Rockford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rockford 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% 9% 3 8% 5% 4 4 4 5% 7% 37%	101423
	Night	14% 10% 4 7% 5% 4 4 3 5% 6% 39%	97709
Transparency	Day	44% 6% 12% 23% 13% 1	104962
	Night	45% 5% 11% 23% 14% 2	102311
Seeing	Day	18% 10% 28% 25% 14% 5%	15857
	Night	18% 9% 31% 30% 12% 1	25693

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	12% 14% 10% 13% 6% 5% 4 3 4 4 25%	2527
	11th to 20th	Day	13% 13% 5% 16% 4 4 5% 9% 8% 5% 19%	2530
	21st to end	Day	17% 19% 10% 12% 5% 3 4 2 4 5% 19%	2939
February	1st to 10th	Day	12% 14% 6% 8% 6% 7% 5% 4 5% 6% 26%	1710
	11th to 20th	Day	14% 10% 3 8% 5% 6% 4 3 5% 5% 36%	1816
	21st to end	Day	13% 15% 4 11% 5% 4 4 2 5% 7% 31%	1570
March	1st to 10th	Day	13% 10% 4 8% 5% 3 4 3 4 6% 40%	3120
	11th to 20th	Day	12% 6% 2 8% 4 4 4 4 6% 8% 41%	3338
	21st to end	Day	22% 13% 4 12% 5% 5% 5% 3 5% 5% 21%	4133
April	1st to 10th	Day	18% 13% 3 8% 5% 4 4 4 4 6% 31%	2280
	11th to 20th	Day	17% 10% 3 6% 5% 4 5% 4 6% 6% 34%	2254
	21st to end	Day	20% 9% 3 8% 5% 4 4 3 5% 6% 33%	2340
May	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 5% 7% 35%	4136
	11th to 20th	Day	16% 6% 2 6% 4 4 4 3 5% 7% 43%	4399
	21st to end	Day	12% 7% 2 6% 5% 4 5% 5% 6% 9% 39%	4824
June	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 5% 5% 7% 44%	2660
	11th to 20th	Day	11% 5% 2 5% 4 3 5% 4 7% 9% 45%	2660
	21st to end	Day	12% 7% 2 7% 4 4 5% 5% 8% 10% 37%	2660
July	1st to 10th	Day	11% 8% 3 8% 6% 5% 5% 5% 7% 10% 33%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 4 5% 6% 10% 49%	4440
	21st to end	Day	9% 7% 2 7% 6% 5% 5% 4 6% 9% 40%	4813
August	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 7% 9% 42%	4340
	11th to 20th	Day	10% 5% 2 6% 3 4 4 4 7% 10% 45%	3759
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 8% 47%	4180
September	1st to 10th	Day	13% 5% 1 5% 5% 4 4 3 5% 8% 47%	2280
	11th to 20th	Day	13% 4 1 4 3 3 4 3 5% 8% 52%	2204
	21st to end	Day	12% 7% 2 7% 4 4 4 3 5% 7% 45%	2090
October	1st to 10th	Day	14% 5% 3 5% 4 3 4 3 5% 5% 49%	1967
	11th to 20th	Day	20% 8% 3 7% 4 4 4 3 5% 6% 36%	1900
	21st to end	Day	21% 9% 3 6% 4 5% 3 2 4 5% 38%	1912
November	1st to 10th	Day	13% 8% 3 6% 4 3 5% 3 4 6% 45%	1708
	11th to 20th	Day	15% 12% 3 8% 6% 4 4 4 4 6% 32%	1710
	21st to end	Day	17% 14% 4 9% 3 3 2 3 4 5% 36%	1563
December	1st to 10th	Day	15% 14% 3 9% 6% 4 4 3 5% 5% 30%	1520
	11th to 20th	Day	13% 15% 4 10% 5% 5% 5% 4 5% 6% 28%	1918
	21st to end	Day	21% 21% 9% 12% 5% 5% 3 2 3 3 15%	2783
January	1st to 10th	Night	13% 14% 8% 11% 6% 4 3 2 4 4 30%	4428
	11th to 20th	Night	14% 17% 7% 14% 5% 4 4 6% 6% 3 20%	4440
	21st to end	Night	19% 19% 7% 10% 5% 4 4 3 3 5% 20%	4724
February	1st to 10th	Night	14% 14% 5% 8% 5% 5% 4 3 4 5% 33%	2470
	11th to 20th	Night	13% 10% 4 7% 6% 4 4 2 5% 6% 39%	2248
	21st to end	Night	18% 12% 4 8% 4 3 3 3 4 6% 35%	1884
March	1st to 10th	Night	19% 10% 3 5% 4 4 3 3 4 5% 41%	3733
	11th to 20th	Night	9% 8% 2 6% 5% 4 5% 3 5% 7% 47%	3652
	21st to end	Night	24% 11% 5% 10% 4 4 3 3 4 5% 28%	3498
April	1st to 10th	Night	18% 10% 3 6% 4 4 5% 3 4 5% 39%	1900
	11th to 20th	Night	19% 9% 3 6% 5% 4 3 2 4 5% 40%	1875
	21st to end	Night	17% 8% 3 6% 4 4 4 3 6% 6% 38%	1838
May	1st to 10th	Night	16% 7% 2 7% 6% 4 4 4 6% 7% 36%	2758
	11th to 20th	Night	14% 6% 2 6% 5% 4 5% 4 7% 7% 40%	2506
	21st to end	Night	10% 7% 2 6% 5% 4 4 4 7% 8% 43%	2743
June	1st to 10th	Night	8% 5% 1 5% 4 4 5% 5% 7% 8% 47%	1520
	11th to 20th	Night	9% 5% 2 6% 3 5% 5% 4 6% 8% 48%	1520
	21st to end	Night	10% 6% 3 7% 4 5% 5% 4 6% 7% 44%	1520
July	1st to 10th	Night	15% 7% 3 6% 5% 4 5% 3 5% 8% 40%	2530
	11th to 20th	Night	5% 4 1 5% 4 4 4 5% 6% 8% 55%	2530
	21st to end	Night	6% 6% 2 7% 5% 5% 5% 5% 7% 8% 45%	2750
August	1st to 10th	Night	6% 5% 2 5% 4 4 4 3 7% 9% 52%	2597
	11th to 20th	Night	8% 6% 2 5% 4 3 5% 4 6% 8% 49%	3071
	21st to end	Night	8% 5% 1 5% 4 4 4 4 5% 9% 51%	3476
September	1st to 10th	Night	9% 5% 2 6% 3 3 3 2 4 6% 55%	1900
	11th to 20th	Night	11% 4 1 4 4 3 4 4 5% 7% 53%	1957
	21st to end	Night	12% 5% 2 6% 4 3 4 3 5% 7% 49%	2090
October	1st to 10th	Night	12% 7% 2 5% 3 4 4 3 4 5% 51%	2209
	11th to 20th	Night	17% 7% 2 6% 4 3 3 3 4 5% 46%	2280
	21st to end	Night	20% 8% 3 5% 4 4 4 3 5% 6% 37%	2684
November	1st to 10th	Night	12% 8% 2 6% 3 4 3 3 4 5% 49%	2470
	11th to 20th	Night	15% 10% 4 9% 4 4 4 3 5% 5% 37%	2470
	21st to end	Night	17% 11% 3 6% 5% 4 3 3 5% 6% 38%	2615
December	1st to 10th	Night	16% 11% 5% 9% 6% 5% 5% 3 4 6% 31%	2660
	11th to 20th	Night	15% 14% 4 9% 5% 3 4 3 5% 6% 31%	3279
	21st to end	Night	23% 17% 6% 10% 5% 4 5% 3 5% 4 18%	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% 6% 11% 15% 6%	2528
	11th to 20th	Day	59% 8% 13% 12% 8%	2530
	21st to end	Day	67% 5% 10% 13% 5%	2939
February	1st to 10th	Day	57% 5% 12% 16% 9% 1	1710
	11th to 20th	Day	49% 5% 11% 24% 9% 1	1826
	21st to end	Day	54% 6% 10% 20% 10% 1	1570
March	1st to 10th	Day	45% 7% 11% 24% 10% 3	3120
	11th to 20th	Day	39% 7% 12% 31% 10% 1	3338
	21st to end	Day	63% 8% 12% 13% 4 1	4133
April	1st to 10th	Day	54% 6% 10% 21% 9%	2280
	11th to 20th	Day	49% 7% 9% 22% 11% 2	2254
	21st to end	Day	51% 6% 11% 17% 13% 1	2340
May	1st to 10th	Day	46% 8% 11% 20% 14% 1	4174
	11th to 20th	Day	41% 6% 11% 28% 14%	4403
	21st to end	Day	38% 9% 13% 21% 16% 4	4837
June	1st to 10th	Day	36% 9% 12% 25% 17% 1	2660
	11th to 20th	Day	34% 7% 12% 25% 20% 2	2660
	21st to end	Day	39% 9% 14% 23% 13% 2	2660
July	1st to 10th	Day	47% 4 13% 24% 10% 2	4371
	11th to 20th	Day	30% 5% 17% 30% 18% 1	4365
	21st to end	Day	40% 5% 15% 18% 19% 3	4662
August	1st to 10th	Day	37% 6% 16% 29% 12% 1	4325
	11th to 20th	Day	34% 4 12% 35% 14% 1	3795
	21st to end	Day	35% 4 14% 29% 17% 1	4179
September	1st to 10th	Day	35% 7% 12% 25% 19% 2	2280
	11th to 20th	Day	31% 5% 12% 31% 20% 2	2204
	21st to end	Day	38% 6% 10% 27% 18% 1	2090
October	1st to 10th	Day	25% 3 6% 37% 28% 1	3266
	11th to 20th	Day	35% 3 10% 27% 24% 2	3140
	21st to end	Day	44% 3 8% 28% 13% 3	3124
November	1st to 10th	Day	40% 4 15% 24% 15% 2	1708
	11th to 20th	Day	52% 6% 12% 21% 9% 1	1710
	21st to end	Day	51% 4 14% 22% 8%	1563
December	1st to 10th	Day	55% 5% 14% 17% 8% 1	1520
	11th to 20th	Day	56% 5% 14% 16% 7% 2	1915
	21st to end	Day	75% 5% 7% 9% 4	2783
January	1st to 10th	Night	57% 5% 11% 19% 8% 1	4428
	11th to 20th	Night	64% 5% 10% 12% 8%	4440
	21st to end	Night	66% 5% 9% 13% 5% 1	4724
February	1st to 10th	Night	54% 4 11% 18% 12% 1	2470
	11th to 20th	Night	47% 5% 11% 22% 14% 1	2249
	21st to end	Night	50% 5% 11% 20% 11% 4	1884
March	1st to 10th	Night	45% 6% 12% 23% 10% 4	3733
	11th to 20th	Night	36% 6% 10% 29% 17% 2	3652
	21st to end	Night	60% 5% 10% 17% 8% 1	3498
April	1st to 10th	Night	47% 6% 11% 21% 13% 2	1900
	11th to 20th	Night	47% 4 7% 20% 18% 4	1875
	21st to end	Night	45% 6% 12% 23% 11% 2	1838
May	1st to 10th	Night	44% 8% 13% 16% 16% 2	2785
	11th to 20th	Night	38% 10% 14% 25% 12% 1	2507
	21st to end	Night	33% 9% 13% 20% 20% 4	2751
June	1st to 10th	Night	31% 8% 16% 24% 19% 2	1520
	11th to 20th	Night	33% 7% 10% 24% 24% 3	1520
	21st to end	Night	38% 7% 14% 21% 18% 3	1520
July	1st to 10th	Night	45% 4 15% 21% 12% 3	2490
	11th to 20th	Night	27% 4 14% 34% 20% 1	2482
	21st to end	Night	36% 5% 15% 19% 21% 4	2662
August	1st to 10th	Night	30% 4 15% 31% 18% 2	2588
	11th to 20th	Night	33% 4 14% 31% 18% 1	3101
	21st to end	Night	31% 5% 12% 31% 18% 3	3476
September	1st to 10th	Night	31% 6% 10% 27% 24% 3	1900
	11th to 20th	Night	30% 6% 9% 33% 20% 3	1957
	21st to end	Night	35% 5% 10% 30% 19% 2	2090
October	1st to 10th	Night	25% 3 7% 36% 29% 1	3690
	11th to 20th	Night	35% 3 8% 25% 26% 3	3779
	21st to end	Night	43% 3 9% 26% 16% 3	4422
November	1st to 10th	Night	38% 5% 10% 27% 18% 3	2470
	11th to 20th	Night	48% 5% 13% 21% 12% 1	2470
	21st to end	Night	48% 5% 11% 23% 11% 1	2615
December	1st to 10th	Night	55% 5% 11% 21% 8% 1	2660
	11th to 20th	Night	53% 6% 13% 19% 8% 1	3281
	21st to end	Night	68% 6% 10% 11% 4	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	20% 15% 30% 26% 9% 1	270
	11th to 20th	Day	21% 14% 37% 23% 3 1	270
	21st to end	Day	24% 10% 37% 26% 2 2	297
February	1st to 10th	Day	19% 17% 40% 16% 7%	270
	11th to 20th	Day	21% 19% 33% 23% 4	270
	21st to end	Day	29% 18% 34% 18% 1	225
March	1st to 10th	Day	20% 22% 39% 16% 4	270
	11th to 20th	Day	26% 16% 36% 13% 7% 1	270
	21st to end	Day	29% 15% 30% 18% 7% 1	487
April	1st to 10th	Day	26% 15% 33% 22% 5%	460
	11th to 20th	Day	22% 21% 26% 20% 9% 3	452
	21st to end	Day	24% 13% 29% 23% 9% 2	460
May	1st to 10th	Day	21% 15% 29% 23% 8% 3	491
	11th to 20th	Day	22% 11% 28% 25% 12% 2	675
	21st to end	Day	19% 9% 26% 22% 16% 7%	734
June	1st to 10th	Day	10% 8% 31% 29% 17% 5%	680
	11th to 20th	Day	14% 6% 34% 26% 14% 6%	680
	21st to end	Day	14% 8% 27% 31% 16% 3	680
July	1st to 10th	Day	10% 3 18% 31% 24% 13%	671
	11th to 20th	Day	10% 4 25% 31% 21% 8%	668
	21st to end	Day	9% 4 22% 35% 23% 7%	739
August	1st to 10th	Day	10% 2 20% 32% 25% 11%	676
	11th to 20th	Day	11% 6% 19% 26% 23% 15%	497
	21st to end	Day	11% 5% 17% 33% 25% 10%	539
September	1st to 10th	Day	17% 7% 20% 28% 21% 7%	490
	11th to 20th	Day	12% 3 20% 30% 24% 11%	490
	21st to end	Day	16% 12% 24% 26% 16% 7%	490
October	1st to 10th	Day	18% 11% 25% 25% 19% 3	367
	11th to 20th	Day	23% 20% 30% 21% 6%	300
	21st to end	Day	32% 14% 28% 20% 5% 1	330
November	1st to 10th	Day	18% 15% 35% 20% 9% 3	282
	11th to 20th	Day	22% 15% 40% 15% 7%	270
	21st to end	Day	29% 9% 38% 18% 6%	270
December	1st to 10th	Day	19% 18% 40% 15% 5% 3	270
	11th to 20th	Day	20% 12% 38% 20% 9% 1	270
	21st to end	Day	27% 15% 39% 15% 3	297
January	1st to 10th	Night	19% 13% 36% 26% 5%	950
	11th to 20th	Night	21% 13% 36% 24% 5% 1	950
	21st to end	Night	22% 11% 34% 28% 6%	1045
February	1st to 10th	Night	22% 11% 38% 23% 5%	950
	11th to 20th	Night	19% 14% 36% 26% 5%	773
	21st to end	Night	24% 14% 38% 20% 4	628
March	1st to 10th	Night	21% 11% 37% 25% 6%	760
	11th to 20th	Night	16% 12% 36% 30% 6%	677
	21st to end	Night	25% 11% 31% 26% 5% 1	627
April	1st to 10th	Night	23% 13% 36% 24% 5%	570
	11th to 20th	Night	22% 13% 30% 27% 7%	563
	21st to end	Night	21% 10% 31% 29% 8% 1	570
May	1st to 10th	Night	19% 8% 33% 31% 9%	570
	11th to 20th	Night	18% 7% 32% 33% 10%	561
	21st to end	Night	15% 4 29% 35% 16%	617
June	1st to 10th	Night	10% 3 27% 44% 15%	570
	11th to 20th	Night	11% 4 31% 40% 13% 1	570
	21st to end	Night	11% 4 30% 38% 17% 1	570
July	1st to 10th	Night	10% 1 16% 40% 29% 3	555
	11th to 20th	Night	9% 3 20% 41% 25% 2	552
	21st to end	Night	8% 3 17% 47% 25% 1	624
August	1st to 10th	Night	6% 2 14% 46% 30% 2	567
	11th to 20th	Night	8% 3 13% 40% 30% 6%	564
	21st to end	Night	11% 2 16% 43% 27% 3	627
September	1st to 10th	Night	10% 5% 22% 35% 25% 4	570
	11th to 20th	Night	12% 4 20% 33% 28% 3	627
	21st to end	Night	14% 9% 23% 32% 19% 2	760
October	1st to 10th	Night	15% 7% 29% 31% 17% 1	760
	11th to 20th	Night	21% 11% 31% 27% 11%	760
	21st to end	Night	25% 10% 33% 24% 8%	836
November	1st to 10th	Night	16% 9% 39% 24% 10% 1	760
	11th to 20th	Night	20% 14% 36% 24% 6%	760
	21st to end	Night	22% 12% 34% 24% 7%	905
December	1st to 10th	Night	22% 11% 38% 23% 6%	950
	11th to 20th	Night	23% 12% 33% 27% 5% 1	950
	21st to end	Night	30% 12% 33% 22% 3	1045

Page generated at 2024-11-03 01:11:22. Version ac07

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