698
FXUS66 KMFR 192151
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
251 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 humitidities
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...19/18Z TAFs...A moderately moist north to northeast flow
covers southwest Oregon from the Cascades to the coast. The moisture
is pretty much confined to a small layer between 5000 and 7000 ft
msl. This is causing sct to bkn fair weather cumulus clouds. This
moisture will slowly dry during the day so the cloudiness will
slowly dissipate but may not totally dissappear especially in areas
north of the Umpqua divide. For areas east of the Cascades and in
northern California, clear blues skies rule with the addition of
some high thin cirrus.

Another afternoon of gusty north to northwest winds is in store
region-wide through the early evening. Wind speeds will be similar
to yesterday`s and calm towards the late evening. Another marine
surge tonight will result in more scattered to broken stratus decks
along the Coos coast and into western valleys, but expecting VFR
conditions to continue. -CSP/Sargeant

&&

.MARINE...Updated 800 AM Sunday, May 19, 2024...A strong
thermal trough along the coast will produce north gales and very
steep, wind-driven seas south of Cape Blanco 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 is in place for the areas
where these gales are expected to surface. These conditions will be
most severe during the afternoon and evening hours each day through
Monday with both winds and seas easing late at night into the early
morning.

Low pressure approaching from the north will disrupt the thermal
trough by Tuesday with winds diminishing and seas becoming dominated
by longer period swells. -CSP/Smith

&&

.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.

&&

$$