Clearfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clearfield clear sky chart from 2005-11-06 to 2024-01-13.

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	16% 10% 4 7% 6% 3 5% 5% 5% 7% 30%	74662
	Night	15% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	75074
Transparency	Day	52% 7% 12% 18% 10% 1	74372
	Night	50% 8% 12% 19% 10% 1	74883
Seeing	Day	23% 18% 27% 19% 10% 4	13585
	Night	22% 16% 27% 24% 10% 1	23191

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% 7% 11% 9% 4 5% 5% 5% 5% 22%	1542
	11th to 20th	Day	15% 16% 6% 12% 7% 4 6% 5% 5% 6% 18%	1638
	21st to end	Day	14% 15% 7% 13% 11% 4 5% 5% 5% 5% 18%	1782
February	1st to 10th	Day	17% 15% 6% 10% 8% 4 6% 5% 6% 5% 19%	1620
	11th to 20th	Day	14% 12% 6% 11% 8% 4 6% 6% 6% 8% 20%	1573
	21st to end	Day	19% 14% 5% 9% 6% 3 5% 4 4 6% 26%	1445
March	1st to 10th	Day	14% 11% 5% 8% 7% 3 4 4 5% 7% 31%	1980
	11th to 20th	Day	18% 10% 4 10% 6% 3 5% 5% 5% 6% 27%	1980
	21st to end	Day	19% 10% 4 7% 7% 3 5% 4 4 7% 30%	2178
April	1st to 10th	Day	15% 12% 4 7% 6% 3 6% 5% 6% 7% 31%	2150
	11th to 20th	Day	15% 11% 3 6% 6% 4 4 5% 4 7% 34%	2134
	21st to end	Day	20% 10% 4 7% 6% 3 4 3 4 6% 32%	2273
May	1st to 10th	Day	17% 10% 3 7% 7% 3 6% 5% 5% 7% 30%	2340
	11th to 20th	Day	22% 7% 3 6% 6% 3 5% 4 6% 8% 30%	2410
	21st to end	Day	14% 6% 2 5% 6% 4 6% 5% 6% 9% 37%	2725
June	1st to 10th	Day	15% 7% 3 6% 6% 4 6% 6% 5% 8% 34%	2520
	11th to 20th	Day	14% 7% 3 7% 7% 3 5% 5% 6% 9% 34%	2520
	21st to end	Day	15% 5% 3 5% 5% 4 6% 5% 6% 9% 37%	2520
July	1st to 10th	Day	9% 7% 4 6% 6% 4 7% 6% 6% 8% 37%	2520
	11th to 20th	Day	10% 6% 2 6% 7% 4 6% 7% 7% 10% 36%	2464
	21st to end	Day	11% 6% 3 7% 7% 4 7% 6% 6% 9% 34%	2547
August	1st to 10th	Day	10% 7% 3 7% 7% 5% 6% 7% 7% 10% 31%	2327
	11th to 20th	Day	13% 6% 3 7% 7% 4 7% 6% 6% 8% 32%	2303
	21st to end	Day	14% 7% 3 7% 5% 4 6% 5% 7% 8% 35%	2386
September	1st to 10th	Day	18% 7% 3 6% 5% 3 4 3 5% 6% 40%	2160
	11th to 20th	Day	15% 6% 2 5% 5% 3 4 6% 5% 8% 43%	2108
	21st to end	Day	17% 8% 3 7% 6% 3 5% 4 5% 7% 35%	1908
October	1st to 10th	Day	15% 9% 3 8% 5% 3 5% 5% 6% 7% 35%	1800
	11th to 20th	Day	20% 11% 3 6% 6% 3 3 4 6% 6% 32%	1800
	21st to end	Day	21% 11% 3 5% 6% 3 4 4 5% 7% 30%	1980
November	1st to 10th	Day	13% 7% 4 7% 7% 3 4 5% 5% 6% 39%	1777
	11th to 20th	Day	16% 14% 5% 8% 6% 3 5% 4 5% 6% 29%	1530
	21st to end	Day	18% 15% 5% 7% 6% 3 5% 6% 4 7% 25%	1520
December	1st to 10th	Day	18% 18% 8% 12% 8% 3 4 4 5% 5% 16%	1520
	11th to 20th	Day	18% 16% 8% 9% 6% 3 4 4 4 7% 20%	1910
	21st to end	Day	24% 21% 7% 10% 5% 3 4 3 3 5% 15%	2772
January	1st to 10th	Night	15% 14% 6% 9% 8% 4 5% 5% 5% 7% 22%	2621
	11th to 20th	Night	17% 13% 6% 11% 8% 4 5% 5% 5% 6% 19%	2367
	21st to end	Night	13% 13% 8% 11% 8% 5% 5% 4 5% 7% 22%	2574
February	1st to 10th	Night	17% 11% 5% 9% 8% 4 6% 6% 4 5% 24%	2340
	11th to 20th	Night	15% 11% 6% 8% 8% 4 5% 6% 5% 7% 25%	2273
	21st to end	Night	18% 10% 5% 9% 7% 4 5% 4 4 5% 28%	1807
March	1st to 10th	Night	14% 9% 5% 7% 6% 4 5% 5% 6% 8% 32%	1980
	11th to 20th	Night	16% 11% 4 6% 6% 2 3 5% 6% 5% 34%	1980
	21st to end	Night	18% 9% 4 7% 5% 3 4 4 4 6% 35%	2178
April	1st to 10th	Night	16% 11% 6% 8% 6% 3 3 4 5% 7% 31%	1810
	11th to 20th	Night	15% 9% 3 6% 5% 3 5% 5% 6% 5% 38%	1775
	21st to end	Night	16% 9% 3 7% 6% 3 5% 4 5% 7% 34%	1702
May	1st to 10th	Night	19% 8% 3 7% 5% 3 4 4 5% 7% 35%	1620
	11th to 20th	Night	16% 7% 3 6% 6% 3 4 3 6% 8% 38%	1480
	21st to end	Night	10% 6% 3 4 5% 4 4 5% 6% 10% 41%	1550
June	1st to 10th	Night	11% 5% 3 5% 5% 3 5% 5% 6% 8% 42%	1440
	11th to 20th	Night	11% 6% 2 6% 6% 4 5% 6% 6% 10% 39%	1440
	21st to end	Night	12% 6% 2 5% 4 3 5% 5% 6% 9% 43%	1440
July	1st to 10th	Night	11% 4 3 6% 5% 3 4 5% 5% 8% 45%	1440
	11th to 20th	Night	8% 4 3 5% 4 3 5% 5% 6% 11% 47%	1492
	21st to end	Night	11% 6% 2 5% 5% 4 6% 5% 7% 9% 41%	1771
August	1st to 10th	Night	8% 5% 2 5% 6% 3 5% 5% 6% 8% 45%	1611
	11th to 20th	Night	11% 6% 3 6% 6% 4 4 4 7% 7% 42%	1598
	21st to end	Night	11% 6% 3 5% 5% 3 5% 5% 6% 9% 42%	1950
September	1st to 10th	Night	16% 5% 2 5% 6% 2 5% 3 5% 6% 46%	1800
	11th to 20th	Night	11% 5% 2 5% 5% 3 3 4 5% 7% 49%	1849
	21st to end	Night	17% 7% 3 6% 5% 4 4 4 4 6% 40%	2052
October	1st to 10th	Night	15% 6% 3 6% 5% 3 4 4 6% 7% 42%	2160
	11th to 20th	Night	18% 8% 3 6% 5% 3 4 4 5% 7% 38%	2160
	21st to end	Night	21% 9% 3 6% 5% 3 4 4 5% 6% 32%	2376
November	1st to 10th	Night	12% 9% 3 5% 5% 3 5% 3 5% 7% 44%	2301
	11th to 20th	Night	16% 11% 4 7% 6% 4 4 4 5% 7% 30%	2648
	21st to end	Night	17% 12% 5% 7% 6% 3 5% 4 5% 7% 28%	2660
December	1st to 10th	Night	19% 13% 7% 9% 8% 4 5% 5% 6% 6% 18%	2660
	11th to 20th	Night	18% 14% 6% 10% 7% 3 5% 4 4 5% 24%	3285
	21st to end	Night	21% 15% 6% 9% 8% 4 5% 5% 5% 6% 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	65% 6% 12% 12% 4	1543
	11th to 20th	Day	68% 6% 12% 9% 5%	1638
	21st to end	Day	70% 6% 9% 9% 5% 1	1782
February	1st to 10th	Day	67% 6% 11% 10% 5%	1620
	11th to 20th	Day	64% 7% 10% 13% 6%	1582
	21st to end	Day	61% 5% 11% 15% 7% 2	1445
March	1st to 10th	Day	53% 7% 12% 20% 8%	1980
	11th to 20th	Day	58% 5% 10% 17% 7% 3	1980
	21st to end	Day	56% 6% 8% 18% 10% 2	2178
April	1st to 10th	Day	52% 8% 11% 18% 11% 2	2150
	11th to 20th	Day	50% 6% 11% 17% 14% 2	2134
	21st to end	Day	54% 5% 9% 19% 11% 1	2273
May	1st to 10th	Day	53% 7% 12% 16% 10% 2	2340
	11th to 20th	Day	52% 8% 11% 15% 11% 2	2414
	21st to end	Day	43% 9% 17% 21% 9% 1	2725
June	1st to 10th	Day	48% 8% 12% 20% 11% 1	2520
	11th to 20th	Day	47% 9% 13% 19% 12% 1	2520
	21st to end	Day	42% 8% 14% 25% 11%	2520
July	1st to 10th	Day	44% 10% 12% 20% 12% 2	2450
	11th to 20th	Day	40% 11% 15% 22% 12% 1	2389
	21st to end	Day	44% 9% 13% 20% 13% 1	2405
August	1st to 10th	Day	44% 11% 15% 22% 8%	2314
	11th to 20th	Day	46% 10% 15% 20% 9% 1	2303
	21st to end	Day	44% 9% 13% 20% 12% 3	2386
September	1st to 10th	Day	46% 6% 10% 21% 14% 3	2160
	11th to 20th	Day	39% 7% 12% 24% 17% 1	2108
	21st to end	Day	48% 7% 11% 19% 14% 1	1908
October	1st to 10th	Day	48% 7% 13% 17% 13% 1	1800
	11th to 20th	Day	51% 7% 11% 22% 9%	1800
	21st to end	Day	54% 7% 12% 17% 9% 1	1980
November	1st to 10th	Day	45% 7% 12% 18% 15% 3	1777
	11th to 20th	Day	56% 5% 13% 15% 8% 2	1530
	21st to end	Day	60% 7% 11% 16% 7%	1520
December	1st to 10th	Day	72% 6% 10% 9% 3	1520
	11th to 20th	Day	66% 6% 10% 15% 4	1906
	21st to end	Day	74% 6% 9% 10% 2	2772
January	1st to 10th	Night	62% 6% 11% 14% 5% 1	2621
	11th to 20th	Night	66% 7% 12% 11% 4 1	2367
	21st to end	Night	63% 5% 12% 12% 6% 1	2574
February	1st to 10th	Night	62% 7% 11% 14% 6%	2340
	11th to 20th	Night	59% 6% 12% 15% 7%	2275
	21st to end	Night	59% 5% 9% 16% 10% 1	1807
March	1st to 10th	Night	49% 7% 12% 21% 10% 1	1980
	11th to 20th	Night	51% 7% 13% 18% 10% 1	1980
	21st to end	Night	50% 6% 9% 18% 14% 2	2178
April	1st to 10th	Night	53% 7% 10% 17% 12% 1	1810
	11th to 20th	Night	45% 8% 11% 20% 13% 2	1775
	21st to end	Night	48% 7% 10% 20% 12% 3	1702
May	1st to 10th	Night	49% 7% 10% 19% 11% 3	1620
	11th to 20th	Night	46% 8% 12% 20% 14% 2	1481
	21st to end	Night	36% 11% 15% 22% 14% 2	1551
June	1st to 10th	Night	38% 8% 13% 26% 13% 1	1440
	11th to 20th	Night	40% 11% 12% 23% 13% 2	1440
	21st to end	Night	36% 10% 14% 26% 13% 1	1440
July	1st to 10th	Night	37% 9% 14% 22% 16% 3	1400
	11th to 20th	Night	30% 10% 16% 24% 18% 2	1444
	21st to end	Night	35% 11% 17% 20% 15% 2	1672
August	1st to 10th	Night	34% 10% 15% 27% 13% 1	1600
	11th to 20th	Night	39% 9% 15% 24% 12% 1	1598
	21st to end	Night	38% 10% 13% 23% 13% 3	1950
September	1st to 10th	Night	39% 8% 10% 25% 15% 3	1800
	11th to 20th	Night	34% 6% 13% 28% 18% 2	1849
	21st to end	Night	43% 7% 12% 21% 16% 1	2052
October	1st to 10th	Night	41% 7% 14% 22% 14% 1	2160
	11th to 20th	Night	46% 6% 14% 21% 12% 1	2160
	21st to end	Night	51% 7% 12% 19% 10% 1	2376
November	1st to 10th	Night	40% 7% 14% 20% 17% 3	2301
	11th to 20th	Night	52% 8% 11% 18% 9% 2	2648
	21st to end	Night	55% 7% 12% 19% 6% 1	2660
December	1st to 10th	Night	67% 8% 11% 11% 4	2660
	11th to 20th	Night	63% 6% 10% 16% 4	3288
	21st to end	Night	68% 8% 11% 11% 2	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	32% 30% 26% 8% 4 1	193
	11th to 20th	Day	35% 29% 30% 5% 1 1	246
	21st to end	Day	30% 30% 29% 9% 2	264
February	1st to 10th	Day	31% 33% 30% 5% 1	240
	11th to 20th	Day	38% 29% 29% 5%	240
	21st to end	Day	40% 25% 25% 9% 1	296
March	1st to 10th	Day	30% 26% 30% 12% 2	420
	11th to 20th	Day	30% 24% 28% 12% 4 1	420
	21st to end	Day	32% 25% 27% 11% 4 2	462
April	1st to 10th	Day	29% 24% 26% 16% 4 1	420
	11th to 20th	Day	22% 25% 26% 14% 8% 4	412
	21st to end	Day	31% 21% 29% 14% 4 1	420
May	1st to 10th	Day	30% 17% 27% 16% 7% 3	423
	11th to 20th	Day	26% 15% 32% 15% 8% 4	447
	21st to end	Day	16% 14% 26% 21% 16% 6%	485
June	1st to 10th	Day	19% 14% 29% 25% 11% 3	450
	11th to 20th	Day	18% 17% 26% 22% 13% 4	450
	21st to end	Day	14% 14% 30% 29% 9% 3	450
July	1st to 10th	Day	11% 9% 25% 27% 17% 11%	445
	11th to 20th	Day	9% 8% 31% 30% 16% 7%	444
	21st to end	Day	13% 7% 32% 28% 14% 6%	488
August	1st to 10th	Day	11% 9% 24% 27% 22% 7%	446
	11th to 20th	Day	14% 8% 25% 28% 16% 10%	439
	21st to end	Day	16% 8% 26% 27% 14% 10%	495
September	1st to 10th	Day	20% 8% 22% 24% 16% 9%	450
	11th to 20th	Day	14% 7% 22% 27% 20% 9%	450
	21st to end	Day	22% 15% 25% 20% 14% 5%	450
October	1st to 10th	Day	21% 14% 22% 20% 19% 3	450
	11th to 20th	Day	27% 18% 28% 17% 8% 1	450
	21st to end	Day	30% 20% 28% 16% 6%	495
November	1st to 10th	Day	20% 21% 28% 18% 13% 1	417
	11th to 20th	Day	31% 25% 27% 12% 4 1	190
	21st to end	Day	27% 28% 34% 9% 2	180
December	1st to 10th	Day	33% 31% 25% 7% 3 1	180
	11th to 20th	Day	36% 22% 28% 12% 1	180
	21st to end	Day	37% 25% 27% 9% 3	198
January	1st to 10th	Night	30% 26% 30% 11% 3	760
	11th to 20th	Night	29% 25% 29% 15% 3	729
	21st to end	Night	26% 27% 30% 15% 2	792
February	1st to 10th	Night	32% 21% 29% 17% 2	720
	11th to 20th	Night	30% 29% 31% 9% 1	703
	21st to end	Night	31% 25% 29% 14% 2	592
March	1st to 10th	Night	25% 22% 30% 19% 3	720
	11th to 20th	Night	30% 21% 24% 19% 5% 1	720
	21st to end	Night	23% 20% 34% 17% 5% 1	792
April	1st to 10th	Night	25% 21% 30% 19% 4	720
	11th to 20th	Night	23% 19% 30% 19% 9% 1	711
	21st to end	Night	22% 14% 30% 27% 6%	622
May	1st to 10th	Night	23% 12% 25% 30% 9% 1	540
	11th to 20th	Night	19% 9% 32% 30% 10%	419
	21st to end	Night	11% 8% 27% 31% 22% 1	389
June	1st to 10th	Night	12% 7% 28% 38% 16%	360
	11th to 20th	Night	13% 8% 26% 38% 14% 1	360
	21st to end	Night	12% 6% 31% 39% 13%	360
July	1st to 10th	Night	12% 5% 19% 39% 21% 3	350
	11th to 20th	Night	8% 4 23% 39% 25% 2	400
	21st to end	Night	12% 4 22% 39% 22% 1	591
August	1st to 10th	Night	10% 3 20% 40% 25% 2	537
	11th to 20th	Night	13% 7% 13% 37% 26% 4	534
	21st to end	Night	14% 5% 20% 34% 25% 4	762
September	1st to 10th	Night	18% 6% 19% 32% 22% 3	720
	11th to 20th	Night	14% 5% 18% 31% 27% 4	720
	21st to end	Night	18% 11% 22% 27% 18% 4	720
October	1st to 10th	Night	18% 12% 23% 27% 18% 2	720
	11th to 20th	Night	23% 17% 28% 23% 8% 1	720
	21st to end	Night	28% 16% 28% 24% 4 1	792
November	1st to 10th	Night	19% 15% 29% 27% 10% 1	740
	11th to 20th	Night	27% 19% 28% 20% 5% 2	760
	21st to end	Night	26% 19% 31% 18% 5%	760
December	1st to 10th	Night	31% 24% 28% 13% 4	760
	11th to 20th	Night	29% 24% 27% 17% 3	760
	21st to end	Night	29% 23% 29% 17% 1	836

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