Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 170923
AFDDMX

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

.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...17/06Z
ISSUED AT 1128 PM CST SUN NOV 16 2014

WINDS WILL REMAIN FROM THE NORTHWEST THROUGH PERIOD...AND WILL
INCREASE THROUGHOUT THE OVERNIGHT. WILL SEE STRONG AND GUSTY WINDS
BEGINNING NEAR 12Z AT SITES...WITH GUSTS UP TO 35KT IN THE
AFTERNOON MONDAY. STRONG WINDS WILL ALLOW FOR BLSN AT SITES...WITH
MVFR OR LOWER VISIBILITIES EXPECTED THROUGH THE AFTERNOON. MAY
ALSO SEE MVFR OR LOWER CEILINGS AT TIMES. SN IS POSSIBLE...THOUGH
HAVE NOT INCLUDED MENTION ATTM DUE TO UNCERTAINTY IN TIMING AND
LOCATION. SN WITH STRONG WINDS COULD ALSO OCCASIONALLY REDUCE
CONDITIONS TO MVFR OR LOWER. WINDS WILL LESSEN NEAR 00Z...WITH VFR
CONDITIONS EXPECTED FOR END OF PERIOD.


&&

.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...AWB



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