Prognostic Meteorological Discussion
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000
FXUS21 KWNC 051843
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 05 2015

SYNOPSIS: AN AREA OF UPPER-LEVEL LOW PRESSURE IS EXPECTED TO SHIFT EAST FROM
THE WESTERN U.S. EARLY IN THE PERIOD, WHILE AN AREA OF UPPER-LEVEL HIGH
PRESSURE PERSISTS OVER THE WESTERN ATLANTIC. A COLD FRONT IS FORECAST TO SLOWLY
ADVANCE FROM THE GREAT PLAINS THIS WEEKEND TO THE EASTERN U.S. EARLY NEXT WEEK.
A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO REMAIN NEARLY STATIONARY NEAR OR
OFFSHORE OF THE SOUTHEAST COAST FROM FRIDAY THROUGH SUNDAY. A SURFACE LOW IS
EXPECTED TO DEVELOP OVER THE NORTHERN GULF OF ALASKA BY FRIDAY.

HAZARDS

PERIODS OF HEAVY RAIN ACROSS THE FRONT RANGE OF THE ROCKY MOUNTAINS AND PARTS
OF THE GREAT PLAINS, FRI-SUN, MAY 8-10.

SEVERE WEATHER FOR PARTS OF THE CENTRAL AND SOUTHERN GREAT PLAINS, FRI-SAT, MAY
8-9.

HIGH WINDS FOR PARTS OF THE SOUTHERN ROCKIES AND CENTRAL/SOUTHERN HIGH PLAINS,
SAT-SUN, MAY 9-10.

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, FRI-SAT, MAY 8-9.

HIGH WINDS FOR COASTAL SOUTH CAROLINA, FRI-SAT, MAY 8-9.

FLOODING OCCURRING ALONG THE ALTAMAHA RIVER ACROSS SOUTHEAST GEORGIA.

HEAVY RAIN FOR PARTS OF WEST AND SOUTH TEXAS, WED-THU, MAY 13-14.

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 FRIDAY MAY 08 - TUESDAY MAY 12: DOWNSTREAM OF A STRONG 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
DRYLINE AND COLD FRONT INITIATE DAILY CONVECTION FROM FRIDAY THROUGH SUNDAY.
TOTAL RAINFALL AMOUNTS COULD LOCALLY EXCEED 5 INCHES ACROSS THE CENTRAL AND
SOUTHERN GREAT PLAINS DURING THE NEXT WEEK. THE UPPER-LEVEL TROUGH IS EXPECTED
TO MOVE AWAY FROM THE GREAT PLAINS EARLY NEXT WITH CONVECTION SHIFTING EAST
ALONG AND EAST OF THE MISSISSIPPI RIVER.



THE POTENTIAL FOR SEVERE WEATHER INCREASES ACROSS THE CENTRAL AND SOUTHERN
GREAT PLAINS ON FRIDAY AND SATURDAY AS THE POTENT SHORTWAVE TROUGH APPROACHES
FROM THE FOUR CORNERS REGION. VERTICAL WIND SHEAR AND INSTABILITY ARE LIKELY TO
BE SUFFICIENT TO SUPPORT SEVERE THUNDERSTORMS ALONG THE DRYLINE. HIGH WINDS ARE
EXPECTED BEHIND THE DRYLINE THIS WEEKEND ACROSS PARTS OF THE CENTRAL AND
SOUTHERN HIGH PLAINS. SEVERE WEATHER IS POSSIBLE BEYOND SATURDAY, BUT
UNCERTAINTY ON LOCATION PRECLUDES DESIGNATING A SPECIFIC AREA AT THIS TIME.



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 WESTERN 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. RAIN MAY CHANGE TO SNOW BY SUNDAY
MORNING ACROSS THE FOOTHILLS OF NORTHEAST COLORADO.



MODEL GUIDANCE INDICATES SURFACE LOW DEVELOPMENT ACROSS THE NORTHERN BAHAMAS BY
THURSDAY. AS OF 10AM EDT ON TUESDAY, THE NATIONAL HURRICANE CENTER STATES THAT
THIS SYSTEM HAS A 40 PERCENT CHANCE OF ACQUIRING SUBTROPICAL CHARACTERISTICS
DURING THE NEXT 5 DAYS. THE LATEST 0Z MODEL CONSENSUS ON MAY 5 FAVORS A MORE
OFFSHORE POSITION OF THE SURFACE LOW COMPARED TO PREVIOUS DAYS WHICH WOULD
LIMIT THE CHANCES OF HEAVY RAIN AFFECTING THE COASTAL CAROLINAS. HOWEVER, THE
12Z GFS MODEL BRINGS THE SURFACE LOW WITH HEAVY RAIN INLAND TO THE EASTERN
CAROLINAS ON FRIDAY. POOR MODEL AGREEMENT PRECLUDES DESIGNATION OF A HEAVY RAIN
HAZARDS ACROSS THE CAROLINAS AT THIS TIME. HIGH WINDS ARE MORE LIKELY TO AFFECT
COASTAL SOUTH CAROLINA ON FRIDAY AND SATURDAY. 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 SATURDAY.



MODERATE FLOODING ALONG THE ALTAMAHA RIVER ACROSS SOUTHEAST GEORGIA IS EXPECTED
TO CONTINUE THROUGH AT LEAST FRIDAY.



AN INCREASE IN RAIN AND WINDS CAN BE EXPECTED ACROSS THE ALASKA PENINSULA AS A
SURFACE LOW STRENGTHENS ACROSS THE NORTHERN GULF OF ALASKA LATER THIS WEEK.
RAINFALL AMOUNTS AND WIND SPEEDS ARE EXPECTED TO REMAIN BELOW HAZARDS CRITERIA.


FOR WEDNESDAY MAY 13 - TUESDAY MAY 19: THE 0Z/6Z GFS AND 0Z ECMWF ENSEMBLE
MEANS FEATURE AN AMPLIFIED 500-HPA TROUGH NEAR THE WEST COAST. UPSLOPE FLOW
ALONG THE TAIL END OF A FRONT, SOUTHWEST FLOW ALOFT, AND ENHANCED MOISTURE AT
THE LOW TO MIDDLE LEVELS OF THE ATMOSPHERE ARE EXPECTED TO RESULT IN HEAVY RAIN
ACROSS PARTS OF WEST AND SOUTH TEXAS ON MAY 13 AND 14. THE HIGH RESOLUTION
MODEL RUNS OF THE 12Z GFS AND 0Z ECMWF SUPPORT THE DEPICTION OF THIS WEEK-2
HEAVY RAIN HAZARD. LATE IN WEEK-2, THE PREDICTED LONGWAVE PATTERN ACROSS THE
WESTERN U.S. IS LIKELY TO RESULT IN A RENEWED RISK FOR SEVERE WEATHER ACROSS
THE GREAT PLAINS.



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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