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 2026-09-14.

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	13% 11% 4 10% 5% 4 4 3 5% 6% 34%	148690
	Night	14% 14% 6% 13% 6% 5% 4 3 4 5% 27%	142690
Transparency	Day	49% 6% 12% 21% 11% 1	152170
	Night	59% 6% 10% 16% 8% 1	147297
Seeing	Day	17% 8% 21% 30% 19% 5%	18270
	Night	21% 9% 25% 29% 14% 2	27934

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% 23% 15% 29% 7% 4 2 1 2 2 4	4691
	11th to 20th	Day	12% 20% 10% 29% 14% 8% 2 1 1 1 2	4679
	21st to end	Day	9% 17% 8% 21% 11% 10% 7% 2 3 3 10%	5156
February	1st to 10th	Day	9% 19% 7% 18% 15% 7% 4 3 4 4 11%	1775
	11th to 20th	Day	13% 15% 6% 16% 11% 6% 5% 3 4 5% 16%	2043
	21st to end	Day	12% 16% 6% 13% 8% 5% 5% 4 5% 5% 21%	1730
March	1st to 10th	Day	13% 9% 3 12% 7% 4 4 3 4 6% 33%	4578
	11th to 20th	Day	11% 11% 4 12% 6% 6% 5% 4 6% 6% 28%	4941
	21st to end	Day	21% 10% 6% 14% 5% 5% 4 3 4 4 24%	5815
April	1st to 10th	Day	17% 12% 3 9% 6% 5% 5% 3 5% 6% 30%	2520
	11th to 20th	Day	18% 11% 3 6% 4 3 4 3 5% 6% 36%	2602
	21st to end	Day	14% 8% 3 9% 5% 4 5% 4 5% 7% 35%	2730
May	1st to 10th	Day	11% 7% 3 6% 4 4 4 3 5% 7% 47%	7642
	11th to 20th	Day	11% 7% 3 8% 5% 4 4 3 5% 6% 43%	7979
	21st to end	Day	11% 7% 2 6% 4 3 4 3 5% 7% 49%	9061
June	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 7% 9% 44%	3050
	11th to 20th	Day	11% 6% 2 6% 4 5% 4 4 7% 8% 42%	3150
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 9% 42%	3035
July	1st to 10th	Day	13% 7% 2 5% 3 3 4 4 6% 9% 44%	8279
	11th to 20th	Day	8% 4 2 5% 3 3 4 3 6% 9% 52%	8280
	21st to end	Day	9% 5% 2 5% 4 3 4 3 5% 9% 50%	8992
August	1st to 10th	Day	8% 6% 2 6% 4 4 4 4 6% 9% 47%	6274
	11th to 20th	Day	12% 5% 2 6% 3 4 3 3 5% 7% 49%	5951
	21st to end	Day	14% 7% 3 7% 4 4 4 4 5% 7% 42%	6316
September	1st to 10th	Day	14% 7% 2 6% 3 4 4 4 5% 7% 45%	2499
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 5% 8% 47%	2233
	21st to end	Day	18% 7% 3 6% 4 3 5% 3 6% 8% 38%	2200
October	1st to 10th	Day	18% 9% 2 7% 5% 4 4 3 5% 7% 36%	2200
	11th to 20th	Day	23% 15% 4 10% 5% 5% 5% 3 5% 5% 20%	1881
	21st to end	Day	25% 17% 4 10% 5% 5% 4 3 5% 4 18%	1980
November	1st to 10th	Day	18% 21% 4 7% 5% 4 3 2 5% 6% 24%	1852
	11th to 20th	Day	15% 25% 8% 13% 5% 4 4 3 4 4 15%	1890
	21st to end	Day	21% 25% 8% 14% 5% 3 4 2 3 3 12%	1716
December	1st to 10th	Day	17% 32% 13% 17% 5% 4 2 1 1 1 5%	2350
	11th to 20th	Day	14% 29% 10% 23% 7% 4 3 2 2 2 5%	2691
	21st to end	Day	22% 23% 10% 15% 8% 5% 3 2 3 3 6%	3929
January	1st to 10th	Night	14% 23% 10% 31% 7% 3 2 1 1 2 5%	8233
	11th to 20th	Night	11% 22% 11% 26% 16% 6% 2 1 1 1 4	8236
	21st to end	Night	9% 16% 9% 22% 13% 10% 5% 2 3 3 9%	9058
February	1st to 10th	Night	12% 19% 6% 19% 13% 6% 4 2 3 4 12%	2844
	11th to 20th	Night	12% 15% 6% 17% 10% 5% 5% 3 4 4 18%	2460
	21st to end	Night	16% 17% 6% 12% 7% 5% 4 3 4 5% 21%	2076
March	1st to 10th	Night	17% 11% 3 11% 5% 3 3 2 4 6% 35%	5482
	11th to 20th	Night	11% 14% 5% 9% 5% 4 4 4 6% 8% 31%	5237
	21st to end	Night	20% 11% 5% 12% 5% 4 4 3 5% 6% 26%	5401
April	1st to 10th	Night	18% 13% 3 11% 5% 4 5% 3 5% 5% 29%	2100
	11th to 20th	Night	20% 10% 3 7% 5% 5% 4 4 5% 5% 33%	1967
	21st to end	Night	16% 10% 3 9% 4 5% 5% 3 5% 6% 36%	1890
May	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 4 6% 8% 41%	5257
	11th to 20th	Night	12% 7% 3 8% 4 4 5% 3 6% 7% 39%	4896
	21st to end	Night	14% 7% 3 6% 4 4 3 3 5% 6% 45%	5148
June	1st to 10th	Night	14% 6% 2 7% 4 4 4 3 5% 7% 43%	1565
	11th to 20th	Night	13% 6% 2 6% 5% 5% 5% 5% 6% 7% 39%	1470
	21st to end	Night	13% 8% 2 6% 4 4 4 3 5% 7% 44%	1576
July	1st to 10th	Night	13% 7% 3 7% 4 5% 5% 3 6% 8% 40%	4710
	11th to 20th	Night	6% 5% 2 6% 4 4 4 4 6% 9% 51%	4710
	21st to end	Night	8% 5% 2 6% 4 4 4 4 5% 8% 50%	5118
August	1st to 10th	Night	15% 6% 3 7% 4 4 4 3 5% 7% 42%	3883
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 6% 8% 49%	4095
	21st to end	Night	14% 6% 2 6% 4 4 5% 4 5% 7% 41%	4807
September	1st to 10th	Night	12% 8% 2 6% 4 4 3 3 6% 7% 46%	2100
	11th to 20th	Night	14% 6% 2 6% 3 4 4 3 5% 7% 46%	2233
	21st to end	Night	19% 7% 3 7% 4 4 4 4 6% 7% 36%	2200
October	1st to 10th	Night	19% 10% 3 7% 5% 4 4 3 4 6% 36%	2200
	11th to 20th	Night	24% 13% 4 9% 5% 5% 4 3 4 6% 23%	2516
	21st to end	Night	26% 16% 4 10% 5% 5% 3 3 4 4 21%	2860
November	1st to 10th	Night	19% 18% 4 10% 5% 4 3 2 4 5% 25%	2666
	11th to 20th	Night	18% 25% 6% 12% 5% 3 4 3 3 4 16%	2730
	21st to end	Night	19% 28% 9% 12% 4 4 3 3 3 3 11%	2897
December	1st to 10th	Night	14% 30% 15% 17% 6% 4 3 2 2 2 6%	5060
	11th to 20th	Night	14% 25% 10% 25% 7% 3 2 2 2 2 8%	5736
	21st to end	Night	24% 21% 10% 15% 6% 4 3 2 3 3 8%	7273

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	91% 3 4 2	4692
	11th to 20th	Day	93% 3 2 2	4710
	21st to end	Day	81% 5% 7% 6% 1	5156
February	1st to 10th	Day	76% 6% 9% 8% 1	1775
	11th to 20th	Day	70% 7% 9% 10% 4	2053
	21st to end	Day	62% 9% 10% 14% 5%	1730
March	1st to 10th	Day	51% 6% 16% 16% 10% 1	4580
	11th to 20th	Day	53% 6% 15% 18% 7% 1	4941
	21st to end	Day	62% 6% 10% 15% 6%	5815
April	1st to 10th	Day	53% 6% 11% 20% 10%	2520
	11th to 20th	Day	47% 6% 10% 21% 13% 2	2602
	21st to end	Day	47% 7% 12% 16% 15% 3	2730
May	1st to 10th	Day	35% 7% 11% 27% 19% 2	7651
	11th to 20th	Day	41% 7% 9% 25% 17% 1	7983
	21st to end	Day	34% 7% 10% 25% 21% 4	9061
June	1st to 10th	Day	35% 8% 14% 25% 16% 2	3050
	11th to 20th	Day	37% 8% 14% 23% 17% 1	3150
	21st to end	Day	39% 7% 15% 25% 13% 1	3035
July	1st to 10th	Day	35% 7% 16% 26% 14% 1	8211
	11th to 20th	Day	27% 6% 15% 37% 14% 1	8205
	21st to end	Day	31% 7% 13% 33% 15% 1	8794
August	1st to 10th	Day	33% 7% 16% 29% 14% 1	6259
	11th to 20th	Day	34% 6% 16% 34% 10% 1	5990
	21st to end	Day	41% 7% 15% 28% 8%	6315
September	1st to 10th	Day	38% 8% 14% 26% 14% 1	2499
	11th to 20th	Day	36% 8% 17% 29% 10%	2233
	21st to end	Day	44% 8% 15% 24% 10%	2200
October	1st to 10th	Day	34% 7% 11% 31% 17%	3590
	11th to 20th	Day	57% 6% 10% 20% 8%	3032
	21st to end	Day	61% 6% 15% 16% 3	3180
November	1st to 10th	Day	61% 6% 10% 16% 6%	1852
	11th to 20th	Day	72% 6% 9% 9% 3	1890
	21st to end	Day	78% 6% 9% 5% 2	1716
December	1st to 10th	Day	90% 3 3 3	2350
	11th to 20th	Day	89% 4 4 2 1	2691
	21st to end	Day	83% 7% 5% 3 2	3929
January	1st to 10th	Night	88% 5% 5% 3	8233
	11th to 20th	Night	92% 3 3 2	8280
	21st to end	Night	82% 5% 5% 6% 2	9058
February	1st to 10th	Night	77% 5% 8% 8% 3	2844
	11th to 20th	Night	68% 6% 9% 13% 3	2461
	21st to end	Night	64% 7% 11% 13% 4	2076
March	1st to 10th	Night	50% 5% 17% 20% 8%	5493
	11th to 20th	Night	50% 7% 17% 18% 7% 1	5238
	21st to end	Night	57% 7% 13% 14% 8%	5401
April	1st to 10th	Night	57% 6% 8% 17% 11% 1	2100
	11th to 20th	Night	51% 6% 9% 18% 13% 2	1967
	21st to end	Night	48% 7% 10% 19% 14% 3	1890
May	1st to 10th	Night	38% 8% 11% 25% 15% 3	5264
	11th to 20th	Night	41% 8% 7% 27% 15% 1	4897
	21st to end	Night	38% 6% 10% 23% 16% 7%	5149
June	1st to 10th	Night	39% 7% 10% 26% 16% 2	1565
	11th to 20th	Night	40% 9% 11% 22% 14% 3	1470
	21st to end	Night	39% 7% 11% 26% 14% 2	1576
July	1st to 10th	Night	41% 6% 13% 22% 14% 4	4670
	11th to 20th	Night	29% 7% 12% 35% 16% 1	4662
	21st to end	Night	31% 7% 15% 30% 17% 1	5002
August	1st to 10th	Night	41% 7% 14% 22% 16% 1	3874
	11th to 20th	Night	32% 6% 21% 31% 11%	4122
	21st to end	Night	40% 7% 15% 26% 11% 1	4807
September	1st to 10th	Night	38% 7% 14% 23% 17% 1	2100
	11th to 20th	Night	37% 7% 15% 27% 13%	2233
	21st to end	Night	46% 9% 14% 21% 10%	2200
October	1st to 10th	Night	42% 6% 11% 30% 11% 1	3590
	11th to 20th	Night	53% 6% 11% 19% 11%	4104
	21st to end	Night	59% 6% 12% 18% 5%	4610
November	1st to 10th	Night	61% 7% 10% 15% 6% 1	2666
	11th to 20th	Night	72% 6% 9% 9% 5%	2730
	21st to end	Night	79% 6% 8% 6% 1	2897
December	1st to 10th	Night	87% 4 4 5%	5060
	11th to 20th	Night	85% 4 7% 3 1	5735
	21st to end	Night	80% 7% 7% 4 1	7273

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% 18% 30% 25% 6% 1	330
	11th to 20th	Day	22% 15% 35% 21% 7% 2	330
	21st to end	Day	20% 11% 31% 30% 8%	363
February	1st to 10th	Day	17% 14% 39% 22% 8% 1	330
	11th to 20th	Day	14% 16% 34% 25% 9%	330
	21st to end	Day	17% 14% 41% 24% 4	273
March	1st to 10th	Day	17% 12% 32% 31% 9%	330
	11th to 20th	Day	17% 10% 30% 32% 10% 2	469
	21st to end	Day	25% 8% 26% 29% 11% 1	594
April	1st to 10th	Day	22% 10% 27% 29% 10% 1	540
	11th to 20th	Day	23% 10% 24% 28% 11% 3	532
	21st to end	Day	17% 7% 22% 34% 18% 2	540
May	1st to 10th	Day	17% 5% 24% 35% 17% 3	543
	11th to 20th	Day	12% 4 24% 37% 19% 4	686
	21st to end	Day	13% 3 17% 37% 25% 5%	844
June	1st to 10th	Day	12% 2 20% 37% 24% 4	780
	11th to 20th	Day	14% 3 17% 38% 23% 4	780
	21st to end	Day	16% 4 12% 39% 24% 4	780
July	1st to 10th	Day	9% 2 13% 37% 32% 8%	771
	11th to 20th	Day	10% 4 15% 34% 30% 8%	768
	21st to end	Day	8% 2 13% 39% 32% 7%	849
August	1st to 10th	Day	10% 2 10% 35% 32% 11%	684
	11th to 20th	Day	13% 3 10% 31% 31% 11%	559
	21st to end	Day	16% 6% 13% 31% 26% 8%	627
September	1st to 10th	Day	16% 8% 16% 27% 25% 10%	570
	11th to 20th	Day	13% 5% 13% 25% 32% 12%	542
	21st to end	Day	17% 9% 15% 25% 26% 8%	530
October	1st to 10th	Day	22% 7% 25% 22% 19% 5%	530
	11th to 20th	Day	26% 13% 26% 23% 11% 1	395
	21st to end	Day	29% 11% 26% 23% 9% 2	363
November	1st to 10th	Day	23% 15% 28% 23% 10% 1	330
	11th to 20th	Day	23% 16% 34% 21% 5% 1	330
	21st to end	Day	30% 18% 31% 17% 4	278
December	1st to 10th	Day	34% 13% 27% 17% 7% 1	220
	11th to 20th	Day	25% 27% 28% 16% 4 1	220
	21st to end	Day	33% 19% 32% 13% 2 1	330
January	1st to 10th	Night	24% 14% 33% 22% 6% 1	1050
	11th to 20th	Night	26% 14% 31% 23% 6% 1	1050
	21st to end	Night	22% 11% 34% 26% 7% 1	1155
February	1st to 10th	Night	19% 14% 32% 27% 7% 1	954
	11th to 20th	Night	19% 13% 33% 28% 6%	823
	21st to end	Night	23% 12% 30% 29% 5% 1	692
March	1st to 10th	Night	19% 7% 31% 31% 11% 1	840
	11th to 20th	Night	16% 9% 34% 31% 9% 1	840
	21st to end	Night	19% 7% 27% 34% 11% 1	840
April	1st to 10th	Night	23% 7% 29% 32% 8% 1	630
	11th to 20th	Night	23% 8% 21% 33% 13% 1	623
	21st to end	Night	20% 6% 23% 37% 14% 2	630
May	1st to 10th	Night	16% 4 23% 37% 19% 1	630
	11th to 20th	Night	15% 5% 20% 39% 20% 1	621
	21st to end	Night	14% 2 17% 38% 25% 3	683
June	1st to 10th	Night	15% 3 16% 39% 24% 3	515
	11th to 20th	Night	12% 2 18% 40% 25% 2	420
	21st to end	Night	15% 3 18% 35% 28% 2	526
July	1st to 10th	Night	12% 2 11% 38% 33% 5%	615
	11th to 20th	Night	9% 3 13% 35% 33% 7%	612
	21st to end	Night	9% 2 14% 39% 33% 3	690
August	1st to 10th	Night	10% 3 13% 38% 33% 3	627
	11th to 20th	Night	13% 3 12% 32% 33% 7%	624
	21st to end	Night	15% 5% 14% 37% 28% 2	693
September	1st to 10th	Night	15% 2 18% 33% 26% 6%	630
	11th to 20th	Night	16% 4 15% 30% 27% 8%	812
	21st to end	Night	21% 5% 18% 28% 22% 6%	800
October	1st to 10th	Night	22% 8% 22% 28% 17% 3	800
	11th to 20th	Night	30% 12% 22% 27% 8% 1	800
	21st to end	Night	34% 11% 22% 24% 8% 1	880
November	1st to 10th	Night	32% 11% 23% 25% 8% 1	820
	11th to 20th	Night	31% 14% 30% 19% 5%	840
	21st to end	Night	32% 15% 27% 21% 4	914
December	1st to 10th	Night	28% 20% 30% 18% 4	1050
	11th to 20th	Night	26% 17% 33% 17% 5% 1	1050
	21st to end	Night	33% 12% 32% 19% 3	1155

Page generated at 2026-09-11 04:11:51. Version ac07

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