Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 302321
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
521 PM CST FRI JAN 30 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 340 PM CST FRI JAN 30 2015

SURFACE HIGH PRESSURE WILL CONTINUE TO SLIDE EASTWARD TONIGHT
INTO SATURDAY MORNING AND ALLOW FOR WAA TO DEVELOP OVERNIGHT. A
DECENT SURGE OF MID-LEVEL THETA-E ADVECTION BRINGS INTO CLOUD
COVER OVER THE SOUTHWEST PAST 06Z AND PUSHES FURTHER NORTHEAST
INTO OVER MUCH OF THE FORECAST AREA BY 12Z SATURDAY. THE BETTER
FORCING AND DEEP MOISTURE MOVE INTO SOUTHWEST IOWA PAST 12Z AND
THUS HAVE MINIMAL POPS GOING IN THE FAR SOUTHWEST CORNER OF THE
CWA B/T 10-12Z SATURDAY. FOR TEMPS TONIGHT...WENT CLOSER TO THE
RAP FOR LOWS.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 340 PM CST FRI JAN 30 2015

PLENTY TO DEAL WITH AS SYSTEM APPROACHES AND THE MODEL SOLUTIONS
CONTINUE TO EVOLVE. CURRENTLY...ALL 12Z RUNS INDICATE THE NORTHERN
STREAM SYSTEM WILL BE STRONGER AND DIG SOUTHEAST INTO THE PLAINS
INTO SUNDAY MORNING AND INTO THE OHIO VALLEY BY SUNDAY NIGHT. WITH
THE STRONGER SYSTEM...THE MOISTURE PLUME FROM THE SOUTHWEST WILL
BE PULLED FARTHER NORTH AND WEST THAN PREVIOUS RUNS HAVE INDICATED
WITH MORE PRECIPITATION EXPECTED ACROSS THE FORECAST AREA. IN
ADDITION...THE SURFACE FRONT WILL BE FARTHER NORTH THAN IN
PREVIOUS FORECAST WITH RAIN/SNOW LINE MAKING IT SOMEWHAT FARTHER
NORTH AS WELL. INITIAL PRECIPITATION WILL BE FORCED BY ISENTROPIC
LIFT AND GOOD MID-LEVEL FRONTOGENETICAL FORCING...ESPECIALLY INTO
SATURDAY NIGHT. THEREAFTER...WITH THE APPROACH OF THE UPPER
WAVE...STRONG MID LEVEL KINEMATICS WILL ALLOW THE PRECIPITATION TO
PERSIST INTO SUNDAY BEFORE FINALLY ENDING BY LATE IN THE DAY AS
THE SYSTEM PULLS EAST.

ANTICIPATE THE PRECIPITATION TO SPREAD NORTHWARD ACROSS THE CWA
FROM SOUTHWEST TO NORTHEAST DURING THE DAY SATURDAY. WITH SURFACE
FRONT SETTLING NEAR THE HWY 30/I80 CORRIDOR BY AFTERNOON...
ANTICIPATE RAIN GENERALLY SOUTH OF THE FRONT WITH SNOW NORTH.
HOWEVER...TO THE NORTH...PRECIPITATION WILL NOT ARRIVE UNTIL LATER
AND DONT ANTICIPATE MUCH ACCUMULATION UNTIL THE EVENING. TO THE
SOUTH...RAIN/SNOW TRANSITION LINE WILL MOVE SLOWLY SOUTHWARD WITH
THE FRONT BUT WILL ACCELERATE SOUTHWARD AROUND SUNSET AS DAYTIME
HEATING DIES OFF AND INCREASED LIFT HELPS SOUNDINGS DROP TOWARD
FREEZING IN THE LOW LEVELS. ONCE THE TRANSITION IN THE SOUTH TO
SNOW IS MADE...THE SNOW WILL CONTINUE WITH THE AFOREMENTIONED
FORCING UNTIL IT PASSES BY LATE SUNDAY AFTERNOON. AS FOR SNOWFALL
RATES...ANTICIPATE THE HIGHEST RATES SATURDAY NIGHT ACROSS
SOUTHERN IOWA WHERE FRONTOGENETICAL FORCING SETS UP WITH THOSE
RATES DECREASING BY SUNDAY MORNING. ANOTHER ROUND OF HIGHER RATES
WILL OCCUR AROUND MIDDAY SUNDAY AS STRONG UPPER FORCING MOVES
ACROSS THE STATE AND SOUNDINGS DEVELOP A DEEP DENDRITIC LAYER.
AS FOR AMOUNTS...MODELS CONTINUE TO EXPAND MORE SNOW NORTHWARD
THROUGH THE STATE WITH A GOOD 3 TO 6 INCHES NORTH OF HWY 30 AND 5
TO 9 INCHES WITH LOCALIZED HIGHER AMOUNTS SOUTH OF HWY 30. QUICK
LOOK AT 18Z NAM WOULD SUGGEST THE POSSIBILITY OF HIGHER AMOUNTS
EVEN FARTHER NORTH AND THIS WILL NEED TO BE TAKEN INTO ACCOUNT IN
SUBSEQUENT SHIFTS SHOULD THE OTHER MODELS FOLLOW SUIT. THE WINTER
STORM WATCH WILL REMAIN IN PLACE WITH THE LIKELIHOOD OF ADVISORIES
ANDWARNINGS NEEDED ACROSS THE ENTIRE CWA SEEMING QUITE HIGH.

WINDS WILL ALSO INCREASE BY LATE SATURDAY NIGHT INTO SUNDAY AS THE
PRESSURE GRADIENT TIGHTENS. THIS WILL LIKELY LEAD TO SOME BLOWING
AND DRIFTING OF SNOW ON SUNDAY ALONG WITH REDUCED VISIBILITIES...
ESPECIALLY IN RURAL AREAS. MUCH COLDER AIR WILL ALSO WORK IN
DURING THE DAY WITH WIND CHILLS ALSO CRASHING BELOW ZERO BY SUNDAY
NIGHT AS TEMPERATURES DROP TO NEAR ZERO OR BELOW OVER MUCH OF THE
AREA. AFTER THIS SYSTEM DEPARTS...WARM ADVECTION WILL KICK BACK IN
BY LATE MONDAY TO MONDAY NIGHT WITH ANOTHER THREAT OF SNOW AND A
BRIEF WARMUP ON TUESDAY. THE BROAD NORTHWEST FLOW WILL PERSIST
WITH COLD TEMPERATURES FROM MUCH OF THE WEEK.

&&

.AVIATION...31/00Z
ISSUED AT 518 PM CST FRI JAN 30 2015

HIGH PRESSURE OVER EASTERN IA WILL MOVE EAST AS LOW
PRESSUREDEVELOPSTO THE SOUTHWEST. VFR CONDITIONS TONIGHT WILL
DETERIORATE FROM SOUTHWEST TO NORTHEAST ON SATURDAY WITH MIXED
RAIN AND SNOW SOUTH AND SNOW NORTH ALONG WITH LOWERING CIGS.

OUTLOOK...WIDESPREAD IFR TO LIFR CONDITIONS IN STRATUS AND SNOW
SATURDAY NIGHT INTO SUNDAY MORNING. SOME IMPROVEMENT SUNDAY WITH
CLEARING EXPECTED LATER SUNDAY NIGHT INTO MONDAY.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH SUNDAY
AFTERNOON FOR ADAIR-ADAMS-APPANOOSE-CLARKE-DALLAS-DAVIS-DECATUR-
JASPER-LUCAS-MADISON-MAHASKA-MARION-MONROE-POLK-POWESHIEK-
RINGGOLD-TAYLOR-UNION-WAPELLO-WARREN-WAYNE.

&&

$$

SHORT TERM...PODRAZIK
LONG TERM...COGIL
AVIATION...MS JAN 15



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