705
FXUS02 KWBC 152027
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
426 PM EDT MON MAY 15 2023
VALID 12Z THU MAY 18 2023 - 12Z MON MAY 22 2023
...WARMER THAN AVERAGE TEMPERATURES WILL PERSIST ACROSS THE
NORTHWEST...
...PORTIONS OF THE SOUTH-CENTRAL ROCKIES AND PLAINS COULD SEE
FLASH FLOODING THURSDAY-FRIDAY...
..OVERVIEW
THE OVERALL WEATHER PATTERN THIS WEEK AND INTO EARLY NEXT WEEK
SHOULD REMAIN FAIRLY SIMILAR WITH TIME ACROSS THE COUNTRY WITH AN
ANOMALOUSLY STRONG UPPER RIDGE OVER THE WEST CAUSING WARM TO HOT
TEMPERATURES THERE, WHILE MEAN TROUGHING IS LIKELY DOWNSTREAM
ACROSS EASTERN NORTH AMERICA WHERE INDIVIDUAL SYSTEMS WILL BE
MOVING THROUGH THE PROGRESSIVE FLOW. INDIVIDUAL SHORTWAVES WILL
SUPPORT COLD FRONTS THAT SHOULD PUSH SOUTHEASTWARD TO THE EAST OF
THE ROCKIES AND PRODUCE AREAS OF SHOWERS AND THUNDERSTORMS,
INCLUDING THE POSSIBILITY FOR SOME ENHANCED RAINFALL AMOUNTS
POTENTIALLY CAUSING FLASH FLOODING IN THE SOUTH-CENTRAL ROCKIES
AND PLAINS LATE THIS WORKWEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
DETAILS WITHIN THE MEAN TROUGHING DOWNSTREAM AND RELATED FRONTAL
SYSTEM IN THE EAST SHOW VARIABILITY, WHILE THE EASTERN PACIFIC
ALSO BECOMES AN AREA OF FOCUS FROM A MODEL DIAGNOSTICS STANDPOINT,
WITH THE POTENTIAL FOR AN UPPER LOW OFFSHORE OF CANADA TO FINALLY
SPIN SOME ENERGY/TROUGHING TOWARD THE PACIFIC NORTHWEST FOR SOME
COOLER TEMPERATURES WITH A COLD FRONT OR TWO AS THE PREVAILING
RIDGE WEAKENS A BIT AND PUSHES EASTWARD EARLY NEXT WEEK. OVERALL,
THE 06Z GFS IS ON THE FAST SIDE OF THE GUIDANCE. THE 00Z CANADIAN
WAS UNIQUELY SLOW IN THE EASTERN US AND COULD NOT BE USED. THE
BREADTH OF THE RIDGE UPSTREAM SUGGESTS A BROADER TROUGH WITH
DECENT FLOW THROUGH IT, ARGUING AGAINST THE CANADIAN. OVERALL, A
COMPROMISE OF THE 00Z ECMWF AND 06Z GFS WORKS WELL ACROSS THE
COUNTRY FOR 500 HPA HEIGHTS AND PRESSURES, WITH SOME INPUT FROM
THE 00Z ECMWF AND NAEFS MEANS LATE IN THE PERIOD TO DEAL WITH
UNCERTAINTY. QPF IN THE SOUTHEAST LOOKS OVERDONE IN THE 00Z
ECMWF. WHILE THE APPROACH OF A SHORTWAVE TROUGH SHOULD SPUR A
SURFACE LOW WHICH SHOULD BE CONVECTIVE, IT SHOULD EITHER REMAIN
STATIONARY AND/OR DRIFT SOUTHEAST AS THE UPPER TROUGH MOVES
OVERHEAD AND PASSES BY. USED MINIMAL 00Z ECMWF WEIGHT IN THE QPF.
..WEATHER/HAZARDS HIGHLIGHTS
A FRONT LOOKS HANGS UP IN THE SOUTH-CENTRAL ROCKIES ON THURSDAY
AND FRIDAY, WITH UPSLOPE FLOW ON ITS BACKSIDE IN AN ENVIRONMENT
WITH 90+ PERCENTILE MOISTURE ANOMALIES. THIS WOULD ALSO BE ATOP
WET GROUND WITH HIGH STREAMFLOWS THAT COULD EXACERBATE FLASH
FLOODING RISK. FARTHER EAST INTO THE SOUTH-CENTRAL PLAINS, THE
WEST-EAST ORIENTATION OF THE FRONT AND ITS POSSIBLY SLOW MOVEMENT
LATE THURSDAY COULD LEAD TO TRAINING OF STORMS WITH POSSIBLY HIGH
RAIN RATES THAT FORM ON THE CUSP OF THE INSTABILITY/MOISTURE NEAR
THE BOUNDARY. THE SLIGHT RISK FOR DAY 4/THURSDAY IN THE ERO IS A
LITTLE SMALLER BUT SIMILAR IN PLACEMENT, WHICH IS A BETTER MATCH
TO THE BEST HEAVY RAIN SIGNAL IN THE 15/12Z GUIDANCE. THE FRONT
WILL SHIFT SOUTH AND EAST LATE WEEK, WITH A MARGINAL RISK IN THE
DAY 5/FRIDAY ERO ACROSS PORTIONS OF THE THE SOUTH-CENTRAL ROCKIES
AND THE SOUTH-CENTRAL PLAINS/MISSISSIPPI VALLEY. IT APPEARS THE
FRONT MAY BEGIN TO MOVE FASTER FOR DAY 5, PRECLUDING AN EMBEDDED
SLIGHT RISK, AS STORMS WITH HIGH RAIN RATES MAY HAVE LESS
OPPORTUNITY TO TRAIN. THE COLD FRONT WILL MOVE MORE PROGRESSIVELY
EASTWARD ACROSS THE MIDWEST/OHIO VALLEY ON FRIDAY WITH ENHANCED
RAINFALL CHANCES SHIFTING INTO THE EAST ON SATURDAY ALONG AND
AHEAD OF THE FRONT, PERHAPS LINGERING ALONG PARTS OF THE EAST
COAST SUNDAY.
ELSEWHERE, SHOWERS AND STORMS MAY HAVE SOME FOCUS ALONG A FRONTAL
BOUNDARY IN THE SOUTHEAST ON THURSDAY IN PARTICULAR. WITH AMPLE
MOISTURE AND INSTABILITY IN PLACE, THERE COULD BE SOME LOCALIZED
HEAVY RAIN IN AND AROUND SOUTHERN GEORGIA/NORTHERN FLORIDA. WHILE
AMOUNTS ARE NOT CURRENTLY EXPECTED TO SURPASS THE HIGH FLASH FLOOD
GUIDANCE, IT MAY FALL FAST ENOUGH TO OVERWHELM URBAN ENVIRONMENTS,
SO A MARGINAL RISK WAS ADDED FOR DAY 4/THURSDAY INTO EARLY FRIDAY.
SCATTERED SHOWERS AND THUNDERSTORMS ARE ALSO POSSIBLE IN THE WEST
AT TIMES LATE THIS WEEK INTO EARLY NEXT WEEK ESPECIALLY IN THE
AFTERNOONS/EVENINGS WITH A COMMON DIURNAL CYCLE, AS A MONSOON-LIKE
PATTERN SETS UP WITH ANOMALOUSLY HIGH MOISTURE REMAINING OVER A
LARGE PORTION OF THE WESTERN U.S. UNDER THE BASE OF THE UPPER
RIDGE.
TEMPERATURE-WISE, THE PERSISTENT LARGE SCALE WESTERN NORTH AMERICA
RIDGE WILL SUPPORT WARM TO HOT TEMPERATURES ACROSS MOST OF THE
WEST. THE PACIFIC NORTHWEST IS LIKELY TO BE HOTTEST AROUND FRIDAY
(DURING THE MEDIUM RANGE PERIOD), WITH HIGHS AROUND 20 DEGREES
ABOVE AVERAGE BEFORE SOME GRADUAL MODERATION LATE THIS WEEKEND.
HOWEVER, INTERIOR AREAS LIKE THE GREAT BASIN CAN EXPECT THE HEAT
TO PERSIST THROUGH THE WEEKEND. HIGHS IN THE 90S THERE COULD BE
RECORD-SETTING, ESPECIALLY FRIDAY AND SATURDAY, WHILE LOWS IN THE
50S AND 60S COULD BREAK RECORDS FOR WARM LOW TEMPERATURES ACROSS
AN INCREASING AREA OF THE WEST. HIGHS ABOVE 100F ARE LIKELY IN THE
DESERT SOUTHWEST, PAR FOR THE COURSE FOR MAY. THE NORTHEAST
SHOULD SEE CHILLY TEMPERATURES THURSDAY MORNING, POSSIBLY
APPROACHING THE FREEZING MARK IN INTERIOR AREAS AND SETTING A FEW
RECORDS. PERIODS OF RAIN AND CLOUDS AND THEN POST-FRONTAL COOLER
AIR COULD LEAD TO TEMPERATURES SLIGHTLY BELOW AVERAGE IN THE
PLAINS AT TIMES.
ROTH/TATE
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES AND
PLAINS, THU-FRI, MAY 18-MAY 19.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHERN PLAINS, THE
NORTHERN ROCKIES, THE NORTHERN GREAT BASIN, AND THE NORTHERN
PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE UPPER
MISSISSIPPI VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN
PLAINS, THE NORTHERN ROCKIES, AND THE NORTHERN GREAT BASIN.
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE
CENTRAL GREAT BASIN, THE NORTHERN PLAINS, THE NORTHERN ROCKIES,
THE SOUTHERN ROCKIES, THE NORTHERN GREAT BASIN, THE UPPER
MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE SOUTHWEST.
- MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE PACIFIC
NORTHWEST, GREAT BASIN, AND NORTHERN ROCKIES, THU-SUN, MAY 18-MAY
20.
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page