Current Conditions
Temp1.8 C
RH13 %
WindW 17 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Monday 25 March 2019
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4.5 C this afternoon, -1 C this evening and -1.5 C tomorrow morning. Winds will be from the WNW at 10-20 mph, with seeing near 0.7-0.8 arcseconds. Precipitable water is expected to be in the 0.8-1 mm range for the night.
Discussion
A fairly well-defined inversion near 8 thousand feet, combined with a dry/stable air mass surrounding the area will ensure the summit steers free of fog and precipitation through at least Tuesday night. There is a possibility that minor instability will weaken the inversion and increase the risk for fog, ice and high humidity for the following 3 nights; precipitation is unlikely. Daytime clouds will be minimal and short-lived through Tuesday, but could pick up on Wednesday, Thursday and Friday.

Skies will remain predominately clear throughout the forecast period.

Precipitable water is expected to dip below 1 mm for tonight, increase toward 2 mm for tomorrow night and probably 3-4 mm for Wednesday night, slip toward 1.5 mm for Thursday night, then increase to 3-4 mm again for the following night.

Steady moderate boundary layer turbulence will prevail, contributing to poorer than average seeing probably throughout the forecast period. There is a possibility that instability and/or an increase in free atmospheric turbulence will further degrade seeing after tonight, Wednesday night in particular.

The eastern tip of a mid-level ridge will linger over the state, with a weak low-level ridge prevailing to the north, providing relatively steady large-scale subsidence in the area for the next 48 hours. This subsidence will help maintain a well-defined inversion near 8 thousand feet and ensure a dry/stable summit-level air mass over the next 2 nights. Unfortunately, a rather large trough to the NE will likely keep winds near 20 mph, which will stir up boundary layer turbulence and contribute to poor seeing during this time. In addition, a short-wave trough is expected to dig in from the north, which will help expand the large-scale trough westward and in the process decay and shift the low-level and mid-level ridge, respectively beginning Wednesday. While this could help destabilize the air mass and thus weaken the inversion by early that evening, the bulk of the moisture will pass to the north of the state over the next several days. Nonetheless, the decay of the inversion may allow for periods of fog, ice and high humidity at the summit until the large-scale trough retracts eastward, which unfortunately may not occur until late in the weekend. Summit-level winds are also not expected to subside during this time, and relatively strong flow aloft associated with the westerly jet could increase turbulence in the free atmosphere beyond tonight. This, combined with the instability may further degrade seeing, especially for Wednesday 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)
Mon Mar 25 - 2 PM0-20Clear0 / 04.5WNW/10-20NaN1-1.5
8 PM0-5Clear0 / 0-1WNW/10-200.6-0.90.8-1
Tue Mar 26 - 2 AM0-5Clear0 / 0-1.5NW/10-200.6-0.90.8-1
2 PM0-20Clear0 / 04WNW/10-20NaN1-2
8 PM0-5Clear0 / 0-1.5W/10-200.6-0.91.75-2.25
Wed Mar 27 - 2 AM0-5Clear0 / 0-2W/15-300.6-11.75-2.25
2 PM0-204-560 / 153W/15-30NaN3-6
8 PM0-5Clear60 / 10-3WNW/15-300.6-13-4
Thu Mar 28 - 2 AM0-5Clear50 / 10-3WNW/15-300.7-1.12.5-3.5
2 PM0-204-4.540 / 103.5NE/10-20NaN2-4
Fri Mar 29 - 2 AM0-5Clear30 / 5-1.5SW/15-300.6-11-2
2 PM0-204-550 / 102.5SW/15-30NaN3-6
Sat Mar 30 - 2 AM0-5Clear60 / 10-2.5WSW/15-300.6-1.13-4
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
Mon Mar 25 - Tue Mar 26 18:43 19:48 5:07 6:12 23:24 N/A 67 17 01.0 -19 51
Tue Mar 26 - Wed Mar 27 18:43 19:48 5:06 6:11 0:18 N/A 57 17 54.6 -21 30
Wed Mar 27 - Thu Mar 28 18:44 19:48 5:06 6:10 1:10 N/A 47 18 47.5 -22 05
Thu Mar 28 - Fri Mar 29 18:44 19:49 5:05 6:09 1:59 N/A 37 19 39.2 -21 38
Fri Mar 29 - Sat Mar 30 18:44 19:49 5:04 6:08 2:44 N/A 29 20 29.4 -20 14
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Monday 25 March (0300 UTC Tuesday 26 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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