Current Conditions
Temp7.4 C
RH26 %
WindSE 10 mph
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Thursday 23 October 2014
Cloud Cover and Fog/Precipitation Forecast
There is a slight risk for fog and high humdity toward the end of the night; precipitation is not expected and skies will remain clear.
Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon, 3 C this evening and 2.5 C tomorrow morning. Winds will be from the NNE at 5-15 mph, with seeing around 0.5-0.55 arcseconds. Precipitable water is expected to be in the 0.7-0.9 mm range for the first half of the night and 0.9-1.4 mm range for the second half.
The tradewind inversion is expected to restrengthen through this evening, but may lift toward 12 thousand feet during the second half of the night and perhaps disappear all together for tomorrow night into early Saturday night. This will raise the stakes on fog, high humidtiy and perhaps light rain at the summit during that time. The inversion is slated to restrengthen again near 8 thousand feet by late Saturday night, which will ensure the summit remains dry and stable for the remainder of the forecast period. Daytime clouds will be minimal and short-lived for today, but could pick up on Friday and Saturday, only to taper again thereafter.

Skies will remain predominately clear of organized high clouds through at least the weekend. However, there is a possibility for summit-level clouds mainly for Friday night and light high clouds may pass over and especially along the northern skies for Monday night.

Precipitable water is expected to drop toward 0.8 mm for this evening, but may increase to 1+ mm for the second half of the night and exceed 4 mm for tomorrow night. It should settle back in near 1 mm for much of Saturday night and especially the following 2 nights.

Average to slightly better than average seeing will prevail as minimal turbulence persists in the atmosphere for most of tonight. There is a possibility that low-level turbulence will disrupt seeing mainly for tomorrow night, but seeing should settle in near 0.5-0.6 arcseconds as this turbulence subsides for Saturday, Sunday and Monday night.

Although the mid-level ridge will continue to sit to the north of the state and maintain some level of large-scale subsidence in the area throughout the forecast period, a patch of relatively unstable low-level clouds/moisture is expected to move in from the NE just before sunrise tomorrow, with another more organized cloud field following suit later tomorrow night. These patches are expected to lift/erode the inversion and could increase the chance for fog, high humidity and rain at the summit during those times. I suspect the first patch is a little overdone, but upper-level instability may increase around the arrival of the second one, which will likely result in a higher risk for moisture/clouds at the summit for Friday night. Regardless, these patches of moisture is slated to shift off toward the southwest while a deep upper-level ridge tries to fill in from the northwest over the weekend. The latter feature is expected to enhance the subsidence in the area, which will help rebuild the inversion and ensure the summit remains dry/stable, calm and relatively clear probably for the remainder of the forecast period (though there is a possibility for light cirrus along the ridges western flank late Monday 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)
Thu Oct 23 - 2 PM0-20Clear0 / 08NNE/5-15NaN0.8-1.2
8 PM0-5Clear5 / 03NE/5-150.45-0.550.7-0.9
Fri Oct 24 - 2 AM0-10Clear25 / 02.5NNE/5-150.45-0.550.9-1.4
2 PM40-604-550 / 56ENE/5-15NaN2-4
8 PM0-204-560 / 101ENE/10-200.55-0.954-6
Sat Oct 25 - 2 AM10-304-675 / 150.5ENE/10-200.6-14-8
2 PM40-604-560 / 156NE/10-20NaN4-8
8 PM0-20Clear15 / 01.5ENE/10-200.5-0.72-4
Sun Oct 26 - 2 AM0-5Clear0 / 01.5ENE/10-200.45-0.651-2
2 PM0-20Clear0 / 07ENE/10-20NaN1-2
Mon Oct 27 - 2 AM0-5Clear0 / 02.5E/5-150.4-0.61-1.5
2 PM0-20Clear0 / 07ENE/5-15NaN1-2
Tue Oct 28 - 2 AM10-309-100 / 02SE/5-150.4-0.61-1.5
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
Thu Oct 23 - Fri Oct 24 18:02 19:07 5:06 6:11 6:55 18:11 0 14 19.6 -12 24
Fri Oct 24 - Sat Oct 25 18:01 19:06 5:06 6:11 N/A 18:56 2 15 11.0 -15 11
Sat Oct 25 - Sun Oct 26 18:00 19:05 5:06 6:12 N/A 19:44 7 16 04.6 -17 15
Sun Oct 26 - Mon Oct 27 18:00 19:05 5:07 6:12 N/A 20:36 13 16 59.9 -18 26
Mon Oct 27 - Tue Oct 28 17:59 19:04 5:07 6:12 N/A 21:31 21 17 56.6 -18 37
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 23 October (0300 UTC Friday 24 October) 2014.
Additional Information
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