411
FXUS10 KWNH 150411
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1211 AM EDT MON JUN 15 2020
VALID JUN 15/0000 UTC THRU JUN 18/1200 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..CLOSED LOW DEVELOPING IN SOUTHERN APPALACHIANS MON/TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH TUESDAY NIGHT
NON-NAM WEDNESDAY
CONFIDENCE: ABOVE AVERAGE
THE FORECAST, PROLONGED, STATIONARY CLOSED LOW IS STARTING TO TAKE
UP GENERAL RESIDENCY ACROSS THE CENTRAL TO SOUTHERN APPALACHIANS
WITH THE INNER CORE VORTICITY CENTER CONTINUING TO SC BY 48HRS.
THERE IS VERY STRONG AGREEMENT WITH THIS EVOLUTION AND PLACEMENT.
ITS INFLUENCE ALONG WITH EASTERLY LOW LEVEL FLOW OFF THE UNSTABLE
GULF STREAM WILL SUPPORT A LOW LEVEL WAVE TO RETROGRADE ACROSS THE
COASTAL PLAIN OVER TUES/WED. THE 00Z NAM CONTINUES TO SHOW A VERY
STRONG CONVECTIVE RESPONSE AND BUILDS THE MCV/DEEPER SHORTWAVE
ALLOWING A MATURE CYCLONE TO RETROGRADE FURTHER AWAY FROM THE
PERSISTENT INSTABILITY SOURCE. GIVEN THE INFLOW WILL LIKELY
SUPPORT BACK-BUILDING TO THE WELL OF GULF STREAM WARM WATERS; THE
NAM EVOLUTION LOOKS A BIT OVER-PLAYED AS IT MOVES AWAY FROM
OTHERWISE SOLID CONSENSUS BY WED. AS SUCH A NON-NAM BLEND IS
SUPPORTED AFTER 48HRS 17.00Z AT ABOVE AVERAGE CONFIDENCE. THE
POTENTIAL FOR STATIONARY CONVECTIVE BANDS AND HIGH RAINFALL
RATES/TOTALS NEEDS TO MONITORED CLOSELY (PLEASE SEE EXCESSIVE
RAINFALL DISCUSSIONS FOR FURTHER DETAILS), AS THE UKMET/ECMWF/GFS
SUGGEST SIMILAR BANDS JUST NOT TO THE MAGNITUDE AND UPSCALE
INFLUENCE AS THE NAM.
...INTERACTION OF SHORTWAVE LIFTING THROUGH SW CANADA WITH A
CLOSED LOW ADVECTING ONSHORE WASHINGTON SUNDAY...
..SECONDARY CLOSED LOW MOVING INTO THE NORTHWEST TUESDAY
..NORTHERN PLAINS SURFACE LOWS/N-S FRONTAL ZONE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS BLEND UNTIL 17.18Z THEN
NON-GFS/NAM BLEND THEREAFTER
CONFIDENCE: ABOVE AVERAGE THROUGH 17.00Z, AVERAGE THEREAFTER
INTERACTION OF A SHORTWAVE LIFTING INTO SASKATCHEWAN AND A CLOSED
LOW MOVING ONSHORE WASHINGTON STATE DRIVES THE BLEND THROUGH
17/00Z. GIVEN THE UNCERTAINTY OF THE LEADING SHORTWAVE HAS COME
TO REALITY, THE INTERACTION BETWEEN THE TWO IN THE LARGER GLOBAL
SCALE CLOSED LOW/GYRE ACROSS THE WEST IS BECOMING MUCH BETTER
ALIGNED, ESPECIALLY THROUGH 48HRS. AFTERWARDS, AS THE NOSE/EXIT
OF THE JET CROSSES THE NORTHERN ROCKIES, THE RESULTANT SURFACE LOW
ACROSS MT INTO THE DAKOTAS WILL HAVE SOME SPREAD. THE 00Z GFS IS
ONCE AGAIN FASTER WITH THIS WAVE AND EVEN OUTPACES THE
BULK/MAJORITY OF THE GEFS MEMBERS TO BE AN OUTLIER. THE GEFS MEAN
IS MORE INLINE WITH THE ECENS MEAN AND OTHER GLOBAL GUIDANCE,
PROVIDING GREATER CONFIDENCE IN THIS SLOWER EVOLUTION. THE 00Z
NAM IS MORE ALIGNED SYNOPTICALLY, BUT THE CONVECTIVE ELEMENTS ONCE
AGAIN ALLOW FOR GREATER AMPLIFICATION/DEEPENING THAT IS SUCH A
NEGATIVE BIAS OF THE LATER HOURS OF THE NAM RUNS TO START MOVING
IT OUT OF THE PREFERENCE AS WELL AT 72HRS. SO A 18Z GEFS AND 12Z
ECMWF/ECENS/CMC/UKMET BLEND IS PREFERRED BY THE END OF THE
FORECAST PERIOD, BUT THE 00Z NAM COULD BE ADDED AT LOWER WEIGHT
FROM 17.00Z TO 18.00Z IF FINER RESOLUTION/DETAILS ARE DESIRED IN
THE BLEND.
GALLINA
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