Current Conditions
Temp2.1 C
RH5 %
WindSSE 10 mph
Mauna Kea Observatories Forecast
5 PM HST Wednesday 06 May (0300 UTC Thursday 7 May) 2015
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for light isolated high clouds along the northern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1 C tomorrow morning. Winds will be light and from the east, with seeing around 0.6-0.65 arcseconds. Precipitable water is expected to be in the 0.9-1.1 mm range for the night.
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.

There is a possibility for light isolated high clouds along the northern skies for tonight, but these clouds will shift eastward leaving clear skeis for tomorrow night. Banding high clouds are expected to fill in from the west early Friday evening and pass over or just south of the summit for much of Saturday night. This band will then shift subtly southward for much of Sunday, opening up skies a bit for that night, then slip northward again for the early part of next week.

Precipitable water is expected to increase toward 1 mm for tonight, 1.5-2 mm for tomorrow night and probably 2-3 mm for Friday night and over the weekend.

A patch of mid-level turbulence passing through the area will likely contribute to slightly poorer than average seeing for tonight. This turbulence is slated to shift northward, allowing seeing to improve toward 0.5 arcseconds for tomorrow night. However, an influx of upper-level turbulence will likely degrade seeing back toward 0.6-0.7 arcseconds for the following 3 nights.

Little change since the morning forecast...The persistent mid/low-level ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area well into next week. This will easily negate the weak instability initiated by the large-scale tropical upper-tropospheric trough (TUTT) lingering to the north of the Islands, maintain a well-defined tradewind inversion near 8-9 thousand feet and ensure the summit-levle air mass remains dry and stable throughout the forecast period. However, the TUTT and especially its southern counterpart, the sub-tropical jet (STJ), will still have an impact on cloud cover, PW and seeing over the next several nights. Intially, turbulence along the northern flank of the STJ is slated to build over the summit area, likely contributing to poorer than average seeing for tonight. There is a possibility that seeing will improve as this turbulence shifts further northward, but the jet may start to inject mid/upper-level moisture over the summit, which could drive PW toward 2 mm for tomorrow night and especially the following 3 nights. The jet will also gain access to high clouds drifting out of the tropics, which will likely pass over and especially along the southern skies through much of the weekend and into next week. There is very good chance that the jet will strengthen, increasing turbulence in the free atmosphere and probably degrading seeing again during that time.
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 May 06 - 8 PM10-308-90 / 02ENE/5-150.55-0.750.9-1.1
Thu May 07 - 2 AM0-208-90 / 01ENE/5-150.5-0.70.9-1.1
2 PM0-20Clear0 / 06NE/5-15NaN1-2
8 PM0-5Clear0 / 01NE/0-100.45-0.551-1.5
Fri May 08 - 2 AM0-5Clear0 / 00NE/0-100.45-0.551.5-2
2 PM0-20Clear0 / 05.5NE/5-15NaN2-3
8 PM20-409-100 / 00.5NE/5-150.6-0.82-3
Sat May 09 - 2 AM40-608-100 / 00ENE/5-150.55-0.752-3
2 PM50-708-100 / 04.5E/0-10NaN2-3
Sun May 10 - 2 AM20-409-100 / 0-1ENE/0-100.5-0.82-3
2 PM10-309-100 / 04WNW/0-10NaN2-3
Mon May 11 - 2 AM30-508-100 / 0-1W/5-150.5-0.72-3
2 PM60-808-100 / 05WNW/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 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
Sun May 10 - Mon May 11 18:58 20:08 4:28 5:38 0:40 N/A 50 21 28.6 -11 22
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 7 May 2015.
Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products