701
FXUS10 KWNH 081900
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT FRI MAY 08 2020
VALID MAY 08/1200 UTC THRU MAY 12/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL FINAL EVALUATION INCLUDING LATEST PREFERENCES AND
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..DEEPENING SURFACE LOW MOVING ALONG THE NORTHEAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: ABOVE AVERAGE
19Z UPDATE: THE PREVIOUS CONCERNS ABOUT THE 00Z ECMWF AND UKMET
HAVE RESOLVED THEMSELVES AS THEY CAME NEARLY PERFECTLY ALIGNED
WITH THE GLOBAL CONSENSUS. THE ONLY OUTLIER AT THIS TIME IS THE
CMC WHICH REMAINS SE OF THE MEAN TRACK AND OUTSIDE THE CLUSTERING,
AGAIN LIKELY DUE TO A WEAKER AND LESS POLEWARD JET STREAK. FEEL
INCLUDING THE UKMET AND ECMWF AT FULL WEIGHT IS PREFERENTIAL NOW
IN THE BLEND, LEAVING OUT ONLY THE 12Z CMC.
PREVIUS DISCUSSION:
SURFACE LOW PRESSURE CONSOLIDATING NEAR NEW JERSEY WILL LIFT
NORTHEAST INTO THE GULF OF MAINE LATE TONIGHT AND THEN CONTINUE
NORTHEAST INTO THE CANADIAN MARITIMES LATE SATURDAY INTO SUNDAY.
THIS LOW WILL DEEPEN IN RESPONSE TO AN ANOMALOUSLY STRONG CLOSED
LOW OVER SE CANADA (-4 STANDARD DEVIATIONS FROM CLIMO) INTERACTING
WITH THE SHORTWAVE ENERGY DRIVING THE SURFACE LOW, AS WELL AS
INCREASING DIFFLUENCE OF AN ATYPICAL JET STREAK (+3 STANDARD
DEVIATIONS FROM CLIMO.) THE 00Z/CMC IS THE ONLY CLEAR OUTLIER WITH
THE TRACK OF THIS LOW, AS IT IS E/SE OF THE CONSENSUS, AND HAS
ENSEMBLE SPREAD EVEN FURTHER EAST OF ITS OPERATIONAL RUN. THIS IS
LIKELY DUE TO A MUCH WEAKER 250MB JET STREAK WITH LESS ROBUST
POLE-WARD EXTENT OF THE JET CORE ROTATING AROUND THE UPPER LOW,
ALLOWING THE SURFACE LOW TO DISPLACE TO THE EAST. THE 00Z/ECMWF
HAS AN 850MB LOW WHICH IS A LITTLE SLOW COMPARED TO CONSENSUS
DESPITE ITS SIMILAR PLACEMENT, AND SINCE THE TREND HAS BEEN FOR A
FASTER EJECTION OF THIS SYSTEM, THE SLOWER ECMWF SEEMS LESS
LIKELY, ESPECIALLY WITH THE ECENS SPEED MORE IN LINE WITH THE
REMAINING GUIDANCE.
THE GFS/NAM/GEFS/ECENS ARE VERY WELL CLUSTERED FOR D1 AND CREATE
THE PREFERRED BLEND FOR THIS SYSTEM, ALTHOUGH SOME WEIGHT OF THE
ECMWF AND UKMET WHICH ARE JUST A BIT SLOW OR A TAD SE CAN BE
INCLUDED, BUT WILL TEMPER THE OVERALL GREAT AGREEMENT OF THE
STRONGEST PREFERENCES TO ACCOUNT FOR MODEL SHIFTS THE PAST 24
HOURS.
...DUAL SHORTWAVES DROPPING THROUGH THE NORTHERN PLAINS AND RACING
EAST TO THE MID-ATLANTIC...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS/NON-NAM THROUGH D2
GENERAL BLEND D3
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE NON-NCEP SUITE HAS TRENDED SUBTLY DEEPER WITH ITS
LEAD SHORTWAVE ON D1 FROM ND INTO MN, BUT IS STILL WEAKER OVERALL
WITH AMPLITUDE THAN THE GFS/NAM, WITH A SURFACE LOW THAT IS
DISPLACED JUST A BIT TO THE WEST. ALTHOUGH OVERALL SPREAD IS
MINIMAL, THE DEFORMATION FORCED BAND OF PRECIPITATION IS LIKELY TO
BE NARROW SO SMALL SPREAD COULD LEAD TO SIGNIFICANT DIFFERENCES.
THE MASS FIELDS SUGGEST THE SLIGHTLY SW PREFERENCE REMAINS
PREFERRED, BUT WITH SOME LOCALLY HEAVIER PRECIP TOWARDS THE
NAMNEST POSSIBLE. BY D3 RE-AMPLIFICATION OF THE SHORTWAVE AND
SUBSEQUENT SURFACE LOW POTENTIAL IS WELL CLUSTERED.
PREVIOUS DISCUSSION:
TWO SHORTWAVES DROPPING QUICKLY INTO THE NORTHERN PLAINS WILL
EVENTUALLY COME TOGETHER D3 OVER THE MID-ATLANTIC. THE LEAD
SHORTWAVE IS MOST IMPORTANT AS IT DIGS THROUGH NORTH DAKOTA
SOUTHEAST TOWARDS SOUTHERN LAKE MICHIGAN SATURDAY INTO SUNDAY AS
THIS PRODUCES A WAVE OF LOW PRESSURE AND ASSOCIATED COLD FRONT
WITH PRECIPITATION ACROSS THE REGION. THE 12Z NCEP GUIDANCE (GFS
AND NAM) ARE BOTH STRONG WITH THE LEAD SHORTWAVE SHOWING SHARPER
TROUGHING INTO MINNESOTA. THIS DRIVES THE SURFACE LOW A BIT SE OF
CONSENSUS, BUT ALSO LEADS TO STRONGER MID-LEVEL
STRETCHING/DEFORMATION TO THE NW. THIS LEADS TO STRONGER FORCED
PRECIPITATION AND LIKELY A HEAVIER BAND OF SNOW WHERE THERMALS
SUPPORT FROZEN PRECIPITATION. THE 00Z/CMC BECOMES A BIT STRONGER
WITH ITS 500MB AMPLIFICATION INTO SUNDAY, BUT IS USABLE SATURDAY
/D1./ THE REMAINING GUIDANCE INCLUDING THE ECMWF/ECENS/UKMET AND
HIGH RES NAMNEST ALL ARE WELL CLUSTERED WITH THE SURFACE LOW, AND
THE GEFS IS ALSO WEST OF THE GFSOP, WELL IN LINE WITH THE
PREFERRED CONSENSUS. DESPITE SOMEWHAT WEAKER DEFORMATION THAN
SHOWN IN THE NAM/GFS, A STRIPE OF MODERATE SNOW IS LIKELY FROM ND
INTO MN.
THIS SHORTWAVE SHOULD WEAKEN ON D2 AS IT BECOMES SHEARED INTO THE
WESTERLIES AROUND THE BASE OF THE TROUGH IN THE EAST, BUT IS
LIKELY TO RE-INTENSIFY MONDAY AS THE SECOND SHORTWAVE BEGINS
INTERACTION WITH THE LEAD WHICH IS WEAKENING. SHARPENING OF THIS
MID-LEVEL WAVE TOWARDS THE EAST COAST MAY LEAD TO SECONDARY
SURFACE LOW DEVELOPMENT MONDAY SOUTH OF NEW ENGLAND. THE ECMWF BY
THIS TIME IS A CLEAR SLOW OUTLIER COMPARED TO THE CONSENSUS WHICH
IS OTHERWISE IN GOOD AGREEMENT. FOR THIS REASON THE ECMWF IS
REMOVED FROM THE BLEND FOR D3.
..SHORTWAVE ENERGY CROSSING SOUTHERN CA BY SUN MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
19Z UPDATE: INCLUSION OF THE ENTIRE 12Z NON-NCEP SUITE IS
ACCEPTABLE AS AMPLITUDE AND SPEED DIFFERENCES OF THE GUIDANCE
REMAINS MINIMAL.
PREVIOUS DISCUSSION:
A WEAK SHORTWAVE LIFTING ONSHORE SOUTHERN CA SATURDAY WILL WEAKEN
AS IT SHIFTS EASTWARD INTO THE DESERT SOUTHWEST ON SUNDAY.
ALTHOUGH THE 12Z/GFS IS A BIT AMPLIFIED COMPARED TO CONSENSUS, AND
THE 00Z/CMC IS SUBTLY FLAT, THE OVERALL SPREAD ENVELOPE IS
MINIMAL. A GENERAL MODEL BLEND REMAINS THE PREFERRED OPTION.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
ORRISON/WEISS
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