083
FXUS02 KWBC 082004
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 PM EDT MON MAY 08 2023
VALID 12Z THU MAY 11 2023 - 12Z MON MAY 15 2023
***PERIODS OF HEAVY RAIN EXPECTED FOR PORTIONS OF THE SOUTHERN
PLAINS AND ALSO THE NORTHERN HIGH PLAINS AND VICINITY***
..SYNOPTIC SCALE OVERVIEW
AN AMPLIFIED UPPER LEVEL TROUGH WITH AN ACCOMPANYING SURFACE LOW
WILL BE MAKING WEATHER HEADLINES ACROSS THE ROCKIES/PLAINS TO END
THE WEEK AS THE MAIN UPPER LOW TRACKS FROM THE CENTRAL ROCKIES TO
THE DAKOTAS. THERE WILL LIKELY BE AN ENHANCED SURGE OF GULF
MOISTURE NORTHWARD THAT WILL FUEL SCATTERED TO NUMEROUS SHOWERS
AND STORMS WITH HEAVY RAINFALL POTENTIAL ACROSS MUCH OF THE
PLAINS. AN UPPER RIDGE OVER THE EAST-CENTRAL U.S. AHEAD OF THE
PLAINS STORM SYSTEM WILL LIKELY BREAK DOWN GOING INTO SUNDAY AND
BEYOND WITH A TROUGH LIKELY BUILDING SOUTHWARD FROM EASTERN CANADA
ACROSS THE NORTHEASTERN QUADRANT OF THE NATION. MUCH OF THE
SOUTHERN/EASTERN U.S. WILL REMAIN UNSETTLED UNDER THIS PATTERN.
MEANWHILE, A RIDGE WILL SIGNIFICANTLY AMPLIFY ACROSS THE WEST,
BRINGING ANOMALOUSLY WARM, NEAR RECORD-TYING/BREAKING HIGHS TO
PORTIONS OF THE PACIFIC NORTHWEST THIS WEEKEND AND INTO EARLY NEXT
WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MODEL GUIDANCE SHOWS THE UPPER-LEVEL PATTERN OVER THE CONUS
DURING THE FORECAST PERIOD (12Z THU 11 MAY - 12Z MON 15 MAY)
BEGINNING WITH A SOUTHERN STREAM TROUGH MOVING NORTHEASTWARD OVER
THE PLAINS BEFORE RELATED ENERGY RETROGRADES WESTWARD AS A STEEP
RIDGE/CLOSED HIGH BUILDS TO THE NORTH OVER THE WESTERN CONUS INTO
WESTERN CANADA. BOTH THE DETERMINISTIC GUIDANCE AND ENSEMBLE MEANS
ARE IN GOOD AGREEMENT IN THE OVERALL EVOLUTION OF THIS TRANSITION,
WITH DIFFERENCES MAINLY RELATED TO SUBTLE SMALL-SCALE DIFFERENCES
IN THE EMBEDDED ENERGY WEAKENING/TRANSITIONING WESTWARD AND
POTENTIALLY LINGERING OVER CALIFORNIA/THE SOUTHWEST. BOTH THE GFS
AND ECMWF ALSO SHOW GOOD RUN-TO-RUN CONSISTENCY OVER THE LAST FEW
CYCLES. ONE OTHER AREA WHERE THE SOLUTIONS DIVERGE A BIT IS WITH
RESPECT TO A CLOSED LOW DEVELOPING OVER SOUTHEASTERN CANADA AND
SHORTWAVE ENERGY ROTATING AROUND THE LOW, WHICH MAY IMPACT
PRECIPITATION CHANCES AND TEMPERATURES OVER THE GREAT
LAKES/NORTHEAST. THE GUIDANCE SHOWS THE PROGRESSION OF ONE
PARTICULAR SHORTWAVE/SURFACE COLD FRONT WILL ALSO DICTATE
PRECIPITATION CHANCES AND TEMPERATURES INTO THE SOUTHERN
PLAINS/SOUTHEAST LATE IN THE PERIOD. A GENERAL MODEL BLEND OF THE
DETERMINISTIC GUIDANCE BETWEEN THE 00Z ECMWF/CMC/UKMET AND 06Z GFS
HAS GOOD AGREEMENT/ENSEMBLE SUPPORT WITH A RESULTANT FORECAST THAT
REMAINS VERY SIMILAR TO THE PREVIOUS WPC BLEND. A SMALL
CONTRIBUTION FROM THE MEANS IS INCLUDED TO REPLACE THE
TIME-LIMITED UKMET MID- TO LATE FORECAST PERIOD, WHICH HELPS TO
SMOOTH OUT NATURALLY INCREASING SMALL-SCALE DEVIATIONS IN THE
SOLUTIONS WITH INCREASING FORECAST LEAD TIME.
..WEATHER/HAZARDS HIGHLIGHTS
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL LIKELY
DEVELOP ACROSS MUCH OF THE PLAINS STATES GOING INTO THE LATTER
HALF OF THE WORK WEEK, AS MOISTURE ADVECTION FROM THE GULF OF
MEXICO INCREASES AHEAD OF A SLOWING FRONTAL SYSTEM OVER THE
CENTRAL/SOUTHERN HIGH PLAINS AND THE UPPER TROUGH/LOW APPROACHES
FROM THE WEST. THE DAY 4 (12Z THURSDAY-12Z FRIDAY) EXCESSIVE
RAINFALL OUTLOOK MAINTAINS A SLIGHT RISK OVER PARTS OF EASTERN
MONTANA INTO NORTHEASTERN WYOMING AND WESTERN PORTIONS OF THE
DAKOTAS. GUIDANCE CONTINUES TO INDICATE THE LIKELIHOOD FOR
WIDESPREAD HEAVY RAINFALL IN A FAVORABLE UPSLOPE PATTERN OVER WET
GROUND CONDITIONS DUE TO MODERATE/HEAVY RAINFALL THE PRIOR DAY.
ADDITIONAL MODERATE TO HEAVY RAINFALL MAY SPREAD EASTWARD INTO THE
NORTHERN PLAINS FOLLOWING THE SURFACE LOW TRACK ON FRIDAY. THE DAY
5 (12Z FRIDAY-12Z SATURDAY) EXCESSIVE RAINFALL OUTLOOK MAINTAINS A
SLIGHT RISK ACROSS PORTIONS OF CENTRAL/SOUTHERN TEXAS WHERE THERE
IS A STRONG SIGNAL FOR POTENTIALLY SIGNIFICANT RAINFALL OF SEVERAL
INCHES. ADDITIONAL ROUNDS OF MODERATE TO LOCALLY HEAVY RAINFALL
LOOK PROBABLE INTO THE WEEKEND AS THE SURFACE BOUNDARY STALLS OVER
THE REGION, RAISING CONCERNS OVER FLASH FLOODING GIVEN
INCREASINGLY SATURATED GROUND CONDITIONS. SHOWER AND STORM
CHANCES WILL ALSO SPREAD INTO THE OHIO VALLEY, APPALACHIANS, AND
MIDWEST INTO THE WEEKEND AS THE FRONTAL SYSTEM SLOWLY PUSHES
EASTWARD. AS THE UPPER LOW CROSSES THE GREAT BASIN AND NORTHERN
ROCKIES, THERE SHOULD BE SUFFICIENT COLD AIR ALOFT TO SUPPORT SOME
LATE SEASON HIGHER ELEVATION SNOW, ESPECIALLY FOR PORTIONS OF THE
NORTHERN/CENTRAL ROCKIES.
IN TERMS OF TEMPERATURES, HIGHS WILL LIKELY BE RUNNING 10 TO 15
DEGREES ABOVE EARLY MAY AVERAGES FROM THE UPPER MIDWEST TO THE
NORTHEAST STATES TO CLOSE OUT THE WORK WEEK, AND THEN TRENDING
COOLER GOING INTO THE WEEKEND AS AN UPPER-LOW OVER CANADA SLIDES
SOUTHWARD AND MULTIPLE COLD FRONTS LOOK TO EFFECT THE REGION.
WARMTH WILL BUILD ACROSS THE PACIFIC NORTHWEST BY FRIDAY AND
ESPECIALLY INTO THE WEEKEND WITH HIGHS REACHING 20-25+ DEGREES
ABOVE MID-MAY AVERAGES ACROSS MUCH OF WASHINGTON AND OREGON. SOME
RECORD-TYING/BREAKING HIGHS INTO THE MID-90S LOOK POSSIBLE. LOWS
MAY BE A LITTLE LESS EXTREME BUT COULD STILL CHALLENGE A FEW DAILY
RECORDS FOR WARM LOWS BY THE WEEKEND. HIGHS WILL LIKELY BE
SLIGHTLY BELOW AVERAGE THE INTERMOUNTAIN WEST IN ASSOCIATION WITH
THE UPPER TROUGH THROUGH THURSDAY BEFORE A MODERATING TREND
COMMENCES. OVERNIGHT LOWS OVER THOSE AREAS EARLY IN THE PERIOD
SHOULD BE CLOSER TO AVERAGE WHILE AREAS EAST OF THE ROCKIES SHOULD
SEE MOSTLY ABOVE AVERAGE LOWS WITH INCREASED CLOUD COVER AND
HUMIDITY.
PUTNAM/HAMRICK
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, FRI-SUN, MAY
12-MAY 14.
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHERN/CENTRAL ROCKIES, THE
CENTRAL HIGH PLAINS, THE UPPER
MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS, THU, MAY 11.
- SEVERE WEATHER ACROSS PORTIONS OF THE CENTRAL HIGH PLAINS AND
THE SOUTHERN HIGH PLAINS, THU, MAY
11.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE GREAT LAKES, THE UPPER
MISSISSIPPI VALLEY, AND THE
NORTHERN PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE
UPPER/MIDDLE MISSISSIPPI VALLEY, THE
NORTHERN PLAINS, THE NORTHERN ROCKIES, AND THE NORTHERN GREAT
BASIN.
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL GREAT BASIN, THE
NORTHERN PLAINS, THE
NORTHERN/CENTRAL ROCKIES, THE NORTHERN GREAT BASIN, THE GREAT
LAKES, AND THE SOUTHWEST.
- MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF CALIFORNIA,
THE PACIFIC NORTHWEST, THE NORTHERN
ROCKIES, AND THE NORTHERN GREAT BASIN, SAT-MON, MAY 13-MAY 15.
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
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