EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 158 AM EST WED JAN 22 2014 VALID 12Z SAT JAN 25 2014 - 12Z WED JAN 29 2014 DEEP AND VERY COLD TROUGH WILL PREVAIL ACROSS THE EASTERN THIRD OF NORTH AMERICA THIS PERIOD...WITH A MID-LEVEL NORTHWEST FLOW CARRYING A SERIES OF MID-LEVEL WAVES (CLIPPERS) THAT CUT A SWATH OF WINTER PRECIPITATION ALONG ITS LENGTHY STORM TRACK FROM THE NORTHERN PLAINS TO THE OHIO VALLEY...CENTRAL APPALACHIANS...INTO THE MID ATLANTIC STATES AND NORTHEAST. IN THE WEST...THE UPPER-LEVEL RIDGE SHOWS SOME SIGNS OF WEAKENING ALONG THE WEST COAST OF CANADA EARLY NEXT WEEK AS A DEEP PACIFIC CYCLONE EDGES INTO THE GULF OF ALASKA. ALTHOUGH A HIGHLY-AMPLIFIED PATTERN OVER NORTH AMERICA USUALLY CONTAINS AN ABUNDANCE OF UNCERTAINTY...THERE HAS NEVER BEEN ENOUGH UPSTREAM PACIFIC INFLUENCE TO DRASTICALLY ALTER THE PATTERN AND CREATE "SPREAD/UNCERTAINTY" DOWNSTREAM OVER THE ROCKIES AND PLAINS. THE MEDIUM RANGE FORECAST IS AFFORDED THIS LUXURY...WITH SOME OF THE FINER DETAILS DOWNSTREAM COMING INTO BETTER FOCUS. THAT SAID...THE 21/12Z MODEL CYCLE SHOWED REMARKABLE AGREEMENT AND LIMITED SPREAD WITH THE BREAKDOWN AND SLOW EASTWARD MIGRATION OF THE RIDGE AXIS ALONG THE WEST COAST ON DAY 6. BY DAY 7...THE EC...GEFS AND NAEFS DE-AMPLIFY THE RIDGE AND SHIFT THE RIDGE AXIS ABOUT 7 DEGREES OF LONGITUDE EASTWARD AND FLATTEN THE AMPLITUDE OF THE DOWNSTREAM TROUGH DRAPED ACROSS THE SOUTHEASTERN US AND EASTERN CANADA HEADING INTO THE DAY+ 8 PERIOD. SATURDAY (DAY 3) APPEARS TO BE THE DAY THAT A FRESHENING OF THE ARCTIC BOUNDARY CONTAINING -30C TEMPS AT 850 MBS MAKES A BEE LINE FOR THE UPPER MIDWEST. OUT AHEAD OF THIS BOUNDARY...THE STRONG SHORTWAVE THAT WAS TRACKED OUT OF NUNAVUT 4-5 DAYS AGO...WILL BE MIGRATING ACROSS THE ST LAWRENCE VALLEY...AND A MID-LEVEL TROUGH WITH SHALLOW WARM ADVECTION LIFTS ATOP THE ARCTIC BOUNDARY IN PLACE ACROSS THE NORTHEAST. THE 500 MB VORTICITY AND LOWER HEIGHTS WILL BE MIGRATING THROUGH THE OHIO VALLEY...THE CENTRAL APPALACHIANS AND INTO THE NEW ENGLAND-MID ATLANTIC REGION SATURDAY NIGHT AND SUNDAY. THIS FEATURE HAS BEEN CARRIED BY THE LAST 5 RUNS OF THE GFS...AND PREVIOUS THREE RUNS OF THE ECMWF...AND BOTH TAKE THE WAVE INTO THE GULF OF MAINE SUNDAY AFTERNOON...WITH THE ARCTIC SURGE SPREADING QUICKLY IN BEHIND IT. AROUND SUNDAY NIGHT AND MONDAY (DAY 5)...YET ANOTHER CLIPPER IS TAKING SHAPE OVER THE MIDWEST WITH A FRESH ARCTIC CANADIAN AIRMASS IN PLACE AHEAD OF IT--AND ANOTHER ARCTIC BOUNDARY BEHIND IT. HERE TOO..THE DETERMINISTIC ECMWF/GFS CAPTURE THE FEATURE(S) RATHER WELL...WITH THE UKMET LENDING SUPPORT TO THE OVERALL CONFIDENCE IN THE PATTERN. A QUICK PEEK AT THE 22/00Z DETERMINISTIC GFS AGREES WITH THE DETERMINISTIC 21/12Z ECMWF FOR THE DETAILS REGARDING THIS ORGANIZED CLIPPER (A 1004-1007 MB SYSTEM) TRACKING THROUGH THE MISSOURI VALLEY SATURDAY...THE MIDWEST AND MID-OHIO VALLEY ON SUNDAY...THEN BY MONDAY (DAY5)...THE CURRENT GUIDANCE SUGGESTS A PRIMARY STORM TRACK THROUGH THE NORTHERN MID-ATLANTIC REGION AND OUT TO SEA INVOF THE JERSEY COAST..WITH SOME INTENSIFICATION OF THE SURFACE LOW INVOF THE BENCHMARK. THIS IS THE CONDENSED AND SIMPLIFIED VERSION OF THE CLIPPER PATTERN THROUGH DAY 5. THERE IS LITTLE DOUBT THAT THE COLD AIRMASS WILL BE IN PLACE AHEAD OF THIS CLIPPER...AND ANOTHER CANADIAN HIGH BUILDS IN BEHIND IT. BUT THE QUESTION IS...WHETHER THE STORM TRACK IS THAT RELIABLE EVEN IF THE GLOBAL MODELS AND THEIR MEANS ARE GENERALLY IN LOCK STEP WITH THE DETAILS EMBEDDED IN THE MIDDLE LEVELS. CERTAINLY...THE PATTERN ALOFT IS COMING TO A DETERMINISTIC CONCLUSION...WITH VERY LITTLE VARIATION IN THE TIMING OF THE STRONG SHORTWAVE ORIGINATING IN NUNAVUT FOR A GOOD 4 DAYS NOW. SO USING THE EC/GEFS AND/OR THE NAEFS MEANS AS A BASELINE FOR THE FLOW PATTERN ALOFT SEEMED REASONABLE. AND WITH THERE BEING A STRIKING SIMILAR SURFACE AND THERMAL PATTERN IN THE GFS/ECMWF RUNS...SEE NO REASON TO EXPECT MUCH CHANGE IN THE OVERALL COLD PATTERN IN THE EAST AND SOUTHEAST THROUGH DAY 6. IN THE WEST...THE PATTERN IS AMAZINGLY CONSISTENT...IF NOT EXTREMELY UNIQUE AS THE MEDIUM RANGE FORECAST PERIOD BEGINS WITH A CLOSED HIGH CENTER INVOF 125W. THE WARMTH ALOFT...SOMETHING THAT IS MORE THE RESULT OF A VERY LIMITED FREQUENCY OF PACIFIC FRONTAL PASSAGES THIS 'WET' SEASON...WILL BE ACCOMPANIED BY THE STRANGEST 500MB IMPULSE TRACK I CAN EVER REMEMBER SEEING OUTSIDE OF LAST SUMMER'S CLOSED UPPER LOW THAT TRACKED FROM WEST VIRGINIA INTO ARIZONA! THE UKMET/CANADIAN CARRY IT AS MORE OF A SHEAR AXIS...BUT THE ECMWF/GFS...WHICH ARE PREFERRED DOWNSTREAM...CARRY THE FEATURE AS A CLOSED CIRCULATION...IT APPEAR TO COMPLETELY MIGRATE THE LOW CLOCKWISE AROUND THE UPPER-LEVEL HIGH....THROUGH INTERIOR OREGON...THEN EXIT THE FEATURE ALONG THE NORTHERN CALIFORNIA COAST ON DAY 3. THIS IMPULSE BECOMES ABSORBED BY A SHORTWAVE IN THE GULF OF ALASKA...AND THEN RE-ENTERS THE WEST COAST A SECOND TIME NEAR THE US/CANADIAN BORDER BY DAY 5. WHAT IS SEEMS TO ACCOMPLISH...IF NOTHING ELSE...IS TO DISSIPATE THE CLOSED HIGH...AND WEAKEN THE RIDGE AXIS. THIS SETS THE STAGE FOR A PACIFIC SHORTWAVE TO ENTER THE PAC NORTHWEST ON DAY 6...AND PASS THROUGH THE NORTHERN ROCKIES AND GREAT BASIN ON DAY 7. VOJTESAK