NWS Medford, OR wrote its last area forecast discussion before the first event at Aug 1, 2:10 PM PST, 1 hour 50 minutes earlier.
Area forecast discussion, Aug 1, 2:10 PM PST, 1 hour 50 minutes before
Area Forecast Discussion
National Weather Service Medford OR
310 PM PDT Sun Aug 1 2021
.DISCUSSION...Cu is popping like, well...,popcorn this afternoon.
A few quick thunderstorms have popped east of the Cascades and
just west of Klamath Lake. Instantaneous rainfall rate estimates
are between 1.5"-2". Less has been detected at the surface because
of their short duration, but ones that last over an area long
enough have produced a few inches of rain. Just across the Modoc
County line a flash flood warning was issued for a burn scar. A
similar concern will exist in our area of concern with any slow
moving storms. Ponding on roadways is also possible where drainage
is poor.
Not many changes to the forecast today. The ones that were made
are as follows,
Raised both Max and Min Temps through Tuesday afternoon. This is to
account for some slight slowing in the progression of the upper
level trough expected to swing through the region later this week.
Did not however, only trended the temps upward, avoiding the maximum
temperatures proposed by guidance because of smoke that is
anticipated from emerging fires in N. Cal. over the next few days.
The other change was to the thunderstorm coverage for tomorrow. The
area most favorable for Tstorms has trended NE with new runs today,
so have reduced the area calling for a chance of Tstorms in NE Lake
and Klamath Counties to only extreme NE Klamath County and the
northern half of Lake County. There still remains a slight chance
for Tstorm activity in other portions of Lake and Klamath county,
plus NE Modoc County. What seems most likely though is that this is
the area for CU buildups, then propagate to the NE into more
unstable conditions.
Otherwise the forecast remained much the same. The only change was
to lower winds by 5-8 mph east of the Cascades. The expectation is
that this front will not be elevated and thus less of a seasonally-
strong wind producer. Gusts in the Winter Rim/Summer Lake area for
now could max out around 30 mph. Beyond this though, the extended
discussion from last night still stands, 448 AM PDT Sun Aug 1 2021
Long-term...Our pattern will change as a string of Pacific troughs
move into the area mid-week. Wednesday will have slightly cooler
daily temperatures and this pattern will bring a slight cooling
trend back down to near normal daily temperatures for the remainder
of the week. This change will also bring gusty afternoon and evening
westerly winds. A shortwave or a closed low will push inland with an
addition of an influx of moisture indicates a possibility of showers
and some thunderstorms for areas in Lake County and Klamath County
on Wednesday afternoon into Thursday. The National Blend of Models
(NBM) is showing precipitation chances creeping back into the
forecast Friday into Saturday as a front moves in. This will likely
bring light precipitation for the Umpqua Divide and northward,
including North Bend, Roseburg, and Lakeside. There is a significant
spread among various model ensemble members regarding the
progression of this pattern affecting our area and confidence
remains low on the details in regards to timing, location, and any
risk of thunderstorms. Viken/Keene
-Miles
&&
.AVIATION...For the 01/18Z TAF Cycle...Over the coastal waters,
along the coast, and in the coastal valleys...Marine stratus is
gradually burning off and clearing will occur inland but IFR will
persist just offshore this afternoon. The lower conditions will move
back onshore early this evening and persist into Monday morning.
Over the remainder of the area...VFR conditions are expected through
the TAf period. However, smoke and haze from area wildfires could
result in some visibility limitations very near the fires. The main
concern will be isolated to scattered thunderstorms this afternoon
and evening with gusty winds. -Petrucelli
&&
.MARINE...Updated 200 PM PDT Sunday 1 August 2021...Offshore high
pressure and a thermal trough near the coast will both persist
through Tuesday evening. This will bring gusty north winds with
steep, choppy seas over the outer waters north of Cape Blanco, but
also for most other areas south of Cape Blanco. Areas of marine
stratus and fog will also persist. North winds will weaken Wednesday
as a front approaches the coast. That front will move onshore
Wednesday night. The thermal trough and stronger north winds will
return Friday through next weekend. -Spilde/Petrucelli
&&
.FIRE WEATHER...Updated 300 PM Sunday, 1 August 2021...
Confidence remains high in scattered thunderstorms developing across
Jackson and Josephine counties this afternoon and evening. Thus far,
we've seen some pulse type thunderstorms from the Cascades eastward.
With high precipitable water values and fairly slow storm movement
of 5-10 mph, thunderstorms will put down heavy rainfall in short
periods of time in storm cores, while outlying portions of cells
will see lightning with little to no rainfall. There will be a
shortwave trough moving through this afternoon into this evening that
will cause activity to pick up in coverage, intensity, and
organization as it moves north to northeastward. The RFW for FWZs
620, 622, 623, and NW 624 remain in effect until 10 PM PDT.
We've issued a new RFW for FWZ 625 for Monday afternoon and evening,
from 2-8 PM PDT. Models indicate this is where most of the activity
will occur tomorrow, though we could see some on the northern
fringes of FWZs 624, 623, and eastern 617. Model trends today have
pushed the focus of activity northeastward, but there's still some
spread in the guidance as to where the southern periphery of the
activity will be. All in all, have gone with the better verifying,
rock-steady GFS parameters for keying in on tomorrow's focus area,
Monday will also be a transition day away from thunderstorms and
toward hotter, drier, and, eventually, windier conditions. While we
do not anticipate any RFWs for wind, RH, or Haines Index for
tomorrow, we do expect it to begin to dry out from SW to NE. The
Rogue Valley and the Shasta Valley may see some brief RFW
conditions, but not long enough for a warning. Also, Haines will be
a 5 or lesser, expect over California's River Complex, where a 6 is
expected.
Tuesday into Wednesday it will be hotter and drier, as well as
windier and unstable. We expect some watches and warning will need
to go out for areas from the Cascades eastward then. This will be
followed by a notable cool down late week into the weekend. ~BTL
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 10 PM PDT this evening for
ORZ620-622>624.
Red Flag Warning from 2 PM to 8 PM PDT Monday for ORZ625.
Heat Advisory until 10 PM PDT Tuesday for ORZ024-026.
CA...Heat Advisory until 10 PM PDT Tuesday for CAZ080-081.
Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Tuesday for PZZ356-370-376.