Current Conditions
Temp4.3 C
RH7 %
WindS 0 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Friday 01 May (0300 UTC Saturday 2 May) 2015
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 0 C this evening and -0.5 C tomorrow morning. Winds will be from the NNE at 5-15 mph, while seeing will start out near 0.65 arcseconds, but improve toward 0.5 arcseconds through the night. Precipitable water is expected to be in the 0.7-0.9 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit steers free of moisture 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 banding high clouds will start to develop along the southern skies over the next 24-36 hours and may pass over or just south of the Big Island late tomorrow night and again for Monday and Tuesday night. The second passage may result in extensive cloud cover particularly for much of Tuesday.

Precipitable water will linger near 0.7-0.8 mm for the next 2 nights, then subtly increase toward 0.9 mm for Sunday night, then settle back down to 0.7-0.8 mm again for the early part of next week.

Lingering mid/upper-level turbulence may contribute to poor seeing for this evening, but this turbulence is slated to subside allowing seeing to settle in near 0.5-0.55 arcseconds as relatively calm skies set in aloft likely for the remainder of the forecast period.

Although the mid-level ridge will remain rather indistinct probably well into next week, the low-level ridge will continue to sit to the north of the state with a relatively weak tropical upper-tropospheric trough lingering to the SE during this time. This will allow strong steady large-scale subsidence to prevail in the area, which will easily maintain the tradewind inversion near 8-9 thousand feet and ensure a dry/stable summit-level air mass over the next 5 nights. The position of the TUTT will also keep the sub-tropical jet off toward the south, allowing predominately dry upper-level air mass to persist overhead, which should help keep PW near 0.8-0.9 mm during this time. Seeing should also settle in near 0.5-0.55 arcseconds, with relatively calm skies prevail at and above the summit throughout most of the forecast period. However, there is a possibility that the sub-tropical jet will occasionally kink northward, bringing bringing bands of high clouds to the area along the southern skies and perhaps overhead for Saturday night and especially for Monday and 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 May 01 - 8 PM0-20Clear0 / 00N/5-150.55-0.750.7-0.9
Sat May 02 - 2 AM0-5Clear0 / 0-0.5NNE/5-150.45-0.550.7-0.9
2 PM0-20Clear0 / 06NE/0-10NaN0.8-1.2
8 PM0-209.5-100 / 02.5NE/0-100.45-0.550.7-0.9
Sun May 03 - 2 AM10-309-100 / 02ENE/0-100.45-0.550.7-0.9
2 PM10-309-100 / 08E/0-10NaN0.8-1.2
8 PM0-10Clear0 / 03SE/0-100.5-0.60.8-1
Mon May 04 - 2 AM0-5Clear0 / 03SSE/0-100.45-0.550.8-1
2 PM0-20Clear0 / 08SSE/0-10NaN0.8-1.2
Tue May 05 - 2 AM20-409-100 / 03SE/0-100.4-0.60.8-1
2 PM30-509-100 / 08.5SE/0-10NaN0.8-1.2
Wed May 06 - 2 AM40-609-100 / 03E/0-100.45-0.650.8-1
2 PM40-609-100 / 08ESE/0-10NaN0.8-1.2
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 May 03 - Mon May 04 18:55 20:04 4:33 5:42 18:35 6:35 100 15 01.0 -14 20
Mon May 04 - Tue May 05 18:56 20:05 4:32 5:41 19:28 N/A 98 15 53.5 -16 41
Tue May 05 - Wed May 06 18:56 20:05 4:32 5:41 20:21 N/A 94 16 47.8 -18 13
Wed May 06 - Thu May 07 18:56 20:06 4:31 5:40 21:16 N/A 88 17 43.5 -18 50
Thu May 07 - Fri May 08 18:57 20:06 4:30 5:40 22:09 N/A 81 18 40.1 -18 26
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 4 May 2015.
Additional Information
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This message is also available at the MKWC road conditions page.
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