939
FXUS02 KWBC 130700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT FRI OCT 13 2023
VALID 12Z MON OCT 16 2023 - 12Z FRI OCT 20 2023
..OVERVIEW
MOST GUIDANCE SHARES THE GENERAL THEME OF AN AMPLIFIED EASTERN
U.S. TROUGH (WITH POSSIBLE EMBEDDED UPPER LOW) DEPARTING WHILE
PACIFIC TROUGH ENERGY REACHING THE NORTHWEST BY TUESDAY AMPLIFIES
INTO THE CENTRAL U.S. MID-LATE WEEK. THIS LATTER AMPLIFICATION
SHOULD BE IN RESPONSE TO A STRONG EAST-CENTRAL PACIFIC STORM
ORIGINALLY ASSOCIATED WITH CURRENT TYPHOON BOLAVEN HELPING TO
ENHANCE UPPER RIDGING EXPECTED TO BUILD OVER THE WESTERN U.S.
WESTERN ATLANTIC LOW PRESSURE ASSOCIATED WITH THE INITIAL EASTERN
UPPER TROUGH/LOW MAY AFFECT THE EAST COAST TO SOME DEGREE, WHILE A
FRONT REACHING THE WEST COAST EARLY IN THE WEEK MAY BRING A BRIEF
PERIOD OF ENHANCED PRECIPITATION TO THAT REGION. EASTWARD
PROGRESSION OF THIS FRONT SHOULD BRING LIGHTER TOTALS INTO THE
ROCKIES AND PERHAPS SOMEWHAT HEAVIER ACTIVITY OVER PARTS OF THE
CENTRAL U.S. LATER IN THE WEEK. TEMPERATURES OVER THE WEST WILL
TEND TO BE ABOVE NORMAL ASIDE FROM A BRIEF MIDWEEK MODERATION
WHILE MUCH OF THE EAST WILL SEE BELOW NORMAL READINGS ESPECIALLY
DURING EARLY-MID WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
OVER THE COURSE OF NEXT WEEK THERE ARE TWO PRIMARY FORECAST
ISSUES. THE FIRST INVOLVES DETAILS OF EASTERN U.S. TROUGHING AND
ASSOCIATED OFFSHORE LOW PRESSURE DURING MONDAY-WEDNESDAY.
CURRENTLY, LOW-PREDICTABILITY SHORTWAVE DIFFERENCES HAVE AN
IMPORTANT INFLUENCE ON EXACTLY HOW CLOSED OR DEEP THE UPPER TROUGH
WILL BE BY WEDNESDAY, WITH CORRESPONDING EFFECTS ON ON THE SURFACE
LOW. AMONG 12Z/18Z GUIDANCE, THE GFS WAS ON THE WESTERN SIDE OF
THE MODEL/MEAN SPREAD DUE TO BEING DEEPEST WITH ITS UPPER LOW. ON
THE OTHER HAND SOME OTHER SOLUTIONS ARE NOTICEABLY MORE OPEN
ALOFT, LEADING TO A WEAKER AND MORE OFFSHORE SURFACE LOW.
CONTINUITY HAD BEEN CLOSER TO THE COAST SO ULTIMATELY FAVORED A
12Z/18Z MODEL BLEND THAT YIELDED A GFS/ECMWF COMPROMISE THAT
PROVIDED JUST A MODEST EASTWARD ADJUSTMENT WHILE AWAITING
CONTINUATION OF THE OFFSHORE TREND (WHICH SEEMS TO BE THE CASE SO
FAR IN THE 00Z CYCLE). THE OTHER CHALLENGE IS DETERMINING THE
CHARACTER OF SHORTWAVE ENERGY REACHING THE CENTRAL U.S. MID-LATE
WEEK. IN GENERAL ECMWF RUNS HAVE BEEN SOMEWHAT MORE STABLE IN
DEPICTING A MODERATELY PROGRESSIVE AND PHASED TROUGH THAT IS MORE
SIMILAR TO THE MEANS, WHILE SOME GFS RUNS (INCLUDING THE NEW 00Z
VERSION) HAVE BEEN PULLING OFF SOUTHWESTERN ENERGY INTO A HIGH
PLAINS UPPER LOW. THE 12Z/18Z GFS RUNS WAITED UNTIL LATE DAY 7
FRIDAY TO CLOSE OFF A LOW OVER THE CENTRAL PLAINS/MIDWEST. THE NEW
00Z CMC SHOWS THE MOST EXTREME SOUTHWESTWARD ELONGATION BY NEXT
FRIDAY, THOUGH THIS IS NOT OUTSIDE THE FAIRLY WIDE ENSEMBLE
ENVELOPE. THE 12Z CMC WAS MORE SIMILAR TO THE ECMWF AND ENSEMBLE
MEANS. INCREASING UNCERTAINTY FOR DETAILS AT THIS LATER TIME FRAME
LED TO TRANSITIONING THE FORECAST TO A BLEND OF THE 18Z GFS/GEFS
MEAN AND 12Z ECMWF/ECENS/CMC.
..WEATHER/HAZARDS HIGHLIGHTS
EXPECT SHORTWAVE ENERGY AND A LEADING COLD FRONT TO BRING A BRIEF
PERIOD OF MODERATE TO HEAVY PRECIPITATION TO THE CENTRAL AND
NORTHERN WEST COAST AROUND MONDAY, WITH HIGHEST TOTALS LIKELY OVER
SOUTHWARD FACING TERRAIN OVER THE PACIFIC NORTHWEST. THERE MAY BE
SUFFICIENT INSTABILITY TO PROMOTE SOME ENHANCED RAINFALL INTENSITY
ON A LOCALIZED BASIS BUT THE COMBINATION OF OBSERVED SOIL
MOISTURE/RECENT RAINFALL/STREAM FLOWS SUGGEST ANY RUNOFF ISSUES
SHOULD BE ISOLATED ENOUGH NOT TO MERIT ANY RISK AREA IN THE DAY 4
(MONDAY) EXCESSIVE RAINFALL OUTLOOK. LIGHTER PRECIPITATION SHOULD
SPREAD ACROSS THE NORTHERN AND PERHAPS CENTRAL ROCKIES AS THE
SHORTWAVE ENERGY AND FRONT CONTINUE EASTWARD. COVERAGE AND
INTENSITY OF RAINFALL SHOULD INCREASE OVER THE CENTRAL U.S. BY
WEDNESDAY-FRIDAY BUT DETAILS BECOME INCREASINGLY UNCLEAR, WITH
VARIOUS POTENTIAL UPPER LEVEL AND SURFACE EVOLUTIONS LEADING TO A
WIDE RANGE OF POSSIBILITIES FOR LOCATION AND MAGNITUDE OF HEAVIEST
RAINFALL. ANOTHER AREA OF MOISTURE COULD REACH NORTHERN PARTS OF
THE PACIFIC NORTHWEST BY LATE NEXT WEEK. EARLY-MID WEEK UPPER
TROUGHING AND POSSIBLE EMBEDDED LOW OVER THE EAST SHOULD PROMOTE
OFFSHORE LOW PRESSURE DEVELOPMENT THAT MAY MAINTAIN BRISK WINDS
FOR A TIME NEAR THE EAST COAST. HOWEVER LATEST TRENDS FOR A WEAKER
AND/OR SOMEWHAT MORE OFFSHORE SYSTEM SHOULD KEEP RAINFALL ON THE
LIGHTER SIDE. THE EASTERN GREAT LAKES INTO THE APPALACHIANS MAY
SEE SOME LIGHT PRECIPITATION AS WELL.
THE AMPLIFIED TROUGH OVER THE EAST EARLY IN THE WEEK WILL SUPPORT
BELOW NORMAL TEMPERATURES OVER MUCH OF THE EASTERN HALF OF THE
COUNTRY EARLY IN THE WEEK, WITH A BROAD AREA OF HIGHS 10-15F BELOW
NORMAL. SIMILAR ANOMALIES FOR MORNING LOWS SHOULD BE CONFINED MORE
TO THE CENTRAL PLAINS ON MONDAY AND THE GULF COAST/FLORIDA REGIONS
TUESDAY-WEDNESDAY. EASTERN U.S. TEMPERATURES SHOULD RETURN CLOSER
TO NORMAL THEREAFTER. THE WESTERN U.S. WILL SEE ABOVE NORMAL
TEMPERATURES FOR MOST OF NEXT WEEK, WITH A BRIEF MIDWEEK LULL
SEPARATING WARMTH AHEAD OF A LEADING PACIFIC COLD FRONT AND THEN A
REBOUND IN TEMPERATURES AS UPPER RIDGING BUILDS OVER THE REGION.
SOME LOCATIONS MAY SEE ONE OR MORE DAYS OF PLUS 10-20F ANOMALIES.
RAUSCH
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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