Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 260353
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
953 PM CST TUE NOV 25 2014

.UPDATE...
ISSUED AT 947 PM CST TUE NOV 25 2014

SLOWED THE ONSET OF PRECIP ACROSS THE EAST JUST A BIT THINKING
THAT IT WOULD TAKE JUST A LITTLE LONGER TO SATURATE IN THIS AREA.
PRECIP HAS MOVED INTO THE WEST AND IT IS IN THE FORM OF RAIN
ACROSS WEST CENTRAL AND SOUTHWEST IOWA. ACROSS THE NORTH IT RAINED
OR THERE WAS SOME FREEZING DRIZZLE BRIEFLY BEFORE THE COLUMN
SATURATED AND COOLED CHANGING THE PRECIP OVER TO SNOW. IT MAY TAKE
A BIT LONGER ACROSS THE SOUTH SO I KEPT MIXED PRECIP IN ACROSS THE
SOUTH A BIT PAST 06Z.

UPDATE ISSUED AT 751 PM CST TUE NOV 25 2014

MADE SOME TWEAKS TO THE FORECAST BASED ON SOUNDINGS. SOUNDINGS
ACROSS SOUTHERN IOWA SHOW A SHALLOW WARM NOSE BUT THE COLUMN WAS
NOT SATURATED. I BELIEVE ONCE THE COLUMN SATURATES PTYPE WILL
CHANGE QUICKLY OVER TO SNOW SO OTHER THAN A BRIEF PERIOD OF A
WINTERY MIX...PRECIP SHOULD BE SNOW. THIS NUDGED SOME SNOWFALL
AMOUNTS UP NEGLIGIBLY ACROSS THE SOUTH. ALSO INCREASED POPS ACROSS
THE ADVISORY AREA CO-INCIDENT WITH THE BEST FORCING.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 323 PM CST TUE NOV 25 2014

MAIN CONCERNS TONIGHT WILL BE SNOWFALL TIMING AND AMOUNTS. THE FAST
MOVING CLIPPER WILL MOVE SOUTHEAST TRACKING INTO WEST CENTRAL TO
SOUTHERN IOWA BY 12Z WED WITH A SHIELD OF PRECIPITATION EXPANDING
SOUTHEAST FROM THE WEST FROM THIS AFTERNOON THROUGH TONIGHT. THE
MODELS HAVE GENERALLY SLOWED THE SYSTEM DOWN A FEW HOURS...SO HAVE
BACKED OFF ON THE ARRIVAL TIME AND TRANSLATION THROUGH THE FORECAST
AREA. MILDER AIR THIS AFTERNOON HAS WARMED TEMPERATURES MORE THAN
GUIDANCE HAD ANTICIPATED...BUT OVERALL THE END RESULT OF THE SYSTEM
LOOKS PRETTY MUCH THE SAME. THE ONLY EXCEPTION WILL BE THE
SOUTH...FARTHER NORTH TO NEAR I80 THAT MAY SEE LESS SNOWFALL WITH A
RAIN SNOW MIXTURE MORE LIKELY AT THIS TIME...BUT STILL SOME
CONFIDENCE ISSUES DUE TO PRESENT DRY AIR AND EXPECTATION THAT WET
BULB MAY RISE OVERNIGHT ENOUGH TO KEEP SFC TEMPS JUST ABOVE
FREEZING. ALOFT...THE WARM LAYER ALOFT MAY COOL FASTER THAN
ANTICIPATED...WITH SLIGHTLY MORE SNOW THAN RAIN IN THE RAIN SNOW
MIX. THIS IS GENERALLY OVER THE SOUTHWEST TOWARD THE METRO AND
THEN SOUTHEAST TOWARD OTTUMWA. TO THE NORTH AND NORTHEAST OF THE
H850 LOW TRACK...ALL SNOW WILL FALL. THE CUT OFF OF MIX TO ALL
SNOW IS THROUGH POLK COUNTY SO NORTHERN AREAS WILL LIKELY SEE MORE
SNOW THAN SOUTHERN AREAS HERE. OVERALL BY 12Z WITH AMPLE
ISENTROPIC LIFT AND QG FORCING...ABOUT 1 TO 2 INCHES OF SNOW IS
EXPECTED WITH THE HEAVIER TOTALS FROM NORTHWEST TO CENTRAL. WITH
THE ANTICIPATION OF AMOUNTS OF 2 TO LOCALLY NEAR 4 INCHES
NORTH...WILL ISSUE HEADLINE FOR WINTER WEATHER NORTH AND
NORTHEAST...WITH START/END TIMES STAGGERED TO BETTER REFLECT THE
TIMING OF IMPACTS. THE WESTERN SECTION BEGINS AT 06Z AND THE
EASTERN SECTION AT 09Z...ENDING AT 18Z AND 21Z RESPECTIVELY. SINCE
MUCH OF THE SNOW WILL FALL WEST OVERNIGHT...MORNING IMPACTS WILL
BE GREATEST OVER THE WEST...BUT MUCH OF THE AREA WILL BE SEEING
SNOW BY 12Z. TEMPS WILL STAY MILD OVERNIGHT WITH THE SYSTEM...AND
WINDS POSE ONLY MINOR ADDITIONAL ISSUES AS STRONG WINDS ARE NOT
EXPECTED...GENERALLY 10 TO 15 MPH.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 323 PM CST TUE NOV 25 2014

BIGGEST ISSUE THROUGH THE MID/LONG RANGE WILL BE ON SNOWFALL CHANCES
WEDNESDAY AND THEN MAINLY TEMPS THROUGHOUT THE REMAINDER OF THE
EXTENDED. CLIPPER TYPE SYSTEM TO DROP SOUTHEASTWARD THROUGH THE
STATE MAINLY LATE TONIGHT AND LINGERING INTO WEDNESDAY. ASSOCIATED
SURFACE LOW TO TRACK FROM AROUND SIOUX CITY BY EARLY WEDNESDAY TO
SOUTHEASTERN IOWA/NRN ILLINOIS BY WEDNESDAY EVENING. WAA AHEAD OF
THE SYSTEM...AND MOISTURE WRAPPING AROUND THE NORTH SIDE OF THE
LOW WILL RESULT IN CHANCES FOR MAINLY LIGHT SNOW ACROSS MUCH OF
THE CWA WEDNESDAY. EXPECT MAINLY LIGHT SNOW...WITH ISENTROPIC LIFT
SUGGESTING A NARROW BAND OF MODERATE SNOWFALL TO ROTATE/SLIDE
THROUGH THE AREA AS THE LOW SLIDES THROUGH. THEREFORE TRIED TO GET
THE BASIC TREND WITH HIGHER POPS IN A FEW COUNTY-WIDE NW-SE LINE
THROUGH THE DAY. QPF AMOUNTS EXPECTED TO BE AROUND A TENTH OF AN
INCH TO A FEW TENTHS AT MOST...WITH SNOWFALL RATIOS IN THE 14 TO
15 TO 1 RANGE WITH SOME LIFT IN THE DENDRITIC GROWTH ZONE ACROSS
THE NORTH. WITH THE STRONGER WAA...SFC TEMPS EXPECTED TO RISE TO
NEAR FREEZING OR ABOVE FOR A FEW HOURS. THEREFORE COULD SEE SOME
SNOW CHANGING BACK TO RAIN OR A RAIN/SNOW MIX WITH THE PUSH OF
WARMER AIR AT THE SURFACE AND ALOFT. THEREFORE LIGHT ACCUMULATIONS
OR LITTLE OR NO SNOW ACCUMULATIONS EXPECTED ACROSS THE FAR
SOUTH/SOUTHWEST. HIGHEST SNOW ACCUMULATIONS EXPECTED ACROSS THE
NORTH/NORTHEAST WITH AROUND 3 TO 4 INCHES POSSIBLE. WITH THE
MODERATE SNOWFALL AMOUNTS AND WEDNESDAY EXPECTED TO BE A BUSY
HOLIDAY TRAVEL DAY...WILL ISSUE AN ADVISORY FOR ROUGHLY THE
NORTHERN HALF TO THIRD OF THE CWA. AS THE SYSTEM PULLS
AWAY...COULD SEE SOME GUSTY WINDS FOR A BIT WEDNESDAY EVENING AS
HIGH PRESSURE BUILDS INTO THE AREA FOR THURSDAY. GIVEN THE WINDS
ARRIVING AFTER THE SNOW ENDS...SOME PATCHY BLOWING SNOW IS
POSSIBLE BUT EXPECT MORE OF A DRIFTING OF SNOW ACROSS ROADWAYS
WEDNESDAY EVENING RATHER THAN DRASTIC REDUCTION IN VISIBILITIES
DUE TO BLOWING SNOW ESPECIALLY AS THE SFC PRES GRADIENT IS
RELAXING AS THE SYSTEM MOVES THROUGH.

A COOLER DAY IS EXPECTED FOR THE THANKSGIVING HOLIDAY WITH DRY
CONDITIONS...AND WINDS EXPECTED TO SHIFT AROUND TO THE SOUTH TOWARD
THURSDAY NIGHT INTO FRIDAY AS A WARM FRONT LIFTS NORTH THROUGH THE
CWA. THIS MAY RESULT IN SOME FLURRIES OR A SLIGHT CHANCE OF LIGHT
SNOW ACROSS THE FAR NORTH LATE THURSDAY NIGHT WITH BETTER CHANCES
NORTH OF THE CWA. DRY CONDITIONS THEN EXPECTED INTO THE
WEEKEND...WITH A DRY COLD FRONTAL PASSAGE FOR LATE IN THE WEEKEND.
STRONG WARMING AHEAD OF THIS FRONTAL BOUNDARY SHOULD ALLOW MUCH OF
THE SOUTHERN CWA TO REACH THE 40S TO AROUND 50 DEGREE RANGE. LARGE
AREA OF HIGH PRESSURE TO THEN DOMINATE THE CENTRAL/EASTERN US BY THE
MIDDLE OF NEXT WEEK BRINGING WARMING TEMPERATURES AND DRY
CONDITIONS.

&&

.AVIATION...26/00Z
ISSUED AT 556 PM CST TUE NOV 25 2014

A CLIPPER SYSTEM WILL SWEEP THE STATE TONIGHT THROUGH WEDNESDAY.
CURRENTLY THE AIRMASS IS QUITE DRY AND IS FORECAST TO SATURATE VERY
QUICKLY AS THE SYSTEM MOVES IN.  THERE MAY BE A BRIEF PERIOD OF
DRIZZLE OR RAIN BEFORE CHANGING OVER TO SNOW.  AS A RESULT OF THE
QUICK SATURATION...CIGS WILL BE VFR THEN QUICKLY DROP TO IFR.
NORTHERN TAF SITES MAY SEE AN OCCASIONAL VSBY TO 1/2SM.  IMPROVEMENT
WILL OCCUR SLOWLY FROM WEST TO EAST AFT 15Z.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 3 AM TO 6 PM CST WEDNESDAY FOR
BLACK HAWK-BREMER-BUTLER-CERRO GORDO-FRANKLIN-GRUNDY-HARDIN-
JASPER-MARSHALL-POWESHIEK-STORY-TAMA-WORTH.

WINTER WEATHER ADVISORY UNTIL NOON CST WEDNESDAY FOR BOONE-EMMET-
HAMILTON-HANCOCK-HUMBOLDT-KOSSUTH-PALO ALTO-POCAHONTAS-WEBSTER-
WINNEBAGO-WRIGHT.

&&

$$

UPDATE...FAB
SHORT TERM...REV
LONG TERM...BEERENDS
AVIATION...REV


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