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 2024-01-16.

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	9% 11% 5% 10% 9% 5% 7% 7% 7% 8% 22%	74339
	Night	5% 12% 6% 11% 9% 5% 7% 7% 8% 9% 20%	75462
Transparency	Day	55% 13% 16% 12% 4	73969
	Night	54% 11% 16% 13% 5% 1	75352
Seeing	Day	15% 8% 21% 28% 21% 7%	16018
	Night	11% 6% 18% 33% 26% 7%	22479

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	2 9% 6% 10% 13% 7% 10% 8% 9% 10% 17%	759
	11th to 20th	Day	3 10% 8% 15% 10% 7% 9% 10% 8% 7% 14%	866
	21st to end	Day	2 12% 7% 13% 9% 6% 9% 9% 7% 8% 18%	1188
February	1st to 10th	Day	1 7% 6% 11% 8% 4 8% 13% 7% 11% 23%	1169
	11th to 20th	Day	2 11% 7% 10% 12% 6% 9% 9% 7% 12% 15%	1400
	21st to end	Day	1 8% 5% 10% 13% 9% 13% 8% 7% 10% 17%	1231
March	1st to 10th	Day	1 8% 7% 10% 8% 5% 8% 7% 9% 11% 28%	1787
	11th to 20th	Day	9% 7% 14% 11% 7% 9% 8% 8% 9% 20%	1835
	21st to end	Day	1 8% 6% 11% 10% 5% 8% 7% 7% 10% 28%	2376
April	1st to 10th	Day	3 13% 7% 11% 10% 6% 6% 6% 6% 8% 24%	2224
	11th to 20th	Day	3 14% 7% 11% 9% 6% 7% 7% 6% 7% 24%	2482
	21st to end	Day	3 11% 6% 9% 8% 5% 7% 7% 7% 9% 28%	2605
May	1st to 10th	Day	6% 14% 6% 9% 9% 5% 8% 6% 6% 7% 25%	2844
	11th to 20th	Day	8% 11% 5% 9% 7% 4 6% 6% 6% 8% 31%	2902
	21st to end	Day	6% 10% 4 9% 8% 4 7% 6% 7% 9% 30%	3420
June	1st to 10th	Day	13% 10% 4 8% 8% 4 8% 7% 7% 8% 23%	3240
	11th to 20th	Day	14% 11% 4 9% 9% 5% 7% 7% 7% 7% 19%	3240
	21st to end	Day	14% 10% 4 9% 9% 6% 8% 8% 8% 8% 17%	3240
July	1st to 10th	Day	14% 10% 4 8% 8% 5% 6% 6% 6% 9% 24%	3240
	11th to 20th	Day	15% 10% 5% 10% 9% 6% 8% 7% 6% 7% 17%	3240
	21st to end	Day	14% 9% 4 8% 7% 5% 7% 7% 7% 8% 24%	3201
August	1st to 10th	Day	14% 9% 3 8% 8% 5% 6% 6% 7% 8% 25%	2865
	11th to 20th	Day	20% 11% 4 9% 8% 4 6% 5% 6% 7% 22%	2581
	21st to end	Day	18% 11% 4 10% 9% 5% 6% 6% 6% 7% 16%	2772
September	1st to 10th	Day	17% 13% 5% 9% 8% 4 6% 6% 6% 6% 21%	2261
	11th to 20th	Day	9% 10% 4 9% 8% 6% 6% 6% 6% 9% 28%	2138
	21st to end	Day	12% 16% 5% 10% 8% 4 6% 6% 6% 7% 19%	1945
October	1st to 10th	Day	10% 17% 5% 10% 7% 4 8% 6% 6% 8% 19%	1746
	11th to 20th	Day	9% 18% 6% 10% 7% 6% 7% 7% 7% 7% 17%	1620
	21st to end	Day	5% 13% 6% 12% 10% 5% 7% 8% 7% 8% 18%	1495
November	1st to 10th	Day	3 13% 7% 12% 10% 5% 7% 9% 10% 9% 13%	1297
	11th to 20th	Day	3 11% 7% 12% 13% 7% 8% 8% 8% 9% 12%	1045
	21st to end	Day	2 11% 6% 10% 11% 7% 9% 10% 11% 10% 12%	950
December	1st to 10th	Day	3 11% 5% 14% 12% 7% 11% 8% 9% 8% 13%	787
	11th to 20th	Day	2 14% 7% 11% 9% 6% 8% 7% 9% 8% 20%	962
	21st to end	Day	3 13% 6% 14% 10% 6% 7% 9% 6% 7% 19%	1386
January	1st to 10th	Night	2 12% 6% 12% 10% 8% 9% 7% 9% 9% 17%	3406
	11th to 20th	Night	4 13% 8% 13% 10% 5% 7% 8% 8% 10% 14%	3234
	21st to end	Night	2 13% 8% 13% 10% 5% 7% 7% 7% 10% 17%	3168
February	1st to 10th	Night	2 9% 6% 12% 9% 5% 7% 8% 8% 11% 22%	2788
	11th to 20th	Night	2 10% 8% 13% 10% 6% 8% 7% 9% 9% 18%	2447
	21st to end	Night	7% 7% 12% 9% 5% 9% 7% 9% 11% 22%	2023
March	1st to 10th	Night	1 7% 5% 11% 10% 7% 7% 6% 8% 8% 30%	2173
	11th to 20th	Night	1 9% 7% 12% 9% 7% 8% 8% 7% 8% 23%	2121
	21st to end	Night	1 8% 5% 11% 9% 5% 8% 7% 6% 9% 31%	1980
April	1st to 10th	Night	3 11% 7% 12% 10% 5% 6% 5% 5% 8% 27%	1736
	11th to 20th	Night	2 10% 7% 10% 8% 4 8% 7% 6% 10% 28%	1424
	21st to end	Night	3 11% 4 10% 7% 4 6% 6% 8% 8% 32%	1355
May	1st to 10th	Night	5% 10% 5% 9% 7% 4 6% 7% 6% 8% 33%	1114
	11th to 20th	Night	7% 8% 4 8% 5% 4 5% 6% 6% 10% 38%	993
	21st to end	Night	5% 6% 4 8% 7% 3 6% 7% 6% 9% 39%	853
June	1st to 10th	Night	10% 8% 2 6% 6% 4 6% 8% 9% 10% 31%	720
	11th to 20th	Night	13% 8% 3 9% 7% 3 5% 6% 9% 10% 27%	720
	21st to end	Night	13% 9% 5% 7% 8% 3 7% 7% 8% 11% 23%	720
July	1st to 10th	Night	12% 7% 2 7% 8% 5% 8% 5% 8% 9% 30%	720
	11th to 20th	Night	10% 8% 5% 8% 8% 5% 9% 8% 8% 8% 24%	720
	21st to end	Night	9% 8% 3 9% 9% 5% 7% 7% 8% 10% 25%	1113
August	1st to 10th	Night	13% 9% 3 7% 7% 4 6% 5% 6% 11% 29%	1074
	11th to 20th	Night	16% 12% 3 9% 7% 4 5% 5% 5% 8% 27%	1318
	21st to end	Night	16% 11% 5% 9% 8% 5% 6% 7% 6% 8% 20%	1584
September	1st to 10th	Night	13% 11% 4 8% 7% 4 6% 6% 6% 9% 25%	1696
	11th to 20th	Night	9% 10% 3 7% 8% 4 5% 5% 7% 7% 35%	1822
	21st to end	Night	13% 15% 5% 10% 8% 5% 5% 5% 5% 6% 22%	2012
October	1st to 10th	Night	11% 16% 5% 10% 6% 5% 5% 6% 6% 7% 24%	2214
	11th to 20th	Night	8% 21% 7% 10% 9% 4 6% 6% 6% 7% 17%	2340
	21st to end	Night	5% 16% 7% 12% 10% 5% 7% 7% 7% 8% 17%	2857
November	1st to 10th	Night	4 13% 7% 12% 11% 5% 8% 8% 8% 11% 12%	2780
	11th to 20th	Night	3 13% 9% 13% 13% 7% 9% 8% 7% 10% 9%	3116
	21st to end	Night	4 13% 6% 15% 11% 6% 7% 8% 9% 9% 12%	3230
December	1st to 10th	Night	3 13% 6% 14% 12% 6% 8% 8% 11% 10% 11%	3391
	11th to 20th	Night	2 12% 7% 13% 12% 6% 8% 9% 8% 8% 14%	4230
	21st to end	Night	2 13% 6% 12% 11% 6% 9% 7% 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	55% 8% 16% 12% 8% 1	759
	11th to 20th	Day	60% 9% 14% 9% 6% 1	866
	21st to end	Day	57% 11% 12% 12% 7%	1188
February	1st to 10th	Day	43% 10% 16% 20% 11% 1	1169
	11th to 20th	Day	54% 10% 17% 13% 6% 1	1408
	21st to end	Day	57% 10% 16% 11% 6% 1	1231
March	1st to 10th	Day	47% 11% 13% 16% 11% 3	1787
	11th to 20th	Day	57% 12% 14% 13% 4 2	1835
	21st to end	Day	49% 14% 16% 14% 7%	2376
April	1st to 10th	Day	58% 14% 17% 9% 3	2224
	11th to 20th	Day	56% 14% 15% 11% 4	2482
	21st to end	Day	48% 16% 20% 13% 3	2605
May	1st to 10th	Day	54% 13% 18% 14% 1	2844
	11th to 20th	Day	49% 10% 14% 20% 6%	2906
	21st to end	Day	47% 12% 18% 17% 6%	3421
June	1st to 10th	Day	55% 12% 14% 14% 4	3240
	11th to 20th	Day	59% 13% 13% 13% 2	3240
	21st to end	Day	59% 17% 14% 9% 1	3240
July	1st to 10th	Day	54% 14% 15% 13% 4	3151
	11th to 20th	Day	62% 16% 13% 8% 1	3141
	21st to end	Day	54% 18% 18% 8% 1	3023
August	1st to 10th	Day	52% 15% 20% 10% 2	2846
	11th to 20th	Day	60% 14% 15% 10%	2581
	21st to end	Day	64% 15% 15% 6%	2772
September	1st to 10th	Day	61% 13% 14% 11% 1	2261
	11th to 20th	Day	49% 15% 20% 15% 1	2138
	21st to end	Day	60% 12% 13% 12% 2	1945
October	1st to 10th	Day	57% 14% 17% 11% 1	1746
	11th to 20th	Day	63% 11% 15% 8% 2	1620
	21st to end	Day	60% 11% 18% 10% 1	1495
November	1st to 10th	Day	60% 12% 15% 11% 3	1297
	11th to 20th	Day	61% 10% 13% 12% 3	1045
	21st to end	Day	55% 14% 16% 12% 3	950
December	1st to 10th	Day	57% 12% 17% 9% 4 1	787
	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	55% 9% 16% 12% 6% 1	3406
	11th to 20th	Night	59% 10% 14% 10% 6% 2	3234
	21st to end	Night	59% 9% 11% 11% 8% 1	3168
February	1st to 10th	Night	50% 7% 11% 19% 12% 1	2788
	11th to 20th	Night	53% 10% 15% 15% 5% 1	2450
	21st to end	Night	48% 9% 18% 17% 7% 1	2023
March	1st to 10th	Night	47% 10% 14% 17% 10% 2	2173
	11th to 20th	Night	54% 11% 15% 13% 6% 1	2123
	21st to end	Night	44% 14% 18% 16% 7% 1	1980
April	1st to 10th	Night	52% 10% 19% 15% 3	1736
	11th to 20th	Night	49% 14% 16% 15% 5% 1	1424
	21st to end	Night	44% 14% 19% 19% 4	1355
May	1st to 10th	Night	46% 13% 20% 18% 3	1114
	11th to 20th	Night	40% 11% 16% 24% 8%	993
	21st to end	Night	39% 10% 21% 23% 6%	853
June	1st to 10th	Night	43% 14% 19% 21% 4	720
	11th to 20th	Night	50% 12% 21% 15% 2 1	720
	21st to end	Night	51% 15% 20% 12% 2	720
July	1st to 10th	Night	47% 12% 20% 15% 6%	700
	11th to 20th	Night	50% 16% 20% 11% 2	696
	21st to end	Night	47% 17% 23% 12% 1	1051
August	1st to 10th	Night	47% 13% 22% 16% 2	1068
	11th to 20th	Night	54% 11% 17% 17% 1	1318
	21st to end	Night	58% 14% 19% 9%	1584
September	1st to 10th	Night	52% 15% 16% 15% 2	1696
	11th to 20th	Night	43% 12% 23% 19% 3	1822
	21st to end	Night	60% 10% 13% 15% 2	2012
October	1st to 10th	Night	54% 13% 17% 14% 2	2214
	11th to 20th	Night	63% 11% 14% 10% 2	2340
	21st to end	Night	61% 11% 17% 9% 1	2857
November	1st to 10th	Night	60% 12% 16% 10% 3	2780
	11th to 20th	Night	63% 10% 13% 11% 3	3116
	21st to end	Night	60% 10% 15% 10% 3	3230
December	1st to 10th	Night	58% 14% 14% 10% 4	3391
	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 25% 33% 21% 14%	101
	21st to end	Day	6% 9% 22% 27% 25% 12%	176
February	1st to 10th	Day	7% 6% 16% 35% 28% 9%	244
	11th to 20th	Day	6% 8% 21% 32% 21% 11%	335
	21st to end	Day	4 8% 24% 30% 24% 10%	280
March	1st to 10th	Day	2 7% 24% 30% 25% 12%	340
	11th to 20th	Day	6% 7% 27% 32% 23% 5%	348
	21st to end	Day	6% 8% 27% 31% 22% 7%	462
April	1st to 10th	Day	10% 9% 27% 27% 20% 6%	420
	11th to 20th	Day	7% 9% 27% 30% 22% 6%	586
	21st to end	Day	10% 10% 28% 31% 18% 3	600
May	1st to 10th	Day	13% 12% 24% 27% 18% 6%	603
	11th to 20th	Day	11% 7% 20% 29% 24% 8%	694
	21st to end	Day	11% 9% 20% 27% 24% 9%	874
June	1st to 10th	Day	16% 8% 18% 29% 21% 8%	810
	11th to 20th	Day	19% 6% 18% 28% 25% 5%	810
	21st to end	Day	20% 6% 19% 28% 23% 5%	810
July	1st to 10th	Day	20% 5% 19% 26% 23% 7%	796
	11th to 20th	Day	20% 9% 16% 24% 24% 8%	792
	21st to end	Day	20% 6% 14% 27% 24% 10%	715
August	1st to 10th	Day	17% 8% 20% 28% 20% 8%	626
	11th to 20th	Day	26% 9% 24% 25% 12% 5%	615
	21st to end	Day	26% 8% 19% 27% 17% 3	693
September	1st to 10th	Day	24% 12% 21% 22% 14% 7%	460
	11th to 20th	Day	12% 14% 23% 28% 17% 6%	450
	21st to end	Day	25% 14% 24% 21% 12% 3	432
October	1st to 10th	Day	24% 14% 28% 19% 10% 5%	360
	11th to 20th	Day	21% 13% 22% 24% 16% 4	360
	21st to end	Day	13% 6% 17% 31% 24% 9%	305
November	1st to 10th	Day	12% 4 20% 35% 19% 9%	180
	11th to 20th	Day	9% 3 11% 35% 19% 22%	180
	21st to end	Day	6% 10% 23% 33% 18% 9%	180
December	1st to 10th	Day	9% 8% 20% 29% 25% 10%	102
	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	11% 7% 23% 33% 20% 6%	942
	21st to end	Night	7% 8% 23% 35% 22% 6%	880
February	1st to 10th	Night	6% 4 19% 40% 25% 6%	800
	11th to 20th	Night	7% 5% 22% 38% 22% 6%	784
	21st to end	Night	3 3 18% 43% 26% 6%	658
March	1st to 10th	Night	3 6% 20% 36% 29% 7%	725
	11th to 20th	Night	4 3 22% 34% 31% 6%	700
	21st to end	Night	3 5% 17% 34% 32% 9%	594
April	1st to 10th	Night	6% 7% 16% 32% 30% 9%	540
	11th to 20th	Night	6% 5% 16% 36% 29% 9%	533
	21st to end	Night	9% 6% 21% 33% 27% 4	455
May	1st to 10th	Night	9% 8% 16% 33% 26% 8%	360
	11th to 20th	Night	12% 5% 19% 30% 30% 4	354
	21st to end	Night	7% 5% 12% 30% 40% 6%	272
June	1st to 10th	Night	15% 2 8% 33% 38% 5%	180
	11th to 20th	Night	16% 4 13% 34% 31% 3	180
	21st to end	Night	14% 5% 17% 31% 29% 4	180
July	1st to 10th	Night	18% 3 9% 29% 37% 4	175
	11th to 20th	Night	17% 4 11% 20% 40% 7%	174
	21st to end	Night	14% 5% 13% 20% 39% 9%	359
August	1st to 10th	Night	16% 3 18% 26% 31% 6%	358
	11th to 20th	Night	24% 7% 15% 26% 24% 4	472
	21st to end	Night	20% 6% 12% 28% 28% 6%	594
September	1st to 10th	Night	20% 9% 15% 26% 26% 4	540
	11th to 20th	Night	14% 7% 15% 28% 30% 5%	562
	21st to end	Night	22% 11% 20% 26% 18% 4	720
October	1st to 10th	Night	23% 9% 20% 30% 16% 3	720
	11th to 20th	Night	19% 9% 22% 26% 20% 4	720
	21st to end	Night	14% 6% 16% 35% 23% 6%	888
November	1st to 10th	Night	13% 4 16% 34% 27% 7%	830
	11th to 20th	Night	9% 5% 18% 29% 25% 14%	926
	21st to end	Night	10% 9% 21% 34% 18% 10%	1040
December	1st to 10th	Night	8% 8% 20% 36% 22% 6%	1040
	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 2024-01-13 06:37:57. Version ac07

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