556
FXUS02 KWBC 151836
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
236 PM 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
THE 00Z/06Z SUITE OF MODEL GUIDANCE REMAINS IN REASONABLY GOOD
AGREEMENT REGARDING THE EVOLUTION OF THE LARGE SCALE PATTERN,
INCLUDING A SLOW-MOVING UPPER TROUGH AND CLOSED LOW OVER THE
INTERMOUNTAIN WEST AND FOUR CORNERS, AND A NORTHERN STREAM
SHORTWAVE/CLOSED LOW NORTH OF THE GREAT LAKES AND THE NORTHEAST
THROUGH THE EARLY PART OF THE WEEKEND. MODEL DIFFERENCES BECOME
MORE APPARENT AND IMPACTFUL BY SUNDAY, HOWEVER, AS THE CLOSED LOW
REVERTS BACK TO AN OPEN WAVE BEFORE EJECTING EASTWARD INTO THE
PLAINS. ASIDE FROM THE 00Z CMC, WHICH REMAINED QUITE FAST AND MORE
NEGATIVELY TILTED, THE 00Z ECMWF, 06Z GFS, AND 00Z UKMET WERE ALL
IN A SIMILAR CLUSTER OF KEEPING THE WAVE SLOWER AND FARTHER SOUTH
ACROSS SOUTHERN NEW MEXICO AND FAR WESTERN TEXAS. OTHER THAN THE
GENERALLY MINOR DIFFERENCES IN TIMING/STRENGTH TYPICALLY SEEN AT
THESE EXTENDED RANGES, THE 500 MB AND SURFACE EVOLUTIONS THROUGH
THE REMAINDER OF THE PERIOD WERE HANDLED ROUGHLY THE SAME OVERALL
BY THE DETERMINISTIC GUIDANCE, WITH THE WAVE AND FRONTAL SYSTEM
CONSOLIDATING AND GAINING LATITUDE FROM THE SOUTHERN PLAINS TO THE
UPPER MIDWEST. MORE DRASTIC CHANGES WERE SEEN WITH SOME OF THE NEW
12Z GUIDANCE, ESPECIALLY THE 12Z GFS AND 12Z ECMWF, WHICH WERE BOTH
MUCH FASTER AND FARTHER NORTH COMPARED TO THEIR EARLIER RUNS. THE
12Z CMC ON THE OTHER HAND WAS SLOWER AND FARTHER SOUTH, WHILE THE
12Z UKMET WAS SIMILAR TO 00Z ALBEIT SLIGHTLY FARTHER NORTH. GIVEN
THE ABOVE, IT'S CLEAR THAT THE SYNOPTIC FEATURES IN PLAY STILL
REMAIN QUITE SENSITIVE TO EVEN SMALL CHANGES FROM RUN-TO-RUN, WHICH
THUS LEADS TO LOWER THAN AVERAGE CONFIDENCE OVERALL FOR DAYS 5-7.
LATER IN THE PERIOD, ANOTHER TROUGH IS EXPECTED TO DIG SOUTHWARD
ACROSS THE PACIFIC NORTHWEST, WITH THE 12Z CMC AND 12Z UKMET MORE
AGGRESSIVE COMPARED TO THEIR PREVIOUS RUNS AND THE NEW 12Z GFS AND 12Z
ECMWF (THE LATTER WHICH WAS MORE AGGRESSIVE AT 00Z). A GENERAL
BLEND DEPICTED BROAD TROUGHING FOR DAYS 6 AND 7, WHICH IS A FAIR
COMPROMISE FOR NOW.
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC
GUIDANCE USING THE 00Z ECMWF, 06Z GFS AND TO A LESSER DEGREE THE
00Z UKMET AND 00Z CMC. GRADUALLY INCLUDED SOME ENSEMBLE MEAN
GUIDANCE AND INCREASED THE MEANS TO HALF BY THE END OF THE PERIOD
TO TEMPER THE INDIVIDUAL MODEL DIFFERENCES. OVERALL, THIS RESULTED
IN A SLIGHTLY SLOWER AND FARTHER SOUTH TREND IN THE PROGS COMPARED
TO CONTINUITY.
..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. MAINTAINED A MARGINAL RISK FOR 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 REMAINS 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.
MILLER/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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