000
FXUS66 KMFR 211116
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
403 AM PDT Tue Aug 21 2018

Updated Fire Weather discussion.

.DISCUSSION...
A few minor changes to the forecast this morning. First and
foremost we decided to lower temperatures west of the Cascades
Tuesday. Even though the flow is more easterly and off shore
compared to yesterday, not expecting it to exceed 100 degrees in
the Umpqua valley. Smoke is the primary reason for this, but the
offshore flow isn`t as strong as we would like to see in the
afternoon hours. Most areas will see temperatures in the upper
90`s west of the Cascades.

As for thunderstorms, some high resolution guidance is still
initiating convection in Modoc County and areas east of Modoc
county. Models suggest some potential instability with only 200 to
300 J/kg of CAPE. However, this is enough to produce a handful of
strikes that are fully capable of starting new fires. Hence, the
Red Flag warning looks good for this forecast cycle. Read the
discussion below for more information on the Red Flag Warning.

Beyond today, we`re watching the upcoming cool down towards the
end of next week. Ensemble data shows troughing in the Pacific
Northwest. This is a good thing temperature wise, but winds will
likely pick up cause issues with existing and new fires. Right
now the forecast is calling for highs in the upper 80`s west of
the Cascades late this weekend into next week.

-Smith

&&

.AVIATION...For the 21/06Z TAFs...IFR/LIFR fog and stratus will
prevail along the coast overnight until around 15z Tuesday morning.
Models are still showing some stronger NE offshore winds that may
try to scour out the stratus from some areas earlier than 15z, but
this is when we are currently breaking it out at North Bend. Even if
the stratus/fog leaves early, wildfire smoke should still cause MVFR
visibility through Tuesday. We do expect clearing of the stratus in
most areas north of Gold Beach Tuesday, but north winds will reverse
to southerly and stratus will surge northward again over the coastal
waters/adjacent coastline Tuesday afternoon and evening.

Inland, wildfire smoke in most areas will limit visibility
to MVFR, and occasionally to IFR. However, solid IFR/LIFR visibility
can be expected immediately downwind of the most active wildfires.

Thunderstorms are unlikely tonight, but if one were to occur, it`d
be east of the Cascades. Isolated thunderstorms may develop Tuesday
across SE sections of the area, including Modoc and southern Lake
Counties.

-Spilde


&&

.MARINE...Updated 200 AM PDT Tuesday 21 August 2018...The thermal
trough over the area the last couple of days will weaken and shift
inland today. North winds and steep seas, mainly from Cape Blanco
southward and beyond 8 nm from shore north of Cape Blanco will
gradually subside. Areas of wildfire smoke will persist and bring
haze and minor visibility reductions aside from the normal
reductions associated with the marine layer.

A wind reversal to southerly will occur today into tonight,
especially inside 40 NM from shore. This will occur first near
Brookings, then surge up the coast late Tuesday and Tuesday night.
With the south winds, expect fog/stratus to develop. These
conditions will linger Wednesday, but overall, expect calmer seas
and sub-advisory winds.

Beginning Thursday, another thermal trough will develop resulting in
a return of north winds. Late Thursday and Friday, the thermal
trough will strengthen likely bringing another round of gusty north
winds and steep seas, highest south of Cape Blanco. -CC


&&

.FIRE WEATHER...Updated 300 AM PDT Tuesday 21 August 2018...In
addition to local wildfire smoke sources, substantial smoke
continues to drift southward over the area from wildfires to our
north from northern Oregon, Washington, and British Columbia. From
the Siskiyous southward, and across portions of Modoc County,
however, there`s less smoke, which is allowing fires to burn more
freely.

A weak trough over eastern portions of the area combined with some
mid level moisture is expected to bring a slight risk for showers
and thunderstorms to eastern portions of the area today through this
evening. Models continue to show that thunderstorms will be limited
to far southeast Klamath, far eastern Siskiyou, Lake and Modoc
counties this morning into Tuesday evening. The greatest model
agreement, especially among our standard model suite, as well as the
convective allowing models, is for an area of isolated to widely
scattered thunderstorms to develop over Modoc County this afternoon
and evening. However, there is also a slight chance for showers and
thunderstorms this morning. Due to limited fire fighting resources
available in the Modoc due to the ongoing Stone Fire there, as well
as increased confidence in a mix of wet and dry storms there, a red
flag warning has been issued for lightning for FWZ 285.

Otherwise, there are limited concerns for wind and RH early this
morning, and then again Wednesday and Thursday afternoons. There
will be enhanced east wind along and just west of the Oregon Cascade
Crest with moderate RH recoveries this morning. Then, the next two
afternoons, expect low RHs and breezy winds in west side valleys.

A cooler trend is expected for later this week into early next week
as an upper trough deepens over the region. There is also some
possibility of light rainfall for portions of the area west of the
Cascades Sunday night into Monday. -CC

&&

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

CA...Red Flag Warning until 11 PM PDT this evening for CAZ285.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT early this morning for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 11 AM PDT this
     morning for PZZ356-370-376.

$$

NWS MFR Office Area Forecast Discussion