Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 281925
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 28 2014

SYNOPSIS: A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO STRENGTHEN AS IT TRACKS
TOWARDS THE UPPER MISSISSIPPI VALLEY ON SUNDAY, WHILE A STRONG COLD FRONT
PUSHES EAST FROM THE NORTH-CENTRAL PLAINS TO THE MIDWEST. AN AREA OF
UPPER-LEVEL LOW PRESSURE IS EXPECTED TO DEVELOP ACROSS THE NORTHWESTERN U.S.
AND PERSIST INTO EARLY SEPTEMBER. ELSEWHERE, A SUBTROPICAL RIDGE OF HIGH
PRESSURE IS FORECAST TO BUILD ACROSS THE SOUTHERN PLAINS, LOWER MISSISSIPPI
VALLEY, AND SOUTHEAST. A SERIES OF WEAK LOW PRESSURE SYSTEMS ARE EXPECTED TO
PROGRESS EAST FROM THE BERING SEA AND AFFECT ALASKA DURING THE NEXT WEEK.

HAZARDS

HEAVY RAIN SHIFTING EAST FROM THE NORTHERN/CENTRAL GREAT PLAINS TO THE GREAT
LAKES, SUN-MON, AUG 31-SEP 1.

SEVERE WEATHER FOR PARTS OF THE NORTHERN/CENTRAL PLAINS AND UPPER MISSISSIPPI
VALLEY, SUN, AUG 31.

HEAVY RAIN FOR SOUTH TEXAS, TUE-WED, SEP 2-3.

RIVER FLOODING IS OCCURRING, IMMINENT, OR POSSIBLE ACROSS THE MISSOURI RIVER
VALLEY.

SEVERE DROUGHT FOR THE CENTRAL AND SOUTHERN GREAT PLAINS, SOUTHWEST, PACIFIC
NORTHWEST, GREAT BASIN, AND CALIFORNIA.

DETAILED SUMMARY

FOR SUNDAY AUGUST 31 - THURSDAY SEPTEMBER 04: A VIGOROUS SHORTWAVE TROUGH IS
FORECAST TO REACH THE NORTH-CENTRAL GREAT PLAINS BY SUNDAY. THIS SHORTWAVE
TROUGH AND ANOMALOUS LOW-LEVEL MOISTURE ARE LIKELY TO RESULT IN ANOTHER ROUND
OF HEAVY RAINFALL (1 TO 2 INCHES, LOCALLY MORE) ACROSS PARTS OF THE GREAT
LAKES, UPPER MISSISSIPPI VALLEY, AND MIDWEST ON SUNDAY AND MONDAY. DUE TO
RECENT HEAVY RAINFALL, THIS REGION IS VULNERABLE TO FLASH FLOODING AND ISOLATED
RIVER FLOODING. INSTABILITY, ABUNDANT LOW-LEVEL MOISTURE, AND FAVORABLE WIND
SHEAR ARE PREDICTED TO FAVOR SEVERE THUNDERSTORMS FROM THE NORTH-CENTRAL GREAT
PLAINS EAST TO THE MIDWEST ON SUNDAY. THUNDERSTORMS ARE EXPECTED TO CONTINUE
INTO MONDAY ACROSS THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES, BUT LOWER
INSTABILITY MAY LIMIT THE COVERAGE OF SEVERE THUNDERSTORMS.



AN UPPER-LEVEL TROUGH IS EXPECTED TO BRING RELATIVELY COOL TEMPERATURES TO THE
NORTHERN ROCKIES DURING THE LABOR DAY WEEKEND. MAXIMUM TEMPERATURES ARE
FORECAST TO AVERAGE 5 TO 10 DEGREES F BELOW-NORMAL FROM SUNDAY THROUGH NEXT
TUESDAY ACROSS THE NORTHERN ROCKIES. ALTHOUGH MINIMUM TEMPERATURES ARE FORECAST
TO REMAIN ABOVE FREEZING ACROSS THE LOWER ELEVATIONS OF THE NORTHERN HIGH
PLAINS, FREEZING TEMPERATURES ARE EXPECTED ACROSS THE HIGHER ELEVATIONS OF THE
NORTHERN ROCKIES.



EARLY NEXT WEEK, A TROPICAL WAVE ORIGINATING FROM THE EASTERN CARIBBEAN SEA IS
EXPECTED TO ENTER THE SOUTHWEST GULF OF MEXICO WHERE CONDITIONS COULD BECOME
MORE FAVORABLE FOR TROPICAL CYCLONE DEVELOPMENT. THE GFS MODEL CONTINUES TO
INDICATE MORE ROBUST SURFACE LOW DEVELOPMENT WITH THIS TROPICAL WAVE THAN THE
ECMWF MODEL. REGARDLESS OF ANY TROPICAL CYCLONE DEVELOPMENT, THIS TROPICAL WAVE
ALONG WITH EASTERLY FLOW INCREASE THE POTENTIAL FOR HEAVY RAINFALL ACROSS SOUTH
TEXAS NEXT WEEK.



OCCASIONAL RAIN IS FORECAST TO AFFECT CENTRAL/SOUTHERN INTERIOR ALASKA AND THE
ALASKAN PANHANDLE THROUGHOUT THIS PERIOD, WHILE SOME SNOW IS EXPECTED NORTH OF
THE BROOKS RANGE. RAIN AND SNOW AMOUNTS ARE LIKELY TO REMAIN BELOW HAZARDOUS
CRITERIA.

FOR FRIDAY SEPTEMBER 05 - THURSDAY SEPTEMBER 11: THE 0Z GFS AND 0Z ECMWF
ENSEMBLE MEANS AT 500-HPA INDICATE A WEAK TROUGH PERSISTING ACROSS THE
NORTHWESTERN U.S. WITH A BROAD RIDGE OVER THE EAST-CENTRAL U.S. THIS LONGWAVE
PATTERN IS EXPECTED TO YIELD A CONTINUATION OF RELATIVELY COOL TEMPERATURES
ACROSS THE NORTHERN ROCKIES AND ABOVE-NORMAL TEMPERATURES FROM THE
SOUTH-CENTRAL CONUS TO THE EAST COAST. ALTHOUGH AN ACTIVE PATTERN IS EXPECTED
ACROSS THE MIDWEST AND GREAT LAKES DUE TO THE UPSTREAM TROUGH, UNCERTAINTY ON
THE TIMING OF INDIVIDUAL SHORTWAVE TROUGHS PRECLUDE DESIGNATION OF A HEAVY RAIN
HAZARD FOR THESE AREAS AT THIS TIME.



THE MOST RECENT U.S. DROUGHT MONITOR, RELEASED ON AUGUST 28, INDICATES THE
PERCENTAGE OF CONUS IN SEVERE TO EXCEPTIONAL DROUGHT DECREASING VERY SLIGHTLY
TO 21.55 PERCENT.

FORECASTER: BRAD PUGH

$$



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