Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 231522

Area Forecast Discussion
National Weather Service Boise ID
922 AM MDT Sun Apr 23 2017

.DISCUSSION...Radar at 8AM MDT showed rain showers in Baker County,
OR, and Adams and Valley Counties, ID, but little if any elsewhere.
Models are not in good agreement regarding pcpn this afternoon but
showers will stay in the forecast as weak upper trough comes in
from Oregon.  Instability will produce a chance of thunderstorms
this afternoon mainly on the Idaho side.  After relative drying
tonight a much wetter Pacific storm will bring widespread rain
Monday morning, with a chance of thunderstorms again Monday
afternoon as the air mass destabilizes.  Current forccast already
has a slight chance of thunder everywhere Monday afternoon but
latest models indicate a better chance.  Afternoon package will
addresss that in more detail.  For now though, no updates.


.AVIATION...VFR and occasional MVFR showers and isolated
thunderstorms through 24/06Z, then a brief break, then more showers
and afternoon thunderstorms moving in from west to east after 24/12Z
in E Oregon and after 24/15Z in W Idaho. Surface winds: Generally
10-15 kts, except gusts to 25 kts in SE OR and Magic Valley, and
gusts to 35 kts near stronger storms.  WInds aloft near 10 KFT MSL:
West 15-25 kts, then increasing to 35-45 after 24/12Z.


SHORT TERM...Today through Monday...A weak cold front is
moving across southwest Idaho this morning (around 3 AM MDT) with
showers generally located out ahead of it. Dry air will
temporarily work its way into the southern zones this morning
before an upper level shortwave spreads showers across the region
this afternoon. Increased instability in the afternoon as cold air
aloft moves into the area, bringing a chance of thunderstorms to
southwest Idaho and east central Oregon. Breezy conditions
expected across southeast Oregon and south of the Snake River
Plain. Showers will taper off overnight Sunday and winds will
diminish as the upper level flow turns westerly, ushering in the
next bout of moisture for Monday. Expecting widespread showers and
a slight chance of afternoon thunderstorms across the region.
High temperatures will cool 5 to 10 degrees Sunday and again on
Monday as snow levels drop from 6-8K FT MSL Sunday, north to
south, to 5-6K FT MSL, north to south, Monday.

LONG TERM...Monday night through Sunday. The wave axis will
approach the northeastern portion of the forecast area Monday
evening, with continued showers and thunderstorms expected. The
threat for thunder loses its muster through the evening with loss
of daylight. A brief period of drying will be possible Tuesday as
the trough axis sweeps through the area allowing for drier
northwest flow. However, the next surge of Pacific moisture will
be moving along the coast at the same time, with activity
spreading into eastern Oregon by Tuesday afternoon/evening. Shower
activity to again become fairly widespread by Wednesday morning.
This northwest flow remains over the area through Sunday, with
unsettled conditions expected as models showing the potential for
another atmospheric river along the Pacific coast. By Friday
afternoon, models are in fair agreement at an area of low pressure
developing over the Intermountain West, centered near the
Idaho/Wyoming border. As this system moves off, models gain
confidence in a transition to a ridging pattern, with warming
temperatures. This ridge will continue into Sunday, though an
area of low pressure moving south out of Alaska will flatten the
ridge, with moisture able to reach into the northern reaches of
the forecast area by Sunday afternoon/evening.





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