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 2024-12-09.

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% 12% 5% 11% 7% 6% 6% 4 6% 7% 24%	107795
	Night	7% 13% 6% 13% 7% 6% 6% 5% 7% 7% 22%	100580
Transparency	Day	57% 7% 16% 16% 4	107442
	Night	57% 6% 12% 15% 8% 1	100581
Seeing	Day	16% 5% 14% 27% 26% 12%	18539
	Night	12% 4 11% 30% 31% 11%	23502

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	2 9% 5% 14% 8% 6% 7% 9% 11% 10% 19%	761
	11th to 20th	Day	4 13% 6% 13% 9% 5% 7% 5% 6% 8% 24%	1007
	21st to end	Day	5% 14% 5% 13% 7% 5% 6% 4 6% 8% 25%	1683
February	1st to 10th	Day	1 7% 5% 12% 7% 7% 6% 9% 9% 9% 28%	1121
	11th to 20th	Day	4 9% 3 10% 5% 6% 8% 9% 9% 9% 26%	1295
	21st to end	Day	3 9% 5% 17% 9% 9% 7% 5% 7% 7% 22%	1338
March	1st to 10th	Day	1 10% 9% 20% 10% 6% 5% 4 7% 7% 22%	2874
	11th to 20th	Day	3 14% 8% 19% 10% 9% 8% 5% 5% 5% 14%	3381
	21st to end	Day	2 9% 5% 14% 9% 8% 5% 4 5% 6% 33%	4051
April	1st to 10th	Day	3 12% 5% 17% 10% 8% 7% 6% 6% 6% 20%	2475
	11th to 20th	Day	6% 11% 5% 14% 10% 5% 5% 4 7% 7% 27%	2640
	21st to end	Day	5% 13% 6% 13% 7% 5% 5% 4 6% 8% 29%	2952
May	1st to 10th	Day	7% 15% 6% 15% 8% 7% 6% 4 5% 6% 22%	5178
	11th to 20th	Day	8% 12% 5% 11% 6% 5% 5% 5% 6% 8% 29%	5633
	21st to end	Day	10% 12% 4 9% 6% 5% 5% 5% 7% 8% 28%	6593
June	1st to 10th	Day	11% 11% 4 9% 7% 6% 6% 5% 6% 8% 26%	3814
	11th to 20th	Day	13% 8% 3 8% 6% 6% 6% 5% 7% 8% 29%	3990
	21st to end	Day	16% 8% 3 8% 7% 6% 6% 5% 7% 9% 24%	3990
July	1st to 10th	Day	26% 10% 4 10% 7% 6% 6% 5% 6% 6% 15%	6447
	11th to 20th	Day	19% 8% 3 8% 7% 7% 6% 5% 6% 9% 21%	6067
	21st to end	Day	16% 7% 3 8% 6% 5% 6% 5% 7% 8% 30%	6164
August	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 5% 7% 33%	5271
	11th to 20th	Day	20% 11% 3 9% 6% 5% 5% 4 5% 7% 24%	4783
	21st to end	Day	21% 16% 4 13% 7% 6% 6% 4 5% 6% 12%	4979
September	1st to 10th	Day	19% 12% 4 9% 6% 5% 5% 4 6% 7% 23%	2478
	11th to 20th	Day	21% 12% 4 8% 5% 4 4 4 6% 8% 25%	2280
	21st to end	Day	17% 23% 6% 11% 6% 5% 5% 3 4 5% 16%	2005
October	1st to 10th	Day	9% 14% 9% 10% 5% 4 5% 3 5% 7% 28%	3170
	11th to 20th	Day	9% 15% 8% 17% 7% 5% 4 3 4 5% 25%	2530
	21st to end	Day	6% 18% 10% 18% 7% 6% 5% 3 5% 6% 17%	2489
November	1st to 10th	Day	6% 19% 7% 12% 10% 7% 5% 3 3 5% 22%	1176
	11th to 20th	Day	6% 16% 7% 16% 9% 9% 5% 4 4 4 20%	870
	21st to end	Day	4 16% 9% 14% 9% 7% 6% 4 7% 8% 16%	740
December	1st to 10th	Day	7% 14% 8% 14% 8% 6% 6% 7% 5% 5% 20%	396
	11th to 20th	Day	5% 13% 8% 12% 5% 8% 8% 6% 8% 10% 17%	481
	21st to end	Day	6% 15% 4 9% 5% 5% 5% 5% 8% 12% 25%	693
January	1st to 10th	Night	3 12% 5% 11% 6% 6% 7% 8% 13% 9% 20%	6193
	11th to 20th	Night	4 15% 6% 13% 6% 6% 5% 4 6% 7% 28%	5899
	21st to end	Night	6% 13% 6% 13% 7% 7% 6% 5% 6% 9% 24%	6005
February	1st to 10th	Night	3 10% 5% 10% 8% 6% 6% 7% 8% 10% 27%	3059
	11th to 20th	Night	3 10% 5% 13% 8% 7% 7% 7% 9% 7% 25%	2772
	21st to end	Night	3 9% 5% 16% 9% 9% 7% 5% 5% 5% 27%	2114
March	1st to 10th	Night	1 13% 7% 19% 8% 7% 6% 5% 8% 6% 20%	3990
	11th to 20th	Night	5% 11% 6% 18% 12% 10% 9% 6% 5% 5% 13%	3579
	21st to end	Night	3 10% 6% 13% 8% 7% 6% 6% 7% 9% 25%	3588
April	1st to 10th	Night	4 14% 5% 15% 9% 8% 8% 5% 7% 6% 18%	1703
	11th to 20th	Night	5% 12% 6% 16% 9% 6% 6% 5% 6% 5% 25%	1488
	21st to end	Night	6% 12% 9% 11% 6% 5% 6% 3 6% 7% 29%	1228
May	1st to 10th	Night	8% 17% 8% 16% 7% 6% 4 4 5% 5% 20%	1781
	11th to 20th	Night	8% 11% 4 9% 6% 6% 7% 5% 8% 9% 25%	1262
	21st to end	Night	9% 15% 4 7% 7% 6% 5% 4 6% 8% 29%	990
June	1st to 10th	Night	13% 10% 3 8% 5% 7% 8% 4 5% 6% 30%	363
	11th to 20th	Night	12% 6% 2 11% 5% 7% 4 6% 4 13% 31%	190
	21st to end	Night	11% 7% 5% 7% 4 5% 6% 3 11% 16% 25%	190
July	1st to 10th	Night	31% 8% 5% 7% 4 5% 7% 4 5% 7% 15%	523
	11th to 20th	Night	20% 6% 4 8% 6% 7% 7% 6% 7% 7% 23%	901
	21st to end	Night	17% 8% 2 8% 6% 5% 5% 4 7% 8% 31%	1388
August	1st to 10th	Night	19% 8% 3 9% 5% 6% 6% 3 5% 6% 31%	1660
	11th to 20th	Night	17% 10% 4 9% 5% 5% 7% 4 7% 7% 24%	2048
	21st to end	Night	19% 14% 5% 13% 7% 6% 6% 5% 6% 6% 13%	2688
September	1st to 10th	Night	16% 13% 4 11% 6% 6% 7% 5% 6% 8% 19%	1701
	11th to 20th	Night	16% 13% 4 9% 5% 5% 6% 3 6% 7% 26%	1900
	21st to end	Night	18% 21% 6% 10% 5% 4 5% 4 5% 5% 17%	2173
October	1st to 10th	Night	10% 15% 6% 11% 6% 5% 4 4 5% 7% 28%	3800
	11th to 20th	Night	8% 14% 7% 17% 8% 6% 5% 4 4 5% 23%	4398
	21st to end	Night	6% 15% 11% 20% 8% 6% 4 3 5% 5% 18%	5063
November	1st to 10th	Night	6% 18% 7% 13% 9% 7% 6% 3 5% 6% 20%	3122
	11th to 20th	Night	5% 14% 7% 17% 10% 7% 6% 5% 5% 5% 19%	3509
	21st to end	Night	5% 13% 6% 16% 8% 8% 7% 5% 7% 7% 18%	3658
December	1st to 10th	Night	6% 15% 6% 11% 8% 7% 7% 7% 7% 6% 18%	3967
	11th to 20th	Night	4 14% 6% 12% 9% 7% 8% 6% 8% 10% 16%	4713
	21st to end	Night	6% 14% 5% 11% 6% 6% 6% 5% 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	49% 7% 8% 17% 17% 2	761
	11th to 20th	Day	55% 4 7% 17% 8% 10%	1016
	21st to end	Day	54% 5% 7% 9% 23% 1	1683
February	1st to 10th	Day	44% 7% 11% 22% 15% 3	1121
	11th to 20th	Day	46% 7% 14% 20% 11% 1	1302
	21st to end	Day	56% 7% 13% 14% 8% 2	1338
March	1st to 10th	Day	59% 4 8% 21% 8% 1	2874
	11th to 20th	Day	71% 4 8% 12% 6%	3381
	21st to end	Day	50% 4 23% 17% 6%	4051
April	1st to 10th	Day	61% 6% 15% 12% 5% 1	2475
	11th to 20th	Day	56% 6% 17% 16% 5%	2640
	21st to end	Day	52% 6% 16% 20% 5%	2952
May	1st to 10th	Day	62% 8% 12% 13% 5%	5178
	11th to 20th	Day	50% 7% 20% 21% 2	5637
	21st to end	Day	50% 8% 18% 20% 4	6594
June	1st to 10th	Day	53% 7% 14% 21% 4	3814
	11th to 20th	Day	50% 7% 16% 22% 4	3990
	21st to end	Day	54% 11% 17% 16% 3	3990
July	1st to 10th	Day	67% 9% 15% 8% 1	6348
	11th to 20th	Day	58% 10% 20% 11% 1	5960
	21st to end	Day	48% 9% 23% 17% 3	5968
August	1st to 10th	Day	50% 9% 17% 18% 7%	5251
	11th to 20th	Day	58% 9% 16% 17%	4831
	21st to end	Day	72% 8% 12% 8%	4978
September	1st to 10th	Day	60% 7% 19% 13% 1	2478
	11th to 20th	Day	56% 9% 20% 13% 2	2280
	21st to end	Day	71% 5% 13% 10% 1	2005
October	1st to 10th	Day	54% 7% 19% 15% 4	3170
	11th to 20th	Day	60% 5% 11% 19% 4	2530
	21st to end	Day	67% 5% 15% 11% 2	2489
November	1st to 10th	Day	65% 4 12% 14% 5%	1176
	11th to 20th	Day	67% 4 10% 13% 5%	870
	21st to end	Day	62% 7% 9% 18% 5%	740
December	1st to 10th	Day	62% 6% 12% 15% 6%	396
	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	48% 6% 11% 17% 17% 1	6193
	11th to 20th	Night	53% 5% 6% 14% 11% 12%	5952
	21st to end	Night	54% 5% 7% 9% 22% 3	6005
February	1st to 10th	Night	46% 5% 10% 23% 12% 3	3059
	11th to 20th	Night	50% 5% 12% 19% 13% 1	2776
	21st to end	Night	55% 6% 12% 13% 12% 2	2114
March	1st to 10th	Night	60% 5% 7% 20% 8%	3990
	11th to 20th	Night	70% 4 7% 12% 7%	3581
	21st to end	Night	52% 6% 21% 16% 5% 1	3588
April	1st to 10th	Night	64% 6% 14% 11% 4 2	1703
	11th to 20th	Night	59% 5% 12% 18% 5%	1488
	21st to end	Night	53% 6% 17% 19% 5%	1228
May	1st to 10th	Night	64% 6% 13% 14% 3	1781
	11th to 20th	Night	51% 7% 19% 19% 3	1262
	21st to end	Night	53% 5% 16% 23% 4	990
June	1st to 10th	Night	53% 6% 16% 22% 3	363
	11th to 20th	Night	47% 8% 17% 24% 3 1	190
	21st to end	Night	45% 12% 23% 16% 4	190
July	1st to 10th	Night	62% 13% 16% 7% 2	513
	11th to 20th	Night	59% 9% 20% 11% 1	885
	21st to end	Night	47% 8% 25% 19% 2	1345
August	1st to 10th	Night	53% 7% 16% 16% 6% 1	1655
	11th to 20th	Night	55% 10% 19% 15%	2066
	21st to end	Night	67% 12% 15% 6%	2688
September	1st to 10th	Night	62% 9% 17% 11%	1701
	11th to 20th	Night	58% 6% 19% 15% 2	1900
	21st to end	Night	69% 5% 13% 11% 1	2173
October	1st to 10th	Night	54% 8% 12% 23% 3	3800
	11th to 20th	Night	61% 7% 10% 19% 3	4398
	21st to end	Night	68% 5% 12% 14% 1	5063
November	1st to 10th	Night	64% 4 16% 13% 3	3122
	11th to 20th	Night	65% 5% 12% 12% 5%	3509
	21st to end	Night	62% 5% 10% 18% 5%	3658
December	1st to 10th	Night	60% 7% 12% 14% 7%	3967
	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 8% 34% 30% 12%	90
	21st to end	Day	9% 4 16% 31% 33% 6%	99
February	1st to 10th	Day	3 3 9% 33% 35% 16%	201
	11th to 20th	Day	6% 4 12% 32% 31% 15%	365
	21st to end	Day	5% 5% 16% 30% 26% 19%	307
March	1st to 10th	Day	4 2 15% 32% 25% 21%	370
	11th to 20th	Day	8% 4 14% 32% 31% 11%	370
	21st to end	Day	5% 6% 16% 28% 27% 18%	471
April	1st to 10th	Day	6% 3 15% 35% 30% 11%	631
	11th to 20th	Day	9% 5% 16% 30% 25% 15%	640
	21st to end	Day	8% 6% 14% 30% 30% 13%	650
May	1st to 10th	Day	12% 6% 20% 27% 25% 11%	653
	11th to 20th	Day	14% 6% 17% 26% 26% 11%	848
	21st to end	Day	14% 7% 14% 30% 25% 9%	1094
June	1st to 10th	Day	16% 5% 19% 31% 22% 7%	1060
	11th to 20th	Day	15% 5% 14% 27% 29% 10%	1060
	21st to end	Day	18% 4 11% 24% 30% 13%	1060
July	1st to 10th	Day	20% 5% 14% 23% 26% 11%	1041
	11th to 20th	Day	23% 5% 10% 21% 28% 14%	1036
	21st to end	Day	19% 5% 11% 21% 28% 17%	939
August	1st to 10th	Day	23% 5% 12% 25% 22% 14%	676
	11th to 20th	Day	25% 9% 17% 24% 16% 9%	665
	21st to end	Day	29% 6% 17% 24% 18% 6%	748
September	1st to 10th	Day	23% 8% 15% 22% 21% 13%	650
	11th to 20th	Day	23% 6% 15% 24% 24% 9%	490
	21st to end	Day	27% 7% 15% 18% 23% 10%	403
October	1st to 10th	Day	18% 6% 21% 22% 21% 11%	390
	11th to 20th	Day	20% 5% 12% 26% 22% 14%	390
	21st to end	Day	18% 4 12% 27% 23% 16%	336
November	1st to 10th	Day	10% 5% 10% 35% 28% 14%	200
	11th to 20th	Day	13% 3 9% 25% 28% 22%	129
	21st to end	Day	7% 2 15% 25% 32% 19%	100
December	1st to 10th	Day	14% 4 10% 41% 24% 6%	98
	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 11% 34% 31% 10%	1110
	21st to end	Night	10% 3 12% 34% 31% 10%	983
February	1st to 10th	Night	7% 3 12% 31% 37% 11%	850
	11th to 20th	Night	6% 3 13% 35% 32% 11%	834
	21st to end	Night	5% 3 16% 35% 29% 12%	703
March	1st to 10th	Night	3 4 13% 35% 32% 12%	832
	11th to 20th	Night	5% 2 10% 35% 36% 11%	632
	21st to end	Night	4 3 12% 31% 35% 14%	627
April	1st to 10th	Night	9% 3 9% 31% 34% 13%	570
	11th to 20th	Night	9% 3 10% 34% 30% 13%	563
	21st to end	Night	10% 3 11% 32% 35% 9%	468
May	1st to 10th	Night	14% 5% 11% 32% 32% 6%	313
	11th to 20th	Night	12% 4 13% 29% 34% 6%	187
	21st to end	Night	13% 4 9% 36% 36% 2	206
June	1st to 10th	Night	18% 4 15% 29% 33% 1	190
	11th to 20th	Night	15% 2 12% 39% 31% 2	190
	21st to end	Night	13% 4 9% 33% 39% 3	190
July	1st to 10th	Night	21% 3 10% 30% 33% 3	185
	11th to 20th	Night	22% 3 10% 22% 40% 4	184
	21st to end	Night	20% 2 13% 25% 34% 6%	208
August	1st to 10th	Night	23% 5% 8% 28% 35% 2	235
	11th to 20th	Night	25% 7% 12% 25% 27% 5%	477
	21st to end	Night	26% 6% 12% 23% 26% 7%	627
September	1st to 10th	Night	22% 4 12% 24% 26% 11%	570
	11th to 20th	Night	22% 4 11% 29% 29% 6%	570
	21st to end	Night	27% 5% 11% 28% 23% 6%	679
October	1st to 10th	Night	21% 4 14% 28% 24% 8%	760
	11th to 20th	Night	21% 5% 10% 23% 30% 12%	857
	21st to end	Night	15% 5% 11% 30% 27% 13%	946
November	1st to 10th	Night	13% 2 10% 30% 33% 12%	880
	11th to 20th	Night	10% 5% 10% 27% 30% 19%	1069
	21st to end	Night	10% 3 12% 26% 32% 18%	1115
December	1st to 10th	Night	11% 6% 12% 35% 29% 7%	1189
	11th to 20th	Night	10% 3 11% 32% 33% 11%	1130
	21st to end	Night	7% 4 12% 28% 33% 17%	1243

Page generated at 2024-12-06 00:54:49. Version ac07

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