209
FXUS66 KMFR 200303
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
803 PM PDT Sun May 19 2024

.DISCUSSION...No changes are necessary to the forecast. Please
see the previous discussion for details on the forecast.

&&

.PREV DISCUSSION... /Issued 440 PM PDT Sun May 19 2024/

SHORT TERM...Tonight through Wednesday morning...There is
currently a batch of mid clouds moving southward from northwestern
Oregon, and this is bringing partly sunny skies to Douglas and
Coos counties. Temperatures right now are in the upper 50s and low
60s west side with 40s and low 50s east side. Tonight will be
cooler for more west side valleys with low 40s while elsewhere
will be comparable to tonight with low 40s at the coast and 20s to
low 30s east of the Cascades. There will be a concern for areas
of frost with temperatures falling to the mid-30s outside of the
Umpqua Basin and above 1,500 feet. However, this is looking too
isolated and cloud cover that could stay in the evening will make
it harder to see widespread frost. There have been breezy
northerly winds this afternoon, and afternoon breezes will be a
trend that continues through the start of the workweek.

The main area of focus will be towards the end of the short term
(Tuesday into Wednesday) as an upper level low moving along the
Canadian coast swings into the PNW with a cold front. This will
begin to increase rain chances in southern Oregon starting Tuesday
afternoon. Although the PoPs will increase in coverage through the
day to all southern Oregon counties, the main areas of focus will be
the Coos County Coast and the Cascades. Even so, totals are looking
to be light at the coast with a ~20% probability to see 0.05" at
North Bend Wednesday. The southern ORegon Cascades will see the most
with near 0.25" possible. Northern California will continue seeing
dry conditions although partly sunny to partly cloudy skies will
be present Tuesday and Wednesday.

There is a healthy swath of 85% to near 100% relative  between
700 and 500 mb passing by Wednesday, and this will help keep the
moisture into the mid-levels. However, LIs are still not favorable
and CAPEs are focused in eastern Oregon, so the initiation of
thunderstorms has been capped at below 15%. Rain chances will die
down later Wednesday, and more details on the rest of the week
will be found in the long term discussion. -Hermansen

LONG TERM...Wednesday morning through Saturday night.

Temperatures trend roughly 5 degrees lower on Wednesday as some of
the cooler air filters in behind the cold front. The upper level low
appears to sit right over central Oregon. With very little shear,
limited potential instability and cold air aloft, the weather
pattern suggests pop up showers are most likely. The NBM keeps a low
10 to 20 percent chance of precipitation across sections of the
forecast area on Wednesday with the best chances east of the
Cascades and around Douglas County. In addition, there is about a
10% chance of cloud to ground lightning.  Given the time of year and
the pattern, this seems reasonable and we wouldn`t be surprised with
some lightning activity in the region, although storms will likely
be weak.

Thursday has a high probability of being a break in the action with
an upper level low departing the area.  The NBM still is holding on
to some low probability of precipitation chances across Oregon.
Perhaps there are a few ensemble members that are keeping the upper
level low around, or perhaps the next low is arriving a little
earlier.

In any case, the most likely solution is another upper level
approaching from the north on Friday with precipitation chances
increasing. The whole forecast area has a 10 to 15 percent chance of
precipitation on Friday afternoon and evening. Some ensemble members
are taking a bit longer to bring the low into southern Oregon and
northern California, whereas a smaller majority has it here on
Friday.

Overall, an active weather pattern with minimal weather impacts is
anticipated in the extended forecast. We`ll have to watch out for
some stronger thunderstorms, although it`s hard to see a lot of
instability building under this cooler north to northwest flow.

-Smith

&&

.AVIATION...20/06Z TAFs...VFR conditions will continue through
the TAF period, with gusty north to northwest breezes in the
afternoon and early evening hours, but guidance shows should not
be as strong as they were earlier this afternoon and early
evening.
-Petrucelli


&&

.MARINE...Updated 800 PM Sunday, May 19, 2024...North gales and very
steep, wind-driven seas south of Cape Blanco will continue through
Monday evening. Conditions will be less severe, but still hazardous
to small craft with breezy north winds and steep seas north of Cape
Blanco.

Model guidance continues to suggest periods of off-and-on gales
south of Cape Blanco, and a Gale Warning remains in place for the
areas where these gales are expected to surface. Winds will briefly
diminish at night, then increasing during during the afternoon and
evening hours Monday, with winds easing Monday night.

Low pressure approaching from the north will disrupt the thermal
trough on Tuesday with winds diminishing. Moderate winds will likely
continue into Wednesday with northwest swell gradually increasing
Wednesday afternoon. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Tuesday
     for PZZ356-376.

Small Craft Advisory until 11 PM PDT Monday for PZZ350-370.

     Gale Warning until 11 PM PDT Monday for PZZ356-376.

&&

$$