Bend
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bend clear sky chart from 2005-11-06 to 2025-09-19.

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	4 6% 2 6% 4 4 4 4 6% 7% 54%	135494
	Night	4 7% 2 6% 4 4 4 4 6% 7% 51%	130872
Transparency	Day	28% 9% 11% 22% 20% 10%	130300
	Night	29% 11% 13% 22% 17% 6%	127060
Seeing	Day	9% 16% 27% 27% 17% 5%	15771
	Night	7% 12% 24% 36% 19% 2	24773

By Month

Percentage Cloud Cover SW (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	6% 13% 4 11% 8% 7% 7% 5% 7% 8% 25%	3639
	11th to 20th	Day	7% 8% 3 7% 5% 5% 5% 4 6% 7% 44%	3640
	21st to end	Day	5% 8% 3 6% 4 5% 5% 4 6% 8% 46%	4326
February	1st to 10th	Day	4 10% 3 8% 6% 7% 6% 5% 7% 9% 35%	1800
	11th to 20th	Day	5% 10% 4 7% 5% 5% 5% 4 7% 9% 39%	1761
	21st to end	Day	2 11% 5% 9% 6% 6% 6% 6% 7% 8% 34%	1650
March	1st to 10th	Day	5% 7% 3 7% 5% 6% 6% 5% 8% 12% 37%	4575
	11th to 20th	Day	3 11% 4 9% 6% 5% 6% 4 6% 7% 41%	5000
	21st to end	Day	3 8% 3 9% 7% 7% 8% 6% 8% 10% 31%	5722
April	1st to 10th	Day	6% 12% 4 10% 6% 5% 5% 4 6% 8% 34%	2400
	11th to 20th	Day	6% 10% 3 8% 6% 5% 5% 4 5% 8% 41%	2369
	21st to end	Day	6% 7% 2 7% 5% 4 4 3 6% 8% 47%	2458
May	1st to 10th	Day	8% 7% 2 5% 3 3 4 3 5% 6% 54%	6310
	11th to 20th	Day	5% 5% 3 6% 4 4 5% 4 5% 7% 51%	6277
	21st to end	Day	6% 5% 2 4 4 4 4 4 6% 8% 54%	6902
June	1st to 10th	Day	8% 7% 2 6% 5% 5% 5% 4 5% 7% 47%	2800
	11th to 20th	Day	6% 5% 2 5% 4 3 4 4 5% 7% 55%	2800
	21st to end	Day	3 3 2 3 3 3 3 3 5% 5% 66%	2800
July	1st to 10th	Day	1 1 1 2 2 2 2 2 3 3 81%	6319
	11th to 20th	Day	1 1 1 1 1 2 2 3 3 84%	6320
	21st to end	Day	1 1 2 2 2 2 2 3 6% 79%	6880
August	1st to 10th	Day	2 2 1 3 3 3 4 3 6% 7% 67%	5912
	11th to 20th	Day	2 2 1 3 2 3 3 2 4 5% 73%	5757
	21st to end	Day	4 4 1 3 3 3 3 3 5% 6% 65%	5984
September	1st to 10th	Day	2 2 1 3 2 2 3 2 4 6% 73%	2400
	11th to 20th	Day	3 4 2 5% 3 4 4 4 5% 6% 60%	2377
	21st to end	Day	6% 5% 2 5% 3 3 3 2 5% 6% 61%	2033
October	1st to 10th	Day	4 4 1 4 3 3 3 3 3 5% 67%	3180
	11th to 20th	Day	3 4 2 5% 4 4 5% 5% 6% 9% 52%	3161
	21st to end	Day	7% 8% 2 7% 5% 5% 5% 4 6% 7% 44%	3301
November	1st to 10th	Day	5% 9% 2 8% 5% 6% 6% 4 7% 7% 40%	1764
	11th to 20th	Day	4 7% 2 8% 7% 6% 6% 6% 9% 9% 35%	1625
	21st to end	Day	4 8% 4 6% 5% 4 5% 7% 8% 9% 39%	1600
December	1st to 10th	Day	3 6% 3 4 4 3 3 4 6% 7% 57%	2620
	11th to 20th	Day	6% 13% 4 10% 7% 7% 5% 6% 7% 8% 27%	3028
	21st to end	Day	5% 11% 4 11% 7% 6% 5% 5% 8% 9% 28%	4004
January	1st to 10th	Night	6% 11% 4 11% 7% 8% 7% 6% 7% 8% 24%	6306
	11th to 20th	Night	4 7% 3 8% 5% 4 5% 4 6% 7% 45%	6320
	21st to end	Night	7% 11% 4 8% 4 4 4 3 5% 6% 45%	6627
February	1st to 10th	Night	4 11% 4 9% 6% 4 5% 5% 7% 8% 38%	2600
	11th to 20th	Night	4 10% 3 9% 5% 4 5% 5% 7% 8% 39%	2524
	21st to end	Night	4 10% 4 9% 6% 6% 6% 4 6% 9% 37%	1980
March	1st to 10th	Night	5% 8% 2 5% 5% 5% 7% 6% 9% 11% 38%	5315
	11th to 20th	Night	2 5% 2 6% 5% 5% 5% 5% 7% 9% 49%	5000
	21st to end	Night	4 8% 3 9% 6% 6% 7% 6% 8% 10% 33%	5240
April	1st to 10th	Night	6% 11% 3 7% 5% 5% 5% 4 6% 7% 40%	2000
	11th to 20th	Night	5% 9% 3 6% 5% 4 5% 5% 8% 7% 42%	1979
	21st to end	Night	6% 8% 3 5% 4 4 5% 4 7% 9% 45%	1939
May	1st to 10th	Night	7% 7% 2 5% 3 3 3 3 4 6% 56%	3649
	11th to 20th	Night	4 5% 2 5% 4 5% 5% 4 5% 5% 55%	3616
	21st to end	Night	6% 5% 2 4 4 3 4 3 5% 6% 58%	3972
June	1st to 10th	Night	10% 6% 3 5% 5% 3 4 4 4 7% 50%	1600
	11th to 20th	Night	6% 5% 2 5% 3 2 3 3 5% 7% 60%	1600
	21st to end	Night	3 3 1 2 3 2 3 3 3 7% 69%	1600
July	1st to 10th	Night	2 1 1 2 1 3 3 2 3 3 79%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 2 87%	3640
	21st to end	Night	2 2 1 2 2 3 2 2 3 5% 77%	3970
August	1st to 10th	Night	2 2 2 4 3 3 3 3 5% 6% 66%	3891
	11th to 20th	Night	1 2 1 2 2 2 3 2 4 5% 76%	4093
	21st to end	Night	3 3 1 3 2 2 3 2 4 5% 71%	5015
September	1st to 10th	Night	2 1 1 2 1 2 3 3 3 5% 77%	2000
	11th to 20th	Night	3 3 1 5% 3 3 4 2 6% 6% 64%	1980
	21st to end	Night	6% 4 1 4 3 2 2 3 5% 6% 64%	2142
October	1st to 10th	Night	4 4 1 4 2 2 3 2 3 4 71%	3800
	11th to 20th	Night	4 4 2 5% 4 4 4 4 5% 8% 55%	3777
	21st to end	Night	4 6% 2 8% 6% 5% 5% 5% 6% 8% 45%	4262
November	1st to 10th	Night	6% 9% 3 7% 6% 4 5% 5% 7% 7% 40%	2535
	11th to 20th	Night	6% 8% 3 8% 6% 5% 5% 5% 8% 9% 38%	2772
	21st to end	Night	4 8% 3 6% 4 4 5% 5% 7% 8% 45%	2800
December	1st to 10th	Night	3 6% 2 5% 3 3 3 3 5% 7% 60%	4560
	11th to 20th	Night	7% 11% 4 10% 6% 7% 7% 5% 8% 9% 28%	5176
	21st to end	Night	4 11% 4 9% 6% 6% 6% 5% 7% 8% 35%	6952

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	46% 18% 16% 14% 6%	3639
	11th to 20th	Day	36% 13% 11% 23% 15% 2	3640
	21st to end	Day	32% 14% 12% 17% 19% 7%	4326
February	1st to 10th	Day	44% 14% 14% 18% 9% 1	1800
	11th to 20th	Day	38% 14% 17% 18% 10% 2	1770
	21st to end	Day	43% 18% 16% 14% 9% 2	1650
March	1st to 10th	Day	33% 12% 16% 24% 11% 4	4575
	11th to 20th	Day	37% 12% 13% 25% 13%	5000
	21st to end	Day	37% 18% 16% 19% 8%	5722
April	1st to 10th	Day	45% 13% 14% 18% 9% 2	2400
	11th to 20th	Day	41% 10% 15% 19% 13% 3	2372
	21st to end	Day	33% 10% 17% 24% 13% 2	2458
May	1st to 10th	Day	28% 9% 10% 25% 25% 3	6310
	11th to 20th	Day	29% 8% 12% 25% 23% 3	6280
	21st to end	Day	25% 10% 17% 34% 14%	6904
June	1st to 10th	Day	36% 9% 12% 29% 13% 1	2800
	11th to 20th	Day	29% 7% 12% 30% 20% 3	2800
	21st to end	Day	19% 6% 11% 28% 26% 9%	2800
July	1st to 10th	Day	10% 3 5% 16% 28% 38%	6251
	11th to 20th	Day	8% 2 5% 8% 21% 56%	6245
	21st to end	Day	9% 2 4 28% 35% 21%	6681
August	1st to 10th	Day	17% 3 7% 17% 36% 22%	4305
	11th to 20th	Day	15% 3 6% 26% 35% 15%	4168
	21st to end	Day	16% 3 6% 26% 28% 20%	4311
September	1st to 10th	Day	13% 4 6% 25% 33% 20%	2400
	11th to 20th	Day	22% 7% 11% 24% 25% 11%	2377
	21st to end	Day	23% 7% 12% 25% 22% 10%	2033
October	1st to 10th	Day	22% 5% 10% 21% 25% 17%	3180
	11th to 20th	Day	26% 9% 16% 26% 20% 3	3161
	21st to end	Day	35% 10% 9% 25% 20% 2	3301
November	1st to 10th	Day	39% 12% 14% 20% 14% 1	1764
	11th to 20th	Day	38% 19% 19% 15% 9% 1	1625
	21st to end	Day	37% 16% 14% 15% 16% 2	1600
December	1st to 10th	Day	24% 12% 11% 24% 25% 4	2620
	11th to 20th	Day	49% 14% 17% 14% 6%	3028
	21st to end	Day	46% 14% 14% 19% 7% 1	4004
January	1st to 10th	Night	48% 18% 16% 13% 6%	6306
	11th to 20th	Night	33% 14% 11% 23% 16% 3	6320
	21st to end	Night	38% 11% 11% 14% 18% 8%	6627
February	1st to 10th	Night	41% 16% 17% 15% 9% 1	2600
	11th to 20th	Night	38% 14% 18% 19% 9% 2	2526
	21st to end	Night	39% 19% 15% 17% 8% 1	1980
March	1st to 10th	Night	30% 14% 16% 25% 11% 3	5315
	11th to 20th	Night	26% 12% 18% 28% 16%	5000
	21st to end	Night	36% 20% 18% 20% 6%	5240
April	1st to 10th	Night	40% 14% 19% 18% 8% 1	2000
	11th to 20th	Night	36% 13% 17% 21% 11% 2	1979
	21st to end	Night	34% 14% 18% 23% 10% 1	1939
May	1st to 10th	Night	25% 11% 13% 25% 26% 1	3646
	11th to 20th	Night	25% 10% 17% 29% 18% 1	3616
	21st to end	Night	24% 11% 25% 33% 7%	3972
June	1st to 10th	Night	35% 9% 13% 31% 12% 1	1600
	11th to 20th	Night	24% 8% 15% 34% 17% 2	1600
	21st to end	Night	17% 6% 12% 33% 26% 7%	1600
July	1st to 10th	Night	13% 2 6% 21% 25% 33%	3600
	11th to 20th	Night	7% 1 4 15% 25% 48%	3592
	21st to end	Night	12% 3 3 31% 32% 19%	3857
August	1st to 10th	Night	15% 2 6% 19% 41% 16%	2824
	11th to 20th	Night	12% 4 6% 35% 34% 9%	2957
	21st to end	Night	13% 3 9% 30% 30% 15%	3608
September	1st to 10th	Night	12% 4 7% 26% 36% 16%	2000
	11th to 20th	Night	20% 8% 11% 24% 27% 10%	1980
	21st to end	Night	21% 7% 11% 24% 25% 12%	2142
October	1st to 10th	Night	19% 5% 8% 23% 32% 14%	3800
	11th to 20th	Night	26% 9% 19% 26% 17% 4	3777
	21st to end	Night	31% 11% 12% 28% 15% 2	4262
November	1st to 10th	Night	39% 14% 15% 16% 13% 3	2535
	11th to 20th	Night	39% 17% 15% 19% 9% 1	2772
	21st to end	Night	33% 16% 15% 17% 17% 3	2800
December	1st to 10th	Night	23% 10% 10% 24% 29% 4	4560
	11th to 20th	Night	46% 16% 16% 15% 6%	5176
	21st to end	Night	41% 15% 17% 19% 7% 1	6952

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	16% 24% 33% 19% 9% 2	200
	11th to 20th	Day	18% 13% 31% 26% 11% 3	200
	21st to end	Day	10% 22% 26% 28% 13% 1	360
February	1st to 10th	Day	14% 24% 27% 26% 9% 1	400
	11th to 20th	Day	12% 28% 32% 19% 9% 1	399
	21st to end	Day	13% 25% 29% 24% 8%	414
March	1st to 10th	Day	12% 24% 32% 26% 6%	500
	11th to 20th	Day	11% 25% 26% 25% 11% 1	500
	21st to end	Day	13% 27% 29% 23% 7% 1	550
April	1st to 10th	Day	13% 22% 29% 21% 12% 3	500
	11th to 20th	Day	13% 23% 30% 23% 8% 4	492
	21st to end	Day	9% 23% 29% 23% 13% 4	500
May	1st to 10th	Day	10% 19% 28% 26% 13% 3	503
	11th to 20th	Day	16% 16% 27% 20% 16% 5%	528
	21st to end	Day	11% 12% 25% 27% 18% 6%	573
June	1st to 10th	Day	8% 14% 28% 25% 19% 6%	530
	11th to 20th	Day	7% 18% 31% 24% 16% 3	530
	21st to end	Day	4 7% 26% 31% 24% 8%	530
July	1st to 10th	Day	2 6% 27% 36% 21% 7%	526
	11th to 20th	Day	1 4 32% 31% 23% 8%	524
	21st to end	Day	1 5% 27% 35% 22% 9%	575
August	1st to 10th	Day	2 5% 24% 35% 24% 11%	527
	11th to 20th	Day	2 5% 23% 32% 26% 13%	517
	21st to end	Day	4 8% 22% 32% 24% 10%	583
September	1st to 10th	Day	3 5% 21% 34% 28% 9%	530
	11th to 20th	Day	5% 9% 21% 34% 24% 7%	523
	21st to end	Day	7% 13% 21% 33% 22% 3	490
October	1st to 10th	Day	9% 15% 23% 28% 22% 4	490
	11th to 20th	Day	9% 17% 22% 25% 23% 4	490
	21st to end	Day	11% 18% 30% 21% 16% 5%	454
November	1st to 10th	Day	11% 17% 29% 29% 13% 2	300
	11th to 20th	Day	9% 27% 25% 23% 13% 3	213
	21st to end	Day	13% 23% 21% 29% 13% 2	200
December	1st to 10th	Day	9% 19% 24% 26% 15% 9%	200
	11th to 20th	Day	14% 26% 34% 21% 5% 1	200
	21st to end	Day	15% 23% 29% 24% 8% 1	220
January	1st to 10th	Night	10% 21% 32% 25% 11% 2	800
	11th to 20th	Night	7% 19% 30% 25% 17% 2	800
	21st to end	Night	10% 14% 26% 34% 14% 2	880
February	1st to 10th	Night	8% 18% 31% 31% 10% 1	800
	11th to 20th	Night	8% 14% 32% 33% 12% 1	784
	21st to end	Night	9% 18% 31% 33% 8%	660
March	1st to 10th	Night	9% 20% 27% 33% 10% 2	800
	11th to 20th	Night	6% 16% 28% 35% 14% 1	800
	21st to end	Night	7% 19% 31% 30% 12% 1	880
April	1st to 10th	Night	11% 15% 28% 32% 15% 1	800
	11th to 20th	Night	9% 13% 30% 31% 15% 2	791
	21st to end	Night	9% 11% 27% 35% 16% 1	739
May	1st to 10th	Night	9% 8% 23% 40% 19% 1	409
	11th to 20th	Night	8% 7% 19% 43% 21% 1	394
	21st to end	Night	9% 7% 21% 36% 24% 2	433
June	1st to 10th	Night	9% 7% 21% 43% 20% 1	400
	11th to 20th	Night	7% 5% 22% 46% 20% 1	400
	21st to end	Night	4 2 14% 59% 22%	400
July	1st to 10th	Night	2 1 9% 59% 27% 1	390
	11th to 20th	Night	2 11% 65% 21% 1	388
	21st to end	Night	1 1 10% 57% 30% 1	438
August	1st to 10th	Night	2 1 6% 52% 36% 3	530
	11th to 20th	Night	1 1 7% 44% 41% 6%	609
	21st to end	Night	2 2 17% 47% 30% 2	880
September	1st to 10th	Night	2 2 15% 47% 31% 3	800
	11th to 20th	Night	4 3 14% 43% 31% 5%	792
	21st to end	Night	8% 5% 18% 38% 26% 5%	760
October	1st to 10th	Night	8% 5% 22% 38% 24% 3	760
	11th to 20th	Night	7% 10% 21% 35% 24% 4	760
	21st to end	Night	8% 13% 25% 33% 15% 6%	836
November	1st to 10th	Night	9% 14% 30% 33% 13% 2	780
	11th to 20th	Night	10% 21% 27% 26% 14% 2	800
	21st to end	Night	7% 17% 25% 33% 15% 3	800
December	1st to 10th	Night	9% 13% 26% 33% 18% 2	800
	11th to 20th	Night	8% 20% 30% 29% 12% 1	800
	21st to end	Night	9% 25% 31% 25% 9%	880

Page generated at 2025-09-15 22:49:14. Version ac07

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