NASA Wallops Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NASA Wallops Visitor Center clear sky chart from 2005-11-06 to 2024-02-20.

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% 5% 2 5% 5% 3 4 5% 6% 8% 44%	78419
	Night	14% 6% 3 5% 5% 3 4 4 5% 7% 43%	80773
Transparency	Day	37% 7% 13% 25% 15% 3	78127
	Night	40% 6% 12% 23% 16% 3	80584
Seeing	Day	15% 7% 22% 30% 20% 5%	14187
	Night	17% 8% 25% 31% 16% 3	23743

By Month

Percentage Cloud Cover SE (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% 5% 3 4 4 2 3 4 4 8% 48%	2517
	11th to 20th	Day	13% 7% 2 7% 6% 3 4 3 5% 6% 44%	2780
	21st to end	Day	14% 9% 4 7% 6% 3 4 4 5% 6% 39%	3124
February	1st to 10th	Day	12% 7% 3 6% 6% 3 5% 6% 6% 8% 39%	1710
	11th to 20th	Day	19% 7% 3 3 4 2 4 4 4 5% 44%	1837
	21st to end	Day	18% 9% 3 5% 4 2 5% 4 6% 7% 38%	1480
March	1st to 10th	Day	15% 5% 2 4 4 3 4 4 4 6% 50%	1831
	11th to 20th	Day	17% 5% 2 4 5% 2 4 4 6% 6% 44%	1980
	21st to end	Day	16% 5% 3 5% 5% 3 4 5% 5% 7% 41%	2288
April	1st to 10th	Day	13% 5% 2 4 5% 3 4 4 6% 7% 49%	2160
	11th to 20th	Day	11% 5% 2 4 4 3 4 4 5% 7% 50%	2134
	21st to end	Day	13% 5% 3 4 4 2 4 4 5% 7% 47%	2160
May	1st to 10th	Day	11% 6% 3 6% 4 3 5% 5% 6% 10% 42%	2182
	11th to 20th	Day	16% 7% 3 5% 4 3 4 5% 6% 8% 40%	2435
	21st to end	Day	12% 5% 2 5% 4 2 5% 4 5% 8% 46%	2725
June	1st to 10th	Day	10% 4 2 4 4 3 5% 6% 8% 11% 43%	2520
	11th to 20th	Day	11% 4 2 4 5% 3 4 5% 6% 11% 45%	2520
	21st to end	Day	7% 4 2 4 5% 4 5% 5% 7% 12% 45%	2520
July	1st to 10th	Day	8% 4 2 5% 4 3 6% 5% 7% 11% 45%	2520
	11th to 20th	Day	6% 3 2 4 4 3 4 7% 8% 11% 47%	2520
	21st to end	Day	8% 4 2 5% 5% 3 7% 7% 10% 11% 38%	2572
August	1st to 10th	Day	9% 5% 2 4 6% 4 5% 6% 8% 11% 41%	2284
	11th to 20th	Day	10% 5% 2 5% 6% 4 6% 6% 7% 9% 40%	2126
	21st to end	Day	10% 5% 2 5% 5% 3 5% 6% 7% 9% 41%	2376
September	1st to 10th	Day	14% 4 2 4 6% 3 4 4 6% 9% 44%	2160
	11th to 20th	Day	12% 5% 3 6% 5% 3 4 4 5% 8% 46%	2138
	21st to end	Day	19% 6% 3 6% 6% 2 3 3 5% 8% 39%	1980
October	1st to 10th	Day	14% 5% 2 5% 5% 3 4 5% 4 6% 46%	1800
	11th to 20th	Day	17% 4 2 4 3 3 4 4 5% 5% 49%	1800
	21st to end	Day	13% 6% 2 5% 5% 3 4 5% 4 6% 47%	1980
November	1st to 10th	Day	13% 6% 2 4 3 2 4 4 4 7% 50%	1673
	11th to 20th	Day	12% 6% 3 4 5% 4 4 5% 4 7% 47%	1710
	21st to end	Day	15% 5% 2 4 4 2 4 4 5% 7% 48%	1675
December	1st to 10th	Day	17% 6% 2 5% 4 3 5% 4 6% 7% 40%	1520
	11th to 20th	Day	15% 8% 2 5% 4 3 3 3 4 5% 48%	1910
	21st to end	Day	15% 6% 2 4 5% 3 4 4 6% 7% 44%	2772
January	1st to 10th	Night	13% 7% 3 5% 5% 3 4 4 5% 6% 46%	4429
	11th to 20th	Night	17% 7% 3 5% 5% 3 4 4 4 5% 43%	4176
	21st to end	Night	16% 9% 3 7% 5% 2 5% 3 4 5% 39%	4532
February	1st to 10th	Night	16% 7% 2 6% 5% 2 3 4 5% 6% 43%	2470
	11th to 20th	Night	19% 8% 2 4 4 2 3 4 5% 6% 42%	2213
	21st to end	Night	18% 6% 2 5% 5% 2 4 4 4 5% 45%	1776
March	1st to 10th	Night	15% 6% 2 5% 3 2 3 4 5% 5% 50%	2125
	11th to 20th	Night	16% 6% 3 6% 5% 2 4 4 6% 7% 41%	1980
	21st to end	Night	15% 8% 3 5% 5% 3 3 5% 4 5% 43%	2067
April	1st to 10th	Night	15% 8% 2 5% 6% 3 4 4 6% 8% 39%	1800
	11th to 20th	Night	11% 6% 2 4 4 3 4 5% 5% 7% 50%	1775
	21st to end	Night	15% 6% 2 6% 5% 3 6% 4 6% 7% 41%	1800
May	1st to 10th	Night	16% 8% 2 6% 5% 2 4 4 7% 7% 39%	1778
	11th to 20th	Night	16% 6% 3 4 6% 2 5% 5% 5% 9% 39%	1472
	21st to end	Night	12% 8% 3 5% 5% 4 4 5% 6% 8% 40%	1550
June	1st to 10th	Night	13% 7% 3 5% 5% 2 4 5% 6% 8% 42%	1440
	11th to 20th	Night	9% 4 3 5% 6% 4 5% 6% 7% 11% 40%	1440
	21st to end	Night	8% 5% 4 5% 5% 4 6% 6% 7% 11% 41%	1440
July	1st to 10th	Night	8% 5% 2 5% 6% 4 7% 7% 6% 10% 40%	1440
	11th to 20th	Night	6% 5% 2 5% 7% 4 5% 6% 7% 12% 43%	1440
	21st to end	Night	6% 5% 3 6% 7% 3 6% 5% 8% 10% 41%	1742
August	1st to 10th	Night	7% 5% 2 5% 6% 4 6% 6% 8% 11% 38%	1636
	11th to 20th	Night	9% 6% 3 6% 6% 4 5% 5% 7% 10% 40%	1774
	21st to end	Night	8% 5% 3 6% 5% 4 5% 6% 6% 10% 43%	1980
September	1st to 10th	Night	12% 6% 3 5% 6% 3 4 4 6% 8% 45%	1800
	11th to 20th	Night	9% 6% 3 4 6% 3 4 4 5% 9% 48%	1822
	21st to end	Night	19% 7% 2 5% 6% 3 5% 6% 5% 7% 36%	1980
October	1st to 10th	Night	15% 7% 2 6% 4 3 3 4 5% 7% 45%	2156
	11th to 20th	Night	16% 5% 3 5% 4 2 3 3 4 5% 49%	2160
	21st to end	Night	14% 7% 3 5% 4 3 4 3 5% 6% 47%	2376
November	1st to 10th	Night	14% 7% 2 4 4 2 4 4 4 6% 49%	2402
	11th to 20th	Night	14% 6% 3 5% 4 3 3 4 5% 6% 47%	2470
	21st to end	Night	11% 5% 3 5% 4 2 4 4 5% 7% 50%	2503
December	1st to 10th	Night	16% 8% 3 6% 5% 3 5% 5% 5% 6% 38%	2660
	11th to 20th	Night	18% 6% 2 6% 5% 3 4 4 4 7% 42%	3285
	21st to end	Night	14% 7% 2 5% 5% 3 4 5% 6% 8% 41%	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	36% 5% 8% 32% 18% 2	2518
	11th to 20th	Day	41% 4 10% 21% 20% 4	2780
	21st to end	Day	47% 5% 10% 23% 13% 2	3124
February	1st to 10th	Day	41% 7% 14% 24% 12% 2	1710
	11th to 20th	Day	42% 4 10% 24% 16% 4	1846
	21st to end	Day	46% 5% 12% 20% 14% 4	1480
March	1st to 10th	Day	37% 4 12% 24% 22% 2	1831
	11th to 20th	Day	40% 5% 11% 22% 18% 4	1980
	21st to end	Day	41% 7% 11% 22% 15% 3	2288
April	1st to 10th	Day	36% 6% 12% 21% 20% 5%	2160
	11th to 20th	Day	33% 6% 11% 25% 19% 5%	2134
	21st to end	Day	37% 5% 13% 23% 18% 4	2160
May	1st to 10th	Day	38% 7% 14% 24% 14% 3	2182
	11th to 20th	Day	41% 7% 14% 23% 12% 3	2439
	21st to end	Day	35% 9% 17% 26% 12% 1	2725
June	1st to 10th	Day	33% 9% 17% 26% 14% 1	2520
	11th to 20th	Day	33% 9% 18% 25% 14% 2	2520
	21st to end	Day	30% 9% 18% 26% 15% 1	2520
July	1st to 10th	Day	31% 10% 18% 25% 13% 2	2450
	11th to 20th	Day	27% 10% 21% 32% 9%	2445
	21st to end	Day	31% 10% 18% 26% 14% 1	2428
August	1st to 10th	Day	33% 10% 21% 26% 10% 1	2271
	11th to 20th	Day	36% 9% 17% 25% 12% 1	2126
	21st to end	Day	33% 11% 15% 26% 13% 2	2376
September	1st to 10th	Day	36% 8% 17% 20% 17% 3	2160
	11th to 20th	Day	36% 6% 10% 26% 20% 2	2138
	21st to end	Day	44% 6% 10% 21% 17% 2	1980
October	1st to 10th	Day	38% 6% 10% 25% 18% 4	1800
	11th to 20th	Day	37% 4 11% 27% 19% 3	1800
	21st to end	Day	38% 5% 8% 25% 20% 4	1980
November	1st to 10th	Day	37% 4 10% 28% 16% 4	1673
	11th to 20th	Day	38% 5% 12% 21% 19% 5%	1710
	21st to end	Day	38% 4 9% 29% 16% 3	1675
December	1st to 10th	Day	44% 6% 15% 23% 11% 2	1520
	11th to 20th	Day	39% 4 9% 29% 15% 3	1906
	21st to end	Day	39% 7% 14% 27% 12% 1	2772
January	1st to 10th	Night	38% 4 9% 26% 18% 3	4429
	11th to 20th	Night	44% 5% 8% 23% 17% 2	4176
	21st to end	Night	47% 5% 7% 24% 14% 2	4532
February	1st to 10th	Night	42% 3 11% 26% 15% 2	2470
	11th to 20th	Night	44% 3 8% 23% 17% 4	2215
	21st to end	Night	42% 4 8% 22% 18% 5%	1776
March	1st to 10th	Night	37% 3 11% 27% 18% 3	2125
	11th to 20th	Night	42% 5% 10% 21% 19% 4	1980
	21st to end	Night	43% 5% 9% 21% 16% 5%	2067
April	1st to 10th	Night	42% 7% 11% 18% 18% 5%	1800
	11th to 20th	Night	35% 6% 11% 21% 20% 6%	1775
	21st to end	Night	40% 6% 11% 22% 17% 4	1800
May	1st to 10th	Night	43% 6% 13% 23% 13% 3	1778
	11th to 20th	Night	42% 7% 14% 21% 13% 3	1473
	21st to end	Night	42% 8% 13% 23% 12% 1	1551
June	1st to 10th	Night	40% 8% 13% 22% 16% 1	1440
	11th to 20th	Night	37% 9% 16% 22% 14% 2	1440
	21st to end	Night	36% 10% 16% 22% 15% 2	1440
July	1st to 10th	Night	35% 11% 20% 20% 12% 3	1400
	11th to 20th	Night	31% 11% 18% 28% 12% 1	1392
	21st to end	Night	34% 9% 18% 23% 15% 1	1645
August	1st to 10th	Night	37% 10% 19% 23% 11%	1625
	11th to 20th	Night	38% 9% 17% 22% 13% 1	1774
	21st to end	Night	37% 9% 16% 24% 12% 2	1980
September	1st to 10th	Night	37% 8% 16% 18% 16% 4	1800
	11th to 20th	Night	36% 5% 11% 26% 20% 2	1822
	21st to end	Night	47% 8% 9% 19% 16% 3	1980
October	1st to 10th	Night	39% 6% 10% 24% 17% 3	2156
	11th to 20th	Night	38% 5% 8% 26% 20% 3	2160
	21st to end	Night	40% 4 9% 25% 18% 4	2376
November	1st to 10th	Night	38% 5% 9% 26% 17% 5%	2402
	11th to 20th	Night	40% 4 11% 21% 19% 5%	2470
	21st to end	Night	34% 5% 10% 27% 21% 3	2503
December	1st to 10th	Night	47% 6% 11% 22% 12% 2	2660
	11th to 20th	Night	43% 5% 10% 22% 18% 2	3288
	21st to end	Night	40% 6% 15% 26% 12% 1	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% 16% 32% 29% 6%	180
	11th to 20th	Day	17% 19% 40% 17% 7%	254
	21st to end	Day	16% 13% 33% 30% 7%	297
February	1st to 10th	Day	15% 12% 33% 31% 9%	270
	11th to 20th	Day	25% 16% 34% 22% 3	451
	21st to end	Day	23% 14% 37% 20% 6%	346
March	1st to 10th	Day	16% 15% 31% 31% 6%	420
	11th to 20th	Day	19% 15% 29% 30% 4 2	420
	21st to end	Day	17% 10% 33% 32% 7% 1	462
April	1st to 10th	Day	13% 14% 33% 31% 7% 2	420
	11th to 20th	Day	13% 8% 26% 38% 13% 2	412
	21st to end	Day	17% 8% 26% 34% 14% 1	420
May	1st to 10th	Day	14% 8% 30% 32% 13% 2	423
	11th to 20th	Day	17% 4 24% 36% 17% 2	447
	21st to end	Day	18% 2 17% 30% 25% 8%	485
June	1st to 10th	Day	13% 2 15% 35% 28% 7%	450
	11th to 20th	Day	10% 2 18% 33% 29% 8%	450
	21st to end	Day	8% 1 13% 40% 32% 7%	450
July	1st to 10th	Day	9% 2 9% 33% 34% 12%	445
	11th to 20th	Day	5% 1 6% 32% 44% 11%	444
	21st to end	Day	10% 1 10% 33% 37% 8%	488
August	1st to 10th	Day	9% 2 10% 31% 38% 10%	446
	11th to 20th	Day	11% 1 8% 29% 38% 13%	439
	21st to end	Day	9% 2 13% 29% 34% 14%	495
September	1st to 10th	Day	15% 3 11% 29% 26% 16%	450
	11th to 20th	Day	13% 2 15% 28% 31% 10%	450
	21st to end	Day	22% 6% 20% 27% 21% 4	450
October	1st to 10th	Day	18% 5% 16% 30% 22% 9%	450
	11th to 20th	Day	16% 6% 24% 30% 21% 4	450
	21st to end	Day	15% 8% 28% 29% 15% 4	495
November	1st to 10th	Day	18% 8% 25% 27% 18% 5%	365
	11th to 20th	Day	15% 13% 34% 24% 13% 2	370
	21st to end	Day	19% 16% 21% 26% 15% 3	335
December	1st to 10th	Day	22% 11% 33% 24% 11% 1	180
	11th to 20th	Day	20% 12% 27% 33% 8%	180
	21st to end	Day	20% 10% 29% 28% 11% 2	198
January	1st to 10th	Night	18% 17% 34% 26% 5%	760
	11th to 20th	Night	19% 15% 32% 26% 8%	760
	21st to end	Night	18% 16% 34% 30% 3	836
February	1st to 10th	Night	20% 12% 36% 27% 5%	760
	11th to 20th	Night	24% 16% 39% 19% 2	742
	21st to end	Night	21% 13% 31% 31% 4 1	592
March	1st to 10th	Night	18% 11% 33% 29% 8%	720
	11th to 20th	Night	20% 11% 33% 28% 7% 2	720
	21st to end	Night	19% 8% 32% 33% 7% 1	792
April	1st to 10th	Night	19% 9% 35% 30% 7%	720
	11th to 20th	Night	14% 7% 29% 38% 11% 1	711
	21st to end	Night	17% 4 30% 36% 12% 1	720
May	1st to 10th	Night	18% 7% 28% 36% 10% 1	698
	11th to 20th	Night	19% 3 25% 36% 17% 1	411
	21st to end	Night	17% 2 14% 34% 27% 6%	389
June	1st to 10th	Night	14% 3 16% 40% 25% 2	360
	11th to 20th	Night	8% 1 13% 45% 29% 4	360
	21st to end	Night	11% 1 12% 41% 31% 3	360
July	1st to 10th	Night	9% 9% 45% 32% 5%	350
	11th to 20th	Night	8% 2 6% 34% 43% 9%	348
	21st to end	Night	9% 1 9% 38% 37% 6%	562
August	1st to 10th	Night	9% 1 10% 36% 38% 7%	562
	11th to 20th	Night	12% 2 9% 35% 36% 6%	710
	21st to end	Night	9% 2 11% 33% 35% 10%	792
September	1st to 10th	Night	13% 2 11% 33% 32% 9%	720
	11th to 20th	Night	11% 2 13% 33% 34% 7%	720
	21st to end	Night	21% 5% 15% 32% 23% 3	720
October	1st to 10th	Night	18% 4 18% 31% 22% 7%	720
	11th to 20th	Night	18% 8% 22% 30% 20% 3	720
	21st to end	Night	18% 10% 25% 29% 14% 3	792
November	1st to 10th	Night	16% 8% 26% 29% 16% 4	740
	11th to 20th	Night	17% 11% 31% 30% 10% 1	760
	21st to end	Night	13% 15% 28% 29% 14% 1	760
December	1st to 10th	Night	21% 11% 34% 22% 10% 2	760
	11th to 20th	Night	19% 11% 38% 25% 7%	760
	21st to end	Night	18% 13% 33% 28% 8%	836

Page generated at 2024-02-17 06:28:38. Version ac07

Copyright 2024 Attilla Danko