Current Conditions
Temp1.4 C
RH4 %
WindE 26 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Wednesday 16 April (0300 UTC Thursday 17 April) 2014
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but banding high clouds to the southeast will continue to creep over the summit area, contributing to extensive cloud cover as the night progresses.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C, with winds from the east at 15-25 mph and seeing around 0.7-0.8 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 9 thousand feet and keep the summit-level air mass dry and stable through at least Friday night. While the inversion will remain in tact through the weekend, mid-level moisture is expected to fill into the area, which could increase summit-level humidity toward 60-80% and perhaps the risk for fog, ice and light flurries at the summit for Saturday and Sunday night. Daytime clouds will be minimal and short-lived through Friday, but could pick up over the weekend and into next week.

Banding high clouds to the southeast will continue to creep over the summit area, blanketing skies to the east for much of tonight. These clouds will eventuall shift over the summit around sunrise, blanketing skies for at least Thursday and Friday night. There is a chance that these clouds will start to shift eastward and breakdown on Saturday, but patchy mid-level clouds may also build in the area, contributing to extensive cloud cover for Saturday night and probably most of Sunday night.

Precipitable water is expected to linger near 0.8-1 mm for tonight, increase to 2-3 mm for the next 2 nights, and likely 4+ mm for Saturday and Sunday night.

A mixture of minor boundar layer turbulence, low-level turbulence and/or free atmospheric turbulence will contribute to poor seeing probably throughout the forecast period.

Little change since the morning forecast....The 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. Although this will help maintain a well-defined tradewind inversion at or below 9 thousand feet during this time, it won't ensure a dry/stable air mass over the weekend. The sub-tropical jet is slated to drift in from the SE as the tropical upper-tropospheric trough (TUTT) and develops over the state during the next few days. Initially the TUTT and STJ will bring lots of high clouds into the area, which will likely contribute to extensive cloud cover for tonight and probably blanket skies for Thursday and Friday night. However, there is a chance that the TUTT/STJ will pull up mid-level moisture from the south and could raise humidity toward 60-80% as well as the stakes on fog/ice and light flurries over the weekend. I suspect humidity will linger just below the 80% threshold through most of that time, but I still increased the risk for fog/ice and light flurries at the summit for Saturday and Sunday night. A mixture of turbulence through several layers in the atmosphere (including the boundary layer) will also contribute to poorer than average seeing probably throughout the forecast period.
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 Apr 16 - 8 PM30-509-100 / 02ENE/15-250.6-0.90.8-1
Thu Apr 17 - 2 AM50-708.5-100 / 02ESE/15-250.6-0.90.8-1
2 PM80-1008-100 / 07.5E/10-20NaN1-2
8 PM80-1007-100 / 02.5E/10-200.7-12-3
Fri Apr 18 - 2 AM80-1007-100 / 02.5E/15-250.7-1.12-3
2 PM80-1007-100 / 07.5ESE/15-25NaN2-3
8 PM80-1007-100 / 02.5ESE/15-250.6-12.5-3.5
Sat Apr 19 - 2 AM80-1007.5-100 / 01.5ESE/15-250.6-12.5-3.5
2 PM80-1006-1025 / 205ESE/10-20NaN3-6
Sun Apr 20 - 2 AM60-805-1040 / 30-2ESE/15-250.6-1.14-6
2 PM60-804.5-840 / 303ESE/10-20NaN4-8
Mon Apr 21 - 2 AM40-605-725 / 15-2E/15-250.7-1.14-6
2 PM40-60Clear30 / 204E/15-25NaN4-8
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 Apr 16 - Thu Apr 17 18:49 19:56 4:47 5:53 20:13 N/A 95 15 28.0 -16 59
Thu Apr 17 - Fri Apr 18 18:50 19:56 4:46 5:53 21:11 N/A 89 16 26.0 -18 45
Fri Apr 18 - Sat Apr 19 18:50 19:57 4:45 5:52 22:09 N/A 80 17 25.2 -19 24
Sat Apr 19 - Sun Apr 20 18:50 19:57 4:44 5:51 23:06 N/A 71 18 24.8 -18 54
Sun Apr 20 - Mon Apr 21 18:51 19:58 4:43 5:50 0:01 N/A 60 19 23.8 -17 14
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 17 April 2014.
Additional Information
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