327
FXUS02 KWBC 202048
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
447 PM EDT TUE JUN 20 2023
VALID 12Z FRI JUN 23 2023 - 12Z TUE JUN 27 2023
...PROLONGED HEAT WAVE CONTINUES ACROSS TEXAS AND SOUTHEASTERN NEW
MEXICO THROUGHOUT THIS WEEK WITH SOME EXPANSION ACROSS THE
SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY EARLY NEXT WEEK...
...HEAVY RAIN AND FLOODING ARE POSSIBLE ACROSS THE NORTH-CENTRAL
U.S. LATE THIS WEEK WITH A LOW PRESSURE SYSTEM...
..OVERVIEW
THE MEDIUM RANGE PERIOD WILL BEGIN FRIDAY WITH AN UPPER LOW
FINALLY LIFTING NORTH OUT OF THE TENNESSEE VALLEY, THOUGH WITH
SOME REMAINING SHOWERS AND THUNDERSTORMS ACROSS THE EAST WITH A
LOW PRESSURE/FRONTAL SYSTEM AT THE SURFACE. FARTHER WEST, ANOTHER
UPPER LOW IS FORECAST TO PRESS ACROSS THE WEST INTO THE NORTHERN
PLAINS THROUGH THE WEEKEND AND THEN INTO THE GREAT LAKES REGION,
SPREADING RAIN WITH IT THAT COULD BE HEAVY AND CAUSE FLASH
FLOODING CONCERNS PARTICULARLY IN THE NORTHERN PLAINS/UPPER
MIDWEST. MEANWHILE, A STRONG UPPER HIGH WILL CONTINUE TO MEANDER
AROUND THE RIO GRANDE THROUGH THE WEEK AND INTO NEXT WEEK, CAUSING
PERSISTENT HEAT ACROSS MUCH OF TEXAS AND SOUTHEASTERN NEW MEXICO,
AND HIGH HEAT INDICES ARE LIKELY TO EXPAND FURTHER INTO THE
SOUTHERN PLAINS AND THE LOWER MISSISSIPPI VALLEY AS WELL BY EARLY
NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE INDICATES THE PERSISTENT BLOCKY PATTERN THAT HAS
BEEN IN PLACE ACROSS THE CONUS ON AND OFF FOR SEVERAL WEEKS WILL
INITIALLY START OFF THE FORECAST PERIOD ON FRIDAY (6/23). A
PREVIOUSLY CUTOFF UPPER-LEVEL LOW WILL BE LINGERING OVER THE
SOUTHEAST/TENNESSEE VALLEY WHILE SLOWLY BEING ABSORBED INTO THE
NORTHERN STREAM BRINGING AN END TO A BRIEF REX BLOCK PATTERN, WITH
HIGH PRESSURE TO THE NORTH SHIFTING EASTWARD OVER THE ATLANTIC. TO
THE WEST, AN UPPER-LEVEL HIGH LOOKS TO BE MAINTAINED OVER NORTHERN
MEXICO INTO PORTIONS OF THE SOUTHWEST/TEXAS, WITH RIDGING
EXTENDING NORTHWARD OVER THE PLAINS, AS MEAN TROUGHING REMAINS
OVER THE WEST. THROUGH THE FORECAST PERIOD, THE UPPER-LEVEL
HIGH/RIDGING OVER TEXAS WILL BRIEFLY EXPAND NORTHWESTWARD AS A
PIECE OF SHORTWAVE ENERGY EJECTS FROM THE WESTERN TROUGH
NORTHEASTWARD, BREAKING DOWN THE NORTHWARD EXTENT OF THE RIDGING
OVER THE PLAINS, BEFORE REINFORCING UPPER-LEVEL TROUGHING OVER THE
NORTHEAST FOLLOWING THE ABSORPTION OF THE LOW OVER THE TENNESSEE
VALLEY. MEANWHILE, MID- TO LATE PERIOD, ADDITIONAL UPPER-LEVEL
ENERGY OVER THE GULF OF ALASKA FLOWS SOUTHWARD, REINFORCING THE
MEAN TROUGHING OVER THE WEST COAST AS THE UPPER-LEVEL HIGH/RIDGING
OVER THE SOUTHERN CONUS SHIFTS BACK EASTWARD.
MOST LARGE-SCALE, AND EVEN SMALLER-SCALE, DETAILS ARE RELATIVELY
CONSISTENT ACROSS THE GUIDANCE AT THE START OF THE PERIOD, WITH
DECENT RUN-TO-RUN CONSISTENCY WITHIN THE GFS/ECMWF INDICATING A
GOOD HANDLE ON THE FORECAST. TWO ASPECTS WHERE THE MODEL SOLUTIONS
DIVERGE RELATIVELY QUICKLY INTO THE PERIOD IS THE 00Z UKMET
DEPICTING A MUCH WEAKER SHORTWAVE TRAVERSING THE NORTHERN PLAINS,
AND THE 00Z ECMWF/UKMET TRENDING WEAKER WITH THE UPPER-LEVEL
ENERGY THAT SHIFTS SOUTHWARD FROM THE GULF OF ALASKA OFF THE WEST
COAST. IN CONTRAST, THE GFS HAS ACTUALLY TRENDED STRONGER WITH
THIS FEATURE OVER THE LAST FEW RUNS, WITH A DEEPER CLOSED LOW IN
BOTH THE MOST RECENT 00Z/06Z AND UPDATED 12Z RUNS, WHICH IS ALSO
DEPICTED IN THE 00Z CMC. THE 00Z ECENS AND 06Z GEFS MEANS ARE
NOTABLY LESS DETAILED, BUT DO BOTH SIGNAL THE POTENTIAL FOR A BIT
DEEPER CLOSED LOW AT DIFFERENT TIMES IN THE MID- TO LATE FORECAST
PERIOD, GIVING CREDENCE TO LEAN TOWARDS THIS SOLUTION FOR NOW
DESPITE THE DIFFERENCE BETWEEN THE 06Z GFS/00Z CMC AND 00Z ECMWF.
THE UPDATED WPC FORECAST BLEND IS INITIALLY BASED OFF A
COMBINATION OF THE 00Z ECMWF/CMC AND 06Z GFS, WITH THE 00Z UKMET
NOT INCLUDED GIVEN THE DIFFERENCES WITH RESPECT TO THE SHORTWAVE
OVER THE NORTHERN TIER AND A SIMILAR WEAKER TROUGH ALONG THE WEST
COAST THAT IS ALREADY ACCOUNTED FOR BY THE INCLUSION OF THE 00Z
ECMWF. A CONTRIBUTION FROM THE 00Z ECENS MEAN IS INTRODUCED
MID-PERIOD AS THE 00Z ECMWF CONTRIBUTION IS REDUCED GIVEN THE
WEAKER REPRESENTATION OF THE WESTERN UPPER-LEVEL LOW/TROUGH
COMPARED TO THE OTHER GUIDANCE THAT THE 00Z ECENS MEAN TRENDS MORE
SIMILARLY TOWARDS. GREATER CONTRIBUTIONS OF BOTH THE 00Z ECENS AND
00Z GEFS MEAN ARE INCLUDED TOWARDS THE END OF THE PERIOD AS THE
DETERMINISTIC GUIDANCE BEGINS TO DIVERGE MORE WITH INCREASING LEAD
TIME, ESPECIALLY WITH RESPECT TO THE NORTHERN TIER SHORTWAVE
RE-AMPLIFYING TROUGHING OVER THE GREAT LAKES INTO THE EAST COAST,
WITH THE MEANS PROVIDING A COMPROMISED SOLUTION.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE UPPER LOW MEANDERING OVER THE SOUTHEAST/TENNESSEE VALLEY IN
THE SHORT RANGE WEAKENS AND LIFTS NORTH, IT WILL STILL PROVIDE
SOME SUPPORT FOR RAIN AND THUNDERSTORMS BUT LIKELY WITH REDUCED
WIDESPREAD AMOUNTS COMPARED TO THE SHORT TERM. THE UPPER AND
SURFACE LOWS LIFTING NORTH SHOULD ALLOW FOR RAIN CHANCES TO SPREAD
NORTH INTO THE MID-ATLANTIC AND NORTHEAST AS WELL. FOR FRIDAY, A
MARGINAL RISK OF EXCESSIVE RAINFALL IS IN PLACE ACROSS THE
SOUTHEAST AND MID-ATLANTIC FOR LINGERING CONVECTION OVER WHAT IS
LIKELY TO BE WET GROUND AFTER MULTIPLE DAYS OF RAIN IN SOME AREAS.
THE INSTABILITY IN PLACE COULD SUPPORT LOCALIZED HEAVY RAIN RATES.
BY SATURDAY FOR THE DAY 5 ERO, THERE MAY BE A SOMEWHAT FOCUSED
AXIS OF RAINFALL ACROSS THE NORTHERN MID-ATLANTIC REGION INTO THE
INTERIOR NORTHEAST, SO A MARGINAL RISK IS IN PLACE FOR THOSE
REGIONS, AND AREAS OF LOW FLASH FLOOD GUIDANCE COULD BE OF
PARTICULAR CONCERN. SCATTERED THUNDERSTORMS MAY REMAIN FARTHER
SOUTH TOO. A WET AND STORMY PATTERN LOOKS TO PERSIST ACROSS THE
EAST THROUGH EARLY NEXT WEEK AS A TROUGH RE-AMPLIFIES OVER THE
REGION AND ANOTHER FRONTAL SYSTEM MOVES IN.
FARTHER WEST, SUPPORT STARTS TO BECOME FAVORABLE FOR HEAVY RAIN IN
THE NORTH-CENTRAL U.S. AS A COUPLED UPPER JET (RIGHT ENTRANCE/LEFT
EXIT REGION COMBINATION) SETS UP AROUND MONTANA ON FRIDAY AND INTO
THE NORTHERN PLAINS AND UPPER MIDWEST BY SATURDAY, WHILE AT THE
SURFACE A LOW PRESSURE/FRONTAL SYSTEM CONSOLIDATES. BROAD SLIGHT
RISKS OF EXCESSIVE RAINFALL ARE IN PLACE FOR THIS POTENTIAL,
ACROSS THE NORTHERN HIGH PLAINS ON FRIDAY AND FOR THE NORTHERN
PLAINS/UPPER MIDWEST ON SATURDAY. ENSEMBLE GUIDANCE INDICATES
MODERATE TO HIGH PROBABILITIES FOR AREAL AVERAGE RAINFALL
EXCEEDING AN INCH WITH DETERMINISTIC QPF INDICATING LOCALLY HEAVY
AMOUNTS IN THE 2-4" RANGE EACH DAY ARE POSSIBLE. SHOWER AND STORM
CHANCES WILL LIKELY ALSO EXTEND SOUTHWARD ACROSS THE MISSOURI AND
MISSISSIPPI VALLEYS THIS WEEKEND AHEAD OF THE FRONTAL SYSTEM. AS
THE SYSTEM PICKS UP SPEED AND MOVES EAST EARLY NEXT WEEK, AREAS
WEST OF THE GREAT LAKES SHOULD DRY OUT AS SCATTERED SHOWER AND
STORM CHANCES RETURN FROM THE NORTHWEST INTO THE NORTHERN
ROCKIES/ADJACENT HIGH PLAINS AS ANOTHER UPPER-LEVEL TROUGH
APPROACHES FROM THE WEST.
MEANWHILE, THE EXCESSIVE HEAT WILL CONTINUE THROUGH LATE WEEK,
WITH WIDESPREAD 100S ACROSS PORTIONS OF SOUTHERN NEW MEXICO AND
WESTERN AND SOUTHERN TEXAS, EVENTUALLY EXPANDING INTO CENTRAL AND
EASTERN TEXAS EARLY NEXT WEEK. HIGHS IN THE MID- TO UPPER 90S ARE
ALSO EXPECTED TO EXPAND ACROSS THE SOUTHERN PLAINS AND INTO THE
LOWER MISSISSIPPI VALLEY THIS WEEKEND INTO EARLY NEXT WEEK, WITH
HUMIDITY CONTRIBUTING TO HEAT INDICES BETWEEN 105-110 DEGREES,
LOCALLY AS HIGH AS 115. MANY DAILY RECORD HIGH TEMPERATURES ARE
POSSIBLE, AND SOME MONTHLY RECORDS MAY EVEN BE CHALLENGED. THE
DESERT SOUTHWEST STARTS TO SEE TEMPERATURES WELL OVER 100F BY
EARLY NEXT WEEK TOO, THOUGH NOT REALLY ANOMALOUS FOR THIS
TYPICALLY HOTTEST TIME OF THE YEAR THERE. AS MEAN UPPER RIDGING
EXPANDS FARTHER NORTH, HIGHS IN THE 90S ARE LIKELY ACROSS MUCH OF
THE PLAINS AND MISSISSIPPI VALLEY, WHILE 80S AND LOW 90S IN THE
UPPER MIDWEST/GREAT LAKES REGION LATE THIS WEEK WILL BE 10-15F
ABOVE NORMAL. MEANWHILE THE WEST SHOULD SEE COOLER THAN NORMAL
TEMPERATURES PARTICULARLY FOR HIGHS WITH THE BOUTS OF UPPER
TROUGHING ALOFT, WHILE COOLER THAN AVERAGE TEMPERATURES WILL ALSO
BE PRESENT IN THE SOUTHEASTERN U.S. LATE THIS WEEK GIVEN THE
CLOUDINESS/RAIN CHANCES AND THE UPPER LOW.
PUTNAM/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
- HEAVY RAIN ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY, THE
GREAT LAKES, THE NORTHERN PLAINS,
AND THE NORTHERN ROCKIES, FRI-SAT, JUN 23-JUN 24.
- SEVERE WEATHER ACROSS PORTIONS OF THE CENTRAL PLAINS, THE
SOUTHERN PLAINS, AND THE NORTHERN
PLAINS, FRI, JUN 23.
- SEVERE WEATHER ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE
MISSISSIPPI VALLEY, THE UPPER
MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS, SAT, JUN 24.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHERN
ROCKIES AND THE NORTHERN GREAT
BASIN.
- EXCESSIVE HEAT ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE
LOWER MISSISSIPPI VALLEY, THE
SOUTHERN PLAINS, AND THE SOUTHWEST, FRI-TUE, JUN 23-JUN 27.
- EXCESSIVE HEAT ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER
MISSISSIPPI VALLEY, THE SOUTHERN
PLAINS, AND THE TENNESSEE VALLEY, SAT-TUE, JUN 24-JUN 27.
- EXCESSIVE HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER
MISSISSIPPI VALLEY, THE TENNESSEE
VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHEAST, AND THE
SOUTHERN PLAINS, SAT-SUN, JUN 24-JUN
25.
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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