Prognostic Meteorological Discussion
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FXUS10 KWNH 221849
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT MON SEP 22 2014

VALID SEP 22/1200 UTC THRU SEP 26/0000 UTC

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

...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...NORTHERN STREAM TROF EXITING NEW ENGLAND ON TUESDAY...

FINAL PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

A NEGATIVELY-TILTED TROF IS FORECAST TO CONTINUE LIFTING NORTH AND
EAST THIS EVENING WITH ADDITIONAL SHORTWAVES TRACKING THROUGH
UPPER NEW ENGLAND. ONLY SMALL DIFFERENCES ARE NOTED AMONG THE
AVAILABLE MODELS SO A GENERAL MODEL COMPROMISE WOULD BE BEST
SUITED WITH THIS SECTOR OF THE CONUS.


...UPPER LOW CUTTING OFF OVER THE CAROLINAS...
...INVERTED TROF ALONG THE EASTERN SEABOARD...

FINAL PREFERENCE: 12Z NAM
FORECAST CONFIDENCE: LOW

WATER VAPOR IMAGERY SHOWED A POTENT SHORTWAVE DIVING INTO THE DEEP
SOUTH WITH A WELL DEFINED TONGUE OF DRY AIR SPILLING IN BEHIND IT.
BY 23/1200Z...THERE IS A CLEAR SIGNAL IN THE MODELS THAT THE
SYSTEM WILL NEARLY STALL AS IT BECOMES CUT OFF FROM THE NORTHERN
STREAM. THE GENERAL CLUSTERING IN THE GUIDANCE IS REASONABLE
THROUGH TUESDAY EVENING BEFORE THE FORECAST BECOMES MORE NEBULOUS.
THIS UNCERTAIN FORECAST IS NOTED FROM MID-WEEK ONWARD AS THE
SYSTEM CONTINUES TO SHEAR WITH VORTICITY CENTERS LIFTING NORTHWARD
ALONG THE EAST COAST. THE 12Z ECMWF FAVORS KEEPING THE SHEAR AXIS
FARTHER WEST WHICH ENHANCES THE THREAT FOR HEAVY PRECIPITATION
INLAND. LOOKING AT THE SURFACE...STRONG NORTHEASTERLY FLOW IS
DEPICTED IN ALL GUIDANCE AS A STRONG SURFACE HIGH BUILDS JUST
OFFSHORE OF NEW ENGLAND. THE 12Z NAM SEEMS TO AGREE WITH THE
ENSEMBLE MEANS THROUGH DAY 2 WITH THE POSITION OF THE INVERTED
TROF ALONG THE COAST. THE 12Z ECMWF REMAINS OFF TO THE WEST WHILE
THE 12Z CMC TRENDED EAST MORE OR LESS JOINING THE MORE EASTERN 12Z
GFS. THIS CONTINUES TO BE THE CASE INTO DAY 3 AS WELL.
OVERALL...THE SOLUTIONS DIFFER GREATLY FROM ONE ANOTHER WITH
CONFIDENCE RATHER LOW. FEEL THE 12Z NAM PRESENTS THE MOST
CONSERVATIVE SOLUTION AND SEEMS TO FIT SOMEWHERE IN THE MIDDLE OF
THE SPREAD.


...SLOW-MOVING UPPER TROF MOVING FROM THE CENTRAL GREAT BASIN TO
UPPER MIDWEST...

FINAL PREFERENCE: BLEND OF THE 12Z NAM/UKMET
FORECAST CONFIDENCE: AVERAGE

AN ELONGATED AXIS OF ENERGY IS EXPECTED TO SLIDE FROM THE CENTRAL
GREAT BASIN TOWARD THE NORTH-CENTRAL STATES DURING THE NEXT 24 TO
36 HOURS. THROUGH 24/0000Z...THE MODELS ARE REASONABLY CLUSTERED
WITH ONE ANOTHER. BY WEDNESDAY EVENING...THE 12Z GFS GETS AHEAD OF
THIS CONSOLIDATED SOLUTION AND CONTINUES PUSHING THIS ENERGY
EASTWARD ALONG THE SOUTHERN FRINGE OF THE WESTERLIES. ENSEMBLES
SUPPORT STALLING THE SYSTEM AND ALLOWING SHORTWAVE ENERGY TO
SLOWLY MIGRATE SOUTHWARD. THE 12Z ECMWF/CMC DO KEEP THE SYSTEM A
BIT FARTHER NORTH BUT SHOW MUCH SLOWER MOTION THAN THE QUICKER 12Z
GFS. THE 12Z NAM/UKMET SEEM TO FAVOR THE MORE CUT-OFF SOLUTION
WHICH IS SUGGESTED BY THE ENSEMBLE MEANS. WPC WILL FAVOR A
COMBINATION OF THE 12Z NAM/UKMET AND NOT INCLUDE THE ECMWF THIS
TIME GIVEN ITS MORE NORTHERN DEPICTION.


...WEAK AXIS OF VORTICITY LINGERING OVER THE SOUTHERN HIGH
PLAINS...

FINAL PREFERENCE: BLEND OF THE 12Z NAM/UKMET/ECMWF
FORECAST CONFIDENCE: AVERAGE

MODELS CONTINUE TO ADVERTISE A WEAKNESS IN THE MID-LEVEL FLOW
ACROSS THE SOUTHERN/CENTRAL PLAINS BY WEDNESDAY/THURSDAY. WILL
FAVOR A SOLUTION SIMILAR TO THE SYSTEM ACROSS THE NORTHERN TIER
GIVEN BOTH BECOME EMBEDDED IN SOME FORM OF GENERAL WEAKNESS ACROSS
THE CENTER OF THE COUNTRY BY THURSDAY. THUS...THE RECOMMENDATION
IS A BLEND OF THE 12Z NAM/UKMET WITH THE 12Z ECMWF ALSO
INCORPORATED GIVEN ITS SIMILARITY TO THESE MODELS.


...FULL-LATITUDE TROF ALONG THE IMMEDIATE WEST COAST BY THURSDAY...

FINAL PREFERENCE: BLEND OF THE 12Z GEFS/00Z ECMWF ENSEMBLE MEANS
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE PATTERN BECOMES QUITE AMPLIFIED ACROSS THE EASTERN PACIFIC AND
WESTERN U.S. WITH A RIDGE ANCHORING THE DESERT SOUTHWEST UP INTO
THE GREAT BASIN/ROCKIES. MEANWHILE...MORE IMPRESSIVELY...THE
UPSTREAM TROF CONTAINS 500-MB HEIGHT ANOMALIES OF 3 TO 3.5
STANDARD DEVIATIONS BELOW CLIMATOLOGY. THROUGH 25/0000Z...THE
ENSEMBLE MEANS ARE IN NEAR AGREEMENT WITH ONE ANOTHER WITH
SUFFICIENT SUPPORT FROM THE 12Z GFS. THEREAFTER...THE SPREAD HAS
ACTUALLY GROWN FROM THE PREVIOUS DISCUSSION AS THE 12Z MODELS
DEPART MORE SIGNIFICANTLY FROM ONE ANOTHER. MOST OF THESE
DIFFERENCES ARE MANIFESTED IN THE 564-DM HEIGHT CONTOUR VIA
SPAGHETTI PLOTS WITH MORE AGREEMENT NOTED AT 576-DM. WILL MAINTAIN
THE PREVIOUS PREFERENCE WHILE INCORPORATING THE LATEST 12Z GEFS
MEAN. CONFIDENCE WILL BE SLIGHTLY LOWERED BASED ON THE GROWING
DISAGREEMENT IN SPITE OF NEW GUIDANCE BECOMING AVAILABLE.



...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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