Thunder Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thunder Bay clear sky chart from 2005-11-06 to 2024-11-04.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	101477
	Night	13% 11% 4 9% 5% 5% 5% 4 5% 7% 33%	97671
Transparency	Day	45% 7% 15% 22% 10% 1	104885
	Night	48% 7% 14% 22% 9% 1	102350
Seeing	Day	17% 12% 34% 24% 10% 3	16013
	Night	18% 10% 29% 29% 12% 2	25859

By Month

Percentage Cloud Cover NE (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	9% 12% 5% 9% 6% 6% 6% 4 6% 7% 29%	2527
	11th to 20th	Day	6% 10% 6% 15% 8% 5% 4 4 7% 8% 25%	2530
	21st to end	Day	11% 14% 6% 15% 7% 5% 5% 4 5% 6% 21%	2783
February	1st to 10th	Day	8% 10% 4 12% 5% 4 5% 3 7% 6% 36%	1605
	11th to 20th	Day	8% 11% 3 7% 7% 6% 5% 4 5% 6% 38%	1683
	21st to end	Day	6% 12% 5% 9% 7% 5% 5% 4 6% 7% 35%	1570
March	1st to 10th	Day	11% 9% 3 7% 4 4 5% 3 5% 6% 43%	3118
	11th to 20th	Day	7% 9% 4 9% 5% 6% 5% 4 6% 6% 38%	3315
	21st to end	Day	17% 10% 4 9% 6% 4 4 3 5% 5% 31%	4133
April	1st to 10th	Day	13% 10% 3 7% 6% 5% 6% 4 6% 7% 33%	2280
	11th to 20th	Day	17% 8% 3 9% 4 4 6% 4 6% 6% 31%	2254
	21st to end	Day	16% 10% 3 8% 5% 4 4 3 5% 6% 35%	2539
May	1st to 10th	Day	16% 9% 2 7% 4 4 3 3 5% 6% 40%	4428
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 4 6% 7% 39%	4399
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 5% 6% 6% 38%	4837
June	1st to 10th	Day	15% 6% 3 6% 4 4 5% 5% 6% 9% 38%	2660
	11th to 20th	Day	13% 7% 3 6% 4 5% 5% 4 6% 8% 39%	2840
	21st to end	Day	16% 7% 3 6% 5% 4 5% 5% 6% 8% 35%	2664
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 11% 42%	4440
	11th to 20th	Day	7% 5% 2 5% 4 4 6% 4 8% 10% 43%	4440
	21st to end	Day	9% 5% 2 5% 4 3 4 4 6% 11% 47%	4814
August	1st to 10th	Day	9% 6% 3 8% 6% 5% 6% 5% 7% 9% 36%	4423
	11th to 20th	Day	12% 3 1 4 3 3 5% 4 6% 9% 49%	4273
	21st to end	Day	9% 7% 2 6% 4 4 4 4 7% 10% 42%	4180
September	1st to 10th	Day	11% 5% 3 6% 5% 5% 5% 4 5% 7% 45%	2280
	11th to 20th	Day	13% 6% 3 7% 4 4 5% 4 6% 9% 40%	2228
	21st to end	Day	14% 8% 3 7% 5% 5% 4 4 6% 8% 35%	2090
October	1st to 10th	Day	16% 9% 3 8% 4 4 5% 4 6% 7% 34%	1910
	11th to 20th	Day	17% 11% 3 7% 6% 5% 5% 5% 7% 7% 28%	1835
	21st to end	Day	20% 11% 3 7% 6% 5% 5% 3 5% 6% 27%	1881
November	1st to 10th	Day	13% 10% 4 10% 7% 5% 5% 5% 5% 8% 27%	1677
	11th to 20th	Day	17% 14% 4 10% 6% 6% 5% 4 5% 6% 24%	1520
	21st to end	Day	16% 13% 3 7% 6% 5% 5% 5% 7% 8% 24%	1520
December	1st to 10th	Day	11% 11% 6% 8% 8% 6% 6% 4 8% 8% 24%	1348
	11th to 20th	Day	12% 14% 5% 12% 7% 5% 4 4 6% 8% 23%	1671
	21st to end	Day	26% 21% 4 9% 4 3 3 2 4 4 20%	2782
January	1st to 10th	Night	9% 17% 4 8% 6% 5% 4 3 6% 6% 32%	4428
	11th to 20th	Night	5% 11% 6% 19% 12% 6% 5% 4 5% 7% 21%	4440
	21st to end	Night	8% 17% 7% 13% 8% 6% 4 4 4 6% 23%	4884
February	1st to 10th	Night	8% 10% 5% 11% 6% 6% 5% 5% 5% 6% 33%	2572
	11th to 20th	Night	10% 9% 3 9% 6% 6% 6% 4 6% 6% 36%	2384
	21st to end	Night	7% 12% 5% 11% 7% 4 5% 5% 7% 7% 30%	1884
March	1st to 10th	Night	10% 10% 4 8% 5% 6% 6% 4 5% 6% 36%	3722
	11th to 20th	Night	9% 12% 4 8% 5% 5% 5% 4 6% 7% 33%	3674
	21st to end	Night	18% 12% 3 8% 5% 5% 4 4 4 6% 31%	3498
April	1st to 10th	Night	15% 10% 4 8% 6% 5% 5% 4 5% 7% 31%	1900
	11th to 20th	Night	17% 11% 3 7% 5% 4 5% 5% 5% 7% 32%	1874
	21st to end	Night	17% 11% 2 6% 5% 4 4 3 6% 6% 34%	1639
May	1st to 10th	Night	19% 6% 2 4 4 3 4 4 5% 7% 42%	2523
	11th to 20th	Night	12% 8% 4 8% 6% 5% 6% 4 7% 6% 36%	2506
	21st to end	Night	20% 8% 3 6% 3 4 4 3 5% 6% 38%	2750
June	1st to 10th	Night	16% 8% 3 6% 4 5% 5% 4 6% 7% 36%	1520
	11th to 20th	Night	13% 6% 3 7% 5% 5% 5% 4 6% 7% 39%	1330
	21st to end	Night	14% 8% 3 7% 4 4 4 5% 6% 8% 37%	1504
July	1st to 10th	Night	8% 7% 2 6% 5% 4 5% 4 7% 9% 42%	2530
	11th to 20th	Night	6% 4 2 7% 4 4 5% 4 7% 8% 47%	2530
	21st to end	Night	9% 5% 2 5% 4 4 4 4 6% 9% 49%	2750
August	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 6% 10% 42%	2517
	11th to 20th	Night	11% 4 2 5% 4 3 5% 4 6% 8% 48%	2560
	21st to end	Night	16% 8% 3 6% 4 4 4 3 4 6% 42%	3476
September	1st to 10th	Night	12% 4 2 5% 3 4 4 4 5% 7% 49%	1900
	11th to 20th	Night	13% 7% 3 6% 3 3 4 3 5% 9% 43%	1933
	21st to end	Night	16% 8% 3 7% 4 4 4 4 5% 8% 37%	2090
October	1st to 10th	Night	17% 8% 2 6% 4 5% 5% 4 5% 7% 37%	2268
	11th to 20th	Night	14% 11% 4 8% 5% 4 5% 4 5% 7% 34%	2344
	21st to end	Night	18% 12% 3 9% 5% 5% 5% 4 5% 6% 28%	2717
November	1st to 10th	Night	16% 9% 4 8% 6% 5% 6% 4 7% 6% 28%	2471
	11th to 20th	Night	16% 12% 4 11% 6% 5% 5% 4 5% 6% 24%	2660
	21st to end	Night	15% 15% 4 10% 6% 5% 5% 4 6% 7% 24%	2660
December	1st to 10th	Night	10% 12% 5% 12% 7% 5% 4 5% 8% 7% 25%	2827
	11th to 20th	Night	11% 13% 6% 11% 6% 4 5% 5% 5% 7% 27%	3522
	21st to end	Night	24% 22% 6% 9% 5% 3 3 2 3 4 19%	4884

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	53% 7% 14% 20% 6%	2528
	11th to 20th	Day	54% 7% 12% 25% 2	2530
	21st to end	Day	63% 9% 11% 12% 5% 1	2783
February	1st to 10th	Day	47% 7% 15% 20% 10% 1	1605
	11th to 20th	Day	47% 6% 14% 23% 9% 2	1692
	21st to end	Day	47% 7% 15% 16% 14% 2	1570
March	1st to 10th	Day	41% 7% 13% 21% 15% 2	3120
	11th to 20th	Day	43% 9% 14% 23% 10% 1	3315
	21st to end	Day	53% 8% 9% 14% 14% 2	4133
April	1st to 10th	Day	48% 9% 11% 19% 12% 2	2280
	11th to 20th	Day	50% 8% 12% 21% 8% 1	2254
	21st to end	Day	49% 6% 11% 18% 15% 1	2539
May	1st to 10th	Day	43% 7% 12% 22% 16% 1	4440
	11th to 20th	Day	41% 8% 14% 24% 12% 1	4403
	21st to end	Day	42% 11% 15% 14% 17% 1	4837
June	1st to 10th	Day	40% 9% 15% 21% 14% 1	2660
	11th to 20th	Day	41% 8% 14% 24% 12% 1	2840
	21st to end	Day	44% 7% 16% 22% 10% 1	2664
July	1st to 10th	Day	36% 7% 20% 25% 12% 1	4371
	11th to 20th	Day	34% 5% 21% 33% 7%	4365
	21st to end	Day	32% 6% 16% 36% 10% 1	4662
August	1st to 10th	Day	42% 7% 16% 25% 9% 1	4408
	11th to 20th	Day	31% 6% 23% 30% 10%	4315
	21st to end	Day	37% 6% 16% 31% 9%	4179
September	1st to 10th	Day	38% 8% 17% 29% 9%	2280
	11th to 20th	Day	40% 10% 24% 22% 4 1	2228
	21st to end	Day	46% 9% 17% 20% 6% 1	2090
October	1st to 10th	Day	39% 6% 17% 26% 11% 2	3170
	11th to 20th	Day	48% 6% 14% 27% 5%	3025
	21st to end	Day	56% 5% 15% 19% 5%	3081
November	1st to 10th	Day	54% 8% 16% 15% 6% 1	1677
	11th to 20th	Day	60% 7% 13% 16% 4	1520
	21st to end	Day	55% 8% 17% 15% 5%	1520
December	1st to 10th	Day	55% 9% 16% 16% 4	1348
	11th to 20th	Day	58% 7% 14% 12% 5% 4	1671
	21st to end	Day	69% 4 7% 17% 3	2782
January	1st to 10th	Night	51% 6% 17% 21% 5%	4428
	11th to 20th	Night	62% 7% 11% 17% 3	4440
	21st to end	Night	60% 8% 14% 13% 4	4884
February	1st to 10th	Night	50% 5% 14% 20% 10% 1	2572
	11th to 20th	Night	47% 7% 12% 22% 11% 1	2385
	21st to end	Night	50% 7% 13% 18% 11% 1	1884
March	1st to 10th	Night	46% 7% 13% 17% 15% 2	3733
	11th to 20th	Night	47% 7% 14% 21% 9% 1	3675
	21st to end	Night	52% 7% 9% 18% 13% 2	3498
April	1st to 10th	Night	51% 7% 9% 20% 13%	1900
	11th to 20th	Night	50% 6% 10% 21% 11% 2	1874
	21st to end	Night	48% 6% 10% 22% 12% 2	1639
May	1st to 10th	Night	40% 7% 12% 26% 14% 1	2530
	11th to 20th	Night	44% 9% 11% 23% 10% 4	2507
	21st to end	Night	44% 9% 10% 21% 16% 1	2751
June	1st to 10th	Night	44% 9% 12% 20% 13% 2	1520
	11th to 20th	Night	42% 7% 12% 21% 16% 2	1330
	21st to end	Night	44% 8% 15% 21% 11% 2	1504
July	1st to 10th	Night	38% 6% 21% 21% 13% 1	2490
	11th to 20th	Night	33% 4 17% 36% 10%	2482
	21st to end	Night	31% 6% 14% 36% 12% 1	2662
August	1st to 10th	Night	38% 6% 17% 30% 8% 1	2508
	11th to 20th	Night	34% 5% 19% 33% 10%	2584
	21st to end	Night	44% 5% 14% 28% 10%	3476
September	1st to 10th	Night	33% 7% 16% 30% 13%	1900
	11th to 20th	Night	37% 8% 21% 30% 3	1933
	21st to end	Night	45% 8% 16% 25% 5%	2090
October	1st to 10th	Night	35% 5% 15% 28% 17%	3788
	11th to 20th	Night	45% 5% 13% 28% 9%	3893
	21st to end	Night	58% 5% 15% 17% 6%	4467
November	1st to 10th	Night	53% 9% 14% 19% 5%	2471
	11th to 20th	Night	59% 7% 13% 16% 4	2660
	21st to end	Night	57% 8% 15% 15% 5%	2660
December	1st to 10th	Night	54% 8% 18% 17% 3	2827
	11th to 20th	Night	54% 6% 15% 19% 6%	3521
	21st to end	Night	69% 5% 9% 15% 2	4884

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	14% 13% 38% 29% 6%	270
	11th to 20th	Day	16% 10% 41% 26% 6% 2	270
	21st to end	Day	15% 13% 41% 25% 5%	297
February	1st to 10th	Day	14% 15% 43% 19% 7% 2	270
	11th to 20th	Day	11% 20% 43% 20% 4 1	270
	21st to end	Day	14% 23% 47% 15% 2	225
March	1st to 10th	Day	10% 20% 43% 22% 4 1	270
	11th to 20th	Day	13% 22% 38% 19% 7% 1	270
	21st to end	Day	18% 12% 40% 21% 7% 2	487
April	1st to 10th	Day	17% 15% 34% 27% 7%	460
	11th to 20th	Day	23% 15% 29% 21% 10% 1	452
	21st to end	Day	23% 14% 30% 22% 10% 2	529
May	1st to 10th	Day	18% 15% 38% 19% 7% 2	653
	11th to 20th	Day	16% 11% 39% 25% 8% 3	675
	21st to end	Day	18% 12% 36% 24% 8% 2	734
June	1st to 10th	Day	16% 11% 39% 22% 10% 2	680
	11th to 20th	Day	16% 10% 35% 27% 10% 2	680
	21st to end	Day	17% 8% 30% 30% 13% 2	680
July	1st to 10th	Day	9% 7% 35% 31% 14% 5%	671
	11th to 20th	Day	12% 8% 34% 27% 13% 7%	668
	21st to end	Day	8% 6% 33% 30% 16% 6%	739
August	1st to 10th	Day	12% 7% 34% 32% 11% 4	676
	11th to 20th	Day	12% 7% 28% 29% 18% 6%	654
	21st to end	Day	17% 10% 27% 28% 14% 4	539
September	1st to 10th	Day	13% 10% 29% 27% 16% 5%	490
	11th to 20th	Day	18% 9% 29% 24% 16% 4	490
	21st to end	Day	18% 13% 29% 24% 14% 3	490
October	1st to 10th	Day	22% 15% 28% 27% 8% 1	310
	11th to 20th	Day	19% 16% 37% 20% 7% 1	300
	21st to end	Day	31% 19% 32% 14% 3 1	330
November	1st to 10th	Day	21% 23% 28% 23% 4 2	279
	11th to 20th	Day	27% 21% 36% 11% 4	270
	21st to end	Day	28% 19% 30% 19% 4	270
December	1st to 10th	Day	23% 12% 36% 20% 7% 2	188
	11th to 20th	Day	22% 24% 36% 13% 4 1	180
	21st to end	Day	22% 19% 34% 21% 4	297
January	1st to 10th	Night	16% 13% 39% 26% 6%	950
	11th to 20th	Night	15% 13% 39% 25% 6% 1	950
	21st to end	Night	18% 8% 40% 26% 8% 1	1045
February	1st to 10th	Night	14% 12% 37% 28% 8% 1	950
	11th to 20th	Night	13% 13% 34% 29% 10% 1	910
	21st to end	Night	13% 11% 36% 32% 8%	628
March	1st to 10th	Night	12% 12% 34% 33% 9% 1	760
	11th to 20th	Night	17% 12% 32% 29% 9% 1	687
	21st to end	Night	17% 11% 29% 27% 14% 2	627
April	1st to 10th	Night	19% 9% 30% 32% 9% 1	570
	11th to 20th	Night	20% 11% 24% 29% 13% 1	563
	21st to end	Night	22% 6% 24% 32% 14% 2	570
May	1st to 10th	Night	23% 7% 24% 32% 12% 2	570
	11th to 20th	Night	17% 6% 27% 34% 14% 3	561
	21st to end	Night	20% 7% 21% 35% 15% 1	617
June	1st to 10th	Night	19% 7% 21% 37% 15% 2	570
	11th to 20th	Night	15% 6% 21% 43% 15% 1	380
	21st to end	Night	17% 3 18% 40% 20% 2	554
July	1st to 10th	Night	12% 3 22% 40% 22% 3	555
	11th to 20th	Night	10% 3 23% 35% 25% 3	552
	21st to end	Night	9% 3 22% 35% 27% 4	624
August	1st to 10th	Night	11% 2 24% 40% 21% 2	567
	11th to 20th	Night	12% 4 17% 31% 30% 5%	564
	21st to end	Night	17% 5% 21% 33% 21% 3	627
September	1st to 10th	Night	14% 4 23% 33% 21% 5%	570
	11th to 20th	Night	16% 5% 26% 32% 18% 3	603
	21st to end	Night	20% 9% 23% 29% 18% 2	760
October	1st to 10th	Night	20% 10% 31% 23% 15% 1	760
	11th to 20th	Night	19% 14% 28% 28% 9% 1	760
	21st to end	Night	25% 12% 28% 27% 7%	836
November	1st to 10th	Night	20% 11% 33% 26% 9% 1	774
	11th to 20th	Night	23% 15% 32% 20% 8% 1	950
	21st to end	Night	24% 18% 31% 22% 5%	950
December	1st to 10th	Night	17% 16% 36% 23% 7% 1	950
	11th to 20th	Night	19% 16% 35% 21% 8% 1	950
	21st to end	Night	26% 14% 32% 23% 4 1	1045

Page generated at 2024-11-01 22:47:32. Version ac07

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