Fire Weather Watch 25, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
933 AM PDT Fri Jul 30 2021

.DISCUSSION...Another day of hot temperatures and thunderstorms is
expected today. Despite some cloud cover this morning,
temperatures should reach into the upper 90s and triple digits
again today for west side valleys, and an Excessive Heat Warning
remains in effect for today. Regarding thunderstorms, we're
expecting a stronger shortwave trigger to move through this
afternoon, so we're expecting a greater coverage of thunderstorms
today. 305 strikes were recorded with yesterday's storms, and
today's activity should exceed that. Just about everywhere east
of the Coast Range could see some storms today, however, high
resolution models are showing convection weakening as the cells
move north of the Umpqua Divide. Rainfall amounts with yesterday's
storms were generally in the 0.25"-0.50" range, though there was
a report of 0.65" in Ruch yesterday. This morning's (12z/30th)
KMFR sounding shows 1.32" in precipitable water, which is up from
yesterday afternoon's (00z/30th) sounding of 1.15". So we do
expect storms to be wet again this afternoon, especially under the
storm cores. All of that to say there will likely be some locally
heavy downpours this afternoon under any of these thunderstorms,
especially west of the Cascades.

The only update needed was to expand some shower mention across
the East Side for this morning. Radar is showing returns across
Modoc, Klamath and Lake counties this morning, so the forecast was
updated to better reflect this. Otherwise, the going forecast is
on track and no other updates are needed. For more details on the
upcoming weather, see the previous discussion below. /BR-y

&&

.AVIATION...For the 30/12Z TAF Cycle...LIFR cigs and vsbys at the
coast north of Cape Blanco will continue to extend into the Coquille
Valley and lower Umpqua Valley this morning. The stratus will
gradually erode after 15Z with VFR expected at beaches for a brief
period this afternoon while LIFR continues offshore. This pattern
will repeat early this evening with another inland stratus surge
overnight into Saturday.

Elsewhere, VFR is expected. Smoke from wildfires is not too much of
an issue per monitoring sensors and satellite with the exception for
the Jack Fire (east of KRBG and west of Diamond Lake), and the
Bootleg Fire (northeast of KLMT). However, this smoke is confined to
a small area right around the fires. Hazy conditions are expected
over a wider area.

Scattered thunderstorms are expected to develop this afternoon
mainly east of the Coast Range, but especially along and near the
Cascades. These will last through this evening before tapering off
to showers. Any thunderstorms can produce gusty winds. -Spilde

&&

.MARINE....Updated 800 AM PDT Friday, 30 July 2021...High
pressure to the west and lower pressure inland will continue to
bring general northerly winds to the coastal waters through early
next week. The ingredient that will steepen the seas is gusty
northerly winds near shore from Cape Blanco to Gold Beach, and
extending southward across the southern outer waters. This is due
to a thermal trough, which will persist into early next week.
Models begin to differ around Tuesday, but a majority of solutions
show an improving trend starting Wednesday. -DW/Viken

&&

.PREV DISCUSSION... /Issued 508 AM PDT Fri Jul 30 2021/

DISCUSSION...The southerly flow pattern will likely continue through
early next week, bringing above normal temperatures, plenty of
moisture, and chances of thunderstorms. Temperatures will peak
today at 5 to 10 degrees above normal. The moist air mass will
keep overnight lows warm, at 15 to 20 degrees above normal. The
Excessive Heat Warning continues through this evening. The
dayshift will evaluate the potential need for a Heat Advisory
tonight into Saturday, given that temperatures are not expected to
lower much tonight.

Thunderstorm chance continue this afternoon, and we've expanded the
area of scattered thunderstorms to include portions of Josephine
County, thus expanding our Red Flag Warning for abundant lightning
on dry fuels to include that area. The latest high resolution models
support this change. Additionally, some heavy rain is possible with
these storms, focused mainly west of the Cascades, so have added
this possibility to the forecast. We're still concerned with fire
starts as some lightning will occur outside the heaviest rain cores.

Not much change is expected tomorrow except models indicate less of
a trigger tomorrow and may keep thunderstorms in the isolated
coverage category. The same general portions of the forecast area
will be affected by thunderstorm chances. Temperatures will trend
lower by a few degrees. On Sunday deep southerly flow continues,
maintaining thunderstorm chances. By Monday the upper level flow
shifts slightly to a southwesterly direction, and this will
stabilize the atmosphere some and limit the available moisture,
resulting in decreasing thunderstorm chances. Essentially,
thunderstorm chances will be shifted eastward to areas mainly east
of the Cascades.

The National Blend of Models supports a slight but continued cooling
trend through much of next week. Most model solutions show low
pressure along the British Columbia coastline pushing south and east
towards the area, maintaining relatively dry, stable conditions.
Keene

AVIATION...For the 30/12Z TAF Cycle...LIFR cigs and vsbys at the
coast north of Cape Blanco will continue to extend into the Coquille
Valley and lower Umpqua Valley this morning. The stratus will
gradually erode after 15Z with VFR expected at beaches for a brief
period this afternoon while LIFR continues offshore. This pattern
will repeat early this evening with another inland stratus surge
overnight into Saturday.

Elsewhere, VFR is expected. Smoke from wildfires is not too much of
an issue per monitoring sensors and satellite with the exception for
the Jack Fire (east of KRBG and west of Diamond Lake), and the
Bootleg Fire (northeast of KLMT). However, this smoke is confined to
a small area right around the fires. Hazy conditions are expected
over a wider area.

Scattered thunderstorms are expected to develop this afternoon
mainly east of the Coast Range, but especially along and near the
Cascades. These will last through this evening before tapering off
to showers. Any thunderstorms can produce gusty winds. -Spilde

MARINE...Updated 200 AM PDT Friday, 30 July 2021...
High pressure to the west and lower pressure inland will continue to
bring general northerly winds to the coastal waters through early
next week. The ingredient that will steepen the seas is gusty
northerly winds near shore from Cape Blanco to Gold Beach, and
extending southward across the southern outer waters.

This is due to a thermal trough, which will persist into early next
week. Models begin to differ around Tuesday, but a majority of
solutions show an improving trend starting Wednesday. -DW/Viken

FIRE WEATHER...Updated 200 AM Friday 30 July 2021...A similar
set up compared to yesterday will occur today, but with
additional moisture moving in at the mid levels and a stronger
trigger moving up from the south, the chances for scattered
thunderstorms will spread over a larger area of southern Oregon
and northern California, including areas east of the Cascades. A
Red Flag Warning this afternoon and evening continues for these
expected storms and lightning. See RFWMFR for more details.

We've added Fire Weather Zone 620 to the Red Flag Warning because
the latest high resolution model data, in addition to other
reliable guidance, suggests scattered thunderstorms in this area.

The moisture will continue moving into our area throughout the
weekend, bringing additional cloud cover, some cooler temperatures,
and hopefully some widespread showers. Instability remains
relatively high; so a few showers may produce some lightning, but
storms should remain isolated despite the scattered nature of
showers over the weekend.

Thunderstorm chances will be limited to Lake County Tuesday, and
Wednesday and Thursday look to be dry. -Petrucelli/Keene

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM this afternoon to 11 PM PDT this
     evening for ORZ617-620>625.
     Excessive Heat Warning until 11 PM PDT this evening for
     ORZ023-024-026.

CA...Red Flag Warning from 2 PM this afternoon to 11 PM PDT this
     evening for CAZ280-281-284-285.
     Excessive Heat Warning until 11 PM PDT this evening for
     CAZ080>082.

Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Saturday for PZZ356-376.

MNF/NSK/MAS