799 
FXUS64 KHUN 021130 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
630 AM CDT THU MAY 2 2013

.UPDATE...
FOR 12Z TAFS 

&& 

.DISCUSSION...
/ISSUED 407 AM CDT THU MAY 2 2013/
11-3.9 MICRON SATELLITE IMAGERY AND H5 RAP ANALYSIS INDICATED AN 
ACTIVE UPPER LEVEL PATTERN ACROSS THE CONUS THIS MORNING, WITH AN 
UNSEASONABLY STRONG TROF OVER THE CENTRAL PLAINS, A SLOW-MOVING 
UPPER LOW JUST EAST OF THE ARKLAMISS, AND RIDGING ENCOMPASSING MUCH 
OF THE EAST COAST. REGIONAL RADARS SHOW MUCH OF THE PRECIPITATION 
ASSOCIATED WITH THE UPPER LOW WELL SOUTH OF THE CWA, WITH A SWATH OF 
HEAVY RAINFALL STILL ONGOING ACROSS COASTAL PORTIONS OF AL/MS. TO 
THE NORTHWEST, RAIN AND SNOW ARE BEING REPORTED THIS MORNING WITH 
THE APPROACHING COLD FRONT, WITH UNSEASONABLY COLD AIR IN TOW FOR 
EARLY MAY.

NOT MUCH CHANGE IS REALLY EXPECTED FROM PREVIOUS THINKING WITH 
REGARDS TO TODAY. THE UPPER LOW TO THE SOUTH WILL WEAKEN AND BECOME 
AN OPEN WAVE OVER THE NRN GOMEX AS THE COLD FRONT TO THE NW SLOWLY 
SLIDES SEWRD. AS VORT MAXES ROTATE CCW AROUND THE SYSTEM TO OUR 
SOUTH, ISENTROPIC LIFT ACROSS THE AREA WILL LEAD TO SHRA CLIPPING 
MAINLY OUR SOUTHERN/WESTERN COUNTIES TODAY. SOUNDINGS ARE NEARLY 
SATURATED THRU THE COLUMN, BUT A SMALL AMOUNT OF ELEVATED 
INSTABILITY MAY LEAD TO A FEW RUMBLES OF THUNDER TODAY (THOUGH THE 
WORDING IS PARSED OUT AS ISOLATED IN THE GRIDS). AFTN HIGHS TODAY 
MAY BE TRICKY DEPENDING ON HOW WIDESPREAD THE RAIN IS OR IF MORE 
BREAKS DEVELOP IN THE CLOUD COVER THAN ORIGINALLY THOUGHT. HAVE GONE 
AT/JUST BELOW GUIDANCE FOR TODAY (WHICH IS A COUPLE OF DEGREES 
COOLER THAN YESTERDAY), BUT THIS MAY NEED TO BE UPDATED PENDING 
CONVECTIVE TRENDS THIS AFTN.

SHOWERS WILL BE MORE WIDESPREAD FRIDAY AND ESPECIALLY FRIDAY NIGHT 
INTO SATURDAY MORNING AS THE WAVE TO OUR SOUTH LIFTS NORTH AND EAST 
ACROSS THE REGION. IN ADDITION, SHOWERS/STORMS WILL BE APPROACHING 
FROM THE NW AS THE COLD FRONT FINALLY NEARS THE CWA. GFS/ECMWF ARE 
IN GOOD AGREEMENT ON THE RAINFALL PROGRESSION DURING THIS TIMEFRAME, 
WITH THE HEAVIEST OF RAIN FALLING BETWEEN MIDNIGHT AND DAYBREAK 
SATURDAY. THE PLACEMENT OF THE HEAVY RAINFALL AXIS FROM THE NAM IS 
SLIGHTLY DIFFERENT (AND MORE SPLIT TO THE NW/SE). EITHER WAY, POPS 
WERE INCREASED DURING THIS TIME, WITH HEAVY RAINFALL LIKELY ACROSS 
MUCH OF THE AREA. WILL REISSUE THE ESF FOR THE FRIDAY-SATURDAY
TIMEFRAME TO HIGHLIGHT THE HEAVY RAINFALL AMOUNTS OF 2-4" ACROSS THE
AREA EXACERBATING ANY LINGERING RIVER FLOODING CONCERNS FROM THE LAST
ROUND OF HEAVY RAIN.

IT'S AT THIS POINT IN THE FORECAST THAT THINGS GET TRICKY REGARDING 
THE EVENTUAL TRACK OF AN UPPER LOW THAT BECOMES CUTOFF FROM NRN 
STREAM FLOW (ASSOCIATED WITH THE APPROACHING TROF FROM THE WEST). AS 
USUAL WITH UPPER LEVEL SYSTEMS IN THE VICINITY, CONDITIONS ARE 
COLDER AND MORE CLOUDY THAN MODELS FORECAST THEM TO BE. 
PRECIPITATION IS ALSO USUALLY UNDERDONE. AS SUCH, TEMPERATURES FOR 
THE WEEKEND INTO EARLY NEXT WEEK HAVE BEEN DECREASED, CLOUD COVER 
HAS BEEN INCREASED, AND SLIGHT CHANCES FOR LIGHT RAIN HAVE BEEN 
ADDED TO THE FORECAST. MODELS PROG THE UPPER LEVEL LOW TO BE NEARLY 
OVERHEAD SUNDAY NIGHT INTO MONDAY, AND THOUGH MOS GUIDANCE WAS 
UNDERCUT, IT MAY NOT HAVE BEEN UNDERCUT ENOUGH (DESPITE THE COLD AIR 
WITH THE UPPER LEVEL SYSTEM MODERATING AS THE SYSTEM TRAVERSES THE 
SOUTHEAST).  
 
FEW CHANGES WERE MADE TO THE FORECAST BEYOND THE TUESDAY/WEDNESDAY 
TIMEFRAME OF THE FORECAST AS THE SLOW-MOVING UPPER LEVEL LOW FINALLY 
EXITS THE AREA BY MIDWEEK. ANOTHER SYSTEM COMES ASHORE OFF THE NRN 
CA COAST AND EVENTUALLY MEANDERS ACROSS THE SOUTHERN U.S. STATES. 
MODELS DIFFER IN THEIR TIMING/STRENGTH OF UPPER LEVEL FEATURES AT 
THE END OF NEXT WEEK, SO WILL AWAIT FURTHER MODEL AGREEMENT BEFORE 
MAKING ANY SIGNIFICANT CHANGES TO THE EXTENDED FCST. 
 
12

&&

.AVIATION...
FOR 12Z TAFS...VFR CONDITIONS WILL BE THE RULE THROUGH THE MAJORITY
OF THE UPCOMING FORECAST. WILL CONTINUE WITH A VCSH MENTION AFTER THE 
15Z-16Z TIME FRAME FOR HSV AND MSL. LOWER MVFR CEILINGS ARE EXPECTED
TO MOVE INTO THE REGION BY AROUND 08Z AT MSL AND HSV.

TT

&&

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

$$ 

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