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 2024-01-27.

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	15% 9% 4 7% 6% 4 5% 5% 5% 7% 33%	74875
	Night	16% 9% 4 7% 6% 4 5% 5% 5% 6% 34%	75167
Transparency	Day	51% 4 11% 22% 10% 1	74580
	Night	51% 4 13% 21% 10% 1	74996
Seeing	Day	22% 18% 32% 20% 7% 2	13575
	Night	21% 15% 32% 23% 8% 1	22705

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	12% 12% 5% 11% 8% 5% 6% 5% 6% 6% 23%	1517
	11th to 20th	Day	14% 14% 6% 10% 10% 3 5% 4 5% 5% 25%	1520
	21st to end	Day	8% 12% 5% 11% 9% 5% 6% 6% 5% 6% 25%	1632
February	1st to 10th	Day	14% 14% 6% 10% 9% 5% 6% 5% 5% 5% 21%	1593
	11th to 20th	Day	10% 12% 6% 11% 7% 5% 5% 5% 6% 5% 28%	1695
	21st to end	Day	14% 14% 7% 8% 7% 5% 5% 5% 4 5% 26%	1480
March	1st to 10th	Day	13% 12% 4 10% 8% 4 7% 5% 4 5% 28%	1797
	11th to 20th	Day	13% 12% 5% 8% 7% 4 5% 4 5% 7% 31%	1857
	21st to end	Day	16% 9% 5% 8% 7% 3 4 4 5% 5% 35%	2376
April	1st to 10th	Day	18% 10% 4 7% 6% 3 5% 5% 5% 6% 31%	2160
	11th to 20th	Day	16% 8% 4 6% 6% 4 5% 4 5% 5% 38%	2134
	21st to end	Day	21% 7% 3 7% 5% 3 5% 4 5% 6% 33%	2299
May	1st to 10th	Day	17% 8% 4 7% 5% 4 5% 5% 5% 7% 35%	2437
	11th to 20th	Day	16% 6% 3 6% 6% 4 5% 5% 5% 6% 38%	2478
	21st to end	Day	13% 7% 3 5% 5% 4 6% 5% 6% 9% 37%	2725
June	1st to 10th	Day	20% 6% 3 6% 6% 3 5% 6% 6% 8% 30%	2520
	11th to 20th	Day	13% 5% 3 5% 6% 3 5% 6% 5% 9% 38%	2520
	21st to end	Day	17% 7% 3 7% 6% 4 6% 6% 6% 8% 30%	2520
July	1st to 10th	Day	11% 5% 3 6% 6% 3 7% 6% 7% 8% 39%	2520
	11th to 20th	Day	11% 5% 3 6% 7% 4 7% 7% 7% 9% 36%	2520
	21st to end	Day	12% 5% 2 6% 6% 3 6% 6% 7% 9% 37%	2744
August	1st to 10th	Day	9% 6% 3 7% 6% 4 6% 6% 8% 9% 36%	2506
	11th to 20th	Day	9% 5% 2 5% 6% 4 6% 6% 8% 9% 39%	2240
	21st to end	Day	11% 5% 3 6% 5% 4 6% 6% 6% 7% 41%	2376
September	1st to 10th	Day	11% 5% 2 5% 5% 4 5% 4 5% 8% 45%	2160
	11th to 20th	Day	12% 5% 2 4 5% 3 3 5% 5% 6% 49%	2070
	21st to end	Day	11% 5% 3 5% 5% 4 6% 5% 6% 8% 41%	1980
October	1st to 10th	Day	18% 8% 3 6% 7% 3 4 4 6% 6% 34%	1882
	11th to 20th	Day	15% 8% 3 7% 5% 4 6% 6% 6% 7% 32%	1761
	21st to end	Day	20% 10% 3 7% 7% 4 4 5% 4 6% 29%	1782
November	1st to 10th	Day	12% 10% 4 8% 8% 4 5% 5% 4 7% 33%	1671
	11th to 20th	Day	16% 10% 3 7% 7% 3 6% 5% 5% 6% 32%	1685
	21st to end	Day	16% 11% 4 7% 7% 3 7% 5% 5% 5% 28%	1520
December	1st to 10th	Day	18% 18% 6% 10% 8% 3 5% 4 4 5% 18%	1520
	11th to 20th	Day	19% 13% 5% 8% 6% 3 5% 5% 6% 7% 24%	1906
	21st to end	Day	23% 13% 6% 8% 7% 3 5% 4 4 5% 23%	2772
January	1st to 10th	Night	15% 13% 6% 10% 8% 4 5% 4 6% 6% 23%	2649
	11th to 20th	Night	15% 15% 6% 10% 6% 3 6% 5% 5% 5% 24%	2660
	21st to end	Night	11% 10% 5% 10% 8% 4 5% 5% 4 7% 30%	2868
February	1st to 10th	Night	12% 13% 5% 12% 9% 5% 6% 6% 6% 5% 22%	2365
	11th to 20th	Night	12% 10% 5% 10% 7% 3 6% 5% 5% 6% 31%	2151
	21st to end	Night	13% 11% 6% 10% 6% 3 5% 5% 5% 6% 30%	1776
March	1st to 10th	Night	15% 15% 6% 7% 6% 4 5% 4 4 4 30%	2150
	11th to 20th	Night	15% 12% 5% 7% 6% 4 5% 4 5% 5% 33%	2097
	21st to end	Night	16% 10% 3 7% 6% 3 4 3 4 5% 38%	1980
April	1st to 10th	Night	17% 10% 4 7% 6% 4 5% 5% 6% 6% 31%	1800
	11th to 20th	Night	19% 8% 3 7% 6% 4 5% 4 4 6% 34%	1775
	21st to end	Night	18% 9% 3 6% 6% 3 5% 3 5% 7% 34%	1660
May	1st to 10th	Night	21% 8% 3 6% 5% 3 4 5% 4 7% 34%	1539
	11th to 20th	Night	15% 7% 3 6% 6% 3 4 5% 5% 7% 39%	1415
	21st to end	Night	13% 5% 3 5% 5% 2 5% 6% 6% 10% 41%	1550
June	1st to 10th	Night	21% 6% 2 6% 4 3 4 4 6% 8% 36%	1440
	11th to 20th	Night	15% 6% 3 5% 4 4 4 5% 6% 9% 40%	1440
	21st to end	Night	14% 7% 3 5% 5% 4 4 5% 5% 8% 40%	1440
July	1st to 10th	Night	11% 5% 2 5% 6% 3 5% 5% 6% 9% 44%	1440
	11th to 20th	Night	9% 4 2 4 6% 4 5% 6% 6% 10% 44%	1440
	21st to end	Night	11% 4 2 4 6% 3 5% 6% 7% 8% 44%	1574
August	1st to 10th	Night	10% 5% 1 4 4 3 4 5% 6% 9% 48%	1432
	11th to 20th	Night	10% 5% 2 5% 5% 4 5% 6% 5% 8% 45%	1639
	21st to end	Night	11% 5% 2 5% 4 4 5% 5% 6% 7% 46%	1980
September	1st to 10th	Night	11% 4 2 5% 5% 3 5% 4 5% 8% 49%	1800
	11th to 20th	Night	12% 5% 2 5% 4 3 3 4 4 6% 52%	1889
	21st to end	Night	15% 4 2 4 5% 3 5% 5% 5% 7% 46%	1980
October	1st to 10th	Night	18% 7% 3 5% 6% 4 4 4 4 7% 36%	2075
	11th to 20th	Night	17% 7% 3 6% 6% 4 5% 5% 5% 6% 37%	2197
	21st to end	Night	21% 9% 3 7% 6% 4 5% 5% 5% 6% 29%	2574
November	1st to 10th	Night	16% 9% 4 6% 5% 4 5% 5% 6% 6% 35%	2407
	11th to 20th	Night	16% 10% 3 8% 6% 3 5% 4 5% 6% 34%	2493
	21st to end	Night	16% 13% 4 7% 6% 3 6% 5% 6% 6% 28%	2660
December	1st to 10th	Night	18% 18% 6% 9% 7% 3 5% 4 5% 5% 20%	2660
	11th to 20th	Night	20% 12% 5% 10% 6% 4 5% 5% 4 5% 25%	3288
	21st to end	Night	23% 13% 6% 11% 7% 4 4 3 4 4 21%	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	61% 3 12% 19% 5%	1518
	11th to 20th	Day	62% 4 10% 14% 9% 1	1520
	21st to end	Day	59% 5% 12% 15% 8% 1	1632
February	1st to 10th	Day	65% 5% 8% 16% 5% 2	1593
	11th to 20th	Day	58% 4 11% 18% 8% 1	1704
	21st to end	Day	62% 3 10% 14% 9% 2	1480
March	1st to 10th	Day	57% 4 10% 17% 9% 3	1800
	11th to 20th	Day	54% 3 13% 15% 13% 3	1857
	21st to end	Day	53% 3 7% 20% 13% 4	2376
April	1st to 10th	Day	55% 4 7% 20% 12% 3	2160
	11th to 20th	Day	50% 3 8% 21% 16% 2	2134
	21st to end	Day	54% 4 10% 18% 11% 3	2299
May	1st to 10th	Day	50% 4 8% 21% 16% 2	2437
	11th to 20th	Day	46% 5% 8% 22% 16% 3	2482
	21st to end	Day	45% 6% 14% 22% 12% 2	2725
June	1st to 10th	Day	54% 4 10% 20% 11% 1	2520
	11th to 20th	Day	44% 5% 11% 26% 13% 2	2520
	21st to end	Day	51% 5% 12% 21% 9% 1	2520
July	1st to 10th	Day	41% 6% 11% 27% 14% 1	2450
	11th to 20th	Day	43% 6% 12% 30% 9%	2445
	21st to end	Day	43% 6% 15% 26% 10% 1	2591
August	1st to 10th	Day	42% 7% 17% 26% 9%	2492
	11th to 20th	Day	39% 5% 17% 26% 11%	2240
	21st to end	Day	41% 6% 11% 28% 13% 1	2376
September	1st to 10th	Day	38% 5% 12% 30% 14% 1	2160
	11th to 20th	Day	37% 4 10% 33% 15% 1	2070
	21st to end	Day	41% 5% 16% 28% 9% 1	1980
October	1st to 10th	Day	50% 6% 10% 22% 11%	1882
	11th to 20th	Day	52% 5% 14% 21% 8%	1761
	21st to end	Day	59% 3 13% 18% 7% 1	1782
November	1st to 10th	Day	52% 4 13% 21% 8% 1	1671
	11th to 20th	Day	53% 3 13% 18% 10% 2	1685
	21st to end	Day	58% 4 14% 19% 4 1	1520
December	1st to 10th	Day	70% 3 11% 13% 3	1520
	11th to 20th	Day	59% 4 13% 18% 5%	1906
	21st to end	Day	65% 3 10% 18% 4	2772
January	1st to 10th	Night	62% 4 12% 16% 5% 1	2649
	11th to 20th	Night	63% 4 12% 15% 6% 1	2660
	21st to end	Night	54% 3 11% 20% 11% 1	2868
February	1st to 10th	Night	62% 4 11% 15% 7% 1	2365
	11th to 20th	Night	52% 4 13% 21% 10%	2153
	21st to end	Night	55% 4 10% 18% 12% 1	1776
March	1st to 10th	Night	58% 4 10% 18% 10% 2	2160
	11th to 20th	Night	53% 3 9% 21% 11% 3	2098
	21st to end	Night	50% 3 8% 22% 13% 4	1980
April	1st to 10th	Night	55% 3 7% 20% 13% 2	1800
	11th to 20th	Night	52% 3 9% 21% 13% 1	1775
	21st to end	Night	50% 3 10% 20% 13% 4	1660
May	1st to 10th	Night	52% 3 6% 19% 17% 4	1539
	11th to 20th	Night	44% 4 9% 21% 19% 3	1416
	21st to end	Night	38% 7% 15% 23% 14% 2	1551
June	1st to 10th	Night	47% 4 12% 23% 11% 2	1440
	11th to 20th	Night	41% 6% 12% 24% 15% 2	1440
	21st to end	Night	43% 5% 17% 24% 11%	1440
July	1st to 10th	Night	35% 6% 16% 27% 16% 1	1400
	11th to 20th	Night	35% 5% 16% 32% 11%	1392
	21st to end	Night	36% 6% 17% 29% 11% 1	1486
August	1st to 10th	Night	32% 5% 21% 30% 11%	1422
	11th to 20th	Night	37% 4 19% 27% 13% 1	1639
	21st to end	Night	36% 5% 15% 31% 12% 1	1980
September	1st to 10th	Night	34% 5% 16% 31% 13% 1	1800
	11th to 20th	Night	35% 3 15% 33% 13% 1	1889
	21st to end	Night	37% 5% 14% 30% 13% 1	1980
October	1st to 10th	Night	48% 4 12% 23% 12% 1	2075
	11th to 20th	Night	49% 4 14% 24% 9%	2197
	21st to end	Night	54% 4 14% 17% 9% 1	2574
November	1st to 10th	Night	50% 4 13% 22% 10% 2	2407
	11th to 20th	Night	51% 3 12% 22% 9% 2	2493
	21st to end	Night	55% 4 16% 19% 6%	2660
December	1st to 10th	Night	66% 3 11% 16% 3	2660
	11th to 20th	Night	62% 4 11% 16% 6% 1	3288
	21st to end	Night	67% 2 12% 16% 3	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	23% 20% 35% 14% 8%	180
	11th to 20th	Day	25% 27% 36% 8% 3 1	180
	21st to end	Day	20% 23% 40% 13% 4 1	188
February	1st to 10th	Day	34% 28% 32% 5% 1	228
	11th to 20th	Day	26% 28% 37% 7% 1	363
	21st to end	Day	32% 23% 31% 12% 3	346
March	1st to 10th	Day	28% 21% 34% 14% 3	420
	11th to 20th	Day	25% 26% 33% 13% 3 1	420
	21st to end	Day	29% 26% 26% 13% 5% 1	462
April	1st to 10th	Day	30% 21% 27% 17% 3 1	420
	11th to 20th	Day	25% 24% 29% 15% 6% 2	412
	21st to end	Day	30% 19% 31% 15% 4 1	420
May	1st to 10th	Day	26% 22% 30% 14% 5% 2	423
	11th to 20th	Day	18% 20% 35% 19% 7% 1	447
	21st to end	Day	17% 17% 36% 22% 7% 1	485
June	1st to 10th	Day	25% 13% 36% 20% 5% 1	450
	11th to 20th	Day	17% 18% 32% 22% 9% 2	450
	21st to end	Day	21% 15% 34% 21% 7% 2	450
July	1st to 10th	Day	15% 8% 33% 31% 10% 2	445
	11th to 20th	Day	14% 8% 36% 31% 10% 2	444
	21st to end	Day	15% 7% 38% 30% 8% 2	488
August	1st to 10th	Day	13% 9% 33% 28% 13% 3	446
	11th to 20th	Day	15% 6% 32% 30% 12% 5%	439
	21st to end	Day	16% 13% 25% 30% 13% 4	495
September	1st to 10th	Day	14% 10% 34% 23% 15% 4	450
	11th to 20th	Day	14% 13% 26% 26% 14% 7%	450
	21st to end	Day	14% 13% 33% 25% 12% 3	450
October	1st to 10th	Day	23% 16% 29% 16% 14% 3	450
	11th to 20th	Day	21% 20% 35% 15% 7% 1	430
	21st to end	Day	29% 18% 30% 19% 4	396
November	1st to 10th	Day	23% 20% 30% 20% 6% 1	365
	11th to 20th	Day	26% 27% 27% 15% 4 1	345
	21st to end	Day	31% 20% 29% 17% 2	180
December	1st to 10th	Day	22% 25% 31% 17% 4	180
	11th to 20th	Day	29% 23% 35% 11% 1	180
	21st to end	Day	29% 23% 32% 12% 4 1	198
January	1st to 10th	Night	23% 21% 37% 17% 3	760
	11th to 20th	Night	28% 18% 33% 17% 4	760
	21st to end	Night	16% 20% 41% 19% 4 1	820
February	1st to 10th	Night	21% 18% 37% 21% 4	720
	11th to 20th	Night	19% 21% 39% 19% 2	703
	21st to end	Night	21% 21% 35% 20% 3	592
March	1st to 10th	Night	27% 18% 34% 18% 3	720
	11th to 20th	Night	23% 21% 33% 19% 3 1	720
	21st to end	Night	24% 19% 31% 22% 5% 1	792
April	1st to 10th	Night	24% 19% 33% 21% 3	720
	11th to 20th	Night	25% 22% 28% 19% 6% 1	711
	21st to end	Night	24% 20% 31% 18% 7% 1	580
May	1st to 10th	Night	24% 14% 33% 21% 7% 1	459
	11th to 20th	Night	17% 14% 35% 25% 8%	354
	21st to end	Night	14% 12% 37% 26% 11% 1	389
June	1st to 10th	Night	23% 8% 32% 26% 10% 1	360
	11th to 20th	Night	17% 9% 30% 31% 13%	360
	21st to end	Night	18% 7% 33% 29% 12% 1	360
July	1st to 10th	Night	9% 5% 33% 38% 15%	350
	11th to 20th	Night	9% 3 28% 43% 14% 2	348
	21st to end	Night	11% 4 32% 37% 14% 1	394
August	1st to 10th	Night	13% 3 25% 41% 18% 1	358
	11th to 20th	Night	11% 5% 26% 36% 18% 4	575
	21st to end	Night	13% 7% 27% 35% 17% 2	792
September	1st to 10th	Night	14% 7% 31% 32% 16% 1	720
	11th to 20th	Night	14% 7% 27% 29% 18% 4	720
	21st to end	Night	17% 9% 32% 23% 16% 3	720
October	1st to 10th	Night	22% 13% 28% 24% 12% 1	720
	11th to 20th	Night	22% 13% 30% 24% 9% 1	720
	21st to end	Night	26% 16% 31% 22% 5%	792
November	1st to 10th	Night	23% 18% 31% 21% 6% 1	740
	11th to 20th	Night	22% 20% 31% 18% 8% 1	760
	21st to end	Night	23% 24% 28% 18% 6% 1	760
December	1st to 10th	Night	28% 21% 29% 17% 5%	760
	11th to 20th	Night	27% 22% 30% 16% 4 1	760
	21st to end	Night	30% 19% 31% 18% 3	836

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