Prognostic Meteorological Discussion
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FXUS21 KWNC 041815
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 04 2015

SYNOPSIS: AN AREA OF UPPER-LEVEL LOW PRESSURE IS EXPECTED TO SLOWLY SHIFT EAST
FROM THE WESTERN U.S. DURING THE NEXT WEEK, WHILE AN AREA OF UPPER-LEVEL HIGH
PRESSURE PERSISTS OVER THE WESTERN ATLANTIC. A LOW PRESSURE SYSTEM IS FORECAST
TO DEVELOP ACROSS THE NORTHERN BAHAMAS PRIOR TO THURSDAY AND MAY MOVE INLAND
ACROSS THE SOUTHEAST. A SURFACE LOW IS EXPECTED TO FORM OVER THE NORTHERN GULF
OF ALASKA BY FRIDAY.

HAZARDS

PERIODS OF HEAVY RAIN ACROSS PARTS OF THE GREAT PLAINS, THU-SUN, MAY 7-10.

SEVERE WEATHER FOR PARTS OF THE CENTRAL AND SOUTHERN GREAT PLAINS, SAT, MAY 9.

HIGH WINDS FOR PARTS OF THE CENTRAL AND SOUTHERN HIGH PLAINS, SAT, MAY 9.

HEAVY SNOW FOR THE WASATCH MOUNTAIN RANGE OF UTAH AND WESTERN WYOMING, FRI-SAT,
MAY 8-9.

HEAVY SNOW FOR PARTS OF THE ROCKIES OF NORTHERN COLORADO AND SOUTHERN WYOMING,
FRI-SUN, MAY 8-10.

SIGNIFICANT WAVES FOR THE COASTAL SOUTHEAST, THU-FRI, MAY 7-8.

HIGH WINDS FOR COASTAL SOUTH CAROLINA, THU-FRI, MAY 7-8.

FLOODING OCCURRING ALONG THE ALTAMAHA RIVER ACROSS SOUTHEAST GEORGIA.

FLOODING POSSIBLE ACROSS PARTS OF NORTH TEXAS.

SEVERE DROUGHT FOR THE NORTHERN, CENTRAL AND SOUTHERN GREAT PLAINS, UPPER
MISSISSIPPI VALLEY, SOUTHWEST, GREAT BASIN, CALIFORNIA, THE PACIFIC NORTHWEST,
AND HAWAII.

DETAILED SUMMARY

FOR THURSDAY MAY 07 - MONDAY MAY 11: DOWNSTREAM OF AN UPPER-LEVEL TROUGH,
ABUNDANT LOW-LEVEL MOISTURE IS LIKELY TO RESULT IN PERIODS OF HEAVY RAINFALL
ACROSS PARTS OF THE GREAT PLAINS THROUGH SUNDAY. UPSLOPE FLOW IS EXPECTED TO
ENHANCE RAINFALL AMOUNTS ACROSS THE CENTRAL HIGH PLAINS, WHILE A SLOW-MOVING
FRONT INITIATES DAILY CONVECTION FROM THURSDAY THROUGH SUNDAY. TOTAL RAINFALL
AMOUNTS COULD LOCALLY EXCEED 5 INCHES ACROSS THE CENTRAL OR SOUTHERN GREAT
PLAINS DURING THE NEXT WEEK. THE UPPER-LEVEL TROUGH IS EXPECTED TO MOVE AWAY
FROM THE GREAT PLAINS NEXT MONDAY WITH CONVECTION SHIFTING EAST TO THE
MISSISSIPPI VALLEY.



SATURDAY IS THE MOST LIKELY TIME FOR SEVERE WEATHER THIS WEEK ACROSS THE
CENTRAL AND SOUTHERN GREAT PLAINS WHEN THE POTENT SHORTWAVE TROUGH EJECTS FROM
THE FOUR CORNERS REGION AND CONTRIBUTES TO A STRENGTHENING SURFACE LOW ACROSS
THE CENTRAL HIGH PLAINS. VERTICAL WIND SHEAR AND INSTABILITY ARE LIKELY TO BE
SUFFICIENT TO SUPPORT SEVERE THUNDERSTORMS ALONG A DRYLINE AND COLD FRONT ON
SATURDAY FROM NEBRASKA SOUTH TO NORTH TEXAS. HIGH WINDS ARE EXPECTED BEHIND THE
DRYLINE ON SATURDAY ACROSS PARTS OF THE CENTRAL AND SOUTHERN HIGH PLAINS.



SNOW LEVELS ARE LIKELY TO FALL THIS WEEKEND AS THE UPPER-LEVEL TROUGH CROSSES
THE CENTRAL ROCKIES. DUE TO THE LOWER SNOW LEVELS ALONG WITH GOOD MODEL
AGREEMENT WITH THE TRACK OF THE UPPER-LEVEL TROUGH, A HEAVY SNOW HAZARD IS
POSTED FOR THE WASATCH MOUNTAINS OF UTAH AND NORTHWEST WYOMING, FRIDAY AND
SATURDAY, AND ACROSS THE ROCKIES OF SOUTHERN WYOMING AND NORTHERN COLORADO,
FRIDAY THROUGH SUNDAY. SNOW LEVELS ARE EXPECTED TO FALL TO AS LOW AS 6,000 FEET
WITH SNOWFALL AMOUNTS EXCEEDING 6 INCHES.



MODEL GUIDANCE CONTINUES TO INDICATE SURFACE LOW DEVELOPMENT ACROSS THE
NORTHERN BAHAMAS BY THURSDAY. AS OF 10AM EDT ON MONDAY, THE NATIONAL HURRICANE
CENTER STATES THAT THIS SYSTEM HAS A 30 PERCENT CHANCE OF ACQUIRING SUBTROPICAL
CHARACTERISTICS ON THURSDAY OR FRIDAY. MODEL SOLUTIONS VARY ON THE STRENGTH AND
TRACK OF THE SURFACE LOW WITH THE 0Z/6Z/12Z GFS AND 0Z/12Z CANADIAN MODELS
FAVORING A MORE WESTWARD TRACK COMPARED TO THE 0Z ECMWF. IT REMAINS UNCLEAR IF
HEAVY RAIN WILL EVENTUALLY MOVE ONSHORE INTO THE COASTAL CAROLINAS. HOWEVER,
HIGH WINDS ARE EXPECTED TO AFFECT COASTAL SOUTH CAROLINA ON THURSDAY AND
FRIDAY. PERSISTENT ONSHORE FLOW IS LIKELY TO CAUSE SIGNIFICANT WAVES, SOME
BEACH EROSION, AND INCREASE THE RISK OF RIP CURRENTS ACROSS COASTAL AREAS OF
THE SOUTHEAST THROUGH AT LEAST FRIDAY.



MODERATE FLOODING ALONG THE ALTAMAHA RIVER ACROSS SOUTHEAST GEORGIA IS EXPECTED
TO CONTINUE THROUGH AT LEAST THURSDAY. MEANWHILE, SIGNIFICANT RIVER FLOODING IS
POSSIBLE ACROSS THE UPPER SABINE AND TRINITY RIVER BASINS OF NORTH TEXAS.



NO HAZARDS ARE EXPECTED ACROSS ALASKA WITH THE SURFACE LOW THAT DEVELOPS ACROSS
THE NORTHERN GULF OF ALASKA LATER THIS WEEK.

FOR TUESDAY MAY 12 - MONDAY MAY 18: THE 0Z/6Z GFS AND 0Z ECMWF ENSEMBLE MEANS
FEATURE AN AMPLIFIED 500-HPA TROUGH NEAR THE WEST COAST. THE PREDICTED LONGWAVE
PATTERN ACROSS THE WESTERN U.S. IS LIKELY TO RESULT IN A CONTINUED ACTIVE
PERIOD DURING MID-MAY ACROSS THE GREAT PLAINS WHERE THE RISK FOR ADDITIONAL
HEAVY RAIN AND SEVERE WEATHER IS ELEVATED.



THE MOST RECENT U.S. DROUGHT MONITOR, VALID ON APRIL 28, INDICATES A SLIGHT
INCREASE (TO 20.03 FROM 18.97) IN THE PERCENTAGE OF THE CONUS IN SEVERE TO
EXCEPTIONAL DROUGHT (D2-D4).

FORECASTER: BRAD PUGH

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