Current Conditions
Temp6.2 C
RH18 %
WindS 2 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 10 July (0300 UTC Saturday 11 July) 2020
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this evening and 0.5 C tomorrow morning. Winds will be from the ENE at 5-15 mph, with seeing near 0.5-0.55 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture primarily near 7 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear for tonight, but a narrow strand of high clouds are set to move in from the west and pass overhead beginning tomorrow night. This band is expected to expand and continue to slip overhead, before shifting to the western skies a tad early next week. Still there is a possibility for periods of extensive cloud cover for Sunday, Monday and Tuesday night.

Precipitable water is expected to be in the 1.5-2 mm range for the next 2 nights, slip toward 1-1.5 mm for Sunday night, then drift back to 2 mm for the following 2 nights.

Dissipating low-level turbulence, combined with a drier air mass should allow seeing to improve through the night and settle in near 0.5 arcseconds as moderate upper-level turbulence prevails for the next 3 nights. There is a chance that more laminar/light flow will set in at and above the summit, which may help seeing to improve further for Tuesday night.

No change since the morning forecast...A low-level ridge will persist to the NE of the state, while an upper-level ridge prevails to the SE and the tropical upper-tropospheric trough continues to stretch from the west coast and out to Guam as it lingers to the NW. Fortunately, the latter will remain too far off to the north, which will allow the ridge to promote strong/steady large-scale subsidence in the area, maintain a well-defined inversion primarily near 7 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Skies will remain predominately clear for tonight, but the sub-tropical jet just north of the Big Island is expected to gain access to high clouds flowing out of the tropics for tomorrow night. More widespread high clouds will likely follow suit as a developing upper-level low to the NNW draws more moisture out of the tropics for Sunday night and early part of next week. Fortunately, the bulk of the turbulence associated with the STJ will linger off toward the north, allowing for better than average seeing throughout the forecast period. There is a possibility for excellent seeing as the STJ shifts northward and the upper-level ridge to the SE expands late Tuesday night.
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)
Fri Jul 10 - 8 PM0-5Clear0 / 01ENE/5-150.45-0.651.5-2
Sat Jul 11 - 2 AM0-5Clear0 / 00.5ENE/5-150.4-0.61.5-2
2 PM0-209.5-100 / 06NE/5-15NaN1.5-2.5
8 PM10-309-100 / 01.5NE/0-100.35-0.551.5-2
Sun Jul 12 - 2 AM20-409-100 / 01.5W/0-100.35-0.551.5-2
2 PM40-608.5-100 / 07NNW/0-10NaN1-2
8 PM60-809-100 / 02NW/0-100.4-0.61-1.5
Mon Jul 13 - 2 AM40-609-100 / 01.5NNE/0-100.4-0.61-1.5
2 PM50-709-100 / 07ESE/5-15NaN1.5-2.5
Tue Jul 14 - 2 AM50-709-100 / 02.5SE/5-150.4-0.61.5-2.5
2 PM60-809-100 / 08SE/5-15NaN2-3
Wed Jul 15 - 2 AM60-809-100 / 03SE/5-150.3-0.51.5-2.5
2 PM20-409-100 / 08.5SE/5-15NaN1-2
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
Sun Jul 12 - Mon Jul 13 19:14 20:27 4:29 5:41 0:23 N/A 45 1 47.6 5 28
Mon Jul 13 - Tue Jul 14 19:14 20:27 4:29 5:42 0:57 N/A 36 2 31.8 10 01
Tue Jul 14 - Wed Jul 15 19:14 20:26 4:30 5:42 1:34 N/A 27 3 17.7 14 13
Wed Jul 15 - Thu Jul 16 19:14 20:26 4:30 5:42 2:14 N/A 19 4 06.0 17 52
Thu Jul 16 - Fri Jul 17 19:14 20:26 4:31 5:43 2:58 N/A 12 4 57.1 20 46
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 13 July 2020.
Additional Information
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