Forestville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Forestville clear sky chart from 2005-11-06 to 2024-12-06.

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	16% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	102003
	Night	16% 11% 4 8% 5% 5% 4 4 5% 6% 33%	97795
Transparency	Day	49% 9% 14% 19% 9% 1	105450
	Night	51% 8% 12% 19% 9% 1	102438
Seeing	Day	21% 8% 28% 29% 12% 2	15896
	Night	22% 7% 28% 30% 11% 1	23921

By Month

Percentage Cloud Cover NE (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	13% 16% 4 10% 5% 4 4 3 6% 7% 27%	2207
	11th to 20th	Day	12% 14% 5% 11% 6% 6% 5% 4 4 5% 27%	2458
	21st to end	Day	7% 10% 4 12% 8% 7% 6% 3 5% 6% 31%	2772
February	1st to 10th	Day	7% 13% 5% 10% 8% 6% 5% 3 6% 7% 31%	1569
	11th to 20th	Day	11% 13% 6% 13% 7% 6% 3 3 5% 5% 26%	1689
	21st to end	Day	11% 13% 4 8% 5% 5% 5% 4 6% 8% 32%	1570
March	1st to 10th	Day	13% 12% 3 7% 5% 6% 6% 4 6% 8% 29%	3116
	11th to 20th	Day	18% 20% 3 8% 5% 4 5% 3 4 6% 24%	3445
	21st to end	Day	17% 16% 3 8% 5% 4 3 3 4 6% 31%	3875
April	1st to 10th	Day	19% 12% 4 7% 6% 5% 5% 4 5% 6% 29%	2298
	11th to 20th	Day	16% 10% 3 7% 5% 5% 4 4 5% 7% 36%	2442
	21st to end	Day	21% 10% 3 7% 5% 3 4 3 5% 5% 33%	2470
May	1st to 10th	Day	14% 9% 3 9% 5% 5% 4 4 5% 6% 35%	4132
	11th to 20th	Day	19% 9% 3 6% 5% 4 4 3 5% 7% 36%	4605
	21st to end	Day	17% 10% 3 9% 4 4 4 4 6% 8% 31%	5185
June	1st to 10th	Day	21% 9% 3 7% 5% 5% 4 4 6% 7% 31%	2850
	11th to 20th	Day	17% 6% 3 7% 5% 5% 5% 4 6% 8% 34%	2850
	21st to end	Day	22% 8% 2 8% 5% 5% 5% 4 6% 7% 30%	2850
July	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 5% 6% 10% 34%	4760
	11th to 20th	Day	12% 6% 3 8% 6% 5% 7% 5% 7% 9% 33%	4760
	21st to end	Day	11% 5% 2 7% 5% 5% 6% 5% 7% 9% 38%	4816
August	1st to 10th	Day	12% 6% 2 6% 6% 6% 7% 7% 8% 9% 30%	4331
	11th to 20th	Day	17% 7% 3 8% 5% 5% 6% 4 7% 9% 28%	4045
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 4 5% 8% 38%	4532
September	1st to 10th	Day	15% 6% 2 7% 4 5% 5% 4 5% 7% 39%	2284
	11th to 20th	Day	18% 6% 2 6% 4 4 3 3 5% 6% 43%	2090
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 6% 39%	2090
October	1st to 10th	Day	17% 7% 2 8% 5% 4 5% 4 6% 7% 35%	2014
	11th to 20th	Day	23% 7% 3 7% 5% 5% 5% 3 6% 7% 30%	1791
	21st to end	Day	25% 9% 3 8% 5% 4 4 3 4 5% 30%	1881
November	1st to 10th	Day	17% 10% 3 9% 5% 6% 5% 4 5% 6% 29%	1731
	11th to 20th	Day	21% 11% 4 7% 5% 5% 5% 4 5% 5% 29%	1600
	21st to end	Day	24% 14% 3 7% 5% 4 4 2 4 5% 27%	1431
December	1st to 10th	Day	19% 13% 4 8% 5% 3 4 4 5% 6% 28%	1365
	11th to 20th	Day	18% 16% 4 7% 4 3 3 3 3 4 35%	1668
	21st to end	Day	17% 14% 4 9% 3 3 2 2 3 4 38%	2431
January	1st to 10th	Night	13% 16% 6% 12% 6% 4 4 3 4 4 30%	4748
	11th to 20th	Night	12% 16% 5% 10% 5% 5% 3 3 4 6% 30%	4503
	21st to end	Night	6% 10% 4 11% 6% 5% 5% 4 5% 7% 37%	4884
February	1st to 10th	Night	9% 12% 5% 10% 7% 6% 5% 3 5% 6% 33%	2609
	11th to 20th	Night	11% 16% 5% 11% 6% 5% 6% 4 5% 5% 27%	2375
	21st to end	Night	12% 15% 4 8% 6% 6% 4 4 5% 5% 32%	1884
March	1st to 10th	Night	14% 12% 4 9% 7% 5% 6% 4 5% 5% 28%	3724
	11th to 20th	Night	19% 20% 4 9% 5% 5% 4 3 4 4 24%	3513
	21st to end	Night	18% 17% 4 7% 4 4 3 3 4 5% 31%	3754
April	1st to 10th	Night	22% 13% 4 8% 6% 4 3 3 3 4 30%	1881
	11th to 20th	Night	21% 9% 2 5% 4 5% 5% 4 6% 5% 35%	1688
	21st to end	Night	23% 10% 3 6% 3 3 3 3 3 6% 36%	1710
May	1st to 10th	Night	19% 10% 2 6% 4 4 4 4 6% 7% 35%	2834
	11th to 20th	Night	17% 9% 3 7% 4 3 3 3 7% 8% 36%	2298
	21st to end	Night	17% 9% 4 7% 5% 4 5% 4 7% 8% 30%	2401
June	1st to 10th	Night	20% 6% 2 8% 6% 5% 6% 4 6% 7% 30%	1330
	11th to 20th	Night	17% 7% 2 7% 4 5% 4 3 6% 7% 38%	1330
	21st to end	Night	24% 8% 3 7% 5% 4 4 3 4 5% 31%	1330
July	1st to 10th	Night	14% 6% 2 7% 5% 5% 5% 5% 7% 8% 36%	2210
	11th to 20th	Night	11% 7% 3 6% 5% 4 6% 5% 7% 9% 36%	2210
	21st to end	Night	11% 6% 2 5% 5% 4 5% 5% 6% 9% 43%	2734
August	1st to 10th	Night	17% 6% 3 8% 5% 5% 5% 4 6% 7% 35%	2567
	11th to 20th	Night	15% 7% 3 9% 6% 5% 6% 5% 7% 10% 28%	2782
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 6% 44%	3124
September	1st to 10th	Night	16% 6% 2 7% 5% 4 4 3 6% 8% 40%	1895
	11th to 20th	Night	19% 6% 2 6% 4 4 4 4 4 6% 41%	2090
	21st to end	Night	18% 7% 2 5% 5% 4 3 3 4 5% 44%	2090
October	1st to 10th	Night	17% 7% 2 7% 4 4 4 4 5% 5% 41%	2165
	11th to 20th	Night	25% 7% 3 7% 4 4 3 3 5% 5% 34%	2384
	21st to end	Night	23% 7% 3 7% 4 5% 5% 4 5% 6% 32%	2717
November	1st to 10th	Night	19% 11% 3 8% 5% 4 4 4 5% 6% 32%	2567
	11th to 20th	Night	20% 12% 3 8% 4 5% 4 4 4 5% 32%	2800
	21st to end	Night	20% 16% 4 9% 5% 4 4 3 5% 5% 26%	2965
December	1st to 10th	Night	19% 13% 4 9% 5% 5% 3 2 4 4 30%	2932
	11th to 20th	Night	19% 13% 4 8% 5% 4 4 3 4 5% 30%	3531
	21st to end	Night	15% 13% 5% 9% 5% 5% 4 3 4 6% 31%	5236

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	56% 8% 13% 19% 4	2208
	11th to 20th	Day	56% 8% 9% 20% 5% 1	2458
	21st to end	Day	50% 9% 10% 18% 11% 1	2772
February	1st to 10th	Day	51% 8% 11% 16% 11% 2	1569
	11th to 20th	Day	60% 6% 9% 15% 9%	1697
	21st to end	Day	48% 8% 9% 20% 12% 2	1570
March	1st to 10th	Day	48% 9% 18% 14% 9% 2	3119
	11th to 20th	Day	61% 6% 10% 15% 7% 1	3445
	21st to end	Day	55% 6% 9% 18% 9% 3	3875
April	1st to 10th	Day	54% 6% 11% 15% 13% 2	2298
	11th to 20th	Day	46% 7% 12% 23% 11% 2	2442
	21st to end	Day	51% 6% 9% 19% 12% 2	2470
May	1st to 10th	Day	46% 10% 15% 18% 10% 1	4146
	11th to 20th	Day	45% 11% 14% 20% 10% 1	4609
	21st to end	Day	48% 7% 12% 21% 10% 1	5185
June	1st to 10th	Day	51% 8% 10% 18% 11% 2	2850
	11th to 20th	Day	47% 8% 14% 18% 12% 2	2850
	21st to end	Day	53% 8% 13% 16% 9% 1	2850
July	1st to 10th	Day	43% 10% 16% 25% 7%	4685
	11th to 20th	Day	43% 11% 18% 22% 6%	4679
	21st to end	Day	40% 10% 17% 24% 8%	4662
August	1st to 10th	Day	42% 15% 18% 18% 7%	4317
	11th to 20th	Day	49% 12% 18% 17% 3	4084
	21st to end	Day	42% 10% 16% 20% 10% 1	4532
September	1st to 10th	Day	42% 9% 16% 21% 11%	2284
	11th to 20th	Day	41% 7% 16% 25% 10%	2090
	21st to end	Day	44% 8% 16% 23% 9%	2090
October	1st to 10th	Day	52% 8% 14% 18% 7% 1	3352
	11th to 20th	Day	47% 8% 14% 28% 3	2955
	21st to end	Day	46% 7% 16% 19% 12%	3081
November	1st to 10th	Day	53% 8% 15% 15% 7% 1	1731
	11th to 20th	Day	55% 7% 12% 18% 7%	1600
	21st to end	Day	61% 6% 11% 14% 7%	1431
December	1st to 10th	Day	56% 9% 13% 16% 6%	1365
	11th to 20th	Day	55% 6% 9% 20% 11%	1668
	21st to end	Day	52% 5% 14% 19% 6% 4	2431
January	1st to 10th	Night	60% 5% 9% 16% 10%	4748
	11th to 20th	Night	56% 7% 10% 20% 6% 1	4503
	21st to end	Night	44% 10% 12% 23% 11%	4884
February	1st to 10th	Night	53% 6% 8% 18% 12% 2	2609
	11th to 20th	Night	58% 8% 9% 16% 9%	2378
	21st to end	Night	54% 6% 10% 20% 9% 1	1884
March	1st to 10th	Night	54% 9% 13% 15% 9% 1	3734
	11th to 20th	Night	63% 6% 10% 13% 7% 1	3514
	21st to end	Night	55% 5% 9% 17% 12% 1	3754
April	1st to 10th	Night	59% 4 7% 13% 14% 3	1881
	11th to 20th	Night	49% 6% 9% 19% 15% 2	1688
	21st to end	Night	52% 4 8% 19% 14% 3	1710
May	1st to 10th	Night	47% 8% 14% 14% 15% 1	2840
	11th to 20th	Night	44% 10% 12% 22% 10% 1	2299
	21st to end	Night	49% 10% 9% 22% 10% 1	2402
June	1st to 10th	Night	51% 8% 10% 18% 11% 2	1330
	11th to 20th	Night	46% 6% 13% 19% 14% 3	1330
	21st to end	Night	55% 7% 8% 17% 11% 1	1330
July	1st to 10th	Night	42% 10% 15% 24% 8%	2175
	11th to 20th	Night	41% 9% 17% 27% 5%	2168
	21st to end	Night	36% 10% 23% 18% 13%	2647
August	1st to 10th	Night	46% 10% 15% 22% 7%	2557
	11th to 20th	Night	49% 12% 19% 14% 6%	2809
	21st to end	Night	40% 8% 12% 27% 12%	3124
September	1st to 10th	Night	41% 10% 14% 24% 10% 1	1895
	11th to 20th	Night	44% 8% 16% 23% 10% 1	2090
	21st to end	Night	42% 7% 12% 25% 13%	2090
October	1st to 10th	Night	47% 7% 11% 26% 8% 1	3607
	11th to 20th	Night	47% 7% 12% 29% 5%	3959
	21st to end	Night	48% 10% 14% 20% 8%	4467
November	1st to 10th	Night	53% 7% 13% 18% 9% 1	2567
	11th to 20th	Night	54% 7% 12% 18% 8%	2800
	21st to end	Night	60% 8% 11% 12% 9%	2965
December	1st to 10th	Night	58% 6% 12% 17% 6%	2932
	11th to 20th	Night	56% 7% 10% 17% 9%	3532
	21st to end	Night	54% 8% 12% 14% 10% 2	5236

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	29% 7% 26% 30% 8%	180
	11th to 20th	Day	20% 13% 28% 30% 7% 1	180
	21st to end	Day	14% 9% 32% 27% 15% 4	198
February	1st to 10th	Day	14% 13% 31% 31% 8% 3	229
	11th to 20th	Day	15% 10% 37% 28% 9% 1	379
	21st to end	Day	18% 10% 37% 26% 9% 1	382
March	1st to 10th	Day	23% 8% 30% 28% 10% 1	460
	11th to 20th	Day	23% 11% 28% 24% 11% 3	460
	21st to end	Day	24% 10% 33% 25% 7% 1	506
April	1st to 10th	Day	24% 13% 29% 24% 9% 2	460
	11th to 20th	Day	20% 9% 31% 27% 12% 2	452
	21st to end	Day	24% 8% 29% 30% 9% 1	460
May	1st to 10th	Day	25% 8% 28% 26% 11% 2	463
	11th to 20th	Day	22% 5% 29% 28% 14% 3	603
	21st to end	Day	23% 9% 31% 26% 10% 2	735
June	1st to 10th	Day	26% 4 30% 31% 10% 1	680
	11th to 20th	Day	20% 6% 28% 28% 15% 3	680
	21st to end	Day	23% 4 26% 33% 12% 2	680
July	1st to 10th	Day	19% 3 23% 37% 15% 2	670
	11th to 20th	Day	15% 4 22% 40% 17% 2	668
	21st to end	Day	13% 7% 22% 37% 18% 2	534
August	1st to 10th	Day	17% 5% 20% 38% 19% 2	486
	11th to 20th	Day	19% 4 20% 35% 19% 3	479
	21st to end	Day	15% 8% 22% 33% 19% 3	539
September	1st to 10th	Day	17% 6% 29% 30% 16% 3	490
	11th to 20th	Day	20% 7% 27% 32% 11% 3	490
	21st to end	Day	20% 5% 29% 29% 13% 3	490
October	1st to 10th	Day	19% 6% 32% 26% 13% 4	450
	11th to 20th	Day	27% 10% 27% 23% 10% 3	390
	21st to end	Day	29% 12% 27% 22% 8% 2	429
November	1st to 10th	Day	22% 15% 34% 24% 4 1	395
	11th to 20th	Day	27% 10% 28% 24% 10% 1	400
	21st to end	Day	32% 10% 30% 23% 4 1	231
December	1st to 10th	Day	22% 7% 28% 24% 14% 4	190
	11th to 20th	Day	24% 13% 34% 22% 6% 2	180
	21st to end	Day	25% 12% 30% 24% 8% 1	198
January	1st to 10th	Night	23% 8% 33% 30% 6%	850
	11th to 20th	Night	23% 11% 34% 25% 6%	777
	21st to end	Night	14% 7% 34% 33% 10% 1	836
February	1st to 10th	Night	14% 8% 39% 30% 9% 1	760
	11th to 20th	Night	18% 11% 35% 27% 9% 1	743
	21st to end	Night	18% 8% 32% 31% 10% 1	628
March	1st to 10th	Night	20% 8% 33% 30% 8% 1	760
	11th to 20th	Night	22% 10% 32% 26% 9% 1	760
	21st to end	Night	21% 9% 31% 29% 8% 1	836
April	1st to 10th	Night	28% 6% 31% 26% 9%	741
	11th to 20th	Night	25% 7% 28% 27% 12% 2	564
	21st to end	Night	29% 6% 22% 31% 10% 1	570
May	1st to 10th	Night	29% 5% 21% 34% 11% 1	570
	11th to 20th	Night	23% 2 23% 34% 16% 2	377
	21st to end	Night	23% 3 31% 30% 12% 1	411
June	1st to 10th	Night	21% 3 22% 39% 15% 1	380
	11th to 20th	Night	18% 4 21% 32% 23% 3	380
	21st to end	Night	27% 3 18% 35% 15% 1	380
July	1st to 10th	Night	18% 5% 21% 38% 15% 2	370
	11th to 20th	Night	14% 4 17% 43% 20% 1	368
	21st to end	Night	18% 3 17% 38% 23% 2	416
August	1st to 10th	Night	16% 2 13% 43% 23% 2	413
	11th to 20th	Night	18% 2 17% 40% 21% 2	562
	21st to end	Night	13% 4 17% 43% 19% 4	627
September	1st to 10th	Night	19% 3 26% 35% 15% 1	708
	11th to 20th	Night	23% 4 23% 31% 16% 3	760
	21st to end	Night	20% 4 25% 32% 16% 2	760
October	1st to 10th	Night	20% 5% 29% 31% 13% 2	760
	11th to 20th	Night	27% 6% 27% 26% 14% 1	760
	21st to end	Night	26% 7% 30% 26% 9% 1	836
November	1st to 10th	Night	26% 10% 30% 27% 6% 1	795
	11th to 20th	Night	24% 11% 30% 24% 9% 1	900
	21st to end	Night	29% 9% 28% 28% 5%	900
December	1st to 10th	Night	25% 8% 31% 27% 8% 1	878
	11th to 20th	Night	24% 12% 33% 22% 8% 1	850
	21st to end	Night	25% 11% 31% 24% 7% 1	935

Page generated at 2024-12-03 06:45:14. Version ac07

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