Dawson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dawson clear sky chart from 2005-11-06 to 2024-01-15.

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% 10% 5% 10% 9% 5% 7% 7% 7% 8% 22%	74278
	Night	7% 13% 6% 12% 10% 5% 7% 7% 8% 8% 17%	75504
Transparency	Day	55% 11% 16% 14% 4	73886
	Night	60% 10% 13% 13% 5%	75415
Seeing	Day	13% 5% 15% 27% 27% 13%	16893
	Night	12% 3 12% 33% 31% 9%	22240

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	7% 12% 9% 14% 12% 4 7% 4 10% 10% 13%	569
	11th to 20th	Day	6% 15% 9% 15% 11% 5% 6% 7% 8% 11% 7%	824
	21st to end	Day	5% 13% 8% 15% 11% 6% 9% 4 7% 9% 12%	990
February	1st to 10th	Day	1 9% 7% 13% 10% 5% 8% 8% 8% 11% 18%	1196
	11th to 20th	Day	3 13% 7% 14% 11% 7% 8% 8% 9% 8% 11%	1230
	21st to end	Day	2 13% 4 9% 8% 6% 10% 8% 11% 13% 16%	1332
March	1st to 10th	Day	2 9% 6% 14% 12% 5% 7% 5% 8% 10% 22%	1638
	11th to 20th	Day	3 12% 5% 11% 9% 3 6% 7% 8% 8% 27%	1964
	21st to end	Day	3 8% 4 11% 10% 5% 6% 7% 7% 7% 34%	2268
April	1st to 10th	Day	4 12% 5% 10% 8% 6% 7% 7% 6% 8% 27%	2338
	11th to 20th	Day	4 10% 5% 7% 8% 4 7% 6% 6% 8% 35%	2450
	21st to end	Day	5% 7% 5% 9% 9% 5% 7% 7% 8% 7% 32%	2707
May	1st to 10th	Day	6% 9% 4 9% 8% 6% 7% 7% 7% 9% 28%	2889
	11th to 20th	Day	9% 7% 5% 9% 8% 4 7% 6% 7% 7% 31%	3041
	21st to end	Day	7% 9% 4 9% 8% 5% 7% 7% 8% 10% 25%	3527
June	1st to 10th	Day	9% 8% 4 9% 8% 5% 7% 8% 9% 10% 23%	3420
	11th to 20th	Day	9% 8% 4 10% 9% 5% 8% 7% 7% 9% 23%	3420
	21st to end	Day	14% 8% 4 8% 8% 5% 7% 7% 8% 8% 22%	3420
July	1st to 10th	Day	11% 7% 4 8% 8% 6% 8% 7% 8% 8% 25%	3420
	11th to 20th	Day	13% 10% 4 9% 9% 5% 8% 7% 8% 8% 19%	3352
	21st to end	Day	10% 8% 3 8% 8% 6% 7% 7% 7% 9% 27%	3338
August	1st to 10th	Day	12% 9% 4 9% 8% 5% 7% 6% 6% 7% 26%	2941
	11th to 20th	Day	14% 11% 4 9% 9% 5% 7% 7% 8% 9% 18%	2654
	21st to end	Day	14% 10% 4 10% 9% 5% 7% 7% 7% 8% 18%	2791
September	1st to 10th	Day	14% 11% 4 9% 8% 5% 7% 7% 6% 7% 23%	2322
	11th to 20th	Day	15% 10% 4 9% 8% 5% 6% 5% 8% 8% 23%	2144
	21st to end	Day	13% 12% 4 11% 9% 4 5% 6% 6% 7% 23%	1907
October	1st to 10th	Day	15% 15% 6% 10% 9% 4 5% 5% 5% 6% 19%	1796
	11th to 20th	Day	12% 16% 7% 14% 10% 4 6% 4 5% 5% 17%	1494
	21st to end	Day	8% 17% 5% 14% 13% 6% 9% 6% 6% 7% 10%	1541
November	1st to 10th	Day	7% 19% 6% 12% 9% 5% 6% 6% 9% 10% 9%	1116
	11th to 20th	Day	6% 16% 6% 17% 13% 7% 8% 7% 6% 8% 6%	1026
	21st to end	Day	5% 16% 8% 16% 11% 6% 9% 8% 8% 8% 7%	760
December	1st to 10th	Day	7% 15% 10% 16% 10% 6% 9% 8% 6% 6% 8%	684
	11th to 20th	Day	5% 14% 7% 13% 14% 6% 11% 10% 9% 7% 3	724
	21st to end	Day	3 20% 6% 16% 11% 5% 6% 6% 10% 9% 7%	1045
January	1st to 10th	Night	4 12% 6% 13% 11% 6% 9% 7% 8% 10% 14%	3596
	11th to 20th	Night	7% 16% 9% 14% 11% 5% 7% 5% 7% 9% 9%	3243
	21st to end	Night	4 15% 8% 16% 11% 5% 7% 6% 8% 8% 12%	3366
February	1st to 10th	Night	3 10% 6% 12% 10% 5% 7% 7% 9% 11% 20%	2763
	11th to 20th	Night	2 12% 7% 13% 11% 7% 7% 6% 8% 8% 19%	2617
	21st to end	Night	3 9% 5% 11% 11% 5% 7% 7% 8% 11% 23%	1924
March	1st to 10th	Night	2 9% 6% 11% 9% 5% 6% 5% 6% 10% 30%	2322
	11th to 20th	Night	3 9% 5% 10% 10% 5% 6% 6% 6% 10% 29%	1992
	21st to end	Night	3 10% 6% 9% 8% 5% 5% 6% 6% 7% 36%	2088
April	1st to 10th	Night	4 12% 5% 8% 9% 5% 8% 7% 7% 8% 27%	1620
	11th to 20th	Night	5% 10% 5% 6% 7% 3 7% 7% 8% 10% 32%	1459
	21st to end	Night	4 9% 4 8% 8% 5% 7% 8% 8% 9% 30%	1250
May	1st to 10th	Night	6% 7% 4 8% 9% 6% 8% 7% 9% 9% 27%	1068
	11th to 20th	Night	7% 7% 4 9% 7% 6% 7% 5% 6% 8% 33%	854
	21st to end	Night	6% 8% 3 7% 8% 5% 7% 9% 8% 9% 30%	745
June	1st to 10th	Night	10% 6% 4 8% 8% 5% 8% 8% 10% 11% 22%	540
	11th to 20th	Night	8% 6% 5% 10% 9% 5% 7% 6% 10% 7% 28%	540
	21st to end	Night	13% 8% 2 7% 8% 3 6% 9% 8% 11% 26%	540
July	1st to 10th	Night	6% 9% 5% 9% 8% 4 7% 9% 7% 11% 24%	540
	11th to 20th	Night	11% 9% 4 7% 9% 5% 8% 9% 9% 8% 22%	607
	21st to end	Night	9% 7% 4 7% 6% 4 6% 7% 8% 10% 31%	977
August	1st to 10th	Night	14% 9% 4 7% 6% 4 7% 6% 8% 8% 27%	996
	11th to 20th	Night	14% 9% 4 10% 10% 5% 6% 6% 6% 8% 22%	1246
	21st to end	Night	15% 10% 5% 9% 8% 5% 7% 6% 9% 9% 19%	1563
September	1st to 10th	Night	12% 8% 4 9% 8% 5% 7% 6% 7% 9% 25%	1638
	11th to 20th	Night	12% 9% 4 8% 8% 4 7% 8% 7% 8% 26%	1813
	21st to end	Night	16% 12% 5% 9% 8% 5% 6% 7% 6% 7% 20%	2053
October	1st to 10th	Night	14% 13% 5% 9% 7% 5% 5% 6% 6% 7% 22%	2162
	11th to 20th	Night	12% 19% 6% 10% 7% 5% 6% 5% 5% 7% 17%	2466
	21st to end	Night	8% 15% 7% 12% 11% 5% 8% 8% 7% 7% 14%	2812
November	1st to 10th	Night	8% 19% 9% 13% 9% 4 7% 6% 8% 7% 11%	2962
	11th to 20th	Night	6% 15% 7% 14% 13% 8% 8% 9% 7% 7% 6%	3134
	21st to end	Night	6% 17% 8% 14% 10% 6% 8% 8% 10% 7% 6%	3420
December	1st to 10th	Night	8% 18% 8% 16% 9% 5% 7% 6% 8% 6% 9%	3496
	11th to 20th	Night	5% 13% 8% 16% 13% 8% 9% 10% 7% 6% 4	4470
	21st to end	Night	5% 19% 7% 13% 11% 5% 6% 7% 10% 9% 8%	6622

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% 7% 11% 11% 8% 1	569
	11th to 20th	Day	68% 7% 8% 13% 3	824
	21st to end	Day	67% 7% 8% 9% 8% 1	990
February	1st to 10th	Day	55% 9% 9% 16% 10% 2	1196
	11th to 20th	Day	65% 7% 9% 12% 7%	1237
	21st to end	Day	53% 9% 15% 16% 6% 1	1332
March	1st to 10th	Day	53% 8% 10% 17% 11% 1	1638
	11th to 20th	Day	50% 9% 11% 19% 10% 1	1964
	21st to end	Day	44% 10% 18% 16% 10% 1	2268
April	1st to 10th	Day	52% 11% 17% 15% 5% 1	2338
	11th to 20th	Day	46% 10% 19% 17% 8% 1	2450
	21st to end	Day	46% 10% 17% 20% 6%	2707
May	1st to 10th	Day	48% 10% 18% 20% 4	2889
	11th to 20th	Day	47% 9% 12% 23% 8%	3044
	21st to end	Day	49% 11% 16% 22% 3	3528
June	1st to 10th	Day	50% 13% 17% 17% 3	3420
	11th to 20th	Day	53% 12% 15% 15% 5%	3420
	21st to end	Day	54% 13% 16% 14% 3	3420
July	1st to 10th	Day	51% 13% 18% 15% 3	3326
	11th to 20th	Day	57% 13% 18% 10% 2	3247
	21st to end	Day	50% 13% 24% 12%	3152
August	1st to 10th	Day	53% 13% 19% 13% 2	2921
	11th to 20th	Day	57% 15% 18% 9%	2654
	21st to end	Day	59% 15% 19% 6% 1	2791
September	1st to 10th	Day	58% 10% 18% 13% 1	2322
	11th to 20th	Day	54% 12% 22% 12% 1	2144
	21st to end	Day	57% 9% 18% 14% 2	1907
October	1st to 10th	Day	64% 10% 15% 8% 2	1796
	11th to 20th	Day	69% 8% 15% 7% 1	1494
	21st to end	Day	70% 9% 13% 8%	1541
November	1st to 10th	Day	66% 9% 13% 9% 3	1116
	11th to 20th	Day	72% 9% 12% 6% 1	1026
	21st to end	Day	70% 8% 11% 9% 1	760
December	1st to 10th	Day	71% 11% 7% 9% 2	684
	11th to 20th	Day	71% 8% 9% 9% 3	726
	21st to end	Day	65% 8% 9% 10% 8%	1045
January	1st to 10th	Night	60% 10% 11% 11% 6% 2	3596
	11th to 20th	Night	70% 7% 7% 10% 5%	3243
	21st to end	Night	67% 7% 8% 11% 7%	3366
February	1st to 10th	Night	52% 8% 10% 16% 12% 2	2763
	11th to 20th	Night	59% 8% 11% 15% 7% 1	2621
	21st to end	Night	52% 8% 15% 17% 9%	1924
March	1st to 10th	Night	48% 7% 14% 21% 10% 1	2322
	11th to 20th	Night	48% 8% 11% 22% 9% 1	1994
	21st to end	Night	44% 9% 17% 18% 12%	2088
April	1st to 10th	Night	50% 10% 18% 14% 7% 2	1620
	11th to 20th	Night	43% 12% 16% 20% 9%	1459
	21st to end	Night	45% 10% 18% 20% 6%	1250
May	1st to 10th	Night	48% 12% 16% 22% 2	1068
	11th to 20th	Night	47% 8% 13% 24% 8%	854
	21st to end	Night	45% 11% 17% 23% 4	745
June	1st to 10th	Night	47% 15% 16% 18% 4	540
	11th to 20th	Night	50% 11% 17% 17% 4	540
	21st to end	Night	49% 14% 19% 15% 3	540
July	1st to 10th	Night	50% 13% 19% 14% 5%	525
	11th to 20th	Night	52% 16% 21% 10% 1	589
	21st to end	Night	44% 14% 25% 16% 1	923
August	1st to 10th	Night	51% 14% 21% 13% 2	991
	11th to 20th	Night	57% 12% 18% 12% 1	1246
	21st to end	Night	58% 14% 20% 7%	1563
September	1st to 10th	Night	53% 13% 16% 15% 2	1638
	11th to 20th	Night	52% 14% 17% 16% 1	1813
	21st to end	Night	60% 10% 15% 13% 2	2053
October	1st to 10th	Night	60% 10% 15% 11% 3 1	2162
	11th to 20th	Night	66% 9% 14% 8% 4	2466
	21st to end	Night	64% 11% 15% 10% 1	2812
November	1st to 10th	Night	67% 8% 12% 10% 3	2962
	11th to 20th	Night	70% 11% 11% 7% 1	3134
	21st to end	Night	70% 10% 10% 9% 2	3420
December	1st to 10th	Night	71% 9% 8% 8% 4	3496
	11th to 20th	Night	73% 9% 8% 7% 3	4467
	21st to end	Night	66% 8% 8% 10% 7% 1	6622

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	8% 2 8% 32% 43% 7%	90
	11th to 20th	Day	11% 1 8% 35% 30% 15%	84
	21st to end	Day	10% 5% 11% 32% 28% 14%	88
February	1st to 10th	Day	6% 2 9% 29% 32% 22%	294
	11th to 20th	Day	9% 2 10% 36% 27% 15%	335
	21st to end	Day	6% 3 12% 33% 28% 18%	280
March	1st to 10th	Day	5% 5% 14% 27% 29% 21%	340
	11th to 20th	Day	9% 4 14% 29% 27% 16%	340
	21st to end	Day	7% 4 17% 29% 27% 17%	414
April	1st to 10th	Day	9% 2 20% 29% 30% 10%	598
	11th to 20th	Day	6% 4 17% 31% 29% 13%	590
	21st to end	Day	9% 6% 17% 27% 29% 12%	600
May	1st to 10th	Day	10% 7% 21% 27% 24% 11%	603
	11th to 20th	Day	11% 8% 20% 29% 21% 11%	656
	21st to end	Day	12% 8% 20% 28% 24% 8%	902
June	1st to 10th	Day	13% 5% 13% 27% 31% 11%	990
	11th to 20th	Day	11% 5% 17% 26% 29% 12%	990
	21st to end	Day	15% 4 16% 24% 28% 14%	990
July	1st to 10th	Day	12% 4 15% 26% 30% 12%	971
	11th to 20th	Day	16% 3 11% 24% 31% 14%	898
	21st to end	Day	13% 2 13% 22% 30% 19%	690
August	1st to 10th	Day	15% 6% 13% 23% 27% 15%	626
	11th to 20th	Day	17% 5% 18% 28% 24% 8%	615
	21st to end	Day	19% 5% 15% 24% 27% 11%	693
September	1st to 10th	Day	17% 6% 15% 23% 21% 18%	612
	11th to 20th	Day	15% 5% 17% 21% 28% 13%	441
	21st to end	Day	14% 10% 18% 26% 21% 11%	360
October	1st to 10th	Day	22% 7% 21% 18% 19% 13%	360
	11th to 20th	Day	21% 6% 14% 22% 21% 16%	360
	21st to end	Day	14% 4 13% 29% 26% 14%	388
November	1st to 10th	Day	16% 2 12% 34% 20% 16%	180
	11th to 20th	Day	15% 2 12% 23% 26% 21%	146
	21st to end	Day	11% 2 12% 38% 20% 17%	90
December	1st to 10th	Day	10% 4 14% 41% 28% 2	90
	11th to 20th	Day	10% 3 14% 36% 23% 13%	90
	21st to end	Day	6% 4 17% 30% 29% 13%	99
January	1st to 10th	Night	9% 2 9% 35% 35% 11%	1130
	11th to 20th	Night	13% 2 10% 41% 25% 8%	923
	21st to end	Night	10% 2 11% 41% 27% 8%	880
February	1st to 10th	Night	7% 1 11% 38% 32% 11%	800
	11th to 20th	Night	6% 3 12% 42% 30% 7%	784
	21st to end	Night	6% 1 10% 43% 31% 9%	658
March	1st to 10th	Night	5% 3 12% 35% 37% 9%	792
	11th to 20th	Night	7% 2 12% 31% 41% 7%	554
	21st to end	Night	6% 3 13% 34% 33% 11%	594
April	1st to 10th	Night	11% 3 10% 34% 35% 7%	540
	11th to 20th	Night	8% 3 11% 31% 34% 13%	533
	21st to end	Night	8% 2 15% 30% 36% 9%	530
May	1st to 10th	Night	10% 3 17% 27% 35% 7%	348
	11th to 20th	Night	12% 2 18% 29% 33% 6%	177
	21st to end	Night	10% 3 16% 33% 33% 4	195
June	1st to 10th	Night	13% 2 7% 26% 47% 4	180
	11th to 20th	Night	9% 3 12% 31% 41% 4	180
	21st to end	Night	16% 2 6% 28% 40% 7%	180
July	1st to 10th	Night	8% 1 14% 31% 38% 7%	175
	11th to 20th	Night	14% 1 13% 29% 35% 9%	174
	21st to end	Night	11% 1 9% 21% 43% 15%	197
August	1st to 10th	Night	18% 4 16% 21% 34% 7%	280
	11th to 20th	Night	17% 3 12% 28% 32% 9%	534
	21st to end	Night	19% 3 10% 23% 35% 10%	594
September	1st to 10th	Night	16% 4 13% 26% 31% 11%	540
	11th to 20th	Night	18% 3 12% 27% 34% 7%	540
	21st to end	Night	21% 4 15% 26% 26% 8%	613
October	1st to 10th	Night	20% 5% 15% 30% 24% 7%	722
	11th to 20th	Night	23% 4 12% 27% 27% 7%	810
	21st to end	Night	15% 3 11% 32% 30% 9%	891
November	1st to 10th	Night	18% 3 12% 30% 29% 9%	830
	11th to 20th	Night	13% 3 8% 30% 33% 14%	873
	21st to end	Night	13% 3 12% 33% 28% 12%	1040
December	1st to 10th	Night	14% 3 12% 37% 25% 8%	1076
	11th to 20th	Night	12% 3 13% 37% 26% 10%	1130
	21st to end	Night	9% 2 12% 34% 32% 12%	1243

Page generated at 2024-01-11 20:33:47. Version ac07

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