Current Conditions
Temp7.7 C
RH40 %
WindNE 9 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 23 June (0300 UTC Saturday 24 June) 2017
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 5 C this evening and 4 C tomorrow morning. Winds will be light and from the NW, with seeing near 0.45-0.5 arcseconds. Precipitable water is expected to be in the 2-3 mm range for the night.
Discussion
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 tomorrow evening. Bands of scattered high clouds is set to build in from the WSW late Saturday evening, with more patchy high clouds filling in from the NW on Sunday. The latter is expected to fall apart later that night, while the former becomes more organized and widespread over the following day or two. This will likely lead to extensive cloud cover for Sunday night and perhaps overcast skies for the following 2 nights.

Precipitable water is expected to linger primarily in the 2-3 mm range throughout the forecast period.

Relatively calm skies and deep/uniform WNW flow at and above the summit should allow seeing to linger near 0.45-0.5 arcseconds for the next 2 nights. An increase in upper-level shear is expected to degrade seeing back toward 0.6-0.65 arcseconds for the following 3 nights.

Minor changes have been made to the PW forecast...A ridge in the lower half of the atmosphere will remain quasi-stationary/steady to the NE of the state and continue to promote steady/strong large-scale subsidence in the area well into next week. This subsidence will help maintain a well-defined inversion near 6-8 thousand feet, easily overcome instability associated with a building tropical upper-tropospheric trough (TUTT) to the west and ensure a dry/stable summit-level air mass throughout the forecast period. The TUTT and its associated southern counterpart, the sub-tropical jet (STJ), will remain relatively weak, minimizing shear/turbulence and allowing seeing to linger near 0.45-0.5 arcseconds for the next 2 nights. However, the STJ will gain access to high clouds drifting out of the tropics and stream it over the summit area beginning tomorrow night. The TUTT is expected to dig southward, allowing the STJ to strengthen and pull in more widespread banding high clouds up from the SW on Sunday. The former is expected to increase shear in the free atmosphere and degrade seeing toward more average-like values, while the latter will probably contribute to extensive cloud cover to overcast skies for Sunday night and 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)
Fri Jun 23 - 8 PM0-5Clear0 / 05NW/0-100.4-0.62-3
Sat Jun 24 - 2 AM0-5Clear0 / 04NNW/0-100.35-0.552-3
2 PM0-20Clear0 / 09ENE/0-10NaN2-4
8 PM20-409.5-100 / 04SSE/0-100.35-0.552.5-3.5
Sun Jun 25 - 2 AM40-609-100 / 03.5S/0-100.4-0.62.5-3.5
2 PM40-609-100 / 08S/0-10NaN2-3
8 PM60-809-100 / 03SE/0-100.5-0.72-3
Mon Jun 26 - 2 AM70-909-100 / 02ESE/0-100.5-0.82-3
2 PM80-1008-100 / 07ESE/5-15NaN2-3
Tue Jun 27 - 2 AM80-1008-100 / 02E/5-150.5-0.81.5-2.5
2 PM80-1008-100 / 07ENE/5-15NaN2-3
Wed Jun 28 - 2 AM80-1007-100 / 02NE/5-150.4-0.82-3
2 PM70-907-90 / 07.5NE/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
Sun Jun 25 - Mon Jun 26 19:14 20:28 4:21 5:35 N/A 21:07 8 8 34.4 16 24
Mon Jun 26 - Tue Jun 27 19:14 20:28 4:22 5:36 N/A 21:59 15 9 32.0 13 34
Tue Jun 27 - Wed Jun 28 19:15 20:29 4:22 5:36 N/A 22:46 23 10 26.5 10 01
Wed Jun 28 - Thu Jun 29 19:15 20:29 4:22 5:36 N/A 23:29 33 11 18.0 6 02
Thu Jun 29 - Fri Jun 30 19:15 20:29 4:23 5:37 N/A 0:10 43 12 07.1 1 51
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 26 June 2017.
Additional Information
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