F.Myers Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the F.Myers Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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% 7% 2 6% 4 4 4 4 5% 8% 43%	101082
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 46%	98484
Transparency	Day	38% 6% 11% 23% 19% 4	104785
	Night	36% 6% 10% 23% 20% 5%	102921
Seeing	Day	15% 9% 22% 25% 20% 10%	15388
	Night	16% 8% 24% 31% 19% 3	25167

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	13% 14% 4 8% 3 3 3 2 4 6% 39%	2527
	11th to 20th	Day	20% 9% 2 6% 4 3 2 2 3 4 45%	2731
	21st to end	Day	23% 10% 3 5% 3 4 4 3 4 5% 37%	3201
February	1st to 10th	Day	19% 11% 4 6% 4 3 3 3 4 6% 37%	1900
	11th to 20th	Day	19% 9% 3 7% 4 4 3 3 3 6% 38%	1848
	21st to end	Day	23% 11% 2 6% 5% 3 3 3 5% 5% 34%	1570
March	1st to 10th	Day	19% 13% 4 8% 4 4 4 3 4 5% 33%	3120
	11th to 20th	Day	14% 7% 2 6% 5% 3 3 3 5% 6% 46%	3310
	21st to end	Day	13% 7% 3 7% 5% 4 5% 3 6% 7% 41%	4161
April	1st to 10th	Day	13% 7% 3 6% 4 4 4 3 5% 7% 44%	2280
	11th to 20th	Day	16% 8% 3 6% 3 3 3 3 4 6% 44%	2254
	21st to end	Day	13% 6% 2 6% 5% 4 4 3 5% 8% 42%	2280
May	1st to 10th	Day	17% 6% 2 6% 5% 4 5% 4 6% 10% 35%	3911
	11th to 20th	Day	16% 7% 2 7% 4 4 4 4 6% 8% 37%	4081
	21st to end	Day	11% 7% 3 6% 5% 5% 5% 5% 7% 9% 38%	4533
June	1st to 10th	Day	9% 7% 2 7% 5% 4 5% 4 6% 11% 40%	2660
	11th to 20th	Day	4 4 2 5% 4 5% 5% 4 7% 10% 47%	2660
	21st to end	Day	5% 3 2 5% 5% 5% 5% 6% 8% 11% 46%	2660
July	1st to 10th	Day	6% 5% 2 7% 5% 6% 7% 5% 8% 10% 39%	4440
	11th to 20th	Day	8% 6% 3 6% 5% 4 6% 5% 8% 12% 38%	4440
	21st to end	Day	14% 9% 3 9% 5% 6% 5% 5% 6% 7% 31%	4474
August	1st to 10th	Day	3 3 1 5% 3 4 5% 4 7% 10% 56%	3785
	11th to 20th	Day	8% 5% 2 6% 3 4 5% 5% 6% 9% 46%	3729
	21st to end	Day	5% 4 1 5% 4 4 4 3 5% 8% 56%	4180
September	1st to 10th	Day	9% 6% 2 5% 4 5% 5% 4 6% 8% 46%	2280
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 5% 7% 46%	2157
	21st to end	Day	11% 7% 2 5% 4 4 4 3 4 6% 50%	2090
October	1st to 10th	Day	8% 4 2 4 3 3 4 3 5% 7% 58%	2082
	11th to 20th	Day	11% 5% 2 4 3 3 3 3 5% 7% 54%	1900
	21st to end	Day	18% 8% 2 4 2 2 3 3 3 5% 50%	2025
November	1st to 10th	Day	13% 5% 2 5% 2 2 2 3 4 6% 55%	1762
	11th to 20th	Day	14% 6% 2 6% 3 3 3 3 4 6% 51%	1800
	21st to end	Day	17% 8% 2 5% 3 3 4 3 5% 6% 44%	1773
December	1st to 10th	Day	20% 9% 3 6% 4 4 3 3 4 5% 38%	1710
	11th to 20th	Day	16% 10% 3 5% 4 4 3 4 5% 5% 41%	1985
	21st to end	Day	14% 13% 4 7% 5% 5% 5% 3 5% 6% 34%	2783
January	1st to 10th	Night	19% 11% 2 5% 3 3 3 3 4 5% 41%	4428
	11th to 20th	Night	17% 10% 3 8% 5% 3 3 3 3 4 41%	4234
	21st to end	Night	25% 9% 2 5% 2 2 3 3 3 5% 40%	4461
February	1st to 10th	Night	21% 10% 3 7% 4 4 4 3 4 5% 36%	2280
	11th to 20th	Night	20% 8% 2 7% 5% 4 4 2 3 5% 39%	2218
	21st to end	Night	20% 8% 3 6% 5% 4 3 3 4 6% 38%	1884
March	1st to 10th	Night	21% 10% 3 7% 4 3 3 3 4 5% 36%	3733
	11th to 20th	Night	14% 8% 2 5% 4 3 3 3 4 5% 49%	3677
	21st to end	Night	13% 7% 2 7% 5% 4 4 4 5% 7% 41%	3468
April	1st to 10th	Night	12% 6% 2 6% 4 3 4 4 5% 7% 47%	1900
	11th to 20th	Night	16% 6% 2 5% 3 4 2 3 5% 7% 46%	1875
	21st to end	Night	13% 6% 2 6% 5% 4 4 4 6% 6% 44%	1900
May	1st to 10th	Night	18% 8% 2 7% 4 3 3 3 5% 7% 40%	2983
	11th to 20th	Night	12% 9% 3 6% 4 4 3 3 4 7% 45%	2812
	21st to end	Night	9% 6% 2 7% 5% 5% 4 5% 7% 10% 41%	3018
June	1st to 10th	Night	8% 6% 2 8% 5% 4 5% 4 7% 10% 41%	1520
	11th to 20th	Night	4 4 1 3 3 3 4 4 7% 11% 57%	1520
	21st to end	Night	3 3 1 4 4 4 4 5% 7% 13% 51%	1520
July	1st to 10th	Night	6% 4 2 6% 5% 5% 7% 5% 8% 11% 41%	2530
	11th to 20th	Night	4 3 2 5% 4 4 5% 3 7% 11% 51%	2530
	21st to end	Night	9% 9% 4 8% 5% 5% 5% 4 7% 8% 36%	3077
August	1st to 10th	Night	2 3 1 4 3 3 4 3 6% 9% 63%	3144
	11th to 20th	Night	4 3 1 5% 3 4 4 4 7% 11% 55%	3100
	21st to end	Night	4 3 1 5% 3 3 4 4 6% 8% 60%	3476
September	1st to 10th	Night	8% 5% 2 5% 3 4 3 4 6% 7% 53%	1900
	11th to 20th	Night	9% 6% 2 6% 4 3 3 3 5% 8% 51%	2002
	21st to end	Night	9% 5% 2 4 3 4 3 3 5% 7% 55%	2090
October	1st to 10th	Night	8% 4 1 3 3 2 4 3 4 6% 61%	2095
	11th to 20th	Night	12% 5% 1 3 2 3 3 3 4 6% 57%	2280
	21st to end	Night	16% 7% 1 5% 3 3 3 3 4 5% 51%	2570
November	1st to 10th	Night	13% 6% 2 4 3 3 3 2 5% 5% 54%	2536
	11th to 20th	Night	11% 6% 2 5% 3 3 4 3 5% 7% 52%	2600
	21st to end	Night	16% 7% 2 4 4 3 3 3 4 5% 49%	2562
December	1st to 10th	Night	20% 8% 3 6% 4 3 4 3 4 6% 39%	2470
	11th to 20th	Night	15% 8% 3 6% 3 3 3 3 3 6% 46%	3207
	21st to end	Night	15% 10% 4 9% 5% 5% 5% 4 5% 6% 33%	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	48% 2 8% 22% 18% 2	2528
	11th to 20th	Day	45% 4 8% 22% 21% 1	2731
	21st to end	Day	49% 4 8% 21% 16% 2	3201
February	1st to 10th	Day	49% 4 9% 20% 16% 2	1900
	11th to 20th	Day	49% 3 8% 19% 16% 4	1858
	21st to end	Day	52% 4 8% 15% 14% 6%	1570
March	1st to 10th	Day	53% 4 6% 14% 15% 8%	3120
	11th to 20th	Day	39% 6% 8% 25% 17% 5%	3310
	21st to end	Day	42% 5% 11% 21% 20% 1	4161
April	1st to 10th	Day	38% 6% 9% 23% 21% 3	2280
	11th to 20th	Day	41% 5% 9% 21% 20% 5%	2254
	21st to end	Day	40% 7% 10% 25% 17% 1	2280
May	1st to 10th	Day	42% 8% 13% 22% 14% 1	3946
	11th to 20th	Day	42% 8% 14% 23% 12% 1	4085
	21st to end	Day	39% 9% 12% 24% 15% 1	4546
June	1st to 10th	Day	36% 8% 13% 23% 18% 2	2660
	11th to 20th	Day	28% 8% 16% 27% 18% 3	2660
	21st to end	Day	28% 9% 17% 24% 17% 4	2660
July	1st to 10th	Day	34% 10% 17% 27% 9% 2	4371
	11th to 20th	Day	34% 9% 15% 30% 10% 2	4365
	21st to end	Day	51% 8% 11% 22% 8% 1	4331
August	1st to 10th	Day	21% 8% 17% 29% 23% 2	3773
	11th to 20th	Day	32% 8% 16% 24% 18% 2	3765
	21st to end	Day	26% 7% 11% 29% 25% 2	4179
September	1st to 10th	Day	34% 8% 10% 25% 17% 5%	2280
	11th to 20th	Day	37% 7% 10% 18% 24% 4	2157
	21st to end	Day	35% 6% 10% 21% 23% 6%	2090
October	1st to 10th	Day	17% 3 8% 15% 44% 14%	3459
	11th to 20th	Day	20% 3 6% 24% 31% 16%	3140
	21st to end	Day	29% 3 5% 24% 33% 6%	3315
November	1st to 10th	Day	32% 4 7% 24% 27% 6%	1762
	11th to 20th	Day	36% 4 7% 21% 24% 8%	1800
	21st to end	Day	40% 4 8% 22% 21% 4	1773
December	1st to 10th	Day	48% 4 7% 21% 15% 4	1710
	11th to 20th	Day	45% 5% 8% 20% 19% 3	1982
	21st to end	Day	50% 6% 10% 21% 12% 1	2783
January	1st to 10th	Night	45% 3 8% 24% 18% 2	4428
	11th to 20th	Night	48% 5% 6% 21% 17% 4	4234
	21st to end	Night	48% 3 7% 23% 17% 2	4461
February	1st to 10th	Night	52% 4 9% 16% 17% 3	2280
	11th to 20th	Night	48% 5% 7% 19% 16% 5%	2219
	21st to end	Night	49% 4 8% 16% 17% 5%	1884
March	1st to 10th	Night	49% 4 9% 12% 17% 8%	3733
	11th to 20th	Night	37% 5% 9% 22% 17% 10%	3677
	21st to end	Night	41% 6% 10% 20% 22% 1	3468
April	1st to 10th	Night	35% 6% 11% 23% 20% 5%	1900
	11th to 20th	Night	38% 4 8% 20% 22% 8%	1875
	21st to end	Night	37% 7% 10% 25% 19% 3	1900
May	1st to 10th	Night	43% 8% 11% 22% 14% 2	3013
	11th to 20th	Night	39% 7% 14% 24% 15% 1	2813
	21st to end	Night	34% 9% 14% 26% 15% 2	3026
June	1st to 10th	Night	38% 9% 11% 19% 22% 2	1520
	11th to 20th	Night	20% 6% 17% 32% 20% 4	1520
	21st to end	Night	22% 9% 18% 28% 17% 6%	1520
July	1st to 10th	Night	32% 11% 17% 27% 11% 2	2490
	11th to 20th	Night	24% 8% 14% 38% 12% 4	2482
	21st to end	Night	44% 9% 14% 21% 11%	2980
August	1st to 10th	Night	17% 7% 12% 39% 24% 1	3132
	11th to 20th	Night	21% 9% 19% 30% 18% 2	3130
	21st to end	Night	21% 6% 12% 30% 26% 4	3476
September	1st to 10th	Night	29% 7% 12% 25% 21% 7%	1900
	11th to 20th	Night	32% 6% 11% 19% 28% 4	2002
	21st to end	Night	28% 5% 10% 26% 25% 6%	2090
October	1st to 10th	Night	16% 4 6% 15% 43% 15%	3498
	11th to 20th	Night	17% 3 5% 18% 37% 20%	3779
	21st to end	Night	25% 4 6% 27% 25% 13%	4230
November	1st to 10th	Night	32% 4 7% 23% 26% 7%	2536
	11th to 20th	Night	32% 4 7% 22% 25% 10%	2600
	21st to end	Night	39% 4 6% 23% 23% 5%	2562
December	1st to 10th	Night	47% 5% 8% 19% 18% 4	2470
	11th to 20th	Night	40% 4 7% 24% 21% 4	3209
	21st to end	Night	49% 6% 10% 18% 13% 3	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% 19% 36% 15% 6%	270
	11th to 20th	Day	28% 17% 36% 14% 4 1	270
	21st to end	Day	22% 20% 40% 14% 4	297
February	1st to 10th	Day	26% 19% 31% 18% 5% 1	270
	11th to 20th	Day	32% 19% 35% 10% 3	270
	21st to end	Day	34% 23% 31% 7% 5%	225
March	1st to 10th	Day	25% 17% 38% 14% 6%	270
	11th to 20th	Day	26% 20% 34% 17% 3	270
	21st to end	Day	23% 15% 33% 21% 7% 1	502
April	1st to 10th	Day	19% 17% 29% 25% 9% 1	460
	11th to 20th	Day	21% 13% 30% 24% 10% 2	452
	21st to end	Day	17% 15% 30% 22% 13% 3	460
May	1st to 10th	Day	19% 12% 26% 25% 14% 4	463
	11th to 20th	Day	17% 6% 21% 26% 21% 10%	487
	21st to end	Day	11% 4 19% 30% 22% 13%	560
June	1st to 10th	Day	10% 6% 16% 28% 25% 16%	680
	11th to 20th	Day	6% 2 13% 31% 33% 16%	680
	21st to end	Day	6% 2 17% 34% 26% 15%	680
July	1st to 10th	Day	9% 1 12% 27% 28% 23%	671
	11th to 20th	Day	9% 3 10% 24% 33% 21%	668
	21st to end	Day	8% 2 10% 25% 32% 21%	669
August	1st to 10th	Day	7% 2 8% 29% 35% 18%	486
	11th to 20th	Day	11% 3 13% 30% 33% 11%	479
	21st to end	Day	11% 1 5% 21% 37% 24%	539
September	1st to 10th	Day	9% 2 13% 27% 36% 13%	490
	11th to 20th	Day	12% 3 10% 24% 36% 16%	490
	21st to end	Day	16% 6% 14% 29% 23% 12%	490
October	1st to 10th	Day	8% 3 18% 34% 27% 9%	482
	11th to 20th	Day	9% 11% 35% 27% 14% 3	300
	21st to end	Day	22% 12% 32% 22% 10% 2	330
November	1st to 10th	Day	16% 10% 30% 29% 13% 2	300
	11th to 20th	Day	12% 15% 34% 29% 8% 1	300
	21st to end	Day	24% 13% 30% 19% 12% 2	291
December	1st to 10th	Day	25% 19% 30% 20% 6% 1	270
	11th to 20th	Day	24% 17% 29% 22% 7% 1	270
	21st to end	Day	26% 16% 36% 18% 4	297
January	1st to 10th	Night	22% 15% 34% 25% 4	950
	11th to 20th	Night	26% 15% 33% 22% 4	950
	21st to end	Night	21% 11% 41% 25% 2	1000
February	1st to 10th	Night	24% 13% 34% 25% 4	760
	11th to 20th	Night	25% 13% 35% 24% 2	743
	21st to end	Night	25% 17% 36% 20% 2	628
March	1st to 10th	Night	21% 13% 32% 29% 5%	760
	11th to 20th	Night	22% 12% 33% 27% 5% 1	689
	21st to end	Night	16% 11% 33% 30% 9%	627
April	1st to 10th	Night	15% 9% 35% 29% 11% 1	570
	11th to 20th	Night	19% 9% 30% 29% 13%	563
	21st to end	Night	14% 7% 34% 32% 12% 2	570
May	1st to 10th	Night	15% 6% 28% 34% 15% 2	570
	11th to 20th	Night	13% 4 21% 37% 23% 2	561
	21st to end	Night	7% 3 17% 38% 30% 5%	617
June	1st to 10th	Night	11% 3 13% 39% 29% 5%	570
	11th to 20th	Night	5% 1 10% 37% 44% 3	570
	21st to end	Night	4 1 11% 39% 39% 6%	570
July	1st to 10th	Night	6% 3 7% 32% 42% 10%	555
	11th to 20th	Night	8% 1 7% 28% 43% 12%	552
	21st to end	Night	7% 1 8% 29% 45% 10%	624
August	1st to 10th	Night	5% 1 6% 32% 46% 9%	567
	11th to 20th	Night	6% 1 7% 40% 41% 4	564
	21st to end	Night	8% 1 7% 28% 46% 10%	627
September	1st to 10th	Night	9% 1 8% 33% 43% 6%	570
	11th to 20th	Night	9% 2 12% 31% 40% 6%	672
	21st to end	Night	11% 2 14% 34% 33% 4	760
October	1st to 10th	Night	9% 3 15% 36% 32% 4	760
	11th to 20th	Night	15% 5% 23% 36% 19% 2	760
	21st to end	Night	19% 6% 27% 31% 15% 2	836
November	1st to 10th	Night	15% 7% 25% 35% 17% 2	780
	11th to 20th	Night	13% 10% 31% 34% 11% 1	800
	21st to end	Night	20% 9% 29% 30% 11% 1	789
December	1st to 10th	Night	23% 10% 32% 27% 7%	760
	11th to 20th	Night	22% 10% 28% 32% 7%	878
	21st to end	Night	25% 13% 30% 27% 4	1045

Page generated at 2024-11-24 23:22:19. Version ac07

Copyright © 2024 Attilla Danko.