Harrington Beach State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harrington Beach State Park clear sky chart from 2005-11-06 to 2024-11-06.

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	12% 8% 3 7% 5% 5% 5% 4 6% 7% 39%	101391
	Night	14% 9% 3 7% 5% 4 4 4 5% 6% 37%	97739
Transparency	Day	43% 6% 13% 24% 13% 1	104936
	Night	45% 6% 11% 23% 14% 2	102335
Seeing	Day	15% 4 19% 33% 23% 6%	15916
	Night	18% 7% 24% 31% 17% 3	25764

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	13% 14% 6% 8% 5% 5% 5% 4 7% 6% 28%	2527
	11th to 20th	Day	13% 11% 4 12% 5% 5% 9% 8% 7% 7% 18%	2530
	21st to end	Day	17% 15% 7% 10% 6% 4 4 4 5% 6% 21%	2783
February	1st to 10th	Day	11% 12% 6% 11% 6% 4 4 5% 6% 6% 29%	1695
	11th to 20th	Day	12% 10% 3 8% 6% 5% 5% 4 5% 5% 36%	1848
	21st to end	Day	11% 12% 4 10% 5% 4 4 5% 5% 7% 32%	1570
March	1st to 10th	Day	12% 8% 3 6% 4 4 4 4 6% 6% 43%	3120
	11th to 20th	Day	11% 6% 3 7% 5% 5% 4 4 5% 6% 43%	3250
	21st to end	Day	21% 10% 4 9% 5% 4 4 3 5% 5% 30%	4165
April	1st to 10th	Day	17% 12% 3 6% 5% 4 5% 5% 6% 6% 32%	2280
	11th to 20th	Day	16% 8% 4 7% 5% 5% 5% 4 5% 6% 35%	2254
	21st to end	Day	18% 9% 2 7% 5% 5% 4 4 6% 6% 34%	2434
May	1st to 10th	Day	15% 8% 3 7% 4 4 4 3 5% 7% 38%	4082
	11th to 20th	Day	12% 6% 2 7% 5% 6% 5% 4 6% 7% 39%	4389
	21st to end	Day	11% 7% 2 6% 4 4 5% 4 6% 8% 42%	4824
June	1st to 10th	Day	10% 5% 2 6% 6% 4 4 4 7% 7% 44%	2660
	11th to 20th	Day	11% 6% 2 6% 5% 5% 4 4 6% 9% 42%	2660
	21st to end	Day	8% 5% 2 5% 4 4 5% 5% 7% 10% 44%	2660
July	1st to 10th	Day	12% 6% 3 7% 5% 4 5% 4 7% 8% 38%	4440
	11th to 20th	Day	4 3 1 3 4 4 5% 4 7% 11% 52%	4440
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 49%	4813
August	1st to 10th	Day	10% 5% 2 5% 5% 6% 5% 4 6% 9% 43%	4394
	11th to 20th	Day	10% 4 2 5% 4 4 4 4 5% 7% 51%	3867
	21st to end	Day	8% 5% 2 7% 4 4 5% 4 6% 8% 46%	4180
September	1st to 10th	Day	10% 5% 3 6% 4 5% 4 4 6% 7% 46%	2280
	11th to 20th	Day	12% 5% 2 6% 4 3 4 3 5% 8% 49%	2153
	21st to end	Day	11% 7% 2 7% 4 4 5% 4 6% 8% 43%	2090
October	1st to 10th	Day	14% 6% 3 6% 4 4 4 3 6% 6% 45%	2039
	11th to 20th	Day	20% 8% 3 7% 4 5% 4 4 7% 7% 31%	1848
	21st to end	Day	16% 8% 2 8% 5% 5% 4 4 5% 6% 36%	1881
November	1st to 10th	Day	12% 7% 3 7% 4 4 4 4 5% 7% 42%	1717
	11th to 20th	Day	10% 12% 3 8% 7% 5% 6% 4 6% 8% 31%	1710
	21st to end	Day	17% 11% 3 8% 4 4 4 3 5% 8% 35%	1587
December	1st to 10th	Day	16% 13% 4 7% 7% 6% 6% 4 6% 7% 25%	1520
	11th to 20th	Day	13% 12% 4 8% 6% 6% 5% 4 7% 7% 26%	1918
	21st to end	Day	18% 20% 7% 13% 5% 4 4 3 4 5% 17%	2783
January	1st to 10th	Night	15% 14% 7% 8% 4 4 3 3 5% 5% 30%	4428
	11th to 20th	Night	14% 14% 5% 14% 7% 5% 8% 7% 6% 5% 16%	4440
	21st to end	Night	16% 17% 6% 10% 6% 4 4 4 5% 5% 23%	4884
February	1st to 10th	Night	13% 13% 5% 8% 5% 5% 5% 4 6% 5% 31%	2481
	11th to 20th	Night	12% 10% 4 8% 5% 4 5% 3 5% 5% 39%	2218
	21st to end	Night	17% 14% 3 7% 4 4 3 3 6% 5% 35%	1884
March	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 4 5% 41%	3733
	11th to 20th	Night	10% 7% 2 6% 4 4 5% 4 6% 8% 43%	3736
	21st to end	Night	19% 12% 5% 9% 5% 5% 4 3 4 5% 30%	3468
April	1st to 10th	Night	17% 10% 3 6% 5% 3 4 4 4 6% 37%	1900
	11th to 20th	Night	20% 9% 2 6% 4 3 4 3 5% 5% 39%	1875
	21st to end	Night	18% 8% 2 6% 4 3 4 3 6% 7% 40%	1744
May	1st to 10th	Night	15% 7% 3 8% 5% 4 5% 3 6% 8% 37%	2813
	11th to 20th	Night	14% 6% 3 8% 5% 5% 5% 5% 7% 8% 36%	2512
	21st to end	Night	14% 8% 3 7% 4 4 5% 3 4 7% 40%	2743
June	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 5% 9% 45%	1520
	11th to 20th	Night	12% 5% 2 7% 4 4 4 3 6% 8% 44%	1520
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 6% 6% 47%	1520
July	1st to 10th	Night	12% 6% 2 7% 5% 5% 5% 4 5% 8% 41%	2530
	11th to 20th	Night	4 3 2 4 4 4 5% 4 7% 8% 56%	2530
	21st to end	Night	6% 4 2 5% 4 4 4 4 6% 10% 50%	2750
August	1st to 10th	Night	10% 4 2 6% 4 4 4 3 6% 9% 48%	2542
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 3 6% 8% 49%	2945
	21st to end	Night	8% 4 2 6% 4 5% 5% 4 6% 8% 49%	3476
September	1st to 10th	Night	10% 4 2 6% 5% 3 4 3 5% 7% 52%	1900
	11th to 20th	Night	10% 4 1 5% 4 4 4 3 5% 6% 53%	2007
	21st to end	Night	13% 6% 2 6% 4 4 3 3 6% 6% 46%	2090
October	1st to 10th	Night	13% 6% 2 6% 4 4 3 3 5% 6% 49%	2137
	11th to 20th	Night	18% 8% 2 6% 3 4 4 3 6% 6% 40%	2332
	21st to end	Night	19% 8% 3 6% 4 4 4 4 6% 7% 35%	2717
November	1st to 10th	Night	12% 9% 3 5% 4 4 5% 4 4 6% 44%	2483
	11th to 20th	Night	14% 10% 3 8% 6% 5% 5% 4 5% 6% 34%	2470
	21st to end	Night	16% 10% 3 6% 5% 5% 4 3 5% 6% 36%	2588
December	1st to 10th	Night	16% 13% 4 9% 5% 4 5% 5% 7% 7% 26%	2660
	11th to 20th	Night	15% 15% 3 8% 5% 6% 5% 4 6% 6% 27%	3279
	21st to end	Night	21% 18% 5% 10% 5% 5% 4 3 5% 5% 20%	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	56% 8% 15% 16% 6%	2528
	11th to 20th	Day	60% 14% 8% 15% 3	2530
	21st to end	Day	64% 6% 10% 16% 5%	2783
February	1st to 10th	Day	53% 8% 10% 19% 8% 1	1695
	11th to 20th	Day	49% 5% 11% 22% 11% 2	1858
	21st to end	Day	51% 5% 11% 20% 11% 2	1570
March	1st to 10th	Day	41% 5% 13% 25% 13% 3	3120
	11th to 20th	Day	41% 6% 12% 25% 15% 2	3250
	21st to end	Day	56% 4 13% 19% 7% 1	4165
April	1st to 10th	Day	50% 6% 13% 19% 11%	2280
	11th to 20th	Day	49% 5% 9% 21% 13% 3	2254
	21st to end	Day	49% 6% 15% 17% 11% 2	2434
May	1st to 10th	Day	44% 6% 10% 23% 16% 1	4120
	11th to 20th	Day	37% 11% 11% 25% 14% 2	4393
	21st to end	Day	38% 7% 12% 22% 17% 4	4837
June	1st to 10th	Day	37% 7% 12% 27% 15% 3	2660
	11th to 20th	Day	38% 5% 14% 25% 17% 1	2660
	21st to end	Day	33% 7% 16% 26% 16% 2	2660
July	1st to 10th	Day	43% 4 14% 26% 11% 2	4371
	11th to 20th	Day	26% 4 18% 34% 16% 2	4365
	21st to end	Day	31% 6% 17% 24% 20% 3	4662
August	1st to 10th	Day	38% 4 16% 29% 12% 1	4379
	11th to 20th	Day	33% 3 14% 37% 11% 1	3906
	21st to end	Day	36% 4 15% 25% 19% 1	4179
September	1st to 10th	Day	36% 6% 13% 28% 15% 2	2280
	11th to 20th	Day	34% 6% 13% 31% 15% 1	2153
	21st to end	Day	38% 6% 13% 30% 13%	2090
October	1st to 10th	Day	25% 3 7% 41% 23% 2	3390
	11th to 20th	Day	39% 4 10% 27% 20% 1	3051
	21st to end	Day	42% 3 11% 29% 13% 1	3081
November	1st to 10th	Day	42% 6% 14% 24% 13% 1	1717
	11th to 20th	Day	51% 6% 14% 21% 7% 1	1710
	21st to end	Day	49% 5% 14% 24% 7%	1587
December	1st to 10th	Day	57% 8% 12% 16% 7% 1	1520
	11th to 20th	Day	54% 7% 14% 17% 6% 2	1915
	21st to end	Day	69% 6% 8% 12% 5%	2783
January	1st to 10th	Night	57% 7% 9% 18% 9% 1	4428
	11th to 20th	Night	66% 12% 7% 10% 5%	4440
	21st to end	Night	63% 6% 11% 15% 5%	4884
February	1st to 10th	Night	54% 6% 9% 19% 11% 1	2481
	11th to 20th	Night	47% 5% 10% 23% 13% 2	2219
	21st to end	Night	51% 6% 10% 19% 12% 2	1884
March	1st to 10th	Night	46% 4 14% 25% 9% 2	3733
	11th to 20th	Night	37% 6% 10% 24% 20% 3	3736
	21st to end	Night	58% 5% 8% 18% 10% 2	3468
April	1st to 10th	Night	48% 5% 9% 19% 17% 1	1900
	11th to 20th	Night	48% 4 7% 20% 17% 4	1875
	21st to end	Night	43% 5% 13% 23% 14% 2	1744
May	1st to 10th	Night	45% 6% 11% 19% 16% 3	2840
	11th to 20th	Night	41% 10% 11% 25% 12% 1	2513
	21st to end	Night	44% 5% 10% 18% 15% 8%	2751
June	1st to 10th	Night	34% 6% 11% 29% 17% 2	1520
	11th to 20th	Night	37% 5% 9% 26% 20% 3	1520
	21st to end	Night	34% 7% 14% 24% 18% 2	1520
July	1st to 10th	Night	43% 3 14% 23% 13% 5%	2490
	11th to 20th	Night	25% 4 16% 35% 18% 2	2482
	21st to end	Night	31% 4 16% 22% 24% 3	2662
August	1st to 10th	Night	34% 4 15% 26% 19% 2	2533
	11th to 20th	Night	34% 4 12% 32% 17% 1	2972
	21st to end	Night	34% 4 12% 26% 21% 4	3476
September	1st to 10th	Night	32% 7% 10% 27% 22% 2	1900
	11th to 20th	Night	31% 5% 9% 36% 17% 2	2007
	21st to end	Night	38% 5% 10% 30% 16% 1	2090
October	1st to 10th	Night	26% 3 7% 40% 22% 1	3566
	11th to 20th	Night	36% 4 13% 27% 19% 2	3868
	21st to end	Night	43% 4 9% 26% 17%	4467
November	1st to 10th	Night	40% 6% 11% 25% 17% 2	2483
	11th to 20th	Night	50% 6% 11% 20% 11% 1	2470
	21st to end	Night	48% 7% 15% 21% 8% 1	2588
December	1st to 10th	Night	55% 8% 11% 19% 7% 1	2660
	11th to 20th	Night	57% 7% 11% 16% 9% 1	3281
	21st to end	Night	66% 6% 9% 14% 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	18% 10% 29% 31% 9% 3	270
	11th to 20th	Day	16% 9% 31% 32% 11%	270
	21st to end	Day	21% 5% 26% 35% 12% 1	297
February	1st to 10th	Day	15% 7% 36% 30% 10% 2	270
	11th to 20th	Day	16% 10% 33% 30% 10%	270
	21st to end	Day	18% 5% 37% 36% 3 1	225
March	1st to 10th	Day	13% 7% 38% 34% 9%	270
	11th to 20th	Day	18% 5% 31% 30% 15% 2	307
	21st to end	Day	26% 4 26% 32% 11% 2	506
April	1st to 10th	Day	24% 5% 27% 31% 13%	460
	11th to 20th	Day	20% 5% 26% 30% 15% 4	452
	21st to end	Day	20% 3 20% 36% 18% 3	460
May	1st to 10th	Day	19% 3 21% 40% 16% 2	463
	11th to 20th	Day	19% 3 16% 34% 24% 4	665
	21st to end	Day	15% 2 12% 34% 27% 10%	734
June	1st to 10th	Day	11% 2 13% 37% 30% 7%	680
	11th to 20th	Day	14% 1 13% 40% 25% 7%	680
	21st to end	Day	12% 2 12% 39% 29% 6%	680
July	1st to 10th	Day	8% 1 7% 30% 40% 14%	671
	11th to 20th	Day	9% 2 9% 33% 36% 10%	668
	21st to end	Day	6% 1 8% 39% 37% 9%	739
August	1st to 10th	Day	8% 2 8% 34% 36% 12%	660
	11th to 20th	Day	11% 1 8% 30% 35% 15%	479
	21st to end	Day	10% 2 9% 33% 35% 11%	539
September	1st to 10th	Day	13% 4 12% 31% 31% 9%	490
	11th to 20th	Day	12% 2 11% 29% 33% 13%	490
	21st to end	Day	15% 5% 18% 29% 23% 10%	490
October	1st to 10th	Day	18% 4 19% 28% 24% 6%	439
	11th to 20th	Day	20% 8% 27% 31% 12% 2	300
	21st to end	Day	21% 7% 28% 32% 10% 2	330
November	1st to 10th	Day	16% 6% 25% 34% 17% 2	285
	11th to 20th	Day	14% 11% 35% 28% 12%	270
	21st to end	Day	23% 7% 28% 32% 10%	270
December	1st to 10th	Day	20% 10% 35% 24% 11%	270
	11th to 20th	Day	21% 9% 34% 25% 9% 2	270
	21st to end	Day	25% 11% 33% 24% 6% 1	297
January	1st to 10th	Night	20% 14% 36% 23% 7%	950
	11th to 20th	Night	23% 12% 33% 26% 6% 1	950
	21st to end	Night	20% 11% 34% 27% 8%	1045
February	1st to 10th	Night	18% 10% 35% 30% 6% 1	939
	11th to 20th	Night	17% 10% 37% 27% 9%	743
	21st to end	Night	25% 9% 33% 28% 5%	628
March	1st to 10th	Night	18% 6% 29% 34% 11% 1	760
	11th to 20th	Night	14% 8% 32% 33% 12% 1	760
	21st to end	Night	22% 4 24% 36% 13% 1	629
April	1st to 10th	Night	21% 7% 28% 32% 11% 1	570
	11th to 20th	Night	25% 4 22% 33% 13% 3	563
	21st to end	Night	20% 3 21% 38% 18% 1	570
May	1st to 10th	Night	18% 3 17% 42% 17% 2	570
	11th to 20th	Night	19% 3 16% 34% 25% 3	561
	21st to end	Night	13% 2 13% 34% 30% 8%	617
June	1st to 10th	Night	12% 2 11% 42% 25% 7%	570
	11th to 20th	Night	14% 1 12% 40% 26% 7%	570
	21st to end	Night	10% 2 12% 39% 31% 5%	570
July	1st to 10th	Night	9% 2 5% 33% 41% 10%	555
	11th to 20th	Night	7% 1 8% 39% 36% 10%	552
	21st to end	Night	8% 2 9% 38% 37% 7%	624
August	1st to 10th	Night	7% 1 7% 38% 37% 8%	567
	11th to 20th	Night	9% 2 11% 35% 32% 12%	564
	21st to end	Night	10% 3 11% 34% 37% 5%	627
September	1st to 10th	Night	11% 2 15% 34% 30% 8%	570
	11th to 20th	Night	10% 3 16% 28% 32% 10%	677
	21st to end	Night	17% 4 19% 28% 24% 8%	760
October	1st to 10th	Night	18% 4 22% 30% 22% 4	760
	11th to 20th	Night	22% 9% 26% 29% 14% 1	760
	21st to end	Night	24% 9% 27% 28% 10% 2	836
November	1st to 10th	Night	16% 9% 31% 31% 12% 2	764
	11th to 20th	Night	20% 12% 33% 27% 8%	760
	21st to end	Night	21% 11% 34% 27% 7%	878
December	1st to 10th	Night	22% 15% 34% 23% 6%	950
	11th to 20th	Night	24% 13% 34% 21% 7% 1	950
	21st to end	Night	29% 11% 32% 24% 4	1045

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