Starr Butte
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starr Butte clear sky chart from 2005-11-06 to 2024-11-10.

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	11% 9% 3 6% 4 4 4 3 5% 6% 44%	105162
	Night	13% 10% 3 7% 4 4 4 4 5% 6% 40%	102569
Transparency	Day	40% 6% 13% 21% 14% 6%	104930
	Night	44% 6% 12% 19% 13% 6%	102447
Seeing	Day	17% 11% 23% 25% 18% 6%	14815
	Night	19% 8% 18% 32% 20% 3	23976

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	22% 22% 7% 9% 4 4 5% 3 5% 5% 13%	2539
	11th to 20th	Day	23% 13% 4 8% 6% 5% 5% 4 5% 6% 22%	2516
	21st to end	Day	24% 20% 4 10% 5% 4 4 3 4 4 17%	2794
February	1st to 10th	Day	21% 17% 4 8% 4 5% 4 4 5% 6% 21%	1520
	11th to 20th	Day	19% 18% 6% 8% 4 3 4 4 6% 5% 24%	1791
	21st to end	Day	17% 21% 6% 10% 4 5% 4 3 5% 5% 22%	1570
March	1st to 10th	Day	11% 16% 3 8% 6% 5% 5% 4 7% 7% 28%	3138
	11th to 20th	Day	9% 11% 3 6% 4 4 5% 3 4 6% 45%	3292
	21st to end	Day	16% 17% 4 9% 7% 6% 6% 3 5% 5% 20%	4098
April	1st to 10th	Day	14% 14% 3 8% 5% 6% 5% 5% 6% 8% 25%	2280
	11th to 20th	Day	13% 11% 3 9% 6% 5% 4 3 5% 7% 34%	2323
	21st to end	Day	13% 9% 3 8% 6% 5% 5% 4 6% 7% 35%	2470
May	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 6% 7% 39%	4288
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 7% 10% 46%	4377
	21st to end	Day	10% 8% 3 8% 6% 6% 6% 5% 7% 8% 35%	4831
June	1st to 10th	Day	16% 9% 2 6% 5% 5% 4 3 5% 7% 38%	2850
	11th to 20th	Day	14% 7% 2 6% 5% 4 5% 4 6% 8% 40%	2850
	21st to end	Day	7% 3 2 4 4 4 4 4 6% 7% 56%	2850
July	1st to 10th	Day	2 2 2 2 2 2 2 4 5% 77%	4432
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 80%	4420
	21st to end	Day	1 1 1 2 2 2 2 3 4 5% 75%	4790
August	1st to 10th	Day	3 2 1 3 2 2 3 2 4 6% 70%	4401
	11th to 20th	Day	4 3 1 3 3 3 4 3 5% 7% 65%	4115
	21st to end	Day	3 3 1 4 3 3 3 3 6% 6% 65%	4278
September	1st to 10th	Day	6% 3 1 3 2 3 3 3 4 6% 66%	2280
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 5% 8% 50%	2161
	21st to end	Day	8% 6% 2 6% 4 4 4 4 6% 7% 49%	2090
October	1st to 10th	Day	9% 4 2 5% 3 3 3 3 4 7% 57%	3398
	11th to 20th	Day	12% 7% 2 7% 4 5% 5% 4 5% 7% 43%	2950
	21st to end	Day	18% 11% 5% 7% 3 3 4 3 5% 6% 35%	3101
November	1st to 10th	Day	23% 13% 4 7% 4 5% 4 3 4 8% 25%	1755
	11th to 20th	Day	22% 15% 4 7% 5% 4 5% 4 5% 5% 24%	1644
	21st to end	Day	18% 16% 5% 10% 5% 4 4 4 5% 6% 23%	1388
December	1st to 10th	Day	19% 16% 5% 12% 5% 4 3 4 5% 6% 20%	1330
	11th to 20th	Day	22% 22% 5% 11% 7% 4 4 3 5% 3 13%	1682
	21st to end	Day	18% 19% 4 10% 5% 5% 4 4 5% 7% 19%	2570
January	1st to 10th	Night	24% 19% 5% 9% 5% 5% 5% 3 4 5% 15%	4406
	11th to 20th	Night	19% 16% 5% 9% 5% 4 4 3 5% 7% 24%	4382
	21st to end	Night	24% 17% 5% 8% 4 4 4 4 5% 5% 20%	4862
February	1st to 10th	Night	19% 19% 4 7% 5% 4 3 3 4 6% 25%	2660
	11th to 20th	Night	16% 15% 4 10% 5% 4 5% 3 5% 5% 29%	2273
	21st to end	Night	13% 16% 3 8% 5% 6% 5% 4 6% 6% 28%	1884
March	1st to 10th	Night	11% 10% 3 7% 5% 5% 5% 4 6% 7% 37%	3736
	11th to 20th	Night	10% 10% 2 5% 3 4 3 3 4 5% 50%	3686
	21st to end	Night	13% 10% 3 10% 7% 6% 6% 5% 7% 8% 25%	3550
April	1st to 10th	Night	11% 11% 3 7% 6% 4 5% 4 8% 9% 32%	1900
	11th to 20th	Night	12% 10% 3 8% 6% 4 4 4 5% 5% 40%	1807
	21st to end	Night	10% 10% 2 7% 5% 5% 5% 4 6% 6% 39%	1710
May	1st to 10th	Night	12% 7% 3 7% 5% 5% 6% 5% 6% 8% 38%	2673
	11th to 20th	Night	7% 6% 2 6% 4 3 4 3 5% 9% 49%	2516
	21st to end	Night	14% 6% 2 8% 4 6% 5% 4 7% 8% 37%	2743
June	1st to 10th	Night	13% 6% 1 7% 5% 4 5% 4 5% 9% 42%	1330
	11th to 20th	Night	10% 7% 2 6% 5% 4 4 4 7% 8% 42%	1330
	21st to end	Night	7% 3 2 5% 3 4 5% 3 6% 7% 54%	1330
July	1st to 10th	Night	2 1 1 2 2 2 3 2 4 6% 77%	2523
	11th to 20th	Night	2 1 2 1 1 2 1 3 3 82%	2540
	21st to end	Night	2 2 1 2 2 2 2 2 3 5% 77%	2762
August	1st to 10th	Night	4 3 1 3 2 2 3 3 6% 6% 67%	2529
	11th to 20th	Night	3 3 1 4 4 3 4 4 5% 6% 62%	2719
	21st to end	Night	3 3 1 4 3 3 3 3 5% 6% 65%	3393
September	1st to 10th	Night	4 3 1 4 3 2 3 3 4 6% 67%	1900
	11th to 20th	Night	6% 6% 2 4 4 4 5% 4 5% 6% 54%	2019
	21st to end	Night	9% 4 1 6% 4 3 3 3 5% 8% 53%	2090
October	1st to 10th	Night	7% 4 2 5% 3 3 3 3 5% 7% 58%	3578
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 5% 7% 47%	3979
	21st to end	Night	14% 7% 2 7% 4 4 4 4 5% 7% 42%	4457
November	1st to 10th	Night	21% 12% 3 8% 4 4 4 3 5% 7% 30%	2528
	11th to 20th	Night	21% 13% 4 8% 6% 4 3 4 4 5% 28%	2531
	21st to end	Night	20% 12% 4 8% 4 4 4 4 5% 6% 28%	2769
December	1st to 10th	Night	18% 14% 4 9% 4 4 4 4 5% 5% 28%	2850
	11th to 20th	Night	22% 19% 5% 10% 5% 5% 5% 4 5% 5% 15%	3510
	21st to end	Night	19% 15% 4 10% 6% 5% 5% 5% 6% 6% 19%	5114

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	73% 7% 11% 7% 1	2539
	11th to 20th	Day	62% 7% 12% 14% 3 2	2540
	21st to end	Day	71% 7% 13% 8% 1 1	2794
February	1st to 10th	Day	63% 9% 13% 10% 5%	1520
	11th to 20th	Day	62% 8% 12% 11% 6%	1801
	21st to end	Day	66% 6% 8% 15% 5%	1570
March	1st to 10th	Day	51% 7% 13% 20% 9%	3138
	11th to 20th	Day	41% 6% 16% 33% 4	3292
	21st to end	Day	66% 8% 12% 9% 5% 1	4098
April	1st to 10th	Day	57% 8% 17% 15% 4	2280
	11th to 20th	Day	50% 7% 15% 16% 11% 1	2323
	21st to end	Day	49% 7% 15% 19% 8% 1	2470
May	1st to 10th	Day	42% 6% 14% 29% 8%	4288
	11th to 20th	Day	31% 6% 17% 34% 11% 1	4380
	21st to end	Day	43% 9% 20% 23% 4 1	4832
June	1st to 10th	Day	46% 6% 14% 23% 11%	2850
	11th to 20th	Day	40% 7% 17% 22% 11% 2	2850
	21st to end	Day	26% 5% 15% 29% 21% 3	2850
July	1st to 10th	Day	12% 3 7% 19% 30% 29%	4363
	11th to 20th	Day	11% 2 6% 12% 27% 42%	4345
	21st to end	Day	12% 3 6% 19% 35% 24%	4639
August	1st to 10th	Day	16% 4 5% 20% 39% 16%	4384
	11th to 20th	Day	20% 4 8% 37% 26% 5%	4156
	21st to end	Day	19% 4 11% 32% 28% 6%	4277
September	1st to 10th	Day	20% 4 11% 29% 24% 11%	2280
	11th to 20th	Day	32% 6% 13% 22% 22% 5%	2161
	21st to end	Day	34% 7% 17% 26% 12% 4	2090
October	1st to 10th	Day	28% 4 13% 33% 21% 1	3398
	11th to 20th	Day	42% 5% 17% 23% 13%	2950
	21st to end	Day	51% 6% 13% 19% 9% 1	3101
November	1st to 10th	Day	60% 6% 15% 15% 4 1	1755
	11th to 20th	Day	63% 7% 16% 9% 3 1	1644
	21st to end	Day	61% 8% 13% 14% 3 1	1388
December	1st to 10th	Day	65% 9% 12% 11% 3 1	1330
	11th to 20th	Day	74% 7% 11% 7% 1	1684
	21st to end	Day	63% 7% 16% 10% 5%	2570
January	1st to 10th	Night	70% 6% 13% 9% 1 1	4406
	11th to 20th	Night	60% 6% 13% 14% 6% 1	4420
	21st to end	Night	65% 7% 14% 10% 2	4862
February	1st to 10th	Night	62% 7% 13% 13% 5% 1	2660
	11th to 20th	Night	57% 6% 16% 13% 8%	2274
	21st to end	Night	55% 7% 13% 17% 7% 1	1884
March	1st to 10th	Night	44% 7% 12% 24% 12% 1	3736
	11th to 20th	Night	37% 6% 13% 34% 10%	3687
	21st to end	Night	54% 9% 16% 17% 4	3550
April	1st to 10th	Night	47% 8% 15% 22% 8%	1900
	11th to 20th	Night	45% 5% 12% 23% 13% 2	1807
	21st to end	Night	42% 7% 13% 23% 13% 2	1710
May	1st to 10th	Night	40% 7% 14% 26% 13% 1	2673
	11th to 20th	Night	30% 6% 12% 31% 19% 1	2516
	21st to end	Night	42% 9% 18% 22% 9%	2743
June	1st to 10th	Night	39% 7% 11% 23% 19% 2	1330
	11th to 20th	Night	37% 6% 12% 25% 14% 5%	1330
	21st to end	Night	28% 6% 9% 27% 22% 8%	1330
July	1st to 10th	Night	11% 2 5% 15% 32% 35%	2483
	11th to 20th	Night	10% 2 4 10% 21% 53%	2492
	21st to end	Night	12% 2 3 15% 31% 36%	2674
August	1st to 10th	Night	18% 3 5% 15% 36% 23%	2521
	11th to 20th	Night	21% 5% 7% 29% 30% 9%	2744
	21st to end	Night	20% 4 10% 24% 30% 13%	3393
September	1st to 10th	Night	19% 3 9% 27% 27% 15%	1900
	11th to 20th	Night	30% 4 11% 23% 23% 8%	2019
	21st to end	Night	30% 5% 14% 29% 15% 7%	2090
October	1st to 10th	Night	26% 4 10% 34% 24% 2	3578
	11th to 20th	Night	37% 5% 14% 23% 20% 1	3979
	21st to end	Night	42% 6% 10% 29% 11% 2	4457
November	1st to 10th	Night	55% 7% 16% 16% 5% 1	2528
	11th to 20th	Night	59% 6% 15% 13% 6% 1	2531
	21st to end	Night	56% 7% 15% 16% 6%	2769
December	1st to 10th	Night	58% 7% 16% 15% 4	2850
	11th to 20th	Night	70% 8% 12% 9% 1	3507
	21st to end	Night	61% 8% 17% 11% 4	5114

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	30% 18% 16% 16% 16% 4	180
	11th to 20th	Day	32% 13% 18% 19% 10% 7%	180
	21st to end	Day	30% 13% 28% 17% 11% 1	198
February	1st to 10th	Day	30% 17% 29% 16% 7% 1	180
	11th to 20th	Day	33% 16% 23% 19% 8% 1	423
	21st to end	Day	27% 16% 25% 21% 10% 1	382
March	1st to 10th	Day	26% 20% 24% 19% 9% 3	460
	11th to 20th	Day	21% 13% 21% 25% 16% 4	460
	21st to end	Day	27% 18% 23% 21% 9% 2	506
April	1st to 10th	Day	23% 15% 29% 22% 8% 3	460
	11th to 20th	Day	18% 19% 27% 19% 12% 4	452
	21st to end	Day	17% 15% 27% 24% 14% 3	460
May	1st to 10th	Day	13% 11% 23% 34% 16% 3	463
	11th to 20th	Day	15% 9% 24% 23% 19% 9%	488
	21st to end	Day	11% 11% 21% 26% 21% 9%	534
June	1st to 10th	Day	17% 9% 19% 27% 20% 8%	680
	11th to 20th	Day	15% 14% 28% 25% 15% 4	680
	21st to end	Day	7% 6% 23% 28% 28% 8%	680
July	1st to 10th	Day	4 3 22% 35% 30% 5%	498
	11th to 20th	Day	3 6% 21% 38% 25% 6%	484
	21st to end	Day	2 6% 20% 35% 29% 8%	531
August	1st to 10th	Day	6% 4 21% 31% 28% 10%	487
	11th to 20th	Day	4 3 19% 31% 28% 14%	477
	21st to end	Day	8% 7% 26% 25% 23% 11%	539
September	1st to 10th	Day	8% 6% 24% 27% 23% 12%	490
	11th to 20th	Day	11% 9% 24% 27% 19% 10%	490
	21st to end	Day	12% 11% 24% 28% 20% 6%	490
October	1st to 10th	Day	14% 9% 26% 26% 19% 5%	490
	11th to 20th	Day	19% 13% 20% 23% 18% 8%	369
	21st to end	Day	27% 13% 22% 23% 11% 3	330
November	1st to 10th	Day	29% 19% 16% 25% 11% 1	297
	11th to 20th	Day	35% 14% 13% 20% 15% 3	239
	21st to end	Day	27% 9% 27% 19% 17% 2	180
December	1st to 10th	Day	29% 14% 21% 18% 10% 8%	180
	11th to 20th	Day	41% 13% 22% 16% 8% 2	180
	21st to end	Day	33% 11% 22% 21% 11% 3	198
January	1st to 10th	Night	37% 11% 17% 22% 11% 2	760
	11th to 20th	Night	29% 9% 17% 28% 14% 3	760
	21st to end	Night	25% 7% 18% 31% 17% 1	836
February	1st to 10th	Night	29% 11% 21% 27% 10% 2	760
	11th to 20th	Night	26% 10% 18% 30% 14% 2	744
	21st to end	Night	22% 11% 20% 28% 16% 3	628
March	1st to 10th	Night	21% 10% 19% 30% 18% 1	760
	11th to 20th	Night	19% 12% 18% 30% 20% 1	760
	21st to end	Night	21% 8% 24% 33% 12% 2	836
April	1st to 10th	Night	18% 9% 20% 33% 18% 2	760
	11th to 20th	Night	16% 10% 25% 33% 14% 2	679
	21st to end	Night	14% 8% 25% 32% 19% 2	570
May	1st to 10th	Night	10% 7% 24% 32% 25% 3	461
	11th to 20th	Night	12% 5% 14% 31% 29% 8%	374
	21st to end	Night	15% 6% 15% 31% 27% 6%	411
June	1st to 10th	Night	15% 5% 16% 34% 24% 6%	380
	11th to 20th	Night	12% 9% 23% 32% 21% 3	380
	21st to end	Night	9% 3 14% 38% 31% 5%	380
July	1st to 10th	Night	2 1 13% 42% 39% 4	370
	11th to 20th	Night	3 3 13% 48% 31% 1	368
	21st to end	Night	1 1 13% 40% 38% 6%	416
August	1st to 10th	Night	4 3 11% 39% 38% 6%	378
	11th to 20th	Night	3 2 8% 37% 40% 10%	508
	21st to end	Night	5% 5% 13% 37% 36% 5%	770
September	1st to 10th	Night	6% 3 14% 39% 31% 7%	760
	11th to 20th	Night	9% 4 15% 31% 32% 10%	760
	21st to end	Night	11% 4 19% 33% 27% 5%	760
October	1st to 10th	Night	15% 6% 13% 38% 26% 3	760
	11th to 20th	Night	16% 8% 17% 30% 25% 4	760
	21st to end	Night	21% 8% 20% 31% 15% 4	836
November	1st to 10th	Night	29% 8% 16% 33% 14% 1	778
	11th to 20th	Night	30% 9% 19% 28% 13% 1	760
	21st to end	Night	27% 9% 17% 28% 16% 3	869
December	1st to 10th	Night	26% 8% 19% 31% 16% 1	950
	11th to 20th	Night	34% 9% 16% 29% 11%	950
	21st to end	Night	36% 11% 17% 26% 10% 1	984

Page generated at 2024-11-07 03:55:44. Version ac07

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