432
FXUS10 KWNH 201846
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 PM EDT MON APR 20 2020
VALID APR 20/1200 UTC THRU APR 24/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH INITIAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SURFACE LOW TRACKING OFF THE MID ATLANTIC COAST TODAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: HIGH
SHORTWAVE TROUGH NOW EXITING THE COAST WITH A DUAL-LOW SURFACE
STRUCTURE WILL CONTINUE TO INTENSIFY OFFSHORE AS IT CONSOLIDATES
INTO ONE MAIN SURFACE LOW WELL TO THE SOUTHEAST OF NEW ENGLAND.
THE 00Z CMC RUN WAS A LITTLE SLOWER ONCE THE SYSTEM EXITED THE
COAST, BUT THE 12Z RUN IS NOW COMPARABLE WITH THE TIMING AND NOW A
GENERAL MODEL BLEND CAN BE INCORPORATED FOR THIS EVENT.
DEVELOPING LONG WAVE TROUGH OVER NEW ENGLAND WITH SURFACE LOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/12Z ECMWF/12Z UKMET BLEND
CONFIDENCE: MODERATE-HIGH
SHORT WAVE ENERGY DIVING OUT OF CENTRAL CANADA IN THE FAST MID
LEVEL FLOW DROPS TO THE BASE OF A DEVELOPING LONG WAVE TROUGH OVER
THE UPPER GREAT LAKES BY TUESDAY MORNING, AND THEN THE LONG WAVE
TROUGH TAKES ON A NEGATIVE TILT. THIS WILL SUPPORT A PRIMARY
SURFACE LOW OVER QUEBEC AND A TRIPLE POINT SURFACE LOW FORMING
NEAR THE COAST OF MAINE BY TUESDAY NIGHT. MOST OF THE GUIDANCE IS
CLOSE WITH THE EVOLUTION OF THE LONG WAVE TROUGH, AND THE 12Z CMC
IS A LITTLE CLOSER TO THE CONSENSUS REGARDING THE SURFACE LOWS
COMPARED TO ITS 00Z RUN, BUT STILL ON THE SOUTHERN SIDE OF THE
GUIDANCE. OTHERWISE, THE MODEL DIFFERENCES WITH THE SURFACE LOWS
HAS IMPROVED COMPARED TO EARLIER MODEL RUNS.
MID LEVEL TROUGH TRACKING FROM DESERT SOUTHWEST TO THE DEEP SOUTH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL BLEND THROUGH 00Z WEDNESDAY, THEN 12Z
ECMWF/00Z EC MEAN
CONFIDENCE: LIMITED-MODERATE
A SOUTHERN STREAM SHORTWAVE INITIALLY NEAR CALIFORNIA WILL TRACK
ACROSS THE DESERT SOUTHWEST THROUGH TUESDAY AND THEN EMERGE OVER
THE CENTRAL/SOUTHERN PLAINS ON WEDNESDAY. THIS WILL SPUR SURFACE
CYCLOGENESIS OVER THE WESTERN HIGH PLAINS TUESDAY NIGHT AND LEAD
TO THE NEXT ROUND OF HEAVY RAIN AND STRONG/SEVERE STORMS ACROSS
THE SOUTHERN TIER STATES FOR LATER IN THE WEEK. THE MODELS ARE IN
GENERALLY GOOD AGREEMENT WITH THIS SYSTEM THROUGH TUESDAY EVENING,
AND THEN THE 12Z UKMET BECOMES SLOWER AND ALSO STRONGER THAN THE
OTHER GUIDANCE AND LOSES ENSEMBLE SUPPORT. THE 12Z GFS BECOMES
MORE PROGRESSIVE AFTER 12Z COMPARED TO THE OTHER MODELS AS IT
CROSSES THE SOUTHEASTERN STATES, AND THE NAM SLIGHTLY FARTHER
NORTH WITH THE SURFACE LOW. GIVEN THE VERY CLOSE AGREEMENT
BETWEEN THE 12Z ECMWF AND THE 00Z EC MEAN, A BLEND OF THESE WOULD
BE GOOD AS A STARTING POINT AFTER 00Z WEDNESDAY.
SURFACE LOW TRACKING FROM WESTERN CANADA TO THE NORTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/12Z ECMWF/12Z UKMET
CONFIDENCE: MODERATE
A CLIPPER TYPE SURFACE LOW TRACKS SOUTHEASTWARD OUT OF ALBERTA AND
REACHES THE NORTHERN PLAINS BY WEDNESDAY MORNING IN PROGRESSIVE
NORTHWEST FLOW ALOFT. THE 12Z UKMET CLOSER WITH THE OTHER MODELS
WITH THE ARRIVAL OF THIS LOW, AND THE 12Z NAM IS A LITTLE STRONGER
WITH THE UPPER LEVEL TROUGH THAT ACCOMPANIES IT. A BLEND OF THE
WELL CLUSTERED GFS/ECMWF/UKMET SHOULD WORK AS AN INITIAL BLEND FOR
THIS REGION.
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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