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 2024-11-12.

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	6% 7% 2 6% 4 4 5% 4 6% 7% 48%	105754
	Night	6% 9% 3 7% 4 4 4 4 6% 7% 45%	102023
Transparency	Day	34% 10% 14% 21% 16% 6%	105523
	Night	36% 10% 15% 22% 13% 4	101900
Seeing	Day	10% 19% 34% 25% 10% 2	14582
	Night	10% 11% 32% 32% 14% 1	23241

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% 18% 6% 11% 6% 6% 5% 4 6% 6% 24%	2539
	11th to 20th	Day	8% 14% 4 12% 5% 5% 5% 3 5% 7% 33%	2516
	21st to end	Day	15% 23% 5% 10% 5% 4 3 3 4 6% 22%	2794
February	1st to 10th	Day	4 12% 4 10% 6% 5% 6% 4 8% 9% 33%	1629
	11th to 20th	Day	4 11% 3 8% 4 4 4 4 7% 10% 39%	1665
	21st to end	Day	3 9% 4 11% 7% 6% 5% 5% 7% 10% 33%	1555
March	1st to 10th	Day	4 11% 4 7% 6% 5% 6% 5% 6% 7% 38%	3138
	11th to 20th	Day	3 7% 2 5% 4 4 5% 5% 6% 8% 52%	3382
	21st to end	Day	8% 12% 3 8% 5% 5% 6% 5% 7% 7% 34%	4091
April	1st to 10th	Day	7% 9% 3 8% 7% 6% 6% 6% 7% 8% 34%	2280
	11th to 20th	Day	5% 8% 3 8% 6% 5% 6% 4 8% 9% 38%	2252
	21st to end	Day	5% 8% 3 7% 5% 5% 6% 4 7% 9% 40%	2554
May	1st to 10th	Day	5% 5% 2 6% 5% 4 5% 4 6% 8% 50%	4420
	11th to 20th	Day	5% 5% 2 6% 5% 4 5% 4 7% 8% 49%	4377
	21st to end	Day	13% 9% 3 7% 6% 5% 6% 4 6% 7% 34%	4813
June	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 5% 7% 7% 39%	2660
	11th to 20th	Day	9% 6% 2 7% 5% 4 5% 4 6% 8% 43%	2697
	21st to end	Day	5% 4 2 5% 4 4 5% 4 6% 8% 53%	2850
July	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 75%	4521
	11th to 20th	Day	2 2 1 3 2 2 3 3 3 4 75%	4420
	21st to end	Day	2 2 1 3 3 3 3 3 4 5% 72%	4790
August	1st to 10th	Day	2 1 1 2 3 3 4 4 5% 7% 67%	4401
	11th to 20th	Day	1 1 1 3 3 4 4 4 6% 9% 62%	4187
	21st to end	Day	5% 4 2 5% 3 4 4 3 5% 6% 59%	4215
September	1st to 10th	Day	5% 3 1 3 3 3 3 3 4 6% 67%	2280
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 4 6% 8% 53%	2275
	21st to end	Day	7% 4 2 5% 4 4 4 4 5% 6% 56%	2052
October	1st to 10th	Day	4 3 2 5% 3 4 4 4 5% 8% 58%	3180
	11th to 20th	Day	4 5% 2 6% 5% 5% 5% 5% 6% 9% 47%	3138
	21st to end	Day	7% 7% 2 5% 4 5% 5% 4 7% 8% 47%	3101
November	1st to 10th	Day	8% 10% 3 6% 6% 5% 5% 5% 7% 9% 35%	1695
	11th to 20th	Day	5% 13% 3 8% 7% 5% 5% 4 7% 7% 36%	1528
	21st to end	Day	4 13% 5% 9% 7% 6% 6% 3 7% 7% 34%	1520
December	1st to 10th	Day	6% 13% 4 10% 5% 4 4 5% 5% 8% 36%	1520
	11th to 20th	Day	7% 15% 4 10% 7% 6% 5% 3 7% 7% 30%	1925
	21st to end	Day	10% 18% 6% 11% 7% 5% 5% 4 5% 5% 24%	2794
January	1st to 10th	Night	6% 18% 8% 15% 6% 6% 6% 4 6% 5% 22%	4406
	11th to 20th	Night	8% 16% 4 9% 5% 5% 5% 3 6% 9% 30%	4382
	21st to end	Night	14% 24% 7% 13% 6% 4 4 3 4 4 18%	4862
February	1st to 10th	Night	6% 14% 4 7% 6% 5% 5% 5% 7% 7% 33%	2548
	11th to 20th	Night	5% 10% 3 7% 4 5% 5% 4 6% 9% 42%	2402
	21st to end	Night	4 11% 4 10% 5% 5% 5% 5% 8% 9% 34%	1899
March	1st to 10th	Night	3 10% 4 9% 5% 5% 5% 5% 8% 10% 38%	3736
	11th to 20th	Night	3 7% 2 4 3 3 4 4 5% 7% 57%	3596
	21st to end	Night	6% 11% 3 10% 6% 6% 7% 5% 6% 7% 32%	3561
April	1st to 10th	Night	4 7% 3 7% 6% 5% 5% 5% 8% 11% 39%	1900
	11th to 20th	Night	4 7% 3 5% 4 4 6% 5% 7% 8% 46%	1879
	21st to end	Night	5% 7% 2 6% 4 4 4 4 7% 8% 49%	1624
May	1st to 10th	Night	5% 4 2 7% 4 4 4 4 6% 7% 55%	2540
	11th to 20th	Night	5% 3 2 4 4 4 4 4 5% 7% 59%	2516
	21st to end	Night	7% 4 2 5% 3 4 5% 5% 8% 10% 47%	2762
June	1st to 10th	Night	7% 5% 2 5% 5% 4 4 6% 8% 7% 46%	1520
	11th to 20th	Night	5% 4 2 5% 5% 5% 4 4 7% 8% 52%	1474
	21st to end	Night	4 2 1 3 3 3 4 4 7% 7% 63%	1330
July	1st to 10th	Night	1 1 2 1 2 2 2 3 5% 79%	2430
	11th to 20th	Night	1 1 1 2 1 2 2 3 4 82%	2540
	21st to end	Night	1 1 1 2 2 2 3 2 4 5% 77%	2762
August	1st to 10th	Night	1 2 1 3 2 3 4 3 4 5% 71%	2529
	11th to 20th	Night	1 1 1 3 2 2 3 3 6% 9% 69%	2643
	21st to end	Night	5% 2 1 3 2 4 4 4 5% 6% 65%	3461
September	1st to 10th	Night	3 2 1 3 3 2 3 3 5% 6% 68%	1900
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 8% 61%	1904
	21st to end	Night	6% 4 2 4 4 3 4 4 7% 8% 56%	2126
October	1st to 10th	Night	5% 4 2 3 3 3 4 4 6% 8% 59%	3800
	11th to 20th	Night	7% 6% 2 6% 4 4 4 4 7% 7% 49%	3798
	21st to end	Night	8% 7% 3 7% 5% 4 4 4 6% 7% 46%	4457
November	1st to 10th	Night	11% 12% 3 7% 4 4 6% 4 7% 8% 35%	2600
	11th to 20th	Night	6% 12% 3 8% 6% 5% 5% 4 6% 8% 37%	2674
	21st to end	Night	4 17% 5% 9% 6% 5% 5% 4 6% 6% 31%	2660
December	1st to 10th	Night	7% 14% 4 9% 6% 5% 5% 4 6% 8% 33%	2660
	11th to 20th	Night	7% 17% 7% 13% 8% 6% 7% 4 6% 6% 20%	3280
	21st to end	Night	10% 21% 6% 12% 5% 4 4 3 5% 5% 24%	4862

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	58% 14% 12% 10% 6% 1	2539
	11th to 20th	Day	52% 9% 14% 19% 3 2	2540
	21st to end	Day	64% 11% 11% 10% 4	2794
February	1st to 10th	Day	47% 14% 17% 17% 5% 1	1629
	11th to 20th	Day	41% 14% 18% 19% 8% 1	1674
	21st to end	Day	45% 15% 17% 16% 6% 1	1555
March	1st to 10th	Day	41% 15% 13% 14% 15% 2	3138
	11th to 20th	Day	28% 12% 17% 37% 6%	3382
	21st to end	Day	43% 17% 16% 15% 9% 1	4091
April	1st to 10th	Day	46% 12% 17% 17% 6% 1	2280
	11th to 20th	Day	41% 13% 17% 17% 10% 2	2252
	21st to end	Day	40% 13% 15% 20% 11% 2	2554
May	1st to 10th	Day	30% 11% 15% 19% 24% 2	4420
	11th to 20th	Day	27% 12% 19% 27% 14% 1	4380
	21st to end	Day	44% 15% 15% 20% 6%	4814
June	1st to 10th	Day	42% 11% 12% 18% 13% 4	2660
	11th to 20th	Day	38% 11% 15% 21% 13% 3	2697
	21st to end	Day	28% 8% 16% 26% 19% 4	2850
July	1st to 10th	Day	13% 5% 8% 16% 27% 30%	4452
	11th to 20th	Day	14% 4 6% 13% 27% 37%	4345
	21st to end	Day	14% 4 7% 23% 31% 20%	4639
August	1st to 10th	Day	15% 6% 8% 24% 35% 12%	4384
	11th to 20th	Day	17% 6% 17% 35% 21% 4	4229
	21st to end	Day	25% 7% 16% 24% 23% 5%	4214
September	1st to 10th	Day	18% 7% 12% 29% 27% 6%	2280
	11th to 20th	Day	29% 10% 12% 22% 23% 5%	2275
	21st to end	Day	28% 10% 17% 24% 16% 4	2052
October	1st to 10th	Day	23% 7% 13% 38% 17% 1	3180
	11th to 20th	Day	33% 11% 14% 24% 18%	3138
	21st to end	Day	33% 11% 13% 26% 15% 2	3101
November	1st to 10th	Day	45% 13% 16% 16% 9% 1	1695
	11th to 20th	Day	47% 12% 16% 17% 7% 1	1528
	21st to end	Day	48% 13% 16% 13% 8% 2	1520
December	1st to 10th	Day	47% 12% 16% 17% 9%	1520
	11th to 20th	Day	51% 15% 19% 9% 5%	1928
	21st to end	Day	61% 11% 9% 11% 7% 1	2794
January	1st to 10th	Night	58% 13% 11% 12% 5% 1	4406
	11th to 20th	Night	49% 10% 14% 19% 7% 1	4420
	21st to end	Night	67% 10% 9% 10% 3 1	4862
February	1st to 10th	Night	47% 13% 17% 16% 6% 1	2548
	11th to 20th	Night	39% 11% 18% 20% 9% 2	2404
	21st to end	Night	44% 14% 16% 17% 8% 1	1899
March	1st to 10th	Night	38% 14% 15% 16% 14% 3	3736
	11th to 20th	Night	26% 11% 19% 34% 9%	3597
	21st to end	Night	45% 16% 17% 18% 4 1	3561
April	1st to 10th	Night	37% 14% 18% 22% 7% 1	1900
	11th to 20th	Night	34% 13% 17% 21% 13% 2	1879
	21st to end	Night	31% 11% 18% 26% 13% 1	1624
May	1st to 10th	Night	26% 9% 14% 25% 24% 1	2540
	11th to 20th	Night	22% 10% 18% 31% 16% 1	2516
	21st to end	Night	25% 16% 24% 28% 6% 1	2762
June	1st to 10th	Night	34% 10% 15% 24% 14% 3	1520
	11th to 20th	Night	29% 10% 18% 26% 15% 2	1474
	21st to end	Night	19% 9% 16% 31% 22% 3	1330
July	1st to 10th	Night	11% 5% 8% 21% 30% 26%	2390
	11th to 20th	Night	8% 4 7% 17% 31% 33%	2492
	21st to end	Night	10% 3 9% 27% 31% 20%	2674
August	1st to 10th	Night	14% 5% 9% 28% 30% 14%	2521
	11th to 20th	Night	12% 6% 24% 36% 19% 4	2667
	21st to end	Night	19% 6% 16% 30% 24% 3	3461
September	1st to 10th	Night	17% 8% 12% 30% 27% 6%	1900
	11th to 20th	Night	22% 9% 12% 29% 23% 5%	1904
	21st to end	Night	24% 10% 16% 31% 14% 5%	2126
October	1st to 10th	Night	22% 7% 19% 34% 16% 1	3800
	11th to 20th	Night	32% 9% 16% 28% 14%	3798
	21st to end	Night	35% 8% 16% 26% 13% 1	4457
November	1st to 10th	Night	44% 14% 16% 14% 9% 2	2600
	11th to 20th	Night	44% 13% 16% 17% 7% 2	2674
	21st to end	Night	50% 14% 12% 15% 7% 2	2660
December	1st to 10th	Night	49% 11% 15% 18% 7%	2660
	11th to 20th	Night	57% 16% 12% 10% 5%	3276
	21st to end	Night	60% 10% 10% 12% 8% 1	4862

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% 17% 30% 23% 9% 6%	180
	11th to 20th	Day	16% 17% 23% 30% 11% 3	180
	21st to end	Day	17% 14% 28% 28% 12% 2	198
February	1st to 10th	Day	8% 25% 42% 18% 6% 1	289
	11th to 20th	Day	13% 23% 36% 21% 6% 1	365
	21st to end	Day	7% 24% 39% 24% 6%	375
March	1st to 10th	Day	10% 24% 38% 19% 7% 1	460
	11th to 20th	Day	11% 26% 29% 22% 12% 1	460
	21st to end	Day	13% 25% 39% 17% 6%	506
April	1st to 10th	Day	18% 27% 32% 16% 7% 1	460
	11th to 20th	Day	15% 27% 31% 18% 8% 2	452
	21st to end	Day	14% 27% 33% 17% 8% 1	460
May	1st to 10th	Day	11% 21% 36% 26% 5% 1	463
	11th to 20th	Day	18% 17% 27% 27% 9% 2	488
	21st to end	Day	13% 17% 32% 26% 10% 2	529
June	1st to 10th	Day	12% 23% 35% 21% 7% 1	490
	11th to 20th	Day	12% 25% 36% 19% 7% 1	527
	21st to end	Day	8% 17% 35% 28% 11% 1	680
July	1st to 10th	Day	6% 15% 35% 34% 9%	548
	11th to 20th	Day	6% 15% 33% 32% 12% 2	484
	21st to end	Day	3 12% 33% 35% 14% 2	531
August	1st to 10th	Day	5% 10% 32% 36% 13% 3	487
	11th to 20th	Day	3 10% 29% 36% 17% 5%	477
	21st to end	Day	7% 15% 34% 30% 10% 4	539
September	1st to 10th	Day	7% 14% 36% 25% 14% 4	490
	11th to 20th	Day	7% 15% 31% 30% 14% 3	490
	21st to end	Day	11% 17% 35% 24% 10% 2	490
October	1st to 10th	Day	11% 17% 33% 26% 13% 1	490
	11th to 20th	Day	11% 20% 32% 23% 11% 3	479
	21st to end	Day	14% 18% 32% 25% 9% 2	330
November	1st to 10th	Day	14% 18% 35% 25% 7% 1	265
	11th to 20th	Day	15% 19% 31% 21% 13% 2	182
	21st to end	Day	11% 12% 37% 23% 12% 6%	180
December	1st to 10th	Day	11% 17% 23% 24% 19% 7%	180
	11th to 20th	Day	6% 14% 41% 28% 10% 2	180
	21st to end	Day	8% 13% 32% 30% 16% 2	198
January	1st to 10th	Night	12% 16% 33% 25% 13% 1	760
	11th to 20th	Night	13% 12% 33% 30% 11% 1	760
	21st to end	Night	14% 8% 32% 32% 13% 1	836
February	1st to 10th	Night	13% 13% 38% 27% 9% 2	760
	11th to 20th	Night	10% 11% 34% 33% 13%	744
	21st to end	Night	10% 14% 32% 30% 14% 1	628
March	1st to 10th	Night	10% 10% 33% 34% 11% 1	760
	11th to 20th	Night	9% 11% 34% 33% 13% 1	760
	21st to end	Night	9% 13% 36% 33% 7% 1	836
April	1st to 10th	Night	8% 13% 35% 33% 11% 1	760
	11th to 20th	Night	9% 15% 34% 30% 11% 2	751
	21st to end	Night	9% 12% 43% 27% 9% 1	484
May	1st to 10th	Night	8% 13% 36% 31% 12%	380
	11th to 20th	Night	11% 9% 28% 37% 14%	374
	21st to end	Night	13% 8% 32% 31% 15%	411
June	1st to 10th	Night	7% 14% 35% 32% 11% 1	380
	11th to 20th	Night	8% 15% 38% 29% 10% 1	380
	21st to end	Night	4 10% 36% 33% 17%	380
July	1st to 10th	Night	3 9% 31% 40% 16%	370
	11th to 20th	Night	2 12% 33% 37% 16%	368
	21st to end	Night	2 7% 29% 42% 20%	416
August	1st to 10th	Night	3 8% 20% 42% 25% 1	378
	11th to 20th	Night	1 6% 26% 37% 29% 2	457
	21st to end	Night	5% 9% 27% 38% 19% 2	812
September	1st to 10th	Night	5% 8% 28% 34% 23% 3	760
	11th to 20th	Night	6% 7% 22% 32% 27% 6%	760
	21st to end	Night	8% 6% 31% 33% 19% 3	760
October	1st to 10th	Night	10% 8% 26% 35% 19% 1	760
	11th to 20th	Night	8% 12% 29% 33% 16% 2	760
	21st to end	Night	13% 13% 32% 29% 10% 3	836
November	1st to 10th	Night	16% 11% 34% 31% 7%	780
	11th to 20th	Night	14% 12% 35% 26% 11% 2	764
	21st to end	Night	13% 10% 35% 27% 11% 3	760
December	1st to 10th	Night	13% 8% 33% 32% 11% 2	760
	11th to 20th	Night	14% 9% 37% 33% 7% 1	760
	21st to end	Night	14% 13% 36% 31% 7%	836

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