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 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	4 9% 4 9% 5% 5% 5% 4 6% 7% 42%	105697
	Night	3 8% 4 10% 6% 5% 5% 4 6% 7% 42%	102616
Transparency	Day	40% 7% 12% 20% 15% 6%	105440
	Night	41% 8% 13% 20% 14% 4	102462
Seeing	Day	13% 21% 31% 22% 10% 2	15594
	Night	11% 15% 29% 31% 14% 2	25212

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	2 10% 6% 18% 11% 7% 6% 4 7% 7% 22%	2223
	11th to 20th	Day	2 10% 6% 13% 12% 6% 6% 4 6% 7% 28%	2707
	21st to end	Day	2 20% 12% 18% 5% 4 3 2 3 4 26%	3146
February	1st to 10th	Day	3 16% 8% 17% 9% 7% 5% 5% 5% 6% 21%	1710
	11th to 20th	Day	2 14% 8% 19% 9% 6% 5% 3 5% 6% 23%	1665
	21st to end	Day	2 14% 9% 23% 11% 6% 5% 3 5% 4 19%	1498
March	1st to 10th	Day	1 11% 6% 20% 10% 7% 6% 3 5% 4 28%	3374
	11th to 20th	Day	1 12% 6% 10% 5% 4 4 4 4 6% 43%	3490
	21st to end	Day	3 18% 9% 18% 8% 7% 6% 4 6% 6% 14%	3825
April	1st to 10th	Day	5% 18% 7% 12% 8% 6% 5% 3 5% 6% 26%	2194
	11th to 20th	Day	5% 15% 5% 12% 7% 6% 5% 4 5% 6% 29%	2405
	21st to end	Day	7% 16% 5% 10% 5% 6% 5% 5% 6% 6% 29%	2470
May	1st to 10th	Day	7% 17% 5% 10% 6% 5% 6% 3 6% 7% 29%	4110
	11th to 20th	Day	5% 6% 3 7% 5% 5% 6% 5% 8% 11% 40%	4260
	21st to end	Day	8% 12% 3 8% 6% 5% 6% 4 7% 8% 34%	4825
June	1st to 10th	Day	11% 8% 2 6% 6% 6% 5% 4 7% 9% 36%	2748
	11th to 20th	Day	11% 7% 2 6% 5% 5% 6% 5% 6% 8% 38%	2850
	21st to end	Day	3 3 2 4 4 3 4 4 6% 8% 59%	2850
July	1st to 10th	Day	2 2 1 2 3 4 4 4 6% 8% 64%	4740
	11th to 20th	Day	2 2 1 4 3 4 5% 4 7% 8% 60%	4574
	21st to end	Day	2 2 1 3 3 3 5% 4 6% 8% 62%	4454
August	1st to 10th	Day	4 2 1 4 4 5% 6% 5% 7% 9% 52%	4092
	11th to 20th	Day	3 2 1 3 3 3 4 3 5% 7% 65%	4028
	21st to end	Day	4 3 1 3 2 3 4 3 5% 6% 65%	4495
September	1st to 10th	Day	5% 5% 2 4 3 3 4 2 5% 6% 62%	2271
	11th to 20th	Day	7% 6% 2 4 3 4 4 3 5% 7% 54%	2090
	21st to end	Day	6% 7% 2 4 3 3 3 4 4 8% 56%	2090
October	1st to 10th	Day	6% 7% 2 4 3 3 3 3 4 4 62%	3216
	11th to 20th	Day	4 7% 3 6% 3 3 3 2 4 6% 58%	3150
	21st to end	Day	3 11% 5% 9% 5% 5% 5% 5% 6% 6% 40%	3353
November	1st to 10th	Day	7% 11% 5% 12% 6% 6% 4 4 5% 6% 34%	1707
	11th to 20th	Day	3 15% 5% 11% 6% 5% 5% 4 6% 7% 33%	1600
	21st to end	Day	2 11% 6% 12% 7% 7% 5% 4 5% 6% 37%	1600
December	1st to 10th	Day	2 11% 6% 14% 11% 7% 6% 5% 5% 5% 27%	1528
	11th to 20th	Day	3 13% 7% 17% 8% 6% 6% 5% 7% 7% 22%	1917
	21st to end	Day	2 14% 7% 14% 7% 5% 5% 4 5% 7% 31%	2442
January	1st to 10th	Night	1 8% 5% 18% 10% 8% 7% 4 5% 7% 25%	4726
	11th to 20th	Night	1 9% 5% 15% 12% 8% 7% 5% 5% 7% 24%	4279
	21st to end	Night	1 16% 12% 18% 7% 5% 4 4 5% 6% 22%	4521
February	1st to 10th	Night	3 14% 7% 16% 8% 6% 5% 4 6% 7% 24%	2470
	11th to 20th	Night	2 13% 5% 16% 8% 7% 6% 5% 6% 6% 26%	2402
	21st to end	Night	2 11% 5% 18% 10% 8% 5% 4 6% 7% 22%	1953
March	1st to 10th	Night	1 10% 5% 15% 12% 7% 6% 4 5% 5% 32%	3499
	11th to 20th	Night	1 8% 4 9% 4 4 3 4 5% 7% 50%	3490
	21st to end	Night	2 10% 5% 13% 6% 6% 6% 6% 8% 11% 26%	3828
April	1st to 10th	Night	5% 15% 5% 10% 7% 5% 4 4 6% 7% 33%	1986
	11th to 20th	Night	4 9% 4 8% 6% 5% 5% 5% 8% 7% 38%	1720
	21st to end	Night	7% 12% 4 6% 4 5% 5% 4 7% 7% 40%	1710
May	1st to 10th	Night	5% 11% 5% 8% 5% 5% 6% 4 7% 8% 35%	2860
	11th to 20th	Night	4 5% 2 6% 5% 5% 5% 5% 7% 9% 46%	2628
	21st to end	Night	9% 12% 3 7% 6% 5% 6% 5% 8% 9% 31%	2762
June	1st to 10th	Night	11% 6% 2 6% 4 4 5% 5% 8% 8% 41%	1427
	11th to 20th	Night	8% 5% 2 5% 5% 4 5% 4 7% 8% 47%	1330
	21st to end	Night	3 2 1 3 2 3 3 3 6% 8% 65%	1330
July	1st to 10th	Night	4 2 1 3 2 2 4 3 6% 6% 66%	2220
	11th to 20th	Night	2 2 1 3 2 4 5% 4 6% 7% 65%	2370
	21st to end	Night	2 2 1 2 3 4 4 5% 7% 8% 63%	3109
August	1st to 10th	Night	3 3 1 4 4 4 5% 5% 8% 10% 53%	2847
	11th to 20th	Night	2 2 1 4 3 4 4 4 7% 8% 61%	2811
	21st to end	Night	3 3 1 4 3 2 3 3 4 5% 69%	3171
September	1st to 10th	Night	5% 3 2 4 3 3 4 3 4 6% 64%	1905
	11th to 20th	Night	5% 4 2 4 4 4 4 5% 6% 7% 55%	2090
	21st to end	Night	7% 6% 1 3 3 3 3 2 4 6% 61%	2090
October	1st to 10th	Night	5% 4 1 3 2 2 2 2 4 5% 69%	3755
	11th to 20th	Night	5% 8% 2 5% 3 3 3 3 5% 6% 58%	3778
	21st to end	Night	4 8% 3 7% 4 4 5% 4 6% 8% 46%	4203
November	1st to 10th	Night	6% 12% 4 11% 6% 5% 5% 4 6% 7% 35%	2570
	11th to 20th	Night	4 11% 4 12% 6% 6% 6% 5% 6% 7% 34%	2800
	21st to end	Night	2 9% 5% 10% 7% 5% 5% 4 6% 8% 39%	2800
December	1st to 10th	Night	3 10% 6% 15% 8% 8% 7% 3 5% 7% 28%	2687
	11th to 20th	Night	1 10% 6% 14% 9% 8% 6% 4 8% 7% 27%	3275
	21st to end	Night	2 11% 9% 16% 8% 6% 5% 4 5% 6% 30%	5214

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	63% 8% 11% 15% 3	2223
	11th to 20th	Day	56% 8% 14% 10% 7% 5%	2707
	21st to end	Day	66% 5% 8% 13% 7% 1	3146
February	1st to 10th	Day	67% 7% 11% 12% 4	1710
	11th to 20th	Day	64% 7% 12% 11% 4 1	1674
	21st to end	Day	71% 6% 7% 10% 5% 2	1498
March	1st to 10th	Day	58% 7% 12% 15% 7% 1	3374
	11th to 20th	Day	41% 8% 20% 21% 8% 1	3490
	21st to end	Day	69% 12% 11% 7% 1	3825
April	1st to 10th	Day	60% 6% 13% 14% 7%	2194
	11th to 20th	Day	54% 8% 13% 18% 5% 1	2408
	21st to end	Day	54% 9% 13% 20% 4	2470
May	1st to 10th	Day	49% 8% 13% 22% 7% 1	4110
	11th to 20th	Day	30% 11% 20% 26% 11% 2	4264
	21st to end	Day	46% 12% 14% 23% 5%	4825
June	1st to 10th	Day	43% 10% 19% 23% 5%	2748
	11th to 20th	Day	41% 9% 12% 18% 16% 5%	2850
	21st to end	Day	21% 6% 11% 29% 26% 8%	2850
July	1st to 10th	Day	14% 6% 10% 20% 36% 14%	4666
	11th to 20th	Day	18% 6% 7% 16% 27% 26%	4493
	21st to end	Day	18% 5% 8% 18% 33% 17%	4314
August	1st to 10th	Day	25% 6% 9% 21% 26% 13%	4078
	11th to 20th	Day	18% 6% 8% 25% 34% 10%	4067
	21st to end	Day	19% 4 8% 23% 33% 13%	4494
September	1st to 10th	Day	24% 4 8% 21% 35% 9%	2271
	11th to 20th	Day	30% 5% 12% 25% 22% 6%	2090
	21st to end	Day	27% 6% 12% 30% 19% 5%	2090
October	1st to 10th	Day	28% 4 9% 24% 33% 3	3216
	11th to 20th	Day	30% 5% 12% 34% 15% 4	3150
	21st to end	Day	43% 10% 14% 23% 8% 1	3353
November	1st to 10th	Day	51% 8% 14% 19% 7% 1	1707
	11th to 20th	Day	50% 10% 17% 16% 4 2	1600
	21st to end	Day	51% 8% 15% 16% 9% 1	1600
December	1st to 10th	Day	60% 9% 10% 11% 7% 3	1528
	11th to 20th	Day	61% 9% 12% 14% 3	1915
	21st to end	Day	54% 5% 9% 15% 6% 10%	2442
January	1st to 10th	Night	60% 9% 10% 15% 5% 1	4726
	11th to 20th	Night	61% 9% 10% 9% 6% 4	4279
	21st to end	Night	66% 7% 12% 10% 4 1	4521
February	1st to 10th	Night	64% 8% 9% 13% 6%	2470
	11th to 20th	Night	61% 8% 10% 13% 7% 1	2403
	21st to end	Night	64% 8% 10% 9% 6% 3	1953
March	1st to 10th	Night	54% 9% 11% 17% 6% 2	3499
	11th to 20th	Night	32% 9% 24% 25% 8% 1	3490
	21st to end	Night	51% 14% 18% 14% 2	3828
April	1st to 10th	Night	53% 7% 17% 15% 8% 1	1986
	11th to 20th	Night	40% 10% 18% 24% 7% 1	1720
	21st to end	Night	41% 10% 16% 25% 7%	1710
May	1st to 10th	Night	40% 10% 20% 20% 9%	2860
	11th to 20th	Night	28% 11% 20% 30% 10% 2	2629
	21st to end	Night	41% 13% 18% 22% 6%	2762
June	1st to 10th	Night	36% 12% 19% 25% 7% 1	1427
	11th to 20th	Night	32% 8% 15% 23% 18% 5%	1330
	21st to end	Night	16% 6% 12% 31% 24% 10%	1330
July	1st to 10th	Night	16% 5% 8% 22% 39% 11%	2185
	11th to 20th	Night	14% 5% 9% 21% 26% 25%	2328
	21st to end	Night	16% 5% 7% 25% 32% 15%	3011
August	1st to 10th	Night	22% 7% 10% 24% 26% 11%	2838
	11th to 20th	Night	19% 5% 8% 28% 30% 10%	2838
	21st to end	Night	18% 4 8% 25% 35% 11%	3171
September	1st to 10th	Night	21% 5% 8% 21% 33% 11%	1905
	11th to 20th	Night	26% 7% 13% 24% 24% 6%	2090
	21st to end	Night	25% 5% 12% 31% 23% 4	2090
October	1st to 10th	Night	20% 4 10% 31% 34% 2	3755
	11th to 20th	Night	29% 5% 14% 33% 16% 3	3778
	21st to end	Night	34% 8% 15% 29% 14%	4203
November	1st to 10th	Night	47% 9% 15% 19% 9% 1	2570
	11th to 20th	Night	49% 10% 18% 16% 6% 2	2800
	21st to end	Night	44% 9% 17% 16% 11% 2	2800
December	1st to 10th	Night	60% 7% 13% 10% 6% 2	2687
	11th to 20th	Night	59% 10% 12% 14% 4 1	3276
	21st to end	Night	55% 7% 9% 15% 6% 8%	5214

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	13% 31% 24% 22% 9%	180
	11th to 20th	Day	11% 28% 34% 15% 7% 5%	229
	21st to end	Day	12% 24% 35% 20% 8% 1	297
February	1st to 10th	Day	19% 34% 29% 16% 2	270
	11th to 20th	Day	18% 27% 32% 17% 4 2	270
	21st to end	Day	19% 33% 29% 16% 3	310
March	1st to 10th	Day	20% 31% 34% 12% 3	460
	11th to 20th	Day	12% 28% 32% 20% 7% 1	460
	21st to end	Day	17% 29% 34% 15% 4 1	506
April	1st to 10th	Day	22% 30% 32% 12% 4 1	460
	11th to 20th	Day	19% 29% 33% 15% 5%	452
	21st to end	Day	22% 21% 29% 18% 7% 3	460
May	1st to 10th	Day	16% 19% 30% 24% 9% 2	463
	11th to 20th	Day	15% 13% 30% 25% 14% 3	599
	21st to end	Day	17% 18% 23% 24% 14% 4	734
June	1st to 10th	Day	13% 17% 25% 26% 15% 5%	680
	11th to 20th	Day	18% 21% 31% 21% 8% 1	680
	21st to end	Day	7% 13% 32% 29% 16% 2	680
July	1st to 10th	Day	4 13% 31% 32% 19% 3	671
	11th to 20th	Day	3 12% 40% 28% 16% 1	629
	21st to end	Day	5% 11% 35% 30% 15% 4	531
August	1st to 10th	Day	8% 13% 33% 30% 14% 3	487
	11th to 20th	Day	6% 12% 28% 35% 14% 5%	477
	21st to end	Day	7% 16% 32% 27% 13% 5%	539
September	1st to 10th	Day	7% 12% 37% 27% 13% 4	490
	11th to 20th	Day	16% 16% 31% 23% 11% 3	490
	21st to end	Day	12% 19% 32% 22% 14% 1	490
October	1st to 10th	Day	14% 18% 26% 23% 14% 5%	333
	11th to 20th	Day	17% 23% 23% 18% 13% 7%	300
	21st to end	Day	18% 24% 34% 17% 6% 1	330
November	1st to 10th	Day	17% 28% 31% 14% 8% 3	300
	11th to 20th	Day	17% 29% 31% 19% 4 1	300
	21st to end	Day	14% 23% 36% 19% 7%	300
December	1st to 10th	Day	16% 24% 30% 20% 8% 1	273
	11th to 20th	Day	14% 36% 26% 20% 4 1	266
	21st to end	Day	18% 32% 22% 17% 9% 2	198
January	1st to 10th	Night	11% 21% 29% 29% 9% 1	950
	11th to 20th	Night	10% 22% 32% 23% 11% 2	773
	21st to end	Night	8% 17% 39% 26% 9% 2	836
February	1st to 10th	Night	11% 24% 37% 23% 5% 1	760
	11th to 20th	Night	12% 23% 31% 26% 7% 1	744
	21st to end	Night	12% 22% 35% 22% 8% 1	628
March	1st to 10th	Night	10% 21% 36% 25% 8% 1	760
	11th to 20th	Night	10% 16% 29% 31% 13% 1	760
	21st to end	Night	11% 15% 32% 31% 9% 1	836
April	1st to 10th	Night	15% 17% 34% 24% 8% 2	656
	11th to 20th	Night	12% 16% 36% 27% 8%	563
	21st to end	Night	14% 9% 29% 33% 13% 1	570
May	1st to 10th	Night	12% 13% 27% 34% 15% 1	570
	11th to 20th	Night	10% 10% 28% 32% 17% 2	561
	21st to end	Night	16% 12% 24% 32% 16% 1	617
June	1st to 10th	Night	14% 9% 23% 31% 22% 1	477
	11th to 20th	Night	11% 12% 33% 32% 13%	380
	21st to end	Night	3 3 22% 47% 22% 2	380
July	1st to 10th	Night	3 2 15% 46% 32% 2	370
	11th to 20th	Night	3 2 21% 49% 25%	418
	21st to end	Night	3 3 20% 47% 24% 3	624
August	1st to 10th	Night	6% 3 18% 42% 29% 2	567
	11th to 20th	Night	4 3 18% 45% 29% 2	564
	21st to end	Night	5% 7% 22% 37% 27% 2	627
September	1st to 10th	Night	6% 4 22% 42% 23% 3	575
	11th to 20th	Night	7% 6% 22% 38% 23% 4	760
	21st to end	Night	13% 7% 22% 33% 21% 4	760
October	1st to 10th	Night	13% 8% 24% 35% 18% 2	760
	11th to 20th	Night	15% 11% 24% 31% 16% 3	760
	21st to end	Night	13% 15% 31% 31% 7% 3	836
November	1st to 10th	Night	17% 17% 33% 23% 9% 1	815
	11th to 20th	Night	13% 25% 32% 24% 6%	1000
	21st to end	Night	10% 21% 35% 26% 8% 1	1000
December	1st to 10th	Night	14% 23% 29% 26% 7% 1	960
	11th to 20th	Night	12% 24% 31% 25% 8% 1	950
	21st to end	Night	14% 23% 33% 20% 9% 1	1045

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