807
FXUS02 KWBC 120700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT FRI MAY 12 2023
VALID 12Z MON MAY 15 2023 - 12Z FRI MAY 19 2023
...SOME FLASH FLOODING POTENTIAL COULD LINGER IN/AROUND TEXAS
THROUGH THE FIRST HALF OF NEXT WEEK...
..EARLY SEASON HEAT WAVE TO AFFECT THE PACIFIC NORTHWEST
..OVERVIEW
THE OVERALL WEATHER PATTERN NEXT WEEK WILL CONSIST OF AN
ANOMALOUSLY STRONG UPPER RIDGE OVER THE WESTERN HALF OF THE U.S.
AND INTO WESTERN CANADA THAT WILL BE PERSISTENT ASIDE FROM AN
UPPER LOW GRADUALLY SHEARING OUT/WEAKENING ATOP THE NORTHWEST.
THIS PATTERN WILL RESULT IN AN EARLY SEASON HEAT WAVE ACROSS THE
NORTHWEST AND TO A LESSER EXTENT OVER OTHER PARTS OF THE WEST.
DOWNSTREAM, MEAN TROUGHING IS LIKELY ACROSS EASTERN NORTH AMERICA,
WITH INDIVIDUAL SHORTWAVES SUPPORTING COLD FRONTS THAT DROP INTO
THE NORTHERN/EASTERN PARTS OF THE COUNTRY. MEANWHILE MOIST INFLOW
CONTINUES INTO THE SOUTHERN PLAINS, MAINTAINING SOME RISK OF
EXCESSIVE RAINFALL THERE, THOUGH THE THREAT OF WIDESPREAD FLASH
FLOODING SHOULD DECREASE THROUGH NEXT WEEK GIVEN LESS UPPER-LEVEL
SUPPORT COMPARED TO THE SHORT RANGE PERIOD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE FOR THE MOST PART CONTINUES TO BE REASONABLY
AGREEABLE FOR THE LARGE-SCALE PATTERN OF RIDGING IN THE WEST AND
TROUGHING IN THE NORTHEAST. AT THE START OF THE PERIOD MONDAY,
MODELS INDICATE THAT AN UPPER LOW WILL BE RETROGRADING ACROSS THE
NORTHWEST WHILE WEAKENING AS THE ENERGY BECOMES EMBEDDED IN THE
OVERALL RIDGY FLOW. THERE IS ALSO A GENERAL CONSENSUS FOR TIMING
OF A SHORTWAVE MOVING THROUGH THE EAST, THOUGH THE NORTH-SOUTH
PLACEMENT VARIES ENOUGH TO CAUSE SOME PRECIPITATION FORECAST
DIFFERENCES. BUT THE MAIN OUTLIER FOR THE 12/18Z MODEL CYCLE WAS
THE 12Z CMC, WHICH BROUGHT A SHORTWAVE INTO BRITISH COLUMBIA THAT
IS STRONG ENOUGH TO BASICALLY BREAK DOWN THE RIDGE IN THE INTERIOR
WEST BY AROUND WEDNESDAY, WITH LITTLE SUPPORT FROM THE OTHER
MODELS OR ENSEMBLE MEMBERS THAT SHOW PERSISTENT RIDGING. THE NEWER
00Z CMC TRENDING BACK TOWARD THE LATTER PROVIDES CONFIDENCE THAT
THE 12Z CMC WAS AN OUTLIER. THEN BY WEDNESDAY-FRIDAY, THE 18Z GFS
AND 12Z ECMWF HAPPENED TO AGREE FAIRLY WELL ON TIMING AND
PLACEMENT OF A POTENT SHORTWAVE COMING AROUND THE
SOUTHWESTERN/SOUTHERN PART OF THE TROUGH EXTENDING FROM
EAST-CENTRAL CANADA AND ITS ASSOCIATED SURFACE LOW. THE 12Z GFS
WAS A LITTLE FASTER. THE INCOMING 00Z GUIDANCE IS LOOKING A LITTLE
SLOWER WITH THESE FEATURES TRACKING EAST, BUT AGREEABLE IN
PRINCIPLE ESPECIALLY CONSIDERING THE TYPICAL SPREAD FOR THE LATE
MEDIUM RANGE.
THUS THE WPC FORECAST WAS BASED ON A BLEND OF THE 12Z/18Z GFS AND
THE 12Z ECMWF AND UKMET EARLY IN THE FORECAST PERIOD. FOR THE
MID-PERIOD THE 12Z GFS AND THE UKMET WERE PHASED OUT IN FAVOR OF
THE GEFS AND EC ENSEMBLE MEAN GUIDANCE THAT WERE AGREEABLE WITH
THE 18Z GFS AND 12Z ECMWF.
..WEATHER/HAZARDS HIGHLIGHTS
PERSISTENT MOIST INFLOW IS LIKELY TO CONTINUE INTO THE SOUTHERN
PLAINS THROUGH AT LEAST THE EARLY PART OF NEXT WEEK. THOUGH RAIN
AMOUNTS MAY NOT BE AS HIGH AS IN THE SHORT TERM ACROSS TEXAS,
ANOTHER DAY OF ENHANCED QPF IS POSSIBLE ON MONDAY OVER WHAT IS
LIKELY TO BE VERY WET GROUND, SO A SLIGHT RISK OF EXCESSIVE
RAINFALL/FLASH FLOODING WILL BE MAINTAINED IN THIS FORECAST CYCLE
FOR DAY 4/MONDAY ACROSS SOUTH-CENTRAL TEXAS, WITH A MINOR
EXPANSION WESTWARD PER NEWER MODEL GUIDANCE. THE SURROUNDING
MARGINAL RISK CONTINUES TO ENCOMPASS THE RELATIVE MAJORITY OF
STILL DIVERSE GUIDANCE FOR WHERE HEAVIEST POCKETS OF RAINFALL MAY
BE, WITH THE MARGINAL ALSO EXTENDED WESTWARD INTO PORTIONS OF NEW
MEXICO WHERE A MONSOON-LIKE PATTERN STARTS TO SET UP. BY TUESDAY
AND BEYOND THIS MONSOONAL TYPE OF PATTERN WITH MOISTURE COMING IN
UNDERNEATH RIDGING ALOFT LOOKS TO PERSIST ACROSS THE FOUR CORNERS
STATES AND PERHAPS EVEN FARTHER NORTH THROUGH MUCH OF NEXT WEEK,
WITH TYPICAL DIURNAL ENHANCEMENT. MOISTURE ANOMALIES VARY PER
MODEL (WITH THE ECMWF SUITE SHOWING MUCH HIGHER ANOMALIES THAN THE
GFS SUITE), BUT WITH INSTABILITY IN PLACE THERE COULD BE LOCALIZED
FLASH FLOODING. A MARGINAL RISK OF EXCESSIVE RAINFALL IS PLANNED
FOR DAY 5/TUESDAY FOR THE SOUTHERN HIGH PLAINS, THOUGH PLACEMENT
OF HEAVY TOTALS AND FLASH FLOODING REMAINS UNCERTAIN.
ELSEWHERE, A ROUND OF RAIN IS LIKELY ACROSS THE MID-ATLANTIC
AND/OR CAROLINAS ON MONDAY WITH A SHORTWAVE IMPULSE AND SURFACE
FRONT. LIGHT RAIN IS POSSIBLE FOR THE NORTHEAST ON TUESDAY. AN
INITIALLY STALLING SURFACE FRONT AND ANOTHER FRONT APPROACHING
NEAR/OVER THE GULF COAST COULD LEAD TO SCATTERED SHOWERS AND
STORMS ACROSS THAT AREA THROUGH MUCH OF THE WEEK. THEN A LOW
PRESSURE SYSTEM MOVING ACROSS SOUTHERN CANADA COULD SWEEP A FRONT
ACROSS THE NORTH-CENTRAL U.S. LATE WEEK, BRINGING POTENTIAL FOR
SHOWERS AND STORMS AHEAD OF IT ACROSS THE NORTHERN HALF OF THE
PLAINS INTO THE MIDWEST.
TEMPERATURE-WISE, A HEAT WAVE IS FORECAST TO PERSIST FROM THIS
WEEKEND INTO THE MEDIUM RANGE PERIOD ACROSS THE NORTHWEST AS LARGE
SCALE UPPER RIDGING PREVAILS OVER WESTERN NORTH AMERICA (THOUGH
WITH A WEAKENING EMBEDDED UPPER LOW SETTLING OVER THE REGION).
HIGHS IN THE 80S AND INTO THE LOW 90S WOULD BE 15 TO 20 DEGREES
ABOVE AVERAGE AND COULD SET RECORDS FOR MANY OF THE LOWER
ELEVATIONS IN WASHINGTON AND OREGON. TEMPERATURES ARE FORECAST TO
REMAIN 10-20F ABOVE AVERAGE IN THE WEST THROUGH ALL NEXT WEEK,
THOUGH LESSENING SOMEWHAT (BELOW RECORD LEVELS FOR HIGHS).
HOWEVER, MANY WARM LOW TEMPERATURES COULD KEEP CHALLENGING DAILY
AND PERHAPS EVEN MONTHLY RECORDS FOR HIGH MINIMUM TEMPERATURES IN
THE UPPER 50S AND 60S. FARTHER SOUTH, HIGHS IN THE 90S ARE LIKELY
IN THE CALIFORNIA CENTRAL VALLEY WITH HIGHS ABOVE 100F IN THE
DESERT SOUTHWEST (THOUGH THE LATTER IS NOT TERRIBLY ANOMALOUS FOR
MAY). PERIODS OF WARMER THAN AVERAGE TEMPERATURES SHOULD EXPAND
ACROSS MUCH OF THE NORTHERN TIER, THOUGH COULD EVENTUALLY MODERATE
CLOSER TO NORMAL BY LATE NEXT WEEK. THE NORTHEAST TO MID-ATLANTIC
COULD SEE PERIODS OF SLIGHTLY ABOVE AND BELOW NORMAL TEMPERATURES
VARYING DEPENDING ON A SERIES OF FRONTAL SYSTEMS. MEANWHILE THE
CLOUDY AND RAINY CONDITIONS SHOULD KEEP HIGHS 5-15F BELOW NORMAL
OVER THE SOUTHERN HIGH PLAINS, PERHAPS GRADUALLY MODERATING
THROUGH THE WEEK.
TATE
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
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