Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 281912
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 28 2016

SYNOPSIS: A SURFACE LOW AND TRAILING FRONT ARE FORECAST TO SLOWLY PROGRESS
ACROSS THE EAST-CENTRAL U.S. EARLY IN THE PERIOD. AN AREA OF UPPER-LEVEL HIGH
PRESSURE IS EXPECTED TO BRIEFLY BUILD ACROSS THE WESTERN U.S. DURING THE
BEGINNING OF MAY. THEREAFTER, AN AREA OF UPPER-LEVEL LOW PRESSURE IS FORECAST
TO MOVE INLAND FROM THE EAST PACIFIC BY 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 PARTS OF THE WESTERN GULF COAST, SUN-MON, MAY 1-2.

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

FLOODING OCCURRING, IMMINENT, LIKELY, OR POSSIBLE ACROSS PARTS OF THE CENTRAL
U.S., SUN-MON, MAY 1-2.

HEAVY SNOW FOR THE SANGRE DE CRISTO MOUNTAINS OF SOUTHERN COLORADO, SUN-MON,
MAY 1-2.

MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE ROCKIES AND HIGH PLAINS,
SUN-MON, MAY 1-2.

MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC NORTHWEST, SUN-MON, MAY
1-2.

MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF EASTERN WASHINGTON AND WESTERN
IDAHO, 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 GREAT BASIN
AND ROCKY MOUNTAINS, FRI-SAT, MAY 6-7.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE GREAT PLAINS,
FRI, MAY 6.

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

DETAILED SUMMARY

FOR SUNDAY MAY 01 - THURSDAY MAY 05: A LOW PRESSURE SYSTEM IS FORECAST TO CROSS
THE EASTERN U.S. ON SUNDAY AND MONDAY, MAY 1-2, WITH WIDESPREAD LIGHT TO
MODERATE RAINFALL AMOUNTS (GENERALLY 1 INCH OR LESS).  A CONTINUED RISK OF
HEAVY RAINFALL (LOCALLY MORE THAN 3 INCHES) IS EXPECTED TO PERSIST FOR THE
WESTERN GULF COAST ALONG A TRAILING FRONT. THE DETERMINISTIC 6Z GFS AND 0Z
ECMWF MODELS INDICATE PRECIPITABLE WATER VALUES REMAINING NEAR 1.75 INCHES
ALONG THE TEXAS GULF COAST THROUGH AT LEAST MONDAY, MAY 2. THEREFORE, A HEAVY
RAIN HAZARD IS POSTED FOR THIS REGION ON MAY 1 AND 2. HEAVY RAIN IS ALSO
EXPECTED ACROSS THE EASTERN CAROLINAS ON MAY 3 AND 4 AS A WAVE OF LOW PRESSURE
DEVELOPS ALONG A STATIONARY FRONT.



THE RISK OF HEAVY SNOW (MORE THAN 6 INCHES PER 24 HOURS) IS EXPECTED TO RETURN
TO THE SANGRE DE CRISTO MOUNTAINS OF SOUTHERN COLORADO BY SUNDAY, MAY 1, AS
ANOTHER SHORTWAVE TROUGH APPROACHES FROM THE FOUR CORNERS REGION. THE HEAVIEST
SNOWFALL AMOUNTS ARE FORECAST FOR ELEVATIONS ABOVE 9,000 FEET BUT ACCUMULATING
SNOW MAY OCCUR IN ELEVATIONS AS LOW AS THE RATON PASS. TOTAL SNOWFALL AMOUNTS
FROM MAY 1-2 COULD EXCEED 1 FOOT ALONG THE HIGHEST PEAKS ABOVE 10,000 FEET.
RAIN COULD MIX WITH SNOW ACROSS THE CENTRAL AND SOUTHERN HIGH PLAINS ON SUNDAY
NIGHT. MUCH BELOW-NORMAL TEMPERATURES ARE POSTED FOR THE ROCKIES AND HIGH
PLAINS WHERE MAXIMUM TEMPERATURES ARE FORECAST TO AVERAGE MORE THAN 20 DEGREES
BELOW-NORMAL AND MINIMUM TEMPERATURES COULD FALL BELOW FREEZING.



AN INCREASE IN 500-HPA HEIGHTS IS EXPECTED TO BRING A BRIEF WARMING TREND TO
THE WESTERN U.S. BEGINNING ON SUNDAY, MAY 1. MUCH ABOVE-NORMAL TEMPERATURES ARE
FORECAST TO SHIFT FROM WESTERN OREGON TO EASTERN WASHINGTON DURING THE FIRST
FEW DAYS OF MAY. MAXIMUM TEMPERATURES ARE FORECAST TO AVERAGE 12 TO 20 DEGREES
F ABOVE-NORMAL IN THE HIGHLIGHTED AREAS.



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.



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 FRIDAY MAY 06 - THURSDAY MAY 12: AN UPPER-LEVEL TROUGH IS EXPECTED TO
UNDERCUT AN UPPER-LEVEL RIDGE CENTERED OVER WESTERN CANADA EARLY IN THE WEEK-2.
ALTHOUGH SPREAD CONTINUES AMONG THE GFS AND ECMWF ENSEMBLE MEMBERS WITH THE
PROGRESSION OF THE UPPER-LEVEL TROUGH ENTERING THE WESTERN U.S., THE
DETERMINISTIC MODEL SOLUTIONS AND THEIR ENSEMBLE MEANS REMAIN CONSISTENT THAT
THE UPPER-LEVEL TROUGH RESULTS IN HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION
SNOW) ACROSS PARTS OF THE GREAT BASIN AND ROCKY MOUNTAINS ON MAY 6 AND 7.



DOWNSTREAM OF THE AMPLIFIED TROUGH, A SLIGHT RISK OF MUCH-ABOVE NORMAL
TEMPERATURES IS POSTED FOR MUCH OF THE GREAT PLAINS ON MAY 6. FOR THE
HIGHLIGHTED HAZARD AREA, THE GEFS REFORECAST TOOL INDICATES A 20 PERCENT OR
GREATER CHANCE THAT DAILY MAXIMUM TEMPERATURES EXCEED 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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