Cape Jellison
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cape Jellison clear sky chart from 2005-11-06 to 2024-01-14.

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	18% 7% 3 5% 5% 3 4 4 5% 7% 38%	74584
	Night	19% 8% 3 5% 5% 3 4 4 5% 6% 38%	75166
Transparency	Day	46% 6% 11% 21% 14% 2	74291
	Night	47% 5% 11% 21% 14% 2	74994
Seeing	Day	23% 16% 31% 20% 7% 2	14575
	Night	24% 14% 29% 24% 8% 1	23090

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% 9% 4 7% 5% 3 4 4 4 6% 38%	1517
	11th to 20th	Day	22% 9% 4 5% 4 2 4 4 4 6% 36%	1464
	21st to end	Day	14% 10% 4 7% 5% 3 3 4 5% 6% 40%	1616
February	1st to 10th	Day	18% 10% 3 5% 5% 2 5% 4 5% 7% 35%	1620
	11th to 20th	Day	15% 9% 2 7% 5% 3 6% 5% 6% 6% 37%	1675
	21st to end	Day	13% 10% 4 7% 6% 3 6% 5% 4 7% 35%	1480
March	1st to 10th	Day	17% 8% 3 5% 5% 3 5% 4 5% 7% 36%	1805
	11th to 20th	Day	17% 7% 3 4 6% 3 4 4 5% 7% 40%	1980
	21st to end	Day	19% 8% 3 5% 5% 4 4 4 5% 5% 38%	2178
April	1st to 10th	Day	21% 7% 4 6% 6% 3 4 4 4 6% 33%	2142
	11th to 20th	Day	18% 7% 2 5% 6% 3 5% 4 5% 6% 38%	2284
	21st to end	Day	22% 8% 3 7% 5% 3 4 4 4 6% 34%	2340
May	1st to 10th	Day	22% 8% 2 5% 5% 3 5% 5% 5% 7% 33%	2340
	11th to 20th	Day	21% 6% 3 5% 5% 3 4 4 5% 7% 37%	2301
	21st to end	Day	18% 6% 3 6% 5% 2 5% 5% 6% 9% 36%	2752
June	1st to 10th	Day	22% 6% 3 6% 6% 3 5% 5% 5% 8% 31%	2700
	11th to 20th	Day	18% 7% 2 5% 6% 3 4 4 5% 8% 38%	2700
	21st to end	Day	25% 6% 3 5% 5% 3 5% 5% 5% 7% 30%	2700
July	1st to 10th	Day	17% 6% 2 4 5% 3 4 5% 6% 9% 38%	2572
	11th to 20th	Day	15% 6% 3 4 5% 3 5% 5% 6% 9% 38%	2520
	21st to end	Day	15% 6% 2 5% 5% 3 5% 6% 7% 9% 37%	2704
August	1st to 10th	Day	15% 5% 2 4 4 3 5% 6% 8% 9% 39%	2327
	11th to 20th	Day	14% 6% 3 5% 5% 3 5% 6% 6% 9% 38%	2304
	21st to end	Day	13% 6% 2 4 4 3 4 4 5% 8% 46%	2561
September	1st to 10th	Day	11% 5% 2 5% 5% 2 4 4 5% 8% 49%	2070
	11th to 20th	Day	14% 5% 2 4 4 3 4 3 5% 5% 53%	1980
	21st to end	Day	18% 5% 2 4 4 2 4 4 7% 7% 44%	1980
October	1st to 10th	Day	16% 7% 2 5% 5% 4 4 5% 4 7% 41%	1935
	11th to 20th	Day	20% 6% 2 5% 5% 2 4 4 5% 7% 40%	1787
	21st to end	Day	23% 8% 2 5% 4 3 4 4 5% 5% 36%	1782
November	1st to 10th	Day	19% 6% 2 5% 4 3 5% 4 4 7% 42%	1671
	11th to 20th	Day	21% 5% 2 4 3 2 4 4 6% 7% 42%	1691
	21st to end	Day	22% 7% 3 5% 3 2 3 3 4 6% 42%	1520
December	1st to 10th	Day	23% 9% 3 6% 4 3 3 3 4 6% 35%	1421
	11th to 20th	Day	23% 9% 3 5% 4 1 4 4 4 5% 38%	1668
	21st to end	Day	25% 10% 3 5% 4 3 3 4 4 5% 33%	2497
January	1st to 10th	Night	17% 10% 2 6% 5% 3 4 5% 5% 7% 38%	2649
	11th to 20th	Night	18% 12% 3 7% 6% 3 4 5% 4 6% 32%	2574
	21st to end	Night	12% 9% 3 6% 5% 3 5% 5% 5% 7% 39%	2740
February	1st to 10th	Night	18% 9% 3 6% 6% 4 6% 5% 5% 5% 34%	2340
	11th to 20th	Night	14% 9% 4 7% 6% 4 4 5% 5% 5% 38%	2167
	21st to end	Night	15% 9% 4 6% 5% 3 4 4 4 6% 40%	1776
March	1st to 10th	Night	15% 12% 3 6% 5% 2 5% 3 4 6% 38%	2141
	11th to 20th	Night	18% 8% 4 6% 6% 3 5% 4 5% 6% 34%	1979
	21st to end	Night	18% 8% 3 6% 5% 3 4 4 4 6% 40%	2178
April	1st to 10th	Night	23% 10% 4 6% 5% 2 4 4 4 5% 34%	1816
	11th to 20th	Night	19% 6% 4 6% 4 3 4 5% 6% 7% 35%	1625
	21st to end	Night	25% 9% 3 6% 5% 2 4 4 4 6% 33%	1620
May	1st to 10th	Night	23% 8% 4 7% 5% 2 4 5% 5% 6% 30%	1620
	11th to 20th	Night	23% 8% 2 5% 5% 4 5% 5% 5% 8% 32%	1593
	21st to end	Night	21% 8% 3 5% 6% 3 5% 4 4 6% 35%	1532
June	1st to 10th	Night	23% 9% 3 6% 6% 3 3 4 5% 7% 30%	1260
	11th to 20th	Night	18% 9% 3 5% 4 3 4 5% 4 7% 37%	1260
	21st to end	Night	24% 11% 3 5% 5% 3 4 4 4 6% 30%	1260
July	1st to 10th	Night	18% 7% 2 6% 5% 3 5% 5% 6% 8% 34%	1383
	11th to 20th	Night	18% 7% 4 5% 4 3 5% 4 5% 9% 35%	1440
	21st to end	Night	18% 7% 3 5% 4 3 5% 5% 5% 7% 35%	1596
August	1st to 10th	Night	16% 6% 2 5% 5% 4 5% 5% 5% 8% 39%	1612
	11th to 20th	Night	16% 9% 3 6% 5% 3 4 5% 5% 9% 34%	1596
	21st to end	Night	14% 5% 2 5% 5% 3 3 4 5% 7% 46%	1791
September	1st to 10th	Night	14% 6% 2 4 4 2 4 4 5% 7% 49%	1888
	11th to 20th	Night	17% 6% 1 4 3 2 3 4 4 7% 49%	1980
	21st to end	Night	19% 5% 2 3 4 3 3 4 4 7% 45%	1980
October	1st to 10th	Night	19% 7% 2 5% 4 3 4 5% 4 7% 40%	2024
	11th to 20th	Night	19% 6% 2 5% 4 3 5% 4 5% 6% 42%	2169
	21st to end	Night	25% 8% 2 4 4 2 4 3 4 5% 37%	2574
November	1st to 10th	Night	19% 6% 3 5% 5% 3 4 4 4 5% 42%	2407
	11th to 20th	Night	19% 6% 2 5% 4 3 4 5% 5% 6% 42%	2485
	21st to end	Night	18% 7% 3 5% 4 3 4 4 5% 7% 41%	2660
December	1st to 10th	Night	23% 9% 3 5% 5% 3 4 3 5% 6% 33%	2755
	11th to 20th	Night	23% 8% 2 5% 4 2 3 3 4 5% 40%	3531
	21st to end	Night	25% 8% 3 5% 4 2 4 4 4 6% 36%	5165

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	48% 4 9% 23% 15% 2	1518
	11th to 20th	Day	51% 5% 11% 20% 10% 2	1464
	21st to end	Day	44% 4 10% 23% 17% 2	1616
February	1st to 10th	Day	50% 5% 12% 18% 13% 2	1620
	11th to 20th	Day	48% 5% 11% 20% 15% 2	1683
	21st to end	Day	50% 4 9% 20% 11% 5%	1480
March	1st to 10th	Day	49% 4 12% 17% 15% 3	1808
	11th to 20th	Day	44% 5% 10% 19% 17% 5%	1980
	21st to end	Day	47% 4 10% 17% 16% 5%	2178
April	1st to 10th	Day	51% 5% 7% 16% 16% 4	2142
	11th to 20th	Day	46% 4 10% 22% 15% 2	2284
	21st to end	Day	52% 4 8% 17% 15% 4	2340
May	1st to 10th	Day	51% 5% 8% 19% 14% 3	2340
	11th to 20th	Day	46% 5% 9% 22% 15% 2	2305
	21st to end	Day	48% 6% 12% 21% 11% 2	2752
June	1st to 10th	Day	52% 7% 11% 20% 10% 1	2700
	11th to 20th	Day	46% 6% 9% 20% 16% 3	2700
	21st to end	Day	53% 7% 11% 17% 10% 2	2700
July	1st to 10th	Day	42% 8% 15% 23% 12% 1	2502
	11th to 20th	Day	42% 7% 15% 24% 11% 1	2445
	21st to end	Day	42% 8% 15% 24% 10% 1	2553
August	1st to 10th	Day	38% 10% 15% 29% 9%	2314
	11th to 20th	Day	42% 8% 15% 22% 13%	2304
	21st to end	Day	36% 7% 13% 25% 18% 1	2561
September	1st to 10th	Day	34% 5% 15% 27% 18% 1	2070
	11th to 20th	Day	33% 5% 11% 27% 21% 3	1980
	21st to end	Day	39% 6% 11% 25% 17% 1	1980
October	1st to 10th	Day	43% 6% 10% 24% 15% 2	1935
	11th to 20th	Day	44% 5% 13% 27% 11% 1	1787
	21st to end	Day	49% 5% 10% 21% 14% 1	1782
November	1st to 10th	Day	43% 5% 13% 23% 15% 2	1671
	11th to 20th	Day	42% 5% 10% 22% 18% 3	1691
	21st to end	Day	45% 5% 15% 22% 12% 1	1520
December	1st to 10th	Day	52% 4 10% 21% 11% 1	1421
	11th to 20th	Day	50% 4 10% 19% 14% 2	1668
	21st to end	Day	53% 6% 12% 18% 9% 3	2497
January	1st to 10th	Night	47% 4 12% 23% 13% 2	2649
	11th to 20th	Night	55% 5% 11% 18% 10% 2	2574
	21st to end	Night	45% 4 10% 23% 16% 2	2740
February	1st to 10th	Night	52% 5% 11% 18% 12% 2	2340
	11th to 20th	Night	48% 5% 9% 20% 16% 2	2170
	21st to end	Night	47% 3 10% 20% 16% 4	1776
March	1st to 10th	Night	49% 3 8% 21% 16% 3	2151
	11th to 20th	Night	50% 5% 10% 17% 16% 3	1980
	21st to end	Night	47% 4 8% 19% 19% 3	2178
April	1st to 10th	Night	54% 4 8% 14% 17% 3	1816
	11th to 20th	Night	47% 4 10% 22% 16% 1	1625
	21st to end	Night	53% 3 11% 16% 13% 3	1620
May	1st to 10th	Night	53% 5% 9% 19% 13% 1	1620
	11th to 20th	Night	52% 6% 9% 19% 12% 2	1594
	21st to end	Night	52% 4 10% 20% 12% 1	1533
June	1st to 10th	Night	54% 6% 10% 21% 9% 1	1260
	11th to 20th	Night	47% 5% 13% 20% 12% 2	1260
	21st to end	Night	55% 6% 9% 19% 9% 2	1260
July	1st to 10th	Night	47% 7% 13% 21% 12%	1343
	11th to 20th	Night	48% 5% 14% 22% 11%	1392
	21st to end	Night	48% 5% 14% 22% 9% 1	1507
August	1st to 10th	Night	43% 6% 15% 25% 10%	1600
	11th to 20th	Night	47% 7% 14% 20% 12%	1596
	21st to end	Night	38% 7% 10% 25% 19% 1	1791
September	1st to 10th	Night	35% 5% 14% 30% 16% 1	1888
	11th to 20th	Night	37% 4 11% 27% 20% 2	1980
	21st to end	Night	39% 5% 8% 30% 16% 1	1980
October	1st to 10th	Night	45% 4 10% 24% 14% 2	2024
	11th to 20th	Night	42% 5% 12% 27% 13% 1	2169
	21st to end	Night	51% 4 11% 20% 14% 1	2574
November	1st to 10th	Night	44% 6% 11% 23% 15% 1	2407
	11th to 20th	Night	43% 4 10% 22% 18% 2	2485
	21st to end	Night	45% 4 13% 20% 16% 2	2660
December	1st to 10th	Night	53% 4 9% 21% 12%	2755
	11th to 20th	Night	47% 4 11% 21% 17% 1	3532
	21st to end	Night	49% 5% 13% 18% 12% 2	5165

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	26% 26% 25% 19% 4	180
	11th to 20th	Day	30% 23% 30% 14% 3 1	166
	21st to end	Day	22% 24% 31% 21% 2	208
February	1st to 10th	Day	26% 20% 34% 16% 4	340
	11th to 20th	Day	25% 27% 35% 11% 2	382
	21st to end	Day	21% 24% 35% 16% 3	346
March	1st to 10th	Day	24% 23% 35% 15% 2	420
	11th to 20th	Day	22% 25% 32% 17% 3 1	420
	21st to end	Day	28% 21% 29% 15% 5% 2	462
April	1st to 10th	Day	31% 23% 30% 10% 5% 2	420
	11th to 20th	Day	28% 21% 31% 14% 5% 1	412
	21st to end	Day	25% 21% 33% 16% 4 1	420
May	1st to 10th	Day	27% 22% 34% 13% 3 1	423
	11th to 20th	Day	19% 22% 34% 19% 4 2	447
	21st to end	Day	22% 17% 34% 19% 8% 1	543
June	1st to 10th	Day	24% 14% 29% 22% 10% 2	630
	11th to 20th	Day	22% 12% 30% 23% 10% 1	630
	21st to end	Day	27% 8% 27% 27% 9% 1	630
July	1st to 10th	Day	24% 7% 34% 25% 9% 2	497
	11th to 20th	Day	18% 8% 36% 26% 11% 2	444
	21st to end	Day	16% 7% 38% 25% 10% 3	488
August	1st to 10th	Day	17% 8% 30% 31% 12% 2	446
	11th to 20th	Day	18% 8% 28% 30% 13% 3	439
	21st to end	Day	17% 10% 29% 28% 12% 3	495
September	1st to 10th	Day	16% 7% 36% 26% 12% 3	450
	11th to 20th	Day	19% 12% 30% 22% 12% 6%	450
	21st to end	Day	19% 12% 33% 21% 11% 4	450
October	1st to 10th	Day	20% 14% 27% 24% 13% 2	427
	11th to 20th	Day	21% 15% 33% 20% 8% 3	360
	21st to end	Day	30% 17% 28% 19% 5% 1	396
November	1st to 10th	Day	22% 18% 28% 24% 7% 2	365
	11th to 20th	Day	27% 18% 33% 18% 4 1	370
	21st to end	Day	28% 22% 27% 16% 7%	370
December	1st to 10th	Day	26% 19% 35% 16% 3 1	271
	11th to 20th	Day	32% 28% 29% 7% 3	180
	21st to end	Day	28% 29% 25% 14% 4	198
January	1st to 10th	Night	24% 23% 31% 19% 4	760
	11th to 20th	Night	26% 23% 31% 17% 4	736
	21st to end	Night	19% 24% 33% 20% 4	792
February	1st to 10th	Night	25% 22% 31% 20% 2	720
	11th to 20th	Night	21% 22% 35% 18% 3 1	703
	21st to end	Night	22% 18% 35% 21% 3	592
March	1st to 10th	Night	24% 18% 37% 19% 2	720
	11th to 20th	Night	23% 17% 32% 22% 6%	720
	21st to end	Night	23% 17% 30% 23% 6% 1	792
April	1st to 10th	Night	30% 14% 34% 17% 3 1	720
	11th to 20th	Night	25% 12% 30% 27% 6%	561
	21st to end	Night	31% 10% 30% 23% 7%	540
May	1st to 10th	Night	26% 7% 32% 26% 7% 1	540
	11th to 20th	Night	27% 7% 35% 26% 5%	532
	21st to end	Night	25% 6% 27% 30% 11% 1	433
June	1st to 10th	Night	28% 7% 21% 34% 11% 1	360
	11th to 20th	Night	22% 8% 22% 31% 16% 1	360
	21st to end	Night	31% 3 18% 38% 10%	360
July	1st to 10th	Night	23% 3 19% 39% 14% 1	350
	11th to 20th	Night	23% 1 19% 39% 16% 1	348
	21st to end	Night	21% 2 22% 37% 17% 1	416
August	1st to 10th	Night	19% 3 23% 39% 15% 1	538
	11th to 20th	Night	21% 4 21% 36% 16% 1	532
	21st to end	Night	18% 4 23% 35% 18% 2	603
September	1st to 10th	Night	18% 4 29% 31% 16% 2	720
	11th to 20th	Night	20% 9% 24% 26% 16% 4	720
	21st to end	Night	22% 7% 27% 27% 15% 2	720
October	1st to 10th	Night	23% 8% 24% 27% 17% 1	720
	11th to 20th	Night	22% 11% 30% 25% 10% 2	720
	21st to end	Night	29% 16% 28% 22% 5%	792
November	1st to 10th	Night	25% 13% 27% 26% 8% 1	740
	11th to 20th	Night	24% 17% 30% 20% 8% 1	767
	21st to end	Night	24% 22% 27% 20% 6%	850
December	1st to 10th	Night	29% 16% 34% 16% 5%	850
	11th to 20th	Night	27% 24% 30% 16% 3	850
	21st to end	Night	28% 21% 29% 18% 3	913

Page generated at 2024-01-11 13:31:59. Version ac07

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