PNRO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PNRO clear sky chart from 2005-11-06 to 2024-11-05.

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	7% 6% 3 6% 4 4 4 3 5% 6% 51%	105316
	Night	9% 8% 3 7% 5% 4 4 4 5% 6% 44%	102394
Transparency	Day	17% 47% 6% 12% 10% 7%	105062
	Night	21% 48% 6% 12% 8% 5%	102237
Seeing	Day	10% 9% 21% 26% 23% 10%	14395
	Night	13% 7% 22% 34% 21% 3	23470

By Month

Percentage Cloud Cover SW (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	14% 17% 8% 14% 7% 5% 5% 4 5% 5% 15%	2539
	11th to 20th	Day	19% 19% 6% 9% 5% 4 5% 4 7% 5% 16%	2540
	21st to end	Day	18% 17% 7% 17% 8% 6% 5% 3 4 4 12%	2794
February	1st to 10th	Day	15% 15% 4 10% 7% 6% 4 3 7% 6% 24%	1643
	11th to 20th	Day	13% 13% 5% 9% 5% 5% 5% 3 5% 5% 31%	1748
	21st to end	Day	10% 10% 4 9% 7% 6% 6% 4 8% 7% 29%	1570
March	1st to 10th	Day	7% 9% 2 7% 5% 6% 6% 5% 7% 10% 37%	3138
	11th to 20th	Day	6% 6% 2 6% 5% 3 4 2 4 6% 55%	3288
	21st to end	Day	9% 7% 3 9% 7% 7% 6% 5% 7% 7% 31%	4158
April	1st to 10th	Day	8% 9% 2 6% 6% 4 6% 5% 7% 8% 37%	2280
	11th to 20th	Day	7% 7% 2 6% 5% 4 5% 4 5% 8% 46%	2249
	21st to end	Day	8% 6% 2 5% 4 4 4 4 7% 7% 49%	2437
May	1st to 10th	Day	8% 5% 2 5% 4 4 4 3 6% 8% 52%	4379
	11th to 20th	Day	4 3 1 4 3 3 4 3 5% 6% 64%	4377
	21st to end	Day	6% 6% 2 5% 4 5% 5% 5% 7% 8% 47%	4813
June	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 5% 7% 47%	2660
	11th to 20th	Day	7% 5% 2 5% 4 4 4 3 5% 7% 56%	2660
	21st to end	Day	4 3 1 3 3 3 3 3 6% 6% 67%	2660
July	1st to 10th	Day	1 1 1 2 1 1 2 2 2 3 84%	4420
	11th to 20th	Day	1 1 1 2 1 2 2 2 3 4 82%	4420
	21st to end	Day	1 1 1 2 1 2 2 2 3 4 81%	4790
August	1st to 10th	Day	2 2 1 3 2 2 2 2 4 6% 73%	4400
	11th to 20th	Day	1 1 3 1 2 2 3 4 6% 75%	4040
	21st to end	Day	3 4 1 4 3 3 3 2 3 5% 70%	4180
September	1st to 10th	Day	2 1 1 2 2 2 3 3 4 6% 74%	2280
	11th to 20th	Day	5% 4 1 5% 4 4 4 3 6% 7% 58%	2224
	21st to end	Day	6% 5% 2 5% 4 4 3 3 5% 8% 56%	2090
October	1st to 10th	Day	6% 4 2 4 3 3 3 2 4 6% 64%	3250
	11th to 20th	Day	4 5% 2 6% 4 6% 5% 5% 8% 9% 47%	3111
	21st to end	Day	10% 7% 3 7% 5% 6% 5% 4 6% 7% 40%	3101
November	1st to 10th	Day	14% 9% 3 8% 5% 6% 6% 5% 5% 8% 32%	1710
	11th to 20th	Day	13% 14% 5% 9% 6% 7% 5% 5% 6% 6% 25%	1605
	21st to end	Day	11% 14% 5% 12% 7% 6% 6% 5% 6% 7% 21%	1520
December	1st to 10th	Day	10% 13% 6% 12% 9% 6% 6% 5% 6% 5% 21%	1520
	11th to 20th	Day	14% 17% 11% 18% 8% 5% 5% 3 4 4 12%	1928
	21st to end	Day	14% 12% 6% 17% 10% 7% 6% 3 7% 5% 15%	2794
January	1st to 10th	Night	16% 19% 6% 12% 7% 6% 5% 4 5% 5% 16%	4406
	11th to 20th	Night	18% 14% 5% 11% 5% 5% 5% 4 6% 7% 20%	4420
	21st to end	Night	15% 14% 6% 15% 8% 7% 5% 4 6% 5% 15%	4862
February	1st to 10th	Night	13% 13% 5% 10% 6% 5% 5% 3 6% 6% 28%	2532
	11th to 20th	Night	11% 12% 3 9% 5% 4 5% 4 6% 7% 33%	2317
	21st to end	Night	11% 11% 4 10% 7% 5% 5% 4 5% 7% 31%	1884
March	1st to 10th	Night	7% 8% 3 7% 5% 5% 5% 4 7% 10% 38%	3736
	11th to 20th	Night	7% 7% 2 5% 4 3 4 3 6% 6% 53%	3690
	21st to end	Night	8% 7% 3 8% 7% 8% 8% 6% 9% 8% 28%	3493
April	1st to 10th	Night	13% 10% 2 8% 5% 4 5% 4 5% 8% 36%	1900
	11th to 20th	Night	10% 7% 2 6% 5% 6% 4 3 4 6% 46%	1879
	21st to end	Night	9% 6% 3 7% 5% 4 5% 4 6% 7% 43%	1741
May	1st to 10th	Night	7% 6% 2 6% 4 4 5% 3 6% 7% 50%	2578
	11th to 20th	Night	7% 2 1 4 3 3 4 4 6% 7% 59%	2516
	21st to end	Night	6% 5% 1 6% 4 5% 5% 5% 7% 8% 47%	2762
June	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 4 7% 8% 45%	1520
	11th to 20th	Night	8% 7% 2 5% 4 4 4 4 5% 6% 51%	1520
	21st to end	Night	4 3 1 5% 3 4 4 3 5% 6% 63%	1520
July	1st to 10th	Night	1 1 1 1 1 2 2 4 4 82%	2540
	11th to 20th	Night	1 1 1 2 1 2 2 3 5% 82%	2540
	21st to end	Night	1 1 2 1 2 2 2 3 4 81%	2761
August	1st to 10th	Night	3 3 1 3 2 2 3 2 5% 5% 70%	2529
	11th to 20th	Night	1 2 1 3 2 3 3 3 4 6% 73%	2795
	21st to end	Night	2 2 1 3 3 2 3 3 4 5% 71%	3498
September	1st to 10th	Night	3 2 1 3 2 2 3 2 3 4 74%	1900
	11th to 20th	Night	4 4 1 5% 4 3 4 2 6% 6% 61%	1955
	21st to end	Night	6% 3 1 4 3 3 4 4 5% 7% 59%	2090
October	1st to 10th	Night	5% 3 2 4 3 3 3 3 4 4 67%	3728
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 5% 6% 8% 51%	3824
	21st to end	Night	10% 6% 3 6% 5% 5% 5% 4 6% 8% 42%	4457
November	1st to 10th	Night	15% 9% 3 8% 5% 5% 4 4 5% 6% 35%	2469
	11th to 20th	Night	17% 10% 3 9% 6% 5% 5% 4 5% 6% 29%	2574
	21st to end	Night	13% 11% 3 10% 6% 5% 5% 4 7% 7% 30%	2660
December	1st to 10th	Night	13% 13% 5% 12% 7% 6% 5% 5% 6% 5% 22%	2660
	11th to 20th	Night	16% 18% 7% 15% 7% 5% 5% 4 4 5% 14%	3276
	21st to end	Night	14% 12% 10% 13% 8% 6% 5% 4 5% 5% 18%	4862

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	45% 39% 8% 6% 2	2539
	11th to 20th	Day	45% 42% 7% 6%	2540
	21st to end	Day	49% 45% 3 2	2794
February	1st to 10th	Day	26% 66% 4 3 1	1643
	11th to 20th	Day	22% 66% 5% 5% 2	1757
	21st to end	Day	19% 67% 6% 5% 3 1	1570
March	1st to 10th	Day	21% 43% 6% 19% 10%	3138
	11th to 20th	Day	13% 40% 9% 28% 10%	3288
	21st to end	Day	27% 46% 10% 10% 6%	4158
April	1st to 10th	Day	15% 66% 7% 7% 4	2280
	11th to 20th	Day	13% 66% 6% 8% 5% 1	2252
	21st to end	Day	11% 66% 5% 10% 8% 1	2437
May	1st to 10th	Day	17% 42% 6% 19% 14% 2	4379
	11th to 20th	Day	8% 40% 5% 21% 19% 7%	4380
	21st to end	Day	15% 44% 14% 19% 8% 1	4814
June	1st to 10th	Day	10% 65% 3 10% 10% 2	2660
	11th to 20th	Day	9% 65% 3 10% 10% 2	2660
	21st to end	Day	6% 63% 3 10% 14% 4	2660
July	1st to 10th	Day	5% 35% 2 5% 15% 39%	4351
	11th to 20th	Day	5% 35% 2 4 14% 40%	4345
	21st to end	Day	5% 35% 3 12% 23% 22%	4639
August	1st to 10th	Day	10% 36% 3 6% 22% 24%	4384
	11th to 20th	Day	7% 37% 3 27% 21% 4	4082
	21st to end	Day	13% 37% 5% 19% 20% 6%	4179
September	1st to 10th	Day	5% 60% 5% 13% 13% 4	2280
	11th to 20th	Day	12% 61% 6% 9% 10% 2	2224
	21st to end	Day	12% 61% 6% 14% 6% 1	2090
October	1st to 10th	Day	12% 37% 6% 27% 16% 2	3250
	11th to 20th	Day	19% 40% 14% 18% 9%	3111
	21st to end	Day	27% 39% 8% 19% 7% 1	3101
November	1st to 10th	Day	21% 59% 8% 8% 3	1710
	11th to 20th	Day	26% 61% 5% 6% 1 1	1605
	21st to end	Day	23% 62% 6% 5% 3	1520
December	1st to 10th	Day	27% 64% 4 4 1	1520
	11th to 20th	Day	44% 50% 3 3 1	1928
	21st to end	Day	42% 43% 8% 6% 1	2794
January	1st to 10th	Night	44% 41% 8% 5% 1	4406
	11th to 20th	Night	42% 40% 11% 7% 1	4420
	21st to end	Night	43% 47% 8% 2	4862
February	1st to 10th	Night	24% 67% 5% 4	2532
	11th to 20th	Night	20% 67% 4 8% 1	2319
	21st to end	Night	20% 66% 3 7% 2 1	1884
March	1st to 10th	Night	22% 43% 5% 18% 11% 1	3736
	11th to 20th	Night	13% 41% 7% 28% 11%	3690
	21st to end	Night	28% 46% 12% 11% 3	3493
April	1st to 10th	Night	16% 66% 6% 8% 4	1900
	11th to 20th	Night	14% 65% 4 9% 7% 1	1879
	21st to end	Night	11% 67% 6% 8% 6% 2	1741
May	1st to 10th	Night	20% 41% 6% 14% 16% 2	2578
	11th to 20th	Night	10% 40% 5% 27% 15% 2	2516
	21st to end	Night	15% 44% 16% 21% 4	2762
June	1st to 10th	Night	8% 66% 3 11% 10% 2	1520
	11th to 20th	Night	10% 65% 3 10% 10% 3	1520
	21st to end	Night	8% 63% 3 10% 10% 6%	1520
July	1st to 10th	Night	3 35% 2 8% 14% 39%	2500
	11th to 20th	Night	3 35% 3 5% 13% 42%	2492
	21st to end	Night	6% 34% 2 10% 19% 29%	2674
August	1st to 10th	Night	11% 36% 2 5% 18% 27%	2521
	11th to 20th	Night	8% 37% 4 26% 20% 6%	2819
	21st to end	Night	9% 37% 5% 21% 17% 11%	3498
September	1st to 10th	Night	7% 60% 4 11% 12% 5%	1900
	11th to 20th	Night	11% 61% 5% 11% 7% 5%	1955
	21st to end	Night	10% 60% 5% 13% 10% 1	2090
October	1st to 10th	Night	11% 36% 6% 22% 23% 2	3728
	11th to 20th	Night	17% 39% 12% 17% 15%	3824
	21st to end	Night	25% 38% 6% 23% 7%	4457
November	1st to 10th	Night	20% 59% 7% 10% 3	2469
	11th to 20th	Night	20% 62% 7% 8% 2 1	2574
	21st to end	Night	19% 62% 7% 8% 4	2660
December	1st to 10th	Night	27% 62% 7% 3 1	2660
	11th to 20th	Night	40% 52% 5% 3 1	3276
	21st to end	Night	39% 43% 6% 8% 3	4862

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	23% 10% 22% 22% 18% 5%	180
	11th to 20th	Day	22% 8% 23% 29% 13% 4	180
	21st to end	Day	20% 9% 22% 28% 19% 2	198
February	1st to 10th	Day	22% 13% 24% 24% 13% 3	303
	11th to 20th	Day	21% 13% 21% 25% 17% 3	405
	21st to end	Day	15% 15% 23% 24% 20% 3	382
March	1st to 10th	Day	18% 15% 27% 22% 15% 4	460
	11th to 20th	Day	11% 12% 22% 28% 18% 9%	460
	21st to end	Day	13% 13% 30% 27% 14% 3	506
April	1st to 10th	Day	14% 17% 25% 22% 14% 8%	460
	11th to 20th	Day	10% 15% 31% 22% 15% 6%	452
	21st to end	Day	7% 13% 28% 27% 18% 7%	460
May	1st to 10th	Day	8% 11% 25% 26% 24% 7%	463
	11th to 20th	Day	11% 7% 24% 20% 25% 12%	488
	21st to end	Day	10% 6% 23% 25% 25% 12%	529
June	1st to 10th	Day	10% 11% 19% 21% 26% 14%	490
	11th to 20th	Day	9% 13% 26% 28% 19% 6%	490
	21st to end	Day	3 6% 19% 28% 30% 13%	490
July	1st to 10th	Day	2 2 16% 32% 41% 8%	486
	11th to 20th	Day	1 4 17% 36% 30% 12%	484
	21st to end	Day	1 4 13% 31% 33% 18%	531
August	1st to 10th	Day	2 5% 11% 29% 32% 21%	487
	11th to 20th	Day	2 2 14% 25% 32% 25%	477
	21st to end	Day	6% 6% 18% 26% 27% 17%	539
September	1st to 10th	Day	3 3 15% 28% 33% 17%	490
	11th to 20th	Day	7% 6% 18% 26% 27% 17%	490
	21st to end	Day	8% 8% 17% 28% 27% 12%	490
October	1st to 10th	Day	11% 6% 18% 27% 26% 11%	490
	11th to 20th	Day	10% 10% 19% 23% 26% 12%	465
	21st to end	Day	16% 11% 23% 28% 16% 6%	330
November	1st to 10th	Day	17% 13% 25% 24% 18% 3	282
	11th to 20th	Day	19% 11% 23% 26% 17% 5%	220
	21st to end	Day	13% 11% 22% 23% 27% 6%	180
December	1st to 10th	Day	13% 11% 23% 28% 13% 13%	180
	11th to 20th	Day	20% 12% 22% 33% 11% 3	180
	21st to end	Day	19% 8% 27% 30% 12% 4	198
January	1st to 10th	Night	27% 9% 21% 25% 15% 3	760
	11th to 20th	Night	19% 9% 19% 33% 17% 3	760
	21st to end	Night	19% 6% 17% 34% 20% 3	836
February	1st to 10th	Night	19% 11% 20% 32% 15% 2	760
	11th to 20th	Night	17% 9% 20% 33% 19% 3	744
	21st to end	Night	17% 13% 23% 33% 12% 2	628
March	1st to 10th	Night	14% 10% 25% 31% 17% 2	760
	11th to 20th	Night	12% 8% 23% 34% 21% 2	760
	21st to end	Night	13% 10% 31% 32% 13% 1	836
April	1st to 10th	Night	16% 9% 23% 34% 16% 2	760
	11th to 20th	Night	12% 11% 28% 27% 17% 4	751
	21st to end	Night	10% 9% 28% 31% 19% 2	601
May	1st to 10th	Night	7% 6% 28% 36% 20% 2	405
	11th to 20th	Night	10% 6% 17% 38% 27% 2	374
	21st to end	Night	8% 7% 24% 36% 23% 3	411
June	1st to 10th	Night	11% 7% 27% 33% 19% 3	380
	11th to 20th	Night	11% 9% 33% 34% 12% 1	380
	21st to end	Night	4 5% 27% 38% 23% 3	380
July	1st to 10th	Night	4 3 24% 41% 27% 2	370
	11th to 20th	Night	2 3 29% 43% 20% 2	368
	21st to end	Night	1 4 21% 40% 32% 2	416
August	1st to 10th	Night	4 2 19% 41% 31% 3	378
	11th to 20th	Night	3 2 16% 35% 35% 8%	544
	21st to end	Night	3 3 18% 38% 31% 6%	836
September	1st to 10th	Night	4 2 18% 39% 33% 5%	760
	11th to 20th	Night	4 3 18% 33% 34% 8%	760
	21st to end	Night	7% 5% 19% 32% 31% 7%	760
October	1st to 10th	Night	10% 4 18% 38% 26% 4	760
	11th to 20th	Night	11% 8% 18% 33% 25% 6%	760
	21st to end	Night	12% 7% 25% 31% 19% 5%	836
November	1st to 10th	Night	19% 6% 24% 34% 16% 1	760
	11th to 20th	Night	20% 9% 22% 30% 16% 3	760
	21st to end	Night	16% 8% 16% 35% 21% 4	760
December	1st to 10th	Night	17% 9% 17% 35% 18% 4	760
	11th to 20th	Night	22% 8% 21% 34% 13% 2	760
	21st to end	Night	26% 9% 21% 30% 13% 1	836

Page generated at 2024-11-02 23:11:30. Version ac07

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