094  
FXUS21 KWNC 271849  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT JULY 27 2017  
 
SYNOPSIS: AN UNSEASONABLY STRONG MID-LEVEL LOW IS FORECAST TO SLOWLY EXIT THE  
NORTHERN MID-ATLANTIC EARLY IN THE PERIOD, WHILE A TRAILING FRONT BECOMES  
STATIONARY NEAR THE GULF COAST. THE TAIL END OF THIS FRONT IS EXPECTED TO  
EXTEND BACK TOWARDS THE SOUTHERN HIGH PLAINS. MID-LEVEL HIGH (LOW) PRESSURE  
OVER THE WESTERN U.S. (MAINLAND ALASKA) IS LIKELY TO PERSIST THROUGH THE  
BEGINNING OF AUGUST.  
 
HAZARDS  
 
HEAVY RAIN FOR THE CENTRAL FLORIDA PENINSULA, SUN-TUE, JUL 30-AUG 1.  
 
HEAVY RAIN FOR THE SOUTHERN HIGH PLAINS, SUN-MON, JUL 30-31.  
 
HEAVY RAIN SHIFTING SOUTHEAST ACROSS THE SOUTHERN GREAT PLAINS, TUE-THU, AUG  
1-3.  
 
FLASH FLOODING POSSIBLE FOR PARTS OF THE SOUTHWEST, SUN-THU, JUL 30-AUG 3.  
 
MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN GREAT BASIN, PACIFIC  
NORTHWEST, AND CALIFORNIA, TUE-THU, AUG 1-3.  
 
FLASH FLOODING POSSIBLE FOR PARTS OF THE SOUTHWESTERN U.S., FRI-THU, AUG 4-10.  
 
MODERATE RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR THE CENTRAL VALLEY OF  
CALIFORNIA, FRI-SAT, AUG 4-5.  
 
SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR MUCH OF THE WESTERN U.S. AND  
NORTHERN GREAT PLAINS, FRI-SUN, AUG 4-6.  
 
FLOODING OCCURRING, IMMINENT, OR POSSIBLE FOR PARTS OF THE MIDWEST.  
 
SEVERE DROUGHT ACROSS PARTS OF THE GREAT PLAINS, ARIZONA, CALIFORNIA, AND  
HAWAII.  
 
DETAILED SUMMARY  
 
FOR SUNDAY JULY 30 - THURSDAY AUGUST 03: A VIGOROUS CLOSED LOW AT 500-HPA  
INITIALLY OVER THE MID-ATLANTIC, A PATTERN MORE TYPICAL DURING THE COLD SEASON,  
IS LIKELY TO RESULT IN A COLD FRONT PUSHING SOUTH TO THE NORTHERN GULF OF  
MEXICO AND FLORIDA PENINSULA BY JULY 30. THE PRESENCE OF THIS FRONT, A TROUGH  
ALOFT, AND AMPLE MOISTURE ARE LIKELY TO ENHANCE THE COVERAGE OF SHOWERS AND  
THUNDERSHOWERS ACROSS THE CENTRAL FLORIDA PENINSULA THROUGH AUGUST 1. TOTAL  
RAINFALL AMOUNTS OF 2 TO 5 INCHES, LOCALLY MORE, ARE EXPECTED IN THE OUTLINED  
AREA FOR HEAVY RAINFALL.  
 
THE TAIL END OF A FRONT ALONG WITH UPSLOPE LOW IS LIKELY TO PROMOTE HEAVY  
RAINFALL (TOTAL AMOUNTS LOCALLY EXCEEDING 3 INCHES) ACROSS THE SOUTHERN HIGH  
PLAINS, CONTINUING AT LEAST THROUGH AUGUST 1. THE FOCUS FOR HEAVY RAINFALL  
(MORE THAN 1 INCH PER 24 HOURS) IS EXPECTED TO SHIFT SOUTHEAST TO SOUTHERN  
OKLAHOMA AND NORTHERN TEXAS ON AUGUST 2 AND 3. THE RISK OF FLASH FLOODING IS  
LIKELY TO REMAIN HIGH ACROSS PARTS OF COLORADO AND NEW MEXICO THROUGH AUGUST 1.  
AREAS WITH BURN SCARS AND SATURATED SOILS WILL REMAIN MOST VULNERABLE TO FLASH  
FLOODING.  
 
AS OF JULY 27 AT 8AM PDT, HURRICANE HILARY IS LOCATED AT 17.6/116W OVER THE  
EAST PACIFIC. ALTHOUGH THE INTERACTION BETWEEN HILARY AND TROPICAL STORM IRWIN  
REMAINS UNCERTAIN, THE MODEL CONSENSUS FAVORS A WEST TO NORTHWEST TRACK THROUGH  
THE WEEKEND. THE DETERMINISTIC GFS MODEL RUNS INDICATE AN INCREASE IN  
PRECIPITABLE WATER VALUES, PARTLY ASSOCIATED WITH HURRICANE HILARY, ACROSS THE  
DESERT SOUTHWEST THIS WEEKEND. THEREFORE, A FLASH FLOODING HAZARD IS POSTED FOR  
THIS REGION.  
 
AN AMPLIFIED RIDGE ALOFT IS EXPECTED TO RESULT IN MUCH ABOVE-NORMAL  
TEMPERATURES, WITH MAXIMUM TEMPERATURES 10 TO 15 DEGREES F ABOVE NORMAL, ACROSS  
PARTS OF THE NORTHERN GREAT BASIN, PACIFIC NORTHWEST, AND CALIFORNIA. THE  
HIGHEST TEMPERATURES ARE FORECAST ACROSS THE CENTRAL VALLEY OF CALIFORNIA AND  
EASTERN WASHINGTON WHERE DAILY MAXIMUM TEMPERATURES 100 TO 105 DEGREES F CAN BE  
EXPECTED. THIS ANOMALOUS HEAT MAY BEGIN TO EXPAND EAST TO THE DROUGHT-STRICKEN  
AREAS OF THE NORTHERN GREAT PLAINS LATER NEXT WEEK.  
 
MODERATE TO MAJOR FLOODING CONTINUES ALONG MULTIPLE RIVERS ACROSS EASTERN IOWA,  
NORTHERN ILLINOIS, AND SOUTHERN WISCONSIN. RIVER FLOODING IS EXPECTED TO SLOWLY  
RECEDE DURING THE NEXT DUE TO DRIER WEATHER.  
 
AN UPPER-LEVEL TROUGH IS EXPECTED TO PROMOTE SCATTERED AREAS OF RAINFALL  
THROUGHOUT MAINLAND ALASKA. RAINFALL AMOUNTS ARE NOT EXPECTED TO EXCEED HAZARDS  
CRITERIA.  
 
FOR FRIDAY AUGUST 04 - THURSDAY AUGUST 10: AN AMPLIFIED 500-HPA RIDGE IS  
EXPECTED TO PERSIST ACROSS THE WESTERN U.S. THROUGH AT LEAST THE EARLY PART OF  
WEEK-2. THIS RIDGE SUPPORTS A SLIGHT (AUG 4-6) TO MODERATE (AUG 4-5) RISK OF  
MUCH ABOVE-NORMAL TEMPERATURES FOR MUCH OF THE WESTERN U.S. AND NORTHERN GREAT  
PLAINS. THE MODERATE RISK AREA POSTED FOR THE CENTRAL VALLEY OF CALIFORNIA IS  
BASED ON: GOOD CONSISTENCY AMONG THE ENSEMBLE MEAN SOLUTIONS FOR AN AMPLIFIED  
RIDGE, GUIDANCE FROM THE GEFS REFORECAST TEMPERATURE TOOL, AND RECENT GFS  
ENSEMBLE MEANS INDICATING TEMPERATURES AVERAGING 8 DEGREES F OR MORE ABOVE  
NORMAL ON AUGUST 4 AND 5.  
 
A VARIABLE MONSOON FLOW IS EXPECTED ACROSS THE SOUTHWESTERN U.S.AS THE AXIS OF  
THE SUBTROPICAL RIDGE OSCILLATES DURING EARLY AUGUST. A FACTOR IN THE MOISTURE  
AVAILABILITY IS LIKELY TO BE EAST PACIFIC TROPICAL CYCLONE ACTIVITY. THE CFS  
MODEL INDICATES A ROBUST ATMOSPHERIC KELVIN WAVE PROPAGATING EAST ACROSS THE  
WESTERN HEMISPHERE DURING THE NEXT WEEK TO TEN DAYS WHICH WOULD PROVIDE A  
FAVORABLE ENVIRONMENT FOR ADDITIONAL TROPICAL CYCLONE DEVELOPMENT ACROSS THE  
EAST PACIFIC THROUGH MID-AUGUST. THE RISK OF FLASH FLOODING IS EXPECTED TO BE  
HIGHEST ACROSS PARTS OF THE DESERT SOUTHWEST, SOUTHERN GREAT BASIN, AND BIG  
BEND OF TEXAS DUE TO ANOMALOUS SOUTHEASTERLY FLOW AND THE POTENTIAL FOR  
ENHANCED MOISTURE ASSOCIATED WITH TROPICAL CYCLONES ACROSS THE EAST PACIFIC  
LATER IN WEEK-2. IF A TROUGH DEVELOPS ALONG THE WEST COAST AND CAUSES MORE  
WESTERLY FLOW, A RAPID DRYING TREND WOULD LIKELY OCCUR ACROSS THE SOUTHWESTERN  
U.S.  
 
THE U.S. DROUGHT MONITOR VALID ON JULY 25 INDICATES THAT SEVERE TO EXCEPTIONAL  
(D2-D4) DROUGHT COVERAGE INCREASED TO 5.18 PERCENT ACROSS THE CONTINENTAL U.S.  
THIS INCREASE IS RELATED TO AN EXPANSION OF SEVERE DROUGHT PRIMARILY ACROSS THE  
NORTHERN GREAT PLAINS.  
 
FORECASTER: BRAD PUGH  
 

 
 
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