Old Crow
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Crow clear sky chart from 2005-11-06 to 2026-04-02.

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% 11% 4 11% 7% 6% 6% 5% 7% 8% 26%	136079
	Night	5% 12% 5% 14% 8% 7% 7% 5% 8% 10% 18%	139220
Transparency	Day	52% 7% 17% 18% 5%	135624
	Night	58% 7% 12% 15% 8% 1	139244
Seeing	Day	13% 5% 16% 29% 25% 11%	20977
	Night	12% 4 13% 32% 29% 10%	24966

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	1 8% 5% 16% 13% 5% 6% 8% 8% 14% 16%	278
	11th to 20th	Day	4 9% 4 8% 9% 9% 7% 8% 12% 13% 17%	1293
	21st to end	Day	4 13% 6% 14% 10% 7% 9% 6% 8% 12% 10%	2496
February	1st to 10th	Day	2 7% 3 13% 9% 11% 7% 8% 9% 12% 19%	1072
	11th to 20th	Day	2 6% 4 12% 10% 9% 10% 6% 14% 10% 16%	1435
	21st to end	Day	2 6% 5% 14% 9% 8% 11% 7% 9% 13% 16%	1385
March	1st to 10th	Day	1 7% 5% 20% 11% 8% 7% 5% 7% 10% 18%	4130
	11th to 20th	Day	1 8% 4 13% 8% 8% 6% 7% 11% 11% 22%	4988
	21st to end	Day	2 10% 7% 16% 9% 9% 7% 6% 9% 9% 16%	5971
April	1st to 10th	Day	4 16% 5% 14% 9% 7% 6% 4 7% 6% 23%	2638
	11th to 20th	Day	4 12% 4 9% 6% 6% 6% 5% 7% 9% 32%	2878
	21st to end	Day	3 10% 4 9% 7% 5% 6% 5% 7% 9% 36%	3142
May	1st to 10th	Day	13% 24% 8% 11% 5% 4 3 3 4 6% 17%	7838
	11th to 20th	Day	5% 10% 5% 10% 6% 5% 6% 5% 8% 8% 31%	8433
	21st to end	Day	9% 12% 4 9% 5% 6% 5% 5% 7% 10% 28%	10256
June	1st to 10th	Day	10% 8% 3 7% 6% 6% 6% 6% 7% 8% 34%	4765
	11th to 20th	Day	11% 6% 3 7% 6% 5% 5% 6% 7% 9% 36%	4800
	21st to end	Day	11% 7% 3 7% 6% 6% 7% 6% 8% 10% 31%	4800
July	1st to 10th	Day	13% 9% 4 9% 6% 5% 6% 5% 6% 7% 31%	10880
	11th to 20th	Day	8% 6% 2 8% 6% 5% 6% 5% 8% 11% 34%	9539
	21st to end	Day	11% 7% 3 8% 6% 6% 6% 5% 7% 8% 33%	9385
August	1st to 10th	Day	12% 8% 3 8% 6% 5% 6% 5% 7% 8% 33%	5573
	11th to 20th	Day	14% 8% 4 9% 6% 7% 7% 5% 7% 8% 24%	5107
	21st to end	Day	14% 10% 4 12% 7% 7% 6% 5% 7% 6% 21%	5275
September	1st to 10th	Day	15% 11% 4 10% 6% 6% 5% 5% 7% 6% 25%	2636
	11th to 20th	Day	15% 13% 4 9% 7% 5% 5% 4 6% 8% 24%	2411
	21st to end	Day	17% 22% 8% 12% 7% 4 5% 4 4 3 15%	2118
October	1st to 10th	Day	9% 18% 8% 12% 5% 5% 4 4 6% 8% 21%	3148
	11th to 20th	Day	8% 20% 8% 20% 9% 7% 6% 4 4 4 11%	2615
	21st to end	Day	9% 14% 4 14% 11% 8% 9% 5% 7% 8% 11%	2366
November	1st to 10th	Day	6% 20% 9% 15% 7% 7% 8% 6% 7% 7% 8%	1096
	11th to 20th	Day	3 11% 6% 18% 12% 9% 9% 6% 9% 6% 10%	819
	21st to end	Day	8% 14% 6% 13% 11% 8% 8% 6% 11% 7% 8%	435
December	1st to 10th	Day	3 13% 3 10% 4 5% 1 8% 24% 24% 5%	78
	January	1st to 10th	Night	2 6% 3 11% 8% 10% 10% 7% 9% 14% 19%	13152
11th to 20th		Night	3 10% 5% 13% 8% 8% 8% 5% 9% 11% 20%	11621
21st to end		Night	4 12% 6% 15% 8% 8% 8% 6% 8% 12% 13%	11764
February	1st to 10th	Night	2 9% 5% 12% 9% 10% 9% 7% 11% 13% 16%	3548
	11th to 20th	Night	3 8% 4 14% 10% 7% 6% 7% 10% 12% 20%	3072
	21st to end	Night	2 7% 4 14% 9% 9% 7% 7% 9% 10% 21%	2420
March	1st to 10th	Night	1 8% 5% 21% 11% 7% 8% 5% 6% 7% 21%	5964
	11th to 20th	Night	2 7% 4 13% 7% 7% 6% 6% 10% 13% 25%	5193
	21st to end	Night	1 9% 6% 18% 8% 7% 7% 6% 6% 9% 23%	5199
April	1st to 10th	Night	5% 13% 7% 12% 8% 7% 6% 5% 5% 6% 25%	1785
	11th to 20th	Night	5% 12% 3 10% 6% 6% 6% 4 7% 8% 33%	1470
	21st to end	Night	2 10% 3 9% 5% 4 6% 4 6% 9% 41%	1258
May	1st to 10th	Night	14% 27% 8% 9% 5% 4 3 3 4 6% 18%	2122
	11th to 20th	Night	6% 11% 4 9% 7% 6% 6% 5% 7% 9% 31%	1476
	21st to end	Night	8% 14% 5% 8% 4 5% 6% 6% 7% 7% 29%	641
July	11th to 20th	Night	9% 5% 3 10% 5% 5% 5% 4 8% 8% 39%	465
	21st to end	Night	11% 8% 3 10% 6% 6% 7% 5% 7% 10% 29%	1479
August	1st to 10th	Night	11% 7% 3 9% 6% 6% 7% 5% 6% 8% 33%	1576
	11th to 20th	Night	12% 7% 3 10% 8% 7% 8% 5% 7% 9% 24%	1945
	21st to end	Night	16% 12% 5% 9% 6% 6% 6% 5% 7% 7% 22%	2634
September	1st to 10th	Night	18% 10% 3 8% 6% 5% 6% 4 6% 7% 27%	1762
	11th to 20th	Night	18% 11% 3 9% 5% 5% 4 4 6% 7% 27%	1989
	21st to end	Night	20% 21% 6% 11% 4 5% 5% 4 4 4 16%	2282
October	1st to 10th	Night	9% 17% 6% 11% 6% 5% 5% 4 5% 8% 25%	4042
	11th to 20th	Night	8% 18% 9% 16% 7% 6% 6% 4 6% 7% 14%	4533
	21st to end	Night	7% 17% 6% 16% 9% 9% 8% 5% 7% 6% 11%	5426
November	1st to 10th	Night	6% 20% 7% 16% 9% 7% 6% 5% 6% 8% 9%	3399
	11th to 20th	Night	4 12% 6% 18% 12% 10% 9% 6% 7% 8% 9%	3801
	21st to end	Night	6% 16% 6% 15% 10% 9% 7% 5% 9% 8% 9%	4185
December	1st to 10th	Night	4 16% 6% 14% 8% 7% 7% 6% 9% 13% 11%	7590
	11th to 20th	Night	3 10% 5% 13% 8% 7% 7% 5% 10% 14% 17%	9195
	21st to end	Night	3 17% 8% 15% 8% 7% 6% 5% 8% 11% 11%	12232

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	58% 3 11% 8% 20%	278
	11th to 20th	Day	53% 6% 14% 20% 6% 1	1301
	21st to end	Day	65% 5% 8% 15% 7%	2497
February	1st to 10th	Day	53% 8% 11% 17% 9% 1	1072
	11th to 20th	Day	52% 11% 12% 17% 7%	1442
	21st to end	Day	55% 11% 14% 12% 8%	1385
March	1st to 10th	Day	59% 6% 10% 14% 9% 2	4130
	11th to 20th	Day	47% 7% 10% 20% 15% 1	4988
	21st to end	Day	59% 6% 14% 11% 9%	5971
April	1st to 10th	Day	60% 8% 13% 12% 6%	2638
	11th to 20th	Day	46% 12% 21% 17% 5%	2878
	21st to end	Day	41% 10% 22% 21% 7%	3142
May	1st to 10th	Day	67% 5% 10% 16% 2	7838
	11th to 20th	Day	44% 9% 17% 22% 8%	8437
	21st to end	Day	49% 7% 19% 20% 5%	10257
June	1st to 10th	Day	43% 11% 16% 20% 9%	4765
	11th to 20th	Day	41% 9% 15% 27% 8%	4800
	21st to end	Day	44% 11% 17% 22% 5%	4800
July	1st to 10th	Day	51% 5% 18% 16% 10% 1	10761
	11th to 20th	Day	42% 5% 28% 23% 2	9418
	21st to end	Day	48% 6% 23% 22% 2	9121
August	1st to 10th	Day	47% 8% 23% 20% 2	5552
	11th to 20th	Day	55% 8% 23% 13%	5157
	21st to end	Day	61% 7% 19% 14%	5274
September	1st to 10th	Day	55% 11% 21% 10% 2	2636
	11th to 20th	Day	56% 10% 21% 12% 1	2411
	21st to end	Day	72% 6% 11% 10% 1	2118
October	1st to 10th	Day	62% 5% 16% 16% 1	3148
	11th to 20th	Day	78% 5% 9% 8% 1	2615
	21st to end	Day	70% 6% 11% 14%	2366
November	1st to 10th	Day	71% 10% 13% 5% 1	1096
	11th to 20th	Day	68% 12% 11% 8% 2	819
	21st to end	Day	66% 11% 9% 9% 4 1	435
December	1st to 10th	Day	41% 10% 10% 13% 26%	78
	January	1st to 10th	Night	51% 6% 7% 17% 18%	13153
11th to 20th		Night	57% 5% 13% 14% 8% 4	11674
21st to end		Night	62% 5% 10% 12% 10%	11764
February	1st to 10th	Night	52% 10% 12% 15% 10% 1	3548
	11th to 20th	Night	52% 9% 12% 18% 9%	3076
	21st to end	Night	53% 11% 14% 14% 8%	2420
March	1st to 10th	Night	60% 6% 9% 16% 7% 3	5964
	11th to 20th	Night	46% 7% 10% 20% 17% 1	5195
	21st to end	Night	56% 7% 11% 16% 10%	5199
April	1st to 10th	Night	57% 9% 15% 12% 5% 1	1785
	11th to 20th	Night	47% 11% 20% 18% 5%	1470
	21st to end	Night	38% 9% 21% 25% 7%	1258
May	1st to 10th	Night	68% 4 11% 14% 3	2119
	11th to 20th	Night	46% 9% 19% 20% 6%	1476
	21st to end	Night	48% 8% 20% 19% 5%	641
July	11th to 20th	Night	43% 6% 20% 28% 3	461
	21st to end	Night	50% 6% 19% 24% 1	1438
August	1st to 10th	Night	47% 10% 19% 22% 2	1572
	11th to 20th	Night	55% 7% 23% 14%	1961
	21st to end	Night	59% 6% 24% 11%	2634
September	1st to 10th	Night	54% 11% 21% 12% 2	1762
	11th to 20th	Night	54% 10% 22% 13% 1	1989
	21st to end	Night	69% 8% 12% 10% 1	2282
October	1st to 10th	Night	58% 5% 16% 21% 1	4042
	11th to 20th	Night	70% 5% 13% 11% 1	4533
	21st to end	Night	72% 7% 11% 10% 1	5426
November	1st to 10th	Night	71% 8% 13% 7% 1	3399
	11th to 20th	Night	69% 10% 12% 8% 1	3801
	21st to end	Night	68% 8% 9% 11% 4 1	4185
December	1st to 10th	Night	62% 7% 9% 13% 8%	7590
	11th to 20th	Night	52% 5% 9% 19% 14%	9195
	21st to end	Night	63% 7% 9% 15% 7%	12232

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	2 2 18% 41% 25% 12%	51
	11th to 20th	Day	9% 3 15% 35% 29% 9%	110
	21st to end	Day	9% 5% 18% 28% 26% 13%	121
February	1st to 10th	Day	2 2 14% 44% 27% 11%	132
	11th to 20th	Day	5% 1 13% 36% 29% 15%	425
	21st to end	Day	3 4 18% 32% 28% 15%	355
March	1st to 10th	Day	6% 2 12% 29% 32% 19%	430
	11th to 20th	Day	7% 4 11% 36% 27% 15%	430
	21st to end	Day	7% 5% 15% 27% 25% 22%	584
April	1st to 10th	Day	8% 6% 14% 32% 32% 9%	706
	11th to 20th	Day	8% 5% 15% 32% 29% 11%	690
	21st to end	Day	5% 4 14% 31% 29% 16%	700
May	1st to 10th	Day	15% 6% 18% 30% 23% 8%	763
	11th to 20th	Day	10% 6% 17% 30% 28% 9%	1048
	21st to end	Day	11% 7% 20% 32% 23% 6%	1222
June	1st to 10th	Day	13% 7% 19% 32% 23% 6%	1313
	11th to 20th	Day	11% 6% 17% 31% 25% 10%	1330
	21st to end	Day	13% 4 13% 30% 29% 11%	1330
July	1st to 10th	Day	13% 6% 16% 27% 25% 12%	1306
	11th to 20th	Day	14% 4 19% 27% 24% 12%	1117
	21st to end	Day	13% 4 17% 27% 27% 12%	1232
August	1st to 10th	Day	16% 7% 17% 27% 21% 13%	761
	11th to 20th	Day	17% 8% 20% 26% 21% 8%	715
	21st to end	Day	26% 5% 16% 22% 23% 8%	803
September	1st to 10th	Day	18% 8% 17% 23% 22% 13%	730
	11th to 20th	Day	21% 5% 16% 26% 22% 10%	548
	21st to end	Day	27% 6% 15% 23% 19% 10%	420
October	1st to 10th	Day	20% 9% 18% 27% 19% 8%	420
	11th to 20th	Day	17% 4 17% 27% 22% 13%	420
	21st to end	Day	23% 6% 14% 24% 23% 10%	342
November	1st to 10th	Day	11% 5% 13% 32% 26% 13%	176
	11th to 20th	Day	4 2 8% 29% 34% 24%	110
	21st to end	Day	10% 4 10% 24% 36% 16%	110
December	1st to 10th	Day	15% 11% 7% 30% 19% 19%	27
	January	1st to 10th	Night	9% 3 13% 32% 27% 16%	1319
11th to 20th		Night	8% 4 13% 35% 29% 10%	1270
21st to end		Night	8% 5% 14% 32% 30% 10%	1261
February	1st to 10th	Night	5% 3 11% 35% 33% 12%	950
	11th to 20th	Night	6% 4 13% 39% 30% 9%	934
	21st to end	Night	6% 3 15% 37% 29% 10%	783
March	1st to 10th	Night	4 2 11% 41% 32% 11%	950
	11th to 20th	Night	5% 2 9% 40% 36% 8%	675
	21st to end	Night	4 4 14% 34% 34% 11%	693
April	1st to 10th	Night	10% 3 15% 35% 29% 8%	603
	11th to 20th	Night	8% 2 13% 37% 32% 7%	593
	21st to end	Night	5% 2 16% 41% 33% 3	458
May	1st to 10th	Night	16% 7% 14% 34% 28% 2	200
	11th to 20th	Night	9% 2 14% 40% 35%	197
	21st to end	Night	10% 8% 20% 38% 23% 1	191
July	11th to 20th	Night	14% 4 22% 35% 22% 2	166
	21st to end	Night	18% 4 20% 32% 22% 3	219
August	1st to 10th	Night	18% 6% 15% 31% 27% 3	199
	11th to 20th	Night	21% 5% 18% 29% 24% 3	396
	21st to end	Night	22% 5% 15% 23% 31% 5%	660
September	1st to 10th	Night	23% 4 11% 27% 27% 8%	600
	11th to 20th	Night	22% 4 17% 28% 24% 6%	600
	21st to end	Night	27% 5% 16% 27% 19% 6%	682
October	1st to 10th	Night	20% 7% 18% 29% 21% 6%	839
	11th to 20th	Night	21% 4 16% 22% 28% 9%	910
	21st to end	Night	20% 5% 13% 25% 25% 11%	1001
November	1st to 10th	Night	15% 4 15% 30% 28% 9%	967
	11th to 20th	Night	8% 4 12% 24% 33% 20%	1171
	21st to end	Night	12% 3 10% 28% 30% 17%	1270
December	1st to 10th	Night	11% 4 13% 37% 26% 9%	1311
	11th to 20th	Night	9% 4 11% 33% 32% 11%	1380
	21st to end	Night	7% 3 12% 33% 32% 13%	1518

Page generated at 2026-03-29 22:18:39. Version ac07

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