Forillon National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Forillon National Park clear sky chart from 2005-11-06 to 2024-01-16.

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	18% 9% 3 7% 6% 3 5% 5% 5% 7% 32%	74710
	Night	18% 10% 4 7% 6% 3 5% 5% 5% 6% 31%	75100
Transparency	Day	52% 5% 13% 20% 8% 1	74399
	Night	57% 4 12% 19% 7% 1	74947
Seeing	Day	23% 11% 28% 25% 11% 2	15516
	Night	25% 11% 25% 26% 11% 2	23134

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	15% 17% 6% 9% 8% 3 6% 3 6% 6% 20%	1327
	11th to 20th	Day	15% 15% 6% 9% 8% 4 5% 6% 5% 6% 21%	1295
	21st to end	Day	10% 10% 5% 11% 8% 3 5% 5% 6% 8% 29%	1611
February	1st to 10th	Day	10% 11% 5% 8% 7% 3 5% 5% 7% 7% 31%	1620
	11th to 20th	Day	11% 17% 4 10% 7% 3 5% 4 5% 7% 27%	1573
	21st to end	Day	10% 8% 4 8% 7% 5% 6% 6% 5% 7% 33%	1332
March	1st to 10th	Day	14% 13% 5% 7% 6% 3 5% 4 6% 6% 31%	1900
	11th to 20th	Day	14% 12% 3 8% 7% 4 5% 5% 5% 7% 30%	1980
	21st to end	Day	15% 13% 4 7% 5% 4 6% 5% 4 6% 33%	2183
April	1st to 10th	Day	20% 11% 4 8% 6% 3 5% 5% 5% 7% 28%	2160
	11th to 20th	Day	17% 11% 3 6% 6% 2 4 5% 5% 6% 35%	2292
	21st to end	Day	25% 8% 3 7% 4 3 5% 4 4 7% 31%	2340
May	1st to 10th	Day	24% 10% 3 6% 5% 3 4 3 4 6% 32%	2506
	11th to 20th	Day	21% 8% 3 5% 5% 3 4 5% 5% 7% 34%	2478
	21st to end	Day	19% 8% 3 6% 5% 3 4 5% 5% 7% 34%	2843
June	1st to 10th	Day	24% 8% 2 6% 5% 3 5% 5% 5% 6% 30%	2700
	11th to 20th	Day	20% 7% 2 5% 5% 3 5% 4 5% 7% 37%	2700
	21st to end	Day	24% 8% 3 5% 6% 3 5% 5% 6% 6% 27%	2700
July	1st to 10th	Day	17% 6% 2 5% 5% 3 6% 5% 6% 9% 34%	2700
	11th to 20th	Day	13% 5% 3 6% 6% 4 5% 6% 6% 7% 38%	2700
	21st to end	Day	16% 7% 3 6% 6% 4 5% 6% 6% 8% 33%	2833
August	1st to 10th	Day	15% 6% 2 5% 6% 3 5% 6% 7% 8% 35%	2409
	11th to 20th	Day	16% 6% 3 6% 5% 3 5% 5% 6% 8% 37%	2304
	21st to end	Day	14% 5% 2 6% 6% 4 5% 6% 6% 9% 37%	2543
September	1st to 10th	Day	20% 6% 2 5% 4 3 3 5% 5% 7% 40%	2160
	11th to 20th	Day	21% 6% 2 5% 4 2 3 4 4 5% 43%	2097
	21st to end	Day	19% 6% 2 4 5% 4 5% 4 6% 7% 39%	1922
October	1st to 10th	Day	16% 5% 3 6% 6% 3 4 5% 7% 7% 38%	1800
	11th to 20th	Day	24% 9% 3 6% 5% 3 4 5% 4 6% 32%	1800
	21st to end	Day	24% 11% 3 6% 6% 3 5% 4 5% 6% 27%	1834
November	1st to 10th	Day	18% 11% 4 8% 6% 4 6% 4 5% 6% 29%	1485
	11th to 20th	Day	20% 12% 5% 7% 7% 4 6% 5% 3 6% 24%	1520
	21st to end	Day	19% 15% 5% 10% 6% 3 5% 5% 4 5% 23%	1520
December	1st to 10th	Day	19% 12% 7% 11% 5% 4 6% 5% 6% 6% 21%	1444
	11th to 20th	Day	14% 14% 6% 13% 11% 5% 5% 5% 5% 6% 18%	1668
	21st to end	Day	16% 13% 5% 12% 7% 4 6% 6% 5% 6% 21%	2431
January	1st to 10th	Night	16% 14% 4 12% 9% 5% 5% 4 6% 7% 19%	2838
	11th to 20th	Night	15% 13% 5% 9% 7% 4 6% 6% 6% 7% 22%	2787
	21st to end	Night	11% 12% 5% 8% 8% 3 5% 6% 6% 6% 31%	2742
February	1st to 10th	Night	10% 12% 4 8% 8% 4 6% 5% 6% 6% 32%	2340
	11th to 20th	Night	14% 14% 5% 8% 7% 4 5% 5% 5% 6% 28%	2273
	21st to end	Night	12% 13% 4 6% 7% 3 5% 5% 5% 6% 32%	1924
March	1st to 10th	Night	16% 12% 4 6% 7% 4 6% 4 5% 5% 32%	2042
	11th to 20th	Night	14% 12% 5% 10% 5% 4 4 5% 5% 5% 30%	1979
	21st to end	Night	18% 13% 3 6% 6% 3 4 4 5% 6% 32%	2172
April	1st to 10th	Night	24% 9% 3 8% 6% 3 5% 4 6% 5% 27%	1800
	11th to 20th	Night	20% 11% 3 5% 5% 3 4 4 4 5% 35%	1616
	21st to end	Night	24% 10% 3 5% 5% 2 4 4 4 5% 34%	1620
May	1st to 10th	Night	23% 8% 3 6% 5% 3 5% 4 3 5% 34%	1454
	11th to 20th	Night	20% 9% 3 4 4 3 4 5% 5% 6% 37%	1416
	21st to end	Night	20% 7% 3 7% 4 3 3 5% 6% 7% 35%	1446
June	1st to 10th	Night	26% 8% 3 6% 5% 3 5% 4 5% 5% 30%	1260
	11th to 20th	Night	21% 5% 2 6% 6% 3 4 4 4 7% 38%	1260
	21st to end	Night	21% 7% 3 7% 6% 4 5% 6% 5% 7% 30%	1260
July	1st to 10th	Night	17% 6% 2 6% 4 3 5% 5% 6% 8% 38%	1260
	11th to 20th	Night	15% 7% 2 5% 5% 3 5% 6% 6% 7% 40%	1260
	21st to end	Night	16% 7% 3 7% 6% 3 6% 5% 6% 8% 33%	1466
August	1st to 10th	Night	16% 5% 2 5% 4 3 5% 5% 5% 7% 42%	1527
	11th to 20th	Night	17% 6% 3 5% 5% 2 5% 4 5% 7% 41%	1596
	21st to end	Night	14% 6% 2 5% 5% 3 5% 6% 7% 8% 40%	1813
September	1st to 10th	Night	20% 5% 2 5% 4 3 4 4 5% 6% 43%	1800
	11th to 20th	Night	19% 6% 2 5% 4 3 3 3 3 7% 45%	1862
	21st to end	Night	19% 6% 2 4 4 2 3 4 5% 5% 45%	2037
October	1st to 10th	Night	19% 7% 3 4 6% 3 4 4 5% 6% 40%	2160
	11th to 20th	Night	24% 8% 3 5% 5% 3 3 5% 5% 5% 33%	2160
	21st to end	Night	23% 9% 2 5% 4 3 4 4 5% 7% 34%	2519
November	1st to 10th	Night	21% 10% 3 6% 5% 3 4 5% 5% 6% 32%	2593
	11th to 20th	Night	21% 12% 4 8% 5% 3 5% 5% 6% 7% 24%	2660
	21st to end	Night	20% 15% 6% 10% 6% 3 4 4 5% 6% 22%	2660
December	1st to 10th	Night	20% 14% 4 9% 6% 4 5% 6% 6% 5% 20%	2731
	11th to 20th	Night	20% 15% 5% 10% 9% 4 5% 4 6% 6% 18%	3531
	21st to end	Night	19% 12% 5% 12% 8% 4 5% 5% 5% 6% 20%	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	74% 4 11% 9% 3	1328
	11th to 20th	Day	68% 3 11% 13% 4	1295
	21st to end	Day	58% 3 11% 22% 6%	1611
February	1st to 10th	Day	53% 4 14% 19% 8% 1	1620
	11th to 20th	Day	59% 4 13% 19% 5%	1581
	21st to end	Day	50% 7% 8% 26% 8% 1	1332
March	1st to 10th	Day	55% 4 9% 19% 11% 1	1904
	11th to 20th	Day	53% 5% 10% 20% 11% 1	1980
	21st to end	Day	53% 5% 10% 19% 10% 2	2183
April	1st to 10th	Day	56% 5% 7% 19% 12% 1	2160
	11th to 20th	Day	48% 4 9% 23% 14% 2	2292
	21st to end	Day	53% 4 12% 17% 12% 2	2340
May	1st to 10th	Day	53% 4 9% 21% 11% 2	2506
	11th to 20th	Day	49% 4 11% 24% 10% 1	2482
	21st to end	Day	46% 8% 12% 21% 11% 1	2843
June	1st to 10th	Day	53% 5% 12% 20% 9%	2700
	11th to 20th	Day	45% 6% 12% 25% 10% 1	2700
	21st to end	Day	55% 6% 13% 18% 8%	2700
July	1st to 10th	Day	45% 8% 19% 21% 8%	2625
	11th to 20th	Day	42% 6% 17% 25% 10%	2619
	21st to end	Day	47% 6% 17% 22% 8%	2675
August	1st to 10th	Day	41% 9% 22% 23% 5%	2395
	11th to 20th	Day	44% 6% 21% 21% 7% 1	2304
	21st to end	Day	42% 6% 18% 26% 7%	2543
September	1st to 10th	Day	43% 5% 16% 26% 9%	2160
	11th to 20th	Day	43% 5% 15% 27% 10%	2097
	21st to end	Day	44% 6% 12% 26% 11% 1	1922
October	1st to 10th	Day	44% 5% 16% 25% 8% 2	1800
	11th to 20th	Day	52% 4 15% 21% 7% 1	1800
	21st to end	Day	57% 5% 12% 17% 8% 1	1834
November	1st to 10th	Day	57% 5% 14% 16% 8% 1	1485
	11th to 20th	Day	62% 5% 14% 14% 5%	1520
	21st to end	Day	68% 4 13% 10% 5%	1520
December	1st to 10th	Day	70% 4 13% 11% 3	1444
	11th to 20th	Day	75% 2 9% 10% 3	1668
	21st to end	Day	68% 5% 11% 11% 3 1	2431
January	1st to 10th	Night	71% 4 13% 10% 2	2838
	11th to 20th	Night	68% 4 12% 13% 3	2787
	21st to end	Night	59% 3 12% 19% 7%	2742
February	1st to 10th	Night	55% 5% 10% 19% 9% 2	2340
	11th to 20th	Night	58% 5% 12% 18% 7%	2276
	21st to end	Night	53% 5% 9% 22% 10% 1	1924
March	1st to 10th	Night	55% 4 8% 20% 11% 1	2051
	11th to 20th	Night	57% 3 8% 19% 11% 1	1980
	21st to end	Night	55% 4 11% 19% 8% 3	2172
April	1st to 10th	Night	60% 4 9% 15% 12% 1	1800
	11th to 20th	Night	51% 4 8% 25% 11% 1	1616
	21st to end	Night	55% 3 10% 17% 14% 1	1620
May	1st to 10th	Night	54% 4 8% 19% 13% 2	1454
	11th to 20th	Night	48% 4 11% 25% 12% 1	1417
	21st to end	Night	48% 5% 10% 22% 13% 1	1447
June	1st to 10th	Night	56% 4 9% 21% 9%	1260
	11th to 20th	Night	47% 6% 13% 19% 14% 1	1260
	21st to end	Night	54% 6% 15% 18% 7% 1	1260
July	1st to 10th	Night	45% 6% 19% 24% 6% 1	1225
	11th to 20th	Night	44% 5% 15% 28% 8% 1	1218
	21st to end	Night	52% 6% 14% 19% 9%	1385
August	1st to 10th	Night	43% 5% 20% 25% 7%	1516
	11th to 20th	Night	44% 5% 19% 24% 7% 1	1596
	21st to end	Night	42% 6% 17% 27% 7%	1813
September	1st to 10th	Night	45% 5% 12% 27% 10% 1	1800
	11th to 20th	Night	44% 3 13% 28% 11%	1862
	21st to end	Night	42% 5% 12% 28% 12% 1	2037
October	1st to 10th	Night	46% 4 14% 24% 11% 1	2160
	11th to 20th	Night	55% 3 14% 22% 6%	2160
	21st to end	Night	54% 4 14% 21% 7% 1	2519
November	1st to 10th	Night	55% 4 15% 18% 7% 1	2593
	11th to 20th	Night	63% 4 14% 14% 5%	2660
	21st to end	Night	69% 4 12% 11% 3	2660
December	1st to 10th	Night	72% 4 12% 11% 2	2731
	11th to 20th	Night	75% 3 8% 11% 3	3532
	21st to end	Night	70% 3 14% 11% 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% 15% 29% 23% 2 1	180
	11th to 20th	Day	32% 16% 28% 17% 6% 1	170
	21st to end	Day	18% 17% 36% 18% 9% 1	293
February	1st to 10th	Day	23% 16% 36% 15% 9% 1	340
	11th to 20th	Day	20% 21% 34% 19% 4 1	336
	21st to end	Day	18% 14% 31% 23% 11% 3	280
March	1st to 10th	Day	21% 15% 35% 19% 7% 2	401
	11th to 20th	Day	23% 14% 30% 22% 9% 2	420
	21st to end	Day	23% 19% 30% 20% 6% 2	462
April	1st to 10th	Day	27% 19% 26% 21% 6%	420
	11th to 20th	Day	23% 12% 33% 21% 8% 2	412
	21st to end	Day	26% 8% 28% 25% 10% 2	420
May	1st to 10th	Day	30% 9% 25% 24% 10% 3	589
	11th to 20th	Day	25% 10% 24% 26% 10% 4	624
	21st to end	Day	25% 13% 27% 25% 8% 1	680
June	1st to 10th	Day	29% 8% 25% 27% 9% 2	630
	11th to 20th	Day	22% 9% 21% 31% 13% 4	630
	21st to end	Day	27% 5% 28% 23% 15% 2	630
July	1st to 10th	Day	20% 4 27% 34% 13% 2	620
	11th to 20th	Day	17% 4 26% 35% 16% 2	618
	21st to end	Day	19% 6% 18% 33% 19% 4	685
August	1st to 10th	Day	17% 5% 22% 29% 25% 2	528
	11th to 20th	Day	15% 5% 22% 36% 19% 4	439
	21st to end	Day	17% 7% 26% 32% 15% 3	495
September	1st to 10th	Day	22% 6% 32% 24% 12% 3	450
	11th to 20th	Day	26% 10% 28% 24% 9% 3	450
	21st to end	Day	22% 12% 36% 21% 8% 1	421
October	1st to 10th	Day	17% 15% 32% 22% 10% 4	360
	11th to 20th	Day	29% 13% 29% 15% 11% 2	360
	21st to end	Day	28% 17% 28% 18% 8% 1	396
November	1st to 10th	Day	28% 14% 30% 20% 7% 1	365
	11th to 20th	Day	27% 18% 29% 17% 7% 2	370
	21st to end	Day	34% 18% 26% 20% 3	370
December	1st to 10th	Day	26% 11% 38% 21% 4 1	294
	11th to 20th	Day	28% 23% 31% 14% 3 1	180
	21st to end	Day	26% 24% 29% 17% 4 1	198
January	1st to 10th	Night	25% 17% 29% 22% 6% 1	850
	11th to 20th	Night	23% 17% 30% 22% 7%	829
	21st to end	Night	19% 16% 31% 24% 9% 1	832
February	1st to 10th	Night	18% 14% 30% 29% 8% 1	720
	11th to 20th	Night	24% 14% 32% 22% 7% 1	703
	21st to end	Night	21% 13% 29% 23% 11% 3	592
March	1st to 10th	Night	23% 12% 30% 23% 10% 2	720
	11th to 20th	Night	22% 14% 30% 24% 9% 2	720
	21st to end	Night	25% 13% 26% 25% 10% 1	786
April	1st to 10th	Night	30% 11% 24% 25% 9%	540
	11th to 20th	Night	25% 9% 28% 26% 10% 2	534
	21st to end	Night	29% 7% 19% 31% 10% 3	540
May	1st to 10th	Night	26% 5% 21% 29% 15% 3	540
	11th to 20th	Night	23% 6% 24% 27% 17% 2	532
	21st to end	Night	21% 9% 26% 32% 11% 2	479
June	1st to 10th	Night	28% 5% 21% 29% 17% 2	360
	11th to 20th	Night	24% 5% 15% 34% 18% 3	360
	21st to end	Night	25% 4 15% 36% 19% 2	360
July	1st to 10th	Night	19% 3 12% 39% 23% 3	350
	11th to 20th	Night	18% 4 14% 41% 22% 1	348
	21st to end	Night	21% 3 12% 37% 25% 2	483
August	1st to 10th	Night	18% 4 12% 38% 25% 3	538
	11th to 20th	Night	21% 2 14% 35% 26% 3	532
	21st to end	Night	18% 5% 18% 32% 24% 3	594
September	1st to 10th	Night	23% 4 23% 33% 15% 2	540
	11th to 20th	Night	23% 7% 22% 33% 14% 2	602
	21st to end	Night	23% 8% 27% 29% 12% 1	720
October	1st to 10th	Night	26% 8% 28% 26% 10% 2	720
	11th to 20th	Night	29% 10% 24% 24% 12% 1	720
	21st to end	Night	28% 12% 26% 24% 9%	825
November	1st to 10th	Night	29% 14% 26% 23% 7% 1	830
	11th to 20th	Night	30% 14% 29% 19% 6% 2	850
	21st to end	Night	31% 16% 28% 19% 5% 1	850
December	1st to 10th	Night	29% 15% 33% 17% 5%	850
	11th to 20th	Night	29% 22% 29% 16% 4	850
	21st to end	Night	29% 17% 28% 19% 5% 1	935

Page generated at 2024-01-13 09:37:55. Version ac07

Copyright 2024 Attilla Danko