947
FXUS02 KWBC 140721
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
321 AM EDT MON APR 14 2025
VALID 12Z THU APR 17 2025 - 12Z MON APR 21 2025
...HEAVY RAINFALL AND FLOODING POSSIBLE IN PARTS OF THE CENTRAL
U.S. BY THE WEEKEND...
..OVERVIEW
AS THE MEDIUM RANGE PERIOD BEGINS THURSDAY, A POTENT UPPER TROUGH
WILL BE DIVING INTO THE NORTHWEST WHILE SOUTHERN STREAM TROUGHING
REACHES THE SOUTHWEST. THESE FEATURES WILL COMBINE AND DEVELOP AN
UPPER LOW ATOP THE GREAT BASIN LATE WEEK THAT SHOULD GRADUALLY
PIVOT SOUTH AND EASTWARD OVER THE WEEKEND. COOLER TEMPERATURES AND
INCREASED PRECIPITATION CHANCES ARE EXPECTED WITH THIS DEVELOPING
LOW, INCLUDING THE POTENTIAL FOR HEAVY SNOW IN THE NORTHERN/CENTRAL
ROCKIES THURSDAY-FRIDAY. MEANWHILE A NORTHERN STREAM TROUGH IS
FORECAST TO MOVE THROUGH THE NORTH-CENTRAL AND NORTHEASTERN U.S.
ACCOMPANIED BY A LOW PRESSURE SYSTEM, AS AN ELONGATED FRONTAL
SYSTEM STRETCHES FROM THE NORTHERN TIER SOUTHWESTWARD THROUGH THE
SOUTH-CENTRAL U.S. LATE WEEK INTO THE WEEKEND. THIS WILL LEAD TO
RAIN AND THUNDERSTORM CHANCES, INCLUDING POSSIBLE SEVERE WEATHER.
MOISTURE STREAMING IN AHEAD OF THE SOUTHWEST UPPER LOW COMBINING
WITH FRONTAL SYSTEMS ATOP THE SOUTH-CENTRAL U.S. WILL LEAD TO SOME
HEAVY RAINFALL AND FLOODING POTENTIAL THERE, PERHAPS BEGINNING
FRIDAY BUT CERTAINLY OVER THE WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE HAS BECOME MORE STABLE WITH THE PATTERN DESCRIBED
ABOVE. MINOR DIFFERENCES IN THE COMBINATION OF NORTHERN AND
SOUTHERN STREAM TROUGHING LATE WEEK COULD BE TAKEN CARE OF WITH A
MULTI-MODEL BLEND. MEANWHILE FARTHER EAST, THERE ARE SOME MODEL
DIFFERENCES IN THE TIMING OF THE NORTHERN STREAM TROUGH AND THE
ASSOCIATED SURFACE LOW. THE 12Z GFS WAS THE MAIN OUTLIER WITH ITS
TIMING AS IT WAS SLOWER THAN THE GUIDANCE CONSENSUS. THEN INTO
EARLY NEXT WEEK, THE SOUTHWEST UPPER LOW SHOULD SHIFT EAST AND THEN
NORTHEAST AS THE WORKWEEK BEGINS, WHILE A SURFACE LOW CONSOLIDATES
AND DEEPENS. ONCE AGAIN THE 12Z GFS WAS SLOWER WITH THIS UPPER
LOW, AND THERE IS A FAIR AMOUNT OF MODEL SPREAD WITH THE EXACT
POSITION AND DEPTH OF THE SURFACE LOW, INCLUDING IN THE 00Z MODELS,
SO THIS WILL CONTINUE TO BE REFINED.
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC
GUIDANCE USING THE 12Z ECMWF, 18Z GFS, 12Z CMC, AND 12Z UKMET FROM
MOST TO LEAST AT THE BEGINNING OF THE PERIOD. SINCE THE LARGE SCALE
PATTERN WAS REASONABLY AGREEABLE, MAINTAINED A MAJORITY OF
DETERMINISTIC MODELS THROUGH THE PERIOD WHILE BLENDING IN SOME
ENSEMBLE MEANS TO TEMPER THE MODEL DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
LATER THIS WEEK, STRONG UPPER-LEVEL ENERGY WILL PROVIDE SUPPORT
FOR MODERATE TO HEAVY PRECIPITATION ACROSS PARTS OF THE WEST,
STRETCHING FROM THE NORTHERN/CENTRAL ROCKIES AND HIGH PLAINS ACROSS
THE INTERMOUNTAIN WEST INTO THE SIERRA NEVADA. WITH THE COLD
TROUGH ALOFT, ACCUMULATING SNOW IN HIGHER ELEVATIONS IS LIKELY. THE
HEAVIEST SNOW EXPECTED IN THE HIGHER ELEVATIONS OF WYOMING AND
SOUTHERN MONTANA WHILE SOME SNOW IS LIKELY IN THE WASATCH AND
SIERRA. SOME PRECIPITATION IS FORECAST TO CONTINUE IN THE FOUR
CORNERS STATES INTO THE WEEKEND, WITH POSSIBLY MULTIPLE DAYS OF
SNOW IN THE COLORADO ROCKIES.
FARTHER EAST, THE NORTHERN STREAM UPPER TROUGH AND A SURFACE LOW
PRESSURE SYSTEM WILL TRAVERSE THE NORTH-CENTRAL PLAINS AND MIDWEST
ON THURSDAY, SUPPORTING SHOWER AND THUNDERSTORM CHANCES. THE STORM
PREDICTION CENTER INDICATES A SEVERE THREAT IN PARTS OF THESE
AREAS. LOCALLY HEAVY RAIN RATES MAY BE POSSIBLE IN THUNDERSTORMS,
BUT STORMS SHOULD BE MOVING QUICKLY WITH THE PROGRESSIVE LOW
PRESSURE SYSTEM, LIMITING FLOODING CONCERNS. THERE IS ALSO A FAIR
AMOUNT OF UNCERTAINTY IN THUNDERSTORM PLACEMENT. THUS THERE MAY BE
A NONZERO FLASH FLOODING RISK BUT LIKELY LESS THAN THE 5 PERCENT
REQUIRED FOR ANY MARGINAL RISK IN THE EXCESSIVE RAINFALL OUTLOOK.
THEN ON FRIDAY, RAIN/THUNDERSTORM CHANCES WILL CONTINUE EAST INTO
THE GREAT LAKES REGION AND UPPER OHIO VALLEY. ONCE AGAIN THERE MAY
BE SOME LOCALLY HEAVY RAIN. INDIVIDUAL THUNDERSTORMS SHOULD MOVE
QUICKLY BUT THERE MAY BE REPEATED ROUNDS MOVING WEST TO EAST
SOMEWHERE IN THE VICINITY OF LOWER MICHIGAN AND/OR INDIANA/OHIO.
WITH ANTECEDENT DRY CONDITIONS AND UNCERTAINTY WITH THE AXIS OF
POTENTIAL HEAVY RAIN, WILL INDICATE A LESS THAN 5 PERCENT RISK IN
THE ERO, BUT WILL CONTINUE TO MONITOR FLOODING POTENTIAL. FARTHER
SOUTH, THE TAIL END OF THE FRONTAL SYSTEM IN THE SOUTHERN PLAINS
SHOULD HELP TO FOCUS MOISTURE ADVECTION AHEAD OF THE SOUTHWEST
UPPER LOW. SOME RAIN AND STORMS BECOME LIKELY BY FRIDAY EVENING OR
NIGHT OVER PARTS OF TEXAS AND OKLAHOMA, WITH SOME LIKELY LESSER
AMOUNTS OVER ARKANSAS/MISSOURI. MODELS VARY IN HOW MUCH RAIN COULD
FALL THROUGH FRIDAY NIGHT, THAT IS THROUGH THE DAY 5 ERO PERIOD.
SINCE IT IS THE BEGINNING OF THE HEAVY RAIN EVENT, HAVE NO ERO
AREAS OUTLOOKED THROUGH 12Z SATURDAY, BUT FUTURE FORECASTS WILL
CONTINUE TO ASSESS THE RISK. BY SATURDAY HEAVY RAIN IS LIKELY TO
CONTINUE IN THE SOUTHERN PLAINS, AND THIS SHOULD WARRANT ERO AREAS,
BUT THIS IS BEYOND THE DAY 5 ERO PERIOD. BY SUNDAY AS THE SURFACE
LOW AND FRONTAL SYSTEM SHIFT NORTHEAST, RAIN AND THUNDERSTORMS WILL
SPREAD INTO THE CENTRAL/SOUTHERN PLAINS AND THE MIDDLE/LOWER
MISSISSIPPI VALLEY. HEAVIEST RAINFALL AMOUNTS ARE LIKELY TO BE WEST
OF THE MOST SENSITIVE AREAS OF THE MISSISSIPPI VALLEY AND OHIO
VALLEY FROM RECENT FLOODING. HOWEVER, SOME RAIN ATOP RECENTLY
FLOODED AREAS, AND RUNOFF FROM OTHER AREAS INTO THESE RIVERS, COULD
EXACERBATE ONGOING FLOODING ISSUES IN SOME AREAS. THE FORECAST
DETAILS COULD CHANGE OVER THE NEXT FEW DAYS AND SHOULD BE CLOSELY
MONITORED TO ASSESS ANY POSSIBLE IMPACTS.
INITIAL UPPER RIDGING ACROSS THE PLAINS WILL ALLOW FOR ABOVE
NORMAL TEMPERATURES THERE ON THURSDAY. ABOVE NORMAL HIGHS BY 20-25
DEGREES WILL RAISE HIGHS INTO THE 90S FROM TEXAS TO KANSAS.
MEANWHILE COOLER THAN NORMAL TEMPERATURES, ESPECIALLY FOR HIGHS,
ARE LIKELY TO SPREAD ACROSS THE INTERIOR WEST THURSDAY AND FRIDAY
UNDER THE UPPER TROUGH. WARMER THAN AVERAGE TEMPERATURES ARE
FORECAST TO MODERATE AND SHIFT EAST INTO LATE WEEK AND FOCUS ACROSS
THE SOUTHEASTERN U.S. BY SUNDAY.
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 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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