Plattsburgh
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Plattsburgh clear sky chart from 2005-11-06 to 2026-06-01.

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	14% 10% 3 9% 6% 5% 5% 4 6% 7% 32%	132093
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 31%	131078
Transparency	Day	50% 6% 12% 21% 10% 1	135549
	Night	51% 5% 13% 20% 10% 1	135709
Seeing	Day	22% 18% 32% 19% 7% 2	16587
	Night	21% 16% 32% 23% 8% 1	25632

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	11% 16% 6% 16% 8% 5% 5% 4 5% 5% 20%	4661
	11th to 20th	Day	10% 16% 6% 15% 8% 6% 6% 4 5% 5% 19%	4650
	21st to end	Day	10% 12% 4 11% 10% 7% 6% 5% 6% 6% 23%	5124
February	1st to 10th	Day	12% 14% 4 13% 8% 7% 6% 4 5% 5% 22%	1859
	11th to 20th	Day	10% 13% 5% 13% 6% 6% 5% 4 5% 6% 27%	1986
	21st to end	Day	13% 15% 5% 9% 6% 6% 5% 4 4 5% 26%	1730
March	1st to 10th	Day	16% 13% 4 12% 6% 5% 5% 3 4 5% 27%	4576
	11th to 20th	Day	10% 13% 4 10% 5% 6% 5% 3 5% 6% 32%	4792
	21st to end	Day	17% 10% 4 8% 5% 5% 5% 4 4 4 34%	6102
April	1st to 10th	Day	18% 12% 3 8% 5% 4 5% 4 5% 6% 30%	2520
	11th to 20th	Day	17% 9% 3 7% 6% 5% 4 3 5% 5% 36%	2494
	21st to end	Day	20% 8% 3 7% 5% 4 5% 4 5% 6% 34%	2683
May	1st to 10th	Day	24% 11% 4 9% 5% 5% 5% 4 5% 6% 23%	6286
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	6458
	21st to end	Day	18% 9% 3 6% 4 5% 5% 4 7% 8% 32%	7103
June	1st to 10th	Day	19% 7% 2 7% 5% 5% 5% 4 6% 8% 30%	2800
	11th to 20th	Day	12% 6% 3 6% 6% 5% 5% 5% 7% 9% 37%	2800
	21st to end	Day	18% 7% 2 8% 5% 5% 6% 4 7% 8% 31%	2800
July	1st to 10th	Day	9% 6% 3 8% 6% 6% 7% 5% 7% 9% 34%	6360
	11th to 20th	Day	9% 4 2 6% 5% 5% 6% 5% 8% 10% 39%	6360
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 9% 43%	6926
August	1st to 10th	Day	12% 7% 3 8% 5% 5% 6% 5% 8% 8% 33%	4563
	11th to 20th	Day	10% 6% 3 8% 5% 6% 6% 5% 8% 8% 36%	4036
	21st to end	Day	12% 5% 2 7% 5% 5% 5% 5% 6% 7% 40%	4312
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 8% 47%	2400
	11th to 20th	Day	11% 5% 2 5% 4 3 4 4 5% 6% 50%	2300
	21st to end	Day	12% 6% 3 6% 5% 6% 5% 4 6% 8% 41%	2200
October	1st to 10th	Day	17% 8% 3 7% 6% 4 4 3 6% 6% 37%	2090
	11th to 20th	Day	15% 8% 3 7% 4 5% 6% 4 6% 7% 34%	1956
	21st to end	Day	19% 11% 3 9% 6% 5% 4 4 4 6% 31%	1980
November	1st to 10th	Day	13% 11% 4 8% 7% 6% 4 4 4 6% 33%	1851
	11th to 20th	Day	15% 12% 3 8% 6% 5% 6% 4 5% 5% 33%	1861
	21st to end	Day	16% 13% 4 9% 6% 5% 5% 4 5% 5% 28%	1680
December	1st to 10th	Day	13% 20% 7% 15% 8% 5% 4 3 4 4 16%	2680
	11th to 20th	Day	16% 12% 5% 8% 5% 4 4 4 6% 7% 29%	3066
	21st to end	Day	19% 14% 5% 9% 6% 4 5% 3 4 5% 26%	4048
January	1st to 10th	Night	12% 19% 7% 15% 6% 5% 4 3 4 4 21%	8234
	11th to 20th	Night	11% 16% 8% 16% 7% 6% 5% 4 5% 5% 19%	8235
	21st to end	Night	11% 12% 4 13% 8% 7% 6% 4 6% 6% 22%	9057
February	1st to 10th	Night	11% 13% 4 13% 7% 7% 5% 4 6% 5% 24%	2759
	11th to 20th	Night	11% 11% 5% 13% 6% 5% 6% 3 5% 5% 30%	2519
	21st to end	Night	12% 13% 5% 11% 5% 5% 5% 4 5% 5% 30%	2076
March	1st to 10th	Night	18% 13% 4 9% 6% 5% 5% 4 4 5% 28%	5484
	11th to 20th	Night	13% 14% 3 8% 5% 5% 5% 4 6% 6% 32%	5382
	21st to end	Night	13% 13% 4 11% 6% 5% 4 3 4 5% 31%	5072
April	1st to 10th	Night	17% 11% 4 8% 5% 5% 5% 4 5% 6% 31%	2100
	11th to 20th	Night	20% 10% 3 7% 5% 6% 4 3 4 5% 32%	2075
	21st to end	Night	17% 10% 3 7% 5% 4 4 3 5% 6% 36%	1936
May	1st to 10th	Night	24% 12% 3 8% 6% 5% 5% 4 5% 6% 23%	3918
	11th to 20th	Night	19% 9% 4 8% 5% 4 4 4 5% 6% 32%	3655
	21st to end	Night	16% 8% 4 8% 5% 4 5% 4 6% 8% 32%	4014
June	1st to 10th	Night	20% 7% 2 6% 5% 4 4 3 6% 8% 35%	1600
	11th to 20th	Night	14% 6% 2 6% 4 5% 4 5% 6% 8% 40%	1600
	21st to end	Night	14% 7% 3 7% 4 5% 4 4 6% 7% 39%	1600
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 5% 7% 9% 39%	3600
	11th to 20th	Night	11% 4 2 6% 5% 5% 5% 4 5% 7% 45%	3600
	21st to end	Night	8% 5% 2 7% 6% 5% 4 4 6% 8% 45%	3926
August	1st to 10th	Night	13% 7% 3 7% 5% 4 4 4 6% 7% 41%	2586
	11th to 20th	Night	11% 6% 3 7% 5% 5% 6% 5% 5% 7% 41%	2975
	21st to end	Night	11% 5% 2 5% 4 5% 5% 3 6% 8% 46%	3586
September	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 7% 50%	2000
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 4 6% 52%	2099
	21st to end	Night	15% 5% 2 5% 4 4 5% 4 5% 6% 46%	2200
October	1st to 10th	Night	18% 7% 3 6% 5% 4 4 3 5% 7% 38%	2307
	11th to 20th	Night	16% 8% 2 7% 5% 5% 5% 4 5% 6% 38%	2442
	21st to end	Night	20% 9% 3 8% 4 5% 4 4 5% 6% 31%	2860
November	1st to 10th	Night	16% 10% 3 8% 4 5% 5% 4 6% 6% 35%	2667
	11th to 20th	Night	15% 10% 3 9% 6% 4 5% 3 5% 6% 34%	2756
	21st to end	Night	15% 14% 4 8% 5% 5% 5% 5% 6% 6% 28%	2940
December	1st to 10th	Night	15% 20% 7% 12% 7% 5% 4 4 5% 4 17%	4720
	11th to 20th	Night	19% 14% 5% 11% 5% 5% 4 3 4 5% 25%	5348
	21st to end	Night	19% 14% 6% 11% 5% 5% 4 3 5% 7% 22%	7150

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	62% 6% 13% 17% 3	4662
	11th to 20th	Day	64% 7% 10% 10% 7% 2	4680
	21st to end	Day	58% 7% 12% 13% 9% 1	5124
February	1st to 10th	Day	62% 4 8% 18% 6% 2	1859
	11th to 20th	Day	57% 4 11% 19% 8% 1	1995
	21st to end	Day	60% 4 10% 15% 9% 2	1730
March	1st to 10th	Day	58% 5% 9% 15% 9% 4	4579
	11th to 20th	Day	53% 4 16% 15% 10% 2	4792
	21st to end	Day	53% 3 6% 17% 18% 2	6102
April	1st to 10th	Day	55% 5% 7% 20% 12% 2	2520
	11th to 20th	Day	52% 4 7% 20% 16% 1	2494
	21st to end	Day	53% 4 10% 19% 12% 3	2683
May	1st to 10th	Day	63% 4 7% 17% 8% 1	6297
	11th to 20th	Day	51% 5% 14% 19% 9% 1	6462
	21st to end	Day	50% 5% 12% 24% 8% 1	7103
June	1st to 10th	Day	53% 5% 10% 20% 12% 1	2800
	11th to 20th	Day	43% 5% 11% 25% 13% 2	2800
	21st to end	Day	50% 5% 12% 22% 9% 2	2800
July	1st to 10th	Day	43% 9% 14% 22% 12%	6290
	11th to 20th	Day	36% 11% 13% 27% 12%	6285
	21st to end	Day	36% 7% 13% 35% 9%	6728
August	1st to 10th	Day	44% 8% 16% 23% 9% 1	4549
	11th to 20th	Day	41% 8% 16% 28% 7%	4076
	21st to end	Day	39% 9% 15% 23% 14%	4312
September	1st to 10th	Day	36% 5% 12% 33% 14% 1	2400
	11th to 20th	Day	36% 4 11% 33% 15% 1	2300
	21st to end	Day	41% 5% 15% 27% 10% 1	2200
October	1st to 10th	Day	37% 8% 14% 30% 11%	3402
	11th to 20th	Day	41% 6% 17% 26% 10%	3159
	21st to end	Day	41% 5% 17% 28% 8% 1	3180
November	1st to 10th	Day	52% 4 13% 21% 9% 1	1851
	11th to 20th	Day	52% 4 14% 18% 10% 2	1861
	21st to end	Day	59% 4 13% 19% 4 1	1680
December	1st to 10th	Day	69% 5% 10% 13% 2	2680
	11th to 20th	Day	52% 6% 14% 19% 9% 1	3066
	21st to end	Day	60% 4 9% 18% 9%	4048
January	1st to 10th	Night	61% 6% 14% 13% 5% 1	8234
	11th to 20th	Night	63% 6% 11% 13% 6% 1	8280
	21st to end	Night	56% 6% 11% 15% 11% 1	9057
February	1st to 10th	Night	60% 4 11% 17% 7% 1	2759
	11th to 20th	Night	52% 4 13% 21% 9%	2521
	21st to end	Night	54% 4 11% 19% 11% 1	2076
March	1st to 10th	Night	57% 4 9% 16% 13% 2	5494
	11th to 20th	Night	51% 4 16% 18% 10% 1	5383
	21st to end	Night	55% 4 6% 22% 12% 2	5072
April	1st to 10th	Night	54% 4 7% 20% 13% 2	2100
	11th to 20th	Night	54% 4 9% 20% 12% 1	2075
	21st to end	Night	48% 3 9% 20% 15% 3	1936
May	1st to 10th	Night	63% 4 8% 16% 7% 2	3924
	11th to 20th	Night	50% 6% 11% 21% 10% 1	3656
	21st to end	Night	48% 5% 12% 21% 13% 1	4015
June	1st to 10th	Night	48% 4 12% 22% 12% 2	1600
	11th to 20th	Night	41% 6% 13% 24% 15% 2	1600
	21st to end	Night	42% 6% 16% 24% 12% 1	1600
July	1st to 10th	Night	38% 8% 19% 25% 10%	3560
	11th to 20th	Night	34% 9% 15% 29% 13%	3552
	21st to end	Night	36% 9% 15% 29% 11%	3809
August	1st to 10th	Night	40% 7% 16% 27% 10%	2576
	11th to 20th	Night	40% 6% 20% 23% 10% 1	3001
	21st to end	Night	34% 7% 16% 28% 15% 1	3586
September	1st to 10th	Night	32% 5% 16% 33% 13% 1	2000
	11th to 20th	Night	34% 3 15% 34% 14% 1	2099
	21st to end	Night	37% 5% 14% 28% 14% 1	2200
October	1st to 10th	Night	41% 6% 14% 28% 11%	3775
	11th to 20th	Night	39% 5% 13% 28% 15%	3978
	21st to end	Night	43% 5% 15% 26% 11% 1	4610
November	1st to 10th	Night	50% 4 13% 22% 10% 2	2667
	11th to 20th	Night	51% 3 12% 22% 10% 2	2756
	21st to end	Night	55% 5% 16% 19% 5%	2940
December	1st to 10th	Night	65% 7% 11% 14% 3	4720
	11th to 20th	Night	60% 5% 11% 14% 11% 1	5348
	21st to end	Night	61% 4 11% 16% 8%	7150

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	22% 22% 36% 13% 7%	220
	11th to 20th	Day	25% 28% 35% 8% 3	220
	21st to end	Day	19% 27% 36% 13% 4 1	242
February	1st to 10th	Day	31% 25% 35% 8% 1	314
	11th to 20th	Day	26% 28% 35% 9% 1	474
	21st to end	Day	30% 22% 34% 12% 2	446
March	1st to 10th	Day	28% 23% 33% 13% 3	540
	11th to 20th	Day	29% 25% 31% 12% 2 1	540
	21st to end	Day	31% 28% 25% 11% 4 1	594
April	1st to 10th	Day	31% 23% 28% 14% 3 1	540
	11th to 20th	Day	30% 24% 28% 13% 5% 1	532
	21st to end	Day	29% 22% 30% 13% 5% 1	540
May	1st to 10th	Day	29% 23% 29% 13% 5% 1	543
	11th to 20th	Day	19% 20% 34% 19% 7% 1	567
	21st to end	Day	19% 18% 35% 21% 6% 1	617
June	1st to 10th	Day	23% 13% 37% 21% 5% 1	530
	11th to 20th	Day	16% 18% 34% 21% 9% 2	530
	21st to end	Day	22% 16% 35% 20% 7% 1	530
July	1st to 10th	Day	14% 10% 35% 30% 9% 2	525
	11th to 20th	Day	13% 9% 35% 31% 10% 2	524
	21st to end	Day	13% 10% 37% 30% 8% 2	576
August	1st to 10th	Day	12% 9% 32% 30% 13% 3	526
	11th to 20th	Day	15% 7% 33% 29% 12% 5%	519
	21st to end	Day	15% 12% 27% 29% 13% 4	583
September	1st to 10th	Day	14% 12% 33% 24% 14% 4	530
	11th to 20th	Day	12% 12% 25% 27% 16% 8%	530
	21st to end	Day	14% 14% 33% 25% 11% 3	530
October	1st to 10th	Day	21% 15% 30% 17% 13% 3	530
	11th to 20th	Day	21% 21% 34% 16% 7% 1	505
	21st to end	Day	29% 18% 30% 20% 4	462
November	1st to 10th	Day	26% 22% 29% 18% 5% 1	425
	11th to 20th	Day	25% 25% 27% 17% 4 1	401
	21st to end	Day	32% 21% 30% 15% 2	220
December	1st to 10th	Day	23% 25% 33% 15% 4	220
	11th to 20th	Day	29% 24% 35% 11% 1	220
	21st to end	Day	27% 23% 33% 12% 4 1	242
January	1st to 10th	Night	22% 21% 38% 16% 3	840
	11th to 20th	Night	28% 19% 33% 17% 4	840
	21st to end	Night	16% 19% 40% 19% 5% 1	924
February	1st to 10th	Night	19% 17% 38% 22% 4	840
	11th to 20th	Night	20% 21% 38% 19% 2	823
	21st to end	Night	20% 22% 35% 21% 3	692
March	1st to 10th	Night	27% 19% 34% 17% 3	840
	11th to 20th	Night	24% 21% 32% 19% 3	840
	21st to end	Night	25% 20% 30% 20% 4 1	924
April	1st to 10th	Night	25% 19% 33% 20% 3	840
	11th to 20th	Night	27% 21% 28% 18% 5%	831
	21st to end	Night	24% 20% 32% 18% 6%	676
May	1st to 10th	Night	24% 14% 34% 21% 6% 1	534
	11th to 20th	Night	18% 15% 35% 25% 8%	414
	21st to end	Night	15% 12% 36% 27% 10% 1	455
June	1st to 10th	Night	23% 8% 32% 27% 10% 1	400
	11th to 20th	Night	16% 10% 31% 32% 11%	400
	21st to end	Night	18% 7% 34% 29% 11% 1	400
July	1st to 10th	Night	9% 6% 33% 39% 13%	390
	11th to 20th	Night	10% 4 28% 44% 13% 2	388
	21st to end	Night	10% 6% 32% 38% 13% 1	438
August	1st to 10th	Night	13% 3 25% 41% 18% 1	398
	11th to 20th	Night	11% 6% 26% 35% 18% 4	641
	21st to end	Night	13% 7% 26% 36% 16% 1	880
September	1st to 10th	Night	13% 8% 31% 31% 16% 1	800
	11th to 20th	Night	13% 7% 25% 30% 21% 4	800
	21st to end	Night	17% 9% 32% 24% 16% 3	800
October	1st to 10th	Night	21% 13% 27% 24% 14% 1	800
	11th to 20th	Night	22% 14% 31% 25% 9% 1	800
	21st to end	Night	26% 15% 31% 23% 5%	880
November	1st to 10th	Night	24% 19% 31% 21% 5% 1	820
	11th to 20th	Night	22% 20% 31% 18% 8% 1	840
	21st to end	Night	23% 24% 28% 18% 6% 1	840
December	1st to 10th	Night	27% 21% 29% 18% 5%	840
	11th to 20th	Night	28% 22% 30% 16% 4	840
	21st to end	Night	30% 20% 29% 18% 3	924

Page generated at 2026-05-29 01:53:31. Version ac07

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