Norway House
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norway House clear sky chart from 2005-11-06 to 2025-02-21.

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% 10% 4 9% 6% 6% 5% 4 6% 7% 31%	112451
	Night	10% 12% 5% 11% 7% 6% 6% 5% 6% 6% 26%	114856
Transparency	Day	49% 8% 14% 21% 7%	112194
	Night	55% 7% 12% 18% 7%	114760
Seeing	Day	16% 12% 33% 26% 10% 2	16740
	Night	17% 9% 32% 30% 11% 1	26558

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	7% 13% 7% 17% 10% 8% 7% 9% 8% 4 10%	3179
	11th to 20th	Day	3 11% 7% 16% 11% 10% 9% 7% 11% 6% 9%	3159
	21st to end	Day	6% 18% 7% 17% 7% 6% 6% 6% 7% 6% 14%	3654
February	1st to 10th	Day	7% 11% 6% 10% 8% 8% 10% 7% 9% 7% 19%	1600
	11th to 20th	Day	6% 11% 4 11% 7% 6% 7% 7% 9% 7% 25%	1709
	21st to end	Day	4 10% 5% 10% 8% 8% 8% 6% 9% 9% 24%	1448
March	1st to 10th	Day	6% 13% 4 9% 6% 7% 6% 4 6% 8% 31%	3130
	11th to 20th	Day	9% 14% 5% 12% 6% 9% 8% 5% 5% 5% 22%	3473
	21st to end	Day	5% 10% 4 7% 6% 4 5% 5% 6% 7% 42%	3832
April	1st to 10th	Day	7% 10% 5% 9% 5% 4 4 4 5% 7% 39%	2399
	11th to 20th	Day	12% 9% 4 9% 6% 5% 5% 4 4 6% 36%	2442
	21st to end	Day	8% 7% 3 8% 6% 5% 5% 4 6% 6% 41%	2470
May	1st to 10th	Day	14% 10% 4 9% 5% 5% 4 4 5% 7% 35%	4683
	11th to 20th	Day	17% 8% 2 7% 5% 4 5% 4 6% 7% 35%	4705
	21st to end	Day	20% 12% 4 8% 4 4 4 3 5% 6% 32%	5173
June	1st to 10th	Day	15% 7% 3 6% 6% 5% 5% 5% 7% 7% 34%	2850
	11th to 20th	Day	18% 8% 3 7% 4 5% 5% 4 6% 8% 33%	2926
	21st to end	Day	14% 8% 2 6% 4 5% 5% 4 6% 8% 38%	3040
July	1st to 10th	Day	14% 5% 2 6% 5% 4 5% 4 7% 9% 40%	4843
	11th to 20th	Day	9% 4 2 5% 5% 5% 5% 5% 6% 10% 45%	4750
	21st to end	Day	10% 5% 2 5% 4 5% 4 4 6% 10% 45%	5150
August	1st to 10th	Day	12% 5% 2 5% 4 4 5% 4 6% 7% 47%	4614
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 5% 6% 8% 46%	4142
	21st to end	Day	20% 7% 2 6% 4 4 4 4 5% 7% 36%	4532
September	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 35%	2434
	11th to 20th	Day	20% 10% 2 7% 4 4 4 4 6% 5% 34%	2090
	21st to end	Day	14% 11% 3 7% 5% 4 5% 4 4 7% 37%	2090
October	1st to 10th	Day	15% 13% 3 8% 5% 5% 5% 4 6% 8% 28%	3206
	11th to 20th	Day	13% 15% 4 9% 6% 5% 6% 4 5% 5% 28%	2906
	21st to end	Day	17% 19% 7% 11% 6% 5% 4 4 4 4 21%	2981
November	1st to 10th	Day	14% 19% 7% 16% 9% 6% 5% 3 4 4 13%	1567
	11th to 20th	Day	13% 18% 6% 14% 10% 9% 5% 3 4 4 15%	1447
	21st to end	Day	9% 18% 7% 16% 9% 8% 7% 4 4 5% 13%	1400
December	1st to 10th	Day	8% 17% 5% 15% 11% 12% 8% 7% 5% 4 9%	2290
	11th to 20th	Day	11% 11% 4 15% 8% 6% 8% 7% 8% 8% 14%	2639
	21st to end	Day	5% 15% 6% 20% 9% 8% 6% 4 5% 4 17%	3498
January	1st to 10th	Night	5% 14% 8% 17% 9% 8% 8% 8% 7% 4 14%	6787
	11th to 20th	Night	4 11% 6% 20% 10% 8% 8% 9% 11% 4 8%	6759
	21st to end	Night	7% 19% 8% 17% 6% 7% 6% 4 6% 5% 14%	7321
February	1st to 10th	Night	6% 12% 5% 9% 7% 8% 10% 7% 9% 7% 19%	2800
	11th to 20th	Night	5% 10% 4 9% 8% 6% 8% 8% 8% 7% 25%	2578
	21st to end	Night	4 11% 6% 11% 10% 7% 6% 4 6% 5% 30%	2023
March	1st to 10th	Night	9% 13% 4 9% 6% 5% 5% 3 5% 9% 32%	3734
	11th to 20th	Night	8% 13% 6% 13% 9% 6% 5% 5% 4 5% 26%	3484
	21st to end	Night	6% 9% 4 9% 4 6% 6% 4 6% 7% 39%	3797
April	1st to 10th	Night	9% 12% 3 8% 6% 4 4 3 5% 6% 40%	1780
	11th to 20th	Night	12% 10% 5% 10% 6% 5% 6% 4 4 6% 34%	1689
	21st to end	Night	5% 7% 3 6% 6% 5% 6% 5% 6% 9% 42%	1710
May	1st to 10th	Night	16% 11% 3 8% 4 4 5% 5% 6% 6% 31%	2283
	11th to 20th	Night	17% 9% 3 9% 5% 5% 4 4 6% 6% 33%	2201
	21st to end	Night	18% 10% 3 7% 4 4 5% 3 5% 5% 35%	2414
June	1st to 10th	Night	14% 7% 3 6% 5% 5% 4 4 5% 7% 39%	1330
	11th to 20th	Night	15% 6% 2 8% 5% 5% 6% 5% 6% 6% 35%	1248
	21st to end	Night	13% 8% 3 7% 4 4 5% 4 5% 10% 39%	1140
July	1st to 10th	Night	12% 4 2 5% 5% 5% 5% 4 6% 8% 43%	2119
	11th to 20th	Night	8% 5% 2 5% 4 5% 4 4 6% 8% 49%	2220
	21st to end	Night	7% 4 2 5% 4 4 5% 5% 7% 9% 47%	2414
August	1st to 10th	Night	11% 4 2 4 4 4 4 4 7% 8% 49%	2324
	11th to 20th	Night	11% 4 2 5% 3 3 4 3 6% 10% 50%	2697
	21st to end	Night	16% 7% 2 6% 4 4 4 3 5% 7% 39%	3135
September	1st to 10th	Night	14% 8% 3 6% 4 4 4 3 4 8% 44%	1743
	11th to 20th	Night	18% 10% 2 7% 4 5% 4 3 5% 7% 35%	2090
	21st to end	Night	14% 8% 3 7% 6% 5% 5% 4 4 7% 37%	2090
October	1st to 10th	Night	15% 12% 3 8% 6% 5% 6% 5% 6% 7% 28%	3721
	11th to 20th	Night	12% 13% 4 8% 5% 5% 4 4 6% 9% 31%	4019
	21st to end	Night	17% 19% 5% 11% 5% 4 4 3 4 4 23%	4577
November	1st to 10th	Night	15% 18% 8% 15% 9% 5% 4 3 4 4 16%	2731
	11th to 20th	Night	14% 17% 7% 14% 11% 7% 4 4 3 4 15%	2950
	21st to end	Night	8% 21% 8% 16% 10% 6% 5% 3 4 5% 14%	3000
December	1st to 10th	Night	8% 19% 7% 16% 10% 9% 8% 5% 5% 4 8%	4900
	11th to 20th	Night	8% 14% 5% 11% 6% 7% 9% 9% 7% 7% 17%	5568
	21st to end	Night	7% 16% 7% 18% 8% 6% 6% 3 5% 5% 18%	7480

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	69% 6% 8% 13% 4 1	3179
	11th to 20th	Day	67% 6% 7% 16% 5%	3180
	21st to end	Day	65% 7% 10% 12% 6%	3654
February	1st to 10th	Day	57% 9% 13% 15% 6% 1	1600
	11th to 20th	Day	51% 7% 13% 21% 8%	1718
	21st to end	Day	52% 7% 11% 20% 9%	1448
March	1st to 10th	Day	48% 8% 14% 23% 7%	3130
	11th to 20th	Day	57% 11% 11% 16% 5% 1	3475
	21st to end	Day	37% 8% 12% 26% 16% 1	3832
April	1st to 10th	Day	42% 8% 12% 23% 14% 1	2399
	11th to 20th	Day	48% 7% 9% 21% 16%	2442
	21st to end	Day	40% 8% 12% 26% 13% 2	2470
May	1st to 10th	Day	46% 8% 12% 27% 7%	4683
	11th to 20th	Day	41% 11% 15% 22% 10% 2	4709
	21st to end	Day	51% 8% 11% 21% 8%	5173
June	1st to 10th	Day	45% 10% 14% 20% 11%	2850
	11th to 20th	Day	47% 7% 14% 21% 10%	2926
	21st to end	Day	42% 9% 16% 24% 9%	3040
July	1st to 10th	Day	37% 9% 24% 23% 7%	4769
	11th to 20th	Day	30% 9% 22% 33% 7%	4669
	21st to end	Day	34% 8% 22% 28% 7% 1	4988
August	1st to 10th	Day	34% 8% 17% 34% 7%	4597
	11th to 20th	Day	34% 8% 23% 29% 6%	4183
	21st to end	Day	45% 8% 18% 23% 6%	4531
September	1st to 10th	Day	44% 9% 20% 21% 5% 1	2434
	11th to 20th	Day	50% 8% 18% 20% 2	2090
	21st to end	Day	47% 7% 19% 22% 5%	2090
October	1st to 10th	Day	52% 6% 18% 17% 6%	3206
	11th to 20th	Day	57% 6% 12% 17% 7%	2906
	21st to end	Day	67% 6% 12% 13% 1	2981
November	1st to 10th	Day	74% 8% 9% 7% 1	1567
	11th to 20th	Day	72% 6% 12% 8% 1	1447
	21st to end	Day	74% 7% 10% 8% 1	1400
December	1st to 10th	Day	76% 8% 7% 7% 2	2290
	11th to 20th	Day	62% 7% 11% 16% 4	2640
	21st to end	Day	67% 7% 7% 15% 4	3498
January	1st to 10th	Night	66% 8% 9% 11% 6%	6787
	11th to 20th	Night	68% 6% 7% 15% 4	6800
	21st to end	Night	69% 6% 8% 10% 7%	7321
February	1st to 10th	Night	56% 8% 13% 17% 6%	2800
	11th to 20th	Night	51% 6% 12% 22% 9%	2579
	21st to end	Night	54% 4 10% 21% 10%	2023
March	1st to 10th	Night	48% 5% 12% 27% 8%	3734
	11th to 20th	Night	56% 9% 10% 17% 6% 1	3484
	21st to end	Night	39% 7% 12% 25% 17% 1	3797
April	1st to 10th	Night	43% 5% 9% 24% 17% 2	1780
	11th to 20th	Night	50% 7% 7% 19% 16% 2	1689
	21st to end	Night	36% 7% 12% 29% 15% 2	1710
May	1st to 10th	Night	49% 8% 9% 25% 8%	2283
	11th to 20th	Night	47% 9% 12% 18% 11% 2	2201
	21st to end	Night	48% 9% 10% 21% 10% 1	2414
June	1st to 10th	Night	42% 8% 12% 22% 14% 1	1330
	11th to 20th	Night	43% 10% 12% 21% 12% 1	1248
	21st to end	Night	40% 8% 17% 26% 9%	1140
July	1st to 10th	Night	37% 8% 24% 22% 9%	2084
	11th to 20th	Night	30% 8% 20% 35% 7% 1	2178
	21st to end	Night	31% 8% 23% 27% 11%	2337
August	1st to 10th	Night	30% 7% 15% 41% 7%	2317
	11th to 20th	Night	30% 6% 23% 35% 5%	2722
	21st to end	Night	44% 7% 19% 22% 8%	3135
September	1st to 10th	Night	38% 9% 20% 25% 8% 1	1743
	11th to 20th	Night	48% 8% 17% 24% 3	2090
	21st to end	Night	46% 8% 16% 23% 7%	2090
October	1st to 10th	Night	54% 6% 16% 19% 5%	3721
	11th to 20th	Night	49% 7% 16% 21% 7%	4019
	21st to end	Night	63% 6% 14% 14% 2	4577
November	1st to 10th	Night	71% 8% 11% 6% 4	2731
	11th to 20th	Night	74% 6% 9% 9% 2	2950
	21st to end	Night	73% 7% 11% 8% 1	3000
December	1st to 10th	Night	78% 7% 8% 5% 2	4900
	11th to 20th	Night	61% 6% 14% 14% 5%	5566
	21st to end	Night	66% 5% 8% 13% 7% 1	7480

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	12% 9% 40% 30% 8%	300
	11th to 20th	Day	9% 10% 42% 29% 9% 1	300
	21st to end	Day	18% 13% 33% 27% 8%	330
February	1st to 10th	Day	10% 9% 40% 30% 8% 2	300
	11th to 20th	Day	9% 11% 39% 27% 13% 1	300
	21st to end	Day	8% 15% 41% 20% 13% 3	225
March	1st to 10th	Day	11% 13% 36% 21% 16% 3	270
	11th to 20th	Day	10% 18% 41% 20% 9% 2	270
	21st to end	Day	11% 14% 35% 30% 7% 3	303
April	1st to 10th	Day	11% 8% 40% 28% 12% 2	579
	11th to 20th	Day	18% 13% 29% 28% 10% 2	640
	21st to end	Day	10% 14% 36% 30% 9% 2	650
May	1st to 10th	Day	17% 13% 36% 26% 8%	653
	11th to 20th	Day	13% 17% 33% 25% 10% 1	675
	21st to end	Day	20% 14% 32% 25% 8% 1	734
June	1st to 10th	Day	19% 15% 31% 23% 11% 2	680
	11th to 20th	Day	21% 14% 32% 23% 8% 3	680
	21st to end	Day	17% 10% 29% 32% 9% 3	680
July	1st to 10th	Day	13% 9% 33% 31% 10% 4	671
	11th to 20th	Day	14% 9% 31% 29% 13% 4	668
	21st to end	Day	15% 10% 27% 29% 14% 5%	739
August	1st to 10th	Day	14% 12% 30% 28% 12% 3	676
	11th to 20th	Day	14% 9% 30% 27% 15% 5%	665
	21st to end	Day	23% 11% 27% 25% 13% 2	748
September	1st to 10th	Day	19% 15% 35% 23% 8% 1	644
	11th to 20th	Day	27% 16% 29% 21% 7% 1	300
	21st to end	Day	20% 17% 34% 22% 7%	300
October	1st to 10th	Day	25% 15% 38% 13% 6% 3	300
	11th to 20th	Day	27% 16% 36% 15% 6% 1	300
	21st to end	Day	32% 12% 24% 24% 8% 1	330
November	1st to 10th	Day	18% 16% 34% 25% 6% 1	300
	11th to 20th	Day	20% 14% 42% 18% 5% 1	300
	21st to end	Day	23% 17% 34% 21% 5% 1	300
December	1st to 10th	Day	12% 10% 39% 26% 12% 1	300
	11th to 20th	Day	14% 14% 41% 22% 7% 1	300
	21st to end	Day	12% 8% 33% 34% 12% 1	330
January	1st to 10th	Night	14% 10% 34% 31% 10% 1	1000
	11th to 20th	Night	12% 9% 36% 32% 10% 1	1000
	21st to end	Night	19% 9% 35% 28% 10%	1100
February	1st to 10th	Night	11% 8% 37% 33% 11% 1	1000
	11th to 20th	Night	11% 8% 30% 34% 15% 4	979
	21st to end	Night	8% 8% 37% 31% 14% 1	767
March	1st to 10th	Night	12% 8% 29% 34% 15% 2	760
	11th to 20th	Night	15% 13% 35% 25% 11% 1	574
	21st to end	Night	15% 8% 33% 28% 14% 2	627
April	1st to 10th	Night	13% 8% 33% 31% 14% 2	570
	11th to 20th	Night	16% 7% 30% 34% 11% 2	563
	21st to end	Night	9% 7% 38% 33% 13% 1	570
May	1st to 10th	Night	20% 7% 35% 28% 9% 1	570
	11th to 20th	Night	18% 12% 28% 30% 10% 1	561
	21st to end	Night	19% 10% 33% 29% 9%	617
June	1st to 10th	Night	18% 7% 29% 31% 14% 1	570
	11th to 20th	Night	18% 7% 30% 30% 13% 1	488
	21st to end	Night	14% 7% 28% 36% 15% 1	380
July	1st to 10th	Night	13% 6% 29% 35% 16% 1	493
	11th to 20th	Night	15% 6% 24% 34% 19% 3	552
	21st to end	Night	11% 6% 21% 36% 21% 4	624
August	1st to 10th	Night	11% 5% 26% 37% 19% 1	567
	11th to 20th	Night	13% 6% 23% 34% 21% 2	564
	21st to end	Night	20% 7% 29% 31% 12%	627
September	1st to 10th	Night	18% 8% 30% 31% 13% 1	570
	11th to 20th	Night	25% 8% 26% 32% 8% 1	570
	21st to end	Night	19% 8% 34% 30% 9%	570
October	1st to 10th	Night	25% 9% 32% 26% 7% 1	707
	11th to 20th	Night	30% 11% 26% 23% 9% 1	898
	21st to end	Night	31% 11% 29% 22% 5% 1	1045
November	1st to 10th	Night	22% 15% 31% 24% 8% 1	975
	11th to 20th	Night	23% 10% 33% 25% 9% 1	1000
	21st to end	Night	17% 14% 36% 25% 6% 1	1000
December	1st to 10th	Night	14% 9% 35% 30% 10% 2	1000
	11th to 20th	Night	17% 11% 36% 26% 10% 2	1000
	21st to end	Night	16% 7% 31% 31% 13% 2	1100

Page generated at 2025-02-18 02:26:26. Version ac07

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