Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS66 KMFR 152245
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
245 PM PST Fri Nov 15 2019

.DISCUSSION...Short-term...Tonight through Monday....A weak front has 
passed through the forecast area, and some rain with the front 
has been observed over the past 24 hours, primarily from Cascades 
westward. The highest rainfall (0.88in) was observed in 
northwestern Douglas County. No rainfall was observed east of the 
Cascades and in northern California...or in the Rogue Valley. 

Tonight, rain is not expected, and skies will clear some. We expect 
fog in the coastal, Umpqua, and Illinois Valley tonight. Farther 
east where there has been no measurable rainfall, we don't expect 
much if any fog tonight. 

Quiet weather continues after the front on Saturday through Monday 
under low amplitude upper ridging. Fog will impact travel more 
Saturday and Sunday night as high pressure builds some and 
inversions strengthen. Some dense fog is possible in the 
aforementioned valleys.

Regarding the Air Stagnation Advisory, the current hazard area
looks fine with stagnant air expected to continue in the Rogue
Valley and most valleys east of the Cascades. Mixing heights will
be close to the thresholds, but without any rain today and light 
winds continuing, we don't expect the air mass to change much. 
Farther north, the rain has helped to clear the air some in the 
Umpqua Basin, and we expect mixing heights to be higher than 1000 
ft AGL through the weekend. Therefore we won't be re-issuing the 
Air Stagnation Advisory for that area. 

Long-term...(Monday evening through Friday)...The frontal 
boundary moving through on Tuesday will continue through southern 
Oregon and northern California through the day. This front is not 
expected to bring significant rainfall. Maybe a quarter of an inch
of rain for the coast, with a tenth of an inch or less for the 
Cascades with a couple hundreths of an inch in the West Side 
Valleys with much less east of the Cascades. Snow levels will 
start off around 7000 feet and drop to around 4000 feet by 
Wednesday night, after the front goes through. Precipitation 
should end by the time by the snow levels reach the passes. As 
such, limited travel impacts, if any, are expected. (Roads may 
become slippery due to oils washing away-- especially in areas 
that did not see rain today.) 

Then we move towards another ridge pattern with gusty east winds and 
dry air aloft.  This means that we'll get some cold temperatures 
(near or below freezing for most of our valleys in southern Oregon 
and northern California) at night with some rapid drying out, 
especially on ridges. This pattern will continue for the next 
several days. Temperatures will moderate out into the weekend, 
being closer to normal or slightly above normal. -Schaaf


&&

.AVIATION...For the 15/18Z TAFs...Over the coastal waters, along the 
coast, in the Coast Range, and in the Umpqua Basin...Areas of MVFR 
cigs/vsbys in low clouds and rain with higher terrain obscured will 
persist through this morning. The precipitation will end this 
afternoon but the lower cigs will persist into this evening. Areas 
of IFR cigs/vsbys in low clouds and fog will develop tonight, 
persisting into Saturday morning. Over the remainder of the 
area...VFR conditions will persist into this evening with scattered 
light precipitation. Areas of higher terrain will be obscured. Areas 
of MVFR cigs will develop in the valleys tonight, and persist into 
Saturday morning. -BPN 

&&

.MARINE...Updated 800 AM PST Friday 15 November 2019...Despite 
light and variable winds, steep and hazardous seas will persist 
through Saturday evening. Meanwhile, long period west swell could 
create hazardous bar conditions through Saturday. A weak thermal 
trough will build along the coast Sunday, producing a brief period 
of north winds south of Cape Blanco through Monday morning. The 
next front will move onshore Monday night, followed by gusty north 
winds and steep to very steep seas Tuesday into Wednesday night.   
-BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until noon PST Tuesday for 
     ORZ026-029>031. 

CA...None.

National Weather Service Glossary of Abbreviations