Current Conditions
Temp-0.2 C
RH95 %
WindENE 17 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 18 September (0300 UTC Tuesday 19 September) 2017
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for patches of high clouds filling in from the north through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this evening and 2 C tomorrow morning. Winds will be from the ENE at 15-30 mph for the first half of the night, increasing to 20-35 mph by the ending of the night. Seeing will be near 0.7-0.8 arcseconds, while precipitable water is expected to be in the 2-3 mm range for the night.
A well-defined tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure the summit remains dry and stable for tonight. There is a possibility that the inversion will briefly lift/weaken toward 10-12 thousand feet, which could raise the stakes on short-periods of fog and high humidity at the summit between for tomorrow night and early Wednesday night; precipitation is not expected. The inversion is set to recover again during the latter night, ensuring the summit steers free of moisture for the remainder of the forecast period. Daytime clouds will be minimal and short-lived for today, but could pick up for Tuesday and Wednesday, taper again for the following 2 days, then could pick up again over the weekend.

There is a possibility that patches of high clouds will move in from the north and west and pass through the summit area for tonight and tomorrow night, respectively. These clouds are set to shift eastward on Wednesday, leaving predominately clear skies overhead for the following 2 nights. However, there is a possiblity that banding high clouds will set up along the southern skies and could be visible from the summit, particularly during the latter night. This band may eventually drift northward, increasing cloud cover for Friday night.

Precipitable water is expected to linger near 2.5-3 mm for the next 2 nights, slip toward 2 mm for Wednesday night and perhaps 1-1.5 mm for Thursday night, then increase back to 2-3 mm for the following night.

Boundary layer turbulence induced by winds near 20-30 mph will contribute to poor seeing over the next 2 nights. While the boundary layer turbulence is set to taper thereafter, an increase in turbulence in the free atmosphere will only allow for a modest improvement in seeing (toward more average-like values) for the following 3 nights.

Not much change since the morning forecast....The mid/low-level ridge to the NE combined with a departing upper-level ridge to the SW will help promote steady/strong large-scale subsidence in the area, which will maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass for tonight. However, a mid-level low meandering just south of the Big Island is expected to send small patches of moisture toward the Big Island and disrupt the stability of the atmosphere a bit between early tomorrow afternoon and Wednesday evening. This could weaken/lift the inversion and combined with another increase in summit winds, may allow for short-periods of fog/high humidity at the summit during this period. The inversion is set to recover again as this moisture shifts westward with the easterly trades and the low dissipates thereafter. The tropical upper-tropospheric trough is expected to redevelop over the state, with an embedded rather broad quasi-stationary low forming to the NE during the second half of the week. Initially this low or the TUTT will not affect the stability of the atmosphere, but could bring an increase in free atmospheric turbulence as the sub-tropical jet sets up over the Big Island for Wednesday, Thursday and Friday night. However, there is a chance that the TUTT will sharpen and dig southwestward, which could destabilize the air mass over the weekend. This, coupled with an ample supply of moisture creeping in from the SE as the ridge decays to the north could bring wet condiitions to the summit over 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)
Mon Sep 18 - 8 PM0-209.5-100 / 03ENE/15-300.5-0.92-3
Tue Sep 19 - 2 AM10-309-100 / 02E/20-350.6-12-3
2 PM10-304-560 / 107.5E/15-30NaN3-6
8 PM10-309-1025 / 02E/15-300.55-0.952.5-3.5
Wed Sep 20 - 2 AM0-209.5-1040 / 01.5E/10-200.5-0.92-3
2 PM0-204-560 / 107.5NE/5-15NaN3-5
8 PM0-5Clear25 / 02.5NE/5-150.5-0.81.75-2.25
Thu Sep 21 - 2 AM0-5Clear0 / 02NE/0-100.5-0.71.75-2.25
2 PM0-20Clear0 / 07WSW/0-10NaN1-2
Fri Sep 22 - 2 AM0-209.5-100 / 01.5WNW/5-150.5-0.71-1.5
2 PM40-609-100 / 07.5W/5-15NaN1.5-2.5
Sat Sep 23 - 2 AM60-808.5-100 / 02W/5-150.5-0.82-3
2 PM70-904-1060 / 205W/5-15NaN4-8
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 Sep 18 - Tue Sep 19 18:30 19:35 4:57 6:01 5:35 17:49 1 11 13.9 6 43
Tue Sep 19 - Wed Sep 20 18:29 19:34 4:57 6:02 6:30 18:32 0 12 04.2 2 28
Wed Sep 20 - Thu Sep 21 18:28 19:33 4:57 6:02 N/A 19:13 2 12 53.2 -1 50
Thu Sep 21 - Fri Sep 22 18:27 19:32 4:58 6:02 N/A 19:52 5 13 41.2 -5 59
Fri Sep 22 - Sat Sep 23 18:26 19:31 4:58 6:02 N/A 20:32 10 14 28.9 -9 48
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 19 September 2017.
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.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products