Timber Point:
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Timber Point: clear sky chart from 2005-11-06 to 2024-01-14.

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% 12% 6% 10% 9% 5% 6% 6% 6% 7% 22%	74433
	Night	8% 14% 6% 11% 9% 5% 7% 6% 6% 7% 20%	75326
Transparency	Day	59% 9% 14% 14% 4	74070
	Night	61% 8% 12% 13% 5% 1	75208
Seeing	Day	16% 11% 23% 25% 19% 6%	16009
	Night	15% 8% 20% 31% 22% 4	22647

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	5% 13% 8% 16% 12% 6% 8% 6% 6% 7% 13%	857
	11th to 20th	Day	8% 16% 8% 16% 12% 5% 8% 5% 7% 7% 8%	1098
	21st to end	Day	7% 16% 8% 11% 10% 5% 6% 7% 7% 7% 15%	1188
February	1st to 10th	Day	6% 12% 6% 11% 8% 4 7% 6% 8% 9% 23%	1299
	11th to 20th	Day	6% 16% 9% 10% 9% 6% 7% 6% 7% 7% 18%	1400
	21st to end	Day	3 10% 8% 11% 9% 6% 5% 6% 7% 9% 25%	1278
March	1st to 10th	Day	3 11% 6% 11% 11% 7% 7% 7% 6% 7% 23%	1800
	11th to 20th	Day	2 13% 8% 16% 10% 6% 7% 6% 5% 8% 18%	1835
	21st to end	Day	4 12% 8% 11% 10% 6% 7% 6% 6% 7% 23%	2376
April	1st to 10th	Day	4 14% 8% 12% 11% 4 6% 7% 7% 7% 20%	2204
	11th to 20th	Day	4 14% 7% 11% 10% 5% 6% 6% 5% 8% 23%	2440
	21st to end	Day	5% 11% 5% 9% 9% 6% 7% 6% 6% 8% 28%	2556
May	1st to 10th	Day	10% 14% 6% 8% 7% 5% 6% 6% 6% 8% 24%	2760
	11th to 20th	Day	8% 13% 5% 8% 8% 4 6% 6% 6% 8% 29%	2833
	21st to end	Day	10% 9% 4 8% 9% 4 6% 6% 7% 7% 31%	3257
June	1st to 10th	Day	13% 12% 5% 10% 8% 5% 6% 6% 6% 6% 23%	3176
	11th to 20th	Day	16% 11% 5% 9% 8% 5% 6% 6% 6% 7% 21%	3240
	21st to end	Day	10% 9% 5% 10% 9% 5% 7% 7% 7% 8% 23%	3240
July	1st to 10th	Day	14% 8% 4 8% 7% 5% 7% 7% 7% 8% 25%	3240
	11th to 20th	Day	18% 11% 5% 10% 8% 5% 6% 7% 7% 8% 15%	3006
	21st to end	Day	16% 9% 4 8% 8% 4 6% 6% 6% 7% 27%	3135
August	1st to 10th	Day	13% 9% 4 8% 7% 5% 6% 6% 7% 7% 30%	2839
	11th to 20th	Day	20% 11% 4 9% 7% 4 5% 5% 5% 7% 22%	2476
	21st to end	Day	21% 11% 4 8% 8% 3 6% 6% 6% 7% 20%	2746
September	1st to 10th	Day	19% 11% 5% 9% 7% 5% 5% 6% 6% 6% 19%	2229
	11th to 20th	Day	15% 10% 3 7% 9% 3 6% 6% 6% 8% 27%	2128
	21st to end	Day	16% 15% 5% 11% 8% 5% 4 6% 5% 6% 18%	1962
October	1st to 10th	Day	13% 17% 5% 9% 9% 5% 5% 5% 6% 7% 18%	1760
	11th to 20th	Day	13% 17% 5% 13% 9% 4 7% 5% 5% 5% 16%	1620
	21st to end	Day	10% 15% 7% 11% 11% 4 6% 5% 7% 7% 17%	1590
November	1st to 10th	Day	8% 17% 9% 13% 11% 6% 7% 6% 6% 5% 13%	1302
	11th to 20th	Day	8% 17% 9% 15% 10% 6% 7% 6% 6% 6% 9%	1228
	21st to end	Day	6% 17% 6% 16% 10% 4 8% 6% 8% 6% 12%	970
December	1st to 10th	Day	8% 13% 6% 13% 11% 7% 8% 8% 7% 7% 12%	950
	11th to 20th	Day	4 12% 8% 10% 10% 7% 7% 7% 8% 9% 18%	1029
	21st to end	Day	7% 16% 6% 11% 10% 5% 5% 8% 9% 8% 15%	1386
January	1st to 10th	Night	5% 14% 8% 12% 13% 8% 8% 6% 5% 6% 15%	3325
	11th to 20th	Night	8% 17% 7% 13% 11% 5% 7% 5% 6% 6% 14%	2934
	21st to end	Night	7% 15% 7% 14% 10% 5% 8% 6% 6% 7% 16%	3168
February	1st to 10th	Night	5% 13% 6% 12% 9% 5% 9% 6% 6% 8% 20%	2659
	11th to 20th	Night	4 14% 6% 14% 11% 7% 7% 6% 7% 7% 17%	2447
	21st to end	Night	3 11% 8% 12% 8% 4 5% 6% 7% 7% 30%	1978
March	1st to 10th	Night	4 12% 6% 12% 9% 5% 6% 5% 5% 6% 31%	2160
	11th to 20th	Night	1 14% 10% 13% 10% 6% 8% 7% 5% 6% 20%	2123
	21st to end	Night	3 13% 7% 13% 10% 7% 7% 7% 4 6% 23%	1980
April	1st to 10th	Night	4 11% 6% 11% 10% 5% 8% 6% 5% 6% 28%	1756
	11th to 20th	Night	4 10% 6% 10% 8% 5% 6% 7% 6% 8% 30%	1469
	21st to end	Night	6% 12% 5% 9% 9% 6% 7% 6% 7% 7% 27%	1404
May	1st to 10th	Night	9% 9% 4 9% 7% 5% 7% 7% 9% 9% 25%	1198
	11th to 20th	Night	9% 9% 5% 7% 6% 5% 5% 5% 8% 7% 34%	1062
	21st to end	Night	7% 7% 3 8% 7% 4 6% 6% 7% 9% 34%	1018
June	1st to 10th	Night	11% 5% 3 8% 7% 4 8% 7% 7% 10% 31%	782
	11th to 20th	Night	12% 9% 4 8% 6% 2 6% 6% 7% 11% 28%	720
	21st to end	Night	9% 7% 4 7% 7% 4 7% 7% 8% 10% 30%	720
July	1st to 10th	Night	12% 5% 4 7% 8% 4 6% 8% 10% 8% 29%	720
	11th to 20th	Night	15% 8% 3 9% 10% 5% 8% 7% 8% 9% 19%	950
	21st to end	Night	13% 8% 4 6% 8% 4 6% 7% 7% 8% 31%	1182
August	1st to 10th	Night	13% 7% 3 6% 6% 4 5% 6% 8% 9% 32%	1098
	11th to 20th	Night	16% 8% 2 7% 9% 3 6% 7% 7% 8% 27%	1424
	21st to end	Night	20% 11% 6% 8% 6% 4 5% 5% 5% 6% 25%	1610
September	1st to 10th	Night	15% 12% 4 8% 8% 4 5% 6% 6% 7% 25%	1728
	11th to 20th	Night	11% 9% 4 7% 6% 5% 6% 5% 6% 8% 34%	1831
	21st to end	Night	17% 16% 5% 9% 7% 4 6% 5% 6% 6% 21%	1997
October	1st to 10th	Night	13% 14% 4 9% 8% 4 5% 6% 5% 7% 25%	2200
	11th to 20th	Night	14% 19% 6% 9% 8% 4 5% 5% 5% 6% 17%	2340
	21st to end	Night	8% 18% 7% 11% 8% 4 6% 5% 6% 7% 20%	2766
November	1st to 10th	Night	9% 15% 7% 12% 12% 7% 8% 7% 5% 6% 12%	2776
	11th to 20th	Night	8% 16% 9% 15% 10% 6% 7% 5% 6% 7% 11%	2949
	21st to end	Night	7% 17% 8% 14% 11% 6% 7% 6% 5% 7% 11%	3190
December	1st to 10th	Night	7% 17% 8% 13% 13% 6% 7% 7% 6% 7% 9%	3230
	11th to 20th	Night	5% 16% 7% 14% 12% 6% 7% 5% 6% 8% 14%	4162
	21st to end	Night	7% 16% 6% 10% 9% 6% 7% 8% 7% 6% 17%	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	69% 6% 9% 7% 7% 1	857
	11th to 20th	Day	73% 6% 9% 7% 4 1	1098
	21st to end	Day	66% 9% 9% 11% 6%	1188
February	1st to 10th	Day	56% 8% 8% 14% 11% 2	1299
	11th to 20th	Day	63% 8% 11% 11% 7% 1	1408
	21st to end	Day	54% 10% 12% 17% 6% 1	1278
March	1st to 10th	Day	57% 8% 9% 17% 8% 2	1800
	11th to 20th	Day	62% 6% 13% 13% 6%	1835
	21st to end	Day	58% 9% 14% 11% 8% 1	2376
April	1st to 10th	Day	61% 7% 16% 12% 4	2204
	11th to 20th	Day	58% 8% 14% 16% 5%	2440
	21st to end	Day	54% 8% 17% 16% 6%	2556
May	1st to 10th	Day	57% 8% 17% 14% 3	2760
	11th to 20th	Day	52% 7% 12% 21% 7%	2836
	21st to end	Day	50% 9% 14% 22% 6%	3258
June	1st to 10th	Day	60% 7% 13% 16% 4	3176
	11th to 20th	Day	60% 8% 13% 16% 3	3240
	21st to end	Day	56% 11% 17% 13% 4	3240
July	1st to 10th	Day	53% 11% 17% 15% 4	3151
	11th to 20th	Day	64% 11% 17% 8%	2911
	21st to end	Day	54% 10% 19% 15% 2	2961
August	1st to 10th	Day	51% 9% 22% 15% 2	2820
	11th to 20th	Day	61% 9% 17% 12% 1	2476
	21st to end	Day	61% 11% 17% 10% 1	2746
September	1st to 10th	Day	62% 10% 12% 12% 3	2229
	11th to 20th	Day	53% 9% 16% 19% 4	2128
	21st to end	Day	66% 8% 12% 12% 3	1962
October	1st to 10th	Day	64% 7% 15% 12% 2	1760
	11th to 20th	Day	69% 7% 12% 11% 1	1620
	21st to end	Day	63% 9% 12% 13% 3	1590
November	1st to 10th	Day	69% 8% 11% 10% 2	1302
	11th to 20th	Day	73% 7% 7% 11% 2	1228
	21st to end	Day	67% 9% 9% 10% 5%	970
December	1st to 10th	Day	68% 9% 11% 9% 3 1	950
	11th to 20th	Day	59% 8% 5% 19% 10%	1031
	21st to end	Day	64% 7% 6% 15% 7% 1	1386
January	1st to 10th	Night	69% 7% 9% 8% 6% 1	3325
	11th to 20th	Night	69% 7% 9% 8% 6%	2934
	21st to end	Night	66% 8% 8% 12% 5%	3168
February	1st to 10th	Night	60% 7% 7% 13% 11% 1	2659
	11th to 20th	Night	63% 8% 10% 12% 5% 1	2450
	21st to end	Night	51% 6% 16% 18% 8% 1	1978
March	1st to 10th	Night	53% 7% 10% 20% 8% 3	2160
	11th to 20th	Night	63% 7% 10% 14% 6%	2125
	21st to end	Night	58% 8% 14% 12% 8%	1980
April	1st to 10th	Night	54% 7% 15% 18% 6%	1756
	11th to 20th	Night	48% 10% 16% 19% 6%	1469
	21st to end	Night	53% 7% 16% 17% 6%	1404
May	1st to 10th	Night	50% 12% 20% 15% 4	1198
	11th to 20th	Night	46% 6% 16% 22% 9% 1	1062
	21st to end	Night	45% 6% 17% 25% 8%	1018
June	1st to 10th	Night	46% 10% 18% 22% 4 1	782
	11th to 20th	Night	47% 11% 20% 17% 5%	720
	21st to end	Night	44% 12% 22% 20% 3	720
July	1st to 10th	Night	44% 10% 21% 20% 4 1	700
	11th to 20th	Night	58% 11% 19% 12%	922
	21st to end	Night	48% 10% 23% 16% 2	1116
August	1st to 10th	Night	44% 11% 25% 18% 2	1092
	11th to 20th	Night	52% 13% 15% 18% 2	1424
	21st to end	Night	61% 7% 19% 13%	1610
September	1st to 10th	Night	57% 9% 18% 15% 1	1728
	11th to 20th	Night	47% 8% 19% 21% 4	1831
	21st to end	Night	63% 6% 13% 14% 3	1997
October	1st to 10th	Night	57% 9% 18% 13% 3	2200
	11th to 20th	Night	66% 8% 14% 11% 2	2340
	21st to end	Night	62% 8% 15% 13% 3	2766
November	1st to 10th	Night	69% 8% 10% 11% 2	2776
	11th to 20th	Night	70% 8% 10% 10% 2	2949
	21st to end	Night	71% 6% 9% 11% 3	3190
December	1st to 10th	Night	73% 7% 8% 9% 3	3230
	11th to 20th	Night	67% 7% 8% 12% 6%	4159
	21st to end	Night	63% 8% 7% 10% 10% 2	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	5% 7% 21% 37% 26% 5%	117
	11th to 20th	Day	11% 6% 26% 25% 25% 7%	166
	21st to end	Day	15% 18% 18% 26% 19% 5%	176
February	1st to 10th	Day	11% 6% 25% 35% 17% 6%	306
	11th to 20th	Day	10% 13% 28% 28% 14% 7%	335
	21st to end	Day	9% 9% 31% 28% 17% 6%	280
March	1st to 10th	Day	9% 9% 26% 30% 17% 9%	340
	11th to 20th	Day	11% 10% 31% 27% 19% 3	350
	21st to end	Day	9% 15% 23% 28% 20% 6%	462
April	1st to 10th	Day	11% 16% 26% 25% 20% 3	420
	11th to 20th	Day	9% 14% 23% 26% 22% 6%	544
	21st to end	Day	12% 11% 30% 26% 18% 4	600
May	1st to 10th	Day	14% 13% 24% 26% 17% 6%	603
	11th to 20th	Day	13% 11% 20% 25% 21% 10%	625
	21st to end	Day	12% 11% 20% 24% 24% 8%	826
June	1st to 10th	Day	17% 10% 20% 24% 22% 7%	810
	11th to 20th	Day	19% 9% 22% 25% 21% 5%	810
	21st to end	Day	15% 9% 21% 26% 22% 6%	810
July	1st to 10th	Day	16% 7% 20% 26% 24% 7%	796
	11th to 20th	Day	21% 11% 16% 24% 21% 7%	691
	21st to end	Day	20% 9% 18% 23% 20% 10%	684
August	1st to 10th	Day	15% 11% 21% 26% 19% 8%	626
	11th to 20th	Day	28% 15% 21% 21% 12% 3	615
	21st to end	Day	25% 11% 24% 20% 16% 3	667
September	1st to 10th	Day	27% 14% 25% 16% 14% 4	450
	11th to 20th	Day	18% 11% 26% 21% 18% 6%	450
	21st to end	Day	28% 15% 25% 20% 11% 2	441
October	1st to 10th	Day	25% 16% 29% 20% 8% 2	360
	11th to 20th	Day	28% 14% 28% 18% 9% 4	360
	21st to end	Day	14% 10% 23% 31% 19% 3	348
November	1st to 10th	Day	13% 13% 27% 27% 16% 4	180
	11th to 20th	Day	17% 5% 29% 26% 16% 8%	180
	21st to end	Day	11% 14% 29% 26% 11% 9%	180
December	1st to 10th	Day	11% 4 27% 36% 16% 6%	180
	11th to 20th	Day	7% 11% 24% 24% 26% 8%	122
	21st to end	Day	10% 7% 23% 27% 19% 13%	99
January	1st to 10th	Night	11% 7% 21% 35% 21% 5%	1017
	11th to 20th	Night	16% 8% 22% 32% 18% 3	817
	21st to end	Night	13% 11% 23% 31% 19% 3	880
February	1st to 10th	Night	12% 7% 18% 41% 18% 3	800
	11th to 20th	Night	10% 10% 23% 34% 18% 4	784
	21st to end	Night	8% 7% 22% 39% 20% 4	650
March	1st to 10th	Night	9% 8% 21% 32% 25% 5%	720
	11th to 20th	Night	7% 8% 21% 33% 27% 4	707
	21st to end	Night	7% 7% 16% 31% 29% 10%	594
April	1st to 10th	Night	6% 8% 14% 31% 33% 6%	540
	11th to 20th	Night	8% 6% 17% 33% 30% 5%	533
	21st to end	Night	11% 7% 19% 28% 28% 7%	504
May	1st to 10th	Night	13% 6% 16% 30% 28% 6%	360
	11th to 20th	Night	12% 5% 16% 28% 34% 5%	354
	21st to end	Night	10% 6% 16% 29% 33% 6%	389
June	1st to 10th	Night	15% 3 16% 33% 29% 3	242
	11th to 20th	Night	19% 3 13% 31% 30% 3	180
	21st to end	Night	11% 4 16% 27% 38% 4	180
July	1st to 10th	Night	12% 5% 14% 31% 35% 3	175
	11th to 20th	Night	16% 6% 16% 28% 28% 5%	302
	21st to end	Night	15% 6% 17% 28% 28% 7%	394
August	1st to 10th	Night	17% 6% 16% 26% 31% 4	358
	11th to 20th	Night	20% 8% 21% 26% 21% 4	534
	21st to end	Night	25% 8% 19% 22% 22% 4	594
September	1st to 10th	Night	23% 7% 17% 32% 19% 2	540
	11th to 20th	Night	14% 8% 20% 26% 25% 6%	571
	21st to end	Night	28% 9% 20% 25% 13% 4	720
October	1st to 10th	Night	21% 11% 22% 29% 14% 3	720
	11th to 20th	Night	28% 9% 17% 29% 14% 3	720
	21st to end	Night	17% 8% 21% 32% 18% 4	864
November	1st to 10th	Night	16% 7% 20% 35% 18% 4	830
	11th to 20th	Night	17% 6% 19% 30% 23% 6%	850
	21st to end	Night	16% 8% 26% 29% 17% 4	1000
December	1st to 10th	Night	15% 8% 22% 33% 20% 2	1040
	11th to 20th	Night	15% 7% 18% 37% 18% 5%	1040
	21st to end	Night	15% 9% 21% 31% 19% 6%	1144

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