NWS Medford, OR wrote its last area forecast discussion before the first event at Jul 28, 2:01 PM PST, 44 minutes earlier.
Area forecast discussion, Jul 28, 2:01 PM PST, 44 minutes before
Area Forecast Discussion
National Weather Service Medford OR
301 PM PDT Sun Jul 28 2019
.DISCUSSION...Satellite imagery is showing some congested cumulus
forming across the SE portion of the forecast area this afternoon.
No lightning yet, but a few isolated cells are beginning to show
up on radar and a couple of these could develop into thunderstorms
through this evening, mainly in eastern Modoc and SE Lake
Counties. There probably won't be much, if any, rain with these
since the air mass below the cloud base is so dry. These will move
northeastward and away from the forecast area overnight.
The rest of the area is mainly sunny, but with plenty of smoke
originating from the Milepost 97 fire along I-5 just south of
Canyonville. The thickest smoke right now is near Azalea extending
southward to Grants Pass, Rogue River and the Applegate Valley.
The smoke plume is shifting eastward a bit and visibility will
deteriorate across the remainder of the Rogue Valley late this
afternoon into this evening with the thickest smoke in
Medford/Ashland between about 4 and 9 pm. The smoke plume will
probably waver westward again overnight into Monday morning, but
significant visibility reductions are possible all along I-5 from
Canyonville southward into northern California, including the
Shasta Valley. The worst visibility will probably be near or just
south of Azalea.
We are expecting a bit more of a marine push tonight into Monday
morning such that higher humidity will move in over much of the
Umpqua Valley and some clouds could even develop and bank up
against the Umpqua Divide. This will help with respect to slowing
the fire's spread, but probably also inhibit air attack
operations. Coastal stratus/fog and even perhaps a bit of drizzle
are possible from Cape Blanco northward and also near Brookings.
Overall, on Monday, with the air mass aloft cooling slightly,
temperatures should be a few degrees lower than today. Aside from
wildfire smoke, it should be mostly sunny. Convection allowing
models are showing some build-ups again Monday afternoon and/or
evening near Winter Rim and perhaps across northern Lake County.
But, any activity once again will be isolated at best.
The weather pattern remains fairly benign through much of the
remainder week with temperatures mostly within a couple of degrees
of normal. An upper trough and associated weak frontal system
will approach from the Pacific on Thursday and low pressure will
move in near Vancouver Island on Friday. But, the front will
probably get hung up and dissipate near the coast or just offshore
as the flow aloft becomes parallel to the front. We've kept slight
chance POPs over the coastal waters, but don't bring precipitation
onshore. We'll probably see slight warming into next weekend, but
no heat waves. -Spilde
&&
.AVIATION...For the 28/18Z TAFs...IFR/LIFR stratus/fog near
Brookings should clear out for a while this afternoon. MVFR with
local IFR visibility in wildfire smoke will cover a large portion of
Josephine, Jackson and Siskiyou Counties this afternoon through
Monday morning. Worst visibility at Medford likely between 23z this
afternoon and 05z this evening. Isolated thunderstorms may
develop in portions of southern Modoc/southern Lake Counties this
afternoon/evening, then dissipate overnight. MVFR/IFR ceilings will
likely return to coastal areas tonight, with some spreading into the
lower Umpqua Valley, and perhaps to Roseburg, by sunrise. -Spilde
&&
.MARINE...Updated 230 PM PDT Sunday 28 July 2019...A thermal
trough near the coast will strengthen through tonight, then slowly
weaken Monday through Wednesday. Strong north winds and steep to
very steep wind-driven seas will persist into Monday morning with
the strongest winds and heaviest seas south of Cape Blanco. From
Monday into Tuesday, the steep seas will be limited to areas south
of Gold Beach in the afternoons and evenings. Winds and seas will be
relatively light Wednesday into Thursday. A weak front will approach
the coastal waters Thursday. -Sven
&&
.FIRE WEATHER...Updated 215 PM PDT Sunday, 28 July 2019...
There is a slight chance for thunderstorms over eastern Modoc and
southeastern Lake County this afternoon and evening. Overnight and
this morning, high resolution convection allowing models began to
show the potential for isolated thunderstorms. Meanwhile,
satellite imagery depicting altocumulus fields this morning and
extensive cumulus fields early this afternoon have underlined this
potential. The dry air at the surface will likely limit development,
but would also create the potential for dry lightning due to high
cloud bases and the likelihood that any precipitation would evaporate
before reaching the ground. Guidance also is beginning to show some
potential for convection farther north Monday, but confidence is
very low. If thunderstorms do develop either day, they should be
isolated.
Other than lightning, the primary concern for the rest of today and
tomorrow will be dry and warm conditions and breezy afternoon and
early evening winds. While overnight recoveries have been and should
continue to be good, daytime humidities will be low, particularly
east of the Cascades, and especially over the Modoc and far southern
Lake County. Dry air in the midlevels and just above the higher
ridgelines will likely mix down to the surface with daytime heating.
When the breezy winds kick in during afternoon and evening, we
should see several areas approach critical conditions in the Modoc
or far southern Lake County, but not for the duration required for a
watch or warning. The same setup is expected again on Monday,
although a very gradual cooling trend with slightly higher humidity
is expected for the majority of the area through Wednesday.
Regarding dryness and instability as indicated by the Haines Index,
we're still expecting a 5 over the the Milepost 97 Fire near
Canyonville, as well as the fires along the Klamath River in
Siskiyou County, this afternoon and evening, which equates to a
moderate potential for plume dominated fire activity. We
then expect it to lower to a 3-4 for the remainder of the week. East
of the Cascades, Haines values of 5 and 6 are expected today and
again, although to a lesser extent, on Monday. These areas that
experience Haines 6 conditions are likely to see flare-ups or
even plume dominated activity on any new or undiscovered wildfires.
-BPN
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.
CA...None.
Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Tuesday
for PZZ356-376.
Hazardous Seas Warning until 11 AM PDT Monday for PZZ356-376.
Small Craft Advisory until 11 AM PDT Monday for PZZ350-370.
MAS/BPN/SBN