Prognostic Meteorological Discussion
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000
FXUS10 KWNH 200442
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 AM EDT MON OCT 20 2014

VALID OCT 20/0000 UTC THRU OCT 23/1200 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...NEGATIVELY-TILTED SHORTWAVE LIFTING UP COASTAL NEW ENGLAND...

PRELIMINARY PREFERENCE: GENERAL MODEL CONSENSUS
FORECAST CONFIDENCE: HIGH

A PROGRESSIVE SHORTWAVE EXISTING THE VA CAPES EARLIER ON SUNDAY
HAS ATTAINED A NEGATIVE TILT WHILE LIFTING OFFSHORE OF COASTAL NEW
ENGLAND. THIS HAS ALLOWED A SURFACE LOW TO DEEPEN AS IT MOVES
TOWARD NEWFOUNDLAND EARLY MONDAY. WHILE THE SYSTEM IS STILL ACROSS
THE MAP DOMAIN...MODELS SHOW SUFFICIENT AGREEMENT TO WARRANT A
GENERAL MODEL CONSENSUS SOLUTION.


...CLIPPER-LIKE SYSTEM RACING THROUGH THE UPPER MIDWEST...
...UPPER LOW CLOSING OFF OVER THE MID-ATLANTIC
WEDNESDAY/THURSDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z ECMWF/UKMET
FORECAST CONFIDENCE: BELOW AVERAGE

THE HIGH AMPLITUDE FLOW SETTING IN THE NORTHERN STREAM WILL FAVOR
ABOVE NORMAL HEIGHTS IN THE CENTER OF THE COUNTRY WHILE A POTENT
SHORTWAVE DIVES THROUGH THE UPPER MIDWEST. THIS FEATURE IS WELL
IDENTIFIED ON WATER VAPOR IMAGERY AS IT RACES FROM THE MN/WI/IA
SOUTHEASTWARD TOWARD THE LOWER GREAT LAKES/UPPER OH VALLEY. BY
TUESDAY ONWARD...THE EASTWARD PROGRESSION NEARLY HALTS AS THE
SYSTEM BECOMES CUT-OFF FROM THE MAIN STEERING FLOW. THE 12Z ECMWF
ENSEMBLE MEMBERS SUPPORT A SLIGHTLY DEEPER SOLUTION ALOFT PER THE
NUMBER OF MEMBERS PLOTTED ON THE 552-DM SPAGHETTI PLOT. IT HAS
TRENDED STRONGER RELATIVE TO THE PAST DAY OF RUNS. EVENTUALLY THE
12Z CMC/UKMET GRAB ON TO THIS DEEPER SOLUTION BY MID-WEEK. WITH
REGARD TO TIMING...THE 00Z NAM IS THE SLOWEST MODEL IN GENERAL TO
TRACK THIS CUT-OFF LOW TOWARD THE EAST. NORMALLY PREFER TO STAY ON
THE MORE WESTERN SIDE OF THE SPREAD WITH CUT OFF SYSTEMS BUT IT
DIVERGES TOO MUCH FROM THE CONSENSUS TO INCLUDE. WILL FAVOR THE
12Z ECMWF/UKMET AS THEY ALIGN WELL WITH THE 12Z ECMWF ENSEMBLE
MEAN AND CAPTURE THE SLIGHTLY DEEPER SOLUTION. THE CONFIDENCE WILL
BE KEPT BELOW AVERAGE GIVEN THE AMOUNT OF SPREAD NOTED IN THE
ENSEMBLE LOW PLOTS. THE 12Z GEFS MEMBERS FAVOR A SURFACE LOW MUCH
CLOSER TO THE COAST WHILE THE 12Z ECMWF/CMC ENSEMBLE MEMBERS ARE
MORE SCATTERED ABOUT OFFSHORE.


...CLOSED LOW GRADUALLY SHEARING OVER NORTHERN MX ON MONDAY
EVENING...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

AN UPPER LOW SPINNING OVER NORTHWESTERN MX HAS HELPED INVIGORATE
AN AREA OF RAINFALL OVER SOUTH-CENTRAL NM/FAR WEST TX WITHIN A
NARROW AXIS OF MOISTURE RETURN. THIS FEATURE WILL GRADUALLY LOSE
ITS IDENTITY OVER NORTH-CENTRAL MX AS IT BEGINS TO SHEAR LATE
MONDAY. MODELS VARY SLIGHTLY WITH HOW MUCH ENERGY REMAINS WHILE
CROSSING INTO CENTRAL TX ON TUESDAY. WILL FAVOR A GENERAL MODEL
COMPROMISE GIVEN THE SPREAD REMAINS ON THE LOW SIDE.


...AMPLIFIED TROF REACHING THE WEST COAST BY 20/1800Z...
...EVENTUAL SPLIT FLOW ACROSS THE GREAT PLAINS BY MID-WEEK...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z ECMWF/UKMET WITH THE 12Z
ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: BELOW AVERAGE

A SINUSOIDAL PATTERN IS IN PLACE ACROSS THE MID-LATITUDES WITH
HEIGHTS BUILDING IN THE CENTER OF THE COUNTRY. MEANWHILE...AN
AMPLIFIED TROF WILL APPROACH THE WEST COAST AND ADVANCE INLAND BY
MONDAY AFTERNOON/EVENING. THE KEY FEATURE IN THIS PATTERN IS A
SHORTWAVE CROSSING INTO NORTHERN CA BY MONDAY NIGHT. THE 00Z
NAM/12Z CMC ARE SLOWER EARLY IN THE PERIOD...PARTICULARLY THE 00Z
NAM AS IT CARRIES ENERGY INTO WEST-CENTRAL NV WHILE OTHER GUIDANCE
ARE UP NEAR THE OR/ID BORDER. MODEL SPREAD GROWS MARKEDLY BY LATE
TUESDAY INTO WEDNESDAY AS THE UPPER FLOW BEGINS TO SPLIT OVER THE
HIGH PLAINS. THE 12Z CMC SHOWS TOO MUCH ENERGY SETTLING INTO THE
SOUTHERN ROCKIES WITH VERY LITTLE SUPPORT SEEN IN THE 576-DM
SPAGHETTI PLOTS. THE SPREAD OVER THE NORTHERN SIDE OF THE SPLIT IS
RATHER HIGH WITH THE 00Z GFS SUPPORTING A ROBUST SYSTEM CROSSING
THE NORTHERN TIER MID-WEEK. THE 12Z ECMWF/UKMET ALLOW MORE OF THE
ENERGY TO LIFT INTO CENTRAL CANADA LEAVING A WEAKER SYSTEM OVER
THE CONUS. WILL PLAY IT MORE CONSERVATIVE FOR NOW FOLLOWING THE
12Z ECMWF/UKMET WHILE ADDING THE 12Z ECMWF ENSEMBLE MEAN GIVEN THE
INHERENT UNCERTAINTY.


...LONGWAVE TROF ANCHORING THE NORTHEASTERN PACIFIC TUESDAY
THROUGH THURSDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE
MEANS
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

BROAD CYCLONIC FLOW OVER THE NORTHEASTERN PACIFIC WILL ALLOW A
MYRIAD OF SHORTWAVES TO RACE TOWARD THE PACIFIC NORTHWEST AND
BRITISH COLUMBIA. THE LOW-AMPLITUDE/PROGRESSIVE FLOW IS
CHARACTERIZED BY BUILDING SPREAD GIVEN THE UNCERTAINTIES IN THIS
FLOW REGIME. THE ENSEMBLE MEANS APPEAR TO AT LEAST HAVE A HANDLE
ON THE SYNOPTIC-SCALE PATTERN SO WILL LEAN ON THEIR OUTPUT WITH
THIS ISSUANCE. THE CONFIDENCE IS A TAD HIGHER THAN THE PREVIOUS
SECTIONS GIVEN THE AGREEMENT IN THE MEANS.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

RUBIN-OSTER

$$




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