Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 021905
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 02 2016

SYNOPSIS: DURING WEEK-1 HIGH AMPLITUDE FLOW IS EXPECTED ACROSS THE CONUS,
BEFORE BEING SUBSEQUENTLY FORECAST TO FLATTEN OUT AS TIME PROGRESSES INTO
WEEK-2 AND BECOME A MORE ZONAL PATTERN.  THE HIGHLIGHT OF THIS PATTERN WILL BE
A CLOSED LOW INITIALLY IN THE CENTRAL ROCKIES THAT WILL YIELD VARIOUS HAZARDS
ACROSS THE CENTRAL AND SOUTHERN CONUS FOR WEEK-1 BEFORE OPENING UP AND SHIFTING
EAST IN WEEK-2.  MULTIPLE SURFACE LOWS ARE EXPECTED TO IMPACT SOUTHERN ALASKA
AND THE ALASKA PANHANDLE DURING THE NEXT TWO WEEKS.

HAZARDS

MUCH ABOVE NORMAL TEMPERATURES FOR THE NORTHERN PLAINS THROUGH MINNESOTA,
THU-FRI, MAY 5-6.

FLOODING OCCURRING, IMMINENT, OR LIKELY FOR ACROSS PARTS OF THE CENTRAL U.S.,
THU-FRI, MAY 5-6.

FLOODING LIKELY FOR PARTS OF WASHINGTON STATE, THU-FRI, MAY 5-6.

HEAVY PRECIPITATION FOR SOUTHERN ALASKA AND THE ALASKA PANHANDLE, FRI, MAY 6.

HEAVY PRECIPITATION FOR THE CENTRAL ROCKIES, FRI-SAT, MAY 6-7.

MUCH ABOVE NORMAL TEMPERATURES FOR NORTHWESTERN OREGON AND MUCH OF WASHINGTON,
SAT-SUN, MAY 7-8.

HEAVY RAIN FOR THE CENTRAL PLAINS AND MID-MISSISSIPPI VALLEY, SUN, MAY 8.

HEAVY RAIN FOR THE SOUTHERN PLAINS, MON, MAY 9.

HEAVY RAIN FOR EAST TEXAS THROUGH THE LOWER TENNESSEE VALLEY, TUE-WED, MAY
10-11.

A SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC
NORTHWEST, TUE-THU, MAY 10-12.

A SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PARTS OF THE DESERT
SOUTHWEST, WED-THU, MAY 11-12.

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

DETAILED SUMMARY

FOR THURSDAY MAY 05 - MONDAY MAY 09: DYNAMICAL MODEL GUIDANCE IS IN GOOD
AGREEMENT REGARDING THE PROGRESSION OF A CLOSED 500-HPA LOW ACROSS THE WESTERN
U.S. INTO THE CENTRAL ROCKIES IN WEEK-1.  THIS SYSTEM WILL BRING HEAVY
PRECIPITATION (IN EXCESS OF 1 INCH LIQUID EQUIVALENT IN 24 HOURS) TO MUCH OF
WYOMING AND CENTRAL COLORADO ON FRIDAY, MAY 6 AND SATURDAY, MAY 7.  THIS
PRECIPITATION IS EXPECTED TO BE IN THE FORM OF SNOW AT HIGHER ELEVATIONS, WITH
RAIN FAVORED AT LOWER ALTITUDES.  AS THIS SYSTEM SHIFTS EASTWARD, THE FOCUS FOR
HEAVY RAINFALL WILL BE FOR CENTRAL KANSAS NORTHEASTWARD THROUGH THE MISSOURI
RIVER VALLEY AND SOUTHWEST IOWA ON SUNDAY, MAY 8TH WHERE 24 HOUR RAINFALL
TOTALS COULD AGAIN EXCEED 1 INCH.  ON SUNDAY, MAY 8 OVER AN INCH OF RAIN IN 24
HOURS IS EXPECTED FOR MUCH OF CENTRAL AND EASTERN TEXAS WITH THE SAME SYSTEM
THAT MAY EXACERBATE ONGOING FLOODING CONCERNS FOR MUCH OF THIS REGION.
CURRENTLY SPC PRODUCTS DO NOT DEPICT A SEVERE WEATHER HAZARD FOR THIS SYSTEM,
BUT POTENTIAL FOR CONVECTIVE ACTIVITY ALONG A DRYLINE IN WESTERN TEXAS SAT-SUN,
MAY 7TH AND 8TH BEARS MONITORING.  ONE FINAL IMPACT FROM THIS SYSTEM MAY BE THE
POTENTIAL FOR HIGHER-ELEVATION SNOWFALL ACROSS THE SIERRA NEVADAS ON FRIDAY,
MAY 6 AND SATURDAY, MAY 7, HOWEVER LIQUID EQUIVALENT AMOUNTS APPEAR UNLIKELY TO
MEET HAZARDS CRITERIA.



GIVEN THE INITIAL HIGH AMPLITUDE PATTERN WITH THE CLOSED 500-HPA LOW, RIDGING
OUT AHEAD OF AND BEHIND THE SYSTEM WILL GIVE RISE TO ABOVE NORMAL TEMPERATURES
FOR PORTIONS OF THE NORTHERN CONUS.  ON THURSDAY, MAY 5 AND FRIDAY, MAY 6
MAXIMUM TEMPERATURE ANOMALIES ARE FORECAST TO EXCEED 16 DEGREES FAHRENHEIT FOR
EASTERN MONTANA AND MUCH OF THE DAKOTAS.  RIDGING BUILDING IN BEHIND THE CLOSED
LOW IS EXPECTED TO YIELD ANOMALOUS WARMTH WITH HIGHS INTO THE MID-80S FOR MUCH
OF WASHINGTON STATE ON SATURDAY MAY 7 AND SUNDAY MAY 8 THAT MAY APPROACH RECORD
VALUES.



STRONG ONSHORE FLOW IN ADVANCE OF A LOW-PRESSURE CENTER IN THE GULF OF ALASKA
IS ANTICIPATED TO BRING HEAVY RAINFALL OF 2-3 INCHES OR MORE TO SOUTHERN ALASKA
AND THE ALASKA PANHANDLE ON FRIDAY, MAY 6TH.



ANTECEDENT RAINFALL AND SUBSEQUENT EXPECTED RAINS DURING THE FORECAST PERIOD
LEAD TO OCCURRING, IMMINENT, AND LIKELY FLOODING FOR PARTS OF THE CENTRAL
PLAINS AND SOUTHERN MISSISSIPPI VALLEY.  EXPECTED ABOVE NORMAL TEMPERATURES AND
MELTING SNOWPACK ALSO RESULT IN FLOODING LIKELY FOR PARTS OF WASHINGTON STATE.

FOR TUESDAY MAY 10 - MONDAY MAY 16: THE CLOSED LOW PRESSURE DOMINATING WEEK-1
IS EXPECTED TO OPEN UP IN WEEK-2 AND BEGIN TO PROGRESS EASTWARD AS MORE ZONAL
FLOW COMES TO DOMINATE THE MID-LEVELS.  AN AREA OF HEAVY RAINFALL IS EXPECTED
TO CONTINUE WITH THIS SYSTEM FOR TUESDAY, MAY 10 FROM EAST TEXAS THROUGH THE
SOUTHERN MISSISSIPPI RIVER VALLEY.  POTENTIAL EXISTS FOR THIS HEAVY RAINFALL
EVENT TO CONTINUE BEYOND THIS DATE, HOWEVER MODEL GUIDANCE DISAGREES ON THE
DEGREE OF EASTWARD PROGRESSION WITH THE LOW PRESSURE CENTER.  AS SUCH, AN
EXPLICIT HAZARD SHAPE IS LEFT OFF THE MAP, BUT CONDITIONS WILL CONTINUE TO BE
MONITORED.



WEAK RIDGING ACROSS THE WESTERN CONUS WILL BRING A SLIGHT RISK FOR MUCH
ABOVE-NORMAL TEMPERATURES EARLY IN WEEK-2.  FOCAL REGIONS ARE ANTICIPATED TO BE
EASTERN WASHINGTON FOR TUESDAY, MAY 10 THROUGH THURSDAY, MAY 12 WHERE THE GEFS
REFORECAST TOOL SUGGESTS MAXIMUM TEMPERATURES TO EXCEED THE 85TH PERCENTILE
GREATER THAN 20% OF THE TIME.  A SIMILAR RISK IS EXPECTED ACROSS PARTS OF THE
DESERT SOUTHWEST FOR WEDNESDAY, MAY 10 AND THURSDAY, MAY 11 WHERE TEMPERATURES
COULD EXCEED 100 FAHRENHEIT.



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: DANIEL HARNOS

$$




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