Sarles
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sarles clear sky chart from 2005-11-06 to 2024-02-20.

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	11% 8% 4 7% 6% 4 5% 5% 6% 7% 35%	77926
	Night	9% 9% 4 9% 7% 4 5% 5% 6% 7% 35%	81306
Transparency	Day	32% 37% 11% 15% 6%	77616
	Night	33% 36% 10% 15% 6% 1	81138
Seeing	Day	14% 9% 31% 29% 14% 3	15118
	Night	14% 8% 33% 32% 12% 1	25274

By Month

Percentage Cloud Cover SW (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	4 17% 6% 12% 8% 7% 7% 6% 7% 6% 21%	2218
	11th to 20th	Day	4 7% 5% 12% 14% 7% 13% 13% 8% 7% 11%	2458
	21st to end	Day	7% 11% 5% 13% 11% 5% 6% 5% 6% 6% 25%	2794
February	1st to 10th	Day	9% 13% 6% 10% 8% 4 8% 7% 7% 7% 21%	1562
	11th to 20th	Day	5% 10% 5% 10% 11% 5% 9% 9% 9% 6% 22%	1682
	21st to end	Day	8% 9% 5% 10% 9% 6% 7% 9% 5% 6% 25%	1480
March	1st to 10th	Day	9% 13% 8% 14% 10% 4 5% 6% 5% 6% 21%	1800
	11th to 20th	Day	7% 10% 5% 8% 9% 4 6% 5% 6% 8% 32%	1957
	21st to end	Day	14% 11% 6% 10% 7% 4 5% 4 6% 7% 27%	2200
April	1st to 10th	Day	10% 11% 5% 8% 6% 3 4 4 6% 8% 34%	2178
	11th to 20th	Day	15% 11% 4 8% 7% 4 5% 4 6% 6% 31%	2309
	21st to end	Day	16% 10% 3 8% 6% 4 4 4 6% 6% 34%	2340
May	1st to 10th	Day	15% 9% 3 6% 5% 3 5% 5% 5% 6% 38%	2348
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 4 5% 7% 39%	2592
	21st to end	Day	19% 7% 3 5% 4 3 5% 5% 6% 8% 37%	2918
June	1st to 10th	Day	14% 6% 3 5% 5% 3 4 6% 6% 8% 41%	2700
	11th to 20th	Day	16% 6% 3 5% 6% 3 6% 5% 6% 8% 37%	2700
	21st to end	Day	12% 5% 2 6% 5% 4 6% 5% 6% 9% 39%	2700
July	1st to 10th	Day	8% 3 2 4 5% 3 5% 5% 6% 9% 49%	2700
	11th to 20th	Day	9% 5% 2 5% 4 3 5% 5% 6% 9% 46%	2700
	21st to end	Day	7% 3 1 3 3 2 4 4 6% 10% 55%	2751
August	1st to 10th	Day	9% 6% 2 5% 5% 3 5% 4 6% 9% 47%	2482
	11th to 20th	Day	11% 4 2 4 4 3 5% 5% 6% 9% 47%	2301
	21st to end	Day	11% 5% 2 4 5% 2 4 4 5% 7% 51%	2574
September	1st to 10th	Day	12% 5% 2 4 4 3 4 4 4 7% 51%	2184
	11th to 20th	Day	15% 5% 2 4 4 3 5% 4 5% 7% 46%	1980
	21st to end	Day	13% 6% 2 5% 4 3 5% 4 6% 9% 42%	1980
October	1st to 10th	Day	17% 11% 3 6% 4 3 4 4 4 5% 38%	1908
	11th to 20th	Day	12% 10% 4 6% 5% 2 4 5% 6% 7% 38%	1689
	21st to end	Day	14% 13% 4 8% 5% 3 5% 4 5% 8% 30%	1782
November	1st to 10th	Day	15% 13% 5% 9% 6% 3 4 4 4 5% 31%	1639
	11th to 20th	Day	7% 13% 8% 13% 10% 3 6% 4 4 4 26%	1520
	21st to end	Day	10% 13% 6% 10% 9% 3 5% 5% 4 6% 29%	1345
December	1st to 10th	Day	7% 12% 6% 11% 10% 5% 7% 7% 7% 8% 19%	1330
	11th to 20th	Day	10% 12% 7% 13% 10% 4 6% 5% 6% 7% 19%	1683
	21st to end	Day	8% 9% 3 11% 8% 4 5% 6% 7% 6% 34%	2442
January	1st to 10th	Night	6% 14% 7% 13% 8% 4 6% 7% 6% 7% 22%	4737
	11th to 20th	Night	5% 8% 5% 13% 12% 6% 10% 9% 7% 7% 17%	4498
	21st to end	Night	7% 12% 7% 15% 10% 4 5% 5% 5% 5% 26%	4873
February	1st to 10th	Night	9% 10% 5% 10% 8% 5% 7% 6% 7% 6% 25%	2618
	11th to 20th	Night	6% 9% 3 11% 9% 5% 7% 6% 6% 7% 31%	2387
	21st to end	Night	7% 9% 5% 7% 7% 4 8% 6% 7% 8% 32%	1776
March	1st to 10th	Night	10% 13% 7% 11% 8% 4 6% 5% 6% 7% 24%	2160
	11th to 20th	Night	7% 11% 4 7% 6% 4 4 5% 5% 7% 39%	2003
	21st to end	Night	11% 10% 4 9% 7% 4 4 5% 6% 6% 34%	2154
April	1st to 10th	Night	8% 8% 3 6% 7% 4 5% 5% 7% 7% 41%	1782
	11th to 20th	Night	13% 12% 3 6% 6% 3 4 5% 5% 7% 36%	1599
	21st to end	Night	15% 8% 3 5% 5% 4 4 5% 7% 7% 37%	1620
May	1st to 10th	Night	13% 7% 3 6% 6% 3 3 5% 5% 8% 42%	1611
	11th to 20th	Night	14% 6% 2 4 4 3 4 6% 6% 8% 42%	1300
	21st to end	Night	16% 8% 3 5% 4 2 2 4 5% 8% 42%	1358
June	1st to 10th	Night	11% 4 2 4 4 2 4 5% 5% 9% 49%	1260
	11th to 20th	Night	11% 5% 3 5% 6% 4 6% 5% 6% 8% 41%	1260
	21st to end	Night	9% 3 2 4 4 2 5% 4 8% 11% 48%	1260
July	1st to 10th	Night	7% 3 1 4 3 2 4 4 6% 7% 59%	1260
	11th to 20th	Night	5% 2 1 4 4 2 4 4 6% 8% 57%	1260
	21st to end	Night	5% 2 1 3 4 2 4 4 7% 8% 60%	1565
August	1st to 10th	Night	6% 4 2 4 3 3 4 4 5% 8% 57%	1456
	11th to 20th	Night	6% 4 1 4 4 2 4 5% 6% 8% 56%	1600
	21st to end	Night	9% 3 2 3 4 2 3 4 4 7% 59%	1782
September	1st to 10th	Night	8% 5% 2 4 4 3 4 4 5% 7% 55%	1773
	11th to 20th	Night	11% 5% 2 4 4 3 3 4 5% 7% 51%	1980
	21st to end	Night	14% 6% 2 6% 5% 3 3 4 5% 7% 44%	1980
October	1st to 10th	Night	14% 8% 4 5% 6% 3 4 4 4 6% 41%	2034
	11th to 20th	Night	14% 9% 2 6% 5% 3 5% 5% 5% 7% 38%	2268
	21st to end	Night	11% 11% 4 8% 6% 3 4 5% 6% 6% 35%	2574
November	1st to 10th	Night	11% 10% 5% 9% 6% 3 5% 5% 5% 8% 34%	2438
	11th to 20th	Night	9% 13% 5% 12% 8% 4 4 4 6% 7% 29%	2660
	21st to end	Night	10% 11% 5% 10% 8% 4 5% 4 5% 6% 31%	2831
December	1st to 10th	Night	8% 10% 6% 10% 10% 6% 7% 6% 6% 6% 25%	2850
	11th to 20th	Night	10% 13% 6% 13% 8% 4 6% 4 5% 7% 22%	3514
	21st to end	Night	10% 10% 5% 10% 8% 4 5% 4 5% 6% 33%	5225

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	49% 27% 12% 10% 2	2219
	11th to 20th	Day	55% 28% 9% 5% 2	2458
	21st to end	Day	44% 24% 8% 19% 5%	2794
February	1st to 10th	Day	40% 36% 6% 13% 4 1	1562
	11th to 20th	Day	36% 38% 9% 11% 6% 1	1691
	21st to end	Day	41% 36% 9% 8% 4 1	1480
March	1st to 10th	Day	44% 38% 8% 7% 2	1800
	11th to 20th	Day	33% 39% 9% 13% 5%	1957
	21st to end	Day	35% 39% 9% 14% 2	2200
April	1st to 10th	Day	30% 37% 11% 15% 6% 1	2178
	11th to 20th	Day	35% 37% 7% 14% 7%	2312
	21st to end	Day	35% 38% 12% 11% 4	2340
May	1st to 10th	Day	31% 37% 8% 15% 7% 1	2348
	11th to 20th	Day	27% 38% 9% 18% 7% 1	2596
	21st to end	Day	32% 39% 10% 14% 5% 1	2918
June	1st to 10th	Day	29% 39% 12% 13% 6%	2700
	11th to 20th	Day	28% 39% 11% 15% 5% 1	2700
	21st to end	Day	25% 39% 15% 17% 4	2700
July	1st to 10th	Day	19% 39% 13% 22% 6% 1	2626
	11th to 20th	Day	21% 40% 14% 18% 6%	2619
	21st to end	Day	18% 40% 14% 19% 8% 1	2598
August	1st to 10th	Day	25% 39% 12% 16% 7% 1	2466
	11th to 20th	Day	21% 38% 13% 21% 7% 1	2301
	21st to end	Day	22% 38% 9% 20% 10%	2574
September	1st to 10th	Day	21% 38% 12% 18% 11%	2184
	11th to 20th	Day	24% 37% 12% 20% 7%	1980
	21st to end	Day	22% 38% 11% 23% 6%	1980
October	1st to 10th	Day	31% 36% 9% 17% 7%	1908
	11th to 20th	Day	31% 38% 10% 17% 4	1689
	21st to end	Day	34% 38% 11% 13% 3	1782
November	1st to 10th	Day	34% 41% 8% 9% 7% 1	1639
	11th to 20th	Day	38% 40% 9% 8% 4	1520
	21st to end	Day	34% 42% 8% 12% 3	1345
December	1st to 10th	Day	39% 41% 10% 8% 1	1330
	11th to 20th	Day	44% 35% 8% 8% 4	1680
	21st to end	Day	36% 25% 11% 16% 12%	2442
January	1st to 10th	Night	45% 29% 10% 13% 3	4737
	11th to 20th	Night	50% 28% 11% 8% 3	4498
	21st to end	Night	47% 24% 7% 17% 5%	4873
February	1st to 10th	Night	39% 35% 7% 12% 6% 1	2618
	11th to 20th	Night	33% 38% 8% 11% 10%	2388
	21st to end	Night	34% 38% 10% 12% 6%	1776
March	1st to 10th	Night	39% 39% 10% 9% 2	2160
	11th to 20th	Night	30% 38% 8% 18% 6%	2003
	21st to end	Night	32% 38% 12% 13% 5%	2154
April	1st to 10th	Night	27% 38% 7% 15% 11% 2	1782
	11th to 20th	Night	33% 37% 8% 13% 8% 1	1599
	21st to end	Night	30% 38% 12% 14% 5%	1620
May	1st to 10th	Night	26% 37% 11% 17% 7% 1	1611
	11th to 20th	Night	25% 38% 10% 16% 10% 1	1301
	21st to end	Night	28% 39% 10% 17% 6% 1	1358
June	1st to 10th	Night	24% 39% 12% 17% 7% 2	1260
	11th to 20th	Night	24% 39% 13% 16% 7% 1	1260
	21st to end	Night	18% 40% 15% 22% 5%	1260
July	1st to 10th	Night	14% 39% 12% 24% 10% 1	1225
	11th to 20th	Night	16% 40% 12% 22% 9%	1218
	21st to end	Night	14% 39% 11% 24% 11% 1	1478
August	1st to 10th	Night	18% 39% 11% 23% 8% 1	1448
	11th to 20th	Night	16% 39% 14% 21% 9% 1	1600
	21st to end	Night	17% 37% 10% 22% 13% 1	1782
September	1st to 10th	Night	17% 38% 9% 23% 12% 1	1773
	11th to 20th	Night	20% 37% 10% 21% 11% 1	1980
	21st to end	Night	25% 37% 9% 22% 7% 1	1980
October	1st to 10th	Night	29% 37% 9% 17% 8%	2034
	11th to 20th	Night	31% 38% 10% 16% 6%	2268
	21st to end	Night	33% 39% 9% 15% 4	2574
November	1st to 10th	Night	28% 42% 10% 12% 6% 2	2438
	11th to 20th	Night	36% 41% 9% 9% 4	2660
	21st to end	Night	31% 42% 12% 11% 4	2831
December	1st to 10th	Night	36% 42% 12% 7% 3	2850
	11th to 20th	Night	43% 34% 12% 7% 2 1	3516
	21st to end	Night	37% 26% 9% 16% 10% 1	5225

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	9% 11% 34% 32% 11% 4	270
	11th to 20th	Day	10% 13% 31% 34% 11% 1	270
	21st to end	Day	13% 9% 37% 27% 10% 3	297
February	1st to 10th	Day	12% 10% 39% 32% 5% 2	270
	11th to 20th	Day	10% 12% 38% 30% 9% 1	267
	21st to end	Day	6% 6% 38% 35% 12% 3	198
March	1st to 10th	Day	12% 14% 33% 32% 8% 2	240
	11th to 20th	Day	12% 10% 34% 28% 14% 3	240
	21st to end	Day	15% 10% 32% 26% 13% 4	286
April	1st to 10th	Day	14% 15% 35% 26% 9% 2	438
	11th to 20th	Day	19% 10% 32% 25% 12% 1	590
	21st to end	Day	17% 11% 33% 25% 12% 2	600
May	1st to 10th	Day	15% 10% 26% 30% 16% 2	603
	11th to 20th	Day	19% 8% 31% 25% 14% 3	625
	21st to end	Day	19% 9% 24% 30% 15% 3	679
June	1st to 10th	Day	14% 9% 29% 27% 15% 6%	630
	11th to 20th	Day	15% 10% 34% 26% 10% 5%	630
	21st to end	Day	13% 7% 28% 30% 18% 4	630
July	1st to 10th	Day	8% 5% 27% 34% 20% 6%	621
	11th to 20th	Day	11% 7% 30% 29% 18% 5%	618
	21st to end	Day	6% 4 26% 36% 21% 7%	684
August	1st to 10th	Day	9% 5% 22% 35% 21% 7%	626
	11th to 20th	Day	12% 6% 24% 30% 22% 7%	615
	21st to end	Day	11% 7% 25% 31% 22% 4	693
September	1st to 10th	Day	15% 8% 35% 26% 13% 3	474
	11th to 20th	Day	19% 8% 27% 34% 11% 1	270
	21st to end	Day	21% 10% 33% 25% 10% 1	270
October	1st to 10th	Day	24% 11% 27% 25% 12% 1	270
	11th to 20th	Day	20% 9% 35% 23% 10% 2	270
	21st to end	Day	26% 11% 36% 20% 5% 2	297
November	1st to 10th	Day	24% 13% 29% 23% 11%	270
	11th to 20th	Day	13% 12% 37% 30% 9%	270
	21st to end	Day	17% 12% 39% 26% 5% 1	270
December	1st to 10th	Day	11% 9% 35% 32% 10% 2	270
	11th to 20th	Day	16% 14% 40% 24% 5% 1	270
	21st to end	Day	13% 8% 39% 29% 7% 3	297
January	1st to 10th	Night	11% 10% 38% 29% 11% 1	950
	11th to 20th	Night	14% 10% 39% 29% 8% 1	950
	21st to end	Night	12% 11% 37% 30% 9% 1	1045
February	1st to 10th	Night	13% 10% 35% 32% 9% 1	950
	11th to 20th	Night	10% 9% 36% 32% 10% 3	917
	21st to end	Night	10% 7% 33% 34% 12% 2	592
March	1st to 10th	Night	15% 9% 33% 28% 13% 3	720
	11th to 20th	Night	12% 8% 35% 33% 11% 1	563
	21st to end	Night	15% 7% 30% 30% 15% 2	594
April	1st to 10th	Night	12% 7% 36% 33% 10% 1	540
	11th to 20th	Night	19% 7% 30% 35% 9% 1	533
	21st to end	Night	16% 7% 31% 31% 14% 1	540
May	1st to 10th	Night	16% 7% 30% 31% 14% 1	540
	11th to 20th	Night	18% 6% 27% 34% 14%	531
	21st to end	Night	20% 7% 28% 31% 13% 1	584
June	1st to 10th	Night	12% 7% 33% 32% 13% 1	540
	11th to 20th	Night	14% 5% 32% 33% 15% 1	540
	21st to end	Night	10% 6% 26% 40% 19%	540
July	1st to 10th	Night	8% 1 25% 42% 22% 1	525
	11th to 20th	Night	8% 6% 27% 43% 15% 1	522
	21st to end	Night	6% 3 22% 47% 19% 3	591
August	1st to 10th	Night	9% 2 22% 46% 19% 2	537
	11th to 20th	Night	6% 4 25% 43% 19% 2	534
	21st to end	Night	11% 4 28% 40% 16% 1	594
September	1st to 10th	Night	11% 4 31% 35% 18% 3	540
	11th to 20th	Night	13% 6% 31% 38% 12% 1	540
	21st to end	Night	18% 9% 30% 29% 13% 1	540
October	1st to 10th	Night	18% 9% 32% 32% 9%	594
	11th to 20th	Night	19% 10% 31% 31% 9%	828
	21st to end	Night	17% 10% 36% 27% 8% 1	990
November	1st to 10th	Night	16% 11% 37% 28% 7% 1	925
	11th to 20th	Night	14% 11% 39% 25% 9% 2	950
	21st to end	Night	16% 14% 37% 26% 5% 1	950
December	1st to 10th	Night	11% 11% 37% 29% 10% 1	950
	11th to 20th	Night	17% 12% 33% 29% 7% 2	950
	21st to end	Night	20% 6% 34% 31% 9% 1	1045

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