Mauna Kea Weather Center Forecast

Mauna Kea Observatories Forecast
5 PM HST Thursday 02 July (0300 UTC Friday 3 July) 2009

Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this evening and 2 C tomorrow morning.Precipitable water is expected to be in the 2-3 mm range, with seeing around 0.6 arcseconds.Winds will be from the ESE at 5-15 mph for this evening, switching to a more southerly component toward the end of the night.

Discussion
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies overhead and especially to the east will remain predominately clear for at least the next 3 nights. There is a very good chance that scattered to broken cirrus will start to creep in from the west late Sunday night and could result in extensive cloud cover for Monday night.

Precipitable water will likely linger near 2 mm for the next 3 nights, briefly jump to 4+ mm for Sunday night, then slip back to 2 mm for Monday night.

Light winds aloft should result in minimal shear/turbulence in the free atmosphere and likely better than average seeing for at least the next 2 nights. Upper-level flow is slated to increase, strengthening shear a bit and degrading seeing toward more average-like values for Saturday, Sunday and probably Monday night.

Minimal change since the morning forecast...The mid and surface ridge will continue to rebound northward from the SE and nearly directly overhead, respectively, until it becomes firmly planted near 30 N late in the weekend and into next week. This return of the ridge will coincide perfectly with the redevelopment of the tropical upper-tropospheric trough (TUTT) just west of the state and easily negate any of its associated instability. In fact, the air mass near the Big Island will remain very dry and stable with a strong/prominent tradewind inversion at or below 9 thousand feet throughout the forecast period. Light winds at and above the summit will also result in minimal shear in the free atmosphere and likely better than average seeing, at least until the return of the TUTT. The TUTT will likely allow the sub-tropical jet to build just west of the state and increase shear and/or mesoscale turbulence in the area, which will probably degrade seeing a bit late in the weekend. The STJ may also start to transport mid/upper-level moisture to the area mainly for Sunday and Monday night.

Please Note: There will no forecasts tomorrow, July 3, in observance of the Independence Day. I will try to issue a brief forecast on Sunday morning and the normal forecast schedule will resume on Monday, July 6.

WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles

5 Day Forecast Summary (Graphical Trend)

HST	Cloud Cover (%)	Fog Prob (%)	Precip Prob (%)	Temp (C)	Wind Spd (mph)	Wind Dir (deg)	Seeing (arcsec)	PW (mm)
Thu Jul 02 - 8 PM	0-5	0	0	3	5-15	ESE	0.5-0.7	2-3
Fri Jul 03 - 2 AM	0-5	0	0	2	5-15	SSE	0.5-0.7	2-3
2 PM	0-20	0	0	7	5-15	SW	NaN	2-3
8 PM	0-5	0	0	3	5-15	W	0.5-0.8	2-3
Sat Jul 04 - 2 AM	0-5	0	0	2	5-15	W	0.5-0.7	2-3
2 PM	0-20	0	0	8	5-15	WSW	NaN	2-3
8 PM	0-5	0	0	3	5-15	W	0.5-0.8	2-3
Sun Jul 05 - 2 AM	0-5	0	0	3	5-15	SW	0.5-0.9	2-3
2 PM	0-20	0	0	8.5	5-15	SW	NaN	2-3
Mon Jul 06 - 2 AM	40-60	0	0	3.5	5-15	SSW	0.5-1	3-5
2 PM	60-80	0	0	9	5-15	SSE	NaN	3-5
Tue Jul 07 - 2 AM	50-70	0	0	4	10-20	E	0.5-0.9	2-3
2 PM	60-80	0	0	8	15-25	ENE	NaN	2-3

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
Thu Jul 02 - Fri Jul 03	19:15	20:29	4:24	5:37	N/A	2:51	86	15 35.3	-24 46
Fri Jul 03 - Sat Jul 04	19:15	20:29	4:24	5:38	N/A	3:39	92	16 28.9	-26 34
Sat Jul 04 - Sun Jul 05	19:15	20:28	4:25	5:38	N/A	4:30	96	17 23.2	-27 06
Sun Jul 05 - Mon Jul 06	19:15	20:28	4:25	5:38	18:00	5:22	99	18 16.9	-26 22
Mon Jul 06 - Tue Jul 07	19:15	20:28	4:25	5:39	18:47	6:15	100	19 09.3	-24 27

Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 3 July 2009.

Additional Information
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This message is also available at the MKWC road conditions page.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products

Current Conditions
Temp		3.5 C
RH		45 %
Wind		SE 4 mph
Road		Open