698
FXUS02 KWBC 121837
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
237 PM EDT WED MAR 12 2025
VALID 12Z SAT MAR 15 2025 - 12Z WED MAR 19 2025
...HEAVY RAIN/FLOODING AND SEVERE WEATHER POSSIBLE FOR THE
OHIO/TENNESSEE VALLEYS TO EAST COAST THIS WEEKEND...
...WIDESPREAD HIGH WINDS CAUSE FIRE DANGER IN THE SOUTHERN PLAINS
AND LOCALIZED BLIZZARD CONDITIONS IN THE NORTH-CENTRAL U.S. INTO
SATURDAY...
..MULTIPLE ROUNDS OF PRECIPITATION LIKELY IN THE WEST
..OVERVIEW
THE FIRST WEATHER FEATURE OF CONCERN THIS WEEKEND WILL BE AN UPPER
LOW SUPPORTING A STRONG SURFACE LOW IN THE UPPER MIDWEST WITH
POTENT COLD FRONTS TO ITS SOUTH AS THE PERIOD BEGINS SATURDAY.
HAZARDS ASSOCIATED WITH THE SURFACE LOW PRESSURE SYSTEM WILL
INCLUDE HEAVY RAIN AND SEVERE THUNDERSTORMS IN THE SOUTHEAST AND
TENNESSEE/OHIO VALLEYS SATURDAY AND MOVING INTO THE EASTERN
SEABOARD SUNDAY. SNOW IS POSSIBLE ON THE BACKSIDE OF THE LOW IN THE
NORTHERN PLAINS INTO THE UPPER MIDWEST SATURDAY. MEANWHILE AREAS
OF STRONG WINDS ARE LIKELY, WHICH COULD CAUSE LOCALIZED BLIZZARD
CONDITIONS WHERE IT SNOWS, AS WELL AS FIRE DANGER PARTICULARLY IN
THE SOUTHERN PLAINS. WARMER THAN NORMAL TEMPERATURES WILL BE COMMON
AHEAD OF THE LOW AND ITS COLD FRONTS, WITH COOLER TEMPERATURES
BEHIND, BUT REBOUNDING INTO NEXT WEEK. BEHIND THAT LOW, ANOTHER
UPPER TROUGH IS FORECAST TO MOVE INTO THE WEST THIS WEEKEND AND
EARLY NEXT WEEK AND SPREAD ADDITIONAL PRECIPITATION THERE, WITH
POSSIBLY HEAVY RAIN AND SNOW.
..GUIDANCE/PREDICTABILITY ASSESSMENT
DETERMINISTIC GUIDANCE IS IN GENERALLY GOOD AGREEMENT WITH THE
PROGRESSION OF AN INITIAL UPPER-WAVE, NOW CLOSED LOW, WITHIN BROAD-
SCALE TROUGHING OVER THE CENTRAL U.S. WHICH WILL BE RESPONSIBLE FOR
THE ACTIVE WEATHER TO END THE WORK WEEK AND LAST INTO THE WEEKEND.
THE UPPER-LOW WILL LIFT NORTHEASTWARD OVER THE GREAT LAKES AND
INTO SOUTHEASTERN CANADA WHILE ADDITIONAL SOUTHERN STREAM ENERGY
SPREADS OVER THE SOUTH-CENTRAL U.S. GUIDANCE IS ALSO IN GOOD
AGREEMENT THAT THE MAIN UPPER-TROUGH WILL CONTINUE TO MOVE SLOWLY
EASTWARD FROM THE CENTRAL TO EASTERN U.S. THROUGH THE WEEKEND.
HOWEVER, THE SURFACE REFLECTION WITH RESPECT TO THE ADDITIONAL
SOUTHERN STREAM ENERGY LIFTING NORTHWARD TOWARDS THE MIDWEST DOES
DIFFER BETWEEN THE GUIDANCE, WITH THE MOST RECENT RUNS OF THE
00/06Z GFS TRENDING TOWARDS THE 00Z UKMET IN SHOWING A MUCH
STRONGER SECONDARY LOW LIFTING NORTHEASTWARD THROUGH THE GREAT
LAKES COMPARED TO THE 00Z ECMWF AND CMC. BOTH THE 00Z ICON AND THE
SUITE OF AI GUIDANCE SUPPORT A WEAKER SECONDARY SURFACE LOW. TO THE
WEST, THE GUIDANCE IS IN BETTER AGREEMENT WITH THE TIMING AND
GENERAL PLACEMENT WITH AN UPPER-LEVEL TROUGH AND ACCOMPANYING
PACIFIC STORM SYSTEM/POTENTIAL AR MOVING INTO THE PACIFIC NORTHWEST
THIS WEEKEND.
TYPICAL INCREASES IN GUIDANCE SPREAD FOLLOW HEADING INTO NEXT WEEK
WITH THE PROGRESSION OF THE WESTERN U.S. TROUGH AS IT MOVES
EASTWARD TOWARDS THE CENTRAL U.S. THE GFS HAS BEEN TRENDING FASTER
WHILE THE CMC AND THEN ECMWF ARE SLOWER. THE SUITE OF AI GUIDANCE
FROM THE EC SHOW SOME VARIANCE IN SOLUTIONS, THOUGH MOST ACTUALLY
FAVOR A FASTER PROGRESSION. HOWEVER, THE ICON MODEL FAVORS A SLOWER
PROGRESSION DESPITE SOME POTENTIAL FASTER LEAD SHORTWAVE ENERGY.
THE ENSEMBLE MEANS TEND TO FOLLOW THEIR DETERMINISTIC COUNTERPARTS,
THOUGH WITH LESS VARIANCE. CONTINUITY WITH THE PRIOR WPC FORECAST
WITH RESPECT TO BOTH THE UPPER-TROUGH AND SURFACE LOW REFLECTION
WOULD FAVOR A FASTER SOLUTION, ALBEIT NOT QUITE AS FAST AS THE
LATEST 00/06Z GFS, BUT MORE SIMILAR TO THE 00Z GEFS MEAN WHICH
PROVIDES A MORE FAVORED PROGRESSIVE COMPROMISE. THE NEW 12Z GFS, AS
WELL AS 12Z CMC, CONTINUED TO FAVOR A FASTER PROGRESSION.
THE UPDATED WPC FORECAST FEATURED A MULTI-MODEL BLEND OF THE
GFS/ECMWF/CMC FOR THE FIRST HALF OF THE PERIOD GIVEN NOTED GOOD
OVERALL AGREEMENT. THE UKMET WAS NOT INCLUDED GIVEN THE MORE
INTENSE SECONDARY LOW OVER THE GREAT LAKES, AND THE INCLUSION OF
THE GFS ALREADY ACCOUNTED FOR THIS POTENTIAL. THEN, FOR THE LATTER
HALF, THE BLEND FOCUSED ON A BALANCE OF THE GFS/CMC AND GEFS/CMC
ENSEMBLE MEANS, AND A SMALLER CONTRIBUTION FROM THE ECENS MEAN, TO
FOLLOW MORE CLOSELY THE OVERALL FAVORED FASTER PROGRESSION OF THE
WESTERN TO CENTRAL U.S. TROUGH.
..WEATHER/HAZARDS HIGHLIGHTS
THE STRONG LOW PRESSURE SYSTEM IN THE MIDWEST SATURDAY ALONG WITH
ITS TRAILING COLD FRONTS COULD CAUSE SEVERAL WEATHER HAZARDS. AHEAD
OF THE COLD FRONTS, AMPLE MOISTURE AND INSTABILITY WILL BE IN
PLACE ALONG WITH GOOD DYNAMICS FOR LIFT, CAUSING WIDESPREAD
THUNDERSTORMS IN THE EAST-CENTRAL U.S. SATURDAY. SEVERE WEATHER IS
LIKELY PER SPC. RAINFALL TOTALS COULD BE SUBSTANTIAL AS HIGH RAIN
RATES LIKELY AT LEAST 1-2 INCHES PER HOUR COULD BE COMMON IN THE
TENNESSEE VALLEY AND INTO THE SOUTHERN APPALACHIANS. A SLIGHT RISK
REMAINS IN PLACE FOR DAY 4/SATURDAY IN THE ERO, WITH A LARGER
MARGINAL FROM THE OHIO VALLEY TO CENTRAL GULF COAST. THIS IS
CONSIDERED A HIGHER END SLIGHT RISK, AND A MODERATE RISK MAY BE
NEEDED IN FUTURE ISSUANCES ESPECIALLY ONCE THE HI-RES MODELS COVER
THE SYSTEM AND GIVE A BETTER IDEA OF RAINFALL RATES AND PLACEMENT
OF HEAVIEST AMOUNTS. MEANWHILE ON SATURDAY, SNOW MAY WRAP AROUND
THE SURFACE LOW FOCUSED IN WESTERN MINNESOTA AND THE EASTERN
DAKOTAS. WIDESPREAD HIGH WINDS IN THE CENTRAL U.S. ARE ANOTHER
POTENTIAL HAZARD WITH THE LOW. IN NORTHERN AREAS, LOCATIONS THAT
RECEIVE SNOW COULD EXPERIENCE BLIZZARD CONDITIONS INTO SATURDAY
GIVEN THE STRONG WINDS. MEANWHILE FARTHER SOUTH, HIGH WINDS IN THE
SOUTHERN ROCKIES AND SOUTHERN PLAINS WILL CAUSE FIRE WEATHER
CONCERNS.
AS THE PRIMARY COLD FRONT PROGRESSES EASTWARD ON SUNDAY,
WIDESPREAD CONVECTION IS POSSIBLE ACROSS THE EAST. SEVERE
THUNDERSTORMS ARE POSSIBLE FROM THE MID-ATLANTIC TO CAROLINAS AND
SOUTHEAST. LOCALLY HEAVY RAINFALL IS ALSO POSSIBLE. THE DAY
5/SUNDAY ERO MAINTAINS A MARGINAL RISK STRETCHING ACROSS MUCH OF
THE EASTERN SEABOARD. THERE IS SOME UNCERTAINTY IN HOW QUICKLY THE
COLD FRONT MOVES EASTWARD INTO THE ATLANTIC OFF THE SOUTHEAST
COAST, BUT HEAVY RAIN WITH HIGH RATES IS LIKELY AHEAD OF IT.
MEANWHILE FARTHER NORTH IN THE NORTHERN MID-ATLANTIC AND NORTHEAST,
MOISTURE ANOMALIES ARE GENERALLY OVER THE 95TH PERCENTILE AND SOME
MODEST INSTABILITY IS IN PLACE, SO RAIN RATES FOR THE REGION COULD
BE LOCALLY HEAVY. ALL THIS PROVIDES CONTINUED SUPPORT FOR A
MARGINAL RISK BUT FUTURE ADJUSTMENTS CERTAINLY COULD BE NECESSARY.
RAIN AND STORMS MAY CONTINUE INTO MONDAY FOR COASTAL AREAS BEFORE
MOVING AWAY.
ROUNDS OF PRECIPITATION ARE LIKELY IN THE WEST BY THE WEEKEND WITH
FRONTAL SYSTEMS CHANNELING PACIFIC MOISTURE INLAND. AN ATMOSPHERIC
RIVER OF MODERATE STRENGTH IS FORECAST TO REACH THE WEST COAST
POSSIBLY LATE SATURDAY BUT ESPECIALLY BY SUNDAY, CAUSING CHANCES
FOR HEAVY PRECIPITATION (LOWER ELEVATION RAIN AND HIGHER ELEVATION
SNOW) TO INCREASE FOR OREGON TO NORTHERN CALIFORNIA. WITH THE
MODERATE AR, SOME LOCALIZED RAIN RATES OF OVER AN INCH PER HOUR ARE
LIKELY, AND HAVE A MARGINAL RISK DELINEATED FOR THE DAY 5/SUNDAY
ERO. WILL HAVE TO MONITOR THE TIMING OF THE AR'S ARRIVAL TO SEE IF
SUFFICIENT HEAVY RAIN ENTERS THE COAST BEFORE 12Z SUNDAY, SO DURING
THE DAY 4 ERO PERIOD, TO SHOW A DAY 4 MARGINAL AS WELL. THE AR
CURRENTLY LOOKS TO WEAKEN AS IT PUSHES INTO CENTRAL AND SOUTHERN
CALIFORNIA SUNDAY-MONDAY, HOPEFULLY PRECLUDING TOO MANY FLOODING
ISSUES OVER RECENT BURN SCARS. HEAVY SNOW MAY PILE UP OVER HIGHER
ELEVATIONS OF THE CASCADES, SIERRA NEVADA, AND THE INTERIOR WEST
AND ROCKIES THIS WEEKEND INTO EARLY NEXT WEEK AS PRECIPITATION
CHANCES GRADUALLY SHIFT EAST. UNCERTAINTY REMAINS WITH THE SYSTEM
PROGRESSION EAST OF THE ROCKIES BUT PRECIPITATION CHANCES LOOK TO
RETURN TO THE PLAINS/MIDWEST/SOUTHEAST BY MID-NEXT WEEK WHICH MAY
INCLUDE BOTH AREAS OF RAINFALL AS WELL AS SOME MIXED PRECIPITATION
OR SNOWS NORTHWEST OF THE SYSTEM TRACK FROM THE CENTRAL HIGH PLAINS
TO THE UPPER MIDWEST.
ABOVE NORMAL TEMPERATURES ARE LIKELY ACROSS THE EASTERN THIRD OF
THE U.S. ON SATURDAY, WITH HIGHEST ANOMALIES OF 20-30 DEGREES ABOVE
NORMAL LIKELY IN THE OHIO VALLEY/GREAT LAKES AS SOME LOCATIONS
THERE RISE WELL INTO THE 70S. THE STRONG COLD FRONT GRADUALLY
PUSHING THROUGH THAT AREA AND WARM INFLOW AHEAD OF IT SHOULD PUSH
THESE WARM TEMPERATURES INTO THE MID-ATLANTIC AND NORTHEAST SUNDAY.
WARM MORNING LOWS WILL BE COMMON IN THE EASTERN U.S., WHICH COULD
SET RECORDS FOR WARM MINS--IF THE LOCATIONS DO NOT HAVE THOSE
TEMPERATURES FALL LOWER BEFORE THE CALENDAR DAY AFTER THE COLD
FRONTAL PASSAGE. MILDER THAN AVERAGE TEMPERATURES ARE FORECAST TO
REBUILD IN THE CENTRAL U.S. AND SPREAD INTO THE EAST FOR THE FIRST
HALF OF NEXT WEEK UNDERNEATH UPPER RIDGING. MEANWHILE, PERIODS OF
TROUGHING ACROSS THE WEST WILL PRODUCE BELOW NORMAL TEMPERATURES ON
AVERAGE, WITH HIGHS GENERALLY A BIT MORE BELOW NORMAL GIVEN CLOUDS
AND PRECIPITATION COMPARED TO LOW TEMPERATURES.
PUTNAM/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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