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 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	10% 10% 4 8% 8% 5% 6% 6% 7% 9% 28%	74642
	Night	7% 12% 6% 11% 10% 5% 7% 6% 7% 8% 21%	75111
Transparency	Day	51% 11% 16% 17% 4	74241
	Night	57% 9% 13% 14% 5%	75030
Seeing	Day	16% 6% 18% 29% 22% 8%	16401
	Night	13% 6% 19% 32% 24% 6%	22170

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	5% 11% 5% 12% 12% 6% 9% 8% 7% 9% 16%	569
	11th to 20th	Day	6% 12% 9% 10% 13% 8% 5% 6% 7% 7% 16%	627
	21st to end	Day	4 15% 6% 10% 11% 6% 9% 8% 6% 11% 16%	976
February	1st to 10th	Day	3 9% 3 8% 12% 5% 9% 9% 8% 12% 23%	1109
	11th to 20th	Day	3 10% 5% 13% 12% 8% 9% 7% 9% 9% 15%	1250
	21st to end	Day	2 7% 6% 15% 12% 7% 7% 7% 7% 8% 21%	1260
March	1st to 10th	Day	3 8% 4 9% 9% 6% 8% 8% 8% 10% 28%	1649
	11th to 20th	Day	1 11% 6% 15% 12% 6% 8% 7% 7% 8% 19%	1943
	21st to end	Day	3 9% 6% 12% 11% 6% 8% 7% 6% 8% 24%	2291
April	1st to 10th	Day	7% 14% 7% 10% 8% 5% 6% 7% 6% 7% 24%	2340
	11th to 20th	Day	8% 11% 6% 9% 7% 5% 6% 6% 7% 7% 28%	2508
	21st to end	Day	8% 10% 4 8% 7% 4 5% 6% 7% 9% 33%	2704
May	1st to 10th	Day	10% 11% 4 8% 6% 4 5% 6% 6% 8% 31%	3001
	11th to 20th	Day	10% 9% 3 7% 6% 4 6% 5% 6% 9% 35%	3070
	21st to end	Day	11% 8% 3 5% 5% 4 5% 6% 6% 8% 40%	3684
June	1st to 10th	Day	11% 8% 3 6% 6% 4 6% 6% 6% 10% 32%	3538
	11th to 20th	Day	12% 6% 3 7% 6% 5% 6% 7% 8% 10% 30%	3780
	21st to end	Day	11% 6% 3 5% 6% 3 6% 6% 7% 9% 38%	3780
July	1st to 10th	Day	12% 5% 3 6% 7% 4 7% 7% 7% 9% 31%	3576
	11th to 20th	Day	12% 7% 3 7% 7% 4 6% 7% 8% 10% 28%	3420
	21st to end	Day	9% 6% 3 6% 8% 4 7% 7% 8% 10% 32%	3461
August	1st to 10th	Day	13% 8% 3 6% 6% 3 5% 6% 6% 10% 34%	3027
	11th to 20th	Day	17% 10% 4 7% 7% 4 6% 6% 7% 8% 24%	2666
	21st to end	Day	19% 10% 4 7% 7% 4 6% 5% 7% 8% 22%	2839
September	1st to 10th	Day	14% 8% 3 6% 6% 4 6% 6% 7% 9% 31%	2340
	11th to 20th	Day	13% 10% 3 8% 7% 3 5% 5% 5% 8% 33%	2133
	21st to end	Day	16% 18% 6% 10% 7% 3 4 5% 5% 6% 21%	1952
October	1st to 10th	Day	15% 16% 5% 8% 6% 4 5% 5% 5% 6% 24%	1724
	11th to 20th	Day	10% 18% 7% 14% 9% 4 5% 6% 5% 5% 17%	1524
	21st to end	Day	9% 20% 8% 13% 11% 5% 7% 5% 4 5% 15%	1446
November	1st to 10th	Day	6% 13% 7% 14% 11% 6% 8% 4 5% 9% 17%	1116
	11th to 20th	Day	5% 14% 8% 14% 12% 5% 9% 5% 8% 7% 12%	884
	21st to end	Day	5% 9% 6% 13% 14% 7% 8% 7% 9% 12% 11%	691
December	1st to 10th	Day	4 15% 8% 13% 10% 8% 8% 6% 5% 9% 14%	544
	11th to 20th	Day	3 10% 6% 11% 14% 6% 7% 9% 9% 10% 13%	476
	21st to end	Day	2 7% 2 10% 13% 8% 8% 8% 8% 15% 18%	744
January	1st to 10th	Night	4 11% 7% 13% 12% 7% 10% 7% 6% 8% 13%	3596
	11th to 20th	Night	6% 13% 7% 13% 12% 6% 8% 6% 7% 8% 14%	3458
	21st to end	Night	5% 13% 6% 13% 10% 7% 9% 7% 6% 8% 16%	3380
February	1st to 10th	Night	2 8% 5% 11% 11% 7% 10% 8% 8% 10% 20%	2866
	11th to 20th	Night	3 10% 6% 10% 12% 6% 8% 8% 7% 9% 21%	2594
	21st to end	Night	2 10% 5% 12% 11% 7% 8% 7% 6% 9% 22%	1996
March	1st to 10th	Night	2 7% 4 9% 9% 5% 7% 6% 8% 9% 33%	2309
	11th to 20th	Night	1 9% 7% 14% 12% 8% 8% 5% 5% 6% 24%	2016
	21st to end	Night	2 7% 7% 13% 8% 4 7% 5% 5% 8% 33%	2062
April	1st to 10th	Night	6% 14% 8% 11% 9% 4 5% 5% 6% 6% 26%	1620
	11th to 20th	Night	7% 13% 5% 6% 5% 3 4 4 7% 10% 36%	1401
	21st to end	Night	6% 11% 4 7% 6% 4 7% 6% 7% 9% 33%	1256
May	1st to 10th	Night	11% 11% 5% 6% 6% 4 5% 6% 6% 8% 32%	959
	11th to 20th	Night	11% 5% 2 7% 6% 4 6% 6% 7% 7% 39%	825
	21st to end	Night	11% 8% 3 6% 5% 2 4 5% 7% 11% 39%	590
June	1st to 10th	Night	15% 12% 5% 6% 7% 4 6% 5% 7% 8% 26%	420
	11th to 20th	Night	12% 7% 5% 8% 9% 5% 4 5% 7% 8% 31%	180
	21st to end	Night	13% 7% 3 5% 6% 3 7% 4 7% 9% 37%	180
July	1st to 10th	Night	12% 6% 2 4 6% 4 7% 9% 7% 11% 31%	381
	11th to 20th	Night	11% 7% 5% 8% 7% 5% 6% 9% 7% 7% 28%	540
	21st to end	Night	9% 7% 2 5% 7% 5% 6% 7% 8% 10% 33%	853
August	1st to 10th	Night	16% 9% 3 6% 6% 3 6% 5% 6% 8% 32%	911
	11th to 20th	Night	18% 10% 4 7% 7% 5% 6% 7% 7% 8% 21%	1233
	21st to end	Night	15% 11% 6% 9% 8% 5% 7% 5% 7% 7% 21%	1514
September	1st to 10th	Night	11% 9% 4 7% 8% 5% 5% 5% 7% 8% 31%	1620
	11th to 20th	Night	15% 10% 4 7% 6% 3 5% 6% 6% 7% 31%	1826
	21st to end	Night	17% 16% 5% 10% 7% 4 5% 5% 5% 6% 20%	2008
October	1st to 10th	Night	14% 15% 6% 9% 7% 5% 5% 6% 6% 6% 22%	2235
	11th to 20th	Night	11% 18% 7% 13% 8% 4 5% 4 5% 6% 19%	2437
	21st to end	Night	8% 17% 8% 14% 10% 5% 6% 6% 4 7% 14%	2893
November	1st to 10th	Night	5% 15% 7% 15% 13% 5% 6% 5% 5% 8% 15%	2958
	11th to 20th	Night	6% 15% 8% 15% 12% 6% 6% 7% 6% 6% 12%	3294
	21st to end	Night	4 11% 6% 13% 11% 5% 8% 9% 8% 9% 15%	3486
December	1st to 10th	Night	5% 14% 7% 15% 11% 6% 7% 5% 6% 9% 15%	3634
	11th to 20th	Night	4 12% 6% 14% 11% 6% 7% 7% 8% 9% 15%	4716
	21st to end	Night	4 9% 4 11% 10% 7% 9% 8% 8% 11% 20%	6864

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	60% 9% 10% 15% 6%	569
	11th to 20th	Day	64% 6% 7% 16% 5% 1	627
	21st to end	Day	59% 9% 12% 12% 9% 1	976
February	1st to 10th	Day	48% 11% 13% 19% 9%	1109
	11th to 20th	Day	60% 10% 9% 15% 5%	1257
	21st to end	Day	57% 7% 14% 14% 7%	1260
March	1st to 10th	Day	46% 9% 15% 21% 9%	1649
	11th to 20th	Day	59% 10% 9% 17% 6%	1943
	21st to end	Day	54% 12% 13% 16% 4	2291
April	1st to 10th	Day	58% 11% 13% 11% 5% 1	2340
	11th to 20th	Day	53% 10% 15% 18% 4	2508
	21st to end	Day	47% 10% 18% 21% 4	2704
May	1st to 10th	Day	49% 11% 18% 18% 4	3001
	11th to 20th	Day	45% 10% 15% 24% 7%	3074
	21st to end	Day	40% 9% 13% 25% 12% 1	3685
June	1st to 10th	Day	45% 13% 13% 23% 6%	3538
	11th to 20th	Day	46% 11% 16% 20% 6%	3780
	21st to end	Day	40% 10% 16% 28% 5%	3780
July	1st to 10th	Day	45% 14% 18% 19% 4	3481
	11th to 20th	Day	48% 13% 21% 15% 2	3315
	21st to end	Day	44% 15% 24% 15% 1	3268
August	1st to 10th	Day	44% 13% 25% 14% 3	3007
	11th to 20th	Day	55% 14% 19% 9% 2	2666
	21st to end	Day	57% 13% 21% 8%	2839
September	1st to 10th	Day	47% 14% 25% 12% 1	2340
	11th to 20th	Day	49% 10% 23% 16% 2	2133
	21st to end	Day	64% 9% 14% 12% 2	1952
October	1st to 10th	Day	59% 11% 15% 14% 2	1724
	11th to 20th	Day	67% 10% 11% 10% 2	1524
	21st to end	Day	68% 12% 7% 11% 2	1446
November	1st to 10th	Day	66% 7% 12% 12% 3	1116
	11th to 20th	Day	68% 8% 11% 10% 3	884
	21st to end	Day	61% 12% 10% 12% 5% 1	691
December	1st to 10th	Day	66% 7% 11% 14% 3	544
	11th to 20th	Day	59% 8% 15% 10% 7% 1	476
	21st to end	Day	49% 7% 16% 12% 15% 1	744
January	1st to 10th	Night	65% 7% 10% 13% 5%	3596
	11th to 20th	Night	64% 8% 11% 13% 3 1	3458
	21st to end	Night	61% 8% 12% 11% 8%	3380
February	1st to 10th	Night	54% 9% 12% 15% 9% 1	2866
	11th to 20th	Night	57% 9% 13% 15% 7% 1	2597
	21st to end	Night	57% 10% 11% 16% 6% 1	1996
March	1st to 10th	Night	45% 8% 12% 26% 9% 1	2309
	11th to 20th	Night	59% 8% 9% 15% 8%	2017
	21st to end	Night	47% 9% 13% 25% 6%	2062
April	1st to 10th	Night	57% 7% 15% 14% 6% 2	1620
	11th to 20th	Night	44% 8% 20% 23% 5%	1401
	21st to end	Night	45% 12% 18% 19% 6%	1256
May	1st to 10th	Night	48% 11% 17% 20% 4	959
	11th to 20th	Night	40% 12% 19% 23% 5% 1	825
	21st to end	Night	39% 10% 10% 29% 11% 1	590
June	1st to 10th	Night	54% 12% 12% 17% 5%	420
	11th to 20th	Night	51% 9% 15% 21% 4 1	180
	21st to end	Night	42% 8% 18% 28% 3	180
July	1st to 10th	Night	43% 18% 16% 20% 3	367
	11th to 20th	Night	49% 17% 17% 15% 2	522
	21st to end	Night	41% 17% 24% 17% 1	806
August	1st to 10th	Night	48% 11% 24% 14% 3	906
	11th to 20th	Night	56% 16% 17% 10% 1	1233
	21st to end	Night	59% 13% 18% 9%	1514
September	1st to 10th	Night	48% 12% 24% 14% 2	1620
	11th to 20th	Night	50% 12% 20% 17% 1	1826
	21st to end	Night	63% 11% 13% 11% 2	2008
October	1st to 10th	Night	60% 10% 14% 13% 2	2235
	11th to 20th	Night	64% 8% 14% 11% 2	2437
	21st to end	Night	67% 10% 11% 11% 2	2893
November	1st to 10th	Night	65% 9% 12% 12% 2	2958
	11th to 20th	Night	68% 9% 9% 11% 3	3294
	21st to end	Night	58% 12% 12% 13% 4 1	3486
December	1st to 10th	Night	64% 7% 11% 15% 3	3634
	11th to 20th	Night	61% 8% 12% 12% 7% 1	4715
	21st to end	Night	52% 9% 14% 14% 11%	6864

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	6% 12% 18% 34% 20% 10%	90
	11th to 20th	Day	13% 6% 24% 39% 16% 2	85
	21st to end	Day	11% 6% 22% 34% 21% 8%	170
February	1st to 10th	Day	10% 11% 18% 32% 24% 5%	160
	11th to 20th	Day	8% 9% 20% 30% 23% 11%	185
	21st to end	Day	8% 10% 28% 32% 20% 2	280
March	1st to 10th	Day	4 4 24% 29% 26% 12%	340
	11th to 20th	Day	8% 4 22% 32% 27% 8%	404
	21st to end	Day	7% 7% 23% 32% 23% 8%	462
April	1st to 10th	Day	16% 8% 21% 23% 22% 10%	420
	11th to 20th	Day	14% 5% 18% 29% 26% 8%	495
	21st to end	Day	11% 5% 26% 29% 24% 6%	604
May	1st to 10th	Day	15% 6% 21% 33% 20% 5%	783
	11th to 20th	Day	16% 7% 21% 30% 20% 6%	802
	21st to end	Day	16% 4 20% 35% 21% 4	874
June	1st to 10th	Day	19% 7% 16% 30% 22% 6%	839
	11th to 20th	Day	16% 5% 19% 33% 21% 5%	990
	21st to end	Day	17% 4 20% 30% 21% 7%	990
July	1st to 10th	Day	16% 4 12% 36% 25% 7%	887
	11th to 20th	Day	18% 5% 13% 24% 25% 14%	792
	21st to end	Day	15% 4 15% 28% 27% 12%	881
August	1st to 10th	Day	20% 4 13% 27% 24% 12%	788
	11th to 20th	Day	25% 7% 16% 24% 22% 5%	615
	21st to end	Day	25% 3 13% 28% 21% 10%	624
September	1st to 10th	Day	22% 5% 17% 24% 22% 10%	450
	11th to 20th	Day	18% 7% 22% 28% 18% 7%	450
	21st to end	Day	28% 10% 16% 26% 17% 3	450
October	1st to 10th	Day	24% 10% 19% 24% 14% 8%	412
	11th to 20th	Day	17% 9% 23% 25% 19% 7%	264
	21st to end	Day	22% 6% 17% 21% 23% 11%	198
November	1st to 10th	Day	9% 8% 23% 23% 26% 12%	180
	11th to 20th	Day	14% 6% 13% 33% 24% 9%	180
	21st to end	Day	19% 4 13% 27% 26% 11%	147
December	1st to 10th	Day	10% 3 21% 38% 19% 9%	77
	21st to end	Day	6% 21% 42% 21% 9%	33
January	1st to 10th	Night	8% 7% 21% 29% 26% 9%	1040
	11th to 20th	Night	12% 7% 23% 34% 20% 4	1016
	21st to end	Night	12% 5% 23% 32% 23% 6%	1078
February	1st to 10th	Night	6% 6% 19% 36% 27% 6%	833
	11th to 20th	Night	8% 4 22% 38% 22% 7%	784
	21st to end	Night	6% 7% 22% 36% 22% 6%	624
March	1st to 10th	Night	5% 7% 19% 37% 25% 7%	720
	11th to 20th	Night	4 4 22% 35% 27% 8%	720
	21st to end	Night	6% 7% 19% 31% 27% 10%	725
April	1st to 10th	Night	12% 5% 18% 33% 26% 6%	540
	11th to 20th	Night	13% 4 13% 38% 26% 5%	416
	21st to end	Night	11% 5% 23% 36% 21% 4	360
May	1st to 10th	Night	17% 3 20% 33% 24% 3	360
	11th to 20th	Night	13% 6% 18% 34% 27% 3	354
	21st to end	Night	17% 3 21% 34% 25%	203
June	1st to 10th	Night	20% 5% 19% 33% 21% 2	91
	July	1st to 10th	Night	17% 4 18% 32% 24% 6%	109
11th to 20th		Night	17% 4 10% 32% 36% 2	174
21st to end		Night	13% 2 11% 34% 36% 4	307
August	1st to 10th	Night	21% 4 9% 29% 31% 5%	358
	11th to 20th	Night	27% 3 12% 33% 19% 5%	356
	21st to end	Night	22% 4 11% 33% 24% 6%	455
September	1st to 10th	Night	19% 4 14% 30% 27% 6%	540
	11th to 20th	Night	24% 5% 19% 31% 19% 3	679
	21st to end	Night	30% 6% 15% 25% 19% 4	720
October	1st to 10th	Night	23% 8% 19% 27% 19% 4	720
	11th to 20th	Night	23% 6% 16% 27% 23% 6%	720
	21st to end	Night	17% 5% 14% 29% 25% 9%	852
November	1st to 10th	Night	13% 6% 21% 30% 23% 8%	1012
	11th to 20th	Night	14% 6% 16% 30% 23% 10%	1040
	21st to end	Night	11% 4 18% 31% 25% 10%	1040
December	1st to 10th	Night	14% 6% 23% 31% 21% 5%	1040
	11th to 20th	Night	10% 8% 24% 32% 20% 6%	1040
	21st to end	Night	8% 6% 15% 33% 31% 8%	1144

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