Four Winds Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Four Winds Observatory 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	14% 10% 5% 8% 6% 3 4 4 5% 6% 33%	74409
	Night	16% 13% 6% 10% 7% 3 4 4 4 5% 28%	75317
Transparency	Day	51% 7% 12% 19% 10% 1	74115
	Night	58% 7% 11% 15% 8% 1	75146
Seeing	Day	17% 9% 26% 27% 16% 4	14603
	Night	21% 9% 26% 29% 13% 2	24707

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% 19% 12% 17% 12% 6% 3 3 4 3 8%	1517
	11th to 20th	Day	16% 16% 11% 18% 13% 5% 5% 3 3 3 6%	1485
	21st to end	Day	13% 18% 12% 18% 13% 4 6% 3 3 2 7%	1584
February	1st to 10th	Day	10% 17% 8% 16% 18% 5% 5% 3 3 4 11%	1530
	11th to 20th	Day	13% 13% 7% 16% 14% 5% 5% 3 3 4 16%	1748
	21st to end	Day	14% 15% 9% 11% 9% 4 6% 4 4 4 19%	1480
March	1st to 10th	Day	13% 11% 5% 11% 9% 4 4 4 5% 6% 28%	1798
	11th to 20th	Day	11% 10% 5% 10% 7% 4 4 4 4 5% 35%	1911
	21st to end	Day	17% 10% 5% 7% 6% 3 4 4 6% 6% 31%	2276
April	1st to 10th	Day	19% 13% 4 7% 6% 3 4 4 5% 6% 29%	2160
	11th to 20th	Day	20% 11% 4 5% 4 2 4 4 4 6% 35%	2212
	21st to end	Day	16% 8% 4 8% 5% 3 4 5% 6% 6% 35%	2340
May	1st to 10th	Day	14% 8% 3 6% 6% 2 5% 4 5% 5% 41%	2340
	11th to 20th	Day	14% 7% 3 5% 5% 3 4 4 5% 6% 44%	2407
	21st to end	Day	10% 5% 2 5% 4 4 5% 5% 6% 8% 46%	2725
June	1st to 10th	Day	13% 4 2 6% 5% 3 4 4 6% 8% 46%	2520
	11th to 20th	Day	10% 5% 2 4 5% 3 5% 5% 6% 9% 46%	2526
	21st to end	Day	12% 5% 3 5% 4 2 5% 6% 5% 7% 46%	2520
July	1st to 10th	Day	8% 3 1 3 4 2 4 5% 6% 9% 54%	2520
	11th to 20th	Day	10% 3 2 4 4 3 3 5% 7% 8% 51%	2520
	21st to end	Day	7% 4 2 4 4 2 4 5% 5% 9% 52%	2743
August	1st to 10th	Day	9% 5% 1 5% 5% 3 5% 4 6% 9% 49%	2433
	11th to 20th	Day	11% 4 2 4 4 3 4 4 5% 7% 50%	2303
	21st to end	Day	13% 5% 3 5% 4 3 3 4 4 8% 48%	2450
September	1st to 10th	Day	15% 6% 2 5% 5% 2 5% 5% 6% 6% 44%	2152
	11th to 20th	Day	14% 4 2 5% 5% 2 4 5% 5% 8% 46%	1980
	21st to end	Day	18% 6% 2 4 6% 3 5% 5% 7% 8% 36%	1980
October	1st to 10th	Day	20% 8% 3 7% 6% 3 4 4 4 7% 34%	1980
	11th to 20th	Day	25% 15% 4 8% 6% 3 5% 5% 4 5% 20%	1698
	21st to end	Day	26% 16% 4 8% 7% 4 5% 5% 4 5% 17%	1782
November	1st to 10th	Day	18% 18% 4 6% 5% 3 4 4 5% 6% 26%	1672
	11th to 20th	Day	15% 22% 8% 12% 7% 3 4 4 5% 4 15%	1710
	21st to end	Day	18% 25% 9% 11% 5% 2 4 3 3 4 14%	1614
December	1st to 10th	Day	17% 24% 17% 16% 6% 2 3 3 2 2 8%	1330
	11th to 20th	Day	16% 22% 11% 14% 11% 3 4 4 3 4 8%	1680
	21st to end	Day	21% 20% 12% 12% 9% 4 4 3 3 3 9%	2783
January	1st to 10th	Night	14% 20% 11% 16% 13% 4 4 3 3 3 10%	2648
	11th to 20th	Night	16% 19% 10% 16% 13% 4 4 3 2 3 9%	2603
	21st to end	Night	13% 18% 10% 17% 14% 6% 5% 3 4 3 8%	2772
February	1st to 10th	Night	12% 16% 8% 16% 17% 7% 4 3 3 3 12%	2429
	11th to 20th	Night	13% 13% 8% 16% 12% 4 5% 4 3 4 18%	2098
	21st to end	Night	17% 16% 6% 13% 8% 3 5% 3 4 6% 19%	1776
March	1st to 10th	Night	11% 13% 4 9% 7% 4 4 4 5% 6% 33%	2149
	11th to 20th	Night	11% 10% 5% 10% 7% 4 4 5% 4 5% 34%	2047
	21st to end	Night	17% 11% 4 8% 7% 3 4 4 4 7% 33%	2095
April	1st to 10th	Night	18% 12% 3 8% 6% 3 4 4 5% 5% 30%	1800
	11th to 20th	Night	20% 9% 3 6% 5% 3 5% 4 5% 5% 35%	1697
	21st to end	Night	17% 8% 3 7% 5% 3 5% 5% 4 6% 36%	1620
May	1st to 10th	Night	16% 7% 3 6% 6% 4 6% 5% 5% 7% 35%	1620
	11th to 20th	Night	15% 8% 4 6% 7% 2 6% 6% 6% 5% 35%	1485
	21st to end	Night	11% 5% 3 5% 4 3 5% 5% 7% 9% 45%	1551
June	1st to 10th	Night	14% 5% 2 5% 5% 4 4 5% 5% 7% 44%	1440
	11th to 20th	Night	12% 5% 3 5% 5% 3 5% 5% 6% 8% 43%	1345
	21st to end	Night	11% 6% 2 6% 5% 3 4 4 5% 8% 47%	1440
July	1st to 10th	Night	8% 4 2 4 4 2 4 5% 7% 9% 52%	1440
	11th to 20th	Night	8% 4 2 5% 4 3 5% 5% 6% 7% 50%	1440
	21st to end	Night	10% 3 2 5% 4 3 4 5% 5% 8% 50%	1575
August	1st to 10th	Night	8% 5% 2 5% 5% 3 5% 5% 6% 8% 48%	1503
	11th to 20th	Night	11% 3 2 4 5% 3 4 5% 6% 8% 49%	1598
	21st to end	Night	14% 5% 2 5% 5% 4 3 4 5% 7% 46%	1903
September	1st to 10th	Night	12% 6% 3 5% 5% 3 4 4 5% 7% 48%	1800
	11th to 20th	Night	15% 5% 2 5% 4 3 4 4 5% 7% 46%	1970
	21st to end	Night	18% 6% 3 7% 5% 3 4 4 6% 8% 36%	1980
October	1st to 10th	Night	20% 8% 3 7% 6% 3 4 3 4 5% 36%	1980
	11th to 20th	Night	27% 12% 4 7% 5% 3 4 4 5% 6% 24%	2261
	21st to end	Night	26% 14% 4 7% 7% 4 4 4 3 4 21%	2574
November	1st to 10th	Night	17% 16% 5% 7% 6% 3 5% 3 4 6% 27%	2406
	11th to 20th	Night	17% 22% 8% 10% 7% 3 5% 4 3 4 18%	2470
	21st to end	Night	18% 22% 8% 11% 7% 4 4 4 4 4 14%	2556
December	1st to 10th	Night	15% 24% 13% 17% 8% 3 3 2 2 3 9%	2850
	11th to 20th	Night	15% 21% 10% 19% 9% 3 4 3 3 4 10%	3512
	21st to end	Night	25% 22% 10% 11% 6% 3 3 3 3 4 10%	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	83% 6% 6% 4 1	1518
	11th to 20th	Day	85% 6% 5% 3 1	1485
	21st to end	Day	84% 7% 4 4 1	1584
February	1st to 10th	Day	79% 5% 7% 8% 1	1530
	11th to 20th	Day	73% 7% 8% 8% 3	1758
	21st to end	Day	69% 7% 8% 12% 3 1	1480
March	1st to 10th	Day	57% 8% 13% 16% 6% 1	1800
	11th to 20th	Day	52% 6% 12% 21% 7% 2	1911
	21st to end	Day	53% 8% 13% 19% 7% 1	2276
April	1st to 10th	Day	56% 7% 10% 18% 10%	2160
	11th to 20th	Day	50% 6% 10% 19% 14% 2	2212
	21st to end	Day	48% 7% 13% 15% 15% 3	2340
May	1st to 10th	Day	44% 6% 11% 24% 12% 3	2340
	11th to 20th	Day	41% 6% 12% 23% 16% 3	2411
	21st to end	Day	36% 8% 14% 25% 14% 2	2725
June	1st to 10th	Day	36% 8% 13% 26% 16% 2	2520
	11th to 20th	Day	34% 8% 13% 24% 18% 2	2526
	21st to end	Day	36% 8% 16% 25% 15% 1	2520
July	1st to 10th	Day	26% 7% 15% 30% 19% 2	2451
	11th to 20th	Day	30% 8% 16% 29% 16% 2	2445
	21st to end	Day	29% 8% 16% 27% 19% 1	2591
August	1st to 10th	Day	32% 8% 19% 29% 11% 1	2418
	11th to 20th	Day	33% 7% 16% 29% 13% 2	2303
	21st to end	Day	37% 6% 16% 24% 15% 1	2450
September	1st to 10th	Day	39% 7% 14% 24% 14% 1	2152
	11th to 20th	Day	34% 10% 17% 29% 9% 1	1980
	21st to end	Day	44% 8% 16% 24% 8%	1980
October	1st to 10th	Day	49% 8% 12% 22% 9% 1	1980
	11th to 20th	Day	66% 7% 10% 14% 3	1698
	21st to end	Day	69% 8% 10% 10% 3	1782
November	1st to 10th	Day	58% 8% 11% 17% 7%	1672
	11th to 20th	Day	71% 7% 10% 9% 3	1710
	21st to end	Day	74% 7% 11% 7% 1	1614
December	1st to 10th	Day	85% 4 5% 5% 1	1330
	11th to 20th	Day	80% 9% 6% 4 1	1680
	21st to end	Day	80% 9% 7% 3 1	2783
January	1st to 10th	Night	81% 6% 6% 5% 1	2648
	11th to 20th	Night	81% 7% 6% 5% 1	2603
	21st to end	Night	83% 6% 6% 4 1	2772
February	1st to 10th	Night	79% 6% 7% 7% 2	2429
	11th to 20th	Night	70% 7% 8% 12% 3	2099
	21st to end	Night	66% 7% 11% 13% 3	1776
March	1st to 10th	Night	51% 8% 13% 20% 7%	2160
	11th to 20th	Night	51% 8% 10% 19% 11% 2	2048
	21st to end	Night	51% 7% 11% 20% 10% 1	2095
April	1st to 10th	Night	54% 8% 9% 19% 10% 1	1800
	11th to 20th	Night	50% 6% 10% 18% 13% 3	1697
	21st to end	Night	47% 7% 10% 20% 13% 3	1620
May	1st to 10th	Night	47% 8% 11% 18% 12% 4	1620
	11th to 20th	Night	48% 7% 9% 19% 15% 2	1486
	21st to end	Night	35% 8% 16% 25% 15% 3	1552
June	1st to 10th	Night	38% 9% 11% 27% 14% 1	1440
	11th to 20th	Night	37% 8% 14% 23% 16% 3	1345
	21st to end	Night	36% 8% 12% 27% 15% 2	1440
July	1st to 10th	Night	26% 8% 16% 29% 18% 3	1400
	11th to 20th	Night	31% 8% 15% 23% 21% 2	1392
	21st to end	Night	32% 7% 15% 28% 16% 1	1487
August	1st to 10th	Night	32% 9% 18% 28% 11% 2	1494
	11th to 20th	Night	31% 9% 16% 27% 15% 1	1598
	21st to end	Night	39% 7% 14% 24% 16% 1	1903
September	1st to 10th	Night	36% 7% 14% 22% 20% 1	1800
	11th to 20th	Night	37% 7% 17% 27% 11%	1970
	21st to end	Night	45% 9% 16% 23% 7%	1980
October	1st to 10th	Night	49% 7% 9% 22% 12% 1	1980
	11th to 20th	Night	61% 7% 12% 15% 4	2261
	21st to end	Night	65% 9% 9% 13% 4	2574
November	1st to 10th	Night	57% 8% 11% 17% 6% 1	2406
	11th to 20th	Night	70% 7% 9% 9% 4	2470
	21st to end	Night	73% 8% 10% 8% 1	2556
December	1st to 10th	Night	81% 6% 5% 6% 1	2850
	11th to 20th	Night	78% 8% 8% 3 2	3511
	21st to end	Night	78% 9% 9% 3 1	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	18% 16% 37% 21% 7% 2	270
	11th to 20th	Day	25% 13% 37% 20% 5% 1	257
	21st to end	Day	23% 13% 32% 25% 6% 1	264
February	1st to 10th	Day	22% 19% 39% 16% 4	240
	11th to 20th	Day	18% 18% 41% 18% 5%	240
	21st to end	Day	20% 24% 41% 13% 2	198
March	1st to 10th	Day	21% 15% 39% 20% 5%	240
	11th to 20th	Day	20% 11% 29% 27% 11% 2	351
	21st to end	Day	24% 11% 28% 24% 11% 1	462
April	1st to 10th	Day	24% 10% 29% 27% 8% 1	420
	11th to 20th	Day	25% 13% 27% 19% 12% 3	412
	21st to end	Day	18% 10% 29% 26% 15% 3	420
May	1st to 10th	Day	18% 9% 30% 25% 13% 4	423
	11th to 20th	Day	16% 5% 28% 33% 14% 4	553
	21st to end	Day	13% 6% 23% 30% 24% 5%	679
June	1st to 10th	Day	13% 4 25% 33% 21% 4	630
	11th to 20th	Day	13% 4 24% 34% 20% 5%	630
	21st to end	Day	14% 4 18% 36% 22% 5%	630
July	1st to 10th	Day	8% 2 17% 37% 27% 9%	621
	11th to 20th	Day	10% 4 22% 33% 24% 8%	618
	21st to end	Day	8% 3 21% 36% 28% 5%	684
August	1st to 10th	Day	10% 3 17% 33% 28% 10%	552
	11th to 20th	Day	12% 3 18% 30% 27% 11%	439
	21st to end	Day	16% 4 19% 29% 25% 7%	495
September	1st to 10th	Day	18% 6% 22% 25% 21% 8%	450
	11th to 20th	Day	11% 5% 24% 27% 25% 8%	450
	21st to end	Day	19% 8% 18% 28% 20% 6%	450
October	1st to 10th	Day	22% 11% 22% 25% 16% 4	450
	11th to 20th	Day	29% 14% 29% 20% 6% 1	320
	21st to end	Day	32% 13% 27% 22% 5% 1	297
November	1st to 10th	Day	27% 15% 27% 18% 12% 1	270
	11th to 20th	Day	18% 20% 41% 16% 4	270
	21st to end	Day	27% 21% 33% 15% 3	257
December	1st to 10th	Day	31% 16% 33% 13% 7% 1	180
	11th to 20th	Day	27% 22% 33% 16% 3 1	184
	21st to end	Day	27% 20% 36% 13% 3 1	297
January	1st to 10th	Night	20% 15% 37% 22% 6% 1	950
	11th to 20th	Night	25% 14% 31% 22% 7% 1	930
	21st to end	Night	20% 11% 34% 25% 8% 1	990
February	1st to 10th	Night	18% 15% 34% 26% 7%	824
	11th to 20th	Night	21% 12% 34% 25% 8%	703
	21st to end	Night	24% 15% 30% 26% 5%	592
March	1st to 10th	Night	17% 9% 30% 31% 12% 1	720
	11th to 20th	Night	16% 11% 34% 29% 9% 1	720
	21st to end	Night	21% 7% 26% 34% 11% 1	709
April	1st to 10th	Night	23% 9% 29% 31% 8% 1	540
	11th to 20th	Night	23% 8% 25% 31% 12% 1	533
	21st to end	Night	18% 6% 27% 35% 12% 1	540
May	1st to 10th	Night	17% 4 26% 35% 16% 1	540
	11th to 20th	Night	19% 3 22% 38% 17% 2	531
	21st to end	Night	13% 4 20% 35% 26% 3	584
June	1st to 10th	Night	16% 2 20% 38% 22% 1	540
	11th to 20th	Night	13% 4 19% 39% 24% 2	445
	21st to end	Night	12% 2 18% 39% 27% 2	540
July	1st to 10th	Night	10% 2 12% 42% 29% 5%	525
	11th to 20th	Night	10% 1 18% 37% 29% 5%	522
	21st to end	Night	9% 3 17% 38% 30% 3	591
August	1st to 10th	Night	10% 1 15% 42% 28% 3	537
	11th to 20th	Night	11% 4 15% 32% 32% 6%	534
	21st to end	Night	15% 3 15% 38% 26% 3	594
September	1st to 10th	Night	15% 3 19% 32% 27% 4	540
	11th to 20th	Night	17% 4 19% 31% 24% 5%	710
	21st to end	Night	20% 8% 19% 29% 19% 5%	720
October	1st to 10th	Night	23% 8% 21% 28% 17% 2	720
	11th to 20th	Night	31% 11% 24% 26% 7% 1	720
	21st to end	Night	33% 11% 26% 22% 7% 1	792
November	1st to 10th	Night	26% 14% 24% 29% 6% 1	740
	11th to 20th	Night	28% 17% 31% 20% 4	760
	21st to end	Night	28% 17% 30% 20% 4	826
December	1st to 10th	Night	27% 20% 31% 18% 4	950
	11th to 20th	Night	25% 15% 35% 18% 5% 1	950
	21st to end	Night	30% 13% 35% 20% 2	1045

Page generated at 2024-01-13 19:28:31. Version ac07

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