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 2024-11-12.

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 6% 7% 38%	102265
	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 40%	97009
Transparency	Day	44% 6% 13% 25% 11% 1	105893
	Night	42% 5% 12% 25% 13% 2	101521
Seeing	Day	16% 9% 31% 28% 13% 3	16040
	Night	15% 8% 33% 31% 11% 1	25918

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	10% 17% 4 16% 8% 5% 5% 4 4 6% 20%	2527
	11th to 20th	Day	5% 10% 5% 15% 7% 7% 9% 6% 8% 6% 21%	2662
	21st to end	Day	7% 18% 8% 13% 8% 7% 6% 3 5% 6% 19%	3135
February	1st to 10th	Day	8% 12% 4 11% 7% 6% 5% 4 6% 6% 31%	1710
	11th to 20th	Day	8% 11% 4 10% 6% 6% 6% 5% 6% 7% 32%	1664
	21st to end	Day	10% 11% 3 10% 8% 5% 5% 4 6% 7% 31%	1436
March	1st to 10th	Day	11% 11% 4 9% 5% 4 4 4 5% 7% 37%	3436
	11th to 20th	Day	10% 8% 3 8% 5% 5% 4 3 5% 8% 41%	3480
	21st to end	Day	22% 12% 3 11% 8% 5% 4 3 4 6% 21%	3814
April	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 6% 6% 36%	2256
	11th to 20th	Day	19% 12% 3 8% 4 5% 4 3 5% 5% 33%	2328
	21st to end	Day	23% 10% 3 6% 4 4 4 3 4 6% 32%	2470
May	1st to 10th	Day	17% 6% 2 6% 4 5% 5% 4 5% 7% 38%	4144
	11th to 20th	Day	13% 6% 3 6% 4 4 4 3 5% 7% 45%	4399
	21st to end	Day	17% 6% 3 7% 4 4 5% 4 6% 9% 35%	4824
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 7% 8% 45%	2660
	11th to 20th	Day	13% 7% 3 6% 4 5% 4 4 6% 7% 40%	2805
	21st to end	Day	9% 5% 2 6% 4 4 5% 5% 7% 10% 44%	2850
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 39%	4750
	11th to 20th	Day	5% 4 1 3 3 3 4 3 5% 8% 61%	4450
	21st to end	Day	6% 4 2 5% 4 4 5% 5% 7% 10% 49%	4627
August	1st to 10th	Day	12% 6% 2 6% 4 5% 4 4 6% 8% 43%	4104
	11th to 20th	Day	13% 5% 2 5% 4 5% 5% 5% 7% 9% 40%	4041
	21st to end	Day	9% 5% 2 6% 4 4 4 3 5% 7% 50%	4410
September	1st to 10th	Day	11% 4 2 5% 3 4 4 4 4 8% 51%	2280
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 7% 47%	2180
	21st to end	Day	16% 5% 2 4 4 4 4 3 5% 7% 47%	2043
October	1st to 10th	Day	16% 8% 2 5% 4 4 4 2 5% 6% 43%	1900
	11th to 20th	Day	14% 9% 2 6% 4 5% 4 3 5% 7% 42%	1900
	21st to end	Day	17% 10% 3 7% 3 3 3 3 5% 6% 39%	2090
November	1st to 10th	Day	13% 11% 4 8% 5% 5% 4 3 5% 7% 36%	1621
	11th to 20th	Day	10% 11% 5% 12% 6% 5% 4 3 5% 6% 32%	1528
	21st to end	Day	14% 10% 3 7% 5% 4 5% 4 6% 9% 33%	1520
December	1st to 10th	Day	10% 12% 4 11% 8% 7% 5% 4 5% 6% 27%	1520
	11th to 20th	Day	10% 14% 6% 10% 7% 5% 4 4 4 7% 29%	1918
	21st to end	Day	21% 13% 4 18% 4 4 3 3 4 6% 20%	2783
January	1st to 10th	Night	10% 13% 6% 18% 7% 4 4 3 4 5% 26%	4428
	11th to 20th	Night	6% 10% 5% 13% 9% 8% 9% 6% 8% 5% 21%	4304
	21st to end	Night	8% 18% 9% 12% 5% 5% 4 3 5% 5% 26%	4532
February	1st to 10th	Night	7% 13% 4 9% 6% 6% 4 4 5% 7% 36%	2470
	11th to 20th	Night	6% 8% 3 9% 5% 5% 5% 4 6% 8% 40%	2403
	21st to end	Night	10% 9% 3 9% 6% 4 5% 5% 6% 6% 37%	2032
March	1st to 10th	Night	9% 7% 2 7% 4 4 4 3 5% 7% 48%	3420
	11th to 20th	Night	8% 7% 2 8% 5% 4 5% 4 6% 7% 42%	3480
	21st to end	Night	25% 12% 3 10% 5% 3 2 3 4 5% 28%	3817
April	1st to 10th	Night	14% 9% 3 7% 5% 4 4 4 5% 6% 39%	1923
	11th to 20th	Night	19% 10% 3 7% 5% 3 3 3 6% 5% 36%	1798
	21st to end	Night	18% 9% 3 7% 4 4 4 3 5% 5% 38%	1710
May	1st to 10th	Night	15% 8% 2 5% 4 4 4 4 5% 6% 44%	2759
	11th to 20th	Night	14% 4 2 5% 3 3 3 4 6% 8% 48%	2506
	21st to end	Night	16% 7% 2 5% 3 3 4 3 6% 7% 45%	2743
June	1st to 10th	Night	10% 5% 1 4 3 3 4 3 7% 9% 51%	1520
	11th to 20th	Night	10% 5% 2 5% 5% 4 5% 3 6% 9% 48%	1368
	21st to end	Night	8% 3 1 4 4 3 4 4 6% 6% 57%	1330
July	1st to 10th	Night	11% 4 1 5% 4 4 4 4 7% 9% 45%	2220
	11th to 20th	Night	3 2 1 5% 3 4 4 3 5% 8% 63%	2516
	21st to end	Night	5% 4 2 4 3 3 4 3 6% 8% 58%	2933
August	1st to 10th	Night	13% 6% 2 6% 3 4 3 4 5% 6% 49%	2836
	11th to 20th	Night	13% 4 2 4 4 3 5% 3 5% 8% 49%	2798
	21st to end	Night	9% 4 2 6% 4 4 4 4 5% 7% 52%	3251
September	1st to 10th	Night	8% 4 2 5% 3 3 4 3 5% 6% 57%	1900
	11th to 20th	Night	10% 5% 1 4 3 3 4 4 5% 7% 56%	1995
	21st to end	Night	11% 5% 2 4 3 3 3 3 5% 6% 55%	2118
October	1st to 10th	Night	15% 6% 2 4 3 3 3 3 4 7% 50%	2280
	11th to 20th	Night	14% 9% 2 6% 3 4 4 3 4 6% 44%	2280
	21st to end	Night	16% 10% 3 6% 4 3 3 3 5% 7% 40%	2508
November	1st to 10th	Night	13% 7% 2 6% 5% 4 4 3 6% 6% 44%	2673
	11th to 20th	Night	12% 12% 4 10% 6% 4 4 3 5% 5% 37%	2675
	21st to end	Night	12% 10% 3 7% 5% 4 4 4 5% 6% 39%	2660
December	1st to 10th	Night	9% 11% 4 11% 7% 5% 4 4 5% 7% 33%	2660
	11th to 20th	Night	11% 12% 5% 11% 6% 7% 5% 4 6% 6% 29%	3279
	21st to end	Night	21% 14% 4 13% 6% 4 4 4 5% 5% 22%	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	65% 5% 10% 16% 4	2528
	11th to 20th	Day	60% 5% 12% 18% 5%	2662
	21st to end	Day	65% 6% 11% 14% 4	3135
February	1st to 10th	Day	53% 5% 13% 20% 8% 1	1710
	11th to 20th	Day	50% 5% 15% 22% 8% 1	1673
	21st to end	Day	51% 7% 11% 20% 11%	1436
March	1st to 10th	Day	47% 5% 13% 25% 10% 1	3436
	11th to 20th	Day	41% 5% 9% 31% 11% 3	3480
	21st to end	Day	65% 5% 9% 17% 4	3814
April	1st to 10th	Day	48% 5% 11% 23% 12% 1	2256
	11th to 20th	Day	52% 4 10% 19% 12% 1	2328
	21st to end	Day	54% 4 11% 20% 9% 1	2470
May	1st to 10th	Day	43% 7% 11% 25% 14% 1	4182
	11th to 20th	Day	37% 6% 9% 29% 16% 2	4403
	21st to end	Day	44% 7% 12% 26% 9% 1	4837
June	1st to 10th	Day	35% 7% 14% 30% 13% 1	2660
	11th to 20th	Day	42% 6% 14% 22% 15% 2	2805
	21st to end	Day	34% 7% 18% 28% 11% 2	2850
July	1st to 10th	Day	36% 9% 19% 23% 12%	4676
	11th to 20th	Day	22% 5% 17% 36% 18% 2	4374
	21st to end	Day	29% 7% 16% 32% 15% 1	4481
August	1st to 10th	Day	38% 6% 12% 30% 12% 2	4090
	11th to 20th	Day	39% 7% 15% 31% 8%	4080
	21st to end	Day	34% 6% 18% 28% 14% 1	4409
September	1st to 10th	Day	33% 5% 13% 35% 14%	2280
	11th to 20th	Day	36% 6% 16% 32% 11%	2180
	21st to end	Day	37% 6% 11% 34% 12% 1	2043
October	1st to 10th	Day	32% 3 8% 32% 24%	3160
	11th to 20th	Day	37% 4 12% 24% 21% 1	3140
	21st to end	Day	44% 3 15% 28% 10%	3428
November	1st to 10th	Day	47% 5% 12% 20% 13% 3	1621
	11th to 20th	Day	53% 4 13% 19% 10% 1	1528
	21st to end	Day	47% 5% 17% 22% 7% 1	1520
December	1st to 10th	Day	56% 6% 14% 17% 7%	1520
	11th to 20th	Day	56% 4 17% 17% 5%	1915
	21st to end	Day	67% 4 10% 14% 5%	2783
January	1st to 10th	Night	60% 5% 11% 18% 6%	4428
	11th to 20th	Night	61% 5% 10% 18% 5%	4304
	21st to end	Night	60% 4 10% 19% 6% 1	4532
February	1st to 10th	Night	48% 4 14% 22% 11% 2	2470
	11th to 20th	Night	41% 5% 16% 25% 11% 2	2404
	21st to end	Night	46% 5% 12% 22% 13% 2	2032
March	1st to 10th	Night	35% 5% 13% 28% 17% 2	3420
	11th to 20th	Night	38% 5% 10% 31% 15% 1	3480
	21st to end	Night	60% 4 7% 20% 8% 1	3817
April	1st to 10th	Night	45% 6% 12% 25% 12% 1	1923
	11th to 20th	Night	49% 4 6% 22% 17% 3	1798
	21st to end	Night	48% 5% 9% 22% 14% 2	1710
May	1st to 10th	Night	41% 6% 10% 23% 19% 2	2786
	11th to 20th	Night	33% 6% 12% 24% 21% 4	2507
	21st to end	Night	39% 6% 12% 27% 15% 1	2751
June	1st to 10th	Night	29% 5% 15% 32% 16% 3	1520
	11th to 20th	Night	34% 4 16% 25% 18% 3	1368
	21st to end	Night	26% 6% 15% 32% 17% 3	1330
July	1st to 10th	Night	34% 7% 21% 23% 14% 1	2185
	11th to 20th	Night	18% 5% 15% 38% 20% 3	2469
	21st to end	Night	24% 6% 16% 35% 16% 3	2840
August	1st to 10th	Night	36% 6% 12% 27% 15% 5%	2826
	11th to 20th	Night	34% 6% 14% 32% 13% 1	2825
	21st to end	Night	31% 7% 17% 29% 14% 2	3251
September	1st to 10th	Night	26% 6% 14% 34% 20% 1	1900
	11th to 20th	Night	28% 6% 16% 33% 17% 1	1995
	21st to end	Night	31% 5% 11% 35% 17% 2	2118
October	1st to 10th	Night	23% 3 6% 37% 27% 5%	3800
	11th to 20th	Night	31% 4 12% 28% 22% 3	3779
	21st to end	Night	41% 5% 11% 30% 13% 1	4120
November	1st to 10th	Night	40% 5% 14% 25% 14% 2	2673
	11th to 20th	Night	51% 5% 12% 19% 13% 1	2675
	21st to end	Night	45% 5% 17% 23% 8% 1	2660
December	1st to 10th	Night	51% 5% 17% 20% 7%	2660
	11th to 20th	Night	54% 7% 14% 18% 6% 1	3281
	21st to end	Night	64% 6% 10% 16% 5%	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	16% 9% 33% 26% 14% 2	270
	11th to 20th	Day	15% 13% 36% 31% 5% 1	270
	21st to end	Day	14% 9% 39% 26% 10% 2	297
February	1st to 10th	Day	13% 13% 44% 25% 4	270
	11th to 20th	Day	15% 16% 36% 28% 4 1	270
	21st to end	Day	17% 11% 40% 28% 4	225
March	1st to 10th	Day	19% 12% 40% 23% 5% 1	270
	11th to 20th	Day	19% 11% 35% 25% 8% 1	270
	21st to end	Day	24% 13% 27% 24% 9% 2	297
April	1st to 10th	Day	25% 15% 33% 21% 6%	436
	11th to 20th	Day	28% 13% 25% 24% 9% 1	526
	21st to end	Day	25% 12% 30% 22% 8% 2	650
May	1st to 10th	Day	21% 12% 34% 24% 8% 1	653
	11th to 20th	Day	19% 10% 30% 26% 13% 3	675
	21st to end	Day	18% 9% 31% 27% 13% 3	734
June	1st to 10th	Day	10% 6% 28% 31% 20% 4	680
	11th to 20th	Day	15% 8% 33% 33% 10% 2	680
	21st to end	Day	13% 7% 32% 30% 14% 4	680
July	1st to 10th	Day	8% 5% 23% 36% 20% 8%	671
	11th to 20th	Day	8% 7% 26% 33% 21% 6%	668
	21st to end	Day	7% 4 26% 37% 22% 5%	739
August	1st to 10th	Day	12% 4 22% 36% 22% 4	676
	11th to 20th	Day	15% 4 20% 33% 22% 6%	665
	21st to end	Day	10% 5% 28% 35% 19% 4	678
September	1st to 10th	Day	13% 7% 29% 32% 15% 4	490
	11th to 20th	Day	14% 4 31% 32% 16% 4	390
	21st to end	Day	18% 10% 31% 21% 12% 7%	300
October	1st to 10th	Day	19% 9% 31% 24% 12% 5%	300
	11th to 20th	Day	16% 18% 37% 22% 7% 1	300
	21st to end	Day	26% 13% 37% 16% 7% 1	330
November	1st to 10th	Day	22% 13% 31% 24% 9% 1	300
	11th to 20th	Day	14% 13% 45% 22% 5%	273
	21st to end	Day	21% 14% 39% 21% 6%	270
December	1st to 10th	Day	13% 9% 41% 27% 9% 1	270
	11th to 20th	Day	16% 13% 39% 27% 5%	270
	21st to end	Day	27% 13% 36% 20% 4	297
January	1st to 10th	Night	11% 10% 40% 29% 8% 1	950
	11th to 20th	Night	15% 10% 36% 30% 7% 1	950
	21st to end	Night	17% 11% 35% 30% 7%	1045
February	1st to 10th	Night	14% 10% 39% 30% 7% 1	950
	11th to 20th	Night	11% 11% 40% 29% 7% 1	929
	21st to end	Night	15% 10% 35% 30% 9% 1	776
March	1st to 10th	Night	15% 10% 40% 25% 10% 1	571
	11th to 20th	Night	18% 9% 36% 31% 5% 1	570
	21st to end	Night	23% 10% 31% 23% 11% 2	627
April	1st to 10th	Night	19% 9% 38% 28% 5%	570
	11th to 20th	Night	22% 12% 29% 29% 7% 1	563
	21st to end	Night	22% 10% 33% 25% 8% 1	570
May	1st to 10th	Night	19% 10% 32% 30% 8% 1	570
	11th to 20th	Night	16% 8% 35% 30% 10% 1	561
	21st to end	Night	17% 7% 29% 34% 12% 1	617
June	1st to 10th	Night	12% 3 30% 38% 16%	570
	11th to 20th	Night	12% 4 34% 39% 10%	570
	21st to end	Night	9% 3 28% 43% 16%	570
July	1st to 10th	Night	6% 2 23% 40% 27% 2	555
	11th to 20th	Night	5% 2 25% 48% 19% 1	552
	21st to end	Night	5% 2 23% 47% 20% 3	624
August	1st to 10th	Night	10% 2 17% 47% 22% 2	567
	11th to 20th	Night	11% 2 18% 41% 24% 3	564
	21st to end	Night	7% 4 27% 38% 22% 2	627
September	1st to 10th	Night	10% 4 27% 39% 18% 2	570
	11th to 20th	Night	11% 5% 32% 31% 19% 2	570
	21st to end	Night	12% 9% 33% 31% 14% 1	598
October	1st to 10th	Night	18% 7% 33% 29% 12% 1	760
	11th to 20th	Night	20% 10% 36% 26% 8% 1	760
	21st to end	Night	22% 11% 33% 28% 7%	836
November	1st to 10th	Night	17% 10% 35% 29% 9%	955
	11th to 20th	Night	17% 11% 38% 25% 8% 1	956
	21st to end	Night	17% 12% 38% 25% 7%	950
December	1st to 10th	Night	16% 10% 37% 28% 8% 1	950
	11th to 20th	Night	19% 9% 38% 27% 6% 1	950
	21st to end	Night	24% 11% 32% 27% 5%	1045

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