Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 200244 CCA

Area Forecast Discussion
National Weather Service Boise ID
844 PM MDT Mon Mar 19 2018

.DISCUSSION...Weak upper low off the Oregon coast will track
inland tonight and across our CWA Tuesday.  The low will bring
scattered rain and snow showers to our northern mountains, and
isolated rain showers to southern areas Tuesday.  No impacts
are expected with these showers.  Temps will be a couple degrees
warmer Tuesday, and a few more degrees warmer Wednesday.  Light
east or southeast winds Tuesday and Wednesday.  No updates.


.AVIATION...Lingering MVFR/IFR showers across the mountains, Baker
County through Valley County this evening, tappering off by 20/12Z.
Otherwise, low VFR. Another round of isolated showers expected after
20/12Z, spreading north of a KBNO-KBOI-KJER line, and tapering off
by 21/03Z. Snow levels between 3500-4500 ft with mountains obscured.
Surface winds: variable, 10 kts or less. Winds aloft near 10 KFT
MSL: SW 15-20 kts.


SHORT TERM...Tonight through Wednesday...Scattered afternoon
shower activity will dissipate this evening with loss of daytime
heating. A weak low off the Oregon coast pulls across the area on
Tuesday with clouds and accompanying light precipitation. Snow
levels are 4-5k feet MSL with less than an inch of accumulation
above 6k feet. A warm front lifts through the area on Wednesday
with another round of light rain/snow. Precipitation totals
through Wednesday are 0.10-0.20 inches in the mountains and less
than 0.10 inches in the lower basins and valleys. Clouds and light
precipitation on Tuesday will slow the warming trend, keeping
temperatures near normal. Though cloudy conditions will persist,
the warm frontal passage on Wednesday will push temperatures to
about 5 degrees above normal.

LONG TERM...Wednesday night through Monday...Large upper low off
the  PACNW coast will send in ample moisture for widespread
precipitation Thursday. A cold front moving through later on
Thursday will enhance QPF amounts. Snow levels ahead of the front
will be around 7000 ft, then drop to around 3000 ft by Friday. A
break in precip though on Friday will limit snow accumulations. By
Saturday, the upper trough axis moves inland and brings another
cold front through the area with more enhanced precipitation, and
snow levels will drop to lowest valley floors. Temperatures will
drop to below normal on Friday and about 10 degrees below normal
on Saturday.

...Saturday evening through Tuesday morning... Moist, active
westerly flow as a series of trough/ridge couplets quickly move
through the CWA. Models somewhat in agreement with the GFS ahead
in the timing while hinting at larger breaks in between trough
to ridge dominance/coverage. In leaning more with the GFS, expect
to start off Saturday night with widespread snowfall throughout
the area. This should continue to lessening degrees as we progress
though the period. Breezy westerly winds associated with the
trough as it moves through. Sunny skies and lighter winds by
Sunday afternoon as a ridge moves into the area in advance of the
next trough on our doorstep by Tuesday morning. As we gradually
warm, the Treasure Valley may see rain on Tuesday. High and low
temperatures both expected to be 5 and 7 degrees below normal.





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