Current Conditions
Temp4.1 C
RH5 %
WindSW 10 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 19 March (0300 UTC Wednesday 20 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 3.5 C this evening and tomorrow morning. Winds will be decreasing through today and will be from the NW at 10-20 mph tonight. Seeing will be average/good somewhat improving through the night. Precipitable water will range between 0.7 and 1.1 mm.
Discussion
A strong tradewind inversion is well established between 5 and 7 thousand feet. The inversion is projected to remain in place for at least the next 3/4 days, while it is expected to lift and weaken some, but remaining below summit level, from late Friday and through Saturday. Nevertheless the summit will be dry and stable throughout most of this forecast period with moisture increasing some on Saturday and Sunday. The bulk of the moisture will remain below warning levels. Daytime clouds might become an issue from Friday and onward.

The summit skies will be predominantly clear through the next three days/nights. Some thin high clouds will be visible along the NW horizon on Friday. They will approach on Friday and partially obscure the summit on Saturday nigth and Sunday.

Precipitable water will be in the 0.7-1.1 mm range tonight through Thursday nigth. It is projected to increase some on Friday (1 to 2 mm) and further on Saturday, possibly reaching the 4 mm threshold by Sunday .

Observing conditions will be average to good tonight, with seeing dropping below 0.6 arcsec, as winds at the surface taper. Variability in the free atmosphere might be possible. Similar conditions are expected on Wednesday night, while seeing is projected to gradually degrade from Thursday as more free atmospheric turbulence due to the sub-tropical jet developing over the islands is expected.

Not changes since the morning forecast... The large scale subsidence promoted by ridging north of the State is resulting in stable and very dry airmasses around the summit. Nevertheless the ridge is projected to weaken and shift eastward as an upper level trough and the associated front approaches from the NW on Wednesday. Winds at the summit are expected to weaken from now and through the rest of this forecast period, and observing condtions to improve because of a weaker ground layer for at least the next two nights. More variability and a larger contribution from the free atmosphere is to be accounted for on Wednesday and Thursday as the trough sweeps eastweard and the sub-tropical jet develops overhead. Moreover, some high clouds will start approaching and moisture will increase on Friday as the front nears the islands. Although the front is not expected to largely impact the weather at the summit, summit skies might be partially obscured over the weekend and moisture might increase enough that PW reaches the 4 mm threshold then.
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 Mar 19 - 8 PM0-10Clear0 / 03.5NW/15-250.4-0.80.9-1.3
Wed Mar 20 - 2 AM0-10Clear0 / 03.5NW/10-200.3-0.70.7-1.1
2 PM0-20Clear0 / 09NNW/10-20NaN1-1.5
8 PM0-10Clear0 / 04N/10-200.35-0.750.9-1.3
Thu Mar 21 - 2 AM0-10Clear0 / 03.5NNE/5-150.3-0.70.7-1.1
2 PM0-20Clear0 / 010ESE/0-10NaN0.9-1.3
8 PM0-10Clear0 / 04.5S/0-100.4-0.80.8-1.2
Fri Mar 22 - 2 AM0-10Clear0 / 03.5SSW/0-100.4-0.80.7-1.1
2 PM0-207.5-80 / 07SW/0-10NaN1-2
Sat Mar 23 - 2 AM10-307-80 / 02.5WNW/5-150.5-0.91-2
2 PM20-407-80 / 06WNW/5-15NaN1-2
Sun Mar 24 - 2 AM20-406-80 / 01NW/5-150.6-11.5-2.5
2 PM30-506-80 / 05WNW/10-20NaN4-6
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 Mar 19 - Wed Mar 20 18:42 19:46 5:13 6:17 17:26 6:34 99 11 31.0 7 28
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
Forecast Issued by: Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Wednesday 20 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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