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 2024-01-13.

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% 8% 3 7% 6% 3 5% 5% 5% 7% 38%	75204
	Night	12% 8% 3 7% 6% 3 4 4 5% 7% 41%	74554
Transparency	Day	45% 6% 14% 24% 11% 1	74904
	Night	43% 5% 13% 24% 12% 2	74374
Seeing	Day	16% 9% 31% 29% 13% 3	14831
	Night	15% 8% 33% 31% 11% 1	24861

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% 11% 5% 8% 8% 5% 8% 7% 5% 8% 28%	1517
	11th to 20th	Day	10% 13% 6% 12% 8% 4 6% 5% 5% 7% 25%	1537
	21st to end	Day	8% 12% 5% 9% 10% 7% 8% 6% 6% 8% 21%	1782
February	1st to 10th	Day	8% 11% 4 10% 8% 5% 6% 5% 6% 7% 31%	1620
	11th to 20th	Day	8% 11% 5% 8% 7% 4 6% 7% 6% 7% 31%	1574
	21st to end	Day	11% 11% 4 9% 9% 3 5% 5% 6% 8% 29%	1353
March	1st to 10th	Day	13% 11% 5% 8% 6% 3 5% 5% 5% 7% 32%	1980
	11th to 20th	Day	13% 9% 3 7% 6% 4 5% 4 5% 8% 36%	1980
	21st to end	Day	17% 11% 3 7% 6% 4 5% 5% 5% 7% 29%	2178
April	1st to 10th	Day	16% 10% 4 7% 5% 3 4 4 5% 7% 35%	2137
	11th to 20th	Day	20% 12% 3 7% 4 3 5% 4 5% 6% 33%	2204
	21st to end	Day	23% 10% 3 6% 5% 4 4 4 4 6% 32%	2340
May	1st to 10th	Day	18% 7% 3 6% 6% 4 5% 4 5% 7% 34%	2374
	11th to 20th	Day	17% 6% 3 5% 5% 3 5% 5% 5% 7% 39%	2479
	21st to end	Day	15% 6% 3 7% 6% 3 5% 5% 5% 9% 36%	2725
June	1st to 10th	Day	11% 4 2 4 5% 3 6% 5% 7% 8% 44%	2520
	11th to 20th	Day	13% 6% 3 6% 5% 3 5% 5% 5% 7% 41%	2657
	21st to end	Day	9% 5% 2 5% 5% 3 5% 6% 7% 10% 45%	2700
July	1st to 10th	Day	7% 3 1 3 4 3 4 5% 7% 11% 52%	2700
	11th to 20th	Day	8% 4 1 3 4 3 4 5% 5% 9% 54%	2530
	21st to end	Day	5% 4 2 4 5% 2 5% 5% 7% 10% 52%	2638
August	1st to 10th	Day	9% 5% 2 6% 6% 4 6% 6% 7% 8% 41%	2328
	11th to 20th	Day	13% 6% 2 4 4 3 5% 5% 6% 8% 45%	2301
	21st to end	Day	9% 4 2 4 5% 2 4 4 6% 8% 54%	2508
September	1st to 10th	Day	11% 4 3 4 4 3 4 5% 4 8% 50%	2160
	11th to 20th	Day	13% 6% 2 4 5% 3 4 5% 6% 7% 46%	2066
	21st to end	Day	17% 5% 2 4 5% 2 5% 3 5% 7% 45%	1936
October	1st to 10th	Day	17% 7% 2 5% 5% 3 5% 3 5% 6% 42%	1800
	11th to 20th	Day	14% 9% 2 5% 4 4 4 4 5% 7% 42%	1800
	21st to end	Day	18% 10% 4 7% 5% 2 3 4 5% 5% 38%	1980
November	1st to 10th	Day	12% 10% 4 7% 6% 4 4 4 5% 7% 37%	1539
	11th to 20th	Day	10% 11% 6% 10% 8% 3 4 4 5% 6% 32%	1520
	21st to end	Day	14% 9% 3 6% 6% 3 5% 4 6% 9% 33%	1520
December	1st to 10th	Day	10% 11% 5% 9% 9% 5% 6% 6% 4 7% 28%	1520
	11th to 20th	Day	10% 13% 7% 9% 8% 4 4 5% 5% 7% 29%	1918
	21st to end	Day	21% 12% 5% 17% 5% 3 3 4 4 6% 20%	2783
January	1st to 10th	Night	7% 9% 5% 10% 8% 5% 6% 4 6% 7% 33%	2648
	11th to 20th	Night	10% 12% 6% 10% 8% 5% 6% 5% 6% 7% 27%	2481
	21st to end	Night	11% 14% 6% 9% 8% 4 4 4 7% 7% 26%	2574
February	1st to 10th	Night	7% 12% 5% 7% 7% 4 6% 4 5% 7% 36%	2340
	11th to 20th	Night	6% 8% 4 8% 6% 3 5% 5% 6% 8% 40%	2273
	21st to end	Night	11% 9% 3 8% 6% 3 5% 6% 6% 7% 36%	1916
March	1st to 10th	Night	12% 9% 3 9% 6% 3 5% 4 4 8% 37%	1981
	11th to 20th	Night	12% 10% 3 7% 5% 3 5% 3 5% 6% 40%	1980
	21st to end	Night	17% 10% 4 7% 6% 3 3 4 5% 6% 34%	2178
April	1st to 10th	Night	14% 8% 4 6% 5% 3 3 5% 5% 7% 39%	1822
	11th to 20th	Night	20% 9% 4 6% 6% 2 4 3 5% 5% 35%	1703
	21st to end	Night	18% 8% 4 6% 5% 3 3 4 5% 5% 38%	1620
May	1st to 10th	Night	14% 8% 2 5% 6% 3 4 5% 5% 7% 40%	1584
	11th to 20th	Night	14% 6% 2 5% 4 3 4 5% 6% 8% 43%	1416
	21st to end	Night	14% 5% 3 4 4 4 4 5% 6% 7% 46%	1551
June	1st to 10th	Night	10% 4 2 3 4 2 5% 4 7% 9% 50%	1440
	11th to 20th	Night	9% 4 2 5% 4 3 5% 4 5% 9% 49%	1296
	21st to end	Night	7% 3 1 3 4 2 4 5% 6% 7% 57%	1260
July	1st to 10th	Night	4 3 1 4 4 2 3 4 6% 9% 58%	1260
	11th to 20th	Night	4 3 1 5% 4 2 4 4 5% 8% 60%	1426
	21st to end	Night	4 3 1 3 3 3 4 4 6% 8% 61%	1677
August	1st to 10th	Night	8% 4 2 4 5% 3 5% 5% 6% 8% 50%	1611
	11th to 20th	Night	10% 4 2 3 4 2 4 4 5% 7% 54%	1600
	21st to end	Night	7% 3 1 5% 3 2 3 4 4 6% 61%	1846
September	1st to 10th	Night	8% 4 2 4 4 2 4 4 5% 7% 56%	1800
	11th to 20th	Night	10% 4 1 3 4 2 3 5% 5% 7% 55%	1890
	21st to end	Night	11% 5% 2 4 4 2 4 4 4 6% 53%	2006
October	1st to 10th	Night	15% 6% 3 4 4 2 3 4 4 7% 48%	2160
	11th to 20th	Night	15% 9% 3 5% 4 3 4 4 4 6% 43%	2160
	21st to end	Night	17% 10% 3 5% 5% 2 3 4 4 7% 40%	2376
November	1st to 10th	Night	13% 6% 2 5% 6% 3 4 4 5% 7% 44%	2536
	11th to 20th	Night	12% 11% 5% 9% 6% 3 4 4 5% 5% 37%	2660
	21st to end	Night	12% 9% 4 7% 5% 3 4 5% 5% 6% 40%	2660
December	1st to 10th	Night	9% 10% 4 10% 8% 4 4 5% 5% 7% 33%	2660
	11th to 20th	Night	11% 11% 5% 9% 8% 5% 5% 5% 6% 6% 29%	3279
	21st to end	Night	21% 13% 5% 11% 7% 3 4 5% 4 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	54% 7% 14% 19% 7%	1518
	11th to 20th	Day	60% 5% 11% 16% 7% 1	1537
	21st to end	Day	60% 5% 13% 15% 7%	1782
February	1st to 10th	Day	52% 5% 13% 20% 9% 1	1620
	11th to 20th	Day	51% 5% 14% 20% 8% 1	1583
	21st to end	Day	53% 7% 9% 20% 11%	1353
March	1st to 10th	Day	53% 4 14% 20% 7% 1	1980
	11th to 20th	Day	48% 5% 14% 25% 7% 1	1980
	21st to end	Day	55% 5% 12% 23% 5%	2178
April	1st to 10th	Day	49% 5% 11% 22% 11% 1	2137
	11th to 20th	Day	53% 4 11% 20% 11% 1	2204
	21st to end	Day	55% 4 11% 20% 9% 1	2340
May	1st to 10th	Day	50% 5% 13% 21% 10% 1	2374
	11th to 20th	Day	44% 6% 12% 24% 12% 1	2483
	21st to end	Day	45% 6% 13% 23% 12% 1	2725
June	1st to 10th	Day	36% 7% 15% 30% 12% 1	2520
	11th to 20th	Day	41% 7% 14% 22% 15% 1	2657
	21st to end	Day	33% 7% 19% 28% 11% 2	2700
July	1st to 10th	Day	26% 8% 15% 33% 16% 1	2626
	11th to 20th	Day	28% 6% 15% 28% 19% 4	2454
	21st to end	Day	27% 6% 17% 32% 15% 3	2491
August	1st to 10th	Day	38% 8% 15% 27% 10% 3	2314
	11th to 20th	Day	37% 7% 15% 30% 11% 1	2301
	21st to end	Day	29% 6% 16% 31% 17% 2	2508
September	1st to 10th	Day	34% 5% 12% 34% 14%	2160
	11th to 20th	Day	37% 6% 15% 31% 10%	2066
	21st to end	Day	39% 6% 11% 34% 10% 1	1936
October	1st to 10th	Day	43% 5% 12% 26% 14% 1	1800
	11th to 20th	Day	42% 5% 12% 26% 13% 2	1800
	21st to end	Day	48% 3 13% 24% 10% 1	1980
November	1st to 10th	Day	46% 5% 12% 20% 13% 3	1539
	11th to 20th	Day	53% 4 13% 18% 10% 1	1520
	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	50% 5% 12% 22% 10% 1	2648
	11th to 20th	Night	56% 6% 14% 17% 7%	2481
	21st to end	Night	57% 4 13% 18% 8% 1	2574
February	1st to 10th	Night	48% 4 14% 21% 11% 1	2340
	11th to 20th	Night	41% 5% 17% 24% 12% 2	2274
	21st to end	Night	47% 4 11% 22% 13% 2	1916
March	1st to 10th	Night	47% 6% 16% 23% 8%	1981
	11th to 20th	Night	46% 4 13% 23% 13% 1	1980
	21st to end	Night	51% 5% 11% 24% 8% 1	2178
April	1st to 10th	Night	45% 5% 12% 25% 12% 1	1822
	11th to 20th	Night	50% 4 6% 21% 16% 2	1703
	21st to end	Night	48% 5% 9% 22% 14% 2	1620
May	1st to 10th	Night	43% 6% 12% 24% 14% 1	1584
	11th to 20th	Night	38% 7% 14% 22% 17% 2	1417
	21st to end	Night	38% 6% 14% 25% 16% 2	1552
June	1st to 10th	Night	29% 5% 16% 32% 16% 2	1440
	11th to 20th	Night	33% 4 16% 26% 18% 3	1296
	21st to end	Night	25% 7% 16% 32% 17% 4	1260
July	1st to 10th	Night	22% 6% 15% 35% 20% 2	1225
	11th to 20th	Night	22% 5% 16% 34% 18% 4	1379
	21st to end	Night	21% 6% 17% 36% 16% 5%	1584
August	1st to 10th	Night	30% 7% 15% 29% 15% 4	1601
	11th to 20th	Night	30% 6% 16% 31% 16% 1	1600
	21st to end	Night	25% 6% 13% 32% 20% 4	1846
September	1st to 10th	Night	27% 6% 14% 33% 20% 1	1800
	11th to 20th	Night	29% 6% 15% 33% 17% 1	1890
	21st to end	Night	32% 5% 12% 34% 16% 1	2006
October	1st to 10th	Night	37% 5% 9% 30% 16% 3	2160
	11th to 20th	Night	42% 4 12% 24% 15% 2	2160
	21st to end	Night	45% 5% 12% 25% 13% 1	2376
November	1st to 10th	Night	39% 4 14% 25% 15% 2	2536
	11th to 20th	Night	51% 5% 12% 19% 13% 1	2660
	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	17% 11% 34% 32% 6% 1	248
	21st to end	Day	16% 9% 40% 25% 9% 2	264
February	1st to 10th	Day	14% 13% 45% 25% 3	240
	11th to 20th	Day	16% 16% 36% 28% 3 2	240
	21st to end	Day	19% 11% 37% 28% 5%	198
March	1st to 10th	Day	20% 12% 39% 23% 5% 1	240
	11th to 20th	Day	20% 9% 35% 26% 8% 1	240
	21st to end	Day	24% 13% 26% 24% 10% 2	264
April	1st to 10th	Day	26% 14% 32% 22% 6%	397
	11th to 20th	Day	28% 12% 25% 24% 9% 1	482
	21st to end	Day	25% 13% 29% 23% 9% 2	600
May	1st to 10th	Day	22% 11% 33% 24% 8% 1	603
	11th to 20th	Day	20% 10% 29% 25% 13% 3	625
	21st to end	Day	18% 8% 31% 27% 14% 3	679
June	1st to 10th	Day	10% 5% 27% 32% 21% 4	630
	11th to 20th	Day	15% 7% 32% 35% 10% 2	630
	21st to end	Day	12% 6% 32% 31% 15% 4	630
July	1st to 10th	Day	8% 4 23% 36% 21% 7%	621
	11th to 20th	Day	9% 7% 26% 33% 20% 5%	618
	21st to end	Day	7% 4 26% 37% 21% 5%	684
August	1st to 10th	Day	12% 3 21% 37% 23% 4	626
	11th to 20th	Day	15% 4 19% 33% 23% 6%	615
	21st to end	Day	9% 4 28% 34% 20% 4	627
September	1st to 10th	Day	14% 7% 28% 32% 15% 5%	450
	11th to 20th	Day	15% 4 30% 31% 17% 4	356
	21st to end	Day	20% 11% 32% 22% 9% 6%	270
October	1st to 10th	Day	20% 8% 31% 23% 12% 6%	270
	11th to 20th	Day	16% 19% 34% 22% 8% 1	270
	21st to end	Day	27% 13% 35% 16% 7% 1	297
November	1st to 10th	Day	19% 13% 31% 24% 10% 1	270
	11th to 20th	Day	14% 13% 45% 23% 5%	270
	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	16% 10% 35% 31% 7% 1	915
	21st to end	Night	18% 11% 36% 29% 6%	990
February	1st to 10th	Night	14% 11% 39% 30% 6% 1	900
	11th to 20th	Night	11% 11% 40% 29% 7% 1	879
	21st to end	Night	16% 11% 35% 29% 9% 1	732
March	1st to 10th	Night	15% 10% 38% 26% 11% 1	541
	11th to 20th	Night	19% 7% 35% 31% 5% 1	540
	21st to end	Night	23% 10% 31% 23% 12% 2	594
April	1st to 10th	Night	19% 9% 38% 28% 6%	540
	11th to 20th	Night	23% 12% 28% 29% 8% 1	533
	21st to end	Night	22% 9% 34% 25% 8% 1	540
May	1st to 10th	Night	20% 9% 32% 30% 9% 1	540
	11th to 20th	Night	17% 8% 35% 30% 10% 1	531
	21st to end	Night	17% 7% 29% 35% 12% 1	584
June	1st to 10th	Night	12% 3 29% 39% 16%	540
	11th to 20th	Night	12% 4 33% 40% 11%	540
	21st to end	Night	8% 4 28% 44% 17%	540
July	1st to 10th	Night	6% 2 22% 41% 27% 2	525
	11th to 20th	Night	5% 2 25% 48% 18% 1	522
	21st to end	Night	5% 2 23% 47% 20% 2	591
August	1st to 10th	Night	9% 2 16% 48% 23% 2	537
	11th to 20th	Night	11% 2 19% 40% 24% 3	534
	21st to end	Night	7% 4 26% 38% 23% 2	594
September	1st to 10th	Night	10% 4 26% 40% 18% 2	540
	11th to 20th	Night	12% 5% 31% 31% 19% 2	540
	21st to end	Night	12% 10% 33% 31% 13% 1	566
October	1st to 10th	Night	19% 7% 33% 29% 13% 1	720
	11th to 20th	Night	21% 10% 34% 26% 8% 1	720
	21st to end	Night	23% 10% 32% 27% 7%	792
November	1st to 10th	Night	17% 10% 35% 29% 9%	906
	11th to 20th	Night	17% 11% 38% 25% 7% 1	950
	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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