Horsethief Lake State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Horsethief Lake State Park 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	8% 7% 3 6% 4 4 4 4 5% 7% 49%	105436
	Night	10% 8% 3 7% 4 4 4 4 5% 7% 43%	102417
Transparency	Day	36% 5% 13% 23% 16% 7%	105179
	Night	41% 6% 14% 22% 12% 5%	102263
Seeing	Day	16% 15% 27% 23% 14% 5%	14551
	Night	15% 10% 24% 32% 17% 2	23541

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	17% 19% 6% 11% 6% 6% 5% 5% 5% 6% 13%	2539
	11th to 20th	Day	23% 18% 5% 9% 6% 5% 5% 3 5% 8% 13%	2540
	21st to end	Day	25% 19% 7% 12% 7% 5% 4 3 4 4 10%	2894
February	1st to 10th	Day	13% 14% 4 11% 6% 6% 6% 4 5% 8% 22%	1710
	11th to 20th	Day	11% 11% 3 8% 5% 6% 6% 5% 7% 7% 29%	1665
	21st to end	Day	10% 10% 3 8% 7% 6% 5% 6% 9% 7% 28%	1558
March	1st to 10th	Day	7% 10% 4 9% 7% 6% 8% 6% 8% 9% 25%	3138
	11th to 20th	Day	8% 7% 2 6% 5% 4 4 5% 6% 10% 42%	3485
	21st to end	Day	9% 10% 3 9% 6% 6% 6% 5% 7% 9% 30%	4010
April	1st to 10th	Day	8% 8% 3 7% 6% 5% 6% 5% 7% 8% 35%	2280
	11th to 20th	Day	7% 9% 2 6% 6% 5% 5% 5% 7% 8% 40%	2249
	21st to end	Day	5% 5% 2 5% 4 6% 5% 5% 8% 10% 45%	2418
May	1st to 10th	Day	10% 5% 2 5% 4 4 5% 3 5% 7% 51%	4420
	11th to 20th	Day	4 3 1 3 3 3 3 2 5% 8% 66%	4377
	21st to end	Day	6% 5% 2 6% 5% 4 6% 5% 7% 8% 46%	4813
June	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 6% 8% 48%	2660
	11th to 20th	Day	4 3 1 4 4 4 4 5% 5% 8% 57%	2660
	21st to end	Day	3 2 1 3 3 3 3 3 5% 7% 69%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 3 4 85%	4420
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 3 85%	4420
	21st to end	Day	1 1 1 2 1 1 2 2 3 4 82%	4790
August	1st to 10th	Day	2 2 1 3 2 2 3 2 3 5% 75%	4317
	11th to 20th	Day	1 2 1 3 2 2 3 3 5% 6% 72%	4026
	21st to end	Day	3 3 1 4 3 3 3 3 4 5% 68%	4190
September	1st to 10th	Day	2 2 1 2 1 2 2 2 3 6% 76%	2280
	11th to 20th	Day	4 3 1 4 4 4 4 4 6% 6% 61%	2280
	21st to end	Day	7% 4 1 5% 3 4 4 3 5% 6% 58%	2034
October	1st to 10th	Day	5% 4 1 4 3 3 4 3 6% 7% 60%	3180
	11th to 20th	Day	6% 5% 2 7% 5% 6% 5% 5% 7% 9% 42%	3161
	21st to end	Day	10% 7% 3 9% 6% 6% 6% 5% 7% 8% 35%	3232
November	1st to 10th	Day	15% 11% 3 9% 7% 7% 5% 5% 7% 8% 24%	1740
	11th to 20th	Day	14% 14% 5% 10% 6% 6% 7% 5% 7% 6% 19%	1528
	21st to end	Day	14% 11% 4 11% 6% 7% 5% 5% 5% 7% 25%	1520
December	1st to 10th	Day	13% 15% 7% 11% 5% 6% 4 4 6% 6% 23%	1520
	11th to 20th	Day	17% 18% 8% 15% 8% 5% 5% 3 5% 5% 10%	1928
	21st to end	Day	19% 22% 7% 14% 6% 5% 3 3 4 4 12%	2794
January	1st to 10th	Night	20% 19% 6% 11% 6% 5% 5% 4 5% 5% 13%	4406
	11th to 20th	Night	25% 16% 5% 9% 5% 5% 4 3 5% 10% 14%	4420
	21st to end	Night	26% 17% 6% 13% 7% 5% 4 2 3 4 12%	4763
February	1st to 10th	Night	14% 13% 4 9% 5% 5% 5% 4 6% 7% 27%	2470
	11th to 20th	Night	12% 11% 3 8% 5% 5% 4 4 5% 7% 34%	2402
	21st to end	Night	10% 12% 3 8% 6% 5% 5% 5% 7% 8% 29%	1895
March	1st to 10th	Night	8% 9% 3 9% 6% 6% 8% 7% 8% 8% 27%	3736
	11th to 20th	Night	7% 6% 2 6% 5% 3 4 3 7% 6% 50%	3491
	21st to end	Night	9% 7% 3 7% 7% 7% 7% 5% 8% 9% 30%	3630
April	1st to 10th	Night	9% 8% 2 7% 4 5% 5% 5% 9% 8% 38%	1900
	11th to 20th	Night	6% 6% 3 7% 5% 5% 4 4 7% 7% 46%	1879
	21st to end	Night	6% 5% 2 5% 5% 4 5% 4 7% 9% 48%	1758
May	1st to 10th	Night	10% 6% 2 4 4 3 4 3 5% 5% 54%	2540
	11th to 20th	Night	4 2 1 3 2 3 3 3 5% 7% 68%	2516
	21st to end	Night	3 4 1 4 4 4 5% 5% 6% 10% 55%	2762
June	1st to 10th	Night	9% 5% 1 5% 4 5% 5% 4 6% 7% 48%	1520
	11th to 20th	Night	4 4 1 3 3 3 4 2 6% 8% 61%	1520
	21st to end	Night	2 3 1 3 3 3 3 2 4 5% 70%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 87%	2540
	11th to 20th	Night	1 2 1 1 2 2 2 3 3 83%	2540
	21st to end	Night	1 1 1 1 1 1 2 2 4 86%	2761
August	1st to 10th	Night	3 2 1 3 1 3 3 2 4 5% 75%	2613
	11th to 20th	Night	1 2 2 2 3 3 3 4 6% 74%	2812
	21st to end	Night	1 2 1 3 2 3 3 2 4 6% 73%	3488
September	1st to 10th	Night	1 1 1 2 2 2 3 2 4 5% 77%	1900
	11th to 20th	Night	4 3 1 3 3 3 4 3 5% 6% 63%	1900
	21st to end	Night	6% 4 1 4 3 3 3 3 6% 7% 62%	2141
October	1st to 10th	Night	5% 3 1 3 3 3 4 3 5% 7% 64%	3800
	11th to 20th	Night	6% 5% 2 5% 4 5% 5% 4 8% 9% 47%	3777
	21st to end	Night	10% 6% 2 8% 4 5% 7% 5% 7% 8% 38%	4330
November	1st to 10th	Night	15% 9% 3 8% 5% 6% 5% 5% 6% 7% 31%	2555
	11th to 20th	Night	16% 13% 3 10% 6% 5% 6% 5% 6% 6% 24%	2674
	21st to end	Night	11% 11% 4 9% 6% 6% 6% 5% 6% 7% 29%	2660
December	1st to 10th	Night	16% 15% 5% 11% 6% 4 6% 4 5% 5% 23%	2660
	11th to 20th	Night	20% 16% 6% 14% 8% 6% 5% 3 5% 5% 11%	3276
	21st to end	Night	18% 19% 7% 12% 6% 6% 4 3 4 5% 16%	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	73% 6% 10% 11%	2539
	11th to 20th	Day	72% 4 16% 7% 1	2540
	21st to end	Day	80% 5% 7% 6% 2	2894
February	1st to 10th	Day	61% 9% 17% 11% 2	1710
	11th to 20th	Day	52% 9% 18% 17% 4	1674
	21st to end	Day	51% 10% 17% 14% 8%	1558
March	1st to 10th	Day	50% 10% 12% 21% 7%	3138
	11th to 20th	Day	37% 6% 18% 33% 7%	3485
	21st to end	Day	51% 7% 16% 21% 5%	4010
April	1st to 10th	Day	44% 9% 18% 20% 8%	2280
	11th to 20th	Day	41% 7% 19% 19% 11% 3	2252
	21st to end	Day	33% 8% 20% 25% 12% 2	2418
May	1st to 10th	Day	33% 5% 12% 28% 20% 2	4420
	11th to 20th	Day	20% 3 12% 39% 22% 4	4380
	21st to end	Day	35% 7% 24% 26% 7%	4814
June	1st to 10th	Day	34% 6% 15% 30% 13% 3	2660
	11th to 20th	Day	26% 4 16% 37% 13% 3	2660
	21st to end	Day	18% 3 15% 35% 21% 8%	2660
July	1st to 10th	Day	6% 2 7% 18% 29% 38%	4351
	11th to 20th	Day	8% 2 5% 13% 27% 45%	4345
	21st to end	Day	9% 2 7% 23% 38% 22%	4639
August	1st to 10th	Day	15% 2 6% 20% 34% 23%	4301
	11th to 20th	Day	15% 2 11% 39% 24% 8%	4065
	21st to end	Day	22% 2 11% 26% 31% 7%	4189
September	1st to 10th	Day	12% 2 9% 34% 28% 14%	2280
	11th to 20th	Day	24% 4 16% 26% 22% 7%	2280
	21st to end	Day	29% 4 15% 29% 18% 5%	2034
October	1st to 10th	Day	26% 5% 12% 32% 23% 3	3180
	11th to 20th	Day	39% 5% 18% 23% 13% 1	3161
	21st to end	Day	47% 6% 11% 26% 8% 1	3232
November	1st to 10th	Day	56% 8% 14% 18% 4	1740
	11th to 20th	Day	62% 10% 13% 12% 3	1528
	21st to end	Day	60% 8% 15% 11% 5% 1	1520
December	1st to 10th	Day	64% 6% 12% 15% 4	1520
	11th to 20th	Day	78% 5% 9% 6% 1	1928
	21st to end	Day	79% 4 7% 8% 1	2794
January	1st to 10th	Night	73% 7% 9% 9% 1	4406
	11th to 20th	Night	68% 5% 16% 9% 2	4420
	21st to end	Night	77% 6% 8% 8% 1	4763
February	1st to 10th	Night	55% 10% 19% 14% 2	2470
	11th to 20th	Night	48% 9% 18% 19% 5%	2404
	21st to end	Night	49% 10% 16% 19% 5% 1	1895
March	1st to 10th	Night	47% 10% 14% 24% 5%	3736
	11th to 20th	Night	33% 5% 20% 34% 8%	3491
	21st to end	Night	48% 8% 20% 21% 3	3630
April	1st to 10th	Night	41% 9% 21% 21% 7% 1	1900
	11th to 20th	Night	36% 6% 21% 23% 11% 3	1879
	21st to end	Night	31% 9% 20% 27% 11% 2	1758
May	1st to 10th	Night	33% 4 13% 32% 18% 1	2540
	11th to 20th	Night	17% 4 15% 41% 20% 3	2516
	21st to end	Night	25% 6% 36% 27% 5%	2762
June	1st to 10th	Night	35% 6% 14% 33% 9% 2	1520
	11th to 20th	Night	23% 4 21% 38% 14% 1	1520
	21st to end	Night	18% 3 13% 38% 22% 6%	1520
July	1st to 10th	Night	6% 2 8% 17% 32% 35%	2500
	11th to 20th	Night	9% 2 6% 16% 28% 39%	2492
	21st to end	Night	6% 1 8% 22% 40% 23%	2674
August	1st to 10th	Night	14% 2 5% 22% 35% 22%	2605
	11th to 20th	Night	15% 2 13% 41% 23% 6%	2839
	21st to end	Night	16% 3 14% 29% 31% 8%	3488
September	1st to 10th	Night	11% 3 13% 31% 28% 14%	1900
	11th to 20th	Night	22% 5% 14% 30% 18% 11%	1900
	21st to end	Night	23% 4 15% 30% 22% 6%	2141
October	1st to 10th	Night	22% 3 12% 37% 25% 1	3800
	11th to 20th	Night	35% 5% 20% 26% 13% 1	3777
	21st to end	Night	44% 7% 12% 26% 11% 1	4330
November	1st to 10th	Night	50% 8% 15% 20% 7%	2555
	11th to 20th	Night	58% 9% 14% 15% 4	2674
	21st to end	Night	52% 9% 16% 17% 5% 1	2660
December	1st to 10th	Night	63% 7% 12% 14% 3	2660
	11th to 20th	Night	74% 8% 10% 6% 1	3276
	21st to end	Night	71% 6% 9% 12% 2	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	34% 18% 16% 17% 13% 3	180
	11th to 20th	Day	36% 9% 18% 27% 9% 2	180
	21st to end	Day	25% 9% 24% 25% 15% 2	259
February	1st to 10th	Day	26% 15% 24% 22% 11% 2	370
	11th to 20th	Day	27% 16% 25% 22% 9% 1	365
	21st to end	Day	20% 19% 25% 26% 7% 2	377
March	1st to 10th	Day	21% 17% 28% 23% 9% 2	460
	11th to 20th	Day	20% 16% 23% 25% 13% 3	460
	21st to end	Day	22% 20% 27% 21% 9% 1	506
April	1st to 10th	Day	24% 22% 27% 15% 10% 2	460
	11th to 20th	Day	17% 27% 27% 17% 8% 4	452
	21st to end	Day	17% 23% 30% 20% 8% 2	460
May	1st to 10th	Day	16% 20% 30% 20% 11% 3	463
	11th to 20th	Day	19% 15% 31% 17% 14% 4	488
	21st to end	Day	13% 17% 31% 23% 12% 4	529
June	1st to 10th	Day	14% 20% 29% 19% 14% 4	490
	11th to 20th	Day	15% 24% 33% 16% 10% 2	490
	21st to end	Day	7% 17% 33% 26% 14% 4	490
July	1st to 10th	Day	5% 12% 42% 24% 14% 3	486
	11th to 20th	Day	5% 13% 36% 27% 16% 3	484
	21st to end	Day	3 11% 35% 24% 18% 8%	531
August	1st to 10th	Day	5% 9% 29% 24% 23% 10%	487
	11th to 20th	Day	2 9% 28% 29% 21% 11%	477
	21st to end	Day	8% 13% 27% 23% 20% 9%	539
September	1st to 10th	Day	4 12% 25% 27% 22% 9%	490
	11th to 20th	Day	10% 12% 26% 25% 23% 5%	490
	21st to end	Day	12% 14% 23% 28% 19% 6%	490
October	1st to 10th	Day	13% 13% 24% 24% 16% 10%	490
	11th to 20th	Day	15% 14% 22% 23% 19% 7%	490
	21st to end	Day	19% 16% 23% 22% 15% 5%	411
November	1st to 10th	Day	27% 12% 19% 26% 13% 3	287
	11th to 20th	Day	30% 11% 22% 24% 9% 3	182
	21st to end	Day	26% 8% 17% 29% 17% 3	180
December	1st to 10th	Day	24% 9% 24% 22% 14% 7%	180
	11th to 20th	Day	34% 10% 22% 26% 7% 1	180
	21st to end	Day	28% 12% 20% 27% 12% 1	198
January	1st to 10th	Night	28% 9% 21% 28% 12% 1	760
	11th to 20th	Night	28% 9% 16% 30% 14% 2	760
	21st to end	Night	23% 8% 17% 31% 18% 2	836
February	1st to 10th	Night	23% 12% 17% 33% 14% 1	760
	11th to 20th	Night	19% 13% 22% 29% 17% 1	744
	21st to end	Night	20% 14% 20% 33% 12% 1	628
March	1st to 10th	Night	18% 11% 21% 34% 15% 1	760
	11th to 20th	Night	14% 11% 23% 36% 14% 2	760
	21st to end	Night	16% 16% 27% 30% 10% 1	836
April	1st to 10th	Night	14% 16% 26% 29% 14% 1	760
	11th to 20th	Night	14% 17% 28% 25% 14% 2	751
	21st to end	Night	10% 17% 33% 27% 13% 1	618
May	1st to 10th	Night	10% 14% 31% 29% 15% 1	380
	11th to 20th	Night	9% 10% 28% 33% 17% 2	374
	21st to end	Night	6% 8% 35% 35% 14% 2	411
June	1st to 10th	Night	12% 12% 33% 28% 14% 1	380
	11th to 20th	Night	9% 17% 38% 27% 9%	380
	21st to end	Night	5% 13% 34% 31% 16% 1	380
July	1st to 10th	Night	3 8% 34% 36% 18% 1	370
	11th to 20th	Night	1 8% 41% 35% 13% 1	368
	21st to end	Night	2 9% 30% 38% 20% 1	416
August	1st to 10th	Night	2 6% 26% 41% 22% 3	423
	11th to 20th	Night	3 5% 19% 33% 32% 8%	564
	21st to end	Night	3 11% 28% 31% 23% 4	826
September	1st to 10th	Night	2 7% 27% 31% 30% 3	760
	11th to 20th	Night	6% 6% 26% 26% 31% 5%	760
	21st to end	Night	7% 7% 21% 34% 28% 4	760
October	1st to 10th	Night	11% 8% 19% 38% 21% 4	760
	11th to 20th	Night	13% 7% 20% 31% 26% 3	760
	21st to end	Night	17% 8% 23% 31% 18% 2	836
November	1st to 10th	Night	19% 9% 21% 36% 14% 1	780
	11th to 20th	Night	25% 9% 21% 30% 13% 1	764
	21st to end	Night	16% 8% 23% 34% 16% 3	760
December	1st to 10th	Night	24% 7% 20% 31% 16% 2	760
	11th to 20th	Night	26% 9% 18% 32% 15% 1	760
	21st to end	Night	28% 11% 20% 31% 9% 1	836

Page generated at 2024-11-08 19:45:33. Version ac07

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