Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 251829
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 25 2016

SYNOPSIS: AN AREA OF UPPER-LEVEL LOW PRESSURE ACROSS THE WEST-CENTRAL CONUS IS
EXPECTED TO GRADUALLY WEAKEN DURING THE NEXT WEEK WITH A DISSIPATING SURFACE
FRONT OVER THE GREAT PLAINS. A LOW PRESSURE SYSTEM IS EXPECTED TO AFFECT THE
COASTAL SOUTHEAST DURING THE MEMORIAL DAY WEEKEND. AN AREA OF UPPER-LEVEL HIGH
PRESSURE IS LIKELY TO PERSIST ACROSS ALASKA INTO THE BEGINNING OF JUNE. DURING
WEEK-2, AN AREA OF UPPER-LEVEL HIGH PRESSURE IS EXPECTED TO BUILD ACROSS THE
NORTHWESTERN CONUS WITH AN AREA OF UPPER-LEVEL LOW PRESSURE EXTENDING ACROSS
THE EASTERN AND SOUTH-CENTRAL U.S.

HAZARDS

LOCALLY HEAVY RAIN FOR THE COASTAL SOUTHEAST, SAT-MON, MAY 28-30.

LOCALLY HEAVY RAIN FOR PARTS OF THE GREAT PLAINS AND LOWER MISSOURI RIVER
VALLEY, SUN-TUE, MAY 29-31.

LOCALLY  HEAVY RAIN FOR PARTS OF TEXAS, WED-THU, JUNE 1-2.

MUCH ABOVE NORMAL TEMPERATURES FOR PARTS OF THE GREAT LAKES, OHIO VALLEY,
CENTRAL APPALACHIANS, AND NORTHEAST, SAT, MAY 28.

FLOODING IS OCCURRING, IMMINENT, LIKELY, OR POSSIBLE ACROSS PARTS OF THE
CENTRAL AND SOUTHERN PLAINS, CENTRAL ROCKIES, LOWER MISSOURI RIVER VALLEY, AND
MIDWEST, SAT-SUN, MAY 28-29.

A SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC
NORTHWEST, THU-WED, JUNE 2-8.

SEVERE DROUGHT ACROSS MUCH OF CALIFORNIA AND NEVADA (AND ADJACENT PARTS OF
ARIZONA AND OREGON), NORTH-CENTRAL WYOMING, AND HAWAII.

DETAILED SUMMARY

FOR SATURDAY MAY 28 - WEDNESDAY JUNE 01: SHORTWAVE TROUGHS EJECTING FROM THE
LONGWAVE TROUGH CENTERED OVER THE ROCKIES IS LIKELY TO TRIGGER DAILY CONVECTION
ACROSS THE GREAT PLAINS THROUGH THE END OF MAY. THE MOST LIKELY AREA AND TIMING
FOR LOCALLY HEAVY RAINFALL (MORE THAN 1 INCH PER 24 HOURS) EXTENDS FROM THE
LOWER MISSOURI RIVER VALLEY SOUTH TO NORTHERN TEXAS FROM MAY 29 TO 31. ON JUNE
1, THE RISK FOR HEAVY RAINFALL IS EXPECTED TO SHIFT SOUTH ACROSS TEXAS WHERE
MOIST, SOUTHEASTERLY FLOW INTERACTS WITH A REMNANT FRONT. WEAKENING FLOW AT THE
MID-LEVELS IS EXPECTED TO BECOME LESS FAVORABLE FOR WIDESPREAD SEVERE WEATHER
EVENTS ACROSS THE GREAT PLAINS.



RECENT RAINFALL HAS RESULTED IN MINOR TO MODERATE FLOODING ACROSS PARTS OF THE
CENTRAL U.S. AND IS LIKELY TO CONTINUE INTO THE BEGINNING OF JUNE. FOR EXAMPLE,
MODERATE FLOODING IS FORECAST TO PERSIST ALONG PARTS OF THE NORTH PLATTE RIVER
IN NEBRASKA. ANY HEAVY RAINFALL COULD EXACERBATE ONGOING FLOODING AND MAY CAUSE
ADDITIONAL FLOODING DUE TO THE ANTECEDENT WETNESS.



MODEL GUIDANCE CONTINUES TO INDICATE THAT A MID-LEVEL LOW AND A WEAK SURFACE
LOW WITH TROPICAL ORIGINS APPROACHES THE SOUTHEAST COAST DURING THE WEEKEND.
REGARDLESS OF INTENSITY, LOCALLY HEAVY RAIN (MORE THAN 1 INCH PER 24 HOURS) IS
EXPECTED ACROSS THE COASTAL SOUTHEAST FROM MAY 28-30. DUE TO WEAK STEERING
FLOW, THE SURFACE LOW IS FORECAST TO REMAIN NEAR THE COASTAL SOUTHEAST. PLEASE
REFER TO THE NATIONAL HURRICANE CENTER FOR THE LATEST UPDATES ON THIS POTENTIAL
TROPICAL OR SUBTROPICAL STORM.



STRONG RIDGING ALOFT IS EXPECTED TO RESULT IN MUCH ABOVE-NORMAL TEMPERATURES
ACROSS PARTS OF THE NORTHEAST, EASTERN GREAT LAKES, AND UPPER OHIO VALLEY ON
SATURDAY, MAY 28. MAXIMUM TEMPERATURES ARE FORECAST TO AVERAGE 10 TO 15 DEGREES
F ABOVE-NORMAL ACROSS THESE AREAS WITH SOME LOCATIONS LIKELY REACHING 90
DEGREES F.



UNSEASONABLY WARM TEMPERATURES ARE LIKELY TO PERSIST ACROSS MUCH OF ALASKA AS
RIDGING ALOFT REMAINS DOMINANT THROUGH THE END OF MAY. ALTHOUGH THE 6Z GFS
ENSEMBLE MEAN INDICATES THAT TEMPERATURES WILL AVERAGE MORE THAN 12 DEGREES F
ABOVE-NORMAL ACROSS SOUTHWEST ALASKA, THESE TEMPERATURES ARE NOT CONSIDERED TO
BE HAZARDOUS.

FOR THURSDAY JUNE 02 - WEDNESDAY JUNE 08: THE TAIL END OF A SURFACE FRONT, A
WEAKNESS IN THE SUBTROPICAL RIDGE, AND ABUNDANT LOW-LEVEL MOISTURE ARE LIKELY
TO RESULT IN LOCALLY HEAVY RAINFALL ACROSS PARTS OF SOUTH-CENTRAL TEXAS AND THE
RIO GRANDE VALLEY ON JUNE 2. THE DETERMINISTIC 6Z/12Z GFS AND 0Z ECMWF MODELS
INDICATE LOCAL RAINFALL AMOUNTS NEAR 2 INCHES WITHIN THE AREA HIGHLIGHTED FOR
HEAVY RAINFALL. ELSEWHERE, THE GFS ENSEMBLE MEAN INDICATES THE POTENTIAL FOR
HEAVY RAIN ALONG THE SOUTHERN COAST OF ALASKA BUT THE ECMWF ENSEMBLE MEAN IS
WEAKER WITH THE ONSHORE FLOW.



THE GFS AND ECMWF ENSEMBLE MEANS AND THEIR DETERMINISTIC MODEL RUNS DEPICT AN
INCREASE IN 500-HPA HEIGHTS ACROSS THE WESTERN CONUS BY THE BEGINNING OF
WEEK-2. A SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES IS POSTED FOR PARTS OF
THE PACIFIC NORTHWEST WHERE THE GEFS REFORECAST TOOL INDICATES THAT DAILY
MAXIMUM TEMPERATURES HAVE A 20 PERCENT CHANCE OR MORE OF EXCEEDING THE 85TH
PERCENTILE AND THE POTENTIAL EXISTS FOR MAXIMUM TEMPERATURES TO EXCEED 90
DEGREES F.



ACCORDING TO THE U.S. DROUGHT MONITOR (ISSUED MAY 19), SEVERE, OR GREATER
INTENSITY, DROUGHT COVERS 4.07 PERCENT OF THE U.S. DROUGHT MONITOR AREAS
(INCLUDING ALASKA, HAWAII, AND PUERTO RICO), DOWN FROM 4.49 PERCENT LAST WEEK.
THIS IS THE LOWEST COVERAGE SINCE OCTOBER 2010. A VISUAL COMPARISON BETWEEN THE
TWO LATEST U.S. DROUGHT MONITOR MAPS REVEALS ONE-CATEGORY IMPROVEMENTS IN
PORTIONS OF NORTHERN CALIFORNIA (D2 TO D1), WESTERN NEVADA (D3 TO D2), AND UTAH
(D1 TO D0).

FORECASTER: BRAD PUGH

$$




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