Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXUS21 KWNC 271955
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 27 2017

SYNOPSIS: MID-LEVEL LOW PRESSURE IS ANTICIPATED ACROSS THE CENTRAL CONTIGUOUS
U.S. DURING THE 3-5 DAY PERIOD, WITH A FORECAST TENDENCY TO LIFT NORTHWARD,
TOWARD AND OVER THE UPPER GREAT LAKES REGION. SURFACE LOW PRESSURE NEAR THE
OZARKS IS FORECAST TO INTENSIFY WHILE SIMILARLY LIFTING NORTHWARD TOWARD THE
GREAT LAKES. SEVERAL TYPES OF HAZARDS ARE PREDICTED TO ACCOMPANY THIS LOW
PRESSURE SYSTEM, GIVEN BOTH LARGE TEMPERATURE DIFFERENCES AND THE INFLUX OF
GULF MOISTURE. UNCERTAINTY IS HIGH REGARDING THE WEEK-2 CIRCULATION AND ITS
IMPACTS TO THE CONTIGUOUS U.S. ALASKA IS EXPECTED TO EXPERIENCE PERIODIC
SURFACE LOW PRESSURE SYSTEMS OF SEASONABLE STRENGTH MOVING ACROSS THE BERING
SEA AND GULF OF ALASKA THROUGHOUT THE OUTLOOK PERIOD.

HAZARDS

HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER MISSISSIPPI VALLEY,
THE NORTHERN PLAINS, THE TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE
NORTHEAST, THE UPPER MISSISSIPPI VALLEY, THE SOUTHEAST, THE GREAT LAKES, AND
THE OHIO VALLEY, SUN-MON, APR 30-MAY 1.

HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER MISSISSIPPI VALLEY, AND
THE TENNESSEE VALLEY, TUE-WED, MAY 2-MAY 3.

SEVERE WEATHER ACROSS PORTIONS OF THE SOUTHEAST, THE MIDDLE MISSISSIPPI VALLEY,
THE LOWER MISSISSIPPI VALLEY, THE OHIO VALLEY, AND THE TENNESSEE VALLEY, SUN,
APR 30.

FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER MISSISSIPPI
VALLEY, THE TENNESSEE VALLEY, THE GREAT LAKES, THE MIDDLE MISSISSIPPI VALLEY,
THE UPPER MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE OHIO VALLEY.

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE MID-ATLANTIC, THE
SOUTHERN PLAINS, THE NORTHERN PLAINS, AND THE NORTHERN GREAT BASIN.

FLOODING LIKELY ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE TENNESSEE
VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE MID-ATLANTIC, THE SOUTHEAST, AND THE
SOUTHERN PLAINS.

HIGH WINDS ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER MISSISSIPPI VALLEY,
THE NORTHERN PLAINS, THE GREAT LAKES, THE MIDDLE MISSISSIPPI VALLEY, THE UPPER
MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE OHIO VALLEY, SUN-MON, APR
30-MAY 1.

MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL APPALACHIANS, THE
TENNESSEE VALLEY, THE MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE GREAT LAKES,
AND THE OHIO VALLEY, SUN, APR 30.

MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE
CENTRAL ROCKIES, THE SOUTHERN PLAINS, THE CENTRAL PLAINS, AND THE SOUTHWEST,
SUN, APR 30.

SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE GREAT LAKES,
THE UPPER MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS, FRI-SAT, MAY 5-MAY 6.

SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL GREAT
BASIN, THE NORTHERN PLAINS, THE NORTHERN ROCKIES, THE CENTRAL ROCKIES,
CALIFORNIA, THE NORTHERN GREAT BASIN, THE PACIFIC NORTHWEST, AND THE SOUTHWEST,
FRI-SAT, MAY 5-MAY 6.

SEVERE DROUGHT ACROSS THE TENNESSEE VALLEY, HAWAII, THE SOUTHERN APPALACHIANS,
THE SOUTHEAST, CALIFORNIA, AND THE SOUTHWEST.

DETAILED SUMMARY

FOR SUNDAY APRIL 30 - THURSDAY MAY 04: THE PRIMARY FEATURE OF INTEREST DURING
THE 3-7 DAY PERIOD IS AN ANTICIPATED SURFACE LOW PRESSURE SYSTEM WHICH IS
FORECAST TO TRACK FROM THE OZARKS NORTHWARD ACROSS THE UPPER GREAT LAKES
REGION, BEFORE EXITING INTO EASTERN CANADA. SEVERAL HAZARDS ARE EXPECTED TO
ACCOMPANY THIS SYSTEM. THE FIRST IS THE POTENTIAL FOR SEVERE WEATHER ON APR 30
ACROSS THE LOWER TENNESSEE VALLEY AND CENTRAL GULF COAST REGION. THE STORM
PREDICTION CENTER (SPC) EXPECTS FAVORABLE VERTICAL WIND SHEAR PROFILES AND
MODERATE INSTABILITY WITHIN THIS ENVIRONMENT FOR THE FORMATION OF SEVERE
THUNDERSTORMS. ANOTHER ANTICIPATED HAZARD WITH THIS STORM SYSTEM IS HEAVY
RAINFALL ACROSS THE EAST-CENTRAL AND NORTHEASTERN CONUS. NORTHERN SECTIONS OF
THIS AREA ARE PREDICTED TO RECEIVE BETWEEN 1.5"-2.5" ON APR 30-MAY 1, WHILE
SOUTHERN SECTIONS ARE EXPECTED TO GET BETWEEN 3"-4". DURING THE SUBSEQUENT
TWO-DAY PERIOD, MAY 2-3, THE CENTRAL GULF COAST REGION IS PREDICTED TO RECEIVE
AN ADDITIONAL 2"-3" OF RAIN. THIS IS DUE TO THE ANTICIPATED FORMATION OF A WARM
FRONT OVER TEXAS. A THIRD CONCERN WITH THE ORIGINAL LOW PRESSURE SYSTEM IS FOR
HIGH WINDS (30 KNOTS OR GREATER) ON THE WESTERN SIDE OF THE STORM, FROM THE
SOUTH-CENTRAL GREAT PLAINS NORTHEASTWARD ACROSS THE MIDWEST AND UPPER GREAT
LAKES REGION ON APR 30-MAY 1. A FOURTH POTENTIAL HAZARD WITH THIS STORM SYSTEM
IS UNSEASONABLY WARM AIR (MUCH ABOVE-NORMAL TEMPERATURES) ON ITS EASTERN SIDE,
AND UNSEASONABLY COLD AIR (MUCH BELOW-NORMAL TEMPERATURES) ON ITS WESTERN SIDE.
THE PREDICTED REGION OF MUCH ABOVE-NORMAL TEMPERATURES INCLUDES THE
MID-ATLANTIC, CENTRAL APPALACHIANS, AND OHIO VALLEY, WHERE TEMPERATURES ARE
FORECAST TO RANGE FROM 12-18 DEGREES ABOVE-NORMAL ON APR 30. THIS GENERALLY
MEANS HIGH`S ARE ANTICIPATED TO REACH THE MID-80`S. ON THE WESTERN SIDE OF THE
STORM, MUCH BELOW-NORMAL TEMPERATURES ARE FORECAST FOR PORTIONS OF THE CENTRAL
AND SOUTHERN ROCKIES, AND CENTRAL AND SOUTHERN PLAINS ON APR 30. THE
HIGHLIGHTED AREA ON THE MAP REPRESENTS AN OVERLAP BETWEEN EXPECTED MINIMUM
TEMPERATURES IN THE 20`S TO LOW 30`S (AT OR BELOW FREEZING), AND EXPECTED
MAXIMUM TEMPERATURES AT OR BELOW 50 DEGREES F.



FLOODING IS POSSIBLE, LIKELY, IMMINENT, OR OCCURRING ACROSS THE CAROLINAS AND
SOUTHERN VIRGINIA, THE LOWER OHIO VALLEY/MIDWEST, THE SOUTH-CENTRAL MISSISSIPPI
VALLEY AND PARTS OF ADJACENT STATES, NORTHERN NORTH DAKOTA, AND PARTS OF IDAHO.
A COLD FRONT WHICH STALLED ACROSS NORTH CAROLINA AND TENNESSEE THIS PAST WEEK
BROUGHT SEVERE STORMS TO THE REGION, RAINFALL AMOUNTS OF 2-10", AND FLASH
FLOODING.



ALASKA IS FORECAST TO EXPERIENCE PERIODIC LOW PRESSURE SYSTEMS TRACKING ACROSS
THE BERING SEA AND GULF OF ALASKA DURING THE 3-7 DAY PERIOD. NONE OF THESE
SYSTEMS ARE EXPECTED TO BE UNUSUALLY STRONG FOR THIS TIME OF YEAR.

FOR FRIDAY MAY 05 - THURSDAY MAY 11: SUBSTANTIAL UNCERTAINTY IS APPARENT IN THE
WIDE RANGE OF SPAGHETTI MAP PERSPECTIVES OF THE MID-LEVEL CIRCULATION OVER
NORTH AMERICA IN WEEK-2. SOME EASTWARD PROGRESSION OF THE CIRCULATION PATTERN
IS ANTICIPATED, WITH A TROUGH PREDICTED TO APPROACH THE EAST COAST, A RIDGE
OVER THE NATION`S MIDSECTION, AND ANOTHER TROUGH ENTERING THE WESTERN CONUS.
GIVEN THE EXPECTED PROGRESSIVE PATTERN, AND THE FORECAST OF MODEST 500-HPA
HEIGHT ANOMALIES, LIMITED HAZARDOUS IMPACTS CAN BE DISCERNED AT THIS TIME.



A SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES IS FORECAST FOR APPROXIMATELY
THE WESTERN QUARTER OF THE CONUS EARLY IN THE WEEK-2 PERIOD, IN-BETWEEN AN
APPROACHING TROUGH TO THE WEST, AND A DEPARTING RIDGE TO THE EAST. THE AREA OF
ANTICIPATED MUCH ABOVE-NORMAL TEMPERATURES INDICATED ON THE MAP IS WHERE THE
GEFS HAS AT LEAST A 20% CHANCE OF EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE
OF MAXIMUM TEMPERATURE. A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES EXTENDS
FROM EASTERN NORTH DAKOTA ACROSS THE UPPER MISSISSIPPI VALLEY, AND THE WESTERN
AND CENTRAL GREAT LAKES REGION. HERE LOW TEMPERATURES MAY FALL BELOW FREEZING,
WHILE THE GEFS SUPPORTS AT LEAST A 20% CHANCE OF BEING BELOW THE 15TH
CLIMATOLOGICAL PERCENTILE OF MINIMUM TEMPERATURE.



ACCORDING TO THE U.S. DROUGHT MONITOR RELEASED ON APRIL 27TH (USING DATA
THROUGH 8 AM EDT, APRIL 25TH), COVERAGE OF SEVERE, OR GREATER INTENSITY,
DROUGHT THROUGHOUT THE CONUS DROPPED SLIGHTLY (FROM 1.44 PERCENT LAST WEEK TO
1.07 PERCENT THIS WEEK). THIS IS THE LOWEST COVERAGE OF D2-D4 DROUGHT OVER THE
CONUS SINCE THE INCEPTION OF THE U.S. DROUGHT MONITOR IN 1999.

FORECASTER: ANTHONY ARTUSA

$$



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