117
FXUS02 KWBC 252023
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
423 PM EDT MON SEP 25 2023
VALID 12Z THU SEP 28 2023 - 12Z MON OCT 02 2023
..OVERVIEW
A TROUGH DIGGING SOUTH FROM THE PACIFIC NORTHWEST BECOMES A CUTOFF
LOW OVER THE GREAT BASIN SUNDAY AS RIDGING OVER THE EAST-CENTRAL
CONUS AMPLIFIES. PROLONGED PRECIPITATION, WITH HIGH ELEVATION
SNOW, IS EXPECTED TO DEVELOP ACROSS THE INTERMOUNTAIN WEST,
NORTHERN ROCKIES, AND NORTHERN HIGH PLAINS THIS WEEKEND.
MEANWHILE, A SLOW MOVING COLD FRONT WILL BRING CONTINUED RAIN FOR
THE FLORIDA PENINSULA INTO THIS WEEKEND. WARM CONDITIONS CAN BE
EXPECTED OVER THE GREAT PLAINS THROUGH GREAT LAKES.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
DETERMINISTIC GUIDANCE SHOWS VERY GOOD AGREEMENT WITH THE EXPECTED
FLOW PATTERN OF A CLOSING/CUT OFF LOW OVER THE WEST AND RIDGING
OVER THE EAST-CENTRAL CONUS. BLENDING THE 00Z ECMWF/CMC/UKMET AND
THE 06Z GFS WORKED WELL THROUGH DAY 5 WITH INCLUSION OF THE 00Z
ECENS AND 06Z GEFS MEANS FOR DAYS 6/7. QPF GRIDS WERE GENERALLY A
BLEND OF THE 13Z NBM WITH MAINLY 06Z GFS AND 00Z ECMWF THROUGH DAY
5, THEN THE GFS WAS USED TO TEMPER/REDUCE QPF COVERAGE FROM THE
13Z NBM FOR DAYS 6/7.
..WEATHER/HAZARDS HIGHLIGHTS
A STALLED FRONT OVER THE FLORIDA SHOULD PROGRESS SOUTHWARD AS A
FRONTAL WAVE FORMS TO THEIR EAST, PROGRESSING PAST BERMUDA AHEAD
OF A PROGRESSIVE AND POSITIVELY TILTED UPPER LEVEL TROUGH. THE ERO
FOR DAY 4/THURSDAY INTO FRIDAY MORNING, THE SIGNAL FOR A COOL
SEASON HEAVY RAINFALL SETUP INTO NORTHEAST FL REMAINS, SO DOES THE
MARGINAL RISK. FOR DAY 5/FRIDAY INTO SATURDAY MORNING, THE
MARGINAL RISK WAS TRIMMED A BIT TO THE SOUTH FOR BOTH COOL SEASON,
POST-FRONTAL HEAVY RAINFALL SETTING UP A BIT FARTHER SOUTH THAN
PRIOR GUIDANCE. THIS IS OFF THE VERY WARM WESTERN SUBTROPICAL
NORTH ATLANTIC AND FOR THE CENTRAL AND SOUTHERN PENINSULA CLOSER
TO THE FRONT, WHICH HAVE BEEN A BIT WETTER THAN AVERAGE THIS PAST
WEEK.
A DIGGING WESTERN TROUGH WILL CLOSE INTO A CUT OFF LOW CENTERED
OVER THE GREAT BASIN THIS WEEKEND AND WILL FOCUS MODERATE PRECIP
OVER THE INTERMOUNTAIN WEST THROUGH NORTHERN ROCKIES, AND NORTHERN
HIGH PLAINS. NO EXCESSIVE RAINFALL AREAS APPEAR NEEDED. SNOW AT
HIGHER ELEVATION BECOMES INCREASINGLY FAVORED WITH TIME ACROSS THE
NORTHERN ROCKIES AS THE UPPER LEVEL LOW DEVELOPS.
INCREASED RIDGING OVER THE CENTER OF THE COUNTRY AND TROUGHING
ACROSS THE WEST, WILL SLOWLY SHIFT TEMPERATURES OF 10 TO 15
DEGREES ABOVE NORMAL EAST ACROSS THE CENTRAL PLAINS THROUGH THE
GREAT LAKES WITH TEMPERATURES BELOW NORMAL EXPANDING FROM THE
NORTHWEST TO ACROSS THE WEST. BELOW NORMAL TEMPERATURES OVER THE
MID-ATLANTIC STATES CAN BE EXPECTED INTO FRIDAY BEFORE MODERATING
ON APPROACH OF THE RIDGE AXIS.
JACKSON/ROTH
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
NO SIGNIFICANT HAZARDS ARE EXPECTED OVER THE CONUS DURING THIS
FORECAST PERIOD.
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
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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