Washoe Zephyr Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Washoe Zephyr Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	2 4 1 4 3 3 3 3 5% 6% 66%	105419
	Night	2 4 2 4 3 3 3 3 5% 7% 64%	103090
Transparency	Day	19% 5% 10% 18% 25% 22%	105163
	Night	21% 7% 12% 20% 23% 17%	102935
Seeing	Day	8% 16% 27% 27% 18% 5%	15131
	Night	5% 10% 23% 35% 23% 4	24513

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	1 6% 3 7% 5% 5% 4 4 7% 10% 48%	2539
	11th to 20th	Day	1 5% 2 7% 5% 5% 6% 5% 6% 9% 48%	2581
	21st to end	Day	3 8% 3 8% 6% 6% 7% 5% 7% 9% 39%	3146
February	1st to 10th	Day	3 5% 3 4 4 4 4 4 6% 10% 54%	1719
	11th to 20th	Day	1 6% 3 6% 4 3 5% 5% 6% 8% 53%	1850
	21st to end	Day	1 6% 2 4 4 3 5% 4 8% 10% 55%	1570
March	1st to 10th	Day	1 7% 6% 9% 5% 5% 6% 5% 8% 11% 37%	3138
	11th to 20th	Day	1 4 1 4 3 3 4 4 5% 7% 65%	3419
	21st to end	Day	2 9% 3 6% 5% 4 5% 4 6% 9% 50%	4088
April	1st to 10th	Day	2 5% 2 5% 5% 5% 4 4 6% 9% 54%	2280
	11th to 20th	Day	2 4 2 4 4 3 4 4 6% 9% 57%	2249
	21st to end	Day	3 5% 1 4 4 3 3 4 5% 6% 62%	2280
May	1st to 10th	Day	2 4 1 3 3 3 3 2 4 7% 69%	4007
	11th to 20th	Day	2 3 1 3 3 2 3 2 4 6% 72%	4300
	21st to end	Day	4 3 2 4 3 3 3 3 5% 6% 65%	4813
June	1st to 10th	Day	3 3 1 4 4 3 4 3 5% 8% 61%	2660
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 77%	2660
	21st to end	Day	2 1 1 3 2 2 2 2 4 4 77%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 3 89%	4420
	11th to 20th	Day	3 2 1 3 3 2 2 3 4 4 74%	4420
	21st to end	Day	2 1 1 2 2 2 3 2 3 4 79%	4710
August	1st to 10th	Day	3 2 1 2 2 2 3 2 3 4 76%	4035
	11th to 20th	Day	1 1 1 1 1 2 2 2 3 86%	3724
	21st to end	Day	1 1 1 1 1 1 1 1 2 2 88%	4180
September	1st to 10th	Day	1 1 1 1 1 2 2 3 5% 82%	2280
	11th to 20th	Day	2 2 1 3 2 3 2 2 3 5% 75%	2242
	21st to end	Day	2 1 1 3 2 2 2 2 2 5% 78%	2090
October	1st to 10th	Day	2 2 1 2 2 2 2 2 4 6% 75%	3247
	11th to 20th	Day	2 4 1 2 2 2 2 2 3 4 76%	3161
	21st to end	Day	1 2 1 2 2 3 3 3 5% 7% 69%	3338
November	1st to 10th	Day	2 4 2 4 4 3 4 4 6% 7% 61%	1764
	11th to 20th	Day	2 2 1 3 3 3 4 4 7% 9% 61%	1800
	21st to end	Day	2 4 1 5% 3 4 4 5% 5% 10% 57%	1743
December	1st to 10th	Day	3 5% 2 4 4 4 4 4 8% 10% 52%	1584
	11th to 20th	Day	2 8% 2 8% 6% 6% 5% 6% 9% 9% 37%	1928
	21st to end	Day	2 6% 4 8% 5% 4 5% 5% 8% 11% 42%	2794
January	1st to 10th	Night	1 5% 3 6% 4 4 5% 5% 7% 11% 50%	4406
	11th to 20th	Night	1 6% 3 8% 7% 6% 6% 6% 7% 9% 43%	4376
	21st to end	Night	4 9% 3 8% 5% 5% 5% 4 7% 8% 42%	4521
February	1st to 10th	Night	2 5% 2 5% 4 4 5% 4 6% 8% 55%	2460
	11th to 20th	Night	1 5% 2 5% 3 3 4 5% 7% 9% 55%	2218
	21st to end	Night	2 4 1 6% 4 4 4 4 5% 10% 55%	1884
March	1st to 10th	Night	1 7% 5% 7% 5% 5% 5% 4 7% 9% 44%	3736
	11th to 20th	Night	1 4 2 4 3 3 4 4 5% 7% 63%	3557
	21st to end	Night	3 10% 3 6% 4 4 5% 4 7% 8% 47%	3564
April	1st to 10th	Night	2 4 2 3 4 4 4 4 9% 9% 55%	1900
	11th to 20th	Night	2 4 2 3 3 4 4 4 7% 7% 61%	1879
	21st to end	Night	3 3 1 3 3 3 3 3 4 7% 65%	1900
May	1st to 10th	Night	3 3 1 3 2 2 3 3 4 5% 72%	2965
	11th to 20th	Night	1 2 1 3 1 2 3 2 4 6% 75%	2592
	21st to end	Night	4 3 1 3 2 2 3 3 4 7% 68%	2762
June	1st to 10th	Night	4 4 2 4 3 3 3 3 5% 6% 64%	1520
	11th to 20th	Night	1 1 1 2 2 2 2 2 4 5% 79%	1520
	21st to end	Night	3 2 1 2 2 2 2 2 2 4 79%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 89%	2540
	11th to 20th	Night	4 2 1 3 3 2 2 2 3 4 74%	2540
	21st to end	Night	3 1 2 2 2 2 2 3 4 78%	2840
August	1st to 10th	Night	3 2 1 3 2 2 3 2 4 5% 74%	2903
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 86%	3126
	21st to end	Night	2 2 1 1 1 1 1 1 2 2 86%	3498
September	1st to 10th	Night	2 1 1 1 1 1 1 2 4 85%	1900
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 4 77%	1937
	21st to end	Night	2 2 1 3 2 2 3 2 3 4 78%	2090
October	1st to 10th	Night	2 2 1 2 2 2 2 2 3 4 79%	3728
	11th to 20th	Night	1 2 1 2 1 2 2 2 3 4 81%	3777
	21st to end	Night	2 3 1 4 2 3 3 3 4 6% 70%	4225
November	1st to 10th	Night	2 3 1 4 3 3 4 3 6% 7% 64%	2535
	11th to 20th	Night	1 3 1 4 3 3 3 3 6% 10% 64%	2600
	21st to end	Night	1 4 2 4 3 3 3 4 7% 8% 59%	2655
December	1st to 10th	Night	3 5% 2 5% 3 4 4 3 7% 8% 56%	2778
	11th to 20th	Night	3 7% 3 6% 5% 4 6% 5% 8% 11% 41%	3276
	21st to end	Night	2 7% 3 8% 6% 6% 6% 5% 8% 9% 42%	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	31% 10% 21% 26% 11%	2539
	11th to 20th	Day	33% 11% 17% 25% 10% 4	2581
	21st to end	Day	40% 10% 14% 22% 12% 1	3146
February	1st to 10th	Day	28% 8% 15% 26% 17% 6%	1719
	11th to 20th	Day	29% 6% 16% 28% 17% 4	1860
	21st to end	Day	25% 9% 21% 25% 17% 4	1570
March	1st to 10th	Day	38% 11% 21% 16% 13% 1	3138
	11th to 20th	Day	19% 7% 14% 32% 24% 3	3419
	21st to end	Day	30% 9% 21% 21% 17% 2	4088
April	1st to 10th	Day	27% 9% 17% 22% 19% 5%	2280
	11th to 20th	Day	24% 8% 14% 27% 21% 6%	2252
	21st to end	Day	21% 8% 14% 29% 24% 4	2280
May	1st to 10th	Day	18% 5% 8% 32% 31% 7%	4007
	11th to 20th	Day	14% 4 8% 19% 40% 15%	4303
	21st to end	Day	20% 5% 9% 25% 35% 6%	4814
June	1st to 10th	Day	20% 5% 10% 21% 32% 11%	2660
	11th to 20th	Day	12% 3 7% 20% 35% 24%	2660
	21st to end	Day	12% 3 4 10% 31% 41%	2660
July	1st to 10th	Day	4 2 3 5% 14% 73%	4351
	11th to 20th	Day	14% 2 4 7% 16% 57%	4345
	21st to end	Day	9% 2 4 6% 24% 55%	4561
August	1st to 10th	Day	13% 2 4 6% 21% 54%	4020
	11th to 20th	Day	6% 2 3 3 21% 65%	3760
	21st to end	Day	6% 1 2 7% 36% 47%	4179
September	1st to 10th	Day	8% 2 4 8% 30% 49%	2280
	11th to 20th	Day	13% 3 6% 16% 35% 26%	2242
	21st to end	Day	13% 2 6% 16% 37% 27%	2090
October	1st to 10th	Day	12% 3 5% 12% 37% 31%	3247
	11th to 20th	Day	13% 3 6% 19% 47% 13%	3161
	21st to end	Day	13% 5% 9% 28% 34% 12%	3338
November	1st to 10th	Day	22% 7% 14% 23% 26% 8%	1764
	11th to 20th	Day	18% 8% 18% 26% 26% 4	1800
	21st to end	Day	24% 8% 13% 24% 26% 6%	1743
December	1st to 10th	Day	27% 9% 15% 25% 20% 5%	1584
	11th to 20th	Day	41% 11% 14% 19% 12% 3	1928
	21st to end	Day	32% 11% 20% 23% 13% 2	2794
January	1st to 10th	Night	28% 10% 23% 26% 12% 1	4406
	11th to 20th	Night	36% 11% 21% 18% 11% 4	4376
	21st to end	Night	40% 10% 16% 21% 11% 2	4521
February	1st to 10th	Night	28% 9% 15% 24% 18% 6%	2460
	11th to 20th	Night	23% 9% 18% 30% 18% 3	2219
	21st to end	Night	26% 7% 19% 27% 16% 5%	1884
March	1st to 10th	Night	33% 10% 19% 21% 14% 3	3736
	11th to 20th	Night	20% 8% 13% 38% 17% 3	3557
	21st to end	Night	33% 11% 23% 20% 11% 2	3564
April	1st to 10th	Night	22% 11% 18% 27% 16% 5%	1900
	11th to 20th	Night	21% 9% 17% 30% 18% 6%	1879
	21st to end	Night	20% 8% 16% 32% 21% 3	1900
May	1st to 10th	Night	15% 5% 11% 34% 30% 5%	2965
	11th to 20th	Night	12% 5% 8% 23% 37% 14%	2592
	21st to end	Night	17% 6% 12% 29% 32% 4	2762
June	1st to 10th	Night	21% 7% 9% 23% 29% 11%	1520
	11th to 20th	Night	10% 4 6% 21% 37% 22%	1520
	21st to end	Night	12% 2 6% 12% 33% 35%	1520
July	1st to 10th	Night	4 1 2 4 17% 70%	2500
	11th to 20th	Night	16% 2 3 7% 15% 56%	2492
	21st to end	Night	10% 2 5% 5% 25% 53%	2751
August	1st to 10th	Night	13% 3 4 8% 25% 46%	2894
	11th to 20th	Night	7% 1 3 5% 24% 60%	3156
	21st to end	Night	8% 1 3 9% 37% 42%	3498
September	1st to 10th	Night	6% 2 4 7% 37% 45%	1900
	11th to 20th	Night	12% 2 7% 20% 34% 24%	1937
	21st to end	Night	12% 2 6% 18% 36% 25%	2090
October	1st to 10th	Night	11% 2 6% 12% 34% 35%	3728
	11th to 20th	Night	9% 3 6% 19% 47% 15%	3777
	21st to end	Night	13% 5% 9% 26% 35% 12%	4225
November	1st to 10th	Night	20% 6% 14% 25% 23% 11%	2535
	11th to 20th	Night	18% 7% 14% 29% 27% 5%	2600
	21st to end	Night	21% 9% 12% 26% 25% 7%	2655
December	1st to 10th	Night	27% 10% 15% 24% 20% 5%	2778
	11th to 20th	Night	35% 13% 15% 20% 15% 3	3276
	21st to end	Night	36% 11% 20% 18% 12% 3	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	13% 19% 32% 21% 13% 2	180
	11th to 20th	Day	12% 13% 32% 22% 17% 3	208
	21st to end	Day	7% 13% 32% 28% 16% 4	407
February	1st to 10th	Day	12% 14% 28% 27% 16% 3	374
	11th to 20th	Day	7% 22% 27% 30% 13% 1	455
	21st to end	Day	9% 21% 25% 34% 11%	382
March	1st to 10th	Day	12% 23% 32% 21% 9% 2	460
	11th to 20th	Day	10% 24% 27% 22% 14% 3	460
	21st to end	Day	12% 25% 28% 25% 9%	506
April	1st to 10th	Day	12% 24% 28% 22% 10% 4	460
	11th to 20th	Day	14% 26% 26% 19% 13% 2	452
	21st to end	Day	12% 20% 28% 23% 13% 4	460
May	1st to 10th	Day	13% 22% 27% 24% 11% 3	463
	11th to 20th	Day	12% 22% 23% 23% 14% 6%	488
	21st to end	Day	10% 16% 21% 27% 20% 6%	529
June	1st to 10th	Day	8% 16% 26% 23% 22% 5%	490
	11th to 20th	Day	9% 17% 31% 24% 15% 4	490
	21st to end	Day	3 12% 28% 29% 23% 5%	490
July	1st to 10th	Day	2 11% 31% 29% 21% 6%	486
	11th to 20th	Day	2 9% 28% 31% 22% 7%	484
	21st to end	Day	2 7% 27% 30% 26% 7%	531
August	1st to 10th	Day	3 11% 27% 27% 25% 7%	487
	11th to 20th	Day	2 11% 24% 29% 24% 11%	477
	21st to end	Day	4 7% 29% 31% 24% 5%	539
September	1st to 10th	Day	2 9% 27% 32% 23% 7%	490
	11th to 20th	Day	6% 15% 24% 27% 22% 5%	490
	21st to end	Day	5% 12% 25% 37% 17% 4	490
October	1st to 10th	Day	5% 13% 27% 26% 22% 6%	490
	11th to 20th	Day	8% 12% 21% 30% 23% 6%	490
	21st to end	Day	8% 14% 27% 26% 21% 5%	478
November	1st to 10th	Day	11% 14% 23% 24% 20% 9%	300
	11th to 20th	Day	6% 15% 23% 28% 20% 8%	300
	21st to end	Day	8% 14% 23% 28% 20% 6%	271
December	1st to 10th	Day	12% 11% 23% 22% 22% 10%	196
	11th to 20th	Day	5% 19% 33% 22% 13% 7%	180
	21st to end	Day	15% 16% 23% 29% 15% 3	198
January	1st to 10th	Night	6% 13% 29% 26% 18% 8%	760
	11th to 20th	Night	5% 12% 24% 37% 17% 5%	760
	21st to end	Night	6% 7% 29% 33% 19% 5%	836
February	1st to 10th	Night	5% 12% 25% 35% 19% 3	760
	11th to 20th	Night	4 13% 26% 35% 18% 5%	744
	21st to end	Night	7% 15% 25% 36% 14% 3	628
March	1st to 10th	Night	6% 15% 34% 27% 14% 4	760
	11th to 20th	Night	4 17% 26% 26% 24% 3	760
	21st to end	Night	5% 20% 29% 31% 14% 1	836
April	1st to 10th	Night	5% 14% 29% 31% 19% 1	760
	11th to 20th	Night	7% 16% 25% 32% 17% 4	751
	21st to end	Night	6% 13% 25% 33% 20% 4	760
May	1st to 10th	Night	6% 15% 24% 32% 20% 3	636
	11th to 20th	Night	4 8% 22% 40% 23% 2	424
	21st to end	Night	6% 7% 17% 40% 28% 2	411
June	1st to 10th	Night	5% 5% 22% 38% 26% 4	380
	11th to 20th	Night	1 6% 22% 43% 27% 2	380
	21st to end	Night	3 3 18% 45% 30% 2	380
July	1st to 10th	Night	1 2 14% 51% 31% 2	370
	11th to 20th	Night	1 1 18% 51% 28% 1	368
	21st to end	Night	4 1 10% 45% 36% 5%	459
August	1st to 10th	Night	4 1 14% 43% 36% 3	596
	11th to 20th	Night	2 3 17% 44% 29% 5%	752
	21st to end	Night	3 2 17% 45% 28% 3	836
September	1st to 10th	Night	2 2 17% 38% 35% 5%	760
	11th to 20th	Night	3 5% 19% 32% 35% 6%	760
	21st to end	Night	2 5% 21% 35% 29% 8%	760
October	1st to 10th	Night	4 6% 20% 36% 28% 6%	760
	11th to 20th	Night	4 8% 15% 38% 28% 7%	760
	21st to end	Night	4 8% 19% 32% 26% 11%	836
November	1st to 10th	Night	5% 12% 21% 28% 28% 7%	780
	11th to 20th	Night	5% 10% 27% 35% 19% 5%	800
	21st to end	Night	7% 9% 26% 30% 23% 5%	800
December	1st to 10th	Night	7% 11% 24% 34% 19% 5%	794
	11th to 20th	Night	7% 14% 26% 31% 16% 6%	760
	21st to end	Night	8% 12% 31% 33% 13% 3	836

Page generated at 2024-12-06 00:54:51. Version ac07

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