Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 242146
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
246 PM PDT Thu May 24 2018

.SYNOPSIS...
Low pressure off of the California coast will bring showers and
thunderstorms inland from the coast this afternoon through Friday
evening. Significant wetting rainfall will occur across much of
this area. Friday night through Saturday showers will then
progressively end from west to east across the area. Dry weather
with cool nights and mornings and warm afternoons is then expected
to persist through the Memorial Day holiday weekend.

&&

.SHORT TERM...This afternoon through Sunday night...
Plentiful fields of cumulus and towering cumulus clouds early this
afternoon are now beginning to blossom into showers and isolated
thunderstorms. Thus far, one thunderstorm has formed and since
dissipated north of Diamond Lake in the High Cascades, and another
is currently occuring as of 215 PM PDT near Butte Falls.

This afternoon into this evening we expect showers and
thunderstorms will be possible from eastern and southern Douglas
counties and eastern Curry County eastward. There is a marginal
risk for severe thunderstorm winds across eastern Modoc and
southeastern Lake Counties, per the Storm Prediction Center.
While precipitable water values are above the 90th percentile
today, we expect decent storm movement of 10 to 20 knots will
prevent flooding from occuring. However, isolated urban and small
stream flood concerns do exist if storms should begin to train.

This evening through Friday morning a mesoscale low pressure
impulse is expected to arrive in Modoc County, move northwestward
across the East Side, into the Cascades, and then move onto the
West Side. Thunderstorms and moderate to heavy rainfall is
expected with this impulse, likely on the order of a half of an
inch to an inch from the Cascades eastward, but locally in the 1
to 2 inch range, especially in the more prominent mountains. West
of the Cascades and east of the Coast Range amounts of a quarter
of an inch to a half inch are expected, but locally up to an inch
is expected. There is a slight possibility of urban and small
stream flooding due to this expected heavier rainfall.

Temperatures Friday afternoon are likely to be 15 to 20 degrees
cooler than they are today across the interior under mostly cloudy
skies. While plenty of rain and rain showers are expected Friday
afternoon and evening, thunderstorms Friday afternoon and evening
are expected to remain south of Siskiyous and east of the
Cascades. Thunderstorms across Modoc and Lake counties Friday
afternoon and evening could, again be locally intense with some
small hail and locally heavy rainfall.

Saturday rain and high elevation snow showers will end from west
to east along with clearing skies. After a cool start Sunday
morning, temperatures will rebound Sunday to 5 degrees above
normal for highs. The Curry County coast is likely to warm up
nicely Sunday afternoon due to northeast downslope winds off of
the Coast Range and down the Chetco. Warmer and drier conditions
will continue across the forecast area through Memorial
Day/Monday. BTL


.LONG TERM...Monday through Thursday...
Only slight adjustments were made to the extended. Models are in
pretty good agreement with only minor differences through mid
week.

The warm and dry trend will continue on Memorial Day and with the
upper level ridge axis directly overhead, it`s likely to be the
warmest day of the extended. Tuesday will be a transition day as an
upper level trough approaches the Pacific Northwest. Temperatures
will be a few degrees cooler, and we`ll see the return of
thunderstorm chances east of the Cascades. Conditions will be
similar on Wednesday, but with slightly cooler temperatures.

By Thursday, models diverge on how they handle a secondary shortwave
that swings down the backside of the trough. The GFS drops the
energy further south into northern California and shears it off
briefly into a closed low that lingers over the area through
Thursday. The EC on the other hand, moves the shortwave through the
area by Thursday afternoon. About half of the GFS ensembles agree
with the operational while the other half are similar to the EC
solution. Because of this, went with a general blend for Thursday
and introduced a slight chance for thunderstorms over southwest
Siskiyou County. If the GFS pans out, convection would be a bit more
in coverage over northern California, whereas the EC would keep the
area dry for most of the day Thursday. Either solution will bring
seasonable temperatures. /BR-y


&&

.AVIATION...24/18Z...The marine layer has deepened, and conditions
at the coast and the western half of the Umpqua basin are generally
MVFR and should stay MVFR through Thursday morning. Gradual
improvement after around 16Z should allow some coastal areas to
briefly break out to VFR in the afternoon.

Farther inland, generally east of the line from the Illinois Valley
to Roseburg, showers will gradually diminish overnight into Thursday
morning. Scattered thunderstorms are expected in the same region on
Thursday afternoon and evening. -Schaaf/DW


&&

.MARINE...Updated 130 PM PDT Thursday 24 May 2018...Light northerly
winds today will increase tonight and Friday. Small craft advisory
level winds and steep seas are expected beginning tonight and
continuing on Friday for areas south of Cape Blanco. Winds will
weaken Friday night then increase late Saturday into Sunday as a
thermal trough develops along the coast. North winds will strengthen
further Sunday evening into early next week with small craft
advisory conditions expected over most the waters and gales and very
steep wind-driven seas possible for areas south of Cape Blanco.
-CC/Sven


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...
- Small Craft Advisory for hazardous seas from 2 AM Friday to 5
  AM PDT Saturday for PZZ350-356-370-376.

$$

BTL/MNF/SBN


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