092
FXUS10 KWNH 011901
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT WED APR 01 2020
VALID APR 01/1200 UTC THRU APR 05/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...WESTERN ATLANTIC CLOSED LOW AND OFFSHORE SURFACE LOW THROUGH
FRIDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: ANY OF THE OPERATIONAL MODELS
CONFIDENCE: ABOVE AVERAGE
A MATURING LARGE SCALE CLOSED TROUGH, WITH INTENSE SURFACE LOW
PRESSURE DIPPING DOWN TO NEAR OR BELOW 980 MB, WILL AFFECT THE
EAST COAST AND WESTERN ATLANTIC WITH STRONG WINDS. THE GENERAL
CIRCULATION PATTERN NOW FEATURES THIS AND ANOTHER DEVELOPING HIGH
AMPLITUDE, CLOSED TROUGH OVER THE INTERMOUNTAIN WEST / NORTHERN
PLAINS. SO THE PATTERN IS SLOWING DOWN, AND THE INTENSE CYCLONE
OFF THE COAST WILL BE SLOW TO EXIT. THE GLOBAL MODELS ARE IN
STRONG AGREEMENT IN THEIR HANDLING OF THIS SYSTEM. IF ANY
DIFFERENCE COULD BE NOTED, THE GFS SHOWS ITS TYPICAL BIAS BY DAY 3
WITH THE TROUGH SWINGING FARTHER FORWARD AND OUT TO SEA.
..INTERMOUNTAIN WEST / GREAT PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/ECMWF/UKMET/CANADIAN... LESS
WEIGHT ON GFS AFTER 04/00Z
CONFIDENCE: AVERAGE
AS A LARGE SCALE CLOSED TROUGH DEVELOPS OVER THE MOUNTAINS AND
PARTS OF THE PLAINS, ELONGATED LOW PRESSURE WILL SLIP OUT THROUGH
THE PLAINS AND UPPER MIDWEST ALONG A COLD FRONT, WITH WINTRY
WEATHER IMPACTS FELT ACROSS THE NORTHERN ROCKIES TO THE UPPER
MIDWEST. IN THE 12Z CYCLE THE GLOBAL MODELS TRENDED TOWARD BETTER
AGREEMENT AS TO MOST OF THE DETAILS HERE. THE ECMWF/UKMET/CANADIAN
ARE BEST SYNCED IN TERMS OF THE TIMING AND LOCATION OF INDIVIDUAL
SHORTWAVES, AND BLENDING THEM WILL HELP FORM A CONSENSUS AROUND
THE AMPLITUDE DIFFERENCES. THE NAM IS THE FIRST TO DROP OUT OF THE
LARGER SCALE CONSENSUS. ITS FORECAST IS LARGELY IN STEP WITH THE
OTHER MODELS THROUGH 03/12Z, SO ONLY 48 HOURS INTO THE FORECAST.
BUT EVEN THEN THE SOLUTION IS SLIGHTLY FAST AND DEPICTS A WEAKER
PRESSURE GRADIENT ALONG THE FRONT. IT THEN BECOMES MORE
UNREALISTIC AS IT SIGNIFICANTLY ERODES THE SOUTHERN FLANK OF THE
RIDGE IN CANADA, WHEREAS TYPICALLY A LOW WOULD BECOME TRAPPED
BENEATH THE RIDGE AS DEPICTED IN THE OTHER MODELS.
THE GFS IS NOT FAR OFF FROM MODEL CONSENSUS FOR THE NORTHERN U.S.
WEATHER SYSTEM THROUGHOUT ITS LIFE CYCLE. THE ONLY REASON WE
SUGGEST REDUCING WEIGHT GIVEN TO THE GFS OVER TIME IS THAT IN
BROADER TERMS THE GFS UPPER AIR PATTERN TURNS A LITTLE OUT OF
PHASE GIVEN SOME UPSTREAM PROBLEMS OVER THE EASTERN PACIFIC.
ANOTHER ASPECT OF THIS BROAD SCALE TROUGH IS THE INCREASING
LIKELIHOOD OF GULF RETURN MOISTURE INTERACTING WITH A FRONT AND
SEASONABLY STRONG WESTERLY FLOW TO YIELD THUNDERSTORMS IN THE
SOUTHERN PLAINS. WE NOTE THAT THE NAM QPF INTENSITY DROPS OFF WITH
SOUTHWARD EXTENT. THE OTHER MODELS DO DISPLAY SOME SPATIAL SPREAD,
BUT ALL ARE MORE INDICATIVE OF ROBUST PRECIPITATION, SO THE NAM
APPEARS TO BE A DRY OUTLIER, ESPECIALLY ACROSS SOUTH TEXAS.
..WEST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z ECMWF/UKMET/CANADIAN
CONFIDENCE: SLIGHTLY BELOW AVERAGE
CHALLENGING PATTERN ON THE BACK SIDE OF THE DEVELOPING LARGER
SCALE TROUGH OVER THE INTERMOUNTAIN WEST. TWO NOTEWORTHY SHORTWAVE
TROUGHS COME INTO PLAY ALONG THE WEST COAST. THE FIRST INTO
CALIFORNIA SHOWS THE TELLTALE SIGNS OF A REMARKABLY FAST GFS
SOLUTION THAT STANDS OUT AS AN OUTLIER. ON THE OTHER HAND, THE
ECMWF SUDDENLY WENT FLAT WITH THIS WAVE, DAMPENING IT ON DAY 3...
BUT IT STILL DOES NOT CATCH UP TO THE VERY FAST GFS. THE SECOND,
LARGER WAVE SHOWS A TENDENCY TO FORM A CLOSED CIRCULATION AND
EXPAND ITS INFLUENCE AS IT APPROACHES WASHINGTON/OREGON ON DAY 3.
THE NCEP GUIDANCE WAS FIRST TO BECOME MORE BULLISH IN
STRENGTHENING THIS FEATURE AND DRIVING IT FARTHER SOUTH AND WEST
OFFSHORE. THIS IS ESPECIALLY TRUE OF THE NAM. SPAGHETTI PLOT SHOW
THAT THIS FARTHER SOUTH AND WEST POSITION HAS LOST FAVOR IN THE
ENSEMBLES OVER TIME, BUT NOT ENTIRELY. CONSENSUS DEFINITELY POINTS
TOWARD THE 12Z UKMET/CANADIAN SOLUTIONS (AND 00Z ECMWF/UKMET), BUT
PERHAPS WITH SOME LEGITIMATE TRENDING TOWARD A DEEPER SOLUTION
FARTHER SOUTH AND WEST...PER THE 12Z ECMWF AND GFS. OVERALL, THE
GFS PROBLEMS WITH THE LEAD WAVE INTO CALIFORNIA MAKE IT LESS
DESIRABLE ALONG THE WEST COAST, AND THE NAM IS SO MUCH DEEPER WITH
THE UPSTREAM WAVE OFF WA/OR. SO OUR PREFERENCE REMAINS WITH THE
EC/UK, NOW JOINED BY THE 12Z CANADIAN. BUT IF ONE WANTED TO
INCLUDE THE NAM FOR THE CALIFORNIA WAVE AND GFS FOR THE WA/OR
WAVE, THEY MAY HAVE SOME UTILITY.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
BURKE
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page