North Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Bay clear sky chart from 2005-11-06 to 2024-11-04.

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% 11% 4 8% 5% 4 4 3 5% 7% 32%	101737
	Night	17% 14% 4 9% 5% 4 4 3 5% 6% 29%	97315
Transparency	Day	52% 5% 13% 21% 8% 1	105299
	Night	56% 5% 11% 18% 8% 1	101841
Seeing	Day	21% 9% 27% 28% 12% 3	15077
	Night	23% 8% 28% 29% 11% 1	24046

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	17% 25% 10% 11% 5% 4 3 2 3 4 16%	2208
	11th to 20th	Day	11% 15% 8% 17% 8% 5% 4 3 4 6% 17%	2370
	21st to end	Day	16% 22% 8% 11% 6% 5% 4 2 4 5% 16%	3124
February	1st to 10th	Day	10% 20% 7% 13% 7% 5% 5% 4 5% 6% 19%	1710
	11th to 20th	Day	13% 17% 6% 10% 7% 5% 4 3 5% 6% 24%	1663
	21st to end	Day	16% 16% 5% 11% 6% 6% 6% 3 4 4 23%	1413
March	1st to 10th	Day	20% 15% 3 8% 4 3 4 3 5% 6% 27%	3420
	11th to 20th	Day	12% 15% 5% 14% 7% 4 5% 3 4 5% 25%	3480
	21st to end	Day	12% 10% 5% 11% 5% 6% 3 3 4 5% 35%	3815
April	1st to 10th	Day	20% 12% 4 9% 4 5% 4 3 6% 6% 28%	2263
	11th to 20th	Day	21% 11% 3 7% 5% 4 3 2 5% 6% 34%	2382
	21st to end	Day	22% 12% 2 7% 4 3 3 3 4 5% 35%	2470
May	1st to 10th	Day	20% 9% 3 6% 4 4 4 4 5% 6% 34%	4256
	11th to 20th	Day	14% 8% 3 7% 5% 5% 5% 3 6% 7% 38%	4398
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 7% 41%	4837
June	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 3 5% 7% 32%	2783
	11th to 20th	Day	14% 6% 2 6% 5% 4 5% 4 7% 8% 38%	2850
	21st to end	Day	17% 8% 3 7% 6% 5% 4 4 6% 8% 32%	2850
July	1st to 10th	Day	18% 7% 2 7% 5% 5% 5% 4 5% 8% 34%	4760
	11th to 20th	Day	15% 5% 2 6% 4 5% 4 4 6% 9% 39%	4701
	21st to end	Day	12% 5% 2 6% 4 3 3 4 6% 8% 47%	4735
August	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 4 7% 9% 36%	4104
	11th to 20th	Day	18% 6% 2 5% 4 4 5% 4 7% 9% 37%	4044
	21st to end	Day	11% 5% 2 6% 5% 5% 4 4 6% 9% 44%	4418
September	1st to 10th	Day	17% 7% 3 6% 4 4 4 3 5% 8% 39%	2280
	11th to 20th	Day	16% 6% 2 7% 4 4 3 3 6% 8% 42%	2185
	21st to end	Day	23% 7% 3 7% 4 4 4 3 5% 6% 33%	2043
October	1st to 10th	Day	19% 9% 2 7% 5% 5% 5% 4 5% 6% 34%	1900
	11th to 20th	Day	25% 14% 3 9% 5% 4 4 3 4 6% 23%	1900
	21st to end	Day	29% 14% 5% 8% 5% 3 3 3 5% 5% 20%	2062
November	1st to 10th	Day	22% 13% 4 8% 4 4 4 4 5% 7% 26%	1511
	11th to 20th	Day	21% 17% 5% 10% 6% 4 5% 4 4 6% 19%	1520
	21st to end	Day	27% 22% 5% 10% 5% 4 3 3 3 5% 13%	1520
December	1st to 10th	Day	18% 23% 6% 12% 6% 4 4 4 3 5% 13%	1520
	11th to 20th	Day	19% 19% 5% 12% 4 4 4 2 4 5% 21%	1811
	21st to end	Day	19% 23% 8% 16% 5% 3 3 2 3 4 14%	2431
January	1st to 10th	Night	16% 21% 8% 15% 7% 5% 3 3 4 4 14%	4748
	11th to 20th	Night	13% 16% 6% 16% 8% 6% 4 4 5% 5% 17%	4589
	21st to end	Night	14% 25% 8% 12% 6% 5% 4 3 3 4 15%	4532
February	1st to 10th	Night	12% 16% 6% 14% 8% 6% 4 4 5% 5% 21%	2470
	11th to 20th	Night	13% 18% 7% 11% 7% 5% 4 3 4 4 23%	2403
	21st to end	Night	15% 20% 5% 11% 7% 5% 4 3 4 5% 22%	2041
March	1st to 10th	Night	15% 16% 4 9% 5% 4 3 3 5% 6% 29%	3418
	11th to 20th	Night	15% 20% 4 8% 5% 4 4 3 5% 5% 26%	3479
	21st to end	Night	14% 13% 4 9% 6% 5% 4 3 4 5% 33%	3817
April	1st to 10th	Night	20% 15% 5% 7% 4 4 4 3 4 5% 30%	1916
	11th to 20th	Night	20% 11% 4 6% 4 4 4 2 5% 5% 35%	1763
	21st to end	Night	22% 10% 3 7% 5% 4 4 3 4 6% 31%	1710
May	1st to 10th	Night	18% 9% 3 8% 5% 4 4 3 5% 6% 35%	2683
	11th to 20th	Night	14% 7% 2 6% 5% 5% 4 4 6% 8% 39%	2495
	21st to end	Night	16% 6% 3 7% 5% 4 4 3 5% 8% 39%	2738
June	1st to 10th	Night	14% 9% 3 7% 6% 5% 5% 4 6% 6% 34%	1394
	11th to 20th	Night	16% 6% 1 6% 4 4 3 4 5% 9% 43%	1330
	21st to end	Night	16% 7% 2 7% 5% 4 5% 4 7% 7% 36%	1330
July	1st to 10th	Night	16% 8% 2 6% 4 4 4 3 5% 8% 40%	2210
	11th to 20th	Night	19% 6% 2 6% 4 4 4 4 4 7% 41%	2263
	21st to end	Night	11% 6% 2 5% 4 3 3 3 6% 8% 49%	2815
August	1st to 10th	Night	14% 6% 2 6% 4 3 5% 4 6% 7% 42%	2825
	11th to 20th	Night	17% 6% 2 6% 4 4 4 4 5% 5% 42%	2785
	21st to end	Night	15% 5% 2 4 4 3 3 4 5% 8% 47%	3206
September	1st to 10th	Night	16% 5% 2 5% 4 3 3 3 4 7% 47%	1900
	11th to 20th	Night	15% 6% 2 5% 4 4 4 3 5% 7% 45%	1990
	21st to end	Night	19% 7% 2 6% 4 3 4 3 5% 7% 40%	2137
October	1st to 10th	Night	21% 8% 3 7% 4 5% 4 4 5% 5% 34%	2280
	11th to 20th	Night	27% 12% 3 7% 5% 4 4 3 5% 5% 27%	2280
	21st to end	Night	27% 14% 4 8% 5% 4 4 3 5% 5% 22%	2532
November	1st to 10th	Night	22% 13% 3 7% 5% 4 3 3 4 5% 30%	2639
	11th to 20th	Night	18% 17% 4 10% 6% 5% 5% 4 4 5% 22%	2660
	21st to end	Night	25% 19% 5% 8% 5% 5% 5% 3 4 5% 17%	2660
December	1st to 10th	Night	21% 24% 6% 12% 6% 4 3 4 4 4 14%	2660
	11th to 20th	Night	20% 20% 6% 10% 6% 4 4 3 4 4 18%	3381
	21st to end	Night	21% 21% 7% 17% 5% 4 3 2 3 3 14%	5236

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	72% 5% 10% 10% 2	2209
	11th to 20th	Day	68% 4 12% 10% 5% 1	2370
	21st to end	Day	71% 4 9% 10% 4	3124
February	1st to 10th	Day	65% 6% 10% 13% 5% 1	1710
	11th to 20th	Day	62% 5% 11% 14% 8% 1	1672
	21st to end	Day	64% 4 8% 15% 8% 1	1413
March	1st to 10th	Day	56% 6% 13% 15% 8% 1	3423
	11th to 20th	Day	60% 5% 13% 15% 7% 1	3480
	21st to end	Day	49% 6% 11% 22% 10% 2	3815
April	1st to 10th	Day	55% 5% 11% 18% 9% 1	2263
	11th to 20th	Day	52% 4 9% 23% 12% 1	2382
	21st to end	Day	51% 5% 9% 18% 13% 3	2470
May	1st to 10th	Day	48% 6% 10% 23% 11% 2	4268
	11th to 20th	Day	44% 7% 12% 27% 9% 1	4402
	21st to end	Day	43% 6% 15% 18% 17% 2	4837
June	1st to 10th	Day	50% 6% 10% 22% 11% 1	2783
	11th to 20th	Day	41% 8% 12% 24% 13% 1	2850
	21st to end	Day	47% 8% 13% 19% 11% 1	2850
July	1st to 10th	Day	47% 5% 16% 24% 7%	4686
	11th to 20th	Day	41% 4 17% 31% 6%	4620
	21st to end	Day	35% 5% 15% 32% 13%	4584
August	1st to 10th	Day	43% 5% 12% 32% 7%	4091
	11th to 20th	Day	43% 6% 17% 26% 9%	4083
	21st to end	Day	37% 5% 14% 35% 9%	4418
September	1st to 10th	Day	43% 7% 14% 24% 11%	2280
	11th to 20th	Day	41% 6% 15% 28% 9%	2185
	21st to end	Day	52% 6% 12% 23% 6%	2043
October	1st to 10th	Day	50% 5% 11% 28% 7%	3160
	11th to 20th	Day	53% 6% 15% 21% 5%	3140
	21st to end	Day	67% 4 14% 10% 4	3376
November	1st to 10th	Day	58% 6% 14% 17% 5%	1511
	11th to 20th	Day	65% 8% 11% 10% 5% 1	1520
	21st to end	Day	76% 5% 9% 7% 3	1520
December	1st to 10th	Day	74% 6% 8% 10% 2	1520
	11th to 20th	Day	67% 7% 10% 13% 3	1810
	21st to end	Day	76% 4 7% 12% 2	2431
January	1st to 10th	Night	74% 6% 11% 7% 3	4748
	11th to 20th	Night	68% 7% 11% 11% 3	4589
	21st to end	Night	73% 5% 7% 9% 5% 1	4532
February	1st to 10th	Night	64% 6% 10% 14% 5% 1	2470
	11th to 20th	Night	64% 5% 10% 15% 5% 1	2405
	21st to end	Night	65% 4 9% 14% 7% 1	2041
March	1st to 10th	Night	53% 6% 12% 15% 12% 1	3428
	11th to 20th	Night	59% 6% 12% 15% 8% 1	3480
	21st to end	Night	52% 5% 10% 19% 12% 2	3817
April	1st to 10th	Night	58% 4 8% 18% 11% 2	1916
	11th to 20th	Night	53% 3 7% 21% 14% 2	1763
	21st to end	Night	55% 5% 8% 15% 14% 3	1710
May	1st to 10th	Night	48% 8% 10% 21% 12% 1	2690
	11th to 20th	Night	41% 8% 13% 25% 12% 2	2496
	21st to end	Night	41% 7% 12% 22% 14% 3	2739
June	1st to 10th	Night	48% 8% 10% 21% 10% 3	1394
	11th to 20th	Night	39% 6% 12% 26% 17% 1	1330
	21st to end	Night	44% 8% 14% 21% 11% 1	1330
July	1st to 10th	Night	43% 5% 13% 25% 13% 2	2175
	11th to 20th	Night	44% 4 15% 29% 8% 1	2221
	21st to end	Night	34% 5% 13% 31% 17%	2725
August	1st to 10th	Night	41% 5% 14% 28% 12%	2814
	11th to 20th	Night	43% 6% 16% 26% 9% 1	2812
	21st to end	Night	36% 4 14% 32% 12% 1	3206
September	1st to 10th	Night	37% 6% 15% 28% 11% 1	1900
	11th to 20th	Night	40% 5% 16% 28% 10%	1990
	21st to end	Night	44% 5% 15% 26% 9%	2137
October	1st to 10th	Night	46% 4 9% 31% 10%	3800
	11th to 20th	Night	52% 3 14% 27% 5%	3779
	21st to end	Night	60% 5% 18% 12% 5%	4168
November	1st to 10th	Night	56% 6% 14% 18% 6%	2639
	11th to 20th	Night	65% 6% 12% 11% 5% 1	2660
	21st to end	Night	71% 7% 11% 9% 3	2660
December	1st to 10th	Night	75% 6% 8% 9% 2	2660
	11th to 20th	Night	68% 6% 8% 13% 5%	3381
	21st to end	Night	77% 4 6% 10% 3	5236

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	27% 16% 27% 20% 9% 1	180
	11th to 20th	Day	18% 13% 32% 26% 9% 2	189
	21st to end	Day	26% 9% 27% 26% 9% 2	297
February	1st to 10th	Day	26% 14% 38% 16% 5% 1	270
	11th to 20th	Day	23% 13% 35% 26% 3	270
	21st to end	Day	32% 15% 33% 21%	225
March	1st to 10th	Day	21% 12% 35% 27% 5%	449
	11th to 20th	Day	17% 12% 35% 28% 7% 1	460
	21st to end	Day	22% 12% 29% 29% 6% 2	506
April	1st to 10th	Day	23% 9% 34% 23% 9% 2	460
	11th to 20th	Day	29% 13% 24% 20% 10% 4	452
	21st to end	Day	27% 12% 25% 26% 8% 2	460
May	1st to 10th	Day	25% 6% 25% 29% 14% 1	463
	11th to 20th	Day	20% 8% 24% 28% 18% 3	487
	21st to end	Day	18% 7% 27% 29% 16% 3	529
June	1st to 10th	Day	21% 5% 28% 32% 12% 1	613
	11th to 20th	Day	15% 6% 28% 32% 13% 5%	680
	21st to end	Day	19% 8% 24% 33% 12% 4	680
July	1st to 10th	Day	13% 4 22% 40% 18% 3	671
	11th to 20th	Day	17% 4 22% 32% 21% 4	635
	21st to end	Day	12% 5% 20% 38% 21% 5%	532
August	1st to 10th	Day	16% 4 19% 34% 21% 5%	486
	11th to 20th	Day	18% 4 14% 31% 26% 8%	479
	21st to end	Day	16% 8% 22% 31% 16% 7%	539
September	1st to 10th	Day	18% 7% 24% 29% 17% 5%	490
	11th to 20th	Day	16% 5% 21% 29% 21% 8%	490
	21st to end	Day	25% 8% 21% 25% 18% 4	490
October	1st to 10th	Day	23% 10% 27% 24% 13% 2	490
	11th to 20th	Day	26% 15% 32% 21% 5% 1	490
	21st to end	Day	34% 12% 29% 22% 3 1	511
November	1st to 10th	Day	27% 18% 31% 19% 4 1	186
	11th to 20th	Day	23% 21% 35% 16% 5% 1	180
	21st to end	Day	36% 15% 31% 16% 2 1	180
December	1st to 10th	Day	26% 16% 30% 26% 2	180
	11th to 20th	Day	28% 12% 38% 18% 3 1	180
	21st to end	Day	29% 15% 33% 17% 5% 1	198
January	1st to 10th	Night	28% 7% 29% 28% 7%	950
	11th to 20th	Night	29% 8% 26% 30% 8%	867
	21st to end	Night	19% 6% 28% 33% 11% 2	836
February	1st to 10th	Night	17% 10% 36% 30% 6%	760
	11th to 20th	Night	21% 10% 32% 29% 7% 1	743
	21st to end	Night	23% 11% 29% 33% 4	628
March	1st to 10th	Night	21% 8% 35% 30% 6%	760
	11th to 20th	Night	21% 10% 34% 27% 7% 1	760
	21st to end	Night	20% 7% 33% 32% 7% 1	836
April	1st to 10th	Night	28% 8% 26% 32% 6%	760
	11th to 20th	Night	24% 9% 29% 27% 10% 1	639
	21st to end	Night	24% 8% 27% 30% 11% 1	570
May	1st to 10th	Night	22% 5% 27% 33% 12% 1	485
	11th to 20th	Night	19% 5% 28% 36% 11% 1	374
	21st to end	Night	18% 4 26% 38% 13%	411
June	1st to 10th	Night	15% 4 30% 36% 15%	380
	11th to 20th	Night	18% 5% 24% 37% 16% 1	380
	21st to end	Night	18% 6% 20% 35% 21% 1	380
July	1st to 10th	Night	11% 3 23% 47% 15% 1	370
	11th to 20th	Night	13% 3 23% 38% 23% 1	368
	21st to end	Night	11% 4 20% 43% 21% 1	456
August	1st to 10th	Night	17% 3 18% 36% 23% 2	567
	11th to 20th	Night	14% 3 17% 37% 26% 3	564
	21st to end	Night	20% 6% 21% 31% 18% 4	670
September	1st to 10th	Night	18% 5% 21% 33% 22% 1	760
	11th to 20th	Night	17% 6% 22% 28% 23% 3	760
	21st to end	Night	22% 6% 22% 29% 18% 2	760
October	1st to 10th	Night	24% 7% 27% 29% 11% 1	760
	11th to 20th	Night	31% 12% 26% 23% 6% 1	760
	21st to end	Night	34% 12% 28% 22% 4	836
November	1st to 10th	Night	28% 10% 31% 24% 7% 1	755
	11th to 20th	Night	27% 14% 33% 19% 7%	760
	21st to end	Night	35% 10% 28% 22% 5%	760
December	1st to 10th	Night	31% 13% 31% 19% 6%	760
	11th to 20th	Night	28% 9% 34% 22% 5% 2	816
	21st to end	Night	31% 9% 29% 25% 6% 1	1045

Page generated at 2024-11-01 22:47:35. Version ac07

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