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 2024-03-06.

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% 5% 9% 7% 3 4 4 5% 6% 32%	78165
	Night	16% 14% 6% 11% 8% 3 4 4 4 5% 25%	81372
Transparency	Day	53% 7% 12% 18% 9% 1	77871
	Night	62% 6% 10% 14% 7% 1	81201
Seeing	Day	17% 8% 22% 30% 19% 4	14698
	Night	22% 9% 25% 29% 14% 2	24668

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% 24% 20% 19% 8% 4 2 2 2 2 4	2527
	11th to 20th	Day	14% 18% 10% 23% 19% 4 3 2 2 2 3	2530
	21st to end	Day	16% 21% 11% 17% 9% 4 4 3 3 3 7%	2783
February	1st to 10th	Day	10% 17% 8% 15% 18% 5% 4 3 4 4 11%	1605
	11th to 20th	Day	13% 14% 7% 13% 13% 5% 5% 4 4 5% 16%	1843
	21st to end	Day	12% 14% 8% 11% 8% 4 5% 5% 4 6% 22%	1570
March	1st to 10th	Day	12% 10% 4 11% 8% 3 4 4 5% 6% 31%	1848
	11th to 20th	Day	11% 9% 4 9% 6% 4 5% 5% 4 7% 36%	1918
	21st to end	Day	17% 8% 4 9% 6% 3 5% 4 5% 7% 32%	2264
April	1st to 10th	Day	18% 11% 4 8% 6% 3 5% 4 5% 5% 30%	2160
	11th to 20th	Day	19% 11% 4 5% 4 3 4 4 5% 6% 36%	2226
	21st to end	Day	15% 8% 3 8% 6% 3 5% 5% 5% 7% 35%	2340
May	1st to 10th	Day	14% 7% 3 5% 5% 3 4 4 5% 6% 42%	2340
	11th to 20th	Day	13% 6% 3 6% 7% 3 4 4 5% 6% 43%	2402
	21st to end	Day	11% 5% 2 4 5% 3 5% 5% 6% 9% 45%	2725
June	1st to 10th	Day	13% 5% 2 5% 4 3 4 4 7% 8% 45%	2614
	11th to 20th	Day	11% 5% 2 5% 5% 3 5% 5% 6% 9% 44%	2700
	21st to end	Day	13% 6% 3 5% 4 3 4 5% 5% 9% 43%	2603
July	1st to 10th	Day	7% 3 2 3 3 2 4 5% 7% 9% 54%	2520
	11th to 20th	Day	10% 4 2 3 4 2 4 4 7% 9% 51%	2520
	21st to end	Day	7% 4 2 4 4 3 4 4 6% 9% 51%	2743
August	1st to 10th	Day	8% 5% 2 5% 5% 3 4 4 6% 10% 48%	2429
	11th to 20th	Day	11% 5% 2 4 4 3 4 4 6% 8% 49%	2303
	21st to end	Day	13% 5% 2 5% 4 3 3 4 5% 7% 47%	2470
September	1st to 10th	Day	14% 7% 2 5% 3 3 4 4 5% 7% 45%	2142
	11th to 20th	Day	14% 5% 2 5% 4 3 4 4 5% 8% 46%	1980
	21st to end	Day	19% 7% 3 5% 5% 2 5% 4 6% 9% 36%	1980
October	1st to 10th	Day	20% 9% 3 6% 7% 3 4 4 5% 7% 33%	1980
	11th to 20th	Day	25% 15% 5% 9% 6% 4 4 4 5% 4 19%	1694
	21st to end	Day	27% 17% 5% 8% 7% 4 4 3 4 4 16%	1782
November	1st to 10th	Day	18% 20% 4 6% 5% 3 4 3 4 6% 25%	1672
	11th to 20th	Day	16% 23% 10% 13% 6% 3 4 4 4 4 14%	1710
	21st to end	Day	21% 23% 9% 12% 7% 2 4 3 3 4 12%	1554
December	1st to 10th	Day	18% 25% 17% 16% 5% 3 3 2 2 2 8%	1330
	11th to 20th	Day	17% 22% 12% 18% 10% 3 4 3 2 3 7%	1671
	21st to end	Day	22% 21% 11% 14% 8% 3 4 3 3 4 7%	2687
January	1st to 10th	Night	14% 25% 11% 21% 9% 3 2 2 2 2 8%	4428
	11th to 20th	Night	14% 18% 10% 21% 21% 3 3 2 1 2 6%	4440
	21st to end	Night	17% 22% 10% 16% 12% 4 4 3 2 3 7%	4884
February	1st to 10th	Night	12% 17% 7% 16% 16% 5% 4 3 3 4 13%	2574
	11th to 20th	Night	12% 14% 7% 15% 12% 4 5% 4 4 4 18%	2220
	21st to end	Night	17% 16% 5% 12% 9% 3 4 4 4 5% 21%	1884
March	1st to 10th	Night	13% 11% 4 9% 6% 4 3 4 4 6% 35%	2216
	11th to 20th	Night	11% 10% 5% 9% 7% 4 4 5% 5% 5% 34%	2040
	21st to end	Night	17% 8% 4 8% 6% 3 4 4 6% 7% 32%	2106
April	1st to 10th	Night	19% 12% 3 9% 6% 3 5% 4 5% 5% 29%	1800
	11th to 20th	Night	19% 9% 3 6% 6% 4 4 5% 5% 5% 34%	1683
	21st to end	Night	16% 9% 3 8% 5% 4 4 4 5% 6% 36%	1620
May	1st to 10th	Night	16% 8% 4 6% 5% 4 5% 5% 6% 7% 35%	1620
	11th to 20th	Night	14% 8% 3 7% 7% 3 6% 4 5% 7% 34%	1488
	21st to end	Night	12% 5% 2 5% 5% 3 4 5% 6% 9% 44%	1551
June	1st to 10th	Night	14% 5% 2 6% 5% 3 4 5% 5% 7% 43%	1342
	11th to 20th	Night	11% 6% 2 5% 5% 4 6% 6% 6% 7% 41%	1260
	21st to end	Night	11% 7% 2 5% 5% 2 5% 4 4 8% 46%	1350
July	1st to 10th	Night	10% 3 2 4 4 3 5% 5% 7% 8% 50%	1440
	11th to 20th	Night	8% 5% 3 6% 4 3 4 6% 5% 6% 50%	1440
	21st to end	Night	8% 4 2 5% 5% 3 4 4 6% 8% 50%	1575
August	1st to 10th	Night	8% 4 3 5% 5% 3 4 5% 6% 9% 48%	1507
	11th to 20th	Night	10% 4 1 4 5% 3 4 4 7% 8% 48%	1598
	21st to end	Night	14% 5% 2 5% 4 4 4 4 5% 6% 45%	1883
September	1st to 10th	Night	13% 7% 2 5% 4 3 4 3 5% 7% 47%	1800
	11th to 20th	Night	16% 6% 3 5% 4 2 4 4 4 6% 45%	1979
	21st to end	Night	20% 6% 3 6% 5% 4 4 5% 6% 8% 34%	1980
October	1st to 10th	Night	20% 10% 3 6% 6% 3 4 4 3 6% 35%	1980
	11th to 20th	Night	26% 12% 4 8% 6% 3 5% 4 4 6% 22%	2263
	21st to end	Night	28% 16% 4 9% 6% 3 4 3 4 4 19%	2574
November	1st to 10th	Night	19% 17% 4 8% 6% 3 4 3 4 6% 25%	2406
	11th to 20th	Night	19% 23% 7% 11% 7% 3 3 3 3 4 16%	2470
	21st to end	Night	20% 25% 9% 12% 5% 3 4 3 3 3 12%	2619
December	1st to 10th	Night	17% 27% 15% 15% 6% 2 3 2 2 2 8%	2850
	11th to 20th	Night	16% 22% 10% 19% 9% 3 3 3 3 3 10%	3526
	21st to end	Night	25% 22% 11% 11% 7% 3 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	53% 7% 13% 18% 8% 1	1850
	11th to 20th	Day	49% 6% 13% 23% 6% 2	1918
	21st to end	Day	51% 8% 12% 20% 8% 1	2264
April	1st to 10th	Day	54% 6% 11% 19% 9%	2160
	11th to 20th	Day	48% 6% 11% 19% 14% 2	2226
	21st to end	Day	47% 8% 12% 16% 15% 3	2340
May	1st to 10th	Day	42% 6% 12% 23% 13% 3	2340
	11th to 20th	Day	40% 8% 11% 23% 16% 3	2406
	21st to end	Day	34% 9% 15% 26% 14% 2	2725
June	1st to 10th	Day	35% 8% 14% 26% 16% 2	2614
	11th to 20th	Day	35% 8% 14% 24% 18% 2	2700
	21st to end	Day	38% 7% 16% 24% 14% 1	2603
July	1st to 10th	Day	25% 9% 15% 30% 19% 2	2451
	11th to 20th	Day	28% 8% 15% 31% 17% 1	2445
	21st to end	Day	29% 8% 15% 29% 18% 1	2591
August	1st to 10th	Day	32% 8% 19% 29% 10% 1	2414
	11th to 20th	Day	33% 7% 17% 30% 12% 2	2303
	21st to end	Day	36% 7% 16% 26% 14% 1	2470
September	1st to 10th	Day	38% 8% 13% 25% 15% 1	2142
	11th to 20th	Day	37% 8% 17% 28% 9%	1980
	21st to end	Day	45% 8% 16% 24% 8%	1980
October	1st to 10th	Day	50% 9% 11% 22% 8%	1980
	11th to 20th	Day	68% 7% 10% 13% 3	1694
	21st to end	Day	72% 6% 12% 9% 3	1782
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	51% 5% 14% 22% 7% 1	2227
	11th to 20th	Night	51% 7% 10% 19% 11% 2	2041
	21st to end	Night	51% 6% 12% 19% 12% 1	2106
April	1st to 10th	Night	57% 7% 8% 17% 11% 1	1800
	11th to 20th	Night	50% 6% 10% 18% 13% 3	1683
	21st to end	Night	49% 7% 10% 18% 14% 3	1620
May	1st to 10th	Night	48% 6% 11% 18% 12% 4	1620
	11th to 20th	Night	48% 8% 8% 20% 14% 2	1489
	21st to end	Night	36% 7% 13% 26% 15% 4	1552
June	1st to 10th	Night	39% 8% 11% 26% 14% 2	1342
	11th to 20th	Night	39% 9% 12% 23% 14% 3	1260
	21st to end	Night	37% 7% 12% 26% 16% 2	1350
July	1st to 10th	Night	29% 8% 14% 29% 17% 3	1400
	11th to 20th	Night	32% 8% 14% 24% 20% 2	1392
	21st to end	Night	32% 7% 16% 27% 16% 1	1487
August	1st to 10th	Night	31% 8% 20% 28% 13% 1	1498
	11th to 20th	Night	32% 8% 18% 27% 15% 1	1598
	21st to end	Night	39% 7% 15% 23% 15% 2	1883
September	1st to 10th	Night	38% 7% 13% 22% 19% 1	1800
	11th to 20th	Night	40% 7% 15% 27% 10%	1979
	21st to end	Night	47% 9% 15% 21% 7%	1980
October	1st to 10th	Night	52% 5% 10% 22% 10% 1	1980
	11th to 20th	Night	64% 5% 12% 14% 5%	2263
	21st to end	Night	70% 7% 7% 12% 4	2574
November	1st to 10th	Night	60% 8% 10% 15% 6% 1	2406
	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	16% 12% 33% 31% 9%	255
	11th to 20th	Day	16% 8% 29% 33% 12% 2	358
	21st to end	Day	24% 7% 26% 29% 12% 2	462
April	1st to 10th	Day	24% 9% 27% 28% 11% 1	420
	11th to 20th	Day	24% 9% 27% 25% 11% 4	412
	21st to end	Day	18% 7% 23% 32% 18% 2	420
May	1st to 10th	Day	19% 5% 26% 31% 15% 4	423
	11th to 20th	Day	13% 3 24% 37% 18% 4	548
	21st to end	Day	12% 2 18% 37% 26% 5%	679
June	1st to 10th	Day	11% 2 22% 36% 24% 4	630
	11th to 20th	Day	13% 3 19% 36% 24% 6%	630
	21st to end	Day	15% 4 13% 39% 25% 5%	630
July	1st to 10th	Day	8% 2 14% 37% 31% 9%	621
	11th to 20th	Day	11% 4 17% 33% 29% 8%	618
	21st to end	Day	8% 3 14% 39% 30% 7%	684
August	1st to 10th	Day	11% 2 10% 36% 31% 10%	548
	11th to 20th	Day	12% 3 12% 30% 32% 12%	439
	21st to end	Day	16% 6% 13% 32% 26% 7%	495
September	1st to 10th	Day	16% 6% 16% 28% 24% 9%	450
	11th to 20th	Day	15% 5% 15% 28% 30% 7%	450
	21st to end	Day	18% 10% 17% 24% 24% 8%	450
October	1st to 10th	Day	25% 8% 23% 22% 17% 5%	450
	11th to 20th	Day	28% 13% 29% 19% 9% 1	329
	21st to end	Day	34% 11% 26% 22% 7% 1	297
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% 31% 11% 1	743
	11th to 20th	Night	15% 8% 33% 32% 10% 1	720
	21st to end	Night	19% 6% 26% 35% 13% 1	720
April	1st to 10th	Night	23% 7% 29% 31% 9% 1	540
	11th to 20th	Night	22% 7% 23% 34% 14% 1	533
	21st to end	Night	20% 5% 24% 36% 14% 2	540
May	1st to 10th	Night	17% 4 24% 36% 18% 1	540
	11th to 20th	Night	16% 5% 20% 37% 20% 2	531
	21st to end	Night	15% 1 17% 37% 26% 4	584
June	1st to 10th	Night	16% 2 16% 40% 24% 2	442
	11th to 20th	Night	11% 2 19% 40% 26% 3	360
	21st to end	Night	13% 3 18% 34% 30% 2	450
July	1st to 10th	Night	11% 2 11% 39% 32% 5%	525
	11th to 20th	Night	10% 2 14% 36% 31% 8%	522
	21st to end	Night	10% 1 14% 38% 33% 4	591
August	1st to 10th	Night	9% 2 13% 39% 34% 3	537
	11th to 20th	Night	12% 3 12% 30% 34% 8%	534
	21st to end	Night	16% 4 14% 38% 26% 3	594
September	1st to 10th	Night	16% 2 17% 34% 26% 5%	540
	11th to 20th	Night	18% 4 16% 32% 24% 6%	719
	21st to end	Night	22% 6% 19% 27% 21% 6%	720
October	1st to 10th	Night	24% 8% 22% 27% 17% 3	720
	11th to 20th	Night	32% 12% 22% 25% 8% 1	720
	21st to end	Night	36% 11% 22% 23% 7% 1	792
November	1st to 10th	Night	31% 11% 22% 26% 9% 1	740
	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 2024-03-03 06:28:54. Version ac07

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