Current Conditions
Temp4.8 C
RH4 %
WindW 4 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Wednesday 20 March (0300 UTC Thursday 21 March) 2019
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will be dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4.5 C this evening and 4 C tomorrow morning. Winds will be from the NNW at 5-15 mph. Seeing will be average/good (0.45-0.6) through the night. Precipitable water will range between 0.6 and 1 mm.
Discussion
A strong tradewind inversion will continue to ensure a dry and stable environment for at least the next 3 days. The inversion is projected to lift and weaken starting on Saturday and possibly reach summit level on Sunday, allowing some moisture to slip up the summit then. It will rebuild through Monday. Daytime clouds might become on issue over the weekend days.

Summit skies will be predominantly clear through the next three days. High clouds will be visible along the northern horizon from late Friday and will near during the weekend. The bulk of them should remain North of the Big Island and summit skies will only be partially obscured on Saturday and Sunday night. Clearing will follow at the beginning of the coming week.

Precipitable water will continue to linger close or below 1mm for at least the next three days. It will range between 0.6 and 1 tonight and Thurday night. It will be in the 0.8 to 1.2 mm range on Friday night and will start increasing afterward, lingering close to 1.5 on Saturday night and 3 mm on Sunday night.

Observing conditions will be rather good tonight and tomorrow morning as winds at the summit are weak. Only a small contribution is expected from the free atmosphere tonight and Thursday nigth. Some more variability and a larger contribution from the free atsmophere is likely on Friday and more so on Saturday and Sunday night as the Sub-Tropical Jet strenghtens overhead and shear aloft substantially increases.

No changes since the morning forecast... the high pressure northeast of the State combined with ridging aloft continue to promote very dry conditions and large scale subsidence in the area. As a result the tradewind inversion is well established below summit level, ensuring optimal conditions for operations for at least the next 2/3 nights. The high pressure system is expected to shift more eastward through today while an upper level trough and its associated front are also moving eastward. As a result, aloft, the westerly jet will split and a sub-tropical jet will form and strengthen overhead from Friday and onward, increasing shear in the free atmosphere. At the lower levels, the frontal system is expected to reach the northern portion of the State by Saturday but it is projected to not affect the summit weather too much if not for an increase in PW through the weekend, longer lived daytime clouds, a higher inversion and some high clouds partially obscuring the summit skies then. The front will quickly move easteward by early Monday morning.
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 Mar 20 - 8 PM0-10Clear0 / 04.5NNW/5-150.4-0.70.8-1.2
Thu Mar 21 - 2 AM0-10Clear0 / 04NNW/5-150.35-0.650.6-1
2 PM0-20Clear0 / 010.5SW/0-10NaN1-1.5
8 PM0-10Clear0 / 04WNW/0-100.4-0.70.8-1.2
Fri Mar 22 - 2 AM0-10Clear0 / 04N/0-100.4-0.70.6-1
2 PM0-20Clear0 / 08.5N/5-15NaN1-1.5
8 PM0-10Clear0 / 03.5NW/0-100.4-0.80.9-1.3
Sat Mar 23 - 2 AM0-20Clear0 / 03WNW/0-100.45-0.850.8-1.2
2 PM10-307.5-80 / 07SSW/0-10NaN1-2
Sun Mar 24 - 2 AM20-407-80 / 02NNW/0-100.6-11-2
2 PM30-506-80 / 05NE/0-10NaN1.5-2.5
Mon Mar 25 - 2 AM20-406-80 / 00SW/5-100.6-11.5-2.5
2 PM10-307-80 / 06WNW/5-10NaN2-3
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 Mar 20 - Thu Mar 21 18:42 19:46 5:12 6:16 18:29 N/A 100 12 28.1 1 57
Thu Mar 21 - Fri Mar 22 18:42 19:46 5:11 6:15 19:31 N/A 97 13 23.7 -3 36
Fri Mar 22 - Sat Mar 23 18:42 19:47 5:10 6:15 20:31 N/A 92 14 18.5 -8 49
Sat Mar 23 - Sun Mar 24 18:43 19:47 5:09 6:14 21:30 N/A 85 15 12.9 -13 24
Sun Mar 24 - Mon Mar 25 18:43 19:47 5:08 6:13 22:28 N/A 76 16 07.0 -17 07
Forecast Issued by: Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Thursday 21 March 2019.
Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
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