Mauna Kea Weather Center Forecast

Mauna Kea Observatories Forecast
5 PM HST Tuesday 29 July (0300 UTC Wednesday 30 July) 2014

Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but small patches of high clouds will pass overhead and especially along the southern skies throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C this evening and 2 C tomorrow morning. Winds will be light and from the WNW, with seeing around 0.45-0.5 arcseconds. Precipitable water is expected to be in the 1-1.5 mm range for the night.

Discussion
The tradewind inversion will continue to cap low-level moisture near 7 thousand feet and keep the mid/summit-level air mass dry and stable through at least midnight Thursday. However, an influx of moisture and instability is expected to dismantle the inversion early Friday morning, which could lead to a saturated atmosphere for that night. This will significantly raise the stakes on extensive fog, high humidity and rain at the summit between early Friday morning and late Saturday afternoon. The odds on moisture at the summit will subside as the atmosphere dries out and the inversion rebuilds through Saturday night. Daytime clouds will be minimal and short-lived through Thursday, but could turn extensive for Friday and Saturday, only to taper again on Sunday.

Patches of high clouds will continue to pass overhead and especially along the southern skies through the night. More organized high clouds are slated to fill in from the southwest just after sunrise tomorrow and become more widespread and thicker over the next 2 nights. This will likely lead to extensive cloud cover for Wednesday night and probably overcast skies for Thursday and Friday night. In addition, there is a strong possibility that thick/deep clouds and perhaps convection will fill in from the southeast for much of Friday night. The bulk of these clouds will start to breakdown early Saturday evening, perhaps opening up skies as that night progresses.

Precipitable water is expected to linger near 1.25 mm for tonight, but will likely increase to 3 mm for tomorrow night and probably exceed 4 mm for Thursday, Friday and Saturday night.

Relatively calm skies will likely allow for seeing to linger near 0.5 arcseconds through at least Thursday evening. However, building turbulence and eventually moisture/instability in the atmosphere, will degrade seeing during the latter half of Thursday night and especially for Friday night. There is a chance that seeing will start to improve with conditions and skies through Saturday night.

Changes have been made mainly to tonight's CC forecast...Although the mid-level ridge will remain rather weak/indistinct into the late part of the weekend, the low-level ridge will continue to sit to the north of the state and promote relatively strong large-scale subsidence in the area during that time. This will help maintain the tradewind inversion near 7 thousand feet, negate the affects of an upper-level trough lingering to the west of the state and ensure a dry/stable summit-level air mass through at least Thursday evening. Unfortunately, the trough and its associated sub-tropical jet are expected to transport high clouds out of the tropics and over the summit area particularly after tonight. There is a possibility that these clouds will thicken and become more widespread starting early Thursday morning. In addition, the remnants of TS Genevieve will contribute to the cloud coverage as mid-level clouds begin to fill in from the southeast later that night. Eventually, deep residual tropical moisture is expected to fill into the area, breakdown the inversion and saturate the atmosphere near sunrise Friday morning. This will likely lead to inoperable (wet/foggy/rainy) summit-level conditions, overcast skies and perhaps deep convection in the area for Friday night. Conditions and skies are slated to improve as the moisture slips off toward the west and the mid-level ridge begins to strengthen through Saturday night.

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)
Tue Jul 29 - 8 PM	20-40	9-10	0 / 0	2.5	WNW/0-10	0.45-0.55	1-1.5
Wed Jul 30 - 2 AM	20-40	9-10	0 / 0	2	WNW/0-10	0.4-0.5	1-1.5
2 PM	20-40	8.5-10	0 / 0	8	WSW/0-10	NaN	1-2
8 PM	40-60	8-10	0 / 0	3	WSW/0-10	0.45-0.55	1.5-2.5
Thu Jul 31 - 2 AM	60-80	6-10	0 / 0	3	SW/5-15	0.45-0.55	2.5-3.5
2 PM	80-100	5-10	0 / 0	7	SE/5-15	NaN	4-8
8 PM	80-100	5-10	0 / 0	2	SE/10-20	0.45-0.55	4-8
Fri Aug 01 - 2 AM	80-100	5-10	40 / 20	1.5	SSE/10-20	0.45-0.65	6-10
2 PM	80-100	4-10	90 / 75	5	S/10-20	NaN	8-12
Sat Aug 02 - 2 AM	80-100	4-10	90 / 75	2	SSE/15-30	1-2	8-12
2 PM	60-80	4-10	90 / 60	6	SE/10-20	NaN	6-10
Sun Aug 03 - 2 AM	40-60	6-9	40 / 10	3	ESE/10-20	0.6-1.2	4-8
2 PM	40-60	6-8	20 / 5	8	E/10-20	NaN	3-6

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
Tue Jul 29 - Wed Jul 30	19:09	20:20	4:37	5:48	N/A	20:59	10	10 57.8	2 46
Wed Jul 30 - Thu Jul 31	19:09	20:19	4:38	5:48	N/A	21:35	17	11 42.6	-1 03
Thu Jul 31 - Fri Aug 01	19:08	20:18	4:38	5:48	N/A	22:12	24	12 28.1	-4 53
Fri Aug 01 - Sat Aug 02	19:08	20:18	4:39	5:49	N/A	22:51	33	13 14.9	-8 36
Sat Aug 02 - Sun Aug 03	19:07	20:17	4:39	5:49	N/A	23:32	43	14 03.7	-12 04

Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 30 July 2014.

Additional Information
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Current Conditions
Temp		5.4 C
RH		23 %
Wind		NW 0 mph
Road		Open