872  
FXUS64 KHUN 220002  
AFDHUN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HUNTSVILLE AL  
602 PM CST MON JAN 21 2019  
   
UPDATE
 
 
FOR 00Z TAFS.  
 

 
   
NEAR TERM
 
(TONIGHT)  
ISSUED AT 325 PM CST MON JAN 21 2019  
 
AS HIGH PRESSURE OVER THE OH VALLEY SHIFTS EAST INTO THE MID ATLANTIC  
STATES TONIGHT (AND STRENGTHENS) WHILE THE NEXT LEE-SIDE CYCLONE  
EMERGES INTO THE CENTRAL PLAINS, THE PRESSURE GRADIENT WILL TIGHTEN  
SIGNIFICANTLY ACROSS THE TN VALLEY. THIS WILL RESULT IN INCREASING  
WIND FLOW LATE TONIGHT, AND RESULTANT WARM ADVECTION. WILL FORECAST  
TEMPERATURES THAT ARE NEAR STEADY TONIGHT. DEW POINTS NOW IN THE  
SINGLE DIGITS AND LOWER TEENS WILL RISE INTO FURTHER INTO THE TEENS,  
MAINLY LATER TONIGHT. AT THIS POINT, ONLY A FEW HIGH CLOUDS ARE  
EXPECTED TO STREAM INTO THE AREA.  
   
SHORT TERM
 
(TUESDAY THROUGH WEDNESDAY)  
ISSUED AT 325 PM CST MON JAN 21 2019  
 
A WINDY TUESDAY IS EXPECTED AS THE AFOREMENTIONED PRESSURE GRADIENT  
(ABOUT 6 MB WEST TO EAST ACROSS OUR FORECAST AREA) INCREASES. WINDS  
WILL GUST OVER 25 MPH IN VALLEYS AND AROUND 30-35 MPH IN THE HIGHER  
ELEVATIONS, ESPECIALLY DURING THE AFTERNOON HOURS. MOISTURE TRANSPORT  
WILL INCREASE STEADILY THROUGH THE DAY, BRINGING INCREASING LOWER TO  
MID LEVEL CLOUDS DURING THE AFTERNOON. THIS WILL LIKELY LIMIT  
MAXIMUM TEMPERATURES IN THE M40S-A50 DESPITE WARM ADVECTION  
INCREASING. AS THE LOW-MID LEVELS MOISTEN DURING THE AFTERNOON, A FEW  
SPRINKLES OR SHOWERS ARE POSSIBLE FROM LATE AFTERNOON INTO THE  
EVENING HOURS, MAINLY OVER NORTHWEST AL INTO SOUTHERN MIDDLE TN.  
 
THE LARGER SCALE RAIN SHOWERS ASSOCIATED WITH THE SOLID WARM  
CONVEYOR BELT AND UPPER TROUGH APPROACH WILL SLOWLY SPREAD EAST  
ACROSS THE AREA ON WEDNESDAY. THE ATMOSPHERE APPEARS IT WILL BE TOO  
STABLE FOR THUNDERSTORMS WITH THIS SYSTEM, BUT A GOOD FEED OF 1-1.25  
INCH PWS AND MODERATE SHOWERS ARE CERTAINLY EXPECTED. DEEP CONVECTION  
AND A LIKELY MCS/QLCS WILL TRACK THROUGH SOUTHERN AL INTO GA DURING  
THE AFTERNOON HOURS. THERE MAY BE A PERIOD OF WANING PRECIPITATION  
LOCALLY AS THE 8H PRE-FRONTAL TROUGH SHIFTS CONVERGENCE TO OUR EAST  
BY MID AFTERNOON. THEN A RENEWED BAND OF -DIVQ ASSOCIATED WITH THE  
7-5H TROUGH AXIS WILL ARRIVE DURING THE LATE AFTERNOON/EARLY EVENING  
HOURS. TOP-DOWN APPROACH ON FORECAST SOUNDINGS INDICATE THE SHALLOW  
LOW LEVEL COLD AIR MAY ALLOW FOR A BRIEF CHANGEOVER TO FREEZING RAIN  
BEFORE ENDING ABRUPTLY FROM WEST TO EAST WITH THE UPPER TROUGH  
PASSAGE AND DRY SLOT. A FEW OF THE HIGHER ELEVATIONS ALONG THE  
CUMBERLAND PLATEAU AND FAR NORTHWEST AL WOULD APPEAR TO HAVE THE  
GREATEST CHANCE OF THE BRIEF FREEZING RAIN. RAINFALL AMOUNTS OF  
1.25-1.75 INCHES ARE FORECAST AT THIS TIME. THIS MAY CAUSE BRIEF  
FLOODING PROBLEMS, ESPECIALLY GIVEN THE RECENT RAINFALL OVER THE  
WEEKEND.  
   
LONG TERM
 
(THURSDAY THROUGH SUNDAY)  
ISSUED AT 325 PM CST MON JAN 21 2019  
 
AFTER A COLDER START TO THE MORNING ON THURSDAY, SOME SUNSHINE  
SHOULD ALLOW HIGH TEMPERATURES TO CLIMB INTO THE UPPER 30S TO LOWER  
40S. HOW QUICKLY CLOUD COVER MOVES BACK INTO THE AREA BEHIND A RE-  
ENFORCING COLD FRONT MAY KEEP HIGH TEMPERATURES A BIT COOLER (MID TO  
UPPER 30S). FOR NOW, EXPECTING THICKER AND MORE WIDESPREAD CLOUD  
COVER TO PUSH BACK INTO THE AREA ALONG AND BEHIND THIS NEXT FRONT  
VERY LATE THURSDAY AFTERNOON INTO THE EVENING HOURS ON THURSDAY.  
MOISTURE ALONG THIS FRONT LOOKS TOO MEAGER FOR ANY PRECIPITATION AT  
THIS TIME.  
 
A RETURN TO DRIER AND COLDER TEMPERATURES BEHIND THIS COLD FRONT ARE  
EXPECTED THURSDAY NIGHT INTO FRIDAY NIGHT. COLD AIR ADVECTION INTO  
THE AREA AHEAD OF AN APPROACHING CANADIAN SURFACE HIGH SHOULD DROP  
LOWS INTO THE UPPER TEENS TO MID 20S.  
 
A RETURN OF MORE SUNSHINE AS THE SURFACE HIGH SETTLES OVER THE  
TENNESSEE VALLEY ON FRIDAY SHOULD ALLOW HIGHS TO CLIMB INTO THE LOWER  
TO MID 30S PRIMARILY. AN EVEN COLDER NIGHT IS EXPECTED ON FRIDAY  
NIGHT, AS THE SURFACE HIGH REMAINS CENTERED OVER THE AREA AND WINDS  
BECOME LIGHTER. A GOOD RADIATIONAL COOLING SETUP LOOKS TO BE IN  
STORE. THIS SHOULD ALLOW LOW TEMPERATURES TO DROP AT LEAST INTO THE  
LOWER TO MID 20S...MAYBE EVEN THE TEENS IN MORE LOCATIONS. MODELS  
DIFFER HOW QUICKLY ANOTHER FRONT MOVES SOUTHEAST INTO NORTHERN  
ALABAMA AND HOW MUCH MOISTURE THIS SYSTEM HAS TO WORK WITH. AT THIS  
TIME KEPT CLOSE TO A BLEND OF THE GUIDANCE, KEEPING 20 TO 30 PERCENT  
CHANCE OF PRECIPITATION IN THE AREA SATURDAY EVENING. ENOUGH WARM AIR  
ADVECTION AHEAD OF THE FRONT AND SOME SUNSHINE EARLY SHOULD ALLOW  
HIGHS TO CLIMB INTO THE LOWER TO MID 40S. THE FRONT PUSHES INTO  
NORTHWESTERN ALABAMA AND FURTHER EAST AROUND MIDNIGHT INTO THE  
DAYBREAK HOURS ON SUNDAY. AS THIS OCCURS, MODELS DO SHOW MUCH COLDER  
AIR MOVING IN ALONG AND BEHIND THE FRONT. GFS IS MUCH MORE MOIST WITH  
THIS FRONT, WHILE ECMWF HARDLY SHOWS ANY PRECIPITATION. HOWEVER,  
BOTH MODELS CHANGE PRECIPITATION INTO A MIX OF SNOW AROUND 10 PM.  
THEN MODELS FORECAST A CHANGE TO ALL SNOW IN MOST LOCATIONS AFTER  
MIDNIGHT. GIVEN DIFFERENCE IN MODELS QPF, VERY LOW CONFIDENCE THAT  
ANY SNOWFALL WILL ACCUMULATE, BUT WILL NEED TO MONITOR AS WE GET  
CLOSER TO THE END OF NEXT WEEKEND.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)  
ISSUED AT 602 PM CST MON JAN 21 2019  
 
WINDS ALOFT WILL CONTINUE TO BACK TO WSW OVERNIGHT AS A TROUGH  
SHIFTS EWD ACROSS THE WESTERN CONUS, AND THIS WILL PROVIDE BROKEN VFR  
CIGS ARND FL250 THROUGH THE LATE NIGHT/EARLY MORNING HOURS. AS A SFC  
RIDGE BUILDS EWD INTO THE LEE OF THE CENTRAL APPALACHIANS, WE  
ANTICIPATE LGT ESELY SFC FLOW TO VEER TO THE SE AND INCREASE TO ARND  
10 KNOTS BY 04Z. REGARDLESS OF THE INCREASE IN SFC WINDS, SUBSTANTIAL  
STRENGTHENING OF THE LOW-LEVEL JET WILL OCCUR LATE TONIGHT AND  
WARRANTS INCLUSION OF LLWS DURING THE PERIOD FROM 09-13Z, WHEN FLOW  
IMMEDIATELY ABOVE THE SFC AND SHEAR SHOULD BE MOST SIGNIFICANT. WINDS  
WILL BACK FURTHER TO SSE AND INCREASE INTO THE 13G23 KNOT RANGE BY  
13Z, REDUCING IMPACTS FROM LLWS AT THIS POINT. ATMOSPHERIC LIFT  
DOWNSTREAM FROM THE APPROACHING TROUGH AND GENERATION OF  
PRECIPITATION ALOFT WILL ALSO RESULT IN A RAPID LOWERING OF CLOUD  
CEILINGS, ESPECIALLY DURING THE EARLY AFTERNOON HOURS. ATTM, WE HAVE  
INTRODUCED BROKEN MVFR STRATOCU AT BOTH TERMINALS BY 20Z, WITH EVEN  
LOWER CIGS AND INCLUSION OF -SHRA IN TAFMSL BTWN 22-00Z.  
 

 
   
HUN WATCHES/WARNINGS/ADVISORIES
 
 
AL...NONE.  
TN...NONE.  
 

 
 

 
 
NEAR TERM...17  
SHORT TERM...17  
LONG TERM...KTW  
AVIATION...70/DD  
 
FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE  
AT WEATHER.GOV/HUNTSVILLE.  
 
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