Prognostic Meteorological Discussion
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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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