Richfield Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Richfield Observatory clear sky chart from 2005-11-05 to 2024-10-14.

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	12% 9% 3 8% 5% 4 5% 4 6% 7% 37%	101185
	Night	13% 10% 3 8% 5% 4 4 4 5% 6% 38%	97451
Transparency	Day	45% 5% 12% 24% 13% 1	100975
	Night	46% 4 11% 23% 14% 2	97338
Seeing	Day	17% 11% 30% 26% 13% 4	15838
	Night	18% 10% 31% 29% 12% 1	25661

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	10% 15% 7% 12% 6% 4 5% 3 4 5% 28%	2527
	11th to 20th	Day	10% 13% 6% 16% 5% 4 5% 7% 7% 6% 20%	2530
	21st to end	Day	18% 17% 8% 12% 5% 4 3 3 4 6% 20%	2794
February	1st to 10th	Day	9% 14% 5% 10% 5% 4 5% 4 5% 6% 30%	1710
	11th to 20th	Day	12% 11% 4 8% 5% 5% 5% 3 5% 6% 35%	1836
	21st to end	Day	11% 15% 4 11% 5% 5% 5% 4 4 6% 30%	1570
March	1st to 10th	Day	12% 9% 3 6% 4 4 4 4 5% 5% 42%	3120
	11th to 20th	Day	10% 7% 2 8% 6% 4 5% 4 6% 6% 43%	3272
	21st to end	Day	22% 13% 3 9% 5% 4 3 3 4 5% 29%	4165
April	1st to 10th	Day	18% 13% 4 7% 5% 5% 4 4 5% 7% 29%	2280
	11th to 20th	Day	16% 11% 3 7% 5% 5% 5% 3 5% 6% 34%	2254
	21st to end	Day	18% 10% 3 7% 4 4 5% 4 5% 7% 33%	2403
May	1st to 10th	Day	15% 8% 3 7% 5% 4 4 4 6% 7% 38%	4109
	11th to 20th	Day	13% 7% 2 6% 5% 4 4 4 5% 8% 43%	4399
	21st to end	Day	12% 8% 2 7% 4 4 5% 4 7% 8% 38%	4824
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 4 4 6% 9% 44%	2660
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 4 6% 9% 42%	2660
	21st to end	Day	10% 6% 2 5% 5% 5% 5% 5% 7% 9% 41%	2660
July	1st to 10th	Day	12% 7% 4 7% 5% 5% 6% 5% 7% 9% 33%	4440
	11th to 20th	Day	4 4 1 5% 4 5% 5% 5% 7% 10% 49%	4440
	21st to end	Day	8% 6% 3 6% 5% 5% 5% 4 6% 9% 44%	4813
August	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 8% 40%	4423
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	3803
	21st to end	Day	10% 6% 3 7% 4 4 5% 4 6% 8% 44%	4180
September	1st to 10th	Day	11% 6% 2 7% 4 4 5% 4 6% 6% 44%	2280
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 6% 8% 48%	2174
	21st to end	Day	12% 7% 2 7% 4 4 5% 4 4 7% 43%	2090
October	1st to 10th	Day	14% 7% 3 6% 4 4 4 3 5% 7% 45%	2009
	11th to 20th	Day	19% 11% 3 8% 5% 4 4 3 6% 6% 31%	1807
	21st to end	Day	18% 9% 4 7% 4 4 4 4 5% 5% 35%	1782
November	1st to 10th	Day	10% 10% 4 7% 4 4 4 3 5% 6% 43%	1672
	11th to 20th	Day	11% 12% 4 9% 7% 5% 5% 4 6% 8% 31%	1710
	21st to end	Day	16% 12% 3 7% 5% 4 3 3 4 6% 36%	1568
December	1st to 10th	Day	12% 14% 4 10% 7% 4 5% 3 6% 8% 28%	1520
	11th to 20th	Day	11% 15% 4 9% 6% 6% 5% 4 6% 7% 27%	1918
	21st to end	Day	18% 20% 9% 14% 4 4 3 3 5% 5% 15%	2783
January	1st to 10th	Night	13% 14% 6% 11% 5% 4 4 3 4 5% 32%	4428
	11th to 20th	Night	12% 14% 6% 15% 6% 5% 5% 5% 7% 6% 19%	4440
	21st to end	Night	15% 17% 7% 12% 5% 4 4 3 4 5% 22%	4870
February	1st to 10th	Night	11% 13% 4 9% 6% 4 4 4 5% 5% 34%	2470
	11th to 20th	Night	11% 9% 3 8% 5% 5% 5% 3 4 6% 40%	2228
	21st to end	Night	16% 12% 4 8% 4 4 4 3 6% 5% 35%	1884
March	1st to 10th	Night	16% 9% 3 5% 4 3 4 3 4 5% 42%	3733
	11th to 20th	Night	10% 6% 3 6% 4 4 4 4 7% 8% 44%	3717
	21st to end	Night	20% 12% 4 10% 5% 4 3 3 4 5% 30%	3466
April	1st to 10th	Night	17% 10% 3 7% 5% 4 4 4 6% 6% 35%	1900
	11th to 20th	Night	20% 9% 2 7% 4 4 4 3 5% 5% 38%	1875
	21st to end	Night	17% 9% 3 5% 4 4 4 4 5% 7% 38%	1776
May	1st to 10th	Night	14% 7% 3 7% 4 4 5% 4 6% 7% 37%	2783
	11th to 20th	Night	13% 7% 2 6% 5% 5% 5% 5% 5% 7% 42%	2506
	21st to end	Night	12% 9% 3 6% 5% 4 4 4 5% 7% 41%	2743
June	1st to 10th	Night	9% 5% 2 5% 5% 5% 4 4 6% 9% 47%	1520
	11th to 20th	Night	10% 5% 3 5% 3 4 4 4 7% 8% 46%	1520
	21st to end	Night	9% 8% 2 6% 4 4 4 3 5% 7% 48%	1520
July	1st to 10th	Night	13% 7% 3 6% 5% 4 4 4 5% 8% 41%	2530
	11th to 20th	Night	3 3 1 5% 4 4 5% 4 6% 8% 57%	2530
	21st to end	Night	6% 4 1 5% 5% 5% 6% 5% 6% 9% 48%	2750
August	1st to 10th	Night	10% 4 2 6% 4 3 5% 4 6% 8% 48%	2517
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 6% 8% 48%	3021
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 50%	3476
September	1st to 10th	Night	9% 5% 2 5% 3 4 3 3 5% 7% 55%	1900
	11th to 20th	Night	11% 4 2 5% 3 4 4 4 5% 7% 53%	1986
	21st to end	Night	11% 7% 3 6% 4 5% 3 3 4 6% 48%	2090
October	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 5% 5% 49%	2166
	11th to 20th	Night	17% 8% 3 6% 4 3 4 3 4 7% 40%	2225
	21st to end	Night	18% 10% 3 6% 4 4 4 3 5% 7% 35%	2574
November	1st to 10th	Night	12% 7% 3 6% 5% 4 3 3 5% 6% 46%	2406
	11th to 20th	Night	13% 11% 4 8% 5% 5% 4 4 5% 7% 34%	2470
	21st to end	Night	16% 9% 3 7% 5% 4 4 3 5% 6% 37%	2608
December	1st to 10th	Night	14% 12% 4 9% 5% 5% 4 3 5% 6% 31%	2660
	11th to 20th	Night	13% 14% 5% 10% 6% 5% 5% 4 5% 5% 29%	3279
	21st to end	Night	19% 19% 5% 10% 5% 5% 4 3 4 5% 20%	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	59% 4 13% 17% 7%	2528
	11th to 20th	Day	62% 4 11% 19% 5%	2530
	21st to end	Day	66% 3 9% 17% 5%	2794
February	1st to 10th	Day	53% 4 12% 21% 9% 1	1710
	11th to 20th	Day	49% 4 10% 23% 12% 2	1846
	21st to end	Day	56% 3 10% 19% 11% 3	1570
March	1st to 10th	Day	44% 4 9% 26% 13% 3	3120
	11th to 20th	Day	41% 5% 10% 27% 15% 2	3272
	21st to end	Day	58% 4 11% 18% 8% 1	4165
April	1st to 10th	Day	54% 5% 11% 19% 11%	2280
	11th to 20th	Day	50% 5% 9% 20% 13% 3	2254
	21st to end	Day	49% 6% 12% 18% 12% 1	2403
May	1st to 10th	Day	45% 5% 10% 24% 16% 1	4147
	11th to 20th	Day	39% 5% 11% 30% 14% 1	4403
	21st to end	Day	41% 6% 11% 22% 16% 4	4837
June	1st to 10th	Day	35% 6% 13% 28% 16% 2	2660
	11th to 20th	Day	37% 5% 14% 25% 17% 1	2660
	21st to end	Day	37% 7% 15% 24% 15% 2	2660
July	1st to 10th	Day	45% 6% 12% 25% 10% 2	4371
	11th to 20th	Day	27% 6% 17% 31% 17% 1	4365
	21st to end	Day	36% 7% 15% 21% 20% 2	4662
August	1st to 10th	Day	39% 6% 15% 29% 11% 1	4408
	11th to 20th	Day	39% 5% 12% 31% 12% 1	3841
	21st to end	Day	37% 6% 13% 24% 19% 1	4179
September	1st to 10th	Day	38% 6% 10% 28% 17% 1	2280
	11th to 20th	Day	34% 4 11% 32% 17% 1	2174
	21st to end	Day	41% 4 10% 30% 14% 1	2090
October	1st to 10th	Day	40% 4 8% 30% 16% 1	2009
	11th to 20th	Day	52% 4 11% 21% 11% 1	1807
	21st to end	Day	50% 4 12% 21% 11% 1	1782
November	1st to 10th	Day	42% 4 13% 25% 15% 2	1672
	11th to 20th	Day	51% 4 13% 22% 9% 1	1710
	21st to end	Day	50% 2 13% 25% 8% 1	1568
December	1st to 10th	Day	54% 3 16% 19% 7% 1	1520
	11th to 20th	Day	55% 3 14% 18% 8% 2	1915
	21st to end	Day	71% 3 9% 11% 5%	2783
January	1st to 10th	Night	57% 3 9% 20% 10% 1	4428
	11th to 20th	Night	64% 3 10% 13% 8%	4440
	21st to end	Night	64% 3 11% 15% 6%	4870
February	1st to 10th	Night	52% 3 10% 19% 13% 2	2470
	11th to 20th	Night	45% 4 10% 24% 16% 2	2229
	21st to end	Night	50% 3 11% 20% 12% 3	1884
March	1st to 10th	Night	44% 4 13% 25% 10% 3	3733
	11th to 20th	Night	35% 5% 11% 27% 19% 3	3717
	21st to end	Night	58% 4 7% 18% 11% 2	3466
April	1st to 10th	Night	48% 5% 9% 21% 16% 1	1900
	11th to 20th	Night	49% 3 7% 20% 18% 3	1875
	21st to end	Night	45% 4 12% 23% 14% 2	1776
May	1st to 10th	Night	44% 6% 11% 20% 17% 3	2810
	11th to 20th	Night	40% 6% 11% 29% 13% 1	2507
	21st to end	Night	43% 5% 10% 19% 16% 8%	2751
June	1st to 10th	Night	34% 5% 14% 27% 18% 2	1520
	11th to 20th	Night	35% 5% 10% 27% 20% 2	1520
	21st to end	Night	35% 5% 16% 24% 18% 2	1520
July	1st to 10th	Night	42% 5% 14% 22% 13% 4	2490
	11th to 20th	Night	23% 5% 16% 35% 18% 3	2482
	21st to end	Night	30% 7% 15% 20% 23% 4	2662
August	1st to 10th	Night	34% 5% 15% 26% 19% 2	2508
	11th to 20th	Night	33% 5% 14% 33% 15% 1	3049
	21st to end	Night	31% 4 14% 28% 21% 3	3476
September	1st to 10th	Night	30% 5% 12% 27% 24% 2	1900
	11th to 20th	Night	32% 4 10% 34% 19% 2	1986
	21st to end	Night	38% 4 9% 31% 17% 1	2090
October	1st to 10th	Night	37% 4 8% 32% 17% 2	2166
	11th to 20th	Night	44% 4 13% 23% 15% 1	2230
	21st to end	Night	49% 5% 12% 23% 11% 1	2574
November	1st to 10th	Night	39% 4 10% 27% 17% 2	2406
	11th to 20th	Night	48% 5% 12% 22% 11% 2	2470
	21st to end	Night	48% 4 14% 23% 9% 1	2608
December	1st to 10th	Night	53% 4 12% 21% 9% 1	2660
	11th to 20th	Night	56% 5% 11% 18% 9% 1	3281
	21st to end	Night	66% 4 10% 14% 5%	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	18% 15% 39% 21% 6% 1	270
	11th to 20th	Day	18% 19% 34% 23% 6% 1	270
	21st to end	Day	24% 13% 38% 20% 4 1	297
February	1st to 10th	Day	12% 20% 44% 17% 5% 1	270
	11th to 20th	Day	20% 24% 37% 14% 6%	270
	21st to end	Day	19% 23% 41% 16%	225
March	1st to 10th	Day	18% 24% 41% 15% 2	270
	11th to 20th	Day	24% 20% 29% 19% 6% 1	284
	21st to end	Day	28% 13% 29% 23% 7% 1	506
April	1st to 10th	Day	27% 12% 36% 20% 5%	460
	11th to 20th	Day	23% 19% 25% 22% 8% 2	452
	21st to end	Day	23% 11% 30% 23% 12% 1	460
May	1st to 10th	Day	23% 10% 35% 23% 8% 2	477
	11th to 20th	Day	21% 11% 32% 24% 10% 3	675
	21st to end	Day	17% 8% 29% 28% 13% 5%	734
June	1st to 10th	Day	9% 10% 33% 30% 15% 4	680
	11th to 20th	Day	13% 10% 29% 30% 13% 5%	680
	21st to end	Day	14% 8% 31% 30% 14% 4	680
July	1st to 10th	Day	9% 3 21% 32% 24% 10%	671
	11th to 20th	Day	8% 6% 27% 32% 20% 7%	668
	21st to end	Day	6% 3 28% 36% 19% 8%	739
August	1st to 10th	Day	8% 3 24% 36% 18% 10%	676
	11th to 20th	Day	12% 4 16% 30% 25% 13%	483
	21st to end	Day	13% 6% 19% 30% 22% 9%	539
September	1st to 10th	Day	14% 6% 25% 28% 20% 8%	490
	11th to 20th	Day	12% 3 22% 31% 23% 10%	490
	21st to end	Day	17% 11% 24% 26% 16% 6%	490
October	1st to 10th	Day	19% 9% 26% 28% 12% 6%	409
	11th to 20th	Day	24% 18% 31% 17% 9%	279
	21st to end	Day	28% 13% 38% 15% 4 1	297
November	1st to 10th	Day	17% 17% 33% 22% 9% 1	270
	11th to 20th	Day	16% 21% 36% 20% 7%	270
	21st to end	Day	24% 11% 42% 19% 5%	270
December	1st to 10th	Day	21% 18% 41% 13% 6% 1	270
	11th to 20th	Day	19% 19% 37% 17% 8% 1	270
	21st to end	Day	24% 21% 35% 16% 4	297
January	1st to 10th	Night	18% 18% 35% 22% 6%	950
	11th to 20th	Night	21% 15% 37% 20% 7% 1	950
	21st to end	Night	20% 11% 37% 25% 6%	1045
February	1st to 10th	Night	18% 14% 37% 25% 5%	950
	11th to 20th	Night	17% 18% 35% 25% 5%	753
	21st to end	Night	24% 15% 39% 17% 4	628
March	1st to 10th	Night	20% 13% 34% 24% 8% 1	760
	11th to 20th	Night	16% 13% 37% 26% 7% 1	732
	21st to end	Night	22% 7% 30% 32% 7% 2	627
April	1st to 10th	Night	23% 11% 35% 25% 6%	570
	11th to 20th	Night	26% 9% 32% 25% 7% 1	563
	21st to end	Night	21% 8% 32% 29% 10% 1	570
May	1st to 10th	Night	19% 7% 33% 34% 7% 1	570
	11th to 20th	Night	19% 6% 29% 32% 14% 1	561
	21st to end	Night	14% 4 25% 38% 18% 2	617
June	1st to 10th	Night	11% 4 27% 41% 17% 1	570
	11th to 20th	Night	13% 3 31% 37% 15% 1	570
	21st to end	Night	11% 5% 25% 41% 17% 1	570
July	1st to 10th	Night	9% 1 17% 40% 29% 4	555
	11th to 20th	Night	6% 2 23% 42% 24% 3	552
	21st to end	Night	7% 1 20% 46% 24% 2	624
August	1st to 10th	Night	7% 2 17% 46% 26% 3	567
	11th to 20th	Night	11% 1 15% 40% 28% 5%	564
	21st to end	Night	11% 3 17% 41% 26% 3	627
September	1st to 10th	Night	10% 3 22% 35% 26% 4	570
	11th to 20th	Night	12% 3 21% 31% 27% 5%	656
	21st to end	Night	14% 8% 24% 28% 21% 4	760
October	1st to 10th	Night	16% 9% 27% 31% 17% 1	760
	11th to 20th	Night	21% 11% 33% 25% 8% 1	735
	21st to end	Night	23% 10% 31% 27% 8% 1	792
November	1st to 10th	Night	16% 12% 38% 23% 11% 1	740
	11th to 20th	Night	19% 17% 35% 22% 7%	760
	21st to end	Night	21% 13% 37% 21% 7%	898
December	1st to 10th	Night	23% 15% 37% 21% 4	950
	11th to 20th	Night	22% 13% 37% 21% 6% 1	950
	21st to end	Night	29% 14% 35% 18% 3	1045

Page generated at 2024-10-11 09:50:01. Version ac07

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