Current Conditions
Temp-0.4 C
RH12 %
WindWSW 14 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 26 May (0300 UTC Saturday 27 May) 2017
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will be mostly dry and stable through the first part of the night. Moisture will increase in time during the second half. Isolated high clouds might be visible along the southern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near -0.5 C this evening and -1.5 C tonight and tomorrow mornign. Winds from the West will be rather sustained at 15-30 mph with seeing variable and exceeding 6 arcseconds. Precipitable water is expected to range between 2 and 3 mm during the first half of the night and slowly increase through the second half, possibly reaching 4 mm.
Discussion
The tradewind inversion will start showing signs of weakening from later this evening (Lihue sounding already shows the weakening) as instability moves into the area. Moisture is therefore expected to increase through the night and possibly reach 60%-80% during the second half of tonight. There are risk for periodic fog and possibly light ice at the summit through early Monday morning. Precipitation is unlikely. The inversion is expected to rebuild from late Monday and through the rest of the forecast period. More stable conditions are likely then. Daytime clouds are very likely throughout the long weekend, then taper on Tuesday.

High clouds might be visible tonight and tomorrow along the southern horizon. Mid clouds might also develop from tomorrow and through Monday and block a good portion of the sky. They are expected to shift eastward by late Monday and clear skies will prevail afterward.

Precipitable water is expected to range between 2 and 3 mm during the first half of tonight, to then slowly increase and possibly reach 4 mm by the end of the night. It will exceed the 4 mm threshold through Saturday and part of Sunday to then slowly decrease and range between 3 and 4 mm and possibly stay in this range for the remaining nights.

Increased summit-level winds will increase boundary layer turbulence, which combined with building upper level instability will likely result in less than average seeing for tonight and poor seeing for tomorrow night. A more stable air mass aloft, combined with relatively calm skies should allow for an improvement in seeing for late Sunday and through the rest of this forecast period.

Not much is changed since this morning forecast if not minor touches-up to PW... A mid/upper-level tropical upper-trospheric trough is expected to shift eastward and pass north of the State through this long weekend. Winds at the summit are in fact increasing as gradients increase, and as a result, boundary layer turbulence is strenghtening. From tomorrow, the advected instability will erode most of the tradewind inversion and summit air mass might become nearly saturated, with chances for episodes of fog and possibly light nightime ice through part of Monday. High clouds passing along the southern fringe of the TUTT and within the sub-tropical jet, could also be visible along the southern skies for tonight, Saturday and Sunday night. There is also a chance that thick clouds will develop within the TUTT's axis as it digs southward tomorrow night. The TUTT is set to shift east of the Big Island as a relatively deep ridge fills in from the west and passes to the north during the early part of the week. This should help re-establish large-scale subsidence in the area, strengthen the inversion and decrease the risk for moisture at the summit for Monday night. Seeing will dip toward more average-good/like values as calm skies prevail during that time.
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 26 - 8 PM0-20Clear20 / 0-0.5W/15-250.4-0.82-3
Sat May 27 - 2 AM0-20Clear60 / 10-1.5W/20-300.55-0.953.5-4.5
2 PM30-504-670 / 202.5W/15-25NaN4-8
8 PM40-604-880 / 20-1.55W/15-250.7-1.14-8
Sun May 28 - 2 AM30-504-860 / 10-1W/10-200.8-1.24-8
2 PM30-504-650 / 5-2WNW/10-20NaN4-8
8 PM20-406-730 / 03.5NW/5-250.5-0.93.5-4.5
Mon May 29 - 2 AM10-307-810 / 01WNW/5-250.5-0.93-4
2 PM0-20Clear0 / 00.5NW/5-25NaN3.5-4.5
Tue May 30 - 2 AM0-20Clear0 / 05WNW/5-250.4-0.83-4
2 PM0-20Clear0 / 02N/5-25NaN3-4
Wed May 31 - 2 AM0-20Clear0 / 06S/5-250.3-0.73-4
2 PM10-307-80 / 02.5SW/5-25NaN3.5-4.5
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
Fri May 26 - Sat May 27 19:05 20:17 4:21 5:33 N/A 20:26 4 5 54.3 18 33
Sat May 27 - Sun May 28 19:05 20:18 4:20 5:33 N/A 21:28 10 6 56.9 18 42
Sun May 28 - Mon May 29 19:06 20:18 4:20 5:33 N/A 22:27 18 7 57.8 17 34
Mon May 29 - Tue May 30 19:06 20:19 4:20 5:33 N/A 23:20 27 8 56.0 15 20
Tue May 30 - Wed May 31 19:07 20:19 4:20 5:33 N/A 0:08 38 9 51.1 12 15
Forecast Issued by: Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Monday 29 May 2017.
Additional Information
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