Grand Haven
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Haven 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% 4 4 3 5% 7% 36%	101284
	Night	15% 13% 5% 10% 5% 4 4 3 4 6% 31%	97814
Transparency	Day	47% 6% 12% 22% 12% 1	104842
	Night	53% 5% 10% 19% 11% 1	102384
Seeing	Day	16% 9% 25% 30% 15% 4	15849
	Night	20% 9% 26% 29% 14% 2	25701

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% 26% 12% 15% 7% 6% 3 3 2 3 8%	2527
	11th to 20th	Day	13% 18% 9% 17% 17% 8% 3 3 3 3 6%	2530
	21st to end	Day	19% 25% 7% 20% 7% 5% 3 2 2 2 8%	2783
February	1st to 10th	Day	11% 17% 6% 16% 11% 7% 4 3 4 4 16%	1728
	11th to 20th	Day	12% 16% 6% 15% 10% 6% 5% 3 4 5% 19%	1848
	21st to end	Day	15% 16% 5% 11% 6% 5% 6% 4 6% 5% 21%	1570
March	1st to 10th	Day	13% 11% 5% 9% 6% 5% 5% 3 5% 6% 32%	3120
	11th to 20th	Day	11% 8% 5% 11% 6% 5% 4 4 4 6% 36%	3342
	21st to end	Day	20% 11% 7% 8% 4 4 4 3 5% 6% 29%	4025
April	1st to 10th	Day	18% 11% 4 9% 4 4 3 3 5% 7% 32%	2280
	11th to 20th	Day	17% 9% 3 7% 4 3 4 4 5% 6% 37%	2285
	21st to end	Day	16% 8% 3 7% 5% 4 4 3 6% 7% 37%	2470
May	1st to 10th	Day	15% 6% 3 6% 4 4 4 3 6% 8% 41%	4082
	11th to 20th	Day	13% 7% 3 5% 4 4 4 3 6% 9% 43%	4167
	21st to end	Day	9% 7% 2 5% 4 4 4 4 6% 8% 48%	4824
June	1st to 10th	Day	9% 6% 2 6% 4 5% 4 4 6% 9% 47%	2660
	11th to 20th	Day	11% 5% 1 5% 3 4 4 4 5% 10% 48%	2660
	21st to end	Day	10% 5% 2 5% 4 4 4 3 6% 9% 46%	2660
July	1st to 10th	Day	11% 8% 3 6% 5% 4 4 4 6% 8% 41%	4440
	11th to 20th	Day	5% 3 1 4 4 4 3 4 6% 9% 56%	4440
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 48%	4813
August	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 44%	4209
	11th to 20th	Day	11% 4 2 6% 3 3 4 4 6% 7% 51%	4028
	21st to end	Day	8% 5% 3 6% 4 4 4 3 6% 8% 48%	4180
September	1st to 10th	Day	10% 6% 3 6% 4 4 4 4 6% 8% 47%	2275
	11th to 20th	Day	11% 4 2 4 5% 4 4 4 6% 7% 48%	2090
	21st to end	Day	12% 6% 3 7% 4 4 4 4 6% 8% 42%	2090
October	1st to 10th	Day	16% 7% 3 7% 4 4 4 2 5% 5% 44%	2090
	11th to 20th	Day	22% 11% 3 8% 5% 5% 5% 4 4 7% 25%	1837
	21st to end	Day	23% 12% 4 9% 5% 4 5% 4 5% 7% 23%	1881
November	1st to 10th	Day	15% 14% 4 8% 4 4 5% 4 5% 5% 33%	1708
	11th to 20th	Day	17% 25% 5% 9% 5% 4 3 3 4 5% 21%	1710
	21st to end	Day	22% 21% 6% 9% 5% 4 4 2 3 5% 20%	1710
December	1st to 10th	Day	14% 28% 11% 15% 5% 3 3 2 3 4 12%	1521
	11th to 20th	Day	15% 24% 10% 15% 6% 4 5% 3 4 4 10%	1918
	21st to end	Day	21% 25% 9% 14% 6% 4 3 2 4 4 9%	2783
January	1st to 10th	Night	15% 27% 10% 14% 8% 4 3 2 3 3 11%	4428
	11th to 20th	Night	14% 21% 10% 19% 12% 6% 3 2 3 2 8%	4440
	21st to end	Night	21% 22% 9% 16% 7% 5% 4 2 3 3 8%	4884
February	1st to 10th	Night	12% 20% 5% 16% 10% 7% 3 3 3 3 18%	2446
	11th to 20th	Night	14% 16% 6% 15% 8% 5% 4 3 4 4 21%	2218
	21st to end	Night	16% 17% 5% 11% 6% 5% 4 3 4 5% 24%	1884
March	1st to 10th	Night	16% 9% 4 8% 5% 5% 4 3 5% 6% 36%	3733
	11th to 20th	Night	9% 7% 3 9% 5% 4 4 3 6% 6% 42%	3618
	21st to end	Night	17% 12% 5% 12% 6% 5% 4 3 4 6% 27%	3636
April	1st to 10th	Night	16% 11% 3 7% 5% 4 4 4 5% 6% 34%	1900
	11th to 20th	Night	20% 9% 3 6% 4 5% 4 4 4 5% 35%	1843
	21st to end	Night	16% 8% 3 6% 4 4 4 4 5% 7% 38%	1710
May	1st to 10th	Night	14% 8% 4 9% 5% 5% 4 4 5% 7% 35%	2813
	11th to 20th	Night	16% 6% 3 7% 4 4 4 4 6% 9% 36%	2725
	21st to end	Night	15% 8% 3 7% 5% 5% 4 3 4 6% 41%	2743
June	1st to 10th	Night	10% 6% 2 6% 5% 4 5% 5% 7% 8% 43%	1520
	11th to 20th	Night	9% 5% 2 7% 5% 4 3 4 6% 10% 44%	1520
	21st to end	Night	9% 5% 3 6% 5% 4 4 5% 6% 9% 45%	1520
July	1st to 10th	Night	10% 7% 3 7% 5% 5% 5% 4 6% 9% 40%	2530
	11th to 20th	Night	5% 4 1 4 4 4 4 4 6% 8% 55%	2530
	21st to end	Night	7% 6% 2 7% 4 4 4 3 5% 8% 50%	2750
August	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 6% 8% 48%	2721
	11th to 20th	Night	11% 5% 1 6% 4 4 3 4 5% 7% 50%	2785
	21st to end	Night	8% 6% 2 7% 5% 4 4 4 6% 8% 46%	3476
September	1st to 10th	Night	9% 5% 2 6% 4 4 5% 3 5% 7% 50%	1900
	11th to 20th	Night	11% 4 2 4 3 3 4 4 4 6% 55%	2076
	21st to end	Night	13% 6% 3 7% 5% 5% 5% 3 5% 7% 41%	2090
October	1st to 10th	Night	18% 6% 2 6% 3 3 3 3 4 6% 46%	2090
	11th to 20th	Night	24% 11% 3 7% 3 3 4 2 4 6% 33%	2340
	21st to end	Night	26% 10% 3 7% 4 4 4 3 4 6% 29%	2717
November	1st to 10th	Night	18% 13% 3 7% 5% 4 4 3 4 6% 34%	2470
	11th to 20th	Night	19% 21% 5% 11% 5% 3 3 4 5% 6% 19%	2470
	21st to end	Night	20% 21% 6% 10% 5% 4 3 2 4 5% 21%	2470
December	1st to 10th	Night	18% 28% 8% 12% 5% 3 3 2 3 4 13%	2655
	11th to 20th	Night	16% 24% 9% 13% 6% 4 4 3 4 4 13%	3279
	21st to end	Night	25% 23% 7% 11% 5% 4 3 3 4 4 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	81% 5% 6% 6% 1	2528
	11th to 20th	Day	85% 5% 6% 3 1	2530
	21st to end	Day	84% 4 7% 4 2	2783
February	1st to 10th	Day	71% 5% 7% 14% 3	1728
	11th to 20th	Day	67% 5% 9% 14% 6%	1858
	21st to end	Day	62% 5% 14% 14% 5%	1570
March	1st to 10th	Day	52% 4 14% 21% 8%	3120
	11th to 20th	Day	49% 4 16% 19% 10% 1	3342
	21st to end	Day	57% 3 11% 20% 7% 1	4025
April	1st to 10th	Day	52% 5% 11% 20% 11%	2280
	11th to 20th	Day	46% 5% 11% 21% 14% 2	2285
	21st to end	Day	46% 5% 14% 20% 14% 2	2470
May	1st to 10th	Day	41% 6% 11% 26% 15% 1	4120
	11th to 20th	Day	38% 8% 13% 23% 15% 3	4171
	21st to end	Day	33% 6% 13% 25% 22% 2	4837
June	1st to 10th	Day	34% 6% 13% 29% 17% 2	2660
	11th to 20th	Day	31% 7% 15% 24% 22% 1	2660
	21st to end	Day	34% 7% 16% 25% 17% 2	2660
July	1st to 10th	Day	41% 6% 13% 24% 14% 3	4371
	11th to 20th	Day	23% 6% 16% 34% 19% 2	4365
	21st to end	Day	29% 7% 17% 23% 21% 2	4662
August	1st to 10th	Day	35% 6% 13% 32% 13% 1	4194
	11th to 20th	Day	30% 8% 13% 32% 16% 1	4067
	21st to end	Day	32% 6% 15% 28% 17% 2	4179
September	1st to 10th	Day	34% 6% 15% 28% 15% 2	2275
	11th to 20th	Day	33% 5% 12% 32% 16% 2	2090
	21st to end	Day	40% 6% 12% 26% 15%	2090
October	1st to 10th	Day	29% 4 9% 39% 18% 1	3480
	11th to 20th	Day	44% 6% 13% 25% 13%	3014
	21st to end	Day	52% 5% 15% 20% 8%	3081
November	1st to 10th	Day	51% 6% 11% 21% 10%	1708
	11th to 20th	Day	67% 5% 10% 13% 4	1710
	21st to end	Day	68% 4 12% 12% 4	1710
December	1st to 10th	Day	78% 5% 7% 8% 2	1521
	11th to 20th	Day	77% 6% 9% 6% 1	1915
	21st to end	Day	80% 4 8% 7% 1	2783
January	1st to 10th	Night	79% 5% 6% 7% 2	4428
	11th to 20th	Night	85% 4 5% 4 2	4440
	21st to end	Night	84% 4 7% 4 1	4884
February	1st to 10th	Night	72% 3 8% 12% 5%	2446
	11th to 20th	Night	68% 5% 6% 15% 6%	2219
	21st to end	Night	63% 4 11% 13% 7% 1	1884
March	1st to 10th	Night	50% 4 13% 25% 7%	3733
	11th to 20th	Night	40% 6% 13% 26% 13% 2	3618
	21st to end	Night	59% 4 9% 18% 8% 1	3636
April	1st to 10th	Night	49% 6% 10% 21% 13% 1	1900
	11th to 20th	Night	50% 4 7% 18% 18% 3	1843
	21st to end	Night	46% 5% 11% 20% 15% 4	1710
May	1st to 10th	Night	48% 5% 10% 20% 15% 2	2840
	11th to 20th	Night	45% 6% 8% 23% 15% 4	2726
	21st to end	Night	45% 4 9% 18% 20% 3	2751
June	1st to 10th	Night	35% 7% 10% 29% 17% 3	1520
	11th to 20th	Night	36% 5% 12% 25% 20% 2	1520
	21st to end	Night	36% 7% 14% 24% 16% 3	1520
July	1st to 10th	Night	40% 5% 11% 24% 13% 7%	2490
	11th to 20th	Night	26% 5% 13% 28% 24% 2	2482
	21st to end	Night	33% 6% 12% 21% 26% 3	2662
August	1st to 10th	Night	32% 6% 13% 28% 19% 1	2712
	11th to 20th	Night	33% 6% 10% 32% 18% 1	2812
	21st to end	Night	35% 7% 10% 25% 21% 2	3476
September	1st to 10th	Night	34% 6% 11% 27% 19% 2	1900
	11th to 20th	Night	30% 5% 10% 34% 19% 2	2076
	21st to end	Night	42% 7% 11% 27% 13% 1	2090
October	1st to 10th	Night	31% 4 8% 34% 21% 2	3480
	11th to 20th	Night	41% 5% 13% 25% 16%	3889
	21st to end	Night	46% 5% 9% 26% 13%	4467
November	1st to 10th	Night	51% 7% 9% 21% 11% 1	2470
	11th to 20th	Night	65% 5% 10% 13% 5% 1	2470
	21st to end	Night	67% 4 13% 14% 2	2470
December	1st to 10th	Night	77% 4 7% 8% 3	2655
	11th to 20th	Night	74% 6% 10% 7% 3	3281
	21st to end	Night	78% 4 10% 6% 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	21% 13% 34% 26% 4 2	270
	11th to 20th	Day	23% 16% 31% 22% 7% 1	270
	21st to end	Day	26% 12% 32% 25% 4 1	297
February	1st to 10th	Day	17% 19% 34% 21% 7% 2	270
	11th to 20th	Day	19% 17% 38% 20% 6%	270
	21st to end	Day	20% 17% 40% 18% 4	225
March	1st to 10th	Day	17% 18% 40% 19% 5%	270
	11th to 20th	Day	17% 16% 31% 25% 11% 1	374
	21st to end	Day	25% 11% 27% 28% 8% 1	506
April	1st to 10th	Day	22% 11% 31% 27% 8%	460
	11th to 20th	Day	20% 17% 28% 24% 8% 3	452
	21st to end	Day	22% 10% 26% 29% 12% 1	460
May	1st to 10th	Day	20% 10% 27% 32% 10% 1	463
	11th to 20th	Day	18% 6% 23% 34% 15% 4	534
	21st to end	Day	14% 4 22% 32% 23% 5%	734
June	1st to 10th	Day	10% 5% 23% 41% 17% 4	680
	11th to 20th	Day	14% 5% 23% 35% 20% 4	680
	21st to end	Day	11% 7% 25% 39% 14% 4	680
July	1st to 10th	Day	7% 3 20% 35% 26% 8%	671
	11th to 20th	Day	7% 4 22% 38% 22% 6%	668
	21st to end	Day	8% 2 18% 44% 22% 5%	739
August	1st to 10th	Day	11% 3 16% 32% 29% 9%	553
	11th to 20th	Day	11% 4 15% 33% 26% 11%	479
	21st to end	Day	12% 4 15% 32% 28% 9%	539
September	1st to 10th	Day	13% 5% 19% 32% 23% 9%	490
	11th to 20th	Day	9% 4 15% 27% 32% 13%	490
	21st to end	Day	15% 7% 23% 25% 21% 9%	490
October	1st to 10th	Day	18% 8% 24% 26% 17% 6%	490
	11th to 20th	Day	26% 16% 24% 28% 6%	356
	21st to end	Day	33% 11% 29% 21% 5% 2	330
November	1st to 10th	Day	22% 18% 26% 24% 8% 2	282
	11th to 20th	Day	24% 23% 31% 19% 3	270
	21st to end	Day	27% 16% 37% 16% 4	270
December	1st to 10th	Day	26% 23% 27% 18% 6%	270
	11th to 20th	Day	20% 23% 32% 19% 5% 1	270
	21st to end	Day	28% 20% 34% 15% 3	297
January	1st to 10th	Night	23% 16% 31% 22% 7% 1	950
	11th to 20th	Night	26% 14% 33% 21% 6% 1	950
	21st to end	Night	22% 11% 33% 28% 6%	1045
February	1st to 10th	Night	21% 14% 34% 25% 6% 1	831
	11th to 20th	Night	22% 12% 33% 26% 7%	743
	21st to end	Night	25% 13% 34% 24% 3	628
March	1st to 10th	Night	20% 9% 30% 32% 9% 1	760
	11th to 20th	Night	16% 10% 32% 31% 9% 1	760
	21st to end	Night	22% 8% 27% 31% 12%	732
April	1st to 10th	Night	19% 9% 31% 32% 8% 1	570
	11th to 20th	Night	26% 9% 25% 31% 10% 1	563
	21st to end	Night	20% 6% 28% 34% 11% 1	570
May	1st to 10th	Night	19% 5% 24% 38% 13% 1	570
	11th to 20th	Night	19% 4 23% 33% 20% 1	561
	21st to end	Night	15% 3 19% 34% 24% 4	617
June	1st to 10th	Night	12% 3 21% 40% 22% 2	570
	11th to 20th	Night	12% 2 24% 36% 24% 2	570
	21st to end	Night	10% 4 18% 39% 26% 3	570
July	1st to 10th	Night	9% 2 13% 35% 36% 5%	555
	11th to 20th	Night	8% 2 16% 38% 32% 4	552
	21st to end	Night	8% 2 14% 40% 34% 3	624
August	1st to 10th	Night	9% 2 13% 39% 32% 6%	567
	11th to 20th	Night	12% 3 10% 37% 32% 7%	564
	21st to end	Night	11% 3 12% 39% 30% 4	627
September	1st to 10th	Night	12% 3 16% 38% 24% 6%	570
	11th to 20th	Night	11% 4 15% 34% 30% 6%	746
	21st to end	Night	15% 7% 21% 28% 23% 6%	760
October	1st to 10th	Night	21% 5% 20% 32% 20% 3	760
	11th to 20th	Night	28% 11% 24% 25% 10% 1	760
	21st to end	Night	30% 12% 28% 22% 7% 1	836
November	1st to 10th	Night	24% 11% 27% 26% 11% 1	760
	11th to 20th	Night	30% 15% 30% 19% 5% 1	760
	21st to end	Night	29% 14% 29% 24% 4	760
December	1st to 10th	Night	28% 16% 30% 21% 5%	945
	11th to 20th	Night	27% 14% 35% 19% 4 1	950
	21st to end	Night	32% 15% 32% 20% 2	1045

Page generated at 2024-11-03 02:11:08. Version ac07

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