Fishtrap
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fishtrap clear sky chart from 2005-11-06 to 2024-11-10.

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	8% 7% 3 6% 4 4 4 4 5% 7% 48%	105135
	Night	11% 8% 3 7% 4 4 4 3 5% 7% 43%	102570
Transparency	Day	35% 7% 12% 22% 16% 8%	104903
	Night	40% 7% 11% 21% 15% 7%	102448
Seeing	Day	12% 8% 23% 27% 22% 8%	14585
	Night	15% 6% 21% 34% 21% 3	23787

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	17% 18% 5% 11% 6% 5% 5% 4 5% 6% 18%	2539
	11th to 20th	Day	20% 13% 5% 10% 6% 6% 6% 4 5% 5% 21%	2516
	21st to end	Day	23% 17% 7% 12% 5% 4 3 3 4 4 17%	2794
February	1st to 10th	Day	15% 12% 5% 10% 6% 7% 5% 4 5% 6% 26%	1553
	11th to 20th	Day	14% 13% 4 9% 6% 4 6% 4 5% 6% 30%	1766
	21st to end	Day	12% 15% 5% 9% 4 5% 4 4 5% 6% 31%	1570
March	1st to 10th	Day	9% 11% 3 7% 5% 6% 6% 5% 7% 9% 33%	3138
	11th to 20th	Day	7% 7% 2 5% 4 5% 5% 3 5% 6% 51%	3250
	21st to end	Day	11% 11% 4 9% 7% 6% 6% 5% 6% 7% 28%	4165
April	1st to 10th	Day	10% 11% 4 9% 6% 6% 6% 4 6% 9% 30%	2280
	11th to 20th	Day	8% 8% 3 8% 5% 5% 5% 3 8% 7% 40%	2290
	21st to end	Day	9% 8% 3 7% 4 5% 4 5% 5% 7% 42%	2470
May	1st to 10th	Day	8% 6% 2 6% 4 4 5% 4 6% 8% 47%	4357
	11th to 20th	Day	6% 4 2 5% 5% 4 4 4 6% 8% 51%	4377
	21st to end	Day	8% 7% 3 7% 5% 6% 6% 5% 7% 8% 39%	4813
June	1st to 10th	Day	12% 8% 3 6% 5% 4 4 4 5% 7% 43%	2722
	11th to 20th	Day	9% 7% 3 5% 4 3 4 4 6% 7% 46%	2850
	21st to end	Day	4 3 2 5% 3 4 4 4 5% 7% 60%	2725
July	1st to 10th	Day	2 2 1 2 2 2 2 2 4 4 79%	4420
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 80%	4420
	21st to end	Day	1 1 1 2 2 2 2 2 3 5% 78%	4790
August	1st to 10th	Day	3 2 1 3 1 2 3 2 4 5% 73%	4401
	11th to 20th	Day	2 2 1 3 2 2 3 3 5% 7% 69%	4161
	21st to end	Day	3 3 1 4 3 3 4 3 5% 6% 65%	4194
September	1st to 10th	Day	4 3 1 3 2 2 2 2 4 7% 70%	2280
	11th to 20th	Day	5% 4 2 5% 3 4 4 4 5% 7% 55%	2190
	21st to end	Day	5% 5% 2 6% 4 3 4 4 6% 7% 53%	2090
October	1st to 10th	Day	6% 4 1 6% 4 3 3 2 6% 7% 59%	3318
	11th to 20th	Day	7% 5% 2 6% 4 5% 6% 4 6% 7% 47%	3010
	21st to end	Day	12% 8% 3 6% 5% 4 5% 4 5% 7% 42%	3101
November	1st to 10th	Day	15% 9% 3 9% 5% 4 5% 4 6% 8% 33%	1755
	11th to 20th	Day	17% 12% 4 8% 5% 4 5% 5% 5% 4 30%	1606
	21st to end	Day	14% 14% 4 10% 6% 4 5% 5% 6% 7% 25%	1482
December	1st to 10th	Day	15% 16% 5% 11% 7% 7% 5% 3 5% 6% 20%	1330
	11th to 20th	Day	18% 17% 6% 15% 7% 5% 5% 4 4 5% 15%	1682
	21st to end	Day	15% 17% 6% 12% 6% 5% 5% 4 5% 6% 19%	2730
January	1st to 10th	Night	20% 17% 6% 10% 5% 5% 4 3 5% 5% 18%	4406
	11th to 20th	Night	18% 14% 4 11% 5% 5% 4 3 4 6% 26%	4382
	21st to end	Night	20% 16% 6% 9% 5% 5% 5% 3 5% 6% 21%	4862
February	1st to 10th	Night	16% 15% 4 8% 5% 4 4 4 6% 6% 29%	2623
	11th to 20th	Night	12% 11% 5% 8% 5% 4 4 4 6% 6% 34%	2301
	21st to end	Night	11% 13% 3 9% 5% 5% 4 4 6% 8% 33%	1884
March	1st to 10th	Night	9% 8% 2 8% 5% 5% 5% 4 5% 8% 40%	3736
	11th to 20th	Night	9% 6% 2 5% 4 3 3 3 4 6% 54%	3725
	21st to end	Night	9% 8% 3 9% 8% 7% 7% 5% 7% 9% 26%	3488
April	1st to 10th	Night	10% 10% 3 7% 6% 5% 5% 4 6% 8% 36%	1900
	11th to 20th	Night	8% 11% 3 7% 5% 3 5% 3 5% 6% 44%	1840
	21st to end	Night	7% 7% 4 7% 5% 5% 5% 5% 6% 7% 42%	1710
May	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 4 6% 8% 45%	2590
	11th to 20th	Night	6% 4 2 5% 5% 3 4 3 6% 9% 52%	2516
	21st to end	Night	8% 6% 2 6% 4 5% 4 4 6% 9% 46%	2762
June	1st to 10th	Night	10% 7% 2 6% 4 5% 4 4 5% 7% 47%	1454
	11th to 20th	Night	8% 5% 2 6% 5% 4 5% 4 5% 7% 48%	1330
	21st to end	Night	6% 3 2 4 4 3 5% 4 7% 6% 56%	1447
July	1st to 10th	Night	2 1 2 1 2 3 2 4 5% 79%	2540
	11th to 20th	Night	2 1 1 2 1 2 2 1 3 4 82%	2540
	21st to end	Night	1 2 1 2 2 1 2 2 3 4 81%	2762
August	1st to 10th	Night	4 3 1 3 1 2 2 2 4 6% 72%	2529
	11th to 20th	Night	3 3 2 4 3 3 4 4 5% 6% 64%	2671
	21st to end	Night	2 3 1 3 3 3 4 3 5% 6% 67%	3481
September	1st to 10th	Night	3 2 1 3 2 3 3 3 4 7% 69%	1900
	11th to 20th	Night	4 4 2 6% 4 4 4 3 5% 6% 57%	1990
	21st to end	Night	8% 4 2 5% 3 4 4 2 6% 7% 54%	2090
October	1st to 10th	Night	6% 3 1 4 3 3 3 3 5% 7% 62%	3645
	11th to 20th	Night	9% 4 2 5% 4 4 5% 4 6% 8% 50%	3922
	21st to end	Night	12% 5% 2 6% 5% 4 5% 4 6% 6% 47%	4457
November	1st to 10th	Night	17% 9% 3 7% 5% 4 4 4 5% 7% 34%	2528
	11th to 20th	Night	16% 9% 4 8% 6% 5% 5% 4 5% 6% 31%	2572
	21st to end	Night	16% 11% 5% 8% 6% 5% 4 4 5% 6% 30%	2674
December	1st to 10th	Night	14% 12% 4 9% 5% 5% 5% 4 6% 7% 28%	2850
	11th to 20th	Night	20% 14% 6% 13% 7% 5% 6% 4 5% 6% 14%	3510
	21st to end	Night	18% 14% 5% 13% 6% 5% 5% 4 5% 6% 21%	4953

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	63% 12% 12% 10% 2	2539
	11th to 20th	Day	62% 9% 12% 13% 3 2	2540
	21st to end	Day	70% 8% 13% 8% 2	2794
February	1st to 10th	Day	58% 10% 15% 11% 5% 1	1553
	11th to 20th	Day	54% 9% 14% 16% 7%	1775
	21st to end	Day	52% 9% 12% 18% 8% 1	1570
March	1st to 10th	Day	42% 9% 13% 23% 12% 1	3138
	11th to 20th	Day	33% 7% 15% 38% 7%	3250
	21st to end	Day	51% 11% 16% 15% 6% 1	4165
April	1st to 10th	Day	50% 8% 14% 20% 8% 1	2280
	11th to 20th	Day	41% 5% 16% 22% 13% 2	2290
	21st to end	Day	39% 8% 14% 24% 12% 2	2470
May	1st to 10th	Day	30% 9% 12% 31% 17% 1	4357
	11th to 20th	Day	26% 7% 15% 31% 19% 2	4380
	21st to end	Day	37% 11% 18% 26% 8% 1	4814
June	1st to 10th	Day	41% 6% 11% 23% 17% 3	2722
	11th to 20th	Day	34% 7% 13% 26% 16% 4	2850
	21st to end	Day	23% 5% 11% 29% 25% 7%	2725
July	1st to 10th	Day	11% 3 5% 17% 26% 39%	4351
	11th to 20th	Day	10% 2 5% 11% 27% 45%	4345
	21st to end	Day	12% 2 5% 17% 36% 28%	4639
August	1st to 10th	Day	15% 2 5% 18% 39% 21%	4384
	11th to 20th	Day	17% 3 6% 38% 30% 7%	4203
	21st to end	Day	20% 3 9% 30% 31% 7%	4193
September	1st to 10th	Day	16% 4 10% 28% 28% 13%	2280
	11th to 20th	Day	27% 5% 15% 25% 23% 7%	2190
	21st to end	Day	29% 7% 17% 29% 14% 5%	2090
October	1st to 10th	Day	26% 4 11% 36% 22% 2	3318
	11th to 20th	Day	36% 4 19% 26% 14% 1	3010
	21st to end	Day	42% 5% 13% 26% 12% 2	3101
November	1st to 10th	Day	48% 9% 16% 20% 5% 1	1755
	11th to 20th	Day	56% 9% 16% 14% 4 2	1606
	21st to end	Day	55% 12% 16% 12% 4 1	1482
December	1st to 10th	Day	64% 9% 11% 11% 5%	1330
	11th to 20th	Day	72% 9% 10% 7% 1	1684
	21st to end	Day	63% 10% 13% 10% 4	2730
January	1st to 10th	Night	66% 9% 11% 12% 1 1	4406
	11th to 20th	Night	58% 8% 15% 13% 5% 1	4420
	21st to end	Night	63% 11% 14% 10% 2 1	4862
February	1st to 10th	Night	55% 8% 16% 15% 6% 1	2623
	11th to 20th	Night	48% 8% 19% 15% 9%	2303
	21st to end	Night	48% 7% 15% 20% 9% 1	1884
March	1st to 10th	Night	37% 8% 13% 26% 13% 1	3736
	11th to 20th	Night	31% 6% 12% 36% 14% 1	3726
	21st to end	Night	47% 12% 15% 20% 5%	3488
April	1st to 10th	Night	43% 7% 13% 25% 11% 1	1900
	11th to 20th	Night	39% 7% 11% 24% 17% 3	1840
	21st to end	Night	38% 8% 12% 22% 17% 3	1710
May	1st to 10th	Night	32% 8% 10% 27% 19% 3	2590
	11th to 20th	Night	26% 6% 11% 30% 24% 3	2516
	21st to end	Night	31% 11% 17% 28% 12% 1	2762
June	1st to 10th	Night	36% 6% 9% 22% 22% 4	1454
	11th to 20th	Night	35% 6% 8% 26% 20% 6%	1330
	21st to end	Night	25% 6% 9% 25% 26% 10%	1447
July	1st to 10th	Night	10% 3 3 13% 28% 43%	2500
	11th to 20th	Night	9% 2 4 10% 20% 56%	2492
	21st to end	Night	10% 1 3 15% 30% 41%	2674
August	1st to 10th	Night	15% 2 4 12% 38% 29%	2521
	11th to 20th	Night	21% 3 4 25% 35% 11%	2695
	21st to end	Night	19% 3 8% 27% 28% 15%	3481
September	1st to 10th	Night	16% 4 7% 26% 29% 18%	1900
	11th to 20th	Night	27% 4 10% 24% 23% 11%	1990
	21st to end	Night	28% 5% 13% 29% 17% 8%	2090
October	1st to 10th	Night	23% 3 8% 35% 29% 2	3645
	11th to 20th	Night	32% 4 15% 24% 22% 2	3922
	21st to end	Night	38% 5% 10% 33% 13% 2	4457
November	1st to 10th	Night	48% 8% 16% 20% 7% 1	2528
	11th to 20th	Night	52% 9% 16% 16% 6% 1	2572
	21st to end	Night	54% 8% 15% 17% 6%	2674
December	1st to 10th	Night	55% 10% 14% 17% 5%	2850
	11th to 20th	Night	69% 9% 12% 8% 2	3507
	21st to end	Night	61% 11% 13% 11% 4	4953

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	24% 7% 32% 20% 13% 3	180
	11th to 20th	Day	26% 7% 20% 26% 17% 4	180
	21st to end	Day	27% 10% 24% 23% 16% 1	198
February	1st to 10th	Day	22% 8% 33% 26% 9% 2	213
	11th to 20th	Day	22% 13% 27% 23% 14% 2	414
	21st to end	Day	17% 15% 28% 23% 14% 3	382
March	1st to 10th	Day	17% 11% 34% 20% 14% 4	460
	11th to 20th	Day	15% 9% 24% 27% 18% 7%	460
	21st to end	Day	16% 15% 28% 25% 13% 2	506
April	1st to 10th	Day	16% 13% 26% 27% 14% 5%	460
	11th to 20th	Day	11% 15% 30% 23% 15% 6%	452
	21st to end	Day	10% 11% 27% 28% 19% 5%	460
May	1st to 10th	Day	9% 7% 23% 31% 23% 7%	463
	11th to 20th	Day	14% 7% 19% 28% 21% 12%	488
	21st to end	Day	9% 7% 18% 28% 25% 13%	529
June	1st to 10th	Day	13% 7% 21% 25% 24% 11%	552
	11th to 20th	Day	12% 8% 28% 30% 15% 6%	680
	21st to end	Day	4 4 21% 28% 32% 12%	555
July	1st to 10th	Day	3 3 18% 35% 35% 7%	486
	11th to 20th	Day	3 4 17% 34% 31% 11%	484
	21st to end	Day	2 2 15% 29% 37% 16%	531
August	1st to 10th	Day	5% 4 13% 30% 31% 17%	487
	11th to 20th	Day	2 2 14% 29% 33% 20%	477
	21st to end	Day	6% 5% 21% 25% 28% 15%	539
September	1st to 10th	Day	6% 5% 18% 28% 29% 14%	490
	11th to 20th	Day	8% 4 24% 24% 28% 12%	490
	21st to end	Day	8% 8% 24% 28% 24% 8%	490
October	1st to 10th	Day	12% 6% 24% 26% 24% 8%	490
	11th to 20th	Day	14% 8% 20% 25% 26% 8%	403
	21st to end	Day	19% 10% 23% 31% 12% 5%	330
November	1st to 10th	Day	21% 9% 22% 32% 14% 2	297
	11th to 20th	Day	25% 10% 20% 24% 15% 5%	221
	21st to end	Day	19% 11% 19% 28% 18% 4	180
December	1st to 10th	Day	19% 11% 22% 26% 16% 7%	180
	11th to 20th	Day	28% 10% 23% 24% 13% 1	180
	21st to end	Day	26% 7% 28% 25% 11% 4	198
January	1st to 10th	Night	28% 10% 22% 26% 11% 2	760
	11th to 20th	Night	24% 7% 21% 28% 18% 1	760
	21st to end	Night	21% 4 21% 34% 17% 2	836
February	1st to 10th	Night	22% 10% 24% 30% 13% 1	760
	11th to 20th	Night	19% 8% 23% 31% 17% 1	744
	21st to end	Night	17% 10% 22% 33% 16% 3	628
March	1st to 10th	Night	17% 7% 24% 33% 16% 3	760
	11th to 20th	Night	15% 8% 24% 31% 20% 2	760
	21st to end	Night	17% 7% 28% 34% 13% 2	836
April	1st to 10th	Night	16% 5% 25% 33% 19% 2	760
	11th to 20th	Night	12% 6% 33% 32% 14% 2	712
	21st to end	Night	9% 8% 26% 34% 21% 2	570
May	1st to 10th	Night	7% 5% 28% 32% 24% 4	417
	11th to 20th	Night	11% 6% 14% 33% 28% 7%	374
	21st to end	Night	8% 6% 20% 37% 26% 3	411
June	1st to 10th	Night	13% 3 22% 36% 24% 3	380
	11th to 20th	Night	12% 5% 28% 34% 18% 3	380
	21st to end	Night	8% 4 16% 40% 29% 3	380
July	1st to 10th	Night	4 1 14% 43% 35% 4	370
	11th to 20th	Night	3 2 14% 49% 29% 2	368
	21st to end	Night	1 1 11% 45% 36% 5%	416
August	1st to 10th	Night	3 3 11% 37% 40% 7%	378
	11th to 20th	Night	3 2 10% 39% 35% 10%	472
	21st to end	Night	3 3 17% 38% 33% 5%	819
September	1st to 10th	Night	4 2 13% 44% 31% 6%	760
	11th to 20th	Night	6% 4 17% 33% 33% 8%	760
	21st to end	Night	9% 5% 20% 32% 28% 5%	760
October	1st to 10th	Night	12% 4 17% 38% 26% 3	760
	11th to 20th	Night	12% 5% 21% 35% 24% 3	760
	21st to end	Night	16% 6% 25% 35% 15% 4	836
November	1st to 10th	Night	22% 7% 20% 38% 13% 1	778
	11th to 20th	Night	21% 8% 26% 29% 13% 2	760
	21st to end	Night	21% 6% 20% 32% 19% 2	774
December	1st to 10th	Night	19% 7% 21% 36% 15% 2	950
	11th to 20th	Night	26% 7% 22% 33% 12% 1	950
	21st to end	Night	31% 10% 19% 30% 10% 1	888

Page generated at 2024-11-07 03:55:49. Version ac07

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