Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 241141
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
641 AM CDT THU JUL 24 2014

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
ISSUED AT 326 AM CDT THU JUL 24 2014

TODAY...SURFACE HIGH OVER THE REGION WILL SLOWLY SHIFT FURTHER
EAST TO SOUTHEAST AND ALLOW FOR AN AREA OF LOW PRESSURE MAKE ITS
WAY ACROSS THE DAKOTAS AND NEBRASKA TODAY. SOME WEAK THETA-E
ADVECTION AND FORCING BETWEEN 700-500MB ASSOCIATED WITH A SUBTLE
500MB SHORTWAVE RIDING THE NORTHWEST FLOW AHEAD OF THE SURFACE
LOW. THIS SYSTEM MAY SPAWN A FEW THUNDERSTORMS OVER THE NORTHWEST
PORTIONS OF THE FORECAST AREA BY THE AFTERNOON. HOWEVER...HAVE LOW
CONFIDENCE WITH MUCH PRECIP AS THE SURFACE RIDGE REMAINS FAIRLY
STUBBORN IN MOVING EAST AND THERE IS STILL QUITE A BIT OF DRY AIR
IN PLACE OVER IOWA. HENCE...CUT BACK ON POPS THROUGH 18Z AND
CONFINED THEM TO THE NORTHWEST TO NORTH CENTRAL.

WITH THE DRIER FORECAST...LEANED TOWARD WARMER HIGH TEMPERATURES
TODAY DUE TO THE LESS CLOUD COVER/PRECIP AS WELL AS THE ADDITION
OF WEAK SOUTHERLY FLOW DEVELOPING THIS AFTERNOON.

.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
ISSUED AT 326 AM CDT THU JUL 24 2014

WATER VAPOR IMAGERY SHOWS THE WAVE...ACROSS THE WEST COAST
BEGINNING TO ROUND THE UPPER LEVEL RIDGE...TO IMPACT OUR AREA
TONIGHT AND EARLY FRIDAY MORNING. SIMILAR SOLUTIONS ONCE AGAIN
THIS MODEL PACKAGE FOR TONIGHTS EXPECTED CONVECTIVE EVENT THAT
SHOULD TAKE PLACE GENERALLY ALONG AND EAST OF HIGHWAY 169...WITH
THE BEST LIFT AND CONVERGENCE INTO THE UPPER LEVEL BOUNDARY EAST
OF INTERSTATE 35. TRENDS HAVE BEEN SIMILAR...WITH SOME DIFFERENCES
ON TIMING...GFS/GEM STILL SLIGHTLY SLOWER THAN NAM/12Z EURO
WHICH AGAIN FOCUS MOST OF THE THUNDERSTORMS/POTENTIAL MCS OVER THE
EAST/NORTHEAST LATE TONIGHT AND EARLY FRIDAY. NEWEST 00Z EURO IS
ALSO SLIGHTLY SLOWER...SO WILL DELAY THE ONSET NORTHWEST AND
EXTEND THE EXIT EAST BY ABOUT 3 TO 6 HOURS. OVERALL IT WOULD
APPEAR THAT THE EVENT WILL STILL PEAK BETWEEN 09Z AND 15Z
EAST/NORTHEAST AS STRONG WARM AIR ADVECTION AND MOISTURE ARE
FORCED INTO DEVELOPING H850/H700 FRONTAL ZONE ALONG THE LEADING
EDGE OF A THERMAL CAP AT H700 LATE TONIGHT. GFS CONTINUES TO SHOW
PRECIPITABLE WATER VALUES NEARING 1.5 TO 2.0 INCHES BY 12Z FRIDAY
FROM NORTH CENTRAL THROUGH NORTHEAST IOWA WITH SUFFICIENT WARM
CLOUD DEPTHS FOR EFFICIENT RAINFALL. SOUNDINGS AGAIN TONIGHT
INDICATE THAT ELEVATED CONVECTION WILL PEAK BETWEEN 09Z AND JUST
AROUND SUNRISE OVER NORTHEAST SECTIONS. STILL EXPECT THAT ANY
SEVERE THREATS SHOULD BE LIMITED TO HAIL AND PERHAPS SOME
WIND...THOUGH THERE IS A SIGNIFICANT INVERSION THAT MUST BE
OVERCOME FOR ANY DOWNWARD WIND MOMENTUM TO REACH THE SFC. OVERALL
RAINFALL AMOUNTS WILL GENERALLY BE IN THE HALF TO 1 INCH RANGE
WITH SOME HIGHER TOTALS POSSIBLE...ALL ENDING BY MIDDAY FRIDAY.
THIS WILL MAKE FOR A SOGGY START TO FRIDAY MORNING OVER THE
NORTHEAST/EAST. ONCE THE CONVECTION MOVES EAST WITH THE WAVE AND
EXPECTED SFC LOW TRACKING INTO THE NORTH CENTRAL IOWA BY FRIDAY
AFTERNOON...A H700 WARM LAYER WILL BUILD ACROSS IOWA AND BRING
RATHER WARM/HOT TEMPERATURES BACK INTO THE REGION FOR FRIDAY
AFTERNOON. WITH AMPLE SUNSHINE...HIGHS WILL QUICKLY BUILD BACK
INTO THE LOWER TO MID 90S SOUTH WITH UPPER 80S ACROSS THE
NORTHWEST. SLIGHT COOLER READINGS IN THE LOWER 80S WILL HOLD ON
NORTHEAST WITH LEFTOVER CLOUDS EXITING THE REGION. DESPITE MUCAPE
IN THE 4500 TO 5500 J/KG RANGE FRIDAY AFTERNOON...STRONG CAP ALOFT
LIKELY TO MUTE ANY ADDITIONAL CONVECTION. ALONG WITH THE
HEAT...SOUTHERN SECTIONS LIKELY TO BE BACK TO 100F TO 105F HEAT
INDICES BY LATE AFTERNOON AS WELL. WE WILL STAY IN THE WARM SECTOR
FRIDAY NIGHT AND SATURDAY WITH HUMID LOWS IN THE 70S AND HIGHS IN
THE MID TO UPPER 80S SATURDAY. AS THE FRONT SAGS SOUTH AGAIN
SATURDAY AFTERNOON/EVENING...SOME CONVECTION MAY FIRE ALONG IT
OVER THE SOUTH THIRD OF THE FORECAST AREA THROUGH SATURDAY
EVENING. WE ARE OUTLOOKED FOR SLIGHT RISK...BUT WITH ONLY WEAK SFC
CONVERGENCE AND CAP ALOFT...STORMS WILL BE RATHER CONDITIONAL
THROUGH THE AFTERNOON. OTHERWISE COOLER AND LESS HUMID WEATHER
WILL RETURN WILL BY SUNDAY. LITTLE CHANGE FROM YESTERDAY WITH
REGARDS TO THE EXTENDED. H500 LOW OVER HUDSON BAY WILL PHASE WITH
APPROACHING H500 NORTHERN STREAM SYSTEM BY SUNDAY. THIS WILL ALLOW
UPPER LEVEL TROUGH TO AMPLIFY AND EXPAND SOUTH ACROSS THE EASTERN
CONUS. THIS WILL KEEP OUR AREA IN A PROLONGED NORTHWEST FLOW
PATTERN LASTING THROUGH THE EXTENDED PERIOD WITH HIGHS IN THE 70S
AND LOWS IN THE 50S TO LOWER 60S AND LITTLE ORGANIZED
PRECIPITATION.

&&

.AVIATION...24/12Z
ISSUED AT 633 AM CDT THU JUL 24 2014

HAVE VFR CONDITIONS THROUGH ENTIRE TAF PERIOD. ALTHOUGH MVFR AND
POSSIBLY IFR CONDITIONS MAY BRIEFLY OCCUR AT FOD/MCW AND EVEN ALO
LATE IN THE FORECAST PERIOD WITH THE RAIN OVERNIGHT TONIGHT. ONLY
HAVE VCTS MENTIONED ATTM AS LOW CONFIDENCE WITH THE DURATION IF
ANY IFR/MVFR CONDITIONS DO HAPPEN TONIGHT. OTHERWISE...SOUTHERLY
WINDS WILL INCREASE THIS AFTERNOON WITH MIXING AND SURFACE HIGH
SHIFTING EASTWARD.  PRESSURE GRADIENT WINDS ANTICIPATED TONIGHT.

&&

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

&&

$$

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



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