National Weather Service Raw Text Product

416 
FXUS63 KFSD 291000
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
500 AM CDT WED AUG 29 2012

.DISCUSSION.../ISSUED AT 500 AM CDT/
FIRE WEATHER CONCERNS ARE AT FOREFRONT OF MORNING FORECAST...AND
FINER DETAILS SURROUNDING THE REASONING ARE CONTAINED IN THE FIRE 
WEATHER SECTION BELOW.

STRONG RIDGE WILL EXPAND EASTWARD AND TAKE CONTROL OF THE WEATHER 
OVER THE REGION TODAY. WEAK SURFACE BOUNDARY HAS SETTLED SOUTHWARD 
TO AROUND INTERSTATE 90...THEN DOWN TOWARD NEBRASKA BORDER IN SOUTH 
CENTRAL. MOISTURE POOLING NORTH OF BOUNDARY WILL LIKELY PRODUCE SOME 
PATCHY FOG YET IN THE LATE NIGHT/EARLY MORNING HOURS. SOME VERY HIGH 
BASED INSTABILITY REMAINS...AND EVEN A COUPLE OF WEAK RETURNS ACROSS
NORTHEAST NEBRASKA.

SOME STRONG VARIATION HOW TO DEAL WITH THIS BOUNDARY ON VARIOUS 
SHORT RANGE MODELS...WITH NAM/HRRR SLOWEST ON NORTHWARD RETURN...
AND IN FACT CONTINUE PUSHING SOUTHWARD ALL THE WAY THROUGH KSUX AREA 
THIS MORNING. THIS SEEMS UNREASONABLE WITH LACK OF PUSH SUGGESTED BY
Q VECTORS...AND INSTEAD WILL SHOW A BIT MORE FAVOR TOWARD THE 
GFS/ECMWF SOLUTION. EVEN THEN...NAM DOES TAKE BOUNDARY BACK 
NORTHWARD IN THE LATE AFTERNOON TO AROUND I90 IN CENTRAL SOUTH 
DAKOTA...AND TO AROUND HIGHWAY 18 IN NORTHWEST IOWA. FAIRLY SHALLOW
FEATURE IN ANY REGARD...AND DO NOT EXPECT TO HAVE A MAJOR IMPACT ON 
TEMPERATURES. RECORDS ARE LIKELY TO FALL FOR MANY LOCATIONS IN THE 
WESTERN HALF OF THE AREA THROUGH THE LOWER MISSOURI VALLEY...WHERE 
READINGS WILL EASILY EXCEED 100 DEGREES. HUMIDITY WILL NOT BE AN 
ISSUE WITH THIS HEAT...AS DEWPOINTS ARE LIKELY TO MIX INTO THE MID 
40S TO LOWER 50S NEAR AND SOUTH OF THE BOUNDARY. TECHNICALLY DO
GET WEST AND FAR SOUTH INTO A HEAT ADVISORY CRITERIA...BUT FOR THE 
MOMENT WILL LET THE ACTUAL FORECAST SPEAK AS ANY GREATER MIXING
OR SLIGHTLY COOLER TEMPS WOULD KEEP MARGINAL FOR THE TIME.

TONIGHT...RECOVERY IN DEWPOINTS MAY BE HARD TO COME BY WITH BOUNDARY 
LIFTING NORTHWARD...AND STRONG SOUTHWESTERLY LOW LEVEL JET 
DEVELOPING IN RESPONSE TO WAVE MOVING OVER TOP OF THE RIDGE. 
APPROACHING FRONTAL BOUNDARY WILL BRUSH UP AGAINST THE FAR NORTHWEST 
BY EARLY THURSDAY MORNING. TOOK OUT MENTION OF MEASURABLE 
PRECIPITATION WITH DEEP DRY LAYER MAKING PROSPECT OF ANYTHING 
REACHING THE SURFACE A EXTREMELY UNLIKELY EVENT. THERE IS NOT ANY 
APPRECIABLE MID LEVEL BOUNDARY IN THE AREA...AND DESPITE 8.5 TO 
9C/KM MID LEVEL LAPSE RATES...NO APPRECIABLE ADVECTION OR GRADIENTS 
TO ASSIST IN LIFT...AND KEPT MENTION AS ONLY SPRINKLES WITH POSSIBLE 
THUNDER FOR LATER NIGHT AND EARLY MORNING HOURS THURSDAY. BREEZIER
NIGHT WILL HELP BOOST LOWS OVER LAST COUPLE NIGHTS...BUT WILL HAVE 
TO BE WARY OF THE DRY AIRMASS...AND POTENTIAL FOR SOME SHELTERED 
LOWER ELEVATION LOCATIONS TO DECOUPLE AND DIP COMPARED TO HIGHER 
LOCATIONS.

FRONTAL BOUNDARY SUGGESTED TO PUSH SOUTHWARD ON THURSDAY...WITH NAM 
BY FAR THE MOST AGGRESSIVE...WITH 06Z ITERATION SHOWING FRONT NEAR 
KFSD BY 15Z. THIS MAY BE IN PART TO ITS DEVELOPMENT OF LIGHT 
PRECIPITATION TO THE NORTH OF THE BOUNDARY IN THE MORNING. PREFERRED 
A MORE CONTROLLED SOUTHWARD PUSH PER BLEND OF OTHER MODELS...ABOUT 6 
HOURS SLOWER. THIS WILL PUT THE SOUTHERN TWO THIRDS OF THE CWA IN
A LOCATION TO MIX VERY WELL UNDER A DEEPER SOUTHWEST FLOW. STRONG 
MIXING OF SLOWLY DECAYING LOW LEVEL JET WINDS...LOW DEWPOINTS...AND 
TEMPERATURES LIKELY NEAR OR EXCEEDING 100 DEGREES WILL BE EXTREMELY
CONCERNING FOR FIRE WEATHER...AND CONTINUED FIRE WEATHER WATCH.
FARTHER NORTH...WILL SEE MID TO HIGH CLOUDS CUT BACK ON THE WARMING 
POTENTIAL...BUT STILL SHOULD BE ABLE TO GET CLOSER TO 90 IN THE FAR 
NORTH.

BOUNDARY AGAIN DOES NOT MAKE IT TOO FAR SOUTHWARD...STALLING AS 
ABANDONED BY UPPER WAVE BY EARLY FRIDAY FROM EASTERN NEBRASKA INTO 
WESTERN IOWA. PUSH OF ANY COOLING IS FAIRLY WEAK AND SHALLOW...BUT 
ENOUGH TO REMOVE REALISTIC THREAT OF ANY 100 DEGREE TEMPS. LESSER 
WIND AND DEWPOINT RECOVERY TO THE MID 50S TO LOWER 60S SHOULD EASE
FIRE WEATHER CONCERNS A BIT.

IN THE EXTENDED RANGE /SATURDAY THROUGH TUESDAY/...EARLY ON WILL BE 
WATCHING ENVIOUSLY THE REMNANTS OF ISAAC MOVING WELL SOUTHEAST OF 
THE AREA WITH SHORT WAVE UPPER RIDGE FOLDED ACROSS THE AREA.  
HOWEVER...LOW LEVEL GRADIENT WILL LIKELY BLEED OFF HIGHER DEWPOINTS 
WHICH MAY RESULT IN A BIT MORE OF FLAT CUMULUS FIELD ON 
SATURDAY...AS WELL AS LEAVE A SLIGHTLY COOLER FOOTPRINT FOR THE 
EASTERN HALF OF THE CWA. REESTABLISHMENT OF THE WESTERLIES BY SUNDAY 
WILL PUSH FRONTAL BOUNDARY BACK TOWARD THE AREA. SQUEEZED JUST A BIT
MORE WARMING OUT THAN GUIDANCE VALUES THROUGH HEART OF CWA...WITH 
EVEN CONSERVATIVE GFS SHOWING SOME MID 90S MIXING POTENTIAL IN THE 
WEST. MOST DEEPER DYNAMIC FORCING WILL JUST BRUSH THE NORTHERN CWA 
SUNDAY NIGHT...SO AS MID LEVEL TEMPS FALL OFF A BIT...COULD GET A 
FEW STORMS DEVELOPING MAINLY FROM EAST CENTRAL SOUTH DAKOTA THROUGH 
SOUTHWEST MINNESOTA. MORE ACTIVE WESTERLIES TAKE OVER THE MONDAY 
THROUGH TUESDAY TIME FRAME. SOME SIGNIFICANT DIFFERENCES IN THE 
TIMING AND STRENGTH OF ANOTHER WAVE EXPECTED TO MOVE INTO THE REGION 
ON TUESDAY...WITH GFS TAKING FAMILIAR STANCE OF MOST PROGRESSIVE... 
AND EURO SLOWER AND MORE INTENSE. SOME LOW END POPS RETAINED FOR 
MAINLY MONDAY NIGHT AND TUESDAY WINDOW...BUT COULD AS EASILY SEE 
THIS END UP MORE OF A TUESDAY NIGHT TIMING WHEN ALL IS SAID AND DONE.
/CHAPMAN

&&

.AVIATION.../FOR THE 06Z TAF ISSUANCE/
VFR CONDITIONS EXPECTED THROUGH 06Z THURSDAY. MAY SEE PATCHY FOG 
09Z-13Z WITH VISIBILITY DROPPING TO NEAR 3 MILES AT TIMES IN 
SHALLOW FOG. 

&& 

.FIRE WEATHER...
CONVERSION FROM FIRE WEATHER WATCH TO RED FLAG WARNING THIS MORNING 
WAS COMPLEX DECISION. CRITICAL TO WIND FORECAST WILL BE LOCATION OF 
THE BOUNDARY...WHICH IS NOT AGREED UPON BY MOST SHORT RANGE 
GUIDANCE. WENT ALONG CLOSER TO SLIGHTLY MORE NORTHWARD SOLUTIONS OF 
GFS/ECMWF...BUT EVEN THE SOUTHWARD NAM DOES ALLOW LATER DAY 
NORTHWARD PUSH INTO THE NORTHERN PORTIONS OF THE FIRE WEATHER ZONES.
REALIZATION THAT WINDS MAY COME UP SOMEWHAT SHORT IN A MAJORITY OF 
THE RED FLAG WARNING AREA. HOWEVER...ECMWF/GFS BOTH INDICATE THAT 
THERE WILL BE 20-30 KNOTS AVAILABLE TO MIX DOWN THROUGH AT LEAST THE 
LOWER MISSOURI VALLEY AREA...AS WELL AS LOESS HILLS AREA IN 
NORTHWEST IOWA. MOISTURE PARAMETERS WILL LIKELY BE OF NO LARGE
CHALLENGE IN MUCH OF THE AREA...WITH OVERNIGHT DEWPOINTS ALREADY IN 
THE 40S IN MUCH OF CENTRAL NEBRASKA...AND 50S IN THE EAST.  IN 
FACT...WITH THE RAW PARAMETERS ACTUALLY WORST FOR THIS LATTER 
AREA...INCLUDED THE LOESS HILLS GROUP IN THE RED FLAG WARNING. WITH 
DESICCATED VEGETATION AND EXTREME LOW RH...WAS A BIT MORE LENIENT ON 
THE WIND CRITERIA...ESPECIALLY TOWARD LOWER BRULE LOCATIONS.

ANOTHER FACTOR IN ISSUANCE WAS THE LIKELIHOOD OF LIMITED RH RECOVERY 
TONIGHT. STRENGTHENING LOW LEVEL JET WILL CONTINUE TO PULL THE MIXED 
LOWER DEWPOINT AIR NORTHEASTWARD...AND HIGHER ELEVATION LOCATIONS 
WILL LIKELY HOLD ON TO SOME BETTER WINDS AS WARM FRONT LIFTS 
NORTHWARD. 

RETAINED FIRE WEATHER WATCH FOR THURSDAY FOR ALL BUT THE FAR 
NORTHWEST...WHERE EARLIER FRONTAL PASSAGE WILL ALLEVIATE THE FIRE 
WEATHER THREAT. GRADUALLY WEAKENING PREFRONTAL LOW LEVEL JET WILL
BRING 25 TO 30 KNOTS THROUGH THE MIXED LAYER...AND WITH ESTABLISHED 
LOW DEWPOINTS CONTINUED WITH DEEPER PREFRONTAL MIXING LIKELY LEADING 
TO WIDESPREAD 15 TO 20 PERCENT RH DURING THE AFTERNOON...POTENTIAL
FOR RED FLAG CONDITIONS SEEMS QUITE STRONG. /CHAPMAN

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
IA...RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 9 PM CDT THIS
     EVENING FOR IAZ300.

     FIRE WEATHER WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY 
     EVENING FOR IAZ300-301.

MN...FIRE WEATHER WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY 
     EVENING FOR MNZ900.

NE...RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 9 PM CDT THIS 
     EVENING FOR NEZ249.

     FIRE WEATHER WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY 
     EVENING FOR NEZ249.

SD...RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 9 PM CDT THIS 
     EVENING FOR SDZ255-258.

     FIRE WEATHER WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY 
     EVENING FOR SDZ257-258.

&&

$$