Prognostic Meteorological Discussion
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FXUS21 KWNC 061821
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 06 2016

SYNOPSIS: THE INITIAL FORECAST WEEK IS EXPECTED TO BE ACTIVE EARLY IN
ASSOCIATION WITH A PAIR OF CYCLONES.  THE FIRST SYSTEM IS EXPECTED TO BE
LIFTING NORTHWARD OUT OF THE CENTRAL PLAINS WITH POTENTIAL HAZARDS ACROSS THE
MISSISSIPPI VALLEY AND SOUTHERN PLAINS.  THE SECOND DISTURBANCE IS ANTICIPATED
TO DESCEND FROM CANADA AND IMPACT THE NORTHERN ROCKIES AND NORTHERN PLAINS.
LATER IN WEEK-1 THROUGH WEEK-2, A LESS IMPACTFUL WEATHER PATTERN IS FORECAST,
LEADING TO MINIMAL HAZARD EXPECTATIONS AT THIS TIME.  ALASKA IS EXPECTED TO
EXPERIENCE MID-LEVEL HIGH PRESSURE THROUGHOUT BOTH WEEKS.

HAZARDS

SEVERE WEATHER ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER AND  MIDDLE
MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS, MON, MAY 9.

HEAVY PRECIPITATION ACROSS WESTERN MONTANA, MON, MAY 9.

HEAVY RAIN ACROSS PORTIONS OF THE MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE
MIDWEST, AND THE OHIO VALLEY, MON, MAY 9.

FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL ROCKIES AND THE CENTRAL
PLAINS, MON-TUE, MAY 9-MAY 10.

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE SOUTHERN PLAINS, AND THE UPPER MISSISSIPPI VALLEY, MON-TUE, MAY 9-MAY 10.

HIGH WINDS ACROSS PORTIONS OF THE NORTHERN PLAINS, TUE, MAY 10.

MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE PACIFIC NORTHWEST,
WED-FRI, MAY 11-13.

ENHANCED WILDFIRE RISK ACROSS PORTIONS OF THE THE SOUTHERN PLAINS AND THE
SOUTHWEST, MON, MAY 9.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR THE PACIFIC NORTHWEST,
SAT-SUN, MAY 14-MAY 15.

SEVERE DROUGHT ACROSS THE CENTRAL GREAT BASIN, THE NORTHERN PLAINS, HAWAII, THE
NORTHERN GREAT BASIN, CALIFORNIA, AND THE SOUTHWEST.

DETAILED SUMMARY

FOR MONDAY MAY 09 - FRIDAY MAY 13: THE INITIAL 500-HPA FLOW FORECAST OVER THE
CONUS FOR WEEK-1 FEATURES AN ELONGATED NEGATIVELY-TILTED RIDGE EXTENDING FROM
THE SOUTHERN APPALACHIANS THROUGH THE NORTHERN PLAINS.  FORECAST TO BE
STRADDLING THIS RIDGE ARE A PAIR OF CLOSED LOWS, WITH ONE OVER THE CANADIAN
MARITIMES AND ANOTHER EXITING THE CENTRAL ROCKIES.  ANOTHER TROUGH, WITH AN
ASSOCIATED CLIPPER SYSTEM, IS ANTICIPATED TO DESCEND INTO THE PACIFIC NORTHWEST
FROM CANADA EARLY IN THE WEEK.  BY THE MIDDLE OF WEEK-1, THE TROUGH INITIALLY
ACROSS THE PACIFIC NORTHWEST AND THE CLOSED LOW INITIALLY EXITING THE ROCKIES
ARE EXPECTED TO PHASE TOGETHER AS THE FLOW AMPLITUDE DECREASES.  THE REMAINDER
OF THE WEEK-1 FORECAST FEATURES LOW-AMPLITUDE FLOW THROUGHOUT THE CONUS WITH A
WEAK PREFERENCE FOR RIDGING ACROSS THE WEST AND TROUGHING NEAR THE GREAT LAKES.
 THE MOST RECENT ECMWF ENSEMBLES HAVE BEGUN FAVORING A MORE AMPLIFIED FLOW
PATTERN LATE IN WEEK-1 ACROSS THE CONUS RELATIVE TO BOTH PREVIOUS RUNS AND GEFS
FORECASTS, WHICH WILL REQUIRE MONITORING FOR ANY CHANGES IN CONSISTENCY THROUGH
SUBSEQUENT OUTLOOKS.



THE PRIMARY FOCUS FOR HAZARDS DURING WEEK-1 IS THE SURFACE CYCLONE ASSOCIATED
WITH THE CLOSED LOW EXPECTED TO EXIT THE CENTRAL ROCKIES.  THE STORM PREDICTION
CENTER ANTICIPATES A 15% SEVERE WEATHER RISK FOR MONDAY, MAY 9 ACROSS THE OZARK
PLATEAU AND LOWER MISSISSIPPI VALLEY ASSOCIATED WITH A SHORTWAVE ACTING TO
FORCE CONVECTION ACROSS THE CYCLONE`S WARM SECTOR.  HEAVY RAINFALL (EXCEEDING 1
INCH OVER 24 HOURS) IS ALSO EXPECTED DOWNSTREAM OF THE SEVERE WEATHER THREAT
FOR MONDAY, MAY 9, ACROSS THE MIDDLE MISSISSIPPI VALLEY AND LOWER OHIO VALLEY.
A SECOND REGION OF HEAVY RAINFALL ON MONDAY, MAY 9, IS FORECAST ACROSS THE THE
NORTHERN AND CENTRAL MISSISSIPPI VALLEY ALONG THE WARM FRONT ASSOCIATED WITH
THE AFOREMENTIONED CYCLONE.  BOTH HEAVY PRECIPITATION AREAS AND THE SEVERE
WEATHER FORECAST FOR MONDAY MAY FURTHER EXACERBATE ONGOING FLOODING ACROSS THE
MISSISSIPPI VALLEY.  IN THE WAKE OF THIS SYSTEM`S PASSAGE, ENHANCED FIRE
WEATHER RISK IS FORECAST ACROSS SOUTHEASTERN NEW MEXICO AND WEST TEXAS ON
MONDAY, MAY 9.  HERE DRY AND BREEZY CONDITIONS (NOT MEETING HAZARDOUS WIND
CRITERIA) ARE EXPECTED, WHILE IT SHOULD BE NOTED THAT FIRE HAZARD CONCERNS
EXTEND AROUND THE IMMEDIATE PERIPHERY OF THE HAZARD DEPICTED ON THE MAP FOR
BOTH THIS DATE AND TUESDAY, MAY 10.



THE CLIPPER SYSTEM DESCENDING INTO THE NORTHERN ROCKIES EARLY IN WEEK-1 IS
FORECAST TO BRING A REGION OF HEAVY PRECIPITATION TO WESTERN MONTANA ON MONDAY,
MAY 9.  THIS PRECIPITATION IS EXPECTED TO BE PREDOMINANTLY RAIN, WITH SNOW
POSSIBLE ABOVE 4000-5000 FEET.  AFTER THE CLIPPER IS FORECAST TO SHIFT
EASTWARD, HIGH WINDS EXCEEDING 35 MPH OUT OF THE NORTH ARE FORECAST IN ITS WAKE
ACROSS MUCH OF SOUTH DAKOTA ON TUESDAY, MAY 10.  THE TIGHTENING PRESSURE
GRADIENT FORECAST ACROSS SOUTH DAKOTA LEADING TO THESE WINDS IS ANTICIPATED TO
BE AIDED BY HIGH PRESSURE BUILDING ACROSS THE NORTHERN ROCKIES.  ON THE BACK
SIDE OF THIS HIGH, SOUTHERLY FLOW IS EXPECTED TO ASSIST IN THE DEVELOPMENT OF
MUCH ABOVE NORMAL TEMPERATURES FOR COASTAL OREGON AND SOUTHWESTERN WASHINGTON
STATE ON WEDNESDAY THROUGH FRIDAY, MAY 11-13, WHERE FORECAST MAXIMUM
TEMPERATURE ANOMALIES COULD EXCEED 16 TO 20 DEGREES FAHRENHEIT ABOVE NORMAL.



DURING WEEK-1 ALASKA IS FORECAST TO EXPERIENCE RELATIVELY STATIONARY LOW
PRESSURE ACROSS THE BERING SEA AND HIGH PRESSURE ACROSS THE GULF OF ALASKA.
THIS FORECAST SETUP WOULD BRING PERSISTENT ONSHORE FLOW TO THE SOUTHERN PORTION
OF THE STATE.  A HEAVY PRECIPITATION HAZARD WAS CONSIDERED FOR THE VICINITY OF
THE KENAI PENINSULA FOR THURSDAY, MAY 12, ASSOCIATED WITH THE FORECAST ONSHORE
FLOW AND A SURGE OF MOISTURE INDICATED BY THE DETERMINISTIC GFS.  HOWEVER,
FORECAST PRECIPITATION AMOUNTS FROM BOTH THE ECMWF AND ENSEMBLE GUIDANCE FAILED
TO APPROACH HAZARDOUS CRITERIA AT THIS TIME, AND AS SUCH NO HAZARD IS DEPICTED.

FOR SATURDAY MAY 14 - FRIDAY MAY 20: WEEK-2 ENSEMBLE GUIDANCE GENERALLY FAVORS
LOW-AMPLITUDE 500-HPA FLOW FOR THE CONUS.  AS MENTIONED PREVIOUSLY, THE ECMWF
ENSEMBLES HAVE TRENDED TOWARD SOMEWHAT MORE AMPLIFIED FLOW EARLY IN WEEK-2
RELATIVE TO PREVIOUS RUNS AND THE GEFS, BUT RETURN TO A LARGELY ZONAL PATTERN
BY THE MIDDLE OF WEEK-2.  LATE IN WEEK-2 THE GEFS BEGINS TO DEVELOP A RIDGE
OVER THE MISSISSIPPI VALLEY WHILE A MODEST TROUGH IS FORECAST TO IMPACT
CALIFORNIA, ALTHOUGH THE EUROPEAN ENSEMBLES ARE LESS PROGRESSIVE AND MAINTAIN
LOW-AMPLITUDE FLOW.



THE ONLY PROBABILISTIC HAZARD DEPICTED FOR WEEK-2 IS A SLIGHT RISK OF MUCH
ABOVE NORMAL TEMPERATURES ACROSS THE PACIFIC NORTHWEST ON SATURDAY, MAY 14 AND
SUNDAY, MAY 15.  THIS WARMTH IS EXPECTED TO BE ASSOCIATED WITH RIDGING ACROSS
THE PACIFIC NORTHWEST THAT IS STRONGEST FURTHER NORTH AND WEST ACROSS ALASKA.
HERE THE GEFS PROBABILISTIC EXTREMES TOOL DEPICTS A GREATER THAN 30%
PROBABILITY OF EXCEEDING THE 85TH PERCENTILE OF CLIMATOLOGICAL MAXIMUM
TEMPERATURE.



EARLY IN WEEK-2 SUBSTANTIAL RIDGING IS FORECAST ACROSS EASTERN ALASKA BY BOTH
DYNAMICAL MODELS.  CURRENT EXPECTATIONS FOR THIS RIDGE DURING WEEK-2 ARE A
TENDENCY FOR DEAMPLIFICATION AND THE FEATURE TO RETROGRADE SLIGHTLY WESTWARD.
GIVEN THE STRONG ANOMALOUS RIDGING EARLY IN WEEK-2 THERE IS POTENTIAL FOR MUCH
ABOVE NORMAL TEMPERATURES ACROSS MUCH OF THE STATE, HOWEVER WITH RECORD HIGH
TEMPERATURES FOR THIS TIME OF YEAR BEING GENERALLY AT OR BELOW 80 DEGREES
FAHRENHEIT, NO IMPACTS ON HEALTH ARE CURRENTLY ANTICIPATED.  CONCERNS RELATED
TO THIS WARMTH MAY LEAD TO ENHANCED FIRE WEATHER RISK OR SNOW MELT-RELATED
FLOODING FOR PORTIONS OF ALASKA, AND WILL BE COORDINATED WITH NOAA`S ALASKAN
REGION AS THE PERIOD DRAWS NEARER.



VALID AS OF MAY 3, SEVERE, OR GREATER INTENSITY, DROUGHT COVERS 4.64 PERCENT OF
THE U.S. DROUGHT MONITOR AREAS, A DECREASE OF NEARLY A HALF PERCENT RELATIVE TO
THE PRIOR WEEK.  THIS CONTINUES A GENERAL DECREASE IN OVERALL DROUGHT COVERAGE
DURING THE PAST SIX MONTHS.

FORECASTER: DANIEL HARNOS

$$




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