Hope
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hope clear sky chart from 2005-11-06 to 2026-05-17.

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	17% 16% 4 9% 5% 4 4 3 4 5% 30%	135714
	Night	17% 17% 4 9% 5% 4 4 3 4 5% 27%	135807
Transparency	Day	55% 7% 12% 16% 8% 1	135429
	Night	58% 7% 12% 14% 7% 1	135670
Seeing	Day	29% 18% 27% 19% 7% 1	16963
	Night	32% 12% 23% 23% 9%	25391

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	18% 30% 5% 12% 6% 4 4 3 3 3 13%	4125
	11th to 20th	Day	11% 16% 4 9% 4 3 2 2 4 5% 39%	4450
	21st to end	Day	15% 16% 5% 12% 6% 5% 3 2 3 4 28%	5186
February	1st to 10th	Day	22% 22% 6% 10% 5% 3 3 3 3 6% 17%	1832
	11th to 20th	Day	16% 27% 4 8% 5% 4 4 3 4 4 20%	1845
	21st to end	Day	14% 28% 6% 11% 7% 6% 4 3 3 3 16%	1637
March	1st to 10th	Day	12% 19% 7% 13% 8% 6% 5% 4 4 4 19%	4618
	11th to 20th	Day	10% 25% 7% 13% 6% 5% 4 2 3 3 22%	5082
	21st to end	Day	16% 22% 6% 12% 6% 6% 5% 3 5% 5% 14%	5876
April	1st to 10th	Day	18% 28% 4 9% 5% 4 5% 3 5% 5% 13%	2520
	11th to 20th	Day	17% 25% 5% 8% 5% 4 5% 3 5% 5% 18%	2516
	21st to end	Day	23% 23% 4 8% 4 4 3 3 5% 5% 19%	2866
May	1st to 10th	Day	14% 17% 3 8% 5% 5% 5% 3 4 4 33%	6460
	11th to 20th	Day	22% 20% 5% 9% 5% 4 3 3 4 5% 19%	6362
	21st to end	Day	24% 17% 3 8% 4 4 4 3 5% 6% 21%	6903
June	1st to 10th	Day	29% 12% 3 8% 5% 4 4 2 5% 5% 23%	2949
	11th to 20th	Day	36% 14% 4 8% 5% 3 3 3 4 5% 15%	3000
	21st to end	Day	23% 10% 3 7% 5% 4 4 4 5% 6% 31%	3000
July	1st to 10th	Day	10% 4 1 4 3 3 4 3 5% 6% 57%	6780
	11th to 20th	Day	7% 3 2 3 2 3 3 2 4 5% 67%	6670
	21st to end	Day	9% 5% 2 4 3 3 3 3 5% 6% 56%	6874
August	1st to 10th	Day	9% 3 1 4 3 3 4 3 4 7% 60%	4541
	11th to 20th	Day	10% 10% 3 8% 5% 4 4 3 5% 6% 40%	4258
	21st to end	Day	16% 8% 3 8% 4 5% 5% 4 5% 5% 37%	4458
September	1st to 10th	Day	14% 7% 3 7% 3 4 3 3 5% 6% 45%	2400
	11th to 20th	Day	20% 10% 3 8% 4 4 4 2 4 4 37%	2400
	21st to end	Day	24% 11% 3 6% 3 4 4 3 4 6% 32%	2129
October	1st to 10th	Day	20% 9% 3 9% 6% 6% 5% 4 5% 6% 27%	3280
	11th to 20th	Day	26% 15% 4 9% 5% 5% 3 3 4 4 23%	3261
	21st to end	Day	23% 18% 4 13% 6% 6% 5% 3 4 4 15%	3237
November	1st to 10th	Day	30% 22% 4 7% 4 3 4 3 4 4 16%	1678
	11th to 20th	Day	29% 25% 3 8% 4 3 3 2 2 3 19%	1680
	21st to end	Day	25% 22% 5% 8% 5% 4 3 3 4 4 18%	1680
December	1st to 10th	Day	16% 17% 3 8% 6% 4 5% 4 5% 4 27%	2700
	11th to 20th	Day	15% 25% 6% 14% 7% 6% 4 3 4 4 13%	2886
	21st to end	Day	14% 26% 8% 13% 7% 5% 4 3 5% 4 10%	3575
January	1st to 10th	Night	15% 27% 7% 12% 7% 5% 4 3 4 4 13%	8770
	11th to 20th	Night	15% 15% 4 7% 3 3 4 3 4 6% 37%	8445
	21st to end	Night	14% 14% 4 11% 6% 6% 4 3 4 4 30%	8994
February	1st to 10th	Night	23% 21% 6% 9% 6% 4 3 3 4 5% 17%	2787
	11th to 20th	Night	18% 27% 5% 8% 4 4 4 2 3 4 21%	2662
	21st to end	Night	17% 26% 5% 10% 5% 3 4 3 5% 4 17%	2168
March	1st to 10th	Night	10% 18% 6% 11% 7% 6% 5% 4 5% 6% 22%	5496
	11th to 20th	Night	11% 24% 6% 12% 6% 5% 3 2 4 4 24%	5121
	21st to end	Night	20% 22% 5% 10% 6% 4 4 3 4 5% 16%	5341
April	1st to 10th	Night	16% 27% 4 9% 6% 5% 4 2 4 6% 18%	2100
	11th to 20th	Night	18% 23% 3 8% 5% 4 4 3 3 5% 22%	2052
	21st to end	Night	24% 22% 4 7% 4 4 3 3 4 4 20%	1752
May	1st to 10th	Night	13% 18% 3 8% 5% 5% 5% 3 3 4 35%	3720
	11th to 20th	Night	21% 23% 4 9% 4 4 4 3 3 4 21%	3664
	21st to end	Night	22% 18% 3 7% 4 4 3 3 5% 6% 25%	3972
June	1st to 10th	Night	26% 11% 3 6% 4 4 4 4 6% 5% 26%	1449
	11th to 20th	Night	29% 12% 3 8% 5% 4 4 4 5% 6% 21%	1400
	21st to end	Night	22% 10% 2 5% 4 4 3 3 5% 6% 35%	1400
July	1st to 10th	Night	10% 5% 1 4 3 3 3 2 5% 5% 59%	3180
	11th to 20th	Night	5% 3 1 2 3 2 2 3 4 4 70%	3288
	21st to end	Night	10% 4 1 4 3 3 4 3 4 6% 59%	3969
August	1st to 10th	Night	7% 3 1 3 3 3 3 3 6% 8% 61%	2609
	11th to 20th	Night	13% 10% 2 6% 4 4 4 4 5% 6% 42%	2793
	21st to end	Night	19% 8% 3 6% 4 4 4 4 5% 7% 37%	3457
September	1st to 10th	Night	15% 8% 3 7% 4 4 3 3 4 5% 45%	2000
	11th to 20th	Night	22% 9% 3 7% 4 3 3 2 3 6% 39%	2000
	21st to end	Night	23% 10% 3 7% 5% 4 4 3 5% 6% 31%	2268
October	1st to 10th	Night	21% 11% 3 8% 4 5% 6% 5% 6% 7% 23%	3920
	11th to 20th	Night	29% 14% 4 6% 4 4 3 2 4 4 27%	3897
	21st to end	Night	22% 19% 4 9% 5% 5% 4 3 4 5% 19%	4564
November	1st to 10th	Night	32% 18% 4 8% 3 4 4 3 3 4 16%	2836
	11th to 20th	Night	29% 22% 3 8% 4 4 3 3 3 4 17%	2940
	21st to end	Night	25% 25% 4 8% 4 3 3 2 4 3 17%	2940
December	1st to 10th	Night	16% 15% 5% 8% 4 4 4 3 5% 6% 29%	4700
	11th to 20th	Night	20% 22% 6% 14% 6% 5% 4 3 3 4 13%	5530
	21st to end	Night	15% 26% 7% 13% 7% 5% 5% 3 4 5% 10%	7623

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	76% 6% 6% 10% 2	4125
	11th to 20th	Day	49% 4 9% 23% 12% 3	4473
	21st to end	Day	61% 5% 6% 18% 10%	5187
February	1st to 10th	Day	71% 6% 7% 8% 6% 2	1832
	11th to 20th	Day	67% 6% 8% 10% 7% 1	1854
	21st to end	Day	73% 6% 7% 9% 3 1	1637
March	1st to 10th	Day	64% 8% 10% 12% 7%	4618
	11th to 20th	Day	68% 5% 9% 15% 3	5082
	21st to end	Day	70% 9% 9% 7% 5%	5876
April	1st to 10th	Day	73% 9% 9% 8% 1	2520
	11th to 20th	Day	66% 9% 7% 10% 7% 1	2516
	21st to end	Day	68% 7% 9% 9% 6% 1	2866
May	1st to 10th	Day	50% 9% 14% 22% 5%	6460
	11th to 20th	Day	66% 9% 14% 10% 1	6365
	21st to end	Day	64% 8% 15% 12% 1	6904
June	1st to 10th	Day	64% 7% 11% 11% 4 2	2949
	11th to 20th	Day	72% 7% 9% 10% 2	3000
	21st to end	Day	54% 8% 14% 16% 6% 1	3000
July	1st to 10th	Day	27% 6% 17% 20% 20% 8%	6706
	11th to 20th	Day	21% 5% 17% 29% 25% 3	6589
	21st to end	Day	26% 6% 24% 28% 13% 3	6681
August	1st to 10th	Day	24% 6% 12% 30% 26% 2	4524
	11th to 20th	Day	42% 9% 20% 17% 10% 2	4300
	21st to end	Day	48% 7% 13% 21% 10% 2	4457
September	1st to 10th	Day	39% 8% 13% 22% 14% 4	2400
	11th to 20th	Day	50% 6% 9% 17% 16% 2	2400
	21st to end	Day	53% 8% 14% 16% 8% 2	2129
October	1st to 10th	Day	55% 8% 14% 16% 6%	3280
	11th to 20th	Day	64% 7% 9% 14% 5% 1	3261
	21st to end	Day	69% 8% 8% 9% 5%	3237
November	1st to 10th	Day	72% 6% 9% 8% 4 1	1678
	11th to 20th	Day	73% 5% 7% 9% 5% 2	1680
	21st to end	Day	70% 7% 6% 10% 6% 2	1680
December	1st to 10th	Day	59% 8% 12% 12% 9%	2700
	11th to 20th	Day	72% 10% 7% 7% 3 1	2888
	21st to end	Day	75% 7% 10% 5% 2	3575
January	1st to 10th	Night	74% 7% 7% 9% 3 1	8770
	11th to 20th	Night	48% 7% 11% 19% 13% 2	8484
	21st to end	Night	57% 6% 10% 15% 11%	8994
February	1st to 10th	Night	70% 6% 8% 10% 6% 1	2787
	11th to 20th	Night	69% 5% 7% 10% 7% 2	2664
	21st to end	Night	69% 7% 8% 13% 4	2168
March	1st to 10th	Night	56% 10% 13% 12% 8% 1	5496
	11th to 20th	Night	63% 7% 10% 17% 3	5122
	21st to end	Night	68% 8% 13% 8% 3	5341
April	1st to 10th	Night	69% 7% 13% 9% 2	2100
	11th to 20th	Night	63% 7% 12% 10% 7% 1	2052
	21st to end	Night	67% 7% 10% 9% 5% 1	1752
May	1st to 10th	Night	50% 8% 14% 19% 8%	3717
	11th to 20th	Night	64% 11% 13% 10% 2	3664
	21st to end	Night	60% 8% 18% 12% 1	3972
June	1st to 10th	Night	58% 9% 14% 11% 5% 2	1449
	11th to 20th	Night	62% 13% 11% 11% 3	1400
	21st to end	Night	49% 9% 18% 17% 6% 1	1400
July	1st to 10th	Night	26% 6% 18% 25% 17% 8%	3145
	11th to 20th	Night	18% 6% 20% 28% 26% 3	3246
	21st to end	Night	26% 7% 22% 27% 16% 3	3857
August	1st to 10th	Night	21% 6% 14% 34% 24% 1	2601
	11th to 20th	Night	38% 10% 25% 15% 10% 2	2817
	21st to end	Night	44% 9% 16% 20% 9% 2	3457
September	1st to 10th	Night	40% 7% 14% 20% 15% 3	2000
	11th to 20th	Night	49% 5% 11% 17% 15% 3	2000
	21st to end	Night	54% 8% 13% 15% 8% 2	2268
October	1st to 10th	Night	54% 9% 17% 15% 5%	3920
	11th to 20th	Night	61% 5% 9% 17% 8%	3897
	21st to end	Night	65% 6% 12% 12% 5%	4564
November	1st to 10th	Night	72% 7% 9% 8% 3 1	2836
	11th to 20th	Night	71% 6% 8% 8% 5% 1	2940
	21st to end	Night	72% 5% 5% 9% 7% 2	2940
December	1st to 10th	Night	56% 7% 13% 17% 6% 1	4700
	11th to 20th	Night	75% 7% 7% 9% 2	5527
	21st to end	Night	73% 9% 8% 7% 3	7623

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	31% 25% 23% 15% 5%	220
	11th to 20th	Day	29% 17% 29% 19% 6%	220
	21st to end	Day	27% 17% 33% 17% 6%	242
February	1st to 10th	Day	39% 20% 21% 17% 3	372
	11th to 20th	Day	34% 19% 27% 16% 4	425
	21st to end	Day	34% 22% 28% 13% 3	398
March	1st to 10th	Day	31% 21% 26% 17% 5%	540
	11th to 20th	Day	36% 20% 18% 18% 7%	540
	21st to end	Day	37% 22% 22% 14% 5%	594
April	1st to 10th	Day	38% 19% 21% 17% 5%	540
	11th to 20th	Day	30% 21% 27% 14% 7%	532
	21st to end	Day	37% 20% 21% 15% 6% 1	540
May	1st to 10th	Day	27% 16% 31% 21% 5%	543
	11th to 20th	Day	30% 15% 26% 21% 6% 2	553
	21st to end	Day	35% 17% 24% 17% 6% 2	573
June	1st to 10th	Day	30% 22% 26% 18% 5%	679
	11th to 20th	Day	38% 21% 25% 12% 3 1	730
	21st to end	Day	27% 16% 27% 22% 6% 2	730
July	1st to 10th	Day	21% 15% 35% 23% 6% 1	721
	11th to 20th	Day	16% 17% 39% 21% 6% 2	673
	21st to end	Day	13% 12% 37% 25% 11% 3	575
August	1st to 10th	Day	16% 11% 31% 27% 13% 2	527
	11th to 20th	Day	13% 12% 33% 30% 9% 2	517
	21st to end	Day	20% 17% 29% 22% 11% 1	583
September	1st to 10th	Day	18% 17% 29% 22% 11% 3	530
	11th to 20th	Day	26% 15% 27% 22% 9% 1	530
	21st to end	Day	31% 16% 25% 20% 7% 1	530
October	1st to 10th	Day	28% 18% 24% 20% 9% 1	530
	11th to 20th	Day	37% 16% 19% 18% 10% 1	530
	21st to end	Day	39% 17% 24% 15% 4	388
November	1st to 10th	Day	41% 12% 28% 17% 3	236
	11th to 20th	Day	41% 16% 20% 13% 9%	220
	21st to end	Day	37% 25% 19% 9% 9%	220
December	1st to 10th	Day	42% 12% 16% 21% 7% 1	220
	11th to 20th	Day	42% 16% 23% 15% 2 1	220
	21st to end	Day	31% 23% 26% 17% 2	242
January	1st to 10th	Night	41% 19% 24% 13% 3	950
	11th to 20th	Night	34% 15% 29% 19% 3	889
	21st to end	Night	31% 15% 29% 22% 2	924
February	1st to 10th	Night	35% 17% 29% 16% 3	840
	11th to 20th	Night	34% 16% 27% 21% 2	824
	21st to end	Night	36% 15% 27% 19% 4	692
March	1st to 10th	Night	31% 14% 24% 23% 8%	840
	11th to 20th	Night	37% 15% 21% 21% 5%	840
	21st to end	Night	35% 14% 26% 19% 6%	924
April	1st to 10th	Night	32% 13% 22% 25% 8% 1	840
	11th to 20th	Night	31% 15% 23% 24% 6%	804
	21st to end	Night	36% 12% 20% 22% 10%	492
May	1st to 10th	Night	26% 11% 20% 28% 15%	420
	11th to 20th	Night	30% 9% 16% 29% 16%	406
	21st to end	Night	32% 8% 18% 28% 14% 1	433
June	1st to 10th	Night	31% 7% 23% 27% 13% 1	400
	11th to 20th	Night	32% 12% 17% 26% 14%	400
	21st to end	Night	25% 6% 18% 33% 20% 1	400
July	1st to 10th	Night	16% 5% 16% 36% 25% 1	390
	11th to 20th	Night	14% 6% 17% 38% 23% 2	388
	21st to end	Night	11% 3 14% 39% 32% 1	438
August	1st to 10th	Night	12% 3 12% 35% 34% 3	398
	11th to 20th	Night	14% 3 16% 37% 28% 2	521
	21st to end	Night	19% 6% 20% 32% 23%	781
September	1st to 10th	Night	22% 6% 24% 27% 21% 1	800
	11th to 20th	Night	26% 9% 16% 27% 20% 2	800
	21st to end	Night	31% 9% 19% 31% 10%	800
October	1st to 10th	Night	28% 9% 25% 30% 9%	800
	11th to 20th	Night	39% 10% 18% 26% 6%	800
	21st to end	Night	41% 12% 24% 19% 4	880
November	1st to 10th	Night	45% 12% 28% 14% 1	820
	11th to 20th	Night	43% 15% 25% 15% 2	840
	21st to end	Night	42% 17% 23% 15% 3	840
December	1st to 10th	Night	32% 15% 30% 19% 4	840
	11th to 20th	Night	42% 16% 26% 13% 2	892
	21st to end	Night	37% 18% 33% 12% 1	1045

Page generated at 2026-05-13 22:58:56. Version ac07

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