Mauna Kea Weather Center Forecast

Mauna Kea Observatories Forecast
5 PM HST Friday 07 March (0300 UTC Saturday 8 March) 2014

Warning(s)
Fog/ice and snow
Moderate/strong winds
Large drifts

Cloud Cover and Fog/Precipitation Forecast
Fog, ice, snow and clouds will plague the summit through tonight. There is a strong possibility for periods of heavy snow, large drifts and convection in the area particularly as the night progresses.

Summary of Key Meteorological Variables
Summit temperatures will be near -1 C this evening and -3 C tomorrow morning. Winds will be from the west at 25-40 mph, with stronger gusts. Precipitable water and seeing are expected to exceeding to 4 mm and 1 arcsecond, respectively.

Discussion
The tradewind inversion will continue to breakdown over the next 3 hours, allowing the air mass to become saturated through late Saturday evening. As a result, fog, ice, high humidity and snow will plague the summit for tonight and probably tomorrow night. The upper-half of the air mass is expected to dry out through tomorrow night, but the inversion will remain rather indistinct as instability persists in the area into Tuesday night. Consequently, there is a moderate/high risk for fog, ice and periods of high humidity for Sunday, Monday and Tuesday night; precipitation is unlikely during that time. Extensive daytime clouds are expected through Tuesday, but will taper for Wednesday.

Broken to overcast thick clouds will continue to march in from the northwest, blanketing skies for tonight. The bulk of the upper-level clouds are expected to shift eastward through tomorrow night, but there is a possibility for lingering patches of mid-level clouds in the area for that night. These clouds will gradually dissipate in the area during the remainder of the weekend and there is a small possibility for summit-level clouds mainly for Monday night.

Precipitable water is expected to exceed 6-8 mm for the next 2 nights, but will likely settle in near 3-4 mm for Sunday night and the early part of next week. There is a chance that it will slip toward 2 mm or less late Tuesday night.

Boundary layer turbulence, upper-level turbulence and instability/moisture will inoperable conditions/skies over the next 2 nights. The boundary layer turbulence is expected to subside for Sunday and Monday night, but upper-level turbulence and perhaps instability/moisture will persist in the area during that time. Boundary layer turbulence is also expected to pick up again for Tuesday night. Consequently, poor/bad seeing is expected throughout the forecast period.

No change since the morning forecast...The leading edge of the approaching cold front is expected to reach the Big Island late this afternoon, slowly progress toward the SE before shifting south of the Big Island late tomorrow night. In the process, it will dismantle the inversion, saturate most of the air mass and bring extensive fog, ice and snow to the summit between this afternoon/evening and late tomorrow evening. There is also a possibility for periods of heavy snow and convection in the area particularly for the second half of tonight and perhaps tomorrow afternoon/evening. Moderate to strong winds will also continue to be an issue and could produce large drifts through Sunday afternoon. The upper-half of the air mass is expected to dry out as the front falls a part and/or shifts further off to the southeast on Sunday. However, residual instability and low-level moisture may keep the inversion from rebuilding and allow for more periods of fog, high humidity and ice at the summit for Sunday, Monday and Tuesday night. There is an outside chance for isolated afternoon convection along the slopes during those days. Winds are expected to subside for Sunday and Monday night, but there is a very good chance that it will pick up again (perhaps upwards of 75 mph) as a tight wind gradient drifts through Big Island around the middle part of next 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
HST	Cover (%)	Height (km)	Probability (%)	(Celcius)	(Dir/MPH)	(Arcseconds)	(mm)
Fri Mar 07 - 8 PM	80-100	4-10	100 / 80	-1	WSW/25-40	1-3	8-12
Sat Mar 08 - 2 AM	80-100	4-9	100 / 95	-3	W/25-40	1-3	8-12
2 PM	80-100	4-10	100 / 90	1	WNW/20-35	NaN	8-12
8 PM	60-80	4-7	95 / 75	-3	WNW/20-35	1-3	6-10
Sun Mar 09 - 2 AM	40-60	4-6	75 / 25	-3	W/20-35	1-2	4-8
2 PM	60-80	4-5	80 / 40	2	N/10-20	NaN	4-8
8 PM	0-20	Clear	60 / 15	-1.5	ESE/5-15	0.8-1.2	3-4
Mon Mar 10 - 2 AM	0-20	Clear	50 / 10	-1.5	WSW/5-15	0.7-1.1	3-4
2 PM	60-80	4-5	75 / 25	2	W/10-20	NaN	3-6
Tue Mar 11 - 2 AM	0-20	Clear	60 / 15	-3	WNW/10-20	0.7-1.3	3-4
2 PM	60-80	4-5	75 / 25	1	NNW/20-35	NaN	3-6
Wed Mar 12 - 2 AM	0-20	Clear	40 / 5	-4	NNE/40-60	0.8-1.6	1.5-2.5
2 PM	0-20	Clear	0 / 0	3	NE/40-60	NaN	1-2

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
Sat Mar 08 - Sun Mar 09	18:38	19:43	5:22	6:26	N/A	1:47	57	5 49.0	18 47
Sun Mar 09 - Mon Mar 10	18:39	19:43	5:21	6:25	N/A	2:33	67	6 39.5	18 00
Mon Mar 10 - Tue Mar 11	18:39	19:43	5:20	6:25	N/A	3:17	75	7 29.0	16 26
Tue Mar 11 - Wed Mar 12	18:39	19:43	5:20	6:24	N/A	3:58	83	8 17.6	14 08
Wed Mar 12 - Thu Mar 13	18:40	19:44	5:19	6:23	N/A	4:38	90	9 05.4	11 13

Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 10 March 2014.

Additional Information
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This message is also available at the MKWC road conditions page.
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Current Conditions
Temp		0.5 C
RH		86 %
Wind		W 27 mph
Road		Open