Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 180002

Area Forecast Discussion
National Weather Service Medford OR
500 PM PDT Sat Apr 17 2021

The Aviation section has been updated...

.SHORT TERM...Strong high pressure aloft remains in control of our
weather today with sunny skies and unseasonably warm weather for
all locations inland from the coast. We had a coastally trapped
wind reversal last night which resulted in a surge of marine air
and clouds north along the coast, and these remain in place at
this hour. High resolution guidance shows the cloud deck thinning
through the evening which may allow for some breakup, but with
little change in the overall setup, clouds will likely thicken
and surge back onto the immediate coastal again tonight.

The upper ridge and associated low level thermal trough move
right over us tomorrow, and despite some increase in high cloud,
this will produce the warmest day of the year so far. Inland
temperatures will top out somewhere around 20 degrees above normal
with Medford proper likely reaching the mid- 80s. Marine stratus
will remain along the coast tomorrow and probably deepen and surge
farther inland tomorrow night as onshore flow increases behind the
thermal trough.

The upper ridge moves east of us Monday and this will open the
door for increasing high cloudiness, cooling temperatures, and
breezy afternoon northwest winds for all areas. Marine air will
continue to deepen at the coast and surge even farther inland
Monday night into Tuesday. -Wright

.LONG TERM...Tuesday through Saturday, April 20-24, 2021...The
upper level pattern will change a bit next week. The ridge that
has been dominant across the PacNW will weaken and this will allow
an upper trough offshore to undercut the ridge with a closed low
moving across Oregon and into the Great Basin Tuesday into
Wednesday. This will bring some cooling and higher humidity
compared to the weekend/early week dryness/warmth, but high temps
(inland) probably remain a little above normal.

Some showers are possible along the coast in the morning Tuesday,
then as the upper level cold pool moves through, we expect some
instability Tuesday afternoon and evening for a slight chance of
showers over the mountains and also across portions of the east
side/NE California. Model soundings are showing about 200-500 J/KG
of CAPE in those areas. Have added a slight chance of thunder,
though confidence in this actually occurring still remains on the
low side. Breezy to locally gusty winds are likely to accompany
the trough passage, strongest over the east side, but also in some
west side valleys in the afternoon and evening.

The best moisture and instability will shift to the south and east
of the area on Wednesday. Cumulus could linger in some southern
and eastern areas, but probably without rain. It should be noted
that onshore flow north of Cape Blanco will probably result in
marine stratus Wednesday morning.

Thursday into Friday, upper ridging is likely to return with
mainly dry weather and high temperatures around 10 degrees above

The ridge will probably be more progressive though as models and
ensembles continue to indicate next weekend as a potential pattern
change. Model clusters and ensembles indicate an increasing
probability of a period of wetter weather arriving next weekend as
upper troughing offshore moves eastward. But the timing of this,
just how much and how far inland all remain uncertain. Given the
dry spring so far and the ongoing drought (especially east of the
Cascades), any indication of wetter weather at this range is met
with pause. But, any rainfall at this point would certainly be
welcome. -Spilde


.AVIATION...For the 18/00Z TAF Cycle...
IFR to LIFR conditions generally exist over the coastal waters,
along the coast, and a bit inland from the coast. In general,
conditions along the coast are expected to stay the same in some
areas and deteriorate in others this evening and overnight as
cooling temperatures result in fog that may become locally dense, at
times. This marine layer cloud deck is likely to lift some to IFR
during the day Sunday, but probably will persist for most, if not
all, of the day a bit further inland than it did today.

Elsewhere, a generally light easterly flow over the area tonight
into Sunday morning will switch to northwest Sunday afternoon into
the evening as the surface high pressure area that has been
northwest of the area moves southward. ~BTL


.MARINE...Updated 230 PM PDT Saturday, 17 Apr 2021...Mostly light
winds and low seas persist into Sunday. Marine stratus will also
be persistent and areas of fog could limit visibility at times. A
thermal trough along the coast deepens Sunday night into Monday
with north winds likely. The thermal trough strengthens Tuesday
with conditions deteriorating as north winds strengthen and steep
to very steep seas build across all areas. Winds are expected to
be around 20 to 25 knots with gusts up to 30 knots. Seas are
expected to rise up to around 10 feet 10 nm to 60 nm west of
Brookings. These winds and seas will be slightly lower closer to
shore. Overall, we will probably see conditions hazardous to
smaller crafts Tuesday and Wednesday. Conditions are then expected
to improve Thursday. -Smith




Pacific Coastal Waters...None.

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