Poverty Beach Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Poverty Beach Observatory clear sky chart from 2005-11-06 to 2024-07-03.

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	18% 11% 4 10% 6% 5% 4 4 5% 7% 27%	89932
	Night	19% 12% 4 10% 6% 5% 5% 4 5% 6% 26%	89329
Transparency	Day	55% 7% 13% 17% 7% 1	89650
	Night	58% 7% 13% 15% 6% 1	89166
Seeing	Day	22% 8% 25% 29% 14% 2	17070
	Night	24% 9% 27% 28% 10% 1	24419

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% 13% 7% 23% 7% 6% 4 4 3 5% 15%	2526
	11th to 20th	Day	12% 11% 6% 13% 8% 6% 6% 5% 6% 7% 20%	2530
	21st to end	Day	12% 11% 6% 15% 7% 5% 5% 3 4 6% 25%	3000
February	1st to 10th	Day	18% 13% 4 10% 5% 6% 5% 4 5% 5% 23%	1710
	11th to 20th	Day	15% 14% 4 11% 8% 6% 5% 4 4 6% 22%	1663
	21st to end	Day	11% 13% 6% 9% 7% 7% 4 4 5% 7% 28%	1489
March	1st to 10th	Day	21% 12% 4 9% 5% 5% 4 3 4 6% 28%	3264
	11th to 20th	Day	11% 17% 7% 14% 8% 6% 5% 3 4 5% 20%	3480
	21st to end	Day	21% 17% 6% 13% 6% 4 3 3 4 5% 18%	3926
April	1st to 10th	Day	19% 12% 4 9% 7% 5% 5% 3 4 6% 27%	2280
	11th to 20th	Day	21% 10% 3 6% 5% 5% 4 3 4 7% 32%	2263
	21st to end	Day	20% 12% 4 8% 5% 3 4 4 5% 6% 30%	2470
May	1st to 10th	Day	25% 15% 3 8% 4 4 3 3 5% 5% 25%	4411
	11th to 20th	Day	17% 8% 3 8% 4 4 4 3 5% 7% 37%	4398
	21st to end	Day	17% 9% 3 8% 5% 4 5% 4 6% 8% 29%	4836
June	1st to 10th	Day	24% 12% 3 7% 4 5% 5% 3 5% 8% 23%	2660
	11th to 20th	Day	17% 9% 3 7% 4 4 4 3 6% 7% 36%	2677
	21st to end	Day	21% 9% 4 8% 6% 4 4 3 5% 7% 28%	2850
July	1st to 10th	Day	15% 7% 2 6% 6% 4 5% 4 6% 8% 36%	2579
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 5% 7% 8% 36%	2520
	21st to end	Day	17% 9% 3 9% 6% 5% 4 3 5% 8% 29%	2745
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 5% 7% 9% 35%	2397
	11th to 20th	Day	16% 6% 3 7% 5% 5% 4 5% 6% 9% 34%	2304
	21st to end	Day	13% 6% 3 7% 5% 4 5% 4 6% 9% 38%	2434
September	1st to 10th	Day	15% 7% 2 8% 4 4 5% 3 5% 9% 38%	2160
	11th to 20th	Day	18% 8% 3 7% 5% 4 4 3 5% 7% 35%	2160
	21st to end	Day	18% 7% 2 6% 6% 4 4 3 5% 7% 38%	1888
October	1st to 10th	Day	18% 8% 2 7% 5% 5% 5% 3 6% 6% 34%	1800
	11th to 20th	Day	18% 9% 4 8% 7% 6% 6% 4 7% 7% 24%	1800
	21st to end	Day	20% 14% 4 10% 5% 5% 5% 4 6% 6% 21%	1896
November	1st to 10th	Day	20% 12% 5% 9% 6% 6% 4 4 5% 6% 24%	1567
	11th to 20th	Day	20% 17% 5% 11% 6% 5% 4 4 4 6% 18%	1520
	21st to end	Day	18% 17% 6% 11% 7% 6% 5% 4 6% 6% 16%	1520
December	1st to 10th	Day	23% 15% 8% 11% 7% 5% 5% 4 4 4 13%	1520
	11th to 20th	Day	26% 18% 5% 14% 7% 4 4 3 4 5% 11%	1906
	21st to end	Day	20% 15% 8% 14% 6% 5% 4 3 5% 5% 17%	2783
January	1st to 10th	Night	13% 13% 6% 15% 8% 6% 6% 4 5% 6% 17%	4429
	11th to 20th	Night	18% 11% 4 13% 6% 7% 6% 3 5% 6% 21%	4440
	21st to end	Night	13% 12% 5% 18% 8% 5% 4 4 5% 5% 20%	4657
February	1st to 10th	Night	19% 13% 4 10% 6% 5% 4 4 4 5% 26%	2470
	11th to 20th	Night	16% 14% 4 11% 6% 6% 6% 4 5% 6% 22%	2403
	21st to end	Night	12% 15% 5% 9% 6% 5% 4 3 5% 6% 29%	1965
March	1st to 10th	Night	20% 13% 5% 8% 6% 5% 4 3 4 5% 27%	3576
	11th to 20th	Night	20% 17% 7% 11% 6% 5% 4 2 4 5% 19%	3479
	21st to end	Night	24% 15% 4 10% 6% 6% 5% 3 3 4 20%	3705
April	1st to 10th	Night	23% 12% 3 8% 5% 4 4 3 5% 6% 27%	1900
	11th to 20th	Night	21% 11% 3 6% 4 4 3 3 5% 6% 33%	1864
	21st to end	Night	24% 11% 4 7% 5% 4 4 3 4 5% 30%	1710
May	1st to 10th	Night	25% 17% 3 8% 5% 4 3 3 5% 5% 21%	2538
	11th to 20th	Night	15% 10% 3 7% 5% 6% 4 5% 6% 7% 34%	2506
	21st to end	Night	16% 10% 4 8% 5% 6% 6% 5% 6% 8% 26%	2749
June	1st to 10th	Night	26% 10% 3 7% 5% 4 5% 3 5% 6% 25%	1520
	11th to 20th	Night	19% 9% 2 5% 4 3 4 4 5% 7% 39%	1511
	21st to end	Night	23% 9% 4 8% 6% 4 5% 3 6% 5% 28%	1330
July	1st to 10th	Night	14% 8% 2 6% 5% 5% 6% 5% 6% 8% 34%	1396
	11th to 20th	Night	14% 7% 2 7% 4 7% 5% 4 8% 9% 33%	1440
	21st to end	Night	17% 7% 3 7% 6% 5% 5% 5% 8% 7% 30%	1573
August	1st to 10th	Night	14% 6% 2 6% 4 4 6% 5% 7% 7% 38%	1539
	11th to 20th	Night	16% 7% 2 7% 6% 5% 6% 4 7% 8% 34%	1596
	21st to end	Night	13% 5% 2 6% 4 4 4 4 7% 9% 40%	1921
September	1st to 10th	Night	14% 7% 2 5% 5% 4 5% 3 6% 7% 41%	1800
	11th to 20th	Night	18% 8% 3 4 3 3 4 4 4 8% 40%	1800
	21st to end	Night	18% 6% 2 6% 4 5% 4 3 5% 7% 40%	2068
October	1st to 10th	Night	18% 7% 2 8% 5% 4 4 4 6% 6% 37%	2160
	11th to 20th	Night	19% 8% 3 7% 5% 4 5% 3 6% 7% 32%	2160
	21st to end	Night	24% 11% 4 9% 5% 5% 4 3 4 6% 25%	2458
November	1st to 10th	Night	19% 12% 3 8% 6% 6% 5% 4 5% 7% 26%	2509
	11th to 20th	Night	21% 13% 4 9% 6% 5% 5% 4 5% 7% 20%	2660
	21st to end	Night	23% 15% 4 10% 6% 5% 5% 4 5% 5% 18%	2660
December	1st to 10th	Night	24% 14% 6% 11% 6% 5% 5% 4 5% 6% 15%	2660
	11th to 20th	Night	28% 15% 5% 11% 5% 4 4 3 4 4 17%	3293
	21st to end	Night	27% 14% 5% 13% 5% 3 3 3 4 5% 17%	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	74% 7% 12% 4 3	2527
	11th to 20th	Day	62% 8% 11% 13% 6%	2530
	21st to end	Day	58% 8% 15% 11% 8% 1	3000
February	1st to 10th	Day	59% 5% 13% 14% 8%	1710
	11th to 20th	Day	62% 6% 10% 16% 5% 1	1671
	21st to end	Day	54% 4 14% 16% 10% 2	1489
March	1st to 10th	Day	57% 4 11% 19% 8%	3268
	11th to 20th	Day	60% 9% 10% 13% 6% 1	3480
	21st to end	Day	68% 4 10% 11% 5% 1	3926
April	1st to 10th	Day	56% 7% 10% 14% 11% 2	2280
	11th to 20th	Day	52% 6% 10% 20% 12% 1	2263
	21st to end	Day	52% 6% 12% 17% 11% 2	2470
May	1st to 10th	Day	59% 8% 12% 14% 6% 1	4426
	11th to 20th	Day	46% 8% 14% 24% 8%	4402
	21st to end	Day	48% 11% 14% 18% 8%	4836
June	1st to 10th	Day	58% 7% 12% 18% 5%	2660
	11th to 20th	Day	47% 6% 13% 23% 9% 1	2677
	21st to end	Day	54% 7% 12% 16% 9% 1	2850
July	1st to 10th	Day	42% 9% 16% 23% 9%	2509
	11th to 20th	Day	42% 9% 16% 24% 9% 1	2444
	21st to end	Day	53% 6% 15% 19% 7%	2592
August	1st to 10th	Day	41% 9% 16% 26% 7%	2383
	11th to 20th	Day	43% 9% 18% 23% 6% 1	2304
	21st to end	Day	39% 7% 17% 27% 10%	2434
September	1st to 10th	Day	42% 7% 15% 25% 10%	2160
	11th to 20th	Day	48% 7% 11% 21% 12%	2160
	21st to end	Day	44% 6% 12% 26% 12% 1	1888
October	1st to 10th	Day	48% 6% 13% 24% 9%	1800
	11th to 20th	Day	57% 7% 15% 16% 5%	1800
	21st to end	Day	62% 7% 11% 14% 5%	1896
November	1st to 10th	Day	60% 7% 13% 15% 5%	1567
	11th to 20th	Day	66% 7% 14% 9% 3	1520
	21st to end	Day	68% 9% 13% 7% 2	1520
December	1st to 10th	Day	74% 10% 8% 6% 2	1520
	11th to 20th	Day	78% 8% 7% 5% 2 1	1905
	21st to end	Day	70% 7% 15% 6% 2	2783
January	1st to 10th	Night	63% 10% 18% 6% 2	4429
	11th to 20th	Night	64% 8% 12% 11% 5%	4440
	21st to end	Night	62% 7% 14% 11% 5%	4657
February	1st to 10th	Night	60% 5% 10% 13% 11% 1	2470
	11th to 20th	Night	63% 6% 11% 12% 7% 1	2406
	21st to end	Night	56% 5% 11% 17% 10% 1	1965
March	1st to 10th	Night	59% 5% 8% 17% 9% 2	3585
	11th to 20th	Night	67% 6% 8% 13% 5% 1	3480
	21st to end	Night	69% 4 7% 12% 6% 1	3705
April	1st to 10th	Night	58% 5% 11% 13% 10% 2	1900
	11th to 20th	Night	52% 5% 9% 19% 12% 2	1864
	21st to end	Night	57% 5% 9% 16% 12% 1	1710
May	1st to 10th	Night	65% 4 9% 14% 6% 1	2543
	11th to 20th	Night	46% 9% 16% 20% 8%	2507
	21st to end	Night	52% 10% 16% 16% 5% 1	2750
June	1st to 10th	Night	59% 6% 11% 18% 6%	1520
	11th to 20th	Night	46% 7% 12% 21% 13% 1	1511
	21st to end	Night	56% 7% 14% 14% 8% 1	1330
July	1st to 10th	Night	43% 9% 18% 24% 6%	1357
	11th to 20th	Night	43% 11% 16% 21% 8% 1	1392
	21st to end	Night	49% 9% 17% 18% 6%	1486
August	1st to 10th	Night	40% 11% 17% 25% 7%	1528
	11th to 20th	Night	48% 9% 16% 22% 5%	1596
	21st to end	Night	39% 10% 17% 25% 8%	1921
September	1st to 10th	Night	40% 8% 15% 27% 11%	1800
	11th to 20th	Night	43% 7% 12% 25% 13% 1	1800
	21st to end	Night	43% 7% 13% 25% 11%	2068
October	1st to 10th	Night	47% 7% 12% 23% 11%	2160
	11th to 20th	Night	51% 8% 15% 23% 4	2160
	21st to end	Night	61% 7% 10% 15% 6%	2458
November	1st to 10th	Night	58% 8% 14% 14% 5%	2509
	11th to 20th	Night	62% 9% 15% 9% 5%	2660
	21st to end	Night	68% 9% 14% 7% 2	2660
December	1st to 10th	Night	72% 9% 10% 7% 2	2660
	11th to 20th	Night	72% 6% 10% 8% 3	3295
	21st to end	Night	72% 6% 12% 8% 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	27% 17% 34% 18% 4	370
	11th to 20th	Day	26% 15% 32% 18% 8% 1	370
	21st to end	Day	17% 9% 40% 28% 6%	407
February	1st to 10th	Day	26% 15% 29% 22% 7%	370
	11th to 20th	Day	22% 15% 34% 24% 5%	366
	21st to end	Day	14% 10% 35% 31% 9% 1	307
March	1st to 10th	Day	21% 10% 33% 29% 7% 1	411
	11th to 20th	Day	17% 8% 33% 30% 10% 1	460
	21st to end	Day	26% 11% 29% 24% 9% 1	506
April	1st to 10th	Day	25% 12% 30% 26% 7%	460
	11th to 20th	Day	23% 7% 32% 27% 10% 2	452
	21st to end	Day	23% 7% 21% 35% 13% 2	460
May	1st to 10th	Day	31% 5% 24% 28% 8% 3	639
	11th to 20th	Day	22% 3 20% 32% 19% 3	674
	21st to end	Day	22% 5% 21% 37% 14% 2	735
June	1st to 10th	Day	31% 5% 16% 31% 14% 2	680
	11th to 20th	Day	19% 4 20% 36% 19% 2	680
	21st to end	Day	27% 4 16% 29% 19% 4	680
July	1st to 10th	Day	18% 2 14% 40% 25% 2	630
	11th to 20th	Day	15% 3 14% 39% 26% 4	618
	21st to end	Day	18% 3 14% 38% 23% 2	685
August	1st to 10th	Day	14% 2 13% 37% 29% 5%	516
	11th to 20th	Day	20% 4 13% 33% 23% 8%	439
	21st to end	Day	16% 2 18% 29% 31% 4	495
September	1st to 10th	Day	14% 5% 21% 36% 21% 3	450
	11th to 20th	Day	20% 6% 23% 31% 18% 2	450
	21st to end	Day	20% 6% 26% 29% 14% 5%	392
October	1st to 10th	Day	19% 7% 23% 29% 17% 4	360
	11th to 20th	Day	21% 8% 31% 23% 14% 2	360
	21st to end	Day	23% 15% 31% 23% 7% 2	396
November	1st to 10th	Day	23% 13% 34% 21% 8% 1	365
	11th to 20th	Day	29% 16% 31% 18% 5% 1	370
	21st to end	Day	27% 19% 29% 22% 3	370
December	1st to 10th	Day	29% 13% 34% 19% 4	370
	11th to 20th	Day	28% 24% 31% 16% 1	370
	21st to end	Day	25% 17% 36% 17% 4 1	407
January	1st to 10th	Night	27% 15% 34% 20% 4	850
	11th to 20th	Night	25% 14% 33% 22% 6%	850
	21st to end	Night	21% 11% 39% 23% 7% 1	870
February	1st to 10th	Night	28% 10% 31% 26% 5%	760
	11th to 20th	Night	22% 12% 39% 22% 4 1	743
	21st to end	Night	19% 9% 34% 29% 10%	628
March	1st to 10th	Night	21% 9% 36% 27% 6%	760
	11th to 20th	Night	22% 7% 30% 27% 12% 1	760
	21st to end	Night	25% 9% 28% 27% 10% 1	776
April	1st to 10th	Night	29% 8% 27% 27% 8%	570
	11th to 20th	Night	25% 6% 29% 29% 10% 1	564
	21st to end	Night	28% 4 26% 30% 11% 1	570
May	1st to 10th	Night	32% 3 23% 28% 11% 4	570
	11th to 20th	Night	23% 3 21% 34% 16% 3	562
	21st to end	Night	22% 3 27% 38% 9% 2	616
June	1st to 10th	Night	31% 3 18% 38% 9% 1	570
	11th to 20th	Night	23% 3 20% 38% 16% 1	561
	21st to end	Night	26% 4 15% 37% 17% 2	380
July	1st to 10th	Night	17% 2 15% 41% 23% 1	472
	11th to 20th	Night	18% 2 15% 43% 21% 2	522
	21st to end	Night	19% 2 15% 39% 22% 3	590
August	1st to 10th	Night	15% 2 15% 43% 22% 2	538
	11th to 20th	Night	20% 2 17% 36% 23% 2	532
	21st to end	Night	14% 3 18% 38% 26% 2	594
September	1st to 10th	Night	17% 3 22% 36% 19% 1	540
	11th to 20th	Night	24% 6% 18% 36% 13% 2	540
	21st to end	Night	21% 7% 26% 34% 9% 2	692
October	1st to 10th	Night	21% 5% 28% 32% 13% 1	720
	11th to 20th	Night	24% 9% 28% 27% 11% 1	720
	21st to end	Night	32% 12% 30% 20% 5%	834
November	1st to 10th	Night	24% 14% 32% 22% 6% 1	830
	11th to 20th	Night	28% 18% 29% 20% 5% 1	850
	21st to end	Night	32% 16% 30% 18% 4	850
December	1st to 10th	Night	30% 16% 33% 15% 6%	850
	11th to 20th	Night	30% 20% 32% 15% 2	850
	21st to end	Night	31% 16% 31% 17% 4 1	935

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