Begich Boggs Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Begich Boggs Visitor Center clear sky chart from 2005-11-06 to 2026-09-14.

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	20% 20% 5% 11% 6% 5% 5% 3 4 5% 16%	155896
	Night	15% 23% 6% 12% 6% 5% 5% 3 4 5% 15%	144064
Transparency	Day	67% 9% 11% 9% 3 1	155543
	Night	66% 8% 8% 9% 6% 3	144002
Seeing	Day	35% 13% 16% 19% 14% 3	20449
	Night	34% 12% 18% 19% 14% 2	24760

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% 28% 6% 13% 8% 7% 6% 4 6% 6% 12%	2403
	11th to 20th	Day	15% 24% 5% 10% 5% 5% 4 4 6% 5% 17%	3421
	21st to end	Day	10% 22% 6% 12% 6% 5% 6% 4 5% 6% 17%	3871
February	1st to 10th	Day	9% 20% 6% 12% 6% 6% 6% 4 6% 6% 20%	1482
	11th to 20th	Day	14% 27% 7% 12% 7% 5% 5% 3 5% 3 12%	1639
	21st to end	Day	6% 19% 4 12% 7% 5% 4 4 6% 7% 26%	1487
March	1st to 10th	Day	8% 25% 7% 15% 8% 6% 4 3 4 3 16%	4569
	11th to 20th	Day	4 23% 9% 17% 8% 6% 6% 4 5% 4 13%	4743
	21st to end	Day	10% 26% 9% 15% 6% 5% 4 3 4 4 15%	6101
April	1st to 10th	Day	10% 26% 7% 13% 6% 5% 4 3 4 4 19%	2562
	11th to 20th	Day	10% 23% 6% 10% 5% 5% 5% 3 5% 5% 24%	2887
	21st to end	Day	12% 25% 6% 11% 6% 5% 5% 2 4 5% 20%	2977
May	1st to 10th	Day	19% 34% 6% 11% 5% 4 3 2 3 3 9%	9171
	11th to 20th	Day	17% 27% 5% 11% 6% 5% 4 3 4 4 15%	9381
	21st to end	Day	18% 25% 5% 12% 6% 5% 5% 3 4 4 13%	10892
June	1st to 10th	Day	29% 16% 4 8% 6% 4 4 4 5% 4 17%	3780
	11th to 20th	Day	22% 14% 4 9% 5% 5% 5% 4 5% 5% 22%	3780
	21st to end	Day	27% 14% 4 8% 6% 5% 4 3 5% 5% 19%	3780
July	1st to 10th	Day	22% 15% 5% 11% 6% 5% 6% 4 6% 7% 14%	10620
	11th to 20th	Day	30% 16% 4 10% 6% 4 4 3 4 4 14%	10088
	21st to end	Day	23% 11% 3 8% 5% 5% 5% 4 5% 5% 25%	10251
August	1st to 10th	Day	27% 11% 3 8% 4 4 5% 4 5% 6% 21%	7375
	11th to 20th	Day	24% 12% 4 10% 6% 6% 6% 3 4 5% 21%	6415
	21st to end	Day	33% 11% 3 8% 5% 5% 5% 3 4 4 17%	7085
September	1st to 10th	Day	40% 15% 5% 9% 5% 4 3 3 3 3 11%	2583
	11th to 20th	Day	43% 14% 4 8% 4 3 3 2 2 4 12%	2420
	21st to end	Day	33% 17% 4 9% 5% 4 5% 2 2 5% 14%	2153
October	1st to 10th	Day	21% 20% 6% 14% 7% 6% 5% 3 3 3 10%	3205
	11th to 20th	Day	17% 19% 5% 12% 4 4 5% 4 6% 4 20%	2924
	21st to end	Day	19% 22% 4 11% 5% 4 4 7% 5% 4 15%	2789
November	1st to 10th	Day	15% 26% 6% 14% 5% 4 5% 4 4 5% 13%	1441
	11th to 20th	Day	12% 20% 5% 9% 7% 5% 8% 6% 8% 8% 13%	1311
	21st to end	Day	14% 25% 7% 13% 6% 4 5% 5% 6% 4 11%	1088
December	1st to 10th	Day	19% 30% 6% 12% 7% 6% 7% 3 3 3 4	1619
	11th to 20th	Day	12% 32% 6% 12% 8% 6% 6% 4 3 4 8%	1557
	21st to end	Day	5% 24% 7% 17% 8% 7% 5% 4 5% 6% 13%	2046
January	1st to 10th	Night	9% 26% 6% 13% 6% 5% 4 3 6% 9% 14%	10511
	11th to 20th	Night	13% 26% 7% 14% 7% 5% 4 3 3 3 17%	9509
	21st to end	Night	12% 20% 5% 12% 6% 6% 5% 5% 6% 7% 17%	10342
February	1st to 10th	Night	8% 20% 6% 13% 7% 5% 5% 4 7% 5% 19%	3134
	11th to 20th	Night	14% 27% 5% 15% 7% 5% 5% 3 4 4 11%	2868
	21st to end	Night	7% 17% 4 11% 6% 5% 5% 4 6% 8% 26%	2317
March	1st to 10th	Night	6% 29% 8% 15% 7% 5% 4 3 3 3 16%	5504
	11th to 20th	Night	3 22% 9% 20% 8% 6% 6% 4 5% 4 13%	5432
	21st to end	Night	6% 28% 8% 16% 7% 6% 5% 4 4 4 12%	5072
April	1st to 10th	Night	9% 26% 6% 12% 5% 4 4 3 5% 5% 19%	2058
	11th to 20th	Night	9% 22% 6% 9% 5% 6% 6% 3 6% 7% 23%	1679
	21st to end	Night	12% 23% 7% 10% 5% 5% 4 3 4 4 24%	1643
May	1st to 10th	Night	18% 32% 6% 13% 6% 4 3 3 3 3 8%	3775
	11th to 20th	Night	18% 25% 5% 10% 6% 5% 5% 3 4 4 16%	3510
	21st to end	Night	20% 25% 5% 10% 5% 5% 5% 4 5% 4 12%	3284
June	1st to 10th	Night	29% 15% 4 8% 4 5% 5% 4 4 5% 18%	840
	11th to 20th	Night	22% 15% 3 8% 3 3 4 6% 6% 7% 23%	840
	21st to end	Night	27% 14% 3 7% 6% 5% 5% 3 5% 6% 20%	840
July	1st to 10th	Night	23% 15% 4 9% 6% 6% 5% 4 6% 6% 15%	2370
	11th to 20th	Night	32% 14% 5% 10% 5% 4 5% 3 4 4 16%	2891
	21st to end	Night	24% 11% 3 8% 4 5% 6% 4 5% 6% 24%	3852
August	1st to 10th	Night	29% 11% 3 8% 5% 5% 4 3 4 6% 22%	2793
	11th to 20th	Night	26% 10% 3 9% 6% 6% 6% 4 6% 6% 18%	3650
	21st to end	Night	31% 15% 5% 9% 5% 4 4 3 3 3 19%	4063
September	1st to 10th	Night	41% 15% 5% 8% 4 5% 4 2 2 3 12%	2036
	11th to 20th	Night	42% 15% 4 7% 4 3 3 3 2 2 15%	2047
	21st to end	Night	34% 16% 3 9% 5% 4 3 2 3 3 16%	2245
October	1st to 10th	Night	23% 22% 6% 12% 7% 5% 4 2 3 4 13%	3976
	11th to 20th	Night	18% 20% 4 9% 5% 5% 5% 3 3 4 24%	4224
	21st to end	Night	18% 20% 5% 12% 7% 6% 6% 4 5% 3 14%	5011
November	1st to 10th	Night	17% 25% 5% 13% 7% 5% 4 4 4 3 13%	3077
	11th to 20th	Night	12% 17% 5% 11% 6% 7% 7% 5% 7% 7% 17%	3308
	21st to end	Night	13% 25% 7% 12% 6% 4 4 5% 5% 5% 14%	3530
December	1st to 10th	Night	15% 35% 6% 13% 6% 5% 5% 3 4 3 7%	5779
	11th to 20th	Night	8% 29% 8% 16% 8% 6% 5% 4 4 4 8%	6880
	21st to end	Night	7% 26% 7% 16% 8% 6% 5% 4 5% 7% 9%	9174

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	62% 9% 5% 9% 8% 8%	2403
	11th to 20th	Day	62% 6% 6% 11% 12% 2	3439
	21st to end	Day	59% 9% 7% 8% 12% 4	3872
February	1st to 10th	Day	59% 6% 6% 13% 9% 6%	1482
	11th to 20th	Day	71% 5% 6% 8% 7% 3	1646
	21st to end	Day	53% 7% 7% 13% 16% 4	1487
March	1st to 10th	Day	66% 6% 7% 8% 7% 6%	4569
	11th to 20th	Day	62% 11% 9% 9% 8% 1	4743
	21st to end	Day	66% 8% 11% 8% 7% 1	6101
April	1st to 10th	Day	66% 7% 11% 10% 5% 1	2562
	11th to 20th	Day	59% 8% 11% 15% 7%	2887
	21st to end	Day	66% 7% 8% 12% 6% 1	2977
May	1st to 10th	Day	80% 8% 5% 6% 2	9171
	11th to 20th	Day	68% 11% 7% 11% 2	9384
	21st to end	Day	71% 9% 10% 8% 1	10893
June	1st to 10th	Day	69% 7% 13% 10% 1	3780
	11th to 20th	Day	63% 10% 14% 12% 2	3780
	21st to end	Day	66% 9% 17% 7%	3780
July	1st to 10th	Day	67% 16% 12% 5%	10531
	11th to 20th	Day	73% 10% 13% 3	9990
	21st to end	Day	59% 9% 17% 15%	10030
August	1st to 10th	Day	63% 12% 21% 4	7356
	11th to 20th	Day	64% 12% 15% 8% 1	6457
	21st to end	Day	68% 8% 11% 12% 1	7084
September	1st to 10th	Day	78% 7% 6% 6% 2	2583
	11th to 20th	Day	76% 5% 9% 9% 1	2420
	21st to end	Day	72% 6% 10% 9% 3	2153
October	1st to 10th	Day	75% 10% 7% 7% 1	3205
	11th to 20th	Day	61% 8% 9% 12% 9%	2924
	21st to end	Day	61% 8% 12% 11% 7% 1	2789
November	1st to 10th	Day	70% 4 7% 10% 5% 4	1441
	11th to 20th	Day	56% 6% 8% 19% 10% 1	1311
	21st to end	Day	69% 3 7% 10% 9% 2	1088
December	1st to 10th	Day	78% 6% 7% 4 4 1	1619
	11th to 20th	Day	72% 7% 8% 8% 4 1	1560
	21st to end	Day	61% 9% 7% 8% 7% 8%	2046
January	1st to 10th	Night	62% 6% 4 9% 10% 8%	10511
	11th to 20th	Night	67% 7% 5% 7% 10% 4	9554
	21st to end	Night	56% 7% 9% 10% 11% 6%	10342
February	1st to 10th	Night	60% 6% 7% 12% 10% 6%	3134
	11th to 20th	Night	72% 6% 7% 7% 7% 2	2872
	21st to end	Night	53% 7% 9% 12% 16% 4	2317
March	1st to 10th	Night	67% 6% 6% 7% 8% 6%	5504
	11th to 20th	Night	63% 11% 9% 8% 8% 1	5434
	21st to end	Night	64% 11% 10% 7% 6% 1	5072
April	1st to 10th	Night	65% 6% 10% 14% 5% 1	2058
	11th to 20th	Night	57% 7% 11% 17% 8%	1679
	21st to end	Night	64% 6% 9% 13% 7% 1	1643
May	1st to 10th	Night	78% 10% 5% 6% 1	3772
	11th to 20th	Night	67% 10% 11% 8% 4	3511
	21st to end	Night	72% 12% 8% 7% 2	3288
June	1st to 10th	Night	69% 10% 11% 10% 1	840
	11th to 20th	Night	60% 10% 16% 12% 2	840
	21st to end	Night	67% 8% 18% 7%	840
July	1st to 10th	Night	69% 13% 12% 5%	2350
	11th to 20th	Night	72% 11% 14% 3	2866
	21st to end	Night	58% 10% 20% 12%	3768
August	1st to 10th	Night	64% 13% 17% 6%	2787
	11th to 20th	Night	63% 15% 13% 6% 2	3674
	21st to end	Night	70% 6% 9% 12% 1	4063
September	1st to 10th	Night	79% 6% 7% 7% 1	2036
	11th to 20th	Night	76% 5% 8% 9% 3	2047
	21st to end	Night	70% 6% 10% 10% 3	2245
October	1st to 10th	Night	74% 7% 7% 10% 2	3976
	11th to 20th	Night	62% 7% 7% 13% 11%	4224
	21st to end	Night	62% 7% 13% 12% 5% 1	5011
November	1st to 10th	Night	70% 4 7% 10% 7% 3	3077
	11th to 20th	Night	54% 5% 10% 19% 11% 1	3308
	21st to end	Night	66% 4 7% 11% 9% 3	3530
December	1st to 10th	Night	78% 5% 6% 5% 4 1	5779
	11th to 20th	Night	71% 8% 7% 7% 6% 1	6876
	21st to end	Night	65% 8% 6% 6% 7% 8%	9174

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% 17% 22% 19% 19% 4	126
	11th to 20th	Day	33% 15% 24% 19% 8% 2	320
	21st to end	Day	35% 14% 20% 20% 10% 1	352
February	1st to 10th	Day	20% 17% 21% 23% 14% 6%	345
	11th to 20th	Day	31% 17% 24% 17% 10% 1	425
	21st to end	Day	26% 14% 33% 16% 6% 5%	355
March	1st to 10th	Day	22% 12% 27% 22% 16% 1	430
	11th to 20th	Day	18% 19% 24% 20% 16% 4	469
	21st to end	Day	22% 15% 19% 20% 19% 5%	704
April	1st to 10th	Day	26% 21% 22% 16% 11% 3	662
	11th to 20th	Day	25% 13% 16% 24% 17% 5%	740
	21st to end	Day	31% 12% 15% 20% 16% 5%	750
May	1st to 10th	Day	41% 18% 13% 14% 12% 2	753
	11th to 20th	Day	34% 11% 14% 22% 15% 3	775
	21st to end	Day	32% 14% 17% 21% 14% 3	857
June	1st to 10th	Day	35% 12% 11% 20% 18% 5%	990
	11th to 20th	Day	27% 8% 13% 24% 23% 5%	990
	21st to end	Day	33% 12% 11% 19% 20% 5%	990
July	1st to 10th	Day	35% 11% 13% 22% 16% 3	976
	11th to 20th	Day	40% 13% 12% 17% 15% 3	898
	21st to end	Day	39% 12% 14% 16% 14% 4	849
August	1st to 10th	Day	44% 11% 12% 18% 12% 4	776
	11th to 20th	Day	45% 13% 16% 15% 9% 2	765
	21st to end	Day	46% 10% 18% 16% 10% 1	858
September	1st to 10th	Day	47% 16% 15% 12% 9% 1	696
	11th to 20th	Day	49% 11% 13% 15% 10% 2	616
	21st to end	Day	44% 13% 14% 15% 13% 2	420
October	1st to 10th	Day	44% 13% 16% 13% 10% 2	420
	11th to 20th	Day	39% 16% 19% 15% 9% 3	420
	21st to end	Day	40% 12% 18% 16% 13% 2	462
November	1st to 10th	Day	33% 14% 19% 18% 12% 3	425
	11th to 20th	Day	29% 10% 24% 25% 12% 1	346
	21st to end	Day	31% 14% 20% 21% 10% 4	148
December	1st to 10th	Day	37% 10% 17% 22% 12% 2	110
	11th to 20th	Day	30% 14% 29% 15% 10% 2	110
	21st to end	Day	33% 15% 26% 18% 8%	121
January	1st to 10th	Night	26% 14% 19% 23% 16% 2	1060
	11th to 20th	Night	33% 16% 22% 17% 10% 2	969
	21st to end	Night	34% 11% 23% 20% 10% 2	1045
February	1st to 10th	Night	23% 13% 23% 25% 14% 2	950
	11th to 20th	Night	35% 16% 21% 19% 8%	934
	21st to end	Night	22% 15% 29% 20% 10% 3	678
March	1st to 10th	Night	19% 15% 25% 26% 13% 3	740
	11th to 20th	Night	16% 15% 22% 28% 16% 2	736
	21st to end	Night	27% 11% 16% 22% 18% 5%	693
April	1st to 10th	Night	29% 16% 18% 19% 16% 3	630
	11th to 20th	Night	25% 12% 16% 21% 24% 2	623
	21st to end	Night	29% 11% 18% 18% 20% 3	630
May	1st to 10th	Night	35% 16% 12% 16% 18% 3	511
	11th to 20th	Night	33% 10% 9% 19% 24% 4	414
	21st to end	Night	32% 9% 11% 21% 23% 4	275
June	1st to 10th	Night	35% 12% 9% 17% 23% 4	210
	11th to 20th	Night	31% 7% 9% 17% 32% 4	210
	21st to end	Night	34% 10% 11% 14% 26% 4	210
July	1st to 10th	Night	37% 6% 10% 19% 25% 3	205
	11th to 20th	Night	39% 7% 12% 16% 23% 4	311
	21st to end	Night	43% 8% 12% 14% 19% 3	460
August	1st to 10th	Night	47% 10% 10% 12% 17% 4	418
	11th to 20th	Night	46% 9% 13% 18% 12% 2	616
	21st to end	Night	45% 9% 13% 17% 12% 4	693
September	1st to 10th	Night	51% 11% 12% 11% 13% 1	630
	11th to 20th	Night	53% 9% 11% 13% 12% 1	609
	21st to end	Night	45% 9% 11% 17% 15% 3	625
October	1st to 10th	Night	46% 11% 14% 16% 13% 1	740
	11th to 20th	Night	44% 10% 15% 16% 13% 2	910
	21st to end	Night	39% 9% 18% 17% 15% 2	1001
November	1st to 10th	Night	36% 13% 20% 20% 10% 1	930
	11th to 20th	Night	24% 12% 26% 24% 11% 2	950
	21st to end	Night	31% 12% 22% 21% 11% 2	950
December	1st to 10th	Night	37% 13% 20% 18% 9% 2	968
	11th to 20th	Night	27% 14% 26% 23% 7% 2	1060
	21st to end	Night	33% 18% 18% 20% 9% 2	1166

Page generated at 2026-09-11 00:11:58. Version ac07

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