065
FXUS02 KWBC 291904
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 PM EDT MON APR 29 2024
VALID 12Z THU MAY 02 2024 - 12Z MON MAY 06 2024
..OVERVIEW
A HEAVY RAIN AND FLASH FLOODING THREAT PERSISTS OVER THE SOUTHERN
PLAINS THURSDAY NIGHT AS AN ADVANCING TROUGH OVER THE NORTHERN
PLAINS SHIFTS THE HEAVY RAIN FOCUS TO TO THE MIDWEST. THE HEAVY
RAIN RISK THEN SPREADS TO THE GULF COAST AND DEEP SOUTH FRIDAY. THE
NEXT HEAVY BOUT OF HEAVY RAIN OVERSPREADS THE SOUTHERN PLAINS
SATURDAY INTO SUNDAY. LOW PRESSURE MOVES TOWARD OR OVER THE WEST
COAST THIS WEEKEND, THOUGH GREAT UNCERTAINTY ON TRACK/PROGRESSION
PERSISTS ON IF THIS IMPACTS THE NORTHWEST ONLY, OR WILL CALIFORNIA
RECEIVE SIGNIFICANT PRECIPITATION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE EXIT OF LOW PRESSURE FROM THE NORTHERN PLAINS WITH ITS EFFECTS
TO THE NORTHEAST THROUGH THE WEEKEND AND THE CLOSED LOW THAT SWINGS
SOUTHEAST FROM THE ALEUTIANS WEDNESDAY TO A POINT OFF THE PACNW
LATE FRIDAY ARE THE KEY UPPER LEVEL LOW PRESSURE FEATURES FOR DAYS
4-7. THE NORTHWEST LOW HAS THE GREATEST UNCERTAINTY WITH THE 00Z
ECMWF TRACKING A MORE OPEN WAVE EAST OVER THE NORTHERN TIER TO MN
THROUGH MONDAY, WHILE THE 06Z GFS AND 00Z CMC KEPT A MUCH DEEPER
LOW OFF THE COAST, TRACKING SOUTH TO NORTHERN CA BY LATE SATURDAY
WITH REINFORCING TROUGHS KEEPING LONGWAVE TROUGHING OVER THE WEST
INTO THE WEEKEND. THE 00Z UKMET WAS MORE IN BETWEEN WITH THIS
FEATURE WITH A LOW TRACKING INTO THE GREAT BASIN. HOWEVER, THE 00Z
UKMET WAS MUCH DIFFERENT WITH THE CENTRAL U.S. LOW/TROUGH AND WAS
NOT INCLUDED IN THE FORECAST BLEND FROM THIS MORNING.
NOW ONTO 12Z GUIDANCE FOR TODAY, GFS STILL TRACKS THE LOW INTO CA,
REMAINING THE FARTHEST WEST/SLOWEST WITH THIS FEATURE WHILE THE
CMC TOOK A MORE EASTWARD TRACK, NOT DIGGING AS FAR SOUTH OVER THE
WEEKEND. THE UKMET IS A BIT FARTHER WEST/DUG A LITTLE FARTHER SOUTH
BY 00Z SUNDAY (IT STILL ONLY HAS A 5-DAY FORECAST). AND THE 12Z
ECMWF COMING IN IS FARTHER WEST/SLOWER WITH THE LOW AS IT
APPROACHES/MOVES INTO THE NORTHWEST. 12Z GUIDANCE GENERALLY
SUPPORTS THE GFS/CMC SOLUTION OF A MORE CUTOFF/STALLED LOW.
THE MORNING WPC BLEND FAVORED THE 06Z GFS/00Z CMC BY DAY 5 FOR THE
FORECAST PRESSURE/FRONTS AND ESPECIALLY FOR QPF, THOUGH CONTINUITY
WITH THE PREVIOUS FORECAST WAS ACHIEVED WITH THE GEFSMEAN FOR QPF
IN THE PACNW. ALSO FOR QPF, THE LATE SATURDAY INTO SUNDAY SOUTHERN
PLAINS RAINS WHICH WERE CLOSER TO A 06Z GFS/00Z CMC BLEND THAN THE
13Z NBM, PROVIDING FOCUS FOR REPEATING HEAVY RAIN CONCERNS THERE.
THE COVERAGE OF THE PRECIP FOOTPRINT FROM THE CENTRAL THROUGH
EASTERN U.S. THURSDAY NIGHT THROUGH SUNDAY IN THE 00Z ECMWF-AIFS
(AI GUIDANCE TENDS TO FEATURE THE FOOTPRINT OF QPF WELL, THOUGH IT
IS OFTEN WAY LOW FOR MAGNITUDE IN THAT FOOTPRINT) LINED UP WELL
WITH THE 06Z GFS, SO THE 06Z GFS WAS INCORPORATED INTO THE QPF FOR
THAT TIME AND PLACE.
..WEATHER/HAZARDS HIGHLIGHTS
THE DAY 4 (12Z THURSDAY TO 12Z FRIDAY) SLIGHT RISK OVER THE CENTRAL
U.S. WAS TRIMMED A BIT FROM THE WEST GIVEN TIMING CONFIDENCE
INCREASE IN THE GLOBAL CONSENSUS WHILE ALLOWING FOR ONGOING HEAVY
RAIN FROM WEDNESDAY TO BE ACCOUNTED FOR AND AN EXPANSION IN TO THE
CHICAGO AREA GIVEN THE 12Z GFS INCREASE THERE. A FOCUS FOR MORE
SIGNIFICANT IMPACTS REMAINS FROM NORTH TEXAS THROUGH EASTERN
OKLAHOMA AND WESTERN ARKANSAS FOR HEAVY RAIN ON TOP OF WET
ANTECEDENT CONDITIONS. SHOULD THIS TREND CONTINUE, EMBEDDED
UPGRADES WITHIN THE SLIGHT RISK MAY BE NEEDED.
BY FRIDAY, THE COLD FRONT PROGRESSING EAST IN THE NORTHERN TWO-
THIRDS OF THE COUNTRY OR SO WILL SHIFT RAIN CHANCES TO THE GREAT
LAKES AND OHIO/TENNESSEE VALLEYS, AND TOWARD THE APPALACHIANS TO
EASTERN SEABOARD ON SATURDAY. HOWEVER, THE FRONT LINGERS OVER THE
SOUTHERN PLAINS AND PRODUCE ADDITIONAL ROUNDS OF RAIN AND STORMS
THROUGH THE WEEKEND. A DAY 5 (12Z FRIDAY TO 12Z SATURDAY) MARGINAL
RISK IS EXPANDED FROM FAR EAST TEXAS INTO THE DEEP SOUTH BASED ON
THE LATEST QPF CONSENSUS FOR HEAVIER RAINFALL AND (AT LEAST IN
TEXAS) WET ANTECEDENT CONDITIONS.
HIGHER ELEVATION SNOW CAN BE EXPECTED WHEREVER THIS LOW TRACKS
INTO THE WEST THIS WEEKEND. THE EASTERN THIRD OF THE COUNTRY WILL
BE WARMER THAN AVERAGE BY 10-15 DEGREES THROUGH FRIDAY, WITH 80S
PERSISTING OVER THE OHIO VALLEY AND MID-ATLANTIC. MEANWHILE COOLER
THAN AVERAGE TEMPERATURES ARE FORECAST ACROSS THE ROCKIES AND
NORTHERN PLAINS. THESE COOLER TEMPERATURES WILL PUSH EAST BEHIND A
COLD FRONT AND HELP MODERATE TEMPERATURES A BIT IN THE EAST, THOUGH
GENERALLY REMAINING A FEW DEGREES ABOVE NORMAL. TEMPERATURES
ACROSS THE ROCKIES TO PLAINS ARE FORECAST TO WARM UP INTO EARLY
NEXT WEEK DUE TO UPPER RIDGING AHEAD OF THE PACIFIC TROUGH WHILE
TEMPERATURES ON THE WEST COAST LIKELY BECOME COOLER THAN NORMAL
THIS WEEKEND, PARTICULARLY UNDER THE UPPER LOW.
JACKSON
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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