Middle Fork River Forest Preserve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Middle Fork River Forest Preserve clear sky chart from 2005-11-06 to 2024-10-25.

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 7% 5% 4 4 4 6% 8% 37%	101139
	Night	14% 9% 3 7% 4 4 4 3 5% 6% 39%	97732
Transparency	Day	44% 6% 12% 23% 13% 2	100927
	Night	45% 5% 11% 23% 14% 2	97616
Seeing	Day	16% 8% 27% 26% 16% 7%	15674
	Night	18% 8% 29% 30% 13% 1	25477

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	14% 13% 8% 16% 6% 4 4 3 5% 5% 21%	2527
	11th to 20th	Day	14% 12% 6% 14% 8% 7% 5% 6% 7% 4 17%	2530
	21st to end	Day	22% 23% 6% 10% 5% 3 3 2 4 5% 18%	2942
February	1st to 10th	Day	16% 13% 4 9% 7% 5% 4 3 5% 6% 28%	1806
	11th to 20th	Day	15% 12% 3 8% 5% 6% 4 3 5% 7% 31%	1848
	21st to end	Day	16% 14% 6% 9% 5% 4 2 3 4 7% 30%	1570
March	1st to 10th	Day	18% 18% 5% 8% 4 4 3 2 3 4 31%	3120
	11th to 20th	Day	10% 9% 3 6% 4 4 4 4 7% 8% 41%	3267
	21st to end	Day	15% 12% 6% 9% 6% 5% 5% 4 5% 6% 27%	4165
April	1st to 10th	Day	15% 11% 4 7% 5% 3 4 5% 5% 7% 35%	2280
	11th to 20th	Day	15% 9% 3 7% 5% 4 4 4 5% 7% 38%	2254
	21st to end	Day	21% 8% 3 8% 4 5% 4 3 4 6% 35%	2355
May	1st to 10th	Day	16% 9% 2 6% 5% 5% 5% 5% 7% 9% 29%	4082
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 4 5% 8% 37%	4162
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 45%	4824
June	1st to 10th	Day	9% 5% 3 5% 5% 5% 6% 5% 7% 9% 42%	2660
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 6% 9% 47%	2660
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 5% 7% 9% 40%	2660
July	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 5% 7% 11% 36%	4440
	11th to 20th	Day	6% 5% 2 5% 4 5% 6% 4 7% 11% 44%	4440
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 4 7% 9% 41%	4813
August	1st to 10th	Day	7% 4 2 5% 4 4 5% 4 6% 9% 51%	4172
	11th to 20th	Day	8% 5% 2 5% 4 5% 5% 5% 7% 12% 42%	3729
	21st to end	Day	5% 4 2 5% 4 4 4 4 7% 10% 49%	4180
September	1st to 10th	Day	10% 5% 3 6% 5% 4 3 4 6% 7% 46%	2280
	11th to 20th	Day	10% 5% 2 4 3 4 4 4 5% 7% 51%	2146
	21st to end	Day	12% 6% 2 5% 5% 3 4 4 6% 7% 47%	2090
October	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 4 7% 47%	2070
	11th to 20th	Day	15% 8% 2 6% 4 3 4 3 5% 7% 42%	1900
	21st to end	Day	19% 9% 3 7% 4 4 4 4 5% 7% 34%	1830
November	1st to 10th	Day	11% 7% 2 5% 3 3 4 4 5% 6% 51%	1672
	11th to 20th	Day	16% 11% 3 7% 4 3 4 4 4 5% 39%	1710
	21st to end	Day	17% 10% 4 9% 5% 4 3 3 4 5% 37%	1710
December	1st to 10th	Day	17% 14% 5% 10% 6% 5% 4 3 5% 5% 28%	1544
	11th to 20th	Day	14% 13% 4 12% 5% 4 5% 4 4 6% 28%	1918
	21st to end	Day	21% 20% 7% 14% 6% 4 4 3 3 5% 14%	2783
January	1st to 10th	Night	16% 16% 7% 10% 5% 3 4 3 5% 5% 28%	4428
	11th to 20th	Night	14% 18% 7% 13% 5% 6% 5% 4 4 4 20%	4440
	21st to end	Night	24% 16% 7% 9% 4 3 3 3 3 4 23%	4724
February	1st to 10th	Night	18% 13% 4 9% 6% 5% 3 3 4 6% 29%	2371
	11th to 20th	Night	14% 10% 4 9% 6% 3 4 3 5% 6% 35%	2218
	21st to end	Night	18% 11% 4 9% 4 4 3 3 4 6% 33%	1884
March	1st to 10th	Night	17% 15% 3 6% 5% 3 4 2 4 6% 35%	3733
	11th to 20th	Night	10% 7% 3 7% 4 4 3 3 5% 6% 46%	3720
	21st to end	Night	19% 9% 4 9% 5% 4 4 4 6% 6% 29%	3466
April	1st to 10th	Night	12% 10% 3 6% 4 5% 4 4 5% 7% 41%	1900
	11th to 20th	Night	17% 8% 3 6% 4 4 4 2 4 7% 41%	1875
	21st to end	Night	19% 8% 3 7% 4 5% 5% 3 4 5% 37%	1824
May	1st to 10th	Night	17% 9% 2 8% 4 4 5% 4 6% 8% 34%	2813
	11th to 20th	Night	17% 8% 2 5% 5% 4 4 3 6% 7% 39%	2732
	21st to end	Night	9% 6% 3 6% 4 4 4 4 7% 8% 44%	2743
June	1st to 10th	Night	10% 5% 3 6% 3 3 4 3 5% 8% 50%	1520
	11th to 20th	Night	7% 6% 2 6% 4 4 4 4 6% 9% 49%	1520
	21st to end	Night	7% 5% 2 6% 5% 5% 4 4 8% 9% 43%	1520
July	1st to 10th	Night	11% 4 2 6% 5% 4 5% 4 6% 10% 44%	2530
	11th to 20th	Night	4 3 1 4 4 4 4 4 7% 10% 56%	2530
	21st to end	Night	6% 6% 3 7% 5% 6% 4 4 6% 9% 45%	2750
August	1st to 10th	Night	7% 4 1 5% 4 4 4 3 7% 9% 52%	2754
	11th to 20th	Night	6% 4 2 6% 4 4 5% 4 7% 8% 49%	3100
	21st to end	Night	7% 4 1 5% 3 4 4 4 5% 8% 54%	3476
September	1st to 10th	Night	12% 4 2 4 4 2 3 3 4 7% 54%	1900
	11th to 20th	Night	8% 4 1 4 4 3 3 3 6% 8% 55%	2014
	21st to end	Night	11% 6% 3 5% 4 3 4 4 5% 7% 48%	2090
October	1st to 10th	Night	11% 5% 1 5% 4 3 3 3 5% 5% 55%	2107
	11th to 20th	Night	15% 6% 2 5% 3 3 3 2 5% 6% 50%	2280
	21st to end	Night	19% 8% 3 7% 4 4 4 3 4 6% 39%	2630
November	1st to 10th	Night	11% 7% 2 6% 4 3 4 3 5% 6% 49%	2406
	11th to 20th	Night	13% 8% 3 7% 5% 4 4 3 5% 7% 41%	2470
	21st to end	Night	18% 11% 4 9% 4 3 3 3 4 6% 36%	2470
December	1st to 10th	Night	17% 11% 3 10% 5% 5% 4 3 5% 5% 32%	2631
	11th to 20th	Night	16% 12% 5% 9% 5% 4 4 3 4 5% 35%	3279
	21st to end	Night	25% 18% 7% 11% 5% 4 4 3 3 4 16%	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	63% 5% 9% 15% 6%	2528
	11th to 20th	Day	66% 4 10% 10% 8% 1	2530
	21st to end	Day	70% 3 9% 14% 4	2942
February	1st to 10th	Day	58% 4 11% 17% 9% 2	1806
	11th to 20th	Day	53% 4 11% 22% 9% 1	1858
	21st to end	Day	55% 4 10% 22% 8% 2	1570
March	1st to 10th	Day	59% 3 7% 17% 12% 1	3120
	11th to 20th	Day	38% 6% 12% 28% 15% 1	3267
	21st to end	Day	54% 7% 15% 19% 4 1	4165
April	1st to 10th	Day	48% 5% 12% 21% 13% 1	2280
	11th to 20th	Day	45% 5% 12% 22% 12% 4	2254
	21st to end	Day	50% 5% 12% 19% 12% 2	2355
May	1st to 10th	Day	47% 8% 13% 23% 8%	4120
	11th to 20th	Day	45% 7% 12% 26% 10% 1	4166
	21st to end	Day	33% 7% 12% 21% 23% 4	4837
June	1st to 10th	Day	36% 7% 14% 23% 17% 3	2660
	11th to 20th	Day	33% 6% 11% 25% 21% 4	2660
	21st to end	Day	39% 8% 13% 21% 16% 3	2660
July	1st to 10th	Day	41% 6% 12% 27% 11% 2	4371
	11th to 20th	Day	32% 7% 15% 29% 16% 1	4365
	21st to end	Day	38% 7% 16% 20% 16% 2	4662
August	1st to 10th	Day	29% 6% 17% 32% 15% 1	4157
	11th to 20th	Day	34% 6% 15% 28% 16% 1	3765
	21st to end	Day	29% 6% 15% 31% 15% 4	4179
September	1st to 10th	Day	36% 6% 11% 25% 18% 5%	2280
	11th to 20th	Day	32% 5% 11% 25% 23% 5%	2146
	21st to end	Day	36% 5% 10% 26% 22% 2	2090
October	1st to 10th	Day	37% 6% 10% 25% 20% 3	2070
	11th to 20th	Day	41% 5% 11% 23% 19% 2	1900
	21st to end	Day	49% 5% 11% 22% 13% 1	1830
November	1st to 10th	Day	33% 5% 16% 24% 18% 4	1672
	11th to 20th	Day	47% 3 11% 22% 14% 3	1710
	21st to end	Day	51% 3 11% 20% 12% 2	1710
December	1st to 10th	Day	59% 5% 9% 19% 7%	1544
	11th to 20th	Day	58% 4 8% 23% 6% 1	1915
	21st to end	Day	74% 5% 9% 9% 4	2783
January	1st to 10th	Night	58% 5% 11% 17% 8%	4428
	11th to 20th	Night	68% 4 8% 13% 7%	4440
	21st to end	Night	66% 3 8% 15% 7% 1	4724
February	1st to 10th	Night	57% 4 11% 17% 9% 2	2371
	11th to 20th	Night	50% 4 11% 22% 12% 2	2219
	21st to end	Night	52% 5% 10% 20% 10% 3	1884
March	1st to 10th	Night	50% 5% 10% 23% 10% 2	3733
	11th to 20th	Night	37% 5% 10% 26% 19% 2	3720
	21st to end	Night	52% 7% 13% 21% 6% 1	3466
April	1st to 10th	Night	43% 6% 11% 23% 14% 2	1900
	11th to 20th	Night	44% 4 9% 23% 17% 4	1875
	21st to end	Night	49% 5% 10% 20% 12% 4	1824
May	1st to 10th	Night	48% 6% 12% 24% 10%	2840
	11th to 20th	Night	43% 6% 15% 25% 10% 1	2733
	21st to end	Night	35% 8% 12% 21% 19% 5%	2751
June	1st to 10th	Night	33% 5% 11% 28% 19% 4	1520
	11th to 20th	Night	31% 5% 13% 26% 21% 4	1520
	21st to end	Night	34% 7% 16% 22% 16% 4	1520
July	1st to 10th	Night	37% 5% 14% 27% 12% 5%	2490
	11th to 20th	Night	23% 6% 14% 33% 23% 2	2482
	21st to end	Night	35% 6% 16% 21% 17% 4	2662
August	1st to 10th	Night	27% 6% 18% 30% 17% 2	2745
	11th to 20th	Night	30% 6% 15% 29% 18% 1	3130
	21st to end	Night	28% 6% 11% 33% 18% 4	3476
September	1st to 10th	Night	31% 5% 10% 27% 21% 7%	1900
	11th to 20th	Night	27% 4 9% 27% 28% 5%	2014
	21st to end	Night	35% 5% 8% 25% 22% 4	2090
October	1st to 10th	Night	32% 4 10% 27% 24% 3	2107
	11th to 20th	Night	36% 4 8% 27% 22% 3	2280
	21st to end	Night	47% 3 9% 21% 17% 3	2630
November	1st to 10th	Night	34% 5% 11% 27% 19% 5%	2406
	11th to 20th	Night	43% 4 11% 23% 16% 3	2470
	21st to end	Night	51% 3 9% 24% 13% 1	2470
December	1st to 10th	Night	53% 4 11% 21% 10% 1	2631
	11th to 20th	Night	53% 4 11% 19% 13% 1	3281
	21st to end	Night	73% 4 7% 10% 6%	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% 13% 32% 23% 6% 1	270
	11th to 20th	Day	27% 14% 37% 17% 4 1	270
	21st to end	Day	25% 13% 34% 22% 5%	297
February	1st to 10th	Day	25% 14% 37% 20% 4	270
	11th to 20th	Day	27% 13% 37% 17% 5% 1	270
	21st to end	Day	27% 15% 43% 13% 2	225
March	1st to 10th	Day	23% 19% 38% 18% 3	270
	11th to 20th	Day	25% 16% 37% 17% 5%	301
	21st to end	Day	30% 13% 33% 15% 8% 1	506
April	1st to 10th	Day	23% 13% 33% 22% 8% 1	460
	11th to 20th	Day	20% 16% 31% 19% 11% 2	452
	21st to end	Day	23% 13% 36% 18% 8% 2	460
May	1st to 10th	Day	20% 9% 34% 25% 9% 3	463
	11th to 20th	Day	22% 6% 24% 29% 14% 5%	529
	21st to end	Day	11% 5% 31% 26% 16% 9%	734
June	1st to 10th	Day	11% 7% 24% 32% 20% 6%	680
	11th to 20th	Day	11% 5% 26% 32% 21% 6%	680
	21st to end	Day	11% 6% 28% 30% 19% 6%	680
July	1st to 10th	Day	11% 2 16% 29% 24% 17%	671
	11th to 20th	Day	7% 3 18% 33% 26% 13%	668
	21st to end	Day	11% 2 15% 33% 29% 11%	739
August	1st to 10th	Day	6% 2 14% 32% 30% 16%	563
	11th to 20th	Day	10% 3 17% 29% 29% 12%	479
	21st to end	Day	7% 2 13% 29% 34% 15%	539
September	1st to 10th	Day	12% 5% 16% 29% 30% 9%	490
	11th to 20th	Day	9% 2 12% 29% 30% 17%	490
	21st to end	Day	14% 6% 24% 24% 20% 11%	490
October	1st to 10th	Day	11% 5% 27% 32% 18% 8%	470
	11th to 20th	Day	14% 17% 31% 26% 9% 3	300
	21st to end	Day	29% 14% 33% 17% 5% 2	311
November	1st to 10th	Day	12% 11% 34% 23% 14% 4	270
	11th to 20th	Day	23% 16% 31% 19% 10% 1	270
	21st to end	Day	23% 10% 36% 27% 4	270
December	1st to 10th	Day	19% 13% 41% 18% 7% 1	270
	11th to 20th	Day	18% 13% 41% 21% 6% 1	270
	21st to end	Day	25% 18% 37% 18% 4	297
January	1st to 10th	Night	22% 13% 38% 24% 3	950
	11th to 20th	Night	23% 13% 37% 21% 5%	950
	21st to end	Night	22% 12% 37% 25% 4	1045
February	1st to 10th	Night	26% 11% 36% 24% 3	851
	11th to 20th	Night	19% 15% 37% 25% 4	743
	21st to end	Night	26% 12% 38% 21% 3	628
March	1st to 10th	Night	21% 14% 35% 25% 5%	760
	11th to 20th	Night	18% 12% 37% 26% 6%	751
	21st to end	Night	24% 7% 37% 25% 5% 1	627
April	1st to 10th	Night	16% 13% 37% 27% 6%	570
	11th to 20th	Night	21% 10% 34% 25% 10% 1	563
	21st to end	Night	23% 8% 35% 26% 7% 1	570
May	1st to 10th	Night	20% 4 36% 32% 9%	570
	11th to 20th	Night	19% 4 27% 34% 14% 1	561
	21st to end	Night	11% 4 26% 38% 19% 2	617
June	1st to 10th	Night	12% 3 23% 43% 19%	570
	11th to 20th	Night	10% 3 25% 43% 19% 1	570
	21st to end	Night	10% 2 23% 42% 22% 1	570
July	1st to 10th	Night	11% 1 14% 37% 32% 6%	555
	11th to 20th	Night	6% 2 17% 41% 30% 5%	552
	21st to end	Night	6% 2 13% 46% 32% 2	624
August	1st to 10th	Night	8% 2 9% 46% 32% 4	567
	11th to 20th	Night	7% 2 10% 46% 30% 4	564
	21st to end	Night	8% 3 12% 33% 41% 3	627
September	1st to 10th	Night	15% 2 13% 38% 29% 4	570
	11th to 20th	Night	8% 3 14% 40% 32% 4	684
	21st to end	Night	13% 6% 22% 30% 26% 3	760
October	1st to 10th	Night	13% 5% 23% 37% 21% 3	760
	11th to 20th	Night	18% 10% 30% 28% 14%	760
	21st to end	Night	23% 12% 34% 24% 6%	812
November	1st to 10th	Night	14% 9% 41% 26% 10% 1	740
	11th to 20th	Night	18% 13% 34% 28% 6% 1	760
	21st to end	Night	22% 14% 31% 26% 6%	760
December	1st to 10th	Night	22% 12% 36% 25% 4	921
	11th to 20th	Night	24% 11% 32% 26% 6%	950
	21st to end	Night	30% 14% 31% 22% 3	1045

Page generated at 2024-10-22 19:21:02. Version ac07

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