Prognostic Meteorological Discussion
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FXUS02 KWBC 220617
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
116 AM EST THU FEB 22 2018

VALID 12Z SUN FEB 25 2018 - 12Z THU MAR 01 2018

DUE TO TECHNICAL DIFFICULTIES, SOME PRODUCTS MAY NOT BE AVAILABLE
OR UPDATED.  PLEASE CHECK ISSUANCE TIMES.  WE APOLOGIZE FOR ANY
INCONVENIENCE.


...PATTERN OVERVIEW...

THE MID-LATITUDE FLOW SHOULD BE IN SOME SORT OF TRANSITIONAL STATE
AS THE PERSISTENT POSITIVE HEIGHT ANOMALY OVER THE WESTERN
ATLANTIC FINALLY BUCKLES. HOWEVER...THE BLOCKING RIDGE EAST OF THE
HAWAIIAN ISLANDS SHOULD CONTINUE WHICH FAVORS A SERIES OF TROUGHS
PUSHING ACROSS THE WESTERN U.S. DURING THE PERIOD. WITHIN THIS
TRAIN OF SHORTWAVES...MANY OF THEM HAVE THE POTENTIAL TO BRING
VAST IMPACTS TO THE REGIONS OF INTEREST. THE LEAD SYSTEM WILL WIND
UP OVER THE UPPER GREAT LAKES ON SUNDAY MORNING BEFORE LIFTING
INTO NORTHERN QUEBEC EARLY NEXT WEEK. ON ITS HEELS...A WELL
ADVERTISED UPPER LOW BARRELS DOWN THE WEST COAST ACCOMPANIED BY
IMPRESSIVELY LOW 1000-500 MB THICKNESS VALUES. THIS PARENT TROUGH
SHOULD OPEN UP WHILE MOVING THROUGH THE DESERT SOUTHWEST AND INTO
THE FOUR CORNERS REGION BY MID-WEEK. THIS COULD LEAD TO THE
FORMATION OF ANOTHER DEEP CYCLONE MOVING TOWARD THE OH VALLEY LATE
IN THE PERIOD. MEANWHILE...ANOTHER SHORTWAVE TAKES SHAPE OVER THE
WEST COAST WHICH MAINTAINS THE VERY REPEATABLE SYNOPTIC PATTERN IN
PLACE.


...MODEL GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES...

AS MENTIONED IN THE HEADER...RESOURCES REMAIN SOMEWHAT SCANT SO
WILL FOCUS ON SOME OF THE MORE MEANINGFUL ISSUES. FIRST OF ALL...A
DEEP SURFACE LOW PRIMED TO PUSH INTO THE UPPER GREAT LAKES ON
SUNDAY MORNING HAS THE POTENTIAL TO BE SUB 980-MB BY 25/1200Z.
CONSIDERING THE PAST FEW RUNS OF THE GFS/ECMWF...THE FORMER HAS
BEEN CONSISTENTLY DEEPER WHICH THE 12Z ECMWF APPEARS TO HAVE
TRENDED TOWARD. DOWNSTREAM RIDGING SHOULD FORCE THIS SHORTWAVE
INTO EASTERN CANADA WHILE MID-LEVEL HEIGHTS BRIEFLY BUILD ACROSS
THE CENTRAL U.S. EARLY MONDAY. THE NEXT SYSTEM IN THE CHAIN WILL
BE IN THE FORM OF A CLOSED LOW WHICH HAS BEEN ADVERTISED FOR A FEW
DAYS NOW. POTENTIAL 1000-500 MB THICKNESSES MAY PUSH INTO THE
530-535 DM RANGE WHICH COULD SPREAD WINTRY PRECIPITATION TO SOME
RATHER LOW ELEVATIONS ALONG THE CA COAST. OVERALL...THE 12Z ECMWF
AND PRECEDING RUNS HAVE BEEN THE MOST STABLE WHILE THE GFS FROM
THE PREVIOUS DAY WAS PERHAPS 24-HOURS SLOWER. THE 00Z GFS SPED UP
FROM ITS PRECEDING RUN WHICH TAKES IT OUT AHEAD OF THE CONSENSUS
SOLUTION EARLY TUESDAY. SUCH DIFFERENCES PROJECT FORWARD WITH SOME
VAST SPREAD WHILE THE SYSTEM ACCELERATES ACROSS THE CENTER OF THE
COUNTRY. BY 01/1200Z...THE 00Z GFS DEPICTS A POTENT SHORTWAVE
CROSSING INTO THE OH VALLEY WHILE THE 12Z ECMWF/CMC ARE BACK
TOWARD THE SOUTHERN/CENTRAL HIGH PLAINS. GIVEN THE STAGNANT RIDGE
OVER THE EASTERN PACIFIC...A THIRD SYSTEM TAKES SHAPE ALONG THE
WEST COAST WITH POSITIONS QUITE VARIABLE AMONG THE OPERATIONAL
GUIDANCE.

WITH THE NON-NCEP GUIDANCE UNAVAILABLE FOR USE IN THE MODEL
BLENDER...HAD TO INCORPORATE THE GFS/GEFS SOLUTIONS AS FIT.
UTILIZED A COMBINATION OF THE 18Z/12Z GFS WITH THE 18Z GEFS MEAN
THROUGHOUT THE PERIOD WITH A GRADUAL DEDUCTION OF OPERATIONAL
INFLUENCES TOWARD THE DAY 5-7...FEBRUARY 27-MARCH 1...REALM.
UNFORTUNATELY...WITH THE ECMWF SOLUTIONS BEING AROUND 12 TO 18
HOURS SLOWER BY DAY 7...THE MANUAL FORECAST MAY BE TOO QUICK SO
CONFIDENCE IN IT IS VERY LOW.


...WEATHER HIGHLIGHTS/THREATS...

CONDITIONS WILL GENERALLY REMAIN QUITE MILD FROM THE MS RIVER
EASTWARD...PARTICULARLY ON SUNDAY AND INTO MONDAY MORNING.
RELATIVE TO CURRENT RECORDS...THERE MAY BE SOME OVERNIGHT MINIMA
WHICH BREAK DAILY RECORDS FROM THE MID-SOUTH INTO THE MID-ATLANTIC
ON SUNDAY. EXPECTED LOWS WILL BE ANYWHERE FROM THE MID/UPPER 50S
INTO THE LOWER 60S. SUCH TEMPERATURES WILL RESIDE ANYWHERE FROM 20
TO POSSIBLY 30 DEGREES ABOVE CLIMATOLOGY FOR LATE FEBRUARY.
ANOMALIES SHOULD COME DOWN A BIT AS THE UPPER RIDGE WEAKENS WHILE
UPSTREAM HEIGHTS SEMI-REGULARLY LOWER. OVER THE WESTERN U.S...THE
PERSISTENCE OF UPPER TROUGHING WILL KEEP BELOW AVERAGE
TEMPERATURES IN THE PICTURE ALL THE WAY INTO THE FIRST DAY OF
MARCH. THE SHARPEST DEPARTURES FROM CLIMATOLOGY WILL BE OVER THE
NORTHERN ROCKIES WITH ANOMALIES IN THE 15 TO 20 DEGREE RANGE. THE
WEST COAST IS FORECAST TO ALSO REMAIN CHILLY AS OVERNIGHT LOWS
PUSH BELOW FREEZING IN MANY LOCATIONS.

GIVEN THE INTENSE WAVE OF LOW PRESSURE MOVING INTO THE UPPER GREAT
LAKES ON SUNDAY MORNING...WOULD ANTICIPATE A DEFORMATION ZONE OF
WINTRY PRECIPITATION OVER THE REGION. THIS SHOULD BE IN THE
PROCESS OF EXITING THE REGION WHILE THE TRAILING COLD FRONT WILL
SPREAD RAINFALL ALONG THE ENTIRE EASTERN SEABOARD AS WELL AS ALONG
THE GULF COAST. ACROSS THE WEST COAST...THE UPPER LOW WILL FOCUS
MODERATE/HEAVY RAIN/SNOW OVER WESTERN OR/WA WITH GREATER AMOUNTS
ATTACHED TO THE HIGHER PEAKS OF THE CASCADES. PRECIPITATION SHOULD
SPREAD DOWN THE COAST WITH APPRECIABLY LOW SNOW LEVELS GIVEN THE
MAGNITUDE OF COLD AIR TO WORK WITH. AS THIS SYSTEM BARRELS TOWARD
THE DESERT SOUTHWEST...AMPLE RETURN FLOW IN ADVANCE OF THESE
HEIGHT FALLS WILL BRING WARM ADVECTION RAINFALL TO SECTIONS OF THE
ARKLATEX AND POINTS EASTWARD. THIS COULD BE ACCOMPANIED BY
HYDROLOGIC ISSUES DEPENDING ON THE DEGREE OF RECOVERY OF LOCAL
RIVERS...STREAMS...AND CREEKS FROM THE ONGOING ACTIVITY.
MEANWHILE...UNSETTLED CONDITIONS RETURN TO THE PACIFIC NORTHWEST
WITH THE NEXT SYSTEM PRIMED TO MOVE THROUGH.


RUBIN-OSTER


$$





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