Current Conditions
Temp4.5 C
RH69 %
WindNW 12 mph
Mauna Kea Observatories Forecast
5 PM HST Tuesday 23 August (0300 UTC Wednesday 24 August) 2016
Fog/high humidity
Chance for afternoon convection
Cloud Cover and Fog/Precipitation Forecast
There is a good chance for more periods of fog and high humidity through the night; precipitation is unlikely especially as the night progresses, but there is a possibility patches of clouds and convection in the area, particularly along the southern and western skies.
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C, with light winds from the NNW for the night. Seeing and precipitable water is expected to linger near or exceed 1 arcsecond and 4 mm, respectively, through the night.
Although the inversion is set to gradually start to rebuild this evening, lingering mid/low-level moisture will likely contribute to more periods of fog and high humidity for tonight and maybe even the early part of tomorrow night; nighttime precipitation is unlikely particularly after this evening. There is also a possibility for convection in the area throughout the night. A more well-defined inversion near 7-8 thousand feet will help dry out and stabilize the mid-level air mass by late Wednesday night and ensure the summit steers free of moisture for the remainder of the forecast period. Extensive afternoon clouds are possible for tomorrow, but will become minimal and short-lived for the remainder of the week.

Broken thick clouds will continue to linger in the area likely contributing to extensive cloud cover for tonight, but will also dissipate and start to gradually shift westward during this time. While this should help open up skies for parts of tomorrow night, a patch of high clouds drifting in from the SE is set to pass over the summit area for Thursday night. There is also a possibility that a narrow band of high clouds will begin to develop along the northern skies over the early part of the weekend.

Precipitable water is expected to linger near or exceed 4 mm through tomorrow night, then will slip toward 2-3 mm probably for the remainder of the forecast period (there is a chance it will dip just below 2 mm for Saturday night).

Persistent moisture, instability and turbulence will contribute to poor/bad seeing for tonight. Despite a drier more stable air mass, an increase in boundary layer turbulence will likely limit much improvement in seeing for Wednesday and Thursday night. Calmer skies should allow seeing to return toward more normal-like values or better for the following 2 nights.

No change since the morning forecast period....Residual mid/low-level tropical moisture will continue to linger in the area until it is pushed off toward the SW by strengthening ridge to the NE and its associated building NE trades later tomorrow. This will limit the inversion from rebuilding and allow the atmosphere below 15 thousand feet to remain fairly saturated, likely contributing to another round of fog, clouds and high humidity for tonight. Convection is still possible in the area, particularly along slopes for this afternoon, which could deposit rain at the summit into the early evening. Any convection should move off shore to the south and west of the Big Island overnight and eventually dissipate and shift further off to the SW with the departure of moisture through tomorrow evening. This should allow the ridge to the NE to regain control of the air mass, rebuild the inversion near 7-8 thousand feet and ensure the summit steers free of fog/precipitation for the remainder of the week. Unfortunately, the boost in winds could stir up boundary layer turbulence and contribute to poor seeing through Thursday night. Summit-level winds are set to taper through Friday, which should allow seeing to settle in near average-like values or better as calm skies to prevail at and above the summit for much of the weekend.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Tue Aug 23 - 8 PM70-904.5-9100 / 402.5NNW/0-100.9-1.58-12
Wed Aug 24 - 2 AM60-805-880 / 202.5NNW/0-100.7-1.36-10
2 PM40-604-560 / 107NNE/5-15NaN4-8
8 PM0-20Clear25 / 52.5NNE/10-200.55-0.953.5-4.5
Thu Aug 25 - 2 AM0-20Clear5 / 02.5NE/15-300.6-0.93-4
2 PM20-409.5-105 / 08ENE/15-30NaN3-5
8 PM20-409-100 / 02.5NE/20-350.6-12.5-3.5
Fri Aug 26 - 2 AM20-409-100 / 02NE/15-300.6-0.92-3
2 PM0-209-100 / 08.5NE/5-15NaN2-3
Sat Aug 27 - 2 AM0-209.5-100 / 02.5NE/5-150.5-0.72-3
2 PM0-209.5-100 / 08NNE/5-15NaN2-3
Sun Aug 28 - 2 AM0-209.5-100 / 03NE/5-150.45-0.652-3
2 PM0-209.5-100 / 09.5ENE/5-15NaN2-3
Rise and Set times for the Sun and Moon
Night (HST) Sun Set Twilight End Twilight Beg Sun Rise Moon Rise Moon Set Illumination (%) RA DEC
Tue Aug 23 - Wed Aug 24 18:53 20:00 4:49 5:56 23:02 N/A 58 3 27.0 13 10
Wed Aug 24 - Thu Aug 25 18:52 19:59 4:49 5:56 23:53 N/A 46 4 24.5 15 48
Thu Aug 25 - Fri Aug 26 18:51 19:58 4:50 5:56 0:46 N/A 35 5 22.2 17 26
Fri Aug 26 - Sat Aug 27 18:50 19:57 4:50 5:56 1:42 N/A 25 6 19.8 17 59
Sat Aug 27 - Sun Aug 28 18:50 19:56 4:50 5:57 2:38 N/A 16 7 16.5 17 28
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 24 August 2016.
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