Astro Acres
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro Acres clear sky chart from 2005-11-06 to 2024-11-02.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 36%	101177
	Night	14% 10% 4 7% 5% 4 4 3 5% 6% 37%	97870
Transparency	Day	45% 6% 12% 22% 13% 2	100966
	Night	46% 6% 11% 21% 14% 2	97753
Seeing	Day	16% 10% 28% 25% 15% 6%	15719
	Night	17% 10% 29% 30% 13% 1	25539

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	15% 14% 10% 13% 5% 5% 5% 3 5% 5% 19%	2527
	11th to 20th	Day	14% 15% 8% 16% 6% 4 4 7% 7% 4 16%	2530
	21st to end	Day	23% 23% 6% 11% 4 3 3 3 3 5% 18%	2850
February	1st to 10th	Day	17% 12% 5% 10% 6% 5% 5% 3 5% 5% 27%	1828
	11th to 20th	Day	14% 12% 4 9% 5% 5% 4 4 5% 5% 32%	1848
	21st to end	Day	17% 14% 6% 8% 4 4 4 3 5% 6% 30%	1570
March	1st to 10th	Day	18% 18% 4 7% 5% 4 3 3 4 4 30%	3120
	11th to 20th	Day	11% 8% 3 7% 5% 4 5% 4 6% 8% 38%	3256
	21st to end	Day	16% 11% 6% 10% 6% 5% 5% 4 5% 7% 25%	4151
April	1st to 10th	Day	16% 13% 3 7% 4 4 4 3 6% 6% 35%	2280
	11th to 20th	Day	16% 9% 3 7% 5% 4 4 4 5% 6% 37%	2254
	21st to end	Day	20% 8% 3 8% 5% 5% 4 3 4 7% 33%	2398
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 4 4 7% 8% 30%	4082
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 5% 8% 37%	4131
	21st to end	Day	9% 6% 2 6% 4 4 4 4 6% 9% 46%	4824
June	1st to 10th	Day	10% 6% 2 6% 5% 4 6% 4 6% 9% 44%	2660
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	2660
	21st to end	Day	10% 6% 2 7% 6% 5% 6% 4 7% 8% 39%	2660
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 5% 7% 9% 35%	4440
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 12% 44%	4440
	21st to end	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 8% 41%	4813
August	1st to 10th	Day	7% 5% 2 5% 5% 5% 5% 4 6% 9% 48%	4203
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 5% 7% 9% 44%	3768
	21st to end	Day	6% 4 2 5% 4 5% 5% 4 6% 9% 50%	4180
September	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 6% 7% 47%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 6% 8% 50%	2123
	21st to end	Day	11% 6% 2 6% 4 4 4 3 5% 8% 45%	2090
October	1st to 10th	Day	12% 7% 2 6% 3 4 4 4 6% 7% 47%	2090
	11th to 20th	Day	17% 7% 3 6% 3 4 5% 4 5% 6% 39%	1880
	21st to end	Day	18% 10% 3 9% 5% 4 4 3 6% 6% 32%	1881
November	1st to 10th	Day	12% 7% 2 4 5% 4 4 3 5% 7% 49%	1681
	11th to 20th	Day	17% 11% 4 7% 5% 3 3 3 4 6% 37%	1710
	21st to end	Day	17% 11% 3 9% 4 3 3 3 4 6% 36%	1710
December	1st to 10th	Day	15% 15% 4 10% 7% 4 3 3 4 5% 27%	1558
	11th to 20th	Day	14% 13% 5% 13% 5% 4 4 3 6% 6% 27%	1918
	21st to end	Day	22% 20% 9% 14% 5% 3 3 2 3 4 14%	2783
January	1st to 10th	Night	16% 16% 8% 10% 6% 4 4 3 4 4 24%	4428
	11th to 20th	Night	14% 19% 8% 13% 6% 5% 6% 3 5% 4 17%	4440
	21st to end	Night	24% 18% 7% 9% 5% 3 3 3 3 4 21%	4816
February	1st to 10th	Night	17% 14% 4 8% 6% 5% 4 3 5% 6% 29%	2352
	11th to 20th	Night	14% 11% 4 9% 5% 4 5% 3 5% 6% 35%	2218
	21st to end	Night	19% 13% 3 8% 5% 3 4 3 5% 5% 32%	1884
March	1st to 10th	Night	17% 14% 4 6% 4 4 3 3 4 6% 36%	3733
	11th to 20th	Night	11% 7% 3 6% 4 4 4 3 5% 6% 46%	3704
	21st to end	Night	19% 10% 5% 8% 5% 5% 4 4 5% 6% 29%	3509
April	1st to 10th	Night	13% 9% 3 7% 5% 4 4 3 6% 7% 38%	1900
	11th to 20th	Night	18% 9% 3 6% 5% 4 4 3 4 6% 38%	1875
	21st to end	Night	18% 8% 2 7% 5% 4 4 4 5% 7% 35%	1781
May	1st to 10th	Night	16% 9% 3 7% 5% 5% 4 3 6% 8% 33%	2813
	11th to 20th	Night	19% 6% 2 6% 4 4 4 4 5% 8% 38%	2761
	21st to end	Night	9% 6% 3 7% 5% 5% 4 4 5% 8% 44%	2743
June	1st to 10th	Night	9% 5% 2 7% 4 3 4 2 5% 9% 50%	1520
	11th to 20th	Night	8% 6% 2 6% 4 4 3 3 6% 9% 49%	1520
	21st to end	Night	9% 7% 2 6% 6% 5% 6% 4 6% 9% 43%	1520
July	1st to 10th	Night	10% 4 2 6% 5% 5% 5% 5% 7% 10% 42%	2530
	11th to 20th	Night	5% 4 2 6% 3 4 4 4 5% 9% 55%	2530
	21st to end	Night	5% 6% 2 8% 5% 5% 5% 5% 6% 7% 45%	2750
August	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 9% 48%	2728
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 4 6% 8% 50%	3058
	21st to end	Night	9% 4 2 5% 4 3 4 4 5% 8% 53%	3476
September	1st to 10th	Night	10% 5% 1 5% 3 3 4 2 5% 8% 53%	1900
	11th to 20th	Night	8% 5% 1 4 3 3 4 3 6% 8% 55%	2038
	21st to end	Night	10% 7% 2 7% 4 4 4 4 5% 7% 47%	2090
October	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 4 6% 53%	2090
	11th to 20th	Night	15% 7% 2 6% 3 4 3 3 4 6% 47%	2295
	21st to end	Night	19% 8% 3 7% 4 4 4 3 4 6% 38%	2717
November	1st to 10th	Night	11% 8% 3 6% 4 4 4 3 5% 7% 46%	2431
	11th to 20th	Night	14% 9% 3 7% 5% 4 5% 4 6% 6% 37%	2470
	21st to end	Night	18% 11% 3 7% 5% 4 3 3 4 6% 35%	2470
December	1st to 10th	Night	15% 13% 5% 9% 5% 5% 4 3 4 6% 31%	2617
	11th to 20th	Night	15% 14% 5% 8% 5% 4 4 3 4 4 32%	3279
	21st to end	Night	24% 19% 6% 11% 6% 4 4 3 4 5% 15%	4884

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	66% 6% 10% 12% 6%	2528
	11th to 20th	Day	68% 4 9% 10% 9% 1	2530
	21st to end	Day	72% 3 8% 13% 4	2850
February	1st to 10th	Day	60% 4 12% 15% 7% 2	1828
	11th to 20th	Day	53% 5% 10% 22% 9% 1	1858
	21st to end	Day	54% 6% 11% 20% 7% 2	1570
March	1st to 10th	Day	57% 5% 8% 18% 10% 1	3120
	11th to 20th	Day	41% 6% 11% 28% 13% 1	3256
	21st to end	Day	56% 9% 15% 17% 3	4151
April	1st to 10th	Day	48% 6% 12% 20% 14%	2280
	11th to 20th	Day	47% 6% 10% 21% 12% 3	2254
	21st to end	Day	51% 6% 12% 18% 11% 2	2398
May	1st to 10th	Day	47% 9% 14% 23% 8%	4120
	11th to 20th	Day	43% 7% 14% 25% 10% 1	4135
	21st to end	Day	33% 8% 12% 21% 23% 3	4837
June	1st to 10th	Day	36% 8% 12% 24% 16% 4	2660
	11th to 20th	Day	33% 8% 11% 23% 21% 4	2660
	21st to end	Day	40% 9% 13% 20% 16% 3	2660
July	1st to 10th	Day	44% 6% 12% 22% 13% 2	4371
	11th to 20th	Day	31% 8% 16% 28% 16% 1	4365
	21st to end	Day	38% 8% 16% 17% 18% 3	4662
August	1st to 10th	Day	31% 7% 17% 29% 15% 1	4188
	11th to 20th	Day	33% 8% 13% 29% 16% 1	3805
	21st to end	Day	29% 7% 14% 28% 18% 4	4179
September	1st to 10th	Day	35% 7% 12% 24% 17% 5%	2280
	11th to 20th	Day	32% 6% 11% 24% 22% 4	2123
	21st to end	Day	36% 6% 10% 25% 20% 2	2090
October	1st to 10th	Day	36% 7% 12% 24% 19% 3	2090
	11th to 20th	Day	44% 5% 10% 22% 18% 1	1880
	21st to end	Day	51% 5% 11% 21% 11% 1	1881
November	1st to 10th	Day	35% 5% 15% 25% 18% 3	1681
	11th to 20th	Day	49% 4 11% 22% 13% 1	1710
	21st to end	Day	51% 5% 11% 22% 11% 1	1710
December	1st to 10th	Day	60% 4 11% 17% 8%	1558
	11th to 20th	Day	58% 5% 9% 22% 5%	1915
	21st to end	Day	75% 5% 9% 8% 3	2783
January	1st to 10th	Night	61% 6% 11% 14% 7% 1	4428
	11th to 20th	Night	70% 3 9% 12% 5%	4440
	21st to end	Night	69% 4 8% 13% 6% 1	4816
February	1st to 10th	Night	57% 5% 12% 17% 8% 2	2352
	11th to 20th	Night	51% 5% 11% 20% 12% 1	2219
	21st to end	Night	54% 5% 11% 18% 10% 3	1884
March	1st to 10th	Night	49% 6% 10% 22% 9% 3	3733
	11th to 20th	Night	37% 7% 10% 27% 18% 2	3704
	21st to end	Night	54% 8% 12% 20% 6% 1	3509
April	1st to 10th	Night	43% 6% 12% 22% 14% 2	1900
	11th to 20th	Night	46% 5% 9% 21% 16% 4	1875
	21st to end	Night	47% 7% 11% 20% 12% 4	1781
May	1st to 10th	Night	47% 8% 12% 21% 12% 1	2840
	11th to 20th	Night	43% 9% 14% 24% 10% 1	2762
	21st to end	Night	36% 9% 11% 19% 20% 5%	2751
June	1st to 10th	Night	33% 6% 12% 25% 21% 3	1520
	11th to 20th	Night	30% 6% 12% 26% 21% 4	1520
	21st to end	Night	37% 8% 14% 22% 15% 4	1520
July	1st to 10th	Night	36% 7% 16% 25% 11% 5%	2490
	11th to 20th	Night	25% 7% 12% 28% 26% 2	2482
	21st to end	Night	35% 7% 16% 19% 18% 5%	2662
August	1st to 10th	Night	30% 8% 18% 27% 15% 2	2719
	11th to 20th	Night	29% 7% 15% 28% 19% 1	3087
	21st to end	Night	29% 7% 12% 31% 19% 3	3476
September	1st to 10th	Night	30% 6% 12% 25% 20% 7%	1900
	11th to 20th	Night	26% 6% 9% 28% 27% 5%	2038
	21st to end	Night	36% 7% 9% 25% 21% 3	2090
October	1st to 10th	Night	33% 6% 8% 27% 24% 2	2090
	11th to 20th	Night	38% 4 10% 25% 21% 2	2295
	21st to end	Night	46% 5% 10% 21% 16% 2	2717
November	1st to 10th	Night	37% 5% 10% 26% 19% 3	2431
	11th to 20th	Night	45% 5% 12% 21% 14% 2	2470
	21st to end	Night	51% 4 10% 24% 10% 1	2470
December	1st to 10th	Night	54% 5% 11% 19% 10% 1	2617
	11th to 20th	Night	55% 5% 10% 18% 11% 1	3281
	21st to end	Night	72% 5% 8% 10% 5%	4884

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	24% 13% 36% 18% 7% 1	270
	11th to 20th	Day	23% 17% 38% 16% 4 1	270
	21st to end	Day	26% 15% 31% 21% 6% 1	297
February	1st to 10th	Day	23% 19% 35% 19% 4	270
	11th to 20th	Day	25% 13% 38% 19% 4	270
	21st to end	Day	28% 15% 43% 10% 4	225
March	1st to 10th	Day	23% 18% 37% 20% 2	270
	11th to 20th	Day	27% 14% 33% 20% 6%	327
	21st to end	Day	30% 13% 30% 20% 7% 1	506
April	1st to 10th	Day	24% 14% 29% 26% 6% 1	460
	11th to 20th	Day	20% 15% 34% 16% 12% 4	452
	21st to end	Day	23% 15% 32% 20% 7% 2	460
May	1st to 10th	Day	20% 11% 33% 25% 8% 3	463
	11th to 20th	Day	20% 9% 26% 26% 15% 5%	511
	21st to end	Day	13% 7% 31% 26% 15% 8%	734
June	1st to 10th	Day	10% 8% 28% 29% 19% 6%	680
	11th to 20th	Day	10% 4 29% 33% 19% 6%	680
	21st to end	Day	12% 7% 29% 31% 16% 5%	680
July	1st to 10th	Day	10% 4 18% 27% 22% 18%	671
	11th to 20th	Day	8% 3 22% 31% 23% 13%	668
	21st to end	Day	9% 4 19% 31% 27% 10%	739
August	1st to 10th	Day	7% 3 16% 30% 30% 15%	547
	11th to 20th	Day	9% 5% 17% 30% 22% 16%	479
	21st to end	Day	7% 2 16% 33% 31% 12%	539
September	1st to 10th	Day	12% 5% 18% 29% 29% 8%	490
	11th to 20th	Day	9% 3 14% 29% 31% 14%	490
	21st to end	Day	13% 9% 24% 24% 22% 8%	490
October	1st to 10th	Day	14% 8% 22% 30% 20% 6%	490
	11th to 20th	Day	18% 20% 26% 24% 10% 2	311
	21st to end	Day	28% 12% 36% 16% 7% 1	330
November	1st to 10th	Day	12% 12% 39% 20% 13% 4	273
	11th to 20th	Day	21% 17% 35% 16% 10% 1	270
	21st to end	Day	26% 11% 39% 20% 3	270
December	1st to 10th	Day	17% 19% 39% 17% 9%	270
	11th to 20th	Day	17% 21% 35% 21% 5% 1	270
	21st to end	Day	25% 18% 37% 17% 3	297
January	1st to 10th	Night	23% 17% 35% 20% 5%	950
	11th to 20th	Night	22% 16% 35% 22% 5%	950
	21st to end	Night	22% 14% 35% 25% 4	1045
February	1st to 10th	Night	24% 12% 37% 23% 3	832
	11th to 20th	Night	19% 15% 36% 25% 4	743
	21st to end	Night	26% 13% 37% 21% 3	628
March	1st to 10th	Night	20% 14% 37% 24% 6%	760
	11th to 20th	Night	17% 12% 40% 26% 5%	760
	21st to end	Night	22% 10% 39% 22% 7%	657
April	1st to 10th	Night	16% 13% 39% 26% 5% 1	570
	11th to 20th	Night	21% 11% 34% 24% 9%	563
	21st to end	Night	22% 10% 34% 26% 8%	570
May	1st to 10th	Night	19% 7% 34% 32% 7% 1	570
	11th to 20th	Night	20% 4 28% 34% 14% 1	561
	21st to end	Night	9% 5% 26% 41% 18% 1	617
June	1st to 10th	Night	11% 5% 23% 44% 16%	570
	11th to 20th	Night	11% 3 27% 44% 15% 1	570
	21st to end	Night	10% 5% 25% 40% 20%	570
July	1st to 10th	Night	9% 1 16% 40% 29% 5%	555
	11th to 20th	Night	7% 2 18% 40% 29% 4	552
	21st to end	Night	5% 2 14% 47% 30% 2	624
August	1st to 10th	Night	6% 2 13% 45% 30% 4	567
	11th to 20th	Night	6% 2 15% 40% 32% 4	564
	21st to end	Night	8% 2 13% 37% 37% 4	627
September	1st to 10th	Night	12% 2 16% 41% 26% 3	570
	11th to 20th	Night	8% 5% 14% 37% 32% 4	708
	21st to end	Night	12% 6% 23% 32% 24% 3	760
October	1st to 10th	Night	14% 4 23% 38% 19% 2	760
	11th to 20th	Night	19% 13% 29% 28% 11%	760
	21st to end	Night	22% 15% 31% 25% 7%	836
November	1st to 10th	Night	16% 10% 39% 25% 8% 2	748
	11th to 20th	Night	19% 16% 33% 24% 7% 1	760
	21st to end	Night	22% 13% 33% 25% 7%	760
December	1st to 10th	Night	23% 12% 36% 24% 4	907
	11th to 20th	Night	24% 12% 33% 25% 6%	950
	21st to end	Night	29% 15% 30% 23% 2	1045

Page generated at 2024-10-30 12:19:21. Version ac07

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