Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 152008
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
108 PM MST Sun Jan 15 2017

.SHORT TERM...Tonight through Saturday.

Cold weather remains locked in place over the region. Saw some light
snow around the Magic Valley today. That was due to fog that formed,
and was so cold that the ice crystals were falling out of the fog.
Could see a repeat of that tonight with fog possible once again over
parts of the area. If some areas should see some light snow or
flurries it shouldn`t amounts to much at all. Otherwise, forecasting
persistence for temperatures tonight and Monday. Started to bump
temps up from persistence Monday night as the ridge of high pressure
starts to move away from the area.

Models are continuing to push back the timing of the next system and
snow amounts and the amount of warm air looks much less. Models now
show much of the energy diving well south of the region. As a
result, expect Tuesday to remain mainly dry across the region.
Widespread snow may not arrive in the Sawtooths until sometime late
Wednesday afternoon now. Latest model runs still show precipitation
advancing through the central Idaho mountains Wed night into east
Idaho with precipitation persisting on Thursday. There`s a chance
that precipitation might remain all snow across the entire region,
which would be very good for those with flooding concerns. Snowfall
amounts look much less as well now with amounts from Bellevue to
Stanley in the 6 to 12 inch range with higher amounts at ridgetop
level. That`s about half of what earlier forecasts were indicating.
The rest of the area could see 2 to 5 inches. The question at this
point, will the models flip back to earlier solutions or continue
the trend of sending the energy south which would lessen the impacts
for Idaho. Too early to say right now.

Valle

.LONG TERM...Fri through next Sun night. After the main storm this
week, the 500mb longwave trough at the coast keeps a threat of
precipitation with south to southwest upper level flow continuing
over the Gem State. However, this long wave pattern is of low
amplitude and makes the solutions very much dependent on the
shortwave timing, of which there is little agreement. So have
painted with a very broad brush, especially early. Used more of the
ECMWF as its resolution is less and thus is a little better for
broad-brushing. The GFS and ECMWF start to agree at the end of this
period for a shortwave trough to enter southern Idaho Sun night, so
have increased the PoPs and cloudiness for this period. Using
adjusted ECMWF temperatures for highs and lows. Messick

&&

.AVIATION...Where will the "fog monster" have an impact tonight is
the main question. Both GFS and NAM have KBYI, KIDA, and KPIH shut
down with 100 ft CIGs. Visibility is also expected to be low, but
not expected to be dense fog. The timing is different, with the NAM
bringing it to that condition by 16/09Z, but the GFS waits until
16/15Z. Have made a compromise of IFR conditions, but accessible,
from around 16/07Z to 09Z, and closing KIDA and KBYI at 16/13Z.
Forecasted KPIH to get close with 200 ft CIG at that time. Clearing
not likely until sometime around 16/18Z. KSUN and KDIJ may have a
situation develop with wind shifts potentially bringing stratus in
from the Snake River plain, but at this point it seems more likely
that these two airdromes will stay unlimited in CIGs and VSBYs.
Light wind expected everywhere except KSUN which should have normal
afternoon and early evening upslope and mid-evening and morning down
slope winds. Messick

&&

.HYDROLOGY...

Flooding continues across Cassia, Minidoka, Power and Oneida
counties per conversations with respective Emergency Managers and
Law Enforcement. The worst of the flooding is occurring in Cassia
County and Malta and Oakley in particular. Water remains over roads
across portions of Minidoka County, particularly near the Snake
River and Heyburn. In these two counties, road closures are still
being reported. We have also received reports of water over roads in
Oneida and Power counties as well, thus the Flood Warning continues
for these areas. Below freezing temperatures has ended additional
runoff due to snowmelt, so we`re seeing no new water being added to
existing flooding areas. However, due to the below freezing
temperatures, flooded areas are freezing and this is creating
hazardous driving conditions where water is covering roadways.

With below freezing temperatures (and with many sub-zero lows this
weekend) expected over the region through early next week, the risk
of additional ice jam flooding will increase, with existing
significant ice buildup in many channels. A new storm system will
begin to bring precipitation and warmer temperatures to SE Idaho
beginning Tuesday and possibly lasting through Thursday, with the
heaviest and most widespread precipitation expected Wednesday. At
this time, this system has the potential to bring significant
precipitation to the area, including valley rain and significant
mountain snows. Additional valley rain and above-freezing
temperatures may cause renewed flooding for many areas that are
experiencing or have experienced flooding this week.

A Flood Warning has been issued for the Antelope Creek at Darlington
as an ice jam on this creek along with runoff from recent rain and
mild temperatures has resulted in some homes being flooded in
Darlington.

The Flood Advisory for the Challis River Bridge south of Challis
will continue at the request of the BLM and local law enforcement as
citizens are urged to avoid this area. AD/JAM

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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