Driggs
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Driggs clear sky chart from 2005-11-06 to 2025-04-26.

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	7% 14% 5% 9% 4 4 4 3 5% 6% 40%	117839
	Night	7% 15% 5% 10% 4 4 3 3 4 5% 40%	119637
Transparency	Day	44% 5% 9% 20% 16% 7%	117583
	Night	45% 5% 10% 20% 15% 6%	119482
Seeing	Day	18% 15% 29% 25% 11% 2	16040
	Night	17% 9% 22% 34% 16% 2	25819

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	7% 23% 10% 17% 4 3 3 2 3 3 24%	3340
	11th to 20th	Day	5% 14% 5% 17% 7% 4 3 3 5% 4 31%	4023
	21st to end	Day	4 21% 8% 12% 4 3 2 2 3 4 38%	4510
February	1st to 10th	Day	11% 25% 8% 15% 5% 4 3 2 4 3 20%	1800
	11th to 20th	Day	8% 23% 9% 15% 6% 4 4 3 4 3 21%	1755
	21st to end	Day	7% 23% 9% 20% 7% 4 3 2 3 3 20%	1605
March	1st to 10th	Day	4 21% 8% 15% 4 3 3 3 5% 4 30%	4841
	11th to 20th	Day	4 21% 9% 12% 5% 4 3 2 3 3 35%	5000
	21st to end	Day	7% 29% 11% 15% 7% 5% 3 3 3 3 16%	5486
April	1st to 10th	Day	12% 21% 7% 11% 4 4 3 3 4 5% 25%	2290
	11th to 20th	Day	9% 20% 6% 11% 6% 4 4 3 4 5% 29%	2537
	21st to end	Day	11% 20% 5% 8% 5% 4 4 3 6% 6% 27%	2537
May	1st to 10th	Day	8% 19% 5% 9% 5% 5% 5% 4 5% 6% 29%	4110
	11th to 20th	Day	6% 7% 2 6% 4 5% 5% 4 6% 8% 46%	4165
	21st to end	Day	10% 15% 4 9% 5% 5% 5% 4 5% 6% 33%	4825
June	1st to 10th	Day	12% 7% 3 6% 5% 5% 5% 5% 8% 8% 36%	2704
	11th to 20th	Day	13% 8% 3 6% 5% 4 4 4 5% 6% 41%	2850
	21st to end	Day	4 3 1 4 3 3 4 4 6% 6% 62%	2850
July	1st to 10th	Day	3 2 1 3 2 2 4 3 5% 8% 66%	4740
	11th to 20th	Day	2 3 1 3 3 4 5% 4 6% 9% 59%	4400
	21st to end	Day	3 4 1 5% 4 5% 5% 5% 8% 9% 52%	4454
August	1st to 10th	Day	5% 4 2 6% 5% 4 5% 4 6% 8% 51%	4092
	11th to 20th	Day	3 3 1 4 3 4 4 4 6% 8% 59%	4028
	21st to end	Day	4 3 1 4 3 3 4 3 5% 5% 63%	4498
September	1st to 10th	Day	6% 5% 1 4 4 3 4 3 4 6% 58%	2244
	11th to 20th	Day	9% 8% 2 5% 4 3 3 3 4 6% 52%	2090
	21st to end	Day	11% 7% 1 4 3 3 3 2 4 6% 55%	2090
October	1st to 10th	Day	8% 7% 2 5% 3 3 3 3 3 3 60%	3244
	11th to 20th	Day	8% 10% 3 5% 3 3 3 2 3 4 57%	3150
	21st to end	Day	8% 18% 6% 9% 4 3 4 3 4 6% 36%	3358
November	1st to 10th	Day	16% 15% 7% 9% 3 3 3 3 3 4 34%	1759
	11th to 20th	Day	12% 21% 6% 7% 4 4 3 2 4 6% 31%	1600
	21st to end	Day	8% 17% 6% 13% 4 3 3 2 3 4 36%	1600
December	1st to 10th	Day	7% 12% 5% 12% 5% 3 2 2 3 5% 45%	2620
	11th to 20th	Day	11% 27% 9% 13% 4 3 3 3 4 4 20%	3026
	21st to end	Day	8% 22% 6% 16% 5% 4 4 3 5% 5% 24%	3618
January	1st to 10th	Night	7% 15% 8% 18% 6% 4 4 2 3 5% 26%	6648
	11th to 20th	Night	5% 19% 7% 16% 8% 5% 4 3 3 3 26%	5949
	21st to end	Night	3 22% 7% 10% 4 3 3 2 3 4 39%	6468
February	1st to 10th	Night	9% 23% 8% 16% 6% 4 3 3 3 3 21%	2600
	11th to 20th	Night	8% 24% 11% 13% 5% 4 3 2 3 3 24%	2532
	21st to end	Night	7% 21% 8% 17% 6% 4 5% 4 4 4 21%	2020
March	1st to 10th	Night	4 22% 7% 15% 5% 3 3 2 3 4 32%	5052
	11th to 20th	Night	4 18% 7% 10% 4 4 4 3 5% 5% 37%	5000
	21st to end	Night	8% 21% 8% 11% 5% 5% 4 3 5% 6% 24%	5489
April	1st to 10th	Night	10% 19% 6% 9% 4 4 4 4 5% 5% 29%	2110
	11th to 20th	Night	10% 14% 4 9% 6% 4 4 3 5% 5% 34%	1808
	21st to end	Night	9% 15% 4 6% 4 4 3 4 5% 6% 39%	1759
May	1st to 10th	Night	8% 19% 5% 7% 5% 4 4 3 5% 6% 35%	2860
	11th to 20th	Night	5% 6% 2 6% 5% 4 4 4 7% 8% 48%	2739
	21st to end	Night	9% 12% 3 7% 5% 4 5% 3 6% 7% 38%	2762
June	1st to 10th	Night	11% 7% 2 7% 4 5% 4 5% 7% 7% 40%	1471
	11th to 20th	Night	12% 8% 2 5% 4 3 3 3 6% 8% 47%	1330
	21st to end	Night	4 3 2 3 2 3 3 2 6% 6% 66%	1330
July	1st to 10th	Night	3 2 1 3 3 3 4 4 5% 5% 68%	2220
	11th to 20th	Night	2 1 1 2 3 3 3 4 7% 9% 64%	2558
	21st to end	Night	2 2 2 4 3 4 5% 5% 7% 7% 61%	3109
August	1st to 10th	Night	4 4 1 5% 4 3 5% 4 6% 7% 57%	2847
	11th to 20th	Night	2 3 2 5% 3 4 4 3 6% 9% 60%	2811
	21st to end	Night	4 4 1 3 2 3 2 2 4 5% 69%	3167
September	1st to 10th	Night	6% 4 1 4 4 3 3 3 5% 5% 64%	1933
	11th to 20th	Night	7% 6% 2 4 3 4 3 4 6% 5% 56%	2090
	21st to end	Night	9% 7% 2 4 2 2 2 2 3 6% 61%	2090
October	1st to 10th	Night	8% 6% 1 3 3 2 2 1 3 5% 66%	3728
	11th to 20th	Night	10% 9% 3 5% 2 3 2 2 4 5% 53%	3778
	21st to end	Night	9% 14% 4 7% 4 3 4 3 5% 6% 41%	4199
November	1st to 10th	Night	15% 16% 4 7% 4 3 3 3 4 5% 37%	2535
	11th to 20th	Night	11% 19% 5% 9% 4 3 4 3 4 4 33%	2785
	21st to end	Night	9% 17% 5% 9% 4 4 3 3 5% 6% 36%	2800
December	1st to 10th	Night	6% 14% 4 14% 5% 3 2 2 3 4 43%	4570
	11th to 20th	Night	8% 25% 7% 12% 5% 4 4 3 4 5% 23%	5181
	21st to end	Night	9% 24% 6% 13% 5% 4 4 3 4 5% 24%	7309

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	67% 3 9% 13% 8% 1	3340
	11th to 20th	Day	54% 5% 13% 15% 9% 4	4023
	21st to end	Day	52% 6% 8% 17% 14% 4	4510
February	1st to 10th	Day	70% 5% 9% 12% 4 1	1800
	11th to 20th	Day	65% 4 11% 12% 5% 2	1764
	21st to end	Day	69% 5% 5% 13% 7% 1	1605
March	1st to 10th	Day	53% 7% 9% 18% 9% 4	4841
	11th to 20th	Day	53% 5% 11% 21% 9% 1	5000
	21st to end	Day	71% 6% 10% 11% 2	5486
April	1st to 10th	Day	60% 5% 10% 16% 8% 1	2290
	11th to 20th	Day	57% 4 10% 20% 9% 1	2540
	21st to end	Day	55% 5% 11% 24% 5%	2537
May	1st to 10th	Day	50% 6% 8% 25% 9% 1	4110
	11th to 20th	Day	33% 7% 10% 33% 13% 5%	4168
	21st to end	Day	49% 6% 10% 29% 7%	4825
June	1st to 10th	Day	42% 6% 15% 25% 11% 1	2704
	11th to 20th	Day	41% 4 9% 21% 17% 7%	2850
	21st to end	Day	21% 4 6% 27% 32% 11%	2850
July	1st to 10th	Day	14% 4 4 16% 36% 26%	4666
	11th to 20th	Day	19% 4 6% 14% 24% 33%	4321
	21st to end	Day	23% 6% 6% 18% 30% 16%	4314
August	1st to 10th	Day	27% 6% 6% 17% 28% 16%	4078
	11th to 20th	Day	21% 5% 6% 21% 34% 13%	4067
	21st to end	Day	21% 4 6% 20% 32% 18%	4497
September	1st to 10th	Day	26% 4 6% 17% 31% 15%	2244
	11th to 20th	Day	32% 4 7% 24% 24% 8%	2090
	21st to end	Day	31% 2 10% 28% 23% 6%	2090
October	1st to 10th	Day	30% 2 6% 26% 32% 5%	3244
	11th to 20th	Day	32% 3 10% 33% 18% 4	3150
	21st to end	Day	49% 5% 12% 22% 12% 1	3358
November	1st to 10th	Day	53% 4 11% 21% 9% 2	1759
	11th to 20th	Day	55% 4 14% 18% 7% 1	1600
	21st to end	Day	52% 4 15% 19% 9% 2	1600
December	1st to 10th	Day	45% 5% 20% 20% 8% 2	2620
	11th to 20th	Day	68% 5% 11% 13% 4	3024
	21st to end	Day	62% 5% 8% 13% 7% 6%	3618
January	1st to 10th	Night	60% 5% 8% 18% 8%	6648
	11th to 20th	Night	61% 6% 9% 15% 6% 3	5949
	21st to end	Night	50% 4 10% 14% 16% 6%	6468
February	1st to 10th	Night	67% 5% 9% 13% 6%	2600
	11th to 20th	Night	65% 4 8% 14% 8% 1	2533
	21st to end	Night	63% 5% 8% 14% 7% 3	2020
March	1st to 10th	Night	53% 6% 7% 18% 10% 6%	5052
	11th to 20th	Night	46% 7% 11% 25% 10% 1	5000
	21st to end	Night	58% 7% 13% 19% 4	5489
April	1st to 10th	Night	53% 5% 13% 17% 10% 1	2110
	11th to 20th	Night	50% 4 12% 21% 11% 2	1808
	21st to end	Night	42% 5% 14% 29% 9%	1759
May	1st to 10th	Night	46% 6% 9% 25% 12% 1	2860
	11th to 20th	Night	27% 8% 13% 36% 13% 3	2740
	21st to end	Night	40% 7% 11% 30% 11% 1	2762
June	1st to 10th	Night	39% 7% 14% 27% 12% 1	1471
	11th to 20th	Night	35% 4 10% 25% 19% 8%	1330
	21st to end	Night	18% 4 7% 27% 30% 14%	1330
July	1st to 10th	Night	15% 4 6% 15% 37% 24%	2185
	11th to 20th	Night	12% 5% 4 15% 33% 32%	2515
	21st to end	Night	18% 6% 6% 17% 32% 21%	3011
August	1st to 10th	Night	24% 6% 5% 18% 30% 18%	2838
	11th to 20th	Night	21% 4 5% 27% 28% 15%	2838
	21st to end	Night	17% 3 5% 24% 31% 20%	3167
September	1st to 10th	Night	22% 3 5% 20% 32% 19%	1933
	11th to 20th	Night	28% 4 10% 23% 25% 10%	2090
	21st to end	Night	27% 2 9% 27% 29% 6%	2090
October	1st to 10th	Night	24% 2 7% 27% 35% 4	3728
	11th to 20th	Night	33% 4 8% 33% 18% 4	3778
	21st to end	Night	40% 6% 13% 24% 15% 1	4199
November	1st to 10th	Night	50% 3 11% 23% 11% 2	2535
	11th to 20th	Night	53% 4 13% 20% 8% 2	2785
	21st to end	Night	49% 5% 13% 20% 11% 2	2800
December	1st to 10th	Night	48% 3 16% 23% 8% 2	4570
	11th to 20th	Night	63% 5% 15% 12% 4	5182
	21st to end	Night	62% 5% 7% 15% 6% 5%	7309

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	25% 22% 22% 21% 11% 1	200
	11th to 20th	Day	15% 19% 33% 23% 9% 2	282
	21st to end	Day	16% 14% 34% 25% 9% 1	330
February	1st to 10th	Day	29% 26% 29% 13% 3	300
	11th to 20th	Day	25% 22% 31% 16% 5% 1	300
	21st to end	Day	23% 22% 33% 16% 5%	369
March	1st to 10th	Day	25% 23% 32% 17% 3	500
	11th to 20th	Day	21% 19% 30% 23% 7% 1	500
	21st to end	Day	30% 20% 27% 19% 4	550
April	1st to 10th	Day	31% 19% 25% 20% 4 1	500
	11th to 20th	Day	23% 24% 30% 17% 5% 1	492
	21st to end	Day	25% 17% 25% 22% 10% 2	481
May	1st to 10th	Day	17% 18% 29% 25% 10% 1	463
	11th to 20th	Day	20% 10% 27% 25% 15% 2	543
	21st to end	Day	22% 10% 20% 25% 19% 4	734
June	1st to 10th	Day	13% 13% 24% 28% 18% 4	680
	11th to 20th	Day	22% 15% 29% 23% 10% 1	680
	21st to end	Day	8% 12% 30% 30% 15% 4	680
July	1st to 10th	Day	7% 11% 27% 33% 18% 4	671
	11th to 20th	Day	6% 8% 39% 35% 11% 1	556
	21st to end	Day	6% 8% 29% 40% 14% 3	531
August	1st to 10th	Day	9% 9% 34% 33% 12% 2	487
	11th to 20th	Day	6% 11% 29% 35% 16% 4	477
	21st to end	Day	11% 13% 26% 32% 14% 4	539
September	1st to 10th	Day	9% 11% 33% 29% 16% 3	490
	11th to 20th	Day	18% 18% 26% 23% 14% 2	490
	21st to end	Day	17% 12% 27% 29% 13% 2	490
October	1st to 10th	Day	16% 13% 26% 27% 17% 1	348
	11th to 20th	Day	18% 17% 22% 26% 12% 5%	300
	21st to end	Day	26% 16% 27% 24% 6% 1	330
November	1st to 10th	Day	24% 20% 29% 18% 6% 3	300
	11th to 20th	Day	24% 20% 28% 19% 8% 2	300
	21st to end	Day	17% 16% 34% 25% 8%	300
December	1st to 10th	Day	21% 14% 32% 22% 9% 2	300
	11th to 20th	Day	26% 20% 30% 19% 4 1	300
	21st to end	Day	26% 19% 28% 19% 6% 2	247
January	1st to 10th	Night	18% 13% 23% 34% 11% 1	947
	11th to 20th	Night	19% 11% 24% 32% 12% 2	800
	21st to end	Night	14% 10% 30% 34% 11% 1	880
February	1st to 10th	Night	22% 14% 25% 29% 8% 2	800
	11th to 20th	Night	19% 13% 25% 31% 10% 2	784
	21st to end	Night	19% 13% 28% 29% 10% 2	660
March	1st to 10th	Night	20% 12% 26% 32% 10% 1	800
	11th to 20th	Night	19% 9% 24% 33% 13% 1	800
	21st to end	Night	19% 11% 26% 31% 12% 1	880
April	1st to 10th	Night	21% 13% 23% 30% 11% 2	710
	11th to 20th	Night	20% 9% 28% 33% 10% 1	593
	21st to end	Night	18% 6% 23% 32% 20% 2	587
May	1st to 10th	Night	17% 7% 20% 34% 21% 2	570
	11th to 20th	Night	15% 3 22% 35% 22% 3	561
	21st to end	Night	20% 7% 16% 34% 20% 3	617
June	1st to 10th	Night	16% 6% 20% 36% 20% 2	521
	11th to 20th	Night	17% 8% 20% 38% 17%	380
	21st to end	Night	5% 2 20% 42% 28% 3	380
July	1st to 10th	Night	4 2 16% 46% 28% 4	370
	11th to 20th	Night	4 3 18% 45% 28% 1	453
	21st to end	Night	4 3 16% 43% 31% 3	624
August	1st to 10th	Night	8% 4 15% 41% 30% 2	567
	11th to 20th	Night	4 3 16% 41% 32% 4	564
	21st to end	Night	7% 6% 17% 38% 30% 3	627
September	1st to 10th	Night	8% 3 19% 39% 28% 3	603
	11th to 20th	Night	9% 6% 16% 35% 27% 6%	760
	21st to end	Night	13% 3 21% 36% 21% 6%	760
October	1st to 10th	Night	17% 5% 19% 38% 19% 3	760
	11th to 20th	Night	19% 7% 15% 36% 20% 3	760
	21st to end	Night	18% 9% 20% 37% 13% 3	836
November	1st to 10th	Night	23% 10% 24% 29% 12% 2	780
	11th to 20th	Night	23% 13% 24% 32% 6% 1	985
	21st to end	Night	19% 12% 24% 32% 11% 2	1000
December	1st to 10th	Night	22% 10% 27% 32% 9% 1	1000
	11th to 20th	Night	24% 13% 23% 33% 8% 1	1000
	21st to end	Night	24% 13% 24% 29% 9% 2	1100

Page generated at 2025-04-23 07:25:08. Version ac07

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