Area Forecast Discussion
Issued by NWS Boise, ID
FXUS65 KBOI 182153
Area Forecast Discussion
National Weather Service Boise ID
253 PM MST Wed Jan 18 2017
.SHORT TERM...Tonight through Friday...Our latest winter storm is
well underway this afternoon, as a large area of snow is presently
working its way into the CWA. Temperatures are such that rain,
snow, sleet, and freezing rain have all occurred over parts of the
area today. Latest sounding information indicates that this
temperature profile will continue through the night with only
small changes. Therefore, we have altered the forecast for more
snow this evening than previously forecast. This will be heavy wet
snow for most folks, limiting the depth. Even with that, there
will still be substantial totals in some areas. Baker County will
see totals from 4 to 12 inches, the Lower Treasure Valley will
range from 6 to 9 inches, the Upper Treasure Valley will see from
around an inch up to 7. The Western Magic Valley should end up
seeing 3 to 8 inches. Snow levels are higher to the north and
south of the Snake River Plain, and therefore some of the usual
places that get the most snow won`t see too much more than the
valley for this storm. This includes McCall, for example, with a
forecast of 5-6 inches by tomorrow afternoon - which is just about
the same as Boise. A cold front will move through late tonight,
but little will change at the surface. However, aloft, snow levels
will beging to come back down. This will bring us back to "normal"
snow conditions, meaning the mountains will get more than the
valleys as of tomorrow afternoon and going forward from then.
This system will lessen in intensity tomorrow and then move off to
the east tomorrow night. The partial clearing of skies will allow
temps to cool back down into the 20s in the valleys, and allow the
new wet snow to freeze almost solid. Friday, a new system will
move into southeast Oregon, spreading snow and rain into mainly
Harney County, but also affecting Baker and Malheur. This may
prompt another advisory for Harney County, but we will move
through this system and then address the Friday one. In
conclusion, and just to be clear, tonight should be mostly snow,
but the temperature profile is very close to what would support
sleet and freezing rain, and some areas may get just above
freezing for overnight lows and experience regular rain (although
this will likely freeze on any pre-existing snow/ice pack and
therefore effectively become freezing rain anyway).
.LONG TERM...Friday night through Wednesday...Pacific system will
continue to progress eastward through the region bringing light snow
to the area as most of the energy moves south of the Nevada border.
Expecting a brief repreive in precipitation Saturday before another
system moves in Sunday. Models are indicating that this system will
bring in more substatial snow amounts than the previous system,
though mostly to the higher elevations. Precipitation will generally
fall as snow for both systems. Will see an amplified ridge begin to
push into the Pacific Northwest Tuesday and over the region
Wednesday, bringing dry conditions with it. Temperatures will range
between 5-10 degrees below normal.
.AVIATION...MVFR/IFR, isolated LIFR in heavier showers. Mountain
obscuration expected. Pockets of VFR during breaks in precip.
Expecting snow to be the predominant precip type through tomorrow
morning, with areas of IP/FZ along the Snake River Plain and in the
Lower Treasure. Areas of mixed rain/snow closer to the Nevada
border. Heaviest precip totals this afternoon and evening,
continuing in the mountains overnight. Surface winds generally
southeast 10-20 kts. Gusts to 30 kts in Baker County. Northeast
winds 30 kts near KJER. BLSN in these areas with winds tapering
offovernight. Winds aloft at 10 kft MSL, southwesterly 35 to 50 kts,
decreasing to 20-30 kts by 19/09Z.
.HYDROLOGY...Model trends indicate lesser amounts of precipitation
falling as rain across the Treasure Valley through the duration of
the storm. Surface temperatures are expected to rise above freezing
but not a dramatic warmup, so melting of the snowpack in the valley
shouldn`t be excessive. Feeling is that the threat of minor flooding
due to rain and snowmelt is pretty small. Impacts are more likely to
occur on Thursday an be limited to standing water along some city
streets and highways where snow and ice may be clogging gutters and
Ice jams on the Snake River around Ontario and Payette downstream to
near Weiser remain a concern. Folks in low-lying areas near the
Snake River, especially around Ontario and Payette should continue
to monitor river conditions and be prepared for fluctuating river
levels and possible lowland flooding due to ice jams.
ID...Winter Storm Warning until 5 PM MST Thursday IDZ016.
Winter Weather Advisory until 5 PM MST Thursday IDZ015-028-030.
Winter Storm Warning until 11 AM MST Thursday IDZ011-012-033.
Winter Weather Advisory until 11 AM MST Thursday IDZ013-014-029.
OR...Winter Storm Warning until 11 AM MST /10 AM PST/ Thursday
Winter Weather Advisory until 4 AM PST Thursday ORZ061.