Current Conditions
Temp-2.5 C
RH74 %
WindSW 46 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 15 December (0300 UTC Saturday 16 December) 2017
Moderate/Strong Winds
Chances for fog/ice.
Cloud Cover and Fog/Precipitation Forecast
Some chances are for fog, high humidity and ice from this evening and through the night. Clouds will be visible along the northern horizon and interest the summit skies at times.
Summary of Key Meteorological Variables
Summit temperatures will be near -5 C this evening and -4.5 C tomorrow morning. Winds will be from the WNW at 25-40 mph for this evening, decreasing to 20-35 mph by the end of the night. Seeing will be poor at 0.8-1 arcsec, while precipitable water is expected to linger close to 4 mm through the night.
The tradewind inversion is lifting and will vanish by late this afternoon. This will increase the risks for fog, high relative humidity and ice from sunset through part of tomorrow. There is also a possibility for isolated convection in the area and light flurries at the summit during this time. The inversion is expected to start rebuilding by early Saturday evening, reducing the risk for moisture at the summit for most of that night. More moisture is expected to reach the area by Sunday. Fog, ice and possibly snow are possible from then through the rest of this forecast period. Daytime clouds will be very likely from Sunday and onward.

Mid/High clouds will be visible along the northern horizon this afternoon. They could approach the area and cover part of the sky tonight, to then move further north and away, leaving mostly clear skies for Saturday night. But more mid level clouds are expected to sip in from the south starting on Sunday and they are expected to result in most overcast skyes for the remaining nights.

Precipitable water will range between 3.5 and 4.5 mm tonight, and between 1.5 and 2 mm on Saturday night. It will linger close to 4 mm on Sunday night to then exceed the 4 mm threshold for the rest of this forecast period.
Observing conditions will be rather poor throughout, both because of strong surface winds, therefore ground layer turbulence, and mid/upper level shears.

Not much is changed since the morning forecast, if not for minor adjustment to PW for tomorrow night... The current weather scenario is dominated aloft by an upper level low located just to the ENE of the Big Island, which is prohibiting the ridge from proceeding eastward in the wake of the passing trough. As a result. strong surface gradients are causing moderate to strong winds at the surface, stirring up quite a bit of ground layer turbulence. As the upper level low moves somewhat backward toward the island today, it will cause the inversion to weaken and lift and will advect some instability over the area, which will increase the risks for fog, high relative humidity and ice tonight. Some convections and flurries are also a possibility (although not as likely). As the low moves Northeastward tomorrow, the inversion should rebuild some, but the following trough will cause mid level moisture to be advected over from the SW starting on Sunday. This will cause the inversion to lift again and the air masses to become saturated then and through most of the remaining part of this forecast period. The weather could be particularly adverse between Monday and Tuesday.
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 Dec 15 - 8 PM20-406-830 / 0-5WSW/25-400.65-1.052-3
Sat Dec 16 - 2 AM30-506-850 / 10-4.5WSW/20-350.7-1.13.5-4.5
2 PM0-20Clear30 / 0-2SW/30-45NaN3-4
8 PM0-20Clear0 / 0-5SW/30-451.3-1.72-2.5
Sun Dec 17 - 2 AM0-20Clear0 / 0-4SW/35-501.3-1.71.5-2
2 PM10-306-830 / 02SW/25-35NaN2.5-3.5
8 PM20-406-850 / 5-2WSW/20-351-1.42.5-3.5
Mon Dec 18 - 2 AM30-506-860 / 10-3SW/20-351-1.43.5-4.5
2 PM60-804-670 / 200SW/20-35NaN4-8
Tue Dec 19 - 2 AM60-804-690 / 40-4WSW/25-401-1.48-12
2 PM80-1004-690 / 40-1WSW/25-40NaN8-12
Wed Dec 20 - 2 AM80-1004-690 / 40-4WSW/20-351-1.44-6
2 PM60-807-870 / 30-1WSW/20-35NaN4-6
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 Dec 17 - Mon Dec 18 17:56 19:05 5:32 6:41 7:00 17:54 0 17 52.2 -19 39
Mon Dec 18 - Tue Dec 19 17:57 19:06 5:33 6:42 7:48 18:41 1 18 41.8 -20 04
Tue Dec 19 - Wed Dec 20 17:57 19:06 5:33 6:42 N/A 19:29 4 19 31.4 -19 38
Wed Dec 20 - Thu Dec 21 17:58 19:06 5:34 6:43 N/A 20:19 8 20 20.7 -18 22
Thu Dec 21 - Fri Dec 22 17:58 19:07 5:34 6:43 N/A 21:09 14 21 09.5 -16 18
Forecast Issued by: Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Monday 18 December 2017.
Additional Information
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