688 
FXUS66 KMFR 052141
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
241 PM PDT Fri Aug 5 2022

.DISCUSSION...Our forecast area remains wedged between an upper
trough to the north and a closed low off the California coast with
a weak frontal boundary extending from Idaho back across SE Oregon
into NorCal. Isolated to scattered thunderstorms are developing
along this boundary in portions of northern California and also 
south-central Oregon early this afternoon. These will continue in
the same general areas into this evening with a focus out east 
near the Warners and Hart Mtn Wildlife refuge. North and west of
the boundary, fair weather prevails with sunshine and temperatures
a few degrees above normal. While an isolated shower or
thunderstorm could affect SE portions of the forecast area 
overnight, most of the convection will wane and dissipate later 
this evening.

A thermal trough and upper ridging will move in overhead this 
weekend, resulting in a period of hot weather. This latest hot 
spell does NOT look nearly as strong as last weeks heat wave and
will be of much shorter duration. It looks like the peak of the
heat will be Sunday into Monday, and there'll probably be some
variability in temperatures due to the potential for convection --
more on that later. Right now, we're forecasting 102F here in 
Medford on Sunday, then 100F on Monday with highs in the mid to
upper 90s over most of the east side and in NE Cal. On Saturday, 
with the ridge axis at its closest, it'll likely be our least 
active day in terms of thunderstorms. That being said, latest CAMs
continue to show at least a slight chance of thunderstorms over 
portions of the east side and in Modoc County, so we have added 
that to the forecast. We think the activity should remain east of 
the current larger fires burning across the area -- the McKinney, 
Yeti and Windigo. 

By Sunday and Monday, the closed low offshore will wobble to a
position very near 40N and 130W. This places the area in a
diffluent flow aloft and is a pretty classic pattern for producing
some of the better thunderstorm outbreaks in these parts. The
tricky part of the forecast, though, is that the model data is at
odds with just how much moisture, instability and forcing can come
together (if at all) and produce a significant outbreak. Sunday, 
for instance, we are seemingly in a good position for convection 
to form, but models aren't showing much, likely due to a capping 
inversion and lack of trigger. NBM thunder probabilities are 
fairly low, 10 percent or less, but SSE flow aloft an minor 
disturbances in the flow should be enough to trigger some build- 
ups near the Cascades, over the East Side/Warner Mtns along with 
a slight chance of thunderstorms. We have deviated from the NBM 
here to increase the thunder probabilities, due to pattern 
recognition and enough indices indicating the potential for at 
least a slight chance. Farther west, including western Siskiyou 
County and most of the west side, moisture is more limited, so we
have maintained a dry forecast there. There is a better chance of
thunderstorms in a similar area (Cascades eastward and into 
Modoc) on Monday afternoon/evening, so we have once again bumped 
up POPs/thunder probs to introduce that wording to the forecast. 

Monday night-Tuesday night, the closed low is expected to move 
northeastward off the coast and then onshore Wednesday. This will
result in a chance of additional showers and thunderstorms over 
parts of the area Tuesday and into Wednesday, but at this point, 
it's too early to say just exactly where and when. Some guidance 
is pegging an area near the coast (N&W), but also another east of
the Cascades, while southern and western areas get little or
nothing. We'll see. Models are showing very low PWs in the SW part
of the CWA, which would account for limited convection. Keep 
checking the forecasts for updates, because forecaster confidence 
at this time is low. 

After the low moves onshore, we should get a respite from
thunderstorms late next week with temperatures near to slightly
above normal. -Spilde

&&

.AVIATION...05/18Z TAFs...Stratus and some patchy fog persist south 
of Cape Blanco this afternoon keeping Brookings in LIFR thresholds. 
Those low ceilings will likely persist through the day as the 
southerly stratus continues to push in.  Elsewhere,  thunderstorms 
are in the forecast east of the Cascades with broken ceilings and 
MVFR to IFR ceilings at times.  VFR will prevail west of the 
Cascades through the TAF period.

In northern California, visibilities will be low around the fires as 
they are still burning with some intensity.  Any low level flights 
around those fires should expect LIFR visibilities at times.

By tonight,  LIFR ceilings will move back in along the coast later 
tonight.  Visibilities are also expected to fall down to IFR levels.

-Smith


&&

.MARINE...Updated 245 PM PDT Friday, 5 August, 2022... Winds and 
seas will begin to ease a bit this afternoon through tonight, but 
seas are expected to remain steep into Saturday. By late Saturday 
morning advisory level conditions are likely to have ended within 
10NM of the coast as a southerly surge makes its way northward 
along and near the coast. Southerly winds are then likely for all 
of the coastal waters area by Sunday afternoon as low pressure 
becomes established west of the area. ~BTL/Smith


&&

.FIRE WEATHER...200 PM PDT Friday, 5 August, 2022...Southern 
Oregon and northern California remain locked between upper level 
troughing to the north, a persistent and troublesome closed upper 
level low to the southwest, and ridging with monsoonal inflow to the 
southeast. This morning, at least a part of the remnants of tropical 
storm Frank made their way into the area, bringing enough moisture 
to fire off a few isolated thunderstorms before and just after 
sunrise. This same lobe of moisture and instability has gradually 
made its way to the east, and by this afternoon and evening, it will 
likely help produce isolated to scattered thunderstorms over Modoc 
and southern Lake and Klamath counties. A Red Flag Warning remains 
in effect through this evening for these areas. Isolated 
thunderstorms are possible again Saturday afternoon due to residual 
moisture, but will likely be relegated to portions of Lake County 
and points east.  

Meanwhile, with an upper trough to the north, expect breezy to gusty 
winds across the region, strongest east of the Cascades where gusts 
of 25 to 35 mph will be common during the afternoons today and 
Friday. While it doesn't look like humidities will be a concern with 
these winds, the concern lies with the wind's potential effects for 
any hold over fires. 

The northern trough will depart the area Saturday, and the ridge 
will expand west and northward. This will produce a warming and 
drying trend Saturday into Monday, with the warmest temperatures 
expected Sunday for areas west of the Cascades, and MOnday to the 
east. 

Meanwhile, offshore low pressure will slowly approach the coastline, 
perhaps finally crossing onshore or leaving the area middle to late 
next week. Typically, a low such as this would result in wind and 
lightning concerns, and while models have been depicting the 
increased winds, they seem very reluctant to produce any 
thunderstorm chances. It seems difficult to follow, given the 
moisture inflow and instability this low would bring with it, that 
no lightning is possible. Although confidence in timing and location 
are low, we are introducing a mention for afternoon thunderstorms 
along and east of the Cascades beginning Sunday, to get some lead 
time on what we suspect will begin to show up in the models over the 
coming days. 

As for the wind concerns with the low, we do expect to see gusty 
south to southwest winds Monday into Wedensday. Mid level winds in 
various models are ranging between 30 and 45 mph, and this is 
usually a good indicator of gust speeds. These types of winds, 
occuring after/during lightning and with the ongoing fires in the 
area, may become a significant concern. We will keep a sharp eye on 
the wind and lightning threat over the coming days, and will update 
the forecast when confidence increases. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 8 PM PDT this evening for ORZ624-625. 

CA...Red Flag Warning until 8 PM PDT this evening for CAZ285. 

Pacific Coastal Waters...
     Small Craft Advisory until 11 AM PDT Saturday for PZZ350-356. 
     Hazardous Seas Warning until 2 PM PDT this afternoon for 
     PZZ356-376. 
     Small Craft Advisory until 8 PM PDT Saturday for PZZ370-376. 

$$

MAS/BPN/CZS