Westfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Westfield clear sky chart from 2005-11-06 to 2024-11-30.

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	19% 9% 3 7% 4 4 4 4 5% 7% 33%	101733
	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 33%	97920
Transparency	Day	49% 8% 12% 20% 10% 1	105266
	Night	51% 7% 11% 20% 10% 1	102464
Seeing	Day	26% 20% 32% 17% 5% 1	16532
	Night	26% 17% 31% 21% 5%	24396

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	14% 12% 4 8% 5% 4 4 3 4 5% 37%	2207
	11th to 20th	Day	16% 12% 3 7% 5% 3 3 2 3 4 42%	2487
	21st to end	Day	15% 8% 3 6% 6% 5% 5% 4 5% 7% 36%	3089
February	1st to 10th	Day	16% 12% 4 7% 5% 5% 4 4 5% 6% 31%	1710
	11th to 20th	Day	15% 12% 3 9% 6% 5% 4 4 5% 6% 32%	1663
	21st to end	Day	11% 12% 3 9% 5% 4 4 4 5% 7% 36%	1521
March	1st to 10th	Day	23% 14% 4 9% 4 3 3 3 4 5% 30%	3307
	11th to 20th	Day	16% 16% 4 9% 6% 6% 5% 3 5% 5% 24%	3480
	21st to end	Day	29% 11% 5% 7% 4 4 4 4 4 4 25%	3816
April	1st to 10th	Day	21% 15% 3 8% 5% 4 3 3 5% 6% 28%	2207
	11th to 20th	Day	19% 11% 3 7% 4 3 4 3 4 6% 36%	2442
	21st to end	Day	24% 10% 2 7% 4 4 3 3 5% 6% 33%	2470
May	1st to 10th	Day	20% 11% 3 8% 5% 5% 5% 4 5% 7% 27%	4106
	11th to 20th	Day	18% 8% 2 7% 5% 4 4 4 5% 8% 33%	4297
	21st to end	Day	17% 8% 3 6% 5% 5% 5% 5% 7% 8% 31%	4892
June	1st to 10th	Day	23% 10% 3 7% 5% 5% 4 3 5% 7% 27%	2850
	11th to 20th	Day	21% 9% 3 7% 4 4 4 3 5% 6% 35%	2850
	21st to end	Day	28% 9% 2 7% 5% 3 4 4 5% 6% 27%	2850
July	1st to 10th	Day	17% 7% 2 8% 5% 5% 5% 3 6% 8% 32%	4760
	11th to 20th	Day	21% 8% 3 6% 4 4 4 4 6% 8% 33%	4737
	21st to end	Day	20% 8% 3 6% 5% 4 4 4 6% 7% 34%	4508
August	1st to 10th	Day	22% 8% 3 8% 4 4 5% 4 6% 8% 28%	4105
	11th to 20th	Day	18% 7% 2 6% 5% 4 5% 4 6% 8% 36%	4045
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 8% 44%	4518
September	1st to 10th	Day	14% 5% 2 6% 4 4 5% 3 6% 7% 45%	2257
	11th to 20th	Day	18% 6% 2 5% 3 3 3 3 4 5% 48%	2090
	21st to end	Day	20% 6% 1 5% 3 3 4 3 4 7% 44%	2090
October	1st to 10th	Day	18% 7% 2 7% 4 4 4 4 4 6% 40%	1929
	11th to 20th	Day	20% 6% 3 6% 5% 3 4 3 4 5% 40%	1900
	21st to end	Day	20% 9% 3 7% 4 5% 4 3 4 6% 35%	1993
November	1st to 10th	Day	21% 8% 2 7% 4 5% 4 3 4 6% 36%	1696
	11th to 20th	Day	20% 6% 2 6% 4 4 3 4 5% 7% 39%	1600
	21st to end	Day	22% 11% 3 6% 4 3 4 4 5% 6% 32%	1599
December	1st to 10th	Day	25% 11% 3 5% 4 5% 4 4 5% 6% 31%	1520
	11th to 20th	Day	25% 14% 3 7% 4 3 3 3 4 5% 29%	1711
	21st to end	Day	22% 9% 3 6% 3 4 3 4 5% 5% 34%	2431
January	1st to 10th	Night	13% 11% 3 7% 5% 5% 5% 4 5% 6% 38%	4748
	11th to 20th	Night	17% 10% 3 8% 5% 4 4 3 6% 5% 35%	4472
	21st to end	Night	14% 12% 3 8% 5% 4 4 4 6% 7% 33%	4564
February	1st to 10th	Night	17% 12% 4 6% 5% 4 4 4 6% 7% 32%	2470
	11th to 20th	Night	16% 12% 3 8% 5% 5% 5% 4 5% 5% 32%	2403
	21st to end	Night	16% 11% 3 8% 6% 4 4 4 5% 6% 33%	1931
March	1st to 10th	Night	24% 13% 4 7% 4 5% 5% 3 3 4 29%	3533
	11th to 20th	Night	17% 14% 4 9% 6% 6% 5% 4 5% 6% 24%	3479
	21st to end	Night	30% 11% 3 6% 4 3 4 3 4 5% 26%	3816
April	1st to 10th	Night	23% 12% 4 7% 5% 4 4 3 4 4 31%	1969
	11th to 20th	Night	23% 9% 3 6% 4 4 4 3 4 6% 33%	1688
	21st to end	Night	24% 9% 3 6% 5% 4 4 4 5% 6% 30%	1710
May	1st to 10th	Night	20% 8% 2 7% 7% 6% 6% 4 6% 6% 28%	2834
	11th to 20th	Night	18% 8% 2 8% 4 5% 5% 4 6% 8% 33%	2602
	21st to end	Night	17% 10% 3 8% 5% 4 5% 4 6% 7% 31%	2721
June	1st to 10th	Night	24% 11% 2 8% 5% 4 5% 3 5% 8% 25%	1330
	11th to 20th	Night	21% 8% 3 6% 6% 3 4 3 5% 6% 33%	1330
	21st to end	Night	30% 9% 2 7% 4 5% 3 3 4 5% 28%	1330
July	1st to 10th	Night	19% 10% 3 10% 6% 5% 5% 4 6% 7% 26%	2210
	11th to 20th	Night	22% 9% 3 8% 5% 5% 5% 4 6% 7% 28%	2229
	21st to end	Night	20% 9% 2 7% 5% 3 4 4 6% 8% 33%	3012
August	1st to 10th	Night	22% 11% 4 7% 4 5% 5% 3 5% 7% 26%	2825
	11th to 20th	Night	16% 9% 3 8% 4 5% 4 4 6% 7% 34%	2782
	21st to end	Night	12% 6% 2 6% 3 4 4 4 6% 7% 45%	3124
September	1st to 10th	Night	18% 6% 2 5% 4 4 5% 3 5% 8% 41%	1919
	11th to 20th	Night	18% 7% 2 6% 3 3 4 3 4 6% 45%	2090
	21st to end	Night	21% 6% 2 5% 3 4 3 3 5% 6% 42%	2090
October	1st to 10th	Night	20% 6% 2 6% 4 4 3 3 5% 7% 40%	2251
	11th to 20th	Night	18% 8% 2 6% 4 3 4 3 5% 6% 40%	2280
	21st to end	Night	22% 10% 3 6% 4 4 4 3 4 5% 35%	2603
November	1st to 10th	Night	21% 6% 2 6% 4 4 4 3 5% 6% 38%	2599
	11th to 20th	Night	20% 8% 2 7% 5% 4 4 4 5% 7% 36%	2800
	21st to end	Night	21% 9% 3 6% 4 3 4 4 5% 6% 34%	2797
December	1st to 10th	Night	26% 11% 3 7% 4 4 4 3 4 5% 30%	2660
	11th to 20th	Night	27% 11% 2 6% 4 4 4 3 4 5% 30%	3483
	21st to end	Night	22% 11% 3 8% 4 4 4 3 4 4 34%	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	49% 7% 18% 17% 8% 1	2208
	11th to 20th	Day	47% 5% 9% 26% 12% 2	2487
	21st to end	Day	45% 10% 14% 17% 14% 1	3089
February	1st to 10th	Day	52% 8% 13% 17% 10% 2	1710
	11th to 20th	Day	52% 6% 12% 18% 11% 2	1671
	21st to end	Day	46% 6% 12% 23% 10% 3	1521
March	1st to 10th	Day	57% 5% 9% 18% 8% 4	3311
	11th to 20th	Day	55% 10% 11% 14% 9% 1	3480
	21st to end	Day	61% 5% 7% 14% 11% 2	3816
April	1st to 10th	Day	56% 6% 8% 14% 12% 3	2207
	11th to 20th	Day	48% 5% 10% 22% 13% 1	2442
	21st to end	Day	52% 6% 10% 17% 12% 3	2470
May	1st to 10th	Day	50% 13% 12% 18% 7% 1	4120
	11th to 20th	Day	45% 10% 17% 20% 8% 1	4301
	21st to end	Day	46% 14% 15% 15% 10% 1	4892
June	1st to 10th	Day	55% 9% 11% 16% 8% 1	2850
	11th to 20th	Day	50% 7% 12% 19% 11% 2	2850
	21st to end	Day	56% 10% 10% 14% 9% 1	2850
July	1st to 10th	Day	50% 9% 14% 16% 10%	4685
	11th to 20th	Day	50% 9% 14% 20% 7%	4656
	21st to end	Day	48% 10% 13% 21% 7%	4364
August	1st to 10th	Day	54% 9% 11% 19% 6%	4092
	11th to 20th	Day	44% 10% 15% 22% 9%	4084
	21st to end	Day	35% 8% 15% 24% 16% 1	4518
September	1st to 10th	Day	37% 9% 14% 25% 14% 1	2257
	11th to 20th	Day	38% 6% 14% 24% 16% 3	2090
	21st to end	Day	41% 6% 9% 27% 16% 1	2090
October	1st to 10th	Day	45% 7% 10% 28% 10%	3202
	11th to 20th	Day	41% 5% 10% 33% 11%	3140
	21st to end	Day	41% 5% 17% 19% 17% 1	3256
November	1st to 10th	Day	49% 6% 12% 21% 11% 1	1696
	11th to 20th	Day	45% 7% 15% 18% 14% 2	1600
	21st to end	Day	54% 7% 12% 20% 7%	1599
December	1st to 10th	Day	54% 7% 11% 20% 7% 1	1520
	11th to 20th	Day	59% 5% 10% 15% 10% 1	1711
	21st to end	Day	52% 6% 13% 18% 10% 2	2431
January	1st to 10th	Night	46% 7% 13% 26% 7% 1	4748
	11th to 20th	Night	50% 9% 10% 22% 9% 1	4472
	21st to end	Night	49% 8% 10% 22% 10% 1	4564
February	1st to 10th	Night	50% 8% 11% 17% 12% 1	2470
	11th to 20th	Night	53% 7% 10% 18% 10% 2	2406
	21st to end	Night	50% 7% 9% 19% 12% 3	1931
March	1st to 10th	Night	58% 6% 7% 17% 11% 1	3542
	11th to 20th	Night	56% 11% 11% 13% 8% 1	3480
	21st to end	Night	61% 4 7% 15% 10% 2	3816
April	1st to 10th	Night	56% 7% 8% 14% 11% 4	1969
	11th to 20th	Night	50% 5% 11% 19% 14% 1	1688
	21st to end	Night	53% 7% 9% 16% 12% 2	1710
May	1st to 10th	Night	51% 12% 12% 17% 6% 1	2840
	11th to 20th	Night	46% 11% 15% 20% 6% 1	2603
	21st to end	Night	50% 11% 15% 17% 7% 1	2722
June	1st to 10th	Night	57% 8% 11% 16% 6% 1	1330
	11th to 20th	Night	52% 6% 12% 20% 8% 1	1330
	21st to end	Night	62% 6% 8% 15% 7% 2	1330
July	1st to 10th	Night	61% 7% 9% 11% 10%	2175
	11th to 20th	Night	59% 7% 8% 18% 7%	2187
	21st to end	Night	51% 8% 12% 19% 10% 1	2916
August	1st to 10th	Night	59% 7% 11% 17% 6%	2813
	11th to 20th	Night	51% 7% 14% 21% 7%	2809
	21st to end	Night	39% 7% 12% 24% 17% 1	3124
September	1st to 10th	Night	42% 6% 11% 26% 14% 1	1919
	11th to 20th	Night	41% 6% 12% 23% 17% 1	2090
	21st to end	Night	42% 6% 10% 26% 14% 2	2090
October	1st to 10th	Night	46% 4 12% 25% 12% 1	3758
	11th to 20th	Night	37% 5% 11% 29% 18%	3779
	21st to end	Night	46% 4 11% 23% 14% 1	4277
November	1st to 10th	Night	46% 7% 13% 20% 12% 1	2599
	11th to 20th	Night	49% 6% 12% 20% 12% 1	2800
	21st to end	Night	51% 7% 14% 18% 10% 1	2797
December	1st to 10th	Night	58% 6% 9% 18% 8%	2660
	11th to 20th	Night	57% 6% 9% 18% 9%	3484
	21st to end	Night	55% 7% 11% 17% 7% 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	32% 26% 28% 12% 2	180
	11th to 20th	Day	37% 22% 32% 6% 3	180
	21st to end	Day	20% 26% 37% 15% 2 1	385
February	1st to 10th	Day	28% 24% 31% 13% 3 1	370
	11th to 20th	Day	26% 31% 31% 10% 2 1	366
	21st to end	Day	25% 26% 33% 15% 1	359
March	1st to 10th	Day	28% 27% 33% 11% 2	460
	11th to 20th	Day	24% 26% 31% 14% 4 1	460
	21st to end	Day	30% 25% 29% 10% 4 1	506
April	1st to 10th	Day	33% 29% 25% 10% 3	460
	11th to 20th	Day	29% 26% 29% 12% 4	452
	21st to end	Day	30% 24% 27% 14% 5% 1	460
May	1st to 10th	Day	30% 22% 33% 12% 4	463
	11th to 20th	Day	25% 19% 31% 17% 5% 1	612
	21st to end	Day	25% 22% 32% 16% 5% 1	735
June	1st to 10th	Day	29% 19% 30% 17% 6%	680
	11th to 20th	Day	24% 16% 33% 20% 7% 1	680
	21st to end	Day	32% 13% 30% 18% 6% 1	680
July	1st to 10th	Day	23% 12% 40% 19% 6%	670
	11th to 20th	Day	24% 8% 34% 23% 9% 1	658
	21st to end	Day	20% 13% 39% 23% 5% 1	532
August	1st to 10th	Day	20% 12% 35% 27% 6% 1	486
	11th to 20th	Day	23% 11% 32% 27% 5% 1	479
	21st to end	Day	18% 16% 30% 26% 8% 2	539
September	1st to 10th	Day	16% 14% 39% 24% 6% 2	490
	11th to 20th	Day	22% 14% 30% 20% 10% 3	490
	21st to end	Day	21% 17% 32% 18% 9% 2	490
October	1st to 10th	Day	20% 18% 27% 22% 10% 3	405
	11th to 20th	Day	23% 19% 31% 19% 7% 2	390
	21st to end	Day	26% 22% 34% 13% 4 1	429
November	1st to 10th	Day	28% 20% 32% 14% 4 2	395
	11th to 20th	Day	28% 22% 32% 14% 4	400
	21st to end	Day	32% 26% 30% 9% 3	400
December	1st to 10th	Day	32% 21% 30% 14% 3	370
	11th to 20th	Day	37% 30% 22% 9% 2	223
	21st to end	Day	30% 28% 31% 9% 2 1	198
January	1st to 10th	Night	25% 24% 32% 17% 2	850
	11th to 20th	Night	28% 23% 29% 16% 4	769
	21st to end	Night	20% 25% 36% 15% 4	836
February	1st to 10th	Night	26% 24% 31% 16% 3	760
	11th to 20th	Night	26% 26% 31% 15% 2	743
	21st to end	Night	23% 21% 33% 19% 3	628
March	1st to 10th	Night	23% 23% 36% 16% 1	760
	11th to 20th	Night	25% 19% 33% 19% 5%	760
	21st to end	Night	25% 18% 35% 17% 5%	836
April	1st to 10th	Night	30% 20% 33% 15% 2	667
	11th to 20th	Night	28% 18% 32% 18% 4	564
	21st to end	Night	28% 15% 31% 20% 5%	570
May	1st to 10th	Night	28% 12% 31% 24% 5%	570
	11th to 20th	Night	27% 13% 34% 22% 4	562
	21st to end	Night	23% 13% 40% 19% 4	601
June	1st to 10th	Night	31% 7% 32% 26% 4	380
	11th to 20th	Night	24% 10% 33% 27% 6%	380
	21st to end	Night	33% 7% 26% 29% 5% 1	380
July	1st to 10th	Night	22% 5% 36% 30% 7% 1	370
	11th to 20th	Night	26% 6% 28% 32% 8% 1	368
	21st to end	Night	25% 7% 31% 30% 7%	574
August	1st to 10th	Night	19% 5% 35% 32% 9%	568
	11th to 20th	Night	23% 9% 28% 32% 9%	562
	21st to end	Night	16% 7% 32% 31% 12% 1	627
September	1st to 10th	Night	21% 6% 39% 23% 10% 1	589
	11th to 20th	Night	21% 11% 25% 29% 12% 1	760
	21st to end	Night	23% 11% 30% 24% 11% 1	760
October	1st to 10th	Night	23% 10% 31% 26% 10% 1	760
	11th to 20th	Night	21% 17% 32% 20% 9% 1	760
	21st to end	Night	29% 20% 28% 20% 3	836
November	1st to 10th	Night	27% 17% 30% 19% 7% 1	812
	11th to 20th	Night	28% 20% 28% 18% 6%	900
	21st to end	Night	29% 21% 27% 18% 4	899
December	1st to 10th	Night	32% 19% 31% 14% 3	850
	11th to 20th	Night	31% 24% 30% 13% 2	850
	21st to end	Night	30% 24% 28% 14% 3	935

Page generated at 2024-11-27 18:30:50. Version ac07

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