Digby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Digby clear sky chart from 2005-11-06 to 2024-01-16.

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	19% 11% 4 8% 6% 3 4 4 4 6% 31%	74768
	Night	20% 13% 5% 9% 7% 3 4 4 4 6% 25%	75008
Transparency	Day	37% 36% 8% 12% 6% 1	74473
	Night	41% 37% 7% 11% 5%	74838
Seeing	Day	30% 20% 30% 14% 4 1	15500
	Night	30% 19% 29% 17% 4	23459

By Month

Percentage Cloud Cover NE (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% 21% 9% 14% 11% 3 5% 3 2 4 11%	1327
	11th to 20th	Day	22% 19% 8% 12% 12% 4 5% 2 2 3 10%	1557
	21st to end	Day	13% 13% 8% 18% 16% 5% 4 4 3 4 12%	1782
February	1st to 10th	Day	18% 18% 9% 15% 12% 4 4 4 3 4 10%	1620
	11th to 20th	Day	18% 16% 7% 14% 12% 4 4 3 3 4 15%	1573
	21st to end	Day	11% 15% 8% 10% 11% 4 5% 4 4 5% 23%	1422
March	1st to 10th	Day	16% 18% 8% 10% 10% 4 3 3 2 5% 21%	1929
	11th to 20th	Day	15% 12% 7% 12% 7% 3 4 4 4 5% 28%	1980
	21st to end	Day	19% 13% 5% 8% 5% 2 4 3 4 5% 31%	2178
April	1st to 10th	Day	23% 15% 4 5% 5% 3 4 4 4 5% 28%	2078
	11th to 20th	Day	20% 9% 3 5% 3 2 4 3 5% 8% 38%	2295
	21st to end	Day	21% 12% 3 6% 5% 2 4 4 5% 6% 33%	2340
May	1st to 10th	Day	21% 10% 3 6% 6% 3 5% 4 5% 6% 31%	2340
	11th to 20th	Day	20% 8% 3 5% 4 3 4 4 4 5% 41%	2415
	21st to end	Day	20% 8% 3 5% 5% 3 4 4 5% 7% 36%	2724
June	1st to 10th	Day	24% 8% 3 5% 5% 3 4 4 5% 7% 32%	2626
	11th to 20th	Day	21% 7% 3 5% 4 3 4 3 5% 7% 37%	2700
	21st to end	Day	22% 7% 3 7% 6% 3 5% 4 5% 6% 33%	2700
July	1st to 10th	Day	16% 7% 2 5% 4 2 4 5% 6% 9% 40%	2700
	11th to 20th	Day	17% 6% 3 5% 4 3 5% 5% 6% 8% 37%	2620
	21st to end	Day	18% 6% 3 6% 5% 3 5% 5% 5% 7% 37%	2548
August	1st to 10th	Day	15% 6% 2 5% 5% 3 5% 5% 6% 7% 41%	2327
	11th to 20th	Day	16% 7% 3 5% 5% 4 5% 5% 5% 7% 39%	2304
	21st to end	Day	14% 6% 2 5% 4 3 3 4 5% 7% 48%	2545
September	1st to 10th	Day	17% 5% 2 4 4 2 3 3 4 6% 50%	2160
	11th to 20th	Day	16% 7% 2 5% 4 2 4 3 4 7% 47%	1980
	21st to end	Day	18% 8% 3 5% 4 2 3 3 3 6% 45%	1980
October	1st to 10th	Day	19% 8% 2 5% 5% 2 4 5% 4 6% 40%	1811
	11th to 20th	Day	20% 10% 3 6% 5% 2 5% 4 5% 6% 34%	1800
	21st to end	Day	23% 12% 4 7% 5% 3 4 4 4 5% 30%	1932
November	1st to 10th	Day	22% 11% 4 7% 5% 2 5% 4 4 6% 30%	1610
	11th to 20th	Day	19% 18% 6% 9% 5% 3 3 3 5% 6% 23%	1520
	21st to end	Day	19% 19% 7% 11% 7% 3 4 3 3 5% 18%	1520
December	1st to 10th	Day	25% 21% 7% 13% 7% 3 3 3 3 4 12%	1520
	11th to 20th	Day	23% 16% 8% 14% 8% 5% 4 3 3 4 11%	1874
	21st to end	Day	23% 18% 11% 14% 8% 2 3 3 3 4 12%	2431
January	1st to 10th	Night	20% 21% 8% 12% 10% 4 3 3 3 3 11%	2838
	11th to 20th	Night	20% 20% 8% 13% 9% 5% 3 3 3 5% 11%	2519
	21st to end	Night	14% 16% 9% 18% 13% 4 4 4 3 4 11%	2574
February	1st to 10th	Night	19% 17% 8% 17% 10% 4 4 4 4 4 11%	2340
	11th to 20th	Night	19% 16% 7% 15% 12% 4 4 3 3 4 12%	2273
	21st to end	Night	12% 15% 7% 15% 9% 3 5% 4 5% 6% 19%	1832
March	1st to 10th	Night	15% 17% 7% 10% 9% 3 4 4 4 4 22%	2017
	11th to 20th	Night	18% 12% 7% 11% 7% 4 6% 3 4 5% 24%	1979
	21st to end	Night	19% 13% 7% 7% 6% 3 4 4 4 5% 29%	2178
April	1st to 10th	Night	24% 14% 4 7% 6% 2 4 4 4 5% 26%	1881
	11th to 20th	Night	22% 10% 3 5% 5% 3 5% 4 5% 7% 30%	1612
	21st to end	Night	23% 12% 3 6% 5% 3 4 4 5% 6% 30%	1620
May	1st to 10th	Night	20% 12% 3 6% 5% 3 5% 4 4 6% 32%	1620
	11th to 20th	Night	23% 10% 3 5% 4 3 4 4 5% 6% 32%	1475
	21st to end	Night	18% 9% 3 6% 7% 2 5% 5% 4 8% 32%	1550
June	1st to 10th	Night	25% 8% 3 5% 5% 4 4 4 7% 8% 28%	1348
	11th to 20th	Night	20% 7% 3 6% 4 3 4 5% 6% 9% 34%	1260
	21st to end	Night	19% 7% 4 9% 6% 4 5% 5% 5% 7% 28%	1260
July	1st to 10th	Night	18% 8% 3 7% 5% 3 4 4 6% 11% 31%	1260
	11th to 20th	Night	15% 9% 4 6% 7% 4 5% 5% 6% 8% 30%	1316
	21st to end	Night	18% 7% 3 7% 5% 4 5% 7% 6% 8% 32%	1770
August	1st to 10th	Night	14% 7% 3 5% 5% 3 5% 5% 5% 8% 38%	1612
	11th to 20th	Night	20% 9% 3 5% 5% 3 5% 5% 5% 8% 33%	1596
	21st to end	Night	14% 6% 3 5% 6% 3 5% 4 6% 8% 41%	1810
September	1st to 10th	Night	15% 5% 2 4 5% 3 4 4 6% 7% 44%	1800
	11th to 20th	Night	18% 7% 3 5% 4 2 4 3 5% 7% 43%	1975
	21st to end	Night	18% 7% 2 6% 5% 3 4 4 5% 6% 39%	1980
October	1st to 10th	Night	19% 7% 2 6% 5% 2 5% 4 5% 7% 38%	2147
	11th to 20th	Night	17% 9% 3 6% 6% 3 4 4 5% 7% 36%	2160
	21st to end	Night	27% 13% 4 6% 5% 3 3 4 3 5% 27%	2420
November	1st to 10th	Night	23% 12% 4 7% 5% 3 3 4 5% 6% 29%	2468
	11th to 20th	Night	20% 19% 5% 8% 6% 3 4 4 4 6% 21%	2660
	21st to end	Night	20% 18% 7% 9% 6% 3 3 3 4 6% 21%	2660
December	1st to 10th	Night	25% 20% 8% 12% 6% 3 3 3 3 4 12%	2660
	11th to 20th	Night	22% 18% 8% 15% 8% 3 3 3 3 4 13%	3302
	21st to end	Night	24% 20% 8% 13% 5% 2 3 2 2 4 16%	5236

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	50% 40% 5% 3 1	1328
	11th to 20th	Day	51% 40% 4 5%	1557
	21st to end	Day	51% 38% 5% 6% 1	1782
February	1st to 10th	Day	52% 37% 6% 3 2	1620
	11th to 20th	Day	52% 37% 6% 4 1	1581
	21st to end	Day	46% 35% 7% 9% 1	1422
March	1st to 10th	Day	47% 35% 5% 9% 4	1933
	11th to 20th	Day	37% 36% 8% 11% 7% 1	1980
	21st to end	Day	37% 35% 6% 14% 6% 1	2178
April	1st to 10th	Day	39% 36% 6% 10% 9% 1	2078
	11th to 20th	Day	33% 35% 6% 16% 9% 1	2295
	21st to end	Day	34% 36% 7% 14% 8% 1	2340
May	1st to 10th	Day	38% 36% 5% 13% 7% 1	2340
	11th to 20th	Day	31% 37% 8% 14% 10% 1	2419
	21st to end	Day	30% 37% 9% 16% 7% 1	2724
June	1st to 10th	Day	37% 37% 7% 13% 5%	2626
	11th to 20th	Day	33% 37% 8% 13% 8% 2	2700
	21st to end	Day	38% 37% 9% 11% 4 1	2700
July	1st to 10th	Day	30% 38% 11% 15% 6% 1	2625
	11th to 20th	Day	30% 38% 11% 14% 6%	2539
	21st to end	Day	31% 37% 10% 16% 6%	2406
August	1st to 10th	Day	31% 37% 9% 15% 8%	2314
	11th to 20th	Day	30% 36% 10% 16% 9%	2304
	21st to end	Day	26% 36% 9% 19% 9% 1	2545
September	1st to 10th	Day	28% 35% 8% 17% 11% 1	2160
	11th to 20th	Day	27% 35% 8% 18% 11% 1	1980
	21st to end	Day	30% 35% 6% 16% 11% 1	1980
October	1st to 10th	Day	29% 36% 8% 19% 8%	1811
	11th to 20th	Day	34% 37% 8% 16% 5%	1800
	21st to end	Day	37% 36% 6% 12% 8%	1932
November	1st to 10th	Day	34% 40% 7% 12% 6%	1610
	11th to 20th	Day	37% 39% 8% 11% 3 1	1520
	21st to end	Day	44% 40% 7% 8% 1	1520
December	1st to 10th	Day	48% 40% 5% 6% 1	1520
	11th to 20th	Day	56% 32% 6% 5% 1	1873
	21st to end	Day	61% 25% 10% 3 1	2431
January	1st to 10th	Night	50% 39% 5% 4 1	2838
	11th to 20th	Night	50% 40% 5% 4 1	2519
	21st to end	Night	51% 38% 5% 6% 1	2574
February	1st to 10th	Night	52% 37% 4 5% 2	2340
	11th to 20th	Night	52% 37% 6% 4 1	2276
	21st to end	Night	46% 37% 7% 8% 2	1832
March	1st to 10th	Night	44% 37% 6% 8% 4	2026
	11th to 20th	Night	42% 36% 9% 9% 4 1	1980
	21st to end	Night	36% 36% 6% 13% 7% 1	2178
April	1st to 10th	Night	40% 36% 6% 10% 7% 1	1881
	11th to 20th	Night	35% 36% 6% 14% 9%	1612
	21st to end	Night	36% 36% 7% 12% 8% 1	1620
May	1st to 10th	Night	37% 36% 7% 13% 6%	1620
	11th to 20th	Night	33% 39% 5% 16% 6% 1	1476
	21st to end	Night	33% 39% 8% 14% 5% 1	1551
June	1st to 10th	Night	37% 37% 9% 13% 3 1	1348
	11th to 20th	Night	33% 38% 8% 13% 7% 1	1260
	21st to end	Night	41% 38% 9% 8% 3 1	1260
July	1st to 10th	Night	32% 40% 10% 12% 5%	1225
	11th to 20th	Night	35% 38% 10% 12% 4	1274
	21st to end	Night	32% 40% 9% 13% 6%	1672
August	1st to 10th	Night	31% 37% 8% 17% 6%	1600
	11th to 20th	Night	35% 36% 9% 13% 7%	1596
	21st to end	Night	29% 37% 10% 17% 7%	1810
September	1st to 10th	Night	28% 36% 7% 18% 9% 1	1800
	11th to 20th	Night	27% 36% 6% 18% 12% 1	1975
	21st to end	Night	32% 37% 5% 14% 11% 1	1980
October	1st to 10th	Night	30% 37% 8% 17% 8%	2147
	11th to 20th	Night	32% 37% 9% 16% 6%	2160
	21st to end	Night	41% 37% 5% 10% 7%	2420
November	1st to 10th	Night	33% 42% 7% 12% 6%	2468
	11th to 20th	Night	38% 41% 7% 9% 4	2660
	21st to end	Night	40% 40% 9% 9% 1	2660
December	1st to 10th	Night	48% 40% 7% 5% 1	2660
	11th to 20th	Night	54% 33% 4 7% 2	3304
	21st to end	Night	59% 25% 7% 9% 1	5236

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	43% 28% 21% 8%	180
	11th to 20th	Day	42% 27% 22% 8% 1	260
	21st to end	Day	28% 30% 33% 8% 1	374
February	1st to 10th	Day	37% 26% 30% 6% 1	340
	11th to 20th	Day	42% 28% 22% 7% 2	336
	21st to end	Day	33% 28% 27% 12% 1	320
March	1st to 10th	Day	34% 28% 31% 5% 2	420
	11th to 20th	Day	35% 29% 24% 9% 2 1	420
	21st to end	Day	34% 28% 23% 11% 3 1	462
April	1st to 10th	Day	44% 24% 24% 6% 2	420
	11th to 20th	Day	34% 24% 27% 11% 3	412
	21st to end	Day	35% 21% 26% 13% 5%	420
May	1st to 10th	Day	36% 22% 29% 9% 3	423
	11th to 20th	Day	30% 20% 30% 15% 4	561
	21st to end	Day	30% 18% 30% 18% 3 1	680
June	1st to 10th	Day	33% 18% 27% 17% 4	630
	11th to 20th	Day	25% 17% 34% 18% 5% 1	630
	21st to end	Day	29% 13% 34% 18% 4 1	630
July	1st to 10th	Day	22% 14% 37% 19% 6% 1	620
	11th to 20th	Day	22% 9% 39% 21% 8% 1	599
	21st to end	Day	22% 13% 40% 20% 5%	488
August	1st to 10th	Day	16% 14% 41% 23% 5% 1	446
	11th to 20th	Day	21% 13% 35% 21% 9% 1	439
	21st to end	Day	19% 15% 32% 24% 8% 2	495
September	1st to 10th	Day	18% 16% 39% 21% 6%	450
	11th to 20th	Day	25% 18% 31% 18% 6% 3	450
	21st to end	Day	24% 18% 32% 16% 8% 2	450
October	1st to 10th	Day	27% 18% 25% 18% 9% 2	365
	11th to 20th	Day	30% 17% 29% 17% 6% 2	360
	21st to end	Day	34% 22% 27% 13% 4 1	396
November	1st to 10th	Day	35% 18% 32% 11% 4 1	365
	11th to 20th	Day	39% 24% 22% 11% 4	370
	21st to end	Day	36% 29% 26% 6% 3	370
December	1st to 10th	Day	39% 26% 24% 10% 1	370
	11th to 20th	Day	46% 28% 20% 6%	351
	21st to end	Day	40% 30% 23% 6% 1 1	198
January	1st to 10th	Night	37% 25% 25% 12% 1	850
	11th to 20th	Night	40% 22% 25% 11% 2	749
	21st to end	Night	29% 29% 27% 13% 2	792
February	1st to 10th	Night	35% 27% 28% 9% 1	720
	11th to 20th	Night	39% 25% 26% 8% 2	703
	21st to end	Night	26% 29% 28% 14% 3	592
March	1st to 10th	Night	30% 25% 31% 13% 1	720
	11th to 20th	Night	31% 21% 27% 18% 3	720
	21st to end	Night	29% 23% 29% 14% 5%	792
April	1st to 10th	Night	38% 20% 27% 13% 2	621
	11th to 20th	Night	30% 22% 30% 16% 2	534
	21st to end	Night	30% 19% 28% 17% 5%	540
May	1st to 10th	Night	28% 16% 32% 19% 4 1	540
	11th to 20th	Night	29% 17% 31% 21% 3	532
	21st to end	Night	21% 15% 40% 18% 4 1	583
June	1st to 10th	Night	29% 15% 31% 21% 4	448
	11th to 20th	Night	23% 12% 32% 27% 5% 1	360
	21st to end	Night	21% 11% 41% 19% 8%	360
July	1st to 10th	Night	18% 7% 44% 25% 4	350
	11th to 20th	Night	20% 11% 35% 23% 11%	388
	21st to end	Night	20% 9% 36% 31% 4	590
August	1st to 10th	Night	18% 8% 36% 31% 7% 1	538
	11th to 20th	Night	23% 9% 31% 29% 8% 1	532
	21st to end	Night	17% 9% 35% 30% 10% 1	594
September	1st to 10th	Night	17% 11% 35% 28% 9% 1	540
	11th to 20th	Night	23% 10% 30% 26% 10% 1	715
	21st to end	Night	23% 13% 31% 22% 10% 1	720
October	1st to 10th	Night	24% 11% 28% 26% 11%	720
	11th to 20th	Night	21% 22% 30% 18% 8% 1	720
	21st to end	Night	37% 21% 22% 16% 3	792
November	1st to 10th	Night	34% 17% 26% 17% 6% 1	769
	11th to 20th	Night	34% 22% 24% 14% 5%	850
	21st to end	Night	34% 24% 24% 15% 3	850
December	1st to 10th	Night	41% 22% 24% 11% 2	850
	11th to 20th	Night	39% 29% 23% 8% 2	850
	21st to end	Night	40% 24% 22% 11% 2	935

Page generated at 2024-01-13 10:37:58. Version ac07

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