Humboldt
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Humboldt 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	9% 9% 3 9% 6% 5% 5% 4 6% 8% 36%	141659
	Night	7% 9% 4 10% 7% 6% 5% 4 6% 8% 34%	139431
Transparency	Day	45% 6% 15% 24% 9% 1	141360
	Night	46% 6% 14% 23% 10% 1	139315
Seeing	Day	13% 8% 28% 30% 17% 5%	18115
	Night	13% 6% 31% 34% 14% 2	27451

By Month

Percentage Cloud Cover NW (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	5% 12% 5% 17% 11% 7% 7% 5% 7% 7% 17%	3799
	11th to 20th	Day	4 8% 3 10% 10% 11% 8% 6% 10% 8% 22%	4119
	21st to end	Day	5% 12% 5% 12% 8% 6% 6% 4 5% 9% 27%	5125
February	1st to 10th	Day	7% 12% 5% 13% 8% 7% 8% 6% 8% 8% 17%	1696
	11th to 20th	Day	6% 12% 4 10% 7% 7% 8% 7% 7% 8% 25%	1845
	21st to end	Day	4 11% 4 13% 9% 8% 8% 6% 8% 8% 20%	1644
March	1st to 10th	Day	5% 13% 6% 16% 9% 8% 7% 4 7% 6% 19%	4600
	11th to 20th	Day	6% 13% 5% 16% 7% 5% 4 3 5% 7% 28%	4892
	21st to end	Day	10% 11% 4 8% 5% 5% 5% 4 6% 7% 36%	6006
April	1st to 10th	Day	6% 10% 3 8% 6% 5% 5% 3 6% 8% 39%	2520
	11th to 20th	Day	13% 12% 4 11% 6% 4 5% 4 5% 7% 29%	2570
	21st to end	Day	12% 11% 3 9% 5% 5% 4 4 5% 7% 34%	2940
May	1st to 10th	Day	10% 9% 4 6% 4 3 4 3 5% 7% 45%	8224
	11th to 20th	Day	14% 9% 3 8% 5% 5% 5% 4 6% 8% 31%	8191
	21st to end	Day	10% 8% 3 6% 4 4 5% 4 5% 7% 44%	9845
June	1st to 10th	Day	14% 8% 3 8% 5% 4 5% 5% 7% 9% 33%	3360
	11th to 20th	Day	21% 8% 2 8% 5% 5% 6% 4 7% 7% 27%	3360
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	3360
July	1st to 10th	Day	7% 4 2 5% 4 5% 6% 4 7% 9% 48%	7241
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 6% 10% 43%	6880
	21st to end	Day	6% 4 2 5% 4 4 5% 4 6% 9% 51%	7038
August	1st to 10th	Day	11% 5% 3 7% 5% 5% 5% 4 6% 8% 42%	4552
	11th to 20th	Day	8% 5% 3 6% 4 5% 5% 3 6% 9% 46%	4483
	21st to end	Day	12% 6% 2 5% 3 4 4 3 5% 7% 50%	4517
September	1st to 10th	Day	10% 5% 2 7% 4 4 4 3 5% 8% 47%	2400
	11th to 20th	Day	14% 7% 3 7% 5% 4 4 4 5% 7% 39%	2400
	21st to end	Day	10% 7% 2 4 4 4 5% 3 5% 8% 49%	2147
October	1st to 10th	Day	10% 9% 2 6% 4 4 4 4 5% 7% 44%	3270
	11th to 20th	Day	8% 7% 3 6% 4 5% 6% 5% 8% 11% 38%	3092
	21st to end	Day	8% 10% 4 9% 6% 6% 5% 5% 6% 7% 34%	3190
November	1st to 10th	Day	17% 15% 4 10% 5% 4 4 4 4 6% 26%	1653
	11th to 20th	Day	9% 14% 7% 15% 9% 6% 4 3 5% 4 23%	1621
	21st to end	Day	8% 14% 7% 13% 8% 6% 5% 4 6% 5% 24%	1470
December	1st to 10th	Day	7% 11% 4 16% 10% 7% 6% 5% 7% 6% 21%	2232
	11th to 20th	Day	6% 12% 7% 18% 10% 9% 7% 4 4 5% 18%	2319
	21st to end	Day	3 8% 4 15% 8% 5% 5% 4 6% 7% 34%	3058
January	1st to 10th	Night	4 13% 6% 16% 11% 7% 6% 4 6% 9% 19%	9089
	11th to 20th	Night	3 8% 4 13% 11% 9% 7% 5% 8% 9% 24%	8779
	21st to end	Night	4 8% 4 12% 9% 7% 6% 5% 7% 8% 30%	9084
February	1st to 10th	Night	6% 12% 5% 13% 9% 7% 6% 5% 6% 8% 23%	2940
	11th to 20th	Night	4 9% 4 12% 6% 7% 6% 5% 8% 7% 32%	2667
	21st to end	Night	4 9% 3 10% 7% 6% 6% 6% 8% 11% 32%	2161
March	1st to 10th	Night	5% 12% 5% 13% 7% 7% 8% 5% 6% 8% 23%	5494
	11th to 20th	Night	7% 10% 4 12% 6% 6% 5% 5% 6% 9% 29%	5303
	21st to end	Night	8% 10% 4 8% 6% 6% 5% 5% 8% 8% 32%	5193
April	1st to 10th	Night	6% 8% 3 8% 5% 6% 5% 4 7% 7% 42%	2100
	11th to 20th	Night	11% 12% 3 8% 6% 4 5% 4 6% 7% 34%	1998
	21st to end	Night	13% 9% 4 8% 5% 4 5% 3 6% 8% 34%	1680
May	1st to 10th	Night	10% 7% 2 6% 4 4 5% 4 6% 7% 46%	4724
	11th to 20th	Night	14% 11% 4 8% 5% 5% 5% 4 5% 7% 30%	4702
	21st to end	Night	10% 8% 3 7% 5% 4 4 4 5% 7% 43%	4329
June	1st to 10th	Night	12% 5% 3 6% 4 4 4 3 7% 10% 42%	1260
	11th to 20th	Night	17% 9% 2 6% 5% 5% 4 3 5% 8% 36%	1260
	21st to end	Night	13% 5% 2 6% 4 4 5% 5% 6% 8% 42%	1260
July	1st to 10th	Night	9% 4 2 5% 4 4 5% 5% 7% 12% 44%	2720
	11th to 20th	Night	8% 4 2 5% 3 4 4 4 6% 9% 51%	3078
	21st to end	Night	4 3 2 4 3 4 4 4 5% 8% 59%	3820
August	1st to 10th	Night	8% 4 2 5% 4 4 5% 4 6% 9% 51%	2608
	11th to 20th	Night	6% 4 1 5% 3 4 5% 5% 7% 11% 49%	2576
	21st to end	Night	8% 4 2 4 3 3 4 4 5% 9% 53%	3387
September	1st to 10th	Night	9% 5% 1 5% 3 4 5% 4 6% 7% 50%	2000
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 5% 8% 44%	2000
	21st to end	Night	9% 5% 2 5% 3 3 4 4 5% 8% 52%	2250
October	1st to 10th	Night	10% 8% 3 5% 3 4 4 3 5% 7% 48%	3920
	11th to 20th	Night	6% 7% 2 7% 4 5% 5% 5% 6% 7% 46%	4024
	21st to end	Night	7% 9% 4 9% 5% 5% 5% 4 6% 8% 40%	4610
November	1st to 10th	Night	15% 16% 4 11% 5% 4 5% 3 5% 7% 26%	2862
	11th to 20th	Night	8% 14% 7% 14% 8% 6% 5% 4 5% 5% 25%	2998
	21st to end	Night	7% 13% 6% 12% 7% 6% 5% 5% 6% 8% 25%	3150
December	1st to 10th	Night	7% 14% 6% 16% 10% 8% 6% 4 5% 5% 18%	5172
	11th to 20th	Night	5% 13% 6% 13% 8% 8% 7% 5% 7% 7% 21%	6093
	21st to end	Night	3 8% 3 14% 9% 6% 5% 4 5% 5% 38%	8140

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% 8% 12% 11%	3799
	11th to 20th	Day	53% 5% 13% 20% 8% 1	4140
	21st to end	Day	54% 5% 16% 15% 10%	5125
February	1st to 10th	Day	61% 7% 11% 13% 8%	1696
	11th to 20th	Day	52% 6% 12% 20% 10%	1854
	21st to end	Day	56% 8% 10% 17% 8%	1644
March	1st to 10th	Day	63% 6% 13% 11% 8%	4600
	11th to 20th	Day	56% 6% 13% 18% 8%	4893
	21st to end	Day	46% 5% 10% 23% 16%	6006
April	1st to 10th	Day	42% 6% 16% 24% 12% 1	2520
	11th to 20th	Day	53% 6% 12% 18% 8% 1	2570
	21st to end	Day	48% 7% 14% 22% 9%	2940
May	1st to 10th	Day	38% 4 10% 33% 14% 1	8224
	11th to 20th	Day	48% 7% 11% 25% 9% 1	8195
	21st to end	Day	37% 6% 11% 28% 17% 1	9845
June	1st to 10th	Day	45% 8% 14% 21% 11% 1	3360
	11th to 20th	Day	54% 9% 12% 19% 6% 1	3360
	21st to end	Day	42% 10% 18% 24% 7%	3360
July	1st to 10th	Day	30% 8% 25% 30% 7%	7162
	11th to 20th	Day	35% 7% 15% 38% 4	6796
	21st to end	Day	29% 7% 20% 34% 10%	6841
August	1st to 10th	Day	38% 7% 20% 27% 7%	4536
	11th to 20th	Day	34% 7% 20% 33% 6%	4525
	21st to end	Day	34% 5% 20% 33% 8%	4516
September	1st to 10th	Day	35% 7% 15% 30% 11% 2	2400
	11th to 20th	Day	44% 7% 16% 25% 7% 1	2400
	21st to end	Day	33% 7% 16% 31% 13% 1	2147
October	1st to 10th	Day	39% 5% 21% 27% 8%	3270
	11th to 20th	Day	39% 6% 18% 28% 9% 1	3092
	21st to end	Day	48% 6% 18% 23% 5%	3190
November	1st to 10th	Day	60% 6% 12% 17% 6%	1653
	11th to 20th	Day	64% 7% 11% 13% 5%	1621
	21st to end	Day	59% 6% 13% 17% 5%	1470
December	1st to 10th	Day	61% 7% 12% 13% 6% 1	2232
	11th to 20th	Day	67% 6% 13% 10% 4	2320
	21st to end	Day	50% 4 9% 20% 13% 4	3058
January	1st to 10th	Night	61% 4 10% 17% 7%	9090
	11th to 20th	Night	54% 5% 13% 19% 9%	8820
	21st to end	Night	50% 7% 17% 18% 8%	9084
February	1st to 10th	Night	58% 6% 11% 17% 8% 1	2940
	11th to 20th	Night	47% 7% 12% 22% 12% 1	2668
	21st to end	Night	44% 7% 14% 24% 10%	2161
March	1st to 10th	Night	56% 7% 16% 15% 6%	5494
	11th to 20th	Night	49% 7% 15% 19% 9%	5303
	21st to end	Night	45% 6% 10% 22% 16% 1	5193
April	1st to 10th	Night	40% 5% 15% 25% 14% 1	2100
	11th to 20th	Night	47% 6% 13% 20% 11% 3	1998
	21st to end	Night	47% 6% 13% 21% 12% 1	1680
May	1st to 10th	Night	36% 6% 10% 29% 17% 2	4724
	11th to 20th	Night	51% 6% 10% 22% 11%	4702
	21st to end	Night	38% 6% 9% 27% 19% 1	4333
June	1st to 10th	Night	35% 6% 18% 26% 12% 2	1260
	11th to 20th	Night	46% 8% 15% 20% 9% 1	1260
	21st to end	Night	37% 9% 20% 24% 9% 1	1260
July	1st to 10th	Night	31% 9% 23% 31% 6%	2690
	11th to 20th	Night	28% 7% 15% 44% 6%	3039
	21st to end	Night	22% 7% 23% 37% 11% 1	3712
August	1st to 10th	Night	29% 8% 22% 31% 10%	2600
	11th to 20th	Night	27% 8% 20% 36% 9%	2600
	21st to end	Night	28% 6% 20% 34% 12%	3387
September	1st to 10th	Night	30% 8% 16% 29% 14% 3	2000
	11th to 20th	Night	38% 7% 15% 30% 9% 1	2000
	21st to end	Night	30% 5% 14% 32% 17% 2	2250
October	1st to 10th	Night	36% 5% 17% 34% 9%	3920
	11th to 20th	Night	36% 5% 15% 32% 12%	4024
	21st to end	Night	42% 6% 18% 28% 6%	4610
November	1st to 10th	Night	59% 6% 12% 15% 7% 1	2862
	11th to 20th	Night	59% 7% 14% 15% 5% 1	2998
	21st to end	Night	56% 8% 14% 18% 4	3150
December	1st to 10th	Night	66% 6% 10% 13% 4	5172
	11th to 20th	Night	60% 5% 16% 15% 5%	6091
	21st to end	Night	48% 5% 8% 22% 14% 3	8140

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	12% 8% 30% 29% 17% 4	220
	11th to 20th	Day	10% 6% 35% 37% 10% 2	220
	21st to end	Day	10% 11% 33% 30% 13% 2	351
February	1st to 10th	Day	11% 10% 38% 29% 11% 2	330
	11th to 20th	Day	8% 5% 30% 34% 19% 5%	330
	21st to end	Day	6% 7% 37% 32% 16% 3	273
March	1st to 10th	Day	12% 9% 31% 32% 14% 2	330
	11th to 20th	Day	10% 8% 33% 32% 14% 2	440
	21st to end	Day	15% 7% 29% 32% 15% 1	594
April	1st to 10th	Day	10% 8% 36% 28% 13% 5%	540
	11th to 20th	Day	16% 11% 29% 30% 12% 3	578
	21st to end	Day	14% 9% 26% 31% 16% 4	750
May	1st to 10th	Day	12% 6% 28% 32% 18% 4	753
	11th to 20th	Day	14% 9% 27% 25% 19% 5%	775
	21st to end	Day	15% 8% 22% 31% 18% 6%	844
June	1st to 10th	Day	15% 11% 28% 27% 14% 5%	780
	11th to 20th	Day	22% 9% 27% 25% 14% 4	780
	21st to end	Day	15% 8% 24% 27% 20% 7%	780
July	1st to 10th	Day	9% 5% 21% 34% 25% 7%	722
	11th to 20th	Day	11% 6% 22% 33% 21% 8%	718
	21st to end	Day	8% 6% 24% 29% 24% 9%	794
August	1st to 10th	Day	11% 6% 21% 31% 23% 8%	726
	11th to 20th	Day	11% 7% 21% 30% 22% 9%	715
	21st to end	Day	12% 8% 24% 31% 20% 5%	614
September	1st to 10th	Day	13% 12% 29% 26% 17% 3	530
	11th to 20th	Day	18% 7% 26% 33% 14% 2	530
	21st to end	Day	13% 9% 30% 31% 13% 2	334
October	1st to 10th	Day	18% 5% 31% 25% 18% 3	330
	11th to 20th	Day	14% 9% 34% 28% 14% 2	330
	21st to end	Day	17% 12% 36% 24% 10% 1	363
November	1st to 10th	Day	22% 9% 33% 24% 8% 3	330
	11th to 20th	Day	16% 10% 43% 26% 5% 1	330
	21st to end	Day	11% 8% 38% 32% 9% 2	330
December	1st to 10th	Day	7% 7% 36% 33% 15% 3	289
	11th to 20th	Day	12% 9% 39% 33% 7%	220
	21st to end	Day	9% 3 38% 28% 17% 5%	242
January	1st to 10th	Night	12% 7% 36% 32% 12% 1	1050
	11th to 20th	Night	11% 9% 41% 29% 9% 1	1050
	21st to end	Night	12% 9% 39% 31% 9% 1	1155
February	1st to 10th	Night	12% 6% 33% 34% 13% 2	1050
	11th to 20th	Night	9% 6% 28% 39% 14% 3	829
	21st to end	Night	7% 6% 28% 36% 21% 3	692
March	1st to 10th	Night	13% 6% 32% 34% 14% 2	840
	11th to 20th	Night	11% 6% 33% 35% 13% 2	840
	21st to end	Night	14% 5% 27% 36% 15% 2	740
April	1st to 10th	Night	9% 6% 29% 37% 17% 3	630
	11th to 20th	Night	16% 8% 27% 36% 13%	623
	21st to end	Night	17% 7% 30% 34% 12%	630
May	1st to 10th	Night	14% 6% 28% 34% 16% 1	630
	11th to 20th	Night	16% 7% 29% 32% 16% 1	621
	21st to end	Night	17% 4 24% 36% 15% 4	585
June	1st to 10th	Night	14% 8% 27% 34% 16% 1	420
	11th to 20th	Night	20% 6% 23% 32% 16% 3	420
	21st to end	Night	16% 4 22% 36% 20% 1	420
July	1st to 10th	Night	7% 4 22% 41% 25% 1	390
	11th to 20th	Night	10% 4 22% 42% 19% 2	388
	21st to end	Night	6% 4 22% 40% 24% 4	587
August	1st to 10th	Night	7% 4 23% 36% 27% 4	597
	11th to 20th	Night	9% 3 21% 36% 28% 2	594
	21st to end	Night	13% 4 25% 37% 20% 1	660
September	1st to 10th	Night	11% 3 26% 39% 18% 3	600
	11th to 20th	Night	15% 4 22% 41% 15% 2	600
	21st to end	Night	12% 6% 31% 38% 12% 1	655
October	1st to 10th	Night	19% 4 29% 35% 12% 1	800
	11th to 20th	Night	12% 7% 32% 35% 12% 2	875
	21st to end	Night	16% 10% 33% 31% 9% 1	1100
November	1st to 10th	Night	24% 7% 30% 31% 6% 1	1025
	11th to 20th	Night	14% 9% 38% 28% 9% 2	1050
	21st to end	Night	12% 8% 40% 31% 8% 2	1050
December	1st to 10th	Night	11% 6% 35% 32% 13% 4	1050
	11th to 20th	Night	13% 9% 36% 30% 11% 1	1050
	21st to end	Night	12% 4 30% 35% 15% 3	1155

Page generated at 2026-06-28 00:10:43. Version ac07

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