000
FXUS66 KMFR 102157
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
257 PM PDT Fri Jul 10 2020

.DISCUSSION...

Quiet weather will continue through this weekend except for the
fire weather concerns discussed in the fire weather discussion
below. Otherwise, the main feature we looked at today was the
stratus and the potential for some drizzle along the coast
tonight. The NAM model usually picks up on this when the marine
layer is pretty condensed. Since the NAM is showing some spotty
precipitation off the coast, then we should see some low stratus
and perhaps some drizzle along the coast tonight and Saturday
night.

Outside of the coastal features, we`ll see a trough swing through the
region with the four corners high in place for this weekend. This
will result in some rather breezy conditions across most of
southern Oregon and northern California this weekend. This is
discussed in more detail in the fire weather discussion below.

After this weekend, the thermal trough begins to build along the
coast and we`ll start to see some offshore winds along the coast
and over most of the west side. Next week, temperatures will be
warmer than normal by only a couple of degrees. Highs will likely
punch through the 90`s in most of southern valleys west of the
Cascades with 80`s east of the Cascades. Brookings will be worth a
visit with highs in the lower 80`s during the afternoons next
week.

The last thing worth mentioning is the potential for thunderstorms
towards the end of next week on the 16th and 17th. The GFS and
the National Blend of Models are picking up on 15 to 20 percent
chance for thunder. We didn`t throw it in the forecast officially
since the probability of precipitation is near zero. This could
be a symptom that the thunderstorms will be on the drier side.
This thunderstorm potential will be something to pay attention to
for the next few forecast cycles.

-Smith

&&

.AVIATION...For the 10/18Z TAF Cycle... IFR to MVFR exists this
morning north of Port Orford along the coast and inland into the
Coast Range and Umpqua Basin, and in a small area along the coats
near Brookings, where partial terrain obscurations exist. Expect the
stratus and fog to dissipate by afternoon. Mostly clear skies are
then likely to prevail until low clouds redevelop in the IFR to MVFR
range tonight, around 06Z at KOTH, then spreading inland, possibly
to KRBG, by early morning. ~BTL/BPN


&&

.MARINE...Updated 200 PM PDT Friday, 10 July 2020...
High pressure centered well to the southwest off of the California
coast combined with an upper level trough across the northeastern
Pacific will maintain a light to moderate northerly flow through
Sunday morning. Conditions could near advisory level for a small
area from 5 to 20NM from the coast this afternoon and evening west
of Port Orford to Point Saint George. The upper level trough will
shift inland Sunday allowing the high to expand northeastward behind
it, rapidly developing a thermal trough along and near the coast.
The thermal trough and the resulting gusty north winds and steep
seas will continue through much of the week, with Gales and very
steep seas possible in the afternoons and evening south of Gold
Beach.

A Gale Watch is in effect for offshore waters south of Gold Beach
through Tuesday evening, but gales will likely expand in size
heading into the second half of the week. Meanwhile, Small Craft
Advisory conditions could develop as early as Sunday afternoon south
of Cape Blanco, then spread to all of the southern Oregon coastal
waters by Monday morning. Conditions are not expected to improve
until the thermal trough pushes inland next Friday or Saturday.
~BTL/BPN

&&

.FIRE WEATHER...Updated 200 PM PDT Friday, 10 July 2020...The main
concern over the next several days will be gusty winds with low
relative humidity Saturday afternoon and evening for portions of
Fire Weather zones 624, 625 and 285 and just for Fire Weather Zone
285 Sunday afternoon and evening. Details on this will follow below.

Confidence is higher for Red Flag conditions to be met Saturday
afternoon and evening due to a combination of Gusty winds and low
relative humidity for most of Fire Weather Zone 285 and portions of
Fire Weather Zones 624 and 625 and the Fire Weather Watch has been
upgraded to a Red Flag Warning. Details can be found at RFWMFR.

There a few reasons for this. First, 700mb winds are expected to be
between 15-25 kts with stronger winds pushing close to 30 kts moving
in from the northwest late Saturday afternoon. At the same time, 600
mb winds are expected to be stronger (25-30 kts), covering a larger
portion of the area, and there`s a chance these could mix down near
or at the surface as we reach max heating. Second, pressure
gradients will be tighter which will be another contributing factor
leading to gusty winds. Third, guidance supports lower relative
humidity with some areas bottoming out below 10 percent.

An upper trough will swing north of the area (Southern B.C.)
Saturday night into Sunday, which will squash down the four
corners high southeast of our area. In it`s wake will be a stable
west to northwest flow aloft. However like Saturday, the surface
pressure gradients will tighten up east of the Cascades resulting
in gusty winds and low relative humidity Sunday afternoon and
evening. The one difference is relative humidities are expected to
be slightly higher in Fire Zones 624 and 625, so were not
expecting any critical conditions there. However, guidance does
suggest relative humidities will be lower in Fire Zone 285 and
could be on the borderline of reaching Red Flag conditions for
mainly the southeast part of the zone. There`s some indications if
Red Flag conditions develop, it may only be for a few hours. Even
then, we`ll lean on the side of caution given the high fire
danger in this area and a Fire Weather Watch has been issued. For
more details please see RFWMFR.


In the meantime, gusty breezes are expected in the Rogue and
Applegate Valleys south and eastward to the Mount Shasta highlands,
most notably over Siskiyou Summit into the northern end of the
Shasta Valley Saturday afternoon and evening and again Sunday
afternoon and evening, but were not expecting critical conditions.

Other than the days noted above, no concerns are expected for the
next 6 days. Recoveries expected to be fairly good at night for
along and north of the Umpqua Divide and coast. Onshore flow will
continue allowing marine stratus to return for most of the coast,
especially north of Cape Blanco Coquille and Umpqua Basin.

Temperatures will warm up through Saturday, but only around 3-5
degrees above average for inland locations. Slight cooling is
expected Sunday. Warming is expected for next week, but we`ll still
be under the influence of a weak upper trough with the four corners
high remaining southeast of our area, thus no heatwave.

The general consensus among the ensembles, individual ensemble
members and cluster analysis remain the same. A general troughiness
remaining over the PAC NW. There will be times where the four
corners ridge will try and nudge its way towards our area, but not
enough to where it would bring significant heating for next week and
a continued low or almost zero chance of precipitation and
thunderstorms.

However, the operational GFS and to a lesser extent the ECMWF shows
a south to southeast flow towards the end of the week which could
tap into some monsoonal moisture with a weak trigger. If this pans
out, then we could be looking at our first chance of thunderstorms.
It`s a ways out there, so a lot can change and so far none of the
individual ensemble members show anything. We`ll continue to keep
a close watch on this.

-Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM to 10 PM PDT Saturday for ORZ624-625.

CA...Red Flag Warning from 2 PM to 10 PM PDT Saturday for CAZ285.
     Fire Weather Watch from Sunday afternoon through Sunday evening
     for CAZ285.

Pacific Coastal Waters...Gale Watch from Sunday afternoon through late Tuesday night for
     PZZ376.

$$

NWS MFR Office Area Forecast Discussion