Upper Geyser Basin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Upper Geyser Basin clear sky chart from 2005-11-06 to 2026-03-03.

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	4 8% 3 8% 5% 5% 5% 4 6% 7% 45%	140129
	Night	3 7% 4 9% 6% 5% 5% 4 6% 8% 44%	138461
Transparency	Day	38% 7% 13% 20% 16% 6%	134842
	Night	39% 8% 14% 21% 14% 4	134753
Seeing	Day	14% 21% 31% 22% 10% 2	17202
	Night	11% 15% 29% 30% 13% 1	26933

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 9% 5% 17% 9% 8% 7% 6% 8% 6% 22%	4142
	11th to 20th	Day	1 6% 3 9% 9% 5% 5% 4 5% 6% 47%	5075
	21st to end	Day	1 11% 7% 13% 6% 5% 5% 3 4 5% 41%	5844
February	1st to 10th	Day	3 16% 8% 16% 9% 6% 5% 5% 5% 6% 22%	1890
	11th to 20th	Day	2 14% 8% 19% 9% 7% 5% 4 5% 6% 22%	1845
	21st to end	Day	2 13% 8% 21% 10% 6% 5% 4 5% 4 22%	1651
March	1st to 10th	Day	1 11% 5% 16% 7% 6% 5% 3 5% 5% 36%	4879
	11th to 20th	Day	1 12% 6% 12% 6% 5% 5% 4 5% 7% 37%	5000
	21st to end	Day	2 15% 8% 15% 7% 7% 7% 5% 7% 7% 20%	5486
April	1st to 10th	Day	5% 17% 7% 11% 7% 6% 5% 3 5% 6% 27%	2310
	11th to 20th	Day	5% 15% 5% 12% 7% 6% 5% 4 5% 6% 31%	2534
	21st to end	Day	7% 16% 5% 10% 5% 6% 5% 5% 6% 7% 28%	2600
May	1st to 10th	Day	7% 13% 4 7% 5% 4 5% 3 5% 7% 42%	5880
	11th to 20th	Day	5% 9% 3 7% 5% 5% 6% 5% 8% 11% 36%	6114
	21st to end	Day	6% 9% 2 6% 5% 5% 6% 4 7% 9% 42%	6925
June	1st to 10th	Day	11% 8% 2 6% 5% 5% 5% 4 7% 9% 37%	2893
	11th to 20th	Day	10% 7% 2 6% 5% 5% 6% 5% 6% 9% 40%	3000
	21st to end	Day	3 3 2 4 4 3 4 4 7% 7% 59%	3000
July	1st to 10th	Day	2 2 1 3 3 4 4 4 7% 8% 64%	6779
	11th to 20th	Day	2 2 1 3 3 3 4 3 6% 8% 65%	6547
	21st to end	Day	2 2 1 3 3 3 5% 4 6% 8% 65%	6401
August	1st to 10th	Day	3 2 1 4 3 5% 5% 5% 7% 10% 55%	5779
	11th to 20th	Day	3 1 1 3 3 3 4 3 6% 7% 68%	5798
	21st to end	Day	7% 4 1 4 3 3 4 3 5% 6% 61%	6429
September	1st to 10th	Day	5% 4 2 3 3 3 4 2 5% 6% 62%	2390
	11th to 20th	Day	6% 6% 2 5% 4 4 5% 3 5% 7% 54%	2200
	21st to end	Day	6% 7% 2 4 3 4 3 4 4 8% 56%	2200
October	1st to 10th	Day	6% 7% 2 4 3 3 3 3 4 4 62%	3317
	11th to 20th	Day	4 8% 3 6% 3 3 3 2 4 6% 57%	3250
	21st to end	Day	3 11% 5% 9% 5% 5% 5% 5% 6% 6% 41%	3460
November	1st to 10th	Day	7% 11% 5% 11% 6% 6% 4 4 5% 6% 35%	1794
	11th to 20th	Day	3 15% 5% 11% 6% 5% 5% 4 6% 7% 33%	1680
	21st to end	Day	2 11% 5% 12% 6% 7% 5% 4 5% 6% 37%	1680
December	1st to 10th	Day	2 7% 4 10% 7% 5% 4 4 5% 6% 47%	2700
	11th to 20th	Day	2 10% 7% 18% 8% 7% 7% 6% 7% 6% 22%	3082
	21st to end	Day	1 13% 6% 16% 8% 7% 7% 4 5% 6% 25%	3575
January	1st to 10th	Night	1 6% 5% 16% 9% 8% 8% 6% 8% 8% 25%	8768
	11th to 20th	Night	1 5% 3 10% 8% 7% 6% 5% 6% 8% 41%	7923
	21st to end	Night	1 9% 7% 12% 6% 5% 5% 4 5% 7% 41%	8370
February	1st to 10th	Night	3 13% 6% 15% 8% 6% 5% 4 6% 7% 25%	2730
	11th to 20th	Night	2 12% 5% 16% 8% 7% 6% 5% 6% 7% 26%	2662
	21st to end	Night	2 11% 5% 17% 9% 8% 5% 4 6% 7% 25%	2151
March	1st to 10th	Night	1 9% 6% 14% 10% 6% 5% 4 4 5% 37%	5059
	11th to 20th	Night	1 8% 4 9% 4 4 4 4 6% 8% 47%	5000
	21st to end	Night	2 8% 4 11% 6% 6% 7% 6% 8% 11% 31%	5489
April	1st to 10th	Night	4 14% 5% 11% 7% 5% 4 4 6% 7% 33%	2090
	11th to 20th	Night	4 9% 4 8% 6% 5% 5% 5% 8% 7% 39%	1811
	21st to end	Night	7% 12% 4 6% 4 5% 5% 4 7% 8% 40%	1800
May	1st to 10th	Night	5% 9% 4 6% 4 4 5% 4 5% 6% 48%	4100
	11th to 20th	Night	6% 7% 3 6% 5% 5% 5% 5% 7% 10% 41%	3784
	21st to end	Night	7% 9% 2 5% 5% 5% 5% 4 8% 9% 41%	3972
June	1st to 10th	Night	10% 6% 2 5% 4 4 5% 4 8% 8% 43%	1502
	11th to 20th	Night	8% 4 2 5% 5% 4 5% 3 7% 8% 49%	1400
	21st to end	Night	3 2 1 3 2 3 3 3 6% 7% 66%	1400
July	1st to 10th	Night	3 2 1 3 2 3 4 4 7% 7% 65%	3180
	11th to 20th	Night	2 2 1 3 2 4 4 4 6% 8% 66%	3400
	21st to end	Night	2 1 1 2 3 4 4 4 7% 8% 65%	4472
August	1st to 10th	Night	3 2 1 4 3 4 4 5% 8% 11% 56%	4033
	11th to 20th	Night	1 1 1 3 2 3 3 4 7% 8% 67%	4051
	21st to end	Night	5% 4 2 5% 4 3 3 3 4 6% 62%	4547
September	1st to 10th	Night	5% 3 2 4 3 3 4 3 5% 6% 64%	2005
	11th to 20th	Night	5% 5% 2 5% 4 4 4 5% 6% 7% 55%	2200
	21st to end	Night	7% 6% 1 3 3 3 3 2 4 6% 62%	2200
October	1st to 10th	Night	5% 5% 1 3 2 2 2 2 4 5% 68%	3873
	11th to 20th	Night	5% 8% 2 5% 3 3 3 3 5% 6% 57%	3898
	21st to end	Night	4 8% 3 7% 4 4 5% 4 6% 8% 47%	4338
November	1st to 10th	Night	6% 11% 4 11% 6% 5% 5% 4 6% 7% 36%	2702
	11th to 20th	Night	3 11% 4 11% 6% 5% 6% 5% 6% 7% 35%	2940
	21st to end	Night	2 9% 5% 10% 7% 5% 5% 4 6% 8% 40%	2940
December	1st to 10th	Night	2 7% 4 11% 6% 6% 5% 3 5% 6% 45%	4710
	11th to 20th	Night	1 7% 5% 16% 7% 8% 7% 5% 8% 9% 27%	5338
	21st to end	Night	1 9% 7% 17% 8% 7% 6% 5% 7% 7% 27%	7623

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	60% 11% 13% 11% 5%	4143
	11th to 20th	Day	39% 7% 22% 15% 11% 5%	5075
	21st to end	Day	48% 5% 12% 18% 12% 5%	5844
February	1st to 10th	Day	65% 7% 11% 13% 4	1890
	11th to 20th	Day	65% 8% 12% 11% 4 1	1854
	21st to end	Day	67% 6% 7% 13% 6% 2	1651
March	1st to 10th	Day	50% 6% 15% 17% 8% 4	4879
	11th to 20th	Day	45% 9% 17% 21% 8% 1	5000
	21st to end	Day	61% 12% 13% 11% 2	5486
April	1st to 10th	Day	58% 7% 13% 15% 7%	2310
	11th to 20th	Day	53% 8% 14% 19% 6% 1	2537
	21st to end	Day	53% 10% 13% 20% 4	2600
May	1st to 10th	Day	38% 7% 14% 28% 12% 1	5880
	11th to 20th	Day	36% 11% 18% 25% 9% 2	6118
	21st to end	Day	37% 11% 15% 27% 10%	6926
June	1st to 10th	Day	42% 10% 18% 24% 6%	2893
	11th to 20th	Day	39% 8% 12% 19% 17% 5%	3000
	21st to end	Day	21% 6% 11% 29% 26% 7%	3000
July	1st to 10th	Day	15% 6% 8% 20% 32% 19%	6706
	11th to 20th	Day	15% 6% 7% 22% 30% 22%	6466
	21st to end	Day	15% 5% 8% 19% 38% 16%	6217
August	1st to 10th	Day	25% 6% 9% 22% 26% 13%	4208
	11th to 20th	Day	17% 6% 8% 25% 34% 10%	4197
	21st to end	Day	20% 4 8% 22% 33% 13%	4636
September	1st to 10th	Day	23% 4 8% 22% 34% 8%	2390
	11th to 20th	Day	30% 6% 12% 25% 23% 6%	2200
	21st to end	Day	27% 6% 12% 29% 20% 5%	2200
October	1st to 10th	Day	28% 4 9% 24% 32% 3	3317
	11th to 20th	Day	31% 5% 12% 34% 15% 4	3250
	21st to end	Day	43% 10% 14% 24% 8% 1	3460
November	1st to 10th	Day	49% 8% 15% 20% 7% 1	1794
	11th to 20th	Day	50% 10% 17% 16% 4 2	1680
	21st to end	Day	50% 8% 15% 16% 9% 1	1680
December	1st to 10th	Day	40% 8% 24% 21% 6% 2	2700
	11th to 20th	Day	61% 10% 15% 12% 2 1	3080
	21st to end	Day	60% 7% 10% 12% 4 7%	3575
January	1st to 10th	Night	54% 12% 11% 16% 6%	8769
	11th to 20th	Night	41% 8% 22% 16% 8% 5%	7923
	21st to end	Night	45% 6% 13% 17% 13% 5%	8370
February	1st to 10th	Night	62% 7% 10% 13% 7%	2730
	11th to 20th	Night	60% 8% 11% 12% 8% 1	2663
	21st to end	Night	61% 8% 10% 11% 7% 2	2151
March	1st to 10th	Night	50% 7% 13% 16% 9% 6%	5059
	11th to 20th	Night	34% 9% 21% 27% 8% 1	5000
	21st to end	Night	46% 13% 17% 20% 4	5489
April	1st to 10th	Night	52% 7% 17% 16% 8% 1	2090
	11th to 20th	Night	40% 9% 18% 25% 7% 1	1811
	21st to end	Night	41% 10% 16% 26% 7%	1800
May	1st to 10th	Night	32% 9% 16% 29% 14%	4097
	11th to 20th	Night	33% 11% 18% 29% 7% 1	3785
	21st to end	Night	34% 11% 19% 26% 9%	3972
June	1st to 10th	Night	36% 12% 18% 26% 8% 1	1502
	11th to 20th	Night	31% 7% 15% 23% 19% 5%	1400
	21st to end	Night	16% 6% 12% 31% 25% 10%	1400
July	1st to 10th	Night	15% 4 7% 25% 34% 14%	3145
	11th to 20th	Night	13% 6% 8% 26% 29% 19%	3358
	21st to end	Night	14% 5% 7% 23% 37% 14%	4344
August	1st to 10th	Night	22% 7% 10% 25% 26% 11%	2928
	11th to 20th	Night	18% 5% 8% 28% 30% 10%	2928
	21st to end	Night	19% 4 8% 24% 35% 11%	3271
September	1st to 10th	Night	21% 5% 9% 22% 32% 10%	2005
	11th to 20th	Night	26% 7% 13% 24% 24% 6%	2200
	21st to end	Night	25% 5% 12% 31% 23% 4	2200
October	1st to 10th	Night	20% 4 10% 30% 34% 2	3873
	11th to 20th	Night	29% 5% 14% 32% 16% 3	3898
	21st to end	Night	34% 8% 15% 29% 14% 1	4338
November	1st to 10th	Night	46% 10% 15% 20% 9% 1	2702
	11th to 20th	Night	48% 10% 18% 16% 6% 2	2940
	21st to end	Night	44% 9% 17% 17% 11% 1	2940
December	1st to 10th	Night	42% 7% 20% 23% 7% 1	4710
	11th to 20th	Night	54% 12% 18% 12% 3 1	5339
	21st to end	Night	55% 9% 12% 14% 5% 5%	7623

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	17% 33% 24% 18% 8%	220
	11th to 20th	Day	10% 28% 36% 15% 6% 4	281
	21st to end	Day	11% 26% 35% 18% 9% 1	363
February	1st to 10th	Day	22% 31% 28% 15% 3	330
	11th to 20th	Day	18% 29% 30% 18% 4 2	330
	21st to end	Day	23% 32% 28% 14% 2	367
March	1st to 10th	Day	19% 29% 34% 13% 4 1	509
	11th to 20th	Day	15% 28% 31% 19% 6% 1	500
	21st to end	Day	18% 30% 33% 15% 4 1	550
April	1st to 10th	Day	21% 29% 31% 14% 5% 1	500
	11th to 20th	Day	19% 28% 34% 14% 4	492
	21st to end	Day	21% 22% 31% 18% 6% 2	500
May	1st to 10th	Day	16% 18% 31% 24% 10% 2	503
	11th to 20th	Day	15% 15% 30% 24% 13% 3	645
	21st to end	Day	16% 17% 23% 26% 14% 4	789
June	1st to 10th	Day	12% 17% 26% 27% 15% 4	730
	11th to 20th	Day	17% 22% 33% 20% 7% 1	730
	21st to end	Day	8% 14% 32% 28% 16% 2	730
July	1st to 10th	Day	4 13% 31% 32% 18% 2	721
	11th to 20th	Day	3 13% 40% 27% 15% 1	677
	21st to end	Day	5% 12% 36% 29% 14% 3	575
August	1st to 10th	Day	7% 13% 34% 29% 13% 3	527
	11th to 20th	Day	6% 12% 29% 35% 14% 4	517
	21st to end	Day	7% 15% 34% 26% 14% 5%	583
September	1st to 10th	Day	6% 11% 36% 29% 13% 4	530
	11th to 20th	Day	15% 15% 32% 24% 10% 3	530
	21st to end	Day	12% 18% 32% 22% 14% 2	530
October	1st to 10th	Day	14% 20% 26% 22% 13% 5%	364
	11th to 20th	Day	19% 23% 23% 17% 12% 6%	330
	21st to end	Day	18% 23% 34% 17% 6% 2	363
November	1st to 10th	Day	19% 28% 30% 14% 7% 2	330
	11th to 20th	Day	18% 28% 32% 18% 3 1	330
	21st to end	Day	14% 23% 36% 19% 7%	330
December	1st to 10th	Day	19% 24% 28% 19% 8% 2	330
	11th to 20th	Day	20% 33% 27% 16% 3 1	324
	21st to end	Day	23% 30% 24% 14% 8% 2	242
January	1st to 10th	Night	12% 22% 30% 27% 8% 1	1050
	11th to 20th	Night	9% 22% 34% 23% 10% 2	853
	21st to end	Night	8% 18% 39% 25% 8% 2	924
February	1st to 10th	Night	13% 24% 36% 22% 5%	840
	11th to 20th	Night	12% 23% 32% 26% 6% 1	824
	21st to end	Night	14% 22% 34% 21% 8% 1	692
March	1st to 10th	Night	9% 21% 36% 24% 8% 1	808
	11th to 20th	Night	10% 18% 29% 30% 12% 1	800
	21st to end	Night	11% 15% 33% 31% 9% 1	880
April	1st to 10th	Night	14% 18% 33% 24% 9% 1	690
	11th to 20th	Night	12% 16% 36% 27% 8%	593
	21st to end	Night	15% 10% 29% 33% 13% 1	600
May	1st to 10th	Night	11% 13% 26% 35% 15% 1	600
	11th to 20th	Night	10% 11% 29% 31% 17% 2	591
	21st to end	Night	16% 11% 24% 33% 17% 1	650
June	1st to 10th	Night	13% 9% 24% 31% 22% 1	502
	11th to 20th	Night	10% 12% 33% 33% 12%	400
	21st to end	Night	4 3 22% 47% 22% 2	400
July	1st to 10th	Night	3 2 15% 46% 32% 2	390
	11th to 20th	Night	2 3 20% 49% 24%	441
	21st to end	Night	3 4 21% 47% 23% 2	657
August	1st to 10th	Night	6% 3 19% 42% 28% 2	597
	11th to 20th	Night	3 3 18% 45% 28% 2	594
	21st to end	Night	5% 7% 22% 38% 26% 2	660
September	1st to 10th	Night	6% 3 22% 41% 24% 3	605
	11th to 20th	Night	7% 6% 22% 38% 23% 4	800
	21st to end	Night	12% 7% 23% 33% 22% 4	800
October	1st to 10th	Night	13% 8% 25% 36% 18% 2	800
	11th to 20th	Night	15% 13% 24% 30% 15% 3	800
	21st to end	Night	13% 15% 31% 31% 8% 3	880
November	1st to 10th	Night	17% 17% 33% 23% 9% 1	857
	11th to 20th	Night	14% 24% 32% 24% 6%	1050
	21st to end	Night	10% 21% 34% 26% 8% 1	1050
December	1st to 10th	Night	15% 24% 28% 25% 7% 1	1050
	11th to 20th	Night	14% 25% 30% 22% 7% 1	1050
	21st to end	Night	16% 23% 32% 20% 8% 1	1155

Page generated at 2026-02-27 23:40:19. Version ac07

Copyright © 2026 Attilla Danko.