940
FXUS02 KWBC 250635
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 AM EDT MON SEP 25 2023
VALID 12Z THU SEP 28 2023 - 12Z MON OCT 02 2023
..OVERVIEW
THE FLOW PATTERN FEATURES AN EASTWARD MOVING AND REASONABLY STRONG
MID-LEVEL HEIGHT ANOMALY/RIDGE MOVING EASTWARD NEAR THE 45TH
PARALLEL FROM ROUGHLY 160W TO 140W LONGITUDE. THE CONSEQUENCE OF
THIS APPROACHING FEATURE IS AN AMPLIFYING UPPER TROUGH DOWNSTREAM
ACROSS THE WEST WITH BUILDING RIDGING ACROSS THE EASTERN PORTION
OF THE UNITED STATES. EXPECT RAINFALL TO SHIFT INLAND FROM THE
PACIFIC NORTHWEST WITH HIGH ELEVATION SNOW FOR THE NORTHERN
ROCKIES THIS WEEKEND INTO EARLY NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE GUIDANCE SHOWS VERY GOOD AGREEMENT WITH THE EXPECTED FLOW
PATTERN WITH SOME ISSUES WITH DETAILS. TO DEAL WITH THE DETAIL
ISSUES, USED A BLEND OF THE 12Z CANADIAN, 12Z ECMWF, 18Z GFS, AND
12Z UKMET EARLY BEFORE SWAPPING OUT THE UKMET FOR INCREASING
AMOUNTS OF THE 12Z NAEFS AND 12Z ECMWF ENSEMBLE MEAN. THIS LED TO
REASONABLY GOOD AGREEMENT WITH CONTINUITY IN THE PRESSURES AND
FRONTS. THE ABOVE BLEND WAS USED FOR PRESSURES, FRONTS, AND QPF.
THE REMAINDER OF THE GRIDS WERE MORE HEAVILY BASED ON THE 01Z NBM.
..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. THIS
SHOULD ALLOW THE SUNSHINE STATE TO DRY OUT EVENTUALLY. IN THE
MEANTIME, FOR DAY 4/THURSDAY INTO FRIDAY MORNING, THERE'S ENOUGH
OF A SIGNAL OF A COOL SEASON HEAVY RAINFALL SETUP INTO NORTHEAST
FL TO INTRODUCE A MARGINAL RISK. FOR DAY 5/FRIDAY INTO SATURDAY
MORNING, A MARGINAL RISK WAS INTRODUCED FOR BOTH COOL SEASON,
POST-FRONTAL HEAVY RAINFALL 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 DEEPENING WESTERN TROUGH WILL SHIFT ACTIVE WEATHER FROM THE
PACIFIC NORTHWEST THROUGH THE GREAT BASIN/NORTHERN ROCKIES, AND
NORTHERN HIGH PLAINS MIDWEEK THROUGH THIS WEEKEND. RATES WILL
GENERALLY BE LIGHT TO MODERATE, SO NO EXCESSIVE RAINFALL AREAS
APPEAR NEEDED. SNOW AT HIGHER ELEVATION BECOMES INCREASINGLY
FAVORED WITH TIME ACROSS THE NORTHERN ROCKIES AS THE UPPER LEVEL
TROUGH STRENGTHENS.
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.
ROTH/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, 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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