Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 290227

Area Forecast Discussion
National Weather Service Boise ID
827 PM MDT Sun May 28 2017

.DISCUSSION...No changes to current forecast. Weak showers
remain possible across the West-Central Mountains of Idaho as
radar continues to demonstrate some activity just east of the
forecast area boundary. Warm conditions to continue on Memorial
Day, when valley locations will approach 90 degrees. Again, some
instability is possible in the afternoon across the West-Central
and Boise Mountains of Idaho. The warming trend continues through
Tuesday, with cooler temperatures possible Wednesday as a
wave of low pressure impacts the area. Hydrology concerns remain
due to the warmth, and river levels continue to be monitored.


.AVIATION...VFR under mostly clear skies.  Winds, variable and less
than 10 kts, up through 10 KFT MSL. Slight chance of showers and
thunderstorms over the West Central Idaho Mountains, though precip
amounts will be light.


SHORT TERM...Tonight through Tuesday...An upper level ridge axis
centered across eastern Oregon this afternoon will drift slowly
eastward as it weakens through Tuesday. In its place, a large and
strong trough will move toward the PacNW coast late Tue, bringing
SW flow aloft to the region. Warming will occur the next two days,
with highs Tue in the lower 90s in the lower elevations. For this
evening and tomorrow, the chance of showers and thunderstorms
remains constrained to the mtns of SW Idaho. But with the approach
of the trough, there will be a slight chance in Harney and extreme
southwest Baker counties Tue afternoon. Precip, if any, will be
light as it will be difficult for much rain to make it all the way
to the ground without evaporating. Winds will remain generally
light through tomorrow, but increase Tue as pressure falls occur
in advance of the approaching trough. Southeast winds in the Snake
River Plain will lead to additional warming due to downsloping.

LONG TERM...Tuesday night through Sunday...The GFS and ECMWF are
in much better agreement about how to handle the next offshore
trough moving in on Wednesday. Some terrain induced showers and
thunderstorms are possible on Wednesday afternoon in this
southerly flow. This slow moving trough wont actually have the
upper level axis pass over the area until Thursday, which will
bring more moisture and dynamics to support more widespread
showers and thunderstorms on Thursday afternoon. Once models move
that system to the east, they diverge very quickly and very
drastically, such that the GFS shows another ridge overhead for
the weekend and the ECMWF has a closed low nearby. Therefore, the
forecast beyond Friday is quite uncertain.





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