PACMO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PACMO clear sky chart from 2005-11-06 to 2024-10-24.

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% 8% 3 7% 5% 4 5% 4 5% 7% 39%	101314
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 40%	97513
Transparency	Day	43% 7% 13% 23% 13% 2	101102
	Night	43% 6% 12% 23% 14% 2	97395
Seeing	Day	16% 11% 29% 26% 13% 4	15780
	Night	17% 10% 32% 29% 11% 1	25591

By Month

Percentage Cloud Cover SE (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	10% 12% 6% 16% 6% 6% 5% 4 5% 5% 27%	2527
	11th to 20th	Day	12% 12% 4 12% 9% 6% 7% 5% 8% 4 21%	2530
	21st to end	Day	16% 20% 10% 11% 5% 4 3 3 3 4 20%	3117
February	1st to 10th	Day	15% 13% 5% 8% 5% 4 5% 3 4 7% 31%	1710
	11th to 20th	Day	14% 10% 3 7% 6% 5% 5% 3 5% 7% 36%	1769
	21st to end	Day	14% 12% 5% 10% 4 3 4 3 5% 5% 34%	1570
March	1st to 10th	Day	15% 13% 4 6% 4 3 3 2 5% 6% 38%	3120
	11th to 20th	Day	10% 7% 2 6% 4 4 5% 4 6% 7% 46%	3480
	21st to end	Day	21% 12% 4 10% 5% 4 5% 3 5% 6% 26%	4035
April	1st to 10th	Day	15% 12% 4 7% 6% 4 4 3 5% 6% 34%	2280
	11th to 20th	Day	16% 11% 3 7% 4 5% 4 3 4 6% 37%	2254
	21st to end	Day	20% 9% 2 7% 5% 5% 4 3 4 6% 35%	2280
May	1st to 10th	Day	16% 7% 2 7% 5% 4 5% 5% 6% 8% 35%	4168
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 3 5% 7% 41%	4399
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 44%	4824
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 4 4 6% 10% 44%	2660
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 5% 8% 46%	2660
	21st to end	Day	10% 6% 3 6% 4 5% 5% 5% 7% 7% 41%	2660
July	1st to 10th	Day	9% 7% 3 8% 6% 5% 6% 5% 6% 10% 35%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 8% 52%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 11% 41%	4813
August	1st to 10th	Day	8% 4 2 6% 5% 5% 5% 5% 7% 11% 43%	4114
	11th to 20th	Day	11% 5% 2 6% 3 5% 5% 5% 7% 9% 42%	3829
	21st to end	Day	7% 4 2 6% 4 4 4 3 6% 9% 50%	4180
September	1st to 10th	Day	12% 6% 2 5% 4 4 5% 3 5% 8% 48%	2280
	11th to 20th	Day	11% 4 2 4 4 3 4 3 5% 8% 54%	2256
	21st to end	Day	10% 5% 1 6% 4 5% 3 4 6% 7% 47%	2073
October	1st to 10th	Day	13% 6% 2 5% 3 3 3 3 5% 6% 50%	1900
	11th to 20th	Day	16% 8% 3 5% 4 4 4 3 4 6% 44%	1900
	21st to end	Day	19% 8% 2 5% 4 4 3 3 5% 6% 41%	1924
November	1st to 10th	Day	10% 8% 2 5% 4 4 4 3 5% 6% 46%	1672
	11th to 20th	Day	14% 12% 3 8% 4 3 4 4 6% 7% 36%	1709
	21st to end	Day	16% 12% 3 8% 5% 3 4 3 4 4 38%	1520
December	1st to 10th	Day	14% 14% 4 8% 6% 4 4 4 4 6% 34%	1520
	11th to 20th	Day	13% 12% 4 11% 5% 5% 4 4 6% 6% 32%	1918
	21st to end	Day	23% 19% 9% 11% 5% 3 3 3 3 4 17%	2783
January	1st to 10th	Night	14% 12% 6% 12% 5% 5% 4 3 4 5% 30%	4428
	11th to 20th	Night	13% 16% 6% 12% 6% 5% 4 4 7% 5% 22%	4440
	21st to end	Night	18% 17% 7% 11% 5% 4 4 3 4 4 23%	4534
February	1st to 10th	Night	14% 12% 4 8% 6% 4 4 3 4 5% 34%	2470
	11th to 20th	Night	12% 10% 4 7% 4 4 4 3 6% 6% 40%	2297
	21st to end	Night	15% 11% 3 8% 4 4 3 3 3 5% 40%	1884
March	1st to 10th	Night	19% 9% 3 5% 4 4 4 3 4 5% 42%	3733
	11th to 20th	Night	11% 6% 3 6% 4 4 4 2 5% 6% 48%	3495
	21st to end	Night	22% 12% 5% 11% 6% 4 3 3 4 5% 24%	3595
April	1st to 10th	Night	16% 11% 3 6% 4 4 4 3 5% 6% 40%	1900
	11th to 20th	Night	18% 9% 2 6% 4 4 4 3 4 6% 42%	1875
	21st to end	Night	17% 7% 3 8% 4 4 4 4 6% 7% 37%	1900
May	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 4 6% 7% 34%	2716
	11th to 20th	Night	13% 6% 2 6% 5% 5% 5% 3 6% 8% 41%	2506
	21st to end	Night	7% 6% 2 6% 4 4 4 4 7% 8% 48%	2743
June	1st to 10th	Night	9% 5% 2 5% 4 3 4 3 6% 8% 51%	1520
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 7% 9% 46%	1520
	21st to end	Night	10% 5% 2 6% 5% 4 5% 4 5% 7% 48%	1520
July	1st to 10th	Night	14% 5% 2 6% 5% 4 5% 4 6% 8% 40%	2530
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 9% 59%	2530
	21st to end	Night	5% 4 2 6% 5% 5% 5% 5% 6% 9% 46%	2750
August	1st to 10th	Night	5% 3 2 5% 3 4 4 3 7% 9% 55%	2823
	11th to 20th	Night	7% 4 2 6% 4 4 4 3 5% 8% 53%	3003
	21st to end	Night	6% 3 2 5% 4 3 4 3 6% 8% 55%	3476
September	1st to 10th	Night	10% 5% 1 5% 3 3 3 2 5% 7% 57%	1900
	11th to 20th	Night	9% 5% 2 5% 4 3 4 4 6% 7% 53%	1904
	21st to end	Night	9% 4 2 5% 4 4 5% 3 6% 8% 50%	2104
October	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 4 5% 55%	2280
	11th to 20th	Night	15% 7% 2 5% 4 3 4 2 3 7% 48%	2280
	21st to end	Night	17% 9% 3 6% 5% 3 4 3 4 5% 40%	2498
November	1st to 10th	Night	10% 7% 2 5% 4 2 3 3 4 6% 53%	2406
	11th to 20th	Night	14% 8% 4 6% 4 4 4 3 6% 7% 40%	2470
	21st to end	Night	16% 10% 3 7% 5% 4 3 2 4 6% 40%	2660
December	1st to 10th	Night	14% 13% 4 8% 6% 4 4 3 4 5% 36%	2660
	11th to 20th	Night	14% 13% 4 8% 5% 5% 3 4 4 6% 34%	3279
	21st to end	Night	22% 16% 6% 11% 5% 5% 4 4 4 4 19%	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	58% 8% 11% 16% 6%	2528
	11th to 20th	Day	62% 6% 11% 13% 8%	2530
	21st to end	Day	69% 4 10% 11% 6%	3117
February	1st to 10th	Day	55% 4 15% 18% 7% 1	1710
	11th to 20th	Day	48% 6% 12% 22% 10% 1	1778
	21st to end	Day	51% 6% 11% 22% 8% 2	1570
March	1st to 10th	Day	46% 6% 12% 21% 13% 2	3120
	11th to 20th	Day	35% 7% 14% 28% 15% 1	3480
	21st to end	Day	57% 9% 14% 17% 3 1	4035
April	1st to 10th	Day	50% 6% 11% 22% 11%	2280
	11th to 20th	Day	47% 6% 9% 22% 13% 2	2254
	21st to end	Day	50% 6% 10% 18% 13% 2	2280
May	1st to 10th	Day	43% 9% 13% 20% 15%	4205
	11th to 20th	Day	42% 8% 9% 29% 11%	4403
	21st to end	Day	36% 9% 12% 23% 18% 3	4837
June	1st to 10th	Day	34% 8% 15% 24% 16% 2	2660
	11th to 20th	Day	35% 6% 12% 22% 22% 3	2660
	21st to end	Day	37% 9% 14% 23% 14% 2	2660
July	1st to 10th	Day	44% 7% 12% 25% 10% 2	4371
	11th to 20th	Day	28% 6% 15% 31% 17% 2	4365
	21st to end	Day	35% 8% 19% 19% 17% 2	4662
August	1st to 10th	Day	33% 8% 17% 29% 12% 1	4099
	11th to 20th	Day	36% 8% 15% 25% 15% 1	3867
	21st to end	Day	31% 6% 13% 31% 17% 2	4179
September	1st to 10th	Day	34% 7% 10% 24% 20% 4	2280
	11th to 20th	Day	28% 5% 12% 27% 23% 3	2256
	21st to end	Day	34% 7% 11% 27% 20% 2	2073
October	1st to 10th	Day	35% 5% 10% 29% 20% 1	1900
	11th to 20th	Day	42% 4 9% 24% 19% 2	1900
	21st to end	Day	45% 5% 13% 23% 11% 3	1924
November	1st to 10th	Day	37% 6% 14% 25% 15% 3	1672
	11th to 20th	Day	47% 5% 14% 22% 11% 1	1709
	21st to end	Day	50% 5% 14% 22% 10%	1520
December	1st to 10th	Day	53% 5% 13% 20% 8% 1	1520
	11th to 20th	Day	50% 7% 13% 22% 6% 2	1915
	21st to end	Day	72% 5% 8% 10% 4	2783
January	1st to 10th	Night	55% 7% 12% 18% 8%	4428
	11th to 20th	Night	61% 4 12% 14% 9%	4440
	21st to end	Night	64% 6% 9% 14% 6% 1	4534
February	1st to 10th	Night	52% 4 12% 19% 12% 1	2470
	11th to 20th	Night	45% 5% 13% 23% 14% 1	2298
	21st to end	Night	48% 4 10% 23% 14% 2	1884
March	1st to 10th	Night	44% 6% 11% 23% 13% 2	3733
	11th to 20th	Night	34% 5% 12% 28% 17% 2	3495
	21st to end	Night	61% 8% 11% 15% 5% 1	3595
April	1st to 10th	Night	44% 6% 10% 24% 13% 2	1900
	11th to 20th	Night	44% 5% 7% 23% 17% 4	1875
	21st to end	Night	45% 7% 11% 21% 13% 3	1900
May	1st to 10th	Night	46% 9% 12% 17% 14% 2	2743
	11th to 20th	Night	38% 10% 15% 26% 12% 1	2507
	21st to end	Night	30% 9% 12% 25% 21% 2	2751
June	1st to 10th	Night	30% 8% 15% 25% 19% 3	1520
	11th to 20th	Night	32% 8% 11% 22% 23% 4	1520
	21st to end	Night	35% 8% 15% 20% 20% 3	1520
July	1st to 10th	Night	41% 7% 14% 22% 13% 3	2490
	11th to 20th	Night	23% 6% 14% 34% 22% 2	2482
	21st to end	Night	31% 9% 16% 22% 18% 4	2662
August	1st to 10th	Night	24% 7% 18% 33% 17% 2	2814
	11th to 20th	Night	29% 6% 16% 31% 17% 1	3031
	21st to end	Night	27% 6% 14% 30% 19% 4	3476
September	1st to 10th	Night	28% 5% 11% 25% 27% 4	1900
	11th to 20th	Night	29% 7% 9% 29% 21% 5%	1904
	21st to end	Night	30% 7% 12% 25% 22% 3	2104
October	1st to 10th	Night	32% 5% 11% 26% 23% 4	2280
	11th to 20th	Night	38% 5% 9% 24% 21% 3	2280
	21st to end	Night	46% 5% 10% 21% 16% 2	2498
November	1st to 10th	Night	33% 6% 12% 26% 19% 4	2406
	11th to 20th	Night	44% 4 12% 25% 14% 2	2470
	21st to end	Night	47% 4 11% 25% 13% 1	2660
December	1st to 10th	Night	51% 5% 12% 22% 9% 1	2660
	11th to 20th	Night	50% 6% 12% 24% 8% 1	3281
	21st to end	Night	67% 7% 9% 11% 5%	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	20% 18% 32% 23% 6%	270
	11th to 20th	Day	24% 21% 38% 14% 4	270
	21st to end	Day	23% 21% 36% 16% 3 1	297
February	1st to 10th	Day	22% 20% 40% 14% 4	270
	11th to 20th	Day	26% 19% 33% 17% 4 1	270
	21st to end	Day	25% 18% 44% 10% 3	225
March	1st to 10th	Day	21% 24% 34% 18% 3	270
	11th to 20th	Day	23% 19% 37% 14% 6% 1	270
	21st to end	Day	31% 18% 30% 16% 4 1	428
April	1st to 10th	Day	23% 18% 33% 19% 6% 1	460
	11th to 20th	Day	21% 18% 31% 20% 8% 2	452
	21st to end	Day	24% 16% 32% 19% 7% 2	460
May	1st to 10th	Day	20% 11% 36% 24% 7% 2	547
	11th to 20th	Day	20% 13% 29% 23% 13% 2	675
	21st to end	Day	15% 10% 28% 26% 13% 7%	734
June	1st to 10th	Day	9% 7% 27% 34% 18% 6%	680
	11th to 20th	Day	9% 5% 32% 32% 17% 5%	680
	21st to end	Day	10% 10% 32% 29% 14% 5%	680
July	1st to 10th	Day	10% 4 21% 29% 24% 13%	671
	11th to 20th	Day	9% 5% 24% 34% 19% 9%	668
	21st to end	Day	6% 2 24% 37% 25% 5%	739
August	1st to 10th	Day	6% 3 22% 38% 24% 7%	676
	11th to 20th	Day	12% 5% 19% 30% 23% 11%	543
	21st to end	Day	7% 4 21% 32% 27% 9%	539
September	1st to 10th	Day	13% 6% 19% 33% 22% 7%	490
	11th to 20th	Day	9% 4 20% 34% 23% 11%	490
	21st to end	Day	12% 10% 26% 26% 19% 6%	473
October	1st to 10th	Day	17% 9% 27% 28% 15% 5%	300
	11th to 20th	Day	18% 23% 32% 19% 8%	300
	21st to end	Day	27% 17% 32% 18% 4 1	306
November	1st to 10th	Day	12% 15% 44% 18% 8% 3	270
	11th to 20th	Day	22% 19% 34% 17% 5% 2	270
	21st to end	Day	26% 13% 40% 18% 3	270
December	1st to 10th	Day	16% 19% 39% 19% 5% 3	270
	11th to 20th	Day	17% 18% 37% 23% 5%	270
	21st to end	Day	27% 20% 39% 13% 2	297
January	1st to 10th	Night	17% 15% 39% 22% 6%	950
	11th to 20th	Night	19% 16% 37% 22% 5% 1	950
	21st to end	Night	20% 13% 36% 25% 5%	1045
February	1st to 10th	Night	22% 13% 38% 23% 4	950
	11th to 20th	Night	18% 15% 38% 26% 4	822
	21st to end	Night	23% 15% 39% 19% 3 1	628
March	1st to 10th	Night	22% 14% 37% 23% 4	760
	11th to 20th	Night	15% 14% 35% 29% 7%	585
	21st to end	Night	26% 12% 36% 22% 5%	627
April	1st to 10th	Night	21% 15% 36% 23% 4 1	570
	11th to 20th	Night	21% 15% 29% 28% 7% 1	563
	21st to end	Night	19% 11% 31% 32% 5% 1	570
May	1st to 10th	Night	18% 9% 38% 28% 6% 1	570
	11th to 20th	Night	19% 7% 32% 34% 9%	561
	21st to end	Night	12% 6% 32% 33% 16% 1	617
June	1st to 10th	Night	10% 4 27% 44% 14% 2	570
	11th to 20th	Night	9% 5% 31% 40% 15% 1	570
	21st to end	Night	10% 5% 29% 38% 16% 1	570
July	1st to 10th	Night	10% 3 15% 40% 27% 5%	555
	11th to 20th	Night	5% 2 25% 40% 25% 3	552
	21st to end	Night	6% 3 19% 42% 29% 1	624
August	1st to 10th	Night	4 4 16% 43% 29% 4	567
	11th to 20th	Night	6% 2 17% 42% 29% 5%	564
	21st to end	Night	9% 1 18% 44% 26% 3	627
September	1st to 10th	Night	12% 2 22% 38% 22% 4	570
	11th to 20th	Night	11% 3 21% 36% 24% 5%	574
	21st to end	Night	8% 9% 25% 34% 22% 2	760
October	1st to 10th	Night	12% 7% 32% 29% 19% 1	760
	11th to 20th	Night	18% 13% 30% 28% 11%	760
	21st to end	Night	23% 12% 34% 24% 7%	805
November	1st to 10th	Night	16% 9% 40% 26% 8% 1	740
	11th to 20th	Night	18% 17% 36% 24% 5%	760
	21st to end	Night	21% 13% 36% 24% 6%	950
December	1st to 10th	Night	20% 14% 38% 23% 5%	950
	11th to 20th	Night	23% 12% 34% 26% 6%	950
	21st to end	Night	27% 16% 33% 21% 3	1045

Page generated at 2024-10-21 01:20:03. Version ac07

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