Tidewater Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tidewater Area clear sky chart from 2005-11-06 to 2025-04-11.

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% 6% 2 6% 4 4 5% 4 6% 7% 42%	113314
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	114973
Transparency	Day	38% 7% 13% 22% 17% 4	116950
	Night	38% 6% 11% 22% 18% 4	119477
Seeing	Day	16% 11% 27% 26% 15% 5%	15801
	Night	16% 9% 28% 31% 14% 2	25499

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	14% 4 1 4 3 3 3 3 4 4 56%	3809
	11th to 20th	Day	12% 6% 2 5% 3 3 3 3 5% 4 53%	4060
	21st to end	Day	11% 9% 3 7% 4 4 4 3 4 5% 44%	4466
February	1st to 10th	Day	14% 8% 2 6% 3 5% 5% 4 6% 6% 41%	1800
	11th to 20th	Day	20% 6% 2 6% 4 3 4 3 4 5% 43%	1927
	21st to end	Day	15% 8% 2 6% 4 4 3 4 6% 8% 40%	1650
March	1st to 10th	Day	20% 8% 2 6% 4 3 4 3 4 6% 40%	4745
	11th to 20th	Day	11% 6% 2 5% 3 3 3 3 4 6% 52%	4980
	21st to end	Day	13% 6% 2 5% 4 5% 4 3 5% 6% 47%	5647
April	1st to 10th	Day	13% 5% 1 5% 4 3 3 3 6% 7% 50%	2400
	11th to 20th	Day	10% 4 2 6% 6% 4 4 3 5% 7% 51%	2254
	21st to end	Day	13% 6% 2 6% 5% 4 4 4 5% 6% 45%	2280
May	1st to 10th	Day	15% 6% 3 7% 5% 5% 5% 4 6% 9% 35%	3765
	11th to 20th	Day	21% 7% 2 8% 4 5% 6% 4 6% 7% 32%	4187
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 9% 46%	4823
June	1st to 10th	Day	11% 5% 2 5% 5% 5% 5% 5% 8% 10% 39%	2660
	11th to 20th	Day	11% 5% 2 5% 5% 4 6% 5% 7% 10% 40%	2660
	21st to end	Day	7% 6% 2 6% 5% 6% 6% 5% 7% 12% 38%	2660
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 6% 10% 12% 35%	4440
	11th to 20th	Day	12% 6% 3 9% 6% 5% 6% 5% 7% 9% 32%	4216
	21st to end	Day	9% 7% 3 9% 7% 7% 7% 5% 7% 8% 30%	4466
August	1st to 10th	Day	17% 9% 3 9% 6% 6% 6% 5% 7% 10% 22%	4047
	11th to 20th	Day	10% 6% 3 8% 5% 7% 5% 5% 8% 9% 34%	3730
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 39%	4180
September	1st to 10th	Day	14% 5% 2 6% 5% 5% 5% 4 7% 9% 37%	2280
	11th to 20th	Day	15% 6% 3 7% 5% 4 4 4 6% 6% 39%	2280
	21st to end	Day	21% 7% 3 6% 4 4 5% 4 5% 7% 35%	2040
October	1st to 10th	Day	17% 6% 2 5% 4 4 5% 3 4 5% 45%	1900
	11th to 20th	Day	14% 5% 3 5% 3 4 5% 3 4 5% 49%	1900
	21st to end	Day	12% 5% 2 6% 3 3 4 3 4 6% 51%	2090
November	1st to 10th	Day	15% 6% 2 5% 3 3 4 3 4 6% 48%	1857
	11th to 20th	Day	16% 7% 2 4 4 3 4 2 4 6% 48%	1800
	21st to end	Day	14% 5% 1 5% 4 4 4 3 5% 6% 49%	1765
December	1st to 10th	Day	10% 5% 3 6% 4 4 3 2 5% 5% 53%	2600
	11th to 20th	Day	14% 8% 3 7% 4 4 4 3 4 5% 44%	2990
	21st to end	Day	13% 5% 2 5% 4 3 3 4 5% 7% 49%	3960
January	1st to 10th	Night	12% 7% 3 5% 3 3 3 3 4 5% 53%	6120
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 4 5% 51%	5900
	21st to end	Night	15% 7% 2 6% 4 3 3 3 4 7% 46%	6490
February	1st to 10th	Night	17% 7% 2 6% 4 3 3 4 6% 5% 43%	2600
	11th to 20th	Night	21% 8% 3 6% 3 3 4 3 4 6% 40%	2358
	21st to end	Night	15% 7% 2 5% 4 4 3 3 4 5% 47%	1980
March	1st to 10th	Night	20% 6% 2 6% 4 4 4 3 4 5% 42%	5103
	11th to 20th	Night	13% 6% 3 6% 4 4 4 3 4 5% 48%	4980
	21st to end	Night	15% 8% 2 5% 3 4 4 3 4 5% 47%	5284
April	1st to 10th	Night	14% 5% 2 6% 4 4 5% 4 6% 7% 44%	2000
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 7% 50%	1882
	21st to end	Night	15% 5% 1 5% 5% 4 3 3 5% 6% 47%	1900
May	1st to 10th	Night	15% 7% 3 8% 6% 5% 5% 3 5% 8% 35%	3130
	11th to 20th	Night	22% 7% 2 6% 4 4 4 3 5% 7% 35%	2733
	21st to end	Night	11% 6% 2 7% 5% 4 5% 4 6% 9% 42%	2732
June	1st to 10th	Night	10% 6% 3 4 5% 5% 5% 4 8% 10% 40%	1520
	11th to 20th	Night	7% 5% 3 7% 5% 5% 6% 5% 6% 11% 41%	1520
	21st to end	Night	7% 4 3 6% 5% 5% 5% 5% 7% 9% 44%	1520
July	1st to 10th	Night	7% 5% 2 7% 5% 6% 6% 5% 8% 13% 37%	2520
	11th to 20th	Night	8% 7% 3 8% 5% 5% 6% 5% 8% 10% 36%	2738
	21st to end	Night	14% 8% 4 9% 6% 5% 5% 5% 7% 7% 30%	3087
August	1st to 10th	Night	17% 8% 3 8% 5% 5% 5% 4 7% 8% 29%	2852
	11th to 20th	Night	9% 7% 3 7% 6% 5% 5% 5% 6% 8% 39%	3097
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 7% 8% 44%	3476
September	1st to 10th	Night	11% 5% 3 6% 4 4 4 3 6% 8% 46%	1900
	11th to 20th	Night	14% 6% 2 7% 4 4 4 4 4 7% 44%	1900
	21st to end	Night	19% 7% 3 8% 5% 4 4 3 4 8% 36%	2134
October	1st to 10th	Night	15% 6% 2 5% 3 5% 4 3 4 6% 48%	2280
	11th to 20th	Night	15% 5% 2 6% 4 3 4 3 4 6% 51%	2280
	21st to end	Night	13% 5% 2 5% 4 3 4 3 4 5% 53%	2508
November	1st to 10th	Night	15% 6% 2 5% 4 3 3 3 5% 6% 48%	2438
	11th to 20th	Night	15% 7% 3 5% 4 3 3 3 5% 6% 47%	2600
	21st to end	Night	13% 5% 2 5% 4 3 4 3 5% 6% 51%	2630
December	1st to 10th	Night	9% 5% 3 6% 4 4 4 3 4 5% 53%	4580
	11th to 20th	Night	16% 8% 3 7% 5% 6% 5% 3 5% 6% 38%	5205
	21st to end	Night	12% 5% 2 6% 4 4 4 3 5% 7% 49%	6996

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	31% 3 6% 26% 21% 12%	3810
	11th to 20th	Day	34% 4 6% 19% 32% 6%	4060
	21st to end	Day	41% 5% 9% 25% 17% 3	4466
February	1st to 10th	Day	42% 5% 12% 24% 13% 3	1800
	11th to 20th	Day	44% 5% 9% 18% 19% 5%	1936
	21st to end	Day	41% 7% 12% 19% 17% 5%	1650
March	1st to 10th	Day	45% 5% 7% 20% 16% 7%	4745
	11th to 20th	Day	33% 4 8% 18% 26% 10%	4980
	21st to end	Day	37% 5% 14% 19% 20% 5%	5647
April	1st to 10th	Day	34% 5% 14% 21% 21% 5%	2400
	11th to 20th	Day	33% 6% 11% 24% 20% 5%	2254
	21st to end	Day	38% 7% 12% 22% 16% 4	2280
May	1st to 10th	Day	44% 11% 16% 19% 8% 2	3800
	11th to 20th	Day	48% 10% 13% 20% 7% 1	4191
	21st to end	Day	31% 10% 15% 26% 14% 2	4837
June	1st to 10th	Day	35% 11% 17% 23% 14% 1	2660
	11th to 20th	Day	35% 10% 17% 22% 14% 1	2660
	21st to end	Day	35% 11% 17% 23% 13% 1	2660
July	1st to 10th	Day	36% 12% 20% 20% 10% 2	4370
	11th to 20th	Day	46% 9% 23% 17% 5% 1	4144
	21st to end	Day	46% 10% 15% 17% 11% 1	4324
August	1st to 10th	Day	55% 8% 17% 16% 4	4034
	11th to 20th	Day	42% 8% 15% 23% 12%	3766
	21st to end	Day	36% 8% 14% 25% 16% 2	4180
September	1st to 10th	Day	40% 10% 15% 16% 16% 3	2280
	11th to 20th	Day	44% 7% 10% 21% 16% 2	2280
	21st to end	Day	48% 7% 11% 18% 14% 2	2040
October	1st to 10th	Day	33% 4 9% 25% 25% 3	3160
	11th to 20th	Day	27% 4 6% 21% 33% 9%	3140
	21st to end	Day	22% 4 9% 28% 28% 9%	3428
November	1st to 10th	Day	37% 5% 11% 25% 19% 3	1857
	11th to 20th	Day	38% 4 13% 20% 20% 5%	1800
	21st to end	Day	36% 4 10% 25% 21% 4	1765
December	1st to 10th	Day	34% 4 9% 28% 22% 3	2600
	11th to 20th	Day	43% 4 12% 20% 14% 5%	2986
	21st to end	Day	35% 4 13% 30% 17% 1	3960
January	1st to 10th	Night	33% 5% 6% 21% 26% 9%	6120
	11th to 20th	Night	36% 4 5% 20% 29% 5%	5900
	21st to end	Night	39% 5% 8% 24% 20% 4	6490
February	1st to 10th	Night	42% 5% 11% 23% 16% 3	2600
	11th to 20th	Night	46% 4 9% 20% 17% 5%	2360
	21st to end	Night	39% 5% 9% 21% 19% 7%	1980
March	1st to 10th	Night	44% 5% 8% 18% 17% 8%	5103
	11th to 20th	Night	38% 5% 9% 15% 22% 10%	4980
	21st to end	Night	40% 5% 9% 24% 16% 6%	5284
April	1st to 10th	Night	39% 7% 12% 17% 22% 4	2000
	11th to 20th	Night	34% 6% 11% 23% 20% 6%	1882
	21st to end	Night	37% 6% 12% 24% 17% 4	1900
May	1st to 10th	Night	45% 12% 14% 20% 8% 2	3160
	11th to 20th	Night	47% 10% 13% 22% 7% 1	2734
	21st to end	Night	34% 12% 18% 22% 12% 1	2739
June	1st to 10th	Night	35% 10% 16% 25% 13% 1	1520
	11th to 20th	Night	35% 12% 17% 21% 14% 1	1520
	21st to end	Night	33% 10% 17% 24% 14% 2	1520
July	1st to 10th	Night	37% 13% 19% 21% 9% 2	2480
	11th to 20th	Night	39% 10% 25% 19% 6% 1	2688
	21st to end	Night	49% 11% 12% 17% 11%	2988
August	1st to 10th	Night	51% 7% 19% 19% 4	2841
	11th to 20th	Night	41% 8% 15% 24% 12%	3127
	21st to end	Night	35% 7% 12% 27% 19% 1	3476
September	1st to 10th	Night	35% 9% 17% 21% 15% 3	1900
	11th to 20th	Night	41% 6% 11% 21% 18% 2	1900
	21st to end	Night	47% 7% 12% 18% 14% 2	2134
October	1st to 10th	Night	38% 5% 8% 24% 24% 2	3800
	11th to 20th	Night	28% 4 6% 20% 33% 10%	3779
	21st to end	Night	21% 3 7% 30% 27% 12%	4120
November	1st to 10th	Night	38% 5% 9% 22% 22% 3	2438
	11th to 20th	Night	39% 5% 10% 20% 18% 8%	2600
	21st to end	Night	34% 6% 10% 26% 22% 4	2630
December	1st to 10th	Night	33% 4 8% 24% 26% 5%	4580
	11th to 20th	Night	48% 4 11% 16% 15% 5%	5208
	21st to end	Night	34% 6% 15% 27% 16% 1	6996

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	19% 28% 34% 14% 4	247
	11th to 20th	Day	19% 26% 36% 16% 2	300
	21st to end	Day	19% 19% 40% 18% 3 1	330
February	1st to 10th	Day	19% 21% 39% 15% 5%	300
	11th to 20th	Day	28% 20% 35% 14% 3	475
	21st to end	Day	19% 21% 37% 20% 3 1	414
March	1st to 10th	Day	18% 20% 37% 19% 5%	500
	11th to 20th	Day	20% 20% 36% 18% 4 2	500
	21st to end	Day	17% 17% 40% 21% 5% 1	550
April	1st to 10th	Day	16% 20% 39% 18% 6% 1	500
	11th to 20th	Day	12% 16% 34% 26% 10% 3	452
	21st to end	Day	17% 12% 34% 26% 10% 2	460
May	1st to 10th	Day	17% 13% 33% 25% 10% 2	463
	11th to 20th	Day	19% 7% 29% 31% 11% 3	487
	21st to end	Day	18% 5% 22% 30% 20% 6%	529
June	1st to 10th	Day	11% 4 22% 32% 25% 4	490
	11th to 20th	Day	12% 8% 18% 33% 22% 7%	490
	21st to end	Day	9% 3 21% 38% 22% 6%	490
July	1st to 10th	Day	10% 1 10% 38% 32% 8%	485
	11th to 20th	Day	9% 3 9% 31% 37% 11%	484
	21st to end	Day	9% 3 17% 34% 30% 7%	532
August	1st to 10th	Day	15% 2 14% 37% 24% 8%	486
	11th to 20th	Day	10% 3 14% 30% 29% 14%	479
	21st to end	Day	12% 4 15% 29% 28% 12%	539
September	1st to 10th	Day	14% 3 21% 27% 20% 15%	490
	11th to 20th	Day	18% 6% 14% 32% 22% 9%	490
	21st to end	Day	24% 8% 22% 23% 18% 6%	490
October	1st to 10th	Day	20% 5% 21% 26% 20% 8%	490
	11th to 20th	Day	17% 11% 25% 27% 18% 3	490
	21st to end	Day	15% 9% 31% 26% 13% 5%	539
November	1st to 10th	Day	17% 10% 31% 24% 13% 4	445
	11th to 20th	Day	19% 15% 32% 25% 9% 2	400
	21st to end	Day	16% 18% 29% 24% 13% 2	365
December	1st to 10th	Day	21% 16% 42% 15% 6% 1	200
	11th to 20th	Day	15% 20% 38% 20% 7% 1	200
	21st to end	Day	22% 15% 33% 20% 9% 1	220
January	1st to 10th	Night	18% 19% 35% 24% 5%	800
	11th to 20th	Night	21% 15% 34% 25% 5%	800
	21st to end	Night	18% 15% 40% 25% 2	880
February	1st to 10th	Night	21% 12% 40% 24% 4	800
	11th to 20th	Night	25% 16% 39% 17% 2	783
	21st to end	Night	19% 16% 38% 23% 4	660
March	1st to 10th	Night	18% 13% 36% 27% 6%	800
	11th to 20th	Night	19% 12% 41% 22% 6%	800
	21st to end	Night	19% 12% 38% 26% 4	880
April	1st to 10th	Night	17% 13% 41% 24% 5%	800
	11th to 20th	Night	14% 12% 35% 29% 10%	754
	21st to end	Night	18% 6% 34% 35% 6% 1	760
May	1st to 10th	Night	16% 10% 33% 34% 7% 1	760
	11th to 20th	Night	16% 4 26% 40% 12% 1	521
	21st to end	Night	14% 3 15% 43% 23% 3	411
June	1st to 10th	Night	12% 3 18% 45% 20% 3	380
	11th to 20th	Night	6% 3 19% 45% 24% 3	380
	21st to end	Night	8% 2 16% 49% 24% 1	380
July	1st to 10th	Night	8% 2 13% 46% 29% 2	370
	11th to 20th	Night	7% 1 9% 42% 35% 5%	493
	21st to end	Night	10% 1 15% 44% 27% 3	624
August	1st to 10th	Night	10% 1 13% 42% 30% 3	581
	11th to 20th	Night	10% 2 12% 40% 31% 4	750
	21st to end	Night	11% 2 11% 34% 36% 5%	836
September	1st to 10th	Night	12% 2 14% 38% 27% 7%	760
	11th to 20th	Night	15% 3 15% 33% 28% 5%	760
	21st to end	Night	21% 4 18% 32% 23% 1	760
October	1st to 10th	Night	15% 5% 18% 33% 24% 5%	760
	11th to 20th	Night	17% 8% 24% 31% 17% 2	760
	21st to end	Night	15% 8% 25% 31% 17% 3	836
November	1st to 10th	Night	17% 8% 27% 31% 15% 3	780
	11th to 20th	Night	17% 11% 33% 27% 11% 1	800
	21st to end	Night	14% 11% 31% 31% 13% 1	800
December	1st to 10th	Night	19% 13% 34% 26% 9%	800
	11th to 20th	Night	17% 10% 37% 29% 7%	800
	21st to end	Night	18% 10% 31% 32% 7%	880

Page generated at 2025-04-08 09:17:23. Version ac07

Copyright © 2025 Attilla Danko.