Current Conditions
Temp3.3 C
RH9 %
WindWSW 0 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Wednesday 17 December (0300 UTC Thursday 18 December) 2014
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but scattered high clouds are slated to fill from the west as the night progresses.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C, with winds from the east at 10-20 mph and seeing around 0.45-0.5 arcseconds. Precipitable water is expected to be in the 0.8-1 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure a dry and stable mid/summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived through Sunday, but could pick up for the early part of next week.

A patch of scattered high clouds is expected to fill in from the west late this evening and pass over/near the area through Thursday. These clouds will abruptly shift off toward the southeast early Friday morning, leaving predominately clear skies for the remainder of the forecast period.

Precipitable water is expected to linger near 0.9-1 mm for the next 3 nights, then increase toward 1-1.5 mm for Saturday and Sunday night.

Minimal turbulence in the atmosphere will allow seeing to linger near 0.45-0.5 arcseconds for tonight. However, increasing turbulence within the boundary layer will likely contribute to poor/bad seeing for the next 3 nights. The boundary layer turbulence is slated to subside for Sunday night, but there is a possibility that upper-level turbulence will build in the area, which will limit much improvement in seeing for that night.

No change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state, while flow aloft will remain relatively light and/or mostly zonal through the weekend. The former will promote strong/steady large-scale subsidence in the area, while the latter will keep turbulence and instability to a minimum during that time. This will allow the inversion to remain well-estabilished near 7-8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Calm skies should also make for better than average seeing for tonight. A patch of scattered high clouds is expected to briefly pass overhead as the sub-tropical jet tries to fill in from the southeast in response to a passing weak trough to the east of the Big Island through tomorrow. However, skies will open up again as these clouds and the STJ shifts off toward the SE as a new ridge wills in from the west on late tomorrow night. This ridge is slated to increase summit-level winds, which will likely stir up boundary layer turbulence and contribute to poor/bad seeing for Thursday, Friday and Saturday night. The ridge will start to shift off toward the east (allowing winds to weaken) in response to a trough deepening to the west late in the weekend. This trough is not expected in affect the stability of the atmosphere until perhaps Monday/Tuesday, but free atmospheric turbulence out ahead of the trough will limit much improvement in seeing for Sunday 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)
Wed Dec 17 - 8 PM0-209.5-100 / 02E/10-200.4-0.50.8-1
Thu Dec 18 - 2 AM10-309-100 / 02E/10-200.45-0.550.8-1
2 PM20-408-100 / 06E/15-30NaN0.8-1.2
8 PM10-308-90 / 01E/20-350.7-1.10.9-1.1
Fri Dec 19 - 2 AM0-208-8.50 / 00.5E/20-350.8-1.20.9-1.1
2 PM0-20Clear0 / 05E/20-35NaN0.8-1.2
8 PM0-5Clear0 / 00.5E/25-400.8-1.20.8-1
Sat Dec 20 - 2 AM0-5Clear0 / 00E/25-400.8-1.20.8-1
2 PM0-20Clear0 / 05E/20-35NaN0.8-1.2
Sun Dec 21 - 2 AM0-5Clear0 / 00E/15-300.6-11-1.5
2 PM0-20Clear0 / 06E/10-20NaN1-2
Mon Dec 22 - 2 AM0-5Clear0 / 00ESE/5-150.5-0.81-1.5
2 PM20-404-4.525 / 104SSW/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
Wed Dec 17 - Thu Dec 18 17:56 19:05 5:32 6:41 3:26 N/A 15 14 36.1 -13 07
Thu Dec 18 - Fri Dec 19 17:56 19:05 5:32 6:41 4:21 N/A 8 15 28.7 -15 47
Fri Dec 19 - Sat Dec 20 17:57 19:06 5:33 6:42 5:19 16:15 4 16 24.1 -17 41
Sat Dec 20 - Sun Dec 21 17:57 19:06 5:33 6:42 6:18 17:09 1 17 21.7 -18 37
Sun Dec 21 - Mon Dec 22 17:58 19:07 5:34 6:43 7:16 18:07 0 18 21.0 -18 26
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 18 December 2014.
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