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fxus66 kmfr 210558 

Area forecast discussion
National Weather Service Medford or
1054 PM PDT Tue Aug 20 2019

Updated aviation discussion. of 8:45 PM, the initial cloud shield has moved
east of the coast, and is about to exit Medford. These clouds have
a distinct north-south line and should also be exiting the west
side in the next half hour to 45 minutes. Areas east of the
Cascades will take a bit longer to clear out.

The front that will provide US more fall-like conditions is still
positioned offshore. Have started looking extensively at
precipitation amounts, temperatures, and winds. Have not found
anything that would indicate any need for changes in the next 6

For tomorrow, want to take a closer look at the next model data;
but it is Worth noting that the past runs of the models,
including ensembles, have been underdispersive regarding this
system. So, will have to continue checking into things. The logic
of the previous forecast makes sense, and encourage you to read
the discussion below. -Schaaf


Previous discussion... /issued 539 PM PDT Tue Aug 20 2019/

Discussion...overall, conditions are similar to what they were
yesterday and we expect the warm and dry conditions to continue
into this evening. Satellite indicates an increase in high level
clouds that will stream over the area as the afternoon progresses,
and this will be the first indication of a front expected to move
through during the day Wednesday.

This front is quite unusual for this time of year. If it was mid-
October, it would be considered weak among our more stronger fall-
like systems. However, since it is late August, this front seems a
little more significant, especially in terms of moisture. As far as
winds go, we'll see an increase in afternoon winds on Wednesday,
especially east of the Cascades, but nothing that warrants any
headlines. The moisture on the other hand, is a bit more unusual,
especially by August standards. Technically it does have tropical
origins and is considered an atmospheric river. However, the bulk of
the moisture is expected to be north of the forecast area, but the
southern fringe of the front will deliver some beneficial rain to
the northern portions of the forecast area. While it was previously
thought that wetting rains would be isolated at best, models have
trended wetter. Now wetting rains look more widespread but still
resigned to the coastal locations north of Cape Blanco and the
higher terrain of Coos County. Some of the guidance is indicating
much higher amounts than what we have in the forecast, but it's
difficult to buy into those solutions given the time of year and
that this front is coming into a dry air mass. Decided to go with
the mean solution for this scenario which results in roughly 0.20"-
0.30" north of Cape Blanco and west of I-5, with 0.10"-0.20" roughly
north of a line from Gold Beach to the Umpqua Divide and Crater
Lake. For the rest of the area north of the or/California border and west of
the Cascades, only a few hundreths are expected and even that may be
too optimistic for the usually drier places, like the Rogue Valley.
Expect rain to begin at the coast by early Wednesday morning,
spreading inland through the day.

Temperatures on Wednesday will be around 5 to 10 degrees cooler than
today, but this cool down will be short lived. Once this front
passes through Wednesday night, the thermal trough will quickly
redevelop and hot, dry conditions with nightly intrusions of marine
stratus along the coast will return Thursday and into the weekend.
Beyond the weekend, models show a strong ridge building over the
area with temperatures climbing higher, possibly into the triple
digits by mid-week. /Br-y

Aviation...for the 21/06z tafs...VFR conditions are expected at all
locations through the early evening hours. Widespread ceilings are
no longer expected to develop at the coast, though isolated IFR
conditions could form in coastal valleys. A front will arrive
Wednesday morning and ceilings will likely to lower to MVFR
conditions then IFR in the early afternoon.

At inland locations, expect MVFR ceilings with the front to arrive
in the Umpqua basin and at krbg Wednesday afternoon. Rain and
mountain obscuration will impact the Coast Range late Wednesday
morning into Wednesday afternoon and will spread east into the
Cascades Wednesday evening. Gusty winds and increased turbulence
ahead of the front will impact areas east of the Cascades Wednesday
afternoon. Keene

Marine...updated 230 PM PDT Tuesday 20 August 2019...a Small Craft
Advisory is in effect beyond about 20 nm from shore and north of
Cape Blanco tonight into Wednesday due to gusty south-southwest
winds, steep south-southwest wind waves and increasing west swell
associated with a cold front. Most areas can also expect a period of
rain to accompany the front, though impacts from the front will be
much less for areas farther south and east.

Short period waves ease Wednesday afternoon, but swell will persist
into Thursday. Then, a thermal trough will restrengthen quickly on
Thursday with rapidly increasing north winds and steepening short
period seas. Gale force winds and very steep seas are possible south
of Cape Blanco by late Thursday afternoon/evening, so we have
hoisted a gale watch for areas mainly beyond 5nm from shore and
south of Port Orford. Conditions hazardous to small craft will also
expand north of Cape Blanco during this time frame.

Late Thursday night into Friday, the thermal trough won't be as
strong, so gales will most likely end. However, small craft
conditions are likely to persist. Further weakening of the thermal
trough Friday night into Saturday will cause winds and seas to lower
briefly, but it will strengthen again Sunday with gales possible
again by Monday. -Spilde


Mfr watches/warnings/advisories...


Pacific coastal waters...gale watch from Thursday afternoon through

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