Prognostic Meteorological Discussion
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FXUS21 KWNC 191846
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 19 2017

SYNOPSIS: AT THE BEGINNING OF THE PERIOD, SURFACE LOW PRESSURE IS FORECAST TO
FORM OVER THE UPPER MISSISSIPPI VALLEY AND TRACK NORTHEASTWARD TO THE NORTHEAST
BY JULY 24. ITS ASSOCIATED TRAILING FRONT IS EXPECTED TO REMAIN RELATIVELY
STATIONARY ACROSS THE CENTRAL TIER OF THE LOWER 48 STATES THROUGHOUT MOST OF
THE 3 TO 7 DAY PERIOD. THE SOUTHWEST MONSOON IS FORECAST TO CONTINUE TO BE
ACTIVE THROUGHOUT THE 3 TO 7 DAY AND WEEK-2 PERIODS. SURFACE LOW PRESSURE IS
FORECAST TO FORM OVER THE NORTHERN COAST OF MAINLAND ALASKA AT THE BEGINNING OF
THE 3 TO 7 DAY PERIOD, BRINGING UNSETTLED WEATHER TO COASTAL REGIONS.
MEANWHILE, A WEAK SURFACE LOW IS PREDICTED TO FORM OVER GULF OF ALASKA
THROUGHOUT THE DAY 3 TO 7 PERIOD. WEEK-2 IS EXPECTED TO BE DOMINATED BY
MID-LEVEL RIDGING ACROSS THE WESTERN HALF OF THE CONTIGUOUS U.S., WITH
TROUGHING ACROSS THE EASTERN HALF.

HAZARDS

HEAVY RAIN ACROSS PORTIONS OF THE GREAT LAKES, THE MID-ATLANTIC, THE NORTHEAST,
AND THE OHIO VALLEY, SAT, JUL 22.

SEVERE WEATHER ACROSS PORTIONS OF THE GREAT LAKES AND THE UPPER MISSISSIPPI
VALLEY, SAT, JUL 22.

HEAVY RAIN ACROSS PORTIONS OF THE FOUR CORNERS REGION, SAT-MON, JUL 22-JUL 24.

EXCESSIVE HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI
VALLEY, THE GREAT LAKES, AND THE OHIO VALLEY, SAT, JUL 22.

EXCESSIVE HEAT ACROSS PORTIONS OF THE SOUTHEAST AND THE MID-ATLANTIC, SAT-SUN,
JUL 22-JUL 23.

FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS, THE CENTRAL ROCKIES,
THE CENTRAL GREAT BASIN, THE SOUTHERN ROCKIES, THE SOUTHERN PLAINS, AND THE
SOUTHWEST EXTENDING THROUGH WEEK-2.

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE GREAT LAKES.

HIGH WINDS ACROSS COASTAL PORTIONS OF NORTHERN MAINLAND ALASKA, SAT, JUL 22.

HIGH SIGNIFICANT WAVE HEIGHTS FOR HIGH WINDS ACROSS COASTAL PORTIONS OF
NORTHERN MAINLAND ALASKA, SAT, JUL 22.

EXCESSIVE HEAT ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, AND LOWER
AND MIDDLE MISSISSIPPI VALLEY, THU-WED, JUL 27-AUG 2.

SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE WESTERN HALF
OF THE CONUS, THU-WED, JUL 27-AUG 2.

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

DETAILED SUMMARY

FOR SATURDAY JULY 22 - WEDNESDAY JULY 26: SURFACE LOW PRESSURE IS ANTICIPATED
TO DEVELOP OVER THE UPPER MISSISSIPPI VALLEY AND TRACK NORTHEASTWARD TO THE
NORTHEAST BY JUL 24. THIS LOW AND ITS ASSOCIATED TRAILING FRONT IS EXPECTED TO
BRING HEAVY RAIN (1.5 INCHES OF RAINFALL OR GREATER IN A 24 HOURS) TO PORTIONS
OF THE GREAT LAKES, THE MID-ATLANTIC, THE NORTHEAST, AND THE OHIO VALLEY, JUL
22. ATMOSPHERIC CONDITIONS MAY ALSO BE CONDUCIVE TO SEVERE THUNDERSTORMS ACROSS
PARTS OF THE GREAT LAKES AND THE UPPER MISSISSIPPI VALLEY JUL 22.



MONSOON MOISTURE IS FORECAST TO CONTINUE STREAMING NORTHWARD ACROSS THE
SOUTHWEST, SUPPORTING HEAVY RAINFALL (ONE INCH OF RAINFALL OR GREATER IN A
24-HOUR PERIOD) ACROSS PARTS OF THE FOUR CORNERS REGION JULY 22 TO 24. EXPECTED
RAIN MAY LEAD TO LOCALIZED FLOODING ACROSS THE FOUR CORNERS REGION. CAUTION
SHOULD BE TAKEN ESPECIALLY IN CANYONS AND ARROYOS WHERE FLOODING CAN QUICKLY
OCCUR.



SURFACE HIGH PRESSURE IS EXPECTED TO BUILD ACROSS MANY PARTS OF THE EASTERN
HALF OF THE CONUS SOUTH OF THE AFOREMENTIONED SURFACE LOW AND FRONTAL
BOUNDARIES. THIS PATTERN FAVORS AN INCREASED LIKELIHOOD FOR EXCESSIVE HEAT
ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI VALLEY, THE GREAT
LAKES, AND THE OHIO VALLEY, JUL 22, AND THE SOUTHEAST, AND THE MID-ATLANTIC JUL
22 TO 23. SOME OF THESE AREAS MAY EXPERIENCE DAILY MAXIMUM HEAT INDEX VALUES OF
105 DEGREES F OR GREATER, WITH PARTS OF VIRGINIA POSSIBLY EXCEEDING 110 DEGREES
F.



SURFACE LOW PRESSURE IS ANTICIPATED TO APPROACH THE NORTHERN COAST OF MAINLAND
ALASKA BY JUL 22, INCREASING CHANCES FOR HIGH WINDS (SUSTAINED WIND SPEEDS OF
30 KNOTS OR GREATER) AND HIGH SIGNIFICANT WAVE HEIGHTS ON JUL 22. BROAD WET,
WESTERLY FLOW IS EXPECTED OVER INTERIOR ALASKA, BRINGING RAIN TO THE AREA JUL
24TH TO 25TH, LIKELY ENDING THE FIRE WEATHER SEASON ACROSS ALASKA. THE 6Z GFS
AND 0Z ECMWF FAVORS THE NORTHWESTERN PORTION OF MAINLAND ALASKA AS WELL AS A
LOCALIZED AREA NORTH OF THE SUSITNA RIVER AS REGIONS WITH THE HEAVIEST RAINFALL
POSSIBLE. CUMULATIVE IMPACTS OF EXPECTED RAIN IN COMBINATION WITH ALREADY HIGH
RIVERS MAY LEAD TO LOCALIZED FLOODING OVER PARTS OF INTERIOR ALASKA. DUE TO
HIGH MODEL UNCERTAINTY REGARDING SPECIFIC LOCATIONS THAT MAY REACH THE HEAVY
RAIN CRITERIA, A RELATED HAZARDS AREA IS NOT DELINEATED AT THIS TIME.



AS OF JULY 19 AT 8AM PDT, HURRICANE FERNANDA, LOCATED AT 17.4N AND 135.5W IN
THE EAST PACIFIC, IS FORECAST TO BECOME A TROPICAL STORM BY THURSDAY. AS IT
CONTINUES TO TRACK WEST-NORTHWEST, INCREASING SWELLS ARE EXPECTED FOR THE
HAWAIIAN ISLANDS TOWARD THE MIDDLE OF THE 3 TO 7 DAY PERIOD. THIS STORM MAY
BRING HIGH SURF AND HEAVY RAINFALL TO HAWAII.

FOR THURSDAY JULY 27 - WEDNESDAY AUGUST 02: ENHANCED MONSOONAL MOISTURE IS
EXPECTED TO EXTEND AT LEAST THROUGHOUT THE EARLY PART OF WEEK-2 ACROSS PARTS OF
THE FOUR CORNERS REGION, CONTINUING THE INCREASED LIKELIHOOD FOR POSSIBLE
FLOODING DURING WEEK-2. THE HIGHLIGHTED POSSIBLE FLOOD AREA REFLECTS THE AREA
MOST LIKELY TO RECEIVE SIGNIFICANT RAINFALL DURING WEEK-2.



MUCH OF WEEK-2 IS PREDICTED TO BE DOMINATED BY MID-LEVEL RIDGING ACROSS THE
WESTERN TWO-THIRDS OF THE CONUS AND TROUGHING ACROSS THE EASTERN THIRD OF THE
CONUS. THIS PATTERN SUPPORTS A SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES
ACROSS MANY PARTS OF THE WESTERN HALF OF THE CONUS, JUL 27 TO AUG 2. THE
IDENTIFIED SLIGHT RISK AREA IS BASED ON WHERE THE GEFS REFORECAST TOOL
INDICATES A 20 PERCENT CHANCE OR GREATER OF EXCEEDING THE 85TH PERCENTILE AND
95 DEG F. AN EXCESSIVE HEAT AREA IS HIGHLIGHTED FOR PARTS OF THE CENTRAL AND
SOUTHERN PLAINS, AND LOWER AND MIDDLE MISSISSIPPI VALLEY JUL 27 TO AUG 2, WHERE
THE SKILL WEIGHTED CPC HEAT INDEX TOOL INDICATES A 20 PERCENT CHANCE OR GREATER
OF EXCEEDING THE 90TH PERCENTILE (COMPARED TO NORMAL). MUCH OF THIS AREA,
ESPECIALLY ACROSS THE SOUTHERN AND CENTRAL PLAINS, HAVE A 20 PERCENT CHANCE OR
GREATER OF EXCEEDING THE 95TH PERCENTILE. LOCALIZED AREAS ACROSS THE SOUTHERN
PLAINS MAY EXPERIENCE HEAT INDEX VALUES EXCEEDING 105 DEGREES.



THE U.S. DROUGHT MONITOR VALID ON JULY 11 SHOWS D2-D4 DROUGHT COVERAGE OVER THE
CONUS 4.31%, A SLIGHT INCREASE FROM 3.83% ONE WEEK AGO. THIS INCREASE IS
RELATED TO AN EXPANSION OF SEVERE DROUGHT ACROSS THE NORTHERN GREAT PLAINS.

FORECASTER: MELISSA OU

$$




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