Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 281855
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 28 2017

SYNOPSIS: A SURFACE LOW IS FORECAST TO ADVANCE EAST INTO SOUTHEAST CANADA ON
JULY 1, WHILE A TRAILING COLD FRONT BECOMES STATIONARY FROM NEW ENGLAND
SOUTHWEST TO THE SOUTHERN GREAT PLAINS. THIS FRONT IS THEN EXPECTED TO LIFT
NORTH AS A WARM FRONT TO THE CENTRAL GREAT PLAINS AND MIDWEST ON JULY 2 AND 3.
AN AREA OF UPPER-LEVEL HIGH PRESSURE IS EXPECTED TO STRENGTHEN OVER THE HIGH
PLAINS EARLY NEXT WEEK AND EXPAND ACROSS THE CENTRAL AND EASTERN U.S. EARLY IN
WEEK-2. ANOTHER AREA OF UPPER-LEVEL HIGH PRESSURE IS EXPECTED TO PERSIST OVER
EASTERN MAINLAND ALASKA THROUGH THE FIRST WEEK OF JULY.

HAZARDS

HEAVY RAIN FOR PARTS OF THE NORTHEAST, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST
OKLAHOMA, SAT, JUL 1.

HEAVY RAIN SHIFTING EAST FROM THE CENTRAL GREAT PLAINS TO THE MIDDLE
MISSISSIPPI VALLEY, SUN-MON, JUL 2-3.

HEAVY RAIN FOR PARTS OF KODIAK ISLAND, THE KENAI PENINSULA, AND THE PRINCE
WILLIAM SOUND, SAT, JUL 1.

MUCH ABOVE NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN AND CENTRAL GREAT
PLAINS, MON-WED, JUL 3-5.

MUCH ABOVE NORMAL TEMPERATURES FOR THE UPPER YUKON VALLEY OF ALASKA, SAT-MON,
JUL 1-3.

EXCESSIVE HEAT FOR PARTS OF THE CENTRAL U.S., THU-FRI, JUL 6-7.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE CENTRAL AND
EASTERN U.S., THU-SAT, JUL 6-8.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE WESTERN U.S.,
THU-WED, JUL 6-12.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF EASTERN MAINLAND
ALASKA, THU-SUN, JUL 6-9.

FLOODING OCCURRING, IMMINENT, OR LIKELY FOR PARTS OF THE SOUTHEAST ANDWYOMING.

FLOODING POSSIBLE FOR PARTS OF THE MIDDLE MISSISSIPPI VALLEY AND THE MIDWEST.

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

DETAILED SUMMARY

FOR SATURDAY JULY 01 - WEDNESDAY JULY 05: A LOW PRESSURE SYSTEM AND ITS
ASSOCIATED COLD FRONT ARE EXPECTED TO RESULT IN LOCALLY HEAVY RAIN (1 TO 2
INCHES, LOCALLY MORE) ACROSS PARTS OF THE NORTHEAST ON JULY 1, WITH THE TAIL
END OF THIS FRONT BECOMING A FOCUS FOR HEAVY RAIN (LOCALLY MORE THAN 1 INCH)
ACROSS SOUTHEAST OKLAHOMA, ARKANSAS, AND THE LOWER MISSISSIPPI VALLEY. A WARM
FRONT IS FORECAST TO MOVE NORTH TO THE CENTRAL GREAT PLAINS ON JULY 2, IN
ADVANCE OF A SHORTWAVE TROUGH EJECTING FROM THE WESTERN U.S.



A SHORTWAVE TROUGH WITHIN NORTHWEST FLOW ALOFT, ALONG WITH A NOCTURNAL
LOW-LEVEL JET, IS EXPECTED TO RESULT IN THE DEVELOPMENT OF A MESOSCALE
CONVECTIVE SYSTEM (MCS) ACROSS THE NORTHERN OR CENTRAL GREAT PLAINS ON JULY 2.
DAMAGING WINDS AND LARGE HAIL ARE EXPECTED TO ACCOMPANY THIS MCS, BUT LOW
PREDICTABILITY ON ITS EXACT LOCATION PRECLUDES DESIGNATION OF A SEVERE WEATHER
HAZARD AT THIS TIME. HEAVY RAIN (1 TO 3 INCHES, LOCALLY MORE) IS LIKELY WITH
THIS MCS ON JULY 2 ACROSS THE CENTRAL GREAT PLAINS WITH HEAVY RAIN SHIFTING TO
THE MIDDLE MISSISSIPPI VALLEY ON JULY 3. THE 6Z GFS AND 0Z ECMWF ENSEMBLE MEANS
REMAIN IN GOOD AGREEMENT ON THE SPATIAL COVERAGE OF THE HEAVY RAIN. DUE TO
ABUNDANT LOW-LEVEL MOISTURE (PRECIPITABLE WATER VALUES OF 1.5 TO 2 INCHES), AN
ELEVATED RISK OF FLASH FLOODING EXISTS WITH THE STRONGEST THUNDERSTORMS ACROSS
THE CENTRAL U.S. ON JULY 2 AND 3.



AN UPPER-LEVEL RIDGE IS EXPECTED TO STRENGTHEN OVER THE HIGH PLAINS BY EARLY
NEXT WEEK AND BEGIN TO EXPAND EAST ACROSS THE CENTRAL U.S. THEREFORE, MUCH
ABOVE-NORMAL TEMPERATURES (10 DEGREES F OR MORE) ARE FORECAST TO AFFECT THE
NORTHERN AND CENTRAL PLAINS FROM JULY 3 TO 5. MAXIMUM TEMPERATURES ARE EXPECTED
TO WARM WELL INTO THE 90S TO NEAR 100 DEGREES F BY JULY 4 ACROSS THIS REGION.
THIS HEAT IS LIKELY TO WORSEN ONGOING DROUGHT CONDITIONS ACROSS EASTERN MONTANA
AND THE DAKOTAS.



ON JULY 1, A LOW PRESSURE SYSTEM WITH ONSHORE LOW IS EXPECTED TO BRING HEAVY
RAINFALL (LOCALLY MORE THAN 1.5 INCH PER 24 HOURS) ACROSS KODIAK ISLAND, THE
SOUTHEAST KENAI PENINSULA, AND THE PRINCE WILLIAM SOUND. STRONG RIDGING ALOFT
IS EXPECTED TO RESULT IN MUCH ABOVE-NORMAL TEMPERATURES ACROSS THE YUKON RIVER
VALLEY WHERE MAXIMUM TEMPERATURES ABOVE 85 DEGREES F ARE FORECAST DURING JULY 1
TO 3.

FOR THURSDAY JULY 06 - WEDNESDAY JULY 12: THE RECENT ENSEMBLE MEANS (CANADIAN,
GFS, AND ECMWF) CONTINUE TO FEATURE AN AMPLIFIED RIDGE CENTERED OVER THE
WEST-CENTRAL U.S. DURING WEEK-2. THE EXPECTED LONGWAVE PATTERN ALONG WITH
TEMPERATURE GUIDANCE FROM THE GFS AND ECMWF MODELS SUPPORT A SLIGHT RISK OF
MUCH ABOVE-NORMAL TEMPERATURES FOR: PARTS OF THE CENTRAL AND EASTERN U.S. (JULY
6 TO 8), THE WESTERN U.S. (JULY 6 TO 12), AND ALASKA (JULY 6 TO 9).  ALTHOUGH
ONLY A SLIGHT RISK FOR MUCH ABOVE-NORMAL TEMPERATURES IS POSTED FOR THE CENTRAL
AND EASTERN U.S., HEAT INDEX VALUES MAY EXCEED 105 DEGREES F IN THE MORE HUMID
AREAS OF THESE AREAS. BASED ON 850-HPA TEMPERATURES PREDICTED BY THE
DETERMINISTIC 0Z ECMWF, THE GEFS AND ECMWF CALIBRATED HEAT INDEX FORECASTS, AND
CLIMATOLOGY, AN EXCESSIVE HEAT HAZARD IS POSTED FOR PARTS OF THE CENTRAL U.S.
ON JULY 6 AND 7.



AN UPPER-LEVEL RIDGE IS FORECAST TO SHIFT NORTH TO THE FOUR CORNERS REGION
WHICH WOULD LEAD TO INCREASED MOISTURE ACROSS THE DESERT SOUTHWEST. THIS
INCREASING MOISTURE IS EXPECTED TO RESULT IN MORE CONVECTION AND A HIGHER RISK
OF FLASH FLOODING ACROSS EASTERN ARIZONA AND NEW MEXICO DURING WEEK-2.



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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