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 2026-07-01.

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	9% 9% 3 9% 6% 5% 5% 4 6% 8% 34%	141780
	Night	7% 10% 4 11% 6% 6% 5% 4 6% 7% 33%	139163
Transparency	Day	46% 7% 15% 23% 7% 1	141458
	Night	49% 7% 15% 21% 7%	139070
Seeing	Day	15% 11% 27% 28% 15% 4	18777
	Night	13% 7% 28% 33% 16% 2	27026

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% 16% 10% 8% 7% 4 5% 5% 24%	3211
	11th to 20th	Day	3 8% 3 12% 7% 6% 6% 5% 7% 8% 34%	3716
	21st to end	Day	4 14% 6% 17% 8% 6% 5% 4 6% 7% 24%	4531
February	1st to 10th	Day	6% 12% 5% 12% 8% 7% 7% 6% 5% 6% 28%	1612
	11th to 20th	Day	4 11% 5% 11% 5% 6% 6% 5% 7% 6% 33%	1729
	21st to end	Day	4 10% 4 11% 8% 6% 6% 5% 8% 8% 29%	1557
March	1st to 10th	Day	2 9% 5% 11% 7% 7% 7% 5% 9% 10% 29%	4528
	11th to 20th	Day	5% 12% 5% 10% 7% 6% 6% 4 7% 8% 30%	5096
	21st to end	Day	4 12% 6% 11% 5% 4 4 4 5% 6% 39%	5668
April	1st to 10th	Day	8% 13% 4 10% 6% 6% 5% 4 5% 7% 31%	2693
	11th to 20th	Day	8% 13% 4 10% 7% 5% 5% 4 6% 6% 31%	2700
	21st to end	Day	11% 11% 4 11% 7% 6% 6% 4 6% 8% 27%	2903
May	1st to 10th	Day	8% 11% 3 8% 5% 5% 6% 4 6% 7% 37%	8793
	11th to 20th	Day	15% 10% 4 11% 7% 5% 6% 4 6% 7% 25%	8755
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 5% 6% 8% 36%	10245
June	1st to 10th	Day	17% 8% 3 8% 6% 5% 6% 4 6% 7% 28%	3570
	11th to 20th	Day	18% 10% 3 9% 6% 6% 5% 5% 6% 7% 26%	3570
	21st to end	Day	13% 8% 2 8% 5% 5% 6% 5% 7% 8% 33%	3570
July	1st to 10th	Day	8% 6% 2 8% 6% 6% 7% 6% 8% 11% 33%	7701
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 6% 8% 53%	7300
	21st to end	Day	13% 5% 2 5% 5% 5% 5% 5% 6% 9% 40%	7384
August	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 6% 8% 47%	4870
	11th to 20th	Day	14% 7% 2 6% 5% 5% 5% 5% 7% 9% 36%	4488
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 4 6% 7% 37%	4664
September	1st to 10th	Day	15% 8% 2 7% 4 4 4 3 5% 8% 37%	2590
	11th to 20th	Day	11% 8% 3 8% 5% 5% 5% 3 6% 7% 39%	2234
	21st to end	Day	10% 8% 3 8% 4 5% 5% 4 8% 7% 39%	2200
October	1st to 10th	Day	9% 12% 4 9% 4 5% 5% 3 7% 8% 34%	3313
	11th to 20th	Day	10% 13% 3 10% 6% 4 5% 3 6% 6% 33%	2943
	21st to end	Day	10% 12% 4 12% 5% 5% 5% 3 6% 6% 31%	2946
November	1st to 10th	Day	9% 16% 5% 11% 7% 5% 4 4 5% 6% 27%	1574
	11th to 20th	Day	11% 14% 3 12% 9% 6% 5% 5% 4 5% 25%	1470
	21st to end	Day	7% 12% 5% 14% 6% 5% 4 4 5% 7% 30%	1286
December	1st to 10th	Day	6% 12% 4 13% 7% 6% 6% 6% 9% 10% 21%	1900
	11th to 20th	Day	8% 19% 5% 11% 6% 5% 5% 3 5% 8% 25%	1929
	21st to end	Day	3 9% 5% 14% 7% 6% 7% 4 5% 6% 34%	2541
January	1st to 10th	Night	5% 13% 6% 17% 9% 6% 6% 5% 7% 6% 19%	9668
	11th to 20th	Night	4 8% 4 10% 6% 6% 7% 6% 7% 7% 35%	9180
	21st to end	Night	4 14% 6% 14% 7% 6% 7% 4 5% 6% 27%	9650
February	1st to 10th	Night	5% 11% 5% 12% 7% 5% 5% 5% 6% 7% 31%	3026
	11th to 20th	Night	5% 12% 5% 9% 7% 7% 6% 4 7% 7% 32%	2777
	21st to end	Night	3 10% 4 11% 8% 6% 6% 5% 6% 8% 33%	2249
March	1st to 10th	Night	2 9% 5% 13% 8% 7% 6% 5% 7% 8% 31%	5571
	11th to 20th	Night	3 10% 5% 13% 8% 7% 6% 5% 7% 7% 29%	5123
	21st to end	Night	6% 10% 4 11% 6% 5% 5% 4 6% 7% 38%	5534
April	1st to 10th	Night	8% 11% 4 12% 6% 6% 6% 4 6% 6% 33%	1926
	11th to 20th	Night	8% 10% 4 8% 6% 5% 4 4 7% 8% 34%	1871
	21st to end	Night	9% 13% 4 9% 7% 5% 5% 4 5% 7% 31%	1714
May	1st to 10th	Night	11% 8% 2 8% 4 5% 5% 4 6% 7% 39%	4126
	11th to 20th	Night	16% 8% 3 9% 5% 5% 5% 5% 7% 7% 29%	4105
	21st to end	Night	11% 7% 3 8% 6% 5% 6% 5% 7% 9% 33%	3908
June	1st to 10th	Night	17% 9% 3 7% 6% 5% 6% 5% 5% 9% 30%	1050
	11th to 20th	Night	17% 9% 2 6% 6% 4 7% 3 5% 7% 33%	1050
	21st to end	Night	11% 6% 3 6% 4 4 4 4 7% 9% 41%	1050
July	1st to 10th	Night	9% 4 1 6% 6% 6% 6% 6% 8% 11% 36%	2260
	11th to 20th	Night	6% 4 1 4 3 3 4 4 6% 9% 56%	2644
	21st to end	Night	12% 4 1 5% 4 4 4 4 7% 8% 46%	3457
August	1st to 10th	Night	7% 4 2 5% 4 4 5% 5% 7% 8% 50%	2280
	11th to 20th	Night	11% 5% 2 6% 4 5% 4 5% 8% 9% 42%	2559
	21st to end	Night	14% 6% 3 6% 4 4 4 4 7% 9% 40%	3245
September	1st to 10th	Night	11% 8% 2 7% 4 5% 4 4 6% 8% 41%	1810
	11th to 20th	Night	11% 6% 3 8% 4 4 5% 4 6% 8% 41%	2164
	21st to end	Night	10% 7% 3 7% 4 6% 5% 4 7% 8% 40%	2200
October	1st to 10th	Night	11% 8% 3 7% 5% 4 4 3 6% 7% 42%	3878
	11th to 20th	Night	10% 10% 4 7% 4 5% 5% 4 6% 8% 37%	4202
	21st to end	Night	11% 13% 4 12% 7% 5% 6% 4 6% 7% 27%	4821
November	1st to 10th	Night	11% 14% 5% 10% 6% 5% 5% 3 5% 6% 30%	2941
	11th to 20th	Night	9% 14% 5% 12% 7% 5% 5% 4 5% 6% 27%	3150
	21st to end	Night	7% 13% 5% 14% 8% 5% 5% 4 5% 6% 28%	3334
December	1st to 10th	Night	7% 11% 5% 15% 9% 7% 6% 4 6% 6% 25%	5500
	11th to 20th	Night	6% 15% 6% 14% 8% 7% 6% 4 6% 6% 21%	6483
	21st to end	Night	3 10% 4 12% 8% 8% 5% 4 5% 7% 34%	8657

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	61% 6% 11% 16% 6%	3211
	11th to 20th	Day	46% 7% 17% 19% 10% 1	3734
	21st to end	Day	59% 6% 13% 14% 7%	4531
February	1st to 10th	Day	54% 7% 12% 17% 10%	1612
	11th to 20th	Day	48% 8% 14% 22% 8%	1737
	21st to end	Day	49% 8% 13% 22% 8% 1	1557
March	1st to 10th	Day	46% 7% 15% 24% 7%	4528
	11th to 20th	Day	49% 7% 15% 22% 7%	5097
	21st to end	Day	44% 5% 9% 23% 16% 3	5668
April	1st to 10th	Day	51% 7% 12% 18% 12% 1	2693
	11th to 20th	Day	50% 7% 10% 20% 12% 1	2700
	21st to end	Day	52% 7% 11% 22% 6% 1	2903
May	1st to 10th	Day	44% 6% 12% 26% 11% 1	8793
	11th to 20th	Day	55% 6% 8% 22% 8%	8759
	21st to end	Day	41% 8% 17% 23% 9% 2	10246
June	1st to 10th	Day	51% 8% 11% 21% 8%	3570
	11th to 20th	Day	55% 8% 11% 20% 6%	3570
	21st to end	Day	46% 9% 15% 22% 8% 1	3570
July	1st to 10th	Day	40% 9% 25% 21% 4 1	7617
	11th to 20th	Day	27% 7% 16% 38% 12%	7211
	21st to end	Day	38% 8% 19% 33% 3	7176
August	1st to 10th	Day	32% 8% 19% 37% 3	4852
	11th to 20th	Day	42% 9% 18% 22% 7% 1	4533
	21st to end	Day	45% 8% 23% 22% 3	4663
September	1st to 10th	Day	45% 8% 20% 22% 5%	2590
	11th to 20th	Day	43% 8% 22% 24% 4	2234
	21st to end	Day	41% 9% 18% 25% 8%	2200
October	1st to 10th	Day	47% 7% 14% 27% 5%	3313
	11th to 20th	Day	50% 5% 15% 24% 5%	2943
	21st to end	Day	51% 6% 18% 21% 3	2946
November	1st to 10th	Day	57% 7% 13% 18% 5%	1574
	11th to 20th	Day	60% 8% 14% 15% 3	1470
	21st to end	Day	52% 8% 16% 18% 5%	1286
December	1st to 10th	Day	54% 9% 16% 17% 3	1900
	11th to 20th	Day	57% 5% 13% 22% 3	1930
	21st to end	Day	50% 6% 16% 23% 5% 1	2541
January	1st to 10th	Night	61% 7% 11% 15% 5%	9669
	11th to 20th	Night	45% 8% 17% 20% 11%	9224
	21st to end	Night	57% 7% 16% 14% 6%	9650
February	1st to 10th	Night	50% 7% 14% 18% 11%	3026
	11th to 20th	Night	49% 8% 14% 20% 9%	2779
	21st to end	Night	47% 7% 17% 20% 8%	2249
March	1st to 10th	Night	48% 6% 15% 23% 7%	5571
	11th to 20th	Night	51% 7% 14% 22% 5%	5123
	21st to end	Night	43% 5% 12% 19% 19% 1	5534
April	1st to 10th	Night	50% 7% 12% 20% 10% 1	1926
	11th to 20th	Night	45% 5% 11% 20% 15% 3	1871
	21st to end	Night	51% 7% 11% 22% 8% 1	1714
May	1st to 10th	Night	42% 5% 11% 27% 13% 1	4126
	11th to 20th	Night	51% 6% 10% 22% 10%	4105
	21st to end	Night	43% 9% 16% 24% 8% 1	3912
June	1st to 10th	Night	49% 7% 11% 22% 12%	1050
	11th to 20th	Night	49% 8% 12% 24% 7% 1	1050
	21st to end	Night	38% 8% 17% 26% 11%	1050
July	1st to 10th	Night	36% 10% 27% 23% 4	2235
	11th to 20th	Night	23% 6% 15% 46% 10%	2610
	21st to end	Night	33% 8% 18% 37% 4	3360
August	1st to 10th	Night	29% 8% 17% 42% 4	2273
	11th to 20th	Night	35% 9% 24% 24% 8%	2580
	21st to end	Night	40% 6% 29% 21% 4	3245
September	1st to 10th	Night	41% 9% 23% 22% 5%	1810
	11th to 20th	Night	39% 9% 17% 26% 8%	2164
	21st to end	Night	41% 7% 19% 24% 9% 1	2200
October	1st to 10th	Night	41% 6% 15% 28% 10%	3878
	11th to 20th	Night	44% 6% 16% 29% 5%	4202
	21st to end	Night	55% 8% 16% 17% 4	4821
November	1st to 10th	Night	54% 7% 14% 19% 6%	2941
	11th to 20th	Night	57% 9% 14% 17% 3	3150
	21st to end	Night	56% 6% 14% 19% 4	3334
December	1st to 10th	Night	60% 6% 12% 16% 7%	5500
	11th to 20th	Night	62% 6% 14% 14% 3	6481
	21st to end	Night	49% 6% 15% 23% 7%	8657

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	5% 7% 30% 33% 20% 5%	220
	11th to 20th	Day	14% 14% 25% 26% 18% 2	220
	21st to end	Day	12% 12% 34% 26% 13% 2	242
February	1st to 10th	Day	10% 9% 34% 26% 16% 4	220
	11th to 20th	Day	6% 11% 32% 31% 15% 5%	267
	21st to end	Day	10% 11% 35% 29% 12% 3	273
March	1st to 10th	Day	7% 12% 36% 32% 11% 2	498
	11th to 20th	Day	9% 17% 31% 29% 11% 3	540
	21st to end	Day	10% 15% 31% 27% 13% 4	594
April	1st to 10th	Day	14% 15% 34% 24% 9% 3	540
	11th to 20th	Day	16% 17% 29% 24% 11% 2	532
	21st to end	Day	18% 13% 30% 26% 10% 3	650
May	1st to 10th	Day	14% 13% 30% 25% 15% 3	753
	11th to 20th	Day	13% 11% 24% 30% 19% 3	775
	21st to end	Day	13% 10% 24% 34% 16% 4	907
June	1st to 10th	Day	24% 10% 24% 26% 14% 2	990
	11th to 20th	Day	20% 8% 25% 28% 15% 3	990
	21st to end	Day	13% 6% 21% 31% 23% 6%	990
July	1st to 10th	Day	13% 8% 24% 32% 20% 4	917
	11th to 20th	Day	11% 6% 21% 31% 21% 10%	912
	21st to end	Day	14% 5% 24% 26% 21% 9%	802
August	1st to 10th	Day	15% 7% 17% 27% 25% 9%	726
	11th to 20th	Day	15% 9% 31% 28% 13% 3	580
	21st to end	Day	17% 6% 27% 28% 17% 5%	583
September	1st to 10th	Day	19% 12% 27% 23% 16% 4	530
	11th to 20th	Day	14% 11% 24% 34% 12% 4	530
	21st to end	Day	18% 14% 31% 24% 12% 2	530
October	1st to 10th	Day	18% 17% 28% 24% 9% 3	360
	11th to 20th	Day	18% 14% 34% 25% 7% 2	330
	21st to end	Day	21% 11% 31% 23% 12% 2	363
November	1st to 10th	Day	18% 12% 34% 21% 14% 1	291
	11th to 20th	Day	15% 11% 38% 22% 11% 3	220
	21st to end	Day	13% 13% 26% 29% 14% 6%	220
December	1st to 10th	Day	10% 10% 30% 38% 9% 3	220
	11th to 20th	Day	12% 13% 30% 30% 14% 1	220
	21st to end	Day	10% 7% 23% 35% 19% 7%	242
January	1st to 10th	Night	12% 7% 29% 34% 15% 2	1160
	11th to 20th	Night	12% 8% 30% 35% 13% 2	1124
	21st to end	Night	13% 11% 32% 32% 11% 1	1155
February	1st to 10th	Night	9% 5% 32% 33% 18% 4	926
	11th to 20th	Night	11% 6% 30% 36% 15% 2	824
	21st to end	Night	5% 6% 31% 37% 17% 2	692
March	1st to 10th	Night	7% 8% 32% 35% 17% 2	840
	11th to 20th	Night	13% 9% 31% 33% 14% 1	840
	21st to end	Night	10% 7% 27% 36% 17% 3	924
April	1st to 10th	Night	13% 8% 29% 34% 15% 1	666
	11th to 20th	Night	11% 12% 28% 35% 13% 1	623
	21st to end	Night	17% 7% 28% 32% 13% 2	564
May	1st to 10th	Night	13% 9% 26% 34% 18% 1	420
	11th to 20th	Night	15% 7% 26% 32% 17% 2	414
	21st to end	Night	13% 6% 24% 36% 19% 2	455
June	1st to 10th	Night	21% 8% 22% 30% 18% 2	420
	11th to 20th	Night	20% 5% 19% 33% 22% 2	420
	21st to end	Night	13% 3 17% 38% 26% 4	420
July	1st to 10th	Night	10% 5% 18% 41% 24% 2	390
	11th to 20th	Night	11% 3 19% 36% 28% 4	388
	21st to end	Night	11% 4 16% 35% 28% 7%	438
August	1st to 10th	Night	13% 3 15% 33% 30% 7%	398
	11th to 20th	Night	9% 5% 24% 41% 20% 1	441
	21st to end	Night	17% 3 23% 34% 22% 1	660
September	1st to 10th	Night	16% 6% 24% 30% 21% 3	600
	11th to 20th	Night	14% 5% 22% 36% 23% 1	764
	21st to end	Night	14% 9% 29% 32% 15% 2	800
October	1st to 10th	Night	19% 9% 32% 26% 13% 2	800
	11th to 20th	Night	17% 8% 27% 33% 13% 2	800
	21st to end	Night	21% 9% 30% 26% 12% 1	1013
November	1st to 10th	Night	17% 9% 28% 32% 13% 1	1025
	11th to 20th	Night	16% 7% 34% 29% 11% 2	1050
	21st to end	Night	13% 10% 34% 30% 12% 1	1050
December	1st to 10th	Night	12% 9% 29% 32% 17% 1	1086
	11th to 20th	Night	12% 8% 32% 35% 12% 2	1160
	21st to end	Night	11% 5% 26% 34% 20% 4	1276

Page generated at 2026-06-28 00:10:42. Version ac07

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