Snoqualmie Point Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Snoqualmie Point Park clear sky chart from 2005-11-06 to 2024-12-09.

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	25% 11% 3 7% 4 4 4 3 4 5% 30%	106339
	Night	28% 12% 3 7% 4 3 3 3 4 5% 28%	102037
Transparency	Day	56% 6% 11% 16% 9% 2	106099
	Night	59% 6% 11% 14% 8% 2	101923
Seeing	Day	29% 10% 22% 25% 12% 2	15030
	Night	34% 7% 16% 25% 16% 2	23449

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	42% 19% 4 8% 3 3 3 2 2 3 11%	2539
	11th to 20th	Day	27% 15% 4 9% 4 3 3 3 3 6% 22%	2516
	21st to end	Day	43% 15% 4 7% 3 3 2 2 3 4 12%	2836
February	1st to 10th	Day	35% 14% 5% 8% 4 4 3 3 4 5% 15%	1710
	11th to 20th	Day	33% 18% 3 7% 5% 3 2 3 4 4 18%	1665
	21st to end	Day	32% 19% 4 8% 4 4 3 2 3 3 18%	1497
March	1st to 10th	Day	21% 18% 5% 10% 6% 5% 5% 3 4 5% 19%	3182
	11th to 20th	Day	22% 16% 3 7% 4 3 3 2 2 3 35%	3490
	21st to end	Day	30% 18% 4 8% 5% 4 4 3 4 5% 14%	3977
April	1st to 10th	Day	30% 18% 4 8% 6% 4 5% 3 4 4 14%	2280
	11th to 20th	Day	26% 16% 4 7% 5% 4 4 3 5% 4 21%	2252
	21st to end	Day	29% 16% 4 10% 6% 4 4 3 4 4 17%	2527
May	1st to 10th	Day	23% 12% 3 6% 5% 4 4 4 4 5% 29%	4420
	11th to 20th	Day	23% 9% 3 6% 4 4 4 4 5% 8% 30%	4377
	21st to end	Day	34% 14% 4 8% 4 4 4 3 4 5% 15%	4813
June	1st to 10th	Day	30% 11% 3 7% 4 4 4 4 5% 5% 22%	2660
	11th to 20th	Day	31% 13% 3 9% 5% 4 4 4 4 5% 17%	2824
	21st to end	Day	17% 10% 3 7% 4 4 4 4 5% 7% 34%	2850
July	1st to 10th	Day	10% 5% 2 4 3 3 3 2 3 4 60%	4740
	11th to 20th	Day	8% 5% 1 4 3 3 3 2 3 4 65%	4425
	21st to end	Day	15% 5% 1 4 3 3 3 3 4 5% 53%	4790
August	1st to 10th	Day	8% 4 1 4 3 3 4 3 5% 6% 60%	4356
	11th to 20th	Day	17% 7% 3 8% 4 4 5% 4 6% 7% 36%	4026
	21st to end	Day	21% 8% 2 6% 3 3 3 3 4 5% 41%	4304
September	1st to 10th	Day	14% 7% 2 6% 3 3 3 3 5% 6% 48%	2280
	11th to 20th	Day	20% 9% 3 6% 5% 4 4 4 4 6% 36%	2280
	21st to end	Day	22% 9% 3 6% 4 4 3 3 4 5% 37%	2017
October	1st to 10th	Day	21% 8% 2 5% 3 4 4 3 5% 8% 38%	3180
	11th to 20th	Day	33% 9% 2 7% 4 3 3 3 4 5% 26%	3161
	21st to end	Day	35% 11% 3 8% 4 4 4 3 4 5% 20%	3227
November	1st to 10th	Day	40% 12% 3 6% 4 3 4 4 3 5% 16%	1635
	11th to 20th	Day	39% 14% 3 6% 4 3 3 3 3 4 19%	1600
	21st to end	Day	35% 15% 4 6% 3 4 4 2 3 4 20%	1600
December	1st to 10th	Day	32% 13% 4 5% 4 3 3 3 5% 4 24%	1584
	11th to 20th	Day	35% 13% 4 8% 4 3 3 3 5% 3 19%	1925
	21st to end	Day	29% 16% 4 9% 6% 5% 4 3 4 4 16%	2794
January	1st to 10th	Night	43% 19% 3 7% 4 3 3 2 3 3 10%	4406
	11th to 20th	Night	30% 16% 3 8% 4 2 3 3 4 6% 21%	4382
	21st to end	Night	40% 13% 3 8% 4 4 4 2 4 5% 14%	4817
February	1st to 10th	Night	34% 16% 3 8% 5% 3 4 2 4 5% 16%	2470
	11th to 20th	Night	32% 15% 3 7% 4 4 3 2 4 4 21%	2402
	21st to end	Night	32% 19% 3 6% 4 3 3 3 4 4 18%	1956
March	1st to 10th	Night	20% 17% 4 8% 6% 5% 5% 4 5% 5% 19%	3688
	11th to 20th	Night	25% 13% 3 6% 3 3 2 1 3 4 37%	3489
	21st to end	Night	34% 17% 4 8% 4 3 3 3 4 4 14%	3675
April	1st to 10th	Night	30% 17% 4 8% 4 4 3 3 6% 6% 16%	1900
	11th to 20th	Night	26% 16% 3 7% 4 4 4 3 4 5% 25%	1879
	21st to end	Night	33% 12% 3 6% 5% 4 4 3 5% 5% 19%	1649
May	1st to 10th	Night	27% 11% 2 6% 4 2 2 2 3 4 37%	2540
	11th to 20th	Night	21% 11% 3 6% 3 3 4 3 4 6% 34%	2516
	21st to end	Night	35% 17% 4 9% 4 2 3 2 2 4 18%	2762
June	1st to 10th	Night	28% 10% 3 8% 6% 5% 4 2 3 4 27%	1520
	11th to 20th	Night	29% 13% 4 8% 5% 4 4 4 3 5% 22%	1350
	21st to end	Night	18% 8% 2 6% 4 4 3 3 4 8% 40%	1330
July	1st to 10th	Night	14% 6% 1 5% 2 2 2 2 3 4 59%	2220
	11th to 20th	Night	6% 4 1 3 2 2 2 2 3 3 71%	2532
	21st to end	Night	19% 4 1 3 2 2 2 2 4 5% 56%	2762
August	1st to 10th	Night	7% 4 1 3 2 2 2 2 4 6% 66%	2560
	11th to 20th	Night	20% 6% 2 5% 3 3 3 2 3 5% 47%	2812
	21st to end	Night	25% 7% 2 5% 2 2 2 2 3 4 48%	3370
September	1st to 10th	Night	15% 5% 2 6% 3 3 3 3 3 5% 52%	1900
	11th to 20th	Night	22% 9% 2 7% 3 3 4 3 4 4 39%	1900
	21st to end	Night	22% 8% 3 7% 4 3 3 3 4 5% 39%	2159
October	1st to 10th	Night	21% 9% 2 5% 4 3 3 3 5% 8% 37%	3800
	11th to 20th	Night	34% 8% 2 5% 3 4 4 3 4 5% 29%	3777
	21st to end	Night	37% 13% 3 6% 3 3 3 3 4 5% 21%	4335
November	1st to 10th	Night	37% 12% 3 7% 4 4 4 3 4 4 17%	2659
	11th to 20th	Night	39% 12% 3 7% 4 3 3 2 3 3 20%	2800
	21st to end	Night	35% 13% 3 7% 4 4 4 2 4 4 20%	2800
December	1st to 10th	Night	31% 12% 3 7% 5% 4 3 3 4 4 23%	2778
	11th to 20th	Night	34% 16% 3 9% 4 3 4 2 3 4 17%	3280
	21st to end	Night	30% 17% 4 9% 5% 4 5% 4 4 4 14%	4862

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	78% 6% 5% 7% 3 1	2539
	11th to 20th	Day	64% 6% 9% 13% 7% 2	2540
	21st to end	Day	78% 4 6% 7% 4 1	2836
February	1st to 10th	Day	73% 5% 10% 8% 3 1	1710
	11th to 20th	Day	72% 5% 7% 9% 6% 1	1674
	21st to end	Day	72% 5% 7% 11% 4	1497
March	1st to 10th	Day	63% 9% 12% 12% 4	3182
	11th to 20th	Day	55% 6% 10% 26% 2	3490
	21st to end	Day	73% 8% 11% 8% 1	3977
April	1st to 10th	Day	73% 7% 12% 7% 1	2280
	11th to 20th	Day	66% 7% 10% 11% 6% 1	2252
	21st to end	Day	73% 5% 9% 9% 4 1	2527
May	1st to 10th	Day	53% 8% 13% 18% 8%	4420
	11th to 20th	Day	50% 11% 21% 15% 3	4380
	21st to end	Day	72% 9% 12% 7%	4814
June	1st to 10th	Day	63% 7% 15% 10% 5%	2660
	11th to 20th	Day	69% 7% 12% 9% 3	2824
	21st to end	Day	49% 7% 17% 18% 8% 2	2850
July	1st to 10th	Day	29% 6% 8% 19% 22% 16%	4666
	11th to 20th	Day	24% 5% 7% 25% 36% 3	4349
	21st to end	Day	32% 5% 13% 33% 15% 2	4639
August	1st to 10th	Day	24% 5% 11% 36% 21% 2	4339
	11th to 20th	Day	46% 8% 16% 20% 8% 1	4065
	21st to end	Day	46% 5% 11% 24% 12% 1	4303
September	1st to 10th	Day	37% 6% 15% 23% 14% 5%	2280
	11th to 20th	Day	50% 6% 11% 16% 14% 3	2280
	21st to end	Day	49% 7% 15% 16% 10% 3	2017
October	1st to 10th	Day	44% 6% 12% 29% 9% 1	3180
	11th to 20th	Day	61% 5% 11% 14% 9% 1	3161
	21st to end	Day	67% 5% 10% 9% 8% 2	3227
November	1st to 10th	Day	72% 5% 9% 10% 3	1635
	11th to 20th	Day	71% 6% 7% 8% 6% 2	1600
	21st to end	Day	71% 5% 5% 9% 8% 3	1600
December	1st to 10th	Day	64% 6% 9% 11% 9% 2	1584
	11th to 20th	Day	70% 5% 10% 11% 4 1	1928
	21st to end	Day	71% 6% 10% 9% 3	2794
January	1st to 10th	Night	81% 4 6% 6% 2 1	4406
	11th to 20th	Night	64% 6% 6% 15% 7% 2	4420
	21st to end	Night	75% 5% 7% 6% 5% 1	4817
February	1st to 10th	Night	72% 6% 9% 8% 4 1	2470
	11th to 20th	Night	67% 6% 10% 9% 6% 2	2404
	21st to end	Night	70% 6% 8% 10% 4	1956
March	1st to 10th	Night	62% 10% 13% 11% 5%	3688
	11th to 20th	Night	51% 6% 14% 24% 4 1	3490
	21st to end	Night	73% 8% 12% 7% 1	3675
April	1st to 10th	Night	70% 10% 11% 8% 1	1900
	11th to 20th	Night	61% 7% 11% 12% 7% 2	1879
	21st to end	Night	70% 7% 8% 9% 5% 1	1649
May	1st to 10th	Night	52% 6% 14% 18% 9%	2540
	11th to 20th	Night	50% 10% 19% 17% 3 1	2516
	21st to end	Night	72% 8% 12% 6% 1	2762
June	1st to 10th	Night	62% 6% 15% 12% 4	1520
	11th to 20th	Night	65% 8% 15% 9% 3	1350
	21st to end	Night	46% 8% 19% 18% 7% 2	1330
July	1st to 10th	Night	32% 6% 10% 17% 16% 20%	2185
	11th to 20th	Night	21% 3 9% 26% 40% 2	2485
	21st to end	Night	32% 6% 13% 27% 19% 3	2674
August	1st to 10th	Night	20% 4 12% 37% 25% 2	2552
	11th to 20th	Night	42% 8% 20% 20% 8% 2	2839
	21st to end	Night	44% 4 13% 24% 15% 1	3370
September	1st to 10th	Night	35% 6% 15% 23% 16% 5%	1900
	11th to 20th	Night	51% 6% 9% 17% 12% 5%	1900
	21st to end	Night	49% 7% 14% 16% 11% 3	2159
October	1st to 10th	Night	46% 4 12% 29% 9% 1	3800
	11th to 20th	Night	59% 4 9% 15% 12% 1	3777
	21st to end	Night	67% 4 10% 10% 8%	4335
November	1st to 10th	Night	70% 6% 10% 10% 4	2659
	11th to 20th	Night	71% 5% 8% 9% 5% 3	2800
	21st to end	Night	69% 5% 7% 8% 9% 1	2800
December	1st to 10th	Night	65% 5% 8% 11% 8% 2	2778
	11th to 20th	Night	70% 6% 10% 9% 5%	3276
	21st to end	Night	73% 7% 10% 7% 3	4862

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	44% 9% 19% 15% 8% 4	180
	11th to 20th	Day	37% 16% 15% 21% 11% 2	180
	21st to end	Day	48% 10% 18% 16% 7% 1	227
February	1st to 10th	Day	44% 12% 20% 16% 8% 1	370
	11th to 20th	Day	48% 10% 21% 15% 6%	365
	21st to end	Day	40% 16% 19% 22% 4	348
March	1st to 10th	Day	36% 16% 21% 20% 6% 1	460
	11th to 20th	Day	33% 13% 21% 22% 8% 2	460
	21st to end	Day	42% 12% 24% 14% 7%	506
April	1st to 10th	Day	40% 12% 22% 16% 8% 2	460
	11th to 20th	Day	31% 19% 25% 15% 8% 2	452
	21st to end	Day	34% 13% 26% 20% 7% 1	460
May	1st to 10th	Day	26% 10% 28% 27% 8% 1	463
	11th to 20th	Day	32% 10% 22% 22% 11% 3	488
	21st to end	Day	34% 9% 22% 24% 9% 2	529
June	1st to 10th	Day	29% 8% 23% 26% 11% 2	490
	11th to 20th	Day	31% 14% 24% 20% 9% 2	654
	21st to end	Day	18% 7% 25% 33% 14% 3	680
July	1st to 10th	Day	16% 6% 22% 38% 16% 2	671
	11th to 20th	Day	13% 7% 23% 37% 17% 4	488
	21st to end	Day	10% 4 21% 41% 20% 4	531
August	1st to 10th	Day	14% 5% 18% 38% 20% 7%	487
	11th to 20th	Day	9% 4 20% 38% 22% 6%	477
	21st to end	Day	18% 9% 22% 34% 12% 5%	539
September	1st to 10th	Day	14% 9% 25% 35% 14% 3	490
	11th to 20th	Day	22% 8% 20% 32% 16% 2	490
	21st to end	Day	24% 7% 24% 26% 16% 3	490
October	1st to 10th	Day	28% 9% 22% 20% 19% 2	490
	11th to 20th	Day	35% 9% 18% 22% 13% 4	490
	21st to end	Day	37% 12% 20% 19% 8% 3	406
November	1st to 10th	Day	41% 13% 17% 20% 8% 1	235
	11th to 20th	Day	45% 15% 11% 14% 14% 3	200
	21st to end	Day	41% 6% 18% 20% 10% 6%	200
December	1st to 10th	Day	44% 9% 13% 14% 14% 6%	196
	11th to 20th	Day	43% 11% 22% 18% 7%	180
	21st to end	Day	40% 10% 20% 20% 10% 1	198
January	1st to 10th	Night	51% 9% 17% 16% 7%	760
	11th to 20th	Night	42% 10% 15% 24% 8% 1	760
	21st to end	Night	41% 8% 16% 26% 8%	836
February	1st to 10th	Night	42% 7% 22% 22% 7%	760
	11th to 20th	Night	39% 8% 17% 27% 8%	744
	21st to end	Night	42% 9% 20% 21% 7% 1	628
March	1st to 10th	Night	36% 9% 19% 22% 12% 1	760
	11th to 20th	Night	36% 8% 20% 25% 10% 1	760
	21st to end	Night	40% 10% 19% 23% 7% 1	836
April	1st to 10th	Night	37% 9% 19% 24% 10% 2	760
	11th to 20th	Night	31% 9% 21% 27% 11% 1	751
	21st to end	Night	37% 8% 17% 27% 11%	509
May	1st to 10th	Night	29% 7% 14% 33% 17% 1	380
	11th to 20th	Night	29% 5% 12% 29% 21% 3	374
	21st to end	Night	32% 5% 16% 22% 23% 3	411
June	1st to 10th	Night	31% 5% 11% 30% 21% 2	380
	11th to 20th	Night	35% 6% 13% 26% 18% 1	380
	21st to end	Night	20% 4 12% 33% 28% 3	380
July	1st to 10th	Night	16% 4 11% 30% 35% 4	370
	11th to 20th	Night	15% 2 9% 34% 36% 4	368
	21st to end	Night	12% 4 7% 30% 43% 5%	416
August	1st to 10th	Night	13% 2 7% 26% 45% 7%	396
	11th to 20th	Night	12% 2 7% 26% 41% 11%	564
	21st to end	Night	20% 4 8% 29% 35% 4	760
September	1st to 10th	Night	17% 2 10% 37% 30% 4	760
	11th to 20th	Night	23% 6% 11% 26% 30% 5%	760
	21st to end	Night	26% 5% 12% 31% 25% 2	760
October	1st to 10th	Night	27% 5% 15% 29% 22% 2	760
	11th to 20th	Night	34% 6% 16% 25% 17% 3	760
	21st to end	Night	38% 8% 17% 25% 9% 2	836
November	1st to 10th	Night	42% 10% 21% 23% 4	780
	11th to 20th	Night	44% 9% 19% 21% 6% 1	800
	21st to end	Night	40% 10% 18% 24% 8%	800
December	1st to 10th	Night	37% 8% 19% 25% 11% 1	794
	11th to 20th	Night	47% 9% 21% 18% 5% 1	760
	21st to end	Night	51% 10% 17% 18% 3	836

Page generated at 2024-12-06 00:54:51. Version ac07

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