Willow Slough Fish and Wildlife Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Willow Slough Fish and Wildlife Area clear sky chart from 2005-11-06 to 2024-04-10.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	83040
	Night	15% 10% 4 7% 5% 3 4 4 5% 6% 37%	85806
Transparency	Day	47% 6% 11% 21% 12% 2	82741
	Night	48% 6% 11% 21% 13% 2	85626
Seeing	Day	17% 9% 28% 25% 15% 6%	14853
	Night	18% 9% 30% 29% 12% 1	24884

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	17% 13% 11% 10% 6% 3 6% 5% 5% 4 20%	2527
	11th to 20th	Day	14% 16% 7% 14% 8% 4 4 7% 7% 4 16%	2530
	21st to end	Day	23% 22% 7% 9% 5% 2 3 3 3 5% 17%	2850
February	1st to 10th	Day	18% 11% 5% 8% 7% 4 6% 4 5% 6% 27%	1818
	11th to 20th	Day	14% 10% 4 7% 7% 4 5% 4 5% 6% 33%	1848
	21st to end	Day	17% 14% 5% 9% 5% 3 4 4 4 6% 30%	1570
March	1st to 10th	Day	19% 16% 4 7% 5% 2 4 4 3 5% 31%	3120
	11th to 20th	Day	11% 8% 4 6% 6% 4 5% 5% 6% 8% 38%	3251
	21st to end	Day	18% 10% 6% 9% 7% 3 5% 5% 5% 7% 24%	4155
April	1st to 10th	Day	17% 11% 3 6% 6% 3 4 4 5% 7% 35%	2269
	11th to 20th	Day	17% 9% 4 5% 6% 3 5% 4 4 7% 38%	2134
	21st to end	Day	21% 7% 3 7% 7% 3 5% 5% 5% 6% 32%	2269
May	1st to 10th	Day	18% 9% 3 7% 5% 4 5% 6% 5% 7% 32%	2340
	11th to 20th	Day	20% 7% 3 6% 5% 3 5% 4 6% 7% 34%	2336
	21st to end	Day	12% 6% 3 6% 6% 4 5% 6% 7% 9% 39%	2725
June	1st to 10th	Day	10% 5% 2 5% 6% 3 5% 5% 6% 9% 44%	2520
	11th to 20th	Day	9% 4 2 5% 6% 4 5% 5% 6% 8% 45%	2520
	21st to end	Day	11% 5% 3 6% 6% 4 6% 7% 6% 9% 39%	2520
July	1st to 10th	Day	9% 4 3 6% 6% 3 6% 6% 6% 10% 43%	2520
	11th to 20th	Day	8% 4 2 4 5% 4 6% 6% 6% 9% 46%	2520
	21st to end	Day	8% 4 2 4 5% 4 5% 6% 7% 11% 44%	2743
August	1st to 10th	Day	8% 4 2 5% 6% 4 5% 5% 6% 9% 46%	2395
	11th to 20th	Day	8% 5% 2 5% 7% 3 4 6% 7% 9% 44%	2150
	21st to end	Day	7% 5% 2 4 5% 3 5% 5% 6% 9% 49%	2376
September	1st to 10th	Day	11% 5% 2 5% 5% 3 5% 5% 6% 7% 46%	2160
	11th to 20th	Day	12% 5% 2 3 4 3 4 4 5% 8% 49%	2016
	21st to end	Day	10% 4 3 5% 5% 3 5% 5% 6% 9% 46%	1980
October	1st to 10th	Day	12% 6% 2 5% 4 3 5% 5% 5% 7% 44%	1980
	11th to 20th	Day	19% 7% 2 5% 5% 3 5% 4 5% 6% 38%	1779
	21st to end	Day	20% 9% 3 8% 6% 3 4 4 5% 6% 31%	1782
November	1st to 10th	Day	12% 6% 2 4 5% 3 4 4 5% 7% 48%	1672
	11th to 20th	Day	18% 10% 4 7% 5% 3 3 4 4 7% 36%	1710
	21st to end	Day	18% 11% 3 9% 4 3 3 4 4 6% 36%	1710
December	1st to 10th	Day	16% 14% 5% 9% 6% 4 4 5% 4 6% 27%	1544
	11th to 20th	Day	15% 12% 6% 10% 6% 3 5% 5% 5% 6% 27%	1918
	21st to end	Day	23% 20% 9% 12% 6% 3 3 3 3 4 15%	2783
January	1st to 10th	Night	18% 15% 9% 9% 5% 3 4 3 4 4 26%	4428
	11th to 20th	Night	16% 19% 7% 12% 7% 3 5% 5% 6% 3 18%	4440
	21st to end	Night	25% 17% 7% 8% 5% 3 3 3 3 4 21%	4816
February	1st to 10th	Night	17% 13% 6% 8% 7% 3 4 3 4 6% 30%	2361
	11th to 20th	Night	15% 10% 4 8% 6% 3 4 4 5% 6% 36%	2218
	21st to end	Night	19% 13% 4 7% 5% 3 4 4 5% 5% 32%	1884
March	1st to 10th	Night	18% 12% 3 5% 5% 2 3 4 4 5% 37%	3733
	11th to 20th	Night	11% 6% 3 5% 5% 3 4 5% 4 7% 46%	3709
	21st to end	Night	20% 9% 6% 7% 6% 3 5% 4 5% 6% 29%	3504
April	1st to 10th	Night	14% 8% 3 7% 5% 3 5% 4 4 8% 39%	1900
	11th to 20th	Night	18% 8% 3 6% 6% 3 4 4 5% 5% 38%	1775
	21st to end	Night	18% 7% 3 6% 6% 3 4 5% 6% 7% 35%	1689
May	1st to 10th	Night	17% 7% 4 6% 6% 3 5% 5% 6% 8% 34%	1620
	11th to 20th	Night	17% 6% 3 5% 5% 3 6% 4 5% 7% 39%	1555
	21st to end	Night	9% 5% 2 6% 7% 3 5% 5% 6% 10% 41%	1551
June	1st to 10th	Night	10% 6% 2 5% 4 3 4 4 6% 8% 50%	1440
	11th to 20th	Night	8% 5% 3 4 5% 3 4 4 6% 10% 49%	1440
	21st to end	Night	10% 5% 3 6% 6% 4 5% 5% 6% 9% 43%	1440
July	1st to 10th	Night	7% 4 2 4 5% 3 4 4 6% 10% 49%	1440
	11th to 20th	Night	7% 4 1 4 4 3 5% 3 5% 8% 57%	1440
	21st to end	Night	5% 4 2 4 5% 3 5% 4 6% 8% 54%	1575
August	1st to 10th	Night	6% 4 1 4 5% 3 4 5% 6% 11% 50%	1543
	11th to 20th	Night	6% 3 2 4 5% 4 5% 5% 6% 9% 50%	1748
	21st to end	Night	8% 4 2 5% 4 2 4 5% 5% 8% 53%	1980
September	1st to 10th	Night	11% 5% 1 5% 4 3 3 4 4 8% 52%	1800
	11th to 20th	Night	9% 4 2 3 4 3 4 4 6% 7% 55%	1926
	21st to end	Night	9% 5% 3 5% 5% 3 5% 4 5% 8% 48%	1980
October	1st to 10th	Night	12% 5% 2 5% 4 3 4 3 4 6% 51%	1980
	11th to 20th	Night	16% 7% 2 5% 4 2 3 4 4 6% 46%	2177
	21st to end	Night	21% 8% 3 7% 5% 3 3 3 4 6% 38%	2574
November	1st to 10th	Night	12% 8% 2 4 5% 3 4 4 5% 7% 46%	2406
	11th to 20th	Night	14% 9% 4 7% 5% 3 5% 5% 6% 6% 38%	2470
	21st to end	Night	18% 10% 4 6% 5% 3 3 3 4 6% 36%	2470
December	1st to 10th	Night	17% 12% 5% 9% 6% 3 4 4 5% 6% 32%	2631
	11th to 20th	Night	16% 13% 5% 8% 5% 4 5% 4 4 4 33%	3279
	21st to end	Night	24% 18% 6% 10% 7% 3 4 4 4 4 16%	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	66% 5% 10% 13% 6%	2528
	11th to 20th	Day	68% 4 8% 11% 8% 1	2530
	21st to end	Day	72% 4 8% 13% 4	2850
February	1st to 10th	Day	59% 5% 11% 16% 7% 2	1818
	11th to 20th	Day	52% 5% 10% 22% 10% 1	1858
	21st to end	Day	55% 6% 10% 21% 6% 2	1570
March	1st to 10th	Day	57% 5% 9% 18% 11% 1	3120
	11th to 20th	Day	42% 6% 11% 28% 12% 1	3251
	21st to end	Day	58% 8% 14% 17% 3	4155
April	1st to 10th	Day	49% 6% 11% 19% 14%	2269
	11th to 20th	Day	47% 6% 10% 22% 12% 3	2134
	21st to end	Day	51% 6% 12% 17% 12% 2	2269
May	1st to 10th	Day	50% 7% 12% 22% 8%	2340
	11th to 20th	Day	48% 8% 12% 18% 13% 1	2340
	21st to end	Day	41% 9% 11% 21% 16% 3	2725
June	1st to 10th	Day	35% 8% 12% 25% 17% 3	2520
	11th to 20th	Day	36% 6% 11% 23% 21% 4	2520
	21st to end	Day	39% 10% 14% 19% 16% 2	2520
July	1st to 10th	Day	36% 7% 12% 25% 16% 4	2451
	11th to 20th	Day	33% 9% 14% 27% 15% 2	2445
	21st to end	Day	33% 9% 15% 24% 16% 3	2591
August	1st to 10th	Day	33% 9% 15% 28% 14% 1	2380
	11th to 20th	Day	34% 8% 14% 26% 16% 2	2150
	21st to end	Day	30% 8% 15% 24% 18% 5%	2376
September	1st to 10th	Day	36% 8% 11% 24% 15% 5%	2160
	11th to 20th	Day	33% 6% 11% 25% 20% 4	2016
	21st to end	Day	36% 6% 9% 26% 21% 2	1980
October	1st to 10th	Day	37% 7% 12% 24% 18% 3	1980
	11th to 20th	Day	46% 6% 10% 22% 16% 1	1779
	21st to end	Day	53% 4 11% 20% 10% 1	1782
November	1st to 10th	Day	36% 6% 14% 24% 18% 3	1672
	11th to 20th	Day	50% 4 11% 22% 12% 1	1710
	21st to end	Day	51% 5% 11% 22% 11% 1	1710
December	1st to 10th	Day	58% 5% 11% 17% 7%	1544
	11th to 20th	Day	57% 5% 10% 21% 6% 1	1915
	21st to end	Day	75% 4 8% 9% 4	2783
January	1st to 10th	Night	62% 5% 11% 14% 7% 1	4428
	11th to 20th	Night	70% 3 10% 11% 6%	4440
	21st to end	Night	68% 4 8% 14% 6%	4816
February	1st to 10th	Night	56% 5% 10% 18% 9% 2	2361
	11th to 20th	Night	50% 4 11% 21% 12% 2	2219
	21st to end	Night	54% 6% 10% 18% 10% 3	1884
March	1st to 10th	Night	49% 6% 11% 23% 9% 2	3733
	11th to 20th	Night	38% 6% 10% 27% 18% 2	3709
	21st to end	Night	55% 8% 11% 20% 6%	3504
April	1st to 10th	Night	45% 5% 12% 23% 14% 2	1900
	11th to 20th	Night	47% 5% 7% 21% 16% 4	1775
	21st to end	Night	47% 7% 10% 20% 13% 3	1689
May	1st to 10th	Night	47% 7% 12% 22% 12%	1620
	11th to 20th	Night	44% 8% 11% 21% 15% 1	1556
	21st to end	Night	38% 9% 13% 18% 17% 4	1552
June	1st to 10th	Night	32% 6% 12% 25% 22% 3	1440
	11th to 20th	Night	31% 6% 12% 25% 23% 3	1440
	21st to end	Night	38% 8% 14% 22% 14% 4	1440
July	1st to 10th	Night	31% 8% 15% 25% 17% 4	1400
	11th to 20th	Night	26% 6% 14% 28% 23% 3	1392
	21st to end	Night	27% 7% 15% 26% 20% 5%	1487
August	1st to 10th	Night	27% 9% 16% 29% 18% 2	1534
	11th to 20th	Night	30% 7% 15% 25% 21% 2	1748
	21st to end	Night	29% 7% 11% 26% 21% 6%	1980
September	1st to 10th	Night	32% 6% 12% 25% 19% 7%	1800
	11th to 20th	Night	27% 6% 9% 28% 26% 4	1926
	21st to end	Night	34% 6% 9% 26% 22% 3	1980
October	1st to 10th	Night	35% 5% 9% 26% 23% 2	1980
	11th to 20th	Night	40% 4 8% 26% 20% 2	2177
	21st to end	Night	48% 5% 8% 22% 14% 2	2574
November	1st to 10th	Night	38% 6% 9% 26% 18% 3	2406
	11th to 20th	Night	46% 5% 12% 21% 14% 2	2470
	21st to end	Night	50% 4 11% 24% 11% 1	2470
December	1st to 10th	Night	54% 6% 11% 19% 10% 1	2631
	11th to 20th	Night	55% 5% 10% 18% 11% 1	3281
	21st to end	Night	73% 5% 7% 10% 5%	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	25% 11% 36% 20% 7% 1	270
	11th to 20th	Day	23% 15% 39% 19% 3 1	270
	21st to end	Day	24% 18% 32% 19% 6% 1	297
February	1st to 10th	Day	25% 16% 36% 19% 5%	270
	11th to 20th	Day	25% 15% 35% 21% 3 1	270
	21st to end	Day	24% 18% 41% 11% 5%	225
March	1st to 10th	Day	21% 22% 36% 19% 2	270
	11th to 20th	Day	24% 14% 35% 20% 7%	322
	21st to end	Day	30% 13% 29% 22% 5% 1	506
April	1st to 10th	Day	24% 13% 31% 24% 8% 1	457
	11th to 20th	Day	20% 13% 34% 16% 13% 3	412
	21st to end	Day	22% 15% 31% 21% 7% 3	420
May	1st to 10th	Day	22% 12% 32% 21% 11% 3	423
	11th to 20th	Day	22% 7% 29% 23% 14% 5%	482
	21st to end	Day	14% 6% 30% 26% 15% 9%	679
June	1st to 10th	Day	11% 6% 28% 30% 18% 7%	630
	11th to 20th	Day	12% 4 27% 32% 20% 6%	630
	21st to end	Day	12% 6% 33% 28% 16% 6%	630
July	1st to 10th	Day	10% 4 17% 28% 24% 17%	621
	11th to 20th	Day	8% 2 22% 32% 23% 13%	618
	21st to end	Day	9% 3 21% 33% 26% 9%	684
August	1st to 10th	Day	7% 3 16% 28% 32% 14%	514
	11th to 20th	Day	10% 2 20% 27% 27% 15%	439
	21st to end	Day	7% 2 18% 32% 28% 12%	495
September	1st to 10th	Day	12% 5% 18% 29% 28% 9%	450
	11th to 20th	Day	12% 3 16% 29% 27% 14%	450
	21st to end	Day	10% 8% 25% 24% 22% 9%	450
October	1st to 10th	Day	13% 6% 28% 27% 20% 6%	450
	11th to 20th	Day	20% 19% 30% 23% 8%	275
	21st to end	Day	30% 13% 34% 18% 4 1	297
November	1st to 10th	Day	14% 11% 39% 20% 11% 4	270
	11th to 20th	Day	22% 16% 35% 16% 9% 1	270
	21st to end	Day	25% 13% 37% 21% 4	270
December	1st to 10th	Day	18% 17% 40% 18% 7% 1	270
	11th to 20th	Day	18% 19% 36% 21% 6%	270
	21st to end	Day	27% 20% 35% 15% 3	297
January	1st to 10th	Night	23% 16% 35% 21% 5%	950
	11th to 20th	Night	23% 16% 34% 22% 5%	950
	21st to end	Night	24% 13% 35% 25% 3	1045
February	1st to 10th	Night	25% 11% 38% 23% 3	841
	11th to 20th	Night	20% 13% 36% 26% 4	743
	21st to end	Night	24% 14% 38% 20% 3	628
March	1st to 10th	Night	21% 14% 38% 23% 5%	760
	11th to 20th	Night	18% 11% 41% 26% 5% 1	760
	21st to end	Night	23% 11% 37% 22% 7%	652
April	1st to 10th	Night	17% 13% 39% 25% 5% 1	570
	11th to 20th	Night	21% 9% 35% 26% 8% 1	533
	21st to end	Night	21% 10% 34% 29% 7% 1	540
May	1st to 10th	Night	19% 7% 34% 32% 7% 1	540
	11th to 20th	Night	18% 4 30% 32% 15% 1	531
	21st to end	Night	11% 4 24% 41% 18% 2	584
June	1st to 10th	Night	10% 4 22% 47% 15%	540
	11th to 20th	Night	10% 3 28% 41% 16% 1	540
	21st to end	Night	11% 4 26% 38% 20% 1	540
July	1st to 10th	Night	9% 2 15% 40% 30% 4	525
	11th to 20th	Night	8% 2 17% 40% 29% 4	522
	21st to end	Night	5% 3 15% 45% 32% 1	591
August	1st to 10th	Night	7% 1 12% 44% 31% 5%	537
	11th to 20th	Night	6% 1 13% 42% 32% 5%	534
	21st to end	Night	9% 1 16% 37% 34% 3	594
September	1st to 10th	Night	12% 2 14% 40% 29% 2	540
	11th to 20th	Night	9% 4 17% 34% 32% 5%	666
	21st to end	Night	11% 5% 23% 31% 27% 3	720
October	1st to 10th	Night	14% 5% 24% 37% 19% 2	720
	11th to 20th	Night	19% 13% 31% 27% 10%	720
	21st to end	Night	25% 12% 32% 24% 7%	792
November	1st to 10th	Night	16% 10% 38% 26% 9% 1	740
	11th to 20th	Night	19% 16% 34% 24% 7% 1	760
	21st to end	Night	22% 13% 34% 25% 7%	760
December	1st to 10th	Night	23% 13% 36% 24% 4	921
	11th to 20th	Night	24% 12% 33% 25% 5%	950
	21st to end	Night	29% 14% 31% 23% 2	1045

Page generated at 2024-04-07 08:28:09. Version ac07

Copyright © 2024 Attilla Danko.