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 2024-05-10.

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	14% 10% 5% 8% 6% 3 4 4 5% 7% 34%	83380
	Night	16% 13% 5% 9% 7% 3 4 4 4 6% 29%	86120
Transparency	Day	51% 5% 12% 20% 11% 1	83081
	Night	57% 5% 10% 18% 9% 1	85940
Seeing	Day	17% 9% 25% 30% 16% 4	15078
	Night	20% 9% 26% 29% 14% 2	25107

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% 25% 12% 13% 9% 4 4 3 2 3 9%	2527
	11th to 20th	Day	14% 17% 10% 15% 19% 6% 4 3 3 3 6%	2530
	21st to end	Day	19% 23% 8% 18% 9% 4 4 3 2 2 8%	2783
February	1st to 10th	Day	12% 15% 8% 13% 13% 5% 5% 4 4 4 16%	1728
	11th to 20th	Day	12% 14% 7% 13% 11% 5% 6% 4 4 5% 19%	1848
	21st to end	Day	15% 14% 6% 10% 8% 4 5% 5% 6% 5% 21%	1570
March	1st to 10th	Day	14% 10% 5% 8% 6% 4 5% 4 5% 6% 32%	3120
	11th to 20th	Day	11% 8% 5% 10% 7% 4 4 4 4 6% 36%	3342
	21st to end	Day	20% 11% 7% 7% 5% 3 4 4 5% 5% 29%	4025
April	1st to 10th	Day	18% 10% 5% 8% 5% 3 4 4 5% 7% 32%	2280
	11th to 20th	Day	17% 9% 3 6% 5% 2 4 4 5% 7% 37%	2285
	21st to end	Day	16% 7% 3 6% 6% 3 4 4 5% 7% 37%	2470
May	1st to 10th	Day	15% 7% 3 5% 5% 3 5% 4 6% 8% 39%	2457
	11th to 20th	Day	17% 6% 3 5% 4 4 4 4 5% 7% 41%	2345
	21st to end	Day	10% 6% 2 4 5% 3 4 5% 5% 8% 46%	2725
June	1st to 10th	Day	10% 5% 2 5% 5% 3 4 5% 6% 9% 47%	2520
	11th to 20th	Day	11% 4 2 4 4 3 4 5% 5% 10% 49%	2520
	21st to end	Day	10% 5% 2 5% 4 3 4 5% 6% 10% 47%	2520
July	1st to 10th	Day	5% 4 2 3 4 3 4 4 5% 9% 57%	2520
	11th to 20th	Day	8% 4 2 3 5% 2 4 4 6% 9% 53%	2520
	21st to end	Day	7% 3 2 4 4 2 5% 5% 7% 9% 51%	2743
August	1st to 10th	Day	9% 4 2 4 4 3 4 5% 6% 9% 49%	2391
	11th to 20th	Day	10% 3 2 5% 4 3 3 5% 6% 8% 50%	2301
	21st to end	Day	9% 5% 2 5% 4 2 4 4 6% 9% 49%	2376
September	1st to 10th	Day	10% 6% 3 5% 5% 3 4 5% 6% 8% 46%	2156
	11th to 20th	Day	12% 4 2 4 6% 3 4 5% 6% 7% 47%	1980
	21st to end	Day	12% 6% 3 7% 5% 3 4 5% 6% 8% 41%	1980
October	1st to 10th	Day	17% 7% 3 6% 5% 3 4 4 5% 5% 42%	1980
	11th to 20th	Day	24% 11% 4 7% 7% 4 5% 5% 4 6% 24%	1742
	21st to end	Day	25% 11% 4 9% 6% 4 4 5% 4 7% 22%	1782
November	1st to 10th	Day	15% 13% 4 7% 5% 3 5% 4 5% 5% 34%	1672
	11th to 20th	Day	18% 23% 6% 8% 5% 3 4 4 4 5% 21%	1710
	21st to end	Day	22% 19% 7% 8% 6% 3 4 3 3 5% 20%	1710
December	1st to 10th	Day	14% 25% 14% 14% 5% 2 3 3 3 4 12%	1521
	11th to 20th	Day	16% 22% 11% 13% 8% 4 4 4 4 4 10%	1918
	21st to end	Day	21% 24% 10% 12% 7% 3 4 3 4 4 9%	2783
January	1st to 10th	Night	15% 25% 11% 13% 9% 3 4 3 3 3 11%	4428
	11th to 20th	Night	15% 20% 11% 17% 15% 6% 3 3 2 2 8%	4440
	21st to end	Night	21% 21% 10% 14% 9% 4 4 3 2 3 8%	4884
February	1st to 10th	Night	13% 18% 7% 14% 11% 6% 4 3 4 3 18%	2446
	11th to 20th	Night	14% 14% 7% 14% 9% 4 5% 4 4 4 21%	2218
	21st to end	Night	17% 15% 6% 9% 7% 4 5% 4 4 5% 24%	1884
March	1st to 10th	Night	16% 8% 4 7% 6% 4 4 4 5% 6% 36%	3733
	11th to 20th	Night	10% 6% 3 8% 7% 3 5% 4 6% 6% 42%	3618
	21st to end	Night	17% 11% 5% 11% 7% 4 4 4 4 6% 27%	3636
April	1st to 10th	Night	16% 9% 3 7% 5% 3 5% 5% 6% 6% 34%	1900
	11th to 20th	Night	20% 8% 3 6% 4 3 5% 5% 4 6% 35%	1843
	21st to end	Night	17% 8% 3 6% 5% 3 4 5% 5% 7% 38%	1710
May	1st to 10th	Night	16% 6% 4 8% 6% 3 5% 5% 5% 7% 34%	1707
	11th to 20th	Night	17% 4 3 6% 4 3 4 5% 6% 9% 38%	1544
	21st to end	Night	12% 7% 3 5% 7% 5% 5% 4 5% 7% 41%	1551
June	1st to 10th	Night	10% 5% 2 5% 5% 2 5% 5% 8% 9% 44%	1440
	11th to 20th	Night	10% 5% 3 6% 5% 2 3 4 6% 10% 45%	1440
	21st to end	Night	9% 5% 3 6% 5% 3 5% 5% 6% 9% 45%	1440
July	1st to 10th	Night	7% 4 2 4 4 3 5% 5% 5% 10% 52%	1440
	11th to 20th	Night	6% 4 2 3 5% 3 5% 5% 7% 9% 50%	1440
	21st to end	Night	8% 5% 2 4 4 3 5% 4 5% 9% 51%	1575
August	1st to 10th	Night	8% 4 2 4 4 3 4 5% 6% 9% 50%	1545
	11th to 20th	Night	10% 4 1 5% 4 3 5% 5% 6% 9% 50%	1598
	21st to end	Night	10% 5% 3 5% 5% 2 3 4 5% 7% 50%	1980
September	1st to 10th	Night	10% 5% 2 5% 4 3 5% 5% 5% 7% 48%	1800
	11th to 20th	Night	11% 4 2 4 4 2 4 4 4 6% 55%	1966
	21st to end	Night	13% 6% 3 6% 6% 4 5% 4 4 8% 41%	1980
October	1st to 10th	Night	19% 6% 2 5% 4 3 3 3 4 7% 44%	1980
	11th to 20th	Night	25% 11% 3 6% 5% 3 3 3 4 5% 32%	2216
	21st to end	Night	27% 10% 3 6% 5% 3 4 4 4 6% 28%	2574
November	1st to 10th	Night	17% 12% 3 6% 5% 3 4 3 4 6% 35%	2406
	11th to 20th	Night	19% 20% 5% 10% 5% 3 3 4 5% 6% 20%	2470
	21st to end	Night	21% 19% 6% 9% 6% 3 3 3 4 5% 21%	2470
December	1st to 10th	Night	18% 23% 12% 11% 6% 2 4 3 3 4 13%	2655
	11th to 20th	Night	16% 22% 11% 11% 8% 3 4 4 4 4 13%	3279
	21st to end	Night	25% 23% 8% 10% 6% 3 3 4 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	43% 6% 12% 26% 12% 1	2457
	11th to 20th	Day	43% 5% 13% 22% 15% 2	2349
	21st to end	Day	36% 6% 14% 28% 14% 2	2725
June	1st to 10th	Day	33% 6% 13% 29% 17% 2	2520
	11th to 20th	Day	32% 7% 15% 24% 22% 1	2520
	21st to end	Day	33% 7% 17% 25% 17% 2	2520
July	1st to 10th	Day	25% 6% 14% 34% 17% 4	2451
	11th to 20th	Day	28% 6% 14% 31% 19% 3	2445
	21st to end	Day	28% 6% 15% 29% 19% 3	2591
August	1st to 10th	Day	31% 5% 15% 34% 13% 2	2376
	11th to 20th	Day	30% 7% 16% 30% 15% 2	2301
	21st to end	Day	31% 6% 14% 29% 18% 3	2376
September	1st to 10th	Day	36% 6% 15% 26% 14% 2	2156
	11th to 20th	Day	35% 6% 13% 33% 13% 2	1980
	21st to end	Day	40% 6% 12% 27% 14%	1980
October	1st to 10th	Day	45% 5% 9% 27% 14% 1	1980
	11th to 20th	Day	59% 6% 13% 15% 6%	1742
	21st to end	Day	63% 5% 11% 15% 6% 1	1782
November	1st to 10th	Day	51% 6% 11% 21% 10%	1672
	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	50% 4 11% 21% 13% 2	1707
	11th to 20th	Night	44% 6% 10% 20% 17% 4	1545
	21st to end	Night	43% 5% 11% 24% 15% 2	1552
June	1st to 10th	Night	35% 7% 10% 29% 17% 3	1440
	11th to 20th	Night	35% 5% 12% 25% 20% 2	1440
	21st to end	Night	36% 7% 14% 25% 16% 3	1440
July	1st to 10th	Night	29% 5% 12% 29% 21% 4	1400
	11th to 20th	Night	29% 5% 14% 28% 22% 3	1392
	21st to end	Night	30% 6% 13% 27% 20% 4	1487
August	1st to 10th	Night	29% 6% 16% 30% 17% 2	1536
	11th to 20th	Night	31% 7% 12% 32% 16% 2	1598
	21st to end	Night	32% 6% 11% 27% 21% 3	1980
September	1st to 10th	Night	35% 7% 11% 27% 18% 2	1800
	11th to 20th	Night	31% 5% 10% 35% 17% 2	1966
	21st to end	Night	41% 7% 11% 28% 12% 1	1980
October	1st to 10th	Night	42% 4 8% 29% 16% 1	1980
	11th to 20th	Night	55% 4 12% 19% 9% 1	2216
	21st to end	Night	58% 6% 11% 16% 8%	2574
November	1st to 10th	Night	51% 7% 9% 21% 11% 1	2406
	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% 31% 10% 1	459
	11th to 20th	Day	19% 6% 23% 34% 15% 4	491
	21st to end	Day	14% 4 22% 31% 23% 5%	679
June	1st to 10th	Day	10% 5% 22% 41% 17% 4	630
	11th to 20th	Day	14% 4 20% 36% 21% 4	630
	21st to end	Day	11% 4 25% 41% 15% 4	630
July	1st to 10th	Day	6% 2 18% 37% 28% 9%	621
	11th to 20th	Day	7% 4 21% 39% 23% 6%	618
	21st to end	Day	8% 1 18% 45% 23% 5%	684
August	1st to 10th	Day	10% 2 14% 33% 31% 10%	510
	11th to 20th	Day	11% 3 13% 33% 28% 12%	439
	21st to end	Day	12% 4 14% 33% 28% 9%	495
September	1st to 10th	Day	14% 4 17% 33% 23% 9%	450
	11th to 20th	Day	10% 4 16% 26% 31% 13%	450
	21st to end	Day	15% 7% 22% 25% 21% 10%	450
October	1st to 10th	Day	19% 7% 24% 25% 18% 7%	450
	11th to 20th	Day	28% 16% 21% 27% 6%	324
	21st to end	Day	33% 9% 29% 21% 5% 2	297
November	1st to 10th	Day	20% 18% 27% 24% 8% 3	270
	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	20% 5% 23% 38% 13% 1	569
	11th to 20th	Night	20% 4 23% 33% 20% 1	531
	21st to end	Night	15% 3 19% 34% 24% 5%	584
June	1st to 10th	Night	12% 3 19% 40% 23% 3	540
	11th to 20th	Night	12% 2 21% 37% 25% 2	540
	21st to end	Night	10% 3 17% 40% 27% 3	540
July	1st to 10th	Night	8% 2 11% 34% 38% 6%	525
	11th to 20th	Night	7% 2 15% 39% 32% 4	522
	21st to end	Night	8% 2 14% 40% 33% 3	591
August	1st to 10th	Night	9% 1 12% 39% 32% 6%	537
	11th to 20th	Night	11% 2 9% 37% 34% 7%	534
	21st to end	Night	11% 3 12% 39% 30% 5%	594
September	1st to 10th	Night	12% 3 16% 39% 24% 6%	540
	11th to 20th	Night	12% 4 16% 32% 29% 7%	706
	21st to end	Night	15% 7% 21% 27% 24% 6%	720
October	1st to 10th	Night	22% 4 19% 31% 20% 3	720
	11th to 20th	Night	29% 11% 24% 25% 10% 1	720
	21st to end	Night	32% 11% 28% 21% 7% 1	792
November	1st to 10th	Night	23% 12% 27% 26% 11% 1	740
	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 2024-05-07 07:25:00. Version ac07

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