530
FXUS66 KMFR 161033
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
333 AM PDT Tue Jul 16 2024

.DISCUSSION...Heat will continue for the area today, with triple
digit highs expected for all valleys west of the Cascades. Smoke
may be a limiting factor for heat in some areas, but the effect
should be small. Clouds, on the other hand, especially if
convection gets started early, will make much more of an impact,
perhaps keeping highs for some locations several degrees cooler
than forecast. A Heat Advisory remains in effect for the valleys
of Jackson and Josephine counties through this evening.

The upper low off the coast will lift northward on Tuesday with a
short wave wrapping from SW to N-NE across the forecast area.
This, in conjunction with the ample moisture flowing into the
region from the south, will produce a 20-30 percent chance for
thunderstorms roughly along and north of a line from Lakeview to
Roseburg, with a few stray thunderstorms possible across the rest
of Douglas and coos counties. Not much rain is expected with the
activity in general - mainly a tenth of an inch or less, but local
amounts of a quarter are possible with some training cells.
Outflow winds will be a concern, as shown by the thunderstorm
activity Monday.

Winds are a concern for Tuesday afternoon as the low moves north
up the coast. Deep, very warm and dry layer of the atmosphere will
be unstable and model indications are that lower atmospheric
winds will be significant (greater than 20 kts) from the south
and southwest. Should see some afternoon gustiness from the south
then from the west over the West Side, and mainly southwesterly
over the East Side. 15 mph gusting to 25-30 mph looks reasonable
for most areas.

Cooler weather by 5-10 degrees will prevail Wednesday through
Friday in the wake of the low. However, the longer range solution
supports high pressure strengthening over the area again with the
NWS Heat Risk forecasts indicating more heat highlights possible
starting again Saturday or Sunday. -Stavish/BPN

&&

.AVIATION...16/12Z TAFS...Another surge of mid-level moisture and
elevated instability will move in later this morning and overspread
the area this afternoon into the evening. This will bring another
round of isolated to scattered thunderstorms. Once again, these
cells will have high bases and a very dry sub-cloud layer, so this
will create the risk for strong outflow winds that can propagate a
very far distance from the storms themselves. Wind gusts could be 35-
45 kt in the stronger cells. And, with any thunderstorm, there is a
risk of cloud to ground lightning. These could pop up just about
anywhere, but are most likely in an arc from northern Josephine
County, across Coos and Douglas counties, and southeast across
Klamath, Lake, and Modoc counties...to the Warner Mountains. Also,
gusts of 20 to 30 kt are likely this afternoon and evening without
thunderstorms in the Shasta and southern Rogue valleys, strongest
near Montague.

Marine stratus is impacting the coast and will bring IFR/LIFR to
North Bend through much of this morning. With a bit more onshore
flow, expect stratus to be a bit more stubborn to break in some
areas than yesterday, especially along the south coast.

Main visibility reductions with the Shelly fire will be in the
immediate vicinity of the fire. Otherwise, VFR will prevail in most
areas for the next 24 hours. -Spilde/DW


&&

.MARINE...Updated 300 AM Tuesday, July 16, 2024...Low pressure
offshore has disrupted the thermal trough pattern. A slight chance
of thunderstorms will extend into the waters north of Cape Blanco
this evening with gusty outflow winds possible. Otherwise, weak
winds and low seas will persist into Friday morning. The thermal
trough will restrengthen Friday into the weekend, with the strongest
winds south of Cape Blanco. Advisory strength northerly winds and
steep seas are possible Friday into Saturday, then gales and steep
to very steep seas are possible on Sunday. -DW


&&

.FIRE WEATHER...Issued 300 AM Tuesday July 16, 2024...

There are two main fire weather threats today: abundant lightning
from scattered thunderstorms across fire weather zones 617, 623,
624, and 625, and gusty winds and low humidity within and around the
Rogue and Shasta valleys. Red Flag Warnings are in effect for
both of these areas.

High pressure remains in control across the western United States. A
weak trough offshore of California will move northward just offshore
of the California coast, then pass over western Oregon today, before
exiting to the north tonight. This will be the trigger for
thunderstorm activity this afternoon and evening. The best chances
for convection today looks to be along an arc from southern Lake
County northwestward across Klamath County/Crater Lake into fire
weather zone 617 and eastern Douglas County east of the I-5
corridor. Meanwhile, the trough will be taking on a negatively
tilted orientation which is a common wind maker pattern for the area
as well. Gusty south winds are expected across northern California,
especially in the Shasta Valley as well as in the Rogue Valley,
particularly between Ashland and Medford. These winds will combine
with low daytime RHs to result in near critical to critical fire
weather conditions for Tuesday afternoon.

Tuesday night into Wednesday, low pressure finally swings through
and out of our region. Given the negative tilt of the trough, it
could kick off some nocturnal storms, but it looks more like a
situation where storms develop along the Douglas/Lane County border
and then moves north out of our area. Moisture looks to be well
north and east of the region on Wednesday, so thunderstorm chances
drop out of the forecast after Wednesday afternoon and typical
summer weather conditions return. -BPN/BR-y


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM this afternoon to 11 PM PDT this
     evening for ORZ617-623>625.

     Heat Advisory until 8 PM PDT this evening for ORZ024-026.

     Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for ORZ622.

CA...Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for CAZ281.

PACIFIC COASTAL WATERS...None.

&&

$$