Mauna Kea Weather Center Forecast

Mauna Kea Observatories Forecast
5 PM HST Friday 27 February (0300 UTC Saturday 28 February) 2015

Warning(s)
Fog/ice, high humidity and flurries
Chance for convection and heavy snow

Cloud Cover and Fog/Precipitation Forecast
Extensive fog, ice, high humidity, thick clouds and light/moderate snow are expected to plague the summit, particularly as the night progresses.

Summary of Key Meteorological Variables
Summit temperatures will be near -2.5 C for the night. Winds will be light and from the south, while precipitable water and seeing are expected to exceed 4 mm and 1 arcsecond, respectively.

Discussion
The tradewind inversion will continue to breakdown as deep moisture and instability fills into the area over the next 6 hours and persists probably well into the middle part of next week. This will saturate the air mass (particularly above 10 thousand feet) and contribute to extensive fog, ice, high humidity and light/moderate snow at the summit through the next 5 nights. Periods of convection in the area and heavy snow at the summit are possible, especially after tonight. Daytime clouds will turn very extensive for the next 5 days.

Thick clouds are slated to develop over the summit area during the next 12-24 hours, with more widespread dense clouds filling in during the weekend and into next week. Regardless, these clouds will contribute to broken to overcast skies throughout most of the forecast period.

Precipitable water is expected to exceed 4 mm through the next 5 nights.

An influx of upper-level turbulence, moisture and instability will contribute to poor/bad seeing and/or inoperable conditions through the next 5 nights.

No change since the morning forecast...The mid/low-level ridge will continue to rapidly fall apart as residual (decaying) low/trough fills in from the east over the next 12 hours and a large developing trough becomes quasi-stationary to the west of the state for the next 5-7 days. The trough will provide widespread (albeit weak) instability, while the low will supply lots of moisture to the area probably for the next week or so. Together this will help saturate the air mass over the next 3-6 hours, and likely contribute to overcast skies, high humidity, extensive fog, ice and stratiform flurries at the summit probably through the remainder of the forecast period. Initially, the air mass below 9 thousand feet may remain a bit dry/stable (for the next 24 hours), which should help minimize the risk convection in the area and heavy snow at the summit. However, an embedded short-wave trough (SWT) may change that by reorganizing the surrounding moisture into a stationary front which is expected to linger over/near the Big Island beginning late Saturday night. This SWT will also provide fresh instability to the area, that together with the abundant moisture may fire up a band of convection and allow for periods of heavy snow at the summit late in the weekend and again as another reinforcing SWT swings by to the north around Wednesday of next week. While its difficult to anticipate snowfall accumulations (which is highly dependent on location/development of convection - though it could potentially exceed 1-2 feet), expect inoperable conditions/skies to plague the summit probably through the next 6-7 nights. There is a chance that conditions will start to improve once the second SWT pushes the moisture and instability to the east around Thursday/Friday 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 Feb 27 - 8 PM	60-80	4-8	90 / 75	-2.5	SSE/5-15	0.7-1.3	8-12
Sat Feb 28 - 2 AM	80-100	4-9	95 / 90	-2.5	SSW/5-15	1-2	8-12
2 PM	80-100	4-9	100 / 95	-1	SSW/5-15	NaN	8-12
8 PM	80-100	4-10	100 / 95	-4	W/0-10	1-2	8-12
Sun Mar 01 - 2 AM	80-100	4-10	100 / 95	-4	WSW/5-15	1-2	8-12
2 PM	80-100	4-10	100 / 95	-2	WSW/5-15	NaN	8-12
8 PM	80-100	4-10	100 / 95	-3.5	N/5-15	1-2	8-12
Mon Mar 02 - 2 AM	80-100	4-10	100 / 95	-3	SSW/0-10	1-2	8-12
2 PM	80-100	4-10	95 / 90	-1.5	W/5-15	NaN	8-12
Tue Mar 03 - 2 AM	80-100	4-10	90 / 75	-2.5	SW/5-15	1-2	8-12
2 PM	80-100	4-10	90 / 75	-0.5	WSW/10-20	NaN	8-12
Wed Mar 04 - 2 AM	80-100	4-10	95 / 90	-2	W/5-15	1-2	8-12
2 PM	80-100	4-10	95 / 90	0	NW/10-20	NaN	8-12

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 Feb 28 - Sun Mar 01	18:36	19:40	5:28	6:33	N/A	4:03	83	7 34.2	16 20
Sun Mar 01 - Mon Mar 02	18:36	19:40	5:28	6:32	N/A	4:46	90	8 23.9	14 15
Mon Mar 02 - Tue Mar 03	18:36	19:41	5:27	6:31	N/A	5:26	95	9 12.3	11 34
Tue Mar 03 - Wed Mar 04	18:37	19:41	5:26	6:30	16:59	6:05	98	9 59.4	8 24
Wed Mar 04 - Thu Mar 05	18:37	19:41	5:25	6:30	17:48	6:42	100	10 45.7	4 54

Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 2 March 2015.

Additional Information
For public road conditions and snow report message please call (808) 935-6268.
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		-3.6 C
RH		95 %
Wind		NW 23 mph
Road		Closed