387
FXUS10 KWNH 231826
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
226 PM EDT THU APR 23 2020
VALID APR 23/1200 UTC THRU APR 27/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z EVALUATION WITH MODEL PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
OHIO VALLEY SYSTEM TODAY THROUGH NORTHEAST FRI INTO EARLY SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE ECMWF SLOWED A BIT, WHILE THE CMC/UKMET TRENDED A
BIT FASTER. THERE REMAINS A MODEST SPREAD IN PLACEMENT OF THE
COASTAL SURFACE LOW, BUT OVERALL A GENERAL MODEL BLEND WILL
SUFFICE AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.
---PRIOR DISCUSSION---
MATURE CLOSED LOW ACROSS TRI-RIVERS OF W KENTUCKY CONTINUES TO
PRESS EAST, WITH ACTIVE WARM CONVEYOR BELT WELL DISPLACED FROM THE
COLD FRONT ACROSS THE LOWER MS VALLEY. GUIDANCE IS FAIRLY SOLID
INITIALLY, BUT FASTER SOLUTIONS OF THE 12Z GFS/NAM BOTH SUGGEST A
STRONGER MCV GROWTH OUT OF THE SOUTHEAST SUPPORTING A COASTAL LOW
TO TAKE OVER THE FILLING SURFACE WAVE THROUGH THE OHIO VALLEY BY
LATER FRIDAY. WHILE THE GFS APPEARS TO BECOME A TAD TO FAST (OUT
OF ENSEMBLE/CONTINUITY TOLERANCE BY 36HRS), A BLEND WITH THE
SLIGHTLY SLOWER 00Z ECMWF AND NAM SHOULD OFFSET THE NEGATIVE BIAS.
THE 00Z CMC IS SIGNIFICANTLY SLOWER AND LINGERS ACROSS THE
SOUTHEAST AND WESTERN ATLANTIC A TAD TOO MUCH IN THIS PROGRESSIVE
PATTERN. THE 00Z UKMET IS ALSO SLOW, BUT THAT APPEARS TO BE DUE
TO THE FACT THERE IS NO MCV REFLECTION/UPSCALE GROWTH MOVING OFF
THE EAST COAST INTO FRIDAY; SO IT FAVORS A STRONGER INNER CORE TO
THE FILLING CLOSED LOW, WHICH APPEARS INCREASINGLY LESS LIKELY
GIVEN OBSERVATIONAL TRENDS. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE
IN A 12Z NAM/GFS AND 00Z ECMWF BLEND.
CONGLOMERATION OF SHORTWAVES TOWARD MID-MS/OHIO VALLEY SAT/SUN...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/ECMWF BLEND (INCL GEFS/ECENS BY D3)
CONFIDENCE: SLIGHTLY BELOW AVERAGE
19Z UPDATE: THE CMC TRENDED A BIT WEAKER ACROSS AR AND SHIFTED
NORTH, CLOSER TO THE ECMWF/GFS/NAM SOLUTIONS, BUT EVENTUALLY SLOW
A BIT. GIVEN THE ECMWF DID TREND SLOWER/SOUTH AS WELL, IT IS
PLAUSIBLE THE CMC HAS SOME SORT OF HANDLE ON THIS EVOLUTION;
HOWEVER, WILL CONTINUE TO SUGGEST ITS EXCLUSION AND REMAIN WITH A
GFS/ECMWF BLEND AT SLIGHTLY BELOW AVERAGE CONFIDENCE.
---PRIOR DISCUSSION---
BROAD LARGE SCALE RIDGE OVER THE EASTERN PACIFIC WITH VERY STRONG
GLOBAL SCALE VORTEX OVER THE ARCTIC LEAVE A VERY DIFFUSE NORTHWEST
FLOW PATTERN ACROSS THE WEST INTO THE PLAINS OVER THE NEXT DAY OR
SO. A JET MAX AND ASSOCIATED SPEED VORTICITY CENTER CURRENTLY
OVER WA/ID WILL DROP SOUTHEAST ACROSS THE CENTRAL PLAINS AND
SUPPORT A SURFACE WAVE OUT OF THE LEE OF THE CENTRAL ROCKIES.
WITH THE EXITING WAVE THERE IS SUBTLE RIDGING AND WITH UPSTREAM
UPPER LEVEL JET ENERGY; THE SHORTWAVE IS ABLE TO AMPLIFY ACROSS E
OK/AR HAVING TAPPED SOME RETURN MOISTURE. THE 00Z CMC BEING MUCH
SLOWER TO EXIT WITH THE PRIOR WAVE, ALLOWS FOR GREATER RIDGING
BETWEEN THE SYSTEMS; ALLOWING FOR THE GREATEST DEEPENING AND WELL
AS SOUTHWARD TRACK. GIVEN THE CMC IS UNFAVORED DOWNSTREAM; IT IS
EQUALLY DISCOURAGED WITH THIS EVOLUTION.
WHILE THE WAVE IS DEEPENING ON FRIDAY, SMALL NORTHERN STREAM
SHORTWAVE ENERGY WILL CARVE OUT ACROSS THE MIDWEST AND HELP TO
DRAW THE GROWING BASE OF THE TROF NORTHWARD. THIS BINARY
INTERACTION IS ALWAYS A LOWER PREDICTABILITY, AS TIMING OF THE
INTERACTION IS CRITICAL. ADDITIONALLY, WITH THE AMPLIFICATION,
ADDITIONAL JET ENERGY IN THE NORTHWEST FLOW WILL FURTHER HELP TO
SLOW/AMPLIFY THE WAVE. THE UKMET/CMC BOTH SUGGEST UPSTREAM
DEVELOPMENT OVER THE NORTHERN PLAINS BY LATE SATURDAY, WHICH WILL
ACT MORE OF A KICKER TO THE SYSTEM THAN HELPING TO AMPLIFY IT.
THE 12Z NAM HAS THIS FEATURE BUT ALSO SHOWS A MUCH STRONGER
COMPACT DEVELOPMENT THROUGH THE MID-MS VALLEY ON SAT...PERHAPS
WITH INCREASED LATENT HEAT RELEASE FROM STRONGER
CONVECTION...EVENTUALLY HAVING A STRONGER WAVE AND AN UPSTREAM
KICKER; THE NAM STARTS TO PRESS EASTWARD THROUGH THE OHIO VALLEY
AND MID-ATLANTIC BY SUNDAY. THE 00Z ECMWF AND 12Z GFS EVENTUALLY
SLOW RELATIVE TO THEIR ENSEMBLE SUITE, SO PERHAPS TRENDING A BIT
MORE TOWARD THE MEANS PARTICULARLY BY SUNDAY IS PRUDENT GIVEN THE
PROGRESSIVE PATTERN, THE CONUS HAS BEEN EXPERIENCING. STILL A 12Z
GFS/00Z ECMWF BLEND IS PREFERRED WITH SOME INCLUSION OF THE 06Z
GEFS/00Z ECENS ON DAY 3 TO ACCOUNT FOR THE MODERATE UNCERTAINTY.
GIVEN THE SPREAD, LOWER PREDICTABILITY PATTERN (DUE TO BROAD
STREAM/BINARY INTERACTIONS) CONFIDENCE IS SLIGHTLY BELOW AVERAGE
IN THE BLEND.
SHORTWAVE ENTERING PACNW LATE SAT, CLIPPING THROUGH NORTHERN TIER
BY SUN...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: ABOVE AVERAGE
19Z UPDATE: THE UKMET REMAINS A BIT NORTH OF THE OVERALL SUITE,
BUT HAS TRENDED TOWARD THE CMC/ECMWF (WHICH KEEP WITH CONTINUITY)
AND THE GFS. AS SUCH, A NON-NAM BLEND IS PREFERRED AT ABOVE
AVERAGE CONFIDENCE.
---PRIOR DISCUSSION---
ACTIVE SOUTHERN PORTION OF THE PACIFIC NORTHERLIES WILL PRESS A
SUBTLE JET MAX AND SHORTWAVE THROUGH VANCOUVER ISLAND BY MIDDAY
FRIDAY...THIS HELPS TO PRESS THE LARGER SCALE PACIFIC RIDGE A BIT
EASTWARD IN ADVANCE OF A STRONGER SHORTWAVE THAT APPROACHES LATE
SAT. THIS WAVE IS FAIRLY COMPACT BUT ALSO A TAD SOUTH. THE 12Z
NAM IS MOST AGGRESSIVE WITH THIS SOLUTION AND SUPPORTS A COMPACT
CLOSED LOW OFF THE NORTHWEST TIP OF VANCOUVER ISLAND. THIS IS
SUPPORTED BY THE GFS, FOLLOWED BY THE CMC AND LESSER SO THE ECMWF
SOLUTIONS, WHILE THE UKMET IS WELL NORTHEAST WITH THE INNER CORE
OF THE UPPER LOW. STILL THE TIMING OF THE TROF/FRONTAL ZONE IS
FAIRLY SOLID WITH SIMILAR FLOW REGIME/STRENGTH MINUS THE NAM.
THIS CONTINUES AS THE SHORTWAVE PRESSES THROUGH THE CANADIAN
ROCKIES SAT INTO SUNDAY WITH STRONG SURFACE LEE-CYCLONE PRESSING
EAST ACROSS NORTH-CENTRAL ALBERTA/SASKATCHEWAN. THIS CLIPS THE
NORTHERN ROW OF COUNTIES WITH SENSIBLE WEATHER BY DAY 3, BUT WITH
LITTLE FANFARE, HAVING WRUNG OUT THE MOISTURE ACROSS THE COASTAL
RANGE AND INTO THE ROCKIES OF ID/W MT. SO FOR AFFECTS IN THE
CONUS, WOULD SUPPORT A NON-UKMET BLEND, BUT WOULD TAMP DOWN OR
REMOVE THE NAM FOR LIKELY BEST POSSIBLE BLEND. OVERALL, THE
SPREAD IS FAIRLY SMALL FOR DAY 2-3 AND THE AFFECTS ARE FAIRLY
SMALL TO HAVE ABOVE AVERAGE CONFIDENCE IN THIS BLEND, ACROSS THE
CONUS.
FRONTAL ZONE OF GULF OF AK CLOSED LOW APPROACHING PACNW LATE SUN...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE UKMET TRENDED A BIT BETTER BUT REMAINS A BIT TOO
FAST GIVEN THE OTHERWISE TIGHTER CLUSTER. THE ECMWF ALSO TRENDED
A BIT SLOWER BUT STILL WELL WITHIN THE ENSEMBLE SUITE AND NEAR THE
12Z CMC, GFS. AS SUCH WILL KEEP WITH NON-UKMET BLEND AT SLIGHTLY
ABOVE AVERAGE CONFIDENCE.
---PRIOR DISCUSSION---
THE NEXT STRONG SHORTWAVE HELPS TO ANCHOR THE LARGER SCALE TROUGH
INTO THE GULF OF AK BY THE END OF THE FORECAST PERIOD. WHILE
THERE ARE SOME RESIDUAL DIFFERENCES DUE TO THE PRIOR SHORTWAVE
EXITING (IE THE ECMWF/CMC A BIT NORTH; GFS/NAM A BIT FURTHER
SOUTH), THERE IS ACTUALLY SOLID MODEL AGREEMENT FOR THE
TIMING/STRENGTH AND POSITION OF CLOSED LOW OFF OF HAIDA GWAII BY
00Z MONDAY. WHILE THE FRONT IS STILL WELL OFFSHORE, ITS AFFECTS
START TO ENCROACH THE PACIFIC NW. BEING A TAD NORTH, THE MOISTURE
TRANSPORT (QPF) IS DELAYED IN THE CMC/ECMWF RELATIVE TO THE
FASTER/SOUTH GFS/NAM. ONLY THE UKMET IS WELL TOO FAST, TOO STRONG
(LIKELY DUE TO TIMING WITH THE PRIOR SYSTEM, ACCELERATING IT
EASTWARD EARLIER), ENOUGH TO SUGGEST A NON-UKMET BLEND THIS FAR
OUT IN THE FORECAST PERIOD AT FAIRLY HIGH CONFIDENCE (SLIGHTLY
ABOVE AVERAGE).
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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