Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 181618
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
918 AM PDT Thu Apr 18 2019

.UPDATE...
Updates this morning were to refine the sky cover forecast for this
morning through this evening. Also added some patchy fog to the
forecast, mainly over the coastal waters. BTL

&&

.DISCUSSION...
Today will be the warmest day of the week, and, likely through
Monday of next week as highs reach 15 to 20 degrees above calendar
day normals.

Tomorrow through Saturday a trough of low pressure will move in
with cooler temperatures and showers and some thunderstorms
across the area before the weather dries out again Sunday into
Monday. Please see the previous forecast discussion for further
details. BTL

&&

.AVIATION...For the 18/12Z TAFS...Along the coast and in the Umpqua
Basin...Local IFR cigs/vsbys in the coastal valleys and near KOTH
will clear to VFR by late Thursday morning. The lower conditions
will be more widespread when they return Thursday evening, spreading
into the Umpqua Basin Thursday night, likely affecting KRBG. Over
the remainder of the area...VFR conditions will prevail through
Thursday night.

&&

.MARINE...Updated 200 AM PDT Thursday 18 April 2019...High pressure
will weaken tonight. A weak front will move through Friday, then a
thermal trough will develop near the coast. This will bring strong
north winds and steep to very steep choppy seas to the area Friday
night through Saturday night. A Hazardous Seas Watch has been issued
for most of the area south of Cape Arago during this interval, but
the conditions will be increasing worse going south. Winds will
also approach gale force south of Cape Blanco, but the more likely
event is the Hazardous seas.  The trough will weaken Saturday night
and winds and seas will subside. High pressure will rebuild over the
area Sunday into Monday.

&&

.PREV DISCUSSION... /Issued 319 AM PDT Thu Apr 18 2019/

SHORT TERM...

The warmest day of the week will arrive later this afternoon
reinforcing the fact that Spring is here and Summer is not that
far away. Highs should reach the mid to lower 80`s in valleys west
of the Cascades and the 70`s east of the Cascades. These
temperatures are roughly 15 to 20 degrees above average in most
valley locations. Even with these abnormally warm temperatures,
we`ll still be roughly 5 degrees short of record high temperatures
across the region.

As for Friday we`ll see a cold front move into the region with a
chance for rain showers and perhaps some thunderstorms east of
the Cascades and within the Shasta valley. There isn`t a massive
amount of instability out there, so thunderstorms should only
produce a few strikes if they are able to get going in the first
place. Upper level winds could really tear the cells apart before
they can start consistently put doing some lightning.

An upper level low will eventually make it`s way into northern
California and southern Oregon. Showers will become widespread
during the early hours of Saturday as this low pushes into the
region. Temperatures aloft will continue to cool and aid in
shower development. Again there is a slight chance for some
thunderstorms east of the Cascades and around the Shasta valley.
Shower coverage will decrease into the evening as the low kicks
through northern California. As for the precipitation, we`re
expecting around 0.25 to 0.75 inches to fall east of the Cascades
Friday and Saturday. Anyone venturing up Mt Shasta Saturday
morning should be prepared for wintry precipitation above 7000
feet. Although this is NOT a full blow winter storm, the weather
could very well cause problems for the unprepared.

-Smith

LONG TERM.../Issued 313 PM PDT Wed Apr 17 2019/
Sunday, April 21 through Wednesday, April 24...
On Sunday, models continue to show a break in the active pattern
with a weak ridge extending into the area and dry weather in
place. With this pattern, expect mostly clear to partly cloudy
skies on Sunday and mild to warm temperatures. High temperatures
on Sunday are forecast to be in the upper 60s to low 70s for most
inland valleys and in the upper 50s to near 60 at the coast.

Two additional fronts are forecast to move  towards the Pacific
Northwest early next week. Current model and ensemble forecasts
indicate the upper ridge may strengthen slightly on Monday and keep
be best chance for precipitation well north of the area.  So have
leaned towards mainly dry weather over the area on Monday. Then,
models and ensembles support somewhat higher chances for
precipitation Tuesday into Wednesday,  showing a front moving
towards the region Tuesday and inland Wednesday. With the front and
a shortwave trough moving inland on Wednesday, there is instability,
so have included a slight chance for thunderstorms as well, mainly
from the Cascades east and Siskiyous south. Of note, there is still
significant variability in the model and ensemble forecasts
concerning the strength of the ridge and strength and timing of the
fronts Monday through Wednesday. So confidence is low in the
details of the forecast for showers or potential thunderstorms.
Will continue to monitor future model runs and adjust as needed.

-Clarstrom

AVIATION...For the 18/12Z TAFS...Along the coast and in the Umpqua
Basin...Local IFR cigs/vsbys in the coastal valleys and near KOTH
will clear to VFR by late Thursday morning. The lower conditions
will be more widespread when they return Thursday evening, spreading
into the Umpqua Basin Thursday night, likely affecting KRBG. Over
the remainder of the area...VFR conditions will prevail through
Thursday night.

MARINE...Updated 200 AM PDT Thursday 18 April 2019...High pressure
will weaken tonight. A weak front will move through Friday, then a
thermal trough will develop near the coast. This will bring strong
north winds and steep to very steep choppy seas to the area Friday
night through Saturday night. A Hazardous Seas Watch has been issued
for most of the area south of Cape Arago during this interval, but
the conditions will be increasing worse going south. Winds will
also approach gale force south of Cape Blanco, but the more likely
event is the Hazardous seas.  The trough will weaken Saturday night
and winds and seas will subside. High pressure will rebuild over the
area Sunday into Monday.

-Stockton

&&

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

CA...None.

Pacific Coastal Waters...Hazardous Seas Watch from Friday evening through late Saturday
     night for PZZ356-370-376.

$$

BTL/CZS/BTL


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