726
FXUS02 KWBC 150659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT TUE APR 15 2025
VALID 12Z FRI APR 18 2025 - 12Z TUE APR 22 2025
...HEAVY RAINFALL AND FLOODING POSSIBLE IN PARTS OF THE CENTRAL
U.S. BY THE WEEKEND...
..OVERVIEW
A POTENT UPPER TROUGH DEVELOPING AN EMBEDDED UPPER LOW WILL BE IN
PLACE OVER THE INTERIOR WEST FRIDAY AND PIVOT EAST OVER THE
WEEKEND. COOLER TEMPERATURES AND INCREASED PRECIPITATION CHANCES
ARE FORECAST WITH THIS DEVELOPING LOW, INCLUDING SNOW IN THE
CENTRAL ROCKIES INTO FRIDAY AND SATURDAY. MEANWHILE A NORTHERN
STREAM UPPER TROUGH WILL ADVANCE THROUGH THE MIDWEST TO NORTHEAST
LATE WEEK, ALONG WITH A SURFACE LOW AND AN ELONGATED FRONT THAT IS
FORECAST TO STRETCH 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
INTERACTING WITH FRONTAL SYSTEMS ATOP THE SOUTH-CENTRAL U.S. WILL
LEAD TO SOME HEAVY RAINFALL AND FLOODING POTENTIAL THERE, BEGINNING
FRIDAY BUT WITH RISING POTENTIAL OVER THE WEEKEND. FARTHER EAST,
WARM UPPER RIDGING WILL TAKE HOLD OVER THE SOUTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE BEGINS IN GOOD AGREEMENT WITH THE OVERALL PATTERN
AS UPPER TROUGHING IN THE WEST CLOSES OFF AN UPPER LOW OVER THE
GREAT BASIN AND FOUR CORNERS WHILE UPPER RIDGING DOMINATES OVER THE
EAST, OTHER THAN A TROUGH POKING INTO THE NORTHERN TIER. SOME
IMPACTFUL MODEL DIFFERENCES START TO ARISE BY AROUND SUNDAY AS THE
UPPER LOW PIVOTS EAST. MODELS VARY WITH THE TIMING OF THE LOW'S
EJECTION AND THE UPPER TROUGH POSSIBLY BECOMING NEGATIVELY TILTED.
THE 12Z/18Z GFS AND 12Z ECMWF AND CMC WERE REASONABLY AGREEABLE
WITH A SOMEWHAT FAST TRACK OF THE UPPER LOW MOVING EAST AND THEN
NORTHEAST, ALONG WITH ITS SURFACE LOW AND QPF. MEANWHILE THE 18Z
AIFS WAS SLOWER TO TILT AND MOVE THE UPPER AND SURFACE LOWS
NORTHEAST. OTHER AI MODELS WERE IN BETWEEN, AND ENSEMBLE MEMBERS
SHOWED SOME TIMING SPREAD, SO THE GOOD AGREEMENT OF THE
DETERMINISTIC MODELS WAS A LITTLE SUSPICIOUS. THE NEWER 00Z ECMWF
AND ESPECIALLY THE 00Z GFS ARE SOMEWHAT FARTHER SOUTH AND SLOWER
THAN THEIR PREVIOUS RUNS, THOUGH THE 00Z CMC IS FAST. THE AIFS,
WHICH WAS ALREADY PARTICULARLY SLOW, NOW SHOWS AN EVEN SLOWER TRACK
IN ITS 00Z RUN. WHILE THESE MODEL DIFFERENCES ARE NOT THE MOST
STARK, THEY DO CAUSE SOME NOTABLE SENSIBLE WEATHER CONCERNS LIKE
SURFACE LOW AND QPF PLACEMENT. SO THE DETAILS WILL CONTINUE TO BE
REFINED IN FUTURE FORECASTS, INCLUDING A POTENTIALLY SLOWER TREND
OF THE SURFACE LOW AND FRONTAL SYSTEM. DID THINK THE NEW 00Z GFS
WAS A SLOW OUTLIER WITH MOVING THE FEATURE NORTHEAST INTO THE GREAT
LAKES OR SO EARLY NEXT WEEK.
UPSTREAM, ANOTHER TROUGH THAT IS NOT AS DEEP LOOKS TO MOVE INTO
THE NORTHWEST EARLY NEXT WEEK. THE 12Z ECMWF SEEMED TO BE A LITTLE
ON THE AGGRESSIVE SIDE WITH THE DEPTH OF THE TROUGH (AND SHOWING AN
EMBEDDED UPPER LOW) COMPARED TO THE OTHER DYNAMICAL AND AI MODELS,
BUT COULD STILL BE USED AS PART OF A BLEND.
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. GRADUALLY INCLUDED
SOME ENSEMBLE MEAN GUIDANCE AND INCREASED THE MEANS TO HALF BY THE
END OF THE PERIOD TO TEMPER THE INDIVIDUAL MODEL DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
PRECIPITATION IS LIKELY ACROSS THE FOUR CORNERS STATES AND NEARBY
ON FRIDAY-SATURDAY, WITH SUPPORT FROM THE TROUGH/LOW ALOFT. SOME
SNOW IS POSSIBLE IN THE WASATCH AND THE MOGOLLON RIM ON FRIDAY
BEFORE THE TROUGH MOVES EAST, AND THE CENTRAL ROCKIES COULD SEE
SNOW PILE UP BOTH FRIDAY AND SATURDAY. THEN ANOTHER TROUGH PUSHING
INTO THE NORTHWEST BY EARLY NEXT WEEK COULD SPREAD SOME MODEST RAIN
AND HIGHER ELEVATION SNOW PARTICULARLY TO THE NORTHERN
ROCKIES/HIGH PLAINS.
FARTHER EAST, A SURFACE LOW PRESSURE SYSTEM WILL TRAVERSE THE
MIDWEST/GREAT LAKES ON FRIDAY, SUPPORTING SHOWER AND THUNDERSTORM
ACTIVITY IN THAT AREA AND SOUTHWEST ALONG THE TRAILING FRONT. THE
STORM PREDICTION CENTER INDICATES A SEVERE THREAT FROM THE UPPER
OHIO VALLEY THROUGH THE MID-MISSISSIPPI VALLEY AND SOUTHERN PLAINS.
THERE MAY BE SOME LOCALLY HEAVY RAIN ON FRIDAY AND FRIDAY NIGHT
WITH THIS CONVECTION. THERE MAY BE SOME FLOODING CONCERNS FROM THE
SOUTH-CENTRAL PLAINS INTO THE MID-MISSISSIPPI VALLEY, WHERE STORMS
MAY TRAIN BY FRIDAY NIGHT AS THE FRONT STARTS TO BECOME MORE WEST-
EAST ORIENTED. HAVE ADDED A MARGINAL RISK TO THE DAY 4/FRIDAY ERO
FOR THIS POTENTIAL. BY SATURDAY, THE SLOW PIVOT OF THE UPPER LOW,
THE CONSOLIDATING FRONTAL SYSTEM, AND PRECIPITABLE WATER ANOMALIES
OVER THE 90TH PERCENTILE ARE LIKELY TO CAUSE WIDESPREAD HEAVY RAIN
OF 3+ INCHES, WITH LOCALLY HIGHER AMOUNTS. A SLIGHT RISK OF
EXCESSIVE RAINFALL STRETCHES FROM NORTH-CENTRAL TEXAS ACROSS
OKLAHOMA AND INTO SOUTHWESTERN MISSOURI (CLIPPING SOUTHEAST KANSAS
AND NORTHWEST ARKANSAS) FOR DAY 5/SATURDAY. A BROADER MARGINAL RISK
SURROUNDS THE SLIGHT AND IS DRAWN ACROSS MUCH OF THE OHIO RIVER
WHERE STREAMFLOWS REMAIN HIGH. BY SUNDAY THERE IS SOME MODEL SPREAD
IN THE TIMING AND PLACEMENT OF THE UPPER AND SURFACE LOWS AND THUS
WHERE RAINFALL WILL FOCUS, BUT BROADLY RAIN AND THUNDERSTORMS
CHANCES ARE LIKELY FROM THE SOUTHERN AND CENTRAL PLAINS INTO MUCH
OF THE MISSISSIPPI VALLEY. THE HEAVIEST RAINFALL IS 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, SO CONTINUE TO
MONITOR. RAIN CHANCES SPREAD FARTHER EAST BY MONDAY.
LATE THIS WEEK, TEMPERATURES WILL BE BELOW AVERAGE ESPECIALLY IN
TERMS OF HIGHS IN THE INTERIOR WEST UNDERNEATH THE UPPER TROUGH.
THESE SHOULD MODERATE TOWARD NORMAL BY EARLY NEXT WEEK, THOUGH
TEMPERATURES IN THE NORTHWEST MAY END UP BELOW NORMAL BY A FEW
DEGREES. MEANWHILE FARTHER EAST, ABOVE AVERAGE TEMPERATURES BY 10
TO 20 DEGREES ARE LIKELY FROM THE SOUTHERN PLAINS INTO MUCH OF THE
EASTERN HALF OF THE U.S. ON FRIDAY. THE PRIMARY COLD FRONT WILL
PUSH ABOVE NORMAL TEMPERATURES TOWARD THE NORTHEAST/MID-ATLANTIC ON
SATURDAY BUT REMAINING OVER THE SOUTHEAST AS AN UPPER RIDGE SETS
UP. THE SOUTHEAST SHOULD REMAIN WARM INTO EARLY NEXT WEEK, WITH
EXPANSIONS OF ABOVE AVERAGE TEMPERATURES NORTHWARD AT TIMES.
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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