Prognostic Meteorological Discussion
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FXUS21 KWNC 281943
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 28 2017

SYNOPSIS: MID-LEVEL LOW PRESSURE IS ANTICIPATED ACROSS THE CENTRAL CONTIGUOUS
U.S. DURING THE FIRST TWO DAYS OF THE OUTLOOK PERIOD, WITH A FORECAST TENDENCY
TO LIFT NORTHWARD, TOWARD AND OVER THE UPPER GREAT LAKES REGION. MODERATELY
STRONG SURFACE LOW PRESSURE INITIALLY NEAR IOWA IS FORECAST TO FOLLOW THE SAME
GENERAL TRACK AS THE MID-LEVEL LOW PRESSURE AREA. SEVERAL TYPES OF HAZARDS ARE
PREDICTED TO ACCOMPANY THIS STORM SYSTEM. UNCERTAINTY REMAINS 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 MID-ATLANTIC, THE LOWER AND MIDDLE
MISSISSIPPI VALLEY, THE CENTRAL APPALACHIANS, THE TENNESSEE VALLEY, THE
NORTHEAST, THE SOUTHERN APPALACHIANS, THE SOUTHEAST, THE SOUTHERN PLAINS, AND
THE OHIO VALLEY, WED-THU, MAY 3-MAY 4.

HEAVY RAIN ACROSS PORTIONS OF THE NORTHEAST AND THE GREAT LAKES, MON-TUE, MAY
1-MAY 2.

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 SOUTHEAST, THE
MID-ATLANTIC, THE SOUTHERN PLAINS, THE NORTHERN PLAINS, AND THE NORTHERN GREAT
BASIN.

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

HIGH WINDS ACROSS PORTIONS OF THE NORTHERN AND CENTRAL PLAINS, THE GREAT LAKES,
THE MIDDLE AND UPPER MISSISSIPPI VALLEY, AND THE OHIO VALLEY, MON-TUE, MAY
1-MAY 2.

MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN AND CENTRAL
PLAINS, AND THE MIDDLE AND UPPER MISSISSIPPI VALLEY, MON, MAY 1.

HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE, WED, MAY 3.

SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTHERN
ROCKIES, THE CENTRAL GREAT BASIN, THE SOUTHWEST, CALIFORNIA, AND THE SOUTHERN
PLAINS, SAT-SUN, MAY 6-MAY 7.

SEVERE DROUGHT ACROSS PARTS OF THE SOUTHEAST, CALIFORNIA, AND HAWAII.

DETAILED SUMMARY

FOR MONDAY MAY 01 - FRIDAY MAY 05: DURING THE FIRST FEW DAYS OF THE OUTLOOK
PERIOD, A SURFACE LOW PRESSURE SYSTEM INITIALLY NEAR IOWA IS PREDICTED TO TRACK
NORTHEASTWARD ACROSS THE UPPER GREAT LAKES REGION AND INTO CANADA. SEVERAL
HAZARDS ARE EXPECTED TO ACCOMPANY THIS SYSTEM. FOR AREAS GENERALLY EAST AND
SOUTH OF THE PREDICTED PATH OF THE LOW PRESSURE CENTER, THE CONCERN IS FOR
HEAVY RAIN (1.5"-2.0") OVER PORTIONS OF UPSTATE NEW YORK AND NORTHERN NEW
ENGLAND ON MAY 1-2, AND 1.5"-4.0" GENERALLY EAST OF A LINE EXTENDING FROM THE
LOWER MISSISSIPPI VALLEY TO SOUTHERN NEW ENGLAND, ON MAY 3-4. ALTHOUGH NO
SEVERE WEATHER SHAPES ARE DRAWN ON THE MAP FOR MAY 1, FAIRLY STRONG
THUNDERSTORMS MAY STILL DEVELOP AHEAD OF THE LOW PRESSURE SYSTEM`S COLD FRONT
IN THE REGION BETWEEN THE LOWER GREAT LAKES AND THE CENTRAL APPALACHIANS. THE
STORM PREDICTION CENTER (SPC) NOTES A CORRIDOR OF STRONG SOUTH-SOUTHWEST
500-HPA FLOW IS EXPECTED TO OVERSPREAD THIS AREA, BUT ANY SIGNIFICANT THREAT OF
SEVERE WEATHER IS PREDICTED TO BE TEMPERED BY A LACK OF STEEPER MID-LEVEL LAPSE
RATES, LIMITED BUOYANCY/INSTABILITY, AND CONCERNS REGARDING CLOUD COVER EARLIER
IN THE DAY.



OTHER HAZARDS THAT ARE FORECAST TO ACCOMPANY THE AFOREMENTIONED LOW PRESSURE
SYSTEM ARE HIGH WINDS AND MUCH BELOW-NORMAL TEMPERATURES. A BROAD AREA OF
MARGINALLY HIGH WIND SPEEDS (APPROACHING 30 KTS) IS DEPICTED FROM EASTERN
PORTIONS OF NEBRASKA AND KANSAS ACROSS THE MIDDLE AND UPPER MISSISSIPPI VALLEY,
PORTIONS OF INDIANA AND OHIO, AND THE WESTERN AND CENTRAL GREAT LAKES REGION,
MAY 1-2. AN AREA OF MUCH BELOW-NORMAL TEMPERATURES IS PREDICTED FOR PORTIONS OF
THE UPPER MISSISSIPPI VALLEY (AND SMALL PARTS OF ADJACENT STATES), ON MAY 1. IN
THIS AREA, DAYTIME MAXIMUM TEMPERATURES ARE ANTICIPATED TO RANGE FROM 20 TO 26
DEGREES F BELOW-NORMAL. THIS WOULD INDICATE A HIGH OF 36 DEGREES F FOR DULUTH,
MN, AND 50 DEGREES F FOR DES MOINES, IA. THESE PREDICTED DAYTIME HIGH
TEMPERATURES ARE TYPICAL OF OVERNIGHT LOW TEMPERATURES FOR THESE LOCATIONS AT
THIS TIME OF YEAR.



FLOODING IS POSSIBLE, LIKELY, IMMINENT, OR OCCURRING ACROSS THE CAROLINAS AND
SOUTHERN VIRGINIA, CENTRAL AND SOUTH-CENTRAL PORTIONS OF THE MISSISSIPPI
VALLEY, EASTERN OKLAHOMA, NORTHERN NORTH DAKOTA, AND PARTS OF IDAHO. AS THESE
FLOOD SHAPES TEND TO CHANGE FAIRLY QUICKLY, IT IS RECOMMENDED THAT THE RIVER
FORECAST CENTER HOME PAGE IS CONSULTED FOR THE VERY LATEST INFORMATION AT:
HTTPS://WATER.WEATHER.GOV/AHPS/RFC/RFC.PHP. A COLD FRONT WHICH RECENTLY STALLED
ACROSS NORTH CAROLINA AND TENNESSEE BROUGHT SEVERE STORMS TO THE REGION,
RAINFALL AMOUNTS OF 2-10", AND FLASH FLOODING.



SEVERAL LOW PRESSURE SYSTEMS ARE FORECAST TO AFFECT SOUTHERN ALASKA DURING THIS
PERIOD, AS THEY TRACK PRIMARILY SOUTH OF THE ALEUTIANS AND ACROSS THE NORTHERN
GULF OF ALASKA. THE 0Z ECMWF AND 6Z GFS (ON APR 28) BOUNDARY LAYER WIND
FORECASTS, ALONG WITH SEA-LEVEL PRESSURE GRADIENTS PREDICTED BY THE WEATHER
PREDICTION CENTER (WPC), ANTICIPATE HIGH WINDS (NEAR 40 KTS) AHEAD OF ONE OF
THESE CYCLONIC SYSTEMS AS IT MOVES ACROSS THE NORTHEASTERN GULF OF ALASKA ON
MAY 3. THE MOST LIKELY AREA TO EXPERIENCE THESE STRONGER WIND SPEEDS SPANS THE
PANHANDLE REGION FROM ABOUT YAKUTAT BAY TO SITKA.

FOR SATURDAY MAY 06 - FRIDAY MAY 12: 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 BE JUST OFF THE EAST COAST, A RIDGE
OVER THE NATION`S MIDSECTION, AND ANOTHER TROUGH TRAVERSING 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 SOUTHERN
CALIFORNIA AND PARTS OF THE SOUTHWEST EARLY IN THE WEEK-2 PERIOD. 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, AND THE DAYTIME HIGH TEMPERATURE IS EXPECTED TO BE AT
LEAST 85 DEGREES F.



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 JANUARY 2000.

FORECASTER: ANTHONY ARTUSA

$$



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