Ambersweet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ambersweet Observatory clear sky chart from 2005-11-06 to 2026-10-14.

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	7% 5% 2 7% 5% 5% 6% 5% 8% 10% 39%	148711
	Night	8% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	143031
Transparency	Day	36% 10% 18% 19% 12% 5%	152421
	Night	36% 10% 17% 19% 13% 6%	147392
Seeing	Day	8% 6% 19% 26% 24% 17%	18184
	Night	10% 5% 20% 33% 25% 7%	28207

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	7% 5% 2 6% 4 3 4 3 5% 7% 55%	5258
	11th to 20th	Day	18% 9% 4 8% 4 4 4 4 5% 6% 34%	5280
	21st to end	Day	11% 5% 2 5% 4 4 4 4 5% 8% 49%	5940
February	1st to 10th	Day	12% 5% 2 6% 4 4 4 4 6% 7% 45%	2100
	11th to 20th	Day	9% 4 2 6% 4 4 4 3 6% 7% 51%	2048
	21st to end	Day	9% 6% 2 6% 5% 4 4 3 5% 7% 50%	1833
March	1st to 10th	Day	8% 6% 2 7% 4 5% 4 4 7% 10% 44%	5045
	11th to 20th	Day	5% 3 2 4 3 3 4 3 6% 9% 59%	5090
	21st to end	Day	8% 5% 2 6% 4 4 4 4 7% 9% 48%	5586
April	1st to 10th	Day	7% 4 2 5% 4 4 4 4 7% 10% 50%	2310
	11th to 20th	Day	7% 5% 2 5% 5% 5% 5% 5% 7% 8% 46%	2327
	21st to end	Day	4 3 1 4 4 4 5% 5% 7% 10% 52%	2520
May	1st to 10th	Day	3 4 2 6% 5% 5% 6% 5% 7% 11% 47%	7554
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 44%	7626
	21st to end	Day	3 3 2 6% 5% 6% 6% 6% 9% 13% 41%	8391
June	1st to 10th	Day	10% 7% 2 8% 7% 7% 8% 6% 8% 9% 27%	2730
	11th to 20th	Day	7% 5% 3 8% 7% 8% 8% 7% 9% 11% 28%	2730
	21st to end	Day	8% 7% 3 8% 8% 6% 8% 5% 7% 11% 29%	2730
July	1st to 10th	Day	5% 5% 2 8% 7% 7% 9% 7% 11% 16% 23%	7680
	11th to 20th	Day	3 4 2 7% 7% 7% 8% 7% 10% 15% 30%	7680
	21st to end	Day	5% 4 2 7% 6% 6% 7% 7% 10% 14% 32%	8340
August	1st to 10th	Day	6% 8% 3 11% 7% 8% 8% 6% 9% 12% 22%	6014
	11th to 20th	Day	3 3 1 6% 5% 6% 8% 6% 9% 13% 39%	5725
	21st to end	Day	6% 5% 3 10% 7% 8% 9% 6% 10% 13% 24%	5566
September	1st to 10th	Day	8% 7% 3 11% 9% 7% 9% 7% 9% 10% 21%	2310
	11th to 20th	Day	9% 7% 3 10% 7% 8% 8% 5% 8% 11% 24%	2310
	21st to end	Day	9% 6% 3 8% 8% 6% 7% 5% 8% 8% 31%	2310
October	1st to 10th	Day	11% 7% 3 8% 7% 6% 7% 5% 6% 8% 31%	2285
	11th to 20th	Day	6% 5% 2 6% 4 5% 5% 4 5% 8% 50%	2030
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 8% 49%	2200
November	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 6% 8% 48%	2057
	11th to 20th	Day	8% 7% 2 6% 5% 5% 5% 3 5% 7% 47%	2100
	21st to end	Day	9% 6% 2 6% 4 4 6% 3 5% 8% 46%	1958
December	1st to 10th	Day	6% 4 1 4 4 4 4 3 6% 8% 56%	3020
	11th to 20th	Day	9% 7% 2 7% 4 5% 5% 5% 8% 9% 40%	3463
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 4 5% 7% 42%	4565
January	1st to 10th	Night	8% 5% 2 4 4 3 3 3 4 8% 57%	7635
	11th to 20th	Night	17% 9% 3 8% 4 4 5% 4 5% 6% 34%	7680
	21st to end	Night	12% 6% 2 6% 4 4 4 3 6% 9% 44%	8224
February	1st to 10th	Night	11% 7% 3 5% 4 3 4 3 5% 7% 48%	2520
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 7% 49%	2458
	21st to end	Night	8% 6% 2 5% 4 3 4 3 6% 7% 53%	1971
March	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 5% 6% 45%	5028
	11th to 20th	Night	6% 4 2 4 4 4 4 4 6% 9% 54%	5090
	21st to end	Night	9% 6% 2 5% 4 4 4 3 5% 7% 50%	5588
April	1st to 10th	Night	8% 4 2 5% 4 3 4 4 6% 9% 52%	2310
	11th to 20th	Night	7% 4 2 6% 4 3 4 3 5% 7% 54%	2238
	21st to end	Night	5% 4 1 4 4 4 5% 4 6% 8% 56%	2100
May	1st to 10th	Night	5% 5% 2 6% 5% 5% 5% 4 7% 10% 47%	5341
	11th to 20th	Night	9% 6% 3 6% 4 4 4 3 6% 9% 47%	5234
	21st to end	Night	4 4 2 6% 5% 5% 6% 5% 8% 11% 46%	5761
June	1st to 10th	Night	10% 6% 3 7% 5% 5% 6% 4 8% 11% 35%	1890
	11th to 20th	Night	5% 8% 3 7% 7% 5% 7% 5% 9% 11% 32%	1890
	21st to end	Night	7% 7% 3 8% 6% 6% 7% 5% 9% 10% 32%	1890
July	1st to 10th	Night	6% 6% 3 9% 7% 7% 8% 7% 11% 13% 23%	5278
	11th to 20th	Night	3 4 2 8% 7% 7% 8% 7% 11% 12% 31%	5277
	21st to end	Night	4 6% 3 9% 7% 7% 7% 6% 9% 11% 32%	5736
August	1st to 10th	Night	5% 6% 3 10% 8% 8% 8% 6% 8% 12% 28%	4135
	11th to 20th	Night	3 3 2 6% 4 5% 6% 6% 8% 14% 43%	4256
	21st to end	Night	5% 5% 3 8% 6% 7% 8% 8% 11% 13% 27%	5559
September	1st to 10th	Night	9% 7% 3 9% 6% 6% 6% 6% 8% 10% 29%	2310
	11th to 20th	Night	9% 8% 3 8% 6% 6% 6% 5% 7% 10% 30%	2310
	21st to end	Night	9% 6% 2 7% 5% 6% 7% 6% 6% 8% 37%	2310
October	1st to 10th	Night	12% 7% 3 7% 4 5% 5% 5% 5% 8% 38%	2332
	11th to 20th	Night	5% 5% 2 5% 4 4 3 4 6% 9% 54%	2437
	21st to end	Night	9% 4 2 5% 4 4 4 3 6% 8% 52%	2640
November	1st to 10th	Night	9% 5% 2 5% 4 4 5% 5% 6% 7% 49%	2461
	11th to 20th	Night	8% 6% 3 5% 4 4 5% 4 5% 6% 49%	2520
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 5% 8% 47%	2657
December	1st to 10th	Night	6% 4 2 5% 4 4 4 3 5% 8% 56%	4380
	11th to 20th	Night	8% 7% 3 7% 4 4 4 3 5% 7% 49%	4952
	21st to end	Night	13% 8% 2 7% 5% 5% 4 4 5% 7% 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	29% 5% 12% 18% 25% 11%	5259
	11th to 20th	Day	51% 4 7% 13% 15% 11%	5280
	21st to end	Day	34% 5% 9% 25% 16% 11%	5940
February	1st to 10th	Day	37% 7% 9% 14% 21% 12%	2100
	11th to 20th	Day	31% 7% 10% 19% 23% 10%	2058
	21st to end	Day	35% 5% 11% 17% 22% 10%	1833
March	1st to 10th	Day	34% 8% 13% 18% 19% 7%	5045
	11th to 20th	Day	23% 5% 10% 22% 22% 18%	5090
	21st to end	Day	31% 7% 11% 26% 17% 8%	5586
April	1st to 10th	Day	28% 9% 14% 22% 19% 8%	2310
	11th to 20th	Day	34% 7% 10% 19% 22% 8%	2327
	21st to end	Day	25% 8% 15% 24% 22% 8%	2520
May	1st to 10th	Day	26% 11% 21% 26% 14% 3	7588
	11th to 20th	Day	33% 9% 15% 30% 12% 1	7630
	21st to end	Day	30% 12% 23% 25% 10% 1	8405
June	1st to 10th	Day	49% 13% 17% 15% 7%	2730
	11th to 20th	Day	45% 15% 21% 17% 2	2730
	21st to end	Day	47% 13% 22% 14% 3	2730
July	1st to 10th	Day	42% 17% 31% 9%	7615
	11th to 20th	Day	37% 16% 35% 12%	7611
	21st to end	Day	37% 15% 27% 20% 1	8156
August	1st to 10th	Day	49% 15% 25% 9% 2	6001
	11th to 20th	Day	31% 16% 31% 19% 3	5764
	21st to end	Day	45% 16% 25% 13% 1	5566
September	1st to 10th	Day	52% 17% 18% 9% 3	2310
	11th to 20th	Day	50% 16% 18% 12% 4	2310
	21st to end	Day	47% 11% 14% 16% 9% 3	2310
October	1st to 10th	Day	56% 10% 12% 10% 7% 5%	3649
	11th to 20th	Day	25% 7% 9% 21% 31% 7%	3270
	21st to end	Day	25% 7% 9% 21% 31% 8%	3538
November	1st to 10th	Day	32% 8% 12% 19% 19% 10%	2057
	11th to 20th	Day	36% 7% 9% 18% 21% 9%	2100
	21st to end	Day	36% 7% 10% 21% 19% 7%	1958
December	1st to 10th	Day	26% 5% 16% 26% 19% 9%	3020
	11th to 20th	Day	37% 10% 12% 16% 17% 9%	3460
	21st to end	Day	39% 7% 11% 21% 17% 4	4565
January	1st to 10th	Night	27% 4 11% 21% 25% 11%	7636
	11th to 20th	Night	50% 5% 8% 15% 14% 9%	7680
	21st to end	Night	36% 6% 12% 21% 13% 11%	8224
February	1st to 10th	Night	35% 6% 10% 16% 18% 14%	2520
	11th to 20th	Night	33% 7% 12% 19% 19% 10%	2459
	21st to end	Night	30% 5% 14% 18% 23% 9%	1971
March	1st to 10th	Night	38% 8% 10% 16% 19% 8%	5028
	11th to 20th	Night	24% 7% 15% 21% 16% 16%	5090
	21st to end	Night	31% 6% 12% 24% 20% 7%	5588
April	1st to 10th	Night	27% 9% 18% 23% 15% 8%	2310
	11th to 20th	Night	28% 7% 11% 25% 20% 9%	2238
	21st to end	Night	23% 9% 15% 26% 21% 7%	2100
May	1st to 10th	Night	28% 12% 21% 25% 11% 3	5368
	11th to 20th	Night	33% 8% 20% 27% 11% 1	5235
	21st to end	Night	29% 13% 22% 25% 11% 1	5771
June	1st to 10th	Night	40% 12% 21% 21% 6%	1890
	11th to 20th	Night	40% 16% 23% 19% 2	1890
	21st to end	Night	42% 14% 23% 16% 4 1	1890
July	1st to 10th	Night	46% 17% 29% 7% 1	5235
	11th to 20th	Night	38% 17% 33% 10% 1	5226
	21st to end	Night	41% 14% 26% 18% 1	5606
August	1st to 10th	Night	44% 16% 30% 9% 1	4124
	11th to 20th	Night	27% 15% 36% 19% 3	4283
	21st to end	Night	42% 19% 26% 10% 1	5559
September	1st to 10th	Night	45% 18% 20% 13% 4	2310
	11th to 20th	Night	46% 15% 20% 16% 3	2310
	21st to end	Night	41% 11% 18% 19% 9% 2	2310
October	1st to 10th	Night	54% 10% 12% 13% 7% 4	3748
	11th to 20th	Night	25% 7% 10% 23% 30% 5%	3936
	21st to end	Night	27% 7% 10% 19% 30% 7%	4252
November	1st to 10th	Night	32% 8% 13% 20% 17% 10%	2461
	11th to 20th	Night	33% 8% 10% 19% 21% 9%	2520
	21st to end	Night	35% 6% 11% 21% 19% 8%	2657
December	1st to 10th	Night	27% 5% 16% 27% 12% 13%	4380
	11th to 20th	Night	35% 8% 12% 21% 15% 9%	4954
	21st to end	Night	42% 8% 12% 19% 14% 5%	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	10% 10% 43% 25% 10% 2	330
	11th to 20th	Day	9% 14% 38% 26% 10% 3	330
	21st to end	Day	13% 18% 42% 22% 4	363
February	1st to 10th	Day	12% 13% 33% 24% 15% 3	330
	11th to 20th	Day	11% 8% 41% 29% 9% 2	330
	21st to end	Day	13% 10% 30% 31% 15% 1	376
March	1st to 10th	Day	7% 14% 31% 33% 14% 2	540
	11th to 20th	Day	10% 11% 29% 31% 16% 2	540
	21st to end	Day	7% 9% 29% 30% 20% 4	594
April	1st to 10th	Day	9% 11% 27% 32% 17% 4	540
	11th to 20th	Day	8% 9% 27% 31% 19% 7%	532
	21st to end	Day	5% 5% 22% 32% 24% 11%	540
May	1st to 10th	Day	6% 5% 20% 33% 25% 11%	543
	11th to 20th	Day	8% 2 19% 28% 28% 13%	567
	21st to end	Day	6% 2 10% 24% 35% 22%	617
June	1st to 10th	Day	12% 1 12% 25% 31% 19%	570
	11th to 20th	Day	8% 2 9% 23% 28% 30%	570
	21st to end	Day	6% 2 5% 18% 32% 38%	570
July	1st to 10th	Day	6% 1 4 13% 27% 49%	565
	11th to 20th	Day	5% 2 3 14% 33% 43%	564
	21st to end	Day	8% 2 5% 15% 30% 40%	620
August	1st to 10th	Day	6% 4 7% 17% 29% 37%	566
	11th to 20th	Day	6% 1 3 14% 30% 46%	559
	21st to end	Day	9% 3 6% 19% 29% 34%	627
September	1st to 10th	Day	10% 2 6% 17% 33% 32%	570
	11th to 20th	Day	8% 2 9% 26% 32% 23%	570
	21st to end	Day	9% 3 11% 22% 31% 25%	570
October	1st to 10th	Day	15% 5% 18% 32% 23% 7%	570
	11th to 20th	Day	6% 6% 17% 33% 29% 9%	542
	21st to end	Day	8% 5% 23% 36% 24% 4	583
November	1st to 10th	Day	9% 6% 24% 31% 26% 4	535
	11th to 20th	Day	13% 6% 24% 33% 19% 5%	540
	21st to end	Day	9% 9% 30% 30% 17% 4	398
December	1st to 10th	Day	9% 9% 37% 27% 15% 3	330
	11th to 20th	Day	11% 11% 34% 31% 12% 1	330
	21st to end	Day	8% 10% 29% 37% 13% 3	363
January	1st to 10th	Night	11% 9% 34% 33% 12% 1	840
	11th to 20th	Night	12% 9% 30% 36% 13% 1	840
	21st to end	Night	14% 11% 35% 33% 6%	924
February	1st to 10th	Night	14% 9% 30% 35% 12%	840
	11th to 20th	Night	12% 8% 32% 37% 10% 1	823
	21st to end	Night	10% 8% 34% 42% 6%	692
March	1st to 10th	Night	7% 9% 34% 38% 12%	840
	11th to 20th	Night	10% 8% 31% 37% 13% 1	840
	21st to end	Night	7% 8% 30% 40% 13% 1	924
April	1st to 10th	Night	9% 7% 30% 39% 15%	840
	11th to 20th	Night	7% 7% 30% 39% 16% 1	831
	21st to end	Night	6% 4 25% 44% 20% 1	840
May	1st to 10th	Night	5% 2 20% 49% 23% 1	669
	11th to 20th	Night	6% 2 14% 44% 30% 3	621
	21st to end	Night	7% 2 10% 35% 40% 6%	683
June	1st to 10th	Night	10% 2 9% 37% 35% 7%	630
	11th to 20th	Night	6% 2 7% 25% 39% 20%	630
	21st to end	Night	8% 2 4 23% 42% 21%	630
July	1st to 10th	Night	8% 1 4 17% 43% 26%	615
	11th to 20th	Night	5% 1 3 14% 46% 30%	612
	21st to end	Night	6% 1 3 16% 50% 24%	690
August	1st to 10th	Night	7% 2 3 15% 48% 25%	627
	11th to 20th	Night	5% 4 13% 45% 32%	645
	21st to end	Night	11% 2 7% 21% 39% 20%	924
September	1st to 10th	Night	11% 2 7% 22% 39% 19%	840
	11th to 20th	Night	11% 4 10% 28% 34% 12%	840
	21st to end	Night	13% 3 8% 28% 39% 10%	840
October	1st to 10th	Night	15% 2 16% 38% 24% 4	840
	11th to 20th	Night	7% 3 15% 38% 33% 4	813
	21st to end	Night	11% 4 17% 41% 26% 2	880
November	1st to 10th	Night	10% 3 24% 35% 26% 2	820
	11th to 20th	Night	9% 7% 22% 40% 20% 3	840
	21st to end	Night	10% 4 29% 40% 16% 1	840
December	1st to 10th	Night	10% 4 28% 38% 20% 1	840
	11th to 20th	Night	11% 7% 27% 37% 17% 1	840
	21st to end	Night	11% 7% 25% 39% 17% 1	924

Page generated at 2026-10-11 05:06:28. Version ac07

Copyright © 2026 Attilla Danko.