Guymon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Guymon clear sky chart from 2005-11-06 to 2025-03-27.

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	5% 4 1 4 3 3 3 3 5% 7% 62%	113403
	Night	5% 4 2 4 3 3 4 3 5% 7% 59%	114712
Transparency	Day	23% 4 9% 23% 28% 12%	113156
	Night	24% 4 9% 23% 27% 13%	114549
Seeing	Day	8% 7% 28% 34% 20% 4	15861
	Night	7% 8% 36% 38% 10%	25990

By Month

Percentage Cloud Cover SW (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% 9% 3 5% 2 3 3 2 4 6% 56%	3638
	11th to 20th	Day	3 5% 3 6% 3 3 3 3 4 6% 63%	3793
	21st to end	Day	5% 5% 2 5% 3 3 3 2 4 5% 61%	4826
February	1st to 10th	Day	6% 7% 2 6% 3 3 3 3 4 6% 57%	2000
	11th to 20th	Day	4 8% 3 6% 4 3 3 3 4 6% 57%	1949
	21st to end	Day	5% 4 2 3 3 3 3 3 4 6% 65%	1650
March	1st to 10th	Day	5% 5% 1 4 2 2 2 2 3 6% 67%	3230
	11th to 20th	Day	6% 5% 2 4 3 3 3 3 5% 7% 60%	3457
	21st to end	Day	7% 6% 2 5% 4 3 4 4 5% 7% 53%	4030
April	1st to 10th	Day	6% 4 1 3 2 3 4 2 5% 5% 65%	2280
	11th to 20th	Day	10% 4 1 4 3 2 2 3 4 6% 60%	2251
	21st to end	Day	9% 5% 1 4 3 3 3 3 5% 6% 58%	2351
May	1st to 10th	Day	9% 4 2 4 3 3 3 3 4 7% 59%	4120
	11th to 20th	Day	7% 4 2 4 3 3 4 3 5% 7% 58%	4082
	21st to end	Day	6% 4 1 3 3 3 3 3 4 7% 63%	4489
June	1st to 10th	Day	4 3 2 4 3 4 4 4 6% 9% 57%	2491
	11th to 20th	Day	5% 3 1 3 2 3 4 3 5% 8% 63%	2660
	21st to end	Day	3 2 1 4 3 3 4 4 6% 10% 59%	2660
July	1st to 10th	Day	5% 3 1 4 3 4 4 4 6% 8% 57%	4430
	11th to 20th	Day	2 2 1 3 2 3 3 3 6% 9% 65%	4347
	21st to end	Day	3 2 1 4 3 3 4 4 6% 9% 61%	4466
August	1st to 10th	Day	7% 4 1 4 3 4 4 4 6% 8% 54%	3987
	11th to 20th	Day	3 3 1 3 3 3 3 3 6% 8% 63%	3726
	21st to end	Day	4 3 1 4 2 3 4 4 7% 9% 59%	4180
September	1st to 10th	Day	9% 5% 1 4 3 2 3 3 4 6% 59%	2260
	11th to 20th	Day	7% 3 1 3 3 3 4 3 4 6% 63%	2090
	21st to end	Day	6% 3 1 3 3 3 2 3 3 6% 67%	2090
October	1st to 10th	Day	7% 2 1 3 2 2 2 2 3 5% 71%	3480
	11th to 20th	Day	6% 4 1 4 2 3 3 2 4 5% 66%	3381
	21st to end	Day	5% 3 1 2 2 2 2 1 3 4 76%	3091
November	1st to 10th	Day	6% 3 1 3 2 2 3 2 3 6% 68%	1763
	11th to 20th	Day	4 4 1 3 2 2 2 2 4 5% 71%	1800
	21st to end	Day	7% 5% 2 3 2 3 2 2 3 6% 65%	1800
December	1st to 10th	Day	1 4 1 2 2 2 2 2 4 5% 74%	2940
	11th to 20th	Day	4 4 1 3 2 2 3 3 5% 7% 67%	3391
	21st to end	Day	6% 9% 3 6% 4 4 3 2 4 5% 52%	4224
January	1st to 10th	Night	6% 7% 2 6% 4 4 4 3 4 5% 54%	6327
	11th to 20th	Night	3 5% 2 5% 3 3 3 3 4 6% 63%	6167
	21st to end	Night	6% 5% 2 5% 4 3 3 2 4 6% 60%	6196
February	1st to 10th	Night	4 7% 2 6% 4 3 3 2 5% 5% 59%	2400
	11th to 20th	Night	5% 6% 3 7% 5% 4 4 4 5% 6% 52%	2338
	21st to end	Night	6% 4 1 4 2 2 3 3 5% 6% 64%	1980
March	1st to 10th	Night	4 5% 2 4 3 3 2 2 4 5% 67%	3854
	11th to 20th	Night	7% 4 2 5% 3 3 4 3 5% 7% 57%	3725
	21st to end	Night	5% 5% 1 4 3 4 4 4 5% 7% 59%	3739
April	1st to 10th	Night	6% 4 1 4 3 3 3 2 4 6% 63%	1900
	11th to 20th	Night	7% 5% 2 4 4 3 3 3 5% 7% 58%	1877
	21st to end	Night	11% 4 1 4 3 3 3 2 6% 8% 54%	1827
May	1st to 10th	Night	9% 5% 1 5% 4 3 4 3 5% 7% 55%	2850
	11th to 20th	Night	9% 5% 2 4 4 3 4 4 6% 8% 52%	2823
	21st to end	Night	8% 4 1 4 4 3 4 4 5% 7% 56%	3098
June	1st to 10th	Night	4 2 1 4 3 5% 4 3 7% 11% 56%	1683
	11th to 20th	Night	4 2 1 4 4 3 5% 4 7% 8% 58%	1520
	21st to end	Night	3 4 1 4 3 4 6% 4 8% 10% 55%	1520
July	1st to 10th	Night	5% 3 2 4 4 4 4 4 7% 10% 52%	2540
	11th to 20th	Night	3 3 1 5% 5% 4 5% 3 8% 11% 51%	2619
	21st to end	Night	3 3 2 5% 4 4 5% 4 8% 11% 49%	3097
August	1st to 10th	Night	9% 4 2 6% 5% 6% 5% 5% 8% 9% 41%	2948
	11th to 20th	Night	4 3 2 4 3 4 5% 5% 9% 14% 46%	3113
	21st to end	Night	4 3 2 5% 4 5% 6% 6% 9% 12% 45%	3487
September	1st to 10th	Night	7% 3 1 3 2 3 3 3 5% 7% 62%	1919
	11th to 20th	Night	7% 3 1 4 3 3 3 4 5% 7% 60%	2090
	21st to end	Night	6% 2 1 3 2 3 2 3 4 5% 68%	2090
October	1st to 10th	Night	6% 2 1 2 1 1 2 2 4 5% 73%	3480
	11th to 20th	Night	7% 3 1 3 3 3 4 2 5% 6% 63%	3511
	21st to end	Night	6% 3 1 3 2 2 2 2 4 4 71%	4461
November	1st to 10th	Night	5% 3 1 3 2 2 2 3 5% 6% 69%	2535
	11th to 20th	Night	2 2 1 3 2 2 3 2 4 5% 73%	2600
	21st to end	Night	7% 5% 2 2 2 2 3 3 4 6% 64%	2600
December	1st to 10th	Night	3 4 1 3 2 2 2 2 4 6% 71%	4250
	11th to 20th	Night	4 3 1 3 2 2 2 2 4 6% 71%	4816
	21st to end	Night	6% 6% 2 5% 3 3 4 3 5% 7% 56%	6732

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	31% 3 7% 29% 24% 6%	3639
	11th to 20th	Day	24% 2 9% 19% 28% 16%	3793
	21st to end	Day	27% 2 7% 21% 35% 8%	4826
February	1st to 10th	Day	30% 3 10% 23% 24% 11%	2000
	11th to 20th	Day	30% 3 7% 26% 22% 11%	1959
	21st to end	Day	22% 3 5% 21% 32% 18%	1650
March	1st to 10th	Day	21% 1 6% 18% 27% 26%	3230
	11th to 20th	Day	25% 4 9% 22% 31% 10%	3457
	21st to end	Day	29% 5% 11% 26% 22% 8%	4030
April	1st to 10th	Day	22% 3 8% 23% 27% 17%	2280
	11th to 20th	Day	26% 4 9% 21% 24% 15%	2254
	21st to end	Day	27% 4 9% 25% 26% 9%	2351
May	1st to 10th	Day	26% 5% 10% 21% 20% 19%	4120
	11th to 20th	Day	26% 6% 12% 24% 24% 8%	4086
	21st to end	Day	22% 7% 11% 17% 24% 20%	4489
June	1st to 10th	Day	22% 8% 15% 26% 20% 9%	2491
	11th to 20th	Day	19% 6% 9% 20% 27% 19%	2660
	21st to end	Day	20% 5% 12% 26% 25% 12%	2660
July	1st to 10th	Day	23% 6% 11% 23% 29% 7%	4361
	11th to 20th	Day	15% 5% 13% 25% 33% 9%	4272
	21st to end	Day	19% 6% 12% 27% 28% 9%	4325
August	1st to 10th	Day	27% 7% 15% 22% 24% 4	3974
	11th to 20th	Day	19% 5% 12% 24% 32% 9%	3762
	21st to end	Day	20% 5% 11% 29% 27% 7%	4179
September	1st to 10th	Day	27% 5% 8% 21% 24% 14%	2260
	11th to 20th	Day	23% 5% 8% 22% 29% 14%	2090
	21st to end	Day	20% 3 8% 24% 29% 15%	2090
October	1st to 10th	Day	18% 3 6% 15% 40% 18%	3480
	11th to 20th	Day	22% 2 7% 22% 34% 13%	3381
	21st to end	Day	15% 2 4 19% 40% 20%	3091
November	1st to 10th	Day	19% 2 8% 20% 34% 16%	1763
	11th to 20th	Day	18% 2 6% 28% 33% 13%	1800
	21st to end	Day	23% 2 6% 20% 31% 17%	1800
December	1st to 10th	Day	14% 3 8% 33% 33% 10%	2940
	11th to 20th	Day	18% 2 5% 24% 42% 9%	3389
	21st to end	Day	35% 4 7% 20% 25% 10%	4224
January	1st to 10th	Night	32% 3 8% 33% 20% 4	6327
	11th to 20th	Night	23% 3 11% 18% 29% 16%	6167
	21st to end	Night	27% 4 9% 17% 35% 9%	6196
February	1st to 10th	Night	28% 4 8% 21% 27% 12%	2400
	11th to 20th	Night	33% 4 8% 21% 24% 10%	2338
	21st to end	Night	22% 2 5% 20% 31% 20%	1980
March	1st to 10th	Night	21% 2 5% 20% 25% 27%	3854
	11th to 20th	Night	26% 4 9% 20% 26% 16%	3725
	21st to end	Night	24% 5% 9% 31% 20% 10%	3739
April	1st to 10th	Night	23% 3 8% 21% 26% 19%	1900
	11th to 20th	Night	27% 4 10% 22% 23% 13%	1877
	21st to end	Night	28% 5% 12% 23% 22% 9%	1827
May	1st to 10th	Night	29% 7% 12% 17% 15% 20%	2850
	11th to 20th	Night	29% 8% 13% 20% 20% 9%	2824
	21st to end	Night	27% 6% 13% 16% 17% 21%	3099
June	1st to 10th	Night	21% 7% 19% 28% 16% 8%	1683
	11th to 20th	Night	20% 9% 14% 21% 23% 13%	1520
	21st to end	Night	22% 7% 12% 26% 20% 13%	1520
July	1st to 10th	Night	25% 6% 12% 31% 22% 4	2500
	11th to 20th	Night	25% 5% 14% 22% 26% 7%	2571
	21st to end	Night	26% 6% 11% 27% 21% 9%	2999
August	1st to 10th	Night	36% 7% 12% 18% 22% 5%	2938
	11th to 20th	Night	25% 6% 13% 27% 22% 7%	3143
	21st to end	Night	28% 6% 13% 24% 24% 5%	3487
September	1st to 10th	Night	22% 5% 12% 21% 25% 14%	1919
	11th to 20th	Night	22% 6% 12% 18% 28% 14%	2090
	21st to end	Night	19% 5% 7% 23% 29% 17%	2090
October	1st to 10th	Night	15% 3 6% 15% 39% 22%	3480
	11th to 20th	Night	24% 3 7% 22% 26% 18%	3511
	21st to end	Night	19% 2 4 19% 40% 16%	4461
November	1st to 10th	Night	17% 3 9% 22% 30% 21%	2535
	11th to 20th	Night	14% 2 6% 25% 36% 16%	2600
	21st to end	Night	22% 3 6% 22% 29% 18%	2600
December	1st to 10th	Night	16% 3 7% 33% 36% 6%	4250
	11th to 20th	Night	18% 2 5% 24% 40% 12%	4817
	21st to end	Night	29% 4 8% 24% 27% 8%	6732

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	7% 7% 35% 36% 13% 1	300
	11th to 20th	Day	10% 13% 33% 30% 13% 1	300
	21st to end	Day	4 8% 42% 28% 15% 4	330
February	1st to 10th	Day	8% 13% 41% 30% 8%	300
	11th to 20th	Day	9% 9% 45% 25% 10% 2	300
	21st to end	Day	6% 9% 50% 28% 6% 1	249
March	1st to 10th	Day	9% 9% 41% 32% 9% 1	300
	11th to 20th	Day	14% 11% 38% 26% 11% 1	300
	21st to end	Day	13% 14% 35% 26% 10% 1	401
April	1st to 10th	Day	10% 14% 41% 25% 9% 2	460
	11th to 20th	Day	11% 16% 38% 28% 6%	452
	21st to end	Day	13% 15% 39% 24% 8% 2	531
May	1st to 10th	Day	10% 11% 34% 34% 11% 1	653
	11th to 20th	Day	11% 7% 29% 34% 16% 3	675
	21st to end	Day	9% 8% 37% 30% 15% 1	734
June	1st to 10th	Day	5% 5% 26% 37% 22% 6%	680
	11th to 20th	Day	5% 4 31% 36% 20% 3	680
	21st to end	Day	4 2 24% 42% 24% 3	680
July	1st to 10th	Day	5% 2 17% 37% 31% 8%	671
	11th to 20th	Day	2 1 13% 40% 34% 9%	668
	21st to end	Day	5% 1 10% 39% 34% 11%	739
August	1st to 10th	Day	4 1 12% 40% 37% 7%	612
	11th to 20th	Day	3 15% 40% 34% 7%	477
	21st to end	Day	4 1 14% 41% 29% 11%	539
September	1st to 10th	Day	10% 2 16% 36% 29% 7%	470
	11th to 20th	Day	5% 3 17% 40% 26% 9%	300
	21st to end	Day	8% 5% 22% 31% 28% 7%	300
October	1st to 10th	Day	11% 6% 25% 28% 23% 7%	300
	11th to 20th	Day	6% 5% 31% 34% 19% 6%	300
	21st to end	Day	14% 9% 27% 28% 17% 5%	330
November	1st to 10th	Day	9% 7% 31% 31% 19% 3	300
	11th to 20th	Day	7% 10% 31% 33% 15% 4	300
	21st to end	Day	11% 12% 27% 29% 15% 6%	300
December	1st to 10th	Day	4 6% 34% 39% 16% 2	300
	11th to 20th	Day	8% 8% 35% 33% 15% 1	300
	21st to end	Day	12% 15% 35% 27% 10% 1	330
January	1st to 10th	Night	6% 8% 37% 41% 8% 1	1000
	11th to 20th	Night	9% 8% 34% 37% 11% 1	1000
	21st to end	Night	6% 6% 39% 40% 9%	975
February	1st to 10th	Night	7% 10% 38% 39% 6%	800
	11th to 20th	Night	8% 11% 49% 27% 5%	784
	21st to end	Night	8% 11% 47% 31% 4	660
March	1st to 10th	Night	7% 12% 43% 33% 4	800
	11th to 20th	Night	11% 11% 39% 31% 8%	683
	21st to end	Night	10% 14% 49% 25% 2	647
April	1st to 10th	Night	8% 14% 45% 29% 3	570
	11th to 20th	Night	10% 15% 50% 23% 3	563
	21st to end	Night	12% 12% 42% 27% 6%	570
May	1st to 10th	Night	9% 11% 45% 31% 4	570
	11th to 20th	Night	9% 8% 38% 36% 10%	561
	21st to end	Night	9% 7% 47% 30% 8%	617
June	1st to 10th	Night	4 5% 39% 39% 12%	570
	11th to 20th	Night	4 7% 49% 35% 5%	570
	21st to end	Night	3 5% 38% 44% 11%	570
July	1st to 10th	Night	5% 3 25% 46% 19% 1	555
	11th to 20th	Night	4 1 22% 50% 22% 1	552
	21st to end	Night	6% 1 19% 52% 22% 1	624
August	1st to 10th	Night	5% 2 18% 48% 26% 1	567
	11th to 20th	Night	7% 2 20% 51% 20% 1	564
	21st to end	Night	5% 2 23% 46% 24% 1	627
September	1st to 10th	Night	8% 1 26% 51% 14%	570
	11th to 20th	Night	7% 2 37% 43% 9% 1	570
	21st to end	Night	6% 5% 28% 46% 14%	570
October	1st to 10th	Night	10% 5% 30% 43% 12%	570
	11th to 20th	Night	7% 7% 37% 38% 11% 1	597
	21st to end	Night	9% 9% 32% 33% 16% 1	1039
November	1st to 10th	Night	6% 5% 33% 45% 10%	975
	11th to 20th	Night	4 7% 40% 39% 10%	1000
	21st to end	Night	9% 9% 30% 38% 13% 1	1000
December	1st to 10th	Night	7% 7% 34% 44% 9%	1000
	11th to 20th	Night	10% 8% 39% 36% 7%	1000
	21st to end	Night	10% 11% 37% 35% 7% 1	1100

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