Salem
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salem clear sky chart from 2005-11-06 to 2024-11-04.

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	16% 8% 3 8% 5% 4 4 3 5% 6% 38%	105421
	Night	18% 9% 3 7% 5% 4 4 3 4 6% 36%	102297
Transparency	Day	46% 7% 13% 17% 12% 4	105165
	Night	49% 7% 13% 17% 11% 3	102142
Seeing	Day	19% 7% 17% 25% 22% 10%	14682
	Night	22% 6% 16% 33% 22% 2	23600

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	35% 15% 6% 13% 6% 5% 4 3 3 3 8%	2539
	11th to 20th	Day	38% 13% 4 11% 6% 4 3 2 3 3 14%	2540
	21st to end	Day	30% 12% 5% 12% 7% 5% 5% 3 4 4 13%	3094
February	1st to 10th	Day	26% 14% 3 12% 6% 5% 6% 4 4 7% 15%	1710
	11th to 20th	Day	27% 12% 5% 10% 6% 5% 5% 3 4 5% 18%	1665
	21st to end	Day	26% 14% 5% 9% 6% 5% 4 3 4 5% 19%	1481
March	1st to 10th	Day	18% 13% 5% 11% 7% 6% 6% 4 5% 6% 17%	3316
	11th to 20th	Day	17% 9% 3 8% 6% 5% 4 4 4 5% 35%	3490
	21st to end	Day	21% 12% 5% 11% 7% 7% 6% 4 5% 6% 17%	3885
April	1st to 10th	Day	22% 12% 4 10% 6% 6% 5% 3 6% 7% 19%	2280
	11th to 20th	Day	20% 12% 3 8% 6% 5% 4 4 6% 6% 26%	2249
	21st to end	Day	18% 9% 3 9% 6% 5% 5% 5% 7% 7% 25%	2470
May	1st to 10th	Day	19% 8% 3 8% 5% 5% 5% 3 4 6% 35%	4317
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 7% 51%	4377
	21st to end	Day	17% 7% 2 7% 6% 6% 6% 5% 7% 8% 28%	4813
June	1st to 10th	Day	18% 9% 3 7% 5% 4 4 3 5% 7% 34%	2660
	11th to 20th	Day	15% 9% 3 8% 5% 5% 7% 5% 6% 8% 30%	2660
	21st to end	Day	7% 5% 2 5% 4 4 4 4 5% 6% 54%	2660
July	1st to 10th	Day	4 2 1 3 2 3 2 3 3 5% 73%	4420
	11th to 20th	Day	4 2 1 3 2 2 2 2 3 5% 76%	4420
	21st to end	Day	5% 2 1 2 2 2 2 2 3 5% 75%	4774
August	1st to 10th	Day	2 3 1 3 2 2 3 3 5% 6% 69%	4091
	11th to 20th	Day	5% 3 1 5% 4 4 4 3 6% 8% 57%	4026
	21st to end	Day	8% 5% 2 5% 3 3 4 3 4 7% 56%	4309
September	1st to 10th	Day	5% 4 1 4 3 3 3 2 6% 6% 63%	2280
	11th to 20th	Day	10% 8% 3 6% 4 4 5% 4 5% 8% 44%	2270
	21st to end	Day	14% 7% 2 6% 3 4 4 4 5% 7% 45%	2005
October	1st to 10th	Day	13% 6% 3 6% 4 5% 4 3 5% 6% 46%	3180
	11th to 20th	Day	15% 7% 3 9% 6% 5% 6% 5% 6% 8% 29%	3161
	21st to end	Day	21% 10% 4 10% 6% 6% 4 4 5% 8% 22%	3400
November	1st to 10th	Day	26% 13% 5% 13% 6% 4 4 4 5% 5% 15%	1597
	11th to 20th	Day	27% 13% 5% 10% 7% 5% 5% 3 4 5% 18%	1520
	21st to end	Day	26% 12% 5% 10% 5% 5% 4 4 4 4 21%	1520
December	1st to 10th	Day	25% 13% 6% 9% 6% 5% 3 2 4 4 22%	1520
	11th to 20th	Day	27% 12% 4 11% 6% 6% 6% 5% 6% 6% 11%	1928
	21st to end	Day	30% 16% 6% 17% 7% 4 4 3 3 3 7%	2794
January	1st to 10th	Night	30% 16% 6% 11% 6% 5% 4 2 4 4 11%	4406
	11th to 20th	Night	36% 16% 3 7% 5% 4 4 2 3 4 16%	4420
	21st to end	Night	34% 12% 4 10% 6% 4 4 3 4 4 15%	4569
February	1st to 10th	Night	24% 12% 5% 9% 7% 5% 4 4 5% 6% 18%	2470
	11th to 20th	Night	26% 10% 4 9% 5% 4 4 3 5% 4 25%	2402
	21st to end	Night	23% 14% 3 9% 6% 4 4 3 5% 6% 22%	1971
March	1st to 10th	Night	16% 13% 4 11% 7% 7% 7% 4 5% 5% 21%	3555
	11th to 20th	Night	14% 8% 3 6% 5% 5% 4 3 5% 6% 40%	3490
	21st to end	Night	21% 11% 4 11% 8% 6% 6% 4 5% 6% 19%	3767
April	1st to 10th	Night	24% 11% 4 8% 5% 5% 4 2 5% 6% 24%	1900
	11th to 20th	Night	19% 9% 3 7% 5% 4 5% 3 6% 7% 32%	1876
	21st to end	Night	19% 8% 3 9% 5% 4 4 4 6% 7% 31%	1710
May	1st to 10th	Night	18% 8% 3 7% 4 3 3 3 4 5% 41%	2645
	11th to 20th	Night	8% 5% 2 4 3 3 3 3 5% 7% 57%	2516
	21st to end	Night	13% 8% 3 6% 5% 4 5% 5% 7% 8% 38%	2762
June	1st to 10th	Night	15% 8% 2 7% 6% 5% 5% 4 6% 6% 36%	1520
	11th to 20th	Night	14% 7% 3 7% 4 5% 4 3 5% 7% 41%	1520
	21st to end	Night	5% 5% 2 5% 4 5% 3 3 4 5% 59%	1520
July	1st to 10th	Night	3 2 2 1 2 2 1 2 4 80%	2540
	11th to 20th	Night	4 2 1 2 1 2 2 2 3 4 78%	2540
	21st to end	Night	3 2 1 2 1 1 1 2 3 4 80%	2775
August	1st to 10th	Night	2 2 1 3 1 2 2 2 4 5% 76%	2848
	11th to 20th	Night	6% 4 2 4 3 4 4 3 5% 6% 59%	2812
	21st to end	Night	9% 4 2 5% 2 2 2 3 3 4 63%	3364
September	1st to 10th	Night	5% 4 1 3 2 2 3 2 4 7% 67%	1900
	11th to 20th	Night	9% 5% 2 7% 5% 4 4 3 4 6% 51%	1909
	21st to end	Night	11% 5% 1 5% 4 3 4 3 4 7% 53%	2175
October	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 4 7% 50%	3800
	11th to 20th	Night	15% 5% 3 6% 5% 5% 5% 4 6% 8% 37%	3777
	21st to end	Night	20% 8% 4 9% 6% 5% 5% 3 6% 6% 28%	4167
November	1st to 10th	Night	27% 9% 3 8% 6% 4 5% 4 6% 6% 23%	2553
	11th to 20th	Night	29% 11% 3 9% 6% 4 4 4 4 5% 22%	2660
	21st to end	Night	22% 10% 3 10% 6% 4 4 4 4 5% 27%	2660
December	1st to 10th	Night	26% 11% 4 9% 5% 4 4 3 5% 6% 24%	2660
	11th to 20th	Night	28% 11% 4 10% 7% 5% 6% 3 5% 6% 16%	3276
	21st to end	Night	26% 14% 5% 13% 8% 6% 4 3 4 4 14%	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	82% 7% 6% 4 1 1	2539
	11th to 20th	Day	78% 4 6% 8% 2 2	2540
	21st to end	Day	73% 8% 7% 7% 5%	3094
February	1st to 10th	Day	67% 10% 10% 9% 4	1710
	11th to 20th	Day	68% 9% 9% 9% 4 2	1674
	21st to end	Day	68% 7% 10% 9% 5% 2	1481
March	1st to 10th	Day	62% 10% 14% 11% 3	3316
	11th to 20th	Day	48% 9% 9% 23% 10% 1	3490
	21st to end	Day	66% 9% 13% 7% 4	3885
April	1st to 10th	Day	65% 7% 13% 12% 3	2280
	11th to 20th	Day	57% 8% 12% 12% 7% 3	2252
	21st to end	Day	56% 8% 15% 12% 7% 1	2470
May	1st to 10th	Day	49% 7% 14% 17% 12%	4317
	11th to 20th	Day	30% 8% 19% 30% 11% 1	4380
	21st to end	Day	50% 13% 21% 14% 2	4814
June	1st to 10th	Day	50% 6% 18% 19% 6% 1	2660
	11th to 20th	Day	49% 9% 21% 16% 6%	2660
	21st to end	Day	29% 6% 18% 30% 12% 4	2660
July	1st to 10th	Day	14% 4 9% 19% 23% 31%	4351
	11th to 20th	Day	13% 3 7% 19% 37% 20%	4345
	21st to end	Day	13% 3 11% 28% 37% 7%	4623
August	1st to 10th	Day	16% 4 11% 29% 27% 12%	4076
	11th to 20th	Day	23% 6% 21% 32% 15% 4	4065
	21st to end	Day	26% 6% 14% 25% 22% 7%	4308
September	1st to 10th	Day	20% 6% 13% 30% 20% 11%	2280
	11th to 20th	Day	39% 8% 14% 20% 14% 6%	2270
	21st to end	Day	39% 6% 15% 20% 14% 5%	2005
October	1st to 10th	Day	38% 6% 9% 23% 21% 3	3180
	11th to 20th	Day	49% 8% 18% 14% 11% 1	3161
	21st to end	Day	59% 7% 9% 15% 9% 1	3400
November	1st to 10th	Day	70% 8% 9% 10% 4	1597
	11th to 20th	Day	69% 7% 9% 8% 6% 2	1520
	21st to end	Day	65% 8% 8% 8% 11%	1520
December	1st to 10th	Day	65% 4 10% 10% 9% 1	1520
	11th to 20th	Day	69% 10% 10% 9% 2	1928
	21st to end	Day	78% 11% 6% 3 2	2794
January	1st to 10th	Night	78% 7% 8% 4 3 1	4406
	11th to 20th	Night	73% 5% 7% 10% 4 1	4420
	21st to end	Night	72% 8% 7% 7% 5% 1	4569
February	1st to 10th	Night	65% 10% 9% 10% 4 1	2470
	11th to 20th	Night	61% 8% 13% 11% 6% 2	2404
	21st to end	Night	62% 8% 11% 11% 5% 2	1971
March	1st to 10th	Night	61% 8% 13% 14% 4	3555
	11th to 20th	Night	41% 10% 15% 22% 10% 1	3490
	21st to end	Night	65% 9% 14% 11% 1	3767
April	1st to 10th	Night	61% 7% 14% 13% 5%	1900
	11th to 20th	Night	52% 7% 19% 14% 6% 3	1876
	21st to end	Night	54% 6% 16% 16% 6% 2	1710
May	1st to 10th	Night	45% 6% 18% 20% 9% 1	2645
	11th to 20th	Night	28% 4 21% 33% 12% 2	2516
	21st to end	Night	40% 13% 31% 12% 3	2762
June	1st to 10th	Night	46% 7% 18% 23% 5% 1	1520
	11th to 20th	Night	44% 6% 21% 22% 7%	1520
	21st to end	Night	28% 5% 18% 31% 13% 4	1520
July	1st to 10th	Night	12% 4 9% 20% 26% 28%	2500
	11th to 20th	Night	13% 3 8% 19% 34% 23%	2492
	21st to end	Night	11% 3 13% 29% 36% 8%	2688
August	1st to 10th	Night	12% 3 10% 37% 29% 9%	2839
	11th to 20th	Night	25% 6% 21% 32% 12% 4	2839
	21st to end	Night	25% 5% 14% 29% 21% 6%	3364
September	1st to 10th	Night	19% 6% 14% 30% 20% 11%	1900
	11th to 20th	Night	33% 8% 15% 23% 13% 9%	1909
	21st to end	Night	31% 7% 16% 23% 16% 8%	2175
October	1st to 10th	Night	34% 6% 9% 29% 20% 2	3800
	11th to 20th	Night	42% 7% 21% 17% 11% 2	3777
	21st to end	Night	55% 7% 12% 14% 10% 1	4167
November	1st to 10th	Night	60% 8% 11% 14% 6%	2553
	11th to 20th	Night	64% 7% 10% 9% 8% 2	2660
	21st to end	Night	58% 9% 8% 10% 12% 2	2660
December	1st to 10th	Night	61% 6% 10% 11% 10% 1	2660
	11th to 20th	Night	66% 10% 10% 10% 3	3276
	21st to end	Night	69% 11% 11% 6% 2	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	44% 8% 14% 19% 12% 3	180
	11th to 20th	Day	39% 4 18% 17% 13% 7%	180
	21st to end	Day	31% 6% 14% 24% 16% 8%	381
February	1st to 10th	Day	32% 10% 18% 17% 17% 6%	370
	11th to 20th	Day	32% 7% 26% 19% 11% 5%	365
	21st to end	Day	33% 12% 17% 23% 12% 3	341
March	1st to 10th	Day	31% 10% 20% 23% 13% 3	460
	11th to 20th	Day	26% 11% 17% 22% 19% 5%	460
	21st to end	Day	30% 10% 23% 21% 14% 2	506
April	1st to 10th	Day	28% 14% 18% 23% 12% 7%	460
	11th to 20th	Day	28% 9% 23% 23% 10% 6%	452
	21st to end	Day	22% 10% 22% 23% 18% 4	460
May	1st to 10th	Day	17% 9% 20% 27% 19% 8%	463
	11th to 20th	Day	20% 8% 16% 23% 21% 11%	488
	21st to end	Day	16% 5% 16% 25% 24% 15%	529
June	1st to 10th	Day	19% 6% 15% 28% 22% 9%	490
	11th to 20th	Day	15% 9% 22% 27% 21% 6%	490
	21st to end	Day	6% 6% 14% 31% 34% 10%	490
July	1st to 10th	Day	6% 3 14% 31% 33% 14%	486
	11th to 20th	Day	4 2 12% 35% 33% 13%	484
	21st to end	Day	4 2 9% 29% 40% 16%	531
August	1st to 10th	Day	3 3 7% 29% 38% 21%	487
	11th to 20th	Day	3 3 7% 31% 34% 23%	477
	21st to end	Day	5% 4 14% 32% 31% 14%	539
September	1st to 10th	Day	7% 2 18% 27% 33% 12%	490
	11th to 20th	Day	12% 6% 13% 26% 30% 13%	490
	21st to end	Day	15% 4 18% 30% 23% 9%	490
October	1st to 10th	Day	17% 6% 18% 27% 21% 11%	490
	11th to 20th	Day	20% 6% 15% 25% 22% 10%	490
	21st to end	Day	28% 8% 25% 21% 11% 8%	515
November	1st to 10th	Day	30% 9% 22% 22% 11% 5%	230
	11th to 20th	Day	28% 8% 22% 15% 17% 9%	180
	21st to end	Day	31% 5% 21% 17% 17% 9%	180
December	1st to 10th	Day	39% 6% 13% 18% 15% 9%	180
	11th to 20th	Day	36% 8% 19% 24% 10% 3	180
	21st to end	Day	37% 9% 18% 22% 11% 4	198
January	1st to 10th	Night	37% 9% 17% 21% 14% 2	760
	11th to 20th	Night	36% 8% 14% 23% 19% 2	760
	21st to end	Night	29% 6% 14% 29% 19% 3	836
February	1st to 10th	Night	26% 9% 17% 28% 18% 2	760
	11th to 20th	Night	29% 6% 19% 26% 19% 1	744
	21st to end	Night	30% 9% 17% 31% 12%	628
March	1st to 10th	Night	27% 8% 19% 29% 16% 1	760
	11th to 20th	Night	22% 8% 19% 33% 17% 1	760
	21st to end	Night	27% 8% 21% 29% 15% 1	836
April	1st to 10th	Night	27% 8% 17% 28% 19% 1	760
	11th to 20th	Night	22% 7% 21% 30% 18% 1	748
	21st to end	Night	23% 5% 18% 36% 17% 1	570
May	1st to 10th	Night	15% 5% 19% 42% 18% 1	446
	11th to 20th	Night	14% 4 15% 40% 25% 2	374
	21st to end	Night	16% 6% 15% 36% 26% 2	411
June	1st to 10th	Night	17% 6% 13% 40% 24% 1	380
	11th to 20th	Night	13% 5% 20% 44% 17% 1	380
	21st to end	Night	8% 2 20% 42% 28% 1	380
July	1st to 10th	Night	5% 3 8% 52% 32% 1	370
	11th to 20th	Night	4 1 16% 48% 29% 1	368
	21st to end	Night	3 2 8% 49% 36% 2	418
August	1st to 10th	Night	4 2 6% 40% 41% 7%	567
	11th to 20th	Night	5% 2 5% 37% 48% 4	564
	21st to end	Night	7% 2 10% 44% 33% 3	754
September	1st to 10th	Night	5% 3 15% 39% 36% 2	760
	11th to 20th	Night	10% 3 10% 34% 37% 5%	760
	21st to end	Night	12% 4 13% 39% 29% 3	760
October	1st to 10th	Night	15% 4 17% 34% 27% 4	760
	11th to 20th	Night	18% 5% 11% 34% 26% 5%	760
	21st to end	Night	25% 6% 18% 30% 17% 4	836
November	1st to 10th	Night	30% 6% 16% 31% 16% 1	754
	11th to 20th	Night	32% 9% 19% 25% 13% 2	760
	21st to end	Night	27% 5% 16% 32% 17% 3	760
December	1st to 10th	Night	31% 7% 13% 30% 16% 3	760
	11th to 20th	Night	34% 8% 17% 25% 15% 1	760
	21st to end	Night	34% 8% 20% 26% 11% 1	836

Page generated at 2024-11-01 19:47:49. Version ac07

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