Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 091718
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1118 AM CST TUE FEB 9 2016

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
ISSUED AT 322 AM CST TUE FEB 9 2016

STILL HAVE SOME LIGHT SNOW FLURRIES ACROSS THE CWA...AND EXPECT
THEM TO SLOWLY WANE THROUGH MID MORNING AS WE LOSE SATURATION IN
THE DENDRITIC ZONE AND IT BECOMES MORE SHALLOW. ADDITIONALLY WINDS
REMAIN GUSTY ACROSS THE CWA...WITH SOUNDINGS INDICATING GUSTY
WINDS TO STICK AROUND THROUGH MUCH OF THE DAY. MIXED LAYER WINDS
DO DIMINISH SOME THROUGH THE DAY...SO EXPECT BLOWING SNOW
CONDITIONS TO EASE WITH TIME ESPECIALLY TOWARD LATE MORNING INTO
THE AFTERNOON HOURS. MAJORITY OF OBSERVATIONS ACROSS THE CWA THIS
AM AROUND 3-5 MILES IN THE AREAS WITH DEEPER SNOW
COVER...THEREFORE EXPECT MORE DRIFTING OF SNOW AND A SHALLOW LAYER
OF BLOWING SNOW NEAR THE GROUND THAN THE CONDITIONS PRESENT MONDAY
WHERE THERE WAS A WIDESPREAD DEEPER LAYER OF BLOWING SNOW.
ADDITIONALLY LOW STRATUS SHOULD BEGIN TO BREAK UP AND CLEAR OUT BY
THIS AFTERNOON WITH MOSTLY CLEAR SKIES ACROSS MUCH OF THE CWA BY
LATE IN THE DAY. THIS SHOULD KEEP THE GUSTINESS GOING THIS
AFTERNOON...WITH WINDS EXPECTED TO LOSE THEIR GUSTINESS AROUND
SUNSET WHEN THEY DECOUPLE.

THEREFORE WITH THE WINDS STAYING UP THROUGH AT LEAST THE
MORNING...AND SOME LIGHT SNOW FLURRIES STILL PRESENT WILL EXTEND
THE ADVISORY THROUGH THE MORNING COMMUTE IN NORTH CENTRAL IOWA
WHERE ROAD CONDITIONS STILL LISTED AS NO TRAVEL ADVISED IN MANY
PLACES. WILL ALLOW THE WESTERN PORTION OF THE ADVISORY TO EXPIRE
WITH CONDITIONS IMPROVING AND SNOW SHOWERS HAVING ENDED IN THAT
AREA FOR THE MOST PART.

.LONG TERM /TONIGHT THROUGH MONDAY/...
ISSUED AT 322 AM CST TUE FEB 9 2016

NOT MUCH CHANGE IN OVERALL FORECAST THINKING TONIGHT. THE LONG
TERM FORECAST REMAINS CHARACTERIZED BY CYCLONIC NORTHWEST FLOW
ALOFT THROUGH SATURDAY...RESULTING IN GENERALLY COOL WEATHER AND
INTERMITTENT CHANCES FOR LIGHT SNOWFALL.

THERE IS NOW BETTER CONSENSUS ON THE PASSAGE OF A SMALL AND SUBTLE
SHORTWAVE TROUGH OVERHEAD ON WEDNESDAY...WHICH IS LIKELY TO SPREAD
A BAND OF LIGHT SNOW ACROSS ABOUT THE SOUTHWEST HALF OF IOWA
DURING THE DAY AND INTO THE EVENING. HAVE INCREASED POPS FAIRLY
SUBSTANTIALLY FOR THAT TIME AND AREA...HOWEVER...THE QUICK
TRANSITION OF THE FORCING ASSOCIATED WITH THE SHORTWAVE...COMBINED
WITH DRY AIR ENTRAINMENT DUE TO A SURFACE HIGH PRESSURE CENTER
DRAPED ACROSS IOWA...WILL KEEP THE SNOW LIGHT AND OF LITTLE IMPACT
AS THERE WILL BE ALMOST NO WIND ASSOCIATED WITH IT. MEANWHILE
MORNING LOW TEMPERATURES ON BOTH WEDNESDAY AND THURSDAY WILL BE
COMPLICATED BY THE RADIATIVE CONDUCIVENESS OF THE HIGH PRESSURE
CENTER MITIGATED BY AN UNCERTAIN EXTENT OF MID AND HIGH LEVEL
CLOUDS ASSOCIATED WITH THE AFOREMENTIONED SYSTEM...SO HAVE STUCK
CLOSE TO PREVIOUS FORECAST AND GUIDANCE FOR NOW.

ANOTHER...SIMILARLY SMALL AND SUBTLE SHORTWAVE WILL MOVE OVERHEAD
AROUND FRIDAY. HOWEVER...THE SENSIBLE EFFECTS OF THIS SYSTEM WILL
BE QUITE DIFFERENT OWING TO STRONGER LOW LEVEL/SURFACE FEATURES
LATE IN THE WEEK. NAMELY...ON THURSDAY NIGHT A WEAK SURFACE LOW
PRESSURE SYSTEM WILL BE DRIFTING ACROSS NEBRASKA WHILE A LARGE AND
COLD HIGH PRESSURE SYSTEM IS BARRELING SOUTHEASTWARD FROM THE
CANADIAN PLAINS. FRONTOGENETICAL FORCING BETWEEN THE TWO
SYSTEMS...ON THE NORTHEAST QUADRANT OF THE SURFACE LOW...WILL BE
COINCIDENT WITH THE SHORTWAVE FORCING ALOFT AND PRODUCE A SOMEWHAT
HIGHER POTENTIAL FOR ACCUMULATING SNOWFALL FROM THURSDAY NIGHT
INTO FRIDAY MORNING. HOWEVER...GIVEN THE DIFFICULTY IN PREDICTING
THE LOCATION OF THESE FEATURES WITHIN THIS TYPE OF STEERING FLOW
SEVERAL DAYS OUT...IT REMAINS UNCERTAIN HOW MUCH OF THIS SNOW MAY
FALL IN OUR AREA VERSUS ADJACENT STATES TO THE NORTH AND EAST. IN
ANY EVENT SNOWFALL AMOUNTS SHOULD NOT BE PARTICULARLY HEAVY AS
ONCE AGAIN THE PARENT SYSTEMS WILL BE MOVING QUICKLY...HOWEVER IF
THE SNOW FALLS IN OUR AREA IT MAY HAVE MORE IMPACT AS FRIDAY WILL
BE QUITE BREEZY WITH THE LARGE CANADIAN HIGH PRESSURE AREA
SPILLING QUICKLY DOWN ACROSS THE MIDWEST. REGARDLESS OF WHETHER
THE SNOW OCCURS...THIS WILL MAKE FOR COLD AND BLUSTERY WEATHER TO
BEGIN THE WEEKEND AND HAVE CONTINUED THE DOWNWARD TREND OF
FORECAST TEMPERATURES ON SATURDAY.

FINALLY...THE CYCLONIC FLOW ALOFT WILL BEGIN TO MOVE OFF TO THE
EAST LATER IN THE WEEKEND ALLOWING FOR WARMING
TEMPERATURES...HOWEVER THE GFS AND ECMWF ARE NOW IN AGREEMENT ON
BRINGING A LONGWAVE TROUGH EASTWARD ACROSS OUR REGION AROUND
SUNDAY/SUNDAY NIGHT WHICH WOULD LIKELY PRODUCE WIDESPREAD
ACCUMULATING PRECIPITATION. AT THIS RANGE THESE SOLUTIONS ARE
VOLATILE AND DETAILS UNCLEAR...BUT IT IS QUITE POSSIBLE THAT THIS
WILL BE THE HIGHEST PRECIPITATION SYSTEM AFFECTING IOWA WITHIN THE
NEXT WEEK.

&&

.AVIATION...09/18Z
ISSUED AT 1115 AM CST TUE FEB 9 2016

MVFR STRATUS LOOKS TO AFFECT ALO/OTM OVER NEXT COUPLE HOURS WITH
SOME FLURRIES FALLING AT OTM. MCW REPORTING FALSE CEILINGS AS MUCH
OF THE WEB CAMERAS AND IDOT PLOW CAMERAS...AND PER VISIBLESATELLITE
REMAINS CLEAR. SOME BLOWING SNOW WILL CONTINUE THROUGH THE
AFTERNOON...MIGHT SEE SOME BRIEF MVFR VIS BUT LOW CONFIDENCE IN
TIMING AND LEFT OUT MENTION ATTM AT MCW. OTHERWISE...WINDS FINALLY
DIMINISH THIS EVENING AS SURFACE HIGH BUILDS INTO THE STATE. VFR
CONDITIONS ARE EXPECTED THROUGH ENTIRE TAF PERIOD EXCEPT AT
OTM/ALO AS MENTIONED ABOVE.

&&

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

&&

$$

SHORT TERM...BEERENDS
LONG TERM...LEE
AVIATION...PODRAZIK



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