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 2026-01-02.

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% 12% 5% 11% 8% 7% 6% 5% 7% 8% 23%	131809
	Night	7% 13% 5% 13% 8% 7% 6% 5% 6% 7% 22%	128158
Transparency	Day	56% 8% 14% 16% 6%	131458
	Night	59% 7% 12% 15% 7% 1	128087
Seeing	Day	16% 11% 24% 25% 18% 6%	18713
	Night	14% 8% 20% 31% 22% 4	25200

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 11% 6% 19% 13% 10% 8% 4 4 5% 18%	2050
	11th to 20th	Day	3 13% 6% 17% 10% 8% 7% 4 6% 8% 18%	2702
	21st to end	Day	6% 16% 5% 12% 6% 7% 6% 5% 8% 8% 22%	2992
February	1st to 10th	Day	5% 13% 5% 12% 8% 5% 9% 4 8% 9% 23%	1445
	11th to 20th	Day	5% 17% 7% 12% 8% 6% 7% 4 7% 7% 20%	1560
	21st to end	Day	3 12% 7% 12% 9% 7% 5% 5% 7% 9% 25%	1425
March	1st to 10th	Day	2 9% 4 14% 12% 11% 8% 5% 5% 7% 23%	4496
	11th to 20th	Day	2 13% 6% 15% 9% 7% 7% 5% 6% 9% 20%	4643
	21st to end	Day	2 10% 6% 14% 8% 7% 7% 5% 7% 9% 26%	5969
April	1st to 10th	Day	4 15% 7% 14% 9% 6% 6% 6% 7% 7% 20%	2450
	11th to 20th	Day	3 15% 5% 12% 9% 7% 6% 5% 6% 8% 25%	2716
	21st to end	Day	4 13% 5% 10% 8% 7% 6% 5% 6% 8% 28%	2840
May	1st to 10th	Day	9% 12% 4 8% 7% 7% 6% 5% 6% 7% 28%	6952
	11th to 20th	Day	6% 13% 5% 12% 8% 7% 7% 5% 7% 8% 22%	7193
	21st to end	Day	8% 9% 3 10% 8% 7% 7% 5% 7% 6% 28%	8291
June	1st to 10th	Day	12% 14% 4 11% 7% 7% 6% 5% 6% 7% 23%	3530
	11th to 20th	Day	14% 11% 4 11% 7% 7% 5% 5% 6% 8% 22%	3600
	21st to end	Day	10% 10% 4 11% 8% 6% 7% 6% 7% 8% 23%	3600
July	1st to 10th	Day	11% 9% 3 9% 7% 7% 7% 5% 8% 9% 25%	8160
	11th to 20th	Day	14% 11% 4 10% 7% 6% 6% 5% 7% 9% 20%	7534
	21st to end	Day	12% 8% 3 9% 7% 7% 7% 6% 7% 9% 26%	7876
August	1st to 10th	Day	8% 6% 3 7% 5% 5% 5% 4 6% 6% 45%	5128
	11th to 20th	Day	15% 9% 3 7% 5% 5% 4 4 6% 9% 33%	4480
	21st to end	Day	19% 11% 3 8% 6% 5% 6% 5% 7% 8% 22%	4971
September	1st to 10th	Day	18% 11% 5% 10% 6% 6% 6% 5% 6% 7% 21%	2476
	11th to 20th	Day	15% 11% 3 9% 7% 5% 6% 4 6% 8% 27%	2364
	21st to end	Day	16% 16% 5% 12% 7% 6% 5% 5% 5% 6% 19%	2180
October	1st to 10th	Day	11% 17% 4 10% 8% 8% 7% 5% 7% 7% 16%	3189
	11th to 20th	Day	9% 15% 7% 13% 6% 6% 5% 5% 6% 6% 22%	2933
	21st to end	Day	8% 17% 7% 15% 9% 7% 7% 5% 6% 5% 13%	2836
November	1st to 10th	Day	7% 18% 8% 15% 10% 8% 6% 5% 6% 5% 13%	1442
	11th to 20th	Day	7% 20% 6% 17% 9% 9% 6% 4 6% 6% 8%	1356
	21st to end	Day	6% 17% 6% 16% 9% 5% 9% 4 9% 7% 12%	1072
December	1st to 10th	Day	6% 15% 6% 16% 10% 8% 8% 7% 7% 6% 10%	1680
	11th to 20th	Day	4 11% 7% 18% 12% 8% 7% 5% 7% 7% 15%	1654
	21st to end	Day	5% 17% 7% 17% 9% 7% 5% 5% 7% 7% 14%	2024
January	1st to 10th	Night	3 13% 7% 18% 13% 11% 8% 3 4 5% 14%	7948
	11th to 20th	Night	4 14% 6% 12% 8% 6% 5% 5% 7% 8% 24%	7196
	21st to end	Night	6% 17% 5% 15% 7% 7% 6% 5% 7% 7% 18%	7964
February	1st to 10th	Night	5% 14% 6% 13% 8% 7% 8% 5% 6% 8% 20%	2953
	11th to 20th	Night	4 15% 5% 15% 9% 8% 6% 5% 7% 7% 19%	2727
	21st to end	Night	3 12% 6% 13% 8% 6% 5% 5% 6% 7% 29%	2204
March	1st to 10th	Night	2 8% 4 13% 9% 8% 7% 5% 7% 8% 28%	5378
	11th to 20th	Night	2 13% 6% 12% 9% 8% 7% 6% 7% 8% 22%	5336
	21st to end	Night	2 10% 6% 13% 7% 7% 7% 6% 8% 8% 26%	4984
April	1st to 10th	Night	3 12% 5% 12% 9% 7% 7% 5% 6% 6% 28%	1950
	11th to 20th	Night	3 12% 5% 12% 7% 6% 6% 5% 6% 8% 31%	1633
	21st to end	Night	5% 12% 4 10% 8% 8% 6% 5% 8% 7% 28%	1560
May	1st to 10th	Night	6% 10% 4 11% 5% 6% 5% 5% 7% 7% 34%	3006
	11th to 20th	Night	6% 11% 5% 12% 8% 8% 7% 5% 7% 7% 25%	2702
	21st to end	Night	6% 7% 3 7% 6% 6% 7% 5% 8% 9% 35%	2584
June	1st to 10th	Night	10% 6% 3 8% 6% 6% 8% 6% 8% 10% 30%	868
	11th to 20th	Night	11% 10% 4 9% 6% 4 6% 5% 7% 11% 28%	800
	21st to end	Night	9% 8% 3 8% 6% 5% 7% 6% 8% 10% 30%	800
July	1st to 10th	Night	9% 6% 3 10% 6% 6% 6% 6% 9% 10% 29%	1800
	11th to 20th	Night	14% 9% 3 9% 7% 5% 5% 5% 6% 7% 29%	2422
	21st to end	Night	17% 8% 3 8% 6% 5% 6% 6% 6% 8% 29%	2967
August	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 7% 8% 49%	2007
	11th to 20th	Night	12% 8% 2 6% 5% 5% 5% 4 7% 9% 37%	2578
	21st to end	Night	18% 13% 5% 10% 5% 6% 5% 4 5% 5% 24%	2938
September	1st to 10th	Night	14% 12% 4 9% 7% 5% 5% 5% 6% 8% 26%	1921
	11th to 20th	Night	10% 10% 4 9% 5% 6% 6% 3 6% 7% 34%	2035
	21st to end	Night	16% 16% 4 11% 6% 6% 5% 4 6% 6% 20%	2219
October	1st to 10th	Night	10% 14% 4 10% 6% 6% 6% 5% 7% 8% 23%	4001
	11th to 20th	Night	10% 18% 6% 12% 7% 6% 6% 4 6% 6% 18%	4215
	21st to end	Night	8% 16% 5% 11% 8% 7% 6% 5% 7% 7% 18%	4948
November	1st to 10th	Night	8% 16% 6% 15% 10% 9% 7% 5% 6% 6% 13%	3076
	11th to 20th	Night	7% 19% 8% 17% 8% 7% 6% 4 6% 6% 11%	3261
	21st to end	Night	6% 17% 7% 16% 9% 9% 6% 5% 6% 7% 11%	3526
December	1st to 10th	Night	8% 19% 7% 15% 9% 8% 7% 5% 5% 8% 9%	5720
	11th to 20th	Night	3 13% 6% 21% 12% 9% 6% 3 6% 7% 15%	6757
	21st to end	Night	5% 16% 7% 15% 9% 8% 7% 6% 6% 6% 15%	9174

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% 5% 7% 6% 10% 3	2050
	11th to 20th	Day	62% 7% 9% 8% 13% 2	2720
	21st to end	Day	59% 10% 9% 13% 8% 1	2992
February	1st to 10th	Day	56% 8% 7% 15% 11% 2	1445
	11th to 20th	Day	61% 8% 11% 12% 8% 1	1568
	21st to end	Day	54% 10% 12% 17% 7% 1	1425
March	1st to 10th	Day	58% 7% 8% 15% 12% 1	4496
	11th to 20th	Day	58% 5% 10% 13% 14%	4643
	21st to end	Day	50% 10% 12% 21% 7%	5969
April	1st to 10th	Day	60% 7% 16% 13% 4	2450
	11th to 20th	Day	56% 8% 13% 16% 6% 1	2716
	21st to end	Day	52% 8% 18% 16% 5%	2840
May	1st to 10th	Day	53% 6% 11% 21% 9%	6952
	11th to 20th	Day	56% 9% 10% 19% 7%	7196
	21st to end	Day	52% 8% 10% 21% 9%	8292
June	1st to 10th	Day	59% 7% 12% 16% 5%	3530
	11th to 20th	Day	58% 8% 14% 17% 3	3600
	21st to end	Day	55% 10% 17% 14% 4	3600
July	1st to 10th	Day	52% 8% 19% 19% 2	8071
	11th to 20th	Day	58% 8% 20% 13% 1	7439
	21st to end	Day	51% 10% 24% 14% 1	7655
August	1st to 10th	Day	38% 7% 18% 23% 13% 2	5109
	11th to 20th	Day	47% 7% 20% 20% 6%	4522
	21st to end	Day	59% 8% 15% 17% 2	4970
September	1st to 10th	Day	60% 10% 13% 14% 3	2476
	11th to 20th	Day	54% 9% 14% 19% 4	2364
	21st to end	Day	66% 7% 11% 13% 3	2180
October	1st to 10th	Day	65% 6% 11% 15% 2	3189
	11th to 20th	Day	61% 6% 14% 17% 2	2933
	21st to end	Day	70% 8% 11% 9% 2	2836
November	1st to 10th	Day	70% 7% 10% 10% 2	1442
	11th to 20th	Day	74% 6% 7% 10% 2	1356
	21st to end	Day	66% 9% 10% 10% 6%	1072
December	1st to 10th	Day	71% 8% 10% 6% 4	1680
	11th to 20th	Day	65% 6% 9% 14% 6%	1656
	21st to end	Day	68% 6% 7% 14% 5%	2024
January	1st to 10th	Night	71% 6% 5% 5% 12% 1	7948
	11th to 20th	Night	56% 7% 9% 12% 13% 3	7240
	21st to end	Night	64% 8% 10% 12% 5% 1	7964
February	1st to 10th	Night	60% 7% 7% 13% 11% 1	2953
	11th to 20th	Night	60% 8% 11% 13% 7% 1	2730
	21st to end	Night	52% 7% 15% 17% 8% 1	2204
March	1st to 10th	Night	50% 7% 10% 21% 11% 1	5378
	11th to 20th	Night	55% 7% 9% 17% 11%	5338
	21st to end	Night	50% 8% 14% 17% 11% 1	4984
April	1st to 10th	Night	52% 8% 15% 19% 6%	1950
	11th to 20th	Night	47% 10% 16% 19% 7% 1	1633
	21st to end	Night	51% 8% 16% 19% 6%	1560
May	1st to 10th	Night	45% 8% 12% 25% 10%	3003
	11th to 20th	Night	52% 9% 13% 18% 8% 1	2702
	21st to end	Night	40% 6% 13% 29% 12%	2584
June	1st to 10th	Night	45% 10% 18% 22% 4	868
	11th to 20th	Night	46% 11% 21% 17% 5%	800
	21st to end	Night	44% 12% 22% 20% 2	800
July	1st to 10th	Night	43% 10% 23% 21% 3	1780
	11th to 20th	Night	52% 7% 25% 14% 2	2394
	21st to end	Night	52% 9% 24% 14% 1	2883
August	1st to 10th	Night	32% 7% 19% 27% 12% 2	2001
	11th to 20th	Night	42% 9% 19% 24% 6%	2602
	21st to end	Night	62% 6% 13% 17% 3	2938
September	1st to 10th	Night	55% 9% 19% 16% 1	1921
	11th to 20th	Night	48% 8% 18% 22% 4	2035
	21st to end	Night	64% 6% 12% 14% 4	2219
October	1st to 10th	Night	55% 8% 15% 19% 3	4001
	11th to 20th	Night	66% 6% 11% 15% 2	4215
	21st to end	Night	62% 9% 14% 12% 3	4948
November	1st to 10th	Night	68% 8% 10% 11% 3	3076
	11th to 20th	Night	71% 7% 9% 10% 2	3261
	21st to end	Night	70% 5% 10% 11% 3	3526
December	1st to 10th	Night	75% 6% 7% 10% 3	5720
	11th to 20th	Night	69% 5% 9% 12% 5%	6754
	21st to end	Night	67% 7% 7% 11% 8% 1	9174

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% 8% 21% 35% 24% 6%	131
	11th to 20th	Day	10% 8% 29% 25% 23% 7%	200
	21st to end	Day	16% 17% 20% 25% 17% 4	220
February	1st to 10th	Day	10% 7% 24% 37% 17% 6%	363
	11th to 20th	Day	9% 12% 26% 28% 18% 7%	395
	21st to end	Day	9% 10% 30% 29% 16% 5%	331
March	1st to 10th	Day	8% 9% 26% 29% 19% 9%	400
	11th to 20th	Day	11% 10% 30% 25% 19% 5%	413
	21st to end	Day	8% 13% 22% 27% 23% 6%	550
April	1st to 10th	Day	10% 16% 29% 25% 18% 3	500
	11th to 20th	Day	8% 14% 25% 25% 22% 6%	640
	21st to end	Day	11% 10% 29% 26% 19% 5%	700
May	1st to 10th	Day	15% 15% 24% 24% 17% 6%	703
	11th to 20th	Day	12% 12% 22% 25% 20% 9%	725
	21st to end	Day	13% 11% 22% 24% 22% 8%	953
June	1st to 10th	Day	18% 12% 21% 23% 20% 6%	930
	11th to 20th	Day	17% 8% 22% 27% 22% 6%	930
	21st to end	Day	14% 8% 19% 27% 23% 8%	930
July	1st to 10th	Day	16% 7% 20% 27% 22% 6%	916
	11th to 20th	Day	21% 12% 18% 23% 20% 6%	799
	21st to end	Day	18% 10% 20% 24% 19% 9%	794
August	1st to 10th	Day	14% 11% 21% 25% 20% 8%	726
	11th to 20th	Day	25% 15% 22% 21% 13% 4	715
	21st to end	Day	24% 12% 24% 21% 15% 4	773
September	1st to 10th	Day	24% 13% 25% 18% 14% 5%	530
	11th to 20th	Day	21% 12% 25% 21% 17% 5%	530
	21st to end	Day	28% 14% 25% 19% 11% 3	519
October	1st to 10th	Day	26% 15% 30% 19% 8% 2	420
	11th to 20th	Day	27% 16% 29% 18% 7% 3	420
	21st to end	Day	14% 11% 25% 29% 19% 3	408
November	1st to 10th	Day	14% 13% 30% 26% 14% 4	220
	11th to 20th	Day	18% 6% 29% 26% 14% 6%	220
	21st to end	Day	10% 13% 29% 25% 16% 8%	220
December	1st to 10th	Day	10% 6% 30% 33% 15% 6%	220
	11th to 20th	Day	7% 9% 23% 27% 25% 8%	148
	21st to end	Day	9% 7% 26% 27% 20% 11%	121
January	1st to 10th	Night	11% 8% 21% 33% 22% 5%	1082
	11th to 20th	Night	15% 9% 24% 32% 17% 3	900
	21st to end	Night	14% 11% 24% 31% 17% 2	990
February	1st to 10th	Night	12% 7% 18% 41% 19% 3	900
	11th to 20th	Night	10% 10% 23% 35% 19% 4	884
	21st to end	Night	8% 7% 24% 38% 20% 4	733
March	1st to 10th	Night	8% 8% 21% 33% 25% 5%	800
	11th to 20th	Night	8% 9% 21% 31% 26% 5%	785
	21st to end	Night	7% 7% 15% 32% 30% 9%	660
April	1st to 10th	Night	6% 8% 17% 32% 31% 6%	600
	11th to 20th	Night	7% 8% 18% 33% 30% 5%	593
	21st to end	Night	10% 6% 19% 29% 28% 8%	560
May	1st to 10th	Night	12% 7% 18% 30% 28% 6%	400
	11th to 20th	Night	11% 5% 16% 30% 32% 5%	394
	21st to end	Night	9% 6% 17% 30% 32% 6%	433
June	1st to 10th	Night	14% 4 18% 33% 28% 3	268
	11th to 20th	Night	18% 4 12% 33% 32% 3	200
	21st to end	Night	11% 4 15% 26% 41% 4	200
July	1st to 10th	Night	11% 5% 14% 33% 35% 3	195
	11th to 20th	Night	16% 7% 18% 27% 28% 4	338
	21st to end	Night	15% 6% 18% 28% 27% 6%	438
August	1st to 10th	Night	16% 6% 15% 27% 32% 4	398
	11th to 20th	Night	20% 8% 20% 26% 21% 4	594
	21st to end	Night	24% 8% 18% 24% 22% 3	660
September	1st to 10th	Night	21% 7% 18% 32% 21% 2	600
	11th to 20th	Night	14% 8% 21% 27% 24% 6%	635
	21st to end	Night	28% 9% 20% 24% 14% 4	800
October	1st to 10th	Night	21% 12% 22% 29% 14% 3	800
	11th to 20th	Night	27% 9% 18% 30% 13% 3	800
	21st to end	Night	17% 9% 22% 31% 17% 4	968
November	1st to 10th	Night	16% 8% 21% 34% 17% 4	930
	11th to 20th	Night	16% 6% 20% 29% 22% 6%	950
	21st to end	Night	14% 8% 26% 30% 18% 4	1116
December	1st to 10th	Night	15% 9% 23% 32% 20% 2	1160
	11th to 20th	Night	14% 6% 19% 38% 19% 5%	1160
	21st to end	Night	14% 9% 22% 31% 19% 5%	1276

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