Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 171133
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
533 AM CST MON NOV 17 2014

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
ISSUED AT 322 AM CST MON NOV 17 2014

STRONG PV ANOMALY ENTERING THE NORTHWEST CORNER OF THE STATE EARLY
THIS MORNING AND WILL CONTINUE TO MOVE SOUTHEAST THROUGH THE
REST OF THE MORNING. MAIN FORECAST CONCERN TODAY IS WITH WINDS AND
VISIBILITY RESTRICTIONS WITH CURRENT SNOW PACK AND POTENTIAL
FALLING LIGHT SNOW.

THE INITIAL GUSTS WITH THE PV ANOMALY LOOK TO BE 20-25 KNOTS
BEFORE DEEP MIXING DEVELOPS LATER THIS MORNING INTO THE
AFTERNOON. VERY STEEP LOW LEVEL LAPSE RATES AROUND 8-9 C/KM
DEVELOP BY AROUND 14-15Z THIS MORNING AND WINDS ATOP THE MIX LAYER
NEAR 40 KNOTS AT TIMES THROUGHOUT THE DAY ACROSS NORTHERN IOWA.
HAVE GUSTS HIGHEST FROM 34- 38 KNOTS GOING IN THE ADVISORY PAST
17Z INTO THE AFTERNOON. RAP/NAM SOUNDINGS AT FOD/MCW/ALO ALL
DEPICT SATURATION IN THE DENDRITIC LAYER LATER THIS MORNING WHICH
IS VERY NEAR THE SURFACE AND SHOULD NOT TAKE MUCH FOR FLURRIES OR
SNOW SHOWERS TO DEVELOP TODAY. HENCE...CONTINUED WITH BLOWING SNOW
ACROSS THE NORTH IN THE ADVISORY. CERTAINLY CAN EXPECT SOME
DETERIORATING ROAD CONDITIONS...PARTICULARLY IN OPEN AREAS WHERE
SNOW SHOULD BLOW OVER ROADS MUCH EASIER. ONE CAVEAT IS HOW MUCH
DID THE SUN CRUST THE SNOW PACK ON SUNDAY OVER NORTHERN IOWA...BUT
WITH THE STRONG WINDS ANTICIPATED...THE MOST LIKELY SCENARIO WOULD
BE FOR THE WINDS TO BREAK THROUGH THE CRUSTED OVER SNOW. THAT
BEING SAID...STILL LOW CONFIDENCE WITH WIDESPREAD BLIZZARD
CONDITIONS ACROSS NORTHERN IOWA TODAY...BUT CERTAINLY WITH THE
EXPECTED WINDS AND POTENTIAL FALLING SNOW...SOME BRIEF WHITEOUT
CONDITIONS CANNOT BE COMPLETELY RULE OUT ATTM IN THE ADVISORY AREA
LATER THIS MORNING INTO THE AFTERNOON.

FURTHER SOUTH...WINDS LOOK SLIGHTLY LESS BUT STILL SHOULD SEE SOME
GUSTS SLIGHTLY OVER 30 KNOTS TODAY. BUT WITH THE LESSER SNOW
PACK...ONLY ANTICIPATING SOME PATCHY BLOWING SNOW. THIS TYPICALLY
RESULTS IN SNOW MELTING AND REFREEZING TO ROAD SURFACES IN AREAS
PRONE TO BLOWING SNOW.

TEMPERATURES WILL STRUGGLE TO WARM ANY TODAY WITH THE BLAST OF CAA
INTO THE STATE THROUGH MUCH OF THE DAY. WIND CHILL VALUES WILL NEAR
CRITERIA EARLY THIS MORNING OVER THE FAR NORTHWEST AND POSSIBLY
LATE IN THE PERIOD AS WELL. THE REST OF THE FORECAST AREA...WIND
CHILLS LOOK TO REMAIN NEAR ZERO TO AROUND 10 BELOW FOR MUCH OF THE
DAY.

.LONG TERM /TONIGHT THROUGH SUNDAY/...
ISSUED AT 322 AM CST MON NOV 17 2014

MAIN CHALLENGES FOR MOST OF THE PERIOD WILL BE THE TIMING OF THE
COLD AND THE EVENTUAL WARMING INTO THE WEEKEND WITH A STORM TOWARD
SUNDAY AS A PATTERN SHIFT OCCURS LATE IN THE PERIOD. COLD AIR
SETTLING INTO THE REGION TONIGHT WITH WINDS RELAXING AND FIRST
NIGHT OF SUB ZERO READINGS OCCURS ACROSS THE NORTH AND NORTHWEST.
LARGE UPPER LEVEL TROUGH WILL BEGIN TO DRIFT EAST WITH CLOUDS
THINNING TOWARD SUNRISE SOUTH. DESPITE CLOUD COVER TONIGHT...COLD
AIRMASS AND LITTLE RISE IN TEMPERATURES TODAY WILL RESULT IN
COLDEST NIGHT SO FAR THIS SEASON. WNW WINDS WILL CONTINUE AT A
SLOWER PACE OVERNIGHT BUT STILL RESULT IN RATHER COLD WIND CHILL
VALUES OVER THE AREA. NORTH OF HIGHWAY 20...VALUES WILL BE VERY
NEAR -20F FOR SEVERAL HOURS EARLY TUESDAY MORNING. WILL PROBABLY
NEED HEADLINES THERE BY LATER TODAY. SOUTH OF THAT AREA NOT MUCH
BETTER AS MOST OF THE REGION WILL SEE VALUES BETWEEN 10 AND 15
BELOW DURING THE MORNING/SCHOOL COMMUTE. RATHER RARE FOR NOVEMBER
TO HAVE WIND CHILL ADVISORIES SO EARLY IN THE SEASON. THOUGH WE
CONTINUE TO BE TRAPPED IN A BROAD H500 NORTHWEST FLOW...THERE ARE
SIGNS THAT THE MAIN ANCHOR LOW OVER THE EASTERN CONUS IS GRADUALLY
SHIFTING EAST OVER THE NEXT 3 TO 4 DAYS. THIS WILL RESULT IN
OCCASIONAL MILD INTRUSIONS ACROSS IOWA WHICH SHOULD MODIFY AREA
HIGHS FOR WEDNESDAY AND THURSDAY. MOST THE MODELS HAVE HINTED AT
SEVERAL FAST MOVING WAVES MOVING SOUTHEAST ON THE BACK SIDE OF THE
UPPER LEVEL TROUGH THROUGH FRIDAY. THIS WILL RESULT IN PERIODS OF
CLOUDS AND NEAR NEUTRAL ADVECTION...WITH HIGHS IN THE 20S AND
LOWS IN THE SINGLE DIGITS. FRIDAY MORNING LOOKS TO BE THE COLDEST
MORNING WITH HIGH PRESSURE SETTLING ACROSS THE AREA PRIOR TO
TEMPERATURES IMPROVING INTO THE WEEKEND. FINALLY BY FRIDAY OUR
H500 PATTERN BECOMES MORE ZONAL WHICH WILL FORCE SOME LEE SIDE
WARMING TOWARD THE CENTRAL PLAINS. WITH A RETURN OF SOUTHWEST FLOW
ALOFT AND WARM AIR ADVECTION OVERNIGHT FRIDAY NIGHT...MINS WILL
ACTUALLY BE WARMER IN SOME CASES THAN TODAYS HIGHS. BY SATURDAY A
GATHERING SOUTHERN STREAM STORMS WILL BE SPREADING GULF MOISTURE
TOWARD THE REGION IN THE FORM OF ISENTROPIC LIFT AND GRADUALLY
OVERCAST SKIES BY DAYS END. DESPITE THAT...TEMPERATURES WARM
ENOUGH TO SUPPORT 30S TO LOWER 40S OVER THE AREA. THE MAIN SYSTEM
TAKES UNTIL LATE SAT NIGHT TO ARRIVE...BRINGING A CHANCE FOR
RAIN/SNOW TO THE REGION FROM LATE SATURDAY NIGHT AND RAIN ON
SUNDAY. THE FAR NORTHWEST MAY BE COLD ENOUGH TO SUPPORT A MIXTURE.
THE SYSTEM IS EXPECTED TO DEEPEN RAPIDLY ON SUNDAY WITH THE H500
LOW DEEPENING FROM 544DM TO 533DM IN 12 HOURS BY 18Z SUNDAY. THE
COOLING ALOFT WILL MOST LIKELY CHANGE THE RAIN BACK TO RAIN/SNOW
BY AFTERNOON/EVENING OVER MOST OF CENTRAL AND NORTHEAST IOWA.
THERE WILL BE A POTENTIAL FOR SOME ACCUMULATING SNOWFALL IF THE
SYSTEM IS A BIT SLOWER TO EXIT THE REGION. CONFIDENCE AT THIS TIME
REGARDING THE EVOLUTION REMAINS LOW GIVEN THE DIFFERENCES IN THE
MODEL SOLUTIONS BETWEEN THE EURO/GFS. FORTUNATELY THERE IS LITTLE
COLD AIR IMMEDIATELY BEHIND THE DEPARTING SYSTEM SO TEMPERATURES
ARE NOT LIKELY TO FALL OFF A CLIFF ONCE THE SYSTEM EXITS.

&&

.AVIATION...17/12Z
ISSUED AT 529 AM CST MON NOV 17 2014

STRONG WINDS JUST DEVELOPING AND WILL CONTINUE TO INCREASE THROUGH
THE MORNING HOURS. HAVE MVFR VIS AND CIGS MENTIONED AT FOD/MCW/ALO
LATE THIS MORNING INTO TONIGHT AS HIGHER CONFIDENCE SEE SOME LOW
STRATUS WITH THE MIXING INCREASING TODAY. HOWEVER...THE MVFR
VIS/CIGS CONDITIONS MAY NOT BE CONTINUOUS. KEPT DSM/OTM AT VFR
CONDITIONS AS LOWER CONFIDENCE WITH ANY BLSN.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR CERRO
GORDO-EMMET-FRANKLIN-HANCOCK-HUMBOLDT-KOSSUTH-PALO ALTO-
POCAHONTAS-WINNEBAGO-WORTH-WRIGHT.

&&

$$

SHORT TERM...PODRAZIK
LONG TERM...REV
AVIATION...PODRAZIK



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