Ypsilanti
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ypsilanti 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	14% 9% 3 8% 5% 5% 5% 4 6% 8% 34%	100856
	Night	15% 10% 4 8% 5% 4 4 4 5% 7% 35%	98161
Transparency	Day	45% 8% 13% 20% 12% 1	104471
	Night	46% 7% 12% 21% 13% 1	102686
Seeing	Day	17% 11% 28% 24% 14% 6%	15490
	Night	19% 9% 29% 30% 13% 1	25468

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% 18% 6% 11% 5% 6% 4 4 5% 5% 21%	2527
	11th to 20th	Day	16% 18% 7% 12% 7% 7% 7% 4 6% 6% 11%	2530
	21st to end	Day	27% 20% 7% 12% 5% 4 3 2 3 3 13%	3067
February	1st to 10th	Day	14% 15% 5% 10% 8% 6% 5% 4 6% 5% 22%	1710
	11th to 20th	Day	14% 11% 4 13% 8% 6% 5% 4 4 6% 25%	1811
	21st to end	Day	15% 16% 4 10% 6% 4 4 3 5% 6% 27%	1570
March	1st to 10th	Day	18% 16% 5% 9% 6% 5% 3 3 5% 6% 26%	3179
	11th to 20th	Day	13% 10% 4 9% 6% 5% 4 3 5% 7% 33%	3480
	21st to end	Day	19% 12% 4 10% 5% 5% 4 4 5% 6% 26%	3815
April	1st to 10th	Day	16% 11% 4 8% 5% 5% 4 4 5% 7% 31%	2219
	11th to 20th	Day	17% 9% 3 8% 4 5% 4 4 5% 7% 35%	2394
	21st to end	Day	19% 9% 3 8% 4 4 4 2 5% 7% 34%	2470
May	1st to 10th	Day	18% 8% 2 7% 5% 4 4 4 6% 7% 34%	4082
	11th to 20th	Day	16% 8% 3 7% 5% 5% 4 4 5% 9% 34%	4081
	21st to end	Day	10% 6% 2 7% 5% 4 4 4 5% 8% 45%	4476
June	1st to 10th	Day	9% 6% 3 6% 6% 5% 5% 5% 7% 8% 41%	2646
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 4 8% 10% 39%	2660
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 5% 8% 9% 38%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 6% 5% 4 7% 9% 39%	4440
	11th to 20th	Day	7% 4 2 5% 5% 5% 4 4 7% 10% 46%	4440
	21st to end	Day	6% 5% 3 7% 5% 5% 6% 5% 7% 9% 42%	4539
August	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 44%	4104
	11th to 20th	Day	9% 6% 3 7% 6% 5% 6% 5% 8% 9% 37%	4044
	21st to end	Day	8% 5% 3 6% 5% 5% 6% 5% 7% 10% 40%	4446
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 5% 8% 42%	2155
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 6% 10% 47%	2090
	21st to end	Day	15% 6% 3 6% 5% 4 5% 4 6% 9% 38%	2090
October	1st to 10th	Day	12% 6% 3 6% 4 4 4 4 5% 8% 43%	2049
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 4 5% 6% 35%	1900
	21st to end	Day	18% 10% 3 8% 5% 4 5% 4 5% 7% 32%	1929
November	1st to 10th	Day	12% 8% 3 8% 6% 4 4 3 6% 7% 39%	1699
	11th to 20th	Day	14% 13% 4 8% 5% 5% 6% 3 5% 6% 31%	1710
	21st to end	Day	18% 11% 5% 8% 6% 4 5% 4 5% 6% 29%	1687
December	1st to 10th	Day	14% 14% 6% 11% 7% 5% 5% 5% 5% 6% 21%	1520
	11th to 20th	Day	16% 15% 5% 9% 6% 5% 4 4 6% 7% 23%	1854
	21st to end	Day	25% 22% 7% 11% 6% 4 4 3 3 5% 11%	2783
January	1st to 10th	Night	16% 16% 6% 10% 6% 4 4 3 4 5% 24%	4428
	11th to 20th	Night	15% 18% 7% 13% 5% 5% 6% 5% 5% 6% 15%	4440
	21st to end	Night	24% 17% 7% 13% 5% 4 4 3 3 3 17%	4587
February	1st to 10th	Night	16% 15% 4 11% 7% 5% 5% 3 4 5% 24%	2470
	11th to 20th	Night	14% 13% 5% 10% 6% 5% 5% 3 5% 7% 28%	2252
	21st to end	Night	19% 10% 4 10% 6% 4 4 3 4 6% 30%	1884
March	1st to 10th	Night	17% 11% 4 8% 4 4 4 3 5% 6% 35%	3673
	11th to 20th	Night	10% 7% 2 6% 4 5% 5% 4 7% 7% 44%	3480
	21st to end	Night	17% 8% 3 8% 5% 5% 4 4 4 6% 35%	3817
April	1st to 10th	Night	15% 10% 3 7% 5% 4 4 4 5% 6% 37%	1976
	11th to 20th	Night	18% 9% 2 6% 4 4 5% 4 6% 6% 37%	1735
	21st to end	Night	17% 9% 2 6% 4 4 4 4 5% 6% 38%	1710
May	1st to 10th	Night	16% 10% 3 7% 4 5% 4 4 5% 8% 34%	2813
	11th to 20th	Night	16% 7% 2 7% 5% 5% 4 3 5% 7% 40%	2812
	21st to end	Night	10% 5% 2 6% 4 3 4 4 6% 8% 48%	3079
June	1st to 10th	Night	12% 4 1 5% 3 5% 4 4 6% 8% 47%	1530
	11th to 20th	Night	10% 4 3 7% 5% 5% 4 5% 6% 8% 44%	1520
	21st to end	Night	9% 6% 3 5% 4 3 3 4 7% 8% 48%	1520
July	1st to 10th	Night	9% 3 2 4 4 5% 4 4 6% 10% 49%	2530
	11th to 20th	Night	8% 4 2 4 3 3 3 4 6% 9% 54%	2530
	21st to end	Night	5% 4 2 6% 5% 5% 5% 5% 7% 10% 47%	3014
August	1st to 10th	Night	11% 5% 2 6% 4 3 4 4 5% 8% 47%	2825
	11th to 20th	Night	8% 6% 2 6% 4 4 5% 4 5% 7% 49%	2785
	21st to end	Night	8% 5% 2 7% 4 5% 4 3 6% 7% 48%	3206
September	1st to 10th	Night	9% 6% 2 5% 3 4 4 3 6% 7% 50%	2005
	11th to 20th	Night	8% 6% 2 4 3 4 4 2 5% 8% 54%	2090
	21st to end	Night	14% 6% 2 7% 4 4 5% 4 5% 6% 43%	2090
October	1st to 10th	Night	12% 7% 3 7% 4 3 3 3 4 6% 47%	2129
	11th to 20th	Night	16% 8% 3 8% 5% 4 4 4 5% 6% 37%	2280
	21st to end	Night	20% 8% 3 7% 5% 4 5% 3 4 6% 35%	2665
November	1st to 10th	Night	13% 8% 2 5% 5% 4 5% 3 5% 7% 43%	2452
	11th to 20th	Night	15% 11% 3 7% 6% 5% 4 3 6% 7% 32%	2470
	21st to end	Night	19% 14% 5% 7% 5% 4 4 3 5% 5% 29%	2488
December	1st to 10th	Night	18% 14% 6% 10% 6% 5% 5% 3 4 6% 23%	2660
	11th to 20th	Night	15% 15% 5% 11% 6% 4 5% 4 6% 6% 24%	3332
	21st to end	Night	28% 21% 5% 10% 4 4 4 3 4 4 12%	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	62% 9% 12% 12% 5%	2528
	11th to 20th	Day	68% 9% 12% 8% 3	2530
	21st to end	Day	75% 6% 8% 7% 3 1	3067
February	1st to 10th	Day	61% 8% 10% 13% 7%	1710
	11th to 20th	Day	57% 8% 10% 16% 7% 1	1821
	21st to end	Day	56% 8% 13% 15% 6% 2	1570
March	1st to 10th	Day	58% 7% 12% 16% 6% 1	3179
	11th to 20th	Day	47% 9% 15% 20% 7% 2	3480
	21st to end	Day	56% 8% 12% 15% 8% 1	3815
April	1st to 10th	Day	51% 7% 11% 18% 12%	2219
	11th to 20th	Day	47% 8% 11% 20% 12% 2	2394
	21st to end	Day	48% 7% 13% 17% 14% 1	2470
May	1st to 10th	Day	45% 9% 13% 21% 11% 1	4120
	11th to 20th	Day	43% 10% 14% 22% 9% 1	4085
	21st to end	Day	35% 8% 12% 19% 22% 5%	4489
June	1st to 10th	Day	37% 9% 13% 25% 14% 3	2646
	11th to 20th	Day	37% 9% 14% 21% 17% 2	2660
	21st to end	Day	37% 11% 14% 21% 15% 2	2660
July	1st to 10th	Day	39% 8% 14% 20% 16% 2	4371
	11th to 20th	Day	29% 8% 14% 31% 18% 1	4365
	21st to end	Day	35% 10% 13% 18% 21% 2	4395
August	1st to 10th	Day	35% 7% 14% 27% 16% 1	4091
	11th to 20th	Day	38% 10% 12% 28% 11% 1	4083
	21st to end	Day	36% 8% 13% 28% 12% 2	4445
September	1st to 10th	Day	37% 9% 16% 20% 15% 2	2155
	11th to 20th	Day	31% 8% 12% 31% 16% 1	2090
	21st to end	Day	41% 8% 13% 23% 14%	2090
October	1st to 10th	Day	29% 5% 12% 31% 22% 1	3400
	11th to 20th	Day	39% 6% 11% 25% 19%	3140
	21st to end	Day	43% 6% 14% 24% 13% 1	3153
November	1st to 10th	Day	43% 7% 12% 24% 13% 1	1699
	11th to 20th	Day	53% 6% 13% 18% 9% 2	1710
	21st to end	Day	55% 7% 13% 17% 7%	1687
December	1st to 10th	Day	61% 8% 12% 13% 4	1520
	11th to 20th	Day	58% 9% 14% 14% 4	1851
	21st to end	Day	77% 6% 8% 6% 3	2783
January	1st to 10th	Night	59% 8% 11% 15% 6% 1	4428
	11th to 20th	Night	66% 8% 13% 10% 4	4440
	21st to end	Night	70% 7% 10% 10% 3 1	4587
February	1st to 10th	Night	61% 7% 11% 13% 6% 1	2470
	11th to 20th	Night	56% 6% 10% 18% 8% 1	2253
	21st to end	Night	55% 6% 12% 18% 8% 2	1884
March	1st to 10th	Night	49% 6% 14% 24% 7%	3673
	11th to 20th	Night	35% 9% 15% 22% 19% 1	3480
	21st to end	Night	47% 8% 13% 22% 9% 1	3817
April	1st to 10th	Night	46% 7% 11% 20% 14% 2	1976
	11th to 20th	Night	44% 9% 11% 18% 17% 1	1735
	21st to end	Night	45% 7% 13% 17% 16% 3	1710
May	1st to 10th	Night	46% 8% 11% 20% 13% 2	2840
	11th to 20th	Night	42% 8% 12% 25% 12% 1	2813
	21st to end	Night	30% 9% 14% 22% 21% 4	3087
June	1st to 10th	Night	33% 7% 12% 28% 18% 2	1530
	11th to 20th	Night	36% 9% 12% 24% 17% 2	1520
	21st to end	Night	32% 8% 14% 25% 20% 1	1520
July	1st to 10th	Night	30% 7% 13% 30% 15% 6%	2490
	11th to 20th	Night	26% 6% 15% 30% 21% 2	2482
	21st to end	Night	30% 9% 18% 18% 22% 2	2918
August	1st to 10th	Night	35% 7% 13% 27% 17% 1	2814
	11th to 20th	Night	31% 9% 12% 35% 12% 2	2812
	21st to end	Night	34% 7% 12% 30% 16% 1	3206
September	1st to 10th	Night	32% 9% 12% 27% 19% 2	2005
	11th to 20th	Night	29% 7% 10% 30% 22% 2	2090
	21st to end	Night	41% 6% 11% 27% 14% 1	2090
October	1st to 10th	Night	26% 5% 10% 32% 27% 1	3558
	11th to 20th	Night	40% 5% 11% 24% 19%	3779
	21st to end	Night	38% 4 10% 32% 15% 1	4391
November	1st to 10th	Night	39% 7% 13% 25% 15% 1	2452
	11th to 20th	Night	49% 6% 15% 20% 9% 1	2470
	21st to end	Night	55% 7% 13% 18% 7%	2488
December	1st to 10th	Night	62% 7% 12% 13% 6%	2660
	11th to 20th	Night	58% 9% 13% 14% 6% 1	3334
	21st to end	Night	73% 8% 10% 7% 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	24% 16% 35% 18% 5% 1	270
	11th to 20th	Day	22% 15% 44% 15% 4 1	270
	21st to end	Day	30% 13% 32% 20% 4 1	297
February	1st to 10th	Day	23% 20% 37% 14% 3 1	270
	11th to 20th	Day	24% 17% 38% 17% 3	270
	21st to end	Day	26% 24% 36% 13% 1	225
March	1st to 10th	Day	24% 21% 34% 16% 4	303
	11th to 20th	Day	23% 12% 32% 25% 7% 1	460
	21st to end	Day	25% 15% 32% 21% 6% 1	506
April	1st to 10th	Day	20% 16% 34% 22% 8% 1	460
	11th to 20th	Day	22% 19% 32% 15% 8% 4	452
	21st to end	Day	25% 13% 31% 18% 11% 2	460
May	1st to 10th	Day	23% 13% 29% 21% 10% 4	463
	11th to 20th	Day	20% 10% 25% 24% 15% 7%	487
	21st to end	Day	13% 8% 22% 28% 21% 9%	529
June	1st to 10th	Day	11% 9% 27% 33% 17% 4	666
	11th to 20th	Day	12% 9% 29% 30% 17% 4	680
	21st to end	Day	12% 8% 29% 29% 16% 5%	680
July	1st to 10th	Day	9% 4 22% 28% 26% 10%	671
	11th to 20th	Day	10% 6% 25% 30% 21% 9%	668
	21st to end	Day	8% 4 24% 31% 22% 11%	579
August	1st to 10th	Day	7% 3 21% 27% 27% 14%	486
	11th to 20th	Day	12% 5% 19% 30% 23% 12%	479
	21st to end	Day	11% 2 18% 29% 28% 11%	539
September	1st to 10th	Day	11% 6% 23% 25% 22% 13%	490
	11th to 20th	Day	8% 4 16% 27% 29% 16%	490
	21st to end	Day	17% 10% 22% 23% 20% 8%	490
October	1st to 10th	Day	16% 8% 27% 23% 18% 8%	490
	11th to 20th	Day	18% 16% 28% 28% 9% 2	490
	21st to end	Day	25% 14% 34% 18% 7% 1	378
November	1st to 10th	Day	13% 18% 33% 24% 10% 2	279
	11th to 20th	Day	22% 18% 32% 20% 6% 2	270
	21st to end	Day	25% 15% 40% 14% 5%	259
December	1st to 10th	Day	20% 18% 39% 14% 6% 2	180
	11th to 20th	Day	23% 15% 44% 14% 3 1	207
	21st to end	Day	28% 19% 34% 17% 2	297
January	1st to 10th	Night	23% 14% 36% 21% 5% 1	950
	11th to 20th	Night	26% 13% 33% 22% 5% 1	950
	21st to end	Night	19% 13% 35% 27% 6%	865
February	1st to 10th	Night	24% 13% 35% 25% 3	760
	11th to 20th	Night	23% 14% 34% 26% 4	743
	21st to end	Night	24% 13% 38% 21% 3	628
March	1st to 10th	Night	21% 11% 34% 27% 6%	760
	11th to 20th	Night	17% 17% 36% 24% 6% 1	760
	21st to end	Night	23% 10% 31% 28% 7%	836
April	1st to 10th	Night	19% 14% 34% 29% 4 1	646
	11th to 20th	Night	22% 10% 35% 25% 7% 1	563
	21st to end	Night	22% 8% 31% 31% 8%	570
May	1st to 10th	Night	19% 8% 31% 30% 10% 1	570
	11th to 20th	Night	22% 3 26% 35% 13% 1	561
	21st to end	Night	12% 3 24% 36% 23% 2	617
June	1st to 10th	Night	13% 2 23% 46% 15% 1	570
	11th to 20th	Night	12% 4 21% 44% 19%	570
	21st to end	Night	11% 3 22% 43% 20% 1	570
July	1st to 10th	Night	8% 2 18% 40% 28% 4	555
	11th to 20th	Night	9% 3 19% 39% 26% 4	552
	21st to end	Night	5% 2 17% 47% 25% 3	624
August	1st to 10th	Night	8% 2 17% 42% 28% 2	567
	11th to 20th	Night	9% 2 17% 37% 31% 3	564
	21st to end	Night	9% 2 16% 38% 31% 4	627
September	1st to 10th	Night	12% 5% 18% 32% 27% 5%	675
	11th to 20th	Night	10% 3 16% 33% 32% 5%	760
	21st to end	Night	17% 6% 21% 30% 23% 4	760
October	1st to 10th	Night	14% 7% 27% 31% 18% 3	760
	11th to 20th	Night	21% 12% 30% 26% 10% 1	760
	21st to end	Night	24% 10% 33% 27% 6%	836
November	1st to 10th	Night	17% 11% 30% 28% 12% 1	755
	11th to 20th	Night	22% 13% 35% 22% 7% 1	760
	21st to end	Night	25% 13% 32% 22% 7%	760
December	1st to 10th	Night	24% 14% 35% 21% 6%	760
	11th to 20th	Night	23% 14% 37% 22% 4	859
	21st to end	Night	31% 13% 33% 20% 3	1045

Page generated at 2024-11-01 22:47:31. Version ac07

Copyright © 2024 Attilla Danko.