Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 220911
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
411 AM CDT SUN MAR 22 2015

.SHORT TERM /TODAY/...
ISSUED AT 410 AM CDT SUN MAR 22 2015

A LARGE HIGH PRESSURE RIDGE WILL BUILD ACROSS THE GREAT LAKES REGION
TODAY...WHILE AN INVERTED LOW PRESSURE TROUGH DEEPENS OVER THE HIGH
PLAINS AND APPROACHES IOWA FROM THE WEST. BETWEEN THESE TWO SYSTEMS
OUR CURRENT EAST NORTHEAST SURFACE FLOW WILL TURN A BIT TO EAST
SOUTHEAST BUT LARGELY REMAIN STEADY TODAY. THIS WILL RESULT IN
CONTINUOUS INTRUSION OF DRY AND STABLE AIR OUT OF THE PERIPHERY OF
THE HIGH PRESSURE RIDGE AS WELL EVIDENCED BY FORECAST SOUNDINGS.
SATELLITE IMAGERY AND AUTOMATED OBSERVATIONS CURRENTLY SHOW CLOUDS
DEVELOPING ACROSS SOUTHERN MINNESOTA AND FAR NORTHERN IOWA...BUT
WITH BASES AROUND 10 KFT AND NO SIGN OF PRECIPITATION DEVELOPING.

AS THE DAY PROGRESSES THERE IS A PERSISTENT SIGNAL FOR
FRONTOGENETICAL FORCING AND RESULTING PRECIPITATION DEVELOPING
ACROSS MINNESOTA AND WISCONSIN...AS HAS BEEN WELL ADVERTISED FOR THE
PAST SEVERAL DAYS. HOWEVER...GIVEN CURRENT SATELLITE TRENDS AND
RECENT HIGH RESOLUTION MODEL RUNS IT APPEARS INCREASINGLY LIKELY
THAT THIS PRECIPITATION WILL REMAIN NORTH AND NORTHEAST OF OUR
FORECAST AREA TODAY...PERHAPS GRAZING OUR CORNER UP AROUND MASON
CITY WITH SOME LIGHT PRECIPITATION. HAVE THUS CUT POPS BACK TO JUST
THE FAR NORTH TODAY. ANY PRECIPITATION THAT DOES OCCUR IN OUR AREA
BEFORE 00Z APPEARS LIKELY TO BE ALL RAIN WITH PERHAPS A BRIEF WINTRY
MIX RIGHT ALONG THE MINNESOTA BORDER...SO NO IMPACTS ARE ANTICIPATED
AT THIS TIME. MEANWHILE IN SOUTHWEST IOWA MOSTLY SUNNY SKIES IN THE
WARM SECTOR AHEAD OF THE APPROACHING TROUGH SHOULD ALLOW FOR GOOD
WARMING DESPITE THE EASTERLY FLOW...AND HAVE INCREASED TEMPERATURES
INTO THE LOWER 60S AROUND DES MOINES AND LOWER 70S DOWN AROUND
CORNING AND BEDFORD.


.LONG TERM /TONIGHT THROUGH SATURDAY/...
ISSUED AT 410 AM CDT SUN MAR 22 2015

VERY ACTIVE WEATHER PATTERN THROUGH WEDNESDAY. SFC LOW PRESSURE
WILL MOVE SOUTHEAST THROUGH EASTERN NEBRASKA AND SOUTHWEST IOWA
THEN TOWARD NORTHERN MISSOURI BY MONDAY MORNING. THE 850 MB
BOUNDARY WILL PUSH WELL NORTH OF THE SFC BOUNDARY BY THIS EVENING
WITH A GOOD THERMAL GRADIENT DEVELOPING OVER NORTHEAST IOWA AND
INTO SOUTH DAKOTA. STRONG THETA-E ADVECTION WILL FEED INTO THIS
REGION. THE THERMAL PROFILE OVER THE FAR NORTHEAST FORECAST AREA
SHOWS THAT PRECIPITATION TYPE ALONG AND NORTHEAST OF A WAVERLY TO
MASON CITY LINE IS STILL PROBLEMATIC. THIS REGION WILL BE VERY
CLOSE TO MODERATE SNOW FALL ACCUMULATIONS THAT ARE FORECAST JUST
NORTHEAST OF THIS AREA. STILL POTENTIAL FOR A WARM WEDGE TO
PROMOTE MELTING PROCESSES ALOFT. ANOTHER ISSUE IS THE EASTERLY LOW
LEVEL FLOW ORIGINATING FROM HIGH PRESSURE TO THE EAST RESULTING IN
WEEK WEAK SFC COLD ADVECTION AND SUPPLYING ENOUGH DRY AIR TO
PROMOTE EVAPORATIVE COOLING THAT CAN COUNTER ACT LATENT HEAT
RELEASE FROM THE PRECIPITATION. THIS WOULD ALLOW SFC TEMPERATURES
TO COOL BELOW FREEZING WITH A PERIOD OF FREEZING RAIN POSSIBLE.
MAY REQUIRE WINTER HEADLINES FOR OVERNIGHT INTO EARLY MONDAY BUT
WILL NOT ISSUE AT THIS TIME DUE WITH BETTER RESOLUTION EXPECTED
WITH NEW SOLUTIONS THIS MORNING. A FEW THUNDERSTORMS ARE EXPECTED
SOUTHWEST AS THE UPPER LEVEL SHORT WAVE APPROACHES AND LAPSE RATES
STEEPEN. SOME DRIZZLE/FREEZING DRIZZLE STILL POSSIBLE AT THE END
OF THE EVENT LATE TONIGHT/EARLY MONDAY WITH MID LEVEL DRY AIR
ARRIVING WITH THE UPPER WAVE PASSAGE THOUGH LOW LEVEL SATURATION
WITH GOOD FRONTOGENESIS IN ADVANCE OF THE SFC BOUNDARY PROMOTING
COALESCENCE.

THIS SYSTEM WILL DEPART QUICKLY MONDAY HOWEVER THE EASTERLY SFC
FLOW AND LINGERING CLOUDS WILL KEEP TEMPERATURES COOL MUCH OF THE
DAY BEFORE SOME PEAKS OF AFTERNOON SUN. RETURN FLOW QUICKLY
BECOMES ESTABLISHED MONDAY NIGHT WITH THE DEVELOPMENT OF A 50 KT
PLUS LOW LEVEL JET BRING TREMENDOUS MOISTURE ADVECTION NORTH TO
THE STATE. ELEVATED CONVECTION SHOULD ARRIVE OVER SOUTHERN IOWA
OVERNIGHT ESPECIALLY AFTER 06Z. ADDITIONAL THUNDERSTORMS ARE
POSSIBLE SOUTH OF HIGHWAY 20 DURING THE DAY AS A VIGOROUS PV
ANOMALY ARRIVES FROM THE WEST AND MID LEVEL LAPSE RATES APPROACH
7.5 C/KM AND THETA-E LAPSE RATES BECOME NEGATIVE. POTENTIAL FOR
MARGINAL SEVERE HAIL WITH A FEW OF THE STORMS GIVEN THE LOW
MELTING LEVELS AND GOOD FORCING TO PROMOTE ADEQUATE UPDRAFTS.
PRECIPITATION TYPE OVER THE FAR NORTH WILL AGAIN BE PROBLEMATIC
AND CERTAINLY POTENTIAL FOR A WINTRY MIX BEFORE ENDING WITH SOME
ACCUMULATIONS NOT OUT OF THE QUESTION. THE SYSTEM WILL SHIFT
QUICKLY NORTHEAST TUESDAY NIGHT AS THE MID LEVEL DRY SWEEPS
THROUGH THE AREA.

THE REMAINDER OF THE EXTENDED GENERALLY CONSIST OF NORTHWEST FLOW
WITH BELOW SEASONAL TEMPERATURES. THURSDAY IN PARTICULAR COULD BE
QUITE COOL AS THE THERMAL TROUGH MOVES THROUGH WITH 850 MB
TEMPERATURES NEAR -10C.

&&

.AVIATION...22/06Z
ISSUED AT 1139 PM CDT SAT MAR 21 2015

VFR CONDITIONS LOOK TO PREVAIL THROUGH THE TAF PERIOD WITH MCW AND
FOD MAIN CONCERN TOMORROW NIGHT WITH ONSET OF RAIN MOVING INTO THE
STATE. KEPT STRONG EAST TO SOUTHEAST WINDS THROUGH SUNDAY EVENING
WITH A TIGHT PRESSURE GRADIENT IN PLACE.


&&

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

$$

SHORT TERM...LEE
LONG TERM...DONAVON
AVIATION...PODRAZIK



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