Prognostic Meteorological Discussion
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FXUS21 KWNC 261821
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 26 2017

SYNOPSIS: SURFACE HIGH PRESSURE IS FORECAST TO BECOME CENTERED OFFSHORE OF THE
EAST COAST LATER THIS WEEK WITH A WARMING TREND ACROSS THE EASTERN U.S.  AN
AREA OF UPPER-LEVEL LOW PRESSURE IS EXPECTED TO SLOWLY CROSS THE NORTH-CENTRAL
U.S. FROM JUNE 29 TO JULY 2. HURRICANE DORA IN THE EAST PACIFIC IS FORECAST TO
TURN WEST AND TRACK ALONG THE 20TH PARALLEL DURING MID-WEEK. AN AREA OF
UPPER-LEVEL HIGH PRESSURE IS EXPECTED TO PERSIST OVER EASTERN MAINLAND ALASKA
INTO THE BEGINNING OF JULY.

HAZARDS

SEVERE WEATHER FOR PARTS OF THE CENTRAL GREAT PLAINS AND MIDDLE MISSISSIPPI
VALLEY, THU, JUN 29.

HEAVY RAIN FOR PARTS OF THE CENTRAL GREAT PLAINS, MIDDLE MISSISSIPPI VALLEY,
MIDWEST, AND GREAT LAKES, THU-FRI, JUN 29-30.

HEAVY RAIN FOR PARTS OF THE CENTRAL AND SOUTHERN GREAT PLAINS EAST TO THE LOWER
OHIO VALLEY, SAT-SUN, JUL 1-2.

HEAVY RAIN FOR PARTS OF KODIAK ISLAND, THE KENAI PENINSULA, AND THE PRINCE
WILLIAM SOUND, THU-FRI, JUN 29-30.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR THE NORTHERN GREAT PLAINS,
TUE-MON, JUL 4-10.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF EASTERN MAINLAND
ALASKA, TUE-SAT, JUL 4-8.

SEVERE DROUGHT ACROSS CALIFORNIA, HAWAII, THE NORTHERN PLAINS, AND THE
SOUTHWEST.

DETAILED SUMMARY

FOR THURSDAY JUNE 29 - MONDAY JULY 03: THE MAJOR HAZARDS DURING THIS PERIOD
WILL BE HEAVY RAINFALL, FLASH FLOODING, AND SEVERE THUNDERSTORMS ASSOCIATED
WITH A SHORTWAVE TROUGH AND A COLD FRONT ACROSS THE CENTRAL U.S. AN
INCREASINGLY MOIST AIRMASS IS EXPECTED ACROSS THE GREAT PLAINS, MISSISSIPPI
VALLEY, AND MIDWEST IN ADVANCE OF A SHORTWAVE TROUGH. THE DETERMINISTIC 6Z GFS
MODEL INDICATES THAT PRECIPITABLE WATER VALUES INCREASE ABOVE 1.75 INCHES THIS
WEEK ACROSS IOWA, ILLINOIS, AND MISSOURI. A SHORTWAVE TROUGH IS LIKELY TO
RESULT IN CONVECTION WITH HEAVY RAINFALL (1 TO 3 INCHES, LOCALLY MORE PER 24
HOURS) FROM THE CENTRAL GREAT PLAINS AND MIDDLE MISSISSIPPI VALLEY EAST TO THE
GREAT LAKES JUNE 29 AND 30. THIS HEAVY RAINFALL IS THEN EXPECTED TO BRIEFLY
SHIFT SOUTH TO THE SOUTHERN GREAT PLAINS AND LOWER OHIO VALLEY ON JULY 1 AND 2.
THE HEAVY RAIN HAZARD SHAPES ARE BASED ON THE PRECIPITATION FORECASTS FROM THE
GFS AND ECMWF ENSEMBLE MEANS. HEAVY RAINFALL ACROSS THE CENTRAL U.S. WILL BE
CAPABLE OF TRIGGERING FLASH FLOODING THIS WEEK.



ON JUNE 29, WIND SHEAR AND INSTABILITY ARE EXPECTED TO BE SUFFICIENT TO SUPPORT
SEVERE THUNDERSTORMS ACROSS THE CENTRAL GREAT PLAINS AND MIDDLE MISSISSIPPI
VALLEY. DURING THE REMAINDER OF THE WEEK, THE RISK OF SEVERE THUNDERSTORMS
REMAINS ELEVATED ACROSS THE CENTRAL U.S. WHERE MULTIPLE MESOSCALE CONVECTIVE
SYSTEMS (MCS) ARE EXPECTED TO DEVELOP. HOWEVER, THE LOWER PREDICTABILITY ON THE
EXACT LOCATION OF A MCS BEYOND THE SHORT-TERM PRECLUDES DESIGNATION OF A SEVERE
WEATHER HAZARD AT THIS TIME.



THE PROTRACTED HEAT WAVE THAT AFFECTED THE WESTERN U.S. IS EXPECTED TO END
EARLY THIS WEEK. ALTHOUGH ABOVE-NORMAL TEMPERATURES ARE FORECAST TO PERSIST
ACROSS THIS REGION THROUGH THE END OF JUNE, MAXIMUM TEMPERATURE ANOMALIES AND
HEAT INDEX VALUES ARE NOT EXPECTED TO BE HIGH ENOUGH TO WARRANT ANY HEAT
RELATED HAZARDS. MOISTURE ASSOCIATED WITH HURRICANE DORA IN THE EAST PACIFIC IS
NOT EXPECTED TO SHIFT NORTH INTO THE DESERT SOUTHWEST.



ON JUNE 29 AND 30, A LOW PRESSURE SYSTEM WITH ONSHORE LOW IS EXPECTED TO BRING
HEAVY RAINFALL (LOCALLY MORE THAN 2 INCHES) ACROSS KODIAK ISLAND, THE SOUTHEAST
KENAI PENINSULA, AND THE PRINCE WILLIAM SOUND. RIDGING ALOFT IS LIKELY TO
MAINTAIN ABOVE-NORMAL TEMPERATURES ACROSS EASTERN MAINLAND ALASKA, ESPECIALLY
THE UPPER YUKON VALLEY, DURING THIS PERIOD. SINCE THE MOST ANOMALOUS
TEMPERATURES ARE FORECAST TO BE OVER WESTERN CANADA, A MUCH ABOVE-NORMAL
TEMPERATURES HAZARD IS NOT POSTED FOR ALASKA THROUGH JULY 3.

FOR TUESDAY JULY 04 - MONDAY JULY 10: THE GFS AND ECMWF MODEL GUIDANCE
INDICATES THAT THE LOCATION OF THE LONGWAVE FEATURES WILL BE TYPICAL FOR EARLY
JULY WITH TROUGHS OVER THE PACIFIC NORTHWEST AND NORTHEAST AND A BROAD RIDGE
CENTERED OVER THE WEST-CENTRAL U.S. THE ENSEMBLE MEMBERS FROM THESE MODELS
INDICATE THAT THE RIDGE WILL BE STRONGER THAN NORMAL. THIS ANOMALOUS RIDGING
SUPPORTS AT LEAST A SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF
THE CENTRAL U.S. THROUGHOUT WEEK-2. THE ANOMALOUS WARMTH IS EXPECTED TO
INTENSIFY DROUGHT CONDITIONS ACROSS EASTERN MONTANA AND THE DAKOTAS. THE RISK
FOR EXCESSIVE HEAT (HEAT INDEX VALUES OF MORE THAN 105 DEGREES F FOR
CONSECUTIVE DAYS) WILL HAVE TO BE CLOSELY MONITORED ACROSS THE MIDWEST AND
NORTHEAST DURING EARLY TO MID-JULY.



A SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES IS ALSO POSTED FOR PARTS OF
EASTERN MAINLAND ALASKA THROUGH JULY 8 DUE TO PERSISTENT RIDGING ALOFT. THE
DETERMINISTIC 12Z GFS MODEL INDICATES MAXIMUM TEMPERATURES WARMING TO NEAR 90
DEGREES F ACROSS THE UPPER YUKON VALLEY EARLY IN WEEK-2.



THE PREDICTED LOCATION OF THE 500-HPA RIDGE AXIS IS EXPECTED TO LIMIT ANY
MONSOONAL MOISTURE TO SOUTHEAST ARIZONA AND SOUTHERN NEW MEXICO DURING WEEK-2.
CONVECTION ASSOCIATED WITH MONSOONAL MOISTURE TYPICALLY INCREASES DURING EARLY
JULY ACROSS THE DESERT SOUTHWEST.



THE U.S. DROUGHT MONITOR VALID ON JUNE 20 SHOWS D2-D4 DROUGHT COVERAGE OVER THE
CONUS NOW AT 2.13%, A SLIGHT INCREASE FROM 1.57% ONE WEEK AGO. THIS INCREASE IS
TIED TO THE EMERGENCE OF SEVERE DROUGHT IN THE NORTHERN PLAINS.

FORECASTER: BRAD PUGH

$$



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