306
FXUS10 KWNH 211645
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1245 PM EDT TUE APR 21 2020
VALID APR 21/1200 UTC THRU APR 25/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...DEVELOPING LONG WAVE TROUGH OVER NEW ENGLAND WITH AN ASSOCIATED
SURFACE LOW...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE 12Z NAM AND GFS CONTINUE TO REMAIN ON TRACK/CONSISTENT WITH
THE TIMING AND DEPTH OF THE SHORTWAVE HELPING TO SWING THE LARGER
SCALE TROF NEGATIVE TILT THROUGH THE NORTHEAST WED. THE RESULTANT
TRIPLE POINT WILL TRACK NEAR THE GULF OF MAINE AND QUICKLY INTO
SOUTHEAST CANADA. AS SUCH A GENERAL MODEL BLEND WILL CONTINUE TO
BE PREFERRED AT ABOVE AVERAGE CONFIDENCE.
...MID LEVEL TROUGH TRACKING FROM ACROSS THE SOUTHWEST AND
SOUTHERN PLAINS TO THE MID ATLANTIC...
..SURFACE LOW ASSOCIATED WITH THE MID LEVEL TROUGH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/ECENS AND 06Z GEFS BLEND (WITH SOME LOW 12Z
NAM THRU 60HRS)
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE
MEDIUM-SIZED SHORTWAVE IS STARTING TO TAKE BETTER SHAPE ACROSS THE
SOUTHWEST TODAY, SUPPORTING LEE-CYCLOGENESIS ACROSS EASTERN NM.
THERE IS SOLID MODEL AGREEMENT INITIALLY, THOUGH THE CMC IS A TAD
SOUTH. THIS SMALL DIFFERENCE WITH THE 00Z CMC GROWS GREATER
THROUGH THE MID-MS VALLEY THURSDAY AND IS CLEARLY LAGGING. THE
WAVE IS WEAKENING SLIGHTLY THROUGH THE OHIO VALLEY INTO
INCREASINGLY CONFLUENT FLOW...THIS LEADS TO INCREASED SPREAD IN
TIMING OF THE SURFACE WAVE TRACKING THROUGH THE OHIO VALLEY TOWARD
THE EAST COAST INTO FRIDAY. LIKE THE 00Z CMC, THE 00Z UKMET WILL
LAG TOO, EVENTUALLY BECOMING LESS FAVORABLE. THE 12Z NAM
CONTINUES A TREND OF STRONGER BUT ALSO FASTER INTO THIS CONFLUENT
FLOW, WHILE THE GFS IS A BIT SLOWER BUT EQUALLY COMPACT AND
FAVORING STRONGER FLUX CONVERGENCE INTO THE DEVELOPING DEFORMATION
ZONE, OVER STRONGER CONVECTION; EVENTUALLY SLOWING ITS PROGRESS
THROUGH THE OHIO VALLEY INTO THE EAST. THESE ARE KNOWN NEGATIVE
BIASES OF THE GFS WOULD FAVOR THE 06Z GFS TIMING/INFLUENCE OVER
THE OPERATIONAL 12Z GFS. THE NAM APPEARS TOO FAST, GIVEN ITS
STRENGTH RELATIVE TO THE ENSEMBLE SUITE, SO A BIT
COUNTER-INTUITIVE, STILL IT MAY NOT BE TOO OUT OF PHASE FOR SOME
INCLUSION, ESPECIALLY THROUGH THE OHIO VALLEY.
THE 00Z ECMWF IS TIMED WELL INITIALLY WITH THE GFS AND NAM AND
ALSO FAVORS STRONGER CONVECTIVE DEVELOPMENT SOUTH, OPPOSITE TO THE
GFS, AND MORE IN LINE WITH TYPICAL SPRING (RECENT) PATTERN. THIS
HELPS TO ELONGATE/SHEAR THE LARGER SCALE SHORTWAVE, MAKING IT
GENERALLY WEAKER THROUGH THE EAST COAST, PERHAPS A TAD TOO MUCH
GIVEN INTER-COMPARISON WITH ECENS MEMBERS. AS SUCH A ECMWF HEAVY
BLEND WITH THE 06Z GEFS AND 12Z NAM AND 00Z ECENS MEAN.
CONFIDENCE IS SLIGHTLY BELOW AVERAGE IN THIS BLEND GIVEN THE LOWER
PREDICTABILITY GIVEN IMPORTANCE OF CONVECTIVE SCALE INFLUENCE ON
THE HIGHER LEVEL MASS FIELDS.
...SHORT WAVE AND SURFACE LOW TRACKING FROM WESTERN CANADA TO THE
NORTHERN PLAINS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
A SUBTLE SHORTWAVE/SPEED MAX IN NW FLOW OUT OF NW CANADA WILL DROP
INTO THE NORTHERN PLAINS BY EARLY WED WITH SOLID MODEL AGREEMENT.
THE 12Z NAM/GFS CONTINUE STRONG AGREEMENT WITH THE EVOLUTION OF
THE THIS WAVE BEFORE IT WEAKENS ACROSS IA INTO THE GREAT LAKES,
UNDER CONFLUENT FLOW REGIME AND APPROACHING STRONGER
SHORTWAVE/CYCLONE FROM THE SOUTHERN PLAINS. THE 00Z ECMWF/UKMET
ARE ALSO IN GOOD AGREEMENT WITH THE MASS FIELDS, AND MUCH LIKE THE
GFS AND NAM CAN TAP SOME OF THE OVERRUNNING MOISTURE FROM THE
PACIFIC/GULF MOISTURE TO PRODUCE A SOLID/NARROW SWATH OF QPF
ACROSS THE SOUTHWEST-SOUTHERN GREAT LAKES REGION INTO THURSDAY.
THE CMC MASS FIELDS ARE A BIT OFF WITH THE SURFACE LOW TRACK BUT
THE PLACEMENT OF THE FRONTOGENESIS/QPF MAY BE TOLERABLE WITHIN A
BLEND; YET ITS REMOVAL FOR MASS FIELDS WOULD LIKELY PRESENT A
BETTER BLEND. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE
THE 00Z NAM/GFS ARE CLOSE TO THE CONSENSUS TRACKING SHORT WAVE
ENERGY FROM WESTERN CANADA IN THE VERY FAST MID LEVEL FLOW ACROSS
THE NORTHERN PLAINS BEFORE 23/00Z. THE 00Z NAM BECOMES SLOWER THAN
THE 00Z GFS AFTER THIS TIME, EVENTUALLY PLACING THE TROUGH OVER
WESTERN ND (AS DOES THE 00Z CMC, THOUGH NOT AS FAR WEST AS THE 00Z
NAM). THE 00Z GFS IS CLOSE TO THE 00Z ECMWF/UKMET WITH THE TROUGH
POSITION EXTENDING FROM ND SOUTH THROUGH NE BY 24/12Z. THERE IS
MORE SPREAD WITH THE PLACEMENT OF THE RESULTING SURFACE LOW FROM
ND INTO NE. SINCE THERE HAS BEEN SOME CONSISTENCY WITH THE 00Z
GFS/00Z ECMWF/00Z UKMET WITH THIS FEATURE, THESE MODELS COMPRISE
THE PREFERRED BLEND. HOWEVER, DUE TO THE SLOWER SOLUTIONS OF THE
00Z NAM/00Z CMC AND THE SPREAD IN THE PLACEMENT OF THE SURFACE LOW
AT THE END OF THE PERIOD, FORECAST CONFIDENCE IS ONLY AVERAGE.
...SHORT WAVE ENERGY TRACKING FROM THE PACIFIC NORTHWEST TO THE
SOUTHERN PLAINS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 24.00Z
NON-NAM THEREAFTER
CONFIDENCE: AVERAGE
A STRONG ANTICYCLONICALLY CURVED 250MB PACIFIC JET WILL HELP TO
TAMP DOWN THE LARGER SCALE RIDGE IN THE EASTERN PACIFIC AND USHER
SMALLER SCALE EMBEDDED SHORTWAVES ACROSS THE PACIFIC NORTHWEST
STARTING LATE WED, THAT WILL PROGRESS THROUGH THE ROCKIES INTO
MORE BAGGY, FLATTER/BROAD TROUGHING. THIS WILL ALLOW THE LEAD
WAVE TO START TO AMPLIFY ACROSS THE BITTERROOTS BEFORE STRETCHING
VERTICALLY ALONG THE LEE OF THE ROCKIES, SUPPORTING A LEE TROUGH
AND SURFACE LOW IN THE HIGH PLAINS, THAT BUILDS SOUTH BY 24.00Z,
WITH A STRONGER/DEEPER SURFACE WAVE IN THE TX PANHANDLE. THE DEEP
SOUTHERLY RETURN FLOW WILL SUPPORT ACTIVE CONVECTION THROUGHOUT
THE PLAINS INTO THE MS VALLEY. OVERALL, THIS IS A DIFFICULT
PATTERN TO LOCK DOWN THE PRECISE PLACEMENT OF THESE CONVECTIVE
CLUSTERS, THOUGH GIVEN THIS THE MODEL SPREAD IS FAIRLY CONSISTENT
TO HAVE MODERATE CONFIDENCE IN A GENERAL MODEL BLEND THROUGH ABOUT
72HRS (24.12Z). BY THIS TIME, THE 12Z NAM IS VERY STRONG AND
FAST; TYPICAL OF DAY 3 NEGATIVE BIAS. THE 12Z IS A TAD FASTER, IN
LINE WITH BIAS BUT NOT TERRIBLY SO. THE 06Z GEFS IS BETTER
TIMED...AND FOR A MORE SOLID BLEND, PERHAPS SHOULD BE USED ON DAY
3 OVER THE OPERATIONAL GFS. HOWEVER, WPC PREFERENCE AT THIS TIME,
IS A GENERAL MODEL BLEND THROUGH 24.00Z, SHIFTING MORE NON-NAM
THEREAFTER. CONFIDENCE IS AVERAGE GIVEN SMALL SPREAD BUT LOWER
PREDICTABILITY/ FLOW REGIME.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
GALLINA
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