129
FXUS10 KWNH 241835
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 PM EDT FRI APR 24 2020
VALID APR 24/1200 UTC THRU APR 28/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z EVALUATION WITH FINAL MODEL PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
LOW PRESSURE CROSSING MID-ATLANTIC ON FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
GOES-EAST WV SUITE DEPICTS A SHEARING WAVE MOVING ACROSS THE
MID-ATLANTIC CURRENTLY, WITH A VERY STRONG WARM CONVEYOR BELT
ALONG THE GULF STREAM. THE SURFACE WAVE ASSOCIATED WITH THE
STACKED BUT FILLING LOW WILL SLIDE THROUGH VA TODAY AND GIVE WAY
TO THE DEVELOPING COASTAL LOW. THE 12Z NAM IS A BIT STRONGER
THROUGHOUT THE CYCLE WITH RESPECT TO THE WAVE, BUT IS NICELY TIMED
WITH THE REST OF THE GUIDANCE SUITE. THIS GIVES SOME PAUSE TO ITS
INCLUSION BUT GIVEN THE LOW IS A BIT STRONGER THAN SOME OF THE
OTHER GUIDANCE, WILL INCLUDE THE NAM; AND SUPPORT A GENERAL MODEL
BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.
LOW PRESSURE TRACKING FROM TEXAS TO THE OHIO VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: OVERALL, THE LATE ARRIVING MODELS INCLUDING THE 12Z
GEFS ALL GENERALLY SLOWED A BIT, PARTICULARLY BY DAY 3 AND THE
OVERALL DEPTH OF MASS DIFFERENCES REMAIN VERY SMALL OVERALL. THE
SHIFT BRINGS THE GFS BACK INTO QUESTION, BUT THE STRENGTH OF
CONVECTION ALONG THE WESTERN PERIPHERY/DEFORMATION ZONE ACROSS THE
LOWER OHIO/MID-MS VALLEY SUGGESTS THIS LATENT HEAT INJECTION STILL
IS TROUBLESOME WITH INCLUSION IN A BLEND, BUT ONLY LESSER SO. SO
IF ONE IS RETICENT OF POINT, GFS COULD BE INCORPORATED IN A BLEND
ELSEWHERE. SILL, WPC PREFERENCE WILL CONTINUE TO BE A NON-GFS
BASED BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.
---PRIOR DISCUSSION---
IN THE WAKE OF THE DEPARTING WAVE ALONG THE EAST, BROAD SCALE
TROUGHING REMAINS ACROSS THE MID-MS VALLEY INTO THE OHIO VALLEY.
THIS ALLOWS A SHORTWAVE EMERGING FROM THE COLORADO ROCKIES TODAY
TO SHARPEN AND DEVELOP A ENHANCE A SURFACE WAVE IN THE SOUTHERN
PLAINS THAT MOVES THROUGH THE MID-MS VALLEY SAT AND INTO THE
OHIO/TN VALLEY BY EARLY SUNDAY. UPSTREAM SHORTWAVE FEATURES/SMALL
JET IMPULSES OUT OF THE BROAD NORTHWEST FLOW ACROSS THE ROCKIES
INTO THE PLAINS, WILL ENHANCE THE TROF, BUT LEAD TO INCREASED
BINARY INTERACTION, WHICH CAN MAKE PRECISE SMALLER SCALE FEATURES
MORE DIFFICULT TO PREDICT IN THIS RANGE. THIS IS PARTICULARLY THE
CASE LATE SUNDAY INTO MONDAY, WHEN THE SHORTWAVE OVER THE NORTHERN
PLAINS SWINGS UNDER THE BASE OF THE FORMER. EVENTUALLY, THE
COMBINED BINARY TROF EXPANDS OVER THE MID-ATLANTIC ON MONDAY AND
TRANSFERS TOWARD A COASTAL LOW DEVELOPMENT THAT SLIDES THROUGH THE
SOUTHEAST OF NEW ENGLAND.
THE 12Z NAM/GFS ARE INITIALLY STRONGER EMERGING FROM THE SOUTHERN
PLAINS, WITH THE GFS A TAD NORTH, EVEN COMPARED TO THE GEFS
SOLUTIONS. THE 00Z UKMET/ECMWF/CMC ARE A BIT WEAKER, FASTER BUT
ALSO LESS PRONE TO THE TRICORDIAL WOBBLES THAT MANIFEST,
PARTICULARLY IN THE 12Z GFS. WHEN THE UPSTREAM SHORTWAVE MERGES
ON SUNDAY AND MONDAY, THE GFS WOBBLES BECOME EVEN LARGER AND MOVE
IT OUT OF THE OTHERWISE SOLID CLUSTERING. 00Z UKMET TRENDS TOWARD
A STRONGER INITIAL WAVE THROUGH THE OHIO VALLEY, HOLDING ONTO THE
WAVE/SURFACE LOW A BIT LONGER THAN THE NAM/CMC/ECMWF AND THE
ECENS/GEFS SOLUTIONS, BUT IT DOESN'T MOVE TOO MUCH OUT OF
TOLERANCE FOR A DAY 3 FORECAST TO HAVE IN REMOVED FULLY. AS SUCH
WILL SUPPORT A NON-GFS BLEND EVENTUALLY REDUCING INFLUENCE OF THE
UKMET BY THE END OF THE FORECAST PERIOD. GIVEN THE AMOUNT OF
INFLUENCE OF BINARY INTERACTION/CONVECTIVE UPSCALE INFLUENCE TO
THE TIMING OF THE WAVE...THE OTHER AGREEMENT IS FAIRLY STRONG TO
HAVE SLIGHTLY ABOVE AVERAGE CONFIDENCE IN THIS NON-GFS BLEND.
PAIR OF TROUGHS AFFECTING THE NORTHWESTERN U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL BLEND,
EXCEPTION(S): NON-UKMET AFTER 60HRS WITH 2ND WAVE
LIMIT NAM ON DAY 3 IN ID/WY (QPF MAINLY)
CONFIDENCE: ABOVE AVERAGE
19Z UPDATE: THE EVOLUTION, TIMING OF THE LEAD WAVE CONTINUES TO BE
SOLID AGREEMENT TO CONTINUE A GENERAL MODEL BLEND FOR THAT WAVE.
WITH THE SECOND WAVE, THE 12Z UKMET IS SO QUICK IN ROTATING THE
TOP OF THE WAVE INTO THE LARGER PARENT CYCLONE, OLDER VORTICITY
HUB, DROPS SOUTHEAST AND CAPTURES OR DELAYS THE TRAILING EDGE OF
THE TROF THROUGH THE NORTHEAST PACIFIC ON MONDAY. THIS LEADS TO A
SLOWING OF THE FRONTAL ZONE AND RELOADS A STRONGER TROF ALOFT.
THIS IS A MINOR MASS DIFFERENCE THAT HAS LIMITED SENSIBLE EFFECTS;
HOWEVER, WILL REMOVE THE UKMET AFTER 60HRS IN THE PACIFIC NW FOR A
CLEANER/TIGHTER BLEND PREFERENCE.
---PRIOR DISCUSSION---
AN ELONGATED GLOBAL SCALE TROF WILL START TO SLIDE SOUTHEAST TO
ANCHOR IN THE GULF OF AK BY THE WEEKEND AS A STRONG PACIFIC
SHORTWAVE MOVES THROUGH TOWARD VANCOUVER ISLAND EARLY SATURDAY.
THIS INITIAL WAVE WILL STRETCH INITIALLY LOSING SOME OF THE TOP OF
THE WAVE TO THE GLOBAL TROF, BUT THE REMAINING BASE QUICKLY
TRANSLATES ACROSS THE CANADIAN ROCKIES. THIS WAVE WILL CLIP THE
NORTHERN TIER WITH LIMITED SENSIBLE EFFECTS UNTIL LATE SUNDAY
ACROSS THE UPPER MIDWEST AND UPPER GREAT LAKES. THE GUIDANCE IS
FAIRLY AGREEABLE WITH THE EVOLUTION AND CAN SUPPORT A GENERAL
MODEL BLEND THROUGH THE FORECAST PERIOD WITH THIS SYSTEM.
UPSTREAM, A SECOND PACIFIC SHORTWAVE WILL TRANSLATE ALONG THE BASE
OF THE CONSOLIDATING CLOSED LOW OVER THE GULF OF AK. THIS WAVE IS
DRAWN MORE NORTHWARD WITH ONLY THE BASE RAPIDLY SWINGING MORE
NEGATIVE TILT THROUGH VANCOUVER ISLAND LATE SUNDAY INTO EARLY
MONDAY. THE TRAILING COLD FRONT AND MOISTURE PLUME PRESS ACROSS
THE COASTAL RANGE AND INTO THE NORTHERN US ROCKIES WITH SOLID
MODEL AGREEMENT IN MASS FIELDS. THE ONLY STRANGE OUTLIER IN THE
12Z NAM BEING QUITE DRY RELATIVE TO THE OTHER SOLUTIONS ESPECIALLY
OVER EASTERN ID INTO THE RANGES SURROUNDING YELLOWSTONE AND THE
JACKSON RANGE. AS SUCH A GENERAL MODEL BLEND COULD BE SUPPORTED
THROUGH WOULD REMOVE THE NAM FOR ANY QPF/SNOW REASONS ON DAY 3.
CONFIDENCE IS 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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