Foscoe Overview
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Foscoe Overview clear sky chart from 2005-11-06 to 2026-09-29.

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	13% 7% 2 7% 5% 5% 5% 4 6% 8% 37%	149041
	Night	13% 6% 2 6% 4 4 4 4 6% 8% 42%	142376
Transparency	Day	39% 11% 14% 18% 13% 4	152713
	Night	36% 10% 15% 20% 14% 5%	146763
Seeing	Day	20% 18% 25% 20% 12% 5%	17672
	Night	18% 16% 22% 25% 16% 3	27691

By Month

Percentage Cloud Cover SE (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	14% 6% 2 5% 3 4 3 3 5% 7% 49%	5258
	11th to 20th	Day	8% 6% 3 5% 4 4 3 2 4 6% 55%	5280
	21st to end	Day	13% 7% 3 6% 4 5% 4 3 5% 6% 45%	5780
February	1st to 10th	Day	11% 9% 3 5% 5% 5% 6% 4 6% 7% 38%	1903
	11th to 20th	Day	16% 10% 3 6% 5% 4 4 3 5% 7% 38%	2048
	21st to end	Day	15% 7% 2 6% 5% 4 4 4 6% 8% 38%	1730
March	1st to 10th	Day	18% 6% 2 5% 4 4 5% 3 5% 6% 42%	5030
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 7% 50%	5090
	21st to end	Day	15% 6% 2 6% 5% 4 4 3 5% 7% 42%	5586
April	1st to 10th	Day	11% 6% 2 5% 4 5% 4 4 6% 8% 43%	2310
	11th to 20th	Day	15% 7% 2 5% 4 4 4 4 7% 8% 41%	2511
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 5% 6% 41%	2730
May	1st to 10th	Day	11% 7% 3 8% 6% 6% 6% 5% 7% 8% 33%	7616
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 8% 33%	7626
	21st to end	Day	16% 8% 2 7% 5% 5% 6% 5% 7% 10% 28%	8391
June	1st to 10th	Day	13% 6% 2 7% 7% 7% 6% 5% 7% 8% 31%	2730
	11th to 20th	Day	9% 6% 3 7% 6% 7% 7% 6% 8% 9% 32%	2730
	21st to end	Day	8% 6% 2 7% 6% 7% 7% 6% 9% 10% 31%	2730
July	1st to 10th	Day	6% 5% 2 8% 7% 7% 7% 6% 9% 11% 33%	7680
	11th to 20th	Day	12% 7% 3 9% 7% 7% 7% 6% 8% 9% 25%	7680
	21st to end	Day	15% 9% 3 9% 7% 7% 6% 5% 8% 10% 21%	8340
August	1st to 10th	Day	17% 9% 3 9% 7% 7% 7% 6% 9% 9% 18%	6014
	11th to 20th	Day	7% 5% 2 7% 5% 6% 7% 6% 8% 13% 33%	5951
	21st to end	Day	8% 5% 2 6% 5% 6% 6% 5% 7% 10% 40%	6242
September	1st to 10th	Day	12% 7% 3 8% 5% 5% 6% 5% 6% 9% 34%	2310
	11th to 20th	Day	17% 8% 3 7% 5% 5% 6% 4 7% 7% 30%	2310
	21st to end	Day	20% 7% 2 6% 5% 5% 5% 5% 6% 7% 32%	2288
October	1st to 10th	Day	17% 5% 2 6% 4 3 4 4 5% 6% 46%	2118
	11th to 20th	Day	12% 6% 1 5% 3 4 4 3 4 6% 52%	2000
	21st to end	Day	15% 6% 1 5% 3 3 4 3 5% 6% 50%	2200
November	1st to 10th	Day	11% 7% 2 4 3 3 3 4 4 7% 53%	2001
	11th to 20th	Day	11% 5% 2 4 4 4 4 4 5% 7% 51%	1890
	21st to end	Day	13% 5% 3 6% 4 3 4 3 4 7% 48%	1890
December	1st to 10th	Day	10% 6% 3 5% 5% 4 4 4 4 7% 47%	3020
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 6% 7% 42%	3463
	21st to end	Day	17% 9% 2 5% 3 4 5% 3 5% 8% 40%	4565
January	1st to 10th	Night	12% 6% 2 5% 3 3 3 4 4 8% 50%	7635
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 4 5% 53%	7680
	21st to end	Night	13% 7% 3 5% 4 4 4 3 5% 6% 47%	8401
February	1st to 10th	Night	11% 7% 2 6% 4 4 5% 5% 7% 8% 41%	2714
	11th to 20th	Night	16% 8% 2 5% 4 4 5% 4 6% 7% 40%	2458
	21st to end	Night	13% 7% 2 7% 6% 4 5% 4 7% 7% 38%	2076
March	1st to 10th	Night	18% 8% 2 5% 4 4 4 3 5% 6% 40%	5041
	11th to 20th	Night	10% 5% 1 4 3 4 4 4 6% 8% 51%	5090
	21st to end	Night	15% 6% 2 5% 4 5% 5% 4 5% 9% 43%	5588
April	1st to 10th	Night	11% 6% 2 6% 4 4 5% 4 7% 9% 43%	2310
	11th to 20th	Night	14% 5% 2 5% 4 3 4 4 6% 8% 46%	2072
	21st to end	Night	11% 7% 2 6% 4 4 4 5% 6% 8% 43%	1890
May	1st to 10th	Night	13% 6% 2 6% 4 5% 4 5% 9% 10% 35%	5237
	11th to 20th	Night	17% 6% 2 6% 4 4 5% 4 7% 9% 36%	5234
	21st to end	Night	21% 7% 2 6% 4 4 5% 4 6% 10% 30%	5761
June	1st to 10th	Night	10% 6% 3 7% 4 5% 6% 5% 8% 10% 36%	1890
	11th to 20th	Night	9% 7% 2 5% 5% 5% 5% 4 9% 11% 40%	1890
	21st to end	Night	7% 5% 2 5% 6% 4 6% 5% 9% 12% 40%	1890
July	1st to 10th	Night	7% 5% 2 6% 4 5% 6% 5% 9% 13% 37%	5278
	11th to 20th	Night	12% 5% 2 6% 5% 5% 6% 5% 8% 12% 35%	5277
	21st to end	Night	13% 8% 3 8% 6% 6% 6% 6% 8% 12% 25%	5736
August	1st to 10th	Night	19% 8% 2 7% 5% 5% 5% 5% 7% 11% 25%	4135
	11th to 20th	Night	8% 5% 2 5% 4 5% 6% 4 7% 13% 41%	4095
	21st to end	Night	8% 6% 2 5% 4 4 4 4 7% 10% 47%	4830
September	1st to 10th	Night	12% 8% 2 7% 4 4 5% 4 5% 7% 43%	2310
	11th to 20th	Night	19% 7% 2 6% 4 4 4 3 5% 7% 38%	2310
	21st to end	Night	21% 8% 2 6% 3 4 4 3 4 5% 41%	2289
October	1st to 10th	Night	16% 7% 2 5% 3 4 3 3 5% 6% 46%	2280
	11th to 20th	Night	13% 6% 2 5% 4 3 3 2 5% 6% 51%	2400
	21st to end	Night	14% 5% 1 5% 3 3 3 3 4 5% 54%	2640
November	1st to 10th	Night	13% 8% 2 5% 3 3 3 2 5% 7% 50%	2514
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 5% 8% 50%	2730
	21st to end	Night	12% 6% 2 5% 3 4 4 4 6% 7% 47%	2730
December	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 7% 49%	4380
	11th to 20th	Night	14% 9% 3 7% 5% 5% 5% 3 4 6% 38%	4952
	21st to end	Night	19% 7% 2 5% 4 4 4 3 5% 8% 40%	6633

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	32% 6% 12% 22% 23% 5%	5259
	11th to 20th	Day	29% 7% 8% 14% 31% 13%	5280
	21st to end	Day	38% 6% 9% 19% 20% 8%	5780
February	1st to 10th	Day	41% 10% 12% 19% 15% 4	1903
	11th to 20th	Day	44% 8% 10% 18% 16% 4	2058
	21st to end	Day	42% 9% 12% 16% 15% 6%	1730
March	1st to 10th	Day	40% 7% 9% 17% 17% 10%	5030
	11th to 20th	Day	31% 7% 9% 21% 17% 15%	5090
	21st to end	Day	39% 7% 11% 25% 14% 4	5586
April	1st to 10th	Day	35% 9% 13% 23% 16% 3	2310
	11th to 20th	Day	38% 9% 12% 20% 17% 4	2511
	21st to end	Day	40% 11% 12% 22% 12% 2	2730
May	1st to 10th	Day	43% 12% 14% 18% 11% 1	7651
	11th to 20th	Day	44% 12% 15% 20% 9% 1	7630
	21st to end	Day	46% 12% 13% 15% 11% 2	8405
June	1st to 10th	Day	45% 13% 15% 18% 9%	2730
	11th to 20th	Day	42% 13% 16% 17% 11% 1	2730
	21st to end	Day	41% 14% 16% 18% 11% 1	2730
July	1st to 10th	Day	38% 17% 18% 18% 7% 1	7615
	11th to 20th	Day	48% 15% 18% 14% 4 1	7611
	21st to end	Day	52% 14% 15% 11% 7% 1	8156
August	1st to 10th	Day	54% 18% 15% 11% 2	6001
	11th to 20th	Day	33% 16% 27% 17% 5% 2	5990
	21st to end	Day	31% 14% 19% 27% 8% 1	6242
September	1st to 10th	Day	42% 11% 12% 18% 14% 3	2310
	11th to 20th	Day	46% 11% 11% 18% 12% 2	2310
	21st to end	Day	47% 9% 12% 15% 12% 5%	2288
October	1st to 10th	Day	27% 7% 12% 16% 25% 13%	3443
	11th to 20th	Day	23% 4 7% 21% 24% 21%	3240
	21st to end	Day	25% 7% 11% 25% 16% 16%	3538
November	1st to 10th	Day	31% 7% 11% 19% 26% 7%	2001
	11th to 20th	Day	31% 7% 9% 22% 23% 7%	1890
	21st to end	Day	35% 6% 10% 23% 21% 4	1890
December	1st to 10th	Day	35% 7% 9% 19% 25% 6%	3020
	11th to 20th	Day	38% 8% 11% 18% 19% 5%	3460
	21st to end	Day	39% 8% 15% 23% 12% 3	4565
January	1st to 10th	Night	31% 7% 13% 27% 14% 8%	7636
	11th to 20th	Night	30% 8% 8% 17% 24% 12%	7680
	21st to end	Night	37% 6% 10% 16% 22% 8%	8401
February	1st to 10th	Night	36% 10% 14% 21% 16% 4	2714
	11th to 20th	Night	43% 8% 12% 18% 15% 5%	2459
	21st to end	Night	41% 10% 12% 18% 14% 5%	2076
March	1st to 10th	Night	40% 9% 9% 18% 17% 8%	5041
	11th to 20th	Night	28% 8% 10% 22% 17% 15%	5090
	21st to end	Night	36% 9% 13% 25% 11% 5%	5588
April	1st to 10th	Night	34% 10% 17% 21% 15% 4	2310
	11th to 20th	Night	33% 9% 13% 23% 16% 5%	2072
	21st to end	Night	36% 10% 16% 23% 14% 1	1890
May	1st to 10th	Night	40% 13% 16% 20% 11% 1	5264
	11th to 20th	Night	41% 12% 19% 20% 8%	5235
	21st to end	Night	46% 12% 17% 16% 8% 1	5771
June	1st to 10th	Night	39% 14% 17% 20% 9% 1	1890
	11th to 20th	Night	34% 13% 23% 22% 8% 1	1890
	21st to end	Night	32% 15% 19% 21% 11% 2	1890
July	1st to 10th	Night	34% 16% 24% 20% 5% 1	5235
	11th to 20th	Night	39% 16% 25% 17% 3 1	5226
	21st to end	Night	46% 16% 20% 10% 6% 2	5606
August	1st to 10th	Night	50% 16% 21% 11% 3	4124
	11th to 20th	Night	31% 14% 29% 20% 6% 1	4122
	21st to end	Night	28% 12% 23% 29% 6% 2	4830
September	1st to 10th	Night	38% 11% 15% 19% 14% 3	2310
	11th to 20th	Night	43% 10% 14% 19% 14% 1	2310
	21st to end	Night	45% 8% 12% 17% 15% 3	2289
October	1st to 10th	Night	27% 9% 12% 19% 18% 14%	3722
	11th to 20th	Night	23% 5% 9% 21% 22% 20%	3899
	21st to end	Night	28% 7% 8% 22% 20% 15%	4252
November	1st to 10th	Night	34% 7% 10% 21% 21% 7%	2514
	11th to 20th	Night	31% 7% 10% 21% 22% 8%	2730
	21st to end	Night	33% 8% 10% 22% 22% 5%	2730
December	1st to 10th	Night	32% 9% 12% 20% 23% 4	4380
	11th to 20th	Night	44% 8% 11% 16% 17% 4	4954
	21st to end	Night	38% 10% 17% 20% 12% 3	6633

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	38% 32% 22% 7% 1	330
	11th to 20th	Day	35% 27% 29% 8% 1	330
	21st to end	Day	32% 35% 25% 7% 1	363
February	1st to 10th	Day	23% 36% 31% 8% 1	330
	11th to 20th	Day	44% 32% 20% 4	330
	21st to end	Day	36% 34% 26% 4	273
March	1st to 10th	Day	25% 28% 29% 14% 4	525
	11th to 20th	Day	28% 33% 24% 12% 2 1	540
	21st to end	Day	28% 29% 27% 12% 4	594
April	1st to 10th	Day	24% 27% 26% 16% 6% 1	540
	11th to 20th	Day	21% 28% 24% 18% 8% 2	532
	21st to end	Day	21% 20% 30% 15% 11% 3	540
May	1st to 10th	Day	18% 24% 34% 13% 7% 4	543
	11th to 20th	Day	21% 14% 28% 21% 10% 6%	567
	21st to end	Day	21% 12% 24% 20% 14% 9%	617
June	1st to 10th	Day	15% 10% 29% 25% 14% 7%	570
	11th to 20th	Day	11% 8% 26% 30% 16% 9%	570
	21st to end	Day	9% 10% 30% 28% 16% 8%	570
July	1st to 10th	Day	8% 5% 21% 29% 25% 12%	565
	11th to 20th	Day	10% 6% 16% 33% 24% 11%	564
	21st to end	Day	11% 7% 21% 29% 19% 12%	620
August	1st to 10th	Day	20% 9% 22% 23% 14% 12%	566
	11th to 20th	Day	11% 6% 24% 27% 23% 10%	559
	21st to end	Day	14% 7% 18% 27% 19% 15%	627
September	1st to 10th	Day	12% 5% 19% 28% 24% 12%	570
	11th to 20th	Day	16% 8% 18% 24% 25% 9%	570
	21st to end	Day	23% 11% 25% 23% 14% 4	562
October	1st to 10th	Day	20% 11% 20% 24% 18% 6%	530
	11th to 20th	Day	17% 20% 25% 21% 15% 2	530
	21st to end	Day	21% 18% 26% 23% 10% 2	583
November	1st to 10th	Day	19% 19% 29% 21% 9% 3	479
	11th to 20th	Day	22% 28% 32% 15% 3 1	330
	21st to end	Day	25% 24% 32% 15% 4 1	330
December	1st to 10th	Day	28% 29% 31% 9% 2	330
	11th to 20th	Day	25% 22% 38% 12% 3	330
	21st to end	Day	29% 24% 33% 9% 4 1	363
January	1st to 10th	Night	23% 28% 27% 18% 4	840
	11th to 20th	Night	23% 27% 27% 19% 4	840
	21st to end	Night	18% 32% 29% 18% 3	924
February	1st to 10th	Night	16% 27% 31% 24% 3	840
	11th to 20th	Night	26% 31% 27% 15% 1	823
	21st to end	Night	22% 29% 31% 16% 2	692
March	1st to 10th	Night	18% 26% 31% 22% 4	840
	11th to 20th	Night	23% 21% 31% 18% 7%	840
	21st to end	Night	21% 22% 31% 20% 7%	924
April	1st to 10th	Night	20% 23% 25% 25% 7%	840
	11th to 20th	Night	20% 20% 25% 23% 12% 1	784
	21st to end	Night	15% 16% 24% 33% 12% 1	630
May	1st to 10th	Night	15% 16% 32% 24% 13% 1	630
	11th to 20th	Night	15% 12% 24% 29% 17% 2	621
	21st to end	Night	20% 7% 16% 26% 25% 6%	683
June	1st to 10th	Night	11% 5% 20% 33% 26% 5%	630
	11th to 20th	Night	10% 4 22% 27% 31% 6%	630
	21st to end	Night	6% 5% 20% 33% 32% 4	630
July	1st to 10th	Night	11% 2 12% 28% 41% 5%	615
	11th to 20th	Night	9% 4 11% 27% 41% 8%	612
	21st to end	Night	8% 4 13% 29% 38% 9%	690
August	1st to 10th	Night	18% 3 11% 27% 35% 6%	627
	11th to 20th	Night	14% 4 13% 31% 32% 6%	624
	21st to end	Night	14% 4 12% 28% 35% 8%	785
September	1st to 10th	Night	14% 5% 13% 29% 34% 6%	840
	11th to 20th	Night	21% 4 12% 25% 33% 5%	840
	21st to end	Night	24% 7% 15% 26% 25% 2	833
October	1st to 10th	Night	18% 12% 18% 22% 23% 7%	800
	11th to 20th	Night	19% 15% 23% 28% 13% 2	800
	21st to end	Night	19% 16% 21% 31% 11% 2	880
November	1st to 10th	Night	18% 15% 20% 31% 13% 2	820
	11th to 20th	Night	19% 20% 23% 28% 9% 1	840
	21st to end	Night	18% 20% 24% 26% 10% 1	840
December	1st to 10th	Night	21% 24% 26% 23% 6%	840
	11th to 20th	Night	19% 22% 26% 26% 5% 1	840
	21st to end	Night	25% 21% 26% 23% 4	924

Page generated at 2026-09-26 04:18:40. Version ac07

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