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 2026-02-16.

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	7% 11% 5% 13% 8% 7% 7% 5% 7% 8% 22%	133926
	Night	5% 13% 6% 15% 9% 7% 7% 5% 7% 8% 17%	135650
Transparency	Day	55% 8% 17% 15% 5%	133544
	Night	61% 7% 12% 12% 7% 1	135612
Seeing	Day	12% 5% 16% 27% 27% 13%	19702
	Night	12% 3 12% 33% 31% 9%	25033

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	3 13% 5% 17% 10% 7% 5% 3 8% 12% 16%	1763
	11th to 20th	Day	3 12% 6% 17% 8% 7% 6% 5% 9% 11% 16%	2629
	21st to end	Day	5% 11% 5% 15% 11% 13% 8% 7% 8% 8% 9%	3215
February	1st to 10th	Day	1 10% 6% 15% 10% 8% 8% 6% 7% 11% 17%	1396
	11th to 20th	Day	3 13% 6% 15% 10% 9% 7% 5% 9% 9% 14%	1408
	21st to end	Day	1 13% 5% 10% 8% 9% 10% 6% 13% 10% 17%	1485
March	1st to 10th	Day	1 12% 8% 22% 11% 7% 6% 4 7% 7% 16%	4100
	11th to 20th	Day	4 11% 5% 17% 10% 6% 7% 5% 7% 8% 21%	4951
	21st to end	Day	1 11% 7% 20% 8% 6% 6% 5% 6% 6% 24%	5707
April	1st to 10th	Day	4 13% 5% 11% 7% 8% 7% 5% 6% 8% 26%	2598
	11th to 20th	Day	4 11% 4 8% 7% 6% 6% 5% 7% 7% 35%	2727
	21st to end	Day	4 9% 4 10% 8% 6% 6% 6% 8% 7% 31%	3009
May	1st to 10th	Day	6% 12% 4 11% 8% 8% 7% 6% 8% 9% 22%	7277
	11th to 20th	Day	6% 10% 4 10% 6% 6% 6% 5% 7% 7% 33%	7737
	21st to end	Day	7% 10% 4 11% 8% 7% 8% 6% 9% 9% 20%	8995
June	1st to 10th	Day	9% 8% 3 10% 8% 6% 7% 6% 9% 10% 22%	3800
	11th to 20th	Day	9% 8% 4 10% 8% 7% 7% 6% 7% 9% 25%	3800
	21st to end	Day	13% 9% 3 9% 7% 7% 7% 6% 9% 9% 22%	3800
July	1st to 10th	Day	11% 9% 3 10% 7% 7% 7% 6% 9% 10% 21%	8620
	11th to 20th	Day	11% 11% 4 11% 7% 7% 6% 6% 8% 8% 21%	8440
	21st to end	Day	9% 10% 4 11% 7% 7% 6% 5% 7% 9% 24%	8383
August	1st to 10th	Day	10% 9% 3 8% 6% 6% 6% 5% 6% 7% 34%	5333
	11th to 20th	Day	11% 9% 3 8% 6% 6% 6% 5% 8% 9% 29%	4804
	21st to end	Day	12% 11% 5% 14% 8% 7% 7% 6% 7% 8% 17%	5049
September	1st to 10th	Day	13% 11% 4 11% 6% 7% 7% 5% 6% 7% 22%	2580
	11th to 20th	Day	15% 10% 4 10% 7% 7% 5% 4 7% 8% 22%	2382
	21st to end	Day	13% 13% 5% 13% 7% 5% 5% 4 6% 7% 22%	2118
October	1st to 10th	Day	10% 14% 6% 13% 6% 5% 5% 4 6% 7% 24%	3252
	11th to 20th	Day	9% 16% 6% 13% 7% 6% 6% 4 5% 6% 22%	2701
	21st to end	Day	7% 17% 8% 19% 12% 10% 7% 4 5% 5% 7%	2757
November	1st to 10th	Day	7% 22% 6% 15% 8% 6% 6% 5% 9% 9% 8%	1236
	11th to 20th	Day	6% 17% 6% 21% 11% 8% 7% 4 7% 7% 6%	1133
	21st to end	Day	5% 16% 8% 18% 9% 8% 9% 6% 9% 6% 6%	840
December	1st to 10th	Day	8% 14% 7% 20% 11% 8% 7% 4 5% 9% 7%	1208
	11th to 20th	Day	4 16% 7% 16% 10% 7% 10% 5% 8% 6% 11%	1164
	21st to end	Day	3 22% 7% 19% 10% 6% 5% 3 8% 10% 7%	1529
January	1st to 10th	Night	3 12% 6% 16% 11% 8% 6% 4 6% 11% 18%	11160
	11th to 20th	Night	3 12% 6% 15% 9% 8% 7% 5% 9% 9% 17%	10333
	21st to end	Night	3 11% 6% 17% 12% 12% 9% 6% 8% 7% 8%	10965
February	1st to 10th	Night	2 11% 5% 14% 9% 7% 6% 7% 8% 10% 19%	3222
	11th to 20th	Night	2 12% 6% 14% 9% 8% 6% 5% 8% 9% 20%	2990
	21st to end	Night	3 11% 6% 13% 10% 7% 7% 5% 8% 10% 21%	2145
March	1st to 10th	Night	1 12% 10% 24% 10% 6% 5% 3 5% 6% 18%	5774
	11th to 20th	Night	3 11% 5% 15% 9% 8% 7% 5% 8% 10% 20%	5006
	21st to end	Night	3 13% 7% 16% 7% 7% 6% 4 6% 6% 26%	5235
April	1st to 10th	Night	4 12% 5% 10% 7% 7% 7% 7% 7% 9% 26%	1800
	11th to 20th	Night	5% 10% 4 8% 6% 5% 6% 6% 8% 11% 33%	1622
	21st to end	Night	4 9% 4 9% 7% 7% 7% 6% 9% 9% 29%	1388
May	1st to 10th	Night	6% 10% 4 11% 8% 8% 8% 7% 10% 9% 20%	2680
	11th to 20th	Night	7% 11% 4 9% 6% 6% 6% 4 5% 8% 34%	2158
	21st to end	Night	7% 9% 3 10% 8% 8% 9% 6% 8% 8% 25%	1881
June	1st to 10th	Night	10% 7% 3 9% 6% 8% 6% 7% 11% 11% 23%	600
	11th to 20th	Night	7% 7% 5% 10% 7% 6% 7% 5% 9% 9% 29%	600
	21st to end	Night	11% 8% 2 8% 7% 5% 8% 6% 9% 11% 25%	600
July	1st to 10th	Night	11% 8% 4 10% 6% 6% 7% 6% 8% 9% 24%	1360
	11th to 20th	Night	10% 11% 4 9% 9% 7% 9% 6% 9% 7% 20%	1531
	21st to end	Night	9% 9% 4 9% 6% 6% 7% 5% 9% 9% 28%	2458
August	1st to 10th	Night	11% 9% 3 9% 5% 5% 5% 5% 5% 7% 36%	1816
	11th to 20th	Night	10% 8% 3 10% 6% 6% 6% 5% 6% 9% 31%	2254
	21st to end	Night	14% 10% 4 11% 7% 6% 6% 5% 8% 9% 19%	2858
September	1st to 10th	Night	11% 9% 4 10% 8% 7% 7% 5% 7% 8% 25%	1820
	11th to 20th	Night	12% 10% 4 10% 7% 7% 7% 6% 7% 7% 24%	2015
	21st to end	Night	15% 13% 5% 11% 7% 6% 6% 5% 6% 6% 19%	2282
October	1st to 10th	Night	9% 14% 4 11% 5% 5% 5% 4 7% 7% 28%	3936
	11th to 20th	Night	8% 14% 5% 11% 6% 7% 6% 5% 7% 9% 22%	4447
	21st to end	Night	7% 15% 8% 20% 8% 8% 8% 6% 6% 5% 9%	5040
November	1st to 10th	Night	7% 21% 8% 15% 7% 6% 6% 5% 8% 6% 10%	3282
	11th to 20th	Night	6% 16% 6% 17% 12% 9% 8% 6% 7% 6% 6%	3465
	21st to end	Night	6% 17% 7% 17% 9% 9% 8% 7% 10% 6% 5%	3780
December	1st to 10th	Night	8% 17% 7% 19% 11% 7% 6% 5% 6% 6% 8%	6196
	11th to 20th	Night	3 15% 7% 21% 10% 8% 8% 6% 6% 6% 8%	7260
	21st to end	Night	4 22% 8% 18% 10% 6% 6% 4 8% 7% 7%	9691

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	59% 4 8% 8% 19% 2	1763
	11th to 20th	Day	59% 6% 12% 11% 10% 2	2644
	21st to end	Day	67% 6% 9% 10% 7% 2	3216
February	1st to 10th	Day	57% 9% 9% 15% 10% 1	1396
	11th to 20th	Day	62% 7% 10% 12% 9%	1415
	21st to end	Day	53% 9% 14% 16% 7% 1	1485
March	1st to 10th	Day	63% 6% 10% 13% 8%	4100
	11th to 20th	Day	56% 7% 8% 15% 12% 2	4951
	21st to end	Day	55% 9% 14% 12% 10%	5707
April	1st to 10th	Day	52% 10% 17% 15% 5% 1	2598
	11th to 20th	Day	45% 9% 19% 18% 9% 1	2727
	21st to end	Day	46% 10% 18% 20% 6%	3009
May	1st to 10th	Day	51% 9% 14% 17% 9%	7277
	11th to 20th	Day	43% 8% 11% 24% 12% 2	7740
	21st to end	Day	51% 10% 13% 20% 6%	8996
June	1st to 10th	Day	50% 12% 16% 18% 3	3800
	11th to 20th	Day	51% 11% 16% 16% 6%	3800
	21st to end	Day	53% 12% 17% 15% 3	3800
July	1st to 10th	Day	54% 7% 24% 13% 3	8526
	11th to 20th	Day	58% 5% 26% 10% 1	8335
	21st to end	Day	53% 6% 25% 15%	8147
August	1st to 10th	Day	46% 8% 22% 18% 6%	5313
	11th to 20th	Day	48% 9% 21% 20% 2	4849
	21st to end	Day	62% 9% 21% 7% 1	5048
September	1st to 10th	Day	59% 9% 19% 12% 1	2580
	11th to 20th	Day	55% 10% 22% 12% 1	2382
	21st to end	Day	59% 8% 17% 14% 2	2118
October	1st to 10th	Day	56% 6% 19% 16% 2	3252
	11th to 20th	Day	62% 6% 13% 18% 1	2701
	21st to end	Day	76% 5% 11% 7%	2757
November	1st to 10th	Day	68% 9% 12% 8% 3	1236
	11th to 20th	Day	73% 8% 11% 7% 1	1133
	21st to end	Day	72% 8% 11% 9% 1	840
December	1st to 10th	Day	73% 9% 6% 10% 2	1208
	11th to 20th	Day	67% 6% 12% 9% 5%	1166
	21st to end	Day	69% 6% 7% 12% 5%	1529
January	1st to 10th	Night	59% 5% 6% 8% 19% 2	11161
	11th to 20th	Night	60% 5% 12% 12% 9% 3	10380
	21st to end	Night	70% 6% 8% 9% 5% 2	10965
February	1st to 10th	Night	54% 7% 10% 15% 12% 2	3222
	11th to 20th	Night	56% 7% 11% 16% 9% 1	2994
	21st to end	Night	54% 8% 14% 15% 9%	2145
March	1st to 10th	Night	66% 4 9% 13% 9%	5774
	11th to 20th	Night	53% 8% 9% 17% 12% 1	5008
	21st to end	Night	54% 9% 14% 12% 11%	5235
April	1st to 10th	Night	49% 10% 18% 14% 6% 2	1800
	11th to 20th	Night	41% 11% 16% 21% 10%	1622
	21st to end	Night	45% 9% 19% 21% 6%	1388
May	1st to 10th	Night	50% 9% 16% 20% 5%	2677
	11th to 20th	Night	46% 6% 12% 19% 15% 1	2158
	21st to end	Night	48% 10% 15% 21% 5%	1881
June	1st to 10th	Night	47% 14% 16% 20% 4	600
	11th to 20th	Night	49% 10% 18% 19% 5%	600
	21st to end	Night	48% 13% 22% 15% 3	600
July	1st to 10th	Night	53% 8% 22% 13% 3	1345
	11th to 20th	Night	58% 7% 27% 8%	1513
	21st to end	Night	49% 6% 29% 15% 1	2389
August	1st to 10th	Night	47% 8% 20% 18% 7% 1	1811
	11th to 20th	Night	48% 7% 19% 21% 5%	2275
	21st to end	Night	58% 8% 23% 10%	2858
September	1st to 10th	Night	54% 12% 17% 15% 2	1820
	11th to 20th	Night	54% 12% 18% 15% 1	2015
	21st to end	Night	61% 9% 15% 12% 2	2282
October	1st to 10th	Night	55% 7% 15% 21% 2	3936
	11th to 20th	Night	57% 6% 15% 18% 4	4447
	21st to end	Night	72% 6% 14% 8%	5040
November	1st to 10th	Night	69% 8% 11% 9% 2	3282
	11th to 20th	Night	71% 10% 11% 8% 1	3465
	21st to end	Night	71% 9% 10% 9% 2	3780
December	1st to 10th	Night	74% 7% 7% 9% 3	6196
	11th to 20th	Night	72% 6% 11% 8% 4	7257
	21st to end	Night	71% 7% 6% 11% 5% 1	9691

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% 3 8% 29% 43% 10%	110
	11th to 20th	Day	10% 1 9% 38% 29% 13%	110
	21st to end	Day	10% 4 9% 38% 26% 12%	121
February	1st to 10th	Day	6% 2 9% 30% 35% 18%	374
	11th to 20th	Day	8% 2 9% 36% 29% 16%	411
	21st to end	Day	6% 2 12% 33% 29% 18%	331
March	1st to 10th	Day	5% 4 14% 26% 31% 21%	400
	11th to 20th	Day	9% 4 14% 28% 28% 18%	400
	21st to end	Day	7% 4 18% 28% 26% 18%	491
April	1st to 10th	Day	8% 2 21% 31% 28% 10%	698
	11th to 20th	Day	6% 4 19% 29% 29% 12%	690
	21st to end	Day	9% 6% 16% 26% 29% 14%	700
May	1st to 10th	Day	10% 9% 22% 26% 23% 10%	703
	11th to 20th	Day	10% 8% 21% 28% 22% 11%	760
	21st to end	Day	12% 8% 20% 27% 25% 8%	1038
June	1st to 10th	Day	12% 6% 15% 28% 30% 10%	1130
	11th to 20th	Day	10% 4 15% 26% 31% 14%	1130
	21st to end	Day	14% 4 14% 23% 29% 16%	1130
July	1st to 10th	Day	12% 4 15% 26% 30% 12%	1111
	11th to 20th	Day	16% 3 11% 24% 31% 15%	1030
	21st to end	Day	12% 2 14% 25% 29% 18%	800
August	1st to 10th	Day	15% 5% 13% 24% 27% 16%	726
	11th to 20th	Day	16% 5% 17% 28% 24% 10%	715
	21st to end	Day	19% 5% 15% 24% 26% 11%	803
September	1st to 10th	Day	16% 6% 16% 25% 20% 17%	710
	11th to 20th	Day	16% 5% 18% 21% 28% 12%	519
	21st to end	Day	16% 9% 17% 25% 21% 12%	420
October	1st to 10th	Day	21% 6% 21% 21% 18% 12%	420
	11th to 20th	Day	22% 6% 14% 21% 22% 15%	420
	21st to end	Day	15% 4 13% 29% 26% 14%	452
November	1st to 10th	Day	15% 3 12% 34% 21% 15%	220
	11th to 20th	Day	13% 4 11% 22% 26% 24%	178
	21st to end	Day	10% 3 11% 35% 23% 19%	110
December	1st to 10th	Day	10% 4 14% 40% 25% 7%	110
	11th to 20th	Day	10% 4 12% 36% 25% 14%	110
	21st to end	Day	7% 3 17% 30% 28% 14%	121
January	1st to 10th	Night	9% 2 9% 35% 34% 11%	1270
	11th to 20th	Night	12% 2 11% 43% 25% 7%	1064
	21st to end	Night	9% 3 11% 43% 27% 7%	1045
February	1st to 10th	Night	7% 1 11% 39% 32% 9%	950
	11th to 20th	Night	6% 2 12% 44% 30% 7%	909
	21st to end	Night	6% 1 10% 42% 32% 9%	743
March	1st to 10th	Night	5% 3 11% 35% 38% 8%	889
	11th to 20th	Night	7% 2 12% 31% 40% 8%	615
	21st to end	Night	6% 3 13% 35% 33% 10%	660
April	1st to 10th	Night	10% 3 11% 35% 35% 7%	600
	11th to 20th	Night	8% 3 11% 33% 34% 12%	593
	21st to end	Night	8% 2 14% 28% 37% 10%	588
May	1st to 10th	Night	10% 4 19% 27% 33% 7%	386
	11th to 20th	Night	12% 2 18% 28% 34% 6%	197
	21st to end	Night	10% 3 17% 32% 34% 4	217
June	1st to 10th	Night	13% 3 7% 29% 45% 4	200
	11th to 20th	Night	9% 3 11% 30% 43% 5%	200
	21st to end	Night	15% 3 6% 27% 42% 9%	200
July	1st to 10th	Night	9% 2 13% 32% 38% 7%	195
	11th to 20th	Night	13% 1 13% 28% 36% 9%	194
	21st to end	Night	12% 1 8% 22% 42% 15%	219
August	1st to 10th	Night	17% 4 15% 21% 36% 7%	312
	11th to 20th	Night	16% 3 12% 28% 32% 9%	594
	21st to end	Night	18% 2 10% 25% 34% 10%	660
September	1st to 10th	Night	16% 3 13% 28% 30% 10%	600
	11th to 20th	Night	18% 3 12% 27% 33% 7%	600
	21st to end	Night	21% 4 14% 25% 27% 10%	682
October	1st to 10th	Night	20% 4 15% 31% 23% 6%	803
	11th to 20th	Night	22% 5% 12% 26% 27% 8%	910
	21st to end	Night	16% 3 11% 32% 29% 9%	1001
November	1st to 10th	Night	18% 3 12% 30% 28% 9%	930
	11th to 20th	Night	12% 3 8% 29% 32% 16%	976
	21st to end	Night	12% 3 11% 32% 28% 14%	1160
December	1st to 10th	Night	14% 3 12% 38% 25% 8%	1204
	11th to 20th	Night	11% 3 13% 36% 26% 10%	1270
	21st to end	Night	9% 2 11% 35% 31% 13%	1397

Page generated at 2026-02-12 22:42:15. Version ac07

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