Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 190955
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
355 AM CST WED NOV 19 2014

.SHORT TERM /TODAY/...
ISSUED AT 355 AM CST WED NOV 19 2014

MAIN CONCERNS TODAY WILL BE CLOUDS...WIND AND FLURRIES. FAST
MOVING SHORTWAVE WITH BRIEF SHOT OF WARM AIR THIS EARLY MORNING
TRANSITIONS TO COLD AIR ADVECTION AND BRISK NORTHWEST WINDS
THROUGH THE MORNING AND AFTERNOON HOURS. MID LEVEL CLOUDS CONTINUE
FOLLOWING BOUNDARY AND SHOULD BE PRESENT MUCH OF THE DAY...GIVEN
UPSTREAM FETCH THAT EXTENDS WELL BACK TO US CANADIAN BORDER AT
PRESENT. WITH THE SHALLOW MOISTURE AND COLD AIR ALOFT... BUFR
SOUNDINGS REGION WIDE SHOW THAT SATURATED LAYER CONTINUES TO
INTERSECT THE DENDRITIC ZONE TODAY AND ESPECIALLY THIS AFTERNOON.
HAVE BLANKETED THE AREA WITH SCT FLURRIES FOR THE BALANCE OF THE
FORECAST PERIOD GIVEN THAT THERE WILL EITHER BE PERIODS OR
INTERMITTENT FLURRIES TODAY. SOME MINOR RECOVERY IN TEMPS TODAY
THOUGH IN SOME CASES OUR HIGHS MAY BE REACHED BETWEEN 6 AM AND
ABOUT 10 AM AS COLDER AIR SPILLS INTO THE AREA FOR THE BALANCE OF
THE AFTERNOON. WITH MIXING TODAY EXPECTING WINDS TO GUST TO AROUND
30 TO 35 MPH AT TIMES EARLY THIS MORNING AND AGAIN THIS AFTERNOON.

.LONG TERM /TONIGHT THROUGH MONDAY/...
ISSUED AT 355 AM CST WED NOV 19 2014

HIGHLY AMPLIFIED LONGWAVE PATTERN OVER NORTH AMERICA WILL BREAK
DOWN FOR THE END OF THE WEEK AND THE WEEKEND...WITH THE CANADIAN
ANCHOR LOW RETROGRADING NORTHWARD AND WEST COAST RIDGE FLATTENING
AND MIGRATING EAST. IOWA AND THE REST OF THE UPPER MIDWEST WILL
REMAIN IN A WEST TO NORTHWESTERLY FLOW REGIME THROUGH FRIDAY
MORNING...WHICH WILL KEEP UNSEASONABLY COOL TEMPERATURES IN PLACE.
ELONGATED SURFACE HIGH PRESSURE CELL CURRENTLY OVER WESTERN CANADA
WILL WORK ACROSS IOWA ON THURSDAY AND THURSDAY NIGHT. COLDEST
OVERNIGHT TEMPERATURE READINGS ARE LIKELY ON THURSDAY NIGHT AS THE
CENTER OF THE HIGH PASSES OVERHEAD. CONTINUED GOING AT OR BELOW
MOST GUIDANCE ON LOWS FOR THURSDAY NIGHT...ESPECIALLY OVER
NORTHERN IOWA GIVEN THE CURRENT SNOW PACK.

SOUTHERLY RETURN FLOW SETS IN BEHIND THE DEPARTING HIGH ON FRIDAY
AFTERNOON AND EVENING WITH STRONG THETA-E ADVECTION TAKING PLACE
OVER IOWA DURING THIS TIME. THIS WAA IS BEING DRIVEN IN PART BY AN
UPSTREAM SHORTWAVE TROUGH DIGGING ACROSS THE SOUTHWEST UNITED
STATES. THIS THERMODYNAMIC FORCING/WEAK ISENTROPIC LIFT ALONG THE
290K SURFACE WILL DRIVE PRECIP CHANCES LATE FRIDAY NIGHT INTO
SATURDAY MORNING...WITH A STRENGTHENING 100KT JET AT 300 MB
SUPPLING KINEMATIC FORCING FOR ASCENT DURING THE DAY ON SATURDAY.
BUT OVERALL FORCING REMAINS BROAD AND WEAK AND QPF AMOUNTS WILL BE
LIGHT GIVEN THE RATHER SHALLOW MOISTURE PROFILE BELOW 850MB.

THE FLY IN THE OINTMENT PERTAINS TO PRECIP TYPE ON FRIDAY NIGHT
INTO SATURDAY MORNING. MODEL SOUNDINGS DEPICT A STOUT 900-700 MB
WARM NOSE ACROSS THE CWA WITH MAX TEMPS IN THIS INVERSION PUSHING
+3 TO +5 C BY 06Z SATURDAY. SATURATION IS ONLY ACHIEVED UP TO
850MB (0 C TO -1 C) DURING THIS TIMEFRAME WITH A LARGE SLAB OF
DRY AIR FURTHER ALOFT. COUPLED WITH SURFACE TEMPS IN THE UPPER 20S
TO LOW 30S....THE STAGE IS SET FOR A FREEZING DRIZZLE/LIGHT
FREEZING RAIN EVENT. COMPARED TO YESTERDAY...MODEL SOLUTIONS HAVE
SLOWED THE OVERALL PROGRESSION OF THIS SYSTEM...WHICH HAS RESULTED
IN A LONGER PERIOD OF FAVORABLE FREEZING PRECIP CONDITIONS.
THANKFULLY...ANY GLAZING OF ICE WILL QUICKLY MELT BY MID MORNING
AS CONTINUED WAA PUSHES SURFACE TEMPS ABOVE FREEZING.

HIGHS ON SATURDAY (AND SUNDAY) LOOK TO REACH THE MID 40S WITH THE
BEST POP CHANCES IN THE EAST TIED INTO THE WARM ADVECTION WING OF
A DEVELOPING SURFACE LOW OVER TEXAS. THIS LOW WILL RAPIDLY DEEPEN
FROM 997 MB TO 979 MB BETWEEN 06Z SUNDAY AND 06Z MONDAY AS IT
LIFTS ACROSS THE CENTRAL PLAINS AND INTO THE WESTERN GREAT LAKES.
THIS LOW WILL FOLLOW A CLIMATOLOGICALLY FAVORABLE TRACK FOR HEAVY
SNOW IN CENTRAL/EASTERN IOWA...BUT THANKFULLY THE THERMAL PROFILES
DURING THIS TIME WILL REMAIN ABOVE FREEZING AND IOWA WILL SEE
JUST RAIN. BEYOND SUNDAY...MEDIUM RANGE MODEL SOLUTIONS BEGIN TO
DIVERGE AS THE NEGATIVELY TILTED 500 MB TROUGH TIED INTO THE
AFOREMENTIONED SURFACE CYCLONE INTERACTS WITH A SECONDARY WAVE
DROPPING SOUTHEAST FROM ALBERTA. IN ANY CASE...COLDER AIR WILL
SPILL IN BEHIND THE SURFACE LOW LATE ON SUNDAY AND CHANGE ANY
REMAINING PRECIP INTO SNOW. MULTIPLE INVERTED TROUGHS MAY WRAP
AROUND THE NOW COMPLEX UPPER LEVEL LOW THROUGH EARLY TUESDAY AND
BRING CONTINUED CHANCES OF SNOW THROUGH THEN.

&&

.AVIATION...19/06Z
ISSUED AT 1138 PM CST TUE NOV 18 2014

FRONTAL BOUNDARY MOVING SOUTHEAST THROUGH SOUTH DAKOTA AND
NEBRASKA WILL MOVE ACROSS THE STATE OVERNIGHT AND BRING A SWITCH
TO GUSTY NORTHWEST WINDS. MVFR CIGS WILL FOLLOW THE BOUNDARY THEN
LINGER INTO WEDNESDAY. AREAS OF FLURRIES OR VERY LIGHT SNOW LIKELY
THROUGH THE DAY WEDNESDAY WITH MINOR VSBY RESTRICTIONS POSSIBLE.
THE GUSTY WINDS WILL PREVAIL THROUGH THE DAY BEFORE DIMINISHING BY
LATE AFTERNOON.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...REV
LONG TERM...SKOW
AVIATION...DONAVON


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