Current Conditions
Temp-2.1 C
RH86 %
WindW 40 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Friday 17 May (0300 UTC Saturday 18 May) 2013
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry, stable and predominantly clear through the night but for some high clouds visible along the southeastern horizon.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening, and 0.5 C tomorrow morning. Winds will be light and from the W, with seeing around 0.55-0.6 arcseconds. Precipitable water is expected to be in the 2 to 2.5 mm during the first part of the night and increasing through the rest of the night, possibly reaching the 4 mm threshold.
Discussion
The tradewind inversion, still established at 8-9 thousand feet, is expected to weaken and lift through tonight in response to the instability that is moving in into the area. The inversion is expected to remain rather weak and indistinct through most of this forecast period. Although precipitation is unlikely, the risk for fog will increase from tomorrow. The inversion is expected to strenghten again toward the end of this forecast period.

Summit skies will be predominantly clear tonight, but for some high clouds visible along the southeastern horizon. Mid-high clouds will start approaching the area tomorrow but they are expected to remain rather North for most of the time. Cloud coverage is therefore expected to remain below 40-50% through the weekend and the rest of this forecast period.

Precipitable water will be in the 2 to 2.5 mm range during the first part of tonight and will increase through the rest of the night, possibly reaching the 4 mm threshold. It will linger close to 4 mm on Saturday night and range between 3 and 4 mm on Sunday night to then exceed the 4 mm threshold through the remainin part of this forecast period.

Observing conditions are on a degrading trend... Average but variable seeing is expected for tonight, while entering instability and turbulence aloft, along with increasing surface winds will make it for less than average to poor seeing conditions for the weekend nights and possibly into the beginning of the coming week.

Not much is changed since the morning forecast... The mid-low level ridge is slowling breaking down and moving eastward as a trough is developing Northwest of the State and slowly making is way into the area. This system will bring over instability and upper level turbulence while increasing moisture availability. Nevertheless the system is expected to remain North of the islands, and this, combined with the scarse low level support in term of mostly moisture, will reduce the risk for fog and very adverse weather at the summit. Therefore the odd for fog/ice will be relatively low. Observing conditions will degrade because of the increased turbulence in both the ground and free atmosphere. The trough is expected to move eastward through the weekend and the beginning of the coming week. Moisture might linger in the environment well into the beginning of the coming week...
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 May 17 - 8 PM0-20Clear0 / 02NNE/10-200.4-0.72-2.5
Sat May 18 - 2 AM0-20Clear20 / 00.5W/10-200.4-0.73-4
2 PM20-404-550 / 07WSW/10-20NaN4-6
8 PM0-20Clear40 / 01W/10-200.4-0.84-6
Sun May 19 - 2 AM0-20Clear30 / 0-0.5WSW/15-250.6-13.5-4.5
2 PM10-308-960 / 05W/15-25NaN3-5
8 PM10-308-930 / 00.5W/15-250.6-13-4
Mon May 20 - 2 AM20-407-820 / 00WSW/20-300.6-13-4
2 PM20-407-820 / 06WSW/20-30NaN3-5
Tue May 21 - 2 AM20-406-740 / 00.5SW/120-300.6-14-6
2 PM30-506-750 / 07SW/15-25NaN4-6
Wed May 22 - 2 AM30-506-750 / 00.5WSW/15-250.4-0.84-6
2 PM20-407-840 / 08WSW/10-20NaN4-6
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 May 19 - Mon May 20 19:02 20:13 4:23 5:35 N/A 2:17 72 11 35.9 -2 32
Mon May 20 - Tue May 21 19:02 20:14 4:23 5:34 N/A 2:59 81 12 27.3 -7 08
Tue May 21 - Wed May 22 19:03 20:15 4:22 5:34 N/A 3:44 89 13 21.7 -11 33
Wed May 22 - Thu May 23 19:03 20:15 4:22 5:34 N/A 4:34 95 14 19.6 -15 29
Thu May 23 - Fri May 24 19:04 20:16 4:22 5:34 17:36 5:29 99 15 21.0 -18 32
Forecast Issued by: Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Monday 20 May 2013.
Additional Information
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This message is also available at the MKWC road conditions page.
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