Prognostic Meteorological Discussion
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FXUS21 KWNC 171709
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 17 2015

SYNOPSIS: EARLY IN THE PERIOD, A WARM FRONT AND WAVE OF SURFACE LOW PRESSURE
ARE EXPECTED TO IMPACT THE EASTERN U.S.  A DEEP SURFACE LOW PRESSURE SYSTEM TO
THE WEST IS FORECAST TO BRING ACTIVE SPRING WEATHER ACROSS THE UPPER MIDWEST
AND GREAT LAKES EARLY NEXT WEEK. A DEEP AREA OF SURFACE LOW PRESSURE IS
EXPECTED TO WEAKEN OVER WESTERN ALASKA EARLY IN THE PERIOD. ACTIVE WEATHER IS
FORECAST FROM THE ROCKIES ACROSS THE SOUTHERN TIER OF THE U.S. LATER IN THE
PERIOD, WHILE UNSEASONABLY CHILLY AIR DOMINATES THE NORTHERN TIER OF THE
COUNTRY.

HAZARDS

HEAVY RAIN ADVANCES NORTHEASTWARD ALONG PARTS OF THE NORTHEAST COAST, MON-TUE,
APR 20-21.

HIGH WINDS FOR PARTS OF THE NORTHERN PLAINS, UPPER MISSISSIPPI VALLEY, AND
GREAT LAKES, MON-TUE, APR 20-21.

HIGH WINDS FOR PARTS OF THE MID-ATLANTIC AND NORTHEAST, MON-TUE, APR 20-21.

FLOODING LIKELY FOR PARTS OF EAST-CENTRAL AND WESTERN KENTUCKY.

FLOODING POSSIBLE FOR PARTS OF SOUTHEASTERN TEXAS.

FLOODING POSSIBLE NEAR THE CONFLUENCE OF THE OHIO AND WABASH RIVERS IN WESTERN
KENTUCKY/SOUTHEASTERN ILLINOIS.

FLOODING OCCURRING OR IMMINENT FOR PARTS OF THE SOURIS RIVER IN NORTH DAKOTA
DUE TO WATER RELEASE FROM LAKE DARLING.

FLOODING OCCURRING OR IMMINENT FOR PARTS OF INDIANA.

SEVERE DROUGHT FOR THE CENTRAL AND SOUTHERN GREAT PLAINS, SOUTHWEST, GREAT
BASIN, CALIFORNIA, THE PACIFIC NORTHWEST, SOUTHERN ALABAMA, SOUTHERN FLORIDA,
AND HAWAII.

DETAILED SUMMARY

FOR MONDAY APRIL 20 - FRIDAY APRIL 24: LOW PRESSURE IS FORECAST TO FORM ALONG A
WARM FRONT AND PROPAGATE NORTHEASTWARD EARLY NEXT WEEK NEAR THE EASTERN
SEABOARD. THIS LEADS TO HEAVY RAIN (IN EXCESS OF 1 INCH IN 24 HOURS) THAT IS
FORECAST TO ADVANCE NORTHEASTWARD FROM THE MID-ATLANTIC TO THE NORTHEAST, APR
20-21. AHEAD OF THIS FRONT/LOW PRESSURE SYSTEM, STRONG SOUTHEASTERLY WINDS IN
EXCESS OF 30 KNOTS ARE EXPECTED OVER PARTS OF THE MID-ATLANTIC AND NORTHEAST ON
MONDAY AND TUESDAY. THIS COULD LEAD TO LOCALIZED COASTAL FLOODING IN MORE
FAVORABLE REGIONS INCLUDING PARTS OF LONG ISLAND AND COASTAL NEW ENGLAND.



AN AREA OF LOW PRESSURE DROPPING SOUTHEASTWARD FROM SOUTH-CENTRAL CANADA IS
FORECAST TO SLOWLY COMBINE WITH A SURFACE CYCLONE FORMING IN THE LEE OF THE
ROCKIES BEFORE THE PERIOD. THIS RATHER COMPLEX, STRENGTHENING AREA OF LOW
PRESSURE IS EXPECTED TO CAUSE HIGH WINDS (IN EXCESS OF 30 KNOTS) FOR PARTS OF
THE NORTHERN PLAINS, UPPER MISSISSIPPI VALLEY, AND GREAT LAKES, APR 20-21.
WIDESPREAD RAINFALL AMOUNTS OF 0.25-0.5 INCHES ARE EXPECTED WITH THIS SYSTEM IN
THE GREAT LAKES REGION. HOWEVER, LOCALLY HEAVIER RAIN IS LIKELY IN SOME
REGIONS, THOUGH MODEL UNCERTAINTY PRECLUDES A SPECIFIC HAZARD DESIGNATION AT
THIS TIME. CHECK WITH THE LOCAL WEATHER FORECAST OFFICE FOR THE LATEST
INFORMATION REGARDING FORECAST RAINFALL AMOUNTS. ADDITIONALLY, SOME
ACCUMULATING SNOW IS POSSIBLE IN THE COLD SECTOR NORTHWEST OF SURFACE LOW.
THERE IS A LARGE DEGREE OF MODEL UNCERTAINTY, BUT SOME LOCATIONS COULD SEE
SNOWFALL TOTALS IN EXCESS OF 4 INCHES.



ANTECEDENT RAINFALL LEADS TO THE LIKELIHOOD OF FLOODING FOR PARTS OF
EAST-CENTRAL AND WESTERN KENTUCKY. IN ADDITION, FLOODING IS POSSIBLE NEAR THE
CONFLUENCE OF THE OHIO AND WABASH RIVERS IN WESTERN KENTUCKY/SOUTHEASTERN
ILLINOIS.



DEEP LOW PRESSURE IS FORECAST TO MEANDER AROUND THE ALEUTIANS, WESTERN ALASKA,
AND THE BERING SEA, AT THE VERY BEGINNING OF THE PERIOD, WEAKENING THEREAFTER.
THERE ARE NOT CURRENTLY ANY HAZARDS DEPICTED ASSOCIATED WITH THIS SYSTEM.
ACTIVE WEATHER LOOKS TO RESUME TOWARD THE END OF THE PERIOD AS ANOMALOUS
MID-LEVEL TROUGHING IS FORECAST UPSTREAM.



FLOODING IS OCCURRING OR IMMINENT FOR PARTS OF THE SOURIS RIVER IN NORTH DAKOTA
BECAUSE OF RELEASES FROM LAKE DARLING. THE WATER RELEASES ARE DUE TO RISING
LEVELS CAUSED BY SNOW MELT.



AN UPPER-LEVEL TROUGH IS FORECAST TO IMPACT THE WEST COAST, BRINGING SOME
NEEDED PRECIPITATION ANOMALOUSLY FAR SOUTH THROUGH CALIFORNIA DURING THE
PERIOD. AT THIS TIME, PRECIPITATION AMOUNTS ARE NOT EXPECTED TO REACH HAZARD
CRITERIA. THIS TROUGH IS EXPECTED TO PRODUCE SOME LOCALLY HEAVY RAIN AND VERY
HIGH ELEVATION SNOWS LATE NEXT WEEK, BUT CONFIDENCE IS LOW WITH RESPECT TO
SPECIFIC HAZARDS. THIS PRECIPITATION IS LIKELY GOING TO EXTEND EASTWARD ALONG A
STATIONARY BOUNDARY LATE NEXT WEEK IN THE CENTRAL PLAINS, BUT ENSEMBLE SPREAD
IS TOO LOW TO DEPICT ANY SPECIFIC HAZARDS.

FOR SATURDAY APRIL 25 - FRIDAY MAY 01: DURING WEEK-2, THE PATTERN IS EXPECTED
TO REMAIN ACTIVE EARLY ON ACROSS THE ROCKIES AND PLAINS, AS UPPER-LEVEL HEIGHT
FALLS ADVANCE EASTWARD FROM THE WEST COAST. THIS LEADS TO ELEVATED CHANCES OF
HEAVY MOUNTAIN SNOW AND SEVERE WEATHER BY NEXT WEEKEND ACROSS THE
CLIMATOLOGICALLY FAVORED REGIONS. HOWEVER, THE CURRENT SUITE OF ENSEMBLE
FORECASTS EXHIBIT ENOUGH SPREAD TO PRECLUDE A HAZARD DEPICTION AT THIS TIME.



THE MOST RECENT U.S. DROUGHT MONITOR, RELEASED YESTERDAY, INDICATES A VERY
SLIGHT DECREASE (TO 19.14 FROM 19.17) IN THE PERCENTAGE OF THE CONUS IN SEVERE
TO EXCEPTIONAL DROUGHT (D2-D4). THIS WEEK`S MAP IS VERY SIMILAR TO LAST WEEK`S,
WITH RELATIVELY MINOR ADJUSTMENTS MADE.

FORECASTER: STEPHEN BAXTER

$$




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