786
FXUS02 KWBC 160656
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 AM EDT TUE MAY 16 2023
VALID 12Z FRI MAY 19 2023 - 12Z TUE MAY 23 2023
...WARMER THAN AVERAGE TEMPERATURES WILL PERSIST ACROSS THE
NORTHWEST...
..OVERVIEW
THE OVERALL WEATHER PATTERN THIS WEEK SHOULD REMAIN FAIRLY
STAGNANT INTO THE MEDIUM RANGE, AS AN ANOMALOUSLY STRONG UPPER
RIDGE OVER THE WEST CAUSES WARM TO HOT TEMPERATURES THERE, WHILE
MEAN TROUGHING IS LIKELY DOWNSTREAM ACROSS EASTERN NORTH AMERICA
AS MULTIPLE SHORTWAVES AND COLD FRONTS MOVE THROUGH. THESE SHOULD
PUSH SOUTHEASTWARD EAST OF THE ROCKIES AND PRODUCE AREAS OF
SHOWERS AND THUNDERSTORMS, INCLUDING THE POSSIBILITY FOR SOME
ENHANCED RAINFALL AMOUNTS POTENTIALLY CAUSING FLASH FLOODING IN
THE SOUTH-CENTRAL ROCKIES AND PLAINS THROUGH FRIDAY. EVENTUALLY
EARLY NEXT WEEK SOME UPPER TROUGHING MAY COME INTO THE WEST,
WEAKENING THE RIDGE SOMEWHAT WHILE PUSHING IT EASTWARD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE MODEL GUIDANCE CONTINUES TO BE AGREEABLE WITH THE WESTERN
U.S. TROUGHING LATE WEEK, DOWNSTREAM THERE ARE STILL NOTABLE
DIFFERENCES WITH THE TIMING OF A POTENT SHORTWAVE OR COMPACT UPPER
LOW TRACKING NEAR THE GREAT LAKES WITH A SURFACE LOW REFLECTION
AND THE ASSOCIATED FRONTAL TIMING EVEN BY DAY 3/FRIDAY. FOR THE
12/18Z MODEL CYCLE, THE VARIOUS MODEL SUITES' ENSEMBLE MEMBERS
CLUSTER WITH THEIR DETERMINISTIC RUNS WITHOUT MUCH OVERLAP IN THE
ENSEMBLE SPREAD (THEY ARE UNDERDISPERSED). THE CMC WAS ON THE
SLOWER SIDE, THE ECMWF IN THE MIDDLE ALONG WITH THE DETERMINISTIC
UKMET, AND THE GFS RUNS ON THE FASTER SIDE. THE WPC FORECAST
FAVORED THE ECMWF DETERMINISTIC RUN AND ENSEMBLE MEAN ALONG WITH
THE UKMET, AS THEY WERE A GOOD MIDDLE GROUND OF THE GUIDANCE AND
HAD SIMILAR TIMING TO THE PREVIOUS FORECAST. THE INCOMING 00Z
MODEL CYCLE MAY OFFER SOME SLIGHT MODEL CONVERGENCE THROUGH LATE
WEEK, AS THE CMC AND ECMWF SPED UP A TAD WHILE THE GFS SLOWED.
HOWEVER, THE 00Z ECMWF DOES EJECT MORE QUICKLY BY LATE
SATURDAY-SUNDAY THAN EXPECTED. THE PROGRESSION OF THESE FEATURES
MAY ALSO IMPACT A SHORTWAVE FARTHER SOUTH ATOP THE SOUTHEAST OR
NEARBY WESTERN ATLANTIC AND SOME POTENTIAL SURFACE LOW REFLECTION.
THESE RELATIVELY WEAK AND SMALL LOWS STILL HAVE LOW PREDICTABILITY
AT THIS POINT, SO ADDITIONAL REFINEMENT IS LIKELY. HOWEVER, ONE
PREFERENCE WAS AWAY FROM THE ECMWF RUNS THAT HAD HIGH QPF REACHING
ONSHORE OF THE CAROLINA COASTS, WHICH SEEMS UNLIKELY, AND IN FACT
THE MOST RECENT EC ADJUSTED BY PUTTING HEAVY QPF OFFSHORE.
BY EARLY NEXT WEEK, THERE IS SOME GENERAL AGREEMENT THAT AN UPPER
LOW OFFSHORE OF CANADA COULD FINALLY SPIN SOME ENERGY/TROUGHING
TOWARD THE PACIFIC NORTHWEST FOR SOME COOLER TEMPERATURES WITH A
COLD FRONT OR TWO AS THE PREVAILING RIDGE WEAKENS A BIT AND PUSHES
EASTWARD. THE DETAILS OF THIS FEATURES SUCH AS THE DEPTH THE
ENERGY REACHES AND THE TIMING ARE MORE NEBULOUS. BUT THE ENSEMBLE
MEANS HAD SIMILAR PROGRESSIONS AND THE 12Z ECMWF SEEMED TO MATCH
THEIR TIMING/TRACK THE BEST OUT OF THE 12/18Z DETERMINISTIC
MODELS. FOR THESE REASONS, THE WPC FORECAST HAD A VERY ECMWF-HEAVY
BLEND ALONG WITH SOME UKMET FOR THE FIRST HALF OF THE PERIOD
(OTHER THAN REDUCING THE ECMWF COMPONENT WITH THE SOUTHEAST QPF
LATE WEEK), AND MAINTAINED AN ECMWF/ECENS MEAN MAJORITY THROUGH
THE MEDIUM RANGE TIMEFRAME ALONG WITH SOME GEFS MEAN FOR THE
LATTER PART OF THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
A COLD FRONT MOSTLY PUSHING SOUTHEASTWARD DOES LOOK TO HANG UP A
BIT IN THE SOUTH-CENTRAL ROCKIES FROM THURSDAY (SHORT RANGE) INTO
FRIDAY, WITH UPSLOPE FLOW ON ITS BACKSIDE IN AN ENVIRONMENT WITH
90+ PERCENTILE MOISTURE ANOMALIES. ADDITIONAL RAINFALL THAT OCCURS
ON FRIDAY IN THAT REGION WOULD BE ATOP WET GROUND WITH HIGH
STREAMFLOWS THAT COULD EXACERBATE FLASH FLOODING RISK, SO A
MARGINAL RISK WAS MAINTAINED IN THE DAY 4/FRIDAY ERO. FARTHER
EAST, CONVECTION WITH POSSIBLY HIGH RAIN RATES COULD OCCUR OVER
SOUTH-CENTRAL PARTS OF THE PLAINS AND MISSISSIPPI VALLEY AS WELL,
LEADING TO ANOTHER MARGINAL RISK. THE PROGRESSIVE NATURE OF THE
FRONT SHOULD NOT ALLOW FOR TOO MUCH TRAINING OF STORMS, PRECLUDING
ANY HIGHER RISK LEVEL. THE COLD FRONT WILL MOVE MORE PROGRESSIVELY
EASTWARD ACROSS THE MIDWEST/OHIO VALLEY ON FRIDAY. WHILE THE
TIMING IS STILL SOMEWHAT UNCERTAIN, IT SEEMS MOST LIKELY THAT
ENHANCED RAINFALL CHANCES SHOULD SHIFT INTO THE EAST ON SATURDAY
ALONG AND AHEAD OF THE FRONT, LINGERING ALONG PARTS OF THE EAST
COAST SUNDAY. THERE MAY BE SOME CHANCE OF LOCALLY HEAVY RAIN
SOMEWHERE IN THE EAST AS ATLANTIC MOISTURE AND PERHAPS ANOTHER
SURFACE SYSTEM COULD ENHANCE TOTALS. MEANWHILE, SCATTERED SHOWERS
AND THUNDERSTORMS ARE ALSO POSSIBLE IN THE WEST AT TIMES LATE THIS
WEEK INTO EARLY NEXT WEEK ESPECIALLY IN THE AFTERNOONS/EVENINGS
WITH A COMMON DIURNAL CYCLE, AS A MONSOON-LIKE PATTERN SETS UP
WITH ANOMALOUSLY HIGH MOISTURE REMAINING OVER A LARGE PORTION OF
THE WESTERN U.S., FIRST UNDER THE UPPER RIDGE AXIS AND THEN AS
TROUGHING EDGES INTO THE NORTHWEST.
TEMPERATURE-WISE, THE PERSISTENT LARGE SCALE WESTERN NORTH AMERICA
RIDGE WILL SUPPORT WARM TO HOT TEMPERATURES ACROSS MOST OF THE
WEST. THE PACIFIC NORTHWEST COULD SEE ABOVE AVERAGE TEMPERATURES
LASTING INTO LATE WEEK, BUT MODERATED A BIT COMPARED TO THE HEAT
IN THE NEAR TERM, WITH TEMPERATURES LOOKING CLOSER TO NORMAL BY
SUNDAY. HOWEVER, INTERIOR AREAS LIKE THE GREAT BASIN MAY SEE THEIR
HOTTEST TEMPERATURES OF THE WEEK ON FRIDAY AND SATURDAY, WITH
HIGHS IN THE 90S THAT COULD BE RECORD-SETTING. LOW TEMPERATURES IN
THE 50S AND 60S COULD ALSO BREAK RECORDS FOR WARM MINIMUM
TEMPERATURES ACROSS WIDESPREAD AREAS OF THE WEST. THE NORTHWEST
CAN EXPECT MODERATING TEMPERATURES EARLY NEXT WEEK WHILE
TEMPERATURES AROUND 10-15F ABOVE NORMAL SHIFT INTO THE
NORTH-CENTRAL U.S. FARTHER SOUTH, PERIODS OF RAIN AND CLOUDS AND
THEN POST-FRONTAL COOLER AIR COULD LEAD TO TEMPERATURES SLIGHTLY
BELOW AVERAGE IN THE PLAINS AT TIMES.
TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
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