Medford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Medford clear sky chart from 2005-11-06 to 2024-11-03.

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	10% 8% 2 5% 4 3 3 3 4 6% 51%	101442
	Night	13% 9% 3 6% 4 3 4 3 4 6% 45%	97721
Transparency	Day	34% 6% 11% 20% 19% 10%	101193
	Night	40% 7% 11% 20% 15% 6%	97559
Seeing	Day	16% 15% 27% 26% 13% 3	14934
	Night	16% 8% 18% 32% 23% 3	23964

By Month

Percentage Cloud Cover SW (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	18% 16% 4 11% 6% 4 5% 4 5% 7% 19%	2539
	11th to 20th	Day	29% 15% 3 7% 4 4 4 3 4 5% 23%	2696
	21st to end	Day	20% 11% 4 8% 5% 4 4 4 5% 7% 28%	3146
February	1st to 10th	Day	11% 12% 5% 8% 6% 5% 6% 5% 7% 7% 29%	1710
	11th to 20th	Day	13% 12% 3 9% 5% 5% 4 4 5% 7% 34%	1665
	21st to end	Day	13% 17% 5% 8% 6% 4 4 3 4 7% 28%	1530
March	1st to 10th	Day	17% 16% 5% 11% 6% 5% 5% 3 4 5% 25%	3354
	11th to 20th	Day	11% 10% 3 5% 4 4 4 3 5% 5% 48%	3490
	21st to end	Day	16% 14% 5% 10% 5% 5% 5% 5% 6% 8% 21%	3874
April	1st to 10th	Day	14% 14% 4 9% 6% 4 5% 4 6% 7% 27%	2280
	11th to 20th	Day	16% 14% 4 6% 5% 4 4 4 6% 7% 32%	2249
	21st to end	Day	13% 10% 3 7% 4 4 4 4 7% 8% 37%	2383
May	1st to 10th	Day	11% 9% 2 7% 4 4 4 3 4 6% 46%	4166
	11th to 20th	Day	8% 6% 2 4 3 3 3 3 4 5% 61%	4377
	21st to end	Day	12% 6% 2 5% 3 3 3 3 5% 7% 51%	4813
June	1st to 10th	Day	11% 9% 2 5% 4 4 4 3 6% 8% 44%	2660
	11th to 20th	Day	8% 5% 2 5% 3 4 3 3 5% 7% 54%	2660
	21st to end	Day	4 3 1 3 2 2 2 3 4 5% 70%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 2 87%	4420
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 3 80%	4420
	21st to end	Day	1 1 1 1 1 1 2 2 3 86%	4559
August	1st to 10th	Day	2 2 1 3 2 2 2 3 4 4 75%	4091
	11th to 20th	Day	1 2 1 2 1 2 3 2 4 5% 79%	4026
	21st to end	Day	3 2 1 2 2 2 2 2 2 4 78%	4216
September	1st to 10th	Day	2 2 2 2 2 2 2 3 5% 78%	2280
	11th to 20th	Day	4 4 2 4 3 3 4 4 6% 6% 60%	2271
	21st to end	Day	7% 4 1 4 3 2 3 3 3 7% 63%	2003
October	1st to 10th	Day	8% 4 2 4 3 4 4 3 4 6% 58%	1900
	11th to 20th	Day	10% 5% 2 5% 4 5% 3 3 5% 7% 51%	1900
	21st to end	Day	12% 8% 3 6% 4 5% 4 3 4 7% 44%	2090
November	1st to 10th	Day	16% 11% 3 7% 5% 4 4 4 6% 8% 32%	1732
	11th to 20th	Day	18% 9% 2 7% 5% 4 5% 5% 7% 9% 28%	1520
	21st to end	Day	14% 12% 3 8% 5% 5% 5% 3 4 7% 34%	1520
December	1st to 10th	Day	14% 9% 3 6% 4 5% 4 4 6% 8% 38%	1520
	11th to 20th	Day	18% 13% 3 7% 6% 4 4 4 6% 9% 24%	1928
	21st to end	Day	18% 15% 4 10% 5% 5% 6% 4 6% 8% 20%	2794
January	1st to 10th	Night	19% 17% 4 9% 5% 5% 5% 4 5% 6% 19%	4406
	11th to 20th	Night	25% 16% 4 8% 4 4 3 3 4 6% 25%	4265
	21st to end	Night	25% 15% 4 9% 4 4 4 2 4 5% 24%	4521
February	1st to 10th	Night	13% 13% 4 7% 5% 4 4 3 6% 7% 33%	2470
	11th to 20th	Night	15% 14% 4 8% 5% 5% 4 3 5% 5% 32%	2402
	21st to end	Night	12% 17% 3 8% 5% 5% 5% 3 5% 8% 29%	1922
March	1st to 10th	Night	18% 16% 3 10% 5% 4 5% 4 5% 6% 24%	3504
	11th to 20th	Night	11% 11% 2 6% 4 3 3 3 3 4 49%	3490
	21st to end	Night	15% 15% 5% 10% 7% 5% 5% 4 5% 6% 22%	3777
April	1st to 10th	Night	15% 16% 4 7% 5% 4 5% 4 4 6% 30%	1900
	11th to 20th	Night	14% 15% 3 6% 4 4 4 4 5% 6% 35%	1879
	21st to end	Night	18% 10% 3 5% 4 3 4 4 6% 9% 34%	1795
May	1st to 10th	Night	16% 10% 3 6% 4 3 3 3 4 5% 43%	2801
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 4 4 60%	2516
	21st to end	Night	17% 6% 2 4 3 2 3 3 4 6% 51%	2762
June	1st to 10th	Night	12% 7% 2 5% 4 3 5% 4 7% 6% 45%	1520
	11th to 20th	Night	9% 5% 2 4 4 4 3 3 4 7% 55%	1520
	21st to end	Night	5% 3 1 3 2 2 2 2 4 4 72%	1520
July	1st to 10th	Night	2 1 2 1 1 2 2 2 2 85%	2540
	11th to 20th	Night	2 2 1 1 2 2 1 1 3 4 81%	2540
	21st to end	Night	1 1 1 1 1 1 2 2 3 86%	2998
August	1st to 10th	Night	2 2 2 2 2 2 2 4 4 79%	2848
	11th to 20th	Night	1 1 1 2 2 2 2 3 6% 79%	2812
	21st to end	Night	5% 3 1 3 2 1 2 2 2 3 75%	3460
September	1st to 10th	Night	2 2 1 1 1 1 2 2 3 5% 80%	1900
	11th to 20th	Night	5% 4 1 3 3 2 3 3 5% 8% 64%	1905
	21st to end	Night	8% 4 1 4 3 2 2 2 4 6% 63%	2176
October	1st to 10th	Night	7% 5% 2 5% 3 3 3 3 4 6% 61%	2280
	11th to 20th	Night	11% 5% 2 5% 3 3 3 2 5% 6% 54%	2280
	21st to end	Night	13% 6% 2 6% 3 4 4 3 5% 7% 45%	2508
November	1st to 10th	Night	18% 11% 3 7% 5% 4 5% 4 5% 6% 34%	2386
	11th to 20th	Night	19% 8% 3 7% 5% 5% 5% 4 7% 8% 29%	2660
	21st to end	Night	16% 11% 2 7% 4 4 4 3 5% 7% 37%	2660
December	1st to 10th	Night	15% 10% 2 6% 5% 4 4 4 5% 7% 38%	2660
	11th to 20th	Night	16% 13% 4 10% 6% 4 5% 4 6% 7% 24%	3276
	21st to end	Night	18% 15% 4 8% 5% 5% 4 4 5% 6% 25%	4862

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% 9% 10% 13% 4 1	2539
	11th to 20th	Day	63% 7% 7% 11% 7% 5%	2696
	21st to end	Day	53% 9% 13% 15% 7% 3	3146
February	1st to 10th	Day	51% 9% 16% 13% 10% 2	1710
	11th to 20th	Day	50% 9% 12% 18% 9% 2	1674
	21st to end	Day	55% 7% 11% 15% 9% 2	1530
March	1st to 10th	Day	62% 6% 10% 16% 6%	3354
	11th to 20th	Day	39% 8% 11% 18% 23% 2	3490
	21st to end	Day	58% 11% 13% 14% 3	3874
April	1st to 10th	Day	56% 8% 13% 13% 7% 2	2280
	11th to 20th	Day	52% 8% 15% 13% 8% 4	2252
	21st to end	Day	45% 7% 17% 19% 11% 1	2383
May	1st to 10th	Day	40% 7% 12% 24% 15% 2	4166
	11th to 20th	Day	26% 5% 9% 29% 27% 4	4380
	21st to end	Day	32% 7% 20% 33% 8%	4814
June	1st to 10th	Day	39% 7% 16% 27% 10%	2660
	11th to 20th	Day	30% 7% 13% 32% 16% 2	2660
	21st to end	Day	18% 4 11% 31% 27% 8%	2660
July	1st to 10th	Day	7% 2 6% 16% 23% 47%	4351
	11th to 20th	Day	11% 3 4 15% 30% 38%	4345
	21st to end	Day	7% 2 5% 19% 46% 22%	4415
August	1st to 10th	Day	13% 3 6% 18% 40% 20%	4076
	11th to 20th	Day	10% 3 7% 34% 34% 12%	4065
	21st to end	Day	13% 3 7% 31% 33% 13%	4215
September	1st to 10th	Day	11% 3 5% 22% 34% 24%	2280
	11th to 20th	Day	23% 6% 11% 25% 25% 11%	2271
	21st to end	Day	23% 4 11% 25% 23% 14%	2003
October	1st to 10th	Day	29% 5% 13% 18% 21% 15%	1900
	11th to 20th	Day	32% 6% 13% 22% 19% 7%	1900
	21st to end	Day	40% 6% 12% 17% 16% 9%	2090
November	1st to 10th	Day	49% 8% 13% 16% 12% 2	1732
	11th to 20th	Day	50% 9% 14% 12% 10% 4	1520
	21st to end	Day	48% 7% 13% 13% 12% 6%	1520
December	1st to 10th	Day	44% 8% 12% 19% 14% 3	1520
	11th to 20th	Day	55% 8% 16% 12% 8% 1	1928
	21st to end	Day	57% 10% 11% 16% 4 1	2794
January	1st to 10th	Night	63% 10% 10% 12% 4 2	4406
	11th to 20th	Night	61% 7% 8% 12% 8% 5%	4265
	21st to end	Night	62% 7% 7% 12% 9% 3	4521
February	1st to 10th	Night	50% 8% 15% 15% 11% 2	2470
	11th to 20th	Night	54% 8% 10% 18% 8% 2	2404
	21st to end	Night	52% 11% 13% 15% 7% 2	1922
March	1st to 10th	Night	57% 8% 14% 16% 4	3504
	11th to 20th	Night	40% 7% 10% 21% 19% 2	3490
	21st to end	Night	59% 12% 14% 12% 3	3777
April	1st to 10th	Night	55% 8% 15% 15% 6% 1	1900
	11th to 20th	Night	49% 10% 16% 15% 7% 3	1879
	21st to end	Night	46% 10% 18% 19% 6% 1	1795
May	1st to 10th	Night	43% 7% 16% 21% 11% 2	2801
	11th to 20th	Night	29% 5% 11% 40% 13% 2	2516
	21st to end	Night	36% 7% 27% 28% 3	2762
June	1st to 10th	Night	39% 9% 17% 29% 5%	1520
	11th to 20th	Night	30% 8% 16% 32% 13% 1	1520
	21st to end	Night	18% 3 14% 39% 21% 4	1520
July	1st to 10th	Night	8% 3 6% 18% 22% 44%	2500
	11th to 20th	Night	10% 3 4 17% 36% 30%	2492
	21st to end	Night	6% 2 5% 22% 48% 16%	2904
August	1st to 10th	Night	11% 3 6% 21% 51% 8%	2839
	11th to 20th	Night	8% 3 12% 40% 28% 9%	2839
	21st to end	Night	16% 2 8% 33% 31% 9%	3460
September	1st to 10th	Night	10% 3 6% 26% 36% 19%	1900
	11th to 20th	Night	20% 5% 13% 27% 26% 9%	1905
	21st to end	Night	25% 4 12% 25% 18% 16%	2176
October	1st to 10th	Night	26% 7% 12% 19% 24% 13%	2280
	11th to 20th	Night	32% 5% 13% 22% 18% 9%	2280
	21st to end	Night	38% 9% 13% 15% 15% 10%	2508
November	1st to 10th	Night	51% 8% 11% 14% 11% 5%	2386
	11th to 20th	Night	52% 10% 12% 12% 10% 5%	2660
	21st to end	Night	48% 6% 12% 12% 15% 8%	2660
December	1st to 10th	Night	44% 9% 10% 19% 16% 3	2660
	11th to 20th	Night	57% 10% 10% 13% 10% 1	3276
	21st to end	Night	57% 8% 12% 16% 6% 2	4862

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	33% 18% 24% 19% 4 2	180
	11th to 20th	Day	30% 12% 28% 17% 9% 4	271
	21st to end	Day	28% 14% 21% 25% 12% 1	407
February	1st to 10th	Day	18% 21% 26% 28% 7%	370
	11th to 20th	Day	26% 21% 22% 22% 7%	365
	21st to end	Day	28% 18% 27% 21% 5% 1	364
March	1st to 10th	Day	28% 20% 28% 17% 7%	460
	11th to 20th	Day	25% 16% 26% 24% 10%	460
	21st to end	Day	25% 24% 28% 18% 5%	506
April	1st to 10th	Day	21% 22% 29% 20% 7% 1	460
	11th to 20th	Day	24% 22% 26% 19% 6% 2	452
	21st to end	Day	22% 20% 27% 20% 8% 2	460
May	1st to 10th	Day	18% 22% 29% 20% 9% 3	463
	11th to 20th	Day	21% 18% 26% 20% 11% 3	488
	21st to end	Day	19% 13% 27% 26% 9% 5%	529
June	1st to 10th	Day	14% 19% 28% 22% 13% 4	490
	11th to 20th	Day	12% 20% 29% 24% 11% 3	490
	21st to end	Day	3 11% 34% 30% 14% 7%	490
July	1st to 10th	Day	5% 12% 32% 31% 15% 6%	486
	11th to 20th	Day	3 8% 37% 30% 15% 7%	484
	21st to end	Day	1 6% 35% 34% 15% 9%	531
August	1st to 10th	Day	2 7% 33% 33% 16% 9%	487
	11th to 20th	Day	3 11% 25% 35% 18% 9%	477
	21st to end	Day	5% 9% 27% 34% 20% 5%	539
September	1st to 10th	Day	3 9% 28% 36% 20% 4	490
	11th to 20th	Day	8% 11% 28% 33% 18% 2	490
	21st to end	Day	10% 12% 24% 33% 18% 2	490
October	1st to 10th	Day	11% 10% 26% 31% 20% 1	490
	11th to 20th	Day	15% 11% 21% 30% 23% 1	490
	21st to end	Day	18% 15% 26% 24% 16% 2	539
November	1st to 10th	Day	21% 15% 20% 29% 14% 1	318
	11th to 20th	Day	21% 9% 26% 28% 12% 4	180
	21st to end	Day	22% 12% 23% 30% 13% 1	180
December	1st to 10th	Day	23% 13% 23% 24% 12% 4	180
	11th to 20th	Day	28% 15% 21% 26% 8% 2	180
	21st to end	Day	30% 12% 22% 25% 11% 1	198
January	1st to 10th	Night	25% 10% 28% 25% 9% 3	760
	11th to 20th	Night	22% 12% 22% 28% 13% 3	760
	21st to end	Night	22% 11% 19% 32% 14% 3	836
February	1st to 10th	Night	21% 10% 20% 37% 11% 1	760
	11th to 20th	Night	23% 11% 20% 31% 14% 2	744
	21st to end	Night	20% 12% 24% 33% 10%	628
March	1st to 10th	Night	25% 12% 22% 28% 10% 3	760
	11th to 20th	Night	20% 11% 21% 29% 17% 2	760
	21st to end	Night	20% 17% 23% 27% 12% 1	836
April	1st to 10th	Night	22% 13% 22% 26% 16% 2	760
	11th to 20th	Night	20% 11% 23% 27% 16% 3	751
	21st to end	Night	22% 8% 17% 30% 20% 3	655
May	1st to 10th	Night	15% 9% 18% 33% 22% 3	537
	11th to 20th	Night	16% 6% 15% 30% 30% 3	374
	21st to end	Night	18% 7% 14% 31% 27% 2	411
June	1st to 10th	Night	16% 7% 10% 33% 33% 2	380
	11th to 20th	Night	11% 6% 17% 38% 26% 2	380
	21st to end	Night	6% 3 9% 38% 41% 2	380
July	1st to 10th	Night	3 1 8% 36% 50% 2	370
	11th to 20th	Night	5% 1 6% 44% 42% 2	368
	21st to end	Night	1 1 4 29% 57% 9%	552
August	1st to 10th	Night	3 1 4 31% 52% 9%	567
	11th to 20th	Night	2 1 6% 31% 52% 8%	564
	21st to end	Night	3 2 15% 34% 41% 5%	811
September	1st to 10th	Night	3 3 13% 36% 40% 6%	760
	11th to 20th	Night	6% 4 13% 32% 37% 7%	760
	21st to end	Night	10% 5% 12% 36% 29% 7%	760
October	1st to 10th	Night	9% 4 15% 38% 31% 4	760
	11th to 20th	Night	14% 5% 14% 36% 27% 5%	760
	21st to end	Night	16% 6% 18% 33% 21% 6%	836
November	1st to 10th	Night	20% 9% 22% 31% 14% 4	748
	11th to 20th	Night	23% 8% 20% 35% 12% 1	760
	21st to end	Night	22% 8% 23% 31% 15% 1	760
December	1st to 10th	Night	21% 11% 19% 32% 14% 2	760
	11th to 20th	Night	25% 13% 24% 24% 13% 2	760
	21st to end	Night	29% 16% 23% 25% 7% 1	836

Page generated at 2024-10-31 00:39:22. Version ac07

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