EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1146 PM EST MON FEB 12 2018 VALID 12Z FRI FEB 16 2018 - 12Z TUE FEB 20 2018 ...SIGNIFICANT TROUGH POSSIBLE FOR THE WEST NEXT WEEK... ...OVERVIEW... MAIN DRIVERS OF THE MEDIUM RANGE FORECAST WILL BE UPPER RIDGING NEAR THE GULF OF ALASKA AND OVER THE SOUTHEAST US AND A PERSISTENT UPPER LOW OVER NORTHERN HUDSON BAY. THAT WILL FAVOR A RELATIVELY STABLE LONGWAVE PATTERN WITH SYSTEMS MOVING THROUGH THE FLOW -- OUT OF THE NORTHEASTERN PACIFIC AND THROUGH THE WEST. BY NEXT WEEK, ENSEMBLES WERE STRONGLY SHOWING INCREASING HEIGHTS IN THE EAST AS THE UPPER HIGH EXPANDS NORTHWARD AND THE POTENTIAL FOR THE UPSTREAM TROUGH TO DIG SMARTLY INTO CALIFORNIA AND THE INTERIOR SOUTHWEST. ...GUIDANCE PREFERENCES... LATEST MODELS/ENSEMBLES WERE GENERALLY CLUSTERED ENOUGH TO ALLOW FOR A PRIMARILY DETERMINISTIC BLEND TO START (FRI/SAT FORECAST) WITH A TREND TOWARD A MAJORITY ENSEMBLE MEAN BLEND BY NEXT TUESDAY GIVEN THE UNCERTAINTY IN THE STRENGTH OF THE WESTERN TROUGH AND EMBEDDED SHORTWAVES COMING OUT OF THE NORTHEASTERN PACIFIC. NOTEWORTHY IS THE VERY GOOD AGREEMENT ON THE EASTERN RIDGING THAT CONTINUES TO TREND STRONGER IN THE ENSEMBLES. TYPICAL VERIFICATION SHOWS BETTER RELIABILITY FOR STRONG RIDGES RATHER THAN DEEP TROUGHS IN THE ENSEMBLES AND THE UPPER PATTERN CONFIGURATION CERTAINLY SUPPORTS IT. ...WEATHER HIGHLIGHTS/THREATS... TEMPERATURES... SURGE OF MILD TEMPERATURES AHEAD OF THE LEAD FRONTAL BOUNDARY PUSHING THROUGH THE EAST ON FRIDAY WILL BE REPLACED BY NEAR TO BELOW AVERAGE TEMPERATURES IN ITS WAKE FROM THE PLAINS EASTWARD. TEMPERATURES WILL AGAIN RISE SUN/MON IN THE EAST AHEAD OF THE WESTERN SYSTEM. TEMPERATURES MAY AGAIN RISE TO 10-20 DEGREES ABOVE AVERAGE. FOR THE WEST, TEMPERATURES WILL GENERALLY TREND DOWNWARDS FROM THE WEEKEND INTO NEXT MON/TUE AS THE TROUGH SINKS IN AND THE ARCTIC FRONT TO THE NORTH SLIPS SOUTHWARD AS WELL. TEMPERATURES WILL BE ANYWHERE FROM 5-30 DEGREES BELOW AVERAGE. PRECIPITATION... EXPECT A FOCUS OF PRECIPITATION ALONG THE FRONT FROM THE SOUTHERN PLAINS EAST-NORTHEASTWARD TO THE CENTRAL APPALACHIANS LATER THIS WEEK INTO THE WEEKEND. BY NEXT SUN-TUE, PRECIPITATION WILL EXPAND THROUGH THE WEST, FIRST THROUGH OR/WA (WITH SNOW FOR THE COASTAL RANGES AND CASCADES), BUT THEN ESPECIALLY THROUGH THE INTERIOR AND PERHAPS THROUGH MUCH OF CALIFORNIA. SNOW LEVELS WILL LOWER AS COLDER AIR WORKS IN (POSSIBLY 1500-2000 FT) ALL THE WAY TO SOME VALLEY LOCATIONS IN NORTHERN CALIFORNIA AND OREGON/NEVADA. PRECIPITATION COVERAGE WILL DEPEND ON THE DEPTH OF THE TROUGHING (12Z/12 ECMWF FARTHER WEST THAN MOST MODELS/ENSEMBLES) BUT FOCUS AS OF NOW WILL BE FROM OREGON THROUGH NEVADA INTO UTAH/ARIZONA/COLORADO. THIS WILL INCLUDE THE COASTAL RANGES OF WA/OR LATER THIS WEEKEND. FARTHER EAST, WITH EXPANDING RIDGING OVER THE SOUTHEAST, THE SLOWLY MOVING COLD FRONT MAY ACT AS A FOCUS FOR MODEST RAINFALL FROM THE LOWER MISSISSIPPI VALLEY INTO THE OHIO AND TENNESSEE VALLEYS MON/TUE WITH SOME WINTRY WEATHER FOR THE NORTHERN FRINGE. FRACASSO