Current Conditions
Temp8.0 C
RH10 %
WindSSE 12 mph
RoadOpen
Mauna Kea Observatories Forecast
9 AM HST (1900 UTC) Tuesday 05 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 7.5 C this afternoon, 3 C this evening and 2.5 C tomorrow morning. Winds will be light and from the ESE, with seeing near 0.5-0.55 arcseconds. 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 predominately near 8-9 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 overhead will remain predominately clear through early Friday evening, but there is a possibility thin cirrus along the northern skies mainly for much of Wednesday. A narrow band of cirrus is slated to fill in from the west late Friday evening and continue to pass over the summit area probably well into next week. This could result in periods of extensive cloud cover particularly for Saturday night (there is a chance that this band will shift subtly southward later in the weekend).

Precipitable water will continue to linger near 0.7-0.8 mm for the next 2 nights, increase a tad to 1 mm for Thursday night, then jump to 2-3 mm for Friday and Saturday night.

Relatively calm skies should allow for better than average seeing for most of tonight. However, an influx of mid turbulence will lkely contribute to poorer than average seeing for tomorrow night. There is a possibility for some improvement in seeing as this source of turbulence subsides for Thursday night, but increasing upper-level turbulence may degrade seeing again for the following 2 nights.

The mid/low-level ridge will continue to sit to the north of the state, promote steady large-scale subsidence in the area, which will easily negate the weak instability initiated by the tropical upper-tropospheric trough (TUTT) to the west through the week. This subsidence will help maintain the tradewind inversion primarily near 8-9 thousand feet and ensure the summit remains dry and stable throughout the forecast period. Very dry clear skies will prevail in the upper half of the atmosphere as the sub-tropical jet lingers to the south of the Big Island for the next 3 nights. And while better than average seeing will prevail for tonight, there is a possibility that northern fringe of the STJ will start to bring mid/upper-level turbulence to the area which will degrade seeing for tomorrow night. Calmer skies should prevail as this northern fringe spreads further northward for Thursday night, but more steady/strong upper-level turbulence may start to build as the jet intensifies for Friday night and much of the weekend. The STJ will also start to gain access to high clouds moving out of the tropics as a weak upper-level trough pushes the large-scale TUTT closer to the state over teh 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 May 05 - 2 PM0-20Clear0 / 07.5ESE/0-10NaN0.7-0.9
8 PM0-5Clear0 / 03ESE/0-100.45-0.550.7-0.9
Wed May 06 - 2 AM0-5Clear0 / 02.5ESE/0-100.45-0.650.7-0.9
2 PM0-20Clear0 / 07SE/0-10NaN0.7-0.9
8 PM0-5Clear0 / 02E/0-100.55-0.750.7-0.9
Thu May 07 - 2 AM0-10Clear0 / 01.5E/5-150.55-0.750.8-1
2 PM0-20Clear0 / 06ESE/0-10NaN0.8-1.2
8 PM0-10Clear0 / 01.5E/0-100.5-0.70.9-1.1
Fri May 08 - 2 AM0-5Clear0 / 00.5E/0-100.5-0.60.9-1.1
2 PM0-20Clear0 / 05.5NE/0-10NaN1-2
Sat May 09 - 2 AM20-409-100 / 00.5ENE/0-100.55-0.752-3
2 PM40-608-100 / 05.5E/0-10NaN2-3
Sun May 10 - 2 AM60-808-100 / 00SSE/0-100.55-0.752-3
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
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
Fri May 08 - Sat May 09 18:57 20:07 4:30 5:39 23:01 N/A 71 19 36.8 -17 00
Sat May 09 - Sun May 10 18:58 20:07 4:29 5:39 23:52 N/A 61 20 33.1 -14 36
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 05 May (0300 UTC Wednesday 6 May) 2015.
Additional Information
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This message is also available at the MKWC road conditions page.
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