Dempster Hwy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dempster Hwy clear sky chart from 2005-11-06 to 2026-04-02.

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	11% 11% 5% 12% 7% 6% 6% 5% 6% 7% 24%	134816
	Night	6% 12% 6% 14% 8% 7% 6% 5% 7% 8% 21%	135790
Transparency	Day	56% 8% 16% 16% 5%	134410
	Night	56% 6% 12% 16% 8% 1	135777
Seeing	Day	16% 6% 14% 27% 26% 12%	20158
	Night	12% 4 12% 30% 31% 11%	25443

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 11% 5% 15% 6% 5% 7% 8% 16% 11% 13%	1423
	11th to 20th	Day	4 12% 5% 14% 8% 6% 8% 5% 6% 7% 26%	1892
	21st to end	Day	4 13% 6% 15% 7% 6% 7% 4 6% 10% 22%	3132
February	1st to 10th	Day	1 7% 5% 12% 8% 7% 6% 8% 9% 9% 28%	1239
	11th to 20th	Day	4 8% 3 11% 5% 7% 9% 9% 9% 10% 25%	1435
	21st to end	Day	3 8% 5% 19% 9% 8% 7% 5% 7% 7% 21%	1476
March	1st to 10th	Day	1 8% 6% 16% 8% 6% 6% 4 8% 10% 28%	4224
	11th to 20th	Day	2 10% 6% 15% 9% 11% 12% 7% 8% 7% 14%	4949
	21st to end	Day	1 8% 6% 16% 10% 10% 6% 5% 7% 6% 25%	5927
April	1st to 10th	Day	3 12% 5% 16% 10% 8% 7% 6% 6% 6% 20%	2618
	11th to 20th	Day	6% 12% 5% 14% 10% 5% 5% 4 7% 7% 26%	2781
	21st to end	Day	5% 13% 6% 13% 7% 5% 5% 4 6% 8% 28%	3108
May	1st to 10th	Day	10% 15% 8% 18% 7% 6% 5% 3 5% 5% 18%	7414
	11th to 20th	Day	7% 12% 5% 16% 5% 5% 4 4 5% 8% 29%	8079
	21st to end	Day	8% 10% 4 10% 6% 6% 6% 6% 9% 9% 27%	9467
June	1st to 10th	Day	12% 11% 4 9% 7% 6% 6% 5% 6% 8% 25%	4015
	11th to 20th	Day	13% 8% 3 8% 6% 6% 6% 5% 7% 9% 31%	4200
	21st to end	Day	16% 8% 3 8% 7% 6% 7% 5% 7% 9% 24%	4200
July	1st to 10th	Day	22% 8% 4 9% 6% 6% 6% 4 7% 7% 21%	9239
	11th to 20th	Day	16% 7% 3 9% 7% 7% 7% 5% 7% 9% 22%	8695
	21st to end	Day	15% 7% 3 9% 6% 6% 6% 5% 7% 8% 30%	8847
August	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 5% 7% 33%	5438
	11th to 20th	Day	20% 11% 3 9% 6% 5% 5% 4 5% 7% 24%	4937
	21st to end	Day	20% 16% 4 13% 7% 6% 6% 4 5% 6% 13%	5136
September	1st to 10th	Day	18% 12% 4 9% 6% 5% 5% 4 6% 7% 23%	2608
	11th to 20th	Day	21% 13% 4 8% 5% 4 4 4 6% 8% 25%	2400
	21st to end	Day	17% 22% 5% 11% 6% 5% 5% 4 4 5% 16%	2110
October	1st to 10th	Day	9% 14% 9% 11% 5% 4 5% 3 5% 7% 28%	3270
	11th to 20th	Day	9% 16% 8% 17% 6% 4 4 3 4 5% 25%	2610
	21st to end	Day	7% 18% 10% 18% 7% 6% 5% 3 5% 5% 16%	2569
November	1st to 10th	Day	7% 20% 7% 12% 10% 7% 5% 3 3 4 21%	1236
	11th to 20th	Day	6% 15% 7% 16% 8% 9% 5% 4 5% 4 20%	913
	21st to end	Day	3 16% 10% 15% 9% 7% 6% 4 7% 8% 16%	776
December	1st to 10th	Day	6% 13% 7% 11% 7% 5% 5% 7% 11% 7% 20%	670
	11th to 20th	Day	5% 10% 5% 11% 5% 7% 9% 7% 8% 16% 17%	771
	21st to end	Day	4 17% 5% 12% 6% 6% 6% 5% 6% 10% 22%	1012
January	1st to 10th	Night	3 10% 5% 13% 7% 6% 6% 8% 15% 12% 16%	11485
	11th to 20th	Night	4 13% 6% 14% 8% 7% 6% 4 5% 6% 28%	11029
	21st to end	Night	4 12% 5% 16% 9% 8% 6% 5% 6% 8% 21%	11108
February	1st to 10th	Night	3 11% 5% 11% 7% 6% 6% 6% 8% 10% 27%	3380
	11th to 20th	Night	2 9% 5% 13% 8% 7% 7% 7% 9% 8% 25%	3072
	21st to end	Night	3 10% 5% 16% 9% 9% 7% 5% 5% 5% 25%	2328
March	1st to 10th	Night	1 10% 5% 15% 8% 6% 7% 6% 9% 11% 21%	5870
	11th to 20th	Night	3 9% 5% 14% 11% 11% 10% 8% 7% 9% 14%	5234
	21st to end	Night	2 8% 5% 16% 11% 9% 8% 6% 7% 8% 20%	5261
April	1st to 10th	Night	4 14% 5% 15% 9% 8% 8% 5% 7% 6% 19%	1803
	11th to 20th	Night	6% 13% 6% 15% 9% 6% 6% 5% 5% 5% 24%	1567
	21st to end	Night	6% 12% 9% 11% 7% 5% 6% 3 6% 7% 27%	1292
May	1st to 10th	Night	12% 17% 8% 20% 8% 6% 3 3 4 5% 14%	2545
	11th to 20th	Night	7% 10% 4 16% 6% 5% 6% 4 8% 8% 25%	1816
	21st to end	Night	7% 12% 3 8% 7% 6% 6% 5% 9% 10% 26%	1424
June	1st to 10th	Night	14% 10% 3 8% 6% 7% 8% 4 5% 6% 29%	382
	11th to 20th	Night	12% 6% 2 10% 5% 8% 4 6% 5% 12% 33%	200
	21st to end	Night	12% 7% 5% 8% 4 5% 7% 3 10% 17% 25%	200
July	1st to 10th	Night	29% 7% 4 7% 4 6% 6% 4 6% 7% 20%	741
	11th to 20th	Night	19% 7% 4 8% 7% 6% 7% 5% 7% 7% 23%	1283
	21st to end	Night	15% 7% 2 7% 6% 5% 5% 4 7% 8% 33%	1998
August	1st to 10th	Night	19% 8% 3 9% 5% 6% 5% 3 5% 6% 31%	1713
	11th to 20th	Night	16% 10% 4 9% 5% 5% 7% 5% 6% 7% 24%	2114
	21st to end	Night	19% 14% 5% 12% 7% 6% 6% 5% 6% 6% 14%	2773
September	1st to 10th	Night	16% 13% 4 11% 6% 6% 7% 5% 6% 8% 19%	1791
	11th to 20th	Night	16% 14% 4 9% 5% 5% 6% 3 6% 6% 25%	2000
	21st to end	Night	17% 21% 6% 10% 5% 4 5% 4 5% 5% 17%	2288
October	1st to 10th	Night	10% 15% 6% 11% 6% 5% 4 4 5% 6% 27%	3920
	11th to 20th	Night	8% 14% 7% 17% 7% 6% 5% 4 4 5% 23%	4538
	21st to end	Night	6% 15% 10% 20% 8% 6% 4 3 5% 5% 18%	5225
November	1st to 10th	Night	6% 18% 7% 14% 9% 7% 6% 3 5% 6% 19%	3282
	11th to 20th	Night	5% 14% 7% 17% 9% 7% 6% 5% 5% 5% 19%	3685
	21st to end	Night	5% 13% 7% 15% 8% 8% 7% 5% 7% 8% 17%	3842
December	1st to 10th	Night	7% 14% 6% 12% 8% 7% 7% 7% 9% 8% 15%	6740
	11th to 20th	Night	4 11% 4 10% 7% 6% 9% 8% 11% 13% 17%	7653
	21st to end	Night	5% 15% 6% 13% 7% 6% 5% 5% 7% 8% 22%	10208

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	49% 5% 8% 19% 18% 1	1423
	11th to 20th	Day	56% 5% 15% 15% 5% 5%	1901
	21st to end	Day	55% 6% 7% 16% 14% 1	3133
February	1st to 10th	Day	44% 6% 11% 21% 15% 3	1239
	11th to 20th	Day	45% 8% 14% 19% 13% 2	1442
	21st to end	Day	58% 7% 12% 13% 8% 2	1476
March	1st to 10th	Day	48% 4 7% 26% 12% 3	4224
	11th to 20th	Day	63% 5% 8% 13% 8% 2	4949
	21st to end	Day	56% 5% 18% 15% 7%	5927
April	1st to 10th	Day	61% 7% 15% 12% 5% 1	2618
	11th to 20th	Day	56% 6% 17% 16% 5%	2781
	21st to end	Day	54% 7% 16% 19% 5%	3108
May	1st to 10th	Day	68% 7% 10% 12% 4	7414
	11th to 20th	Day	51% 6% 17% 20% 4	8083
	21st to end	Day	48% 8% 17% 21% 5%	9468
June	1st to 10th	Day	55% 7% 14% 21% 4	4015
	11th to 20th	Day	48% 7% 16% 24% 5%	4200
	21st to end	Day	54% 10% 17% 16% 3	4200
July	1st to 10th	Day	60% 8% 17% 14% 1	9140
	11th to 20th	Day	55% 11% 23% 10%	8588
	21st to end	Day	48% 11% 24% 15% 2	8597
August	1st to 10th	Day	50% 9% 17% 18% 7%	5418
	11th to 20th	Day	58% 9% 16% 17% 1	4985
	21st to end	Day	71% 8% 13% 8%	5135
September	1st to 10th	Day	59% 7% 19% 14% 1	2608
	11th to 20th	Day	56% 9% 20% 13% 2	2400
	21st to end	Day	71% 6% 13% 9% 1	2110
October	1st to 10th	Day	55% 7% 18% 15% 4	3270
	11th to 20th	Day	61% 5% 11% 19% 4	2610
	21st to end	Day	68% 5% 14% 11% 2	2569
November	1st to 10th	Day	67% 4 11% 13% 4	1236
	11th to 20th	Day	67% 4 10% 14% 4	913
	21st to end	Day	62% 7% 9% 18% 5%	776
December	1st to 10th	Day	54% 7% 13% 19% 8%	670
	11th to 20th	Day	49% 8% 13% 18% 11%	772
	21st to end	Day	57% 4 8% 15% 13% 3	1012
January	1st to 10th	Night	48% 5% 9% 15% 23%	11486
	11th to 20th	Night	54% 5% 11% 17% 7% 6%	11082
	21st to end	Night	57% 6% 8% 15% 13% 2	11108
February	1st to 10th	Night	47% 5% 10% 22% 13% 2	3380
	11th to 20th	Night	50% 6% 11% 18% 14% 1	3076
	21st to end	Night	57% 6% 11% 13% 11% 2	2328
March	1st to 10th	Night	51% 5% 7% 24% 11% 2	5870
	11th to 20th	Night	62% 6% 7% 14% 8% 3	5236
	21st to end	Night	56% 7% 18% 13% 5%	5261
April	1st to 10th	Night	64% 6% 13% 11% 5% 2	1803
	11th to 20th	Night	60% 5% 12% 18% 5%	1567
	21st to end	Night	54% 6% 16% 18% 5%	1292
May	1st to 10th	Night	71% 7% 10% 10% 3	2542
	11th to 20th	Night	52% 7% 16% 20% 4	1816
	21st to end	Night	47% 8% 19% 21% 4	1424
June	1st to 10th	Night	54% 6% 16% 21% 3	382
	11th to 20th	Night	46% 8% 17% 27% 4 1	200
	21st to end	Night	45% 12% 22% 17% 4	200
July	1st to 10th	Night	57% 12% 18% 12% 1	731
	11th to 20th	Night	57% 10% 22% 10% 1	1267
	21st to end	Night	45% 10% 27% 17% 1	1943
August	1st to 10th	Night	53% 7% 17% 16% 6% 1	1708
	11th to 20th	Night	55% 11% 19% 15%	2132
	21st to end	Night	66% 12% 16% 7%	2773
September	1st to 10th	Night	60% 9% 18% 12%	1791
	11th to 20th	Night	58% 6% 19% 15% 2	2000
	21st to end	Night	69% 5% 13% 11% 1	2288
October	1st to 10th	Night	54% 8% 12% 22% 3	3920
	11th to 20th	Night	61% 6% 10% 19% 3	4538
	21st to end	Night	68% 5% 12% 14% 1	5225
November	1st to 10th	Night	66% 4 15% 12% 3	3282
	11th to 20th	Night	65% 5% 12% 13% 6%	3685
	21st to end	Night	62% 5% 10% 18% 5%	3842
December	1st to 10th	Night	59% 7% 12% 15% 7%	6740
	11th to 20th	Night	50% 7% 15% 19% 9%	7651
	21st to end	Night	56% 5% 9% 15% 13% 1	10208

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% 3 15% 23% 45% 9%	110
	11th to 20th	Day	9% 8% 11% 35% 27% 10%	110
	21st to end	Day	10% 4 20% 29% 31% 7%	121
February	1st to 10th	Day	3 3 12% 34% 33% 14%	239
	11th to 20th	Day	6% 4 12% 33% 32% 14%	425
	21st to end	Day	5% 4 17% 31% 26% 17%	355
March	1st to 10th	Day	4 3 15% 32% 24% 22%	430
	11th to 20th	Day	7% 3 13% 31% 31% 15%	430
	21st to end	Day	5% 5% 14% 27% 28% 21%	551
April	1st to 10th	Day	7% 3 15% 35% 29% 11%	685
	11th to 20th	Day	9% 5% 18% 30% 24% 14%	690
	21st to end	Day	8% 6% 15% 29% 29% 13%	700
May	1st to 10th	Day	13% 6% 20% 26% 24% 10%	703
	11th to 20th	Day	14% 6% 17% 27% 26% 11%	907
	21st to end	Day	13% 8% 14% 30% 26% 9%	1168
June	1st to 10th	Day	17% 6% 19% 30% 21% 7%	1130
	11th to 20th	Day	14% 5% 13% 27% 30% 11%	1130
	21st to end	Day	17% 4 10% 23% 30% 15%	1130
July	1st to 10th	Day	20% 5% 14% 23% 26% 11%	1111
	11th to 20th	Day	22% 5% 10% 21% 29% 14%	1106
	21st to end	Day	18% 5% 11% 22% 28% 17%	1004
August	1st to 10th	Day	22% 5% 12% 24% 22% 14%	726
	11th to 20th	Day	24% 9% 17% 23% 18% 10%	715
	21st to end	Day	28% 7% 17% 25% 17% 6%	803
September	1st to 10th	Day	22% 7% 15% 22% 21% 12%	698
	11th to 20th	Day	24% 6% 15% 24% 23% 8%	530
	21st to end	Day	26% 8% 14% 18% 24% 11%	434
October	1st to 10th	Day	18% 7% 21% 22% 21% 10%	420
	11th to 20th	Day	21% 6% 12% 25% 22% 14%	420
	21st to end	Day	18% 3 12% 26% 23% 18%	364
November	1st to 10th	Day	11% 5% 10% 33% 27% 13%	220
	11th to 20th	Day	12% 4 8% 24% 27% 25%	142
	21st to end	Day	6% 2 15% 25% 32% 21%	110
December	1st to 10th	Day	12% 5% 11% 40% 24% 8%	110
	11th to 20th	Day	8% 5% 5% 39% 31% 12%	110
	21st to end	Day	12% 5% 18% 26% 28% 12%	121
January	1st to 10th	Night	7% 4 10% 29% 36% 14%	1270
	11th to 20th	Night	11% 4 14% 34% 29% 9%	1245
	21st to end	Night	9% 5% 14% 33% 30% 10%	1097
February	1st to 10th	Night	7% 3 13% 32% 35% 10%	950
	11th to 20th	Night	6% 3 13% 36% 31% 10%	934
	21st to end	Night	5% 3 15% 36% 30% 11%	783
March	1st to 10th	Night	3 4 13% 36% 33% 12%	928
	11th to 20th	Night	5% 2 10% 33% 37% 12%	698
	21st to end	Night	4 3 12% 30% 35% 16%	693
April	1st to 10th	Night	9% 3 10% 31% 34% 13%	603
	11th to 20th	Night	10% 4 11% 34% 29% 12%	593
	21st to end	Night	10% 3 12% 32% 34% 10%	492
May	1st to 10th	Night	15% 5% 11% 31% 31% 6%	329
	11th to 20th	Night	12% 5% 13% 31% 34% 7%	197
	21st to end	Night	12% 4 10% 35% 37% 2	217
June	1st to 10th	Night	19% 5% 14% 30% 32% 1	200
	11th to 20th	Night	14% 2 11% 39% 33% 2	200
	21st to end	Night	13% 4 9% 31% 41% 4	200
July	1st to 10th	Night	21% 4 10% 30% 33% 3	195
	11th to 20th	Night	22% 3 9% 22% 40% 4	194
	21st to end	Night	19% 3 13% 25% 34% 5%	219
August	1st to 10th	Night	23% 5% 8% 27% 36% 2	248
	11th to 20th	Night	24% 7% 12% 25% 28% 5%	503
	21st to end	Night	25% 7% 12% 25% 25% 7%	660
September	1st to 10th	Night	21% 4 13% 25% 26% 11%	600
	11th to 20th	Night	22% 4 12% 29% 28% 6%	600
	21st to end	Night	26% 5% 12% 28% 24% 6%	715
October	1st to 10th	Night	21% 5% 15% 28% 24% 7%	800
	11th to 20th	Night	21% 6% 11% 23% 29% 11%	907
	21st to end	Night	14% 4 11% 29% 27% 14%	1001
November	1st to 10th	Night	13% 3 9% 30% 33% 12%	930
	11th to 20th	Night	9% 5% 9% 27% 30% 20%	1128
	21st to end	Night	9% 3 12% 26% 32% 18%	1177
December	1st to 10th	Night	11% 5% 13% 36% 29% 7%	1270
	11th to 20th	Night	9% 3 11% 31% 35% 11%	1270
	21st to end	Night	7% 4 11% 28% 34% 16%	1397

Page generated at 2026-03-29 22:18:38. Version ac07

Copyright © 2026 Attilla Danko.