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 2024-09-29.

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% 9% 3 9% 6% 5% 5% 4 6% 7% 33%	102012
	Night	8% 10% 4 10% 6% 5% 5% 4 6% 7% 33%	96232
Transparency	Day	46% 8% 15% 22% 7%	101735
	Night	47% 8% 16% 21% 7%	96155
Seeing	Day	15% 10% 27% 28% 16% 4	16462
	Night	13% 7% 28% 33% 17% 2	24612

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	5% 12% 6% 16% 12% 9% 7% 4 6% 4 19%	1721
	11th to 20th	Day	4 10% 3 10% 7% 6% 7% 6% 8% 9% 30%	1978
	21st to end	Day	6% 15% 6% 19% 8% 5% 5% 3 5% 6% 23%	2442
February	1st to 10th	Day	6% 11% 5% 11% 8% 7% 7% 6% 5% 7% 28%	1458
	11th to 20th	Day	4 11% 5% 12% 5% 6% 6% 5% 7% 6% 32%	1560
	21st to end	Day	3 9% 4 11% 9% 7% 7% 5% 8% 8% 30%	1413
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%	2069
October	1st to 10th	Day	13% 13% 4 9% 4 5% 5% 3 6% 7% 31%	1828
	11th to 20th	Day	10% 13% 3 10% 6% 4 5% 3 6% 7% 32%	1631
	21st to end	Day	13% 16% 4 8% 6% 6% 4 3 5% 6% 28%	1644
November	1st to 10th	Day	10% 16% 4 11% 8% 5% 5% 4 5% 6% 27%	1422
	11th to 20th	Day	12% 13% 3 12% 10% 6% 5% 5% 4 5% 25%	1330
	21st to end	Day	8% 11% 5% 14% 6% 5% 4 4 5% 7% 31%	1164
December	1st to 10th	Day	6% 10% 5% 14% 8% 6% 6% 5% 6% 8% 26%	1079
	11th to 20th	Day	7% 17% 6% 11% 6% 5% 4 4 6% 8% 27%	1199
	21st to end	Day	4 8% 3 8% 6% 5% 7% 4 6% 8% 40%	1738
January	1st to 10th	Night	5% 13% 5% 15% 11% 7% 6% 6% 7% 5% 19%	5210
	11th to 20th	Night	4 10% 5% 12% 7% 7% 8% 8% 7% 7% 26%	4918
	21st to end	Night	4 14% 6% 17% 7% 5% 5% 4 5% 6% 26%	5214
February	1st to 10th	Night	4 11% 5% 12% 6% 5% 6% 5% 7% 7% 32%	2738
	11th to 20th	Night	6% 13% 6% 9% 7% 7% 6% 4 6% 6% 31%	2506
	21st to end	Night	2 9% 4 11% 8% 6% 6% 5% 7% 9% 34%	2041
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%	2079
October	1st to 10th	Night	14% 10% 4 8% 6% 4 4 3 5% 6% 37%	2132
	11th to 20th	Night	10% 11% 4 7% 4 5% 5% 4 5% 7% 37%	2326
	21st to end	Night	12% 16% 4 11% 7% 4 5% 4 6% 6% 26%	2693
November	1st to 10th	Night	11% 14% 5% 10% 6% 5% 5% 3 5% 6% 30%	2653
	11th to 20th	Night	9% 14% 4 12% 7% 5% 5% 4 5% 6% 27%	2850
	21st to end	Night	8% 14% 5% 13% 7% 5% 5% 4 5% 6% 28%	3016
December	1st to 10th	Night	6% 10% 4 11% 9% 7% 6% 4 7% 7% 29%	3101
	11th to 20th	Night	8% 13% 5% 12% 8% 7% 6% 4 6% 6% 25%	3993
	21st to end	Night	3 8% 3 8% 6% 6% 5% 4 6% 9% 42%	5918

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	64% 7% 10% 14% 5%	1721
	11th to 20th	Day	46% 9% 17% 21% 7% 1	1996
	21st to end	Day	62% 7% 12% 14% 5%	2442
February	1st to 10th	Day	54% 7% 12% 16% 10%	1458
	11th to 20th	Day	49% 8% 15% 22% 6%	1568
	21st to end	Day	48% 8% 13% 22% 8% 1	1413
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%	2069
October	1st to 10th	Day	51% 8% 16% 20% 4	1828
	11th to 20th	Day	50% 6% 15% 22% 6%	1631
	21st to end	Day	55% 9% 13% 19% 4	1644
November	1st to 10th	Day	59% 7% 14% 17% 4	1422
	11th to 20th	Day	60% 9% 15% 14% 3	1330
	21st to end	Day	52% 9% 17% 17% 4 1	1164
December	1st to 10th	Day	53% 9% 14% 18% 5%	1079
	11th to 20th	Day	55% 7% 13% 22% 2	1200
	21st to end	Day	39% 8% 15% 30% 7% 1	1738
January	1st to 10th	Night	61% 9% 11% 13% 5%	5210
	11th to 20th	Night	52% 9% 14% 20% 4 1	4962
	21st to end	Night	59% 7% 14% 15% 5%	5214
February	1st to 10th	Night	48% 7% 15% 19% 11%	2738
	11th to 20th	Night	51% 8% 15% 19% 7%	2508
	21st to end	Night	46% 8% 18% 20% 8%	2041
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	2079
October	1st to 10th	Night	48% 6% 14% 23% 8% 1	2132
	11th to 20th	Night	46% 8% 18% 23% 5% 1	2326
	21st to end	Night	57% 9% 15% 14% 5%	2693
November	1st to 10th	Night	54% 7% 15% 18% 5%	2653
	11th to 20th	Night	57% 10% 15% 16% 3	2850
	21st to end	Night	56% 7% 15% 19% 3	3016
December	1st to 10th	Night	53% 8% 15% 17% 7%	3101
	11th to 20th	Night	58% 9% 15% 15% 4	3991
	21st to end	Night	38% 7% 19% 26% 10% 1	5918

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	7% 6% 29% 33% 20% 5%	180
	11th to 20th	Day	12% 12% 25% 28% 21% 3	180
	21st to end	Day	13% 11% 31% 29% 13% 3	198
February	1st to 10th	Day	9% 8% 34% 28% 17% 4	180
	11th to 20th	Day	6% 10% 33% 32% 14% 5%	218
	21st to end	Day	8% 12% 35% 29% 13% 4	225
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	17% 12% 30% 25% 13% 2	483
October	1st to 10th	Day	19% 14% 28% 26% 9% 3	298
	11th to 20th	Day	18% 13% 34% 25% 9% 2	270
	21st to end	Day	22% 10% 29% 23% 13% 2	297
November	1st to 10th	Day	18% 13% 31% 23% 15% 1	239
	11th to 20th	Day	15% 11% 38% 22% 11% 3	180
	21st to end	Day	14% 12% 28% 31% 10% 4	180
December	1st to 10th	Day	7% 9% 33% 36% 10% 4	180
	11th to 20th	Day	11% 13% 31% 28% 16% 2	180
	21st to end	Day	7% 7% 23% 34% 21% 8%	198
January	1st to 10th	Night	12% 7% 29% 35% 15% 2	1040
	11th to 20th	Night	12% 7% 28% 37% 14% 2	1011
	21st to end	Night	12% 9% 31% 34% 12% 1	1045
February	1st to 10th	Night	9% 5% 31% 33% 18% 4	838
	11th to 20th	Night	12% 6% 31% 34% 15% 2	744
	21st to end	Night	5% 6% 32% 37% 18% 2	628
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	756
October	1st to 10th	Night	20% 7% 31% 26% 13% 3	720
	11th to 20th	Night	16% 8% 27% 32% 14% 3	720
	21st to end	Night	21% 9% 29% 26% 13% 2	911
November	1st to 10th	Night	17% 8% 27% 33% 14% 2	925
	11th to 20th	Night	16% 7% 33% 30% 12% 2	950
	21st to end	Night	14% 10% 35% 30% 11% 1	950
December	1st to 10th	Night	12% 9% 29% 32% 17% 2	979
	11th to 20th	Night	12% 8% 31% 35% 12% 3	1040
	21st to end	Night	10% 5% 26% 34% 21% 4	1144

Page generated at 2024-09-26 07:52:21. Version ac07

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