Hutchinson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hutchinson clear sky chart from 2005-11-06 to 2026-01-02.

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% 4 4 4 6% 7% 39%	128498
	Night	11% 8% 3 8% 5% 4 4 4 5% 6% 40%	123118
Transparency	Day	43% 5% 13% 25% 12% 1	132086
	Night	43% 5% 12% 25% 13% 2	127606
Seeing	Day	16% 9% 31% 28% 13% 3	17588
	Night	15% 9% 33% 31% 10% 1	27539

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	8% 14% 4 15% 10% 7% 7% 4 5% 7% 19%	3625
	11th to 20th	Day	6% 9% 5% 13% 6% 7% 9% 8% 11% 7% 19%	3822
	21st to end	Day	5% 14% 7% 13% 8% 6% 5% 3 5% 6% 29%	4488
February	1st to 10th	Day	8% 12% 4 12% 7% 6% 5% 4 6% 6% 30%	1800
	11th to 20th	Day	8% 11% 4 10% 6% 5% 6% 5% 6% 7% 33%	1754
	21st to end	Day	10% 11% 3 9% 7% 5% 5% 4 6% 7% 33%	1510
March	1st to 10th	Day	11% 9% 3 7% 4 3 4 4 5% 8% 43%	4936
	11th to 20th	Day	9% 9% 3 7% 4 4 4 4 6% 8% 42%	4980
	21st to end	Day	21% 11% 3 10% 7% 5% 4 3 5% 6% 25%	5462
April	1st to 10th	Day	17% 10% 3 7% 4 3 4 3 6% 6% 36%	2375
	11th to 20th	Day	18% 12% 3 8% 4 5% 4 3 5% 6% 32%	2452
	21st to end	Day	23% 10% 3 6% 4 4 4 3 4 6% 32%	2600
May	1st to 10th	Day	13% 5% 2 5% 4 4 4 3 5% 6% 49%	5952
	11th to 20th	Day	17% 7% 2 5% 3 3 3 3 5% 6% 45%	6319
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 5% 8% 36%	6935
June	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 7% 8% 45%	2800
	11th to 20th	Day	14% 7% 3 7% 5% 5% 4 4 6% 7% 39%	2953
	21st to end	Day	10% 5% 2 5% 4 4 5% 5% 7% 10% 43%	3000
July	1st to 10th	Day	8% 4 2 6% 4 4 5% 4 7% 10% 45%	6800
	11th to 20th	Day	8% 4 1 4 3 3 3 3 4 8% 57%	6370
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 7% 10% 47%	6654
August	1st to 10th	Day	12% 6% 2 6% 4 5% 4 4 6% 8% 43%	4234
	11th to 20th	Day	13% 5% 2 5% 4 5% 5% 5% 7% 9% 40%	4171
	21st to end	Day	9% 5% 2 6% 4 4 4 3 6% 7% 50%	4549
September	1st to 10th	Day	11% 4 2 5% 3 4 4 4 4 8% 50%	2400
	11th to 20th	Day	12% 6% 2 5% 5% 4 4 4 6% 7% 46%	2295
	21st to end	Day	15% 5% 2 4 4 3 4 3 5% 7% 48%	2150
October	1st to 10th	Day	15% 8% 2 5% 4 4 4 2 5% 7% 44%	2000
	11th to 20th	Day	15% 10% 2 6% 3 5% 4 3 5% 7% 41%	2000
	21st to end	Day	18% 11% 3 7% 3 3 3 3 5% 6% 38%	2200
November	1st to 10th	Day	12% 11% 4 8% 5% 5% 4 3 6% 7% 36%	1704
	11th to 20th	Day	10% 11% 5% 12% 6% 5% 4 3 5% 6% 33%	1680
	21st to end	Day	13% 10% 4 9% 5% 4 5% 4 6% 8% 32%	1680
December	1st to 10th	Day	7% 10% 4 12% 9% 9% 6% 5% 6% 7% 26%	2690
	11th to 20th	Day	10% 15% 6% 10% 7% 5% 5% 4 5% 7% 26%	3088
	21st to end	Day	19% 17% 6% 21% 5% 4 3 3 3 5% 16%	4070
January	1st to 10th	Night	7% 10% 5% 17% 9% 7% 5% 3 5% 6% 27%	6363
	11th to 20th	Night	5% 10% 4 11% 8% 8% 10% 7% 7% 5% 24%	6154
	21st to end	Night	6% 14% 8% 9% 5% 4 4 3 6% 6% 34%	6490
February	1st to 10th	Night	8% 13% 4 8% 6% 6% 4 4 5% 7% 35%	2600
	11th to 20th	Night	6% 9% 3 9% 5% 5% 5% 4 6% 8% 40%	2533
	21st to end	Night	10% 9% 3 9% 5% 4 5% 4 6% 7% 38%	2135
March	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 5% 7% 50%	4920
	11th to 20th	Night	9% 6% 2 7% 5% 4 5% 4 7% 9% 42%	4980
	21st to end	Night	24% 11% 3 9% 5% 4 3 3 4 5% 29%	5467
April	1st to 10th	Night	14% 9% 3 7% 5% 4 4 4 5% 6% 39%	2024
	11th to 20th	Night	18% 10% 3 7% 5% 3 3 3 6% 5% 36%	1894
	21st to end	Night	19% 9% 3 7% 4 4 4 3 5% 5% 37%	1800
May	1st to 10th	Night	11% 6% 1 4 4 4 3 3 4 5% 54%	3961
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 5% 7% 48%	3596
	21st to end	Night	17% 8% 3 7% 4 3 3 3 5% 7% 40%	3942
June	1st to 10th	Night	10% 5% 1 4 3 3 4 3 7% 9% 51%	1600
	11th to 20th	Night	10% 5% 2 5% 5% 4 4 3 6% 9% 47%	1440
	21st to end	Night	9% 3 1 4 4 3 4 4 6% 6% 55%	1400
July	1st to 10th	Night	9% 4 1 5% 4 4 4 4 7% 9% 51%	3178
	11th to 20th	Night	4 3 2 5% 4 4 4 3 6% 8% 57%	3590
	21st to end	Night	9% 5% 2 5% 4 4 4 3 6% 7% 50%	4214
August	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 5% 6% 48%	2926
	11th to 20th	Night	13% 4 2 4 4 3 4 3 5% 8% 49%	2888
	21st to end	Night	9% 4 2 6% 3 4 4 4 5% 7% 52%	3354
September	1st to 10th	Night	8% 4 2 5% 3 3 4 3 5% 7% 56%	2000
	11th to 20th	Night	10% 5% 1 4 3 3 4 4 5% 7% 55%	2100
	21st to end	Night	10% 5% 2 4 3 3 3 3 5% 6% 56%	2230
October	1st to 10th	Night	14% 6% 2 4 3 3 3 3 4 6% 51%	2400
	11th to 20th	Night	15% 9% 3 6% 3 4 4 3 4 6% 44%	2400
	21st to end	Night	17% 10% 3 6% 4 3 3 3 4 7% 40%	2640
November	1st to 10th	Night	13% 7% 2 6% 5% 4 4 3 6% 7% 43%	2810
	11th to 20th	Night	12% 12% 4 10% 5% 4 3 3 5% 5% 37%	2940
	21st to end	Night	12% 11% 4 8% 5% 4 4 4 5% 6% 38%	2940
December	1st to 10th	Night	6% 8% 3 12% 9% 6% 6% 4 6% 8% 32%	4720
	11th to 20th	Night	10% 13% 7% 12% 7% 6% 5% 3 6% 5% 26%	5339
	21st to end	Night	20% 16% 5% 17% 6% 4 4 3 4 4 18%	7150

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	64% 5% 9% 15% 7%	3626
	11th to 20th	Day	57% 5% 11% 18% 9%	3822
	21st to end	Day	57% 5% 14% 15% 9%	4488
February	1st to 10th	Day	54% 5% 12% 19% 9% 1	1800
	11th to 20th	Day	49% 5% 14% 23% 8% 1	1763
	21st to end	Day	50% 7% 12% 21% 11%	1510
March	1st to 10th	Day	39% 4 16% 27% 11% 2	4936
	11th to 20th	Day	40% 5% 13% 30% 11% 2	4980
	21st to end	Day	61% 4 11% 19% 6%	5464
April	1st to 10th	Day	48% 5% 11% 23% 12% 1	2375
	11th to 20th	Day	52% 5% 11% 19% 12% 1	2452
	21st to end	Day	54% 4 11% 21% 9% 1	2600
May	1st to 10th	Day	35% 5% 12% 29% 17% 1	5990
	11th to 20th	Day	40% 5% 8% 23% 18% 6%	6323
	21st to end	Day	45% 6% 10% 30% 9% 1	6949
June	1st to 10th	Day	35% 7% 14% 30% 13% 1	2800
	11th to 20th	Day	43% 6% 14% 21% 14% 2	2953
	21st to end	Day	34% 7% 18% 27% 12% 2	3000
July	1st to 10th	Day	32% 8% 18% 31% 10%	6726
	11th to 20th	Day	26% 5% 16% 36% 15% 2	6294
	21st to end	Day	31% 6% 16% 31% 14% 1	6465
August	1st to 10th	Day	38% 6% 13% 29% 12% 2	4220
	11th to 20th	Day	39% 7% 15% 30% 8%	4210
	21st to end	Day	34% 6% 18% 28% 13% 1	4548
September	1st to 10th	Day	33% 5% 13% 35% 13%	2400
	11th to 20th	Day	36% 6% 16% 31% 10%	2295
	21st to end	Day	36% 5% 11% 34% 13% 1	2150
October	1st to 10th	Day	32% 3 8% 33% 24%	3260
	11th to 20th	Day	38% 4 12% 24% 22% 1	3240
	21st to end	Day	45% 3 15% 28% 10%	3538
November	1st to 10th	Day	47% 5% 13% 20% 13% 2	1704
	11th to 20th	Day	52% 4 13% 20% 10% 1	1680
	21st to end	Day	49% 5% 16% 22% 7% 1	1680
December	1st to 10th	Day	56% 6% 14% 18% 5%	2690
	11th to 20th	Day	59% 4 16% 16% 6%	3085
	21st to end	Day	73% 3 8% 10% 5%	4070
January	1st to 10th	Night	58% 4 10% 20% 7%	6363
	11th to 20th	Night	58% 5% 9% 16% 11% 1	6154
	21st to end	Night	50% 4 13% 25% 8%	6490
February	1st to 10th	Night	48% 4 14% 21% 12% 2	2600
	11th to 20th	Night	41% 5% 16% 25% 11% 2	2534
	21st to end	Night	45% 4 13% 23% 13% 2	2135
March	1st to 10th	Night	34% 4 13% 31% 16% 2	4920
	11th to 20th	Night	37% 4 14% 30% 14% 1	4980
	21st to end	Night	58% 4 8% 19% 10% 1	5467
April	1st to 10th	Night	45% 5% 12% 25% 12% 1	2024
	11th to 20th	Night	48% 4 7% 22% 16% 2	1894
	21st to end	Night	49% 5% 9% 21% 14% 2	1800
May	1st to 10th	Night	32% 5% 10% 30% 21% 2	3988
	11th to 20th	Night	35% 5% 9% 20% 21% 9%	3597
	21st to end	Night	43% 5% 10% 28% 12% 1	3950
June	1st to 10th	Night	29% 5% 15% 32% 16% 3	1600
	11th to 20th	Night	35% 4 16% 25% 18% 3	1440
	21st to end	Night	27% 6% 15% 31% 17% 3	1400
July	1st to 10th	Night	29% 7% 20% 28% 16% 1	3145
	11th to 20th	Night	24% 5% 16% 37% 16% 2	3546
	21st to end	Night	32% 6% 16% 31% 12% 2	4092
August	1st to 10th	Night	36% 6% 12% 27% 14% 5%	2916
	11th to 20th	Night	34% 6% 14% 31% 13% 1	2915
	21st to end	Night	30% 7% 17% 29% 14% 2	3354
September	1st to 10th	Night	27% 6% 15% 33% 19% 1	2000
	11th to 20th	Night	29% 6% 16% 32% 16% 1	2100
	21st to end	Night	30% 5% 11% 35% 18% 2	2230
October	1st to 10th	Night	23% 3 6% 37% 27% 5%	3920
	11th to 20th	Night	31% 4 12% 27% 22% 3	3899
	21st to end	Night	41% 5% 11% 30% 13% 1	4252
November	1st to 10th	Night	40% 4 14% 25% 14% 2	2810
	11th to 20th	Night	50% 5% 12% 19% 13% 1	2940
	21st to end	Night	47% 5% 16% 23% 8% 1	2940
December	1st to 10th	Night	48% 6% 19% 20% 6%	4720
	11th to 20th	Night	59% 5% 11% 19% 5% 1	5341
	21st to end	Night	70% 5% 9% 13% 4	7150

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	15% 10% 35% 25% 13% 2	303
	11th to 20th	Day	15% 13% 37% 30% 5% 1	300
	21st to end	Day	14% 9% 40% 26% 9% 2	330
February	1st to 10th	Day	15% 13% 44% 24% 4	300
	11th to 20th	Day	15% 15% 38% 27% 4 1	300
	21st to end	Day	16% 11% 41% 27% 4	249
March	1st to 10th	Day	18% 11% 42% 24% 4 1	300
	11th to 20th	Day	19% 12% 35% 25% 8% 1	300
	21st to end	Day	24% 14% 29% 23% 8% 2	330
April	1st to 10th	Day	25% 16% 32% 21% 5%	475
	11th to 20th	Day	27% 14% 26% 23% 8% 1	570
	21st to end	Day	25% 14% 30% 22% 8% 2	700
May	1st to 10th	Day	20% 11% 32% 24% 10% 2	703
	11th to 20th	Day	20% 10% 29% 26% 13% 2	725
	21st to end	Day	18% 8% 30% 27% 13% 3	789
June	1st to 10th	Day	11% 7% 28% 31% 20% 4	730
	11th to 20th	Day	16% 8% 32% 32% 9% 2	730
	21st to end	Day	14% 7% 33% 29% 14% 3	730
July	1st to 10th	Day	8% 4 23% 37% 20% 8%	721
	11th to 20th	Day	9% 7% 26% 33% 21% 5%	718
	21st to end	Day	7% 4 27% 37% 21% 5%	794
August	1st to 10th	Day	12% 4 23% 35% 22% 4	726
	11th to 20th	Day	15% 4 20% 32% 23% 6%	715
	21st to end	Day	10% 4 28% 35% 19% 5%	729
September	1st to 10th	Day	12% 8% 28% 31% 15% 5%	530
	11th to 20th	Day	13% 4 30% 33% 16% 4	425
	21st to end	Day	18% 9% 29% 23% 15% 7%	330
October	1st to 10th	Day	18% 10% 32% 25% 12% 5%	330
	11th to 20th	Day	18% 18% 37% 20% 7% 1	330
	21st to end	Day	26% 13% 36% 16% 7% 1	363
November	1st to 10th	Day	21% 15% 32% 23% 8% 1	330
	11th to 20th	Day	17% 13% 43% 22% 4	330
	21st to end	Day	20% 15% 37% 22% 5%	330
December	1st to 10th	Day	15% 8% 42% 26% 8% 1	330
	11th to 20th	Day	17% 15% 38% 25% 5%	330
	21st to end	Day	27% 13% 37% 19% 4	363
January	1st to 10th	Night	11% 11% 40% 29% 8% 1	1006
	11th to 20th	Night	15% 10% 37% 30% 7% 1	1000
	21st to end	Night	17% 11% 37% 29% 6%	1100
February	1st to 10th	Night	14% 11% 39% 28% 6% 1	1000
	11th to 20th	Night	11% 12% 41% 29% 7% 1	979
	21st to end	Night	15% 11% 36% 29% 8% 1	815
March	1st to 10th	Night	15% 9% 40% 26% 9% 1	601
	11th to 20th	Night	18% 10% 36% 31% 5% 1	600
	21st to end	Night	24% 10% 32% 23% 11% 2	660
April	1st to 10th	Night	19% 10% 37% 29% 5%	600
	11th to 20th	Night	22% 13% 29% 28% 7% 1	593
	21st to end	Night	23% 10% 33% 25% 8% 1	600
May	1st to 10th	Night	19% 10% 32% 29% 10% 1	600
	11th to 20th	Night	17% 8% 34% 30% 10% 1	591
	21st to end	Night	17% 7% 29% 35% 11% 1	650
June	1st to 10th	Night	13% 4 30% 38% 15%	600
	11th to 20th	Night	13% 5% 33% 40% 10%	600
	21st to end	Night	10% 4 28% 42% 16%	600
July	1st to 10th	Night	7% 2 22% 41% 27% 2	585
	11th to 20th	Night	5% 3 25% 48% 18% 1	582
	21st to end	Night	5% 2 24% 47% 19% 2	657
August	1st to 10th	Night	9% 3 17% 46% 23% 2	597
	11th to 20th	Night	11% 3 19% 41% 23% 3	594
	21st to end	Night	7% 4 26% 39% 22% 2	660
September	1st to 10th	Night	10% 4 27% 39% 18% 3	600
	11th to 20th	Night	12% 5% 32% 31% 19% 2	600
	21st to end	Night	11% 9% 31% 32% 15% 1	630
October	1st to 10th	Night	17% 8% 32% 29% 12% 1	800
	11th to 20th	Night	21% 10% 35% 25% 8% 1	800
	21st to end	Night	23% 11% 33% 27% 6%	880
November	1st to 10th	Night	17% 10% 36% 29% 8%	1004
	11th to 20th	Night	17% 13% 38% 24% 7% 1	1050
	21st to end	Night	18% 12% 38% 25% 6%	1050
December	1st to 10th	Night	15% 10% 38% 28% 8% 1	1050
	11th to 20th	Night	19% 12% 37% 26% 6% 1	1050
	21st to end	Night	24% 11% 33% 26% 5%	1155

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