Current Conditions
Temp1.5 C
RH31 %
WindENE 21 mph
Mauna Kea Observatories Forecast
5 PM HST Tuesday 22 August (0300 UTC Wednesday 23 August) 2017
Chance for fog/high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a small/moderate risk for fog and high humidity, mainly during the first half of the night; precipitation is unlikely. Broken clouds will continue to linger overhead for this evening then move to the western skies as the night progresses.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C, with winds from the east at 10-20 mph and seeing near 0.7-0.8 arcseconds. Precipitable water is expected to exceed 4 mm for the night.
While the air mass near the Big Island will continue to dry out and stabilize as the inversion rapidly rebuilds through the night, there is a possibility for a periods of fog and high humidity mainly for early this evening; precipitation is unlikely and the summit will steer free of moisture for the following 4 nights. Daytime clouds will be minimal and short-lived for the next 5 days.

Broken high clouds will continue to linger overhead for this evening then move to the western skies as the night progresses and for tomorrow night. These clouds are expected to make a move to the northern skies for Thursday night, then dissipate on Friday, leaving relatively clear skies for the remainder of the forecast period.

Precipitable water is expected to linger near or exceed 4 mm through tomorrow evening, trend toward 1.2-1.3 mm for Thursday night, then subtly increase to 1.75 mm for the following 2 nights.

Although the atmosphere is set to stabilize, persistent upper-level turbulence will likely contribute to poorer than average seeing for tonight. A minor increase in boundary layer turbulence will likely prohibit much improvement in seeing for Wednesday and Thursday night. There is a possibility that calmer skies and deep subsidence will allow seeing to settle in near 0.35-0.4 arcseconds for the following 2 nights.

Little change since the morning forecast...The upper-level low responsible for the instability and drawing moisture into the area over the last 2 days will continue to shift off toward the west and allow the ridge to the north to strengthen and regain control of the air mass over the course of the night. Unfortuntely, lingering moisture/instability may still permit the development fog and and periods of high humidity at the summit mainly through this evening. The atmosphere is expected to rapidly dry out and stabilize as the inversion strengthens thereafter, ensuring the summit steers free of fog/precipitation for the remainder of the forecast period. Skies are also expected to open up as an upper-level ridge building in from the SE, shoves the high clouds in the area off toward the west of the summit for the next 2 nights. However, there is a possibility that the upper-level ridge will aid in an increase in summit-level winds, which could stir up minor boundary layer turbulence for Wednesday and Thursday night. The clouds will eventually shift off to the northern skies as the ridge settles in overhead on Friday, and will eventually dissipate as the weekend progresses. Summit-level winds are also set to taper on Friday, which could allow seeing to improve toward excellent-like values for that night and most 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 22 - 8 PM60-806-1030 / 52ENE/10-200.6-14-8
Wed Aug 23 - 2 AM40-606-810 / 02ENE/10-200.55-0.854-8
2 PM40-607-90 / 08ENE/10-20NaN4-6
8 PM30-508-90 / 03ENE/15-250.5-0.83.5-4.5
Thu Aug 24 - 2 AM20-408-90 / 03ENE/15-250.5-0.82.5-3.5
2 PM20-408-90 / 08.5ENE/15-25NaN1.5-2.5
8 PM10-308-90 / 03NE/15-250.5-0.81-1.5
Fri Aug 25 - 2 AM10-308-90 / 02.5ENE/15-250.45-0.751-1.5
2 PM0-20Clear0 / 07.5ENE/10-10NaN1.5-2.5
Sat Aug 26 - 2 AM0-20Clear0 / 02.5NE/5-150.25-0.451.5-2
2 PM0-20Clear0 / 08.5NE/5-15NaN1.5-2.5
Sun Aug 27 - 2 AM0-20Clear0 / 03SSE/5-150.3-0.51.5-2
2 PM0-20Clear0 / 07.5S/5-15NaN2-4
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 22 - Wed Aug 23 18:54 20:01 4:48 5:55 N/A 19:57 3 11 31.3 5 11
Wed Aug 23 - Thu Aug 24 18:53 20:00 4:49 5:56 N/A 20:38 8 12 21.3 0 53
Thu Aug 24 - Fri Aug 25 18:52 19:59 4:49 5:56 N/A 21:19 15 13 09.9 -3 22
Fri Aug 25 - Sat Aug 26 18:51 19:58 4:50 5:56 N/A 21:58 23 13 57.6 -7 24
Sat Aug 26 - Sun Aug 27 18:51 19:57 4:50 5:56 N/A 22:38 31 14 45.1 -11 02
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 23 August 2017.
Additional Information
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