Norman Wells
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norman Wells 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	8% 10% 4 10% 7% 6% 6% 5% 7% 9% 27%	134929
	Night	5% 11% 5% 14% 8% 7% 7% 5% 7% 9% 21%	135452
Transparency	Day	50% 10% 16% 18% 5% 1	134531
	Night	56% 8% 13% 16% 6%	135431
Seeing	Day	16% 6% 19% 30% 22% 7%	19340
	Night	13% 6% 19% 32% 24% 6%	25081

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 7% 5% 17% 10% 8% 10% 6% 9% 14% 14%	1733
	11th to 20th	Day	3 8% 6% 11% 9% 9% 6% 5% 7% 6% 29%	1984
	21st to end	Day	3 10% 5% 17% 12% 9% 7% 7% 9% 7% 13%	3175
February	1st to 10th	Day	3 10% 4 12% 10% 6% 9% 6% 8% 10% 22%	1295
	11th to 20th	Day	3 10% 4 14% 11% 11% 8% 6% 9% 10% 16%	1465
	21st to end	Day	2 7% 6% 17% 12% 9% 7% 5% 7% 8% 20%	1473
March	1st to 10th	Day	1 7% 5% 16% 10% 9% 10% 7% 7% 8% 22%	4235
	11th to 20th	Day	3 11% 5% 16% 12% 10% 8% 6% 7% 9% 13%	5015
	21st to end	Day	2 10% 7% 17% 8% 7% 7% 6% 8% 8% 20%	5907
April	1st to 10th	Day	6% 15% 6% 11% 8% 7% 6% 5% 6% 7% 24%	2614
	11th to 20th	Day	6% 12% 5% 10% 6% 7% 6% 5% 7% 7% 29%	2792
	21st to end	Day	7% 12% 4 10% 6% 5% 5% 5% 7% 9% 30%	3006
May	1st to 10th	Day	12% 16% 5% 10% 5% 5% 5% 5% 6% 8% 22%	7557
	11th to 20th	Day	7% 11% 4 10% 6% 7% 7% 5% 7% 9% 27%	7822
	21st to end	Day	11% 10% 3 8% 6% 5% 6% 5% 7% 8% 31%	9404
June	1st to 10th	Day	11% 9% 3 8% 6% 6% 6% 4 7% 9% 31%	3932
	11th to 20th	Day	11% 7% 3 8% 5% 6% 6% 6% 9% 10% 32%	4200
	21st to end	Day	10% 7% 2 6% 5% 4 5% 5% 7% 10% 39%	4200
July	1st to 10th	Day	10% 8% 4 9% 7% 6% 7% 6% 8% 8% 26%	9000
	11th to 20th	Day	9% 6% 3 7% 6% 6% 7% 6% 9% 10% 32%	8620
	21st to end	Day	10% 6% 3 7% 5% 5% 6% 4 7% 9% 38%	8689
August	1st to 10th	Day	8% 6% 2 5% 5% 4 5% 4 6% 9% 47%	5494
	11th to 20th	Day	15% 8% 3 6% 5% 5% 5% 5% 7% 9% 32%	4808
	21st to end	Day	14% 12% 4 10% 7% 6% 6% 4 6% 8% 22%	5132
September	1st to 10th	Day	14% 9% 3 7% 6% 5% 5% 5% 7% 8% 31%	2600
	11th to 20th	Day	12% 9% 3 10% 6% 5% 5% 4 6% 8% 32%	2369
	21st to end	Day	16% 19% 5% 11% 6% 4 4 4 5% 6% 20%	2168
October	1st to 10th	Day	9% 13% 6% 10% 5% 4 4 3 6% 6% 35%	3130
	11th to 20th	Day	6% 13% 4 15% 7% 6% 6% 5% 6% 7% 26%	2748
	21st to end	Day	6% 15% 6% 17% 11% 8% 8% 5% 5% 5% 13%	2589
November	1st to 10th	Day	6% 15% 7% 17% 8% 8% 7% 3 5% 9% 16%	1236
	11th to 20th	Day	5% 17% 7% 16% 10% 8% 7% 4 8% 6% 12%	976
	21st to end	Day	5% 10% 6% 16% 11% 9% 6% 5% 9% 11% 11%	763
December	1st to 10th	Day	7% 21% 8% 12% 5% 8% 5% 4 4 11% 14%	944
	11th to 20th	Day	2 11% 5% 11% 11% 6% 7% 5% 10% 14% 17%	756
	21st to end	Day	1 8% 4 15% 10% 9% 8% 6% 8% 12% 18%	1098
January	1st to 10th	Night	2 7% 5% 16% 9% 9% 10% 6% 9% 13% 14%	11160
	11th to 20th	Night	4 10% 5% 14% 10% 8% 7% 4 7% 8% 23%	10911
	21st to end	Night	3 11% 5% 16% 11% 10% 8% 7% 8% 7% 14%	11006
February	1st to 10th	Night	2 10% 5% 13% 9% 9% 9% 6% 8% 9% 19%	3343
	11th to 20th	Night	2 10% 5% 13% 10% 9% 7% 6% 7% 9% 22%	3039
	21st to end	Night	2 10% 5% 15% 12% 9% 7% 5% 6% 8% 21%	2333
March	1st to 10th	Night	1 8% 4 15% 8% 7% 7% 6% 9% 11% 24%	5857
	11th to 20th	Night	4 10% 5% 12% 10% 13% 10% 7% 6% 8% 15%	5200
	21st to end	Night	1 11% 7% 17% 6% 5% 7% 5% 6% 9% 27%	5299
April	1st to 10th	Night	5% 16% 6% 14% 7% 5% 6% 4 7% 5% 26%	1809
	11th to 20th	Night	6% 15% 4 7% 5% 4 4 3 7% 9% 36%	1557
	21st to end	Night	6% 13% 4 9% 6% 5% 6% 5% 7% 8% 31%	1394
May	1st to 10th	Night	13% 18% 5% 10% 4 5% 5% 4 6% 7% 23%	2403
	11th to 20th	Night	7% 9% 4 10% 7% 6% 6% 6% 8% 7% 30%	2073
	21st to end	Night	10% 8% 2 8% 6% 5% 6% 5% 8% 9% 31%	1470
June	1st to 10th	Night	14% 13% 4 9% 6% 5% 5% 4 7% 8% 25%	466
	11th to 20th	Night	10% 8% 3 8% 9% 7% 5% 3 8% 10% 32%	200
	21st to end	Night	13% 6% 2 7% 5% 5% 6% 3 10% 8% 38%	200
July	1st to 10th	Night	11% 8% 5% 10% 6% 5% 5% 6% 8% 10% 27%	967
	11th to 20th	Night	7% 8% 4 9% 6% 7% 7% 6% 9% 9% 27%	1340
	21st to end	Night	11% 7% 2 6% 5% 5% 6% 5% 8% 9% 37%	2151
August	1st to 10th	Night	10% 7% 2 6% 4 4 4 3 5% 6% 49%	1655
	11th to 20th	Night	15% 8% 3 7% 5% 6% 6% 5% 7% 9% 29%	2239
	21st to end	Night	15% 12% 5% 11% 7% 7% 7% 4 6% 6% 21%	2767
September	1st to 10th	Night	12% 9% 4 8% 6% 6% 6% 5% 7% 8% 30%	1800
	11th to 20th	Night	14% 10% 4 9% 5% 5% 5% 5% 6% 7% 30%	2030
	21st to end	Night	17% 17% 5% 11% 6% 5% 5% 4 5% 6% 19%	2232
October	1st to 10th	Night	8% 14% 6% 11% 6% 6% 5% 4 6% 6% 28%	4064
	11th to 20th	Night	7% 14% 5% 13% 5% 5% 5% 4 6% 9% 27%	4395
	21st to end	Night	6% 19% 10% 19% 9% 7% 6% 3 4 4 14%	5170
November	1st to 10th	Night	5% 17% 7% 17% 11% 7% 6% 4 5% 7% 14%	3278
	11th to 20th	Night	5% 17% 7% 17% 11% 8% 6% 5% 6% 6% 11%	3642
	21st to end	Night	4 11% 6% 15% 9% 7% 8% 6% 9% 9% 15%	3854
December	1st to 10th	Night	5% 16% 6% 15% 9% 6% 5% 4 7% 10% 17%	6454
	11th to 20th	Night	3 12% 5% 14% 9% 7% 6% 5% 9% 12% 19%	7656
	21st to end	Night	4 10% 4 13% 9% 9% 9% 6% 9% 10% 18%	10038

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% 6% 8% 17% 13%	1733
	11th to 20th	Day	50% 5% 9% 23% 10% 2	1994
	21st to end	Day	61% 8% 13% 10% 8% 1	3175
February	1st to 10th	Day	51% 9% 11% 19% 9% 1	1295
	11th to 20th	Day	58% 9% 9% 14% 8% 1	1472
	21st to end	Day	59% 6% 13% 14% 8%	1473
March	1st to 10th	Day	53% 8% 10% 14% 15%	4235
	11th to 20th	Day	64% 9% 6% 15% 6%	5015
	21st to end	Day	55% 10% 15% 11% 9%	5907
April	1st to 10th	Day	57% 11% 13% 12% 5% 1	2614
	11th to 20th	Day	50% 10% 15% 19% 6%	2792
	21st to end	Day	50% 10% 17% 20% 3	3006
May	1st to 10th	Day	54% 11% 15% 17% 3	7557
	11th to 20th	Day	49% 11% 17% 19% 4	7826
	21st to end	Day	46% 10% 14% 20% 10%	9405
June	1st to 10th	Day	47% 12% 13% 22% 6%	3932
	11th to 20th	Day	44% 11% 16% 23% 7%	4200
	21st to end	Day	39% 10% 16% 29% 7%	4200
July	1st to 10th	Day	51% 10% 17% 18% 3	8905
	11th to 20th	Day	42% 11% 22% 23% 2	8515
	21st to end	Day	40% 10% 23% 22% 4	8445
August	1st to 10th	Day	34% 10% 23% 16% 8% 10%	5474
	11th to 20th	Day	46% 11% 26% 15% 2	4853
	21st to end	Day	58% 11% 21% 10% 1	5131
September	1st to 10th	Day	48% 13% 25% 13% 1	2600
	11th to 20th	Day	48% 10% 23% 17% 2	2369
	21st to end	Day	64% 9% 13% 12% 2	2168
October	1st to 10th	Day	46% 8% 17% 23% 5%	3130
	11th to 20th	Day	55% 9% 13% 20% 3	2748
	21st to end	Day	67% 10% 12% 10% 1	2589
November	1st to 10th	Day	66% 8% 12% 12% 3	1236
	11th to 20th	Day	67% 8% 11% 10% 4	976
	21st to end	Day	61% 11% 10% 12% 6% 1	763
December	1st to 10th	Day	65% 5% 8% 16% 6%	944
	11th to 20th	Day	53% 6% 14% 21% 6% 1	756
	21st to end	Day	52% 8% 14% 12% 13%	1098
January	1st to 10th	Night	56% 6% 9% 18% 12%	11161
	11th to 20th	Night	56% 6% 13% 16% 7% 2	10963
	21st to end	Night	61% 7% 12% 11% 9%	11006
February	1st to 10th	Night	54% 8% 12% 15% 10% 1	3343
	11th to 20th	Night	55% 9% 12% 14% 8% 2	3042
	21st to end	Night	59% 9% 10% 16% 6% 1	2333
March	1st to 10th	Night	48% 7% 9% 24% 12%	5857
	11th to 20th	Night	63% 6% 9% 13% 9%	5201
	21st to end	Night	51% 6% 18% 15% 9%	5299
April	1st to 10th	Night	56% 7% 15% 14% 5% 2	1809
	11th to 20th	Night	43% 8% 19% 23% 6%	1557
	21st to end	Night	47% 11% 17% 18% 6%	1394
May	1st to 10th	Night	57% 9% 14% 17% 3	2403
	11th to 20th	Night	46% 12% 20% 19% 4	2073
	21st to end	Night	42% 12% 12% 22% 12%	1470
June	1st to 10th	Night	54% 12% 11% 18% 5%	466
	11th to 20th	Night	47% 10% 15% 24% 6% 1	200
	21st to end	Night	41% 8% 18% 30% 5%	200
July	1st to 10th	Night	49% 11% 17% 20% 3	953
	11th to 20th	Night	47% 12% 21% 19% 2	1322
	21st to end	Night	40% 10% 25% 22% 3	2090
August	1st to 10th	Night	35% 7% 22% 20% 9% 6%	1650
	11th to 20th	Night	48% 12% 22% 16% 1	2260
	21st to end	Night	60% 10% 19% 10%	2767
September	1st to 10th	Night	49% 12% 24% 14% 2	1800
	11th to 20th	Night	50% 11% 21% 17% 1	2030
	21st to end	Night	63% 11% 14% 11% 2	2232
October	1st to 10th	Night	52% 10% 15% 20% 3	4064
	11th to 20th	Night	50% 8% 18% 19% 4	4395
	21st to end	Night	70% 7% 9% 12% 1	5170
November	1st to 10th	Night	66% 9% 11% 11% 2	3278
	11th to 20th	Night	69% 8% 9% 11% 3	3642
	21st to end	Night	58% 11% 12% 14% 4	3854
December	1st to 10th	Night	61% 6% 11% 19% 3	6454
	11th to 20th	Night	54% 7% 10% 21% 8%	7655
	21st to end	Night	54% 9% 15% 13% 8%	10038

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% 11% 18% 34% 20% 9%	110
	11th to 20th	Day	13% 7% 27% 37% 14% 2	110
	21st to end	Day	11% 9% 24% 33% 18% 6%	234
February	1st to 10th	Day	10% 10% 21% 32% 21% 5%	220
	11th to 20th	Day	7% 9% 22% 31% 21% 10%	250
	21st to end	Day	7% 8% 31% 34% 19% 2	355
March	1st to 10th	Day	4 5% 23% 33% 26% 10%	430
	11th to 20th	Day	8% 3 21% 31% 27% 8%	518
	21st to end	Day	6% 6% 25% 31% 23% 9%	594
April	1st to 10th	Day	14% 8% 21% 23% 22% 11%	505
	11th to 20th	Day	12% 5% 19% 29% 25% 10%	585
	21st to end	Day	11% 6% 25% 31% 22% 6%	706
May	1st to 10th	Day	16% 6% 23% 32% 19% 5%	903
	11th to 20th	Day	16% 7% 20% 31% 19% 6%	922
	21st to end	Day	16% 5% 20% 34% 21% 4	1006
June	1st to 10th	Day	20% 8% 18% 29% 20% 5%	963
	11th to 20th	Day	15% 5% 19% 34% 21% 5%	1130
	21st to end	Day	16% 4 20% 32% 23% 6%	1130
July	1st to 10th	Day	17% 5% 14% 34% 23% 7%	1017
	11th to 20th	Day	17% 7% 14% 25% 24% 13%	912
	21st to end	Day	15% 4 16% 29% 25% 11%	1013
August	1st to 10th	Day	19% 5% 13% 27% 25% 11%	906
	11th to 20th	Day	24% 7% 16% 25% 23% 5%	715
	21st to end	Day	24% 4 15% 27% 20% 9%	726
September	1st to 10th	Day	22% 6% 19% 24% 19% 9%	530
	11th to 20th	Day	16% 8% 24% 28% 18% 7%	530
	21st to end	Day	28% 10% 17% 25% 16% 3	530
October	1st to 10th	Day	24% 11% 19% 24% 14% 7%	483
	11th to 20th	Day	17% 9% 24% 24% 19% 7%	312
	21st to end	Day	19% 10% 19% 21% 22% 9%	242
November	1st to 10th	Day	10% 9% 23% 23% 25% 10%	220
	11th to 20th	Day	12% 6% 15% 33% 25% 9%	220
	21st to end	Day	17% 4 15% 27% 25% 11%	179
December	1st to 10th	Day	12% 4 20% 37% 19% 8%	93
	21st to end	Day	5% 32% 37% 20% 7%	41
January	1st to 10th	Night	8% 7% 22% 28% 26% 9%	1160
	11th to 20th	Night	13% 8% 24% 33% 18% 4	1160
	21st to end	Night	12% 7% 24% 32% 20% 5%	1276
February	1st to 10th	Night	7% 8% 20% 34% 25% 6%	988
	11th to 20th	Night	7% 5% 22% 38% 21% 6%	934
	21st to end	Night	6% 7% 22% 36% 24% 6%	736
March	1st to 10th	Night	5% 6% 20% 38% 25% 6%	840
	11th to 20th	Night	4 4 22% 34% 28% 8%	840
	21st to end	Night	5% 7% 20% 31% 27% 9%	845
April	1st to 10th	Night	12% 5% 18% 32% 27% 6%	603
	11th to 20th	Night	13% 5% 14% 38% 26% 5%	462
	21st to end	Night	11% 5% 25% 35% 21% 4	400
May	1st to 10th	Night	17% 4 21% 34% 22% 3	400
	11th to 20th	Night	13% 6% 19% 35% 25% 3	394
	21st to end	Night	16% 4 21% 35% 25%	225
June	1st to 10th	Night	19% 5% 24% 32% 19% 2	101
	July	1st to 10th	Night	17% 5% 21% 29% 23% 5%	123
11th to 20th		Night	16% 4 11% 32% 35% 2	194
21st to end		Night	13% 2 11% 35% 35% 3	342
August	1st to 10th	Night	20% 5% 10% 29% 30% 5%	398
	11th to 20th	Night	27% 3 12% 33% 20% 5%	396
	21st to end	Night	21% 5% 12% 33% 23% 6%	507
September	1st to 10th	Night	20% 4 16% 29% 26% 6%	600
	11th to 20th	Night	23% 6% 19% 31% 19% 3	755
	21st to end	Night	30% 7% 15% 25% 20% 4	800
October	1st to 10th	Night	22% 9% 20% 27% 19% 4	800
	11th to 20th	Night	22% 7% 16% 26% 23% 5%	800
	21st to end	Night	17% 6% 16% 29% 24% 8%	954
November	1st to 10th	Night	14% 6% 21% 29% 23% 7%	1132
	11th to 20th	Night	13% 7% 17% 30% 24% 9%	1160
	21st to end	Night	11% 4 19% 31% 25% 10%	1160
December	1st to 10th	Night	14% 6% 23% 31% 20% 5%	1160
	11th to 20th	Night	9% 9% 24% 32% 20% 7%	1160
	21st to end	Night	8% 6% 16% 32% 30% 7%	1276

Page generated at 2026-03-30 00:18:45. Version ac07

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