Weather Service Report


600 
FXUS66 KMFR 251602
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
802 AM PST Sat Feb 25 2017

.UPDATE...No significant updates were needed this morning, as the
forecast appears to be on track. RADAR imagery is showing very
little in the way of returns this morning, but do not doubt there
are some local light showers occurring in some areas, mainly in
the southern half of the forecast area, but nothing that should
produce any impacts. Focus for the day will be on the Sunday
system, refining the snow amounts, and confirming the areas of
likely impact. For more information, see the previous discussion
below. -BPN


&&

.AVIATION...25/12z TAF CYCLE...Areas of IFR cigs/vsbys over the 
west side valleys in low clouds and fog will clear to VFR by late 
this morning. Areas of MVFR cigs/vsbys in rain and snow will 
return to the west side late tonight with higher terrain becoming 
obscured. The remainder of the area will remain VFR through this 
evening. Areas of MVFR cigs/vsbys in rain and snow with areas of 
higher terrain becoming obscured will develop late tonight. -JRS

&&

.MARINE...Updated 800 AM PST Saturday 25 February 2017...Low 
pressure off the southern Oregon coast will move south of the area 
later this morning. Southerly winds will become northerly late 
this afternoon. Showers will taper off as high pressure builds 
in. Tonight through Monday, another cold low pressure system will
move through from the north. This will bring small craft winds 
and seas to the area Sunday. The winds will diminish Sunday 
night...but steep seas will persist through Monday. Offshore high 
pressure will build Tuesday into Wednesday. -JRS



&&

.PREV DISCUSSION... /Issued 356 AM PST Sat Feb 25 2017/ 

DISCUSSION...The most recent coastal low is pushing to the south, 
and it's effects on the forecast area are diminishing. Some snow 
is still being observed at Alturas, and about another inch of snow
is expected there before snow tapers off. Some morning fog is 
impacting West Side valleys this morning, and there is a Dense Fog
Advisory out for the Umpqua Basin. We expect visibilities to 
improve later this morning. Temperatures today should be about 10 
degrees below normal under a continued cold air mass. 

The third low, and likely most significant, in a string of cold low 
pressure systems will swing through on Sunday, and tonight's 
forecast efforts have focused on that. Timing, temperatures, and 
shower intensity/coverage are critical factors in the forecast 
for Sunday. A cold front will bring moderate to heavy 
precipitation with it on Sunday from northwest to southeast. We 
have kept forecast temperatures below MOS guidance for Sunday 
based on thick cloud cover and precipitation expected for much of 
the day. Heavy showers at times will bring down the cold air 
aloft, so we have forecast snow levels at 1000-1500 feet below 
freezing levels. The current thinking is that roadways won't be 
covered all day because of any breaks allowing late Feb solar 
effects to warm roadways, but occasional snow covered roadways are
likely on the lower mountain passes on Interstate 5 
(Sexton/Canyon Mtn Pass) and Highway 199 (Hayes Hill). Colder 
temperatures will be more favorable for continual snow covered 
roadways in the higher Cascades. For lower valleys like the Rogue,
snow is expected, but we are expecting Sunday afternoon 
temperatures to prevent continual accumulation of snow, so we 
haven't issued an advisory for Medford, etc. We'll of course 
continue to monitor latest data for snow potential there. If 
showers continue into Sunday evening, more snow will be possible 
in the Rogue Valley. We have issued some Winter Weather Advisories
for the aforementioned expected impacts, and we have continued 
Winter Storm Watches for the Cascades foothills where unusually
heavy snow accumulations are still possible above 2500 feet.

After the main batch of precipitation Sunday and Sunday night, most 
models show continued shortwave activity in the cold northwest flow, 
bringing continued chances for low elevation snow. Much of the snow 
will likely impact areas from the Umpqua Divide northward, so the 
lower passes of Interstate 5 (Sexton Pass, etc) could still see 
winter weather impacts into early next week. Conditions dry out and 
warm up late Tuesday into Wednesday. Please see the previous
long-term discussion which is still relevant to the upcoming
weather pattern.

Tuesday through Friday...The operational models are 
in pretty good agreement in this time period. The pattern will be 
rather quiet with little or no chance of precipitation. A 
northwest flow continues Tuesday with increasing 500 mb heights. 
The models still show some QPF, but they are not as bullish as 
they were yesterday. Even then suspect they are still overdone 
given 500mb heights will be on the rise as the upper trough moves 
east of our area. However the ECMWF shows weak pva moving in the 
northwest flow during the day, so we'll keep a slight chance 
mention. Confidence is high it will be dry from next Wednesday 
through the end of next week as the storm track shifts well north 
of the area. Of note, the GFS shows more of a dirty ridge 
scenario, but still keeps all of the QPF north of our area, but it
could mean more cloud cover and slightly cooler afternoon 
temperatures. 

We could be dealing with an increasing subsidence inversion next 
Wednesday through Friday which means the valleys could stay cool and 
the ridges milder. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 10 AM Sunday to 4 AM PST Monday for 
     ORZ027-028. 
     Winter Weather Advisory from 7 AM Sunday to 4 AM PST Monday 
     for ORZ023-024. 
     Winter Storm Watch from Sunday morning through late Sunday 
 night for ORZ024. 

CA...Winter Weather Advisory from 10 AM Sunday to 4 AM PST Monday for 
     CAZ082. 
     Winter Weather Advisory from 7 AM Sunday to 4 AM PST Monday for 
     CAZ080. 

Pacific Coastal Waters...Small Craft Advisory for hazardous seas from 
     7 AM Sunday to 10 PM PST Monday for PZZ350-356-370-376. 

$$

BPN/NSK/JRS/MAP

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Western Regional Climate Center, wrcc@dri.edu