869
FXUS02 KWBC 100700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT WED JUL 10 2024
VALID 12Z SAT JUL 13 2024 - 12Z WED JUL 17 2024
...HOT TEMPERATURES PERSIST IN THE WEST AND SPREAD EASTWARD, BUT
NOT QUITE AS EXTREME AS RECENT/SHORT RANGE HEAT...
..OVERVIEW
A PERSISTENT UPPER RIDGE OVER THE WEST WILL GRADUALLY DRIFT EAST
AND AT TIMES COMBINE WITH RIDGING STRETCHING WESTWARD FROM A STRONG
ATLANTIC UPPER HIGH THIS WEEKEND INTO EARLY NEXT WEEK. THIS WILL
CAUSE HEAT TO SPREAD ACROSS THE CENTRAL AND EASTERN U.S., BUT AS
THE RIDGE WEAKENS, TEMPERATURES SHOULD BECOME SLIGHTLY LESS EXTREME
DURING THE PERIOD. THE RIDGE SHIFTING EAST WILL ALLOW FOR SOME
MONSOONAL MOISTURE TO SPREAD INTO THE WEST. TO THE NORTH OF THE
UPPER RIDGE, PROGRESSIVE SHORTWAVES MOVING ACROSS CANADA AND THE
U.S. NORTHERN TIER WILL PUSH POSSIBLY MULTIPLE SURFACE FRONTS INTO
THE NORTHERN STATES. ACCOMPANYING ROUNDS OF SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE FROM THE NORTH-CENTRAL U.S. TO
NORTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE AGREES FAIRLY WELL WITH THE LARGE SCALE PATTERN
EVOLUTION DURING THE PERIOD, SHOWING RIDGING ACROSS THE WESTERN
U.S. ALONG WITH RIDGING STEMMING WEST FROM A STRONG ATLANTIC RIDGE
(ANCHORED BY A 600+ DM HIGH NEAR 60W LONGITUDE) GRADUALLY WEAKENING
A BIT BY MONDAY-TUESDAY. TO THE NORTH OF THE RIDGE, SHORTWAVES
PASSING THROUGH THE MEAN FLOW ARE LOWER PREDICTABILITY. MODELS HAVE
GENERALLY SHOWN BROADER BUT SHALLOW TROUGHING COMING INTO THE
NORTH-CENTRAL TO NORTHEASTERN U.S. SETTING UP NEXT WEEK, BUT VARY
WITH THE SOUTHERN EXTENT OF THE TROUGH AND WITH PLACEMENT AND
STRENGTH OF CANADIAN LOW PRESSURE THAT SHOULD PUSH SURFACE FRONT(S)
INTO THE NORTHERN TIER. WHILE THERE ARE MODEL DIFFERENCES IN THE
DYNAMICAL AND AI MODELS, NO REAL OUTLIERS SEEM EVIDENT. FARTHER
WEST, MEAN RIDGING LOOKS TO REBUILD IN THE INTERIOR NORTHWEST, BUT
MODELS LIKE THE ECMWF AND CMC HAVE SHOWN MORE SHORTWAVES DISRUPTING
THE RIDGE AT TIMES. THESE SMALLER DETAILS MAY NOT BE RESOLVED FOR
A WHILE.
WITH THE GENERAL MODEL AGREEMENT AT LEAST ON THE LARGER SCALE, A
BLEND OF DETERMINISTIC MODELS FAVORING THE 12Z ECMWF AND 18Z GFS
WAS USED EARLY IN THE PERIOD. INCLUDED SOME GEFS AND EC ENSEMBLE
MEANS BY DAY 5 AND GRADUALLY INCREASED TO ABOUT HALF BY DAY 7 WITH
INCREASING MINOR MODEL SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
INCREASING MOISTURE WILL FEED INTO THE FOUR CORNERS STATES IN A
MONSOONAL PATTERN OVER THE WEEKEND AND BEYOND, AS THE UPPER RIDGE
FINALLY WEAKENS SOME AND DRIFTS EAST. A MARGINAL RISK REMAINS IN
PLACE FOR MUCH OF ARIZONA INTO NORTHWESTERN NEW MEXICO AND
SOUTHWESTERN COLORADO ON DAY 4/SATURDAY. A MARGINAL RISK EXPANDS
SOMEWHAT TO COVER MUCH OF THE FOUR CORNERS STATES BY DAY 5/SUNDAY
AS MOISTURE CONTINUES TO STREAM IN AND INCREASE. SUNDAY'S RISK
INCLUDES MORE SENSITIVE AREAS LIKE THE SLOT CANYONS OF SOUTHERN
UTAH AND THE SACRAMENTO MOUNTAINS OF SOUTH-CENTRAL NEW MEXICO THAT
HAVE RECENT BURN SCARS. THIS MOISTURE PLUME IS FORECAST TO EXPAND
FARTHER NORTH INTO EARLY NEXT WEEK FOR INCREASING RAIN/THUNDERSTORM
CHANCES FOR THE ROCKIES TO HIGH PLAINS.
THROUGH THE WEEKEND AND EARLY NEXT WEEK, THE COMBINATION OF
NORTHERN TIER U.S./SOUTHERN CANADA SHORTWAVES AND A COUPLE SURFACE
FRONTS WILL PROMOTE ONE OR MORE CLUSTERS OF SHOWERS/STORMS FROM THE
DAKOTAS/UPPER MIDWEST INTO THE GREAT LAKES. THERE REMAINS LOW
PREDICTABILITY IN THE MAGNITUDE AND LOCATION OF HEAVY RAIN AMOUNTS,
PRECLUDING ANY ERO RISKS AT THIS POINT. BUT MUCH OF THIS REGION
WILL BE SENSITIVE TO ADDITIONAL RAINFALL AFTER RECENT WEEKS OF
HEAVY RAIN, SO WILL CONTINUE TO MONITOR THE POTENTIAL FOR FLASH
FLOODING. AMPLE INSTABILITY WILL BE IN PLACE, ALLOWING FOR HIGH
RAIN RATES, BUT STORMS LOOK TO BE MOVING QUICKLY/NOT TRAINING, SO
THERE ARE COMPETING FACTORS. ROUNDS OF RAIN/STORMS WILL ALSO
PROGRESS INTO THE APPALACHIANS/NORTHEAST BY EARLY NEXT WEEK.
LINGERING RAIN IS POSSIBLE ACROSS THE EASTERN SEABOARD ON
SATURDAY, BUT THE HEAVIEST RAINFALL SHOULD BE OVER BY THEN COMPARED
TO THE SHORT RANGE PERIOD. EXPECT SCATTERED SHOWER AND
THUNDERSTORM CHANCES TO CONTINUE AND EXPAND THROUGH THE
SOUTHEASTERN U.S. (LOWER MISSISSIPPI VALLEY INTO THE
SOUTHEAST/FLORIDA AND THE CAROLINAS) OVER THE WEEKEND INTO EARLY
NEXT WEEK, WITH LOCALLY HEAVY RAIN POSSIBLE.
THE DANGEROUS HEAT WAVE THAT HAS BEEN ONGOING ACROSS THE WEST
SHOULD BE EASING SOMEWHAT BY THE MEDIUM RANGE PERIOD, BUT STILL
REMAINING HOT. TEMPERATURES IN THE 110S ARE LIKELY TO CONTINUE
ACROSS THE DESERT SOUTHWEST, A FEW DEGREES ABOVE AVERAGE. FARTHER
NORTH, TEMPERATURE ANOMALIES WILL SLOWLY TREND DOWN FROM AROUND
+10F ABOVE NORMAL SATURDAY TO NEAR NORMAL NEXT WEEK IN THE CENTRAL
GREAT BASIN, BUT IN THE NORTHERN GREAT BASIN THE ANOMALIES WILL
ONLY DROP FROM AROUND +15F ABOVE NORMAL TO +10F. MEANWHILE, THE
NORTHERN HALF OF THE ROCKIES AND PLAINS CAN EXPECT TEMPERATURES
AROUND 10-15F ABOVE NORMAL THIS WEEKEND, WITH SOME AREAS SHOWING
TEMPERATURES OVER 100F. THE NORTHERN AREAS ARE LIKELY TO MODERATE
TO NEAR OR SLIGHLY BELOW AVERAGE FOR HIGHS AFTER A COLD FRONT
PASSES, BUT HIGH HEAT INDICES ARE LIKELY MONDAY-TUESDAY FROM THE
CENTRAL PLAINS AND MID-MISSISSIPPI VALLEY SOUTHWARD. AREAS ACROSS
THE OHIO VALLEY INTO THE APPALACHIANS CAN EXPECT ABOVE NORMAL
TEMPERATURES THIS WEEKEND AND EXPANDING INTO THE EASTERN SEABOARD
EARLY NEXT WEEK. OVERALL, MOST AREAS OF THE LOWER 48 WILL HAVE AT
LEAST SOME HEAT CONCERNS DURING THE PERIOD.
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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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