982
FXUS10 KWNH 240647
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 AM EDT FRI APR 24 2020
VALID APR 24/0000 UTC THRU APR 27/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z EVALUATION WITH FINAL MODEL PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
7Z UPDATE: THE NON-NCEP GUIDANCE GENERALLY TRENDED SLIGHTLY
CLOSER TO THE COAST FOR THE COASTAL LOW NEAR NEW ENGLAND FOR DAY
3, AND NOT QUITE AS AMPLIFIED WITH THE SECOND STORM SYSTEM TO
IMPACT THE PACIFIC NORTHWEST EARLY IN THE WEEK. THE UKMET TRENDED
CLOSER TO THE CONSENSUS WITH THE SURFACE LOW ACROSS THE MID-SOUTH
THROUGH SATURDAY, AND STRONGER THAN ITS 12Z RUN ACROSS THE OHIO
VALLEY, SO A GENERAL MODEL BLEND WORKS WELL THROUGH 12Z SUNDAY FOR
THIS STORM SYSTEM, AND A UKMET/ECMWF/12Z EC MEAN BLEND BEYOND
THAT. FOR THE PACIFIC NORTHWEST, THE UKMET IS STILL SLIGHTLY MORE
AMPLIFIED WITH THE UPPER LEVEL TROUGH AXIS, WITH THE ORIGINAL
PREFERENCE REMAINING VALID.
LOW PRESSURE CROSSING MID-ATLANTIC ON FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/00Z NAM/00Z GFS
CONFIDENCE: MODERATE-HIGH
THE SOUTHERN STREAM STORM SYSTEM WITH SURFACE LOW INITIALLY OVER
THE CENTRAL APPALACHIANS WILL CONTINUE TRACKING EAST ACROSS THE
MID-ATLANTIC ON FRIDAY, WITH A SECONDARY LOW LIKELY DEVELOPING
SOUTHEAST OF NEW ENGLAND BY FRIDAY EVENING THAT BECOMES THE MAIN
LOW PASSING SOUTH OF NOVA SCOTIA. THE 12Z CMC IS A LITTLE BIT
WEAKER WITH THE ACCOMPANYING 500MB SHORTWAVE, AND ONCE THE SYSTEM
EMERGES OFFSHORE, THE UKMET BECOMES SLIGHTLY SLOWER WITH THE
CONSOLIDATED SURFACE LOW.
LOW PRESSURE TRACKING FROM TEXAS TO THE OHIO VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/00Z UKMET/12Z EC MEAN/00Z GFS
CONFIDENCE: MODERATE
A SOMEWHAT COMPLICATED UPPER LEVEL PATTERN EVOLUTION ACROSS THE
NORTH-CENTRAL U.S. WITH BROAD NORTHWEST FLOW WILL BE IN PLACE TO
END THE WEEK. A STRONGER LEAD TROUGH WILL BE FOLLOWED BY A MORE
SUBTLE SECONDARY TROUGH, TRACKING FROM THE NORTHERN ROCKIES TO THE
MIDWEST STATES, AND EVENTUALLY CONSOLIDATE INTO ONE MAIN UPPER
LEVEL TROUGH AND THEN CLOSED LOW OVER THE NORTHEAST U.S. BY THE
END OF THE FORECAST PERIOD MONDAY MORNING. A SURFACE LOW WILL
BECOME BETTER ORGANIZED ACROSS THE SOUTHERN PLAINS AND THEN CROSS
THE MID-SOUTH AND OHIO VALLEY BY SATURDAY NIGHT, FOLLOWED BY
LIKELY SECONDARY CYCLOGENESIS NEAR NEW ENGLAND AS A POTENTIAL
NOR'EASTER FOR EARLY NEXT WEEK.
IN TERMS OF THE MODELS, THE 00Z NAM APPEARS SLIGHTLY SLOWER WITH
THE TRACK OF THE LOW, THE 12Z UKMET A LITTLE WEAKER AND SOUTH OF
THE MODEL CONSENSUS, AND THE CMC A BIT MORE AMPLIFIED WITH THE
UPPER TROUGH CROSSING THE MID-SOUTH ON SATURDAY. MUCH OF THIS
WILL DEPEND ON THE SHORTWAVE ENERGY ROUNDING THE APPARENT TROUGH
AXIS AND THEREFORE INFLUENCE THE TIMING OF PRECIPITATION AS
WELL. THE ENERGY DIVING SOUTH FROM CANADA INTO PORTIONS OF NORTH
DAKOTA AND INTO MINNESOTA SEEM TO BE WEAKER AND SLOWER WITH THE
ECMWF. FOR DAY 3, THE NAM SEEMS SLIGHTLY SLOWER WITH THE UPPER
LEVEL LOW, AND THE UKMET A BIT MORE SUPPRESSED WITH THE SURFACE
LOW. THE 00Z GFS IS REASONABLY WELL CLUSTERED WITH THE LOW NEAR
THE NORTHEAST COAST ALBEIT A LITTLE FASTER, ALTHOUGH THE 18Z GEFS
MEAN IS DISPLACED SOME TO THE NORTH.
PAIR OF TROUGHS AFFECTING THE NORTHWESTERN U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL BLEND FOR FIRST TROUGH, AND 00Z GFS/00Z
NAM/12Z EC MEAN FOR SECOND TROUGH
CONFIDENCE: MODERATE
THE UPPER LEVEL RIDGE THAT IS CURRENTLY IN PLACE ACROSS THE WEST
COAST REGION WILL BEGIN TO BE ERODED BY A MODERATELY STRONG STORM
SYSTEM APPROACHING BRITISH COLUMBIA ON SATURDAY WITH A COLD FRONT
REACHING THE PACIFIC NORTHWEST COAST. THERE WILL BE A BRIEF BREAK
BEFORE A SECOND AND POTENTIALLY STRONGER SYSTEM APPROACHES FROM
THE NORTHEAST PACIFIC SUNDAY NIGHT INTO MONDAY MORNING WITH
ANOTHER FRONTAL PASSAGE. FOR THE FIRST SYSTEM, THERE IS ENOUGH
DETERMINISTIC MODEL AGREEMENT TO MERIT THE USE OF A GENERAL BLEND.
FOR THE SECOND SYSTEM, THE 12Z UKMET IS A BIT FASTER WITH THE
SURFACE LOW AND FRONT, AND THE ECMWF BECOMES SLIGHTLY STRONGER
WITH THE SHORTWAVE BY MONDAY MORNING.
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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