Current Conditions
Temp-0.4 C
RH46 %
WindW 44 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Tuesday 21 May (0300 UTC Wednesday 22 May) 2013
Warning(s)
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but a narrow band/patch of high clouds will likely linger over or just north of the summit particularly for the first half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 0.5 C this evening and -0.5 C tomorrow morning. Winds will be from the SW at 15-30 mph, with seeing around 0.7 arcseconds. Precipitable water is expected to be in the 2.5-3.5 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. However, due to minor mid-level moisture in the area and daytime heating, there is a possibility for afternoon clouds particularly over the weekend.

A narrow band/patch of high clouds is expected to linger over or just north of the summit during the first half of the night, then dissipate through the morning hours. While this will likely leave clear skies for tomorrow night, more scattered to perhaps broken high clouds are slated to spread in the from the southwest and pass over or just south of the Big Island for at least Thursday and Friday night. These clouds are expected to shift eastward late Saturday afternoon, probably leaving mostly clear skies for that night.

Precipitable water is expected to linger near 2.5-3 mm for the next 3 nights, and could jump toward 4 mm for Friday and Saturday night.

Minor boundary layer turbulence will likely contribute to poorer than average seeing for tonight and probably part of tomorrow night. Although this source of turbulence is expected to subside during the latter night, increasing free atmospheric turbulence will limit any improvement in seeing until it diminishes, which should allow seeing improve for Saturday night.

No change since the morning forecast...Although the mid-level ridge will continue to linger to the south of the Big Island as a trough/low sits to the north over the next several days, the latter is expected to gradually weaken and the low-level ridge will remain in the area through the week. This will allow large-scale subsidence to prevail in the area, which will help maintain a fairly well-defined tradewind inversion near 7-8 thousand feet and ensure the summit-level air mass stays dry and stable throughout the forecast period. The aforementioned trough will still affect summit skies by pulling patches of high clouds through the area for the next 12-18 hours and probably produce boundary layer turbulence, contributing to poorer than average seeing through tomorrow evening. This turbulence is expected to subside as the trough weakens, but free atmospheric turbulence along the northern half of a building sub-tropical jet will limit any improvement in seeing starting early Thursday morning. There is a good chance that this turbulence will subside as the jet becomes better established over the area, which should allow seeing to improve over the 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 21 - 8 PM20-409-100 / 00.5SW/15-300.65-0.952.5-3.5
Wed May 22 - 2 AM10-309.5-100 / 0-0.5WSW/15-300.6-0.82.5-3.5
2 PM0-20Clear0 / 06WSW/15-30NaN2-3
8 PM0-10Clear0 / 01WSW/10-200.55-0.852-3
Thu May 23 - 2 AM0-10Clear0 / 00.5WSW/10-200.6-0.92-3
2 PM10-309-100 / 06W/5-15NaN3-4
8 PM30-508-100 / 01NW/5-150.55-0.852.5-3.5
Fri May 24 - 2 AM50-708-100 / 01NW/0-100.55-0.752.5-3.5
2 PM40-608-100 / 06NNW/0-10NaN3-5
Sat May 25 - 2 AM20-409-100 / 01NE/0-100.5-0.93-5
2 PM10-304-4.525 / 05NE/0-10NaN3-6
Sun May 26 - 2 AM0-20Clear0 / 00.5ESE/0-100.35-0.753-5
2 PM10-304-4.515 / 06SSE/5-15NaN2-4
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 21 - Wed May 22 19:03 20:15 4:22 5:34 N/A 3:44 89 13 21.7 -11 33
Wed May 22 - Thu May 23 19:03 20:15 4:22 5:34 N/A 4:34 95 14 19.6 -15 29
Thu May 23 - Fri May 24 19:04 20:16 4:22 5:34 17:36 5:29 99 15 21.0 -18 32
Fri May 24 - Sat May 25 19:04 20:16 4:21 5:33 18:41 6:29 100 16 25.3 -20 23
Sat May 25 - Sun May 26 19:04 20:17 4:21 5:33 19:46 N/A 98 17 30.9 -20 47
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 22 May 2013.
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