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 2024-03-06.

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	23% 18% 5% 8% 6% 3 4 4 4 5% 18%	76844
	Night	18% 21% 6% 10% 7% 4 5% 4 4 5% 17%	82649
Transparency	Day	67% 6% 10% 10% 5% 1	76496
	Night	65% 5% 8% 10% 8% 3	82580
Seeing	Day	36% 12% 16% 19% 14% 3	16821
	Night	35% 12% 18% 20% 14% 2	21745

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% 35% 6% 12% 7% 5% 4 5% 5% 5% 12%	1283
	11th to 20th	Day	15% 22% 6% 7% 5% 3 3 4 5% 7% 24%	1820
	21st to end	Day	9% 21% 8% 13% 7% 4 6% 5% 4 6% 18%	2090
February	1st to 10th	Day	9% 20% 6% 11% 7% 5% 6% 5% 6% 7% 19%	1339
	11th to 20th	Day	15% 27% 7% 12% 8% 4 5% 4 4 3 11%	1479
	21st to end	Day	7% 19% 5% 9% 8% 4 4 5% 6% 7% 26%	1349
March	1st to 10th	Day	9% 19% 6% 11% 8% 5% 4 4 4 4 26%	1848
	11th to 20th	Day	5% 18% 7% 11% 8% 3 5% 6% 5% 6% 25%	1837
	21st to end	Day	8% 26% 8% 10% 6% 3 4 4 4 6% 22%	2376
April	1st to 10th	Day	11% 24% 8% 11% 8% 4 4 4 3 4 18%	2196
	11th to 20th	Day	10% 19% 6% 10% 6% 4 5% 4 6% 6% 26%	2469
	21st to end	Day	12% 22% 6% 9% 7% 3 5% 4 4 5% 22%	2551
May	1st to 10th	Day	19% 25% 6% 9% 6% 4 4 4 4 5% 16%	2798
	11th to 20th	Day	17% 19% 4 8% 6% 3 4 4 4 5% 24%	2833
	21st to end	Day	23% 14% 4 6% 6% 3 4 4 4 6% 26%	3272
June	1st to 10th	Day	30% 13% 5% 6% 7% 3 4 5% 5% 5% 18%	3240
	11th to 20th	Day	24% 13% 5% 9% 6% 4 5% 5% 5% 5% 19%	3240
	21st to end	Day	29% 13% 4 6% 6% 3 4 4 5% 5% 19%	3240
July	1st to 10th	Day	25% 15% 5% 7% 6% 3 5% 5% 5% 7% 18%	3240
	11th to 20th	Day	30% 14% 4 7% 6% 3 4 4 4 6% 18%	3084
	21st to end	Day	36% 14% 4 6% 4 3 3 4 4 4 18%	3137
August	1st to 10th	Day	38% 17% 4 6% 4 2 3 3 3 3 15%	2858
	11th to 20th	Day	41% 15% 3 6% 6% 2 4 2 3 4 14%	2485
	21st to end	Day	40% 12% 3 6% 5% 3 4 4 4 5% 14%	2768
September	1st to 10th	Day	43% 14% 5% 8% 6% 3 2 3 2 3 11%	2214
	11th to 20th	Day	44% 14% 4 6% 5% 2 3 3 3 3 13%	2145
	21st to end	Day	35% 15% 4 7% 6% 3 5% 3 2 5% 15%	1939
October	1st to 10th	Day	34% 22% 5% 6% 5% 2 3 3 3 3 13%	1773
	11th to 20th	Day	26% 23% 7% 12% 6% 2 4 3 3 3 11%	1620
	21st to end	Day	21% 20% 5% 11% 7% 3 4 4 4 4 16%	1567
November	1st to 10th	Day	16% 24% 6% 12% 6% 4 5% 4 4 5% 14%	1301
	11th to 20th	Day	14% 20% 5% 7% 7% 3 7% 7% 8% 8% 14%	1187
	21st to end	Day	15% 24% 8% 13% 6% 2 4 5% 6% 5% 11%	985
December	1st to 10th	Day	21% 21% 8% 11% 9% 5% 5% 5% 3 5% 6%	917
	11th to 20th	Day	15% 25% 6% 10% 10% 4 7% 7% 5% 4 8%	967
	21st to end	Day	8% 21% 7% 13% 10% 5% 5% 5% 5% 7% 14%	1397
January	1st to 10th	Night	9% 31% 7% 12% 8% 5% 5% 4 5% 5% 11%	5659
	11th to 20th	Night	15% 20% 7% 9% 5% 3 3 3 3 4 29%	5087
	21st to end	Night	10% 20% 6% 12% 8% 4 5% 4 5% 6% 19%	5577
February	1st to 10th	Night	9% 19% 7% 12% 8% 4 6% 5% 6% 5% 19%	2837
	11th to 20th	Night	15% 28% 6% 14% 8% 3 5% 4 3 4 10%	2588
	21st to end	Night	7% 17% 5% 10% 7% 4 6% 5% 6% 7% 27%	2103
March	1st to 10th	Night	10% 19% 6% 9% 7% 3 6% 5% 5% 5% 25%	2227
	11th to 20th	Night	5% 17% 6% 11% 8% 5% 5% 5% 6% 6% 26%	2118
	21st to end	Night	8% 24% 8% 11% 6% 3 5% 4 4 5% 22%	1980
April	1st to 10th	Night	11% 25% 7% 11% 7% 2 3 4 4 5% 20%	1764
	11th to 20th	Night	9% 19% 5% 8% 6% 4 6% 5% 6% 8% 25%	1437
	21st to end	Night	11% 21% 8% 9% 6% 4 4 4 3 5% 25%	1409
May	1st to 10th	Night	15% 25% 5% 11% 4 3 4 4 5% 5% 18%	1159
	11th to 20th	Night	18% 18% 5% 7% 5% 3 4 3 4 4 28%	1062
	21st to end	Night	24% 14% 4 7% 5% 3 5% 4 5% 6% 25%	999
June	1st to 10th	Night	30% 12% 4 7% 5% 3 5% 5% 4 6% 19%	720
	11th to 20th	Night	25% 15% 3 8% 4 2 4 5% 7% 7% 20%	720
	21st to end	Night	29% 14% 3 6% 6% 4 5% 3 4 6% 20%	720
July	1st to 10th	Night	26% 13% 4 6% 5% 3 4 3 6% 6% 23%	720
	11th to 20th	Night	31% 11% 5% 6% 5% 3 4 3 4 5% 23%	874
	21st to end	Night	36% 16% 4 6% 5% 3 3 3 2 5% 18%	1182
August	1st to 10th	Night	38% 16% 4 7% 4 2 3 3 3 4 17%	1079
	11th to 20th	Night	40% 14% 4 8% 5% 3 3 3 3 3 14%	1415
	21st to end	Night	36% 14% 4 6% 4 3 3 3 3 3 21%	1588
September	1st to 10th	Night	43% 15% 5% 6% 4 3 4 3 2 3 12%	1745
	11th to 20th	Night	43% 14% 4 6% 5% 2 3 3 2 2 16%	1815
	21st to end	Night	35% 14% 3 8% 5% 3 3 3 3 3 17%	2020
October	1st to 10th	Night	34% 20% 5% 7% 5% 2 2 2 2 4 16%	2186
	11th to 20th	Night	27% 24% 6% 8% 6% 4 4 3 3 3 13%	2340
	21st to end	Night	21% 21% 6% 9% 7% 4 5% 4 4 4 16%	2788
November	1st to 10th	Night	19% 23% 5% 11% 8% 4 5% 5% 4 3 14%	2777
	11th to 20th	Night	14% 16% 5% 9% 7% 5% 7% 6% 7% 7% 18%	2992
	21st to end	Night	14% 24% 8% 11% 6% 3 4 6% 5% 6% 13%	3193
December	1st to 10th	Night	19% 25% 7% 10% 8% 4 5% 5% 4 5% 10%	3259
	11th to 20th	Night	11% 25% 7% 13% 10% 4 5% 6% 4 5% 10%	4240
	21st to end	Night	9% 23% 7% 12% 9% 5% 6% 5% 5% 9% 11%	6270

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	68% 4 4 8% 12% 4	1283
	11th to 20th	Day	57% 2 4 14% 20% 3	1838
	21st to end	Day	59% 7% 5% 8% 15% 7%	2090
February	1st to 10th	Day	60% 5% 6% 13% 9% 6%	1339
	11th to 20th	Day	74% 4 5% 8% 7% 3	1486
	21st to end	Day	53% 7% 7% 14% 16% 3	1349
March	1st to 10th	Day	59% 4 7% 12% 12% 7%	1848
	11th to 20th	Day	57% 6% 7% 14% 13% 3	1837
	21st to end	Day	63% 6% 10% 10% 8% 3	2376
April	1st to 10th	Day	68% 5% 10% 10% 5% 1	2196
	11th to 20th	Day	57% 8% 12% 16% 8%	2469
	21st to end	Day	66% 6% 8% 13% 6% 1	2551
May	1st to 10th	Day	72% 5% 10% 9% 4	2798
	11th to 20th	Day	61% 7% 9% 17% 6%	2836
	21st to end	Day	59% 8% 13% 17% 3	3273
June	1st to 10th	Day	67% 7% 14% 10% 1	3240
	11th to 20th	Day	67% 9% 12% 10% 2	3240
	21st to end	Day	67% 8% 18% 7%	3240
July	1st to 10th	Day	67% 11% 14% 8%	3151
	11th to 20th	Day	68% 9% 19% 4	2986
	21st to end	Day	72% 8% 15% 5%	2963
August	1st to 10th	Day	74% 7% 14% 5%	2839
	11th to 20th	Day	77% 5% 10% 6% 1	2485
	21st to end	Day	73% 6% 12% 7% 2	2768
September	1st to 10th	Day	80% 5% 6% 7% 2	2214
	11th to 20th	Day	77% 5% 9% 9% 1	2145
	21st to end	Day	72% 5% 10% 10% 3	1939
October	1st to 10th	Day	77% 5% 8% 8% 2	1773
	11th to 20th	Day	77% 4 7% 7% 4	1620
	21st to end	Day	70% 5% 6% 8% 9% 2	1567
November	1st to 10th	Day	69% 3 7% 11% 6% 4	1301
	11th to 20th	Day	57% 5% 8% 18% 11% 1	1187
	21st to end	Day	71% 3 6% 9% 9% 3	985
December	1st to 10th	Day	76% 4 6% 6% 6% 2	917
	11th to 20th	Day	69% 6% 10% 11% 5% 1	970
	21st to end	Day	56% 8% 7% 8% 9% 11%	1397
January	1st to 10th	Night	68% 5% 5% 8% 10% 3	5659
	11th to 20th	Night	59% 2 4 11% 17% 8%	5132
	21st to end	Night	55% 7% 6% 10% 12% 10%	5577
February	1st to 10th	Night	61% 4 6% 11% 11% 7%	2837
	11th to 20th	Night	75% 4 6% 7% 6% 2	2592
	21st to end	Night	53% 6% 9% 13% 17% 3	2103
March	1st to 10th	Night	58% 4 6% 12% 12% 8%	2227
	11th to 20th	Night	57% 5% 6% 13% 16% 3	2120
	21st to end	Night	62% 6% 8% 11% 10% 3	1980
April	1st to 10th	Night	66% 3 9% 14% 6% 1	1764
	11th to 20th	Night	56% 5% 11% 18% 9%	1437
	21st to end	Night	64% 5% 9% 13% 8% 1	1409
May	1st to 10th	Night	70% 6% 11% 11% 3	1159
	11th to 20th	Night	59% 6% 12% 16% 6%	1063
	21st to end	Night	59% 7% 14% 16% 3	999
June	1st to 10th	Night	67% 10% 11% 11% 1	720
	11th to 20th	Night	64% 8% 15% 10% 2	720
	21st to end	Night	68% 8% 18% 6% 1	720
July	1st to 10th	Night	63% 9% 18% 10%	700
	11th to 20th	Night	65% 8% 22% 5%	849
	21st to end	Night	73% 7% 16% 4	1116
August	1st to 10th	Night	73% 8% 13% 6%	1073
	11th to 20th	Night	76% 5% 9% 8% 1	1415
	21st to end	Night	69% 6% 13% 9% 3	1588
September	1st to 10th	Night	79% 6% 7% 7% 1	1745
	11th to 20th	Night	76% 4 7% 9% 3	1815
	21st to end	Night	70% 6% 11% 10% 3	2020
October	1st to 10th	Night	74% 3 8% 11% 3	2186
	11th to 20th	Night	77% 3 7% 8% 5%	2340
	21st to end	Night	69% 3 8% 10% 8% 2	2788
November	1st to 10th	Night	70% 3 7% 10% 7% 3	2777
	11th to 20th	Night	56% 4 8% 19% 11% 1	2992
	21st to end	Night	69% 3 6% 10% 9% 3	3193
December	1st to 10th	Night	74% 3 6% 8% 7% 1	3259
	11th to 20th	Night	67% 5% 10% 10% 7% 1	4236
	21st to end	Night	59% 6% 6% 8% 10% 11%	6270

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% 14% 22% 19% 20% 4	104
	11th to 20th	Day	33% 14% 23% 19% 9% 3	280
	21st to end	Day	34% 14% 20% 22% 9% 1	308
February	1st to 10th	Day	21% 15% 21% 24% 13% 6%	300
	11th to 20th	Day	32% 16% 23% 18% 10% 2	365
	21st to end	Day	27% 12% 31% 17% 7% 5%	307
March	1st to 10th	Day	20% 14% 29% 20% 15% 2	356
	11th to 20th	Day	19% 19% 23% 19% 16% 4	373
	21st to end	Day	23% 16% 19% 19% 17% 5%	572
April	1st to 10th	Day	27% 21% 22% 17% 12% 1	536
	11th to 20th	Day	24% 11% 14% 25% 21% 6%	590
	21st to end	Day	30% 12% 13% 22% 17% 5%	600
May	1st to 10th	Day	39% 16% 14% 16% 13% 2	603
	11th to 20th	Day	33% 10% 14% 24% 16% 4	625
	21st to end	Day	33% 10% 18% 22% 15% 3	689
June	1st to 10th	Day	34% 9% 11% 20% 20% 5%	810
	11th to 20th	Day	30% 8% 13% 23% 21% 4	810
	21st to end	Day	37% 10% 11% 17% 20% 6%	810
July	1st to 10th	Day	36% 8% 11% 23% 18% 4	796
	11th to 20th	Day	39% 12% 12% 19% 16% 4	730
	21st to end	Day	44% 11% 10% 16% 15% 4	684
August	1st to 10th	Day	48% 9% 12% 17% 11% 3	626
	11th to 20th	Day	51% 11% 14% 15% 8% 2	615
	21st to end	Day	48% 8% 15% 16% 11% 1	693
September	1st to 10th	Day	49% 12% 14% 13% 10% 1	567
	11th to 20th	Day	49% 11% 11% 15% 11% 2	525
	21st to end	Day	46% 11% 15% 15% 12% 2	360
October	1st to 10th	Day	48% 12% 16% 12% 11% 2	360
	11th to 20th	Day	42% 14% 17% 15% 10% 3	360
	21st to end	Day	41% 10% 17% 17% 13% 2	396
November	1st to 10th	Day	34% 12% 19% 19% 14% 3	365
	11th to 20th	Day	32% 11% 22% 24% 11% 1	302
	21st to end	Day	34% 11% 20% 20% 11% 3	125
December	1st to 10th	Day	37% 9% 18% 23% 12% 1	90
	11th to 20th	Day	31% 13% 28% 17% 9% 2	90
	21st to end	Day	36% 12% 27% 17% 7%	99
January	1st to 10th	Night	26% 14% 19% 23% 16% 2	940
	11th to 20th	Night	33% 15% 22% 18% 11% 2	866
	21st to end	Night	33% 11% 23% 22% 9% 1	935
February	1st to 10th	Night	24% 13% 23% 25% 13% 2	850
	11th to 20th	Night	37% 15% 21% 19% 9%	834
	21st to end	Night	23% 14% 28% 22% 11% 2	608
March	1st to 10th	Night	21% 14% 24% 25% 14% 3	641
	11th to 20th	Night	18% 14% 22% 28% 15% 2	618
	21st to end	Night	29% 12% 17% 20% 17% 5%	594
April	1st to 10th	Night	30% 15% 17% 19% 16% 2	540
	11th to 20th	Night	25% 10% 14% 22% 27% 3	533
	21st to end	Night	29% 11% 17% 18% 21% 4	540
May	1st to 10th	Night	32% 15% 12% 18% 20% 3	439
	11th to 20th	Night	33% 9% 8% 19% 26% 4	354
	21st to end	Night	33% 6% 8% 22% 26% 4	236
June	1st to 10th	Night	33% 13% 8% 18% 24% 4	180
	11th to 20th	Night	34% 7% 7% 17% 30% 4	180
	21st to end	Night	37% 8% 12% 13% 26% 5%	180
July	1st to 10th	Night	37% 6% 9% 17% 28% 3	175
	11th to 20th	Night	38% 5% 10% 18% 24% 5%	265
	21st to end	Night	47% 7% 10% 12% 19% 4	394
August	1st to 10th	Night	50% 8% 11% 13% 16% 2	358
	11th to 20th	Night	51% 7% 12% 17% 11% 2	526
	21st to end	Night	47% 7% 11% 17% 14% 4	594
September	1st to 10th	Night	54% 8% 10% 12% 15% 1	540
	11th to 20th	Night	55% 8% 10% 13% 12% 2	540
	21st to end	Night	45% 7% 11% 17% 16% 3	560
October	1st to 10th	Night	48% 9% 13% 16% 13% 1	656
	11th to 20th	Night	46% 9% 14% 16% 13% 2	810
	21st to end	Night	40% 8% 18% 18% 15% 2	891
November	1st to 10th	Night	37% 12% 19% 21% 10% 1	830
	11th to 20th	Night	26% 12% 26% 24% 11% 2	850
	21st to end	Night	33% 12% 22% 21% 10% 2	850
December	1st to 10th	Night	37% 13% 19% 18% 9% 3	864
	11th to 20th	Night	28% 14% 25% 24% 7% 3	940
	21st to end	Night	34% 17% 18% 19% 9% 2	1034

Page generated at 2024-03-03 02:28:56. Version ac07

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