Current Conditions
Temp7.4 C
RH70 %
WindSE 13 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 26 August (0300 UTC Saturday 27 August) 2016
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while high clouds spread in from the south, perhaps contributing to periods of extensive cloud cover mainly for the second half of tonight.
Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C this evening and 3 C tomorrow morning. Winds will be from the NNE at 5-15 mph, with seeing around 0.45-0.5 arcseconds. Precipitable water is expected to be in the 1.75-2.25 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 6-7 thousand feet and ensure the summit remains dry and stable for at least tonight. There is a slight chance that upper-level instability will begin to enhance the low-level cloud flow, lifting the inversion toward 10-12 thousand feet and thus increasing the risk for periods of fog and high humidity at the summit for Saturday and Sunday night; precipitation is not expected. While the inversion is set to recover near 8 thousand feet as this instability dissipates, allowing ensuring dry conditions for at least Monday night, there is a chance that deep tropical moisture will spread into the area and increase the chance for fog/precipitation for the following night. Daytime clouds will be minimal and short-lived through tomorrow, but could pick up for Sunday, taper a bit on Monday, then perhaps turn extensive again on Tuesday and Wednesday.

Scattered high clouds are set to spread in from the south, perhaps contributing to periods of extensive cloud cover mainly for the second half of tonight. The bulk of these clouds will shift off toward the NE by early tomorrow evening, leaving residual high clouds filling out of the tropics and decaying along the southern skies for the remainder of the weekend and into Monday night. However, there is a possibility for thick clouds building in from the ESE for Tuesday night.

Precipitable water is expected to linger near 2 mm for tonight, trend toward 1 mm through tomorrow night, then increase to 2-3 mm for Sunday and Monday night and perhaps higher for Tuesday night.

Relatively calm skies should allow for better than average seeing for at least the next 2 nights (there is a chance for good/excellent seeing for tomorrow morning/evening). Building instability and pockets of turbulence may contribute to slightly poorer than average seeing for Sunday night, but seeing should improve again as this source of turbulence/instability dissipates for the early part of next week. There is a chance for low-level turbulence moving into the area, which could degrade seeing for Tuesday night.

Little change in the short/middle-term forecast, but things could take another turn for extensive moisture for the long-term forecast...The mid/low-level ridge will continue to sit to the north of the Islands and promote steady large-scale subsidence in the area into the early part of next week. While this subsidence will help maintain the inversion near 7 thousand feet for tonight, instability associated with a building tropical upper-tropospheric trough (TUTT) to the NNW may weaken/lift the inversion toward 10-12 and enhance the low-level cloud flow between late tomorrow evening and Monday afternoon. This could raise the stakes on periods of fog/high humidity at the summit for Saturday and especially Sunday night. Still, dry and stable conditions will prevail for tonight and as the TUTT shifts further off toward the NW and weakens for Monday night. In addition, there is a possibility for good to excellent seeing as an upper-level ridge briefly fills in from the SE over the next 24 hours. And while turbulence associated with the TUTT may contribute to slightly poorer than average seeing mainly for Sunday night, seeing should improve again for the early part of next week. Now for the longer-term forecast...I suspect this is a little overdone, but a pair of tropical cyclones/systems are expected to develop well to the east of the Islands over the next 24 hours (one near 135 W and another at 115 W) and make a pass through/near the area around the middle and/or later part of next week. The GFS has not been consisten with the track and intensity outlook for either cyclone, but the latest run now expects the first storm may start to affect summit-level conditions and erode the inversion as early as Tuesday night. It's still way to early to anticipate what either cyclone will do and the margin of error is large, I did increase the risk for fog/precipitation at the summit for Tuesday 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)
Fri Aug 26 - 8 PM30-509-100 / 03.5NNE/5-150.45-0.551.75-2.25
Sat Aug 27 - 2 AM50-708.5-100 / 03NNE/5-150.4-0.51.75-2.25
2 PM60-808-100 / 08N/5-15NaN1.5-2.5
8 PM20-408-910 / 03NE/5-150.4-0.51.25-1.75
Sun Aug 28 - 2 AM0-209.5-1015 / 02.5ENE/0-100.5-0.61-1.5
2 PM60-804-560 / 157.5N/0-10NaN3-6
8 PM0-209.5-1040 / 102ENE/5-150.5-0.82-3
Mon Aug 29 - 2 AM0-209.5-1040 / 102ENE/5-150.5-0.82-3
2 PM20-404-4.550 / 108NE/5-15NaN2-4
Tue Aug 30 - 2 AM0-209.5-100 / 03ENE/5-150.4-0.63-6
2 PM40-604-1025 / 106NE/5-15NaN3-5
Wed Aug 31 - 2 AM20-404-825 / 101NE/10-200.5-14-8
2 PM60-804-1040 / 206NE/15-30NaN3-6
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
Sun Aug 28 - Mon Aug 29 18:49 19:55 4:51 5:57 3:34 N/A 9 8 11.6 15 58
Mon Aug 29 - Tue Aug 30 18:48 19:54 4:51 5:57 4:30 17:06 4 9 04.7 13 38
Tue Aug 30 - Wed Aug 31 18:47 19:53 4:51 5:57 5:24 17:51 1 9 55.8 10 39
Wed Aug 31 - Thu Sep 01 18:46 19:52 4:52 5:58 6:17 18:34 0 10 44.8 7 13
Thu Sep 01 - Fri Sep 02 18:45 19:51 4:52 5:58 N/A 19:14 1 11 32.3 3 30
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 29 August 2016.
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