917
FXUS02 KWBC 162004
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
404 PM 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
IT REMAINS THE CASE THAT 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 RECENT MODEL GUIDANCE CONTINUES TO BE AGREEABLE WITH THE
WESTERN U.S. TROUGHING LATE WEEK, DOWNSTREAM THERE HAVE BEEN
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.
IT IS STILL IMPORTANT TO NOTE THAT FOR THE RECENT 12/18Z MODEL
CYCLE, THE VARIOUS MODEL SUITES' ENSEMBLE MEMBERS CLUSTER WITH
THEIR DETERMINISTIC RUNS WITHOUT MUCH OVERLAP IN THE ENSEMBLE
SPREAD. THE CMC/CANADIAN ENSEMBLES WERE ON THE SLOWER SIDE, THE
ECMWF/ECMWF ENSEMBLES IN THE MIDDLE ALONG WITH THE DETERMINISTIC
UKMET, AND THE GFS/GEFS RUNS ON THE FASTER SIDE. THE LATEST WPC
FORECAST FAVORED THE 00 UTC ECMWF DETERMINISTIC RUN AND ENSEMBLE
MEAN ALONG WITH THE 00 UTC UKMET, AS THEY REMAINED A GOOD MIDDLE
GROUND OF THE GUIDANCE AND HAD SIMILAR TIMING TO THE PREVIOUS
FORECAST. HOWEVER, GUIDANCE UNDERDISPERSION SEEMS TO BE GRADUALLY
IMPROVING FOR THE MORE RECENT MODEL CYCLES. THE CMC IN PARTICULAR
HAS TREND MORE PROGRESSIVE WITH THE 12 UTC RUN MORE IN LINE WITH
THE WPC PREFERRED COMPOSITE. THE 12 UTC ECMWF/UKMET ARE A TAD MORE
PROGRESSIVE, BUT THE 12 UTC GFS HAS NOT SLOWED. 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.
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 CONTINUE TO HAVE QUITE SIMILAR PROGRESSIONS AND AMPLITUDES
AND REMAIN PREFERRED. THIS SOLUTION ALSO SEEMS BROADLY REASONABLE
DOWNSTREAM ACROSS THE CENTRAL AND EASTERN STATES AND ACTS TO
PROVIDE GOOD PRODUCT CONTINUITY VERSUS CHASING TOO MUCH OF ANY
INDIVIDUAL MODEL DETAIL.
..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. THE SOUTHWARD
DIGGING OF THE TRAILING FRONT THROUGH THE PLAINS INTO SATURDAY MAY
ACT TO FOCUS GULF MOISTURE AND INSTABILITY OVER THE CENTRAL RIO
GRANDE VALLEY WHERE A DAY 5 ERO MARGINAL RISK AREA IS PLANNED TO
BE ADDED IN A REGION WITH MOIST SOILS FROM RECENT RAINFALL. WHILE
THE TIMING IS STILL SOMEWHAT UNCERTAIN, IT SEEMS MOST LIKELY THAT
ENHANCED RAINFALL CHANCES SHOULD ALSO SHIFT INTO THE EAST ON
SATURDAY ALONG AND AHEAD OF THE FRONT BACK UP TO THE MAIN LOW,
LINGERING ALONG PARTS OF THE EAST COAST SUNDAY. THERE MAY BE SOME
CHANCE OF LOCALLY HEAVY RAIN UP THE EAST COAST 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/SCHICHTEL
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE
MISSISSIPPI VALLEY, THE LOWER MISSISSIPPI VALLEY, AND THE SOUTHERN
PLAINS, FRI, MAY 19.
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, SAT, MAY 20.
- SEVERE WEATHER ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY
AND THE SOUTHERN PLAINS, FRI, MAY 19.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS, THE
NORTHERN ROCKIES, AND THE NORTHERN GREAT BASIN.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHERN
PLAINS, THE NORTHERN ROCKIES, THE MIDDLE MISSISSIPPI VALLEY, THE
NORTHERN GREAT BASIN, THE UPPER MISSISSIPPI VALLEY, AND THE
SOUTHERN PLAINS.
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE
CENTRAL GREAT BASIN, THE NORTHERN PLAINS, THE NORTHERN GREAT
BASIN, THE SOUTHERN ROCKIES, THE UPPER MISSISSIPPI VALLEY, THE
PACIFIC NORTHWEST, AND THE SOUTHWEST.
- MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF CALIFORNIA,
THE CENTRAL GREAT BASIN, THE PACIFIC NORTHWEST, THE NORTHERN
ROCKIES, AND THE NORTHERN GREAT BASIN, FRI-MON, MAY 19-MAY 22.
- MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN
PLAINS AND THE NORTHERN ROCKIES, SAT-MON, MAY 20-MAY 22.
- FLOODING POSSIBLE ACROSS PORTIONS OF MAINLAND ALASKA, FRI, MAY
19.
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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