Hearst
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hearst clear sky chart from 2005-11-06 to 2026-07-01.

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	15% 13% 4 10% 6% 5% 5% 4 5% 6% 28%	138283
	Night	13% 14% 5% 12% 7% 6% 5% 4 5% 5% 23%	134352
Transparency	Day	56% 6% 11% 19% 8% 1	141680
	Night	61% 5% 10% 16% 7% 1	139043
Seeing	Day	23% 15% 32% 20% 7% 2	17706
	Night	22% 12% 31% 25% 8% 1	26882

By Month

Percentage Cloud Cover NE (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% 18% 8% 20% 8% 8% 7% 4 5% 3 10%	4094
	11th to 20th	Day	7% 14% 7% 20% 9% 7% 7% 5% 9% 4 12%	4339
	21st to end	Day	7% 12% 7% 14% 8% 8% 10% 8% 7% 4 15%	5156
February	1st to 10th	Day	8% 14% 4 10% 7% 8% 11% 5% 7% 6% 20%	1727
	11th to 20th	Day	8% 17% 6% 13% 8% 6% 7% 5% 6% 6% 18%	1843
	21st to end	Day	8% 16% 6% 13% 7% 6% 8% 6% 6% 5% 19%	1719
March	1st to 10th	Day	12% 19% 5% 11% 6% 6% 5% 4 5% 5% 23%	4578
	11th to 20th	Day	12% 19% 7% 14% 8% 5% 5% 3 4 5% 18%	5079
	21st to end	Day	14% 16% 5% 15% 6% 6% 5% 3 4 4 22%	5649
April	1st to 10th	Day	17% 16% 6% 11% 5% 4 4 3 3 5% 26%	2571
	11th to 20th	Day	19% 14% 4 9% 5% 4 4 3 4 5% 28%	2702
	21st to end	Day	17% 13% 5% 8% 5% 4 4 3 5% 6% 31%	2730
May	1st to 10th	Day	16% 15% 4 9% 5% 5% 4 3 4 4 32%	7696
	11th to 20th	Day	18% 13% 4 8% 4 4 4 3 4 6% 32%	8812
	21st to end	Day	18% 11% 2 5% 3 3 4 3 5% 6% 40%	9716
June	1st to 10th	Day	23% 9% 3 6% 4 4 4 4 5% 7% 32%	3150
	11th to 20th	Day	17% 7% 3 7% 4 4 4 4 6% 8% 35%	3150
	21st to end	Day	20% 8% 2 6% 5% 4 5% 5% 5% 7% 32%	3150
July	1st to 10th	Day	14% 8% 3 7% 5% 5% 5% 4 6% 8% 36%	6820
	11th to 20th	Day	15% 7% 2 6% 4 5% 5% 4 7% 9% 36%	6820
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 7% 10% 38%	7118
August	1st to 10th	Day	17% 7% 2 7% 4 5% 5% 4 6% 9% 35%	4511
	11th to 20th	Day	16% 6% 2 5% 4 3 4 3 5% 7% 45%	4174
	21st to end	Day	14% 9% 3 8% 5% 5% 4 3 5% 7% 37%	4675
September	1st to 10th	Day	20% 9% 3 8% 5% 5% 4 3 4 6% 35%	2434
	11th to 20th	Day	22% 10% 3 7% 5% 4 4 3 5% 7% 30%	2200
	21st to end	Day	22% 12% 3 7% 5% 4 3 3 4 5% 32%	2200
October	1st to 10th	Day	19% 17% 3 7% 4 4 4 3 4 6% 29%	2095
	11th to 20th	Day	25% 20% 5% 7% 5% 3 4 3 4 6% 19%	1890
	21st to end	Day	23% 24% 6% 9% 4 4 3 2 4 4 17%	1980
November	1st to 10th	Day	19% 21% 6% 12% 5% 4 3 2 4 5% 17%	1756
	11th to 20th	Day	18% 24% 7% 15% 6% 4 3 3 4 4 12%	1680
	21st to end	Day	18% 23% 8% 16% 8% 6% 4 3 3 4 9%	1475
December	1st to 10th	Day	10% 22% 8% 20% 15% 5% 4 3 2 3 7%	2350
	11th to 20th	Day	10% 17% 8% 13% 8% 11% 6% 7% 6% 5% 10%	2691
	21st to end	Day	16% 21% 8% 13% 7% 6% 5% 3 5% 5% 11%	3553
January	1st to 10th	Night	6% 16% 8% 18% 9% 9% 8% 5% 5% 4 10%	8831
	11th to 20th	Night	6% 18% 8% 19% 10% 7% 8% 7% 8% 3 6%	8561
	21st to end	Night	6% 13% 7% 14% 8% 8% 10% 6% 8% 5% 15%	9058
February	1st to 10th	Night	7% 13% 5% 13% 8% 8% 10% 7% 5% 6% 19%	2893
	11th to 20th	Night	8% 17% 5% 14% 9% 6% 6% 5% 6% 5% 18%	2663
	21st to end	Night	7% 16% 6% 12% 8% 6% 7% 5% 5% 6% 22%	2086
March	1st to 10th	Night	16% 16% 4 10% 5% 6% 5% 4 6% 5% 23%	5482
	11th to 20th	Night	13% 17% 7% 14% 8% 4 3 2 3 4 23%	5100
	21st to end	Night	14% 14% 5% 12% 8% 6% 7% 3 4 5% 23%	5555
April	1st to 10th	Night	16% 15% 4 10% 5% 5% 4 3 4 4 30%	2048
	11th to 20th	Night	18% 12% 3 10% 4 4 4 4 5% 6% 29%	1867
	21st to end	Night	18% 13% 4 9% 5% 3 3 3 3 5% 34%	1890
May	1st to 10th	Night	15% 16% 5% 10% 5% 4 4 3 4 5% 30%	5203
	11th to 20th	Night	16% 13% 4 8% 4 4 4 3 6% 6% 32%	4079
	21st to end	Night	16% 10% 3 6% 3 4 3 3 4 6% 43%	4492
June	1st to 10th	Night	19% 8% 2 6% 3 3 4 3 6% 8% 38%	1470
	11th to 20th	Night	16% 8% 3 5% 4 5% 6% 4 5% 7% 37%	1470
	21st to end	Night	20% 6% 2 6% 4 4 5% 4 6% 8% 36%	1470
July	1st to 10th	Night	14% 6% 3 6% 5% 5% 4 5% 7% 8% 38%	3160
	11th to 20th	Night	14% 6% 3 6% 5% 4 4 5% 5% 9% 39%	3160
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 5% 8% 42%	3754
August	1st to 10th	Night	12% 7% 2 6% 5% 4 5% 4 5% 8% 43%	2645
	11th to 20th	Night	15% 7% 2 5% 3 4 4 4 6% 8% 44%	2875
	21st to end	Night	12% 6% 2 5% 4 4 4 3 4 7% 48%	3223
September	1st to 10th	Night	18% 7% 3 7% 4 4 5% 3 5% 7% 38%	1941
	11th to 20th	Night	22% 9% 2 6% 3 3 4 3 4 6% 38%	2200
	21st to end	Night	22% 11% 2 5% 4 3 3 3 5% 6% 37%	2200
October	1st to 10th	Night	20% 13% 3 6% 4 4 3 2 5% 6% 33%	2304
	11th to 20th	Night	24% 17% 5% 8% 4 4 4 3 5% 5% 21%	2508
	21st to end	Night	20% 22% 6% 9% 5% 4 3 3 5% 5% 17%	2860
November	1st to 10th	Night	20% 18% 6% 12% 5% 6% 4 4 4 5% 16%	2761
	11th to 20th	Night	19% 21% 6% 14% 8% 5% 4 3 4 3 12%	2940
	21st to end	Night	19% 22% 8% 16% 7% 5% 3 2 3 3 11%	3140
December	1st to 10th	Night	9% 23% 10% 20% 11% 7% 4 2 3 3 8%	5060
	11th to 20th	Night	9% 17% 6% 15% 10% 10% 6% 5% 5% 5% 13%	5736
	21st to end	Night	17% 21% 7% 13% 7% 7% 5% 5% 5% 5% 9%	7667

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	77% 5% 7% 7% 4	4095
	11th to 20th	Day	72% 3 8% 14% 2	4368
	21st to end	Day	68% 4 7% 15% 5% 1	5156
February	1st to 10th	Day	63% 5% 10% 17% 6%	1727
	11th to 20th	Day	64% 4 12% 13% 6%	1852
	21st to end	Day	65% 4 9% 14% 7% 1	1719
March	1st to 10th	Day	63% 5% 7% 13% 10% 3	4580
	11th to 20th	Day	69% 6% 8% 12% 5% 1	5079
	21st to end	Day	65% 5% 5% 16% 8% 1	5649
April	1st to 10th	Day	61% 5% 7% 17% 8% 1	2571
	11th to 20th	Day	59% 4 8% 18% 10% 1	2702
	21st to end	Day	54% 5% 9% 17% 14% 2	2730
May	1st to 10th	Day	55% 5% 7% 17% 15% 2	7705
	11th to 20th	Day	52% 7% 10% 17% 12% 2	8816
	21st to end	Day	44% 5% 9% 26% 14% 1	9717
June	1st to 10th	Day	50% 7% 10% 18% 13% 1	3150
	11th to 20th	Day	46% 7% 12% 23% 12%	3150
	21st to end	Day	49% 7% 13% 22% 9% 1	3150
July	1st to 10th	Day	45% 7% 11% 31% 6%	6747
	11th to 20th	Day	43% 7% 18% 24% 7%	6739
	21st to end	Day	40% 7% 19% 28% 6%	6915
August	1st to 10th	Day	44% 8% 16% 26% 5%	4496
	11th to 20th	Day	39% 6% 17% 33% 5%	4213
	21st to end	Day	46% 6% 14% 25% 7% 1	4674
September	1st to 10th	Day	50% 7% 14% 22% 7% 1	2434
	11th to 20th	Day	53% 8% 18% 18% 3	2200
	21st to end	Day	55% 6% 11% 21% 7%	2200
October	1st to 10th	Day	55% 6% 19% 15% 6%	3407
	11th to 20th	Day	62% 5% 8% 20% 5%	3054
	21st to end	Day	71% 5% 11% 9% 5%	3180
November	1st to 10th	Day	69% 6% 11% 11% 3	1756
	11th to 20th	Day	78% 5% 9% 7% 1	1680
	21st to end	Day	82% 4 5% 7% 1	1475
December	1st to 10th	Day	84% 3 6% 5% 2	2350
	11th to 20th	Day	72% 7% 13% 6% 2	2691
	21st to end	Day	75% 4 7% 13% 1	3553
January	1st to 10th	Night	76% 5% 9% 6% 3 1	8831
	11th to 20th	Night	77% 4 7% 8% 3	8607
	21st to end	Night	66% 5% 8% 16% 4	9058
February	1st to 10th	Night	63% 7% 8% 14% 7%	2893
	11th to 20th	Night	65% 5% 10% 14% 6%	2665
	21st to end	Night	62% 5% 11% 15% 6% 1	2086
March	1st to 10th	Night	62% 4 9% 12% 12% 2	5493
	11th to 20th	Night	66% 4 7% 15% 7%	5101
	21st to end	Night	63% 5% 7% 14% 10% 1	5555
April	1st to 10th	Night	57% 6% 7% 18% 11% 1	2048
	11th to 20th	Night	55% 6% 9% 17% 12% 1	1867
	21st to end	Night	54% 4 9% 15% 15% 2	1890
May	1st to 10th	Night	56% 6% 7% 16% 14% 1	5210
	11th to 20th	Night	50% 6% 12% 21% 10% 1	4080
	21st to end	Night	43% 4 9% 23% 18% 2	4493
June	1st to 10th	Night	45% 6% 11% 22% 14% 2	1470
	11th to 20th	Night	45% 7% 11% 23% 14% 1	1470
	21st to end	Night	44% 8% 13% 23% 12%	1470
July	1st to 10th	Night	40% 8% 14% 31% 6%	3125
	11th to 20th	Night	40% 8% 18% 25% 9%	3118
	21st to end	Night	41% 6% 15% 29% 9%	3643
August	1st to 10th	Night	39% 8% 18% 30% 5%	2636
	11th to 20th	Night	37% 7% 17% 31% 7%	2902
	21st to end	Night	35% 7% 13% 35% 9%	3223
September	1st to 10th	Night	46% 6% 16% 24% 7% 1	1941
	11th to 20th	Night	47% 8% 20% 21% 5%	2200
	21st to end	Night	49% 6% 15% 22% 8%	2200
October	1st to 10th	Night	52% 5% 13% 23% 8%	3772
	11th to 20th	Night	56% 5% 15% 18% 5%	4083
	21st to end	Night	67% 6% 14% 11% 2	4610
November	1st to 10th	Night	70% 7% 10% 11% 3 1	2761
	11th to 20th	Night	77% 5% 8% 8% 1	2940
	21st to end	Night	80% 5% 7% 6% 2	3140
December	1st to 10th	Night	83% 4 5% 5% 2	5060
	11th to 20th	Night	72% 6% 9% 10% 3	5735
	21st to end	Night	76% 5% 6% 10% 2	7667

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	18% 15% 42% 19% 5% 2	220
	11th to 20th	Day	16% 13% 36% 26% 7% 2	267
	21st to end	Day	16% 16% 34% 26% 6% 2	363
February	1st to 10th	Day	18% 23% 37% 17% 4 1	330
	11th to 20th	Day	17% 18% 41% 19% 4 1	330
	21st to end	Day	22% 23% 38% 14% 3	273
March	1st to 10th	Day	22% 16% 42% 18% 2 1	330
	11th to 20th	Day	23% 18% 32% 21% 4 2	529
	21st to end	Day	23% 16% 36% 20% 5% 1	594
April	1st to 10th	Day	20% 20% 34% 18% 5% 2	540
	11th to 20th	Day	27% 19% 28% 17% 6% 2	532
	21st to end	Day	25% 18% 30% 17% 8% 2	540
May	1st to 10th	Day	25% 14% 34% 17% 8% 2	559
	11th to 20th	Day	23% 18% 30% 21% 6% 2	775
	21st to end	Day	26% 14% 32% 21% 6% 1	844
June	1st to 10th	Day	27% 14% 32% 18% 7% 2	780
	11th to 20th	Day	22% 13% 35% 20% 8% 1	780
	21st to end	Day	23% 12% 30% 21% 11% 2	780
July	1st to 10th	Day	19% 13% 32% 24% 10% 3	722
	11th to 20th	Day	19% 12% 30% 26% 11% 2	718
	21st to end	Day	16% 10% 33% 27% 10% 3	794
August	1st to 10th	Day	18% 10% 32% 25% 11% 3	700
	11th to 20th	Day	17% 11% 27% 24% 15% 5%	519
	21st to end	Day	20% 14% 29% 22% 11% 4	583
September	1st to 10th	Day	23% 16% 31% 21% 8% 2	530
	11th to 20th	Day	27% 13% 31% 17% 9% 3	530
	21st to end	Day	29% 11% 29% 20% 10% 1	530
October	1st to 10th	Day	29% 17% 28% 20% 5% 1	530
	11th to 20th	Day	33% 19% 30% 15% 3	420
	21st to end	Day	35% 18% 26% 17% 4 1	363
November	1st to 10th	Day	33% 23% 29% 11% 3	279
	11th to 20th	Day	37% 20% 30% 10% 3	220
	21st to end	Day	32% 24% 32% 10% 2	220
December	1st to 10th	Day	23% 16% 30% 22% 7% 2	220
	11th to 20th	Day	22% 18% 40% 16% 3 1	220
	21st to end	Day	28% 14% 32% 19% 5% 1	242
January	1st to 10th	Night	20% 14% 37% 21% 7% 1	1050
	11th to 20th	Night	20% 13% 33% 27% 6% 1	1050
	21st to end	Night	16% 11% 34% 28% 10% 2	1155
February	1st to 10th	Night	14% 14% 33% 29% 9% 1	1003
	11th to 20th	Night	15% 15% 34% 27% 8% 1	823
	21st to end	Night	16% 14% 34% 27% 7% 1	692
March	1st to 10th	Night	17% 14% 34% 27% 7% 1	840
	11th to 20th	Night	20% 16% 35% 22% 7% 1	840
	21st to end	Night	17% 15% 35% 24% 8% 1	916
April	1st to 10th	Night	23% 14% 31% 23% 7% 1	630
	11th to 20th	Night	25% 12% 29% 25% 8% 1	623
	21st to end	Night	24% 12% 29% 24% 9% 1	630
May	1st to 10th	Night	21% 10% 32% 30% 8%	630
	11th to 20th	Night	22% 11% 34% 26% 6% 1	418
	21st to end	Night	22% 11% 33% 27% 7%	455
June	1st to 10th	Night	23% 12% 28% 26% 10% 1	420
	11th to 20th	Night	20% 11% 27% 35% 8%	420
	21st to end	Night	20% 8% 28% 31% 11% 1	420
July	1st to 10th	Night	17% 8% 29% 32% 12% 1	390
	11th to 20th	Night	16% 8% 33% 33% 10% 1	388
	21st to end	Night	17% 6% 29% 33% 15%	567
August	1st to 10th	Night	14% 6% 32% 32% 14% 2	597
	11th to 20th	Night	16% 7% 26% 34% 15% 2	594
	21st to end	Night	18% 8% 28% 30% 14% 2	660
September	1st to 10th	Night	21% 9% 30% 26% 12% 2	636
	11th to 20th	Night	26% 10% 31% 23% 10% 1	800
	21st to end	Night	27% 9% 27% 26% 10% 1	800
October	1st to 10th	Night	27% 14% 29% 22% 8% 1	800
	11th to 20th	Night	35% 11% 29% 20% 5% 1	800
	21st to end	Night	32% 12% 25% 24% 7%	880
November	1st to 10th	Night	30% 18% 30% 18% 5% 1	820
	11th to 20th	Night	31% 14% 30% 18% 6%	840
	21st to end	Night	31% 15% 32% 16% 6%	1040
December	1st to 10th	Night	20% 15% 35% 22% 7% 1	1050
	11th to 20th	Night	20% 13% 36% 22% 7% 1	1050
	21st to end	Night	25% 15% 29% 20% 9% 2	1155

Page generated at 2026-06-28 02:10:47. Version ac07

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