Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1
000
FXUS21 KWNC 051823
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 05 2016

SYNOPSIS: EARLY IN WEEK-1, A SURFACE LOW PRESSURE SYSTEM IS EXPECTED TO BRING
AN ARRAY OF METEOROLOGICAL HAZARDS TO THE WESTERN AND CENTRAL CONUS.  IN THE
WAKE OF THIS SYSTEM DRY AND WINDY CONDITIONS ARE ANTICIPATED ACROSS PARTS OF
THE WEST.  AS THE SYSTEM MOVES OUT, A MORE BENIGN WEATHER PATTERN IS EXPECTED
FOR WEEK-2 WITH TRENDS TOWARDS GENERAL HIGH PRESSURE ACROSS THE WEST AND LOW
PRESSURE ACROSS THE EAST.  DURING WEEK-1, ALASKA IS FORECAST TO HAVE A SURFACE
LOW PRESSURE STAGNATE ACROSS THE BERING SEA WITH HIGH PRESSURE ACROSS THE GULF
OF ALASKA.  THE LATTER HIGH PRESSURE IS EXPECTED TO BUILD ACROSS ALASKA IN
WEEK-2.

HAZARDS

SEVERE WEATHER ACROSS PORTIONS OF THE PLAINS, SUN, MAY 8.

SEVERE WEATHER ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS IN ADDITION
TO THE MISSISSIPPI VALLEY, MON, MAY 9.

HEAVY PRECIPITATION ACROSS PORTIONS OF THE NORTHERN PLAINS AND THE NORTHERN
ROCKIES, MON, MAY 9.

HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MISSISSIPPI VALLEY, AND
THE OHIO VALLEY, SUN-MON, MAY 8-MAY 9.

FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL AND NORTHERN ROCKIES, THE
CENTRAL AND NORTHERN PLAINS, AND THE NORTHERN GREAT BASIN, SUN-MON, MAY 8-MAY 9.

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE SOUTHERN PLAINS, THE UPPER MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS,
SUN-MON, MAY 8-MAY 9.

ENHANCED FIRE WEATHER RISK FOR SOUTHEASTERN NEW MEXICO, SUN, MAY 8.

HIGH WINDS ACROSS PORTIONS OF THE SOUTHERN ROCKIES, AND THE CENTRAL AND
SOUTHERN PLAINS, SUN, MAY 8.

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

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR THE PACIFIC NORTHWEST,
FRI-SAT, MAY 13-MAY 14.

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

DETAILED SUMMARY

FOR SUNDAY MAY 08 - THURSDAY MAY 12: THE CONUS 500-HPA FLOW PATTERN FOR WEEK-1
IS INITIALLY FORECAST TO FEATURE AN OMEGA BLOCK ACROSS THE CENTRAL U.S. WITH A
RIDGE THAT IS IN THE PROCESS OF FLATTENING OUT, STRADDLED BY CLOSED LOWS ACROSS
THE SOUTHWEST AND MID-ATLANTIC.  THE CLOSED LOW INITIALLY ACROSS THE WEST IS
ANTICIPATED TO SUBSEQUENTLY BECOME THE PRIMARY FEATURE OF THE PATTERN, WITH
SPLIT FLOW FORECAST ACROSS THE WESTERN CONUS IN WEEK-1.  AS THIS LOW SHIFTS
INTO THE CENTRAL ROCKIES IT IS FORECAST AND OPENS UP LATE MONDAY, ANOTHER
MID-LEVEL TROUGH IS EXPECTED TO DESCEND INTO THE NORTHERN ROCKIES.  THE TWO
TROUGHS ARE THEN FORECAST TO DEAMPLIFY WITH THE FLOW BECOMING INCREASINGLY
ZONAL LATE IN THE WEEK.



THE LOW-PRESSURE IMPACTING THE WESTERN CONUS IS EXPECTED TO BRING SEVERE
WEATHER THREATS TO THE CENTRAL AND SOUTHERN PLAINS ON SUNDAY, MAY 8.  A 15%
RISK OF SEVERE WEATHER IS FORECAST BY THE STORM PREDICTION CENTER (SPC), WITH
PRIMARY HAZARDS OF LARGE HAIL AND SEVERE WINDS ASSOCIATED WITH CONVECTION ALONG
A DRY LINE.  HIGH WINDS IN EXCESS OF 35 MPH ARE ALSO EXPECTED FROM EASTERN NEW
MEXICO THROUGH SOUTH-CENTRAL KANSAS ASSOCIATED WITH THE LOW-LEVEL JET WITH THIS
CYCLONE.  THE SEVERE WEATHER THREAT IS FORECAST TO SHIFT EASTWARD TO THE MIDDLE
AND LOWER MISSISSIPPI VALLEY FOR MONDAY, MAY 9 WITH SPC AGAIN ANTICIPATING A
15% SEVERE WEATHER RISK.  HEAVY RAINFALL (IN EXCESS OF 1 INCH OVER 24 HOURS) IS
EXPECTED ACROSS THE MIDDLE AND LOWER MISSISSIPPI VALLEYS ON SUNDAY AND MONDAY,
MAY 8 AND 9, FOCUSED INITIALLY ACROSS THE NORTH WITH A WARM FRONT BEFORE A
SECOND ROUND OF RAIN ASSOCIATED WITH THE COLD FRONT PUSHES THROUGH.  THE
AFOREMENTIONED RAINFALL MAY EXACERBATE ONGOING FLOODING ACROSS PARTS OF THE
MISSISSIPPI VALLEY.  REGIONS OF ELEVATED FIRE RISK ARE ALSO FORECAST FOR
SOUTHEASTERN NEW MEXICO ON SUNDAY, MAY 8 ASSOCIATED WITH DRY CONDITIONS AND
HIGH WINDS BEHIND THE DRYLINE.  OUTSIDE OF THIS FIRE WEATHER RISK FOCAL REGION,
LESSER ENHANCEMENTS TO RISK MAY EXTEND ACROSS SOUTHERN NEW MEXICO AND WEST
TEXAS FOR SUNDAY, MAY 8 AND MONDAY, MAY 9.



HEAVY PRECIPITATION IS FORECAST ACROSS SOUTH CENTRAL MONTANA, NORTHWESTERN
WYOMING, AND EASTERN IDAHO ON MONDAY, MAY 9 IN ADVANCE OF AN UPPER-LEVEL TROUGH
AND CLIPPER SYSTEM EXPECTED TO DESCEND INTO THE REGION FROM CANADA.  THIS
PRECIPITATION IS ANTICIPATED TO BE RAIN EXCEPT FOR HIGHER ELEVATIONS WHERE SNOW
IS POSSIBLE.  IN THE WAKE OF THE CLIPPER SYSTEM A TIGHT PRESSURE GRADIENT IS
EXPECTED AS HIGH PRESSURE LOOKS TO BUILD IN, WITH WINDS IN EXCESS OF 35 MPH
FORECAST ACROSS NORTH-CENTRAL MONTANA FOR TUESDAY, MAY 10.



A STATIONARY LOW-PRESSURE SYSTEM IS ANTICIPATED BE SITUATED ACROSS THE BERING
SEA WITH ITS EASTWARD PROGRESS STAGNATED BY A BLOCKING RIDGE ACROSS ALASKA
THROUGHOUT WEEK-1.  A HEAVY RAINFALL HAZARD WAS CONSIDERED FOR KODIAK ISLAND
AND THE KENAI PENNINSULA LATE IN WEEK-1 WITH PERSISTENT ON-SHORE FLOW FORECAST,
BUT PRECIPITATION AMOUNTS CURRENTLY APPEAR MARGINAL RELATIVE TO HAZARDS
CRITERIA WHILE DYNAMICAL MODEL ENSEMBLE SOLUTION UNCERTAINTY FURTHER LIMITS
CURRENT CONFIDENCE REGARDING A SPECIFIC HAZARD AREA.  POTENTIAL HEAVY RAINFALL
FOR ALASKA ASSOCIATED WITH ANY ONSHORE FLOW FROM THIS SETUP WILL BE
RECONSIDERED IN SUBSEQUENT OUTLOOKS.

FOR FRIDAY MAY 13 - THURSDAY MAY 19: THE CONUS WEEK-2 500-HPA PATTERN IS
FORECAST TO INITIALLY BE RELATIVELY ZONAL WITH WEAK RIDGING FAVORED IN THE WEST
AND TROUGHING IN THE EAST.  THE GEFS PREDICTS MORE AMPLIFIED FLOW THAN THE
ECMWF EARLY IN WEEK-2, HOWEVER, BOTH MODELS DEPICT LOW-AMPLITUDE FLOW IN THE
LATTER HALF OF THE WEEK.  BOTH DYNAMICAL ENSEMBLES CURRENTLY PROJECTS A MODEST
500-HPA TROUGH OFF THE PACIFIC NORTHWEST BY LATE WEEK-2.



GIVEN THE LIMITED AMPLITUDE PATTERN EXPECTED FOR WEEK-2 THE ONLY HAZARD
DEPICTED IS A SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES ACROSS THE PACIFIC
NORTHWEST ON FRIDAY, MAY 13 AND SATURDAY, MAY 14.  THE GEFS FORECAST TOOL
SUPPORTS A GREATER THAN 30% CHANCE OF EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE OF MAXIMUM TEMPERATURE HERE.  THIS WARMTH IS ASSOCIATED WITH A
FORECAST RIDGE STRETCHING ACROSS THE PACIFIC NORTHWEST, ALTHOUGH THE STRONGEST
500-HPA HEIGHT ANOMALIES ARE FURTHER NORTH ACROSS ALASKA.



THIS RIDGE EARLY IN WEEK-2 EXPECTED FOR NORTHWESTERN NORTH AMERICA WAS ALSO
CONSIDERED FOR A WARMTH-RELATED HAZARD FOR ALASKA.  HOWEVER, WITH RECORD HIGH
TEMPERATURES TYPICALLY PEAKING NEAR 80 FAHRENHEIT, ANY HEALTH-RELATED IMPACTS
SHOULD BE MINOR.  SHOULD THIS RIDGE SOLUTION COME TO FRUITION, ALASKA MAY
NECESSITATE MONITORING FOR ENHANCED FIRE WEATHER RISK AND FLOODING HAZARDS FROM
MELTING SNOWPACK DURING WEEK-2.  DYNAMICAL MODELS HAVE TRENDED FURTHER EASTWARD
FROM YESTERDAY`S FORECAST REGARDING THE RIDGE AXIS POSITION.



ACCORDING TO THE U.S. DROUGHT MONITOR VALID ON 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

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.