Current Conditions
Temp3.1 C
RH8 %
WindESE 18 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Wednesday 23 April (0300 UTC Thursday 24 April) 2014
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for lingering patches of mid-level clouds in the area mainly for this evening and thin cirrus may spread in from the SW just before sunrise.
Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this eveing and 0.5 C tomorrow morning. Winds will be from the east at 5-15 mph, with seeing around 0.4-0.5 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. Daytime clouds will be minimal and short-lived throughout the forecast period.

There is a possibility for lingering patches of mid-level clouds in the area mainly for this evening. More high clouds will start to stream in from the southwest around sunrise tomorrow increasing cloud cover through that night, and will probably blanket skies for Friday and Saturday night. This stream will start to shift eastward Sunday, which may help to open up skies to the west as that night progresses.

Precipitable water is expected to linger near 2-3 mm probably throughout the forecast period.

Relatively calm skies will likely allow for seeing near 0.4-0.5 arcseconds for tonight. However, increasing turbulence in the free atmosphere will likely degrade seeing over the next 48 hours, and will probably contribute to poorer than average seeing for Friday, Saturday and Sunday night.

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 through the week. This will easily maintain the tradewind inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Skies will continue to open up as the bulk of the mid-level clouds detrain into the surrounding atmosphere and/or shifts northward over the next 12 hours. However, the sub-tropical jet is expected to rapidly rebuild overhead and will start to transport high clouds out of the tropics and over the summit area around sunrise tomorrow. These clouds will gradually thicken and become more widespread over the following 24 hours, and will probably blanket skies for at least Friday and Saturday night. Free atmospheric turbulence associated with the jet will also contribute to poorer than average seeing through the weekend (better than average seeing will prevail for tonight and perhaps part of tomorrow night). The jet is slated to shift eastward as a trough digs in from the northwest late in the weekend. While this could help to open up skies through Sunday night, there is a possibility that moisture/instability associated with this trough could weaken the inversion early 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 Apr 23 - 8 PM0-206-70 / 01ENE/5-150.4-0.52.5-3.5
Thu Apr 24 - 2 AM0-209.5-100 / 00.5ENE/5-150.4-0.52.5-3.5
2 PM20-409-100 / 07ENE/5-15NaN2.5-3.5
8 PM40-608.5-100 / 02ENE/10-200.45-0.652-3
Fri Apr 25 - 2 AM60-808-100 / 02E/10-200.5-0.72-3
2 PM80-1008-100 / 07E/10-20NaN2.5-3.5
8 PM80-1008-100 / 02E/10-200.6-0.82.5-3.5
Sat Apr 26 - 2 AM80-1008-100 / 02ESE/10-200.65-0.852.5-3.5
2 PM80-1008-100 / 07E/5-15NaN2.5-3.5
Sun Apr 27 - 2 AM80-1008-100 / 02SE/5-150.6-0.92.5-3.5
2 PM80-1008-100 / 06W/5-15NaN2.5-3.5
Mon Apr 28 - 2 AM60-809-100 / 00WNW/5-150.6-12.5-3.5
2 PM40-609-100 / 06W/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 Apr 23 - Thu Apr 24 18:52 19:59 4:41 5:48 2:27 N/A 26 22 12.0 -6 58
Thu Apr 24 - Fri Apr 25 18:52 20:00 4:40 5:47 3:12 N/A 17 23 05.2 -2 33
Fri Apr 25 - Sat Apr 26 18:52 20:00 4:39 5:47 3:56 N/A 9 23 57.8 1 57
Sat Apr 26 - Sun Apr 27 18:53 20:01 4:38 5:46 4:40 N/A 4 0 50.0 6 16
Sun Apr 27 - Mon Apr 28 18:53 20:01 4:37 5:45 5:25 17:49 1 1 42.4 10 11
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 24 April 2014.
Additional Information
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