Portage (MI)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Portage (MI) 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	13% 10% 4 8% 5% 5% 5% 4 5% 7% 34%	101203
	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 33%	97902
Transparency	Day	49% 4 11% 23% 13% 1	104802
	Night	51% 4 11% 21% 13% 1	102444
Seeing	Day	17% 13% 28% 24% 13% 4	15767
	Night	19% 10% 29% 29% 11% 1	25601

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	15% 19% 8% 13% 7% 5% 5% 3 4 5% 16%	2527
	11th to 20th	Day	14% 18% 8% 15% 9% 11% 7% 3 3 4 8%	2530
	21st to end	Day	24% 22% 9% 14% 6% 3 3 3 3 4 9%	2791
February	1st to 10th	Day	14% 15% 6% 14% 11% 6% 4 3 4 4 19%	1790
	11th to 20th	Day	14% 13% 6% 15% 9% 5% 5% 3 4 5% 21%	1848
	21st to end	Day	15% 15% 8% 13% 6% 5% 3 4 4 6% 21%	1570
March	1st to 10th	Day	15% 14% 5% 9% 5% 5% 4 3 5% 7% 28%	3120
	11th to 20th	Day	11% 8% 7% 9% 7% 6% 5% 4 6% 7% 30%	3400
	21st to end	Day	19% 13% 6% 10% 6% 5% 4 3 5% 5% 24%	3937
April	1st to 10th	Day	17% 15% 3 7% 6% 4 4 4 5% 6% 29%	2280
	11th to 20th	Day	16% 11% 3 6% 4 4 4 3 5% 6% 36%	2300
	21st to end	Day	17% 9% 4 7% 5% 4 5% 3 6% 7% 34%	2470
May	1st to 10th	Day	18% 8% 3 7% 4 4 5% 4 5% 8% 34%	4082
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 4 6% 8% 37%	4081
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 45%	4749
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 4 6% 8% 44%	2660
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 5% 6% 9% 43%	2660
	21st to end	Day	10% 7% 2 6% 6% 4 5% 5% 7% 8% 39%	2660
July	1st to 10th	Day	11% 6% 3 8% 5% 5% 5% 4 6% 10% 37%	4440
	11th to 20th	Day	8% 4 2 4 4 4 4 4 7% 11% 49%	4440
	21st to end	Day	7% 6% 2 6% 5% 5% 6% 5% 7% 9% 44%	4792
August	1st to 10th	Day	11% 5% 2 6% 4 4 5% 5% 5% 9% 44%	4104
	11th to 20th	Day	11% 6% 2 5% 5% 4 5% 4 6% 7% 46%	4044
	21st to end	Day	8% 4 2 7% 4 5% 5% 4 6% 9% 46%	4212
September	1st to 10th	Day	11% 7% 2 7% 5% 4 5% 4 5% 6% 46%	2241
	11th to 20th	Day	11% 5% 2 5% 4 3 5% 3 6% 9% 48%	2090
	21st to end	Day	12% 7% 3 7% 5% 5% 4 3 5% 9% 39%	2090
October	1st to 10th	Day	14% 7% 2 7% 5% 4 4 4 5% 6% 43%	2090
	11th to 20th	Day	18% 9% 3 9% 5% 5% 5% 4 5% 7% 30%	1875
	21st to end	Day	21% 13% 3 7% 6% 4 5% 2 5% 7% 26%	1881
November	1st to 10th	Day	12% 10% 3 8% 5% 5% 4 3 6% 6% 37%	1708
	11th to 20th	Day	16% 17% 5% 11% 6% 5% 4 4 5% 5% 24%	1710
	21st to end	Day	20% 17% 7% 9% 5% 5% 3 3 4 6% 21%	1710
December	1st to 10th	Day	15% 21% 9% 11% 6% 4 4 3 5% 4 18%	1620
	11th to 20th	Day	13% 20% 10% 14% 5% 4 4 4 5% 5% 16%	1918
	21st to end	Day	21% 24% 7% 14% 6% 4 3 2 4 6% 10%	2783
January	1st to 10th	Night	16% 19% 9% 14% 6% 4 4 3 4 4 16%	4428
	11th to 20th	Night	14% 19% 10% 16% 7% 7% 6% 3 4 4 10%	4440
	21st to end	Night	26% 17% 8% 16% 6% 5% 4 2 3 4 10%	4875
February	1st to 10th	Night	14% 18% 5% 12% 10% 6% 3 3 4 6% 20%	2389
	11th to 20th	Night	13% 15% 6% 12% 7% 6% 4 3 4 6% 24%	2218
	21st to end	Night	18% 12% 5% 11% 6% 4 5% 3 5% 6% 26%	1884
March	1st to 10th	Night	16% 11% 4 8% 5% 4 4 3 4 7% 35%	3733
	11th to 20th	Night	10% 7% 3 7% 5% 5% 4 4 5% 7% 42%	3559
	21st to end	Night	18% 11% 6% 11% 6% 4 4 3 5% 6% 27%	3722
April	1st to 10th	Night	14% 11% 3 7% 4 5% 4 3 6% 7% 35%	1900
	11th to 20th	Night	19% 9% 3 6% 5% 4 4 4 5% 5% 37%	1829
	21st to end	Night	17% 8% 3 7% 5% 3 4 4 6% 7% 38%	1710
May	1st to 10th	Night	14% 9% 3 8% 5% 4 5% 3 5% 9% 34%	2813
	11th to 20th	Night	18% 8% 2 6% 3 3 3 3 4 7% 42%	2812
	21st to end	Night	13% 6% 2 6% 5% 4 4 3 6% 8% 42%	2813
June	1st to 10th	Night	10% 4 2 4 5% 3 4 4 7% 10% 47%	1520
	11th to 20th	Night	10% 5% 2 6% 5% 4 4 4 8% 9% 44%	1520
	21st to end	Night	9% 4 2 6% 5% 4 5% 4 6% 11% 44%	1520
July	1st to 10th	Night	9% 4 2 5% 4 5% 6% 4 7% 10% 44%	2530
	11th to 20th	Night	7% 4 1 5% 4 3 3 3 5% 8% 57%	2530
	21st to end	Night	7% 6% 2 5% 4 4 5% 4 7% 9% 47%	2770
August	1st to 10th	Night	10% 5% 2 5% 4 4 5% 4 6% 9% 46%	2825
	11th to 20th	Night	10% 5% 2 6% 4 5% 4 3 6% 7% 48%	2785
	21st to end	Night	9% 6% 2 7% 4 4 4 4 6% 6% 48%	3441
September	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 6% 8% 50%	1919
	11th to 20th	Night	10% 5% 3 5% 3 3 3 3 4 7% 54%	2090
	21st to end	Night	14% 7% 3 6% 4 3 4 4 4 6% 44%	2090
October	1st to 10th	Night	15% 6% 2 6% 4 3 4 3 5% 6% 47%	2090
	11th to 20th	Night	18% 11% 3 7% 5% 5% 4 2 4 6% 36%	2302
	21st to end	Night	23% 10% 3 7% 4 4 5% 3 4 6% 32%	2717
November	1st to 10th	Night	14% 11% 4 8% 5% 4 4 3 4 6% 39%	2470
	11th to 20th	Night	16% 15% 4 11% 5% 4 5% 4 5% 6% 25%	2470
	21st to end	Night	18% 16% 5% 9% 6% 4 4 3 5% 5% 25%	2470
December	1st to 10th	Night	17% 21% 7% 12% 6% 5% 3 3 4 5% 16%	2555
	11th to 20th	Night	15% 19% 9% 14% 6% 4 4 3 4 4 18%	3279
	21st to end	Night	26% 21% 7% 11% 6% 4 4 3 4 5% 11%	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	71% 2 10% 14% 2	2528
	11th to 20th	Day	80% 2 8% 8% 2	2530
	21st to end	Day	80% 2 8% 9% 2	2791
February	1st to 10th	Day	70% 2 9% 12% 6% 1	1790
	11th to 20th	Day	65% 4 8% 16% 8% 1	1858
	21st to end	Day	64% 3 12% 14% 5% 1	1570
March	1st to 10th	Day	58% 2 11% 21% 7%	3120
	11th to 20th	Day	52% 3 11% 25% 7% 1	3400
	21st to end	Day	64% 3 9% 18% 6% 1	3937
April	1st to 10th	Day	55% 3 9% 21% 12%	2280
	11th to 20th	Day	49% 3 9% 23% 13% 2	2300
	21st to end	Day	50% 3 12% 19% 15% 2	2470
May	1st to 10th	Day	50% 3 10% 25% 13%	4120
	11th to 20th	Day	45% 2 14% 27% 11% 1	4085
	21st to end	Day	38% 3 11% 23% 24% 2	4762
June	1st to 10th	Day	37% 4 12% 28% 17% 2	2660
	11th to 20th	Day	36% 5% 13% 26% 19% 2	2660
	21st to end	Day	40% 5% 15% 22% 16% 2	2660
July	1st to 10th	Day	42% 6% 13% 21% 15% 3	4371
	11th to 20th	Day	29% 5% 14% 33% 17% 2	4365
	21st to end	Day	36% 7% 14% 19% 21% 2	4641
August	1st to 10th	Day	36% 6% 14% 27% 16% 1	4091
	11th to 20th	Day	35% 6% 11% 31% 16% 1	4083
	21st to end	Day	34% 6% 12% 30% 16% 2	4211
September	1st to 10th	Day	39% 3 14% 24% 17% 3	2241
	11th to 20th	Day	34% 4 10% 31% 20% 2	2090
	21st to end	Day	43% 4 10% 25% 17% 1	2090
October	1st to 10th	Day	30% 3 9% 40% 18% 1	3480
	11th to 20th	Day	40% 4 11% 25% 20%	3091
	21st to end	Day	49% 3 10% 26% 10% 2	3081
November	1st to 10th	Day	47% 3 12% 24% 13% 1	1708
	11th to 20th	Day	62% 4 9% 18% 6% 1	1710
	21st to end	Day	66% 3 12% 15% 5%	1710
December	1st to 10th	Day	68% 2 12% 14% 4	1620
	11th to 20th	Day	71% 3 12% 13% 2	1915
	21st to end	Day	78% 3 8% 9% 3	2783
January	1st to 10th	Night	72% 2 8% 12% 5% 1	4428
	11th to 20th	Night	77% 3 9% 8% 3	4440
	21st to end	Night	80% 2 9% 7% 2	4875
February	1st to 10th	Night	67% 3 9% 13% 6% 1	2389
	11th to 20th	Night	61% 3 8% 19% 7% 1	2219
	21st to end	Night	60% 3 11% 17% 7% 2	1884
March	1st to 10th	Night	52% 2 12% 26% 8% 1	3733
	11th to 20th	Night	40% 4 12% 25% 16% 2	3559
	21st to end	Night	59% 2 11% 18% 8% 1	3722
April	1st to 10th	Night	47% 4 11% 23% 13% 1	1900
	11th to 20th	Night	49% 3 8% 19% 18% 3	1829
	21st to end	Night	46% 4 10% 21% 16% 2	1710
May	1st to 10th	Night	49% 2 10% 25% 12% 1	2840
	11th to 20th	Night	44% 2 10% 25% 17% 1	2813
	21st to end	Night	41% 4 11% 21% 21% 2	2821
June	1st to 10th	Night	31% 4 12% 31% 19% 2	1520
	11th to 20th	Night	35% 5% 13% 26% 19% 2	1520
	21st to end	Night	35% 5% 16% 25% 17% 3	1520
July	1st to 10th	Night	34% 5% 14% 26% 14% 7%	2490
	11th to 20th	Night	26% 6% 13% 29% 25% 2	2482
	21st to end	Night	31% 6% 15% 18% 26% 3	2682
August	1st to 10th	Night	33% 6% 13% 31% 16% 1	2814
	11th to 20th	Night	34% 5% 12% 32% 16% 1	2812
	21st to end	Night	35% 6% 9% 30% 18% 2	3441
September	1st to 10th	Night	32% 4 11% 27% 21% 3	1919
	11th to 20th	Night	32% 3 7% 33% 23% 1	2090
	21st to end	Night	41% 3 9% 28% 17% 1	2090
October	1st to 10th	Night	27% 4 9% 35% 25% 1	3480
	11th to 20th	Night	41% 4 9% 24% 22%	3825
	21st to end	Night	42% 3 8% 30% 17% 1	4467
November	1st to 10th	Night	48% 4 9% 24% 14% 1	2470
	11th to 20th	Night	58% 3 12% 18% 7% 1	2470
	21st to end	Night	60% 4 12% 19% 4	2470
December	1st to 10th	Night	70% 3 9% 12% 5%	2555
	11th to 20th	Night	70% 3 10% 12% 4 1	3281
	21st to end	Night	77% 2 10% 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	23% 19% 32% 20% 6% 1	270
	11th to 20th	Day	23% 18% 40% 13% 5% 1	270
	21st to end	Day	23% 19% 32% 23% 3	297
February	1st to 10th	Day	24% 21% 30% 19% 4 1	270
	11th to 20th	Day	27% 21% 33% 17% 2	270
	21st to end	Day	24% 32% 32% 10% 2	225
March	1st to 10th	Day	19% 26% 37% 14% 4	270
	11th to 20th	Day	21% 18% 33% 20% 7% 1	406
	21st to end	Day	27% 18% 30% 18% 5% 1	506
April	1st to 10th	Day	25% 15% 33% 21% 5% 1	460
	11th to 20th	Day	25% 21% 28% 15% 8% 2	452
	21st to end	Day	25% 14% 33% 18% 10% 1	460
May	1st to 10th	Day	22% 17% 29% 22% 8% 2	463
	11th to 20th	Day	21% 12% 28% 23% 12% 5%	487
	21st to end	Day	13% 10% 28% 27% 18% 5%	685
June	1st to 10th	Day	12% 9% 31% 30% 13% 5%	680
	11th to 20th	Day	13% 9% 29% 30% 15% 4	680
	21st to end	Day	13% 11% 30% 29% 13% 4	680
July	1st to 10th	Day	8% 5% 24% 31% 22% 10%	671
	11th to 20th	Day	11% 5% 27% 28% 21% 8%	668
	21st to end	Day	8% 4 26% 32% 23% 7%	730
August	1st to 10th	Day	11% 4 20% 26% 23% 16%	486
	11th to 20th	Day	11% 4 22% 29% 26% 8%	479
	21st to end	Day	11% 5% 21% 31% 24% 9%	539
September	1st to 10th	Day	14% 7% 23% 25% 23% 9%	490
	11th to 20th	Day	8% 4 21% 25% 31% 11%	490
	21st to end	Day	16% 14% 22% 24% 17% 7%	490
October	1st to 10th	Day	16% 10% 28% 26% 15% 5%	490
	11th to 20th	Day	23% 17% 27% 26% 7%	414
	21st to end	Day	28% 17% 36% 15% 4	330
November	1st to 10th	Day	17% 19% 32% 23% 7% 1	282
	11th to 20th	Day	25% 24% 26% 19% 6%	270
	21st to end	Day	29% 16% 37% 15% 3	270
December	1st to 10th	Day	23% 31% 26% 13% 7%	270
	11th to 20th	Day	20% 23% 39% 15% 3	270
	21st to end	Day	23% 28% 33% 15% 2	297
January	1st to 10th	Night	22% 16% 34% 21% 6%	950
	11th to 20th	Night	24% 15% 35% 23% 3 1	950
	21st to end	Night	21% 12% 35% 28% 4	1036
February	1st to 10th	Night	25% 13% 37% 21% 4	760
	11th to 20th	Night	20% 16% 34% 26% 4	743
	21st to end	Night	25% 15% 37% 20% 3	628
March	1st to 10th	Night	21% 14% 33% 26% 6% 1	760
	11th to 20th	Night	17% 12% 40% 24% 6%	760
	21st to end	Night	23% 12% 32% 27% 6% 1	779
April	1st to 10th	Night	17% 14% 34% 28% 5% 1	570
	11th to 20th	Night	24% 11% 34% 25% 5% 1	563
	21st to end	Night	21% 9% 36% 27% 7%	570
May	1st to 10th	Night	19% 8% 34% 30% 8% 1	570
	11th to 20th	Night	21% 7% 27% 32% 12%	561
	21st to end	Night	14% 5% 29% 35% 17% 1	617
June	1st to 10th	Night	11% 4 26% 44% 14% 1	570
	11th to 20th	Night	12% 4 26% 41% 16%	570
	21st to end	Night	11% 3 24% 40% 20% 2	570
July	1st to 10th	Night	8% 3 19% 39% 27% 4	555
	11th to 20th	Night	8% 4 18% 40% 25% 4	552
	21st to end	Night	7% 3 15% 46% 27% 1	624
August	1st to 10th	Night	9% 2 11% 46% 27% 3	567
	11th to 20th	Night	10% 2 16% 40% 28% 4	564
	21st to end	Night	9% 3 17% 37% 29% 4	627
September	1st to 10th	Night	10% 5% 19% 38% 24% 4	589
	11th to 20th	Night	11% 3 18% 36% 28% 4	760
	21st to end	Night	16% 8% 24% 29% 18% 4	760
October	1st to 10th	Night	17% 7% 24% 33% 18% 1	760
	11th to 20th	Night	22% 12% 29% 28% 8% 1	760
	21st to end	Night	28% 13% 31% 22% 6%	836
November	1st to 10th	Night	21% 13% 30% 26% 9%	760
	11th to 20th	Night	23% 17% 32% 23% 4 1	760
	21st to end	Night	24% 11% 36% 24% 4	760
December	1st to 10th	Night	26% 16% 34% 19% 4	845
	11th to 20th	Night	25% 13% 38% 21% 3	950
	21st to end	Night	31% 16% 33% 18% 1	1045

Page generated at 2024-11-03 02:11:27. Version ac07

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