Mauna Kea Weather Center Forecast

Mauna Kea Observatories Forecast
5 PM HST Friday 06 November (0300 UTC Saturday 7 November) 2009

Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable throughout tonight. Summit skies will be mostly clear although dissipating high clouds will be approaching the islands from the west.

Summary of Key Meteorological Variables
Summit temperatures will be near 4.5 C this evening and 3 C tomorrow morning. Winds will be from the NE at 10-20 mph. Seeing will be in the 0.55-0.6 arcsec throughout most of the night. Precipitable water is expected to be in the 1.1 to 1.4 mm range.

Discussion
The tradewind inversion will continue to cap the low-level moisture below 9 thousand feet, keeping the mid/summit-level air mass dry and stable through the next 2-3 nights. The inversion is expected to lift and weaken starting late on Sunday and through Monday and Tuesday when short episodes of fog are also possible. The atmosphere should start stabilizing again by mid-week. Daytime clouds will be minimal and short-lived until Sunday, while they will become more extended at the beginning of the week.

Scattered high clouds will approach the summit skies from the west today and, although dissipating, they may be visible along the western sector of the sky tonight and through Sunday. The more organized clouds to the far west are expected to move eastward on Sunday and may significantly increase cloud cover until they will move to the east on Tuesday.

Precipitable water is expected to range between 1.1 and 1.4 mm tonight while it will be in the 2 to 3 mm range Saturday night and Sunday night. It is then expected to exceed 4 mm by Monday.

A weak flow aloft will result in minimal shear/turbulence in the free atmosphere for tonight. This, along with low boundary layer turbulence will make it for average-good seeing.Unfortunately, flow aloft is expected to strengthen and veer back to a more westerly direction, significantly increasing shear/turbulence in the free atmosphere. Seeing is expected to increase to 0.65 on Saturdy and probably result in poor/bad seeing for Sunday and throughout the beginning of next week.

Not much is changed since this morning forecast...Large scale subsidence in the area, promoted by the high pressure area North of the State, will maintain the tradewind inversion near 9 thousand feet today and through part of tomorrow and as a result the atmosphere will be rather stable until then. Shear aloft will remain week and observing conditions at the summit will be average to good tonight and average on Saturday night. High clouds may be visible along the western sector of the skies, both tonight and particularly tomorrow.On Sunday a trough will start pushing the upper level ridge southward, increasing shear/turbulence in the free-atmosphere and advecting mid and high clouds over the State. Seeing will start degrading then and will worsen through the rest of the forecast period. The atmosphere will start destabilize late on Sunday and the tradewind inversion will start weakening and lifting then. Relative humidity at the summit will increase and there are small chances for short episodes of fog/high humidity on Monday and Tuesday night. Longer term projections also suggest the development of an upper-level trough North of the State, which migh cut-off just east of the Hawaiian islands and reinforce the destabilization at least until mid-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 Nov 06 - 8 PM	0-20	9.5-10	0 / 0	4.5	NE/5-15	0.5-0.8	1.25-1.75
Sat Nov 07 - 2 AM	0-20	9.5-10	0 / 0	3	NE/10-20	0.4-0.7	1.1-1.4
2 PM	0-20	9.5-10	0 / 0	6.5	SE/5-15	NaN	1.5-2
8 PM	10-30	9-10	0 / 0	3.5	ENE/5-15	0.55-0.85	1.75-2.25
Sun Nov 08 - 2 AM	10-30	9-10	0 / 0	2.5	ESE/5-15	0.5-0.8	2-3
2 PM	20-40	8.5-10	0 / 0	5.5	S/5-15	NaN	2.5-3.5
8 PM	30-50	8-10	0 / 0	2.5	SSE/5-15	0.5-0.9	2-3
Mon Nov 09 - 2 AM	40-60	7.5-10	0 / 0	1.5	S/10-20	0.7-1.1	2-3
2 PM	40-60	7-9	20 / 0	2	WSW/10-20	NaN	4-8
Tue Nov 10 - 2 AM	60-80	7-9	40 / 0	-1	WSW/15-25	0.8-1.2	4-10
2 PM	80-100	6.5-9	40 / 0	1	WNW/15-25	NaN	4-10
Wed Nov 11 - 2 AM	80-100	6.5-9	30 / 0	-2	WNW/10-20	0.8-1.2	4-8
2 PM	40-60	7-10	30 / 0	1	WSW/5-15	NaN	4-8

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 Nov 06 - Sat Nov 07	17:54	19:00	5:11	6:17	21:32	N/A	74	7 11.7	23 04
Sat Nov 07 - Sun Nov 08	17:54	19:00	5:11	6:18	22:36	N/A	63	8 11.2	19 24
Sun Nov 08 - Mon Nov 09	17:54	19:00	5:12	6:18	23:39	N/A	52	9 07.2	14 37
Mon Nov 09 - Tue Nov 10	17:53	19:00	5:12	6:19	0:39	N/A	41	10 00.1	9 07
Tue Nov 10 - Wed Nov 11	17:53	18:59	5:13	6:19	1:37	N/A	30	10 50.7	3 13

Forecast Issued by: Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Monday 9 November 2009.

Additional Information
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Current Conditions
Temp		4.8 C
RH		21 %
Wind		NNE 8 mph
Road		Open