Special Weather Statement, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
229 AM MST Tue Feb 21 2017

.SHORT TERM...Today through Thursday night.
Expect precipitation to continue today but likely not as heavy
with winter storm warnings continuing for central mountains and
upper Snake River Highlands near the Montana and Wyoming borders.
Another 3 to 6 inches of snow may fall in those regions. Lower
elevations will continue to see rain showers with isolated
thunderstorms possible this afternoon in all areas with
instability in place and cold frontal passage. Expect windy
conditions in the southern highlands and Snake River Plain and
Magic Valley with wind advisories in effect until 8 pm with gusts
over 40 mph expected. Snow levels will drop to valley floors
overnight but precipitation should mainly end other than very
light showers. Upper trof will approach Wednesday with snow
showers returning to all areas. Expect light accumulations
everywhere Wednesday through Thursday night with most likely snow
areas in Snake River Plain and southeast highlands. Generally 1
to 4 inches of snow are possible everywhere in this time frame.
GK

.LONG TERM...Friday through next Tuesday. Both the GFS and ECMWF
appear to be trending further off shore as the next trough drops
south across WRN Canada into the NW coastal waters Friday afternoon
which leaves SE Idaho falling between an exiting wave to the east
and a developing Low to the WNW. The low continues to drift SSW
Saturday as a backdoor Canadian trough settles south across the NRN
Rockies. The main change with this model cycle is that the low off
the California coast becomes invigorated and infused with sub-
tropical moisture Saturday night before lifting inland Sunday and
Monday with attending moderate to heavy precipitation. The models
also warm things up introducing a mix of rain and snow throughout
the Snake River Plain whereas previously we remained under a cold
trough. Gave this new wrinkle some space in the mix of the new
forecast and if the trend continues we can bump the precipitation
chance up even further. Drier and cooler NW flow breaks into the
region by Tuesday. Huston
&&

.AVIATION...A strong moist SW flow was present over SE Idaho early
this morning as a swath of moderate rain lifted north through the
Snake River Plain. Statistical guidance is indicating that the very
strong winds aloft will mix down toward the surface today especially
behind the advancing swath of precipitation. Instability showers
should return to the area this afternoon dying out by early evening.
Snake Plain terminals should see prevailing VFR conditions with
TEMPO MVFR CIGS in -SHRA this afternoon along with the strong winds.
KSUN is expected to remain at or below airfield minimums until later
this afternoon or evening when the instability helps mix things out.
Again, the models are showing a deep saturated layer over KDIJ and
remain of little help in preparing the terminal forecast. Would
expect some brief improvement this afternoon as the atmosphere
destabilizes but then filling back in with convection until partial
clearing late tonight. Huston
&&

.HYDROLOGY...Moderate precipitation amounts and mild low to mid
elevation temperatures the past several days have maintained and
potentially worsened low land flooding threat across the region.
Minidoka county has, in particular, seen increased low land
flooding. Will continue all low land flood headlines. With
significant rain expected overnight through tomorrow below 6500
feet, some of the flood advisory areas may see increased flooding.
These areas, to include Eastern Custer, Central Blaine, Jefferson,
Southeast Butte, Northwestern Bonneville, Western Madison, and
Southwest Caribou counties, may need to be upgraded to flood
warnings. Some rises have been seen in area creeks, and continuing
to see small responses on the rivers as well. Have also issued a
flood warning for Portneuf River at Pocatello with river forecasted
to rise to flood stage Tuesday morning. Current trend is to decrease
crest and shorten time the gage spends above flood stage. Wyatt

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 8 PM MST this evening for IDZ017-020>022.

Winter Storm Warning until 3 PM MST this afternoon for IDZ018-
019-031.

&&

Special Weather Statement
National Weather Service Pocatello ID
821 AM MST TUE FEB 21 2017

IDZ019-020-023-211545-
Caribou Highlands ID-Upper Snake Highlands ID-
Upper Snake River Plain ID-
821 AM MST TUE FEB 21 2017

...STRONG WINDS AND SMALL HAIL HEADING FOR TETON...FREMONT...CENTRAL
JEFFERSON...NORTHEASTERN BONNEVILLE AND MADISON COUNTIES UNTIL 845
AM MST...

At 815 AM MST, Doppler radar was tracking line of gusty winds near
Teton, or 7 miles east of Rexburg, moving northeast. Small pea size
hail is possible within this line as well.

Wind gusts up to 55 mph will be possible with this storm.

Locations impacted include...
Rexburg, Driggs, Ashton, Felt, Marysville, Victor, Sugar City, Teton,
Parker, Tetonia, Drummond, Egin, Ponds Lodge, St Anthony, Plano,
Chester, Last Chance, Island Park Reservoir, Ashton Reservoir and
Warm River.

LAT...LON 4356 11113 4376 11165 4380 11235 4442 11151
      4444 11110 4413 11109 4412 11105 4366 11105
TIME...MOT...LOC 1515Z 240DEG 49KT 4379 11165

NP/DMH