001
FXUS02 KWBC 011848
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 PM EDT WED MAY 1 2024
VALID 12Z SAT MAY 04 2024 - 12Z WED MAY 08 2024
...RENEWED HEAVY RAIN THREAT IN THE SOUTH-CENTRAL U.S. THIS
WEEKEND...
..OVERVIEW
AN UPPER LOW THAT IS STRONG FOR THIS TIME OF YEAR IS FORECAST TO
MOVE INTO THE WEST THIS WEEKEND AND TRACK EAST INTO THE PLAINS AS
NEXT WEEK PROGRESSES. THIS WILL SUPPORT COOLER THAN NORMAL
TEMPERATURES, GUSTY WINDS, AND PRECIPITATION INCLUDING HIGHER
ELEVATION SNOW IN THE WEST. AHEAD OF THIS, A SUBTROPICAL JET COMING
INTO THE SOUTH-CENTRAL U.S. AND THE WESTERN SIDE OF A FRONT
STALLING WILL LEAD TO RAIN AND THUNDERSTORMS IN THE SOUTHERN HALF
OF THE PLAINS AND MISSISSIPPI VALLEY THIS WEEKEND, POTENTIALLY IN
SOME AREAS THAT HAVE RECEIVED AMPLE RAINFALL RECENTLY AND/OR WILL
DURING THE SHORT RANGE PERIOD. RAIN AND STORMS ARE ALSO POSSIBLE
FARTHER EAST AND TO THE NORTH/WEST ASSOCIATED WITH A STRONG LOW
PRESSURE SYSTEM ACROSS THE NORTHERN U.S.. THEN MEAN UPPER RIDGING
DOWNSTREAM WILL LEAD TO WARMING TEMPERATURES IN MUCH OF THE CENTRAL
AND EASTERN U.S. INTO NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MAIN FEATURE OF CONCERN DURING THE PERIOD WILL BE WITH THE UPPER
LOW THAT DROPS THROUGH THE EAST PACIFIC AND ENTERS THE WEST THIS
WEEKEND, SHIFTING EAST AND NORTHWARD AS IT STRENGTHENS AGAIN OVER
THE NORTHERN PLAINS EARLY NEXT WEEK. COMPARED TO RECENT RUNS,
MODELS HAVE TRENDED MORE AGREEABLE IN TERMS OF TRACK AND STRENGTH
WITH THIS SYSTEM, ALL SUGGESTING A REASONABLY DEEP UPPER AND
SURFACE LOW EARLY NEXT WEEK OVER THE NORTHERN PLAINS. MODELS ALSO
TRENDED TOWARDS HEAVIER QPF ACROSS THE NORTHERN HIGH PLAINS REGION
AS WELL AND THAT IS REFLECTED IN TODAYS ISSUANCE OF THE WPC QPF. A
GENERAL MODEL COMPROMISE BETWEEN THE GFS, ECMWF, CMC, AND UKMET
WORKED WELL FOR THE SATURDAY-MONDAY PERIOD.
BY TUESDAY AND WEDNESDAY, THERE IS GREATER UNCERTAINTY IN THE
EXACT TRACK OF THE LOW, DEPENDING ON BLOCKY DOWNSTREAM RIDGING
ACROSS THE EAST. LATEST 12Z GUIDANCE TODAY IS TRENDING BLOCKIER,
FORCING THE UPPER LOW MORE NORTHWARD THAN PREVIOUS GUIDANCE WHICH
BROUGHT IT MORE EASTWARD INTO THE UPPER MIDWEST/GREAT LAKES.
ADDITIONALLY, UPSTREAM, ANOTHER ROUND OF ENERGY AND TROUGHING MAY
DIVE THROUGH THE PACIFIC MONDAY-WEDNESDAY AND WHETHER ENERGY MAKES
IT FAR ENOUGH SOUTH TO IMPACT THE NORTHWEST U.S.. THE CANADIAN
MODEL (ESPECIALLY THE NEW 12Z RUN) CONTINUES TO BE MOST
AGGRESSIVE/SOUTH WITH THIS ENERGY COMPARED TO THE GFS/ECMWF. THE
TUESDAY-WEDNESDAY BLEND FOR NEXT WEEK TRENDED TOWARDS THE ENSEMBLE
MEANS ALONG WITH SMALLER CONTRIBUTIONS FROM THE GFS/ECMWF AMIDST
GROWING FORECAST UNCERTAINTY IN THE LATE PERIODS. OVERALL,
MAINTAINED REASONABLE CONTINUITY WITH THE PREVIOUS WPC SHIFT
BESIDES A MUCH STRONGER NORTHERN PLAINS SURFACE LOW.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE UPPER LOW TRACKS INTO AND THROUGH THE WEST, WIDESPREAD
PRECIPITATION IS LIKELY. MOISTURE STREAMING PERPENDICULAR INTO THE
FOOTHILLS OF THE SIERRA NEVADA COULD CAUSE A HEAVY RAIN AND
FLOODING THREAT THERE, AND A MARGINAL RISK REMAINS IN PLACE FOR DAY
4/SATURDAY. MEANWHILE THE HIGHER ELEVATIONS OF THE SIERRA, NORTH
INTO THE CASCADES, AND EAST INTO THE INTERMOUNTAIN WEST/ROCKIES
WILL SEE SOME MAY SNOW. PRECIPITATION IS FORECAST TO MOVE STEADILY
EASTWARD THROUGH THE WEEKEND INTO EARLY NEXT WEEK, REACHING THE
NORTHERN PLAINS TO MIDWEST MONDAY AND TUESDAY. RAINFALL ON THE WEST
SIDE OF THE STRONG SURFACE LOW COULD BE HEAVY ACROSS EASTERN
MONTANA INTO THE DAKOTAS. THE TROUGH/LOW ALOFT AND FRONTAL
BOUNDARIES COULD ALSO PRODUCE SOME HIGH WINDS ACROSS THE GREAT
BASIN TO ROCKIES.
MEANWHILE THIS WEEKEND, THE SUBTROPICAL JET LOOKS TO BE ACTIVE
COMING INTO THE SOUTH-CENTRAL U.S., FOCUSING CONVECTION IN A MOIST
AND UNSTABLE ENVIRONMENT. MANY AREAS IN THE SOUTH-CENTRAL U.S. WILL
HAVE QUITE SATURATED ANTECEDENT CONDITIONS BECAUSE OF RECENT AND
UPCOMING SHORT RANGE EVENTS, SO THIS WILL BE A FACTOR FOR FLOODING
AS WELL. ON SATURDAY AND SUNDAY, MARGINAL RISKS ARE DELINEATED IN
THE ERO ACROSS SOUTHERN/CENTRAL PORTIONS OF THE PLAINS AND
MISSISSIPPI VALLEY. WILL ALSO MAINTAIN AN EMBEDDED SLIGHT RISK ON
DAY 4/SATURDAY FOR PORTIONS OF SOUTHWEST OKLAHOMA AND INTO PORTIONS
OF NORTHWEST TEXAS WHERE POTENTIAL EXISTS FOR AN MCS WITH HEAVIER
RAINFALL RATES, THOUGH THE POSITION VARIES SOMEWHAT BETWEEN MODELS.
FARTHER EAST ON SATURDAY, AN AXIS OF INSTABILITY IS FORECAST
ACROSS THE SOUTHERN/CENTRAL APPALACHIANS AND INTO THE PIEDMONT
BETWEEN THE SYNOPTIC COLD FRONT AND BACKDOOR FRONT IN THE EAST AS A
SHORTWAVE ALOFT MOVES THROUGH. THESE INGREDIENTS COULD PRODUCE
HEAVY RAINFALL AND A MARGINAL RISK IS IN PLACE THERE FOR DAY 4 AS
WELL. SHOWERS AND THUNDERSTORMS SHOULD CONTINUE FOR PARTS OF THE
EASTERN U.S. ON SUNDAY.
FOR THE WEEKEND, PORTIONS OF THE EAST-CENTRAL U.S. ARE FORECAST TO
SEE ABOVE AVERAGE TEMPERATURES, BUT THE NORTHEAST AND MID-ATLANTIC
COULD BE COOLER THAN AVERAGE AT LEAST FOR HIGHS DUE TO A BACKDOOR
FRONT. TEMPERATURES THIS WEEKEND SHOULD WARM IN THE INTERMOUNTAIN
WEST TO NORTHERN PLAINS AHEAD OF THE WEST UPPER LOW, WHILE COOLER
THAN NORMAL TEMPERATURES BY 10-20 DEGREES FOR HIGHS WILL IMPACT THE
WEST. AS THE UPPER LOW/TROUGH SHIFTS EAST, THIS SHOULD COOL DOWN
TEMPERATURES TOWARD THE NORTH-CENTRAL U.S. WHILE STAYING BELOW
AVERAGE IN THE NORTHWEST. ON THE OTHER HAND, MEAN UPPER RIDGING
WILL CAUSE WARM TEMPERATURES TO SPREAD ACROSS THE SOUTH-CENTRAL AND
EAST-CENTRAL U.S. INTO THE EASTERN SEABOARD. 90S ARE FORECAST TO
BECOME MORE WIDESPREAD ACROSS THE SOUTHERN TIER, WITH TEMPERATURES
OVER 100F (AND EVEN HIGHER HEAT INDICES) INTO SOUTHWEST TEXAS AND
POSSIBILITY FOR THE FIRST EXCESSIVE HEAT DAYS OF THE YEAR.
SANTORELLI/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page