Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 291844
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 29 2016

SYNOPSIS: A SERIES OF LOW PRESSURE SYSTEMS ARE EXPECTED TO DEVELOP ALONG A
FRONT NEAR THE EAST COAST THROUGH MID-WEEK. AN AREA OF UPPER-LEVEL HIGH
PRESSURE IS EXPECTED TO BRIEFLY BUILD ACROSS THE WEST-CENTRAL U.S. DURING THE
BEGINNING OF MAY. AN AREA OF UPPER-LEVEL LOW PRESSURE IS FORECAST TO MOVE
INLAND FROM THE EAST PACIFIC PRIOR TO THE WEEK-2 PERIOD. MULTIPLE SURFACE LOWS
ARE EXPECTED TO AFFECT SOUTHERN ALASKA AND THE ALASKA PANHANDLE DURING THE NEXT
TWO WEEKS.

HAZARDS

HEAVY RAIN FOR THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST TEXAS, MON, MAY 2.

HEAVY RAIN FOR THE EASTERN CAROLINAS, TUE-WED, MAY 3-4.

FLOODING OCCURRING, IMMINENT, LIKELY, OR POSSIBLE ACROSS PARTS OF THE CENTRAL
U.S., MON-TUE, MAY 2-3.

FLOODING POSSIBLE ACROSS PARTS OF WASHINGTON, MON-TUE, MAY 2-3.

MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE ROCKIES AND HIGH PLAINS, MON,
MAY 2.

MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC NORTHWEST, MON, MAY 2.

MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF EASTERN WASHINGTON, TUE-WED, MAY
3-4.

MUCH ABOVE-NORMAL TEMPERATURES FOR THE DESERT SOUTHWEST, WED, MAY 4.

HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW) FOR PARTS OF THE SIERRA
MOUNTAINS, GREAT BASIN, NORTH-CENTRAL ROCKY MOUNTAINS, AND NORTH-CENTRAL HIGH
PLAINS, SAT-SUN, MAY 7-8.

SLIGHT RISK OF MUCH-ABOVE NORMAL TEMPERATURES FOR MUCH OF THE GREAT PLAINS,
SAT, MAY 7.

SEVERE DROUGHT ACROSS PARTS OF CALIFORNIA, THE GREAT BASIN, SOUTHWEST, WYOMING,
SOUTHERN GREAT PLAINS, HAWAII, AND PUERTO RICO.

DETAILED SUMMARY

FOR MONDAY MAY 02 - FRIDAY MAY 06: THE RISK OF HEAVY RAINFALL (LOCALLY MORE
THAN 2 INCHES) ALONG A TRAILING FRONT IS EXPECTED TO PERSIST ACROSS THE LOWER
MISSISSIPPI VALLEY AND SOUTHEAST TEXAS THROUGH MONDAY, MAY 2. THE DETERMINISTIC
6Z GFS AND 0Z ECMWF MODELS ON APRIL 29 INDICATE PRECIPITABLE WATER VALUES
REMAINING AROUND 1.75 INCHES ACROSS THIS REGION UNTIL DRIER NORTHERLY FLOW
ARRIVES ON TUESDAY, MAY 3. MEANWHILE, WAVES OF LOW PRESSURE ARE EXPECTED TO
DEVELOP ALONG A FRONT NEAR THE EAST COAST AND RESULT IN HEAVY RAINFALL ACROSS
THE EASTERN CAROLINAS ON TUESDAY AND WEDNESDAY, MAY 3 AND 4. THE HEAVIEST
RAINFALL AMOUNTS (2 INCHES OR MORE IN THE 48-HOUR PERIOD) ARE EXPECTED ACROSS
THE OUTER BANKS OF NORTH CAROLINA.



AN UPPER-LEVEL TROUGH IS EXPECTED TO BRING A BRIEF PERIOD OF MUCH-BELOW NORMAL
TEMPERATURES TO PARTS OF THE SOUTH-CENTRAL ROCKIES AND HIGH PLAINS ON MONDAY,
MAY 2. MAXIMUM TEMPERATURES ARE FORECAST TO AVERAGE MORE THAN 20 DEGREES F
BELOW-NORMAL AND MINIMUM TEMPERATURES COULD FALL BELOW FREEZING IN THE
HIGHLIGHTED AREA ON THE MAP.



A STRONG RIDGE ALOFT IS EXPECTED TO PROMOTE MUCH ABOVE-NORMAL TEMPERATURES (10
TO 20 DEGREES F) ACROSS THE PACIFIC NORTHWEST FROM MAY 2 TO 4. THE ANOMALOUS
WARMTH IS EXPECTED TO ACCELERATE SNOW MELT AND MAY TRIGGER RIVER FLOODING
ACROSS PARTS OF WASHINGTON. THE SUMMER-LIKE WARMTH, WITH MAXIMUM TEMPERATURES
INTO THE 80S, IS EXPECTED TO END LATER IN THE WEEK WHEN 500-HPA HEIGHTS
DECREASE.



ELSEWHERE, MUCH ABOVE-NORMAL TEMPERATURES ARE POSTED FOR THE DESERT SOUTHWEST
ON WEDNESDAY, MAY 4, WHEN MAXIMUM TEMPERATURES ARE FORECAST TO PEAK NEAR 10
DEGREES F ABOVE-NORMAL AND COULD REACH 100 DEGREES F IN THE LOWER DESERTS.



MODEL GUIDANCE REMAINS CONSISTENT THAT A VIGOROUS UPPER-LEVEL TROUGH SHIFTS
EAST INTO THE WESTERN U.S. BY FRIDAY, MAY 6. THE DETERMINISTIC 6Z GFS MODEL ON
APRIL 29 IS MOST PROGRESSIVE WITH THIS UPPER-LEVEL TROUGH AND INDICATES HEAVY
RAIN AND HIGH-ELEVATION SNOW DEVELOPING OVER THE NORTH-CENTRAL ROCKIES ON MAY
6. HOWEVER, THE DETERMINISTIC 0Z ECMWF MODEL IS SLOWER WITH THE PROGRESSION OF
THIS UPPER-LEVEL TROUGH AND DELAYS THE RISK OF HEAVY RAIN AND HIGH-ELEVATION
SNOW ACROSS THE INTERIOR WEST UNTIL WEEK-2. DUE TO THESE MODEL DIFFERENCES, A
HEAVY PRECIPITATION HAZARD IS POSTED IN THE WEEK-2 PERIOD.



ANTECEDENT HEAVY RAINFALL RESULTS IN AREAS OF FLOODING OCCURRING, IMMINENT,
LIKELY, OR POSSIBLE ACROSS PORTIONS OF THE CENTRAL U.S. MULTIPLE RIVERS ARE
CURRENTLY IN MINOR TO MODERATE FLOOD STAGE FROM LOUISIANA AND TEXAS NORTH TO
THE MISSOURI RIVER VALLEY.



A SERIES OF LOW PRESSURE SYSTEMS ARE EXPECTED TO BRING PERIODS OF RAIN TO THE
SOUTHERN COASTAL AREAS OF ALASKA AND THE ALASKA PANHANDLE. HOWEVER, RAINFALL
AMOUNTS ARE FORECAST TO REMAIN BELOW HAZARDS CRITERIA.

FOR SATURDAY MAY 07 - FRIDAY MAY 13: A VIGOROUS UPPER-LEVEL TROUGH IS LIKELY TO
BE CENTERED OVER THE ROCKY MOUNTAINS EARLY IN THE WEEK-2 PERIOD. BASED ON
EXCELLENT MODEL CONSISTENCY, HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW)
IS MOST LIKELY ACROSS PARTS OF THE SIERRA MOUNTAINS, GREAT BASIN, NORTH-CENTRAL
ROCKY MOUNTAINS, AND HIGH PLAINS ON MAY 7 AND 8. THE 0Z ECMWF ENSEMBLE MEAN ON
APRIL 29 INDICATES A 48-HOUR MAX OF MORE THAN 1 INCH (LIQUID EQUIVALENT) IN
WYOMING FROM MAY 7-8.



DOWNSTREAM OF THE UPPER-LEVEL TROUGH ENTERING THE WESTERN U.S., A SLIGHT RISK
OF MUCH ABOVE-NORMAL TEMPERATURES IS POSTED FOR PARTS OF THE GREAT PLAINS WHERE
THE GEFS REFORECAST TEMPERATURE TOOL INDICATES THAT MAXIMUM TEMPERATURES HAVE
AT LEAST A 20 PERCENT CHANCE OF EXCEEDING THE 85TH PERCENTILE COMPARED TO
CLIMATOLOGY.



ACCORDING TO THE U.S. DROUGHT MONITOR VALID ON APRIL 26, SEVERE, OR GREATER
INTENSITY, DROUGHT COVERS 5 PERCENT OF THE U.S. DROUGHT MONITOR AREAS WITH A
CONTINUED DECREASE IN COVERAGE DURING THE PAST SIX MONTHS.

FORECASTER: BRAD PUGH

$$




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