Falls City Starparty
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Falls City Starparty clear sky chart from 2005-11-06 to 2025-11-18.

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	12% 8% 3 7% 5% 5% 5% 4 5% 6% 41%	136130
	Night	13% 8% 3 7% 5% 5% 4 4 5% 6% 41%	131511
Transparency	Day	44% 7% 13% 19% 13% 4	130902
	Night	45% 6% 14% 19% 12% 4	127736
Seeing	Day	16% 12% 23% 27% 17% 4	16022
	Night	17% 8% 20% 34% 19% 2	24941

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	23% 15% 7% 15% 8% 7% 5% 3 4 4 9%	3639
	11th to 20th	Day	20% 9% 3 8% 5% 5% 5% 4 5% 8% 29%	3663
	21st to end	Day	15% 10% 4 9% 5% 5% 6% 4 5% 6% 31%	4510
February	1st to 10th	Day	21% 13% 3 11% 8% 7% 6% 5% 6% 6% 15%	1800
	11th to 20th	Day	18% 15% 4 10% 7% 6% 6% 4 5% 4 19%	1755
	21st to end	Day	17% 16% 5% 10% 9% 6% 5% 4 6% 4 18%	1540
March	1st to 10th	Day	12% 12% 4 11% 7% 7% 7% 5% 6% 7% 21%	4839
	11th to 20th	Day	19% 14% 3 9% 6% 5% 4 3 4 5% 26%	5000
	21st to end	Day	15% 12% 4 12% 9% 8% 8% 5% 7% 7% 13%	5527
April	1st to 10th	Day	16% 14% 5% 9% 9% 7% 7% 4 6% 6% 17%	2400
	11th to 20th	Day	18% 12% 4 9% 5% 6% 5% 3 6% 5% 27%	2389
	21st to end	Day	13% 10% 4 9% 7% 6% 6% 5% 6% 7% 26%	2600
May	1st to 10th	Day	11% 8% 3 7% 5% 4 4 4 5% 6% 43%	6095
	11th to 20th	Day	10% 6% 2 8% 6% 5% 5% 4 6% 7% 41%	6277
	21st to end	Day	10% 7% 2 6% 5% 6% 6% 5% 7% 7% 37%	6902
June	1st to 10th	Day	15% 8% 3 8% 6% 5% 5% 4 5% 5% 36%	2800
	11th to 20th	Day	11% 8% 3 9% 6% 5% 6% 5% 7% 9% 32%	2800
	21st to end	Day	6% 4 2 6% 5% 4 4 4 5% 7% 53%	2800
July	1st to 10th	Day	2 2 1 3 2 2 2 2 3 5% 76%	6319
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 3 81%	6320
	21st to end	Day	4 2 1 2 2 2 2 2 3 5% 76%	6760
August	1st to 10th	Day	2 3 1 3 3 3 3 2 4 6% 69%	5777
	11th to 20th	Day	5% 4 2 5% 4 4 4 4 6% 7% 56%	5796
	21st to end	Day	6% 5% 2 4 3 3 4 3 6% 7% 57%	6205
September	1st to 10th	Day	4 3 1 4 3 3 3 3 5% 7% 62%	2400
	11th to 20th	Day	8% 6% 2 6% 4 5% 5% 4 6% 8% 47%	2357
	21st to end	Day	12% 6% 2 6% 4 4 3 2 5% 6% 49%	2130
October	1st to 10th	Day	10% 6% 2 5% 4 4 3 4 5% 5% 52%	3280
	11th to 20th	Day	12% 6% 2 7% 7% 6% 7% 5% 7% 9% 32%	3261
	21st to end	Day	14% 9% 3 9% 6% 6% 6% 5% 8% 9% 25%	3558
November	1st to 10th	Day	18% 12% 5% 12% 7% 6% 6% 4 5% 7% 17%	1723
	11th to 20th	Day	20% 14% 5% 10% 7% 6% 5% 4 5% 6% 18%	1656
	21st to end	Day	18% 11% 3 12% 7% 6% 6% 4 5% 5% 22%	1600
December	1st to 10th	Day	15% 9% 3 8% 6% 5% 5% 3 5% 6% 33%	2620
	11th to 20th	Day	21% 12% 4 13% 9% 7% 6% 5% 6% 6% 11%	3028
	21st to end	Day	24% 14% 5% 15% 9% 7% 6% 4 5% 5% 7%	4004
January	1st to 10th	Night	23% 16% 6% 12% 7% 6% 5% 4 4 4 12%	6306
	11th to 20th	Night	18% 13% 4 9% 5% 4 4 3 4 5% 33%	6293
	21st to end	Night	18% 12% 4 9% 4 4 4 3 4 4 35%	6468
February	1st to 10th	Night	14% 13% 5% 11% 7% 7% 5% 4 6% 7% 21%	2600
	11th to 20th	Night	16% 11% 4 9% 6% 6% 6% 5% 6% 5% 25%	2532
	21st to end	Night	16% 12% 4 9% 6% 6% 7% 4 5% 6% 24%	2090
March	1st to 10th	Night	10% 8% 3 10% 8% 9% 8% 6% 7% 6% 25%	5053
	11th to 20th	Night	13% 11% 4 9% 6% 5% 5% 4 5% 5% 32%	5000
	21st to end	Night	16% 13% 4 10% 8% 6% 6% 5% 7% 7% 18%	5447
April	1st to 10th	Night	15% 12% 4 8% 7% 6% 6% 4 6% 6% 27%	2000
	11th to 20th	Night	12% 9% 3 7% 6% 5% 5% 3 7% 8% 36%	1954
	21st to end	Night	11% 8% 3 8% 5% 4 6% 5% 6% 8% 36%	1800
May	1st to 10th	Night	13% 6% 2 6% 3 3 3 3 4 6% 52%	3874
	11th to 20th	Night	8% 6% 2 6% 4 5% 4 3 6% 6% 49%	3616
	21st to end	Night	7% 5% 3 5% 5% 4 5% 5% 7% 8% 46%	3972
June	1st to 10th	Night	12% 6% 3 7% 4 5% 4 4 5% 6% 45%	1600
	11th to 20th	Night	7% 6% 2 6% 4 5% 3 4 5% 8% 50%	1600
	21st to end	Night	5% 3 2 4 3 3 3 2 5% 6% 63%	1509
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 3 84%	3640
	11th to 20th	Night	2 1 1 1 2 1 1 2 2 85%	3640
	21st to end	Night	3 1 2 1 1 2 1 3 5% 81%	4093
August	1st to 10th	Night	2 2 1 4 2 3 3 3 4 5% 72%	4035
	11th to 20th	Night	7% 2 1 3 3 3 3 2 4 6% 66%	4052
	21st to end	Night	5% 3 1 4 3 3 3 3 4 6% 66%	4782
September	1st to 10th	Night	5% 2 1 2 2 3 3 3 4 5% 71%	2000
	11th to 20th	Night	7% 4 2 6% 4 4 4 3 5% 7% 55%	2040
	21st to end	Night	8% 5% 1 5% 3 3 3 3 5% 8% 56%	2270
October	1st to 10th	Night	7% 4 2 5% 3 3 3 3 4 7% 59%	3920
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 4 7% 8% 41%	3897
	21st to end	Night	16% 8% 3 9% 5% 5% 5% 4 6% 6% 33%	4253
November	1st to 10th	Night	18% 9% 3 10% 7% 6% 6% 4 6% 6% 26%	2789
	11th to 20th	Night	21% 12% 4 10% 7% 6% 5% 4 5% 5% 21%	2898
	21st to end	Night	16% 10% 3 9% 7% 5% 6% 4 5% 6% 29%	2800
December	1st to 10th	Night	12% 8% 3 7% 5% 5% 5% 3 6% 6% 41%	4560
	11th to 20th	Night	26% 12% 5% 12% 7% 6% 5% 4 5% 6% 14%	5176
	21st to end	Night	23% 12% 5% 11% 7% 6% 5% 4 5% 6% 15%	6952

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	78% 5% 7% 6% 3	3639
	11th to 20th	Day	53% 8% 10% 19% 9% 1	3663
	21st to end	Day	56% 5% 7% 12% 15% 4	4510
February	1st to 10th	Day	69% 9% 8% 10% 4	1800
	11th to 20th	Day	68% 8% 10% 9% 4 2	1764
	21st to end	Day	69% 4 10% 9% 6% 1	1540
March	1st to 10th	Day	58% 9% 17% 13% 4	4839
	11th to 20th	Day	60% 6% 9% 18% 8%	5000
	21st to end	Day	69% 8% 14% 6% 3	5527
April	1st to 10th	Day	67% 6% 12% 11% 3	2400
	11th to 20th	Day	59% 6% 10% 14% 8% 2	2392
	21st to end	Day	56% 9% 12% 14% 7% 1	2600
May	1st to 10th	Day	41% 6% 12% 25% 15%	6095
	11th to 20th	Day	39% 10% 18% 23% 10% 1	6280
	21st to end	Day	42% 10% 26% 18% 4	6904
June	1st to 10th	Day	50% 6% 17% 20% 7% 1	2800
	11th to 20th	Day	47% 8% 21% 18% 7%	2800
	21st to end	Day	31% 6% 20% 26% 12% 4	2800
July	1st to 10th	Day	12% 4 11% 30% 19% 24%	6251
	11th to 20th	Day	11% 2 7% 19% 43% 18%	6245
	21st to end	Day	11% 5% 15% 37% 27% 5%	6563
August	1st to 10th	Day	15% 5% 12% 30% 26% 13%	4206
	11th to 20th	Day	25% 11% 18% 26% 15% 4	4195
	21st to end	Day	24% 7% 15% 25% 22% 7%	4472
September	1st to 10th	Day	21% 5% 14% 30% 19% 11%	2400
	11th to 20th	Day	33% 8% 15% 21% 17% 5%	2357
	21st to end	Day	37% 5% 14% 23% 15% 5%	2130
October	1st to 10th	Day	32% 8% 9% 24% 25% 2	3280
	11th to 20th	Day	46% 10% 17% 15% 11% 1	3261
	21st to end	Day	51% 9% 12% 16% 10% 1	3558
November	1st to 10th	Day	65% 8% 10% 12% 4	1723
	11th to 20th	Day	67% 8% 10% 8% 5% 2	1656
	21st to end	Day	63% 9% 7% 9% 11% 1	1600
December	1st to 10th	Day	48% 9% 11% 17% 14% 1	2620
	11th to 20th	Day	73% 8% 10% 7% 1	3028
	21st to end	Day	77% 9% 7% 5% 2	4004
January	1st to 10th	Night	75% 6% 8% 6% 4 1	6306
	11th to 20th	Night	54% 6% 10% 19% 11% 1	6293
	21st to end	Night	56% 3 7% 13% 16% 5%	6468
February	1st to 10th	Night	64% 8% 12% 11% 5%	2600
	11th to 20th	Night	60% 7% 14% 11% 7% 2	2534
	21st to end	Night	61% 5% 13% 11% 7% 2	2090
March	1st to 10th	Night	57% 7% 13% 16% 6% 1	5053
	11th to 20th	Night	54% 6% 15% 16% 7% 1	5000
	21st to end	Night	63% 10% 15% 11% 1	5447
April	1st to 10th	Night	58% 8% 17% 12% 5%	2000
	11th to 20th	Night	47% 7% 18% 17% 8% 3	1954
	21st to end	Night	48% 7% 17% 19% 7% 2	1800
May	1st to 10th	Night	36% 5% 12% 32% 15% 1	3871
	11th to 20th	Night	35% 7% 19% 28% 10% 2	3616
	21st to end	Night	33% 8% 36% 19% 3	3972
June	1st to 10th	Night	40% 6% 20% 27% 6% 1	1600
	11th to 20th	Night	32% 7% 26% 27% 8%	1600
	21st to end	Night	23% 4 25% 33% 12% 4	1509
July	1st to 10th	Night	8% 2 14% 27% 26% 23%	3600
	11th to 20th	Night	9% 2 9% 17% 35% 28%	3592
	21st to end	Night	9% 3 19% 36% 27% 6%	3978
August	1st to 10th	Night	10% 4 12% 33% 31% 10%	2929
	11th to 20th	Night	16% 7% 22% 37% 12% 5%	2929
	21st to end	Night	19% 6% 16% 28% 24% 7%	3440
September	1st to 10th	Night	17% 5% 16% 29% 22% 10%	2000
	11th to 20th	Night	30% 6% 17% 24% 16% 8%	2040
	21st to end	Night	29% 5% 17% 25% 17% 8%	2270
October	1st to 10th	Night	25% 7% 12% 30% 23% 3	3920
	11th to 20th	Night	40% 7% 21% 20% 10% 2	3897
	21st to end	Night	51% 8% 13% 18% 9% 2	4253
November	1st to 10th	Night	58% 8% 12% 15% 6% 1	2789
	11th to 20th	Night	64% 8% 10% 9% 7% 2	2898
	21st to end	Night	56% 8% 12% 10% 12% 3	2800
December	1st to 10th	Night	43% 6% 12% 21% 18% 1	4560
	11th to 20th	Night	73% 8% 8% 8% 3	5176
	21st to end	Night	70% 10% 11% 8% 2	6952

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	39% 13% 25% 17% 6% 2	200
	11th to 20th	Day	29% 10% 27% 20% 13% 1	210
	21st to end	Day	26% 12% 23% 24% 12% 3	440
February	1st to 10th	Day	27% 20% 21% 19% 12% 2	400
	11th to 20th	Day	26% 18% 30% 16% 9% 2	395
	21st to end	Day	29% 18% 25% 19% 9%	359
March	1st to 10th	Day	26% 16% 29% 23% 6% 1	500
	11th to 20th	Day	26% 15% 23% 22% 10% 3	500
	21st to end	Day	25% 19% 27% 18% 10% 1	550
April	1st to 10th	Day	23% 18% 24% 20% 11% 3	500
	11th to 20th	Day	23% 18% 24% 21% 9% 4	492
	21st to end	Day	18% 15% 31% 21% 12% 3	500
May	1st to 10th	Day	14% 18% 26% 24% 14% 3	503
	11th to 20th	Day	20% 15% 22% 24% 14% 5%	528
	21st to end	Day	13% 12% 23% 27% 20% 5%	573
June	1st to 10th	Day	17% 9% 24% 28% 20% 3	530
	11th to 20th	Day	12% 14% 30% 30% 12% 2	530
	21st to end	Day	5% 8% 22% 35% 25% 5%	530
July	1st to 10th	Day	5% 5% 21% 37% 26% 6%	526
	11th to 20th	Day	3 4 23% 38% 25% 7%	524
	21st to end	Day	2 4 15% 37% 32% 9%	575
August	1st to 10th	Day	3 3 16% 36% 30% 12%	527
	11th to 20th	Day	2 4 14% 36% 33% 11%	517
	21st to end	Day	5% 5% 22% 33% 27% 8%	583
September	1st to 10th	Day	5% 6% 22% 30% 29% 8%	530
	11th to 20th	Day	9% 7% 23% 30% 26% 6%	530
	21st to end	Day	13% 9% 23% 34% 17% 4	530
October	1st to 10th	Day	13% 12% 26% 27% 17% 5%	530
	11th to 20th	Day	15% 14% 19% 28% 18% 5%	530
	21st to end	Day	22% 16% 24% 23% 11% 4	583
November	1st to 10th	Day	22% 17% 27% 23% 10% 1	263
	11th to 20th	Day	28% 14% 25% 19% 12% 2	214
	21st to end	Day	24% 17% 21% 22% 16% 1	200
December	1st to 10th	Day	29% 11% 19% 26% 13% 3	200
	11th to 20th	Day	30% 15% 25% 25% 4 2	200
	21st to end	Day	30% 17% 21% 22% 8% 1	220
January	1st to 10th	Night	32% 11% 23% 21% 12% 1	800
	11th to 20th	Night	28% 11% 20% 23% 16% 2	800
	21st to end	Night	23% 8% 18% 34% 15% 3	880
February	1st to 10th	Night	23% 10% 23% 28% 15% 1	800
	11th to 20th	Night	21% 12% 24% 28% 14% 1	784
	21st to end	Night	23% 12% 23% 31% 11%	660
March	1st to 10th	Night	20% 10% 25% 32% 12% 1	800
	11th to 20th	Night	22% 11% 20% 33% 13% 1	800
	21st to end	Night	24% 11% 24% 28% 12% 1	880
April	1st to 10th	Night	23% 11% 20% 29% 16% 1	800
	11th to 20th	Night	17% 10% 25% 33% 14% 1	766
	21st to end	Night	16% 6% 23% 38% 16% 1	600
May	1st to 10th	Night	11% 6% 27% 38% 18% 1	504
	11th to 20th	Night	13% 4 19% 42% 21% 1	394
	21st to end	Night	11% 6% 21% 39% 21% 1	433
June	1st to 10th	Night	14% 4 19% 42% 22%	400
	11th to 20th	Night	9% 4 28% 44% 16% 1	400
	21st to end	Night	7% 2 22% 47% 22%	400
July	1st to 10th	Night	3 2 14% 52% 29% 1	390
	11th to 20th	Night	3 3 18% 52% 24% 1	388
	21st to end	Night	2 1 12% 48% 35% 2	486
August	1st to 10th	Night	2 2 7% 47% 37% 5%	597
	11th to 20th	Night	4 1 7% 42% 43% 3	594
	21st to end	Night	5% 3 15% 45% 30% 2	777
September	1st to 10th	Night	5% 2 17% 41% 33% 2	800
	11th to 20th	Night	8% 4 15% 35% 32% 5%	800
	21st to end	Night	10% 4 17% 42% 25% 3	800
October	1st to 10th	Night	11% 4 25% 34% 24% 3	800
	11th to 20th	Night	15% 7% 17% 36% 22% 5%	800
	21st to end	Night	19% 9% 24% 28% 16% 3	880
November	1st to 10th	Night	21% 9% 21% 33% 15% 1	820
	11th to 20th	Night	26% 14% 21% 26% 11% 1	828
	21st to end	Night	21% 7% 22% 32% 16% 2	800
December	1st to 10th	Night	23% 9% 21% 30% 16% 2	800
	11th to 20th	Night	28% 12% 23% 25% 11% 1	800
	21st to end	Night	30% 13% 24% 23% 10%	880

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