461
FXUS02 KWBC 210658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT WED JUN 21 2023
VALID 12Z SAT JUN 24 2023 - 12Z WED JUN 28 2023
...PROLONGED HEAT WAVE CONTINUES ACROSS TEXAS AND SOUTHEASTERN NEW
MEXICO AND WILL EXPAND NORTHEAST NEXT WEEK...
...HEAVY RAIN AND FLOODING ARE POSSIBLE ACROSS THE NORTH-CENTRAL
U.S. INTO SATURDAY WITH A LOW PRESSURE SYSTEM...
..OVERVIEW
THE MEDIUM RANGE PERIOD WILL BEGIN SATURDAY WITH A COUPLE OF UPPER
TROUGHS/LOWS HELPING TO PRODUCE RAIN AND THUNDERSTORMS, ONE OVER
THE NORTH-CENTRAL U.S. AND ANOTHER CENTERED NEAR THE LOWER GREAT
LAKES REGION. THESE FEATURES ARE LIKELY TO COMBINE INTO AN UPPER
TROUGH THAT LOOKS TO REMAIN ATOP THE EAST NEXT WEEK, WHILE
ADDITIONAL TROUGHING MOVES FROM THE EASTERN PACIFIC INTO THE WEST.
MEANWHILE, IN BETWEEN THESE TROUGHS, AN UPPER HIGH MEANDERING
AROUND TEXAS WILL CAUSE EXCESSIVE HEAT TO PERSIST THERE AND EVEN
EXPAND IN COVERAGE NEXT WEEK EASTWARD INTO THE LOWER MISSISSIPPI
VALLEY AND NORTH INTO OKLAHOMA/KANSAS AT TIMES.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
RECENT MODEL GUIDANCE INDICATES THAT THE UPPER LOW OVER THE
SOUTHEAST IN THE SHORT TERM SHOULD BE LIFTING NORTH OVER THE
WEEKEND, WHILE UPPER AND SURFACE LOWS TRACK ACROSS THE NORTHERN
PLAINS, AND THE UPPER HIGH ACROSS THE RIO GRANDE PERSISTS. THESE
FEATURES ALL SHOW JUST SOME MINOR DIFFERENCES BETWEEN MODELS, WITH
NOTHING TOO EGREGIOUS. THE FIRST REAL NOTABLE MODEL DIFFERENCES
ARISE EARLY NEXT WEEK WITH AN UPPER TROUGH/POSSIBLY EMBEDDED LOW
COMING ACROSS THE EASTERN PACIFIC. MODELS HAVE BEEN WAFFLING SOME
WITH THE DEPTH AND TIMING/TRACK OF THE TROUGH. THE 12Z UKMET
SEEMED TO BE THE FIRST TO DIVERGE BY SHOWING SPLITTING ENERGY WITH
SOME TRACKING INTO THE PACIFIC NORTHWEST QUICKLY BY EARLY SUNDAY.
THE 18Z GFS ALSO ENDED UP ON THE FAST SIDE BY MONDAY-TUESDAY,
WHEREAS THE 12Z GFS/ECMWF/CMC ALL SEEMED TO BE IN BETTER ALIGNMENT
WITH THE ENSEMBLE MEANS WITH THE TIMING OF THE TROUGH'S PUSH
EASTWARD. THE INCOMING 00Z GUIDANCE SUITE GENERALLY SEEMS WEAKER
WITH THE DEPTH OF THE TROUGH AND SHOWS LESS INDICATION FOR ANY
DEEP CLOSED LOW COMPARED TO THE EARLIER MODEL CYCLE, WHICH PERHAPS
ALLOWS THE TROUGH TO MOVE A LITTLE FASTER. SO THERE IS STILL SOME
UNCERTAINTY WITH THIS PART OF THE PATTERN, WHICH IS OFTEN THE CASE
WHEN FEATURES ARISE/ARE REINFORCED FROM PACIFIC AND HIGH LATITUDE
ENERGIES LIKE THIS.
MOST GUIDANCE AGREES WELL REGARDING THE UPPER HIGH/RIDGE PATTERN
OVER TEXAS AND BEYOND LASTING INTO NEXT WEEK. THERE IS GOOD
AGREEMENT IN PLACEMENT OF THE HIGH, WITH THE EXCEPTION OF THE 18Z
GFS THAT PUSHES THE HIGH EAST SOONER AND FARTHER THAN OTHER
MODELS. SOME ISOLATED 18Z AND 06Z RUNS OF THE GFS HAVE BEEN
SHOWING THAT IN THE PAST FEW DAYS. INSTEAD FAVORED THE MORE
AGREEABLE OTHER 12Z MODELS AND ENSEMBLE MEANS. THIS BUILDS RIDGING
ACROSS THE FOUR CORNERS STATES AROUND MONDAY AND PUSHING INTO THE
PLAINS TUESDAY-WEDNESDAY.
GIVEN THESE CONSIDERATIONS, THE WPC FORECAST WAS BASED ON A BLEND
OF THE 12/18Z GFS AND 12Z ECMWF AND CMC EARLY IN THE PERIOD.
GRADUALLY REDUCED (AND ELIMINATED THE 18Z GFS) THE DETERMINISTIC
MODELS IN FAVOR OF THE ENSEMBLE MEANS, ENDING UP AT ABOUT HALF
MODELS/HALF MEANS BY THE END OF THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE UPPER TROUGHING IN THE EAST LIFTS NORTH AND WEAKENS, IT
WILL STILL PROVIDE SOME SUPPORT FOR RAIN AND THUNDERSTORMS BUT
LIKELY WITH REDUCED WIDESPREAD HEAVY AMOUNTS COMPARED TO THE SHORT
TERM. SCATTERED THUNDERSTORMS COULD PRODUCE LOCALIZED HEAVY RAIN
RATES THOUGH GIVEN THE INSTABILITY IN PLACE. THERE MAY BE A
SOMEWHAT FOCUSED AXIS OF RAINFALL ACROSS THE NORTHERN MID-ATLANTIC
REGION INTO THE INTERIOR NORTHEAST THIS WEEKEND, SO MARGINAL RISKS
ARE IN PLACE THERE FOR SATURDAY AND SUNDAY, WITH AREAS OF LOW
FLASH FLOOD GUIDANCE OF PARTICULAR CONCERN. FARTHER WEST, A
CONSOLIDATING LOW PRESSURE SYSTEM AT THE SURFACE AND COUPLED JETS
(RIGHT ENTRANCE/LEFT EXIT REGION COMBINATION) ALOFT WILL LIKELY
PRODUCE HEAVY RAINFALL (LIKELY AROUND 2-4" WITH LOCALLY HIGHER
AMOUNTS) ACROSS THE NORTH-CENTRAL U.S. ON SATURDAY. A BROAD SLIGHT
RISK OF EXCESSIVE RAINFALL IS FOCUSED ON NORTH DAKOTA AND
NORTHERN/CENTRAL MINNESOTA FOR THIS POTENTIAL, WITH A MARGINAL
RISK FOR LINGERING RAINFALL CENTERED ON THE ARROWHEAD OF MINNESOTA
ON SUNDAY. SHOWER AND STORM CHANCES WILL LIKELY ALSO EXTEND
SOUTHWARD ACROSS THE MISSOURI AND MISSISSIPPI VALLEYS THIS WEEKEND
AHEAD OF THE FRONTAL SYSTEM. THE MID-SOUTH AND VICINITY LOOKS TO
SEE SOME ENHANCED ORGANIZED CONVECTION SUNDAY EVENING/NIGHT WITH
HIGH RAIN RATES, LEADING TO A MARGINAL RISK ISSUANCE THERE FOR
SUNDAY. AS THIS UPPER-LEVEL SYSTEM AND SURFACE LOW PRESSURE/FRONT
PUSH EASTWARD, THESE AREAS SHOULD DRY OUT WHILE ADDITIONAL ROUNDS
OF RAIN AND STORMS ARE LIKELY IN THE EAST THROUGH MIDWEEK.
MEANWHILE, SCATTERED SHOWER AND STORM CHANCES RETURN FROM THE
NORTHWEST INTO THE NORTHERN ROCKIES/ADJACENT HIGH PLAINS BY
MONDAY-TUESDAY AS ANOTHER UPPER-LEVEL TROUGH APPROACHES FROM THE
WEST.
IN TERMS OF TEMPERATURES, THERE IS REALLY NO END IN SIGHT FOR THE
EXCESSIVE HEAT THAT HAS PLAGUED PARTICULARLY SOUTH AND WESTERN
TEXAS/SOUTHEASTERN NEW MEXICO IN RECENT DAYS. IN FACT, FOR THE
WEEKEND AND INTO NEXT WEEK, TEMPERATURES OVER 100F AND HEAT
INDICES MUCH HIGHER WILL EXTEND FARTHER EAST INTO THE DALLAS-FORT
WORTH AND HOUSTON METROS BY SATURDAY AND THEN INTO THE LOWER
MISSISSIPPI VALLEY AS WELL. SEVERAL RECORD TEMPERATURES COULD BE
SET OR TIED. THE DESERT SOUTHWEST STARTS TO SEE TEMPERATURES WELL
OVER 100F BY THE WEEKEND AND 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, WITH
CURRENT FORECASTS SHOWING TEMPERATURES EXCEEDING 100F INTO
OKLAHOMA/KANSAS/ARKANSAS BY NEXT WEDNESDAY. MEANWHILE THE WEST
SHOULD SEE COOLER THAN NORMAL TEMPERATURES PARTICULARLY FOR HIGHS
WITH THE BOUTS OF UPPER TROUGHING ALOFT. THE EAST LOOKS TO BE
WITHIN A FEW DEGREES OF AVERAGE FOR EARLY SUMMER.
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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