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 2024-01-16.

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	12% 11% 5% 9% 8% 5% 6% 6% 6% 7% 24%	74586
	Night	8% 13% 6% 11% 9% 5% 7% 6% 6% 7% 22%	75236
Transparency	Day	57% 7% 16% 16% 4	74176
	Night	58% 6% 13% 16% 7% 1	75166
Seeing	Day	17% 5% 14% 26% 26% 12%	17185
	Night	12% 4 11% 30% 31% 11%	22432

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 10% 5% 11% 11% 7% 7% 10% 10% 7% 20%	459
	11th to 20th	Day	5% 14% 8% 9% 10% 5% 9% 7% 7% 6% 19%	595
	21st to end	Day	5% 14% 7% 12% 9% 5% 7% 7% 6% 7% 20%	963
February	1st to 10th	Day	1 6% 6% 10% 10% 5% 7% 10% 8% 10% 28%	1062
	11th to 20th	Day	4 9% 4 9% 6% 4 8% 10% 10% 10% 25%	1225
	21st to end	Day	3 8% 5% 14% 11% 7% 8% 6% 6% 8% 23%	1262
March	1st to 10th	Day	2 8% 7% 10% 11% 5% 7% 8% 7% 9% 28%	1656
	11th to 20th	Day	2 9% 5% 12% 9% 6% 9% 8% 8% 7% 24%	1920
	21st to end	Day	3 11% 6% 12% 10% 7% 9% 7% 6% 5% 24%	2304
April	1st to 10th	Day	4 11% 5% 15% 11% 7% 7% 7% 6% 6% 21%	2344
	11th to 20th	Day	6% 10% 6% 13% 12% 4 5% 5% 7% 7% 25%	2499
	21st to end	Day	5% 12% 6% 10% 8% 4 6% 5% 6% 8% 30%	2796
May	1st to 10th	Day	7% 14% 6% 9% 8% 4 6% 5% 6% 8% 26%	2942
	11th to 20th	Day	11% 11% 5% 9% 6% 3 4 5% 5% 8% 32%	3173
	21st to end	Day	10% 9% 4 8% 6% 4 6% 6% 7% 8% 35%	3705
June	1st to 10th	Day	12% 10% 4 8% 8% 5% 7% 6% 6% 8% 26%	3613
	11th to 20th	Day	14% 8% 3 7% 7% 5% 6% 6% 7% 8% 29%	3780
	21st to end	Day	17% 7% 3 7% 8% 5% 7% 6% 7% 9% 23%	3780
July	1st to 10th	Day	17% 7% 4 7% 8% 5% 6% 7% 7% 8% 24%	3668
	11th to 20th	Day	22% 9% 4 8% 9% 6% 8% 6% 6% 7% 16%	3453
	21st to end	Day	18% 8% 4 8% 8% 5% 6% 7% 7% 7% 22%	3522
August	1st to 10th	Day	20% 10% 4 8% 8% 4 7% 5% 5% 7% 23%	3002
	11th to 20th	Day	25% 13% 4 8% 7% 4 6% 5% 5% 7% 16%	2734
	21st to end	Day	23% 14% 4 9% 8% 5% 5% 5% 5% 7% 16%	2836
September	1st to 10th	Day	19% 12% 4 9% 7% 4 5% 5% 6% 7% 23%	2348
	11th to 20th	Day	21% 12% 4 6% 5% 3 4 5% 6% 8% 26%	2160
	21st to end	Day	16% 22% 6% 10% 7% 4 5% 5% 4 5% 17%	1900
October	1st to 10th	Day	14% 17% 7% 10% 7% 4 6% 5% 5% 6% 19%	1800
	11th to 20th	Day	12% 18% 9% 14% 9% 3 4 4 4 6% 18%	1445
	21st to end	Day	10% 19% 7% 13% 9% 4 4 3 5% 5% 22%	1438
November	1st to 10th	Day	6% 18% 8% 10% 11% 5% 6% 4 3 5% 23%	1116
	11th to 20th	Day	7% 15% 7% 13% 11% 6% 8% 5% 5% 4 20%	828
	21st to end	Day	4 14% 10% 13% 10% 6% 8% 5% 7% 7% 17%	704
December	1st to 10th	Day	7% 14% 8% 11% 9% 4 6% 9% 4 5% 21%	380
	11th to 20th	Day	5% 11% 8% 11% 7% 6% 7% 8% 8% 11% 18%	481
	21st to end	Day	7% 15% 4 8% 7% 4 5% 6% 8% 13% 25%	693
January	1st to 10th	Night	5% 12% 6% 10% 8% 5% 8% 8% 9% 8% 22%	3705
	11th to 20th	Night	6% 15% 7% 11% 9% 6% 7% 7% 6% 8% 18%	3488
	21st to end	Night	5% 14% 6% 11% 8% 6% 8% 9% 6% 7% 21%	3411
February	1st to 10th	Night	3 10% 5% 9% 10% 5% 6% 7% 8% 11% 27%	2898
	11th to 20th	Night	3 9% 5% 11% 10% 5% 7% 8% 9% 8% 24%	2622
	21st to end	Night	3 9% 5% 14% 10% 6% 8% 6% 5% 6% 28%	1992
March	1st to 10th	Night	2 8% 6% 11% 11% 5% 8% 8% 7% 9% 25%	2304
	11th to 20th	Night	2 8% 6% 11% 12% 6% 9% 8% 8% 8% 23%	2037
	21st to end	Night	2 8% 6% 9% 10% 6% 8% 8% 6% 7% 28%	2052
April	1st to 10th	Night	4 13% 6% 13% 11% 6% 8% 7% 7% 6% 19%	1615
	11th to 20th	Night	6% 10% 7% 15% 10% 5% 6% 7% 6% 5% 23%	1409
	21st to end	Night	7% 12% 8% 9% 6% 4 6% 5% 5% 8% 29%	1164
May	1st to 10th	Night	8% 15% 5% 10% 9% 6% 5% 6% 6% 7% 24%	1017
	11th to 20th	Night	12% 8% 4 9% 8% 2 6% 5% 7% 8% 30%	722
	21st to end	Night	9% 10% 5% 6% 5% 3 6% 3 5% 7% 41%	569
June	1st to 10th	Night	14% 10% 3 8% 6% 6% 9% 6% 3 6% 29%	344
	11th to 20th	Night	12% 6% 3 8% 8% 6% 4 8% 4 12% 29%	180
	21st to end	Night	12% 7% 5% 7% 4 3 6% 6% 11% 17% 23%	180
July	1st to 10th	Night	19% 6% 3 5% 4 6% 7% 7% 8% 10% 24%	292
	11th to 20th	Night	19% 7% 4 7% 9% 7% 8% 7% 5% 8% 19%	505
	21st to end	Night	17% 8% 3 6% 7% 4 5% 5% 9% 11% 24%	793
August	1st to 10th	Night	21% 9% 4 8% 8% 5% 7% 4 6% 8% 21%	938
	11th to 20th	Night	23% 11% 5% 9% 6% 4 5% 6% 4 5% 23%	1163
	21st to end	Night	22% 13% 5% 8% 7% 3 5% 6% 6% 8% 17%	1520
September	1st to 10th	Night	16% 13% 4 9% 6% 5% 7% 7% 6% 8% 19%	1611
	11th to 20th	Night	16% 13% 4 8% 6% 5% 6% 4 6% 7% 26%	1800
	21st to end	Night	17% 21% 6% 9% 6% 3 5% 4 5% 5% 17%	2058
October	1st to 10th	Night	16% 17% 6% 9% 7% 4 5% 5% 5% 6% 22%	2160
	11th to 20th	Night	13% 19% 8% 16% 9% 4 4 3 3 4 17%	2515
	21st to end	Night	9% 17% 7% 11% 8% 3 4 4 5% 7% 23%	2916
November	1st to 10th	Night	6% 17% 7% 11% 10% 5% 7% 5% 5% 6% 21%	2962
	11th to 20th	Night	6% 13% 8% 14% 11% 6% 7% 6% 5% 5% 20%	3333
	21st to end	Night	5% 12% 7% 13% 10% 6% 8% 7% 7% 7% 17%	3474
December	1st to 10th	Night	6% 15% 7% 10% 9% 5% 7% 8% 7% 7% 19%	3800
	11th to 20th	Night	4 13% 6% 11% 10% 5% 8% 7% 8% 11% 16%	4713
	21st to end	Night	6% 13% 5% 10% 7% 4 6% 6% 7% 9% 26%	6974

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	56% 7% 11% 20% 6% 1	459
	11th to 20th	Day	60% 5% 11% 19% 5% 1	595
	21st to end	Day	60% 6% 11% 14% 9% 1	963
February	1st to 10th	Day	44% 7% 11% 21% 14% 3	1062
	11th to 20th	Day	47% 8% 14% 20% 11% 1	1232
	21st to end	Day	56% 7% 14% 14% 7% 2	1262
March	1st to 10th	Day	49% 6% 13% 21% 11% 1	1656
	11th to 20th	Day	55% 4 12% 18% 11%	1920
	21st to end	Day	59% 6% 12% 14% 8% 1	2304
April	1st to 10th	Day	61% 7% 15% 11% 5% 1	2344
	11th to 20th	Day	58% 6% 17% 15% 3	2499
	21st to end	Day	52% 6% 16% 21% 5%	2796
May	1st to 10th	Day	57% 6% 18% 17% 3	2942
	11th to 20th	Day	50% 5% 16% 26% 3	3177
	21st to end	Day	45% 7% 17% 27% 4	3706
June	1st to 10th	Day	55% 7% 14% 20% 4	3613
	11th to 20th	Day	51% 7% 17% 21% 4	3780
	21st to end	Day	55% 11% 17% 14% 3	3780
July	1st to 10th	Day	56% 8% 20% 14% 2	3569
	11th to 20th	Day	66% 10% 16% 8% 1	3346
	21st to end	Day	56% 10% 21% 11% 1	3325
August	1st to 10th	Day	59% 8% 19% 13% 1	2982
	11th to 20th	Day	67% 9% 17% 7%	2734
	21st to end	Day	69% 8% 17% 7%	2836
September	1st to 10th	Day	60% 7% 19% 13% 1	2348
	11th to 20th	Day	55% 9% 20% 13% 2	2160
	21st to end	Day	70% 5% 13% 10% 1	1900
October	1st to 10th	Day	66% 6% 15% 12% 1	1800
	11th to 20th	Day	68% 4 16% 10% 2	1445
	21st to end	Day	64% 4 14% 16% 2	1438
November	1st to 10th	Day	64% 4 12% 15% 5%	1116
	11th to 20th	Day	66% 4 11% 14% 4	828
	21st to end	Day	63% 7% 8% 17% 5%	704
December	1st to 10th	Day	63% 5% 12% 14% 6%	380
	11th to 20th	Day	55% 9% 8% 14% 14% 1	482
	21st to end	Day	50% 4 10% 19% 13% 4	693
January	1st to 10th	Night	53% 6% 13% 19% 8%	3705
	11th to 20th	Night	60% 5% 9% 18% 6% 1	3488
	21st to end	Night	58% 6% 12% 14% 9% 1	3411
February	1st to 10th	Night	47% 5% 11% 23% 12% 2	2898
	11th to 20th	Night	51% 5% 12% 19% 13%	2626
	21st to end	Night	54% 6% 13% 14% 11% 2	1992
March	1st to 10th	Night	50% 6% 12% 22% 11%	2304
	11th to 20th	Night	55% 5% 11% 18% 11%	2039
	21st to end	Night	53% 7% 15% 17% 8% 1	2052
April	1st to 10th	Night	63% 6% 13% 12% 4 2	1615
	11th to 20th	Night	61% 5% 12% 18% 4	1409
	21st to end	Night	52% 6% 17% 19% 5%	1164
May	1st to 10th	Night	57% 6% 18% 15% 4	1017
	11th to 20th	Night	51% 7% 14% 23% 4	722
	21st to end	Night	45% 5% 16% 28% 6%	569
June	1st to 10th	Night	55% 6% 15% 21% 3	344
	11th to 20th	Night	49% 8% 16% 23% 3 1	180
	21st to end	Night	46% 12% 22% 16% 3	180
July	1st to 10th	Night	49% 13% 24% 12% 3	282
	11th to 20th	Night	63% 11% 18% 8% 1	489
	21st to end	Night	50% 9% 27% 13% 1	750
August	1st to 10th	Night	61% 7% 22% 10% 1	933
	11th to 20th	Night	63% 9% 20% 8%	1163
	21st to end	Night	65% 9% 17% 9%	1520
September	1st to 10th	Night	62% 9% 18% 11%	1611
	11th to 20th	Night	58% 6% 19% 15% 2	1800
	21st to end	Night	69% 5% 14% 11% 1	2058
October	1st to 10th	Night	62% 7% 14% 15% 2	2160
	11th to 20th	Night	70% 4 12% 10% 4	2515
	21st to end	Night	60% 5% 16% 18% 1	2916
November	1st to 10th	Night	63% 4 17% 13% 3	2962
	11th to 20th	Night	64% 5% 12% 12% 5%	3333
	21st to end	Night	62% 5% 11% 17% 5%	3474
December	1st to 10th	Night	60% 7% 13% 14% 7%	3800
	11th to 20th	Night	57% 7% 12% 14% 10%	4711
	21st to end	Night	51% 5% 10% 17% 15% 1	6974

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	4 2 17% 23% 43% 10%	90
	11th to 20th	Day	11% 4 6% 34% 33% 13%	85
	21st to end	Day	10% 3 11% 33% 35% 7%	88
February	1st to 10th	Day	4 3 9% 32% 35% 18%	182
	11th to 20th	Day	7% 4 9% 33% 32% 16%	335
	21st to end	Day	5% 5% 18% 29% 25% 19%	280
March	1st to 10th	Day	5% 2 14% 32% 25% 22%	340
	11th to 20th	Day	8% 4 13% 33% 30% 11%	340
	21st to end	Day	6% 6% 16% 27% 28% 18%	430
April	1st to 10th	Day	7% 3 15% 35% 29% 11%	582
	11th to 20th	Day	9% 4 17% 29% 25% 16%	590
	21st to end	Day	8% 6% 14% 30% 28% 14%	600
May	1st to 10th	Day	12% 6% 19% 26% 25% 12%	603
	11th to 20th	Day	15% 6% 18% 26% 25% 11%	788
	21st to end	Day	14% 7% 13% 30% 26% 9%	1019
June	1st to 10th	Day	17% 5% 19% 29% 22% 8%	990
	11th to 20th	Day	16% 6% 15% 27% 29% 8%	990
	21st to end	Day	20% 4 11% 24% 30% 11%	990
July	1st to 10th	Day	19% 5% 14% 24% 27% 12%	971
	11th to 20th	Day	24% 5% 10% 20% 28% 13%	966
	21st to end	Day	19% 5% 11% 21% 28% 16%	874
August	1st to 10th	Day	23% 5% 12% 25% 21% 14%	626
	11th to 20th	Day	26% 8% 17% 24% 17% 8%	615
	21st to end	Day	30% 6% 16% 24% 18% 6%	693
September	1st to 10th	Day	23% 7% 15% 21% 20% 13%	602
	11th to 20th	Day	24% 6% 15% 24% 22% 8%	450
	21st to end	Day	26% 7% 16% 19% 23% 9%	372
October	1st to 10th	Day	20% 7% 22% 21% 21% 9%	360
	11th to 20th	Day	21% 5% 12% 27% 21% 13%	360
	21st to end	Day	19% 2 11% 27% 23% 18%	308
November	1st to 10th	Day	8% 5% 9% 36% 27% 15%	180
	11th to 20th	Day	14% 3 10% 24% 26% 22%	117
	21st to end	Day	8% 1 16% 27% 31% 18%	90
December	1st to 10th	Day	14% 4 10% 40% 24% 7%	90
	11th to 20th	Day	10% 6% 3 41% 29% 11%	90
	21st to end	Day	12% 5% 20% 24% 25% 13%	99
January	1st to 10th	Night	8% 4 10% 28% 36% 15%	1130
	11th to 20th	Night	11% 4 10% 34% 32% 10%	1082
	21st to end	Night	10% 3 12% 33% 32% 11%	925
February	1st to 10th	Night	7% 3 12% 30% 37% 12%	800
	11th to 20th	Night	7% 3 11% 36% 33% 12%	784
	21st to end	Night	6% 3 16% 36% 27% 12%	658
March	1st to 10th	Night	3 4 12% 35% 33% 13%	784
	11th to 20th	Night	5% 3 9% 36% 36% 12%	599
	21st to end	Night	4 3 11% 31% 36% 15%	594
April	1st to 10th	Night	10% 3 9% 31% 34% 13%	540
	11th to 20th	Night	10% 3 10% 32% 31% 13%	533
	21st to end	Night	10% 3 11% 33% 33% 10%	444
May	1st to 10th	Night	13% 4 11% 32% 33% 7%	297
	11th to 20th	Night	13% 4 14% 29% 34% 6%	177
	21st to end	Night	12% 4 8% 36% 37% 2	195
June	1st to 10th	Night	19% 4 14% 29% 33% 1	180
	11th to 20th	Night	15% 2 12% 41% 29% 2	180
	21st to end	Night	13% 4 9% 33% 37% 3	180
July	1st to 10th	Night	19% 3 9% 31% 34% 3	175
	11th to 20th	Night	22% 3 10% 20% 40% 5%	174
	21st to end	Night	20% 3 13% 25% 34% 5%	197
August	1st to 10th	Night	24% 5% 7% 27% 35% 2	222
	11th to 20th	Night	25% 7% 12% 24% 27% 5%	451
	21st to end	Night	27% 6% 12% 23% 25% 7%	594
September	1st to 10th	Night	23% 4 12% 24% 26% 11%	540
	11th to 20th	Night	22% 4 12% 29% 29% 5%	540
	21st to end	Night	27% 4 12% 28% 23% 6%	643
October	1st to 10th	Night	22% 5% 15% 27% 24% 7%	720
	11th to 20th	Night	22% 5% 10% 22% 29% 11%	807
	21st to end	Night	15% 4 11% 29% 28% 14%	891
November	1st to 10th	Night	12% 2 9% 31% 33% 12%	830
	11th to 20th	Night	10% 5% 10% 27% 29% 19%	1010
	21st to end	Night	10% 3 11% 26% 32% 18%	1053
December	1st to 10th	Night	11% 5% 13% 35% 29% 7%	1130
	11th to 20th	Night	10% 3 11% 32% 33% 11%	1130
	21st to end	Night	7% 4 12% 28% 33% 17%	1243

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