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 2025-01-22.

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	19% 16% 4 8% 5% 4 4 3 4 5% 29%	109040
	Night	20% 18% 4 8% 4 4 4 3 4 5% 26%	108920
Transparency	Day	57% 7% 11% 14% 8% 2	108796
	Night	60% 8% 11% 13% 7% 1	108810
Seeing	Day	30% 18% 26% 19% 6% 1	15262
	Night	33% 12% 24% 22% 9%	23733

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	24% 31% 4 9% 4 3 2 2 2 3 15%	2289
	11th to 20th	Day	15% 21% 6% 13% 5% 3 2 2 3 4 26%	2438
	21st to end	Day	26% 23% 5% 11% 5% 4 3 3 3 4 13%	2802
February	1st to 10th	Day	25% 24% 5% 10% 4 3 3 2 3 5% 16%	1657
	11th to 20th	Day	18% 28% 4 8% 5% 3 4 3 4 4 20%	1665
	21st to end	Day	15% 29% 6% 9% 6% 6% 4 3 3 3 16%	1485
March	1st to 10th	Day	13% 22% 7% 13% 8% 5% 4 3 4 4 18%	3138
	11th to 20th	Day	13% 25% 4 8% 4 4 2 2 3 4 31%	3476
	21st to end	Day	17% 25% 6% 10% 5% 5% 4 3 4 4 17%	4010
April	1st to 10th	Day	20% 30% 5% 9% 5% 4 4 3 5% 5% 11%	2280
	11th to 20th	Day	19% 26% 5% 8% 5% 4 4 3 4 5% 17%	2274
	21st to end	Day	25% 24% 5% 8% 4 4 3 3 5% 4 15%	2593
May	1st to 10th	Day	17% 21% 4 8% 4 4 3 2 4 4 29%	4420
	11th to 20th	Day	20% 15% 3 7% 5% 4 3 4 5% 7% 26%	4377
	21st to end	Day	31% 22% 4 9% 4 3 3 2 4 4 14%	4813
June	1st to 10th	Day	30% 12% 4 8% 5% 4 4 2 5% 4 21%	2801
	11th to 20th	Day	37% 14% 4 8% 5% 3 3 3 4 4 15%	2850
	21st to end	Day	23% 10% 3 7% 5% 4 4 4 5% 6% 31%	2850
July	1st to 10th	Day	10% 5% 2 4 3 3 4 3 5% 4 59%	4740
	11th to 20th	Day	9% 4 2 3 2 2 3 2 3 5% 65%	4658
	21st to end	Day	12% 6% 2 4 3 3 3 3 5% 5% 53%	4790
August	1st to 10th	Day	9% 3 1 3 3 3 3 2 4 7% 61%	4401
	11th to 20th	Day	10% 9% 3 8% 5% 4 5% 4 5% 6% 40%	4125
	21st to end	Day	17% 8% 3 8% 4 5% 5% 4 5% 5% 36%	4321
September	1st to 10th	Day	15% 7% 3 7% 4 4 3 3 4 6% 45%	2280
	11th to 20th	Day	21% 10% 3 8% 4 4 4 3 4 4 36%	2280
	21st to end	Day	24% 11% 3 7% 3 3 4 3 4 6% 32%	2023
October	1st to 10th	Day	21% 10% 3 9% 6% 6% 5% 4 5% 6% 26%	3180
	11th to 20th	Day	26% 14% 4 9% 5% 5% 3 3 4 4 23%	3161
	21st to end	Day	23% 18% 4 12% 6% 6% 5% 3 4 4 15%	3137
November	1st to 10th	Day	30% 21% 4 7% 3 3 4 3 4 4 16%	1597
	11th to 20th	Day	28% 25% 3 8% 3 3 3 2 2 3 20%	1600
	21st to end	Day	25% 22% 5% 8% 6% 4 3 3 4 4 18%	1600
December	1st to 10th	Day	15% 16% 3 8% 6% 4 6% 4 5% 5% 28%	2620
	11th to 20th	Day	15% 24% 6% 14% 7% 6% 4 3 4 4 13%	2811
	21st to end	Day	15% 26% 8% 13% 7% 5% 4 3 4 4 10%	3498
January	1st to 10th	Night	23% 29% 6% 9% 5% 4 3 2 3 3 13%	4876
	11th to 20th	Night	19% 19% 4 7% 4 3 4 3 4 6% 26%	4677
	21st to end	Night	24% 22% 5% 11% 5% 5% 4 3 4 4 13%	4876
February	1st to 10th	Night	25% 21% 6% 9% 5% 4 3 3 3 5% 16%	2523
	11th to 20th	Night	19% 28% 5% 7% 4 4 4 2 3 4 20%	2402
	21st to end	Night	18% 26% 5% 9% 5% 3 4 4 5% 4 18%	1968
March	1st to 10th	Night	12% 19% 6% 12% 7% 6% 5% 3 4 6% 20%	3736
	11th to 20th	Night	13% 25% 4 6% 3 3 2 2 4 4 33%	3500
	21st to end	Night	19% 23% 5% 9% 6% 5% 4 3 4 4 19%	3643
April	1st to 10th	Night	16% 28% 4 10% 6% 4 4 2 4 6% 17%	1900
	11th to 20th	Night	19% 24% 3 8% 5% 4 4 2 3 5% 22%	1855
	21st to end	Night	25% 23% 5% 7% 4 4 4 3 5% 4 17%	1586
May	1st to 10th	Night	16% 22% 3 8% 4 4 3 2 3 3 32%	2540
	11th to 20th	Night	19% 17% 3 7% 4 4 4 4 4 5% 30%	2516
	21st to end	Night	30% 23% 3 7% 4 3 3 2 4 5% 17%	2762
June	1st to 10th	Night	28% 11% 3 7% 5% 4 4 3 6% 5% 24%	1377
	11th to 20th	Night	30% 12% 3 8% 5% 4 4 4 5% 6% 20%	1330
	21st to end	Night	21% 9% 2 5% 4 4 3 3 5% 6% 36%	1330
July	1st to 10th	Night	10% 5% 2 4 3 3 2 2 4 5% 60%	2220
	11th to 20th	Night	8% 4 1 2 3 2 2 2 3 4 69%	2300
	21st to end	Night	12% 4 1 4 3 3 3 3 5% 5% 57%	2762
August	1st to 10th	Night	6% 3 1 2 2 3 3 3 6% 8% 62%	2529
	11th to 20th	Night	12% 10% 2 6% 4 4 4 4 6% 7% 42%	2707
	21st to end	Night	19% 8% 3 6% 4 4 4 4 5% 7% 36%	3352
September	1st to 10th	Night	15% 8% 3 6% 4 4 3 2 4 5% 45%	1900
	11th to 20th	Night	23% 9% 3 7% 4 3 3 2 3 5% 38%	1900
	21st to end	Night	24% 10% 3 7% 5% 3 4 3 5% 6% 31%	2154
October	1st to 10th	Night	22% 11% 3 8% 4 5% 6% 5% 6% 7% 23%	3800
	11th to 20th	Night	29% 14% 4 5% 4 4 3 2 4 4 27%	3777
	21st to end	Night	23% 19% 4 9% 5% 5% 4 3 4 5% 19%	4422
November	1st to 10th	Night	32% 18% 4 8% 3 4 4 4 4 4 16%	2697
	11th to 20th	Night	29% 23% 3 7% 4 4 3 3 3 4 18%	2800
	21st to end	Night	25% 25% 4 8% 4 3 3 2 4 3 17%	2800
December	1st to 10th	Night	16% 15% 5% 8% 4 4 4 3 5% 6% 29%	4560
	11th to 20th	Night	20% 22% 6% 14% 6% 5% 4 3 3 4 13%	5385
	21st to end	Night	16% 26% 7% 13% 7% 5% 5% 3 4 5% 10%	7458

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% 5% 6% 10% 3 1	2289
	11th to 20th	Day	64% 4 9% 10% 7% 5%	2461
	21st to end	Day	76% 5% 6% 8% 5%	2802
February	1st to 10th	Day	73% 6% 7% 8% 5% 1	1657
	11th to 20th	Day	69% 7% 8% 9% 7% 1	1674
	21st to end	Day	73% 6% 7% 10% 3 1	1485
March	1st to 10th	Day	66% 8% 11% 10% 5% 1	3138
	11th to 20th	Day	59% 4 12% 21% 3	3476
	21st to end	Day	72% 7% 9% 5% 6%	4010
April	1st to 10th	Day	75% 9% 9% 6% 1	2280
	11th to 20th	Day	69% 8% 6% 9% 7% 1	2274
	21st to end	Day	72% 7% 8% 7% 5%	2593
May	1st to 10th	Day	56% 8% 11% 18% 6%	4420
	11th to 20th	Day	55% 11% 19% 14% 2	4380
	21st to end	Day	76% 7% 9% 7% 1	4814
June	1st to 10th	Day	67% 7% 11% 10% 3 2	2801
	11th to 20th	Day	73% 7% 9% 9% 2	2850
	21st to end	Day	54% 8% 14% 17% 6% 1	2850
July	1st to 10th	Day	28% 7% 8% 22% 24% 12%	4666
	11th to 20th	Day	23% 5% 9% 30% 28% 5%	4577
	21st to end	Day	30% 7% 19% 27% 14% 4	4639
August	1st to 10th	Day	23% 6% 12% 30% 27% 2	4384
	11th to 20th	Day	42% 10% 20% 17% 10% 1	4167
	21st to end	Day	49% 7% 13% 21% 9% 1	4320
September	1st to 10th	Day	40% 8% 13% 22% 13% 4	2280
	11th to 20th	Day	51% 6% 9% 16% 16% 2	2280
	21st to end	Day	53% 8% 13% 15% 9% 2	2023
October	1st to 10th	Day	56% 8% 14% 17% 6%	3180
	11th to 20th	Day	64% 7% 10% 14% 5% 1	3161
	21st to end	Day	69% 8% 9% 9% 5%	3137
November	1st to 10th	Day	73% 6% 9% 8% 4 1	1597
	11th to 20th	Day	72% 5% 7% 9% 6% 2	1600
	21st to end	Day	70% 7% 5% 10% 7% 2	1600
December	1st to 10th	Day	58% 9% 12% 12% 9%	2620
	11th to 20th	Day	72% 11% 6% 8% 3 1	2813
	21st to end	Day	76% 7% 9% 5% 2	3498
January	1st to 10th	Night	76% 6% 5% 9% 3 1	4876
	11th to 20th	Night	59% 7% 10% 12% 9% 4	4716
	21st to end	Night	75% 7% 6% 6% 5% 1	4876
February	1st to 10th	Night	71% 6% 8% 9% 5% 1	2523
	11th to 20th	Night	70% 6% 7% 10% 6% 2	2404
	21st to end	Night	68% 7% 8% 13% 4	1968
March	1st to 10th	Night	61% 10% 12% 9% 8% 1	3736
	11th to 20th	Night	55% 6% 12% 23% 4	3501
	21st to end	Night	66% 9% 14% 7% 4	3643
April	1st to 10th	Night	70% 8% 12% 8% 2	1900
	11th to 20th	Night	64% 7% 10% 10% 7% 1	1855
	21st to end	Night	71% 7% 8% 8% 5% 1	1586
May	1st to 10th	Night	55% 8% 11% 19% 7%	2540
	11th to 20th	Night	52% 14% 17% 15% 3	2516
	21st to end	Night	71% 8% 11% 9% 1	2762
June	1st to 10th	Night	61% 9% 14% 11% 4 2	1377
	11th to 20th	Night	63% 13% 11% 10% 2	1330
	21st to end	Night	48% 9% 18% 18% 6% 1	1330
July	1st to 10th	Night	27% 6% 10% 26% 19% 12%	2185
	11th to 20th	Night	21% 4 11% 28% 31% 5%	2258
	21st to end	Night	28% 7% 17% 22% 21% 4	2674
August	1st to 10th	Night	20% 6% 14% 34% 25% 1	2521
	11th to 20th	Night	37% 10% 25% 16% 10% 2	2731
	21st to end	Night	45% 9% 16% 20% 9% 1	3352
September	1st to 10th	Night	41% 7% 14% 20% 15% 4	1900
	11th to 20th	Night	50% 5% 10% 16% 16% 3	1900
	21st to end	Night	53% 8% 13% 15% 8% 2	2154
October	1st to 10th	Night	55% 9% 17% 15% 5%	3800
	11th to 20th	Night	61% 5% 9% 17% 7%	3777
	21st to end	Night	65% 6% 12% 12% 6%	4422
November	1st to 10th	Night	72% 7% 9% 8% 3 1	2697
	11th to 20th	Night	71% 6% 8% 8% 5% 2	2800
	21st to end	Night	72% 5% 5% 9% 7% 2	2800
December	1st to 10th	Night	55% 8% 13% 17% 6% 1	4560
	11th to 20th	Night	74% 7% 7% 9% 2	5382
	21st to end	Night	73% 9% 8% 7% 3	7458

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% 27% 21% 16% 5% 1	200
	11th to 20th	Day	30% 19% 26% 20% 6% 1	200
	21st to end	Day	33% 16% 30% 17% 6%	200
February	1st to 10th	Day	43% 21% 20% 14% 1	317
	11th to 20th	Day	38% 18% 25% 14% 3 1	365
	21st to end	Day	34% 22% 28% 13% 3	342
March	1st to 10th	Day	30% 22% 27% 16% 4	460
	11th to 20th	Day	32% 21% 19% 19% 8%	460
	21st to end	Day	37% 22% 20% 15% 6%	506
April	1st to 10th	Day	40% 19% 21% 16% 3	460
	11th to 20th	Day	31% 22% 26% 15% 6%	452
	21st to end	Day	40% 20% 20% 13% 6% 1	460
May	1st to 10th	Day	28% 16% 31% 21% 4	463
	11th to 20th	Day	29% 14% 27% 21% 7% 2	488
	21st to end	Day	36% 16% 23% 17% 6% 2	529
June	1st to 10th	Day	31% 23% 25% 17% 4	631
	11th to 20th	Day	40% 20% 24% 12% 4 1	680
	21st to end	Day	27% 16% 27% 22% 6% 2	680
July	1st to 10th	Day	22% 15% 34% 23% 6% 1	671
	11th to 20th	Day	16% 17% 37% 21% 6% 2	625
	21st to end	Day	14% 12% 36% 25% 11% 2	531
August	1st to 10th	Day	16% 11% 31% 27% 13% 2	487
	11th to 20th	Day	12% 11% 33% 31% 9% 3	477
	21st to end	Day	21% 19% 29% 21% 10% 1	539
September	1st to 10th	Day	20% 19% 30% 21% 9% 2	490
	11th to 20th	Day	28% 15% 27% 21% 9% 1	490
	21st to end	Day	32% 16% 23% 20% 8% 1	490
October	1st to 10th	Day	29% 17% 23% 21% 9% 1	490
	11th to 20th	Day	36% 16% 19% 20% 9% 1	490
	21st to end	Day	40% 15% 24% 15% 5%	354
November	1st to 10th	Day	40% 12% 27% 18% 3	215
	11th to 20th	Day	40% 17% 21% 13% 9% 1	200
	21st to end	Day	37% 25% 19% 9% 10% 1	200
December	1st to 10th	Day	39% 12% 18% 23% 8% 1	200
	11th to 20th	Day	40% 16% 24% 17% 3 2	200
	21st to end	Day	32% 22% 27% 16% 2	220
January	1st to 10th	Night	41% 20% 23% 13% 3	900
	11th to 20th	Night	34% 16% 29% 18% 3	845
	21st to end	Night	34% 16% 29% 20% 1	840
February	1st to 10th	Night	37% 17% 29% 14% 3	760
	11th to 20th	Night	36% 17% 27% 18% 2	744
	21st to end	Night	35% 16% 28% 18% 4	628
March	1st to 10th	Night	31% 14% 25% 22% 8%	760
	11th to 20th	Night	36% 16% 21% 21% 5%	760
	21st to end	Night	35% 14% 27% 18% 6%	836
April	1st to 10th	Night	33% 13% 23% 25% 6% 1	760
	11th to 20th	Night	32% 16% 24% 23% 5%	727
	21st to end	Night	37% 13% 21% 21% 8%	446
May	1st to 10th	Night	28% 11% 21% 27% 13%	380
	11th to 20th	Night	29% 9% 17% 30% 16%	374
	21st to end	Night	33% 8% 18% 27% 13% 1	411
June	1st to 10th	Night	32% 7% 23% 25% 12% 1	380
	11th to 20th	Night	34% 12% 17% 25% 12%	380
	21st to end	Night	24% 6% 18% 34% 19% 1	380
July	1st to 10th	Night	17% 5% 17% 36% 24% 1	370
	11th to 20th	Night	14% 6% 17% 38% 23% 2	368
	21st to end	Night	11% 3 14% 40% 31% 1	416
August	1st to 10th	Night	12% 3 12% 35% 35% 3	378
	11th to 20th	Night	13% 3 16% 37% 29% 2	495
	21st to end	Night	19% 6% 21% 32% 21%	742
September	1st to 10th	Night	21% 6% 25% 27% 20%	760
	11th to 20th	Night	27% 9% 16% 26% 19% 2	760
	21st to end	Night	32% 8% 19% 30% 11%	760
October	1st to 10th	Night	29% 9% 24% 29% 9%	760
	11th to 20th	Night	40% 10% 18% 26% 6%	760
	21st to end	Night	42% 12% 24% 18% 4	836
November	1st to 10th	Night	45% 13% 28% 14% 1	780
	11th to 20th	Night	44% 15% 25% 14% 2	800
	21st to end	Night	42% 17% 23% 15% 3	800
December	1st to 10th	Night	30% 15% 32% 19% 4	800
	11th to 20th	Night	41% 17% 27% 13% 2	847
	21st to end	Night	38% 18% 33% 10% 1	990

Page generated at 2025-01-19 00:06:46. Version ac07

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