Current Conditions
Temp8.2 C
RH27 %
WindE 12 mph
RoadClosed
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Thursday 17 October 2019
Warning(s)
Small chances for high relative humidity during the first half of the night
Cloud Cover and Fog/Precipitation Forecast
Summit skies will be mostly clear, dry and stable throughout tonight.
Summary of Key Meteorological Variables
Summit temperatures will be near 8.5 C this afternoon, 3.5 C this evening and 3 C tonight; winds will be from the ENE at 0-10/15 mph through the night. Seeing will be average in the 0.55-0.65 arcseconds range, while precipitable water is expected to linger close to 2 mm.
Discussion
The latest sounding shows a strenghtening tradewind inversion at 9-10 thousand feet which should ensure the summit to remain mostly dry and stable through today and tonight. There is a small chance that a residual patch of mid/low-level moisture might crowl over the mountain slopes later today possibly rising the chances for increased relative humidity, during the first half of tonight, but the air masses would quickly dry out afterward. The inversion is expected to weaken again and lift from Saturday and through early Monday, as a shallow front will pass North of the archipelago. Increased relative humidity and possibly fog are therefore likely during this time. The airmasses will stabilize afterward.

Summit skies will be clear/open tonight and tomorrow night, but light high clouds may occasionally spread in from the west and pass mainly along the northern skies on Friday night. More high clouds may spread in from the south during the latter night and may contribute to brief periods of extensive cloud cover for the following 2 nights.

Precipitable water will linger close to 2 mm tonight. It will decreease further and be close to 1.5 mm on Friday night, to then decrease exceeding the 4 mm range on the weekend nights. It will decrease some and range between 2 and 3 mm on Monday night.

Observing conditions will be average to good tonight and tomorrow night as relatively calm skies prevail at and above the summit. Another round of low-level moisture is likely to degrade and/or contribute to some variability in seeing during the weekend nights with an improvement expected on Monday night instead.

As the mid/upper-level low that is interesting the Central Pacific Area is shifting westaward, the air masses over the Big Island are quickly drying out and stabilizing and the mid-level ridge is strenghtening to the north of the state. Therefore, with a stronger inversion in place, the summit is expected to remain dry and stable through Friday night. Meanwhile, a shallow front approaching from the northwest, is expected to advect some tropical moisture from the south from early Saturday and through the weekend, increasing moisture and instability and rising the chances for fog/high relative humidity during the weekend nights. Also some high clouds, advected over by this system, might interfere with observations then. As the front lifts away from the area, the airmasses will dry and stabilize once again at the beginning of the coming working 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)
Thu Oct 17 - 2 PM20-403.5-4.520 / 08.5E/5-15NaN2.5-3.5
8 PM0-20Clear50 / 03.5ENE/0-100.5-0.91.75-2.25
Fri Oct 18 - 2 AM0-20Clear0 / 03ENE/5-150.4-0.71.75-2.25
2 PM20-403.5-4.50 / 09SE/5-15NaN1.5-2.5
8 PM10-307-80 / 04ENE/5-150.5-0.81.5-2
Sat Oct 19 - 2 AM20-407-80 / 03.5E/5-150.4-0.71.25-1.75
2 PM40-603.5-4.50 / 08S/5-15NaN1.5-2.5
8 PM60-803-530 / 03SW/5-150.6-13-4
Sun Oct 20 - 2 AM60-803-580 / 202W/5-150.6-14-6
2 PM60-803-690 / 307.5NW/5-15NaN4-6
Mon Oct 21 - 2 AM30-503-590 / 302.5NW/5-150.5-0.94-6
2 PM20-303.5-4.520 / 08E/5-15NaN2-3
Tue Oct 22 - 2 AM0-20Clear0 / 03ENE/5-150.4-0.82-3
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
Thu Oct 17 - Fri Oct 18 18:06 19:10 5:04 6:09 20:52 N/A 80 5 06.1 20 33
Fri Oct 18 - Sat Oct 19 18:05 19:10 5:04 6:09 21:42 N/A 71 6 01.9 22 14
Sat Oct 19 - Sun Oct 20 18:04 19:09 5:05 6:09 22:36 N/A 61 6 59.6 22 42
Sun Oct 20 - Mon Oct 21 18:04 19:08 5:05 6:10 23:34 N/A 50 7 58.3 21 50
Mon Oct 21 - Tue Oct 22 18:03 19:08 5:05 6:10 0:35 N/A 39 8 56.8 19 38
Forecast Issued by: Tiziana Cherubini
Next update at 5 PM HST Thursday 17 October (0300 UTC Friday 18 October) 2019.
Additional Information
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This message is also available at the MKWC road conditions page.
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