Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Wednesday 14 February 2018

Warnings
Moderate winds
Chance for fog, ice and high humidity
Possibility for convection and flurries

Cloud Cover and Precipitation Forecast
There is a moderate/high risk for periods of fog, ice and high humidity throughout the night; there is a small/moderate chance for convection in the area (particularly to the northwest) and light flurries. Broken patches of mid/upper-level clouds will continue to linger in the area throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this afternoon, -1.5 C this evening and -3 C tomorrow morning. Winds will be from the WSW at 20-35 mph for today, increase to 25-40 mph for the morning hours. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, through the night.

Graphical Summary

Discussion
Instability building into the area, combined with lingering moisture will help weaken/erode the inversion, increase summit-level humidity into the 60-80% range and raise the stakes on periods of fog, ice and flurries at the summit through Friday evening. There is also an outside chance for isolated convection in the area mainly around Thursday afternoon/evening. There is a good possibility that deeper instability and moisture will fill into the area, allowing the atmosphere to turn saturated and increase the risk for widespread convection and heavy snow at the summit over the remainder of the weekend. Extensive daytime clouds are expected throughout the forecast period.

While the bulk of the overcast mid-level clouds are set to shift off toward the east through the day, there is a good chance that scattered to broken clouds will continue to linger in the area (particularly to the north) and/or drift in from the west through Friday evening. More widespread deep clouds are expected to develop over the Big Island early Saturday morning and will likely blanket summit skies for the remainder of the weekend.

Precipitable water is expected to exceed 4 mm throughout the forecast period.

A mixture of moderate boundary layer turbulence, instability, moisture and/or mid/upper-level turbulence will contribute to poor/bad seeing throughout the forecast period.

The low to the NW will continue to dig southeastward and destabilize the air mass, while sending a rather ragged front-like band through the eastern half of the state over the next 36 hours. The low will begin to rapidly fall apart beginning late Thursday evening, leaving a residual but relatively deep trough over the Big Island on Friday and into the weekend. Another short-wave trough passing through is expected to help revitalize the trough and help spawn a secondary low to the north, that will eventually dig southward and linger over the western half of the state late in the weekend and into the early part of next week. Nonetheless, these lows/trough will allow large-scale instability to persist in the area probably well into next week. This, combined with moisture congregrating in the area, will help dismantle the inversion and increase the odds on high humidity, fog, ice and flurries at the summit throughout the forecast period. There is also a possibility for mostly isolated convection in the area and along the slopes, which could deposit heavier snow at the summit mainly as the frontal band passes through around Thursday afternoon/evening. This risk should subside as the band shifts subtly eastward on Friday. However, the injection of fresh instability from the SWT, combined with a slight westward retrograde of the parent trough and eventually low, could allow this frontal band to build back westward and linger over the Big Island for much of the weekend. This may result in more widespread convection and prolong periods of heavy snow and/or even blizzard like conditions during that time.

Astronomical Observing Quality Guidance
05 pm HST Wednesday 14 February (03 UTC Thursday 15 February)CN2
08 pm HST Wednesday 14 February (06 UTC Thursday 15 February)CN2
11 pm HST Wednesday 14 February (09 UTC Thursday 15 February)CN2
02 am HST Thursday 15 February (12 UTC Thursday 15 February)CN2
05 am HST Thursday 15 February (15 UTC Thursday 15 February)CN2
08 am HST Thursday 15 February (18 UTC Thursday 15 February)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
02 pm HST
Wed 14 Feb
08 pm HST
Wed 14 Feb
02 am HST
Thu 15 Feb
02 pm HST
Thu 15 Feb
08 pm HST
Thu 15 Feb
02 am HST
Fri 16 Feb
02 pm HST
Fri 16 Feb
08 pm HST
Fri 16 Feb
02 am HST
Sat 17 Feb
02 pm HST
Sat 17 Feb
02 am HST
Sun 18 Feb
02 pm HST
Sun 18 Feb
02 am HST
Mon 19 Feb
00 UTC
Thu 15 Feb
06 UTC
Thu 15 Feb
12 UTC
Thu 15 Feb
00 UTC
Fri 16 Feb
06 UTC
Fri 16 Feb
12 UTC
Fri 16 Feb
00 UTC
Sat 17 Feb
06 UTC
Sat 17 Feb
12 UTC
Sat 17 Feb
00 UTC
Sun 18 Feb
12 UTC
Sun 18 Feb
00 UTC
Mon 19 Feb
12 UTC
Mon 19 Feb
Cloud Cover (%) 80 to 100 60 to 80 40 to 60 80 to 100 50 to 70 30 to 50 80 to 100 40 to 60 60 to 80 80 to 100 80 to 100 80 to 100 80 to 100
Cloud Height (km) above sea level 4-8 4.5-8 4.5-7 4-8 4-8 4.5-7 4-8 4.5-6 4-8 4-10 4-10 4-10 4-10
Chance for Fog/Precip (%) 75/25 60/15 75/20 80/50 85/40 80/30 90/60 85/50 95/75 95/90 95/90 95/85 90/80
PW (mm, summit upward) 4 to 8 4 to 6 4 to 6 4 to 8 4 to 6 4 to 6 4 to 8 4 to 6 4 to 8 8 to 12 8 to 12 8 to 12 6 to 10
Mean Seeing (arcsecs) N/A 1.0 ± 0.3 1.2 ± 0.3 N/A 1.5 ± 0.5 1.3 ± 0.4 N/A 1.0 ± 0.3 1.2 ± 0.3 N/A 1.5 ± 0.5 N/A 1.3 ± 0.4
Summit Temp (°C) 3 -1.5 -3 3 -1.5 -1.5 2.5 -1.5 -2.5 -1 -4.5 -2 -6
Wind Dir/Speed (mph)
    Summit (615 hPa)
    19,000 ft (500 hPa)
    24,500 ft (400 hPa)
    31,000 ft (300 hPa)
    35,000 ft (250 hPa)
    40,000 ft (200 hPa)
    46,000 ft (150 hPa)
    54,000 ft (100 hPa)

WSW/20 to 35

WSW/20 to 35

WSW/25 to 40

WSW/25 to 40

WSW/20 to 35

WSW/20 to 35

WSW/15 to 30

WSW/15 to 30

SW/15 to 30

WSW/15 to 30

SW/15 to 30

SSW/20 to 35

SW/25 to 40


 Rise and Set times for the Sun and Moon
Night (HST)
Sun Set
Twilight End
Twilight Beg
Sun Rise
Moon Rise
Moon Set
Illum (%)
RA
Dec
Wed.Feb.14/Thu.Feb.15
18:30
19:35
5:37
6:42
6:41
17:51
0
21 36.0
-14 59
Thu.Feb.15/Fri.Feb.16
18:31
19:36
5:36
6:41
7:22
18:42
0
22 24.2
-11 51
Fri.Feb.16/Sat.Feb.17
18:31
19:36
5:36
6:41
N/A
19:34
2
23 12.0
-8 10
Sat.Feb.17/Sun.Feb.18
18:31
19:36
5:35
6:40
N/A
20:26
6
23 59.7
-4 04
Sun.Feb.18/Mon.Feb.19
18:32
19:37
5:35
6:39
N/A
21:18
12
0 47.6
0 16


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Wednesday 14 February (0300 UTC Thursday 15 February) 2018.
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