Current Conditions
Temp3.1 C
RH20 %
WindN 2 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Tuesday 21 October (0300 UTC Wednesday 22 October) 2014
Warning(s)
Fog/high humidity
Chance for rain and convection
Cloud Cover and Fog/Precipitation Forecast
There is a high risk for fog, high humidity and light rain at the summit, particularly as the night progresses. Thick clouds may also develop over and/or drift in from the northeast through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1.5 C tomorrow morning. Winds will be from the north at 5-15 mph, while seeing will likely be near 0.8-0.9 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
Discussion
The atmosphere is expected to become increasing unstable and saturated through the night, then dry out as the inversion rebuilds near 7 thousand feet through tomorrow night. As a result, there is high risk for fog, high humidity and light rain at the summit as well as isolated convection in the area for tonight and mainly tomorrow evening. Dry/stable conditions will return to the summit likely as early as Thursday morning and especially thatnight, but there is a possibility that the inversion will briefly breakdown and increase the risk for fog, rain and high humidity at the summit for Friday night. The inversion is slated to strengthen near 5-6 thousand feet late Saturday morning, ensuring a dry/stable air mass for that night. Extensive daytime clouds are possible for tomorrow, but will taper for Thursday, pick up again on Friday and Saturday, then become minimal and short-lived for Sunday.

There is a possibility that thick clouds will develop over and/or drift in from the northeast, contributing to extensive cloud cover as the night progresses. These clouds are slated to dissipate and shift off toward the southwest through tomorrow, allowing skies to clear by early Thursday morning. Predominately clear skies will likely prevail for the remainder of the forecast period, though there is a possibility for summit-level clouds for Friday night.

Precipitable water is expected to exceed 4 mm for tonight and perhaps tomorrow evening, then abruptly drop toward 1 mm early Thursday morning. There is a good chance it will slip below 1 mm for Thursday night, but could become more variable and increase to 1-2 mm for Friday night. PW should settle back in near 0.8-1 mm again for Saturday night.

Increasing upper-level turbulence and instability will likely contribute to poor seeing for tonight and early tomorrow evening. Seeing is expected to improve toward slightly better than average values for the second half of tomorrow night and Thursday night, but may deteriorate again in response to low-level turbulence for Friday night. More average-like seeing should return as this source of turbulence subsides for Saturday night.

Little change since the morning forecast...A residual band of moisture from a combination of dissipating Hurricane Ana and an old cold front is expected to pass through the Big Island area between early this evening and early tomorrow evening. This band is slated to breakdown the inversion, saturate the atmosphere and likely result in high humidity, fog and light rain at the summit during that time. There is also an outside chance for isolated convection mainly near sunrise tomorrow. This band is expected to shift off toward the southwest through tomorrow night, allowing the ridge to the north to regain control of the air mass, rebuild the inversion near 6-7 thousand feet and ensure a dry and stable air mass for at least Thursday night. However, another patch of low-level moisture is slated to fill into the area as an upper-level trough to the east shifts over/near the Big Island around Friday night. This patch may lift the inversion toward 13-14 thousand feet and increase the risk for moisture at the summit for that night. The trough and patch of moisture is expected to shift off toward the east and southwest, respectively, allowing very dry/stable conditions to return to the summit for the remainder of 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 Oct 21 - 8 PM20-404-560 / 152N/5-150.6-14-6
Wed Oct 22 - 2 AM60-804-990 / 501.5N/5-150.7-1.14-8
2 PM60-804-675 / 156NE/5-15NaN4-8
8 PM20-405-640 / 52NE/5-150.5-0.82-4
Thu Oct 23 - 2 AM0-20Clear10 / 02N/5-150.4-0.61-2
2 PM0-20Clear0 / 08NE/5-15NaN0.8-1.2
8 PM0-10Clear0 / 03ENE/10-200.45-0.550.8-1
Fri Oct 24 - 2 AM0-10Clear0 / 02.5ENE/10-200.45-0.550.8-1
2 PM40-604-525 / 57ENE/10-20NaN1-2
Sat Oct 25 - 2 AM0-204-4.560 / 150.5E/10-200.5-0.91-2
2 PM0-20Clear0 / 06E/10-20NaN2-4
Sun Oct 26 - 2 AM0-10Clear0 / 02ENE/10-200.4-0.71-2
2 PM0-20Clear0 / 08ENE/10-20NaN1-2
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 Oct 21 - Wed Oct 22 18:03 19:08 5:05 6:10 5:10 16:50 2 12 42.6 -5 29
Wed Oct 22 - Thu Oct 23 18:02 19:07 5:06 6:10 6:02 17:30 0 13 30.2 -9 07
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
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 22 October 2014.
Additional Information
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