Current Conditions
Temp9.9 C
RH27 %
WindESE 19 mph
RoadOpen
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Wednesday 17 September 2014
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for patches of thin high clouds along the northern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 10 C this afternoon, 5 C this evening and 4.5 C tomorrow morning. Winds will be light and from the east, with seeing around 0.5 arcseconds. Precipitable water is expected to be in the 1.25-1.75 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

There is a possibility that a band of isolated to scatterd high clouds will set up along the northern skies for tonight. These clouds are slated to break up through tomorrow morning/afternoon, leaving mostly clear skies for tomorrow night. There is a chance that another small patch of thin high clouds will fill in over the summit area again for Friday evening, but will dissipate early Saturday morning, clearing up skies for the remainder of the weekend.

Precipitable water is expected to linger near 1.5 mm for tonight, increase to 2.5 mm for tomorrow night, then drop back 2 mm for Friday night, eventually settling in near 1.5-1.75 mm for the weekend.

Minimal turbulence will persist in the atmosphere, allowing for better than average seeing for the next 2 nights. There is a possibility that upper-level turbulence will briefly increase, which could contribute to poorer than average seeing for Friday night. This turbulence is slated to subside as deep subsidence fills into the area, which should help to improve seeing over the weekend (there is a possibility for excellent seeing late in the weekend).

The eastern flank of the mid-level ridge will continue to sit to the north of the Islands for the next couple of days, shift off toward the west as a trough passes to the far north, then move back toward its normal climitological position in the NE Pacific late in the weekend and into next week. Nonetheless, it will remain close enough to the area to promote steady large-scale subsidence near the Big Island, which will help maintain the tradewind inversion near 9 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Prior to the passing of the trough, the tropical upper-tropospheric trough and its associated sub-tropical jet will linger to the northwest of the Big Island. The jet may transport isolated to scattered high clouds mainly along the northern skies for tonight, but the TUTT will remain far enough away to limit turbulence in the atmosphere and allow for better than average seeing over the next 2 nights. There is a possibility that the TUTT will bring upper-level turbulence and isolated high clouds over the summit as it slips over the Big Island on Friday night. But clear skies and better than average seeing should prevail as the TUTT shifts east of the Big Island ahead of an advancing upper-level ridge to the northwest on Saturday. There is a chance that seeing could dip toward 0.35-0.4 arcseconds once the ridge starts to settle in to the north of the Islands, provided summit-level winds don't increase too much late in the weekend and for the early part of next week.
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 Sep 17 - 2 PM0-20Clear0 / 010E/0-10NaN1.25-1.75
8 PM10-309.5-100 / 05ENE/0-100.45-0.551.25-1.75
Thu Sep 18 - 2 AM10-309.5-100 / 04.5ENE/0-100.45-0.551.25-1.75
2 PM0-209.5-100 / 09.5WSW/0-10NaN1.5-2.5
8 PM0-10Clear0 / 04.5WSW/0-100.4-0.52-3
Fri Sep 19 - 2 AM0-10Clear0 / 04WSW/5-150.4-0.52-3
2 PM0-20Clear0 / 09WSW/5-15NaN2-3
8 PM0-209.5-100 / 04WNW/0-100.5-0.61.75-2.25
Sat Sep 20 - 2 AM0-209.5-100 / 03.5SW/0-100.5-0.71.5-2
2 PM0-20Clear0 / 09W/5-15NaN1.5-2
Sun Sep 21 - 2 AM0-5Clear0 / 03.5W/0-100.4-0.61.5-2
2 PM0-20Clear0 / 09SW/0-10NaN1.5-2
Mon Sep 22 - 2 AM0-5Clear0 / 04NE/5-150.35-0.551.25-1.75
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 Sep 17 - Thu Sep 18 18:31 19:36 4:57 6:01 1:32 N/A 28 7 32.5 16 08
Thu Sep 18 - Fri Sep 19 18:30 19:35 4:57 6:01 2:21 N/A 20 8 20.5 14 01
Fri Sep 19 - Sat Sep 20 18:29 19:34 4:57 6:02 3:10 N/A 13 9 07.2 11 19
Sat Sep 20 - Sun Sep 21 18:29 19:33 4:57 6:02 3:59 N/A 7 9 53.0 8 10
Sun Sep 21 - Mon Sep 22 18:28 19:32 4:58 6:02 4:48 17:00 3 10 38.1 4 41
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 17 September (0300 UTC Thursday 18 September) 2014.
Additional Information
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