Starr Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starr Mountain clear sky chart from 2005-11-06 to 2024-12-02.

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	14% 7% 3 6% 5% 4 5% 4 6% 7% 39%	101199
	Night	14% 8% 2 6% 4 4 4 4 5% 7% 41%	98405
Transparency	Day	41% 8% 11% 20% 16% 3	104995
	Night	39% 8% 11% 21% 17% 4	102735
Seeing	Day	19% 12% 23% 23% 17% 7%	14883
	Night	17% 10% 22% 29% 18% 3	24924

By Month

Percentage Cloud Cover SE (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	17% 14% 3 7% 4 3 4 4 6% 5% 34%	2836
	11th to 20th	Day	18% 10% 8% 8% 4 4 3 3 4 4 35%	2840
	21st to end	Day	24% 14% 3 5% 3 3 3 3 4 5% 34%	3194
February	1st to 10th	Day	19% 11% 4 8% 4 4 4 3 5% 5% 34%	1900
	11th to 20th	Day	22% 11% 3 8% 4 3 4 3 4 6% 33%	1848
	21st to end	Day	22% 11% 3 8% 5% 3 3 3 4 5% 35%	1570
March	1st to 10th	Day	24% 9% 3 6% 4 3 3 3 5% 7% 32%	3179
	11th to 20th	Day	15% 7% 3 6% 4 3 3 2 4 5% 48%	3480
	21st to end	Day	18% 9% 2 6% 4 4 4 3 4 7% 38%	3815
April	1st to 10th	Day	11% 7% 2 5% 5% 5% 6% 5% 6% 7% 41%	2190
	11th to 20th	Day	15% 7% 2 6% 4 3 4 3 5% 6% 44%	2254
	21st to end	Day	13% 7% 2 7% 5% 5% 4 3 5% 7% 42%	2444
May	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 4 6% 7% 37%	4082
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	4081
	21st to end	Day	10% 6% 2 6% 6% 5% 5% 5% 7% 8% 40%	4476
June	1st to 10th	Day	9% 6% 2 6% 6% 5% 6% 6% 8% 9% 37%	2470
	11th to 20th	Day	6% 4 2 7% 6% 6% 6% 6% 8% 11% 41%	2470
	21st to end	Day	8% 5% 2 7% 6% 6% 6% 5% 7% 11% 38%	2470
July	1st to 10th	Day	6% 5% 2 7% 6% 7% 6% 6% 10% 12% 34%	4120
	11th to 20th	Day	10% 6% 2 7% 5% 6% 6% 5% 8% 10% 36%	4120
	21st to end	Day	15% 10% 4 11% 8% 8% 7% 5% 7% 7% 19%	4466
August	1st to 10th	Day	7% 4 2 6% 5% 6% 6% 6% 7% 11% 40%	4104
	11th to 20th	Day	8% 5% 2 7% 5% 5% 5% 5% 8% 11% 39%	3831
	21st to end	Day	7% 4 2 6% 5% 5% 5% 5% 6% 7% 49%	4180
September	1st to 10th	Day	12% 6% 2 7% 6% 4 5% 4 7% 8% 39%	2123
	11th to 20th	Day	14% 6% 2 7% 5% 5% 3 5% 6% 8% 38%	2090
	21st to end	Day	14% 5% 2 6% 4 4 4 3 4 6% 47%	2090
October	1st to 10th	Day	10% 5% 2 4 4 4 3 3 4 7% 54%	2090
	11th to 20th	Day	13% 5% 2 4 3 3 3 2 4 6% 55%	1981
	21st to end	Day	14% 5% 2 4 2 3 4 3 4 6% 52%	2047
November	1st to 10th	Day	13% 5% 2 4 3 3 3 3 5% 5% 54%	1762
	11th to 20th	Day	13% 7% 2 5% 4 3 3 3 5% 6% 48%	1800
	21st to end	Day	16% 8% 3 4 3 3 5% 3 5% 6% 44%	1800
December	1st to 10th	Day	21% 10% 3 7% 4 4 4 4 6% 5% 34%	1719
	11th to 20th	Day	17% 12% 3 7% 4 4 4 4 4 5% 36%	2153
	21st to end	Day	18% 15% 3 6% 4 4 3 3 5% 7% 32%	3124
January	1st to 10th	Night	18% 13% 3 7% 4 3 3 2 3 6% 37%	4109
	11th to 20th	Night	22% 9% 3 6% 6% 3 2 3 4 4 38%	4120
	21st to end	Night	23% 14% 3 6% 4 3 3 3 4 4 35%	4459
February	1st to 10th	Night	16% 10% 3 7% 4 3 3 3 5% 6% 40%	2280
	11th to 20th	Night	23% 10% 3 7% 4 4 4 3 4 3 36%	2218
	21st to end	Night	23% 9% 3 6% 4 4 4 3 5% 7% 33%	1884
March	1st to 10th	Night	22% 10% 2 7% 5% 4 4 3 4 6% 32%	3674
	11th to 20th	Night	14% 6% 2 4 3 3 4 4 6% 7% 48%	3480
	21st to end	Night	15% 8% 3 7% 5% 5% 4 3 5% 6% 40%	3817
April	1st to 10th	Night	13% 5% 1 5% 4 4 4 4 6% 8% 47%	2005
	11th to 20th	Night	13% 7% 2 5% 4 3 3 3 5% 8% 47%	1875
	21st to end	Night	14% 6% 2 5% 4 4 4 4 6% 7% 46%	1734
May	1st to 10th	Night	14% 6% 2 7% 5% 5% 4 4 6% 8% 38%	2813
	11th to 20th	Night	19% 7% 2 6% 5% 4 4 4 5% 7% 37%	2812
	21st to end	Night	8% 6% 2 7% 5% 5% 6% 4 7% 10% 42%	3079
June	1st to 10th	Night	7% 5% 2 8% 5% 6% 6% 5% 7% 11% 37%	1710
	11th to 20th	Night	4 3 2 4 5% 3 5% 6% 8% 13% 47%	1710
	21st to end	Night	6% 4 2 6% 5% 6% 5% 4 7% 10% 44%	1710
July	1st to 10th	Night	8% 6% 2 7% 6% 7% 6% 5% 7% 11% 35%	2840
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 4 8% 11% 42%	2840
	21st to end	Night	13% 10% 4 8% 6% 7% 6% 5% 8% 9% 23%	3087
August	1st to 10th	Night	6% 4 2 6% 6% 5% 5% 4 7% 10% 44%	2825
	11th to 20th	Night	8% 5% 2 7% 4 4 5% 4 6% 9% 45%	2994
	21st to end	Night	5% 4 2 5% 4 4 5% 5% 7% 11% 49%	3476
September	1st to 10th	Night	11% 5% 3 6% 5% 4 5% 4 6% 7% 43%	2036
	11th to 20th	Night	13% 6% 3 7% 4 4 4 4 6% 8% 41%	2090
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 6% 49%	2090
October	1st to 10th	Night	12% 5% 1 4 3 3 3 2 3 6% 58%	2090
	11th to 20th	Night	15% 4 2 4 4 4 3 2 4 5% 54%	2197
	21st to end	Night	14% 6% 2 4 2 3 3 3 4 5% 54%	2546
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 2 5% 5% 52%	2536
	11th to 20th	Night	13% 8% 2 5% 3 3 3 3 5% 6% 49%	2600
	21st to end	Night	15% 8% 3 5% 4 4 4 3 5% 5% 44%	2600
December	1st to 10th	Night	19% 10% 3 7% 5% 4 4 3 5% 6% 34%	2495
	11th to 20th	Night	18% 10% 3 7% 4 3 3 2 3 6% 40%	3042
	21st to end	Night	18% 12% 3 7% 5% 5% 5% 4 5% 6% 29%	4532

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	48% 6% 8% 15% 21% 1	2837
	11th to 20th	Day	51% 6% 8% 13% 20% 2	2840
	21st to end	Day	51% 5% 8% 18% 16% 2	3194
February	1st to 10th	Day	51% 6% 7% 16% 16% 3	1900
	11th to 20th	Day	53% 4 7% 17% 15% 3	1858
	21st to end	Day	52% 5% 8% 12% 18% 5%	1570
March	1st to 10th	Day	50% 6% 11% 14% 12% 7%	3179
	11th to 20th	Day	39% 5% 7% 20% 21% 7%	3480
	21st to end	Day	46% 7% 9% 24% 13% 2	3815
April	1st to 10th	Day	39% 9% 11% 21% 17% 3	2190
	11th to 20th	Day	40% 5% 8% 18% 24% 5%	2254
	21st to end	Day	40% 7% 10% 26% 14% 2	2444
May	1st to 10th	Day	43% 11% 12% 20% 13% 2	4120
	11th to 20th	Day	47% 10% 11% 22% 9% 1	4085
	21st to end	Day	37% 11% 13% 22% 16% 2	4489
June	1st to 10th	Day	39% 12% 15% 22% 10% 2	2470
	11th to 20th	Day	34% 11% 18% 23% 12% 2	2470
	21st to end	Day	38% 12% 17% 17% 13% 3	2470
July	1st to 10th	Day	37% 14% 21% 19% 8% 1	4055
	11th to 20th	Day	40% 11% 21% 20% 6% 2	4051
	21st to end	Day	61% 10% 12% 12% 4	4324
August	1st to 10th	Day	34% 11% 16% 30% 8% 1	4091
	11th to 20th	Day	34% 11% 18% 23% 13% 1	3870
	21st to end	Day	32% 10% 11% 32% 14% 1	4179
September	1st to 10th	Day	39% 10% 14% 16% 16% 5%	2123
	11th to 20th	Day	41% 11% 10% 20% 16% 2	2090
	21st to end	Day	37% 7% 13% 18% 19% 6%	2090
October	1st to 10th	Day	25% 6% 7% 18% 35% 10%	3480
	11th to 20th	Day	22% 4 5% 22% 31% 16%	3273
	21st to end	Day	25% 5% 7% 28% 25% 10%	3349
November	1st to 10th	Day	33% 4 9% 18% 29% 7%	1762
	11th to 20th	Day	36% 6% 6% 22% 25% 6%	1800
	21st to end	Day	40% 5% 9% 21% 22% 4	1800
December	1st to 10th	Day	51% 7% 7% 19% 14% 3	1719
	11th to 20th	Day	49% 5% 8% 16% 19% 3	2150
	21st to end	Day	50% 6% 9% 22% 11% 2	3124
January	1st to 10th	Night	49% 5% 8% 18% 18% 2	4109
	11th to 20th	Night	49% 6% 6% 15% 17% 7%	4120
	21st to end	Night	53% 5% 7% 14% 19% 1	4459
February	1st to 10th	Night	46% 5% 10% 19% 19% 3	2280
	11th to 20th	Night	53% 5% 6% 16% 15% 5%	2219
	21st to end	Night	52% 6% 7% 15% 15% 4	1884
March	1st to 10th	Night	51% 8% 11% 13% 14% 4	3674
	11th to 20th	Night	34% 7% 10% 22% 19% 9%	3480
	21st to end	Night	43% 7% 10% 21% 17% 2	3817
April	1st to 10th	Night	34% 7% 12% 21% 22% 4	2005
	11th to 20th	Night	35% 6% 10% 21% 21% 6%	1875
	21st to end	Night	37% 7% 12% 27% 16% 1	1734
May	1st to 10th	Night	40% 11% 14% 22% 12% 1	2840
	11th to 20th	Night	44% 11% 14% 21% 11%	2813
	21st to end	Night	31% 14% 15% 24% 14% 1	3087
June	1st to 10th	Night	37% 12% 16% 22% 11% 2	1710
	11th to 20th	Night	26% 11% 22% 26% 13% 1	1710
	21st to end	Night	33% 11% 19% 21% 12% 4	1710
July	1st to 10th	Night	40% 11% 21% 21% 6% 1	2795
	11th to 20th	Night	33% 11% 23% 24% 6% 3	2786
	21st to end	Night	54% 12% 14% 13% 5% 1	2988
August	1st to 10th	Night	32% 9% 17% 31% 10%	2814
	11th to 20th	Night	32% 10% 22% 24% 11% 1	3021
	21st to end	Night	26% 9% 16% 33% 14% 1	3476
September	1st to 10th	Night	39% 8% 16% 17% 14% 5%	2036
	11th to 20th	Night	39% 11% 12% 19% 19% 1	2090
	21st to end	Night	34% 7% 11% 21% 20% 6%	2090
October	1st to 10th	Night	25% 5% 8% 20% 29% 14%	3480
	11th to 20th	Night	22% 4 6% 19% 33% 17%	3644
	21st to end	Night	22% 4 5% 29% 28% 12%	4182
November	1st to 10th	Night	34% 5% 9% 21% 24% 8%	2536
	11th to 20th	Night	36% 5% 6% 20% 24% 8%	2600
	21st to end	Night	41% 5% 6% 22% 22% 4	2600
December	1st to 10th	Night	50% 7% 8% 18% 14% 3	2495
	11th to 20th	Night	45% 6% 8% 15% 24% 2	3044
	21st to end	Night	52% 7% 9% 19% 11% 1	4532

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% 23% 34% 10% 3	270
	11th to 20th	Day	32% 24% 28% 11% 4	270
	21st to end	Day	24% 30% 33% 10% 3	297
February	1st to 10th	Day	28% 23% 34% 12% 3	270
	11th to 20th	Day	39% 28% 24% 9% 1	270
	21st to end	Day	41% 26% 28% 6%	225
March	1st to 10th	Day	29% 22% 27% 18% 4	303
	11th to 20th	Day	28% 22% 28% 17% 5% 1	460
	21st to end	Day	28% 19% 30% 17% 7%	506
April	1st to 10th	Day	22% 20% 27% 20% 10% 1	460
	11th to 20th	Day	23% 16% 29% 22% 8% 2	452
	21st to end	Day	20% 14% 28% 24% 11% 3	460
May	1st to 10th	Day	16% 14% 31% 24% 9% 5%	463
	11th to 20th	Day	15% 8% 24% 29% 17% 7%	487
	21st to end	Day	14% 7% 22% 27% 18% 12%	529
June	1st to 10th	Day	10% 7% 21% 29% 24% 9%	490
	11th to 20th	Day	9% 4 16% 28% 28% 15%	490
	21st to end	Day	10% 4 20% 28% 21% 16%	490
July	1st to 10th	Day	11% 4 12% 26% 30% 17%	485
	11th to 20th	Day	11% 4 10% 27% 30% 18%	484
	21st to end	Day	14% 3 11% 24% 30% 18%	532
August	1st to 10th	Day	15% 4 12% 28% 22% 20%	486
	11th to 20th	Day	14% 4 15% 28% 26% 13%	479
	21st to end	Day	14% 3 11% 24% 32% 16%	539
September	1st to 10th	Day	12% 4 14% 26% 30% 14%	490
	11th to 20th	Day	17% 5% 13% 25% 25% 15%	490
	21st to end	Day	17% 6% 14% 31% 26% 6%	490
October	1st to 10th	Day	13% 6% 21% 31% 22% 7%	490
	11th to 20th	Day	15% 12% 27% 26% 18% 2	490
	21st to end	Day	20% 10% 24% 27% 16% 3	496
November	1st to 10th	Day	21% 14% 28% 22% 14% 1	300
	11th to 20th	Day	20% 17% 33% 25% 5%	300
	21st to end	Day	20% 17% 39% 13% 10%	300
December	1st to 10th	Day	30% 21% 27% 18% 4	273
	11th to 20th	Day	27% 15% 33% 19% 6%	270
	21st to end	Day	25% 24% 31% 17% 3	297
January	1st to 10th	Night	25% 20% 29% 23% 3	760
	11th to 20th	Night	27% 18% 28% 22% 5%	760
	21st to end	Night	23% 17% 31% 26% 2	836
February	1st to 10th	Night	21% 15% 33% 28% 4	760
	11th to 20th	Night	29% 20% 30% 20% 1	743
	21st to end	Night	30% 18% 29% 20% 2	628
March	1st to 10th	Night	21% 16% 32% 26% 4	760
	11th to 20th	Night	22% 18% 29% 23% 7% 1	760
	21st to end	Night	22% 15% 29% 26% 9%	836
April	1st to 10th	Night	15% 19% 27% 29% 8% 1	675
	11th to 20th	Night	16% 13% 33% 27% 11% 1	563
	21st to end	Night	15% 8% 29% 37% 11% 1	570
May	1st to 10th	Night	12% 8% 29% 34% 16% 2	570
	11th to 20th	Night	15% 7% 20% 32% 22% 4	561
	21st to end	Night	10% 4 13% 36% 31% 6%	617
June	1st to 10th	Night	9% 5% 14% 37% 32% 4	570
	11th to 20th	Night	5% 1 13% 34% 36% 11%	570
	21st to end	Night	9% 1 10% 35% 37% 8%	570
July	1st to 10th	Night	11% 2 9% 27% 43% 8%	555
	11th to 20th	Night	11% 1 7% 26% 43% 11%	552
	21st to end	Night	10% 2 8% 28% 44% 9%	624
August	1st to 10th	Night	10% 1 7% 29% 45% 8%	567
	11th to 20th	Night	9% 2 10% 34% 40% 4	564
	21st to end	Night	11% 2 9% 29% 41% 7%	627
September	1st to 10th	Night	12% 3 10% 29% 39% 7%	706
	11th to 20th	Night	15% 4 13% 33% 31% 5%	760
	21st to end	Night	15% 4 17% 37% 26% 2	760
October	1st to 10th	Night	13% 6% 19% 30% 26% 5%	760
	11th to 20th	Night	16% 8% 25% 31% 19% 1	760
	21st to end	Night	16% 9% 23% 35% 15% 2	836
November	1st to 10th	Night	16% 8% 22% 35% 17% 2	780
	11th to 20th	Night	16% 15% 28% 29% 11% 1	800
	21st to end	Night	20% 13% 28% 28% 11% 1	800
December	1st to 10th	Night	26% 16% 24% 27% 7%	768
	11th to 20th	Night	23% 12% 28% 29% 8%	760
	21st to end	Night	26% 15% 25% 30% 4	836

Page generated at 2024-11-29 10:43:10. Version ac07

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