Prognostic Meteorological Discussion
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FXUS21 KWNC 231915
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 23 2017

SYNOPSIS: SURFACE HIGH PRESSURE IS FORECAST TO SLIDE EASTWARD FROM THE MIDDLE
MISSISSIPPI VALLEY TOWARDS THE MID-ATLANTIC OVER THE COURSE OF WEEK-1. IN ITS
WAKE, A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO MOVE ALONG THE NORTHERN TIER
OF THE LOWER-48. MID-LEVEL HIGH PRESSURE IS FORECAST IN THE NORTH PACIFIC EARLY
IN WEEK-1 BEFORE IT IS ANTICIPATED TO WEAKEN. PERIODIC SURFACE LOW PRESSURE
SYSTEMS ARE FORECAST IN THE BERING SEA AND GULF OF ALASKA THROUGHOUT THE
FORECAST PERIOD. TYPICAL SEASONAL CONDITIONS ARE GENERALLY FORECAST ACROSS THE
LOWER-48 FOR WEEK-2, WITH NO ASSOCIATED STRONG SIGNALS TIED TO HAZARDOUS
WEATHER.

HAZARDS

HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE UPPER AND MIDDLE
MISSISSIPPI VALLEY, AND THE GREAT LAKES, WED-THU, JUN 28-JUN 29.

HEAVY RAIN ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, THE GREAT LAKES,
AND THE OHIO VALLEY, FRI, JUN 30.

FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN AND CENTRAL PLAINS, THE
MISSISSIPPI VALLEY, THE CENTRAL APPALACHIANS, THE OHIO AND TENNESSEE VALLEYS,
THE SOUTHEAST, AND THE GREAT LAKES.

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER
MISSISSIPPI VALLEY, THE NORTHERN ROCKIES, AND THE NORTHERN GREAT BASIN.

FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES, THE
SOUTHEAST, AND THE CENTRAL GREAT BASIN.

EXCESSIVE HEAT ACROSS PORTIONS OF CALIFORNIA AND THE SOUTHWEST, MON, JUN 26.

MUCH ABOVE-NORMAL TEMPERATURES ACROSS PORTIONS OF THE GREAT BASIN, THE PACIFIC
NORTHWEST, AND THE NORTHERN ROCKIES, MON, JUN 26.

MUCH ABOVE-NORMAL TEMPERATURES ACROSS PORTIONS OF NORTHEASTERN MAINLAND ALASKA,
TUE-WED, JUN 27-JUN 28.

HEAVY RAIN ACROSS COASTAL PORTIONS OF SOUTHERN MAINLAND ALASKA, TUE-THU, JUN
27-JUN 29.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTHERN
ROCKIES AND THE SOUTHERN PLAINS, SAT-WED, JUL 1-JUL 5.

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

DETAILED SUMMARY

FOR MONDAY JUNE 26 - FRIDAY JUNE 30: HEAT-RELATED HAZARDS CONTINUE TO BE
FORECAST ACROSS THE WESTERN U.S., IN ASSOCIATION WITH ANOMALOUS 500-HPA RIDGING
OVER THE NORTH PACIFIC. EXCESSIVE HEAT IS FORECAST FROM LAS VEGAS SOUTHWARD
ACROSS THE DESERT SOUTHWEST ON JUNE 26, WHERE HIGH TEMPERATURES OF 110-115
DEGREES F ARE FORECAST. FURTHER NORTH, MUCH ABOVE-NORMAL TEMPERATURES ARE
ANTICIPATED FROM THE GREAT BASIN THROUGH THE NORTHERN ROCKIES ON JUNE 26 WHERE
MAXIMUM TEMPERATURE ANOMALIES OF 12-16 DEGREES F ABOVE NORMAL COULD YIELD HIGH
TEMPERATURES INTO THE MID 90S AT LOWER ELEVATIONS. WITH BOTH OF THE
AFOREMENTIONED HEAT HAZARDS, ALL INDIVIDUALS, AND PARTICULARLY VULNERABLE
POPULATIONS SUCH AS THE ELDERLY AND THOSE WITH MEDICAL CONDITIONS, ARE ADVISED
TO LIMIT OUTDOOR ACTIVITIES TO THE EARLY MORNING OR EVENING IF POSSIBLE.
INDIVIDUALS THAT MUST BE OUTDOORS IN THE HEAT THROUGHOUT THE DAYTIME ARE
ADVISED TO PAY EXTRA ATTENTION TO THEIR HYDRATION LEVELS AND SEEK SHADED AREAS
TO REST IN WHEN POSSIBLE.



IN ASSOCIATION WITH THE WARMTH FOR THE WEST, MARGINALLY ELEVATED FIRE WEATHER
CONDITIONS ARE POSSIBLE FOR PARTS OF THE GREAT BASIN, SOUTHWEST, AND SOUTHERN
ROCKIES ON JUNE 26-27, WHERE WARM TEMPERATURES, LOW HUMIDITY, BREEZY WINDS, AND
DRY FUELS ARE FORECAST TO BE PRESENT. DRY THUNDERSTORM ODDS ARE ALSO MARGINALLY
ELEVATED FOR PARTS OF THE NORTHERN GREAT BASIN AND PACIFIC NORTHWEST ON JUNE 26
WHERE DRY FUELS ARE PRESENT FROM THE ANTECEDENT WARM/DRY CONDITIONS.



SURFACE LOW PRESSURE IS PREDICTED TO FORM ACROSS A FRONTAL BOUNDARY STRETCHING
FROM THE CANADIAN PRAIRIES THROUGH THE NORTH PACIFIC EARLY IN WEEK-1, WITH THIS
COLD FRONT ACTING TO FINALLY BREAK THE HEAT IN THE WEST. AS THIS SYSTEM MOVES
EASTWARD, AREAS FROM THE CENTRAL PLAINS THROUGH THE WESTERN GREAT LAKES COULD
SEE HEAVY RAIN (EXCEEDING 1 INCH IN 24 HOURS) ON JUNE 28-29. THE RAIN THREAT IS
FORECAST TO SHIFT EASTWARD ON JUNE 30TH, NOW FOCUSED FROM THE CENTRAL PLAINS
THROUGH THE EASTERN GREAT LAKES. THESE RAINS MAY LEAD TO FLOODING CONCERNS IN
THE FUTURE, AS OBSERVED SOIL MOISTURE VALUES FOR PARTS OF THE GREAT LAKES ARE
CURRENTLY IN THE 95TH CLIMATOLOGICAL PERCENTILE.



ALASKA IS FORECAST TO FACE ITS OWN SET OF HEAT AND PRECIPITATION HAZARDS DURING
WEEK-1. MUCH ABOVE-NORMAL TEMPERATURES ARE FORECAST IN THE VICINITY OF THE
YUKON FLATS ON JUNE 27-28 IN ASSOCIATION WITH SURFACE HIGH PRESSURE. HERE HIGH
TEMPERATURES COULD REACH INTO THE UPPER-80S. HIGH TEMPERATURE ANOMALIES WILL BE
GREATEST CLOSER TO THE NORTH SLOPE WHERE THEY MAY APPROACH +20 DEGREES F, BUT
GIVEN COLDER CLIMATOLOGICAL VALUES FURTHER NORTH IMPACTS WILL BE LESSENED AS
THIS WOULD ONLY YIELD ACTUAL HIGHS IN THE 70S. THE WARMTH IN NORTHERN ALASKA
CAN BE EXPECTED TO INCREASE SNOW MELT AND ASSOCIATED RIVER FLOW DUE TO THE
ENHANCED RUN OFF WHICH MAY IMPACT SOME OUTDOOR ACTIVITIES. SURFACE LOW PRESSURE
IS FORECAST IN THE GULF OF ALASKA DURING THE SECOND HALF OF WEEK-1, WITH
PERSISTENT ONSHORE FLOW BRINGING CHANCES FOR HEAVY RAIN (EXCEEDING 2" IN 24
HOURS) TO WINDWARD PORTIONS OF SOUTHERN MAINLAND ALASKA IN THE VICINITY OF THE
KENAI PENINSULA DURING JUNE 27-29.



THE NATIONAL HURRICANE CENTER IS MONITORING A DISTURBANCE NEAR 12N/98W FOR
POSSIBLE DEVELOPMENT IN THE EAST PACIFIC AS OF 2 PM EDT ON JUNE 23RD. FORECAST
ODDS FOR THE SYSTEM TO UNDERGO TROPICAL CYCLOGENESIS ARE 70% THROUGH THE NEXT
48 HOURS, AND 80% THROUGH 5 DAYS. THE SYSTEM IS FORECAST TO DRIFT
WEST-NORTHWESTWARD, PARALLEL TO THE MEXICAN COASTLINE WITH MODELS FORECASTING
EVENTUAL DISSIPATION OFF BAJA CALIFORNIA WITH NO MOISTURE FROM THE SYSTEM EVER
REACHING THE U.S.

FOR SATURDAY JULY 01 - FRIDAY JULY 07: DURING WEEK-2 FORECAST MID-LEVEL HEIGHT
ANOMALIES ARE GENERALLY SMALL, WITH CLIMATOLOGICAL CONDITIONS FAVORED FOR MUCH
OF THE COUNTRY. ANOMALOUS 500-HPA RIDGING IS GENERALLY STILL FAVORED OVER THE
WEST AND ALASKA WITH A SLIGHT TENDENCY FOR TROUGHING OVER THE UPPER MISSISSIPPI
VALLEY. ENSEMBLE GUIDANCE INDICATES SOME RISK OF HEAVY RAINS FROM THE CENTRAL
PLAINS THROUGH THE MIDWEST IN THE FIRST HALF OF WEEK-2, BUT THERE IS
SUBSTANTIAL SPREAD AMONG ECMWF MEMBERS WHILE THE GEFS EXHIBITS BROAD
DISCREPANCIES BETWEEN ITS DETERMINISTIC RUN THAT APPEARS OVERLY PROGRESSIVE AND
THE ENSEMBLE GUIDANCE WHICH IS MUCH SLOWER. GIVEN THE UNCERTAINTY, NO THREAT IS
SPECIFIED FOR RAINS DURING WEEK-2.



A SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES IS FORECAST FOR THE SOUTHERN
ROCKIES AND SOUTHERN PLAINS FOR JULY 1-5. HERE THE GEFS PROBABILISTIC EXTREMES
TOOL INDICATES A GREATER THAN 20% CHANCE OF EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE OF MAXIMUM TEMPERATURES. REFORECAST GUIDANCE FROM THE ECMWF
ENSEMBLES ALSO INDICATES ENHANCED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES
FOR THESE AREAS DURING WEEK-2, LENDING FURTHER SUPPORT TO THE SLIGHT RISK.



THE U.S. DROUGHT MONITOR RELEASED ON JUNE 22ND 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: CPC FORECASTER

$$




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