Current Conditions
Temp7.0 C
RH20 %
WindSE 19 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 28 July (0300 UTC Wednesday 29 July) 2015
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but broken high clouds will continue to move in from the south, contributing to extensive cloud cover through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C, with light NE winds and seeing around 0.4-0.5 arcseconds. Precipitable water is expected to exceed 4 mm for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure a dry and stable summit-level air mass through at least Friday night. There is a possibility that a patch of tropical moisture will move into the area, weaken the inversion and thus increase the risk for fog and light rain at the summit for Saturday night. Daytime clouds will be minimal and short-lived through Friday, but may pick up over the weekend.

Broken cirrus will continue to move in from the south and contribute to periods of extensive cloud cover through early tomorrow evening. These clouds are slated to shift off toward the NW through tomorrow night, leaving only residual slow-moving very thin high clouds over/near the Big Island through Friday night. There is a possibility for summit-level clouds building in the area and/or mid-level clouds filling in from the east for Saturday night.

Precipitable water is expected to linger near or exceed 4 mm likely through early Thursday evening, but may drift toward 3 mm for much of Friday, then increase back toward 4+ mm for Saturday night.

Relatively calm flow will prevail at and above the summit, which will allow for good/excellent seeing for tonight and early tomorrow evening. Despite strengthening upper-level turbulence, there is a chance that minor boundary layer turbulence will briefly disrupt seeing for the second half of tomorrow night and for Thursday night. While seeing is slated to greatly improve (toward 0.3-0.4 arcseconds) as summit-level winds taper for Friday night, there is a possibility that a pocket of mid/low-level turbulence will fill in from the east and degrade seeing for Saturday night.

Not much change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state likely through the week, while an upper-level ridge filling in from the SE over the next 24-36 hours eventually settles in over the Big Island probably through the weekend. Deep subsidence associated with the ridge will help maintain a fairly well-defined tradwind inversion and ensure a dry and stable summit-level air mass through at least Friday night. However, there is a possibility that the remnant moisture/instability associated with Tropical Depression 08E out to the east will ride in with the low-level trades and erode the inversion late Saturday night. This could increase the risk for fog and light rain at the summit for the second half of the weekend. At any rate, the building upper-level ridge will continue to bring broken high clouds up its western flank and over the summit area for the next 24-36 hours. These clouds will shift off toward the NW through tomorrow night, but residual slow-moving thin high clouds embedded in the upper-level ridge may linger over the Big Island through Friday night. The extra subsidence associated with the upper-level ridge should also keep flow at and above the summit relatively calm and allow for good/excellent seeing through tomorrow evening and especially for Friday night. However, latest model runs suggest that summit-level winds will pick up, which could stir up minor boundary layer turbulence between midnight tomorrow and early Friday 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)
Tue Jul 28 - 8 PM80-1008-100 / 03.5N/0-100.4-0.54-6
Wed Jul 29 - 2 AM80-1008-90 / 03.5NE/0-100.35-0.454-6
2 PM40-608-100 / 09NE/5-15NaN4-6
8 PM20-409.5-100 / 04NE/10-200.4-0.54-6
Thu Jul 30 - 2 AM0-209.5-100 / 04NE/10-200.45-0.654-5
2 PM0-209.5-100 / 010NE/10-20NaN3-5
8 PM10-309.5-100 / 05NE/15-250.5-0.73-4
Fri Jul 31 - 2 AM0-209.5-100 / 05NE/10-200.45-0.652.5-3.5
2 PM0-209.5-100 / 011NE/10-20NaN2-4
Sat Aug 01 - 2 AM0-209.5-100 / 05.5ENE/5-150.25-0.453-4
2 PM60-804-560 / 207ENE/5-15NaN3-6
Sun Aug 02 - 2 AM20-404-560 / 204.5ENE/0-100.5-14-6
2 PM0-204-640 / 158NW/10-20NaN4-8
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
Tue Jul 28 - Wed Jul 29 19:10 20:20 4:36 5:47 N/A 4:24 94 18 35.4 -18 40
Wed Jul 29 - Thu Jul 30 19:09 20:20 4:37 5:47 17:29 5:24 98 19 35.3 -17 22
Thu Jul 30 - Fri Jul 31 19:09 20:19 4:38 5:48 18:23 6:25 100 20 35.6 -14 55
Fri Jul 31 - Sat Aug 01 19:08 20:19 4:38 5:48 19:15 N/A 99 21 35.3 -11 30
Sat Aug 01 - Sun Aug 02 19:08 20:18 4:39 5:49 20:05 N/A 94 22 33.9 -7 20
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 29 July 2015.
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