Mildred Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mildred Lake clear sky chart from 2005-11-06 to 2025-02-25.

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	10% 10% 3 9% 6% 5% 5% 4 6% 7% 33%	111129
	Night	7% 10% 4 11% 6% 6% 5% 4 6% 7% 33%	116110
Transparency	Day	47% 8% 15% 22% 7%	110852
	Night	48% 7% 16% 21% 7%	116033
Seeing	Day	15% 10% 27% 28% 16% 4	16810
	Night	13% 7% 28% 33% 17% 2	25350

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	4 11% 6% 15% 11% 9% 6% 4 5% 5% 23%	2471
	11th to 20th	Day	4 10% 3 12% 7% 6% 6% 5% 7% 8% 31%	2854
	21st to end	Day	5% 14% 6% 17% 7% 5% 5% 4 6% 7% 25%	3498
February	1st to 10th	Day	5% 11% 5% 11% 8% 7% 7% 6% 5% 7% 29%	1535
	11th to 20th	Day	4 11% 5% 12% 5% 7% 6% 5% 7% 6% 32%	1645
	21st to end	Day	4 9% 4 11% 9% 7% 7% 5% 8% 8% 29%	1449
March	1st to 10th	Day	2 10% 5% 10% 6% 6% 6% 5% 8% 10% 32%	3078
	11th to 20th	Day	6% 11% 3 7% 5% 5% 6% 4 8% 9% 34%	3477
	21st to end	Day	4 13% 6% 12% 5% 4 4 4 5% 6% 37%	3872
April	1st to 10th	Day	8% 12% 4 11% 6% 7% 5% 4 6% 7% 30%	2437
	11th to 20th	Day	9% 13% 4 10% 7% 5% 5% 4 6% 6% 32%	2440
	21st to end	Day	11% 11% 4 11% 7% 6% 6% 4 6% 7% 27%	2627
May	1st to 10th	Day	11% 11% 4 9% 5% 4 5% 4 5% 6% 34%	4740
	11th to 20th	Day	18% 11% 3 9% 6% 4 6% 4 5% 6% 27%	4694
	21st to end	Day	12% 9% 3 8% 5% 6% 6% 6% 7% 8% 29%	5477
June	1st to 10th	Day	16% 8% 3 8% 7% 5% 6% 4 6% 7% 29%	3230
	11th to 20th	Day	18% 10% 3 8% 6% 6% 5% 5% 5% 7% 26%	3230
	21st to end	Day	14% 8% 2 8% 5% 5% 6% 5% 7% 7% 32%	3230
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 6% 6% 8% 10% 36%	5380
	11th to 20th	Day	7% 4 2 6% 5% 5% 5% 5% 7% 9% 47%	5106
	21st to end	Day	17% 5% 2 5% 5% 5% 5% 4 6% 8% 37%	5146
August	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 6% 8% 47%	4720
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 36%	4347
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 4 6% 7% 36%	4521
September	1st to 10th	Day	16% 8% 3 7% 5% 4 4 3 5% 8% 36%	2461
	11th to 20th	Day	11% 9% 3 8% 5% 5% 5% 4 6% 7% 37%	2123
	21st to end	Day	10% 8% 3 8% 4 5% 5% 4 8% 7% 38%	2090
October	1st to 10th	Day	9% 12% 4 9% 4 5% 5% 4 7% 8% 34%	3212
	11th to 20th	Day	10% 13% 3 10% 6% 4 5% 3 6% 7% 33%	2853
	21st to end	Day	9% 12% 4 12% 5% 5% 5% 3 6% 6% 31%	2855
November	1st to 10th	Day	10% 16% 5% 11% 8% 5% 5% 4 5% 6% 26%	1498
	11th to 20th	Day	11% 14% 3 12% 10% 6% 6% 5% 4 5% 24%	1400
	21st to end	Day	7% 12% 5% 14% 6% 5% 4 4 5% 7% 30%	1225
December	1st to 10th	Day	6% 12% 5% 13% 7% 6% 6% 6% 9% 10% 21%	1843
	11th to 20th	Day	8% 19% 5% 11% 6% 5% 4 3 5% 8% 26%	1879
	21st to end	Day	3 9% 4 14% 7% 6% 6% 4 5% 6% 34%	2486
January	1st to 10th	Night	5% 12% 5% 16% 9% 7% 6% 6% 7% 6% 21%	7460
	11th to 20th	Night	4 9% 5% 11% 6% 6% 7% 6% 6% 6% 34%	7042
	21st to end	Night	4 14% 6% 16% 6% 5% 5% 4 5% 7% 29%	7458
February	1st to 10th	Night	4 11% 5% 11% 7% 5% 5% 5% 6% 8% 32%	2882
	11th to 20th	Night	6% 12% 5% 9% 7% 7% 6% 4 7% 6% 31%	2641
	21st to end	Night	2 9% 4 11% 8% 6% 6% 5% 6% 9% 33%	2099
March	1st to 10th	Night	3 9% 5% 11% 7% 6% 6% 5% 7% 9% 34%	3783
	11th to 20th	Night	5% 10% 4 9% 7% 7% 6% 5% 8% 8% 33%	3502
	21st to end	Night	6% 11% 4 12% 7% 5% 5% 4 5% 6% 35%	3779
April	1st to 10th	Night	8% 11% 4 12% 6% 6% 6% 4 5% 6% 32%	1743
	11th to 20th	Night	8% 10% 4 8% 6% 5% 4 4 7% 9% 35%	1691
	21st to end	Night	9% 13% 4 10% 7% 5% 5% 4 5% 6% 32%	1550
May	1st to 10th	Night	15% 10% 3 8% 4 4 4 4 5% 5% 38%	2220
	11th to 20th	Night	18% 9% 3 7% 4 4 4 5% 7% 7% 30%	2199
	21st to end	Night	10% 7% 3 8% 6% 5% 6% 5% 8% 8% 33%	2080
June	1st to 10th	Night	16% 9% 3 7% 6% 5% 7% 5% 5% 8% 30%	950
	11th to 20th	Night	17% 9% 2 6% 6% 4 7% 3 5% 8% 32%	950
	21st to end	Night	12% 6% 3 6% 4 5% 4 4 7% 8% 41%	950
July	1st to 10th	Night	6% 3 1 5% 6% 6% 6% 7% 9% 11% 40%	1580
	11th to 20th	Night	6% 4 1 4 3 4 4 4 6% 10% 54%	1852
	21st to end	Night	15% 4 1 4 3 4 4 4 7% 8% 45%	2404
August	1st to 10th	Night	7% 3 2 5% 4 4 5% 5% 7% 7% 51%	2210
	11th to 20th	Night	10% 5% 2 6% 4 5% 4 5% 8% 9% 43%	2480
	21st to end	Night	14% 6% 3 7% 4 4 4 4 7% 9% 40%	3146
September	1st to 10th	Night	11% 8% 3 7% 4 5% 4 4 6% 8% 41%	1719
	11th to 20th	Night	12% 6% 3 8% 4 4 5% 5% 6% 8% 39%	2056
	21st to end	Night	10% 7% 2 7% 4 6% 5% 4 7% 8% 40%	2090
October	1st to 10th	Night	11% 8% 3 7% 5% 4 4 3 6% 7% 42%	3759
	11th to 20th	Night	10% 10% 4 7% 4 5% 5% 4 6% 8% 37%	4072
	21st to end	Night	10% 13% 4 12% 7% 5% 6% 4 6% 7% 27%	4671
November	1st to 10th	Night	11% 14% 5% 10% 6% 5% 5% 3 5% 6% 30%	2797
	11th to 20th	Night	9% 14% 5% 12% 7% 5% 5% 4 5% 6% 26%	3000
	21st to end	Night	7% 14% 5% 14% 8% 5% 5% 4 5% 6% 27%	3175
December	1st to 10th	Night	7% 11% 5% 15% 9% 7% 6% 4 6% 6% 25%	5337
	11th to 20th	Night	6% 16% 6% 14% 8% 7% 6% 4 6% 6% 21%	6313
	21st to end	Night	3 10% 4 12% 8% 8% 5% 4 5% 7% 35%	8470

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	60% 6% 11% 16% 6%	2471
	11th to 20th	Day	48% 8% 15% 18% 11% 1	2872
	21st to end	Day	56% 7% 16% 14% 6%	3498
February	1st to 10th	Day	53% 7% 12% 17% 11%	1535
	11th to 20th	Day	49% 8% 14% 22% 7%	1653
	21st to end	Day	49% 8% 13% 22% 8% 1	1449
March	1st to 10th	Day	45% 7% 16% 24% 8%	3078
	11th to 20th	Day	42% 9% 17% 23% 8%	3478
	21st to end	Day	46% 6% 11% 23% 13% 1	3872
April	1st to 10th	Day	52% 7% 12% 17% 11% 1	2437
	11th to 20th	Day	50% 7% 9% 20% 12% 1	2440
	21st to end	Day	53% 8% 12% 20% 6% 1	2627
May	1st to 10th	Day	47% 7% 10% 22% 13% 1	4740
	11th to 20th	Day	54% 7% 9% 19% 10%	4698
	21st to end	Day	46% 12% 13% 19% 10% 1	5478
June	1st to 10th	Day	51% 9% 11% 21% 8%	3230
	11th to 20th	Day	55% 8% 12% 19% 6%	3230
	21st to end	Day	48% 9% 14% 20% 8% 1	3230
July	1st to 10th	Day	38% 10% 22% 25% 5%	5296
	11th to 20th	Day	31% 9% 18% 31% 11%	5017
	21st to end	Day	42% 9% 20% 25% 3	4983
August	1st to 10th	Day	32% 8% 19% 38% 3	4702
	11th to 20th	Day	42% 9% 19% 22% 7% 1	4392
	21st to end	Day	46% 8% 23% 22% 2	4520
September	1st to 10th	Day	46% 8% 19% 21% 5%	2461
	11th to 20th	Day	45% 8% 22% 23% 3	2123
	21st to end	Day	41% 9% 18% 24% 7%	2090
October	1st to 10th	Day	47% 7% 14% 27% 5%	3212
	11th to 20th	Day	50% 5% 16% 24% 5%	2853
	21st to end	Day	51% 7% 18% 21% 3	2855
November	1st to 10th	Day	58% 7% 14% 17% 4	1498
	11th to 20th	Day	60% 9% 15% 14% 3	1400
	21st to end	Day	52% 9% 17% 17% 4	1225
December	1st to 10th	Day	54% 10% 16% 17% 3	1843
	11th to 20th	Day	57% 5% 13% 22% 2	1880
	21st to end	Day	49% 6% 16% 23% 5% 1	2486
January	1st to 10th	Night	59% 8% 12% 16% 6%	7460
	11th to 20th	Night	47% 8% 13% 20% 11% 1	7086
	21st to end	Night	55% 6% 18% 15% 6%	7458
February	1st to 10th	Night	48% 7% 14% 19% 11%	2882
	11th to 20th	Night	50% 8% 14% 20% 8%	2643
	21st to end	Night	46% 8% 18% 20% 8%	2099
March	1st to 10th	Night	44% 7% 17% 26% 6%	3783
	11th to 20th	Night	45% 10% 16% 24% 5%	3502
	21st to end	Night	47% 5% 12% 21% 15%	3779
April	1st to 10th	Night	51% 7% 12% 19% 10% 1	1743
	11th to 20th	Night	44% 5% 11% 20% 16% 3	1691
	21st to end	Night	51% 7% 11% 21% 9% 1	1550
May	1st to 10th	Night	47% 5% 8% 23% 16% 1	2220
	11th to 20th	Night	48% 8% 12% 18% 13% 1	2199
	21st to end	Night	41% 11% 14% 21% 12% 1	2080
June	1st to 10th	Night	49% 7% 11% 22% 12%	950
	11th to 20th	Night	50% 8% 12% 23% 6% 1	950
	21st to end	Night	39% 8% 17% 26% 11%	950
July	1st to 10th	Night	31% 11% 27% 27% 5% 1	1555
	11th to 20th	Night	25% 7% 16% 38% 13% 1	1818
	21st to end	Night	34% 9% 23% 30% 4	2328
August	1st to 10th	Night	29% 8% 17% 42% 4	2203
	11th to 20th	Night	34% 9% 24% 24% 8%	2501
	21st to end	Night	40% 7% 30% 21% 3	3146
September	1st to 10th	Night	41% 9% 22% 22% 5%	1719
	11th to 20th	Night	40% 10% 18% 25% 8%	2056
	21st to end	Night	40% 7% 19% 24% 9% 1	2090
October	1st to 10th	Night	41% 6% 16% 28% 10%	3759
	11th to 20th	Night	44% 6% 16% 29% 4	4072
	21st to end	Night	55% 8% 16% 17% 4	4671
November	1st to 10th	Night	54% 7% 14% 18% 6%	2797
	11th to 20th	Night	57% 9% 15% 17% 2	3000
	21st to end	Night	57% 6% 14% 19% 3	3175
December	1st to 10th	Night	60% 6% 12% 15% 7%	5337
	11th to 20th	Night	62% 7% 15% 13% 3	6311
	21st to end	Night	48% 6% 16% 23% 7%	8470

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	6% 7% 29% 32% 21% 6%	200
	11th to 20th	Day	12% 13% 26% 28% 20% 3	200
	21st to end	Day	13% 12% 34% 26% 12% 2	220
February	1st to 10th	Day	9% 9% 34% 28% 18% 4	200
	11th to 20th	Day	6% 10% 32% 31% 16% 5%	243
	21st to end	Day	9% 11% 34% 29% 13% 3	237
March	1st to 10th	Day	6% 12% 35% 32% 13% 3	422
	11th to 20th	Day	10% 18% 31% 28% 10% 3	460
	21st to end	Day	11% 14% 33% 27% 12% 3	506
April	1st to 10th	Day	15% 14% 35% 23% 9% 4	460
	11th to 20th	Day	16% 16% 29% 25% 12% 2	452
	21st to end	Day	18% 13% 31% 26% 9% 3	560
May	1st to 10th	Day	13% 13% 30% 26% 16% 4	653
	11th to 20th	Day	13% 11% 25% 29% 19% 3	675
	21st to end	Day	13% 10% 23% 34% 16% 4	791
June	1st to 10th	Day	22% 9% 24% 27% 15% 2	870
	11th to 20th	Day	20% 9% 25% 28% 15% 3	870
	21st to end	Day	15% 6% 21% 30% 22% 6%	870
July	1st to 10th	Day	12% 7% 23% 32% 21% 4	856
	11th to 20th	Day	12% 6% 22% 31% 20% 9%	852
	21st to end	Day	15% 5% 24% 26% 21% 9%	747
August	1st to 10th	Day	15% 7% 17% 28% 25% 9%	676
	11th to 20th	Day	14% 9% 30% 29% 14% 4	537
	21st to end	Day	18% 7% 28% 27% 17% 4	539
September	1st to 10th	Day	20% 12% 27% 23% 14% 4	490
	11th to 20th	Day	15% 12% 25% 33% 12% 3	490
	21st to end	Day	16% 13% 31% 25% 13% 2	490
October	1st to 10th	Day	19% 16% 28% 25% 10% 3	329
	11th to 20th	Day	18% 12% 35% 25% 8% 2	300
	21st to end	Day	21% 12% 32% 22% 12% 2	330
November	1st to 10th	Day	17% 12% 34% 22% 15% 2	265
	11th to 20th	Day	15% 11% 39% 22% 11% 4	200
	21st to end	Day	14% 12% 27% 31% 13% 6%	200
December	1st to 10th	Day	8% 11% 32% 36% 10% 4	200
	11th to 20th	Day	12% 13% 31% 29% 15% 2	200
	21st to end	Day	8% 6% 24% 34% 20% 7%	220
January	1st to 10th	Night	12% 7% 29% 33% 15% 2	1100
	11th to 20th	Night	12% 7% 29% 36% 14% 2	1067
	21st to end	Night	12% 11% 32% 32% 11% 1	1100
February	1st to 10th	Night	8% 5% 32% 33% 18% 4	882
	11th to 20th	Night	11% 6% 30% 36% 15% 2	784
	21st to end	Night	5% 6% 32% 37% 18% 2	646
March	1st to 10th	Night	6% 7% 32% 34% 18% 2	760
	11th to 20th	Night	13% 9% 31% 33% 13% 1	760
	21st to end	Night	11% 6% 28% 36% 17% 3	836
April	1st to 10th	Night	13% 8% 29% 33% 15% 1	603
	11th to 20th	Night	11% 11% 27% 36% 14% 1	563
	21st to end	Night	16% 7% 28% 32% 14% 2	510
May	1st to 10th	Night	12% 9% 25% 33% 19% 1	380
	11th to 20th	Night	14% 8% 28% 30% 17% 2	374
	21st to end	Night	12% 5% 23% 37% 20% 3	411
June	1st to 10th	Night	20% 7% 21% 32% 18% 2	380
	11th to 20th	Night	21% 4 19% 33% 22% 2	380
	21st to end	Night	14% 2 17% 38% 24% 4	380
July	1st to 10th	Night	10% 4 19% 41% 25% 2	370
	11th to 20th	Night	11% 2 20% 36% 27% 5%	368
	21st to end	Night	11% 3 17% 35% 27% 7%	416
August	1st to 10th	Night	13% 3 15% 32% 31% 7%	378
	11th to 20th	Night	9% 5% 23% 41% 21% 1	419
	21st to end	Night	17% 3 24% 33% 21% 1	627
September	1st to 10th	Night	16% 6% 25% 29% 21% 3	570
	11th to 20th	Night	15% 5% 22% 36% 21% 1	726
	21st to end	Night	13% 7% 29% 33% 15% 2	760
October	1st to 10th	Night	19% 8% 31% 27% 13% 3	760
	11th to 20th	Night	16% 8% 27% 33% 13% 2	760
	21st to end	Night	21% 9% 30% 26% 12% 2	962
November	1st to 10th	Night	17% 8% 27% 32% 14% 2	975
	11th to 20th	Night	16% 7% 33% 30% 12% 2	1000
	21st to end	Night	14% 10% 34% 30% 12% 1	1000
December	1st to 10th	Night	12% 9% 29% 31% 17% 1	1033
	11th to 20th	Night	12% 8% 31% 35% 12% 3	1100
	21st to end	Night	10% 5% 26% 34% 21% 4	1210

Page generated at 2025-02-22 04:51:32. Version ac07

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