 3 5% 7% 39%	1875
	21st to end	Night	18% 7% 2 6% 3 4 3 4 4 7% 42%	1800
May	1st to 10th	Night	17% 7% 2 7% 4 4 4 4 6% 6% 39%	2759
	11th to 20th	Night	11% 7% 2 7% 5% 4 4 4 5% 6% 46%	2506
	21st to end	Night	10% 7% 2 5% 5% 4 4 3 5% 7% 47%	2743
June	1st to 10th	Night	6% 6% 2 5% 5% 5% 6% 4 5% 9% 47%	1520
	11th to 20th	Night	8% 5% 2 6% 6% 4 4 4 7% 8% 46%	1520
	21st to end	Night	11% 5% 2 6% 3 4 4 3 6% 8% 48%	1520
July	1st to 10th	Night	8% 6% 2 6% 4 4 5% 5% 6% 9% 44%	2530
	11th to 20th	Night	3 3 1 5% 3 4 3 3 6% 8% 60%	2530
	21st to end	Night	5% 4 1 6% 4 4 5% 4 7% 9% 51%	2964
August	1st to 10th	Night	6% 4 2 5% 4 4 4 5% 6% 8% 53%	2836
	11th to 20th	Night	10% 5% 2 5% 3 2 4 3 4 7% 55%	2798
	21st to end	Night	8% 5% 2 5% 4 4 3 3 5% 7% 54%	3440
September	1st to 10th	Night	9% 5% 2 6% 4 3 3 2 5% 6% 56%	1900
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 4 6% 55%	1900
	21st to end	Night	10% 5% 1 5% 4 3 3 2 5% 6% 57%	2177
October	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 4 7% 52%	2280
	11th to 20th	Night	15% 6% 2 6% 4 3 4 3 5% 6% 46%	2280
	21st to end	Night	16% 9% 3 5% 3 3 4 3 5% 6% 42%	2413
November	1st to 10th	Night	11% 7% 2 5% 3 3 4 2 5% 7% 52%	2384
	11th to 20th	Night	12% 9% 4 8% 5% 4 4 4 5% 5% 41%	2655
	21st to end	Night	14% 10% 3 8% 4 4 4 3 5% 6% 42%	2660
December	1st to 10th	Night	10% 10% 4 9% 6% 6% 6% 3 6% 6% 33%	2660
	11th to 20th	Night	13% 11% 4 9% 6% 5% 4 4 5% 6% 34%	3279
	21st to end	Night	20% 16% 5% 14% 6% 4 4 3 4 4 21%	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	68% 4 10% 11% 7%	2528
	11th to 20th	Day	59% 3 11% 18% 7%	2698
	21st to end	Day	69% 3 11% 12% 4 1	3135
February	1st to 10th	Day	54% 4 14% 18% 9% 1	1710
	11th to 20th	Day	49% 4 11% 23% 10% 2	1673
	21st to end	Day	51% 4 12% 19% 11% 3	1532
March	1st to 10th	Day	46% 3 11% 24% 14% 2	3368
	11th to 20th	Day	40% 4 11% 30% 13% 2	3480
	21st to end	Day	65% 5% 12% 13% 4 1	3867
April	1st to 10th	Day	53% 5% 11% 22% 9% 1	2280
	11th to 20th	Day	51% 4 10% 20% 13% 1	2254
	21st to end	Day	51% 4 10% 22% 12% 1	2376
May	1st to 10th	Day	49% 5% 14% 18% 13% 1	4183
	11th to 20th	Day	42% 5% 12% 28% 12% 1	4403
	21st to end	Day	42% 5% 12% 26% 14% 1	4837
June	1st to 10th	Day	37% 5% 16% 24% 16% 2	2660
	11th to 20th	Day	37% 5% 12% 23% 20% 2	2660
	21st to end	Day	41% 6% 14% 23% 14% 2	2660
July	1st to 10th	Day	43% 7% 13% 28% 8% 1	4371
	11th to 20th	Day	26% 5% 14% 34% 19% 2	4365
	21st to end	Day	33% 8% 19% 22% 17% 1	4450
August	1st to 10th	Day	36% 5% 16% 27% 14% 1	4090
	11th to 20th	Day	40% 6% 15% 26% 12% 1	4080
	21st to end	Day	32% 5% 15% 29% 17% 2	4214
September	1st to 10th	Day	32% 4 14% 27% 21% 3	2280
	11th to 20th	Day	33% 5% 13% 32% 16% 1	2278
	21st to end	Day	35% 5% 10% 31% 17% 1	1981
October	1st to 10th	Day	40% 3 9% 29% 18% 1	1900
	11th to 20th	Day	43% 3 10% 25% 18% 2	1900
	21st to end	Day	45% 3 12% 24% 14% 2	2010
November	1st to 10th	Day	38% 4 13% 26% 16% 2	1692
	11th to 20th	Day	48% 4 13% 22% 13% 1	1520
	21st to end	Day	47% 5% 16% 23% 9% 1	1520
December	1st to 10th	Day	54% 4 14% 19% 8% 2	1520
	11th to 20th	Day	53% 4 18% 17% 8%	1915
	21st to end	Day	71% 4 8% 13% 4	2783
January	1st to 10th	Night	63% 3 11% 14% 8% 1	4428
	11th to 20th	Night	58% 3 12% 17% 9%	4271
	21st to end	Night	65% 3 11% 15% 6% 1	4532
February	1st to 10th	Night	52% 4 11% 20% 12% 1	2470
	11th to 20th	Night	44% 5% 11% 26% 13% 2	2404
	21st to end	Night	49% 3 11% 20% 14% 3	1922
March	1st to 10th	Night	42% 3 8% 28% 16% 2	3515
	11th to 20th	Night	35% 3 10% 32% 17% 3	3480
	21st to end	Night	65% 3 15% 12% 5% 1	3764
April	1st to 10th	Night	44% 3 11% 27% 12% 2	1900
	11th to 20th	Night	46% 4 10% 21% 17% 3	1875
	21st to end	Night	42% 4 12% 28% 13% 2	1800
May	1st to 10th	Night	44% 5% 10% 19% 21% 1	2786
	11th to 20th	Night	39% 4 10% 28% 16% 4	2507
	21st to end	Night	36% 5% 12% 28% 16% 3	2751
June	1st to 10th	Night	33% 7% 15% 27% 16% 3	1520
	11th to 20th	Night	33% 5% 14% 21% 21% 6%	1520
	21st to end	Night	34% 4 14% 28% 16% 4	1520
July	1st to 10th	Night	35% 6% 17% 28% 12% 2	2490
	11th to 20th	Night	22% 5% 16% 36% 18% 3	2482
	21st to end	Night	28% 6% 18% 26% 20% 2	2870
August	1st to 10th	Night	28% 6% 15% 35% 15% 2	2826
	11th to 20th	Night	30% 5% 15% 36% 13% 1	2825
	21st to end	Night	30% 5% 15% 27% 19% 4	3440
September	1st to 10th	Night	30% 4 9% 28% 26% 2	1900
	11th to 20th	Night	32% 4 10% 32% 22% 1	1900
	21st to end	Night	29% 3 12% 31% 23% 2	2177
October	1st to 10th	Night	33% 4 10% 27% 23% 3	2280
	11th to 20th	Night	39% 4 10% 24% 19% 4	2280
	21st to end	Night	43% 3 11% 23% 17% 2	2413
November	1st to 10th	Night	34% 4 14% 26% 18% 4	2384
	11th to 20th	Night	45% 3 12% 25% 13% 1	2655
	21st to end	Night	44% 3 13% 27% 11% 1	2660
December	1st to 10th	Night	50% 4 13% 23% 9% 1	2660
	11th to 20th	Night	50% 5% 13% 25% 7% 1	3281
	21st to end	Night	67% 4 8% 14% 7%	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	19% 11% 40% 21% 8% 1	270
	11th to 20th	Day	21% 12% 42% 20% 4	270
	21st to end	Day	20% 12% 34% 27% 5% 2	297
February	1st to 10th	Day	16% 19% 39% 21% 4 1	270
	11th to 20th	Day	19% 18% 35% 21% 6% 1	270
	21st to end	Day	24% 14% 38% 22% 2	225
March	1st to 10th	Day	16% 19% 41% 19% 6% 1	270
	11th to 20th	Day	25% 13% 30% 24% 6% 1	270
	21st to end	Day	32% 15% 29% 18% 6% 1	325
April	1st to 10th	Day	28% 14% 36% 16% 6%	460
	11th to 20th	Day	24% 19% 28% 21% 7% 1	452
	21st to end	Day	27% 13% 33% 17% 9% 1	556
May	1st to 10th	Day	24% 12% 30% 23% 9% 2	653
	11th to 20th	Day	24% 9% 28% 25% 11% 2	675
	21st to end	Day	15% 10% 27% 29% 16% 4	734
June	1st to 10th	Day	9% 6% 28% 35% 19% 4	680
	11th to 20th	Day	13% 6% 30% 33% 15% 3	680
	21st to end	Day	11% 7% 32% 32% 14% 5%	680
July	1st to 10th	Day	10% 2 19% 35% 23% 11%	671
	11th to 20th	Day	8% 3 26% 35% 21% 6%	668
	21st to end	Day	7% 2 24% 37% 24% 6%	739
August	1st to 10th	Day	9% 2 24% 34% 25% 7%	676
	11th to 20th	Day	13% 3 22% 32% 23% 8%	665
	21st to end	Day	12% 3 21% 35% 25% 5%	561
September	1st to 10th	Day	14% 6% 22% 29% 23% 7%	490
	11th to 20th	Day	10% 3 26% 33% 24% 5%	488
	21st to end	Day	15% 11% 27% 29% 16% 3	300
October	1st to 10th	Day	16% 6% 32% 25% 17% 4	300
	11th to 20th	Day	21% 20% 34% 17% 9%	300
	21st to end	Day	23% 15% 34% 18% 8% 2	306
November	1st to 10th	Day	15% 11% 43% 21% 8% 2	270
	11th to 20th	Day	18% 19% 34% 21% 7% 1	270
	21st to end	Day	23% 11% 40% 23% 1 1	270
December	1st to 10th	Day	15% 13% 43% 20% 8% 1	270
	11th to 20th	Day	18% 13% 35% 24% 8% 1	270
	21st to end	Day	25% 14% 42% 17% 2	297
January	1st to 10th	Night	15% 12% 39% 27% 7%	950
	11th to 20th	Night	17% 12% 36% 29% 5% 1	950
	21st to end	Night	20% 11% 35% 29% 5%	1045
February	1st to 10th	Night	17% 12% 38% 27% 6% 1	950
	11th to 20th	Night	16% 13% 39% 26% 5% 1	929
	21st to end	Night	20% 13% 38% 24% 5%	666
March	1st to 10th	Night	19% 13% 38% 23% 7% 1	632
	11th to 20th	Night	18% 9% 37% 27% 9%	570
	21st to end	Night	24% 10% 37% 22% 6% 1	627
April	1st to 10th	Night	19% 13% 39% 25% 4	570
	11th to 20th	Night	20% 10% 36% 27% 7%	563
	21st to end	Night	22% 10% 34% 26% 7% 1	570
May	1st to 10th	Night	19% 7% 34% 32% 8% 1	570
	11th to 20th	Night	17% 5% 34% 35% 9%	561
	21st to end	Night	16% 5% 27% 37% 15%	617
June	1st to 10th	Night	9% 3 29% 41% 17% 1	570
	11th to 20th	Night	10% 3 32% 43% 12% 1	570
	21st to end	Night	12% 5% 27% 39% 17% 1	570
July	1st to 10th	Night	7% 2 14% 47% 27% 2	555
	11th to 20th	Night	5% 2 24% 41% 26% 3	552
	21st to end	Night	7% 1 19% 47% 24% 2	624
August	1st to 10th	Night	8% 2 17% 45% 27% 2	567
	11th to 20th	Night	11% 2 16% 40% 26% 4	564
	21st to end	Night	11% 2 20% 39% 26% 3	627
September	1st to 10th	Night	11% 3 22% 39% 22% 3	570
	11th to 20th	Night	15% 2 22% 39% 19% 3	570
	21st to end	Night	12% 7% 29% 36% 16% 1	659
October	1st to 10th	Night	14% 6% 31% 34% 13% 1	760
	11th to 20th	Night	18% 10% 35% 28% 8%	760
	21st to end	Night	22% 11% 31% 27% 8%	805
November	1st to 10th	Night	15% 10% 39% 28% 8% 1	740
	11th to 20th	Night	17% 13% 42% 22% 7%	945
	21st to end	Night	18% 11% 39% 24% 8%	950
December	1st to 10th	Night	16% 12% 38% 27% 5% 1	950
	11th to 20th	Night	22% 8% 36% 27% 6% 1	950
	21st to end	Night	26% 12% 33% 24% 5%	1045

Page generated at 2024-10-21 01:20:00. Version ac07

Copyright © 2024 Attilla Danko.