Drummond Island Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Drummond Island Airport clear sky chart from 2005-11-06 to 2024-11-05.

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% 10% 3 8% 5% 4 4 4 5% 7% 37%	101449
	Night	15% 12% 4 9% 5% 4 4 3 5% 6% 32%	97688
Transparency	Day	46% 7% 12% 23% 11% 1	104938
	Night	52% 7% 11% 19% 10% 1	102274
Seeing	Day	17% 5% 19% 34% 21% 5%	15520
	Night	21% 5% 25% 32% 15% 2	24885

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	14% 19% 7% 12% 6% 5% 5% 4 5% 7% 16%	2378
	11th to 20th	Day	12% 18% 6% 13% 11% 7% 5% 3 5% 5% 16%	2530
	21st to end	Day	13% 22% 9% 15% 6% 6% 4 3 5% 5% 13%	2783
February	1st to 10th	Day	9% 13% 6% 13% 8% 5% 5% 4 6% 6% 25%	1684
	11th to 20th	Day	11% 13% 4 10% 7% 5% 5% 3 6% 6% 29%	1734
	21st to end	Day	11% 13% 5% 11% 7% 4 6% 4 5% 6% 29%	1570
March	1st to 10th	Day	11% 12% 4 8% 4 4 4 3 6% 7% 38%	3137
	11th to 20th	Day	9% 13% 4 10% 6% 5% 4 4 5% 7% 34%	3480
	21st to end	Day	13% 9% 6% 10% 6% 5% 5% 3 6% 6% 30%	3815
April	1st to 10th	Day	17% 11% 4 7% 5% 4 4 4 6% 6% 33%	2270
	11th to 20th	Day	18% 9% 3 7% 4 4 4 4 5% 5% 37%	2440
	21st to end	Day	17% 9% 3 7% 5% 4 4 4 5% 7% 35%	2470
May	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 4 6% 7% 39%	4108
	11th to 20th	Day	11% 7% 3 7% 4 4 4 4 5% 6% 45%	4137
	21st to end	Day	13% 6% 2 5% 4 3 4 3 4 8% 46%	5173
June	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 7% 8% 43%	2850
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 4 6% 8% 42%	2850
	21st to end	Day	14% 7% 3 5% 4 4 4 3 6% 7% 44%	2850
July	1st to 10th	Day	16% 7% 3 6% 4 3 4 4 5% 7% 42%	4760
	11th to 20th	Day	8% 5% 2 5% 4 3 4 4 5% 9% 51%	4476
	21st to end	Day	9% 5% 2 5% 3 3 3 3 5% 9% 52%	4814
August	1st to 10th	Day	8% 5% 2 7% 4 4 5% 4 5% 9% 47%	4151
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 6% 7% 46%	4044
	21st to end	Day	12% 6% 2 5% 4 4 3 3 6% 7% 47%	4532
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 3 5% 8% 45%	2217
	11th to 20th	Day	13% 5% 2 6% 3 4 4 3 6% 8% 45%	2090
	21st to end	Day	16% 8% 2 7% 4 4 4 4 5% 8% 39%	2090
October	1st to 10th	Day	19% 8% 3 5% 4 3 4 3 5% 7% 38%	2024
	11th to 20th	Day	20% 10% 4 9% 6% 6% 5% 4 6% 8% 23%	1859
	21st to end	Day	22% 13% 4 7% 5% 4 5% 4 5% 7% 23%	1881
November	1st to 10th	Day	18% 13% 4 9% 5% 5% 4 3 6% 7% 25%	1708
	11th to 20th	Day	14% 19% 5% 11% 7% 6% 4 5% 5% 6% 20%	1592
	21st to end	Day	20% 19% 5% 12% 7% 5% 4 3 5% 5% 16%	1520
December	1st to 10th	Day	14% 21% 6% 10% 7% 5% 5% 4 4 6% 19%	1330
	11th to 20th	Day	16% 19% 5% 14% 7% 5% 4 3 4 5% 17%	1671
	21st to end	Day	25% 24% 6% 13% 6% 3 3 2 3 3 13%	2431
January	1st to 10th	Night	17% 14% 6% 12% 6% 5% 4 3 5% 6% 22%	4574
	11th to 20th	Night	12% 17% 6% 15% 9% 6% 5% 4 5% 5% 17%	4440
	21st to end	Night	14% 20% 8% 14% 7% 5% 4 3 4 4 16%	4884
February	1st to 10th	Night	10% 16% 5% 10% 8% 6% 6% 5% 6% 5% 23%	2494
	11th to 20th	Night	11% 12% 4 11% 8% 5% 5% 4 5% 6% 27%	2331
	21st to end	Night	12% 15% 5% 10% 6% 5% 5% 4 5% 6% 26%	1884
March	1st to 10th	Night	15% 11% 3 6% 4 3 3 2 4 7% 41%	3702
	11th to 20th	Night	9% 13% 4 9% 5% 4 4 4 5% 7% 38%	3479
	21st to end	Night	13% 8% 6% 8% 4 5% 5% 4 5% 7% 35%	3817
April	1st to 10th	Night	19% 11% 3 9% 5% 4 5% 3 6% 6% 31%	1924
	11th to 20th	Night	19% 8% 3 6% 4 4 4 3 6% 5% 37%	1688
	21st to end	Night	19% 9% 3 7% 4 4 4 3 6% 5% 36%	1710
May	1st to 10th	Night	17% 7% 3 8% 5% 5% 5% 4 5% 5% 36%	2833
	11th to 20th	Night	12% 8% 3 9% 6% 5% 4 4 5% 7% 38%	2756
	21st to end	Night	16% 7% 2 5% 4 4 4 4 5% 7% 42%	2411
June	1st to 10th	Night	13% 6% 3 4 5% 4 4 5% 7% 8% 41%	1330
	11th to 20th	Night	11% 6% 3 5% 5% 5% 4 5% 5% 8% 43%	1330
	21st to end	Night	14% 7% 2 6% 5% 4 3 4 5% 7% 43%	1330
July	1st to 10th	Night	14% 6% 2 5% 4 4 5% 4 6% 7% 42%	2210
	11th to 20th	Night	8% 5% 2 6% 4 4 4 3 5% 7% 52%	2490
	21st to end	Night	9% 6% 2 5% 3 3 4 3 6% 8% 51%	2750
August	1st to 10th	Night	8% 6% 2 7% 5% 4 5% 4 6% 7% 45%	2777
	11th to 20th	Night	13% 5% 2 6% 3 4 4 3 5% 9% 45%	2785
	21st to end	Night	11% 5% 2 6% 4 4 4 3 4 6% 52%	3124
September	1st to 10th	Night	14% 6% 2 6% 4 3 5% 4 5% 6% 45%	1940
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 5% 8% 47%	2090
	21st to end	Night	18% 9% 3 6% 4 4 3 4 5% 6% 37%	2090
October	1st to 10th	Night	19% 8% 2 7% 4 3 3 3 5% 7% 37%	2156
	11th to 20th	Night	22% 11% 3 9% 4 4 4 4 5% 6% 28%	2318
	21st to end	Night	27% 13% 3 8% 4 4 4 3 4 5% 24%	2717
November	1st to 10th	Night	17% 13% 4 8% 6% 4 4 3 6% 7% 29%	2470
	11th to 20th	Night	19% 16% 5% 10% 6% 6% 4 3 5% 5% 20%	2587
	21st to end	Night	20% 20% 6% 11% 5% 4 4 3 4 5% 19%	2660
December	1st to 10th	Night	16% 21% 5% 11% 6% 4 5% 3 4 6% 20%	2845
	11th to 20th	Night	18% 18% 4 10% 6% 5% 5% 2 5% 4 22%	3526
	21st to end	Night	26% 23% 7% 11% 5% 3 3 2 3 3 14%	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	66% 12% 11% 8% 3	2379
	11th to 20th	Day	69% 10% 8% 9% 3 1	2530
	21st to end	Day	73% 8% 7% 7% 5% 1	2783
February	1st to 10th	Day	59% 8% 14% 13% 6%	1684
	11th to 20th	Day	56% 7% 10% 17% 9% 1	1743
	21st to end	Day	56% 6% 10% 18% 10%	1570
March	1st to 10th	Day	46% 7% 15% 17% 13% 1	3139
	11th to 20th	Day	49% 6% 12% 24% 7% 2	3480
	21st to end	Day	51% 9% 11% 15% 12% 2	3815
April	1st to 10th	Day	51% 7% 11% 18% 13% 1	2270
	11th to 20th	Day	48% 6% 9% 22% 13% 2	2440
	21st to end	Day	47% 5% 10% 17% 16% 4	2470
May	1st to 10th	Day	42% 8% 9% 24% 16% 2	4120
	11th to 20th	Day	40% 9% 9% 25% 16% 1	4141
	21st to end	Day	36% 7% 12% 22% 20% 3	5173
June	1st to 10th	Day	38% 8% 12% 27% 13% 2	2850
	11th to 20th	Day	38% 7% 12% 26% 15% 1	2850
	21st to end	Day	40% 6% 13% 27% 13% 2	2850
July	1st to 10th	Day	41% 5% 15% 24% 14% 1	4686
	11th to 20th	Day	30% 6% 13% 39% 11% 1	4399
	21st to end	Day	29% 6% 11% 35% 19% 1	4662
August	1st to 10th	Day	34% 6% 13% 33% 12% 1	4136
	11th to 20th	Day	37% 6% 15% 29% 13% 1	4083
	21st to end	Day	37% 6% 16% 31% 9% 1	4531
September	1st to 10th	Day	39% 8% 13% 28% 12% 1	2217
	11th to 20th	Day	36% 7% 16% 32% 9%	2090
	21st to end	Day	44% 7% 15% 24% 9%	2090
October	1st to 10th	Day	34% 5% 13% 30% 17%	3362
	11th to 20th	Day	50% 7% 11% 27% 5%	3062
	21st to end	Day	58% 6% 12% 17% 7%	3081
November	1st to 10th	Day	58% 6% 12% 18% 6%	1708
	11th to 20th	Day	64% 7% 13% 11% 5%	1592
	21st to end	Day	72% 7% 10% 9% 2	1520
December	1st to 10th	Day	68% 9% 8% 10% 5%	1330
	11th to 20th	Day	67% 9% 10% 11% 3	1671
	21st to end	Day	77% 7% 6% 6% 5%	2431
January	1st to 10th	Night	64% 9% 9% 10% 6%	4574
	11th to 20th	Night	68% 9% 10% 9% 4	4440
	21st to end	Night	70% 9% 8% 9% 4	4884
February	1st to 10th	Night	60% 7% 11% 15% 6%	2494
	11th to 20th	Night	56% 8% 12% 17% 6% 1	2333
	21st to end	Night	58% 6% 11% 15% 9%	1884
March	1st to 10th	Night	44% 5% 16% 20% 13% 1	3713
	11th to 20th	Night	44% 7% 14% 24% 9% 2	3480
	21st to end	Night	46% 9% 12% 20% 11% 2	3817
April	1st to 10th	Night	53% 5% 10% 17% 14%	1924
	11th to 20th	Night	47% 5% 7% 24% 14% 2	1688
	21st to end	Night	49% 5% 8% 18% 16% 4	1710
May	1st to 10th	Night	47% 6% 9% 24% 12% 2	2840
	11th to 20th	Night	46% 6% 7% 26% 15% 2	2757
	21st to end	Night	42% 8% 10% 18% 16% 6%	2412
June	1st to 10th	Night	39% 6% 10% 25% 18% 2	1330
	11th to 20th	Night	39% 7% 11% 24% 16% 3	1330
	21st to end	Night	40% 6% 13% 26% 13% 2	1330
July	1st to 10th	Night	40% 5% 13% 25% 15% 2	2175
	11th to 20th	Night	31% 5% 14% 33% 17% 1	2444
	21st to end	Night	32% 5% 11% 30% 21% 1	2662
August	1st to 10th	Night	37% 6% 12% 31% 13% 2	2768
	11th to 20th	Night	36% 8% 13% 28% 13% 1	2812
	21st to end	Night	34% 5% 12% 34% 14% 1	3124
September	1st to 10th	Night	39% 7% 12% 26% 14% 2	1940
	11th to 20th	Night	36% 6% 16% 33% 9%	2090
	21st to end	Night	47% 8% 14% 22% 9%	2090
October	1st to 10th	Night	41% 5% 13% 28% 12%	3598
	11th to 20th	Night	44% 6% 17% 23% 10%	3841
	21st to end	Night	58% 6% 16% 17% 4	4467
November	1st to 10th	Night	55% 7% 12% 19% 8%	2470
	11th to 20th	Night	65% 8% 10% 11% 6%	2587
	21st to end	Night	69% 8% 11% 9% 3	2660
December	1st to 10th	Night	66% 8% 10% 13% 2	2845
	11th to 20th	Night	64% 8% 10% 10% 6% 2	3525
	21st to end	Night	77% 5% 7% 8% 3	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	21% 10% 22% 29% 16% 2	230
	11th to 20th	Day	22% 4 20% 39% 13% 2	270
	21st to end	Day	23% 4 18% 37% 16% 1	297
February	1st to 10th	Day	16% 7% 32% 33% 11% 1	270
	11th to 20th	Day	17% 3 31% 37% 10% 1	270
	21st to end	Day	16% 8% 36% 30% 10%	225
March	1st to 10th	Day	17% 7% 27% 35% 13% 2	276
	11th to 20th	Day	16% 6% 28% 33% 15% 2	460
	21st to end	Day	22% 4 22% 34% 16% 2	506
April	1st to 10th	Day	20% 5% 22% 37% 15% 2	460
	11th to 20th	Day	23% 5% 24% 29% 16% 3	452
	21st to end	Day	22% 4 21% 33% 17% 3	460
May	1st to 10th	Day	20% 3 18% 40% 17% 3	463
	11th to 20th	Day	17% 3 15% 37% 23% 4	517
	21st to end	Day	13% 2 16% 39% 25% 5%	734
June	1st to 10th	Day	12% 3 15% 43% 23% 4	680
	11th to 20th	Day	15% 3 17% 38% 22% 5%	680
	21st to end	Day	18% 4 15% 35% 23% 5%	680
July	1st to 10th	Day	10% 1 14% 39% 29% 7%	671
	11th to 20th	Day	11% 3 14% 36% 29% 7%	668
	21st to end	Day	11% 2 12% 36% 30% 8%	739
August	1st to 10th	Day	12% 2 12% 32% 32% 9%	521
	11th to 20th	Day	13% 2 9% 27% 35% 13%	479
	21st to end	Day	14% 4 13% 34% 28% 7%	539
September	1st to 10th	Day	15% 5% 15% 29% 28% 8%	490
	11th to 20th	Day	15% 3 12% 29% 31% 10%	490
	21st to end	Day	21% 4 16% 27% 26% 6%	490
October	1st to 10th	Day	21% 8% 22% 25% 19% 5%	490
	11th to 20th	Day	21% 8% 27% 31% 12% 1	449
	21st to end	Day	26% 9% 25% 29% 10% 2	330
November	1st to 10th	Day	20% 11% 24% 30% 14% 1	282
	11th to 20th	Day	17% 13% 34% 29% 7%	214
	21st to end	Day	24% 9% 32% 29% 5%	180
December	1st to 10th	Day	24% 11% 27% 26% 12% 2	180
	11th to 20th	Day	24% 15% 28% 25% 6% 2	180
	21st to end	Day	30% 9% 37% 20% 5%	198
January	1st to 10th	Night	22% 8% 30% 30% 9% 1	950
	11th to 20th	Night	24% 6% 28% 30% 11% 1	950
	21st to end	Night	21% 4 27% 36% 12% 1	1045
February	1st to 10th	Night	18% 5% 35% 32% 10% 1	784
	11th to 20th	Night	18% 4 32% 33% 11% 1	743
	21st to end	Night	20% 4 32% 35% 9% 1	628
March	1st to 10th	Night	18% 4 31% 37% 9% 1	760
	11th to 20th	Night	19% 5% 28% 38% 9% 1	760
	21st to end	Night	18% 3 28% 37% 12% 1	836
April	1st to 10th	Night	25% 3 25% 35% 10% 2	594
	11th to 20th	Night	23% 4 19% 38% 14% 2	563
	21st to end	Night	23% 3 24% 33% 16% 2	570
May	1st to 10th	Night	15% 4 21% 41% 17% 2	570
	11th to 20th	Night	18% 2 17% 36% 24% 2	561
	21st to end	Night	15% 3 19% 36% 25% 2	421
June	1st to 10th	Night	14% 3 18% 39% 24% 1	380
	11th to 20th	Night	12% 4 18% 42% 22% 3	380
	21st to end	Night	18% 3 16% 36% 25% 3	380
July	1st to 10th	Night	12% 1 13% 42% 31% 1	370
	11th to 20th	Night	8% 3 13% 39% 30% 8%	527
	21st to end	Night	11% 2 14% 38% 30% 5%	624
August	1st to 10th	Night	11% 1 13% 41% 29% 5%	567
	11th to 20th	Night	12% 1 15% 29% 33% 10%	564
	21st to end	Night	15% 2 13% 37% 29% 3	627
September	1st to 10th	Night	14% 5% 18% 31% 26% 7%	635
	11th to 20th	Night	15% 3 18% 33% 24% 7%	760
	21st to end	Night	22% 4 19% 26% 23% 6%	760
October	1st to 10th	Night	22% 7% 22% 28% 19% 3	760
	11th to 20th	Night	28% 8% 25% 28% 11% 1	760
	21st to end	Night	35% 8% 25% 24% 7% 1	836
November	1st to 10th	Night	24% 9% 29% 26% 11% 1	760
	11th to 20th	Night	25% 12% 31% 23% 8% 1	760
	21st to end	Night	29% 13% 29% 24% 5%	760
December	1st to 10th	Night	25% 12% 32% 23% 8%	945
	11th to 20th	Night	28% 9% 35% 20% 7% 1	950
	21st to end	Night	33% 8% 29% 22% 8%	1045

Page generated at 2024-11-03 02:11:29. Version ac07

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