Current Conditions
Temp9.0 C
RH12 %
WindENE 28 mph
RoadOpen
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Tuesday 09 February 2010
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 9 C this afternoon, 5 C this evening and 4 C tomorrow morning.Winds will be from the NE at 20-35 mph for today, but will likely take on a more easterly direction and taper to 10-20 mph by the end of the night.Precipitable water is expected to be in the 0.9-1.1 mm range, with seeing improving from around 0.6-0.7 arcseconds for the first half of the night to 0.5-0.6 arcseconds for the second half.
Discussion
The tradewind inversion will continue to cap the very limited supply of low-level moisture at or below 6 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will also be minimal and short-lived through this period.

Skies overhead will remain predominately clear throughout the forecast period. There is a slight chance that small patches of thin cirrus will pass through the area mainly during the daytime tomorrow.

Precipitable water is expected to linger near 1 mm for the next 2 nights, then slip toward 0.7-0.8 mm for Thursday, Friday and Saturday night.

Minor boundary layer turbulence may keep seeing near 0.7 arcseconds for this evening, but seeing is expected to improve toward 0.5 arcseconds as winds taper and relatively uniform northerly flow persists aloft for the remainder of the night. That will likely be short-lived as upper-level westerly flow will likely pick up through Wednesday, which will increase shear/turbulence in the free atmosphere a bit and probably degrade seeing toward 0.7 arcseconds probably for the remainder of the forecast period.

A tight deep ridge will begin to settle in over the Islands during the next 24 hours, then will eventually spread out across most of the Pacific as it lingers almost directly over the Big Island probably into next week. In the process, it will lose its upper-level portion of the ridge as the westerly jet sags closer to the Islands over the latter half of the week. Nevertheless, very strong large scale subsidence will prevail in the area and ensure the air mass remain clear, dry and stable throughout the forecast period. Seeing will initially benefit from the deep ridge and should slip toward 0.5 arcseconds for tonight. However, it will likely degrade toward 0.7 arcseconds as the westerly jet shifts overhead and increases shear/turbulence in the free atmosphere for the remainder of the week. PW, on the other hand, is expected to improve from 1 mm for the next 2 nights toward 0.7-0.8 mm once the ridge settles in directly over the Big Island for Thursday and 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 Feb 09 - 2 PM0-5Clear0 / 09NE/20-35NaN1-1.5
8 PM0-2Clear0 / 05ENE/15-250.45-0.850.9-1.1
Wed Feb 10 - 2 AM0-2Clear0 / 04E/10-200.4-0.70.9-1.1
2 PM0-209.5-100 / 08SSW/5-15NaN1-1.5
8 PM0-5Clear0 / 03WNW/5-150.5-0.81-1.5
Thu Feb 11 - 2 AM0-2Clear0 / 02NW/5-150.5-0.81-1.5
2 PM0-5Clear0 / 06.5WSW/10-20NaN1-1.5
8 PM0-2Clear0 / 01.5W/10-200.5-0.80.7-0.9
Fri Feb 12 - 2 AM0-2Clear0 / 01WNW/10-200.5-0.90.7-0.9
2 PM0-5Clear0 / 05NW/10-20NaN0.7-0.9
Sat Feb 13 - 2 AM0-2Clear0 / 00NW/10-200.5-0.90.7-0.9
2 PM0-5Clear0 / 04NNW/10-20NaN0.7-0.9
Sun Feb 14 - 2 AM0-2Clear0 / 0-1NW/10-200.5-10.7-0.9
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 Feb 09 - Wed Feb 10 18:28 19:33 5:39 6:44 4:26 N/A 11 18 52.6 -23 46
Wed Feb 10 - Thu Feb 11 18:28 19:34 5:38 6:44 5:09 N/A 6 19 42.1 -21 11
Thu Feb 11 - Fri Feb 12 18:29 19:34 5:38 6:43 5:48 16:49 3 20 29.5 -17 45
Fri Feb 12 - Sat Feb 13 18:29 19:34 5:38 6:43 6:24 17:40 0 21 14.9 -13 39
Sat Feb 13 - Sun Feb 14 18:30 19:35 5:37 6:42 6:58 18:29 0 21 58.7 -9 03
Forecast Issued by: Tiziana Cherubini
Next update at 5 PM HST Tuesday 09 February (0300 UTC Wednesday 10 February) 2010.
Additional Information
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