Area Forecast Discussion
Issued by NWS Des Moines, IA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
000
FXUS63 KDMX 210843
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
343 AM CDT MON APR 21 2014

.SHORT TERM /TODAY/...
ISSUED AT 343 AM CDT MON APR 21 2014

STUBBORN COLD FRONT WILL FINALLY SWING THROUGH THE STATE
TODAY AND BRING SCATTERED SHOWERS AND A FEW THUNDERSTORMS TO THE
FORECAST AREA DURING MUCH OF THE MORNING. FRONT LOOKS TO CREEP INTO
NORTHWEST PORTIONS OF THE FORECAST AREA BY AROUND 14-15Z AND
CONTINUE TO PUSH SOUTHEAST AND CLEAR MUCH OF THE FORECAST AREA BY
AROUND 00Z TUESDAY OR SLIGHTLY SOONER. LEANED TOWARD THE SLOWER
SREF/GFS/ECMWF WRT TO WINDS AND TEMPERATURES TODAY. 21.05Z HRRR IS A
LITTLE TOO FAST WITH THE PRECIP MOVING EAST AND THE 21.03Z HOPWRF IS
LIGHTER ON THE COVERAGE. REGARDLESS...UTILIZED A BLEND OF THE TWO
FOR POPS/WX TRENDS THROUGH MIDDAY TODAY...THEN THE 21.03Z
SREF/21.00Z HIRES-ARW/NMM FOR TRENDS THIS AFTERNOON.

SURFACE LOW LOCATED OVER NORTHWEST IOWA/SOUTHWEST MINNESOTA WITH
COLD FRONT EXTENDING SOUTHWEST INTO NEBRASKA. WEAK AND BROAD LARGE
SCALE FORCING AHEAD THIS COLD FRONT AS WELL AS ISENTROPIC LIFT WILL
CONTINUE TO FEED MOISTURE INTO THE FORECAST AREA THIS MORNING.
INSTABILITY NOT IMPRESSIVE TODAY BUT ENOUGH AVAILABLE TO KEEP
MENTION OF THUNDER. HAVE BULK OF THE HIGHER POPS OVER WESTERN AND
NORTHERN IOWA THROUGH 12-14Z BEFORE SHIFTING FURTHER SOUTHEAST LATE
THIS MORNING. BELIEVE MUCH OF THE PRECIP WILL QUICKLY DISSIPATE PAST
18-20Z OR BE CONFINED TO THE SOUTHEAST CORNER OF THE FORECAST AREA.

HAVE NON-DIURNAL TEMPERATURE TREND MENTIONED ACROSS THE NORTH AS
SHOULD SEE THE CAA DEVELOP LATE THIS MORNING AND INCREASE THROUGH
THE AFTERNOON. 850MB TEMPS DROP TO +4C TO +6C BY 18Z IN THE NORTH.
GUSTY NORTH TO NORTHWEST WINDS BEHIND THE FRONT WITH WINDS ATOP THE
MIXED LAYER INCREASING TO AROUND 25 TO 30 KNOTS. MUCH DRIER AIR MASS
FILTERS INTO THE STATE AS WELL WITH SURFACE DEW POINTS DROPPING INTO
UPPER 30S AND LOWER 40S OVER THE NORTHWEST. RH VALUES DECREASE TO
NEAR 25 PERCENT ACROSS A SMALL WESTERN PORTION OF FORECAST AREA.
THOUGH AN INCREASED FIRE WEATHER DANGER TODAY...HELD OFF ON RED FLAG
WARNING DUE TO CRITERIA NOT BEING MET WIDESPREAD.

.LONG TERM /TONIGHT THROUGH SATURDAY/...
ISSUED AT 343 AM CDT MON APR 21 2014

EARLY IN THE PERIOD...FEW CONCERNS. SYSTEM ON THE WAY OUT BY 00Z
TONIGHT WITH SECONDARY COLD FRONT NOW OVER NORTHERN MN DROPPING
SOUTHEAST ACROSS THE REGION TONIGHT...BRINGING DRIER AND COOLER AIR
INTO THE REGION BY MORNING. DESPITE WARM TEMPS THE PAST FEW DAYS...
MORNING LOWS TONIGHT WILL BE MUCH COOLER WITH MID 30S NORTH TO MID
40S SOUTH. TUESDAY LOOKS LIKE A NICE DAY WITH GENERALLY SUNNY SKIES
AND A FEW FAIR WX CUMULUS DURING THE MID AFTERNOON AS HIGH PRESSURE
DROPS SOUTHEAST THROUGH THE DAY...KEEPING WINDS LIGHT. LITTLE MIXING
TO PROMOTE MUCH WARMING OTHER THAN SUNSHINE...SO WILL STICK WITH
HIGHS IN THE UPPER 50S NORTHEAST AND MID 60S ACROSS THE WEST. MODELS
DIFFER SLIGHTLY ON TIMING OF UPSTREAM WAVE AND EXPECTED WARM AIR
ADVECTION/CLOUDS AND APPROACHING SHOWERS FOR WED. OVERALL...INCREASE
IN CLOUDS EXPECTED LATE DAY WEST TUESDAY WITH SHOWERS NEARING THE
WESTERN BORDER BY 12Z. THOUGH THUNDER MORE LIKELY ACROSS THE HIGH
PLAINS AND NE...DRY AIR OVER IOWA WILL COOL AND DIMINISH INSTABILITY
WHEN INITIAL PUSH OF MOISTURE ARRIVES. MODELS SHOW LITTLE
INSTABILITY UNTIL AFTERNOON WED AND THAT AGAIN IS LESS THAN
YESTERDAYS SOLUTIONS. THUS...HAVE TRIMMED AREAL COVERAGE OF THUNDER
TO ISO WEST IN THE MORNING AND ISO EAST/SCT FAR WEST IN THE PM HOURS
WEDNESDAY WITH THE FIRST REAL SURGE OF THETAE ADVECTION. AS THE
SYSTEM CROSSES THE REGION...CONFIDENCE IN EVOLUTION OF SYSTEM HAS
LESSENED SLIGHTLY. MODELS CONTINUE TO HAVE GENERAL TRENDS SIMILAR...
BUT DETAILS DIFFER. OVERALL THE BETTER INSTABILITY WILL REMAIN WEST
OF THE AREA UNTIL NEARER 00Z THUR...THEN WEAKEN OVERNIGHT PRIOR TO
INCREASING AGAIN FROM LATE MORNING THUR THROUGH 00Z FRI. STILL SOME
CONCERNS ABOUT OVERNIGHT CONVECTION ACROSS SOUTH/CENTRAL SECTIONS
WED NIGHT AS SOME BULK SHEAR COULD AID SVR POTENTIAL. BOTH THE
00Z GFS AND THE 12Z/NEW 00Z EURO NOW SUGGEST THAT THE LOW WILL
TRACK NORTHEAST ACROSS IA NEARLY EXITING OUR FORECAST AREA BY
18Z THUR...KEEPING THE BEST INSTABILITY AND SVR POTENTIAL EAST OF
THE AREA BY THURSDAY AFTERNOON. FOR NOW...WILL CONTINUE TO MONITOR
POTENTIAL BUT OVERALL CHANCES WOULD REMAIN CONDITIONAL ON ANY
BETTER ALIGNMENT OF FORCING AND STRONGER INSTABILITY THURSDAY.
BEYOND THUR AFTERNOON...MORE UNCERTAINTY IS ARISING IN THE
REMAINDER OF THE FORECAST. MODELS HANDLING THE DEPARTURE OF THE
SYSTEM WITH DIFFERING SPEED THUR NIGHT AND FRIDAY DUE TO A
SECONDARY H500 SYSTEM OVER CENTRAL CANADA POTENTIALLY PHASING WITH
THE DEPARTING H500 LOW. BOTH THE GEM/EURO TAKE THE FIRST SYSTEM
EAST QUICKLY ENOUGH TO PREVENT MUCH PHASING WHILE THE GFS HOLDS ON
TO A TROUGH EXTENDING WEST INTO MN. THIS RESULTS IN A FARTHER WEST
RIDGE AXIS OVER CANADA THAT DROPS SOUTH INTO THE NORTHERN PLAINS
AND DRIVES THE JET STREAM FARTHER SOUTH...DIRECTLY NEXT WEEKENDS
STORM SOUTH OF IOWA. THE GEM/EURO SHOW ONLY A SLIGHT DELAY IN
TIMING AND STILL BRING RAIN BACK INTO THE AREA FOR THE WEEKEND.
FOR NOW THE GFS SHOWS TOO DRASTIC A CHANGE FOR SUCH A SMALL H500
FEATURE. DUE TO UNCERTAINTY...WILL CUT BACK ON POP CHANCE AT ONSET
OF PRECIP EVENT NEXT SATURDAY BUT WILL STILL KEEP POP INCREASING
WITH TIME THROUGH SUNDAY. TEMPS WILL HAVE EVEN GREATER UNCERTAINTY
NOW...AS TIED TO CHANGES IN EVOLUTION AND TRACK OF WEEKEND UPPER
AIR PATTERN AND STORM TRACK. NEWEST 21/00Z EURO STILL KEEPS TREND
OF WET WEATHER NEXT WEEKEND...WHILE THE GFS REMAINS DRY. OVERALL
THE EURO TENDS TO PERFORM MORE CONSISTENTLY AFTER FCST 120 HOURS
SO WILL LEAN TOWARD GEM/EURO SOLUTIONS OF WETTER WEATHER SAT/SUN.
AS MENTIONED IN PREVIOUS NIGHTS AFDS...THERE IS A CONSISTENT
SIGNAL OF ENERGY STRETCHING FROM THE NORTH CENTRAL PACIFIC EAST TO
THE PLAINS...WHICH WOULD FAVOR INCLEMENT WEATHER HERE.

&&

.AVIATION...21/06Z
ISSUED AT 1129 PM CDT SUN APR 20 2014

SHRA AND TSRA HAVE FORMED NEAR BOUNDARY ACROSS NORTHERN IOWA AND
WILL CONTINUE TO AFFECT NORTHERN SITES KMCW/KALO/KFOD BEFORE
SLOWLY PUSHING SOUTH OVERNIGHT...REACHING KDSM NEAR 12Z AND KOTM
AFTER. CEILINGS AND VISIBILITIES WILL REMAIN PRIMARILY
VFR...THOUGH MAY BRIEFLY DROP TO MVFR OR LOWER WITH TSRA. WINDS
WILL BE FROM THE SOUTHWEST AHEAD OF BOUNDARY...MORE VARIABLE NEAR
BOUNDARY AND FROM THE NORTHWEST BEHIND BOUNDARY. WINDS WILL ALSO
BECOME GUSTY DURING THE DAY MONDAY BEFORE DIMINISHING NEAR SUNSET.


&&

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

$$

SHORT TERM...PODRAZIK
LONG TERM...REV
AVIATION...AWB



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.