Galena
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Galena clear sky chart from 2005-11-06 to 2025-03-27.

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% 9% 4 8% 5% 4 4 4 5% 7% 37%	109150
	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 38%	110396
Transparency	Day	27% 43% 7% 15% 8% 1	112705
	Night	29% 41% 6% 14% 9% 1	114981
Seeing	Day	18% 15% 31% 22% 10% 3	16306
	Night	18% 13% 31% 27% 10% 1	26354

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% 11% 9% 18% 7% 6% 5% 3 4 4 25%	3617
	11th to 20th	Day	8% 10% 6% 13% 6% 5% 6% 9% 7% 6% 26%	3620
	21st to end	Day	12% 16% 6% 9% 4 3 3 3 5% 6% 33%	4378
February	1st to 10th	Day	12% 15% 5% 9% 6% 5% 5% 4 5% 6% 29%	1800
	11th to 20th	Day	13% 12% 3 7% 5% 5% 4 3 5% 6% 36%	1839
	21st to end	Day	14% 12% 4 9% 6% 4 3 3 4 6% 34%	1650
March	1st to 10th	Day	15% 9% 4 6% 4 4 3 3 4 5% 43%	3220
	11th to 20th	Day	10% 7% 3 8% 4 4 4 3 5% 7% 44%	3585
	21st to end	Day	22% 15% 4 10% 5% 5% 4 3 5% 5% 22%	4104
April	1st to 10th	Day	19% 13% 3 8% 4 4 4 4 5% 6% 31%	2280
	11th to 20th	Day	17% 11% 3 7% 5% 4 4 4 5% 5% 35%	2254
	21st to end	Day	21% 9% 3 7% 4 4 4 3 4 6% 35%	2280
May	1st to 10th	Day	17% 9% 3 8% 4 4 4 4 5% 6% 35%	4289
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 3 5% 6% 41%	4399
	21st to end	Day	14% 7% 3 6% 5% 4 5% 3 6% 7% 39%	4824
June	1st to 10th	Day	11% 6% 3 6% 5% 5% 5% 4 6% 7% 44%	2660
	11th to 20th	Day	11% 7% 2 6% 4 4 5% 4 6% 8% 43%	2660
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 5% 6% 8% 39%	2660
July	1st to 10th	Day	11% 8% 3 8% 5% 5% 5% 5% 7% 9% 34%	4440
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 6% 10% 52%	4440
	21st to end	Day	8% 6% 3 7% 6% 5% 5% 5% 7% 9% 39%	4813
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 7% 5% 7% 9% 40%	4182
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 8% 45%	3882
	21st to end	Day	9% 6% 2 6% 4 4 4 4 6% 8% 48%	4180
September	1st to 10th	Day	13% 5% 2 6% 5% 3 4 3 5% 7% 46%	2280
	11th to 20th	Day	12% 5% 1 5% 3 3 4 3 5% 7% 52%	2261
	21st to end	Day	14% 6% 2 6% 4 3 4 3 5% 7% 46%	2063
October	1st to 10th	Day	13% 8% 3 6% 4 3 3 2 4 6% 48%	1900
	11th to 20th	Day	20% 9% 3 5% 5% 4 3 4 4 5% 39%	1900
	21st to end	Day	19% 9% 2 6% 3 3 2 3 4 6% 40%	1978
November	1st to 10th	Day	13% 9% 3 6% 4 3 4 3 4 6% 44%	1762
	11th to 20th	Day	15% 14% 4 9% 5% 3 4 3 4 6% 34%	1750
	21st to end	Day	15% 13% 4 9% 5% 3 3 3 4 6% 37%	1600
December	1st to 10th	Day	9% 10% 5% 10% 4 4 5% 3 5% 7% 40%	2610
	11th to 20th	Day	14% 16% 5% 14% 6% 5% 4 4 5% 5% 22%	3008
	21st to end	Day	19% 26% 9% 12% 5% 3 3 3 3 5% 13%	3982
January	1st to 10th	Night	9% 11% 6% 16% 7% 5% 4 3 4 4 30%	6348
	11th to 20th	Night	10% 15% 6% 13% 6% 6% 5% 6% 6% 5% 21%	6360
	21st to end	Night	13% 15% 7% 10% 6% 4 3 3 4 5% 31%	6585
February	1st to 10th	Night	12% 13% 5% 10% 6% 5% 5% 3 4 5% 32%	2600
	11th to 20th	Night	11% 11% 3 10% 5% 4 4 3 5% 5% 39%	2446
	21st to end	Night	14% 13% 4 7% 4 4 4 3 4 5% 37%	1980
March	1st to 10th	Night	18% 10% 3 6% 3 3 4 3 3 4 42%	3853
	11th to 20th	Night	10% 7% 2 6% 5% 4 4 3 4 7% 49%	3624
	21st to end	Night	24% 13% 5% 11% 5% 3 3 3 3 5% 25%	3664
April	1st to 10th	Night	17% 11% 3 6% 4 3 4 3 4 6% 39%	1900
	11th to 20th	Night	17% 10% 3 6% 4 4 4 3 5% 6% 38%	1875
	21st to end	Night	18% 8% 2 7% 5% 4 5% 3 5% 6% 37%	1900
May	1st to 10th	Night	19% 8% 3 6% 4 4 5% 3 6% 7% 34%	2609
	11th to 20th	Night	12% 8% 2 8% 4 5% 4 3 5% 6% 41%	2506
	21st to end	Night	10% 6% 2 6% 3 4 4 4 6% 8% 46%	2743
June	1st to 10th	Night	8% 5% 3 5% 4 4 5% 5% 6% 8% 47%	1520
	11th to 20th	Night	10% 6% 2 5% 3 4 5% 4 7% 9% 46%	1520
	21st to end	Night	10% 6% 2 6% 5% 4 5% 4 6% 7% 44%	1520
July	1st to 10th	Night	14% 7% 2 7% 4 4 4 4 6% 8% 39%	2530
	11th to 20th	Night	5% 4 2 5% 4 4 4 4 6% 8% 57%	2530
	21st to end	Night	6% 4 1 6% 4 6% 4 5% 7% 9% 48%	2750
August	1st to 10th	Night	7% 4 2 5% 4 5% 4 4 6% 8% 52%	2754
	11th to 20th	Night	9% 5% 2 5% 4 3 4 3 5% 7% 52%	2952
	21st to end	Night	10% 5% 2 5% 3 3 3 3 5% 8% 52%	3476
September	1st to 10th	Night	9% 5% 1 4 4 3 3 3 4 7% 56%	1900
	11th to 20th	Night	11% 4 1 5% 4 5% 3 3 5% 8% 50%	1900
	21st to end	Night	9% 5% 2 4 4 4 5% 3 4 7% 52%	2114
October	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 6% 52%	2280
	11th to 20th	Night	16% 8% 2 5% 4 4 3 2 5% 6% 45%	2280
	21st to end	Night	18% 8% 3 7% 4 4 4 2 4 6% 38%	2618
November	1st to 10th	Night	13% 8% 3 6% 4 3 3 3 5% 5% 49%	2536
	11th to 20th	Night	14% 11% 4 9% 6% 4 4 3 5% 5% 36%	2648
	21st to end	Night	17% 10% 4 8% 5% 3 3 3 5% 5% 37%	2800
December	1st to 10th	Night	8% 8% 3 8% 6% 5% 5% 4 5% 7% 41%	4580
	11th to 20th	Night	15% 16% 5% 10% 5% 4 4 3 4 5% 29%	5199
	21st to end	Night	20% 20% 7% 13% 5% 5% 4 3 4 4 15%	6996

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	50% 26% 5% 14% 5%	3618
	11th to 20th	Day	41% 27% 9% 7% 16% 1	3620
	21st to end	Day	38% 28% 11% 15% 8%	4378
February	1st to 10th	Day	22% 61% 4 6% 7%	1800
	11th to 20th	Day	20% 60% 3 11% 5% 1	1848
	21st to end	Day	18% 61% 4 10% 5% 2	1650
March	1st to 10th	Day	25% 39% 6% 19% 9% 3	3220
	11th to 20th	Day	23% 39% 7% 23% 8% 1	3585
	21st to end	Day	42% 39% 8% 8% 2 1	4104
April	1st to 10th	Day	22% 65% 3 8% 3	2280
	11th to 20th	Day	19% 65% 4 8% 5% 1	2254
	21st to end	Day	18% 64% 3 7% 7% 1	2280
May	1st to 10th	Day	29% 40% 5% 13% 13%	4328
	11th to 20th	Day	27% 39% 5% 22% 7%	4403
	21st to end	Day	25% 40% 6% 18% 10% 3	4837
June	1st to 10th	Day	10% 65% 4 11% 9% 1	2660
	11th to 20th	Day	16% 65% 5% 8% 6% 1	2660
	21st to end	Day	16% 63% 5% 10% 4 1	2660
July	1st to 10th	Day	33% 37% 8% 17% 4 1	4371
	11th to 20th	Day	16% 36% 12% 24% 12%	4365
	21st to end	Day	27% 37% 9% 12% 14% 1	4662
August	1st to 10th	Day	26% 38% 11% 17% 8%	4167
	11th to 20th	Day	24% 38% 9% 21% 8%	3921
	21st to end	Day	23% 37% 9% 23% 8%	4179
September	1st to 10th	Day	17% 59% 4 11% 8% 1	2280
	11th to 20th	Day	11% 60% 5% 15% 7% 2	2261
	21st to end	Day	17% 59% 4 12% 7% 1	2063
October	1st to 10th	Day	13% 36% 2 27% 21% 1	3160
	11th to 20th	Day	16% 36% 5% 18% 22% 3	3140
	21st to end	Day	27% 36% 6% 20% 9% 2	3242
November	1st to 10th	Day	23% 55% 6% 10% 6% 1	1762
	11th to 20th	Day	22% 56% 4 11% 6% 1	1750
	21st to end	Day	25% 56% 6% 10% 2	1600
December	1st to 10th	Day	26% 35% 14% 21% 4 1	2610
	11th to 20th	Day	46% 31% 8% 10% 5% 1	3005
	21st to end	Day	62% 25% 4 6% 3	3982
January	1st to 10th	Night	45% 25% 7% 15% 6%	6348
	11th to 20th	Night	48% 26% 6% 7% 12%	6360
	21st to end	Night	41% 27% 8% 15% 9%	6585
February	1st to 10th	Night	21% 61% 4 7% 6% 1	2600
	11th to 20th	Night	20% 60% 3 11% 6%	2447
	21st to end	Night	17% 61% 4 9% 6% 2	1980
March	1st to 10th	Night	29% 39% 5% 15% 10% 3	3853
	11th to 20th	Night	20% 39% 4 25% 12% 1	3624
	21st to end	Night	41% 38% 4 12% 4 1	3664
April	1st to 10th	Night	19% 65% 2 10% 3 1	1900
	11th to 20th	Night	17% 65% 3 7% 7% 1	1875
	21st to end	Night	15% 64% 3 9% 8% 1	1900
May	1st to 10th	Night	32% 40% 4 9% 12% 2	2635
	11th to 20th	Night	27% 40% 7% 16% 10% 1	2507
	21st to end	Night	20% 39% 7% 20% 12% 2	2751
June	1st to 10th	Night	11% 65% 5% 11% 8% 1	1520
	11th to 20th	Night	14% 64% 5% 11% 5% 1	1520
	21st to end	Night	15% 64% 5% 10% 6% 1	1520
July	1st to 10th	Night	33% 37% 10% 12% 6% 2	2490
	11th to 20th	Night	16% 36% 12% 26% 9% 1	2482
	21st to end	Night	21% 38% 12% 12% 14% 3	2662
August	1st to 10th	Night	21% 37% 11% 20% 12%	2745
	11th to 20th	Night	22% 38% 9% 23% 8% 1	2979
	21st to end	Night	23% 38% 8% 19% 10% 1	3476
September	1st to 10th	Night	12% 60% 5% 13% 10%	1900
	11th to 20th	Night	13% 60% 5% 13% 7% 3	1900
	21st to end	Night	16% 60% 3 11% 9% 1	2114
October	1st to 10th	Night	16% 36% 2 25% 21% 1	3800
	11th to 20th	Night	16% 36% 5% 16% 24% 3	3779
	21st to end	Night	30% 36% 5% 17% 10% 2	4304
November	1st to 10th	Night	21% 55% 5% 11% 7% 1	2536
	11th to 20th	Night	21% 56% 4 10% 8%	2648
	21st to end	Night	24% 56% 4 11% 3	2800
December	1st to 10th	Night	24% 36% 12% 22% 6% 1	4580
	11th to 20th	Night	40% 31% 9% 14% 5%	5201
	21st to end	Night	58% 26% 4 9% 3	6996

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	20% 18% 33% 21% 8% 1	300
	11th to 20th	Day	23% 23% 39% 12% 2 1	300
	21st to end	Day	24% 24% 36% 12% 3 1	330
February	1st to 10th	Day	23% 27% 35% 13% 2	300
	11th to 20th	Day	23% 30% 32% 13% 2	300
	21st to end	Day	30% 22% 38% 10% 1	249
March	1st to 10th	Day	20% 29% 39% 10% 2	300
	11th to 20th	Day	24% 24% 35% 13% 3 1	300
	21st to end	Day	32% 20% 29% 13% 4 1	449
April	1st to 10th	Day	30% 22% 30% 15% 4	460
	11th to 20th	Day	30% 20% 26% 16% 7% 2	452
	21st to end	Day	26% 19% 30% 16% 8% 1	460
May	1st to 10th	Day	21% 17% 35% 19% 6% 2	590
	11th to 20th	Day	24% 14% 31% 22% 8% 2	675
	21st to end	Day	18% 14% 28% 25% 11% 4	734
June	1st to 10th	Day	11% 10% 33% 28% 13% 4	680
	11th to 20th	Day	14% 11% 36% 26% 10% 3	680
	21st to end	Day	15% 11% 33% 26% 11% 4	680
July	1st to 10th	Day	10% 6% 26% 30% 18% 10%	671
	11th to 20th	Day	9% 9% 30% 31% 15% 6%	668
	21st to end	Day	8% 7% 30% 34% 15% 6%	739
August	1st to 10th	Day	8% 4 27% 34% 21% 6%	676
	11th to 20th	Day	15% 6% 24% 26% 22% 9%	571
	21st to end	Day	10% 6% 24% 33% 20% 6%	539
September	1st to 10th	Day	14% 10% 28% 27% 17% 4	490
	11th to 20th	Day	12% 4 26% 32% 21% 6%	490
	21st to end	Day	17% 14% 28% 25% 13% 3	463
October	1st to 10th	Day	19% 13% 31% 24% 11% 1	300
	11th to 20th	Day	25% 26% 28% 15% 5%	300
	21st to end	Day	31% 18% 31% 17% 3	330
November	1st to 10th	Day	20% 21% 37% 16% 5% 2	300
	11th to 20th	Day	23% 24% 34% 14% 5% 1	300
	21st to end	Day	28% 16% 39% 14% 3	300
December	1st to 10th	Day	19% 24% 37% 14% 5% 1	300
	11th to 20th	Day	20% 21% 34% 19% 5% 1	300
	21st to end	Day	27% 21% 35% 15% 2	330
January	1st to 10th	Night	16% 19% 35% 23% 6% 1	1000
	11th to 20th	Night	19% 17% 36% 23% 5%	1000
	21st to end	Night	22% 14% 36% 23% 4	1100
February	1st to 10th	Night	22% 17% 36% 21% 5%	1000
	11th to 20th	Night	17% 21% 35% 24% 3	892
	21st to end	Night	25% 17% 37% 18% 3	660
March	1st to 10th	Night	24% 16% 35% 20% 5%	800
	11th to 20th	Night	19% 13% 36% 25% 6%	621
	21st to end	Night	25% 16% 35% 19% 5% 1	647
April	1st to 10th	Night	22% 18% 35% 22% 4	570
	11th to 20th	Night	24% 17% 27% 26% 6% 1	563
	21st to end	Night	22% 13% 31% 26% 8% 1	570
May	1st to 10th	Night	18% 12% 36% 27% 5% 1	570
	11th to 20th	Night	20% 9% 33% 29% 9%	561
	21st to end	Night	12% 7% 33% 32% 14% 1	617
June	1st to 10th	Night	10% 6% 32% 39% 12% 1	570
	11th to 20th	Night	11% 6% 32% 38% 11% 1	570
	21st to end	Night	14% 7% 28% 36% 14% 1	570
July	1st to 10th	Night	9% 3 17% 39% 26% 5%	555
	11th to 20th	Night	7% 4 24% 38% 24% 3	552
	21st to end	Night	9% 2 21% 43% 24% 2	624
August	1st to 10th	Night	6% 2 18% 43% 28% 2	567
	11th to 20th	Night	9% 3 16% 38% 29% 5%	564
	21st to end	Night	11% 3 19% 41% 22% 3	627
September	1st to 10th	Night	11% 5% 22% 36% 22% 4	570
	11th to 20th	Night	12% 5% 24% 31% 24% 4	570
	21st to end	Night	12% 9% 27% 34% 17% 1	760
October	1st to 10th	Night	15% 9% 29% 29% 16% 1	760
	11th to 20th	Night	21% 13% 31% 26% 8%	760
	21st to end	Night	23% 17% 31% 23% 6% 1	836
November	1st to 10th	Night	18% 15% 35% 24% 8% 1	780
	11th to 20th	Night	22% 19% 33% 21% 4	848
	21st to end	Night	22% 17% 34% 21% 7%	1000
December	1st to 10th	Night	21% 18% 33% 22% 5% 1	1000
	11th to 20th	Night	22% 16% 34% 23% 6%	1000
	21st to end	Night	28% 16% 33% 20% 2	1100

Page generated at 2025-03-24 08:04:31. Version ac07

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