Defiance
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Defiance clear sky chart from 2005-11-06 to 2024-01-27.

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	14% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	75018
	Night	15% 9% 4 7% 6% 3 5% 4 5% 6% 35%	75041
Transparency	Day	48% 7% 12% 19% 12% 2	74729
	Night	48% 6% 12% 20% 13% 2	74851
Seeing	Day	19% 8% 27% 24% 15% 7%	14480
	Night	20% 8% 28% 30% 13% 1	24441

By Month

Percentage Cloud Cover SE (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	18% 15% 6% 10% 9% 4 5% 5% 4 5% 20%	1517
	11th to 20th	Day	18% 18% 8% 11% 6% 4 5% 5% 4 5% 17%	1520
	21st to end	Day	17% 18% 7% 9% 8% 4 4 4 4 6% 19%	1793
February	1st to 10th	Day	16% 16% 6% 11% 9% 3 5% 4 4 4 22%	1652
	11th to 20th	Day	16% 13% 5% 11% 10% 4 5% 4 4 5% 22%	1748
	21st to end	Day	17% 15% 5% 10% 6% 3 5% 5% 4 6% 25%	1480
March	1st to 10th	Day	18% 11% 5% 9% 7% 4 5% 3 5% 6% 27%	1804
	11th to 20th	Day	17% 11% 5% 7% 6% 3 4 3 5% 7% 32%	1980
	21st to end	Day	23% 12% 4 7% 6% 3 5% 4 5% 6% 25%	2178
April	1st to 10th	Day	15% 11% 4 7% 7% 4 5% 5% 4 7% 31%	2141
	11th to 20th	Day	18% 8% 3 6% 5% 3 5% 5% 4 6% 35%	2219
	21st to end	Day	19% 8% 4 6% 6% 4 3 4 5% 7% 35%	2340
May	1st to 10th	Day	17% 8% 4 7% 7% 4 6% 5% 5% 7% 31%	2340
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 5% 6% 7% 34%	2301
	21st to end	Day	9% 5% 3 6% 8% 4 6% 6% 6% 9% 39%	2531
June	1st to 10th	Day	11% 6% 2 6% 7% 4 5% 6% 6% 7% 40%	2506
	11th to 20th	Day	10% 5% 2 6% 6% 3 6% 6% 6% 9% 42%	2520
	21st to end	Day	10% 4 3 6% 6% 4 6% 7% 6% 10% 37%	2520
July	1st to 10th	Day	9% 6% 3 6% 5% 4 5% 6% 6% 10% 41%	2520
	11th to 20th	Day	8% 4 2 4 5% 3 6% 6% 6% 10% 45%	2520
	21st to end	Day	7% 5% 3 5% 6% 4 6% 5% 7% 10% 42%	2595
August	1st to 10th	Day	7% 4 2 4 5% 4 6% 6% 6% 9% 46%	2327
	11th to 20th	Day	8% 5% 2 5% 7% 3 6% 7% 8% 9% 40%	2303
	21st to end	Day	8% 5% 2 5% 6% 4 4 5% 5% 10% 46%	2457
September	1st to 10th	Day	11% 6% 3 6% 5% 3 5% 5% 5% 8% 43%	2064
	11th to 20th	Day	10% 5% 3 4 5% 2 5% 6% 6% 9% 45%	1980
	21st to end	Day	14% 6% 2 4 5% 3 4 4 5% 8% 44%	1980
October	1st to 10th	Day	13% 6% 3 6% 6% 4 4 5% 6% 7% 41%	1980
	11th to 20th	Day	16% 8% 2 7% 6% 3 4 4 5% 6% 38%	1804
	21st to end	Day	18% 11% 3 7% 6% 4 4 5% 5% 7% 31%	1804
November	1st to 10th	Day	11% 8% 3 5% 4 3 5% 4 5% 7% 45%	1672
	11th to 20th	Day	16% 13% 4 6% 6% 3 4 5% 4 5% 34%	1710
	21st to end	Day	20% 14% 4 8% 5% 3 5% 4 5% 6% 28%	1710
December	1st to 10th	Day	15% 17% 7% 11% 9% 4 5% 4 4 5% 20%	1710
	11th to 20th	Day	14% 14% 6% 12% 7% 4 5% 5% 5% 5% 23%	2009
	21st to end	Day	21% 21% 8% 10% 7% 4 4 4 4 4 12%	2783
January	1st to 10th	Night	18% 13% 6% 9% 7% 3 5% 4 5% 6% 24%	2648
	11th to 20th	Night	17% 16% 6% 12% 7% 3 5% 4 4 5% 22%	2660
	21st to end	Night	17% 15% 7% 10% 7% 3 5% 4 4 6% 22%	2704
February	1st to 10th	Night	19% 14% 6% 8% 7% 4 4 4 6% 5% 23%	2304
	11th to 20th	Night	14% 14% 6% 8% 7% 4 5% 5% 4 6% 26%	2098
	21st to end	Night	22% 11% 4 8% 6% 3 4 3 4 6% 29%	1776
March	1st to 10th	Night	16% 10% 4 7% 7% 4 5% 5% 4 5% 33%	2155
	11th to 20th	Night	14% 8% 3 6% 5% 4 6% 5% 4 6% 40%	1980
	21st to end	Night	20% 10% 4 6% 5% 3 4 4 5% 5% 34%	2178
April	1st to 10th	Night	15% 9% 4 6% 5% 2 5% 5% 5% 8% 36%	1835
	11th to 20th	Night	19% 6% 3 6% 6% 3 5% 5% 4 6% 36%	1688
	21st to end	Night	17% 7% 4 5% 6% 3 5% 4 5% 7% 37%	1620
May	1st to 10th	Night	19% 8% 3 7% 7% 4 5% 5% 5% 6% 32%	1620
	11th to 20th	Night	19% 7% 3 5% 6% 3 4 4 5% 7% 37%	1592
	21st to end	Night	10% 5% 3 5% 5% 3 5% 5% 7% 8% 44%	1744
June	1st to 10th	Night	10% 4 2 5% 4 2 5% 5% 6% 8% 47%	1450
	11th to 20th	Night	8% 5% 2 5% 6% 3 5% 5% 5% 8% 47%	1440
	21st to end	Night	10% 4 2 5% 5% 4 4 5% 6% 8% 46%	1440
July	1st to 10th	Night	8% 4 2 5% 5% 3 5% 4 6% 10% 49%	1440
	11th to 20th	Night	8% 3 2 5% 4 2 4 4 5% 9% 53%	1440
	21st to end	Night	7% 4 2 5% 5% 3 4 5% 6% 9% 49%	1719
August	1st to 10th	Night	6% 4 1 5% 4 3 5% 6% 7% 9% 49%	1611
	11th to 20th	Night	8% 4 2 4 5% 3 4 5% 7% 9% 49%	1598
	21st to end	Night	7% 4 2 4 5% 3 5% 5% 5% 9% 50%	1896
September	1st to 10th	Night	12% 4 2 5% 5% 3 5% 5% 4 7% 49%	1876
	11th to 20th	Night	10% 4 2 5% 4 3 3 3 5% 7% 54%	1980
	21st to end	Night	11% 6% 2 6% 5% 3 4 5% 4 6% 48%	1980
October	1st to 10th	Night	11% 6% 3 6% 6% 2 4 4 4 7% 47%	1980
	11th to 20th	Night	17% 9% 4 6% 6% 3 4 4 4 6% 38%	2155
	21st to end	Night	21% 8% 3 6% 5% 3 4 4 5% 5% 36%	2550
November	1st to 10th	Night	14% 7% 3 5% 5% 3 5% 4 5% 6% 44%	2406
	11th to 20th	Night	17% 11% 3 7% 5% 3 5% 4 5% 6% 33%	2470
	21st to end	Night	20% 11% 5% 8% 5% 3 4 4 5% 6% 28%	2470
December	1st to 10th	Night	17% 15% 6% 8% 7% 3 4 4 5% 6% 23%	2470
	11th to 20th	Night	18% 15% 6% 8% 7% 4 4 4 4 5% 25%	3184
	21st to end	Night	27% 18% 7% 9% 6% 3 4 4 4 5% 14%	4884

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	66% 6% 10% 13% 5%	1518
	11th to 20th	Day	70% 5% 12% 8% 4	1520
	21st to end	Day	67% 5% 11% 12% 5%	1793
February	1st to 10th	Day	66% 5% 9% 12% 7% 1	1652
	11th to 20th	Day	64% 5% 9% 15% 6%	1758
	21st to end	Day	60% 6% 12% 14% 7% 1	1480
March	1st to 10th	Day	58% 6% 11% 18% 6%	1804
	11th to 20th	Day	52% 5% 12% 18% 10% 2	1980
	21st to end	Day	59% 6% 10% 19% 5%	2178
April	1st to 10th	Day	52% 7% 11% 17% 12%	2141
	11th to 20th	Day	48% 6% 11% 20% 12% 2	2219
	21st to end	Day	49% 6% 12% 19% 10% 3	2340
May	1st to 10th	Day	53% 6% 12% 18% 11% 1	2340
	11th to 20th	Day	48% 7% 11% 19% 13% 2	2305
	21st to end	Day	40% 9% 14% 22% 13% 2	2531
June	1st to 10th	Day	41% 7% 11% 24% 15% 2	2506
	11th to 20th	Day	37% 9% 13% 23% 16% 2	2520
	21st to end	Day	39% 9% 14% 20% 14% 3	2520
July	1st to 10th	Day	37% 7% 12% 22% 18% 4	2451
	11th to 20th	Day	33% 8% 14% 26% 17% 2	2445
	21st to end	Day	34% 9% 13% 23% 18% 2	2451
August	1st to 10th	Day	32% 9% 16% 26% 16% 1	2314
	11th to 20th	Day	36% 10% 14% 25% 14% 1	2303
	21st to end	Day	34% 7% 12% 25% 18% 4	2457
September	1st to 10th	Day	39% 8% 14% 20% 16% 3	2064
	11th to 20th	Day	34% 7% 12% 27% 19% 1	1980
	21st to end	Day	38% 6% 11% 25% 18% 1	1980
October	1st to 10th	Day	40% 6% 12% 25% 14% 2	1980
	11th to 20th	Day	45% 6% 10% 22% 16% 1	1804
	21st to end	Day	53% 5% 13% 18% 10% 1	1804
November	1st to 10th	Day	39% 5% 13% 25% 17% 1	1672
	11th to 20th	Day	53% 5% 11% 18% 12% 1	1710
	21st to end	Day	58% 6% 13% 16% 8%	1710
December	1st to 10th	Day	67% 6% 11% 12% 4	1710
	11th to 20th	Day	60% 7% 13% 15% 4	2006
	21st to end	Day	76% 6% 7% 7% 4	2783
January	1st to 10th	Night	61% 5% 10% 15% 8%	2648
	11th to 20th	Night	65% 4 12% 14% 4	2660
	21st to end	Night	64% 5% 11% 13% 6% 1	2704
February	1st to 10th	Night	62% 5% 13% 13% 6% 1	2304
	11th to 20th	Night	57% 6% 9% 18% 8% 1	2099
	21st to end	Night	57% 5% 10% 17% 9% 1	1776
March	1st to 10th	Night	54% 5% 11% 20% 10% 1	2155
	11th to 20th	Night	45% 6% 12% 20% 14% 3	1980
	21st to end	Night	52% 6% 8% 24% 9% 1	2178
April	1st to 10th	Night	45% 6% 12% 21% 14% 2	1835
	11th to 20th	Night	47% 6% 10% 17% 18% 2	1688
	21st to end	Night	46% 6% 11% 20% 14% 3	1620
May	1st to 10th	Night	53% 7% 10% 17% 10% 3	1620
	11th to 20th	Night	45% 8% 10% 18% 17% 2	1593
	21st to end	Night	34% 9% 14% 26% 14% 3	1745
June	1st to 10th	Night	34% 7% 13% 25% 19% 3	1450
	11th to 20th	Night	34% 9% 12% 25% 17% 3	1440
	21st to end	Night	34% 8% 17% 22% 17% 2	1440
July	1st to 10th	Night	32% 5% 13% 24% 21% 4	1400
	11th to 20th	Night	28% 7% 16% 27% 20% 2	1392
	21st to end	Night	29% 8% 16% 25% 19% 4	1623
August	1st to 10th	Night	28% 8% 16% 29% 18% 2	1600
	11th to 20th	Night	30% 9% 15% 28% 16% 3	1598
	21st to end	Night	29% 7% 15% 23% 22% 4	1896
September	1st to 10th	Night	35% 7% 12% 23% 18% 5%	1876
	11th to 20th	Night	30% 5% 11% 28% 25% 1	1980
	21st to end	Night	36% 6% 11% 25% 19% 2	1980
October	1st to 10th	Night	37% 6% 11% 24% 20% 1	1980
	11th to 20th	Night	48% 4 8% 21% 17% 1	2155
	21st to end	Night	48% 6% 10% 22% 12% 2	2550
November	1st to 10th	Night	40% 7% 12% 24% 17% 1	2406
	11th to 20th	Night	50% 6% 11% 19% 12% 1	2470
	21st to end	Night	57% 5% 11% 20% 7%	2470
December	1st to 10th	Night	60% 7% 11% 15% 7%	2470
	11th to 20th	Night	60% 7% 13% 13% 6% 1	3186
	21st to end	Night	73% 6% 11% 8% 3	4884

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	27% 17% 30% 20% 5% 1	270
	11th to 20th	Day	26% 13% 44% 11% 4 1	270
	21st to end	Day	32% 12% 30% 20% 6%	282
February	1st to 10th	Day	30% 14% 39% 15% 2	240
	11th to 20th	Day	26% 18% 37% 15% 4	240
	21st to end	Day	27% 21% 38% 12% 3	198
March	1st to 10th	Day	24% 16% 39% 17% 4	244
	11th to 20th	Day	28% 9% 31% 21% 10% 1	420
	21st to end	Day	32% 12% 27% 20% 8% 1	462
April	1st to 10th	Day	20% 13% 30% 25% 12% 1	420
	11th to 20th	Day	26% 14% 28% 18% 9% 5%	412
	21st to end	Day	24% 11% 31% 21% 11% 2	420
May	1st to 10th	Day	24% 10% 31% 21% 11% 3	423
	11th to 20th	Day	21% 7% 29% 21% 16% 7%	447
	21st to end	Day	13% 4 26% 26% 18% 12%	485
June	1st to 10th	Day	14% 6% 26% 31% 17% 6%	616
	11th to 20th	Day	15% 5% 27% 27% 20% 6%	630
	21st to end	Day	14% 5% 26% 31% 18% 6%	630
July	1st to 10th	Day	11% 3 18% 30% 24% 14%	621
	11th to 20th	Day	12% 3 22% 30% 23% 10%	618
	21st to end	Day	10% 4 20% 28% 27% 12%	536
August	1st to 10th	Day	9% 2 14% 31% 27% 17%	446
	11th to 20th	Day	10% 3 21% 28% 24% 14%	439
	21st to end	Day	10% 3 15% 29% 27% 16%	495
September	1st to 10th	Day	16% 4 15% 24% 27% 13%	450
	11th to 20th	Day	10% 2 15% 23% 31% 18%	450
	21st to end	Day	17% 7% 20% 24% 21% 10%	450
October	1st to 10th	Day	14% 4 23% 31% 18% 10%	450
	11th to 20th	Day	20% 14% 29% 26% 10% 1	450
	21st to end	Day	27% 12% 36% 21% 3 2	319
November	1st to 10th	Day	14% 13% 34% 23% 12% 4	270
	11th to 20th	Day	28% 13% 30% 16% 11% 1	270
	21st to end	Day	27% 11% 40% 18% 3	270
December	1st to 10th	Day	24% 19% 33% 15% 9% 1	270
	11th to 20th	Day	21% 15% 38% 20% 5%	270
	21st to end	Day	30% 17% 31% 19% 3	297
January	1st to 10th	Night	24% 13% 35% 22% 6%	950
	11th to 20th	Night	25% 12% 36% 21% 5% 1	950
	21st to end	Night	24% 13% 32% 26% 5%	860
February	1st to 10th	Night	27% 11% 35% 23% 4	720
	11th to 20th	Night	22% 12% 39% 25% 3	703
	21st to end	Night	30% 12% 35% 21% 2	592
March	1st to 10th	Night	23% 11% 33% 26% 8%	720
	11th to 20th	Night	19% 12% 35% 27% 7%	720
	21st to end	Night	26% 8% 29% 28% 8% 1	792
April	1st to 10th	Night	19% 11% 35% 29% 5% 1	575
	11th to 20th	Night	22% 8% 34% 26% 9% 2	533
	21st to end	Night	23% 5% 33% 27% 11% 1	540
May	1st to 10th	Night	23% 5% 30% 33% 9% 1	540
	11th to 20th	Night	22% 3 26% 31% 17% 1	531
	21st to end	Night	12% 3 21% 40% 21% 2	584
June	1st to 10th	Night	12% 2 23% 44% 19%	540
	11th to 20th	Night	11% 2 21% 46% 20% 1	540
	21st to end	Night	11% 2 22% 39% 23% 3	540
July	1st to 10th	Night	10% 1 15% 40% 30% 4	525
	11th to 20th	Night	11% 1 15% 39% 30% 4	522
	21st to end	Night	7% 1 14% 45% 30% 2	591
August	1st to 10th	Night	8% 1 12% 44% 30% 4	537
	11th to 20th	Night	11% 1 13% 40% 32% 4	534
	21st to end	Night	7% 3 14% 35% 36% 5%	594
September	1st to 10th	Night	14% 2 17% 33% 30% 4	616
	11th to 20th	Night	12% 2 13% 35% 33% 5%	720
	21st to end	Night	15% 5% 19% 35% 22% 4	720
October	1st to 10th	Night	15% 4 24% 34% 20% 4	720
	11th to 20th	Night	22% 10% 29% 29% 9% 1	720
	21st to end	Night	26% 10% 32% 24% 8%	792
November	1st to 10th	Night	17% 8% 33% 28% 13% 1	740
	11th to 20th	Night	24% 13% 28% 27% 7% 1	760
	21st to end	Night	27% 10% 30% 27% 6%	760
December	1st to 10th	Night	25% 12% 34% 24% 5%	760
	11th to 20th	Night	27% 12% 34% 23% 4	855
	21st to end	Night	32% 10% 33% 22% 3	1045

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