732
FXUS02 KWBC 211914
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 PM EDT FRI JUN 21 2024
VALID 12Z MON JUN 24 2024 - 12Z FRI JUN 28 2024
..HAZARDOUS HEAT POSSIBLE MUCH OF NEXT WEEK FOR THE SOUTH/PLAINS
..OVERVIEW
AN UPPER LEVEL RIDGE WILL REMAIN ANCHORED OVER MUCH OF THE
SOUTHERN HALF OF THE NATION THROUGH THE WEEK, LEADING TO MULTIPLE
DAYS OF ABOVE NORMAL TO POSSIBLY HAZARDOUS HEAT. TO THE NORTH,
INDIVIDUAL SHORTWAVES WITHIN THE WESTERLIES CROSSING SOUTHERN
CANADA AND THE NORTHERN TIER OF THE U.S. TO THE NORTHEAST WILL
SUPPORT A SERIES OF PROGRESSIVE SURFACE LOWS AND TRAILING FRONTS
ACROSS THE NORTHERN HALF TO TWO-THIRDS OF THE LOWER 48. A DEEPER
UPPER LOW WILL BUILD OFF THE NORTHWEST COAST, MOVING INTO THE
REGION SOMETIME LATER IN THE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST DYNAMICAL AND MACHINE LEARNING (ML) GUIDANCE AGREES
FAIRLY WELL FOR THE OVERALL PATTERN BUT DISPLAYS TYPICAL SPREAD AND
RUN-TO-RUN VARIABILITY FOR THE DETAILS. THIS IS TRUE EVEN IN THE
EARLY PART OF THE FORECAST PERIOD, CAUSING SENSIBLE WEATHER
IMPACTS. THE SURFACE LOW AND FRONTAL PLACEMENT IN THE NORTH-CENTRAL
U.S. TO SOUTH-CENTRAL CANADA MONDAY-TUESDAY SHOWS DIFFERENCES WITH
THE WARM FRONT AND THUS AN MCS SETTING UP. THE EC SUITE (INCLUDING
THE DETERMINISTIC, AIFS, AND ENSEMBLE MEAN) IS FARTHER WEST,
LEADING TO HEAVIER RAINFALL IN THE MORE SUSCEPTIBLE AREAS WITH
RECENT AND ONGOING SIGNIFICANT RAINS, WHILE THE GFS/GEFS/GFS
GRAPHCAST WERE FARTHER EAST. ADDITIONALLY, MODEL SPREAD WITH
ANOTHER SHORTWAVE IN THE NORTHEAST LEADS TO QPF DIFFERENCES ON
MONDAY. ECMWF RUNS REMAIN ON THE SLOWER SIDE. THEN FARTHER WEST,
THERE REMAINS SOME TIMING SPREAD FOR TROUGHING IN THE EASTERN
PACIFIC TO NORTHWEST LATER IN THE WEEK, THOUGH MODELS ARE SLOWLY
CONVERGING. EC-BASED ML MODELS WERE FARTHER EAST/MORE LIKE THE GFS
THAN THE DETERMINISTIC ECMWF AND CMC, CREATING A WRINKLE IN
DECIDING WHICH CAMP TO LEAN TOWARD, AND A MIDDLE GROUND SEEMS BEST.
EVENTUALLY THERE WERE SOME OUT OF PHASE DIFFERENCES IN THE NORTH-
CENTRAL U.S. WITH THE 06Z GFS SHOWING DIFFERENT EVOLUTION THAN
OTHER MODELS WITH THIS FEATURE AND ENERGY DOWNSTREAM. HOWEVER, THE
INCOMING 12Z SUITE SHOWS BETTER AGREEMENT WITH THESE FEATURES.
THE UPDATED WPC FORECAST FAVORED A DETERMINISTIC MODEL BLEND FOR
THE FIRST HALF OF THE PERIOD AMIDST GOOD AGREEMENT ON THE LARGE
SCALE. INCLUDED INCREASING PERCENTAGES OF THE GEFS AND EC ENSEMBLE
MEANS AS THE PERIOD PROGRESSED, REACHING OVER HALF BY DAY 7.
OVERALL, THIS MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS WPC
FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
A LOW PRESSURE SYSTEM MOVING THROUGH SOUTH-CENTRAL TO EASTERN
CANADA AND ITS ASSOCIATED FRONTS WILL PROVIDE A FOCUS FOR POSSIBLY
IMPACTFUL CONVECTIVE RAINFALL. ON MONDAY EVENING TO NIGHT, A
MESOSCALE CONVECTIVE SYSTEM WILL LIKELY FORM IN THE NORTH-CENTRAL
U.S. NEAR THE WARM FRONT/CUSP OF THE INSTABILITY AND PROPAGATE
EAST/SOUTHEAST. AS MENTIONED, THERE IS STILL SPREAD IN THE
PLACEMENT OF WHERE THIS MCS WILL FORM AND TRACK, SO THE MARGINAL
RISK ATTEMPTS TO COVER A BROAD AREA ACROSS MINNESOTA AND WISCONSIN
AND SURROUNDING STATES EVEN THOUGH NOT ALL THIS REGION MAY SEE
HEAVY RAINFALL. IF MODELS CONVERGE THE AREA MIGHT BE ABLE TO SHRINK
WITH TIME. CONVERSELY, BY TUESDAY, COPIOUS MOISTURE AND
INSTABILITY IN A TYPICAL SUMMERTIME CONVECTIVE PATTERN SOUTH AND
EAST OF THE COLD FRONT SHOULD LEAD TO A BROAD AREA OF THE CENTRAL
U.S. THAT COULD SEE SCATTERED THUNDERSTORMS IN MULTIPLE ROUNDS. AS
A RESULT, A LARGE MARGINAL ERO TO COVER THUNDERSTORMS THAT FORM IN
THIS FAVORABLE ENVIRONMENT STILL SEEMS WISE AND STRETCHES FROM THE
SOUTH-CENTRAL PLAINS ACROSS THE MISSISSIPPI VALLEY AND INTO THE
MIDWEST AND UPPER GREAT LAKES. NO AREAS REALLY STAND OUT WITHIN THE
MARGINAL AS AREAS OF FOCUS FOR ANY HIGHER RISK LEVEL AT THIS TIME.
CONVECTION AND AT LEAST LOCALLY HEAVY RAINFALL SHOULD ACCOMPANY
THE FRONT AS IT PUSHES INTO THE EAST BY WEDNESDAY AS WELL.
ANOMALOUS MOISTURE AND SUFFICIENT INSTABILITY SHOULD PERSIST OVER
THE FOUR CORNERS STATES DURING THE DAYS 4-5 PERIOD AND POTENTIALLY
LEAD TO SOME LOCALLY HEAVY RAINFALL, WHICH COULD CAUSE FLOODING
IMPACTS PARTICULARLY OVER BURN SCARS. MARGINAL RISKS ARE IN THE
OUTLOOK ACROSS PARTS OF ARIZONA AND NEW MEXICO WHERE THE BEST
MOISTURE TRANSPORT IS FOR SLOW-MOVING CONVECTION. THE LATEST
FORECAST EXTENDED THE DAY 4/MONDAY MARGINAL RISK EAST INTO THE
SACRAMENTO MOUNTAINS OF NEW MEXICO, WHERE RECENT/ONGOING FIRES AND
STORMS ATOP THEM HAVE CAUSED SIGNIFICANT IMPACTS LIKE LANDSLIDES
ALREADY. CONVECTIVE COVERAGE IS LIKELY TO EXPAND NORTH AND EAST
ACROSS THE FOUR CORNERS REGION AND INTO THE CENTRAL HIGH PLAINS BY
WEDNESDAY-THURSDAY AS MOISTURE FUNNELS EAST OF TROUGHING IN THE
NORTHWEST.
ELSEWHERE, THERE REMAINS MODEL SPREAD IN HOW MUCH RAINFALL MAY
AFFECT THE NORTHEAST MONDAY, SO CONSIDERED A MARGINAL RISK THERE
BUT WILL AWAIT HOPEFULLY BETTER MODEL CONSENSUS. PARTS OF THE
SOUTHEAST/FLORIDA MAY ALSO SEE EPISODES OF DIURNALLY ENHANCED
CONVECTION, BUT OVERALL DRY CONDITIONS/HIGH FFGS PRECLUDED ANY
EXCESSIVE RAINFALL RISK AREAS AT THIS TIME. A FRONT REACHING THE
NORTHWEST MAY PRODUCE SOME LIGHT RAINFALL WEDNESDAY INTO THURSDAY.
FOR THE FIRST HALF OF THE WEEK, ABOVE NORMAL TEMPERATURES WILL
STRETCH FROM THE WEST TO THE EAST, THOUGH THE FOCUS FOR HAZARDOUS
HEAT WILL BE ACROSS THE CENTRAL PLAINS STATES INTO THE SOUTHEAST
WHERE DAYTIME HIGHS 10-15F ABOVE NORMAL, HEAT/HUMIDITY COULD LEAD
TO HEAT INDICES NEAR 110F FOR SOME, AND WIDESPREAD MAJOR TO EXTREME
HEATRISK ARE PRESENT. HAZARDOUS HEAT IS ALSO POSSIBLE ACROSS THE
SOUTHWEST WHERE TEMPERATURES 105-115F ARE LIKELY. TEMPERATURES
SHOULD MODERATE BACK TOWARDS NORMAL FOR THE EAST AND WEST STATES AS
UPPER TROUGHING MOVES THROUGH BOTH REGIONS.
TATE/SANTORELLI
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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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