Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 201904
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 20 2015

SYNOPSIS: A STRONG AREA OF UPPER-LEVEL LOW PRESSURE IS EXPECTED TO PERSIST
ACROSS SOUTHEAST CANADA DURING THE NEXT WEEK, WHILE A COUPLE OF LOW PRESSURE
SYSTEMS PROGRESS ACROSS THE WESTERN U.S. SURFACE HIGH PRESSURE IS FORECAST TO
EXTEND SOUTH FROM CANADA INTO THE MIDWEST FROM THURSDAY THROUGH EARLY NEXT
WEEK. A BROAD AREA OF LOW PRESSURE IS EXPECTED TO REMAIN OVER THE GULF OF
ALASKA.

HAZARDS

SEVERE WEATHER FOR PARTS OF LOUISIANA, OKLAHOMA, AND TEXAS, THU, APR 23.

HIGH WINDS FOR PARTS OF THE SOUTHWEST AND SOUTHERN GREAT PLAINS, THU-FRI, APR
23-24.

HEAVY RAIN AND HIGH-ELEVATION SNOW FOR PARTS OF THE PACIFIC NORTHWEST, SAT-MON,
APR 25-27.

FLOODING LIKELY FOR WESTERN KENTUCKY AND SOUTHEAST 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.

MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE EASTERN CORN BELT,
CENTRAL/SOUTHERN APPALACHIANS, AND MID-ATLANTIC, TUE-THU, APR 28-30.

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 THURSDAY APRIL 23 - MONDAY APRIL 27: CYCLONIC FLOW ASSOCIATED WITH THE
ANOMALOUS UPPER-LEVEL TROUGH CENTERED OVER SOUTHEAST CANADA IS LIKELY TO RESULT
IN BELOW-NORMAL TEMPERATURES ACROSS THE GREAT LAKES AND NORTHEAST. SUBFREEZING
TEMPERATURES ARE FORECAST ACROSS THE UPPER MISSISSIPPI VALLEY, GREAT LAKES, AND
PARTS OF THE NORTHEAST, BUT THESE TEMPERATURES ARE NOT TOO ANOMALOUS (5 TO 10
DEGREES F BELOW-NORMAL) FOR LATE APRIL.



A SHORTWAVE TROUGH IS EXPECTED TO PROGRESS ACROSS THE FOUR CORNERS REGION LATER
THIS WEEK AND THEN WEAKEN AS IT ENCOUNTERS CONFLUENT FLOW ACROSS THE EASTERN
U.S. HIGH-ELEVATION SNOW (ABOVE 8-9,000 FEET)  IS EXPECTED TO ACCOMPANY THE
SHORTWAVE TROUGH ACROSS THE CENTRAL ROCKIES. SINCE THE SHORTWAVE TROUGH IS
EXPECTED TO BE PROGRESSIVE, A HEAVY SNOW HAZARD IS NOT POSTED FOR THIS REGION.
HIGH WINDS (GUSTS ABOVE 40 KNOTS) ARE EXPECTED FROM THE DESERT SOUTHWEST EAST
TO THE SOUTHERN HIGH PLAINS ON THURSDAY AND FRIDAY. THESE GUSTY WINDS MAY
GENERATE BLOWING DUST ACROSS THESE AREAS.



ON THURSDAY, SEVERE WEATHER IS POSSIBLE ACROSS SOUTHEAST OKLAHOMA, THE EASTERN
HALF OF TEXAS, AND WESTERN LOUISIANA AHEAD OF THE SHORTWAVE TROUGH EJECTING
FROM THE SOUTHWEST. MODERATE INSTABILITY AND STRONG DEEP-LAYER WIND SHEAR ARE
EXPECTED TO FAVOR THE DEVELOPMENT OF SEVERE WEATHER ACROSS THIS REGION. MODEL
DIFFERENCES WITH THE EVOLUTION OF THE SHORTWAVE TROUGH PRECLUDE DESIGNATION OF
A SEVERE WEATHER HAZARD AREA BEYOND THURSDAY AT THIS TIME.



ONSHORE FLOW IS EXPECTED TO INCREASE ACROSS THE PACIFIC NORTHWEST DURING THE
WEEKEND AND INCREASE THE CHANCES FOR HEAVY RAIN AND HIGH ELEVATION SNOW ACROSS
THE COASTAL RANGES OF WASHINGTON AND NORTHERN OREGON. SINCE THE HIGH RESOLUTION
MODELS INDICATE 2 TO 6 INCHES OF PRECIPITATION, LIQUID EQUIVALENT, FOR THESE
AREAS, A HEAVY PRECIPITATION HAZARD IS POSTED FOR PARTS OF OREGON AND
WASHINGTON. SNOW LEVELS ARE LIKELY TO FLUCTUATE AND RESIDENTS ARE URGED TO
REFER TO THE LATEST FORECASTS/STATEMENTS FROM THEIR LOCAL NWS OFFICES.



ANOMALOUS RAINFALL (MORE THAN 4 INCHES ABOVE-NORMAL) DURING THE PAST MONTH HAS
RESULTED IN MODERATE RIVER FLOODING ACROSS PARTS OF KENTUCKY AND SOUTHEAST
TEXAS. THESE RIVERS ARE EXPECTED TO REMAIN IN MODERATE FLOOD STAGE THROUGH AT
LEAST FRIDAY. MINOR FLOODING IS OCCURRING ALONG THE LOWER OHIO RIVER AND MAY
REACH MODERATE STAGE LATER THIS WEEK.



NO HAZARDS ARE EXPECTED WITH THE BROAD TROUGH OVER THE GULF OF ALASKA WITH THE
HEAVIEST PRECIPITATION REMAINING SOUTH OF THE ALASKA PANHANDLE AND WINDS LIKELY
BELOW HAZARDS CRITERIA.

FOR TUESDAY APRIL 28 - MONDAY MAY 04: AN UPPER-LEVEL TROUGH IS EXPECTED TO
PERSIST ACROSS EASTERN NORTH AMERICA EARLY IN WEEK-2, WHILE ONSHORE FLOW
CONTINUES TO AFFECT THE WESTERN U.S. THIS PREDICTED LONGWAVE PATTERN IS LIKELY
TO MAINTAIN UNSEASONABLY COOL TEMPERATURES ACROSS THE EASTERN U.S. AT THE END
OF APRIL.



THE 12Z HIGH-RESOLUTION GFS AND CANADIAN MODELS INDICATE AN INTENSIFYING LOW
PRESSURE SYSTEM NEAR THE EAST COAST EARLY IN WEEK-2. ALTHOUGH MODEL SPREAD
INCREASES ON THE AMPLITUDE OF THE EASTERN U.S. TROUGH, GUIDANCE FROM THE GEFS
REFORECAST TOOL FAVORS AT LEAST A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES
(APRIL 28-30) ACROSS THE EASTERN CORN BELT, CENTRAL/SOUTHERN APPALACHIANS, AND
THE MID-ATLANTIC WHERE A FROST/FREEZE AT THE END OF APRIL COULD HAVE MORE OF AN
IMPACT THAN ACROSS THE UPPER MIDWEST.



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: BRAD PUGH

$$



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