Prognostic Meteorological Discussion
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FXUS21 KWNC 271811
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 27 2015

SYNOPSIS: UPPER-LEVEL HIGH PRESSURE IS FORECAST TO BUILD ACROSS THE WESTERN
U.S. THIS WEEK, WHILE UPPER-LEVEL LOW PRESSURE BECOMES CENTERED NEAR THE GREAT
LAKES. A COLD FRONT IS EXPECTED TO SHIFT SOUTH ACROSS THE EASTERN U.S. ON
THURSDAY AND BECOME STATIONARY NEAR THE GULF COAST THIS WEEKEND. UPPER-LEVEL
LOW PRESSURE IS EXPECTED TO PERSIST ACROSS ALASKA EARLY IN THE PERIOD.

HAZARDS

PERIODS OF HEAVY RAINFALL ACROSS PARTS OF THE SOUTHEAST, FRI-MON, JUL 31-AUG 3.

EXCESSIVE HEAT ACROSS THE LOWER MISSISSIPPI VALLEY, THU, JUL 30.

MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC NORTHWEST, THU-MON, JUL
30-AUG 3.

A SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC
NORTHWEST, TUE-WED, AUG 4-5.

ONGOING FLOODING ACROSS PARTS OF THE MIDDLE AND LOWER MISSISSIPPI VALLEY.

SEVERE DROUGHT FOR PARTS OF THE WESTERN THIRD OF THE CONUS, SOUTHERN GEORGIA,
AND SOUTHERN FLORIDA.

DETAILED SUMMARY

FOR THURSDAY JULY 30 - MONDAY AUGUST 03: THE UPPER-LEVEL PATTERN IS LIKELY TO
BECOME MORE AMPLIFIED DURING THE NEXT WEEK AS 500-HPA HEIGHTS INCREASE
(DECREASE) ACROSS THE WESTERN (EASTERN) U.S. ON THURSDAY, A COLD FRONT IS
FORECAST TO PROGRESS TOWARDS THE EAST COAST AND THEN BECOME STATIONARY ACROSS
THE SOUTHEAST. THIS FRONT, COUPLED WITH ABUNDANT LOW-LEVEL MOISTURE IS EXPECTED
TO RESULT IN PERIODS OF HEAVY RAINFALL (MORE THAN 1 INCH PER 24 HOURS) ACROSS
PARTS OF THE SOUTHEAST FROM FRIDAY THROUGH NEXT MONDAY. STRONG THUNDERSTORMS
ARE EXPECTED AS THE COLD FRONT PUSHES ACROSS THE NORTHEAST AND MID-ATLANTIC ON
THURSDAY, BUT THE RISK OF SEVERE WEATHER IS LOW AT THIS TIME. NORTHWEST FLOW
ALOFT IS EXPECTED TO PROMOTE ANOTHER COLD FRONT TO ENTER THE UPPER MIDWEST THIS
WEEKEND WHICH WOULD INCREASE THE POTENTIAL FOR SEVERE THUNDERSTORMS ACROSS THIS
REGION.



A LOW TO MODERATE GRADE MONSOON IS EXPECTED ACROSS THE SOUTHWEST. ALTHOUGH
LOCALLY HEAVY RAIN CAN TRIGGER FLASH FLOODING, THE LACK OF A STRONG MONSOON
SIGNAL PRECLUDES A HEAVY RAIN HAZARD ON THE MAP.



EXCESSIVE HEAT IS ANTICIPATED ACROSS THE LOWER MISSISSIPPI VALLEY ON THURSDAY
WHEN MAXIMUM HEAT INDEX VALUES ARE LIKELY TO EXCEED 105 DEGREES F. A DECREASE
IN 500-HPA HEIGHTS IS EXPECTED TO BRING HEAT RELIEF TO THIS REGION ON FRIDAY.
MEANWHILE, AN INCREASE IN 500-HPA HEIGHTS IS EXPECTED TO BRING A RETURN OF
UNSEASONABLY HOT TEMPERATURES TO THE PACIFIC NORTHWEST LATER THIS WEEK. MUCH
ABOVE-NORMAL TEMPERATURES ARE POSTED FOR AREAS WHERE MAXIMUM TEMPERATURES ARE
FORECAST TO AVERAGE 12 DEGREES F OR MORE ABOVE-NORMAL FROM THURSDAY THROUGH
MONDAY.



FLOODING ALONG THE ILLINOIS RIVER IS FORECAST TO RECEDE THIS WEEK, WHILE
MODERATE FLOODING PERSISTS ALONG PARTS OF THE LOWER MISSISSIPPI RIVER. FOR THE
VERY LATEST STREAM AND RIVER FLOODING INFORMATION, PLEASE CONSULT THE RIVER
FORECAST CENTER HOMEPAGE AT: HTTP://WATER.WEATHER.GOV/AHPS/RFC/RFC.PHP



AN UPPER-LEVEL TROUGH ALOFT IS EXPECTED TO MAINTAIN A RELATIVELY WET PATTERN
ACROSS INTERIOR ALASKA THROUGH FRIDAY WHICH WILL AID FIREFIGHTING EFFORTS.
HOWEVER, LIGHTNING COULD IGNITE ADDITIONAL WILDFIRES. ACCORDING TO THE ALASKA
INTERAGENCY COORDINATION CENTER ON JULY 26, NEARLY 5 MILLION ACRES HAVE BEEN
CONSUMED BY WILDFIRES THIS SEASON. THIS VALUE IS ON PAR WITH ACREAGE CONSUMED
BY WILDFIRES IN 2005, AND SLIGHTLY LESS THAN 1957. THIS IS IN COMPARISON TO THE
YEAR 2004, THE MOST ACTIVE ALASKA WILDFIRE SEASON ON RECORD (DATING BACK TO
1950), WHEN 6.5 MILLION ACRES BURNED.

FOR TUESDAY AUGUST 04 - MONDAY AUGUST 10: DURING WEEK-2, THE GFS AND ECMWF
ENSEMBLE MEANS INDICATE A PERSISTENT UPPER-LEVEL PATTERN FEATURING A RIDGE
(TROUGH) OVER WESTERN (EASTERN) NORTH AMERICA. A SLIGHT RISK OF MUCH-ABOVE
NORMAL TEMPERATURES IS POSTED FOR THE PACIFIC NORTHWEST WHICH MAINTAINS
CONTINUITY WITH THE DAY 3-7 HAZARD AND IS CONSISTENT WITH THE POSITION OF THE
UPPER-LEVEL RIDGE. THE UPPER-LEVEL TROUGH CENTERED OVER THE GREAT LAKES IS
EXPECTED TO FAVOR NEAR OR BELOW-NORMAL TEMPERATURES ACROSS THE CORN BELT.



THE MOST RECENT U.S. WEEKLY DROUGHT MONITOR, RELEASED JULY 23, INDICATES A
SLIGHT DECREASE (FROM 17.49 TO 16.74) IN THE PERCENTAGE OF THE CONUS IN SEVERE
TO EXCEPTIONAL DROUGHT (D2-D4) FROM THE PREVIOUS WEEK.

FORECASTER: BRAD PUGH

$$




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