Faro
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Faro clear sky chart from 2005-11-06 to 2024-12-09.

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	7% 12% 5% 11% 8% 7% 7% 5% 7% 8% 23%	106761
	Night	4 12% 6% 13% 8% 8% 7% 5% 8% 9% 20%	101513
Transparency	Day	52% 11% 18% 14% 4	106451
	Night	52% 11% 16% 15% 5% 1	101471
Seeing	Day	15% 8% 21% 28% 21% 7%	17328
	Night	11% 6% 18% 33% 25% 7%	23553

By Month

Percentage Cloud Cover NW (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	1 11% 5% 13% 11% 12% 11% 6% 12% 8% 10%	1259
	11th to 20th	Day	2 9% 5% 16% 10% 13% 9% 6% 6% 6% 19%	1470
	21st to end	Day	3 15% 6% 15% 9% 8% 9% 7% 7% 7% 15%	2090
February	1st to 10th	Day	1 8% 6% 12% 7% 6% 9% 10% 6% 11% 22%	1233
	11th to 20th	Day	2 12% 6% 12% 11% 7% 9% 7% 6% 11% 17%	1480
	21st to end	Day	1 8% 5% 11% 14% 11% 11% 5% 7% 10% 17%	1306
March	1st to 10th	Day	8% 6% 12% 10% 10% 8% 6% 8% 8% 24%	3113
	11th to 20th	Day	13% 8% 18% 10% 8% 8% 5% 7% 7% 16%	3232
	21st to end	Day	1 6% 5% 14% 10% 6% 6% 6% 8% 9% 29%	4165
April	1st to 10th	Day	2 14% 7% 13% 8% 7% 7% 5% 6% 8% 23%	2348
	11th to 20th	Day	2 16% 5% 12% 8% 7% 7% 5% 6% 7% 25%	2622
	21st to end	Day	2 12% 4 10% 7% 7% 7% 5% 8% 9% 28%	2750
May	1st to 10th	Day	6% 15% 4 10% 6% 6% 6% 5% 6% 7% 29%	4996
	11th to 20th	Day	4 12% 4 10% 7% 7% 7% 6% 7% 9% 27%	5138
	21st to end	Day	8% 14% 5% 11% 8% 7% 6% 5% 7% 8% 23%	6070
June	1st to 10th	Day	12% 11% 3 9% 7% 7% 6% 6% 7% 8% 23%	3420
	11th to 20th	Day	14% 11% 3 10% 8% 8% 6% 5% 7% 8% 20%	3420
	21st to end	Day	13% 11% 4 10% 8% 7% 7% 6% 8% 8% 18%	3420
July	1st to 10th	Day	9% 10% 4 11% 8% 7% 7% 6% 8% 9% 20%	5700
	11th to 20th	Day	14% 13% 5% 12% 8% 7% 7% 5% 6% 7% 17%	5700
	21st to end	Day	12% 9% 4 9% 7% 7% 6% 5% 7% 9% 25%	5580
August	1st to 10th	Day	9% 8% 2 8% 5% 5% 5% 4 6% 7% 40%	5037
	11th to 20th	Day	16% 10% 3 8% 5% 5% 5% 3 6% 8% 31%	4507
	21st to end	Day	15% 14% 5% 11% 7% 6% 6% 4 7% 8% 18%	4873
September	1st to 10th	Day	16% 14% 4 11% 7% 6% 6% 4 6% 7% 20%	2386
	11th to 20th	Day	9% 11% 4 11% 6% 7% 6% 4 6% 9% 28%	2256
	21st to end	Day	11% 17% 5% 11% 7% 6% 6% 5% 6% 8% 19%	2053
October	1st to 10th	Day	6% 14% 4 10% 5% 5% 7% 5% 7% 9% 28%	3077
	11th to 20th	Day	5% 11% 4 10% 6% 8% 7% 5% 6% 8% 28%	2843
	21st to end	Day	4 17% 8% 14% 8% 7% 7% 5% 7% 8% 17%	2584
November	1st to 10th	Day	3 15% 6% 14% 9% 7% 8% 7% 9% 9% 13%	1366
	11th to 20th	Day	3 13% 7% 14% 11% 9% 8% 6% 8% 9% 11%	1099
	21st to end	Day	1 12% 5% 13% 9% 9% 8% 8% 10% 12% 12%	1000
December	1st to 10th	Day	3 12% 5% 16% 9% 10% 10% 6% 10% 8% 12%	820
	11th to 20th	Day	2 15% 6% 13% 8% 7% 7% 6% 9% 7% 20%	962
	21st to end	Day	3 14% 6% 16% 8% 8% 7% 7% 5% 7% 18%	1386
January	1st to 10th	Night	2 11% 6% 15% 10% 12% 11% 6% 9% 7% 11%	5686
	11th to 20th	Night	3 11% 5% 15% 11% 9% 6% 5% 6% 12% 17%	5459
	21st to end	Night	4 17% 8% 18% 9% 7% 6% 4 6% 9% 13%	5566
February	1st to 10th	Night	2 11% 6% 14% 8% 7% 7% 6% 8% 10% 22%	2944
	11th to 20th	Night	2 11% 7% 13% 9% 7% 7% 5% 9% 9% 19%	2587
	21st to end	Night	8% 6% 13% 9% 9% 7% 6% 10% 11% 22%	2146
March	1st to 10th	Night	6% 4 10% 9% 11% 9% 7% 9% 9% 26%	3751
	11th to 20th	Night	1 15% 8% 16% 8% 8% 7% 5% 7% 7% 18%	3720
	21st to end	Night	2 8% 5% 14% 10% 8% 9% 7% 8% 7% 23%	3477
April	1st to 10th	Night	2 12% 7% 14% 8% 7% 6% 4 5% 8% 27%	1832
	11th to 20th	Night	1 12% 6% 11% 7% 6% 8% 5% 6% 9% 29%	1504
	21st to end	Night	2 12% 4 10% 7% 6% 6% 5% 8% 8% 33%	1430
May	1st to 10th	Night	4 11% 4 10% 6% 5% 6% 5% 6% 8% 35%	1948
	11th to 20th	Night	5% 7% 4 13% 9% 7% 6% 5% 6% 8% 30%	1757
	21st to end	Night	6% 9% 5% 10% 7% 6% 7% 5% 6% 9% 31%	1503
June	1st to 10th	Night	9% 8% 1 7% 6% 6% 6% 6% 9% 11% 30%	760
	11th to 20th	Night	12% 8% 4 9% 6% 5% 4 5% 10% 10% 27%	760
	21st to end	Night	12% 10% 4 8% 6% 5% 7% 5% 9% 11% 23%	760
July	1st to 10th	Night	10% 11% 4 13% 7% 7% 6% 4 8% 8% 22%	1260
	11th to 20th	Night	11% 10% 4 9% 6% 7% 7% 6% 8% 9% 22%	1260
	21st to end	Night	11% 9% 4 8% 7% 6% 7% 6% 9% 10% 23%	1955
August	1st to 10th	Night	8% 8% 3 6% 5% 5% 4 4 4 8% 45%	1893
	11th to 20th	Night	15% 10% 3 8% 5% 5% 5% 4 6% 8% 32%	2327
	21st to end	Night	12% 13% 5% 11% 8% 8% 7% 5% 6% 7% 19%	2794
September	1st to 10th	Night	13% 11% 4 9% 7% 6% 6% 5% 7% 8% 24%	1791
	11th to 20th	Night	8% 10% 3 9% 7% 5% 5% 4 7% 7% 34%	1924
	21st to end	Night	12% 16% 4 12% 7% 7% 5% 4 5% 6% 22%	2124
October	1st to 10th	Night	6% 12% 5% 10% 5% 6% 8% 4 6% 8% 30%	3893
	11th to 20th	Night	5% 15% 6% 13% 8% 7% 6% 4 6% 8% 20%	4085
	21st to end	Night	4 17% 7% 13% 8% 9% 8% 5% 7% 8% 14%	4965
November	1st to 10th	Night	3 14% 7% 14% 10% 7% 8% 6% 8% 11% 13%	2931
	11th to 20th	Night	3 15% 8% 15% 12% 9% 8% 6% 7% 9% 9%	3280
	21st to end	Night	3 13% 7% 17% 10% 8% 7% 6% 10% 9% 11%	3400
December	1st to 10th	Night	2 14% 6% 15% 10% 8% 7% 6% 11% 9% 11%	3541
	11th to 20th	Night	2 13% 7% 15% 10% 8% 8% 8% 9% 8% 14%	4230
	21st to end	Night	2 14% 6% 14% 9% 8% 8% 6% 8% 11% 14%	6270

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	51% 10% 18% 12% 7% 2	1259
	11th to 20th	Day	57% 9% 11% 8% 12% 4	1484
	21st to end	Day	52% 15% 18% 9% 6%	2090
February	1st to 10th	Day	45% 10% 16% 19% 10% 1	1233
	11th to 20th	Day	53% 10% 16% 13% 6% 2	1488
	21st to end	Day	56% 10% 16% 11% 6% 1	1306
March	1st to 10th	Day	47% 11% 13% 16% 12% 2	3113
	11th to 20th	Day	51% 14% 19% 13% 3 1	3232
	21st to end	Day	40% 19% 25% 12% 4	4165
April	1st to 10th	Day	56% 14% 17% 9% 4	2348
	11th to 20th	Day	55% 14% 14% 12% 5% 1	2622
	21st to end	Day	47% 17% 20% 13% 3	2750
May	1st to 10th	Day	44% 11% 19% 23% 2	4996
	11th to 20th	Day	40% 16% 20% 17% 5%	5142
	21st to end	Day	52% 12% 17% 14% 5%	6071
June	1st to 10th	Day	54% 12% 15% 14% 5%	3420
	11th to 20th	Day	59% 12% 13% 14% 2	3420
	21st to end	Day	58% 16% 14% 11% 1	3420
July	1st to 10th	Day	53% 10% 25% 10% 2	5611
	11th to 20th	Day	63% 9% 14% 13% 1	5601
	21st to end	Day	52% 10% 24% 13% 1	5403
August	1st to 10th	Day	41% 9% 21% 17% 12%	5018
	11th to 20th	Day	50% 8% 23% 17% 1	4553
	21st to end	Day	61% 8% 17% 13%	4872
September	1st to 10th	Day	61% 13% 15% 11% 1	2386
	11th to 20th	Day	49% 14% 20% 15% 2	2256
	21st to end	Day	60% 12% 13% 13% 2	2053
October	1st to 10th	Day	48% 8% 18% 25% 2	3077
	11th to 20th	Day	52% 7% 13% 26% 2	2843
	21st to end	Day	62% 8% 17% 12%	2584
November	1st to 10th	Day	61% 11% 15% 10% 3	1366
	11th to 20th	Day	62% 10% 13% 12% 3	1099
	21st to end	Day	55% 13% 16% 12% 3	1000
December	1st to 10th	Day	57% 12% 17% 9% 4 1	820
	11th to 20th	Day	49% 9% 16% 12% 13%	964
	21st to end	Day	55% 9% 15% 8% 10% 2	1386
January	1st to 10th	Night	53% 12% 19% 10% 5% 1	5686
	11th to 20th	Night	51% 10% 12% 9% 10% 8%	5507
	21st to end	Night	59% 10% 13% 10% 6% 1	5566
February	1st to 10th	Night	50% 7% 12% 18% 11% 1	2944
	11th to 20th	Night	51% 10% 15% 16% 5% 2	2590
	21st to end	Night	47% 10% 19% 16% 7% 1	2146
March	1st to 10th	Night	41% 10% 17% 23% 9% 1	3751
	11th to 20th	Night	51% 14% 18% 12% 4 1	3722
	21st to end	Night	39% 22% 22% 12% 4	3477
April	1st to 10th	Night	52% 10% 19% 15% 3	1832
	11th to 20th	Night	47% 14% 15% 16% 6% 1	1504
	21st to end	Night	43% 14% 19% 20% 4	1430
May	1st to 10th	Night	37% 12% 21% 27% 3	1948
	11th to 20th	Night	44% 13% 16% 20% 7%	1757
	21st to end	Night	45% 12% 16% 22% 5%	1503
June	1st to 10th	Night	42% 14% 18% 21% 5%	760
	11th to 20th	Night	49% 11% 21% 16% 3 1	760
	21st to end	Night	51% 14% 20% 12% 2	760
July	1st to 10th	Night	54% 9% 22% 11% 3	1240
	11th to 20th	Night	53% 9% 22% 16% 1	1236
	21st to end	Night	50% 10% 25% 16%	1893
August	1st to 10th	Night	36% 7% 27% 17% 13%	1887
	11th to 20th	Night	47% 7% 23% 21% 3	2347
	21st to end	Night	60% 8% 16% 14% 1	2794
September	1st to 10th	Night	52% 14% 17% 15% 2	1791
	11th to 20th	Night	44% 12% 23% 19% 3	1924
	21st to end	Night	60% 10% 13% 15% 2	2124
October	1st to 10th	Night	46% 8% 15% 27% 4	3893
	11th to 20th	Night	59% 6% 11% 21% 2	4085
	21st to end	Night	63% 7% 15% 14% 1	4965
November	1st to 10th	Night	60% 11% 16% 11% 3	2931
	11th to 20th	Night	64% 10% 13% 11% 2	3280
	21st to end	Night	61% 10% 15% 11% 3	3400
December	1st to 10th	Night	58% 14% 14% 10% 4	3541
	11th to 20th	Night	56% 11% 15% 10% 8%	4227
	21st to end	Night	53% 10% 15% 12% 7% 3	6270

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	6% 3 8% 38% 32% 13%	90
	11th to 20th	Day	5% 3 23% 32% 24% 13%	108
	21st to end	Day	7% 10% 21% 29% 23% 11%	198
February	1st to 10th	Day	7% 7% 16% 34% 28% 8%	268
	11th to 20th	Day	5% 8% 21% 33% 22% 11%	365
	21st to end	Day	4 7% 25% 30% 23% 10%	307
March	1st to 10th	Day	2 6% 23% 29% 26% 13%	370
	11th to 20th	Day	6% 9% 27% 32% 22% 4	379
	21st to end	Day	6% 8% 26% 32% 22% 7%	506
April	1st to 10th	Day	9% 9% 27% 30% 20% 6%	460
	11th to 20th	Day	6% 8% 26% 30% 23% 6%	636
	21st to end	Day	10% 10% 26% 29% 20% 6%	650
May	1st to 10th	Day	13% 12% 25% 26% 18% 7%	653
	11th to 20th	Day	10% 8% 20% 30% 24% 7%	748
	21st to end	Day	10% 10% 20% 28% 24% 9%	940
June	1st to 10th	Day	15% 8% 20% 30% 20% 7%	870
	11th to 20th	Day	18% 6% 17% 29% 26% 5%	870
	21st to end	Day	19% 6% 17% 28% 23% 7%	870
July	1st to 10th	Day	20% 5% 20% 26% 23% 6%	856
	11th to 20th	Day	21% 9% 16% 24% 23% 8%	852
	21st to end	Day	19% 7% 14% 28% 23% 9%	771
August	1st to 10th	Day	17% 8% 19% 27% 21% 8%	676
	11th to 20th	Day	26% 9% 24% 25% 12% 5%	665
	21st to end	Day	26% 8% 20% 27% 16% 3	748
September	1st to 10th	Day	24% 12% 22% 22% 14% 6%	500
	11th to 20th	Day	12% 14% 23% 27% 17% 6%	490
	21st to end	Day	24% 14% 23% 22% 13% 4	470
October	1st to 10th	Day	23% 14% 29% 19% 10% 5%	390
	11th to 20th	Day	20% 12% 21% 25% 17% 5%	390
	21st to end	Day	13% 5% 19% 31% 23% 8%	332
November	1st to 10th	Day	13% 5% 21% 35% 18% 9%	200
	11th to 20th	Day	9% 5% 12% 34% 20% 22%	200
	21st to end	Day	6% 10% 22% 31% 23% 10%	200
December	1st to 10th	Day	10% 8% 20% 31% 23% 9%	111
	11th to 20th	Day	9% 3 20% 36% 20% 12%	90
	21st to end	Day	2 11% 20% 24% 30% 12%	99
January	1st to 10th	Night	7% 5% 19% 34% 28% 7%	1040
	11th to 20th	Night	10% 7% 22% 33% 21% 6%	963
	21st to end	Night	8% 8% 23% 35% 21% 5%	935
February	1st to 10th	Night	6% 5% 20% 39% 24% 7%	850
	11th to 20th	Night	7% 6% 21% 39% 22% 6%	834
	21st to end	Night	4 4 18% 42% 26% 6%	703
March	1st to 10th	Night	2 5% 20% 36% 30% 7%	765
	11th to 20th	Night	4 4 23% 33% 30% 6%	738
	21st to end	Night	3 5% 17% 35% 31% 9%	627
April	1st to 10th	Night	6% 7% 17% 32% 29% 9%	570
	11th to 20th	Night	5% 5% 16% 36% 29% 8%	563
	21st to end	Night	8% 6% 20% 32% 30% 4	480
May	1st to 10th	Night	9% 8% 16% 33% 26% 8%	380
	11th to 20th	Night	11% 5% 20% 32% 29% 4	374
	21st to end	Night	7% 5% 13% 32% 39% 5%	287
June	1st to 10th	Night	14% 2 9% 34% 36% 5%	190
	11th to 20th	Night	15% 4 12% 35% 31% 3	190
	21st to end	Night	15% 5% 16% 29% 29% 6%	190
July	1st to 10th	Night	18% 3 9% 31% 36% 4	185
	11th to 20th	Night	18% 4 11% 21% 39% 7%	184
	21st to end	Night	13% 5% 13% 22% 37% 9%	379
August	1st to 10th	Night	16% 3 18% 26% 31% 5%	378
	11th to 20th	Night	24% 6% 15% 27% 24% 4	499
	21st to end	Night	21% 5% 13% 28% 27% 6%	627
September	1st to 10th	Night	20% 9% 15% 27% 25% 4	570
	11th to 20th	Night	14% 8% 15% 27% 30% 5%	594
	21st to end	Night	22% 11% 19% 25% 18% 4	760
October	1st to 10th	Night	22% 9% 20% 30% 17% 3	760
	11th to 20th	Night	19% 9% 22% 25% 21% 4	760
	21st to end	Night	14% 6% 16% 36% 22% 5%	943
November	1st to 10th	Night	13% 5% 17% 34% 25% 6%	880
	11th to 20th	Night	9% 5% 18% 28% 25% 15%	980
	21st to end	Night	9% 8% 20% 33% 19% 10%	1100
December	1st to 10th	Night	8% 8% 20% 36% 22% 5%	1091
	11th to 20th	Night	8% 8% 20% 35% 25% 5%	1040
	21st to end	Night	7% 6% 20% 35% 24% 8%	1144

Page generated at 2024-12-06 00:54:53. Version ac07

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