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 2024-01-13.

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	10% 9% 4 7% 6% 4 5% 6% 6% 8% 35%	74624
	Night	8% 9% 4 7% 6% 4 6% 5% 6% 8% 37%	75126
Transparency	Day	44% 8% 16% 21% 9% 2	74308
	Night	43% 8% 15% 21% 10% 2	74960
Seeing	Day	14% 9% 28% 30% 15% 4	14212
	Night	11% 7% 32% 35% 14% 2	23446

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% 10% 5% 9% 7% 3 6% 5% 6% 10% 34%	1329
	11th to 20th	Day	5% 10% 5% 9% 8% 3 6% 5% 6% 9% 35%	1291
	21st to end	Day	6% 10% 6% 9% 8% 5% 5% 7% 7% 8% 29%	1584
February	1st to 10th	Day	5% 12% 6% 8% 8% 6% 6% 5% 7% 8% 30%	1440
	11th to 20th	Day	7% 10% 5% 10% 9% 6% 5% 6% 8% 8% 27%	1554
	21st to end	Day	4 10% 7% 9% 8% 4 6% 7% 7% 8% 30%	1435
March	1st to 10th	Day	4 12% 6% 9% 9% 5% 6% 5% 6% 7% 31%	1800
	11th to 20th	Day	5% 11% 4 8% 7% 4 6% 6% 7% 8% 34%	1950
	21st to end	Day	8% 14% 6% 9% 6% 3 6% 6% 7% 8% 26%	2214
April	1st to 10th	Day	9% 14% 6% 8% 8% 4 5% 6% 7% 8% 25%	2211
	11th to 20th	Day	13% 14% 5% 8% 7% 3 5% 5% 5% 6% 28%	2310
	21st to end	Day	14% 11% 4 7% 6% 4 5% 6% 5% 9% 31%	2340
May	1st to 10th	Day	14% 11% 4 8% 6% 4 7% 5% 6% 8% 28%	2487
	11th to 20th	Day	12% 8% 2 6% 6% 4 6% 5% 7% 8% 36%	2654
	21st to end	Day	21% 8% 3 6% 6% 3 5% 5% 6% 7% 28%	2917
June	1st to 10th	Day	18% 8% 3 6% 7% 4 6% 6% 7% 8% 27%	2700
	11th to 20th	Day	21% 9% 3 6% 7% 4 7% 6% 7% 7% 23%	2700
	21st to end	Day	9% 5% 2 6% 6% 4 6% 7% 7% 9% 37%	2700
July	1st to 10th	Day	11% 5% 2 6% 6% 3 6% 7% 7% 8% 38%	2700
	11th to 20th	Day	13% 5% 2 4 5% 4 5% 6% 7% 9% 42%	2700
	21st to end	Day	8% 4 2 4 4 3 4 6% 7% 8% 50%	2888
August	1st to 10th	Day	12% 4 2 4 5% 3 6% 5% 7% 8% 44%	2507
	11th to 20th	Day	11% 4 2 4 5% 3 4 5% 6% 9% 47%	2338
	21st to end	Day	11% 5% 2 5% 5% 3 5% 5% 6% 8% 46%	2574
September	1st to 10th	Day	12% 6% 2 5% 5% 3 4 5% 5% 7% 47%	2241
	11th to 20th	Day	15% 8% 2 5% 4 3 3 5% 5% 7% 43%	1980
	21st to end	Day	10% 9% 2 6% 5% 4 5% 4 5% 8% 43%	1980
October	1st to 10th	Day	13% 8% 4 7% 5% 2 4 5% 5% 8% 38%	1904
	11th to 20th	Day	10% 10% 3 7% 5% 4 4 5% 5% 8% 38%	1656
	21st to end	Day	8% 9% 4 9% 7% 4 6% 5% 6% 7% 35%	1782
November	1st to 10th	Day	8% 15% 6% 9% 6% 3 4 4 6% 6% 32%	1544
	11th to 20th	Day	7% 11% 4 7% 8% 5% 4 5% 5% 7% 38%	1430
	21st to end	Day	5% 12% 5% 6% 5% 4 6% 5% 7% 11% 34%	1330
December	1st to 10th	Day	6% 9% 5% 11% 8% 5% 6% 4 7% 7% 32%	1330
	11th to 20th	Day	4 10% 5% 10% 8% 6% 5% 6% 7% 9% 31%	1682
	21st to end	Day	3 8% 4 7% 7% 3 5% 6% 6% 8% 43%	2442
January	1st to 10th	Night	3 11% 5% 10% 10% 4 7% 6% 7% 9% 29%	2836
	11th to 20th	Night	5% 11% 4 9% 6% 5% 6% 5% 7% 10% 32%	2745
	21st to end	Night	5% 12% 4 9% 7% 4 6% 6% 7% 8% 33%	2775
February	1st to 10th	Night	5% 9% 5% 10% 10% 6% 6% 5% 5% 8% 31%	2520
	11th to 20th	Night	5% 12% 5% 10% 8% 5% 6% 6% 7% 8% 29%	2292
	21st to end	Night	3 10% 6% 9% 8% 4 6% 6% 6% 9% 34%	1817
March	1st to 10th	Night	5% 11% 5% 9% 8% 5% 7% 5% 7% 8% 30%	2160
	11th to 20th	Night	6% 11% 5% 7% 7% 4 7% 5% 6% 9% 34%	2008
	21st to end	Night	6% 13% 6% 9% 8% 4 6% 6% 6% 8% 28%	2140
April	1st to 10th	Night	8% 11% 5% 8% 8% 4 6% 5% 7% 8% 29%	1748
	11th to 20th	Night	11% 14% 4 8% 7% 4 6% 5% 5% 7% 29%	1601
	21st to end	Night	11% 10% 5% 8% 7% 3 5% 5% 7% 7% 31%	1620
May	1st to 10th	Night	13% 12% 4 7% 6% 4 5% 5% 6% 6% 33%	1469
	11th to 20th	Night	11% 8% 2 5% 6% 3 5% 4 7% 8% 41%	1239
	21st to end	Night	19% 7% 3 5% 6% 4 5% 6% 6% 7% 33%	1358
June	1st to 10th	Night	18% 6% 4 6% 5% 3 6% 5% 6% 9% 31%	1260
	11th to 20th	Night	19% 7% 3 7% 7% 3 7% 7% 6% 6% 27%	1260
	21st to end	Night	11% 5% 2 5% 6% 3 6% 6% 7% 8% 42%	1260
July	1st to 10th	Night	10% 4 2 5% 5% 3 6% 6% 8% 10% 40%	1260
	11th to 20th	Night	10% 4 2 5% 5% 5% 7% 6% 7% 9% 40%	1260
	21st to end	Night	6% 3 2 5% 4 2 5% 5% 6% 9% 55%	1426
August	1st to 10th	Night	10% 4 3 5% 5% 3 6% 6% 6% 9% 44%	1432
	11th to 20th	Night	10% 3 2 5% 4 2 4 6% 7% 10% 48%	1563
	21st to end	Night	9% 5% 2 4 4 2 4 7% 5% 9% 49%	1782
September	1st to 10th	Night	11% 7% 3 4 4 3 3 4 5% 8% 48%	1718
	11th to 20th	Night	14% 7% 2 5% 3 2 4 5% 7% 8% 45%	1980
	21st to end	Night	10% 8% 2 5% 4 3 5% 4 6% 8% 45%	1980
October	1st to 10th	Night	12% 8% 3 6% 6% 4 4 5% 5% 7% 41%	2056
	11th to 20th	Night	9% 8% 3 6% 5% 4 5% 6% 7% 8% 40%	2301
	21st to end	Night	7% 10% 4 8% 7% 4 5% 6% 7% 8% 35%	2574
November	1st to 10th	Night	9% 13% 5% 7% 5% 3 6% 5% 6% 6% 35%	2515
	11th to 20th	Night	4 11% 5% 7% 6% 4 5% 6% 7% 9% 36%	2747
	21st to end	Night	5% 9% 5% 7% 6% 4 6% 6% 6% 9% 37%	2850
December	1st to 10th	Night	5% 9% 5% 10% 7% 4 6% 5% 6% 8% 35%	2850
	11th to 20th	Night	2 9% 5% 9% 9% 4 6% 6% 6% 9% 33%	3510
	21st to end	Night	3 9% 3 7% 6% 4 5% 5% 6% 7% 45%	5214

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	44% 6% 14% 24% 8% 4	1329
	11th to 20th	Day	45% 7% 13% 21% 10% 3	1291
	21st to end	Day	50% 7% 14% 15% 12% 1	1584
February	1st to 10th	Day	50% 7% 16% 15% 9% 3	1440
	11th to 20th	Day	52% 8% 14% 16% 9% 1	1563
	21st to end	Day	48% 8% 13% 19% 11% 1	1435
March	1st to 10th	Day	50% 7% 17% 17% 8% 1	1800
	11th to 20th	Day	45% 8% 13% 21% 11% 2	1951
	21st to end	Day	54% 9% 15% 16% 6% 1	2214
April	1st to 10th	Day	53% 9% 16% 15% 8%	2211
	11th to 20th	Day	55% 7% 10% 19% 9% 1	2310
	21st to end	Day	50% 8% 15% 19% 7% 1	2340
May	1st to 10th	Day	53% 8% 14% 19% 6% 1	2487
	11th to 20th	Day	43% 9% 15% 23% 10% 1	2658
	21st to end	Day	52% 7% 14% 20% 6% 1	2918
June	1st to 10th	Day	51% 8% 16% 17% 6% 1	2700
	11th to 20th	Day	56% 9% 14% 15% 5% 1	2700
	21st to end	Day	39% 10% 19% 23% 7% 1	2700
July	1st to 10th	Day	39% 10% 19% 22% 8% 2	2626
	11th to 20th	Day	37% 10% 21% 25% 7% 1	2619
	21st to end	Day	28% 9% 20% 31% 11% 1	2727
August	1st to 10th	Day	35% 11% 19% 28% 7% 1	2490
	11th to 20th	Day	31% 8% 24% 26% 9% 2	2338
	21st to end	Day	33% 9% 17% 28% 11% 2	2574
September	1st to 10th	Day	36% 7% 17% 25% 12% 4	2241
	11th to 20th	Day	39% 7% 14% 27% 12% 1	1980
	21st to end	Day	39% 7% 16% 24% 12% 2	1980
October	1st to 10th	Day	43% 9% 14% 25% 9% 1	1904
	11th to 20th	Day	43% 7% 16% 24% 8% 2	1656
	21st to end	Day	46% 7% 13% 22% 11% 1	1782
November	1st to 10th	Day	51% 8% 11% 19% 9% 2	1544
	11th to 20th	Day	44% 8% 15% 22% 10% 1	1430
	21st to end	Day	43% 8% 16% 22% 9% 2	1330
December	1st to 10th	Day	50% 7% 13% 16% 13% 3	1330
	11th to 20th	Day	46% 10% 17% 18% 8% 1	1684
	21st to end	Day	36% 7% 12% 21% 19% 6%	2442
January	1st to 10th	Night	49% 9% 12% 17% 10% 4	2836
	11th to 20th	Night	45% 8% 14% 22% 7% 3	2745
	21st to end	Night	46% 8% 13% 18% 13% 2	2775
February	1st to 10th	Night	50% 6% 13% 17% 11% 3	2520
	11th to 20th	Night	50% 8% 12% 18% 10% 1	2293
	21st to end	Night	46% 6% 12% 20% 14% 2	1817
March	1st to 10th	Night	48% 7% 15% 21% 7% 1	2160
	11th to 20th	Night	45% 7% 16% 18% 13% 1	2008
	21st to end	Night	51% 7% 15% 18% 7% 1	2140
April	1st to 10th	Night	49% 8% 13% 18% 11% 1	1748
	11th to 20th	Night	53% 6% 12% 18% 9% 1	1601
	21st to end	Night	49% 7% 15% 19% 7% 2	1620
May	1st to 10th	Night	49% 8% 15% 18% 10% 1	1469
	11th to 20th	Night	39% 8% 15% 26% 12% 1	1239
	21st to end	Night	47% 10% 15% 21% 6% 1	1358
June	1st to 10th	Night	48% 7% 17% 18% 9%	1260
	11th to 20th	Night	53% 9% 14% 15% 7% 2	1260
	21st to end	Night	37% 10% 20% 25% 6% 1	1260
July	1st to 10th	Night	35% 12% 21% 22% 10% 1	1225
	11th to 20th	Night	37% 12% 18% 23% 8% 1	1218
	21st to end	Night	24% 10% 21% 30% 14% 1	1347
August	1st to 10th	Night	35% 10% 19% 27% 8% 1	1424
	11th to 20th	Night	29% 11% 23% 26% 10% 1	1563
	21st to end	Night	30% 9% 18% 28% 14% 2	1782
September	1st to 10th	Night	34% 8% 16% 25% 13% 4	1718
	11th to 20th	Night	36% 8% 15% 25% 12% 4	1980
	21st to end	Night	36% 6% 18% 23% 13% 4	1980
October	1st to 10th	Night	43% 7% 14% 24% 12% 1	2056
	11th to 20th	Night	40% 7% 16% 23% 10% 3	2301
	21st to end	Night	44% 9% 14% 22% 10% 1	2574
November	1st to 10th	Night	47% 7% 13% 19% 11% 2	2515
	11th to 20th	Night	42% 7% 17% 19% 13% 1	2747
	21st to end	Night	42% 8% 17% 20% 10% 3	2850
December	1st to 10th	Night	46% 7% 13% 21% 9% 3	2850
	11th to 20th	Night	45% 10% 17% 21% 7% 1	3507
	21st to end	Night	36% 6% 12% 25% 14% 6%	5214

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	6% 7% 33% 31% 16% 8%	180
	11th to 20th	Day	10% 9% 37% 24% 18% 2	165
	21st to end	Day	9% 9% 30% 32% 16% 3	176
February	1st to 10th	Day	14% 13% 38% 22% 9% 4	160
	11th to 20th	Day	11% 9% 37% 32% 9% 2	231
	21st to end	Day	7% 9% 30% 33% 18% 3	301
March	1st to 10th	Day	10% 12% 35% 29% 11% 4	420
	11th to 20th	Day	8% 13% 33% 31% 10% 5%	420
	21st to end	Day	14% 13% 35% 22% 10% 5%	462
April	1st to 10th	Day	12% 14% 33% 29% 10% 1	420
	11th to 20th	Day	16% 11% 29% 29% 12% 3	412
	21st to end	Day	20% 12% 26% 29% 11% 2	420
May	1st to 10th	Day	19% 13% 23% 27% 15% 3	472
	11th to 20th	Day	17% 5% 25% 30% 20% 3	625
	21st to end	Day	19% 6% 22% 29% 19% 5%	679
June	1st to 10th	Day	17% 9% 28% 29% 12% 3	630
	11th to 20th	Day	22% 10% 25% 29% 13% 2	630
	21st to end	Day	10% 5% 25% 33% 21% 5%	630
July	1st to 10th	Day	12% 6% 22% 34% 21% 4	621
	11th to 20th	Day	14% 6% 25% 31% 22% 2	618
	21st to end	Day	6% 5% 24% 38% 20% 6%	634
August	1st to 10th	Day	13% 5% 26% 30% 20% 5%	447
	11th to 20th	Day	10% 4 24% 37% 20% 5%	437
	21st to end	Day	11% 7% 24% 31% 20% 7%	495
September	1st to 10th	Day	15% 8% 32% 27% 14% 4	450
	11th to 20th	Day	19% 5% 27% 28% 15% 6%	450
	21st to end	Day	15% 15% 28% 28% 12% 3	450
October	1st to 10th	Day	17% 9% 28% 29% 12% 6%	374
	11th to 20th	Day	15% 12% 32% 25% 12% 4	270
	21st to end	Day	15% 13% 34% 27% 8% 2	297
November	1st to 10th	Day	17% 9% 34% 27% 9% 4	270
	11th to 20th	Day	16% 14% 32% 27% 8% 2	228
	21st to end	Day	9% 11% 33% 24% 15% 7%	180
December	1st to 10th	Day	8% 9% 34% 32% 14% 3	180
	11th to 20th	Day	7% 10% 41% 28% 11% 3	180
	21st to end	Day	7% 6% 30% 35% 19% 3	198
January	1st to 10th	Night	8% 10% 37% 33% 11% 1	950
	11th to 20th	Night	10% 8% 39% 33% 10% 1	915
	21st to end	Night	10% 12% 36% 31% 9% 2	795
February	1st to 10th	Night	9% 11% 30% 32% 15% 3	720
	11th to 20th	Night	9% 6% 37% 35% 11% 1	704
	21st to end	Night	6% 7% 31% 31% 20% 5%	592
March	1st to 10th	Night	8% 6% 34% 35% 14% 3	720
	11th to 20th	Night	10% 6% 34% 36% 12% 2	720
	21st to end	Night	14% 6% 29% 35% 13% 3	792
April	1st to 10th	Night	11% 8% 29% 33% 16% 2	668
	11th to 20th	Night	17% 7% 31% 34% 11%	533
	21st to end	Night	16% 9% 29% 36% 9% 1	540
May	1st to 10th	Night	15% 9% 29% 32% 14%	438
	11th to 20th	Night	12% 6% 27% 38% 17%	354
	21st to end	Night	20% 4 23% 36% 16% 1	389
June	1st to 10th	Night	19% 6% 26% 34% 13% 1	360
	11th to 20th	Night	20% 6% 29% 30% 13% 1	360
	21st to end	Night	13% 3 21% 39% 22% 2	360
July	1st to 10th	Night	11% 5% 17% 42% 23% 1	350
	11th to 20th	Night	12% 1 25% 43% 17% 2	348
	21st to end	Night	5% 5% 19% 43% 26% 2	394
August	1st to 10th	Night	12% 2 15% 41% 28% 2	358
	11th to 20th	Night	9% 3 19% 43% 23% 2	495
	21st to end	Night	9% 3 24% 41% 22% 1	594
September	1st to 10th	Night	14% 3 25% 38% 18% 3	630
	11th to 20th	Night	15% 3 22% 38% 18% 2	720
	21st to end	Night	14% 5% 32% 32% 14% 2	720
October	1st to 10th	Night	16% 5% 28% 34% 15% 3	720
	11th to 20th	Night	13% 4 33% 34% 13% 3	720
	21st to end	Night	11% 9% 35% 34% 10% 1	792
November	1st to 10th	Night	15% 8% 36% 28% 11% 1	850
	11th to 20th	Night	10% 10% 43% 28% 8% 1	950
	21st to end	Night	7% 9% 41% 32% 8% 2	950
December	1st to 10th	Night	9% 10% 35% 31% 13% 2	950
	11th to 20th	Night	7% 8% 38% 36% 9% 1	950
	21st to end	Night	10% 6% 35% 36% 10% 2	1045

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