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 2024-01-13.

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% 3 6% 6% 3 5% 5% 6% 8% 45%	75053
	Night	6% 9% 4 6% 6% 3 5% 5% 6% 8% 43%	74699
Transparency	Day	37% 11% 14% 20% 14% 3	74756
	Night	39% 11% 15% 21% 12% 3	74514
Seeing	Day	10% 19% 34% 25% 10% 2	13444
	Night	10% 11% 33% 32% 14% 1	22265

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% 7% 9% 7% 4 6% 5% 6% 6% 26%	1519
	11th to 20th	Day	7% 13% 3 10% 6% 4 6% 4 5% 8% 34%	1459
	21st to end	Day	4 14% 5% 9% 5% 4 4 5% 5% 9% 35%	1584
February	1st to 10th	Day	4 11% 4 10% 6% 4 6% 5% 8% 9% 33%	1544
	11th to 20th	Day	4 10% 4 6% 5% 2 4 5% 6% 11% 41%	1575
	21st to end	Day	4 8% 4 10% 8% 4 5% 6% 7% 10% 33%	1466
March	1st to 10th	Day	6% 10% 4 5% 7% 4 6% 7% 6% 8% 36%	1800
	11th to 20th	Day	5% 9% 4 6% 6% 4 6% 8% 7% 10% 35%	1911
	21st to end	Day	5% 11% 4 7% 7% 4 6% 7% 7% 8% 33%	2328
April	1st to 10th	Day	7% 8% 3 7% 8% 4 7% 7% 6% 8% 34%	2160
	11th to 20th	Day	5% 7% 4 7% 7% 4 7% 6% 7% 9% 37%	2132
	21st to end	Day	5% 8% 3 5% 6% 4 7% 5% 7% 9% 42%	2418
May	1st to 10th	Day	6% 5% 2 6% 5% 4 6% 6% 7% 10% 43%	2520
	11th to 20th	Day	8% 6% 3 8% 7% 4 5% 6% 6% 8% 38%	2477
	21st to end	Day	11% 6% 3 7% 7% 4 7% 6% 6% 8% 36%	2723
June	1st to 10th	Day	10% 6% 2 6% 6% 4 6% 6% 7% 7% 39%	2520
	11th to 20th	Day	10% 5% 3 6% 5% 3 5% 6% 6% 8% 43%	2555
	21st to end	Day	5% 4 2 5% 5% 3 5% 4 6% 8% 53%	2700
July	1st to 10th	Day	4 4 2 4 3 3 4 4 6% 7% 59%	2579
	11th to 20th	Day	3 2 1 3 3 2 4 5% 5% 6% 66%	2520
	21st to end	Day	2 1 1 2 3 2 3 3 4 6% 72%	2741
August	1st to 10th	Day	3 2 1 3 4 3 4 4 4 6% 66%	2507
	11th to 20th	Day	2 2 2 3 3 2 3 3 4 7% 68%	2397
	21st to end	Day	3 3 1 4 4 3 5% 5% 6% 8% 58%	2398
September	1st to 10th	Day	5% 3 1 3 3 2 3 3 4 6% 67%	2160
	11th to 20th	Day	6% 4 2 4 4 3 4 5% 5% 8% 53%	2156
	21st to end	Day	7% 4 2 5% 5% 3 4 5% 4 6% 55%	1944
October	1st to 10th	Day	7% 4 3 5% 5% 4 5% 6% 6% 6% 49%	1800
	11th to 20th	Day	6% 5% 1 5% 6% 5% 6% 6% 5% 9% 47%	1790
	21st to end	Day	9% 7% 2 6% 5% 4 5% 5% 6% 9% 42%	1782
November	1st to 10th	Day	9% 9% 4 6% 6% 4 5% 6% 7% 9% 36%	1609
	11th to 20th	Day	6% 12% 4 6% 8% 4 5% 5% 6% 8% 36%	1520
	21st to end	Day	4 12% 6% 8% 7% 4 7% 4 6% 8% 34%	1520
December	1st to 10th	Day	7% 10% 5% 9% 6% 3 5% 6% 5% 8% 36%	1520
	11th to 20th	Day	7% 14% 5% 8% 8% 4 6% 5% 7% 7% 30%	1925
	21st to end	Day	10% 17% 7% 9% 8% 4 5% 5% 5% 5% 24%	2794
January	1st to 10th	Night	6% 17% 7% 12% 8% 4 6% 5% 6% 6% 23%	2646
	11th to 20th	Night	7% 14% 6% 8% 8% 4 5% 4 6% 8% 30%	2562
	21st to end	Night	6% 13% 6% 9% 8% 3 6% 6% 6% 7% 31%	2772
February	1st to 10th	Night	6% 11% 4 7% 6% 4 6% 6% 7% 8% 34%	2414
	11th to 20th	Night	5% 9% 3 6% 5% 4 5% 5% 6% 9% 42%	2272
	21st to end	Night	5% 10% 4 8% 6% 3 5% 6% 8% 9% 35%	1790
March	1st to 10th	Night	5% 11% 4 6% 7% 4 6% 6% 6% 9% 37%	2160
	11th to 20th	Night	6% 7% 3 5% 5% 3 7% 7% 7% 9% 41%	2047
	21st to end	Night	5% 8% 3 6% 7% 4 6% 8% 7% 8% 37%	2027
April	1st to 10th	Night	4 6% 3 7% 6% 4 5% 6% 7% 11% 39%	1800
	11th to 20th	Night	4 6% 4 5% 5% 3 5% 7% 7% 9% 47%	1779
	21st to end	Night	5% 6% 2 5% 5% 3 5% 5% 6% 9% 50%	1540
May	1st to 10th	Night	5% 3 2 6% 5% 3 5% 4 7% 8% 52%	1440
	11th to 20th	Night	8% 4 2 5% 5% 4 5% 6% 7% 8% 47%	1416
	21st to end	Night	10% 5% 2 5% 4 3 4 6% 6% 9% 45%	1552
June	1st to 10th	Night	7% 4 2 5% 6% 3 4 7% 8% 8% 46%	1440
	11th to 20th	Night	5% 4 2 4 7% 3 4 5% 6% 8% 52%	1397
	21st to end	Night	3 2 1 3 3 3 4 4 7% 7% 62%	1260
July	1st to 10th	Night	2 3 1 3 3 2 4 5% 5% 8% 65%	1372
	11th to 20th	Night	2 2 1 2 3 2 3 3 5% 6% 71%	1440
	21st to end	Night	1 1 1 1 2 1 3 3 4 5% 79%	1576
August	1st to 10th	Night	2 2 3 3 2 3 3 4 5% 73%	1432
	11th to 20th	Night	2 2 1 2 3 1 2 3 5% 8% 72%	1500
	21st to end	Night	3 2 1 3 3 3 4 4 6% 7% 64%	1957
September	1st to 10th	Night	3 2 1 3 3 2 3 4 5% 6% 68%	1800
	11th to 20th	Night	5% 3 1 3 4 2 4 3 5% 7% 61%	1803
	21st to end	Night	6% 4 1 4 4 2 4 5% 7% 7% 55%	2014
October	1st to 10th	Night	8% 5% 2 4 4 3 5% 5% 6% 7% 51%	2160
	11th to 20th	Night	7% 5% 2 5% 6% 3 5% 6% 6% 7% 49%	2169
	21st to end	Night	9% 7% 3 6% 6% 3 4 5% 7% 8% 43%	2574
November	1st to 10th	Night	11% 11% 4 6% 5% 3 5% 5% 7% 7% 35%	2466
	11th to 20th	Night	6% 11% 4 6% 7% 4 5% 5% 6% 8% 37%	2660
	21st to end	Night	5% 15% 7% 9% 6% 4 5% 5% 6% 6% 31%	2660
December	1st to 10th	Night	7% 12% 5% 8% 7% 4 5% 5% 5% 8% 33%	2660
	11th to 20th	Night	7% 16% 7% 11% 9% 5% 7% 6% 6% 7% 20%	3280
	21st to end	Night	11% 20% 6% 10% 6% 3 4 5% 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	60% 12% 13% 10% 4 1	1519
	11th to 20th	Day	50% 12% 15% 18% 4 1	1459
	21st to end	Day	47% 11% 16% 18% 7%	1584
February	1st to 10th	Day	47% 14% 17% 17% 5% 1	1544
	11th to 20th	Day	40% 14% 18% 19% 8% 1	1584
	21st to end	Day	46% 16% 17% 15% 6% 1	1466
March	1st to 10th	Day	45% 12% 16% 17% 9% 1	1800
	11th to 20th	Day	44% 14% 14% 19% 8%	1911
	21st to end	Day	47% 15% 17% 15% 5% 1	2328
April	1st to 10th	Day	47% 12% 17% 18% 6% 1	2160
	11th to 20th	Day	43% 13% 17% 16% 9% 2	2132
	21st to end	Day	39% 12% 15% 20% 10% 2	2418
May	1st to 10th	Day	35% 11% 19% 23% 9% 2	2520
	11th to 20th	Day	42% 12% 17% 21% 8%	2480
	21st to end	Day	44% 12% 15% 21% 7% 1	2724
June	1st to 10th	Day	42% 11% 13% 18% 12% 4	2520
	11th to 20th	Day	38% 11% 16% 20% 13% 2	2555
	21st to end	Day	28% 9% 16% 25% 19% 4	2700
July	1st to 10th	Day	23% 8% 14% 24% 24% 7%	2510
	11th to 20th	Day	20% 6% 9% 22% 28% 13%	2445
	21st to end	Day	14% 5% 9% 24% 34% 14%	2589
August	1st to 10th	Day	19% 7% 11% 26% 28% 10%	2490
	11th to 20th	Day	17% 7% 12% 28% 30% 7%	2397
	21st to end	Day	23% 9% 12% 28% 23% 4	2398
September	1st to 10th	Day	19% 8% 13% 29% 27% 5%	2160
	11th to 20th	Day	29% 10% 11% 21% 23% 5%	2156
	21st to end	Day	29% 10% 17% 23% 17% 4	1944
October	1st to 10th	Day	34% 9% 13% 28% 15% 1	1800
	11th to 20th	Day	34% 13% 14% 24% 14% 1	1790
	21st to end	Day	39% 13% 13% 24% 10% 1	1782
November	1st to 10th	Day	46% 12% 16% 15% 9% 1	1609
	11th to 20th	Day	47% 12% 16% 17% 7% 1	1520
	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	60% 11% 12% 11% 5% 1	2646
	11th to 20th	Night	53% 11% 14% 15% 6% 1	2562
	21st to end	Night	50% 10% 16% 17% 6% 1	2772
February	1st to 10th	Night	46% 13% 17% 17% 6% 1	2414
	11th to 20th	Night	39% 11% 19% 21% 8% 2	2274
	21st to end	Night	43% 14% 17% 17% 8% 1	1790
March	1st to 10th	Night	44% 12% 16% 17% 9% 1	2160
	11th to 20th	Night	39% 14% 15% 23% 9%	2048
	21st to end	Night	44% 14% 20% 17% 5% 1	2027
April	1st to 10th	Night	38% 14% 16% 23% 8% 1	1800
	11th to 20th	Night	34% 13% 17% 21% 13% 2	1779
	21st to end	Night	32% 11% 17% 27% 13% 1	1540
May	1st to 10th	Night	28% 12% 18% 29% 12% 1	1440
	11th to 20th	Night	33% 12% 19% 26% 9% 1	1416
	21st to end	Night	33% 12% 20% 26% 9% 1	1552
June	1st to 10th	Night	34% 10% 15% 24% 13% 4	1440
	11th to 20th	Night	29% 10% 18% 26% 15% 1	1397
	21st to end	Night	20% 9% 17% 31% 20% 3	1260
July	1st to 10th	Night	18% 8% 14% 30% 22% 8%	1332
	11th to 20th	Night	14% 6% 12% 29% 26% 12%	1392
	21st to end	Night	8% 5% 8% 30% 34% 15%	1488
August	1st to 10th	Night	14% 6% 12% 27% 27% 14%	1424
	11th to 20th	Night	12% 6% 14% 31% 30% 6%	1500
	21st to end	Night	18% 8% 14% 27% 29% 4	1957
September	1st to 10th	Night	17% 8% 12% 30% 26% 6%	1800
	11th to 20th	Night	22% 9% 12% 27% 24% 5%	1803
	21st to end	Night	24% 11% 15% 31% 14% 5%	2014
October	1st to 10th	Night	32% 9% 13% 29% 15% 2	2160
	11th to 20th	Night	34% 11% 14% 27% 13% 1	2169
	21st to end	Night	39% 10% 13% 26% 12%	2574
November	1st to 10th	Night	45% 14% 16% 14% 9% 2	2466
	11th to 20th	Night	44% 13% 16% 17% 7% 2	2660
	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	15% 19% 22% 29% 12% 4	165
	21st to end	Day	16% 12% 30% 29% 11% 2	176
February	1st to 10th	Day	7% 26% 43% 19% 6%	264
	11th to 20th	Day	14% 23% 37% 20% 5% 1	335
	21st to end	Day	6% 22% 41% 25% 6%	340
March	1st to 10th	Day	10% 25% 40% 18% 6% 1	420
	11th to 20th	Day	11% 27% 30% 20% 11% 1	420
	21st to end	Day	12% 26% 39% 17% 6%	462
April	1st to 10th	Day	17% 27% 31% 17% 8% 1	420
	11th to 20th	Day	15% 27% 31% 18% 8% 2	412
	21st to end	Day	13% 26% 35% 17% 8% 1	420
May	1st to 10th	Day	11% 22% 36% 25% 5% 1	423
	11th to 20th	Day	18% 16% 27% 27% 9% 2	448
	21st to end	Day	12% 15% 33% 27% 11% 2	485
June	1st to 10th	Day	11% 23% 35% 22% 8% 1	450
	11th to 20th	Day	12% 26% 36% 18% 7% 1	485
	21st to end	Day	7% 17% 35% 28% 11% 1	630
July	1st to 10th	Day	6% 15% 34% 36% 9%	505
	11th to 20th	Day	6% 16% 34% 31% 10% 2	444
	21st to end	Day	2 13% 34% 35% 14% 2	487
August	1st to 10th	Day	5% 11% 32% 36% 13% 2	447
	11th to 20th	Day	2 11% 30% 36% 17% 4	437
	21st to end	Day	6% 15% 35% 31% 9% 3	495
September	1st to 10th	Day	7% 15% 38% 25% 12% 2	450
	11th to 20th	Day	8% 16% 31% 29% 14% 3	450
	21st to end	Day	12% 18% 35% 24% 10% 2	450
October	1st to 10th	Day	11% 17% 33% 26% 13%	450
	11th to 20th	Day	10% 21% 32% 23% 11% 3	440
	21st to end	Day	15% 19% 32% 22% 9% 2	297
November	1st to 10th	Day	14% 19% 35% 23% 8% 1	239
	11th to 20th	Day	14% 19% 31% 21% 13% 2	180
	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% 32% 30% 11% 1	732
	21st to end	Night	13% 8% 32% 32% 14% 1	792
February	1st to 10th	Night	12% 12% 38% 27% 9% 2	720
	11th to 20th	Night	10% 11% 35% 32% 12%	704
	21st to end	Night	9% 13% 32% 32% 14% 1	592
March	1st to 10th	Night	11% 11% 34% 33% 11% 1	720
	11th to 20th	Night	9% 11% 34% 32% 13% 1	720
	21st to end	Night	9% 13% 37% 33% 7% 1	792
April	1st to 10th	Night	7% 13% 34% 33% 12% 1	720
	11th to 20th	Night	8% 14% 35% 30% 11% 2	711
	21st to end	Night	9% 11% 44% 27% 9% 1	460
May	1st to 10th	Night	7% 13% 37% 31% 12%	360
	11th to 20th	Night	11% 8% 27% 39% 15%	354
	21st to end	Night	13% 7% 31% 31% 16% 1	389
June	1st to 10th	Night	8% 14% 35% 32% 11% 1	360
	11th to 20th	Night	8% 15% 38% 29% 9% 1	360
	21st to end	Night	3 10% 36% 33% 18%	360
July	1st to 10th	Night	3 9% 31% 40% 16%	350
	11th to 20th	Night	2 12% 34% 36% 16%	348
	21st to end	Night	2 7% 29% 42% 20%	394
August	1st to 10th	Night	3 9% 21% 41% 25% 1	358
	11th to 20th	Night	1 6% 26% 37% 29% 2	432
	21st to end	Night	5% 9% 27% 38% 19% 2	769
September	1st to 10th	Night	5% 9% 29% 34% 21% 3	720
	11th to 20th	Night	7% 7% 22% 31% 28% 6%	720
	21st to end	Night	8% 7% 30% 32% 19% 3	720
October	1st to 10th	Night	11% 8% 26% 35% 19% 1	720
	11th to 20th	Night	8% 12% 30% 32% 17% 2	720
	21st to end	Night	13% 13% 32% 28% 10% 3	792
November	1st to 10th	Night	16% 12% 35% 30% 7%	740
	11th to 20th	Night	14% 12% 35% 26% 11% 2	760
	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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