Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXUS21 KWNC 251905
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 25 2017

SYNOPSIS: MID-LEVEL LOW PRESSURE IS ANTICIPATED ACROSS THE CENTRAL U.S.
THROUGHOUT WEEK-1, WITH A FORECAST TENDENCY TO LIFT NORTHWARD TOWARD THE GREAT
LAKES DURING THE PERIOD. SURFACE LOW PRESSURE IS FORECAST TO DEVELOP IN THE LEE
OF THE SOUTHERN ROCKIES, AND INTENSIFY WHILE SIMILARLY LIFTING NORTHWARD TOWARD
THE GREAT LAKES. A WIDE ARRAY OF HAZARDS IS POSSIBLE ASSOCIATED WITH THIS
FORECAST SCENARIO, GIVEN THE TRANSITION SEASON TIMING AND ANTICIPATED STRONG
DISTURBANCE THAT IS IN A FAVORABLE LOCATION TO TAP INTO GULF MOISTURE.
UNCERTAINTY IS HIGH REGARDING THE WEEK-2 CIRCULATION AND ITS IMPACTS TO THE
LOWER-48 STATES. ALASKA IS FORECAST TO EXPERIENCE PERIODIC SURFACE LOW PRESSURE
SYSTEMS OF MODEST INTENSITY IN THE BERING SEA AND GULF OF ALASKA THROUGHOUT THE
OUTLOOK PERIOD.

HAZARDS

SEVERE WEATHER SHIFTING EASTWARD ACROSS PORTIONS OF THE LOWER MISSISSIPPI
VALLEY, THE SOUTHERN PLAINS, THE TENNESSEE VALLEY, AND THE SOUTHEAST, FRI-SUN,
APR 28-30.

HEAVY PRECIPITATION ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS AND THE
CENTRAL AND SOUTHERN ROCKIES, FRI-SAT, APR 28-29.

HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, THE MIDDLE AND
LOWER MISSISSIPPI VALLEY, THE OHIO AND TENNESSEE VALLEYS, THE CENTRAL AND
SOUTHERN APPALACHIANS, THE NORTHEAST, THE SOUTHEAST, AND THE GREAT LAKES,
FRI-MON, APR 28-MAY 1.

FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHERN APPALACHIANS, THE OHIO
VALLEY, AND THE TENNESSEE VALLEY.

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHERN PLAINS, THE
NORTHERN GREAT BASIN, THE UPPER AND MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN
APPALACHIANS, THE GREAT LAKES, AND THE OHIO VALLEY.

FLOODING LIKELY ACROSS PORTIONS OF THE SOUTHEAST AND THE MID-ATLANTIC.

EXCESSIVE HEAT ACROSS PORTIONS OF SOUTH TEXAS, FRI-SAT, APR 28-29.

MUCH ABOVE-NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN
APPALACHIANS, THE OHIO AND TENNESSEE VALLEYS, AND THE MID-ATLANTIC, FRI-SUN,
APR 28-30.

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

HIGH WINDS ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE CENTRAL AND SOUTHERN
PLAINS, AND THE SOUTHWEST, FRI-SAT, APR 28-29.

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

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN AND
CENTRAL PLAINS, THE NORTHERN AND CENTRAL ROCKIES, THE UPPER MISSISSIPPI VALLEY,
AND THE GREAT LAKES, WED-SAT, MAY 3-6.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL GREAT
BASIN, CALIFORNIA, AND THE SOUTHWEST, WED-TUE, MAY 3-9.

SEVERE DROUGHT ACROSS THE LOWER MISSISSIPPI VALLEY, THE TENNESSEE VALLEY,
HAWAII, THE NORTHEAST, CALIFORNIA, THE SOUTHEAST, THE SOUTHERN APPALACHIANS,
THE SOUTHERN PLAINS, AND THE SOUTHWEST.

DETAILED SUMMARY

FOR FRIDAY APRIL 28 - TUESDAY MAY 02: THE PRIMARY FEATURE OF INTEREST DURING
WEEK-1 IS AN ANTICIPATED 500-HPA TROUGH STRETCHING FROM SOUTHERN CANADA THROUGH
NORTHERN MEXICO ACROSS THE CENTRAL CONUS. EARLY IN THIS PERIOD THE TROUGH IS
FORECAST TO AMPLIFY OVER THE ROCKIES, BEFORE BECOMING NEGATIVELY TILTED AND
LESSENING IN AMPLITUDE AS IT LIFTS TOWARD THE GREAT LAKES LATER IN THE WEEK.
LEE SURFACE CYCLOGENESIS IS LIKELY OVER THE SOUTHERN ROCKIES ASSOCIATED WITH
THE MID-LEVEL TROUGH, WITH THIS SYSTEM BECOMING THE PRIMARY DRIVER OF HAZARDOUS
WEATHER THROUGHOUT WEEK-1.



DRY, DOWNSLOPE WESTERLY WINDS ARE FORECAST AROUND THE BASE OF THE MID-LEVEL
TROUGH ACROSS TEXAS AS THE PERIOD BEGINS AND THE SURFACE CYCLONE BEGINS TO
DEVELOP. WITH A MORE SOUTHERLY COMPONENT TO THE FLOW FURTHER EAST, A DRYLINE IS
ANTICIPATED TO DEVELOP ACROSS TEXAS WHILE A WARM FRONT EXTENDS EAST OF THE
SURFACE LOW THROUGH THE OZARKS. THE STORM PREDICTION CENTER (SPC) PREDICTS A
30% CHANCE OF SEVERE WEATHER FOR OKLAHOMA AND ARKANSAS ASSOCIATED WITH THESE
FEATURES, PRIMARILY NEAR THE TRIPLE POINT AND ALONG THE WARM FRONT ON FRI, APR
28, WHILE A 15% RISK EXTENDS ACROSS A BROADER REGION. AMPLE MOISTURE AND
INSTABILITY APPEAR TO BE AVAILABLE WITH THE FLOW OF WARM, GULF AIR NORTHWARD,
WHILE WIND SHEAR SHOULD ALSO BE SUBSTANTIAL GIVEN THE DEEPENING SURFACE LOW AND
INTENSIFYING LOW-LEVEL JET, COUPLED WITH SOUTHWESTERLY FLOW ALOFT. THIS
SCENARIO SUGGESTS SUPERCELL DEVELOPMENT WITH ASSOCIATED TORNADO AND LARGE HAIL
RISKS. SEVERE WEATHER IS ALSO FORECAST BY SPC FOR THE ARK-LA-TEX REGION ON SAT,
APR 29, WITH AN EMBEDDED 30% PROBABILITY REGION ONCE MORE. THE THREAT HERE IS
FORECAST TO BE TIED TO AN ADVANCING COLD FRONT INTO THE HIGHLY UNSTABLE WARM
SECTOR, WITH ALL MODES OF SEVERE WEATHER POSSIBLE. THE COLD FRONT IS FORECAST
TO ADVANCE EAST ON SUN, APR 30, WITH A 15% PROBABILITY OF SEVERE WEATHER GIVEN
BY SPC FROM THE TENNESSEE VALLEY THROUGH SOUTHERN MISSISSIPPI. ASIDE FROM THE
SEVERE WEATHER, WIDESPREAD HEAVY RAIN (EXCEEDING 1" IN 24 HOURS) IS FORECAST ON
FRI-SAT, APR 28-29, FROM EAST TEXAS THROUGH THE GREAT LAKES AND ON SUN-MON, APR
30-MAY 1, FROM THE LOWER MISSISSIPPI VALLEY THROUGH NEW YORK STATE. MANY AREAS
IN THE MISSISSIPPI VALLEY ARE FORECAST TO RECEIVE 3-6" OF RAIN OVER THE COURSE
OF THIS EVENT.



ON THE BACK SIDE OF THE SURFACE LOW PRESSURE, HEAVY PRECIPITATION (1" OR
GREATER LIQUID EQUIVALENT IN 24 HOURS) IS FORECAST CENTERED ON COLORADO FOR
FRI-SAT, APR 28-29. SNOW IS POSSIBLE IN THE HIGHER ELEVATIONS OF THE FRONT AND
PARK RANGES, WITH DAILY TOTALS OF AROUND 6" POSSIBLE, WHILE RAIN IS FORECAST AT
LOWER ELEVATIONS. SOME SNOW MAY MAKE IT INTO THE IMMEDIATE DENVER METRO AREA
GIVEN THE STRONG COLD AIR ADVECTION ON THE BACK SIDE OF THE LOW AND SUBSTANTIAL
COLD AIR ALOFT. MUCH BELOW-NORMAL TEMPERATURES ARE FORECAST FOR A SIMILAR
REGION ON SUN, APR 30, WHERE MINIMUM TEMPERATURE ANOMALIES OF -12 DEGREES F OR
MORE ARE POSSIBLE THAT COULD RESULT IN A HARD FREEZE FOR MANY AREAS. WIDESPREAD
HIGH WINDS (EXCEEDING 30 KTS) ARE ALSO POSSIBLE ON THE BACK SIDE OF THE SURFACE
LOW PRESSURE AS IT DEEPENS AND LIFTS NORTHWARD WITH AN ASSOCIATED HAZARD FROM
SOUTHEAST ARIZONA THROUGH CENTRAL TEXAS ON FRI-SAT, APR 28-29, AND CENTRAL
KANSAS THROUGH THE UPPER PENINSULA OF MICHIGAN ON SUN-MON, APR 30-MAY 1.
MARGINALLY ELEVATED FIRE WEATHER CONDITIONS ARE ALSO POSSIBLE FROM LAS VEGAS
SOUTHWARD ALONG THE CALIFORNIA/ARIZONA BORDER AND FROM SOUTHERN NEW MEXICO
THROUGH WEST TEXAS ON FRI, APR 28, WHERE DRY FUELS ARE ANTICIPATED ALONG WITH
LOW HUMIDITY AND BREEZY CONDITIONS. MARGINALLY ELEVATED FIRE WEATHER CONDITIONS
ARE ALSO POSSIBLE IN VICINITY OF LOS ANGELES ON FRI-SAT, APR 28-29, WHERE DRY,
DOWNSLOPE WINDS ARE POSSIBLE WITH ANTECEDENT DRY CONDITIONS. MARGINAL TO
ELEVATED FIRE WEATHER CONDITIONS ARE POSSIBLE ACROSS MUCH OF THE SOUTHWEST
THROUGHOUT WEEK-1, AND WILL BE RE-EVALUATED FOR SUBSEQUENT OUTLOOKS BY SPC.



AHEAD OF THE AFOREMENTIONED LOW PRESSURE SYSTEM, WIDESPREAD WARM ADVECTION IS
FORECAST AND ASSOCIATED HEAT-RELATED HAZARDS ARE POSSIBLE BEFORE RELIEF ARRIVES
FROM THE COLD FRONTAL PASSAGE. FIRST, EXCESSIVE HEAT IS FORECAST FOR PORTIONS
OF SOUTH TEXAS ON FRI-SAT, APR 28-29, AS HEAT INDEX VALUES MAY EXCEED 105
DEGREES F ASSOCIATED WITH THE WARM, HUMID CONDITIONS. AN EASTWARD SHIFTING
THREAT OF MUCH ABOVE-NORMAL TEMPERATURES IS FORECAST EAST OF THE APPALACHIANS
THROUGH THE CAPITAL REGION FOR FRI-SUN, APR 28-30. HIGH TEMPERATURES OF 12 TO
20 DEGREES F ABOVE-NORMAL ARE FORECAST, WITH MANY AREAS APPROACHING OR
EXCEEDING 90 DEGREES F FOR THE FIRST TIME THIS YEAR. ANOMALIES IN NEW ENGLAND
ARE FORECAST TO BE SIMILARLY HIGH AS THOSE FARTHER SOUTH, BUT MAXIMUM
TEMPERATURES ARE NOT LIKELY TO EXCEED THE LOW- TO MID-80S, SUCH THAT NO HAZARD
IS FORECAST.



ALASKA IS FORECAST TO EXPERIENCE RELATIVELY QUIET WEATHER DURING WEEK-1, WITH
DISTURBANCES OF MODERATE INTENSITY BY ALASKAN STANDARDS IN THE GULF OF ALASKA
AND BERING SEA. UNLIKE THE LOWER-48, NO SUBSTANTIAL TEMPERATURE ANOMALIES ARE
FORECAST, GIVEN THE LACK OF ANOMALOUS CIRCULATIONS FORECAST IN THE VICINITY OF
THE STATE.

FOR WEDNESDAY MAY 03 - TUESDAY MAY 09: SUBSTANTIAL UNCERTAINTY IS APPARENT IN
THE WIDE RANGE OF SPAGHETTI PERSPECTIVES OF THE MID-LEVEL CIRCULATION OVER
NORTH AMERICA IN WEEK-2. THERE IS A SLIGHT TENDENCY TOWARD ANOMALOUS 500-HPA
RIDGING OVER THE WEST COAST, WITH NEGATIVE HEIGHT ANOMALIES CENTERED ON THE
GREAT LAKES. GIVEN THE REDUCED AMPLITUDE OF THE CIRCULATION ANTICIPATED DURING
WEEK-2, LIMITED HAZARDOUS IMPACTS CAN BE DISCERNED AT THIS TIME.



A SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES IS FORECAST FOR PORTIONS OF THE
SOUTHWEST AND CALIFORNIA THROUGHOUT WEEK-2, WHERE REFORECAST GUIDANCE IS
CONSISTENTLY WARM BENEATH THE FORECAST ANOMALOUS RIDGING. THE AREA INDICATED ON
THE MAP IS A CONFLUENCE OF REGIONS FORECAST BY THE GEFS TO HAVE AT LEAST A 20%
CHANCE OF BOTH EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE OF MAXIMUM
TEMPERATURE AND REACHING 85 DEGREES F. A SLIGHT RISK OF MUCH BELOW-NORMAL
TEMPERATURES EXTENDS FROM THE CENTRAL ROCKIES THROUGH THE HIGH PLAINS AND
EASTWARD THROUGH THE GREAT LAKES FOR WED-SAT, MAY 3-6. 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. THE BEST
CHANCE OF MUCH ABOVE-NORMAL TEMPERATURE ANOMALIES APPEARS TO BE IN ALASKA
DURING WEEK-2, WITH ANOMALOUS SOUTHERLY FLOW ANTICIPATED, BUT NO HAZARDS ARE
FORECAST GIVEN THE MODEST HIGH TEMPERATURES AT THIS TIME OF YEAR AND FIRE
SEASON REMAINING WELL INTO THE FUTURE.



ACCORDING TO THE U.S. DROUGHT MONITOR RELEASED ON APRIL 20TH (USING DATA
THROUGH 8 AM EDT, APRIL 18TH), COVERAGE OF SEVERE, OR GREATER INTENSITY,
DROUGHT THROUGHOUT THE CONUS REMAINS THE SAME AS LAST WEEK (1.44 PERCENT). THIS
REMAINS THE LOWEST COVERAGE OF D2-D4 DROUGHT OVER THE CONUS SINCE AUG 2010.

FORECASTER: CPC FORECASTER

$$




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