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 2026-08-30.

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	6% 12% 4 9% 4 4 4 3 5% 6% 42%	153244
	Night	6% 13% 5% 9% 4 4 4 3 5% 6% 42%	146443
Transparency	Day	41% 5% 9% 21% 17% 7%	147958
	Night	42% 5% 10% 21% 16% 6%	142736
Seeing	Day	18% 16% 29% 24% 10% 2	17957
	Night	17% 9% 23% 33% 15% 2	27480

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	6% 28% 10% 17% 4 3 2 1 3 3 22%	4341
	11th to 20th	Day	4 11% 4 14% 6% 3 3 3 4 4 44%	5235
	21st to end	Day	3 17% 7% 13% 5% 3 3 2 4 5% 37%	5844
February	1st to 10th	Day	10% 25% 8% 14% 5% 4 3 2 4 3 21%	1890
	11th to 20th	Day	8% 23% 8% 15% 6% 4 4 3 4 4 20%	1845
	21st to end	Day	7% 22% 8% 19% 7% 4 3 2 3 3 21%	1683
March	1st to 10th	Day	4 21% 8% 15% 4 4 3 3 5% 5% 29%	4948
	11th to 20th	Day	5% 21% 9% 11% 4 4 3 2 3 4 35%	5110
	21st to end	Day	7% 28% 11% 15% 7% 5% 3 3 3 3 16%	5607
April	1st to 10th	Day	11% 21% 7% 10% 5% 4 3 3 4 5% 26%	2404
	11th to 20th	Day	9% 20% 6% 11% 6% 4 4 3 5% 5% 28%	2665
	21st to end	Day	11% 20% 5% 8% 5% 4 4 3 6% 6% 26%	2730
May	1st to 10th	Day	5% 11% 3 6% 4 4 4 4 6% 7% 46%	7626
	11th to 20th	Day	6% 12% 4 9% 5% 5% 5% 4 6% 7% 38%	7774
	21st to end	Day	9% 11% 3 7% 4 4 5% 4 6% 8% 40%	9026
June	1st to 10th	Day	11% 7% 2 6% 5% 6% 5% 5% 8% 8% 38%	2989
	11th to 20th	Day	12% 8% 3 6% 4 4 4 4 5% 6% 44%	3150
	21st to end	Day	4 4 2 4 3 3 4 4 6% 6% 61%	3150
July	1st to 10th	Day	2 2 1 4 4 4 5% 4 6% 9% 58%	8819
	11th to 20th	Day	2 3 1 4 3 4 5% 4 6% 9% 61%	8182
	21st to end	Day	3 3 2 6% 4 6% 6% 5% 8% 10% 48%	8304
August	1st to 10th	Day	4 3 2 6% 5% 4 5% 4 6% 8% 54%	5909
	11th to 20th	Day	3 2 1 4 3 4 5% 5% 7% 9% 57%	5928
	21st to end	Day	7% 4 2 5% 3 3 4 3 5% 5% 58%	6550
September	1st to 10th	Day	6% 5% 1 4 4 4 4 4 4 6% 59%	2362
	11th to 20th	Day	9% 7% 2 6% 4 4 3 3 5% 6% 51%	2200
	21st to end	Day	11% 7% 2 4 3 3 3 2 4 6% 55%	2200
October	1st to 10th	Day	8% 7% 2 5% 3 3 3 3 3 4 60%	3346
	11th to 20th	Day	8% 10% 3 5% 3 3 3 2 3 4 56%	3250
	21st to end	Day	7% 18% 6% 9% 4 3 4 3 4 6% 37%	3465
November	1st to 10th	Day	16% 15% 7% 9% 3 3 3 3 3 4 35%	1848
	11th to 20th	Day	12% 21% 6% 8% 4 4 3 3 4 5% 31%	1680
	21st to end	Day	8% 17% 6% 13% 4 3 3 2 3 4 37%	1680
December	1st to 10th	Day	7% 13% 6% 12% 4 3 1 2 3 5% 44%	2700
	11th to 20th	Day	11% 26% 8% 13% 4 3 3 3 4 4 20%	3106
	21st to end	Day	8% 22% 6% 16% 5% 4 4 3 4 5% 24%	3698
January	1st to 10th	Night	8% 20% 9% 18% 6% 4 3 2 3 5% 21%	8608
	11th to 20th	Night	4 15% 5% 12% 6% 4 3 2 3 4 40%	7732
	21st to end	Night	2 18% 7% 12% 6% 4 3 2 3 5% 38%	8370
February	1st to 10th	Night	8% 23% 8% 15% 6% 4 3 3 4 4 22%	2730
	11th to 20th	Night	7% 23% 11% 14% 6% 4 3 2 3 4 25%	2662
	21st to end	Night	8% 20% 7% 17% 6% 4 5% 4 4 5% 22%	2118
March	1st to 10th	Night	4 22% 7% 15% 5% 3 3 2 3 4 32%	5165
	11th to 20th	Night	5% 18% 7% 9% 4 4 4 3 4 4 38%	5110
	21st to end	Night	8% 21% 8% 11% 5% 5% 4 3 5% 6% 24%	5610
April	1st to 10th	Night	10% 19% 6% 9% 4 4 4 4 5% 5% 29%	2216
	11th to 20th	Night	10% 14% 4 9% 6% 5% 4 3 5% 5% 34%	1899
	21st to end	Night	9% 14% 4 6% 5% 4 3 4 6% 6% 38%	1890
May	1st to 10th	Night	5% 12% 3 6% 3 3 4 3 5% 6% 48%	5321
	11th to 20th	Night	6% 9% 3 7% 5% 4 4 4 6% 7% 46%	5117
	21st to end	Night	8% 8% 2 6% 4 4 5% 4 6% 9% 43%	5181
June	1st to 10th	Night	11% 7% 2 7% 4 5% 4 5% 7% 6% 41%	1625
	11th to 20th	Night	11% 8% 2 5% 3 3 3 3 6% 8% 49%	1470
	21st to end	Night	4 3 2 4 2 3 3 2 6% 6% 65%	1470
July	1st to 10th	Night	2 2 1 3 3 3 4 4 6% 8% 62%	4140
	11th to 20th	Night	1 1 1 2 3 3 4 4 6% 9% 65%	4772
	21st to end	Night	2 2 2 4 3 4 5% 5% 8% 8% 57%	5805
August	1st to 10th	Night	4 4 1 5% 3 3 4 3 6% 7% 60%	4123
	11th to 20th	Night	2 2 1 4 3 4 4 3 6% 8% 63%	4141
	21st to end	Night	7% 5% 2 4 2 3 3 2 5% 6% 60%	4624
September	1st to 10th	Night	5% 4 1 4 4 3 3 3 5% 6% 64%	2035
	11th to 20th	Night	7% 6% 2 5% 3 4 4 4 6% 5% 56%	2200
	21st to end	Night	9% 6% 2 4 2 2 2 2 3 6% 61%	2200
October	1st to 10th	Night	8% 6% 1 4 3 2 2 1 3 5% 65%	3846
	11th to 20th	Night	11% 10% 3 5% 3 3 2 2 4 5% 52%	3898
	21st to end	Night	9% 14% 4 7% 3 3 4 3 5% 6% 42%	4334
November	1st to 10th	Night	15% 16% 4 7% 4 3 3 3 4 5% 37%	2665
	11th to 20th	Night	11% 19% 5% 9% 4 4 4 3 4 5% 33%	2924
	21st to end	Night	8% 17% 5% 9% 4 4 3 3 5% 6% 36%	2940
December	1st to 10th	Night	7% 14% 4 14% 5% 3 2 2 3 4 43%	4710
	11th to 20th	Night	8% 24% 7% 12% 5% 4 4 3 4 5% 23%	5321
	21st to end	Night	9% 24% 6% 13% 5% 4 4 3 4 5% 25%	7471

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	70% 2 11% 11% 6% 1	4342
	11th to 20th	Day	43% 4 18% 19% 11% 5%	5235
	21st to end	Day	50% 6% 11% 16% 13% 4	5844
February	1st to 10th	Day	68% 5% 10% 13% 4 1	1890
	11th to 20th	Day	65% 5% 11% 12% 5% 2	1854
	21st to end	Day	67% 5% 5% 15% 7% 1	1683
March	1st to 10th	Day	54% 7% 9% 18% 9% 4	4948
	11th to 20th	Day	53% 5% 11% 21% 9% 1	5110
	21st to end	Day	70% 6% 10% 12% 2	5607
April	1st to 10th	Day	59% 6% 11% 17% 8% 1	2404
	11th to 20th	Day	56% 4 10% 19% 10% 1	2668
	21st to end	Day	55% 5% 10% 24% 6%	2730
May	1st to 10th	Day	34% 6% 10% 35% 15%	7626
	11th to 20th	Day	40% 8% 8% 24% 15% 4	7777
	21st to end	Day	38% 7% 11% 30% 13%	9027
June	1st to 10th	Day	40% 6% 14% 26% 12% 1	2989
	11th to 20th	Day	39% 4 8% 21% 21% 7%	3150
	21st to end	Day	22% 4 6% 26% 32% 10%	3150
July	1st to 10th	Day	19% 6% 6% 16% 30% 23%	8746
	11th to 20th	Day	18% 5% 6% 20% 25% 26%	8103
	21st to end	Day	25% 8% 8% 18% 28% 14%	8120
August	1st to 10th	Day	26% 6% 6% 17% 28% 17%	4338
	11th to 20th	Day	22% 5% 6% 21% 33% 13%	4327
	21st to end	Day	22% 5% 6% 20% 31% 17%	4757
September	1st to 10th	Day	26% 5% 6% 18% 31% 14%	2362
	11th to 20th	Day	32% 4 7% 24% 24% 8%	2200
	21st to end	Day	32% 2 10% 28% 23% 5%	2200
October	1st to 10th	Day	30% 2 6% 25% 32% 5%	3346
	11th to 20th	Day	33% 3 10% 33% 17% 4	3250
	21st to end	Day	48% 5% 12% 23% 12% 1	3465
November	1st to 10th	Day	53% 4 12% 22% 8% 1	1848
	11th to 20th	Day	55% 4 15% 18% 7% 1	1680
	21st to end	Day	52% 4 15% 19% 9% 1	1680
December	1st to 10th	Day	46% 5% 20% 20% 8% 2	2700
	11th to 20th	Day	68% 5% 11% 13% 4	3104
	21st to end	Day	62% 5% 9% 12% 7% 6%	3698
January	1st to 10th	Night	66% 5% 7% 15% 6%	8609
	11th to 20th	Night	47% 5% 18% 20% 6% 4	7732
	21st to end	Night	50% 4 10% 13% 15% 6%	8370
February	1st to 10th	Night	65% 5% 10% 13% 6%	2730
	11th to 20th	Night	64% 4 9% 14% 8% 1	2663
	21st to end	Night	62% 5% 8% 16% 7% 2	2118
March	1st to 10th	Night	53% 6% 7% 18% 10% 6%	5165
	11th to 20th	Night	46% 7% 11% 25% 11% 1	5110
	21st to end	Night	57% 7% 12% 19% 4	5610
April	1st to 10th	Night	53% 5% 13% 18% 10% 1	2216
	11th to 20th	Night	50% 5% 12% 21% 11% 2	1899
	21st to end	Night	43% 5% 15% 28% 9%	1890
May	1st to 10th	Night	33% 6% 8% 30% 21% 1	5319
	11th to 20th	Night	31% 8% 10% 27% 20% 4	5118
	21st to end	Night	32% 8% 12% 29% 18% 1	5182
June	1st to 10th	Night	38% 7% 13% 26% 14% 2	1625
	11th to 20th	Night	32% 4 10% 25% 22% 7%	1470
	21st to end	Night	18% 4 7% 27% 31% 13%	1470
July	1st to 10th	Night	16% 5% 6% 17% 33% 23%	4105
	11th to 20th	Night	13% 5% 7% 18% 31% 26%	4729
	21st to end	Night	20% 8% 7% 17% 29% 20%	5677
August	1st to 10th	Night	23% 5% 5% 18% 30% 19%	3018
	11th to 20th	Night	21% 5% 5% 27% 27% 15%	3018
	21st to end	Night	19% 3 5% 24% 30% 19%	3348
September	1st to 10th	Night	22% 3 5% 21% 32% 18%	2035
	11th to 20th	Night	29% 4 9% 23% 25% 10%	2200
	21st to end	Night	27% 2 9% 27% 30% 6%	2200
October	1st to 10th	Night	24% 2 7% 27% 35% 4	3846
	11th to 20th	Night	34% 4 8% 32% 17% 4	3898
	21st to end	Night	40% 6% 13% 25% 15% 1	4334
November	1st to 10th	Night	49% 3 12% 23% 11% 2	2665
	11th to 20th	Night	53% 4 14% 19% 8% 2	2924
	21st to end	Night	49% 5% 13% 20% 11% 2	2940
December	1st to 10th	Night	49% 3 16% 22% 8% 2	4710
	11th to 20th	Night	63% 6% 15% 12% 4	5322
	21st to end	Night	62% 5% 7% 15% 6% 4	7471

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	26% 23% 22% 19% 10%	220
	11th to 20th	Day	14% 21% 34% 22% 8% 2	310
	21st to end	Day	16% 15% 37% 23% 9% 1	363
February	1st to 10th	Day	28% 25% 30% 13% 3	330
	11th to 20th	Day	26% 23% 31% 15% 5% 1	330
	21st to end	Day	25% 23% 32% 15% 5%	399
March	1st to 10th	Day	26% 23% 31% 17% 3	540
	11th to 20th	Day	24% 19% 29% 21% 7% 1	540
	21st to end	Day	31% 20% 27% 18% 4	594
April	1st to 10th	Day	30% 20% 25% 20% 4 1	540
	11th to 20th	Day	23% 24% 30% 17% 5% 1	532
	21st to end	Day	25% 17% 26% 22% 9% 2	540
May	1st to 10th	Day	16% 17% 29% 27% 10% 1	543
	11th to 20th	Day	22% 13% 27% 23% 13% 2	629
	21st to end	Day	22% 12% 21% 25% 17% 3	844
June	1st to 10th	Day	14% 15% 26% 26% 16% 4	780
	11th to 20th	Day	21% 18% 31% 20% 9% 1	780
	21st to end	Day	11% 15% 29% 28% 13% 4	780
July	1st to 10th	Day	7% 12% 31% 31% 15% 3	771
	11th to 20th	Day	6% 10% 40% 34% 10% 1	644
	21st to end	Day	7% 11% 32% 37% 12% 2	619
August	1st to 10th	Day	8% 14% 35% 30% 11% 2	567
	11th to 20th	Day	7% 12% 31% 32% 14% 4	557
	21st to end	Day	12% 14% 28% 30% 13% 4	620
September	1st to 10th	Day	8% 11% 33% 29% 15% 3	530
	11th to 20th	Day	17% 18% 27% 23% 13% 2	530
	21st to end	Day	17% 12% 26% 29% 14% 2	530
October	1st to 10th	Day	16% 14% 27% 25% 16% 1	380
	11th to 20th	Day	22% 19% 21% 23% 11% 5%	330
	21st to end	Day	25% 17% 28% 23% 6% 1	363
November	1st to 10th	Day	26% 20% 29% 17% 6% 3	330
	11th to 20th	Day	24% 22% 29% 18% 7% 2	330
	21st to end	Day	18% 16% 34% 24% 8%	330
December	1st to 10th	Day	23% 16% 31% 20% 8% 2	330
	11th to 20th	Day	28% 21% 29% 18% 4 1	330
	21st to end	Day	29% 18% 27% 18% 6% 2	272
January	1st to 10th	Night	19% 14% 23% 32% 11% 1	994
	11th to 20th	Night	18% 11% 27% 30% 12% 2	840
	21st to end	Night	13% 10% 32% 33% 10% 1	924
February	1st to 10th	Night	22% 14% 26% 29% 7% 1	840
	11th to 20th	Night	19% 14% 26% 31% 9% 1	824
	21st to end	Night	19% 15% 27% 28% 9% 1	692
March	1st to 10th	Night	20% 12% 26% 31% 9% 1	840
	11th to 20th	Night	20% 10% 24% 31% 13% 1	840
	21st to end	Night	19% 13% 26% 30% 11% 1	924
April	1st to 10th	Night	21% 14% 25% 29% 11% 2	746
	11th to 20th	Night	20% 9% 29% 31% 9% 1	623
	21st to end	Night	18% 7% 25% 30% 18% 2	630
May	1st to 10th	Night	16% 8% 21% 34% 19% 2	630
	11th to 20th	Night	15% 6% 23% 33% 20% 3	621
	21st to end	Night	19% 8% 20% 33% 19% 2	683
June	1st to 10th	Night	16% 7% 21% 36% 18% 2	575
	11th to 20th	Night	17% 8% 24% 35% 15%	420
	21st to end	Night	6% 4 22% 39% 26% 3	420
July	1st to 10th	Night	4 3 20% 44% 25% 4	410
	11th to 20th	Night	3 4 20% 45% 26% 1	502
	21st to end	Night	4 3 20% 41% 28% 3	690
August	1st to 10th	Night	7% 4 20% 40% 27% 2	627
	11th to 20th	Night	4 4 19% 40% 29% 3	624
	21st to end	Night	8% 6% 19% 37% 27% 3	687
September	1st to 10th	Night	7% 3 19% 40% 27% 3	635
	11th to 20th	Night	9% 7% 17% 35% 26% 6%	800
	21st to end	Night	13% 3 22% 36% 20% 6%	800
October	1st to 10th	Night	16% 6% 21% 37% 18% 3	800
	11th to 20th	Night	20% 8% 15% 35% 19% 3	800
	21st to end	Night	18% 9% 22% 36% 12% 3	880
November	1st to 10th	Night	23% 11% 25% 28% 12% 1	820
	11th to 20th	Night	23% 14% 25% 31% 6% 1	1034
	21st to end	Night	19% 12% 25% 31% 11% 2	1050
December	1st to 10th	Night	23% 10% 27% 30% 8% 1	1050
	11th to 20th	Night	25% 13% 23% 31% 7% 1	1050
	21st to end	Night	26% 13% 24% 27% 8% 1	1155

Page generated at 2026-08-27 02:07:14. Version ac07

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