161  
FXUS01 KWBC 200756  
PMDSPD  
 
SHORT RANGE FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
355 AM EDT THU SEP 20 2018  
 
VALID 12Z THU SEP 20 2018 - 12Z SAT SEP 22 2018  
 
...SEVERE WEATHER AND A THREAT FOR FLASH FLOODING ACROSS THE UPPER  
MIDWEST TODAY...  
 
...MODERATE RISK FOR FLASH FLOODING IN PLACE OVER CENTRAL OKLAHOMA  
ON FRIDAY INTO THE OVERNIGHT HOURS...  
 
...SUBSTANTIAL TEMPERATURE CONTRAST ON THE ORDER OF 40-50 DEGREES  
F FROM THE DAKOTAS INTO THE CENTRAL U.S...  
 
...WET CONDITIONS LIKELY ACROSS SECTIONS OF WESTERN WASHINGTON UP  
INTO BRITISH COLUMBIA...  
 
AS AN UPPER TROUGH ACCELERATES FROM THE CENTRAL GREAT BASIN TOWARD  
THE DAKOTAS, A SURFACE CYCLONE WILL DEEPEN WHILE RACING INTO THE  
UPPER MIDWEST THIS EVENING. WHILE ALL SEVERE THREATS ARE POSSIBLE  
OVER NORTHERN IOWA INTO SOUTHERN MINNESOTA AND WESTERN WISCONSIN,  
THERE REMAINS A NOTABLE THREAT FOR TORNADOES GIVEN CONSIDERABLE  
TURNING OF THE WINDS WITH HEIGHT. THE STORM PREDICTION CENTER HAS  
THIS REGION OUTLINED IN AN ENHANCED RISK AS THE WAVE OF LOW  
PRESSURE SWEEPS NORTHEASTWARD TOWARD THE UPPER GREAT LAKES. GIVEN  
SUBSTANTIAL MOISTURE TRANSPORT INTERCEPTING THIS FRONTAL SYSTEM,  
SOME HEAVY RAINFALL CAPABLE OF PRODUCING FLASH FLOODS ARE POSSIBLE  
OVER THE UPPER GREAT LAKES BACK TOWARD WESTERN IOWA. THE ENTIRE  
SYSTEM SHOULD REMAIN PROGRESSIVE WITH MARKED DEEPENING ANTICIPATED  
AS IT CROSSES THE INTERNATIONAL BORDER WITH CANADA. A CONSIDERABLE  
PRESSURE GRADIENT WILL ENSUE LEADING TO GUSTY WINDS ACROSS THE  
GREAT LAKES INTO THE NORTHEASTERN U.S. FOR FRIDAY AND SATURDAY.  
 
THE COMBINATION OF ENERGETICS FROM NORTHERN MEXICO LIFTING TOWARD  
THE SOUTHERN ROCKIES/GREAT PLAINS AND ENHANCED MOISTURE FROM THE  
REMAINS OF TROPICAL DEPRESSION NINETEEN-E WILL LEAD TO A HEAVY  
RAINFALL EVENT ACROSS THE SOUTH-CENTRAL U.S. THERE SHOULD BE A  
PARTICULAR FOCUS ACROSS CENTRAL OKLAHOMA WHERE A WAVY FRONTAL ZONE  
IS FORECAST TO STALL. SEVERAL INCHES OF RAIN ARE POSSIBLE ON  
FRIDAY INTO SATURDAY MORNING WHICH LED TO AN UPGRADE OF THE FLASH  
FLOOD POTENTIAL TO A MODERATE RISK WHICH INCLUDES THE CITY OF  
OKLAHOMA CITY. THE FOOTPRINT OF HEAVIER RAINFALL SHOULD SURROUND  
THIS REGION EXTENDING INTO WESTERN ARKANSAS AND SOUTHWARD ACROSS  
THE RED RIVER INTO NORTH TEXAS.  
 
AMIDST THE ACTIVE WEATHER ACROSS THE MIDDLE OF THE COUNTRY, AN  
IMPRESSIVE TEMPERATURE GRADIENT WILL SET UP FROM THE NORTHERN TIER  
STATES DOWN INTO THE NATION'S MID-SECTION. THE WAVY STATIONARY  
FRONTAL ZONE WILL DEMARCATE THIS TEMPERATURE CONTRAST WITH TODAY'S  
HIGHS ONLY IN THE MID 40S ACROSS NORTH DAKOTAS WHILE UPPER 80S TO  
LOWER 90S ENCOMPASS SOUTHERN NEBRASKA AND IOWA SOUTHWARD. RELATIVE  
TO CLIMATOLOGY, ANOMALIES WILL BE QUITE IMPRESSIVE, PARTICULARLY  
NORTH OF THE BOUNDARY WITH DEPARTURES IN THE 20 TO 25 DEGREE F  
RANGE. THE AIR MASS WITHIN THE COLD SECTOR SHOULD MODIFY A BIT BY  
THE FOLLOWING DAY AS HIGHS STAY IN THE MID TO UPPER 50S ACROSS THE  
NORTHERN PLAINS INTO THE UPPER MIDWEST.  
 
A COMPACT UPPER LOW DROPPING DOWN FROM THE GULF OF ALASKA WILL  
TAKE AIM AT THE PACIFIC NORTHWEST. ENERGETICS FROM THIS UPPER  
TROUGH PASSAGE COUPLED WITH AMPLE ONSHORE FLOW OROGRAPHICS WILL  
SPARK WIDESPREAD PRECIPITATION ACROSS WESTERN WASHINGTON UP INTO  
BRITISH COLUMBIA. AS USUAL, MUCH OF THE PRECIPITATION WILL FOCUS  
AGAINST THE UPSLOPE TERRAIN WITH THE HIGHEST AMOUNTS EXPECTED OVER  
THE OLYMPIC MOUNTAINS.  
 
RUBIN-OSTER  
 
GRAPHICS AVAILABLE AT  
WWW.WPC.NCEP.NOAA.GOV/BASICWX/BASICWX_NDFD.PHP  

 
 
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