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 2024-11-30.

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	8% 11% 5% 12% 8% 7% 7% 5% 7% 8% 22%	106985
	Night	6% 14% 6% 14% 9% 7% 7% 5% 8% 8% 17%	101184
Transparency	Day	55% 9% 17% 15% 4	106653
	Night	60% 9% 13% 13% 5% 1	101163
Seeing	Day	12% 5% 16% 27% 27% 13%	18223
	Night	12% 3 12% 33% 31% 9%	23253

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% 16% 5% 13% 12% 9% 6% 3 10% 10% 10%	949
	11th to 20th	Day	4 13% 6% 14% 8% 7% 6% 5% 12% 12% 13%	1393
	21st to end	Day	7% 14% 6% 14% 8% 7% 6% 7% 9% 10% 11%	1738
February	1st to 10th	Day	1 10% 7% 15% 9% 7% 7% 7% 8% 11% 18%	1262
	11th to 20th	Day	3 14% 6% 15% 10% 9% 8% 5% 9% 9% 12%	1300
	21st to end	Day	1 12% 4 10% 8% 9% 10% 6% 13% 10% 17%	1413
March	1st to 10th	Day	1 11% 8% 19% 10% 6% 5% 4 7% 8% 21%	2856
	11th to 20th	Day	5% 15% 6% 17% 9% 5% 6% 5% 6% 7% 19%	3464
	21st to end	Day	1 12% 7% 16% 7% 6% 6% 5% 6% 7% 26%	3987
April	1st to 10th	Day	4 13% 5% 12% 7% 8% 7% 5% 6% 8% 26%	2468
	11th to 20th	Day	3 11% 4 8% 7% 6% 6% 5% 7% 7% 36%	2589
	21st to end	Day	4 8% 4 10% 8% 6% 6% 6% 8% 7% 32%	2858
May	1st to 10th	Day	7% 12% 4 11% 8% 8% 7% 6% 8% 8% 22%	5083
	11th to 20th	Day	6% 10% 4 11% 7% 6% 7% 5% 8% 8% 29%	5389
	21st to end	Day	9% 12% 5% 11% 8% 6% 7% 5% 8% 8% 21%	6261
June	1st to 10th	Day	9% 8% 3 10% 8% 6% 7% 7% 9% 10% 23%	3610
	11th to 20th	Day	9% 8% 4 11% 8% 7% 8% 6% 7% 9% 23%	3610
	21st to end	Day	13% 9% 3 9% 7% 7% 7% 6% 9% 9% 22%	3610
July	1st to 10th	Day	14% 10% 4 11% 7% 7% 7% 6% 8% 8% 17%	6020
	11th to 20th	Day	13% 12% 4 10% 7% 7% 7% 6% 8% 8% 19%	5896
	21st to end	Day	8% 9% 3 10% 7% 7% 6% 5% 7% 10% 28%	5840
August	1st to 10th	Day	10% 9% 3 8% 6% 6% 6% 5% 6% 7% 34%	5169
	11th to 20th	Day	11% 9% 3 8% 6% 6% 6% 5% 8% 9% 29%	4654
	21st to end	Day	12% 11% 5% 14% 8% 7% 7% 6% 7% 7% 17%	4894
September	1st to 10th	Day	13% 11% 4 11% 6% 7% 7% 5% 6% 7% 22%	2451
	11th to 20th	Day	15% 10% 4 10% 7% 6% 5% 4 8% 8% 22%	2263
	21st to end	Day	14% 13% 5% 13% 7% 6% 5% 4 6% 7% 23%	2012
October	1st to 10th	Day	10% 14% 6% 13% 6% 5% 5% 4 6% 7% 25%	3152
	11th to 20th	Day	8% 16% 6% 13% 7% 6% 6% 4 5% 6% 23%	2618
	21st to end	Day	7% 16% 7% 19% 12% 10% 7% 4 5% 5% 7%	2672
November	1st to 10th	Day	7% 21% 6% 14% 8% 7% 6% 5% 9% 9% 8%	1176
	11th to 20th	Day	6% 17% 6% 20% 11% 8% 7% 4 6% 7% 6%	1079
	21st to end	Day	5% 16% 8% 17% 10% 8% 9% 6% 9% 6% 7%	796
December	1st to 10th	Day	6% 16% 9% 17% 9% 8% 9% 6% 6% 5% 7%	684
	11th to 20th	Day	5% 15% 7% 16% 11% 8% 11% 7% 9% 7% 3	724
	21st to end	Day	3 20% 6% 17% 10% 6% 6% 5% 10% 9% 7%	1045
January	1st to 10th	Night	2 12% 6% 17% 15% 11% 7% 5% 7% 8% 11%	6006
	11th to 20th	Night	4 15% 7% 14% 7% 6% 6% 4 10% 9% 17%	5539
	21st to end	Night	5% 14% 7% 18% 10% 7% 6% 5% 8% 9% 10%	5918
February	1st to 10th	Night	2 10% 5% 14% 9% 7% 6% 7% 9% 11% 20%	2917
	11th to 20th	Night	2 12% 6% 14% 9% 8% 6% 5% 8% 9% 19%	2767
	21st to end	Night	2 9% 5% 12% 10% 7% 7% 6% 9% 11% 22%	2041
March	1st to 10th	Night	1 11% 8% 21% 10% 6% 5% 3 5% 8% 23%	4008
	11th to 20th	Night	5% 15% 6% 13% 8% 7% 6% 5% 7% 9% 20%	3492
	21st to end	Night	4 15% 7% 14% 7% 6% 5% 4 5% 6% 27%	3650
April	1st to 10th	Night	4 12% 5% 10% 7% 7% 7% 7% 6% 8% 26%	1710
	11th to 20th	Night	5% 10% 4 7% 6% 5% 6% 6% 8% 11% 33%	1540
	21st to end	Night	3 9% 5% 9% 7% 7% 7% 6% 8% 9% 30%	1319
May	1st to 10th	Night	7% 11% 4 11% 9% 9% 8% 6% 9% 7% 20%	1874
	11th to 20th	Night	5% 9% 4 11% 7% 8% 7% 5% 6% 7% 32%	1506
	21st to end	Night	7% 9% 4 10% 8% 7% 9% 7% 7% 8% 24%	1313
June	1st to 10th	Night	9% 7% 3 9% 6% 8% 6% 7% 11% 11% 23%	570
	11th to 20th	Night	7% 7% 5% 11% 7% 6% 7% 5% 9% 8% 28%	570
	21st to end	Night	12% 8% 2 8% 7% 4 8% 6% 9% 11% 26%	570
July	1st to 10th	Night	12% 10% 5% 10% 8% 6% 7% 6% 7% 9% 19%	950
	11th to 20th	Night	10% 11% 3 8% 9% 6% 8% 7% 9% 8% 21%	1069
	21st to end	Night	10% 8% 3 7% 5% 5% 6% 5% 8% 10% 33%	1710
August	1st to 10th	Night	11% 9% 3 9% 5% 5% 5% 4 6% 7% 36%	1760
	11th to 20th	Night	10% 8% 3 10% 6% 6% 7% 5% 6% 10% 31%	2184
	21st to end	Night	14% 10% 5% 11% 7% 6% 6% 5% 8% 9% 18%	2771
September	1st to 10th	Night	12% 9% 4 10% 8% 7% 6% 5% 7% 8% 24%	1729
	11th to 20th	Night	12% 10% 4 10% 7% 7% 7% 6% 7% 7% 24%	1914
	21st to end	Night	16% 13% 5% 11% 7% 6% 6% 5% 6% 6% 19%	2168
October	1st to 10th	Night	9% 14% 4 10% 5% 5% 5% 5% 7% 7% 28%	3816
	11th to 20th	Night	8% 14% 5% 11% 6% 7% 6% 5% 7% 9% 22%	4310
	21st to end	Night	7% 15% 8% 20% 8% 8% 8% 6% 6% 5% 9%	4883
November	1st to 10th	Night	8% 20% 8% 15% 7% 6% 6% 5% 8% 6% 10%	3122
	11th to 20th	Night	6% 17% 6% 16% 12% 9% 8% 6% 7% 7% 6%	3300
	21st to end	Night	6% 17% 7% 16% 9% 8% 8% 7% 10% 6% 6%	3600
December	1st to 10th	Night	7% 19% 8% 17% 8% 7% 7% 5% 8% 6% 9%	3496
	11th to 20th	Night	5% 15% 7% 18% 11% 10% 9% 8% 7% 6% 4	4470
	21st to end	Night	5% 20% 6% 16% 10% 6% 6% 5% 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% 12% 8% 6% 5%	949
	11th to 20th	Day	55% 6% 7% 14% 15% 3	1408
	21st to end	Day	60% 7% 8% 11% 10% 3	1738
February	1st to 10th	Day	55% 9% 9% 15% 10% 2	1262
	11th to 20th	Day	63% 7% 10% 12% 8%	1307
	21st to end	Day	52% 10% 15% 16% 7% 1	1413
March	1st to 10th	Day	58% 7% 10% 15% 10%	2856
	11th to 20th	Day	59% 9% 10% 14% 7% 1	3464
	21st to end	Day	50% 11% 20% 13% 6%	3987
April	1st to 10th	Day	52% 11% 16% 15% 5% 1	2468
	11th to 20th	Day	44% 10% 19% 18% 9% 1	2589
	21st to end	Day	45% 10% 18% 21% 6%	2858
May	1st to 10th	Day	52% 11% 16% 17% 4	5083
	11th to 20th	Day	45% 11% 14% 23% 7%	5392
	21st to end	Day	53% 12% 14% 18% 3	6262
June	1st to 10th	Day	49% 13% 17% 18% 3	3610
	11th to 20th	Day	53% 11% 15% 14% 5%	3610
	21st to end	Day	53% 12% 16% 15% 4	3610
July	1st to 10th	Day	60% 9% 21% 9% 2	5926
	11th to 20th	Day	58% 7% 22% 11% 1	5791
	21st to end	Day	48% 8% 26% 18%	5655
August	1st to 10th	Day	47% 8% 22% 17% 6%	5149
	11th to 20th	Day	48% 9% 20% 20% 2	4699
	21st to end	Day	63% 9% 21% 6% 1	4893
September	1st to 10th	Day	59% 10% 18% 12% 1	2451
	11th to 20th	Day	54% 11% 22% 12% 1	2263
	21st to end	Day	58% 9% 17% 14% 2	2012
October	1st to 10th	Day	56% 7% 19% 17% 2	3152
	11th to 20th	Day	61% 6% 13% 19% 1	2618
	21st to end	Day	76% 6% 12% 7%	2672
November	1st to 10th	Day	67% 9% 12% 8% 3	1176
	11th to 20th	Day	73% 8% 11% 6% 1	1079
	21st to end	Day	70% 8% 11% 9% 1	796
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	66% 9% 9% 7% 4 4	6006
	11th to 20th	Night	58% 6% 7% 10% 13% 5%	5586
	21st to end	Night	65% 7% 7% 9% 8% 4	5918
February	1st to 10th	Night	52% 8% 11% 16% 13% 1	2917
	11th to 20th	Night	57% 8% 11% 16% 8% 1	2771
	21st to end	Night	52% 8% 14% 16% 9%	2041
March	1st to 10th	Night	60% 5% 9% 15% 11%	4008
	11th to 20th	Night	55% 10% 11% 15% 7% 1	3494
	21st to end	Night	50% 11% 19% 13% 7%	3650
April	1st to 10th	Night	50% 10% 17% 14% 7% 2	1710
	11th to 20th	Night	41% 12% 16% 21% 10%	1540
	21st to end	Night	43% 10% 19% 22% 6%	1319
May	1st to 10th	Night	52% 12% 17% 16% 3	1874
	11th to 20th	Night	47% 9% 14% 22% 8%	1506
	21st to end	Night	49% 13% 15% 20% 3	1313
June	1st to 10th	Night	46% 15% 17% 19% 4	570
	11th to 20th	Night	50% 11% 17% 18% 4	570
	21st to end	Night	48% 13% 20% 15% 3	570
July	1st to 10th	Night	57% 11% 22% 8% 3	935
	11th to 20th	Night	53% 10% 26% 11% 1	1051
	21st to end	Night	44% 8% 27% 20% 1	1656
August	1st to 10th	Night	47% 8% 19% 18% 7% 1	1755
	11th to 20th	Night	48% 7% 19% 21% 5%	2205
	21st to end	Night	59% 8% 23% 10%	2771
September	1st to 10th	Night	55% 13% 16% 15% 2	1729
	11th to 20th	Night	54% 13% 17% 15% 1	1914
	21st to end	Night	61% 10% 14% 13% 2	2168
October	1st to 10th	Night	55% 7% 15% 21% 2	3816
	11th to 20th	Night	56% 6% 15% 18% 4	4310
	21st to end	Night	72% 7% 14% 8%	4883
November	1st to 10th	Night	69% 8% 11% 9% 2	3122
	11th to 20th	Night	71% 10% 11% 7% 1	3300
	21st to end	Night	70% 9% 10% 9% 2	3600
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 9% 36% 29% 14%	90
	21st to end	Day	11% 5% 11% 33% 26% 13%	99
February	1st to 10th	Day	6% 2 9% 28% 34% 21%	320
	11th to 20th	Day	8% 2 9% 37% 29% 15%	365
	21st to end	Day	6% 3 11% 34% 27% 19%	307
March	1st to 10th	Day	4 5% 14% 27% 29% 21%	370
	11th to 20th	Day	9% 4 15% 29% 26% 17%	370
	21st to end	Day	7% 4 18% 28% 27% 16%	453
April	1st to 10th	Day	8% 2 20% 30% 29% 11%	648
	11th to 20th	Day	5% 4 17% 31% 31% 12%	640
	21st to end	Day	8% 6% 16% 26% 30% 14%	650
May	1st to 10th	Day	10% 8% 21% 26% 24% 11%	653
	11th to 20th	Day	11% 8% 19% 29% 22% 11%	708
	21st to end	Day	12% 8% 20% 28% 24% 8%	970
June	1st to 10th	Day	12% 5% 15% 28% 30% 11%	1060
	11th to 20th	Day	11% 5% 16% 26% 30% 13%	1060
	21st to end	Day	14% 4 15% 23% 29% 15%	1060
July	1st to 10th	Day	13% 4 15% 26% 30% 12%	1041
	11th to 20th	Day	16% 3 11% 24% 31% 14%	964
	21st to end	Day	12% 2 14% 23% 30% 18%	745
August	1st to 10th	Day	16% 5% 14% 23% 27% 15%	676
	11th to 20th	Day	17% 5% 18% 28% 24% 8%	665
	21st to end	Day	19% 5% 15% 23% 27% 11%	748
September	1st to 10th	Day	17% 6% 15% 23% 21% 18%	661
	11th to 20th	Day	16% 5% 18% 21% 28% 13%	480
	21st to end	Day	16% 9% 17% 25% 21% 12%	390
October	1st to 10th	Day	22% 7% 20% 20% 19% 13%	390
	11th to 20th	Day	21% 6% 14% 21% 22% 16%	390
	21st to end	Day	14% 4 13% 29% 25% 14%	420
November	1st to 10th	Day	15% 3 12% 35% 21% 15%	200
	11th to 20th	Day	14% 4 12% 23% 26% 22%	162
	21st to end	Day	10% 2 12% 35% 21% 19%	99
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 11% 42% 25% 8%	953
	21st to end	Night	10% 3 12% 42% 26% 7%	935
February	1st to 10th	Night	7% 1 11% 38% 32% 10%	850
	11th to 20th	Night	6% 2 12% 44% 29% 6%	834
	21st to end	Night	5% 1 11% 43% 32% 9%	703
March	1st to 10th	Night	5% 3 11% 35% 38% 8%	840
	11th to 20th	Night	7% 2 13% 32% 40% 7%	584
	21st to end	Night	6% 3 13% 35% 33% 10%	627
April	1st to 10th	Night	10% 3 10% 33% 36% 7%	570
	11th to 20th	Night	8% 3 10% 32% 35% 13%	563
	21st to end	Night	7% 2 15% 29% 37% 10%	559
May	1st to 10th	Night	10% 4 17% 28% 34% 7%	367
	11th to 20th	Night	12% 2 17% 28% 35% 5%	187
	21st to end	Night	10% 3 17% 33% 33% 4	206
June	1st to 10th	Night	13% 2 7% 29% 45% 4	190
	11th to 20th	Night	9% 3 12% 30% 43% 4	190
	21st to end	Night	15% 2 6% 28% 41% 8%	190
July	1st to 10th	Night	9% 2 14% 31% 38% 7%	185
	11th to 20th	Night	13% 1 14% 29% 34% 9%	184
	21st to end	Night	11% 9% 22% 42% 15%	208
August	1st to 10th	Night	17% 4 16% 22% 35% 7%	296
	11th to 20th	Night	17% 3 13% 28% 31% 9%	564
	21st to end	Night	19% 3 10% 23% 36% 10%	627
September	1st to 10th	Night	16% 4 13% 26% 30% 11%	570
	11th to 20th	Night	18% 3 12% 27% 33% 7%	570
	21st to end	Night	21% 4 15% 25% 26% 10%	648
October	1st to 10th	Night	19% 4 15% 30% 24% 7%	763
	11th to 20th	Night	22% 4 11% 26% 28% 8%	860
	21st to end	Night	15% 3 12% 33% 29% 9%	946
November	1st to 10th	Night	18% 3 12% 30% 29% 8%	880
	11th to 20th	Night	13% 3 8% 29% 32% 16%	925
	21st to end	Night	12% 3 11% 33% 28% 13%	1100
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 2024-11-27 14:30:54. Version ac07

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