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 2026-06-01.

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	13% 10% 4 8% 5% 5% 5% 4 5% 7% 33%	131776
	Night	14% 10% 4 9% 5% 5% 4 4 5% 6% 34%	131477
Transparency	Day	48% 6% 12% 21% 12% 1	135374
	Night	48% 6% 11% 20% 13% 1	135950
Seeing	Day	19% 10% 27% 24% 15% 6%	17685
	Night	20% 8% 28% 30% 13% 1	27565

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	15% 17% 8% 18% 6% 5% 4 3 4 5% 16%	4691
	11th to 20th	Day	11% 16% 6% 14% 9% 7% 6% 4 3 3 19%	4710
	21st to end	Day	19% 16% 7% 12% 7% 5% 6% 4 4 4 15%	5649
February	1st to 10th	Day	14% 16% 6% 11% 8% 4 5% 4 4 5% 23%	1927
	11th to 20th	Day	15% 13% 5% 13% 8% 6% 5% 3 5% 5% 23%	2048
	21st to end	Day	16% 15% 5% 10% 5% 4 5% 4 5% 6% 26%	1730
March	1st to 10th	Day	18% 13% 6% 11% 6% 5% 4 2 4 4 27%	4598
	11th to 20th	Day	11% 11% 3 7% 5% 4 4 3 6% 7% 38%	5090
	21st to end	Day	17% 14% 5% 9% 6% 5% 5% 3 5% 6% 25%	5586
April	1st to 10th	Day	16% 12% 3 9% 5% 5% 5% 4 4 8% 29%	2498
	11th to 20th	Day	17% 9% 3 8% 4 4 5% 4 5% 6% 35%	2594
	21st to end	Day	17% 9% 3 8% 5% 4 4 3 5% 7% 36%	2730
May	1st to 10th	Day	21% 10% 3 7% 6% 5% 5% 4 5% 6% 29%	5992
	11th to 20th	Day	16% 7% 3 6% 5% 4 4 4 6% 9% 36%	5991
	21st to end	Day	15% 6% 2 7% 5% 4 4 4 6% 7% 39%	6576
June	1st to 10th	Day	11% 6% 2 6% 6% 5% 5% 4 6% 7% 41%	2785
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 6% 6% 9% 41%	2800
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 6% 7% 10% 38%	2800
July	1st to 10th	Day	9% 6% 3 6% 4 5% 5% 4 7% 11% 39%	6360
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 5% 8% 11% 41%	6360
	21st to end	Day	8% 6% 3 8% 5% 5% 6% 4 7% 9% 39%	6542
August	1st to 10th	Day	9% 4 2 6% 4 5% 5% 4 7% 9% 44%	4234
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 9% 42%	4174
	21st to end	Day	6% 5% 2 6% 5% 4 4 4 6% 10% 47%	4453
September	1st to 10th	Day	10% 6% 3 7% 4 4 5% 3 5% 7% 46%	2292
	11th to 20th	Day	9% 5% 3 5% 5% 3 5% 4 6% 9% 48%	2200
	21st to end	Day	15% 7% 3 5% 5% 4 4 3 5% 7% 42%	2200
October	1st to 10th	Day	12% 6% 2 7% 4 5% 4 4 6% 7% 44%	2200
	11th to 20th	Day	15% 7% 2 7% 5% 4 4 4 5% 6% 40%	2004
	21st to end	Day	17% 11% 3 8% 5% 5% 5% 3 5% 7% 32%	2004
November	1st to 10th	Day	11% 8% 3 6% 4 5% 4 3 5% 7% 44%	1852
	11th to 20th	Day	16% 14% 3 8% 5% 4 4 3 4 5% 33%	1890
	21st to end	Day	20% 15% 4 9% 5% 4 4 3 5% 6% 26%	1890
December	1st to 10th	Day	12% 15% 6% 12% 7% 6% 5% 3 5% 5% 25%	3020
	11th to 20th	Day	17% 16% 7% 11% 5% 4 5% 3 4 5% 22%	3236
	21st to end	Day	25% 20% 7% 11% 5% 4 3 3 4 4 14%	4070
January	1st to 10th	Night	13% 16% 7% 15% 7% 6% 5% 3 5% 5% 19%	8232
	11th to 20th	Night	9% 17% 8% 16% 7% 6% 5% 4 4 5% 19%	8280
	21st to end	Night	17% 13% 5% 10% 6% 5% 6% 4 5% 6% 22%	8523
February	1st to 10th	Night	17% 14% 5% 10% 6% 5% 4 4 5% 5% 25%	2688
	11th to 20th	Night	14% 14% 5% 9% 6% 6% 4 4 5% 6% 27%	2458
	21st to end	Night	19% 12% 4 10% 5% 4 4 3 4 6% 29%	2076
March	1st to 10th	Night	17% 12% 4 7% 4 4 4 3 4 5% 36%	5460
	11th to 20th	Night	11% 7% 2 7% 5% 5% 5% 3 5% 7% 43%	5090
	21st to end	Night	15% 10% 4 9% 5% 4 4 4 5% 6% 34%	5588
April	1st to 10th	Night	17% 11% 3 7% 5% 4 4 4 5% 7% 34%	2140
	11th to 20th	Night	18% 7% 3 7% 5% 5% 5% 4 5% 6% 36%	1973
	21st to end	Night	16% 8% 3 7% 5% 4 5% 3 5% 6% 37%	1890
May	1st to 10th	Night	21% 10% 3 8% 5% 5% 5% 3 4 6% 30%	4123
	11th to 20th	Night	17% 7% 3 7% 4 4 3 3 5% 7% 39%	4122
	21st to end	Night	14% 6% 2 6% 4 4 4 3 6% 7% 42%	4520
June	1st to 10th	Night	10% 5% 2 6% 4 3 5% 4 6% 8% 47%	1610
	11th to 20th	Night	8% 6% 2 7% 5% 5% 4 5% 6% 8% 45%	1600
	21st to end	Night	9% 4 2 6% 5% 5% 4 4 7% 8% 46%	1600
July	1st to 10th	Night	8% 4 2 6% 4 4 5% 4 7% 10% 47%	3618
	11th to 20th	Night	7% 5% 2 6% 4 4 4 3 6% 9% 47%	3617
	21st to end	Night	9% 6% 2 6% 4 4 4 4 6% 9% 45%	4297
August	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 7% 8% 42%	2915
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 7% 9% 46%	2875
	21st to end	Night	6% 5% 2 6% 4 5% 5% 4 6% 9% 49%	3442
September	1st to 10th	Night	11% 4 2 6% 3 4 4 4 4 6% 52%	2086
	11th to 20th	Night	9% 4 2 6% 3 4 3 2 5% 7% 56%	2200
	21st to end	Night	12% 7% 2 7% 4 4 4 3 4 6% 46%	2200
October	1st to 10th	Night	11% 6% 2 6% 5% 3 4 4 4 7% 49%	2200
	11th to 20th	Night	15% 9% 3 7% 5% 4 4 3 5% 6% 39%	2395
	21st to end	Night	19% 8% 3 6% 4 4 4 4 5% 5% 38%	2834
November	1st to 10th	Night	13% 8% 2 6% 4 4 4 3 5% 6% 44%	2666
	11th to 20th	Night	16% 11% 3 8% 4 5% 4 3 5% 6% 33%	2730
	21st to end	Night	19% 13% 5% 9% 5% 4 4 4 5% 6% 27%	2730
December	1st to 10th	Night	13% 12% 5% 11% 6% 5% 5% 4 6% 7% 25%	4380
	11th to 20th	Night	17% 18% 8% 11% 5% 4 4 3 4 4 22%	5169
	21st to end	Night	27% 19% 6% 10% 5% 4 4 3 4 5% 14%	7150

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	71% 5% 11% 11% 3	4692
	11th to 20th	Day	69% 3 9% 8% 11%	4710
	21st to end	Day	71% 4 9% 10% 5%	5649
February	1st to 10th	Day	63% 6% 10% 14% 6% 1	1927
	11th to 20th	Day	63% 5% 9% 16% 7%	2058
	21st to end	Day	57% 5% 14% 15% 7% 1	1730
March	1st to 10th	Day	60% 4 8% 19% 8% 1	4598
	11th to 20th	Day	44% 6% 14% 26% 9% 1	5090
	21st to end	Day	58% 6% 12% 16% 7%	5586
April	1st to 10th	Day	53% 7% 11% 16% 12% 1	2498
	11th to 20th	Day	48% 6% 11% 21% 12% 2	2594
	21st to end	Day	47% 6% 12% 21% 11% 2	2730
May	1st to 10th	Day	54% 7% 10% 16% 13%	6027
	11th to 20th	Day	43% 7% 14% 22% 12% 1	5995
	21st to end	Day	41% 7% 10% 22% 17% 3	6590
June	1st to 10th	Day	40% 7% 11% 24% 16% 2	2785
	11th to 20th	Day	37% 9% 13% 23% 16% 3	2800
	21st to end	Day	39% 9% 14% 20% 15% 4	2800
July	1st to 10th	Day	37% 6% 11% 26% 17% 2	6291
	11th to 20th	Day	34% 7% 15% 26% 17% 1	6285
	21st to end	Day	38% 8% 12% 22% 18% 2	6356
August	1st to 10th	Day	34% 8% 16% 25% 16% 1	4221
	11th to 20th	Day	34% 8% 12% 29% 16% 1	4213
	21st to end	Day	32% 6% 12% 35% 12% 3	4452
September	1st to 10th	Day	36% 7% 13% 23% 17% 3	2292
	11th to 20th	Day	32% 7% 11% 28% 20% 2	2200
	21st to end	Day	41% 6% 11% 23% 18% 1	2200
October	1st to 10th	Day	28% 4 12% 34% 20% 1	3590
	11th to 20th	Day	36% 5% 10% 27% 20% 1	3244
	21st to end	Day	43% 3 12% 26% 15% 1	3216
November	1st to 10th	Day	39% 5% 13% 25% 17% 1	1852
	11th to 20th	Day	53% 5% 11% 18% 11% 2	1890
	21st to end	Day	59% 5% 12% 17% 7%	1890
December	1st to 10th	Day	60% 6% 15% 16% 3	3020
	11th to 20th	Day	63% 5% 11% 15% 5%	3233
	21st to end	Day	74% 5% 7% 10% 4	4070
January	1st to 10th	Night	66% 6% 9% 15% 5%	8233
	11th to 20th	Night	67% 4 9% 10% 9% 1	8280
	21st to end	Night	61% 5% 14% 13% 7%	8523
February	1st to 10th	Night	60% 5% 13% 14% 7% 1	2688
	11th to 20th	Night	56% 6% 9% 20% 8% 1	2459
	21st to end	Night	56% 5% 12% 17% 9% 1	2076
March	1st to 10th	Night	50% 4 10% 25% 9% 1	5460
	11th to 20th	Night	38% 6% 14% 27% 13% 1	5090
	21st to end	Night	49% 6% 11% 21% 12% 1	5588
April	1st to 10th	Night	48% 6% 11% 20% 13% 2	2140
	11th to 20th	Night	47% 6% 11% 17% 17% 2	1973
	21st to end	Night	46% 6% 11% 21% 14% 2	1890
May	1st to 10th	Night	55% 7% 8% 15% 12% 3	4150
	11th to 20th	Night	43% 7% 11% 23% 15% 1	4123
	21st to end	Night	38% 7% 12% 23% 18% 2	4528
June	1st to 10th	Night	34% 6% 13% 25% 20% 3	1610
	11th to 20th	Night	35% 8% 12% 25% 17% 3	1600
	21st to end	Night	34% 7% 17% 22% 18% 2	1600
July	1st to 10th	Night	31% 6% 12% 26% 19% 5%	3580
	11th to 20th	Night	32% 7% 16% 25% 18% 1	3572
	21st to end	Night	35% 7% 13% 23% 18% 5%	4170
August	1st to 10th	Night	37% 7% 14% 26% 15% 2	2904
	11th to 20th	Night	32% 7% 13% 30% 16% 2	2902
	21st to end	Night	31% 7% 13% 28% 18% 2	3442
September	1st to 10th	Night	32% 7% 12% 26% 19% 5%	2086
	11th to 20th	Night	28% 5% 10% 29% 26% 2	2200
	21st to end	Night	39% 6% 11% 24% 19% 2	2200
October	1st to 10th	Night	24% 4 8% 31% 32% 1	3590
	11th to 20th	Night	37% 4 10% 25% 24% 1	3894
	21st to end	Night	35% 4 8% 33% 18% 2	4572
November	1st to 10th	Night	39% 6% 11% 25% 17% 1	2666
	11th to 20th	Night	49% 6% 11% 20% 12% 2	2730
	21st to end	Night	58% 5% 11% 19% 6%	2730
December	1st to 10th	Night	55% 6% 13% 19% 6% 1	4380
	11th to 20th	Night	65% 5% 12% 10% 7% 1	5171
	21st to end	Night	73% 5% 10% 9% 3	7150

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% 31% 21% 4 1	330
	11th to 20th	Day	25% 17% 43% 10% 3 1	330
	21st to end	Day	30% 15% 31% 19% 4	363
February	1st to 10th	Day	25% 16% 38% 15% 5%	330
	11th to 20th	Day	26% 18% 34% 18% 5%	330
	21st to end	Day	27% 21% 37% 11% 3	273
March	1st to 10th	Day	26% 16% 40% 15% 3	335
	11th to 20th	Day	29% 12% 31% 19% 8% 1	540
	21st to end	Day	30% 14% 30% 19% 7% 1	594
April	1st to 10th	Day	24% 14% 30% 21% 10% 1	540
	11th to 20th	Day	25% 16% 30% 17% 8% 4	532
	21st to end	Day	23% 11% 31% 22% 11% 2	540
May	1st to 10th	Day	25% 10% 32% 20% 10% 2	543
	11th to 20th	Day	22% 8% 28% 21% 15% 6%	567
	21st to end	Day	14% 6% 27% 25% 17% 10%	617
June	1st to 10th	Day	14% 7% 27% 30% 16% 5%	715
	11th to 20th	Day	15% 6% 27% 29% 17% 6%	730
	21st to end	Day	13% 5% 26% 32% 17% 6%	730
July	1st to 10th	Day	12% 4 20% 30% 22% 12%	721
	11th to 20th	Day	11% 4 23% 30% 22% 10%	718
	21st to end	Day	10% 3 20% 29% 27% 11%	629
August	1st to 10th	Day	9% 3 15% 29% 28% 16%	526
	11th to 20th	Day	10% 3 21% 28% 25% 13%	519
	21st to end	Day	9% 3 15% 31% 27% 15%	583
September	1st to 10th	Day	14% 5% 17% 24% 26% 15%	530
	11th to 20th	Day	9% 2 13% 24% 31% 21%	530
	21st to end	Day	19% 6% 21% 24% 20% 10%	530
October	1st to 10th	Day	13% 5% 22% 32% 19% 9%	530
	11th to 20th	Day	18% 13% 28% 27% 11% 2	530
	21st to end	Day	25% 12% 37% 20% 3 2	387
November	1st to 10th	Day	17% 13% 35% 22% 11% 3	330
	11th to 20th	Day	30% 14% 31% 15% 10% 1	330
	21st to end	Day	28% 14% 38% 17% 3	330
December	1st to 10th	Day	23% 19% 33% 17% 7% 1	330
	11th to 20th	Day	23% 18% 35% 19% 5%	330
	21st to end	Day	33% 17% 31% 16% 3	363
January	1st to 10th	Night	24% 13% 35% 22% 5%	1050
	11th to 20th	Night	24% 14% 37% 19% 4 1	1050
	21st to end	Night	24% 14% 34% 24% 5%	968
February	1st to 10th	Night	25% 11% 34% 25% 4	840
	11th to 20th	Night	21% 12% 39% 25% 3	823
	21st to end	Night	28% 13% 36% 21% 2	692
March	1st to 10th	Night	24% 11% 34% 25% 7%	840
	11th to 20th	Night	19% 14% 35% 25% 6%	840
	21st to end	Night	26% 10% 30% 27% 7% 1	924
April	1st to 10th	Night	22% 12% 34% 27% 5%	670
	11th to 20th	Night	22% 10% 34% 25% 8% 1	623
	21st to end	Night	22% 6% 34% 27% 10%	630
May	1st to 10th	Night	23% 5% 30% 33% 8%	630
	11th to 20th	Night	22% 4 29% 29% 16%	621
	21st to end	Night	13% 3 23% 41% 19% 2	683
June	1st to 10th	Night	13% 2 24% 43% 18% 1	600
	11th to 20th	Night	11% 3 22% 46% 19% 1	600
	21st to end	Night	11% 3 23% 38% 22% 3	600
July	1st to 10th	Night	10% 1 16% 42% 28% 4	585
	11th to 20th	Night	10% 2 15% 39% 30% 3	582
	21st to end	Night	8% 1 13% 45% 30% 2	657
August	1st to 10th	Night	8% 2 12% 45% 29% 4	597
	11th to 20th	Night	10% 1 14% 40% 31% 3	594
	21st to end	Night	7% 2 14% 37% 35% 4	660
September	1st to 10th	Night	13% 3 18% 32% 30% 4	686
	11th to 20th	Night	11% 2 13% 36% 34% 5%	800
	21st to end	Night	17% 5% 19% 34% 22% 4	800
October	1st to 10th	Night	14% 4 24% 35% 20% 4	800
	11th to 20th	Night	21% 9% 30% 30% 10% 1	800
	21st to end	Night	24% 10% 32% 25% 8%	880
November	1st to 10th	Night	17% 9% 34% 28% 11% 1	820
	11th to 20th	Night	23% 14% 30% 27% 6% 1	840
	21st to end	Night	28% 11% 30% 25% 6%	840
December	1st to 10th	Night	24% 13% 35% 23% 5%	840
	11th to 20th	Night	27% 13% 34% 22% 4	945
	21st to end	Night	32% 11% 32% 21% 3	1155

Page generated at 2026-05-29 01:53:29. Version ac07

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