568
FXUS10 KWNH 181843
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
242 PM EDT SAT APR 18 2020
VALID APR 18/1200 UTC THRU APR 22/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
19Z UPDATE: THE NON-NCEP GUIDANCE HAS TRENDED A LITTLE STRONGER
WITH THE SHORTWAVE CROSSING THE DEEP SOUTH AND THIS CONTINUES WHEN
THE SYSTEM EXITS THE EAST COAST, WITH THE 12Z NAM REMAINING ON THE
MORE PROGRESSIVE SIDE OF THE 12Z MODEL SUITE. THERE WAS ALSO A
SLIGHTLY STRONGER TREND WITH THE GREAT LAKES TROUGH BY DAY 3, WITH
THE 12Z UKMET INDICATING THE MOST AMPLIFIED SCENARIO, SO THE CMC
REPLACES THE UKMET AS PART OF THE MODEL PREFERENCE. OUT WEST, THE
12Z CMC, AND TO A LESSER EXTENT THE 12Z ECMWF, TRENDED FASTER WITH
THE UPPER LEVEL LOW OVER THE DESERT SOUTHWEST BY THE END OF THE
FORECAST PERIOD. HOWEVER, THE CMC STILL TRAILS THE MAJORITY OF
THE GUIDANCE WITH THIS FEATURE.
STORM INTENSIFYING OFF THE NORTHEAST COAST THIS WEEKEND
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: HIGH
A POTENT SHORTWAVE TRACKING ACROSS THE MID-ATLANTIC REGION TODAY
WILL SUPPORT AN INTENSIFYING SURFACE LOW EAST OF NEW ENGLAND AND
SOUTH OF NOVA SCOTIA THROUGH SUNDAY. THERE IS NOW ENOUGH MODEL
AGREEMENT TO SUPPORT A MULTI-MODEL DETERMINISTIC BLEND.
SOUTHERN STREAM SHORTWAVE WITH SURFACE LOW TRACKING ACROSS GULF
COAST STATES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/12Z UKMET/12Z GFS
CONFIDENCE: AVERAGE
THE SOUTHERN STREAM SHORTWAVE EXITING THE SOUTHERN ROCKIES WILL
GIVE WAY TO LEE CYCLOGENESIS ACROSS THE WESTERN HIGH PLAINS THIS
EVENING, AND A WELL DEVELOPED SURFACE LOW IS PROGGED TO TRACK
EASTWARD ACROSS THE SOUTHERN PLAINS AND DEEP SOUTH THROUGH MONDAY
MORNING, AND THEN EXITING THE SOUTHEAST COAST. THE 12Z NAM IS A
BIT FASTER AND A LITTLE FARTHER NORTH COMPARED TO THE MODEL
CONSENSUS BY SUNDAY NIGHT, AND THE 00Z CMC IS A LITTLE SLOWER WHEN
THE SYSTEM EXITS THE EAST COAST. OTHER THAN SOME SMALL MESOSCALE
DIFFERENCES AMONG THE UKMET, ECMWF, AND 12Z GFS, AN INITIAL BLEND
OF THESE MODELS WOULD SUFFICE AS A GOOD STARTING POINT IN THE
FORECAST PROCESS.
AMPLIFYING VORTEX OVER SOUTHERN CANADA WITH COLD FRONT ACROSS
GREAT LAKES REGION
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/12Z CMC/12Z GFS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
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. WHILE THERE IS
GENERALLY GOOD MODEL AGREEMENT IN THE EVOLUTION OF THIS DEEP UPPER
LEVEL TROUGH AND RESULTING SURFACE LOW, THE 12Z NAM BECOMES MORE
PROGRESSIVE WITH THE COLD FRONT ACROSS THE OHIO VALLEY REGION AND
QUICKER WITH THE ARRIVAL OF HEIGHT FALLS ACROSS SOUTHERN CANADA.
ALTHOUGH THE UKMET IS A LITTLE STRONGER WITH THE SURFACE LOW AND
FRONT, IT SHOULD STILL WORK AS A PART OF THE MODEL BLEND.
UPPER LOW AND TROUGH REACHING THE DESERT SOUTHWEST BY TUESDAY
MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/12Z ECMWF/12Z UKMET BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
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 BY THE END OF THE FORECAST PERIOD, EACH SOLUTION TAKES A
SLIGHTLY DIFFERENT ROUTE GETTING THERE. IN TERMS OF THE MODELS,
THE 12Z GFS APPEARS MORE PROGRESSIVE WITH THE MID LEVEL SYSTEM,
AND THE 00Z CMC IS MUCH SLOWER. WITH THE UKMET, ECMWF, AND NAM
BEING RELATIVELY WELL CLUSTERED THROUGH DAY 3, A BLEND OF THOSE
MODELS SHOULD WORK WELL.
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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