FXUS66 KMFR 202204
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
204 PM PST TUE JAN 20 2009
.SHORT TERM...TODAY THROUGH FRIDAY...THE UPPER LEVEL RIDGE AXIS 
THAT HAS BEEN DOMINATING OUR WEATHER FOR THE LAST WEEK OR SO IS
FINALLY EAST OF THE CWA AND WILL WEAKEN IN STRENGTH OVER THE NEXT
24 HOURS. BEHIND THIS...A WEAK UPPER LEVEL LOW AND TROUGH IS
LOCATED OVER THE EASTERN PACIFIC. THE UPPER LEVEL LOW AND TROUGH
IS EXPECTED TO PUSH INLAND BY THURSDAY EVENING. MOST OF THE DYNAMICS
WITH THIS SYSTEM ARE ASSOCIATED WITH THE TROUGH WHICH IS LOCATED
SOUTH OF OUR AREA AND THUS WILL MAINLY IMPACT CALIFORNIA. THE
HIGHEST POPS FOR THE FORECAST AREA FOR WEDNESDAY IS IN SISKIYOU AND
MODOC COUNTY. FOR SOUTHWESTERN OREGON...THE MAIN IMPACTS OF THIS
SYSTEM WILL BE AN INCREASE IN CLOUD COVER AND THE EROSION OF THE
INVERSION THAT HAS BEEN EVER PRESENT OVER OUR AREA FOR THE LAST
SEVERAL DAYS. BY FRIDAY...THE SYSTEM WILL BE WELL EAST OF THE CWA 
WITH A TRANSITION INTO COOLER DAY TIME HIGHS REGIME.
.LONG TERM...THIS WEEKEND AND NEXT WEEK...MODEL DIFFERENCES HAVE
BEEN RATHER SIGNIFICANT FROM RUN TO RUN ON THE DETAILS OF THE
FORECAST IN THIS PERIOD...AND SIGNIFICANT DIFFERENCES CONTINUE TO
EXIST ON THE STRENGTH AND TIMING OF SHORTWAVE TROUGHS MOVING
THROUGH THE AREA. THEREFORE...FORECASTER CONFIDENCE IN DETAILS
SUCH AS TIMING AND MAGNITUDE OF THE INCOMING LOW PRESSURE SYSTEMS
IS LOW TO MODERATE.
HOWEVER...THERE IS HIGH CONFIDENCE IN THE OVERALL PATTERN EVOLUTION 
DURING THIS PERIOD DUE TO GOOD AGREEMENT AMONG THE MODELS REGARDING 
LONGER WAVE FEATURES. THE GENERAL IDEA IS THAT LARGER SCALE HIGH 
PRESSURE WILL BUILD OVER THE EASTERN PACIFIC...GENERALLY BETWEEN 
ALASKA AND HAWAII. THIS WILL OPEN THE DOOR FOR LOW PRESSURE TROUGHS 
OF INCREASING STRENGTH AND MAGNITUDE WITH TIME ENTERING THE AREA 
FROM THE NORTHWEST. WHILE DETAILS ARE STILL TO BE DETERMINED...THE 
12Z ECMWF IS THE FAVORED MODEL GUIDANCE AT THIS TIME.
THIS TRANSLATES INTO A WEAK SYSTEM BRUSHING SOUTHEASTERN SECTIONS 
EARLY ON SATURDAY WITH LIGHT PRECIPITATION...BUT THE BULK OF THE 
ENERGY MOVING THROUGH THE CENTRAL SIERRAS. IN THE WAKE OF THIS 
SYSTEM NORTHWEST FLOW WILL BE ON THE INCREASE YIELDING INCREASING 
PRECIPITATION CHANCES OVER THE WEST SIDE AND MOUNTAINS WITH TIME DUE 
TO ONSHORE FLOW...COLD AIR ADVECTION...AND OROGRAPHICS. MODELS DO 
AGREE ON A LOW PRESSURE TROUGH OVER THE AREA YIELDING A GOOD CHANCE 
OF PRECIPITATION NORTH AND WEST OF YREKA ON SUNDAY. EARLY NEXT WEEK 
A STRONGER SYSTEM IS BEING INDICATED BY THE ECMWF 12Z MODEL. 
DISCUSSIONS FROM NCEP...NAMELY THE EXTENDED FORECAST DISCUSSION OR 
PMDEPD...AND THE PROJECTED PATTERN EVOLUTION...WOULD FAVOR A 
SCENARIO SIMILAR TO THAT INDICATED BY THE ECMWF. BTL 
&&
.AVIATION...KRBG AND POCKETS OF NORTHERN JOSEPHINE COUNTY ARE THE
PROBLEM SPOT THIS AFTERNOON AS LIFR CONDITIONS CONTINUE TO
PREVAIL. CONDITIONS ARE NOT EXPECTED TO SIGNIFICANTLY IMPROVE FOR
THE AREA AS THE FOG AND STRATUS HAS BEEN SLOW TO DISSIPATE.
OTHERWISE...VFR CONDITIONS WILL CONTINUE FOR MOST OF THE AREA
TONIGHT. LIFR TO IFR CONDITIONS ARE EXPECTED LATE TONIGHT AND INTO
EARLY TOMORROW MORNING FOR THE ROGUE VALLEY WITH ONSET OF FOG
FORMATION.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 10 AM PST WEDNESDAY FOR ORZ023-
     ORZ024-ORZ026-ORZ029-ORZ030-ORZ031.
CA...NONE.
PACIFIC COASTAL WATERS...NONE.
$$
KS/FB/BL/RH