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 2024-07-08.

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% 12% 4 9% 5% 4 4 3 4 6% 29%	89608
	Night	20% 14% 5% 11% 6% 4 4 3 4 5% 24%	89726
Transparency	Day	56% 6% 11% 17% 9% 1	89327
	Night	62% 6% 10% 15% 6% 1	89562
Seeing	Day	31% 20% 30% 14% 4 1	16212
	Night	30% 19% 29% 17% 4	24026

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	16% 21% 7% 16% 10% 4 4 2 3 4 13%	2207
	11th to 20th	Day	18% 17% 8% 22% 8% 5% 4 2 2 3 10%	2654
	21st to end	Day	18% 16% 9% 21% 9% 4 3 2 3 3 11%	3124
February	1st to 10th	Day	18% 20% 8% 16% 9% 5% 4 3 3 4 10%	1710
	11th to 20th	Day	16% 17% 6% 16% 12% 4 4 2 3 4 15%	1663
	21st to end	Day	12% 16% 8% 10% 9% 6% 4 3 5% 5% 23%	1508
March	1st to 10th	Day	25% 19% 6% 9% 7% 4 3 2 3 4 21%	3359
	11th to 20th	Day	16% 18% 5% 12% 5% 4 4 3 4 5% 24%	3480
	21st to end	Day	29% 13% 6% 9% 5% 4 4 2 4 4 21%	3816
April	1st to 10th	Day	22% 16% 3 6% 4 4 4 3 4 5% 29%	2194
	11th to 20th	Day	20% 10% 3 6% 2 3 3 2 5% 7% 39%	2425
	21st to end	Day	20% 13% 3 6% 4 3 3 3 5% 6% 34%	2470
May	1st to 10th	Day	19% 14% 3 7% 4 4 4 3 6% 6% 29%	4106
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 5% 7% 35%	4293
	21st to end	Day	16% 8% 2 6% 5% 4 4 4 6% 8% 38%	4836
June	1st to 10th	Day	23% 9% 2 6% 4 4 4 3 5% 7% 32%	2772
	11th to 20th	Day	21% 7% 2 5% 4 3 4 3 5% 8% 38%	2850
	21st to end	Day	22% 9% 3 7% 5% 4 4 4 5% 5% 32%	2850
July	1st to 10th	Day	16% 8% 2 6% 4 3 5% 4 6% 8% 39%	2809
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 6% 8% 37%	2620
	21st to end	Day	18% 7% 2 7% 4 4 4 4 6% 8% 36%	2548
August	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 6% 7% 41%	2327
	11th to 20th	Day	16% 7% 3 7% 4 5% 5% 3 5% 7% 39%	2304
	21st to end	Day	14% 6% 2 5% 3 3 4 3 5% 7% 48%	2545
September	1st to 10th	Day	17% 6% 2 5% 3 3 2 3 4 6% 50%	2160
	11th to 20th	Day	16% 7% 2 6% 3 3 4 2 4 8% 46%	1980
	21st to end	Day	18% 8% 3 5% 3 3 3 3 3 6% 45%	1980
October	1st to 10th	Day	19% 9% 2 6% 4 3 4 4 4 6% 40%	1811
	11th to 20th	Day	20% 10% 3 7% 4 3 5% 3 5% 6% 34%	1800
	21st to end	Day	23% 13% 3 8% 4 4 4 3 4 5% 30%	1932
November	1st to 10th	Day	22% 12% 4 7% 5% 3 4 3 4 6% 30%	1610
	11th to 20th	Day	18% 20% 5% 10% 4 4 3 3 5% 6% 22%	1520
	21st to end	Day	19% 19% 6% 13% 6% 4 4 3 4 5% 18%	1520
December	1st to 10th	Day	24% 24% 5% 15% 5% 4 3 2 3 4 12%	1520
	11th to 20th	Day	23% 18% 7% 15% 7% 6% 3 3 3 4 11%	1874
	21st to end	Day	23% 19% 11% 16% 6% 3 3 2 3 4 12%	2431
January	1st to 10th	Night	17% 19% 8% 21% 7% 4 4 3 3 3 12%	4748
	11th to 20th	Night	17% 22% 8% 19% 7% 4 3 2 3 4 11%	4301
	21st to end	Night	18% 15% 7% 20% 8% 5% 5% 3 4 4 11%	4532
February	1st to 10th	Night	19% 19% 7% 18% 8% 5% 4 3 4 3 11%	2470
	11th to 20th	Night	18% 18% 6% 16% 11% 5% 4 3 3 4 13%	2403
	21st to end	Night	13% 17% 6% 15% 7% 5% 4 3 5% 6% 20%	1943
March	1st to 10th	Night	22% 17% 6% 11% 9% 4 3 2 3 4 19%	3480
	11th to 20th	Night	16% 18% 6% 13% 7% 6% 5% 3 4 5% 18%	3479
	21st to end	Night	27% 13% 6% 9% 5% 4 4 2 3 4 23%	3816
April	1st to 10th	Night	23% 15% 3 8% 5% 4 3 3 4 5% 27%	1985
	11th to 20th	Night	22% 11% 3 7% 4 4 4 3 5% 7% 30%	1702
	21st to end	Night	22% 12% 3 7% 4 4 3 3 5% 6% 31%	1710
May	1st to 10th	Night	19% 17% 4 7% 4 4 4 3 4 5% 28%	2834
	11th to 20th	Night	19% 10% 3 8% 5% 4 4 4 6% 6% 31%	2604
	21st to end	Night	15% 10% 4 8% 6% 4 5% 4 6% 8% 30%	2749
June	1st to 10th	Night	24% 9% 3 6% 5% 4 3 3 6% 8% 28%	1422
	11th to 20th	Night	19% 8% 3 6% 4 4 4 4 6% 9% 35%	1330
	21st to end	Night	20% 8% 4 10% 5% 5% 5% 4 5% 6% 27%	1330
July	1st to 10th	Night	18% 9% 3 7% 5% 4 4 3 7% 10% 31%	1316
	11th to 20th	Night	15% 9% 4 7% 7% 6% 4 5% 6% 8% 30%	1316
	21st to end	Night	17% 7% 3 8% 4 5% 5% 5% 6% 8% 31%	1770
August	1st to 10th	Night	14% 8% 3 6% 4 4 5% 4 6% 8% 38%	1612
	11th to 20th	Night	20% 9% 2 6% 4 5% 4 4 5% 8% 32%	1596
	21st to end	Night	13% 6% 3 6% 5% 4 4 3 6% 8% 41%	1810
September	1st to 10th	Night	15% 6% 2 4 5% 3 4 4 6% 7% 44%	1800
	11th to 20th	Night	18% 7% 2 6% 3 3 3 3 6% 7% 43%	1975
	21st to end	Night	18% 7% 2 7% 4 4 4 3 5% 6% 39%	1980
October	1st to 10th	Night	19% 7% 2 6% 4 3 4 3 5% 7% 38%	2147
	11th to 20th	Night	16% 10% 3 8% 4 4 4 3 5% 6% 36%	2160
	21st to end	Night	26% 13% 4 7% 4 4 4 3 3 4 27%	2420
November	1st to 10th	Night	22% 12% 3 8% 5% 4 3 3 6% 5% 29%	2468
	11th to 20th	Night	20% 20% 5% 8% 5% 4 4 3 4 6% 21%	2660
	21st to end	Night	20% 19% 7% 10% 5% 3 3 3 4 5% 20%	2660
December	1st to 10th	Night	25% 23% 6% 13% 5% 4 3 2 3 4 12%	2660
	11th to 20th	Night	22% 19% 7% 17% 7% 4 3 2 3 4 12%	3302
	21st to end	Night	24% 21% 7% 14% 4 3 2 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	76% 6% 13% 5% 1	2208
	11th to 20th	Day	79% 7% 6% 6% 2	2654
	21st to end	Day	73% 10% 9% 6% 1	3124
February	1st to 10th	Day	79% 6% 7% 5% 3	1710
	11th to 20th	Day	75% 5% 8% 8% 3	1671
	21st to end	Day	63% 6% 10% 14% 6% 1	1508
March	1st to 10th	Day	69% 3 8% 15% 4 1	3363
	11th to 20th	Day	61% 6% 12% 14% 6% 1	3480
	21st to end	Day	69% 3 6% 12% 8% 1	3816
April	1st to 10th	Day	58% 5% 8% 15% 12% 1	2194
	11th to 20th	Day	47% 5% 10% 24% 13% 1	2425
	21st to end	Day	52% 4 10% 19% 13% 2	2470
May	1st to 10th	Day	54% 7% 13% 19% 7% 1	4120
	11th to 20th	Day	47% 7% 16% 21% 8% 1	4297
	21st to end	Day	43% 7% 17% 18% 13%	4836
June	1st to 10th	Day	52% 6% 10% 21% 10%	2772
	11th to 20th	Day	46% 5% 13% 21% 13% 2	2850
	21st to end	Day	54% 7% 10% 18% 10% 1	2850
July	1st to 10th	Day	42% 7% 15% 22% 13% 1	2734
	11th to 20th	Day	43% 8% 14% 24% 11% 1	2539
	21st to end	Day	46% 7% 15% 23% 9% 1	2406
August	1st to 10th	Day	42% 7% 14% 24% 12%	2314
	11th to 20th	Day	44% 8% 13% 23% 11%	2304
	21st to end	Day	37% 5% 14% 27% 15% 1	2545
September	1st to 10th	Day	38% 5% 12% 28% 16% 2	2160
	11th to 20th	Day	39% 5% 12% 26% 16% 2	1980
	21st to end	Day	42% 4 9% 26% 16% 2	1980
October	1st to 10th	Day	45% 5% 11% 26% 12% 1	1811
	11th to 20th	Day	51% 6% 12% 23% 8%	1800
	21st to end	Day	58% 5% 9% 17% 11%	1932
November	1st to 10th	Day	57% 5% 11% 19% 8%	1610
	11th to 20th	Day	64% 5% 11% 14% 5% 1	1520
	21st to end	Day	70% 6% 11% 11% 2	1520
December	1st to 10th	Day	77% 6% 8% 7% 2	1520
	11th to 20th	Day	78% 6% 7% 6% 3	1873
	21st to end	Day	79% 5% 11% 3 2	2431
January	1st to 10th	Night	77% 7% 8% 7% 1	4748
	11th to 20th	Night	78% 6% 8% 7% 2	4301
	21st to end	Night	75% 7% 9% 8% 2	4532
February	1st to 10th	Night	78% 5% 7% 6% 3	2470
	11th to 20th	Night	78% 4 7% 8% 3	2406
	21st to end	Night	65% 7% 10% 12% 5% 1	1943
March	1st to 10th	Night	69% 6% 7% 11% 6% 1	3489
	11th to 20th	Night	66% 8% 10% 10% 5% 1	3480
	21st to end	Night	66% 4 8% 13% 7% 1	3816
April	1st to 10th	Night	59% 5% 9% 14% 10% 2	1985
	11th to 20th	Night	53% 6% 9% 20% 12% 1	1702
	21st to end	Night	54% 5% 10% 17% 13% 1	1710
May	1st to 10th	Night	57% 7% 11% 18% 6%	2840
	11th to 20th	Night	49% 9% 15% 21% 6% 1	2605
	21st to end	Night	49% 10% 16% 20% 5% 1	2750
June	1st to 10th	Night	52% 7% 12% 20% 7% 1	1422
	11th to 20th	Night	45% 8% 14% 21% 10% 1	1330
	21st to end	Night	55% 8% 12% 14% 9% 2	1330
July	1st to 10th	Night	45% 11% 15% 20% 9%	1281
	11th to 20th	Night	50% 8% 14% 19% 8% 1	1274
	21st to end	Night	48% 8% 14% 20% 9% 1	1672
August	1st to 10th	Night	41% 9% 12% 29% 9%	1600
	11th to 20th	Night	47% 9% 16% 19% 8%	1596
	21st to end	Night	40% 7% 15% 26% 12%	1810
September	1st to 10th	Night	38% 7% 12% 29% 13% 2	1800
	11th to 20th	Night	40% 5% 10% 27% 15% 1	1975
	21st to end	Night	44% 6% 9% 23% 16% 2	1980
October	1st to 10th	Night	45% 6% 11% 23% 12% 1	2147
	11th to 20th	Night	48% 6% 14% 23% 8%	2160
	21st to end	Night	61% 4 8% 16% 9% 1	2420
November	1st to 10th	Night	56% 7% 12% 16% 8%	2468
	11th to 20th	Night	64% 6% 11% 13% 5%	2660
	21st to end	Night	66% 6% 15% 10% 2	2660
December	1st to 10th	Night	76% 5% 9% 8% 2	2660
	11th to 20th	Night	77% 5% 7% 9% 2	3304
	21st to end	Night	74% 5% 8% 10% 2	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	43% 27% 21% 8% 1	274
	21st to end	Day	29% 28% 34% 8% 1	407
February	1st to 10th	Day	37% 25% 29% 7% 2	370
	11th to 20th	Day	41% 29% 22% 6% 2	366
	21st to end	Day	34% 26% 27% 12% 1	352
March	1st to 10th	Day	35% 27% 31% 5% 2	460
	11th to 20th	Day	37% 28% 24% 9% 2 1	460
	21st to end	Day	37% 27% 22% 11% 2 1	506
April	1st to 10th	Day	42% 25% 25% 6% 2	460
	11th to 20th	Day	34% 25% 27% 11% 3	452
	21st to end	Day	33% 22% 26% 13% 4	460
May	1st to 10th	Day	36% 22% 29% 10% 3	463
	11th to 20th	Day	28% 19% 31% 17% 4	608
	21st to end	Day	29% 19% 31% 18% 3 1	735
June	1st to 10th	Day	32% 19% 28% 17% 4	680
	11th to 20th	Day	24% 16% 35% 19% 5% 1	680
	21st to end	Day	30% 15% 33% 18% 3 1	680
July	1st to 10th	Day	23% 14% 37% 19% 6% 1	657
	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	41% 22% 24% 10% 2	765
	21st to end	Night	29% 28% 28% 12% 3	836
February	1st to 10th	Night	35% 26% 28% 10% 1	760
	11th to 20th	Night	38% 25% 26% 8% 2	743
	21st to end	Night	26% 28% 28% 14% 3	628
March	1st to 10th	Night	31% 25% 30% 13% 1	760
	11th to 20th	Night	31% 21% 27% 18% 3	760
	21st to end	Night	30% 23% 28% 13% 5%	836
April	1st to 10th	Night	37% 20% 28% 13% 2	655
	11th to 20th	Night	30% 22% 30% 16% 2	564
	21st to end	Night	30% 19% 29% 18% 5%	570
May	1st to 10th	Night	28% 17% 33% 19% 4 1	570
	11th to 20th	Night	27% 16% 31% 22% 3	562
	21st to end	Night	21% 16% 41% 18% 4 1	616
June	1st to 10th	Night	28% 15% 31% 22% 4	472
	11th to 20th	Night	22% 12% 33% 28% 5% 1	380
	21st to end	Night	22% 11% 40% 19% 8%	380
July	1st to 10th	Night	19% 8% 43% 25% 4	366
	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 2024-07-05 12:05:37. Version ac07

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