Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Monday 12 February 2018

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, but there is a chance that thin patches of high clouds will pass along the southern skies through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 7 C this afternoon, 2 C this evening and 1 C tomorrow morning. Winds will be from the NW at 5-15 mph for today, switching to a more westerly direction through the night. Seeing will likely be near 0.7-0.8 arcseconds, while precipitable water is expected to be in the 3-4 mm range for the first half of the night and 3.5-4.5 mm range for the second half.

Graphical Summary

Discussion
The tradewind inversion will continue to cap low-level moisture at or below 10 thousand feet and ensure the summit remains dry and stable for tonight. An influx of mid-level moisture may increase summit-level humidity toward 60-80% and raise the risk for periods of fog, ice and even light flurries at the summit as tomorrow night progresses. The inversion is set to fall apart on Wednesday as instability builds into and lingers the area, which could further increase the odds on moisture at the summit for the following 3 nights. There is also a possibility for convection in the area (particularly to the north) and brief periods of heavy snow at the summit throughout this period and into the weekend. Daytime clouds will be minimal and short-lived through tomorrow, but could turn extensive for the remainder of the week.

There is a possibility that thin patches of high clouds will fill in from the southwest and pass along the southern skies for tonight. A band of mid-level clouds are set to approach from the west and SW through tomorrow, and will eventually move over the summit area later that night. The bulk of these clouds will disperse eastward on Wednesday, while thicker patches develop along the northern skies for the following 3 nights. There is a chance that these batch of clouds will scrape the northern half of the Big Island mainly on Thursday night.

Precipitable water is expected to climb toward 4 mm over the course of the night and likely exceed that value for the remainder of the forecast period.

Residual mid-level turbulence will likely contribute to slightly poorer than average seeing for tonight. A fresh influx of mid/upper-level instability and turbulence will likely prohibit seeing from improving for tomorrow night, and there is also a possibility for another round of boundary layer turbulence which may further degrade seeing for the following 3 nights (Wednesday and Thursday night, in particular). There is also a chance for an increase in moisture and instability, that may also contribute to degradation in seeing over the weekend.

While the low to the northwest of the state will continue to strengthen and gradually dig southeastward before departing northward as it closes in on the northern half of the state later in the week, the SW flank of mid-level ridge will remain close enough to the area to promote large-scale subsidence in the area, which will help maintain a fairly well-defined inversion near 9-10 thousand feet through sunrise Wednesday. This will be enough to ensure a dry/stable summit-level air mass for tonight, but an influx of moisture associated with the SE flank of the low is set to move in over the Big Island through tomorrow night. This could increase cloud cover and humidity, and raise the stakes on periods of fog, ice and light flurries for that night. Although the bulk of this moisture is expected to slip off toward the east and/or drawn in toward the low on Wednesday, the atmosphere will grow increasingly unstable, which will help erode the inversion and further increase the risk for moisture at the summit for subsequent nights. There is a possibility for convection in the area (particularly to the north and northwest) and along the slopes, which could deposit heavy snow at the summi during the afternoon and early evening hours. Long term projections suggests that this low will leave a relatively large/sharp trough just west of the Islands as it departs northward early in the weekend. This trough will continue to destabilize the air mass and perhaps draw more moisture in from the south over the weekend, then could spawn another low just north of the state early next week. Regardless, this may allow moisture/instability to persist in the area over the weekend and into next week.

Astronomical Observing Quality Guidance
05 pm HST Monday 12 February (03 UTC Tuesday 13 February)CN2
08 pm HST Monday 12 February (06 UTC Tuesday 13 February)CN2
11 pm HST Monday 12 February (09 UTC Tuesday 13 February)CN2
02 am HST Tuesday 13 February (12 UTC Tuesday 13 February)CN2
05 am HST Tuesday 13 February (15 UTC Tuesday 13 February)CN2
08 am HST Tuesday 13 February (18 UTC Tuesday 13 February)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
02 pm HST
Mon 12 Feb
08 pm HST
Mon 12 Feb
02 am HST
Tue 13 Feb
02 pm HST
Tue 13 Feb
08 pm HST
Tue 13 Feb
02 am HST
Wed 14 Feb
02 pm HST
Wed 14 Feb
08 pm HST
Wed 14 Feb
02 am HST
Thu 15 Feb
02 pm HST
Thu 15 Feb
02 am HST
Fri 16 Feb
02 pm HST
Fri 16 Feb
02 am HST
Sat 17 Feb
00 UTC
Tue 13 Feb
06 UTC
Tue 13 Feb
12 UTC
Tue 13 Feb
00 UTC
Wed 14 Feb
06 UTC
Wed 14 Feb
12 UTC
Wed 14 Feb
00 UTC
Thu 15 Feb
06 UTC
Thu 15 Feb
12 UTC
Thu 15 Feb
00 UTC
Fri 16 Feb
12 UTC
Fri 16 Feb
00 UTC
Sat 17 Feb
12 UTC
Sat 17 Feb
Cloud Cover (%) 0 to 20 0 to 20 0 to 20 0 to 20 20 to 40 40 to 60 60 to 80 20 to 40 20 to 40 70 to 90 40 to 60 80 to 100 30 to 50
Cloud Height (km) above sea level 9.5-10 9.5-10 9.5-10 N/A 5-7 4.5-8 4-8 6-7 5-7 4-9 5-8 4-10 4-7
Chance for Fog/Precip (%) 0/0 0/0 0/0 0/0 25/10 50/25 75/40 60/30 60/30 80/50 75/30 85/60 75/35
PW (mm, summit upward) 2 to 4 3 to 4 3.5 to 4.5 4 to 6 4 to 6 4 to 6 4 to 8 4 to 6 4 to 6 4 to 8 4 to 6 4 to 8 4 to 6
Mean Seeing (arcsecs) N/A 0.75 ± 0.15 0.75 ± 0.15 N/A 0.8 ± 0.2 1.0 ± 0.3 N/A 1.2 ± 0.3 1.2 ± 0.3 N/A 1.2 ± 0.3 N/A 1.1 ± 0.3
Summit Temp (°C) 7 2 1 5 0 -1.5 2 -2.5 -3 1 -3 1 -2.5
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)

NW/5 to 15

NW/5 to 15

W/5 to 15

SW/10 to 20

SW/10 to 20

SW/15 to 30

SW/25 to 40

WSW/20 to 35

WSW/20 to 35

SW/30 to 45

SW/25 to 40

SW/15 to 30

SW/15 to 30


 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
Mon.Feb.12/Tue.Feb.13
18:29
19:34
5:38
6:43
5:14
N/A
5
19 57.8
-19 08
Tue.Feb.13/Wed.Feb.14
18:30
19:35
5:37
6:42
5:59
17:00
2
20 47.2
-17 26
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


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Monday 12 February (0300 UTC Tuesday 13 February) 2018.
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