Current Conditions
Temp0.4 C
RH62 %
WindNW 41 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Wednesday 27 May (0300 UTC Thursday 28 May) 2015
Warning(s)
Chance for fog/high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a growing risk for fog and high humidity as the night progresses; precipitation is unlikely and skies will remain predominately clear.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1 C tomorrow morning. Winds will be from the west at 20-35 mph, with seeing around 0.8 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
Discussion
The tradewind inversion will remain rather weak near 10-12 thousand feet as pockets of low-level slightly unstable clouds continue to develop over and particularly to the east of the Big Island likely through most of the forecast period (there is a possibility the inversion will strengthen some on Friday). As a result, there is a moderate risk for periods of fog and high humidity during this time; precipitation is unlikely. Extensive afternoon clouds are possible throughout the forecast period.

Skies overhead will remain predominately clear of organized clouds throughout the forecast period. However, there is a possibility for patches of summit-level clouds in the area (especially to the east) and/or mid-level clouds passing along the northern skies over the next 2 nights. More patches of mid-level clouds may start to litter the western skies late in the weekend.

Precipitable water is expected to linger near or exceed 4 mm through the next 5 nights.

Boundary and/or mid-level turbulence will likely contribute to poor seeing through the next 3 nights. Low-level winds are slated to taper a bit, which should allow for some minor improvement in seeing for Saturday and Sunday night.

Little change since the morning forecast....A persistent low roughly 1500 KM to the NNE will keep the mid-level ridge displaced to the west of the state probably into the early part of next week. Although the low will hardly affect the stability of the atmosphere, it associated stationary front is expected to enhance the low-level cloud field near the Big Island throughout most of the forecast period. This coupled with the absence of a prominent ridge may help weaken the inversion, which could allow for periods of fog and high humidity at the summit over the next 5 nights. Westerly flow along southern fringe of the low will also stir up boundary-layer turbulence and likely contribute to poor seeing throughout most of the forecast period. There is a chance that winds will weaken a tad, which could allow for a minor improvement in seeing as the low subtly lifts northward over the weekend. While skies overhead are expected to remain predominately clear of organized high clouds, the low will constantly pull mid-level moisture from the tropics over the summit area, which will result in high PW probably well into next week. Global models do expect the low to weaken and shift eastward late in the weekend, but leave its parent trough in the area into middle/late part of next week. Although this could help to stabilize the low-level cloud field, it may not allow the mid-level air mass to dry out or seeing to dramatically improve anytime soon.
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 May 27 - 8 PM0-20Clear40 / 52WSW/20-350.6-14-6
Thu May 28 - 2 AM0-20Clear50 / 51WSW/20-350.6-14-6
2 PM40-604-560 / 156W/20-35NaN4-8
8 PM0-20Clear50 / 51W/20-350.7-1.14-6
Fri May 29 - 2 AM0-20Clear40 / 50.5W/20-350.7-1.14-6
2 PM20-404-4.540 / 106W/20-35NaN4-8
8 PM0-10Clear25 / 51W/15-300.7-1.14-6
Sat May 30 - 2 AM0-10Clear25 / 50.5W/15-300.6-14-6
2 PM20-404-550 / 106.5WSW/10-20NaN4-8
Sun May 31 - 2 AM0-10Clear60 / 101.5WSW/10-200.5-0.84-6
2 PM60-804-575 / 156.5WSW/10-20NaN4-8
Mon Jun 01 - 2 AM0-20Clear50 / 51.5W/10-200.5-0.84-6
2 PM60-804-560 / 107NW/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
Wed May 27 - Thu May 28 19:05 20:18 4:21 5:33 N/A 2:30 74 12 19.2 -2 56
Thu May 28 - Fri May 29 19:06 20:18 4:20 5:33 N/A 3:08 82 13 05.5 -6 40
Fri May 29 - Sat May 30 19:06 20:19 4:20 5:33 N/A 3:47 89 13 53.3 -10 12
Sat May 30 - Sun May 31 19:06 20:19 4:20 5:33 N/A 4:30 94 14 43.0 -13 23
Sun May 31 - Mon Jun 01 19:07 20:20 4:20 5:33 17:19 5:15 98 15 35.1 -16 01
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 28 May 2015.
Additional Information
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