Prevost
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prevost 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	17% 9% 4 7% 6% 3 5% 5% 5% 6% 32%	74778
	Night	16% 10% 4 7% 6% 3 4 4 5% 6% 34%	75021
Transparency	Day	51% 5% 11% 20% 11% 1	74483
	Night	51% 5% 11% 21% 11% 1	74850
Seeing	Day	24% 16% 32% 19% 7% 2	13421
	Night	22% 13% 32% 25% 8% 1	22531

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	15% 16% 7% 11% 9% 3 4 4 5% 3 23%	1517
	11th to 20th	Day	16% 16% 5% 10% 7% 3 4 3 4 5% 27%	1480
	21st to end	Day	10% 14% 6% 9% 7% 4 5% 5% 5% 6% 29%	1584
February	1st to 10th	Day	13% 16% 5% 10% 8% 3 5% 5% 4 5% 25%	1587
	11th to 20th	Day	11% 16% 6% 10% 6% 4 5% 4 5% 5% 28%	1645
	21st to end	Day	17% 14% 7% 10% 7% 4 5% 4 4 4 27%	1480
March	1st to 10th	Day	15% 12% 5% 10% 8% 4 4 3 5% 4 30%	1797
	11th to 20th	Day	15% 12% 5% 7% 7% 3 5% 5% 5% 5% 32%	1880
	21st to end	Day	19% 10% 3 7% 6% 3 4 4 4 6% 35%	2361
April	1st to 10th	Day	21% 11% 4 7% 6% 3 4 4 4 5% 32%	2160
	11th to 20th	Day	21% 8% 3 6% 6% 3 4 4 5% 6% 36%	2134
	21st to end	Day	21% 10% 3 7% 6% 3 4 4 5% 6% 31%	2296
May	1st to 10th	Day	20% 9% 4 7% 6% 3 5% 4 4 5% 33%	2515
	11th to 20th	Day	20% 8% 3 6% 6% 3 4 3 5% 8% 34%	2478
	21st to end	Day	19% 7% 2 6% 6% 4 5% 5% 5% 6% 35%	2725
June	1st to 10th	Day	22% 6% 3 6% 7% 3 5% 5% 7% 7% 29%	2520
	11th to 20th	Day	16% 6% 3 6% 6% 4 5% 5% 7% 8% 35%	2520
	21st to end	Day	21% 8% 3 7% 6% 4 6% 5% 6% 7% 27%	2520
July	1st to 10th	Day	13% 5% 3 6% 6% 4 6% 6% 7% 8% 38%	2520
	11th to 20th	Day	14% 5% 3 5% 6% 4 7% 6% 8% 9% 33%	2520
	21st to end	Day	13% 6% 3 5% 7% 4 6% 7% 7% 8% 35%	2744
August	1st to 10th	Day	13% 6% 2 6% 6% 5% 6% 7% 7% 8% 34%	2506
	11th to 20th	Day	12% 5% 3 6% 7% 5% 6% 7% 7% 9% 36%	2297
	21st to end	Day	14% 5% 3 6% 6% 3 5% 4 6% 7% 41%	2376
September	1st to 10th	Day	15% 6% 2 5% 4 4 4 5% 7% 8% 41%	2160
	11th to 20th	Day	14% 5% 2 5% 5% 3 4 3 5% 7% 47%	2098
	21st to end	Day	18% 6% 3 5% 4 3 5% 4 5% 7% 41%	1980
October	1st to 10th	Day	21% 7% 3 5% 5% 3 4 5% 4 7% 36%	1836
	11th to 20th	Day	22% 9% 4 8% 7% 3 5% 5% 5% 6% 27%	1770
	21st to end	Day	25% 11% 3 6% 5% 3 4 4 4 6% 28%	1782
November	1st to 10th	Day	15% 10% 3 6% 6% 3 5% 5% 6% 7% 34%	1671
	11th to 20th	Day	19% 10% 4 7% 7% 3 4 4 6% 6% 28%	1601
	21st to end	Day	21% 12% 3 7% 6% 3 6% 5% 5% 7% 25%	1520
December	1st to 10th	Day	22% 14% 6% 10% 5% 4 4 4 4 5% 22%	1520
	11th to 20th	Day	19% 14% 5% 9% 6% 3 4 5% 4 5% 27%	1906
	21st to end	Day	24% 17% 5% 9% 5% 3 3 4 3 4 22%	2772
January	1st to 10th	Night	14% 14% 7% 11% 8% 4 5% 4 5% 5% 23%	2649
	11th to 20th	Night	14% 15% 7% 10% 7% 3 4 3 4 5% 27%	2602
	21st to end	Night	10% 11% 4 8% 8% 5% 5% 5% 5% 6% 33%	2772
February	1st to 10th	Night	12% 12% 6% 10% 8% 5% 6% 5% 5% 6% 26%	2372
	11th to 20th	Night	11% 12% 5% 10% 7% 3 5% 5% 5% 6% 32%	2201
	21st to end	Night	14% 12% 5% 8% 8% 3 5% 4 4 5% 32%	1776
March	1st to 10th	Night	15% 12% 5% 8% 7% 4 5% 5% 4 6% 30%	2150
	11th to 20th	Night	15% 13% 4 7% 6% 3 4 4 5% 7% 31%	2074
	21st to end	Night	16% 8% 3 7% 6% 3 4 4 4 4 41%	1994
April	1st to 10th	Night	22% 10% 4 7% 6% 3 4 4 5% 6% 32%	1800
	11th to 20th	Night	19% 5% 4 6% 5% 3 4 5% 4 7% 39%	1775
	21st to end	Night	20% 8% 3 6% 5% 3 4 4 4 6% 36%	1663
May	1st to 10th	Night	19% 8% 3 7% 7% 3 5% 4 4 5% 36%	1461
	11th to 20th	Night	19% 7% 2 6% 5% 2 3 4 6% 6% 39%	1415
	21st to end	Night	17% 6% 3 5% 5% 3 5% 4 5% 7% 41%	1550
June	1st to 10th	Night	21% 6% 3 5% 5% 3 5% 5% 5% 9% 33%	1440
	11th to 20th	Night	19% 6% 3 6% 5% 3 5% 4 5% 7% 39%	1440
	21st to end	Night	19% 7% 1 5% 6% 3 4 4 6% 8% 37%	1440
July	1st to 10th	Night	10% 4 3 4 6% 3 4 5% 7% 8% 46%	1440
	11th to 20th	Night	12% 5% 2 6% 5% 3 5% 5% 5% 9% 42%	1440
	21st to end	Night	12% 6% 2 5% 5% 3 4 5% 7% 7% 43%	1574
August	1st to 10th	Night	11% 5% 2 4 6% 3 6% 6% 6% 9% 43%	1432
	11th to 20th	Night	10% 6% 3 7% 4 3 5% 5% 5% 7% 46%	1584
	21st to end	Night	13% 5% 2 5% 4 3 4 4 5% 7% 47%	1980
September	1st to 10th	Night	10% 5% 2 5% 5% 3 5% 5% 6% 7% 47%	1800
	11th to 20th	Night	14% 5% 2 4 4 2 4 4 5% 8% 48%	1862
	21st to end	Night	18% 5% 2 4 4 2 3 4 5% 6% 47%	1980
October	1st to 10th	Night	17% 7% 3 6% 5% 3 4 4 4 5% 41%	2120
	11th to 20th	Night	20% 7% 3 6% 5% 2 4 5% 5% 5% 36%	2188
	21st to end	Night	21% 10% 3 6% 7% 3 4 4 5% 6% 31%	2574
November	1st to 10th	Night	16% 10% 3 6% 6% 3 5% 4 6% 7% 33%	2407
	11th to 20th	Night	16% 10% 3 7% 6% 3 5% 5% 5% 6% 34%	2574
	21st to end	Night	19% 13% 5% 6% 6% 3 4 4 5% 6% 29%	2660
December	1st to 10th	Night	18% 14% 5% 9% 6% 4 6% 5% 5% 6% 22%	2660
	11th to 20th	Night	20% 13% 5% 7% 6% 3 5% 4 4 5% 27%	3288
	21st to end	Night	25% 18% 5% 8% 5% 3 3 3 4 4 24%	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	64% 4 8% 17% 7%	1518
	11th to 20th	Day	60% 3 10% 14% 11% 1	1480
	21st to end	Day	55% 5% 8% 18% 13% 1	1584
February	1st to 10th	Day	61% 3 8% 17% 8% 2	1587
	11th to 20th	Day	59% 4 11% 15% 11% 1	1654
	21st to end	Day	61% 4 8% 15% 10% 3	1480
March	1st to 10th	Day	59% 3 8% 17% 11% 2	1800
	11th to 20th	Day	54% 3 11% 15% 14% 3	1880
	21st to end	Day	51% 3 9% 18% 14% 4	2361
April	1st to 10th	Day	55% 4 8% 18% 12% 3	2160
	11th to 20th	Day	49% 3 9% 23% 14% 2	2134
	21st to end	Day	55% 4 7% 17% 13% 4	2296
May	1st to 10th	Day	52% 4 7% 20% 13% 3	2515
	11th to 20th	Day	49% 4 9% 18% 17% 3	2482
	21st to end	Day	48% 6% 10% 19% 15% 2	2725
June	1st to 10th	Day	52% 6% 10% 18% 12% 2	2520
	11th to 20th	Day	46% 6% 11% 21% 12% 3	2520
	21st to end	Day	55% 6% 11% 17% 9% 1	2520
July	1st to 10th	Day	41% 7% 14% 26% 11% 1	2450
	11th to 20th	Day	43% 7% 15% 25% 10%	2445
	21st to end	Day	44% 7% 16% 24% 9%	2591
August	1st to 10th	Day	45% 7% 18% 23% 8%	2492
	11th to 20th	Day	42% 8% 17% 24% 9% 1	2297
	21st to end	Day	40% 6% 16% 24% 14% 1	2376
September	1st to 10th	Day	39% 6% 14% 27% 14%	2160
	11th to 20th	Day	37% 5% 13% 32% 13% 1	2098
	21st to end	Day	43% 5% 14% 27% 11%	1980
October	1st to 10th	Day	48% 4 12% 23% 12% 1	1836
	11th to 20th	Day	56% 6% 11% 20% 6%	1770
	21st to end	Day	58% 3 13% 16% 8% 1	1782
November	1st to 10th	Day	48% 5% 14% 21% 10% 1	1671
	11th to 20th	Day	54% 5% 12% 17% 11%	1601
	21st to end	Day	58% 6% 14% 15% 7% 1	1520
December	1st to 10th	Day	66% 4 10% 13% 6%	1520
	11th to 20th	Day	60% 4 10% 17% 8%	1906
	21st to end	Day	66% 5% 8% 14% 6%	2772
January	1st to 10th	Night	64% 4 8% 16% 7% 1	2649
	11th to 20th	Night	60% 5% 10% 15% 8% 2	2602
	21st to end	Night	53% 5% 8% 18% 14% 2	2772
February	1st to 10th	Night	58% 4 9% 19% 9% 1	2372
	11th to 20th	Night	53% 5% 11% 20% 11% 1	2203
	21st to end	Night	55% 4 8% 17% 14% 2	1776
March	1st to 10th	Night	56% 4 8% 18% 11% 2	2160
	11th to 20th	Night	53% 4 9% 16% 14% 3	2075
	21st to end	Night	48% 4 8% 20% 16% 5%	1994
April	1st to 10th	Night	54% 3 8% 19% 15% 2	1800
	11th to 20th	Night	47% 4 8% 23% 16% 2	1775
	21st to end	Night	50% 4 8% 21% 14% 3	1663
May	1st to 10th	Night	50% 4 7% 20% 14% 5%	1461
	11th to 20th	Night	46% 5% 7% 20% 19% 4	1416
	21st to end	Night	43% 6% 11% 21% 16% 3	1551
June	1st to 10th	Night	47% 6% 11% 22% 12% 1	1440
	11th to 20th	Night	45% 5% 10% 23% 14% 3	1440
	21st to end	Night	46% 6% 13% 20% 13%	1440
July	1st to 10th	Night	35% 7% 16% 27% 15% 1	1400
	11th to 20th	Night	38% 7% 15% 29% 11%	1392
	21st to end	Night	37% 8% 17% 24% 13%	1486
August	1st to 10th	Night	38% 7% 18% 26% 11%	1422
	11th to 20th	Night	38% 6% 17% 27% 12%	1584
	21st to end	Night	37% 6% 15% 29% 13%	1980
September	1st to 10th	Night	36% 6% 15% 28% 15% 1	1800
	11th to 20th	Night	35% 4 14% 33% 12% 1	1862
	21st to end	Night	38% 5% 12% 30% 14%	1980
October	1st to 10th	Night	46% 5% 9% 24% 15% 1	2120
	11th to 20th	Night	49% 5% 14% 23% 9%	2188
	21st to end	Night	54% 5% 12% 19% 10% 1	2574
November	1st to 10th	Night	50% 5% 12% 23% 9% 1	2407
	11th to 20th	Night	51% 4 13% 20% 10% 2	2574
	21st to end	Night	56% 5% 11% 19% 8% 1	2660
December	1st to 10th	Night	63% 5% 10% 17% 5%	2660
	11th to 20th	Night	59% 5% 8% 19% 8% 1	3288
	21st to end	Night	65% 4 7% 17% 6%	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	18% 21% 37% 20% 3	180
	11th to 20th	Day	31% 15% 36% 12% 5% 1	170
	21st to end	Day	20% 20% 39% 15% 5% 1	176
February	1st to 10th	Day	37% 24% 33% 5% 1	226
	11th to 20th	Day	25% 24% 38% 12% 2	312
	21st to end	Day	29% 20% 31% 16% 3	346
March	1st to 10th	Day	28% 19% 32% 17% 4	420
	11th to 20th	Day	26% 21% 34% 15% 4 1	420
	21st to end	Day	31% 20% 27% 16% 6% 2	462
April	1st to 10th	Day	30% 15% 33% 15% 6% 1	420
	11th to 20th	Day	32% 18% 26% 16% 7% 1	412
	21st to end	Day	30% 18% 30% 15% 5% 1	420
May	1st to 10th	Day	26% 17% 36% 15% 4 1	423
	11th to 20th	Day	25% 18% 32% 20% 4 1	447
	21st to end	Day	22% 20% 32% 19% 5% 1	485
June	1st to 10th	Day	26% 16% 35% 16% 6% 1	450
	11th to 20th	Day	20% 17% 34% 19% 10% 1	450
	21st to end	Day	26% 11% 32% 21% 8% 2	450
July	1st to 10th	Day	13% 11% 36% 28% 10% 3	445
	11th to 20th	Day	16% 10% 35% 28% 9% 2	444
	21st to end	Day	14% 9% 35% 28% 12% 1	488
August	1st to 10th	Day	15% 9% 31% 30% 14% 2	446
	11th to 20th	Day	12% 7% 32% 29% 12% 7%	439
	21st to end	Day	18% 11% 30% 22% 12% 6%	495
September	1st to 10th	Day	18% 6% 37% 23% 11% 6%	450
	11th to 20th	Day	13% 12% 31% 24% 15% 5%	450
	21st to end	Day	22% 13% 27% 22% 12% 5%	450
October	1st to 10th	Day	26% 17% 27% 19% 11% 1	450
	11th to 20th	Day	24% 17% 29% 22% 7% 1	435
	21st to end	Day	33% 14% 31% 18% 4	396
November	1st to 10th	Day	28% 16% 32% 18% 5% 1	365
	11th to 20th	Day	26% 19% 33% 16% 5%	261
	21st to end	Day	29% 19% 33% 16% 4	180
December	1st to 10th	Day	27% 16% 32% 19% 4 1	180
	11th to 20th	Day	30% 21% 37% 10% 2 1	180
	21st to end	Day	36% 21% 25% 13% 5% 1	198
January	1st to 10th	Night	23% 16% 34% 22% 5%	760
	11th to 20th	Night	23% 17% 32% 22% 5%	744
	21st to end	Night	16% 15% 39% 23% 6% 1	792
February	1st to 10th	Night	18% 17% 40% 21% 3 1	720
	11th to 20th	Night	21% 17% 38% 18% 5%	703
	21st to end	Night	22% 16% 35% 25% 2	592
March	1st to 10th	Night	23% 17% 33% 23% 3	720
	11th to 20th	Night	24% 16% 35% 19% 6%	720
	21st to end	Night	22% 13% 34% 24% 6% 1	792
April	1st to 10th	Night	28% 14% 31% 23% 4	720
	11th to 20th	Night	24% 14% 32% 24% 5% 1	711
	21st to end	Night	27% 15% 32% 18% 7%	583
May	1st to 10th	Night	24% 14% 32% 22% 6% 2	381
	11th to 20th	Night	24% 12% 29% 28% 6% 1	354
	21st to end	Night	21% 8% 40% 24% 8%	389
June	1st to 10th	Night	23% 10% 35% 23% 8%	360
	11th to 20th	Night	24% 8% 29% 28% 11%	360
	21st to end	Night	21% 6% 28% 29% 15% 1	360
July	1st to 10th	Night	10% 9% 34% 34% 13% 1	350
	11th to 20th	Night	11% 5% 28% 42% 14%	348
	21st to end	Night	12% 5% 29% 39% 12% 2	394
August	1st to 10th	Night	15% 5% 21% 42% 16% 1	358
	11th to 20th	Night	13% 4 27% 32% 21% 3	520
	21st to end	Night	15% 6% 29% 30% 17% 2	792
September	1st to 10th	Night	13% 6% 31% 36% 13% 1	720
	11th to 20th	Night	16% 7% 26% 31% 18% 2	720
	21st to end	Night	19% 9% 25% 29% 15% 3	720
October	1st to 10th	Night	22% 11% 28% 28% 10% 1	720
	11th to 20th	Night	24% 12% 29% 25% 8% 1	720
	21st to end	Night	28% 12% 32% 23% 5%	792
November	1st to 10th	Night	24% 14% 30% 23% 8% 1	740
	11th to 20th	Night	26% 14% 32% 20% 8% 1	760
	21st to end	Night	28% 17% 28% 21% 5% 1	760
December	1st to 10th	Night	27% 16% 32% 19% 6%	760
	11th to 20th	Night	28% 18% 31% 19% 4 1	760
	21st to end	Night	32% 16% 31% 17% 4	836

Page generated at 2024-01-13 09:37:53. Version ac07

Copyright 2024 Attilla Danko