511
FXUS10 KWNH 191856
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EDT SUN APR 19 2020
VALID APR 19/1200 UTC THRU APR 23/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
19Z UPDATE: THE MAIN TREND NOTED IN THE ARRIVAL OF THE 12Z
NON-NCEP GUIDANCE IS A FASTER PROGRESSION OF THE SOUTHERN STREAM
TROUGH REACHING THE SOUTHERN PLAINS BY DAY 3, AND REPRESENTS A
RATHER NOTEWORTHY CHANGE WITH RESPECT TO TIMING. THIS NOW LEAVES
THE 12Z NAM AS THE SLOWEST SOLUTION, AND THE GFS REMAINS A LITTLE
FASTER THAN THE OTHER GUIDANCE, ALBEIT NOT TO THE SAME DEGREE
EARLIER TODAY. GIVEN THE RUN-TO-RUN MODEL VARIABILITY, THE 00Z EC
MEAN WILL BE SUBSTITUTED FOR THE 12Z NAM AS PART OF THE MODEL
PREFERENCE FOR THIS STORM SYSTEM. THE 12Z UKMET REMAINS THE MOST
AMPLIFIED WITH THE TROUGH EXITING THE EAST COAST ON MONDAY.
STORM TRACKING ACROSS THE GULF COAST REGION
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/12Z ECMWF BLEND
CONFIDENCE: MODERATE
THE SOUTHERN STREAM SHORTWAVE CURRENTLY OVER THE SOUTHERN PLAINS
WILL CONTINUE TRACKING EASTWARD ACROSS THE DEEP SOUTH THROUGH
TONIGHT AND THEN EXIT THE EAST COAST BY MONDAY AFTERNOON,
SUSTAINING A WELL DEVELOPED SURFACE LOW THAT WILL RESULT IN
WIDESPREAD HEAVY RAIN AND SEVERE WEATHER. A DUAL-LOW SURFACE LOW
STRUCTURE IS APPEARING LIKELY BY MONDAY MORNING AS A SECOND LOW
DEVELOPS OFF THE MID-ATLANTIC COAST, AND PASSES WELL SOUTH OF NEW
ENGLAND BASED ON CURRENT GUIDANCE.
THE 12Z GFS BECOMES FASTER AS EARLY AS MONDAY MORNING, AND THIS
TREND CONTINUES AS THE LOW EXITS THE COAST. THIS IS SIMILAR TO
WHAT THE 6Z GFS WAS PORTRAYING. THE SURFACE LOW TRACKS ARE
SIMILAR IN POSITION AMONG THE NON-GFS GUIDANCE THROUGH MONDAY
AFTERNOON, SO THE MAIN DIFFERENCES BETWEEN THE MODELS REMAINS THE
PLACEMENT OF THE AXIS OF HIGHEST RAINFALL, WHICH HAS MORE TO DO
WITH MESOSCALE INTERACTIONS AND THE OVERLAY OF THE INSTABILITY AND
MID LEVEL LIFT. THE 00Z UKMET REMAINS SLOWER AND LEFT OF THE
CONSENSUS WITH THE SHORTWAVE AND THE SURFACE LOW ONCE IT EXITS THE
COAST, LIKELY DUE TO THE SLOWER SHORT WAVE ENERGY IN THE
DEVELOPING TROUGH. BECAUSE OF THIS, THIS MODEL WAS ALSO EXCLUDED
FROM THE PREFERRED BLEND. BECAUSE OF THE DIFFERENCES WITH THE QPF
PLACEMENT AND THE TRACK OF THE SURFACE LOW OFF THE COAST, FORECAST
CONFIDENCE REMAINS AVERAGE.
BUILDING TROUGH OVER THE GREAT LAKES AND THE NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/12Z ECMWF BLEND
CONFIDENCE: MODERATE
THE LARGE SYNOPTIC SCALE TROUGH OVER CENTRAL/EASTERN CANADA AND
THE NORTHERN TIER OF THE U.S. GETS REINFORCED WITH A STRONG
SHORTWAVE TRACKING SOUTHWARD ACROSS MANITOBA, AND THEN EVOLVING
INTO A COLD UPPER LOW OVER SOUTHERN ONTARIO AND QUEBEC. THIS WILL
SUSTAIN A COLD FRONT CROSSING THE GREAT LAKES AND OHIO VALLEY, AND
THEN REACHING THE EAST COAST BY TUESDAY EVENING.
THE 12Z GFS/NAM ARE CLOSE TO THE CONSENSUS TRACKING SHORT WAVE
ENERGY IN THE PROGRESSIVE MID LEVEL FLOW FROM MANITOBA ACROSS THE
UPPER GREAT LAKES THROUGH TUESDAY AFTERNOON. BEYOND THAT TIME,
THE 12Z NAM IS SLIGHTLY SLOWER AND A LITTLE MORE AMPLIFIED WITH
THE DEVELOPING LONG WAVE TROUGH APPROACHING NORTHERN NEW ENGLAND.
THE 00Z CMC BECOMES EVEN MORE AMPLIFIED ACROSS NEW ENGLAND BY
WEDNESDAY MORNING AS THE TROUGH ACQUIRES NEGATIVE TILT. SINCE THE
GFS/ECMWF HAVE THE SUPPORT OF THEIR ENSEMBLE MEANS, THESE
SOLUTIONS COMPRISE THE PREFERRED BLEND.
TROUGH ACROSS THE SOUTHWEST AND THEN THE SOUTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z EC MEAN/12Z UKMET/12Z ECMWF BLEND
CONFIDENCE: LIMITED-MODERATE
THE NEXT SHORT WAVE IN THE FLOW TRACKS TOWARD THE CENTRAL
CALIFORNIA COAST AFTER MONDAY MORNING. THERE IS STILL SOME MODEL
SPREAD CONCERNING THE TIMING OF THIS SHORT WAVE, AS IT UNDERCUTS
MID LEVEL RIDGING ACROSS THE PACIFIC NORTHWEST. THOUGH THERE IS A
LOOSE CONSENSUS TAKING THE MID LEVEL SYSTEM OVER NEVADA AND
ARIZONA ON TUESDAY, MORE NOTEWORTHY DIFFERENCES BECOME APPARENT BY
TUESDAY NIGHT AND INTO WEDNESDAY AS THE SYSTEM CROSSES THE
SOUTHERN ROCKIES AND EVENTUALLY THE SOUTHERN PLAINS. SIMILAR TO
YESTERDAY, THE GFS REMAINS MORE PROGRESSIVE AND ALSO AHEAD OF ITS
ENSEMBLE MEAN, AND THE 00Z CMC IS ON THE OTHER END OF THE SPECTRUM
WITH A SLOWER SOLUTION AND WEAKER WITH THE SURFACE LOW THAT
EMERGES OVER THE PLAINS. THE ECMWF IS SLIGHTLY WEAKER WITH THE
TROUGH BUT IS CLOSE TO THE CONSENSUS REGARDING TIMING, WHILST THE
UKMET IS SLIGHTLY STRONGER. THE 12Z NAM IS ALSO CLOSE TO TO
ECMWF/UKMET REGARDING TIMING, SO A BLEND OF THOSE THREE SOLUTIONS
SHOULD SERVE WELL AS A STARTING POINT IN THE FORECAST.
CLIPPER SYSTEM REACHING NORTHERN PLAINS BY WEDNESDAY MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/12Z UKMET/12Z ECMWF BLEND
CONFIDENCE: MODERATE
A SUBTLE MID-LEVEL SHORTWAVE TRACKING AROUND THE UPPER RIDGE
ACROSS SOUTHWESTERN CANADA WILL PROGRESS QUICKLY TOWARDS THE
NORTHERN PLAINS IN STRONG NORTHWEST FLOW, ALONG WITH A
CLIPPER-TYPE SURFACE LOW REACHING NORTH DAKOTA AND THEN MINNESOTA
BY EARLY WEDNESDAY ALONG AN EXISTING QUASI-STATIONARY FRONT. THE
12Z NAM IS DISPLACED TO THE NORTHEAST WITH THE TRACK OF THIS LOW
AND THE 00Z CMC HAS A SLIGHTLY WEAKER LOW.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
HAMRICK
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