Twisp
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twisp 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	5% 7% 2 6% 4 4 5% 4 6% 8% 49%	131776
	Night	5% 9% 3 7% 4 4 5% 4 6% 8% 46%	128293
Transparency	Day	32% 10% 14% 23% 16% 5%	131503
	Night	35% 10% 16% 23% 13% 3	128143
Seeing	Day	10% 18% 33% 26% 10% 2	15945
	Night	10% 11% 32% 33% 14% 1	24670

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	8% 16% 5% 9% 5% 5% 5% 5% 6% 7% 30%	3647
	11th to 20th	Day	5% 10% 3 8% 4 4 4 2 6% 7% 47%	3616
	21st to end	Day	10% 17% 4 8% 4 4 4 3 4 7% 36%	4004
February	1st to 10th	Day	4 12% 4 10% 6% 5% 6% 4 8% 9% 34%	1715
	11th to 20th	Day	4 11% 3 8% 5% 4 5% 4 6% 10% 39%	1755
	21st to end	Day	3 9% 4 12% 7% 6% 5% 5% 7% 10% 33%	1635
March	1st to 10th	Day	3 8% 3 6% 5% 5% 5% 6% 9% 10% 41%	4518
	11th to 20th	Day	2 7% 3 7% 5% 5% 6% 5% 7% 8% 45%	4840
	21st to end	Day	7% 10% 3 8% 5% 5% 6% 5% 8% 9% 34%	5869
April	1st to 10th	Day	6% 9% 3 8% 7% 6% 6% 6% 7% 8% 35%	2400
	11th to 20th	Day	5% 7% 3 8% 6% 5% 6% 4 8% 9% 40%	2372
	21st to end	Day	5% 8% 3 7% 5% 5% 6% 4 7% 9% 42%	2688
May	1st to 10th	Day	4 5% 2 5% 4 3 4 4 7% 8% 54%	6320
	11th to 20th	Day	5% 6% 3 8% 5% 5% 5% 4 7% 8% 43%	6277
	21st to end	Day	9% 7% 2 6% 5% 5% 5% 4 6% 9% 43%	6903
June	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 5% 6% 7% 41%	2800
	11th to 20th	Day	9% 6% 2 7% 5% 4 5% 5% 6% 8% 43%	2839
	21st to end	Day	5% 4 2 5% 4 4 5% 4 6% 8% 54%	3000
July	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 77%	6463
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 78%	6320
	21st to end	Day	2 2 1 3 3 3 4 3 5% 7% 68%	6874
August	1st to 10th	Day	2 2 1 3 3 3 4 4 5% 7% 67%	4541
	11th to 20th	Day	1 1 1 3 3 4 5% 4 6% 9% 62%	4322
	21st to end	Day	5% 4 2 5% 3 4 4 3 5% 6% 59%	4348
September	1st to 10th	Day	4 3 1 3 3 3 3 3 4 6% 67%	2400
	11th to 20th	Day	5% 4 2 5% 4 4 4 4 6% 8% 54%	2395
	21st to end	Day	6% 4 2 5% 4 4 4 4 5% 6% 56%	2160
October	1st to 10th	Day	4 3 2 5% 3 4 4 4 5% 8% 58%	3280
	11th to 20th	Day	5% 5% 2 7% 5% 5% 5% 5% 6% 9% 47%	3237
	21st to end	Day	7% 7% 2 5% 4 5% 5% 5% 7% 8% 46%	3200
November	1st to 10th	Day	8% 11% 3 6% 5% 5% 5% 5% 7% 9% 36%	1781
	11th to 20th	Day	6% 14% 4 8% 7% 5% 5% 3 7% 7% 35%	1680
	21st to end	Day	4 13% 5% 9% 6% 6% 6% 3 7% 8% 33%	1680
December	1st to 10th	Day	4 8% 3 8% 5% 5% 8% 5% 6% 9% 39%	2700
	11th to 20th	Day	6% 17% 5% 10% 7% 6% 5% 4 6% 6% 28%	3105
	21st to end	Day	8% 18% 6% 11% 6% 5% 5% 4 6% 6% 25%	4092
January	1st to 10th	Night	6% 18% 8% 16% 6% 5% 5% 3 5% 6% 23%	6320
	11th to 20th	Night	6% 11% 3 7% 4 4 4 3 6% 10% 42%	6282
	21st to end	Night	10% 17% 5% 10% 5% 6% 5% 4 4 6% 29%	6952
February	1st to 10th	Night	6% 13% 3 7% 6% 6% 6% 4 7% 8% 33%	2682
	11th to 20th	Night	4 10% 3 7% 4 5% 5% 4 6% 9% 42%	2532
	21st to end	Night	4 11% 4 10% 5% 5% 5% 5% 8% 9% 34%	1995
March	1st to 10th	Night	2 8% 3 7% 4 4 5% 5% 9% 12% 41%	5376
	11th to 20th	Night	4 9% 3 5% 4 4 4 4 5% 6% 51%	5158
	21st to end	Night	6% 11% 3 9% 6% 6% 7% 6% 6% 8% 32%	5105
April	1st to 10th	Night	4 7% 3 7% 6% 5% 5% 5% 8% 12% 39%	2000
	11th to 20th	Night	4 6% 3 5% 4 4 5% 5% 7% 8% 48%	1979
	21st to end	Night	5% 7% 2 6% 4 4 4 4 6% 8% 51%	1710
May	1st to 10th	Night	4 3 1 5% 3 3 3 3 5% 7% 63%	3640
	11th to 20th	Night	4 5% 3 6% 4 5% 5% 4 5% 8% 52%	3616
	21st to end	Night	7% 3 1 4 3 3 4 4 8% 11% 51%	3972
June	1st to 10th	Night	6% 5% 2 5% 5% 4 4 5% 8% 7% 48%	1600
	11th to 20th	Night	4 4 2 5% 5% 5% 4 4 7% 7% 52%	1551
	21st to end	Night	4 2 1 3 3 3 4 4 7% 7% 63%	1400
July	1st to 10th	Night	1 2 1 2 2 2 2 2 3 5% 78%	3488
	11th to 20th	Night	1 1 1 1 1 2 2 3 5% 82%	3640
	21st to end	Night	1 1 1 3 2 2 3 2 5% 5% 74%	3969
August	1st to 10th	Night	1 2 1 3 2 3 4 3 4 5% 71%	2609
	11th to 20th	Night	2 2 1 3 2 2 3 3 6% 9% 69%	2727
	21st to end	Night	5% 2 1 3 2 4 4 4 5% 6% 64%	3570
September	1st to 10th	Night	3 2 1 3 2 2 4 3 5% 6% 68%	2000
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 8% 62%	2004
	21st to end	Night	5% 4 1 4 4 3 3 4 7% 8% 56%	2238
October	1st to 10th	Night	5% 4 2 3 3 3 4 4 6% 8% 59%	3920
	11th to 20th	Night	7% 6% 2 6% 4 4 4 4 7% 7% 50%	3919
	21st to end	Night	7% 7% 3 7% 5% 4 4 4 6% 7% 46%	4600
November	1st to 10th	Night	11% 12% 3 7% 4 4 6% 4 7% 8% 34%	2733
	11th to 20th	Night	7% 13% 4 8% 6% 5% 5% 4 7% 8% 35%	2940
	21st to end	Night	4 17% 5% 9% 6% 5% 6% 4 6% 6% 31%	2940
December	1st to 10th	Night	4 9% 3 6% 6% 7% 7% 4 7% 10% 37%	4700
	11th to 20th	Night	6% 18% 7% 12% 8% 7% 7% 4 6% 7% 19%	5320
	21st to end	Night	10% 20% 6% 11% 5% 4 4 4 5% 6% 25%	7106

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% 12% 13% 18% 6%	3647
	11th to 20th	Day	37% 8% 19% 26% 8% 2	3640
	21st to end	Day	47% 10% 14% 20% 8%	4004
February	1st to 10th	Day	46% 13% 16% 16% 7% 2	1715
	11th to 20th	Day	41% 14% 18% 19% 8% 1	1764
	21st to end	Day	45% 15% 16% 16% 6% 1	1635
March	1st to 10th	Day	33% 14% 18% 15% 18% 3	4518
	11th to 20th	Day	32% 11% 15% 32% 9% 1	4840
	21st to end	Day	41% 15% 20% 15% 8% 1	5869
April	1st to 10th	Day	46% 12% 18% 18% 7% 1	2400
	11th to 20th	Day	39% 12% 17% 18% 11% 2	2372
	21st to end	Day	38% 12% 15% 22% 11% 2	2688
May	1st to 10th	Day	25% 9% 12% 26% 24% 3	6320
	11th to 20th	Day	33% 10% 17% 26% 13% 1	6280
	21st to end	Day	35% 12% 17% 26% 10% 1	6904
June	1st to 10th	Day	40% 11% 12% 19% 14% 4	2800
	11th to 20th	Day	36% 11% 15% 21% 15% 3	2839
	21st to end	Day	28% 8% 16% 26% 19% 4	3000
July	1st to 10th	Day	12% 4 10% 23% 28% 24%	6394
	11th to 20th	Day	11% 3 6% 22% 31% 26%	6245
	21st to end	Day	16% 4 8% 28% 29% 15%	6681
August	1st to 10th	Day	15% 6% 8% 24% 35% 12%	4524
	11th to 20th	Day	17% 6% 17% 35% 21% 4	4364
	21st to end	Day	26% 6% 15% 24% 23% 6%	4347
September	1st to 10th	Day	18% 7% 12% 29% 28% 6%	2400
	11th to 20th	Day	28% 10% 12% 23% 23% 5%	2395
	21st to end	Day	28% 10% 17% 26% 16% 4	2160
October	1st to 10th	Day	23% 7% 14% 38% 17% 1	3280
	11th to 20th	Day	33% 11% 14% 24% 18% 1	3237
	21st to end	Day	33% 11% 14% 26% 15% 2	3200
November	1st to 10th	Day	45% 12% 17% 16% 9% 1	1781
	11th to 20th	Day	49% 12% 15% 16% 7% 1	1680
	21st to end	Day	48% 14% 16% 12% 8% 2	1680
December	1st to 10th	Day	40% 14% 19% 20% 7%	2700
	11th to 20th	Day	54% 13% 16% 11% 6%	3108
	21st to end	Day	57% 12% 12% 13% 6%	4092
January	1st to 10th	Night	58% 11% 13% 14% 4	6320
	11th to 20th	Night	37% 10% 18% 25% 9% 1	6320
	21st to end	Night	52% 11% 16% 15% 5%	6952
February	1st to 10th	Night	46% 13% 16% 16% 7% 2	2682
	11th to 20th	Night	40% 11% 18% 20% 9% 2	2534
	21st to end	Night	44% 14% 17% 17% 8% 1	1995
March	1st to 10th	Night	32% 12% 18% 21% 15% 2	5376
	11th to 20th	Night	31% 10% 17% 27% 14%	5159
	21st to end	Night	45% 15% 17% 17% 5%	5105
April	1st to 10th	Night	37% 14% 19% 23% 7% 1	2000
	11th to 20th	Night	32% 12% 17% 22% 14% 2	1979
	21st to end	Night	30% 11% 18% 28% 13% 1	1710
May	1st to 10th	Night	21% 7% 13% 32% 26% 1	3637
	11th to 20th	Night	28% 9% 18% 31% 13% 1	3616
	21st to end	Night	22% 12% 25% 32% 8% 1	3972
June	1st to 10th	Night	33% 10% 14% 25% 15% 4	1600
	11th to 20th	Night	28% 10% 17% 26% 17% 2	1551
	21st to end	Night	19% 9% 17% 31% 21% 3	1400
July	1st to 10th	Night	11% 3 10% 27% 26% 22%	3448
	11th to 20th	Night	7% 3 9% 28% 30% 23%	3592
	21st to end	Night	12% 4 9% 32% 29% 14%	3857
August	1st to 10th	Night	14% 5% 10% 28% 30% 13%	2601
	11th to 20th	Night	12% 6% 24% 36% 19% 4	2751
	21st to end	Night	19% 6% 16% 30% 25% 4	3570
September	1st to 10th	Night	17% 8% 12% 31% 27% 6%	2000
	11th to 20th	Night	21% 8% 12% 30% 23% 5%	2004
	21st to end	Night	24% 10% 16% 32% 14% 5%	2238
October	1st to 10th	Night	22% 7% 19% 35% 16% 1	3920
	11th to 20th	Night	32% 9% 16% 28% 14% 1	3919
	21st to end	Night	35% 8% 16% 27% 13% 1	4600
November	1st to 10th	Night	45% 14% 16% 14% 9% 2	2733
	11th to 20th	Night	45% 13% 15% 18% 7% 2	2940
	21st to end	Night	50% 14% 13% 14% 7% 2	2940
December	1st to 10th	Night	39% 14% 21% 20% 6%	4700
	11th to 20th	Night	58% 14% 13% 10% 5%	5316
	21st to end	Night	56% 10% 13% 14% 6% 1	7106

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	15% 15% 29% 24% 12% 5%	202
	11th to 20th	Day	14% 16% 25% 30% 14% 3	200
	21st to end	Day	15% 12% 28% 29% 13% 2	220
February	1st to 10th	Day	7% 23% 42% 20% 7% 2	315
	11th to 20th	Day	13% 21% 36% 22% 7% 1	395
	21st to end	Day	7% 23% 40% 23% 6%	407
March	1st to 10th	Day	10% 23% 37% 21% 8% 1	500
	11th to 20th	Day	10% 25% 29% 23% 11% 1	500
	21st to end	Day	12% 23% 39% 19% 6% 1	550
April	1st to 10th	Day	17% 25% 31% 18% 8% 1	500
	11th to 20th	Day	15% 26% 31% 19% 8% 1	492
	21st to end	Day	13% 25% 33% 18% 8% 2	500
May	1st to 10th	Day	11% 20% 35% 26% 6% 1	503
	11th to 20th	Day	19% 17% 28% 27% 8% 2	528
	21st to end	Day	13% 17% 31% 27% 10% 2	573
June	1st to 10th	Day	11% 23% 35% 22% 8% 2	530
	11th to 20th	Day	12% 24% 36% 19% 8% 1	569
	21st to end	Day	8% 17% 35% 28% 11% 1	730
July	1st to 10th	Day	6% 16% 35% 34% 10%	591
	11th to 20th	Day	6% 15% 34% 31% 11% 2	524
	21st to end	Day	3 12% 33% 35% 15% 3	575
August	1st to 10th	Day	5% 10% 32% 35% 13% 4	527
	11th to 20th	Day	3 11% 29% 35% 17% 5%	517
	21st to end	Day	7% 15% 32% 31% 11% 5%	583
September	1st to 10th	Day	6% 13% 35% 25% 16% 5%	530
	11th to 20th	Day	7% 15% 31% 30% 15% 4	530
	21st to end	Day	11% 17% 35% 23% 11% 2	530
October	1st to 10th	Day	11% 16% 33% 27% 13% 1	530
	11th to 20th	Day	11% 20% 32% 24% 11% 2	518
	21st to end	Day	14% 17% 33% 25% 10% 2	363
November	1st to 10th	Day	15% 16% 35% 26% 7% 1	291
	11th to 20th	Day	16% 17% 28% 24% 13% 2	220
	21st to end	Day	12% 10% 36% 25% 11% 5%	220
December	1st to 10th	Day	10% 14% 25% 23% 20% 8%	220
	11th to 20th	Day	7% 15% 39% 29% 9% 1	220
	21st to end	Day	8% 12% 29% 32% 16% 2	242
January	1st to 10th	Night	12% 15% 32% 27% 13% 1	804
	11th to 20th	Night	12% 12% 34% 31% 10% 1	800
	21st to end	Night	13% 8% 31% 33% 14% 1	880
February	1st to 10th	Night	12% 12% 38% 28% 9% 2	800
	11th to 20th	Night	9% 11% 34% 33% 12%	784
	21st to end	Night	10% 14% 32% 31% 13% 1	660
March	1st to 10th	Night	10% 10% 33% 35% 11% 1	800
	11th to 20th	Night	9% 11% 34% 33% 13% 1	800
	21st to end	Night	10% 13% 36% 33% 7% 1	880
April	1st to 10th	Night	7% 12% 35% 34% 12% 1	800
	11th to 20th	Night	8% 15% 35% 30% 10% 2	791
	21st to end	Night	8% 12% 43% 26% 10% 1	510
May	1st to 10th	Night	8% 14% 36% 32% 12%	400
	11th to 20th	Night	11% 10% 28% 37% 14%	394
	21st to end	Night	13% 8% 31% 32% 15%	433
June	1st to 10th	Night	8% 14% 35% 32% 11% 1	400
	11th to 20th	Night	7% 16% 39% 29% 9% 1	400
	21st to end	Night	4 10% 35% 34% 17%	400
July	1st to 10th	Night	3 9% 32% 39% 16%	390
	11th to 20th	Night	2 12% 32% 38% 16%	388
	21st to end	Night	2 6% 28% 42% 21%	438
August	1st to 10th	Night	3 8% 20% 43% 26% 1	398
	11th to 20th	Night	1 6% 26% 38% 28% 1	481
	21st to end	Night	5% 9% 26% 38% 21% 2	855
September	1st to 10th	Night	5% 8% 27% 33% 25% 3	800
	11th to 20th	Night	6% 6% 21% 34% 28% 5%	800
	21st to end	Night	8% 7% 30% 34% 19% 3	800
October	1st to 10th	Night	10% 8% 26% 37% 18% 1	800
	11th to 20th	Night	8% 12% 30% 33% 15% 2	800
	21st to end	Night	13% 13% 33% 30% 10% 3	880
November	1st to 10th	Night	17% 12% 34% 31% 7%	820
	11th to 20th	Night	14% 12% 34% 26% 11% 2	840
	21st to end	Night	13% 9% 33% 30% 11% 3	840
December	1st to 10th	Night	12% 8% 34% 32% 12% 2	840
	11th to 20th	Night	14% 10% 37% 32% 7% 1	840
	21st to end	Night	14% 12% 36% 32% 7%	924

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