338
FXUS02 KWBC 130617
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
216 AM EDT THU JUL 13 2023
VALID 12Z SUN JUL 16 2023 - 12Z THU JUL 20 2023
...HAZARDOUS TO EXTREME HEAT IS FORECAST FOR THE ENTIRE SOUTHERN
TIER OF THE U.S. THROUGH EARLY NEXT WEEK AND BEYOND...
..ADDITIONAL HEAVY RAIN THREATS FOR THE NORTHEAST ON SUNDAY
..OVERVIEW
BROAD TROUGHING WILL BE MAINTAINED ACROSS THE EASTERN U.S. DURING
THE MEDIUM RANGE PERIOD AS AN UPPER LOW INITIALLY NEAR HUDSON BAY
DROPS SOUTH AND EAST SKIRTING THE UPPER GREAT LAKES BEFORE IT
LIFTS INTO SOUTHEAST CANADA, AND MULTIPLE SHORTWAVES ROTATE
THROUGH THE BASE OF THIS TROUGH ACROSS THE MIDWEST AND NORTHEAST.
THIS SHOULD TEND TO FOCUS SHOWERS AND STORMS ACROSS THESE REGIONS,
WITH AGAIN POTENTIAL FOR HEAVY RAINFALL IN AN ALREADY SOAKED
NORTHEAST. INITIAL RIDGING OUT WEST WILL SHIFT EAST INTO THE
NORTHERN PLAINS AS AN UPPER LOW/SHORTWAVE MOVES INTO THE NORTHWEST
EARLY NEXT WEEK. UPPER RIDGING MAY BUILD BRIEFLY AGAIN BEHIND IT
MID NEXT WEEK AHEAD OF A DEEP LOW DROPPING OUT OF THE GULF OF
ALASKA. MEANWHILE, AN ANOMALOUSLY STRONG UPPER RIDGE WILL BE
MAINTAINED OVER THE SOUTHERN TIER OF THE U.S. BRINGING HAZARDOUS
TO DANGEROUS HEAT FROM THE SOUTHWEST/CALIFORNIA EASTWARD TO THE
SOUTHERN PLAINS, SOUTHEAST, AND FLORIDA.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
OVERALL, THE LATEST GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON THE
OVERALL SYNOPTIC PATTERN THROUGH THE PERIOD, THOUGH CONTINUES TO
OFFER TYPICAL DIFFERENCES IN THE SMALLER SCALE DETAILS. SOME
UNCERTAINTIES SURROUNDING IMPULSES ROUNDING THROUGH THE MIDWEST,
WHICH HAVE SIGNIFICANT IMPLICATIONS FOR SURFACE FEATURES AND
SENSIBLE WEATHER, INCLUDING POTENTIAL HEAVY RAINFALL/FLOODING,
ESPECIALLY ACROSS PARTS OF THE MIDWEST AND INTO THE NORTHEAST.
TIMING OF THIS SYSTEM BECOMES A CONCERN LATE PERIOD AS THE CMC WAS
QUITE A BIT FASTER LIFTING IT ACROSS SOUTHEAST CANADA. TIMING ALSO
CONTINUES TO IMPROVE WITH THE NEXT LOW/TROUGH INTO THE NORTHWEST
AND WESTERN CANADA, EXCEPT THE 12Z (JULY 12) UKMET WHICH WAS
SIGNIFICANTLY DIFFERENT IN THE BETTER CONSENSUS FOR BOTH THIS LOW
AND THE NEXT IN THE GULF OF ALASKA. OTHERWISE, EVEN LATE IN THE
PERIOD, THIS IS VERY GOOD AGREEMENT THE UPPER HIGH OVER THE
SOUTHWEST MAY SLOWLY SHIFT BACK EASTWARD MORE CENTERED OVER TEXAS
AND NEW MEXICO. TONIGHT'S BLEND FOR THE WPC FORECAST USED A MAINLY
COMPOSITE BLEND OF THE DETERMINISTIC SOLUTIONS THROUGH THE FIRST
HALF OF THE PERIOD, INCREASING THE ENSEMBLE MEANS BY THE SECOND
HALF ALONG WITH THE ECMWF AND GFS. THIS MAINTAINS GOOD CONTINUITY
WITH THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
A FRONT MOVING INTO THE MIDWEST AND OHIO VALLEY AND EVENTUALLY
STALLING EARLY NEXT WEEK WILL BE THE FOCUS FOR SHOWERS AND STORMS
THROUGH MUCH OF THE PERIOD. LOCALLY HEAVY RAIN IS LIKELY IN SPOTS,
BUT STILL ENOUGH UNCERTAINTY TO PRECLUDE ANYTHING MORE THAN A
BROAD MARGINAL RISK ON THE DAYS 4 AND 5 EROS. A SURFACE LOW
LIFTING THROUGH THE NORTHEAST WILL BRING YET ANOTHER ROUND OF
HEAVY RAINFALL AS ANOMALOUS PRECIPITABLE WATER VALUES STREAM
NORTHWARD AHEAD OF A COLD FRONT. SLIGHT RISK HOLDS ON THE DAY 4
ERO ACROSS MUCH OF NEW ENGLAND, WHERE SOME LOCATIONS ARE EXTREMELY
SUSCEPTIBLE TO FLOODING DUE TO RECENT SIGNIFICANT HEAVY RAINFALL.
IT IS POSSIBLE A MODERATE RISK UPGRADE MAY BE NEEDED AS WE GET
CLOSER IN TIME, BUT RIGHT NOW THE MODELS KEEP THE HEAVIEST AXIS
JUST EAST OF THE MORE SUSCEPTIBLE AREAS OF NEW HAMPSHIRE AND
VERMONT. ELSEWHERE, SHOWERS AND STORMS LINGER NEAR THE GULF COAST
AND FLORIDA THROUGH EARLY NEXT WEEK, WITH MONSOONAL MOISTURE
RETURNING TO THE SOUTHWEST. DID OPT TO PLACE A MARGINAL RISK IN
THE AREA ON THE DAY 5 ERO WHERE THE BETTER SIGNAL FOR RAINFALL,
LOCALLY HEAVY, WAS LOCATED. THIS THREAT SHOULD CONTINUE INTO MID
NEXT WEEK AS WELL.
HAZARDOUS TO POTENTIALLY DANGEROUS HEAT WILL IMPACT MUCH OF THE
SOUTHWEST/CALIFORNIA EASTWARD INTO THE SOUTHERN STATES (AND LIKELY
BEYOND PER LATEST CPC FORECASTS). NUMEROUS DAILY HIGH
TEMPERATURES, INCLUDING THE ALL-TIME HIGH TEMPERATURE IN LAS
VEGAS, NV, AND WARM OVERNIGHT LOW RECORDS ARE THREATENED THIS
WEEKEND ACROSS THIS REGION. FARTHER EAST, THE MAIN STORY WILL BE
OPPRESSIVE HUMIDITY LEADING TO HEAT INDICES OF 105-115 (LOCALLY
HIGHER) FOR A LARGE PORTION OF THE SOUTH FROM EASTERN TEXAS INTO
THE SOUTHEAST AND FLORIDA. AGAIN, SOME DAILY TEMPERATURE RECORDS
ARE POSSIBLE. SEE KEY MESSAGES ISSUED BY WPC FOR ADDITIONAL
INFORMATION AND GRAPHICS RELATED TO THIS HEAT WAVE. MUCH ABOVE
NORMAL TEMPERATURES ACROSS THE NORTHWEST ON SUNDAY SHOULD MODERATE
AND SHIFT EAST AS HEIGHTS LOWER EARLY NEXT WEEK OVER THIS REGION.
ABOVE NORMAL TEMPERATURES MAY EXPAND NORTHWARD INTO PARTS OF THE
CENTRAL PLAINS AND MISSISSIPPI VALLEY AND POINTS EAST EARLY NEXT
WEEK.
SANTORELLI
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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