Summerland Key
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Summerland Key clear sky chart from 2005-11-06 to 2026-04-17.

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	5% 4 2 5% 4 5% 6% 5% 8% 12% 44%	131341
	Night	5% 4 2 5% 4 5% 5% 5% 7% 11% 46%	130792
Transparency	Day	18% 40% 16% 18% 7% 1	135069
	Night	18% 39% 14% 18% 8% 2	135133
Seeing	Day	6% 2 7% 25% 37% 22%	17854
	Night	6% 2 8% 27% 37% 19%	28015

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	5% 4 2 5% 4 4 4 4 7% 13% 47%	5258
	11th to 20th	Day	10% 6% 3 8% 5% 6% 6% 6% 8% 10% 32%	5280
	21st to end	Day	9% 7% 3 7% 5% 5% 5% 4 6% 8% 42%	6418
February	1st to 10th	Day	6% 4 2 4 4 4 5% 4 7% 9% 51%	2100
	11th to 20th	Day	5% 4 2 4 3 3 4 4 6% 10% 56%	2095
	21st to end	Day	3 2 1 3 2 3 3 4 6% 10% 61%	1903
March	1st to 10th	Day	2 2 1 3 3 3 5% 4 7% 11% 59%	5045
	11th to 20th	Day	3 2 1 3 3 3 3 4 6% 10% 63%	5090
	21st to end	Day	5% 3 2 5% 4 3 4 4 6% 10% 54%	5586
April	1st to 10th	Day	3 1 1 3 4 4 5% 5% 7% 13% 55%	2310
	11th to 20th	Day	3 3 1 3 3 3 5% 4 8% 11% 57%	2242
	21st to end	Day	4 3 1 4 3 3 4 4 8% 10% 56%	2365
May	1st to 10th	Day	1 1 1 2 2 2 3 3 6% 13% 66%	5405
	11th to 20th	Day	4 3 1 4 3 3 3 4 5% 9% 59%	5627
	21st to end	Day	3 3 1 3 2 3 4 3 6% 10% 62%	6433
June	1st to 10th	Day	11% 8% 3 8% 6% 6% 6% 6% 9% 12% 26%	2600
	11th to 20th	Day	6% 5% 3 8% 6% 7% 7% 7% 11% 12% 27%	2600
	21st to end	Day	4 5% 2 7% 6% 7% 8% 8% 12% 16% 27%	2600
July	1st to 10th	Day	3 3 2 6% 6% 6% 8% 6% 11% 17% 33%	5900
	11th to 20th	Day	2 3 2 6% 5% 6% 8% 7% 11% 17% 32%	5900
	21st to end	Day	2 2 1 3 4 5% 6% 6% 10% 18% 43%	6424
August	1st to 10th	Day	2 3 2 8% 7% 7% 8% 8% 12% 16% 27%	4150
	11th to 20th	Day	2 3 2 7% 6% 8% 9% 7% 11% 17% 29%	3539
	21st to end	Day	4 3 1 6% 6% 8% 10% 8% 13% 17% 24%	3949
September	1st to 10th	Day	5% 4 1 7% 7% 8% 10% 7% 11% 15% 24%	2200
	11th to 20th	Day	4 5% 4 7% 7% 8% 8% 7% 11% 14% 25%	2200
	21st to end	Day	7% 7% 4 10% 6% 7% 7% 7% 9% 12% 25%	2200
October	1st to 10th	Day	5% 7% 2 7% 6% 8% 8% 7% 11% 14% 25%	2200
	11th to 20th	Day	8% 5% 2 7% 6% 6% 6% 6% 9% 12% 33%	2008
	21st to end	Day	7% 6% 2 6% 5% 6% 5% 6% 7% 11% 40%	2200
November	1st to 10th	Day	7% 5% 2 5% 5% 5% 5% 4 7% 10% 45%	2057
	11th to 20th	Day	7% 5% 2 6% 4 5% 6% 5% 7% 9% 44%	2100
	21st to end	Day	5% 5% 2 5% 4 4 5% 4 7% 10% 49%	2100
December	1st to 10th	Day	6% 4 1 4 3 3 4 3 6% 9% 57%	3229
	11th to 20th	Day	6% 6% 3 6% 5% 4 5% 5% 7% 11% 43%	3463
	21st to end	Day	9% 8% 3 9% 6% 6% 6% 5% 7% 9% 33%	4565
January	1st to 10th	Night	4 3 1 4 4 4 5% 4 7% 10% 53%	7635
	11th to 20th	Night	11% 8% 3 8% 5% 6% 6% 5% 7% 9% 33%	7680
	21st to end	Night	10% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	7745
February	1st to 10th	Night	5% 5% 2 6% 5% 4 4 4 6% 9% 50%	2520
	11th to 20th	Night	5% 4 1 4 3 4 4 4 6% 8% 56%	2407
	21st to end	Night	4 3 1 3 3 4 3 3 5% 9% 62%	1903
March	1st to 10th	Night	3 3 1 5% 4 5% 5% 4 7% 8% 55%	5028
	11th to 20th	Night	3 3 1 4 3 3 3 3 5% 8% 64%	5090
	21st to end	Night	4 2 1 5% 4 4 5% 5% 6% 9% 54%	5588
April	1st to 10th	Night	3 3 1 3 3 3 5% 4 7% 9% 58%	2310
	11th to 20th	Night	4 3 1 5% 3 4 5% 4 6% 10% 55%	2240
	21st to end	Night	4 3 2 4 3 4 3 4 6% 9% 58%	2032
May	1st to 10th	Night	2 2 1 2 2 2 3 3 5% 10% 70%	4490
	11th to 20th	Night	5% 4 2 6% 5% 5% 4 4 6% 7% 53%	4293
	21st to end	Night	3 3 1 3 2 2 2 3 5% 9% 67%	4421
June	1st to 10th	Night	11% 10% 3 9% 7% 6% 6% 5% 8% 9% 27%	1800
	11th to 20th	Night	6% 5% 2 6% 6% 6% 6% 6% 10% 13% 35%	1800
	21st to end	Night	3 4 1 5% 7% 7% 6% 6% 10% 14% 36%	1800
July	1st to 10th	Night	2 2 1 5% 5% 6% 7% 6% 11% 18% 37%	4058
	11th to 20th	Night	2 2 2 5% 5% 4 6% 5% 9% 14% 46%	4057
	21st to end	Night	1 2 1 4 3 4 4 5% 8% 14% 53%	4427
August	1st to 10th	Night	2 4 2 6% 5% 5% 7% 6% 10% 18% 35%	2977
	11th to 20th	Night	1 2 1 5% 4 6% 6% 7% 10% 18% 39%	3460
	21st to end	Night	3 3 2 5% 5% 6% 7% 6% 11% 19% 32%	3949
September	1st to 10th	Night	4 3 2 6% 4 6% 8% 8% 10% 16% 33%	2200
	11th to 20th	Night	3 5% 2 7% 7% 7% 10% 6% 11% 13% 29%	2200
	21st to end	Night	7% 7% 3 8% 6% 7% 6% 7% 10% 12% 27%	2200
October	1st to 10th	Night	5% 5% 3 9% 6% 7% 7% 6% 9% 13% 30%	2200
	11th to 20th	Night	8% 5% 2 8% 5% 6% 6% 5% 9% 12% 33%	2390
	21st to end	Night	9% 6% 3 7% 6% 6% 6% 5% 7% 10% 36%	2640
November	1st to 10th	Night	7% 5% 2 6% 5% 3 4 5% 8% 11% 44%	2461
	11th to 20th	Night	7% 6% 2 6% 4 5% 5% 5% 7% 10% 45%	2520
	21st to end	Night	6% 4 2 4 4 4 4 4 7% 10% 50%	2520
December	1st to 10th	Night	4 3 1 4 4 3 4 4 6% 8% 59%	4166
	11th to 20th	Night	6% 6% 2 6% 4 4 5% 5% 7% 10% 47%	4952
	21st to end	Night	9% 8% 3 9% 7% 6% 6% 4 7% 8% 33%	6633

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	20% 25% 11% 30% 13% 1	5259
	11th to 20th	Day	34% 27% 15% 17% 4 2	5280
	21st to end	Day	30% 26% 7% 22% 13% 1	6418
February	1st to 10th	Day	8% 59% 7% 15% 9% 2	2100
	11th to 20th	Day	7% 58% 4 14% 14% 3	2105
	21st to end	Day	7% 59% 6% 13% 11% 4	1903
March	1st to 10th	Day	10% 32% 15% 23% 17% 2	5045
	11th to 20th	Day	9% 30% 16% 21% 15% 9%	5090
	21st to end	Day	17% 30% 9% 25% 16% 3	5586
April	1st to 10th	Day	8% 59% 6% 16% 9% 2	2310
	11th to 20th	Day	7% 61% 7% 11% 11% 4	2242
	21st to end	Day	7% 62% 6% 13% 10% 1	2365
May	1st to 10th	Day	7% 30% 15% 33% 14% 1	5437
	11th to 20th	Day	11% 29% 9% 43% 7%	5631
	21st to end	Day	6% 29% 14% 45% 6%	6447
June	1st to 10th	Day	18% 63% 11% 7%	2600
	11th to 20th	Day	18% 65% 11% 6%	2600
	21st to end	Day	9% 64% 21% 7%	2600
July	1st to 10th	Day	22% 34% 34% 10%	5835
	11th to 20th	Day	22% 34% 35% 8% 1	5831
	21st to end	Day	15% 31% 34% 18% 1	6240
August	1st to 10th	Day	23% 44% 25% 8% 1	4137
	11th to 20th	Day	21% 43% 25% 10% 1	3572
	21st to end	Day	21% 46% 28% 5%	3949
September	1st to 10th	Day	17% 63% 14% 6%	2200
	11th to 20th	Day	15% 62% 16% 7% 1	2200
	21st to end	Day	19% 61% 11% 6% 3	2200
October	1st to 10th	Day	26% 43% 17% 12% 2	3590
	11th to 20th	Day	31% 44% 11% 8% 5% 1	3248
	21st to end	Day	21% 39% 8% 21% 9% 2	3538
November	1st to 10th	Day	13% 55% 9% 15% 6% 1	2057
	11th to 20th	Day	15% 56% 6% 12% 8% 3	2100
	21st to end	Day	12% 55% 7% 12% 13% 2	2100
December	1st to 10th	Day	14% 35% 7% 26% 15% 3	3229
	11th to 20th	Day	21% 34% 12% 18% 12% 3	3460
	21st to end	Day	37% 32% 11% 12% 8%	4565
January	1st to 10th	Night	19% 24% 10% 30% 16% 2	7636
	11th to 20th	Night	36% 27% 15% 16% 5% 1	7680
	21st to end	Night	30% 26% 8% 23% 12% 1	7745
February	1st to 10th	Night	10% 60% 5% 15% 7% 3	2520
	11th to 20th	Night	8% 58% 4 11% 15% 4	2408
	21st to end	Night	8% 59% 6% 11% 12% 5%	1903
March	1st to 10th	Night	17% 32% 8% 21% 18% 3	5028
	11th to 20th	Night	11% 30% 13% 23% 13% 10%	5090
	21st to end	Night	17% 31% 10% 22% 16% 3	5588
April	1st to 10th	Night	8% 59% 6% 17% 8% 1	2310
	11th to 20th	Night	8% 62% 6% 10% 11% 4	2240
	21st to end	Night	8% 62% 5% 14% 10% 1	2032
May	1st to 10th	Night	6% 30% 11% 41% 10% 1	4520
	11th to 20th	Night	19% 31% 8% 29% 13% 1	4294
	21st to end	Night	4 28% 16% 41% 10%	4429
June	1st to 10th	Night	18% 64% 8% 10% 1	1800
	11th to 20th	Night	15% 66% 13% 7%	1800
	21st to end	Night	8% 63% 18% 11%	1800
July	1st to 10th	Night	19% 35% 36% 9%	4015
	11th to 20th	Night	17% 34% 41% 7%	4006
	21st to end	Night	13% 30% 32% 21% 4	4297
August	1st to 10th	Night	20% 42% 26% 10% 1	2966
	11th to 20th	Night	14% 42% 32% 10% 1	3492
	21st to end	Night	17% 48% 29% 5%	3949
September	1st to 10th	Night	13% 63% 17% 6%	2200
	11th to 20th	Night	13% 61% 16% 8% 1	2200
	21st to end	Night	16% 63% 12% 7% 2	2200
October	1st to 10th	Night	26% 42% 16% 14% 2	3590
	11th to 20th	Night	34% 44% 11% 7% 4 1	3889
	21st to end	Night	23% 39% 9% 20% 8% 1	4252
November	1st to 10th	Night	13% 55% 10% 15% 6%	2461
	11th to 20th	Night	17% 55% 6% 12% 8% 2	2520
	21st to end	Night	12% 56% 5% 13% 11% 3	2520
December	1st to 10th	Night	13% 36% 7% 30% 11% 4	4166
	11th to 20th	Night	20% 34% 11% 20% 12% 3	4954
	21st to end	Night	37% 32% 11% 12% 8%	6633

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	7% 3 17% 38% 31% 4	330
	11th to 20th	Day	12% 5% 19% 41% 20% 2	330
	21st to end	Day	11% 5% 21% 41% 21% 2	363
February	1st to 10th	Day	6% 3 13% 42% 30% 6%	330
	11th to 20th	Day	3 2 11% 37% 39% 7%	377
	21st to end	Day	5% 2 15% 31% 42% 5%	446
March	1st to 10th	Day	3 2 15% 43% 34% 4	540
	11th to 20th	Day	8% 2 14% 37% 35% 4	540
	21st to end	Day	5% 2 12% 41% 36% 4	594
April	1st to 10th	Day	3 1 10% 46% 36% 5%	540
	11th to 20th	Day	3 2 13% 49% 30% 3	516
	21st to end	Day	4 5% 49% 39% 2	500
May	1st to 10th	Day	3 4 38% 48% 8%	503
	11th to 20th	Day	9% 1 3 33% 43% 11%	527
	21st to end	Day	8% 2 3 17% 48% 22%	573
June	1st to 10th	Day	12% 1 4 18% 40% 25%	530
	11th to 20th	Day	8% 2 2 13% 38% 38%	530
	21st to end	Day	4 2 1 5% 33% 56%	530
July	1st to 10th	Day	4 1 5% 37% 52%	525
	11th to 20th	Day	3 2 1 4 36% 54%	524
	21st to end	Day	4 1 1 6% 37% 51%	576
August	1st to 10th	Day	5% 2 4 38% 51%	526
	11th to 20th	Day	3 1 5% 38% 53%	519
	21st to end	Day	5% 2 2 9% 39% 43%	583
September	1st to 10th	Day	5% 1 1 4 37% 51%	530
	11th to 20th	Day	5% 1 1 5% 32% 55%	530
	21st to end	Day	8% 3 3 10% 33% 42%	530
October	1st to 10th	Day	6% 3 4 21% 48% 18%	530
	11th to 20th	Day	10% 2 5% 21% 42% 21%	530
	21st to end	Day	9% 2 9% 30% 36% 13%	583
November	1st to 10th	Day	6% 4 11% 30% 39% 9%	535
	11th to 20th	Day	9% 2 12% 31% 39% 6%	540
	21st to end	Day	5% 3 14% 32% 36% 10%	540
December	1st to 10th	Day	7% 4 11% 32% 36% 9%	461
	11th to 20th	Day	7% 2 13% 31% 39% 7%	330
	21st to end	Day	8% 4 15% 31% 34% 9%	363
January	1st to 10th	Night	6% 3 14% 35% 35% 7%	840
	11th to 20th	Night	11% 4 18% 37% 28% 2	840
	21st to end	Night	8% 6% 19% 38% 29% 1	924
February	1st to 10th	Night	7% 4 14% 38% 34% 3	840
	11th to 20th	Night	6% 2 15% 37% 36% 4	823
	21st to end	Night	4 3 11% 36% 41% 5%	692
March	1st to 10th	Night	3 3 15% 44% 32% 4	840
	11th to 20th	Night	5% 2 13% 39% 36% 4	840
	21st to end	Night	3 2 14% 43% 35% 3	924
April	1st to 10th	Night	4 2 8% 44% 39% 3	840
	11th to 20th	Night	4 2 12% 45% 34% 3	816
	21st to end	Night	6% 1 6% 45% 39% 3	800
May	1st to 10th	Night	4 1 5% 35% 47% 10%	800
	11th to 20th	Night	9% 2 3 33% 45% 7%	709
	21st to end	Night	7% 2 5% 21% 48% 17%	650
June	1st to 10th	Night	13% 3 4 20% 42% 19%	600
	11th to 20th	Night	8% 1 2 9% 45% 35%	600
	21st to end	Night	3 1 1 7% 39% 49%	600
July	1st to 10th	Night	2 2 2 5% 33% 56%	585
	11th to 20th	Night	2 1 1 5% 38% 53%	582
	21st to end	Night	4 1 5% 35% 54%	657
August	1st to 10th	Night	4 1 1 6% 42% 47%	597
	11th to 20th	Night	4 1 5% 34% 55%	752
	21st to end	Night	7% 2 2 9% 35% 46%	880
September	1st to 10th	Night	5% 2 1 6% 36% 50%	800
	11th to 20th	Night	5% 1 1 7% 30% 55%	800
	21st to end	Night	10% 2 2 10% 34% 42%	800
October	1st to 10th	Night	8% 3 4 20% 44% 21%	800
	11th to 20th	Night	12% 3 4 20% 42% 20%	800
	21st to end	Night	12% 3 9% 30% 36% 11%	880
November	1st to 10th	Night	10% 3 13% 30% 37% 7%	820
	11th to 20th	Night	8% 2 10% 29% 41% 10%	840
	21st to end	Night	6% 2 11% 35% 38% 7%	840
December	1st to 10th	Night	6% 4 10% 32% 42% 7%	840
	11th to 20th	Night	7% 3 11% 34% 39% 7%	840
	21st to end	Night	7% 4 14% 32% 35% 8%	924

Page generated at 2026-04-14 02:44:23. Version ac07

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