900
FXUS66 KMFR 302201
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
301 PM PDT Sun Jun 30 2024

.DISCUSSION...Low-level cumulus can be seen popping up over elevated
terrain while mid-level clouds have moved east of the Cascades.
Slight thunderstorm chances (10-15%) will be present east of the
Cascades this evening, with the best chances over Modoc and southern
Lake and Klamath counties. Activity is expected to be isolated, but
lightning is always dangerous. Extra caution for anyone traveling
in these areas tonight is encouraged.

An upper pattern chance starts on Monday, with a deep upper ridge
developing behind the departing weak trough. While seasonal
temperatures will continue for one more day, a warming trend will
start on Tuesday and continue through the week. NBM probabilistic
guidance has a 70-80% chance for temperatures to reach 100 degrees
or more in the Rogue Valley on Thursday through Sunday. Other west
side valleys will see similar chances, with the Umpqua Valley
staying a couple degrees cooler. Areas east of the Cascades will
generally be in the mid to high 90s, with 20-50% of triple digit
highs for warmer areas (Klamath Falls, Alturas, Lakeview). Given
additional warming without additional moisture, daytime relative
humidity values are expected to drop to 10-20% over all inland areas
by the end of the week. Gusty winds in the afternoon will also
continue to develop.

This combination of hot, dry, and windy weather presents both health
and fire concerns. Extreme Heat Watches are in place for areas
between the Oregon coast and the Cascades as well as for areas east
of the Cascades from Thursday morning through Saturday evening.
While final heat warning products will likely take a more finely-
tuned shape, the fact is that widespread daytime and nighttime heat
will be high enough to be hazardous to at least vulnerable
individuals if not all individuals in these areas. Additionally,
hazardous heat may continue beyond Saturday, but there is more
uncertainty that far into the future. And while fire concerns are
discussed in more detail below, the amount of fire risk is worth
repeating. Any fuels that were not dry yet will have ample
opportunity to dry out in this pattern, and afternoon winds can
carry sparks or embers to more fuels. Activities that may start
fires are heavily discouraged.

Stable weather does look likely to continue beyond this week,
although there`s some uncertainty in just how hot things will be.
ECMWF and GFS deterministic models do have low pressure challenge
the upper ridge near the end of the weekend, but that may only
change the ridge`s shape rather than a complete pattern change.
Medford`s chances for 100-degree temperatures drop to "only" 40-50%
to start next week. Meteograms for both models show continuing above
seasonal temperatures and absence of rainfall across the area
through mid-July, suggesting hot, dry, and windy continues just with
varying amounts of hot. Highs of 100 degrees instead of 105 might be
a moral victory at best, but we`ll take what we can get. -TAD

&&

.AVIATION...30/18Z TAFS...Low clouds are expected to dissipate
quickly along the coast and in the Umpqua basin, clearing to VFR
afterwards. Low clouds with IFR and MVFR are likely to return to the
coast Sunday evening. Elsewhere, expect VFR across the area. Smoke
from a few wildfires could produce some locally low visibility near
those fires, otherwise the smoke will not be an issue near
terminals. There is a 15 percent chance for an isolated thunderstorm
east of the Cascades this afternoon. -Schaaf/Miles

&&

.MARINE...Updated 100 PM Sunday, June 30, 2024...Winds and seas
will remain low today. However, areas from Brookings south within
about 15 NM of shore could observe brief and isolated advisory level
seas as winds peak in the afternoon, generating a steep wind wave.
But confidence is not high enough to issue a small craft advisory at
this time. If boating in this area, watch Buoy 27 to monitor
conditions to be safe before heading out.

A very strong thermal trough is expected to develop next week
beginning Monday afternoon and lingering towards the end of the
week. The Gale Watch has been upgraded to a Gale Warning, and other
headlines remain in place for this event. The peak should be either
Tuesday or Wednesday evening, and the guidance is trending towards
Tuesday; although very little drop off in intensity is expected
Wednesday. As for the wind speeds expected during the peak of the
thermal trough, the gale force gusts of 35 to 45 kt are expected
south of Cape Blanco, but there is a 20-40% chance that gusts reach
or exceed 50 kt Tuesday or Wednesday evening. With the chance for
gale force gusts remaining below 50% between Cape Blanco and Cape
Arago, the Hazardous Seas Watch was upgraded to a Hazardous Seas
Warning to communicate the very infrequent gale force gusts.
Comparing this event to the past, this is getting into the top end
of events, standing out against climatology. And to summarize, this
occurrence of the thermal trough northerlies will not be one to mess
with. -Schaaf/Miles

&&

.FIRE WEATHER...Updated 200 PM Sunday, June 30, 2024...

...Elevated to critical fire weather possible Tuesday through the
weekend...

Cumulus clouds have begun to build east of the Cascades, where there
is a slight chance for thunderstorms late this afternoon into this
evening. Widespread thunder or severe weather is not expected. but
isolated strikes could occur.

A strong warming and drying trend will begin Monday night as high
pressure builds into the region. This will bring moderate to locally
poor humidity recoveries to ridges. The poorest recoveries and
hottest temperatures are expected from Wednesday morning into the
weekend. The first concern is that western and central Siskiyou
County valleys will approach critical fire weather thresholds of
gusty winds and low humidities on Tuesday afternoon into the evening.
As is common, it will be hottest/driest in the western portion of
the county, while the strongest northerly winds are expected near
Montague in the Shasta Valley. We will monitor the next couple of
new data sets for any drier or windier indications. Much of the
forecast area will have at least elevated concerns through the
weekend.

Additionally, there is concern for both critically poor night-time
ridge top humidity recoveries (including gusty northeast winds at
the higher terrain of Curry and western Josephine counties), and
also, across the area, gusty afternoon winds accompanying a very dry
airmass. The limiting factor in reaching critical thresholds is
likely to be wind speeds, while the hot and dry aspect looks like a
"slam dunk" to occur.

There is a possibility of the very hot and very dry weather
continuing beyond Saturday, but still quite a bit of model
difference in how and when the pattern will transition.

-DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Watch from Thursday morning through Saturday
     evening for ORZ023-024-026-029>031.

CA...Excessive Heat Watch from Thursday morning through Saturday
     evening for CAZ080>082-084-085.

PACIFIC COASTAL WATERS...Gale Warning from noon Monday to 5 AM PDT
     Thursday for PZZ356-376.

     Small Craft Advisory from 5 PM Monday to 5 AM PDT Thursday for
     PZZ350-370.

     Hazardous Seas Warning from 5 PM Monday to 5 AM PDT Thursday for
     PZZ370.

&&

$$