Current Conditions
Temp5.0 C
RH6 %
WindNE 10 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Wednesday 21 June (0300 UTC Thursday 22 June) 2017
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 6 C this evening and 5 C tomorrow morning. Winds will be from the NE at 10-20 mph, with seeing near 0.5 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range for the first half of the night and 2-2.5 mm range for the second half.
The tradewind inversion will continue to cap low-level moisture primarily near 7-8 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 overhead will remain predominately clear through at least Saturday evening. Bands of scattered high clouds building to the northwest and south may merge over the summit area, and could increase cloud cover toward 50% for Sunday night.

Precipitable water is expected to settle in near 2-2.25 mm for most of the next 3 nights, briefly increase to 3-4 mm for Saturday night, then slip back toward 2 mm again for Sunday night.

Relatively calm skies and light uniform westerly flow aloft should allow seeing to settle in near 0.5 arcseconds through most of the next 5 nights. There is a chance for very minor disruption in seeing mainly for tomorrow evening.

Subtle changes have been made mainly to the PW forecast...The mid/low-level ridge will continue to promote steady/strong large-scale subsidence in the area, which will easily maintain a well-defined tradewind inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass into next week. The tropical upper-tropospheric trough is set to slowly redevelop over the next several days, but will have little affect on the stability of the atmosphere anytime soon. The sub-tropical jet will also gradually strengthen with the TUTT, but will maintain a relatively zonal orientation, limiting its access to high clouds flowing out of the tropics through the early part of the weekend. Fortunately, shear/turbulence associated with the STJ will remain quite weak, which should allow for better than average seeing throughout the forecast period. There is a chance that the TUTT/STJ will gain access to high clouds as an embedded short-wave trough digs southward later in the weekend. Still, cloud cover should not exceed 50% until perhaps the early part of next week.
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)
Wed Jun 21 - 8 PM0-5Clear0 / 06NE/10-200.4-0.61.5-2
Thu Jun 22 - 2 AM0-5Clear0 / 05NE/10-200.4-0.62-2.5
2 PM0-20Clear0 / 010.5NE/5-15NaN2-3
8 PM0-5Clear0 / 05.5NNE/5-150.45-0.652-2.5
Fri Jun 23 - 2 AM0-5Clear0 / 05NNE/5-150.4-0.62-2.5
2 PM0-20Clear0 / 010WNW/0-10NaN2-3
8 PM0-5Clear0 / 05NNW/0-100.35-0.552-2.5
Sat Jun 24 - 2 AM0-5Clear0 / 04WNW/0-100.4-0.62-2.5
2 PM0-20Clear0 / 09SW/0-10NaN3-5
Sun Jun 25 - 2 AM0-209.5-100 / 03.5SW/0-100.4-0.63-5
2 PM20-409-100 / 08SSW/5-15NaN2-4
Mon Jun 26 - 2 AM40-609-100 / 02.5S/5-150.45-0.651.5-2.5
2 PM60-808-100 / 07.5ESE/10-20NaN2-3
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
Wed Jun 21 - Thu Jun 22 19:14 20:28 4:20 5:34 4:20 N/A 4 4 25.9 15 59
Thu Jun 22 - Fri Jun 23 19:14 20:28 4:20 5:35 5:19 18:04 1 5 28.0 18 03
Fri Jun 23 - Sat Jun 24 19:14 20:28 4:21 5:35 6:21 19:08 0 6 31.1 18 48
Sat Jun 24 - Sun Jun 25 19:14 20:28 4:21 5:35 N/A 20:10 3 7 33.7 18 13
Sun Jun 25 - Mon Jun 26 19:14 20:28 4:21 5:35 N/A 21:07 8 8 34.4 16 24
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 22 June 2017.
Additional Information
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This message is also available at the MKWC road conditions page.
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