Cathead Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cathead Bay clear sky chart from 2005-11-06 to 2024-11-01.

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	14% 11% 4 9% 5% 4 4 3 5% 6% 34%	101171
	Night	16% 14% 5% 11% 6% 4 4 3 4 5% 28%	97887
Transparency	Day	50% 7% 12% 20% 10% 1	100927
	Night	58% 7% 10% 16% 8% 1	97750
Seeing	Day	17% 8% 22% 30% 19% 5%	15715
	Night	22% 9% 25% 29% 14% 2	25441

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	13% 25% 18% 21% 7% 5% 2 1 2 2 4	2527
	11th to 20th	Day	14% 19% 10% 26% 16% 5% 2 2 2 2 3	2530
	21st to end	Day	16% 23% 10% 18% 8% 6% 4 2 3 3 7%	2783
February	1st to 10th	Day	9% 19% 7% 17% 15% 7% 3 2 5% 4 11%	1605
	11th to 20th	Day	13% 16% 6% 16% 10% 6% 5% 3 4 5% 16%	1843
	21st to end	Day	12% 16% 7% 13% 8% 5% 4 4 4 6% 22%	1570
March	1st to 10th	Day	13% 12% 3 9% 6% 4 4 3 5% 6% 35%	3118
	11th to 20th	Day	8% 12% 5% 14% 6% 5% 4 4 5% 6% 30%	3376
	21st to end	Day	15% 11% 7% 15% 6% 5% 5% 3 4 5% 24%	3969
April	1st to 10th	Day	18% 12% 3 9% 6% 4 4 3 5% 6% 31%	2280
	11th to 20th	Day	18% 11% 3 6% 4 3 4 3 5% 6% 36%	2352
	21st to end	Day	15% 9% 3 8% 5% 4 5% 4 5% 7% 36%	2470
May	1st to 10th	Day	13% 7% 3 6% 4 4 4 3 5% 6% 44%	4108
	11th to 20th	Day	9% 6% 3 7% 5% 4 4 3 5% 7% 47%	4266
	21st to end	Day	11% 6% 2 5% 4 4 5% 4 6% 9% 44%	4837
June	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 7% 9% 44%	2760
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 7% 9% 44%	2850
	21st to end	Day	13% 7% 2 6% 4 4 4 4 5% 8% 43%	2747
July	1st to 10th	Day	16% 8% 2 5% 3 3 4 4 5% 8% 42%	4440
	11th to 20th	Day	7% 4 1 4 3 3 4 3 6% 9% 56%	4440
	21st to end	Day	8% 5% 2 5% 3 4 4 3 6% 9% 52%	4814
August	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	4275
	11th to 20th	Day	13% 5% 2 5% 3 4 3 3 5% 7% 50%	4044
	21st to end	Day	13% 6% 3 6% 4 4 4 3 4 6% 47%	4344
September	1st to 10th	Day	14% 7% 2 6% 3 4 4 4 5% 7% 46%	2261
	11th to 20th	Day	14% 5% 2 6% 4 4 4 3 5% 8% 46%	2090
	21st to end	Day	18% 7% 2 5% 4 3 5% 3 6% 8% 37%	2090
October	1st to 10th	Day	19% 9% 2 8% 5% 4 4 3 5% 7% 35%	2090
	11th to 20th	Day	24% 16% 4 10% 5% 5% 4 3 5% 5% 20%	1787
	21st to end	Day	26% 18% 4 9% 5% 5% 4 3 5% 4 17%	1881
November	1st to 10th	Day	18% 21% 4 7% 5% 4 3 3 4 6% 25%	1672
	11th to 20th	Day	15% 25% 9% 14% 5% 4 4 3 4 4 14%	1710
	21st to end	Day	21% 24% 8% 14% 5% 3 4 2 3 4 12%	1554
December	1st to 10th	Day	17% 30% 14% 15% 4 4 3 1 2 2 8%	1330
	11th to 20th	Day	17% 23% 10% 19% 8% 5% 3 2 2 3 7%	1671
	21st to end	Day	22% 22% 11% 16% 6% 4 3 3 3 3 7%	2687
January	1st to 10th	Night	14% 26% 10% 23% 7% 4 2 1 2 2 8%	4428
	11th to 20th	Night	13% 19% 9% 26% 16% 4 2 1 2 1 6%	4440
	21st to end	Night	17% 23% 10% 18% 10% 6% 3 2 2 3 6%	4884
February	1st to 10th	Night	12% 19% 6% 19% 13% 6% 4 2 3 4 13%	2574
	11th to 20th	Night	12% 16% 7% 17% 10% 5% 4 3 4 4 18%	2220
	21st to end	Night	16% 17% 6% 12% 7% 5% 4 3 4 5% 21%	1884
March	1st to 10th	Night	16% 12% 3 7% 4 3 3 3 4 6% 40%	3722
	11th to 20th	Night	8% 16% 5% 9% 5% 4 4 4 5% 6% 34%	3582
	21st to end	Night	15% 11% 6% 14% 6% 4 4 4 5% 6% 26%	3690
April	1st to 10th	Night	18% 13% 3 10% 5% 4 5% 3 5% 5% 29%	1900
	11th to 20th	Night	19% 9% 3 7% 5% 5% 4 4 5% 5% 33%	1777
	21st to end	Night	16% 10% 3 9% 4 5% 4 3 5% 6% 36%	1710
May	1st to 10th	Night	16% 7% 3 7% 4 4 4 3 5% 6% 40%	2833
	11th to 20th	Night	12% 7% 3 7% 5% 5% 6% 4 6% 7% 39%	2630
	21st to end	Night	19% 6% 2 5% 3 4 4 3 6% 7% 42%	2750
June	1st to 10th	Night	14% 6% 2 7% 5% 4 5% 3 5% 7% 42%	1416
	11th to 20th	Night	11% 6% 2 6% 5% 5% 5% 5% 6% 7% 41%	1330
	21st to end	Night	12% 8% 2 6% 4 4 4 3 5% 8% 45%	1426
July	1st to 10th	Night	14% 7% 3 6% 4 4 5% 3 6% 7% 41%	2530
	11th to 20th	Night	7% 5% 2 7% 4 4 4 4 5% 7% 53%	2530
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 8% 48%	2750
August	1st to 10th	Night	11% 5% 3 8% 4 5% 4 4 5% 8% 42%	2657
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 6% 8% 48%	2785
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 7% 47%	3309
September	1st to 10th	Night	13% 8% 2 6% 4 4 3 2 5% 7% 47%	1900
	11th to 20th	Night	15% 6% 2 6% 3 3 4 3 5% 6% 45%	2089
	21st to end	Night	19% 6% 3 7% 4 4 4 4 6% 8% 36%	2090
October	1st to 10th	Night	19% 10% 3 7% 5% 4 4 3 4 6% 35%	2090
	11th to 20th	Night	24% 13% 4 9% 5% 5% 4 3 4 6% 23%	2390
	21st to end	Night	27% 16% 4 10% 5% 5% 3 3 4 4 19%	2717
November	1st to 10th	Night	18% 18% 4 9% 5% 4 3 3 4 6% 25%	2413
	11th to 20th	Night	18% 25% 6% 13% 5% 4 4 2 3 4 16%	2470
	21st to end	Night	19% 27% 8% 13% 4 4 4 3 3 3 12%	2619
December	1st to 10th	Night	17% 31% 12% 15% 5% 3 2 2 2 2 8%	2850
	11th to 20th	Night	16% 23% 9% 21% 7% 3 3 3 3 3 9%	3526
	21st to end	Night	25% 23% 11% 13% 5% 4 3 2 3 3 9%	4976

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	90% 3 3 3 1	2528
	11th to 20th	Day	91% 4 3 2	2530
	21st to end	Day	83% 7% 7% 3 1	2783
February	1st to 10th	Day	76% 6% 8% 8% 1	1605
	11th to 20th	Day	70% 7% 10% 9% 4	1853
	21st to end	Day	61% 9% 10% 15% 5% 1	1570
March	1st to 10th	Day	49% 6% 14% 20% 11% 1	3120
	11th to 20th	Day	52% 7% 15% 19% 5% 1	3376
	21st to end	Day	60% 7% 10% 16% 6% 1	3969
April	1st to 10th	Day	53% 6% 11% 20% 10%	2280
	11th to 20th	Day	48% 6% 10% 20% 14% 2	2352
	21st to end	Day	46% 8% 12% 16% 15% 3	2470
May	1st to 10th	Day	38% 8% 12% 23% 19% 2	4120
	11th to 20th	Day	34% 8% 12% 28% 16% 2	4270
	21st to end	Day	33% 9% 14% 22% 19% 2	4837
June	1st to 10th	Day	35% 8% 14% 25% 15% 2	2760
	11th to 20th	Day	35% 8% 14% 24% 17% 2	2850
	21st to end	Day	38% 7% 15% 25% 13% 1	2747
July	1st to 10th	Day	40% 7% 15% 24% 13% 1	4371
	11th to 20th	Day	24% 7% 16% 39% 13% 1	4365
	21st to end	Day	29% 8% 13% 31% 19% 1	4662
August	1st to 10th	Day	33% 8% 16% 30% 12% 1	4260
	11th to 20th	Day	34% 6% 14% 32% 13% 1	4083
	21st to end	Day	37% 7% 15% 31% 10% 1	4343
September	1st to 10th	Day	37% 8% 14% 26% 14% 1	2261
	11th to 20th	Day	36% 8% 17% 28% 11%	2090
	21st to end	Day	43% 8% 15% 24% 10%	2090
October	1st to 10th	Day	48% 8% 11% 23% 9%	2090
	11th to 20th	Day	66% 7% 10% 14% 4	1787
	21st to end	Day	70% 6% 12% 10% 2	1881
November	1st to 10th	Day	61% 6% 10% 17% 6%	1672
	11th to 20th	Day	74% 6% 9% 7% 3	1710
	21st to end	Day	77% 6% 10% 5% 1	1554
December	1st to 10th	Day	86% 4 4 5% 1	1330
	11th to 20th	Day	85% 6% 5% 3 1	1671
	21st to end	Day	81% 8% 6% 3 2	2687
January	1st to 10th	Night	83% 6% 5% 5% 1	4428
	11th to 20th	Night	89% 4 4 3	4440
	21st to end	Night	85% 7% 6% 3	4884
February	1st to 10th	Night	77% 5% 7% 7% 3	2574
	11th to 20th	Night	69% 6% 10% 12% 3	2221
	21st to end	Night	64% 7% 11% 12% 5%	1884
March	1st to 10th	Night	46% 5% 17% 24% 8%	3733
	11th to 20th	Night	49% 7% 11% 23% 8% 1	3583
	21st to end	Night	56% 9% 13% 15% 7% 1	3690
April	1st to 10th	Night	56% 7% 8% 17% 11% 1	1900
	11th to 20th	Night	50% 6% 10% 18% 13% 2	1777
	21st to end	Night	49% 7% 9% 18% 14% 3	1710
May	1st to 10th	Night	42% 8% 11% 20% 16% 3	2840
	11th to 20th	Night	41% 10% 9% 26% 14% 1	2631
	21st to end	Night	40% 7% 13% 20% 14% 6%	2751
June	1st to 10th	Night	39% 8% 11% 26% 14% 2	1416
	11th to 20th	Night	39% 9% 11% 22% 15% 3	1330
	21st to end	Night	38% 8% 11% 26% 15% 2	1426
July	1st to 10th	Night	41% 6% 14% 23% 13% 3	2490
	11th to 20th	Night	28% 8% 14% 30% 18% 2	2482
	21st to end	Night	33% 8% 14% 24% 20% 1	2662
August	1st to 10th	Night	38% 8% 16% 24% 13% 1	2648
	11th to 20th	Night	34% 6% 17% 28% 14% 1	2812
	21st to end	Night	36% 7% 15% 26% 16% 1	3309
September	1st to 10th	Night	37% 7% 13% 23% 18% 1	1900
	11th to 20th	Night	38% 7% 15% 27% 12%	2089
	21st to end	Night	46% 8% 15% 22% 9%	2090
October	1st to 10th	Night	51% 6% 10% 22% 11% 1	2090
	11th to 20th	Night	63% 5% 12% 14% 6%	2390
	21st to end	Night	69% 7% 8% 13% 4	2717
November	1st to 10th	Night	60% 8% 10% 15% 6% 1	2413
	11th to 20th	Night	72% 6% 9% 8% 4	2470
	21st to end	Night	78% 6% 9% 6% 1	2619
December	1st to 10th	Night	85% 4 5% 5% 1	2850
	11th to 20th	Night	82% 6% 8% 3 1	3525
	21st to end	Night	81% 8% 8% 3 1	4976

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	20% 17% 30% 25% 7% 1	270
	11th to 20th	Day	23% 15% 32% 21% 7% 2	270
	21st to end	Day	22% 10% 30% 29% 9%	297
February	1st to 10th	Day	18% 14% 39% 20% 7% 1	270
	11th to 20th	Day	14% 18% 36% 23% 9%	270
	21st to end	Day	17% 14% 44% 22% 2	225
March	1st to 10th	Day	17% 11% 33% 31% 9%	270
	11th to 20th	Day	15% 10% 29% 32% 12% 2	395
	21st to end	Day	24% 8% 26% 30% 11% 1	506
April	1st to 10th	Day	23% 10% 28% 28% 10% 1	460
	11th to 20th	Day	23% 11% 26% 26% 10% 4	452
	21st to end	Day	17% 7% 23% 32% 18% 2	460
May	1st to 10th	Day	19% 5% 25% 33% 15% 3	463
	11th to 20th	Day	12% 3 24% 37% 20% 4	594
	21st to end	Day	12% 3 18% 36% 26% 5%	734
June	1st to 10th	Day	12% 3 23% 36% 23% 4	680
	11th to 20th	Day	14% 3 18% 37% 24% 5%	680
	21st to end	Day	16% 5% 13% 38% 24% 4	680
July	1st to 10th	Day	9% 3 14% 37% 30% 8%	671
	11th to 20th	Day	10% 4 16% 32% 30% 8%	668
	21st to end	Day	8% 3 13% 37% 32% 8%	739
August	1st to 10th	Day	10% 2 10% 36% 31% 10%	593
	11th to 20th	Day	12% 3 11% 30% 32% 11%	479
	21st to end	Day	16% 6% 13% 31% 26% 8%	539
September	1st to 10th	Day	16% 7% 17% 27% 25% 9%	490
	11th to 20th	Day	14% 5% 14% 26% 31% 9%	490
	21st to end	Day	17% 9% 16% 25% 25% 8%	490
October	1st to 10th	Day	23% 7% 26% 22% 17% 5%	490
	11th to 20th	Day	27% 13% 27% 21% 11% 1	362
	21st to end	Day	32% 11% 27% 22% 7% 1	330
November	1st to 10th	Day	20% 16% 29% 23% 12% 1	270
	11th to 20th	Day	23% 17% 37% 20% 4	270
	21st to end	Day	29% 18% 32% 16% 4	228
December	1st to 10th	Day	34% 13% 26% 19% 7% 1	180
	11th to 20th	Day	26% 24% 29% 16% 4 1	180
	21st to end	Day	31% 21% 33% 12% 2	270
January	1st to 10th	Night	24% 13% 34% 22% 6% 1	950
	11th to 20th	Night	26% 14% 30% 23% 6% 1	950
	21st to end	Night	23% 9% 32% 27% 7% 1	1045
February	1st to 10th	Night	19% 13% 32% 28% 7% 1	864
	11th to 20th	Night	20% 14% 33% 27% 6%	743
	21st to end	Night	24% 12% 30% 29% 5%	628
March	1st to 10th	Night	19% 7% 31% 30% 11% 1	760
	11th to 20th	Night	14% 9% 34% 32% 10% 1	760
	21st to end	Night	19% 6% 27% 35% 12% 1	760
April	1st to 10th	Night	23% 7% 29% 32% 9% 1	570
	11th to 20th	Night	22% 8% 22% 33% 13% 1	563
	21st to end	Night	20% 5% 24% 36% 14% 2	570
May	1st to 10th	Night	17% 4 23% 36% 19% 1	570
	11th to 20th	Night	15% 5% 20% 39% 20% 1	561
	21st to end	Night	15% 2 18% 36% 26% 4	617
June	1st to 10th	Night	15% 3 17% 39% 24% 2	466
	11th to 20th	Night	11% 2 19% 40% 26% 3	380
	21st to end	Night	14% 3 19% 34% 29% 2	476
July	1st to 10th	Night	12% 2 11% 39% 32% 5%	555
	11th to 20th	Night	10% 3 13% 35% 32% 7%	552
	21st to end	Night	10% 1 14% 37% 34% 4	624
August	1st to 10th	Night	10% 2 14% 38% 33% 3	567
	11th to 20th	Night	13% 3 12% 30% 35% 8%	564
	21st to end	Night	15% 4 14% 37% 27% 2	627
September	1st to 10th	Night	15% 2 18% 33% 26% 5%	570
	11th to 20th	Night	17% 4 16% 31% 25% 7%	759
	21st to end	Night	22% 5% 18% 28% 22% 6%	760
October	1st to 10th	Night	23% 8% 22% 27% 17% 3	760
	11th to 20th	Night	31% 12% 22% 26% 8% 1	760
	21st to end	Night	35% 12% 22% 23% 7% 1	836
November	1st to 10th	Night	32% 11% 22% 26% 8% 1	743
	11th to 20th	Night	31% 14% 30% 19% 5%	760
	21st to end	Night	31% 15% 28% 21% 5%	826
December	1st to 10th	Night	29% 20% 30% 17% 4	950
	11th to 20th	Night	27% 17% 33% 18% 5% 1	950
	21st to end	Night	33% 12% 32% 19% 3	1045

Page generated at 2024-10-29 11:20:52. Version ac07

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