Crossfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crossfield clear sky chart from 2005-11-06 to 2026-01-02.

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% 9% 3 8% 5% 5% 5% 4 7% 8% 37%	131551
	Night	7% 9% 4 9% 6% 5% 5% 4 6% 8% 37%	128506
Transparency	Day	43% 6% 15% 24% 10% 2	131251
	Night	43% 6% 15% 22% 11% 2	128383
Seeing	Day	13% 9% 29% 30% 15% 4	16821
	Night	11% 7% 32% 34% 13% 2	25963

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	2 9% 6% 13% 7% 8% 7% 4 5% 7% 32%	3186
	11th to 20th	Day	2 9% 4 11% 7% 5% 6% 5% 7% 8% 34%	3187
	21st to end	Day	3 7% 3 7% 5% 5% 5% 4 7% 9% 43%	4004
February	1st to 10th	Day	5% 13% 5% 11% 7% 7% 6% 4 6% 7% 29%	1600
	11th to 20th	Day	6% 10% 5% 12% 8% 7% 5% 5% 8% 8% 28%	1732
	21st to end	Day	3 11% 5% 10% 7% 5% 6% 6% 7% 8% 32%	1600
March	1st to 10th	Day	2 10% 4 11% 6% 5% 6% 4 7% 9% 35%	4518
	11th to 20th	Day	4 11% 4 10% 5% 4 4 4 6% 8% 39%	4944
	21st to end	Day	8% 22% 6% 12% 6% 4 5% 4 5% 6% 21%	5573
April	1st to 10th	Day	8% 15% 4 9% 7% 5% 5% 5% 7% 8% 27%	2457
	11th to 20th	Day	12% 15% 4 9% 5% 5% 5% 4 5% 6% 28%	2570
	21st to end	Day	13% 12% 4 8% 5% 5% 5% 5% 5% 8% 31%	2600
May	1st to 10th	Day	14% 10% 3 7% 4 5% 5% 4 5% 6% 37%	6267
	11th to 20th	Day	13% 11% 4 10% 6% 6% 6% 5% 7% 7% 24%	6734
	21st to end	Day	13% 8% 3 8% 6% 6% 5% 4 6% 6% 34%	7405
June	1st to 10th	Day	17% 8% 2 7% 6% 6% 6% 5% 7% 8% 29%	3000
	11th to 20th	Day	19% 10% 3 7% 6% 6% 6% 5% 7% 7% 24%	3000
	21st to end	Day	9% 5% 3 7% 5% 5% 7% 6% 7% 10% 37%	3000
July	1st to 10th	Day	7% 4 2 6% 4 4 5% 5% 7% 9% 45%	6780
	11th to 20th	Day	11% 4 2 4 4 4 5% 5% 8% 10% 42%	6780
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 46%	7245
August	1st to 10th	Day	9% 6% 2 6% 4 5% 6% 5% 7% 8% 41%	4541
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 4 8% 11% 42%	4223
	21st to end	Day	10% 5% 2 5% 4 3 4 3 6% 8% 51%	4664
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 5% 7% 48%	2488
	11th to 20th	Day	14% 8% 2 5% 4 3 4 4 5% 7% 45%	2200
	21st to end	Day	9% 8% 2 7% 4 5% 5% 4 6% 7% 45%	2200
October	1st to 10th	Day	8% 5% 3 7% 4 4 5% 5% 8% 10% 42%	3450
	11th to 20th	Day	6% 7% 2 7% 5% 5% 5% 5% 7% 10% 41%	2996
	21st to end	Day	7% 7% 3 8% 6% 5% 5% 4 5% 7% 44%	3200
November	1st to 10th	Day	7% 16% 5% 10% 5% 4 3 4 6% 6% 33%	1710
	11th to 20th	Day	6% 12% 3 9% 6% 6% 4 3 6% 7% 38%	1580
	21st to end	Day	5% 14% 4 8% 5% 5% 6% 4 7% 10% 32%	1470
December	1st to 10th	Day	4 10% 5% 12% 7% 7% 6% 4 8% 7% 30%	2360
	11th to 20th	Day	4 10% 4 10% 6% 8% 6% 5% 7% 8% 32%	2712
	21st to end	Day	2 9% 4 8% 6% 5% 5% 5% 7% 8% 41%	3575
January	1st to 10th	Night	3 13% 6% 14% 8% 6% 7% 5% 6% 7% 26%	6782
	11th to 20th	Night	2 8% 4 13% 7% 6% 6% 5% 6% 7% 34%	6739
	21st to end	Night	3 9% 4 9% 6% 5% 5% 4 7% 7% 42%	6955
February	1st to 10th	Night	4 10% 4 12% 8% 8% 6% 4 5% 8% 30%	2800
	11th to 20th	Night	5% 12% 5% 11% 7% 6% 5% 5% 7% 8% 30%	2554
	21st to end	Night	2 12% 5% 10% 7% 6% 5% 5% 7% 8% 34%	2026
March	1st to 10th	Night	3 9% 4 12% 7% 6% 6% 4 7% 9% 35%	5376
	11th to 20th	Night	5% 9% 4 10% 5% 6% 5% 5% 7% 9% 36%	5054
	21st to end	Night	7% 19% 6% 14% 7% 5% 5% 4 5% 7% 21%	5387
April	1st to 10th	Night	8% 14% 4 9% 6% 5% 5% 4 7% 8% 30%	1942
	11th to 20th	Night	10% 14% 4 10% 6% 6% 6% 4 5% 7% 29%	1781
	21st to end	Night	11% 10% 4 9% 6% 4 5% 4 7% 7% 31%	1800
May	1st to 10th	Night	15% 11% 3 7% 4 4 4 3 5% 5% 37%	3697
	11th to 20th	Night	13% 10% 3 8% 5% 5% 6% 4 7% 9% 30%	3159
	21st to end	Night	12% 8% 3 8% 7% 5% 6% 4 6% 6% 35%	3470
June	1st to 10th	Night	17% 7% 3 6% 6% 5% 5% 4 6% 9% 32%	1400
	11th to 20th	Night	18% 8% 3 8% 6% 5% 6% 6% 6% 6% 27%	1400
	21st to end	Night	11% 6% 2 5% 5% 4 6% 6% 7% 8% 42%	1400
July	1st to 10th	Night	7% 4 3 7% 5% 5% 6% 5% 7% 9% 43%	3180
	11th to 20th	Night	9% 4 2 6% 3 6% 6% 4 7% 10% 44%	3180
	21st to end	Night	10% 4 2 6% 4 3 4 3 6% 9% 50%	3595
August	1st to 10th	Night	11% 5% 3 6% 4 4 5% 5% 6% 9% 44%	2609
	11th to 20th	Night	7% 4 2 7% 5% 5% 5% 5% 7% 11% 42%	2834
	21st to end	Night	8% 5% 2 5% 3 3 5% 4 5% 8% 51%	3245
September	1st to 10th	Night	11% 7% 2 5% 4 3 3 3 5% 7% 50%	1910
	11th to 20th	Night	14% 7% 2 5% 3 3 4 4 7% 7% 45%	2200
	21st to end	Night	9% 7% 2 6% 3 4 5% 4 6% 8% 46%	2200
October	1st to 10th	Night	8% 6% 2 6% 5% 4 4 4 5% 8% 48%	3745
	11th to 20th	Night	6% 7% 3 7% 5% 5% 5% 4 6% 8% 45%	4149
	21st to end	Night	5% 7% 3 7% 5% 5% 6% 4 7% 8% 43%	4600
November	1st to 10th	Night	8% 13% 4 9% 4 5% 5% 4 7% 7% 34%	2787
	11th to 20th	Night	4 12% 4 8% 6% 5% 5% 5% 7% 9% 36%	3037
	21st to end	Night	5% 10% 4 8% 6% 6% 5% 5% 6% 8% 36%	3150
December	1st to 10th	Night	5% 10% 4 11% 7% 6% 7% 5% 7% 8% 31%	5040
	11th to 20th	Night	4 11% 5% 12% 9% 7% 6% 5% 6% 8% 28%	5700
	21st to end	Night	3 10% 4 9% 5% 5% 5% 4 6% 7% 42%	7623

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	51% 5% 10% 21% 10% 2	3186
	11th to 20th	Day	45% 6% 13% 15% 18% 3	3208
	21st to end	Day	36% 5% 14% 32% 12% 1	4004
February	1st to 10th	Day	52% 7% 16% 14% 9% 2	1600
	11th to 20th	Day	51% 8% 13% 18% 9% 2	1741
	21st to end	Day	47% 8% 13% 20% 11% 2	1600
March	1st to 10th	Day	42% 6% 14% 23% 15% 1	4518
	11th to 20th	Day	41% 5% 14% 23% 15% 1	4945
	21st to end	Day	62% 6% 12% 13% 6% 1	5573
April	1st to 10th	Day	52% 8% 16% 16% 8%	2457
	11th to 20th	Day	53% 7% 11% 19% 9% 1	2570
	21st to end	Day	49% 8% 15% 20% 8% 1	2600
May	1st to 10th	Day	46% 6% 9% 21% 14% 4	6267
	11th to 20th	Day	53% 8% 14% 19% 7%	6738
	21st to end	Day	46% 7% 14% 23% 9%	7406
June	1st to 10th	Day	49% 8% 16% 18% 8% 2	3000
	11th to 20th	Day	55% 9% 13% 16% 6% 2	3000
	21st to end	Day	39% 9% 20% 23% 7% 1	3000
July	1st to 10th	Day	33% 5% 17% 28% 14% 2	6706
	11th to 20th	Day	35% 6% 21% 29% 8% 1	6699
	21st to end	Day	35% 5% 16% 27% 14% 3	7040
August	1st to 10th	Day	38% 7% 17% 32% 6% 1	4524
	11th to 20th	Day	35% 6% 25% 27% 6% 1	4263
	21st to end	Day	31% 6% 18% 33% 11% 1	4663
September	1st to 10th	Day	34% 6% 17% 26% 13% 4	2488
	11th to 20th	Day	38% 6% 14% 27% 13% 1	2200
	21st to end	Day	38% 6% 16% 25% 12% 2	2200
October	1st to 10th	Day	35% 6% 20% 32% 6% 1	3450
	11th to 20th	Day	37% 5% 20% 23% 12% 3	2996
	21st to end	Day	40% 4 10% 33% 12% 1	3200
November	1st to 10th	Day	50% 7% 11% 20% 10% 2	1710
	11th to 20th	Day	44% 7% 15% 22% 10% 1	1580
	21st to end	Day	45% 7% 15% 21% 9% 2	1470
December	1st to 10th	Day	52% 5% 13% 21% 7% 1	2360
	11th to 20th	Day	47% 7% 19% 19% 7% 1	2714
	21st to end	Day	38% 6% 11% 23% 18% 4	3575
January	1st to 10th	Night	55% 7% 11% 20% 6% 2	6782
	11th to 20th	Night	48% 5% 12% 18% 14% 4	6780
	21st to end	Night	39% 6% 15% 25% 14% 1	6955
February	1st to 10th	Night	52% 6% 12% 16% 12% 2	2800
	11th to 20th	Night	49% 8% 12% 19% 11% 2	2555
	21st to end	Night	45% 6% 12% 20% 14% 2	2026
March	1st to 10th	Night	43% 5% 18% 20% 11% 2	5376
	11th to 20th	Night	42% 8% 15% 21% 14% 1	5054
	21st to end	Night	60% 6% 11% 13% 8% 1	5387
April	1st to 10th	Night	48% 7% 13% 19% 11% 1	1942
	11th to 20th	Night	53% 6% 12% 19% 9% 1	1781
	21st to end	Night	49% 7% 14% 20% 8% 2	1800
May	1st to 10th	Night	47% 5% 10% 20% 14% 3	3694
	11th to 20th	Night	46% 8% 16% 22% 7%	3159
	21st to end	Night	44% 9% 15% 24% 7% 1	3470
June	1st to 10th	Night	47% 7% 16% 18% 10% 1	1400
	11th to 20th	Night	53% 9% 14% 16% 7% 2	1400
	21st to end	Night	36% 9% 21% 26% 6% 1	1400
July	1st to 10th	Night	35% 6% 17% 25% 15% 1	3145
	11th to 20th	Night	34% 6% 21% 29% 6% 3	3138
	21st to end	Night	32% 6% 21% 27% 13% 2	3495
August	1st to 10th	Night	36% 7% 15% 33% 9%	2601
	11th to 20th	Night	34% 7% 25% 27% 6% 1	2860
	21st to end	Night	30% 6% 21% 31% 11% 1	3245
September	1st to 10th	Night	32% 7% 16% 26% 14% 5%	1910
	11th to 20th	Night	36% 7% 15% 26% 12% 4	2200
	21st to end	Night	35% 6% 18% 25% 14% 3	2200
October	1st to 10th	Night	34% 5% 18% 26% 16% 1	3745
	11th to 20th	Night	36% 5% 18% 25% 14% 2	4149
	21st to end	Night	37% 6% 11% 32% 14% 1	4600
November	1st to 10th	Night	47% 7% 13% 20% 11% 2	2787
	11th to 20th	Night	42% 7% 17% 20% 12% 1	3037
	21st to end	Night	43% 8% 16% 21% 9% 3	3150
December	1st to 10th	Night	50% 5% 17% 19% 6% 2	5040
	11th to 20th	Night	52% 7% 16% 17% 7% 1	5697
	21st to end	Night	39% 5% 10% 25% 16% 4	7623

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	5% 8% 33% 30% 16% 7%	202
	11th to 20th	Day	10% 10% 40% 23% 16% 2	200
	21st to end	Day	7% 10% 33% 32% 15% 3	220
February	1st to 10th	Day	13% 12% 37% 25% 10% 5%	200
	11th to 20th	Day	9% 8% 37% 33% 10% 2	289
	21st to end	Day	8% 13% 31% 29% 16% 3	364
March	1st to 10th	Day	10% 11% 34% 30% 12% 3	500
	11th to 20th	Day	8% 12% 34% 32% 11% 4	500
	21st to end	Day	15% 13% 33% 24% 10% 5%	550
April	1st to 10th	Day	13% 14% 33% 29% 9% 2	500
	11th to 20th	Day	16% 13% 30% 28% 11% 2	492
	21st to end	Day	19% 12% 28% 28% 11% 2	500
May	1st to 10th	Day	19% 14% 23% 26% 15% 3	558
	11th to 20th	Day	17% 7% 25% 30% 18% 3	725
	21st to end	Day	17% 7% 22% 30% 19% 5%	789
June	1st to 10th	Day	17% 11% 29% 28% 12% 3	730
	11th to 20th	Day	21% 10% 26% 28% 13% 2	730
	21st to end	Day	11% 5% 26% 33% 20% 5%	730
July	1st to 10th	Day	11% 6% 23% 35% 20% 4	721
	11th to 20th	Day	14% 5% 26% 31% 21% 3	718
	21st to end	Day	9% 5% 24% 37% 19% 6%	738
August	1st to 10th	Day	12% 6% 26% 31% 20% 6%	527
	11th to 20th	Day	10% 5% 25% 37% 19% 5%	517
	21st to end	Day	11% 7% 24% 31% 20% 7%	583
September	1st to 10th	Day	13% 8% 30% 28% 16% 6%	530
	11th to 20th	Day	18% 5% 25% 29% 16% 6%	530
	21st to end	Day	13% 15% 32% 27% 10% 3	530
October	1st to 10th	Day	15% 9% 29% 31% 12% 5%	445
	11th to 20th	Day	14% 13% 34% 24% 12% 3	330
	21st to end	Day	14% 17% 34% 25% 7% 3	363
November	1st to 10th	Day	16% 11% 35% 27% 8% 3	330
	11th to 20th	Day	15% 13% 33% 28% 9% 2	278
	21st to end	Day	10% 11% 35% 25% 14% 6%	220
December	1st to 10th	Day	8% 8% 40% 29% 12% 3	220
	11th to 20th	Day	10% 11% 40% 27% 10% 3	220
	21st to end	Day	7% 7% 33% 33% 18% 2	242
January	1st to 10th	Night	8% 11% 37% 32% 11% 1	1006
	11th to 20th	Night	9% 9% 40% 32% 10% 1	1000
	21st to end	Night	10% 12% 37% 31% 9% 1	883
February	1st to 10th	Night	9% 10% 31% 33% 14% 3	800
	11th to 20th	Night	8% 6% 37% 35% 13% 1	784
	21st to end	Night	6% 8% 33% 30% 19% 5%	660
March	1st to 10th	Night	8% 6% 35% 35% 14% 3	800
	11th to 20th	Night	10% 6% 35% 36% 12% 2	800
	21st to end	Night	14% 6% 31% 34% 13% 3	880
April	1st to 10th	Night	12% 8% 30% 32% 15% 2	742
	11th to 20th	Night	16% 8% 34% 32% 10%	593
	21st to end	Night	16% 10% 29% 36% 10% 1	600
May	1st to 10th	Night	15% 10% 29% 33% 13%	486
	11th to 20th	Night	13% 6% 29% 36% 16%	394
	21st to end	Night	19% 4 24% 36% 16% 1	433
June	1st to 10th	Night	19% 8% 27% 34% 13% 1	400
	11th to 20th	Night	20% 6% 30% 31% 14% 1	400
	21st to end	Night	13% 3 22% 40% 21% 2	400
July	1st to 10th	Night	11% 5% 18% 43% 23% 1	390
	11th to 20th	Night	12% 1 26% 41% 18% 2	388
	21st to end	Night	6% 4 19% 43% 25% 2	438
August	1st to 10th	Night	12% 2 17% 41% 27% 2	398
	11th to 20th	Night	9% 3 19% 44% 23% 2	551
	21st to end	Night	9% 3 24% 42% 22% 1	660
September	1st to 10th	Night	13% 3 24% 38% 19% 2	700
	11th to 20th	Night	15% 4 21% 39% 20% 2	800
	21st to end	Night	13% 6% 33% 32% 13% 2	800
October	1st to 10th	Night	14% 6% 29% 35% 14% 3	800
	11th to 20th	Night	12% 6% 34% 34% 12% 2	800
	21st to end	Night	11% 10% 35% 33% 10% 1	880
November	1st to 10th	Night	15% 9% 38% 27% 10% 1	942
	11th to 20th	Night	9% 10% 43% 28% 8% 1	1050
	21st to end	Night	8% 8% 41% 32% 8% 2	1050
December	1st to 10th	Night	9% 10% 37% 30% 12% 2	1050
	11th to 20th	Night	8% 9% 38% 35% 9% 1	1050
	21st to end	Night	9% 7% 37% 35% 10% 2	1155

Page generated at 2025-12-29 23:14:11. Version ac07

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