261
FXUS02 KWNH 030717
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
316 AM EDT MON AUG 3 2026
VALID 12Z THU AUG 06 2026 - 12Z MON AUG 10 2026
...HEAT WAVE CONTINUES THROUGH THE WEEK ACROSS THE SOUTHWEST AND
INTERMOUNTAIN WEST, EXPANDING NORTHEASTWARD WITH TIME...
..OVERVIEW
THE UPPER RIDGE CAUSING EXCESSIVE HEAT ATOP THE SOUTHWEST MIDWEEK
WILL GRADUALLY INTENSIFY AND EXPAND NORTH AND EAST LATE WEEK INTO
NEXT WEEKEND, BRINGING HOT TEMPERATURES ACROSS THE INTERMOUNTAIN
WEST TO PLAINS AND POTENTIALLY INTO THE SOUTH. MEANWHILE, A HANDFUL
OF FRONTAL SYSTEMS IN THE CENTRAL AND EASTERN U.S. WILL TRIGGER
SCATTERED SHOWERS AND THUNDERSTORMS THERE, WITH MONSOON CONVECTION
IN THE SOUTHWEST AS WELL.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS SHOW GOOD AGREEMENT ON THE LARGE SCALE PATTERN EVOLUTION
THROUGH THE PERIOD, WHICH FEATURES A NORTHERN STREAM TROUGH THROUGH
THE NORTH-CENTRAL AND THEN THE NORTHEAST U.S. AND A SPRAWLING
SOUTHERN TIER RIDGE. THE MAIN FOCUS OF UNCERTAINTY CONTINUES TO BE
WITH THE POSITIONS OF VARIOUS ENERGIES ALOFT WITHIN THE BROADER
TROUGH, AS WELL AS THE TIMING OF A SHORTWAVE INTO THE NORTHWEST
WHICH MAY FINALLY ACT TO ERODE THE RIDGE OVER THE SOUTHWEST. MODELS
CONTINUE TO TREND TOWARDS MORE SEPARATION BETWEEN THE RIDGE OVER
THE SOUTHWEST AND THE SUBTROPICAL ATLANTIC RIDGE WITH SOME WEAK
ENERGY IN BETWEEN THEM. THIS WOULD ALLOW FOR MORE TROPICAL MOISTURE
INTRUSION AND A WET PATTERN ACROSS THE SOUTHEAST INTO AT LEAST
EARLY NEXT WEEK. OVERALL, THERE ARE NOT REALLY CONSIDERABLE
OUTLIERS WITH THE PATTERN WITH DIFFERENCES WELL WITHIN THE NORMAL
SPREAD FOR THE MEDIUM RANGE. THUS THE WPC FORECAST USED A BLEND OF
DETERMINISTIC GUIDANCE FOR THE EARLY PART OF THE PERIOD, TRENDING
TOWARDS 50/50 ENSEMBLE MEANS WITH DETERMINISTIC GUIDANCE FOR DAYS 6
AND 7. THIS MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
FOR MIDWEEK, A SLIGHTLY WEAKER UPPER RIDGE WILL ALLOW FOR
LESSENING HEATRISK ACROSS THE SOUTHWEST COMPARED TO THE SHORT RANGE
PERIOD, THOUGH MODERATE HEATRISK WILL STILL BE WIDESPREAD WITH
ISOLATED MAJOR AND EXTREME VALUES. HEAT SHOULD BUILD GRADUALLY
NORTHWARD ACROSS THE INTERMOUNTAIN WEST AND ROCKIES TO THE HIGH
PLAINS, AS WELL AS EASTWARD IN THE MID-SOUTH AS THE UPPER RIDGE
EXPANDS. SEE KEY MESSAGES ISSUED BY WPC FOR THIS EVENT FOR
ADDITIONAL INFORMATION REGARDING THIS LONG LASTING AND DANGEROUS
HEAT WAVE. TEMPERATURES ACROSS THE NORTHERN TIER AND INTO THE EAST
SHOULD BE GENERALLY NEAR AVERAGE MOST OF THE PERIOD.
A REASONABLY STRONG FRONT WILL BE MOVING THROUGH THE MIDWEST AND
CENTRAL PLAINS BY THURSDAY AND TRIGGER A CORRIDOR OF POTENTIALLY
HEAVY RAIN AND THUNDERSTORMS ALONG AND AHEAD OF IT. MEANWHILE, WEAK
FRONTAL BOUNDARIES WILL ALLOW FOR SHOWERS AND THUNDERSTORMS TO BE
SCATTERED ACROSS THE EAST, WITH SOME LOCALLY HEAVY TO EXCESSIVE
RAINFALL POSSIBLE THERE AS WELL. THESE INTERACTING FEATURES SHOULD
ALLOW FOR ADDITIONAL ROUNDS OF RAIN AND STORMS ACROSS THE NORTH-
CENTRAL TO EASTERN U.S. THROUGH LATE WEEK AS THE MEAN FRONTAL
BOUNDARY MAY STALL FOR A BIT. A WET PATTERN MAY SET UP BY NEXT
WEEKEND AND EARLY NEXT WEEK, ESPECIALLY FOR THE SOUTHEAST, AS
TROPICAL MOISTURE ROUNDS THE WEST SIDE OF THE RIDGE. ELSEWHERE,
MONSOONAL CONVECTION IS LIKELY FOR ARIZONA AND NEW MEXICO IN
PARTICULAR, WITH SCATTERED CONVECTION OCCASIONALLY REACHING
PORTIONS OF UTAH AND COLORADO. THE REMAINDER OF THE WEST INTO THE
NORTHERN PLAINS SHOULD BE MOSTLY DRY DURING THE PERIOD.
SANTORELLI
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, 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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