Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 261128
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
628 AM CDT SAT JUL 26 2014

.SHORT TERM /TODAY/...
ISSUED AT 345 AM CDT SAT JUL 26 2014

RATHER COMPLEX FORECAST FOR TODAY AS CONFIDENCE OF EVOLUTION OF MESO
SCALE ONLY MODEST AT THIS TIME...BUT COULD BE AN RATHER ACTIVE
AFTERNOON AND EVENING OVER THE SOUTH. AFTER EARLY MORNING PATCHY FOG
POTENTIAL FOR SEVERE WEATHER THIS AFTERNOON FOR ABOUT THE SOUTHERN
HALF OF THE FORECAST AREA. EARLY THIS MORNING A SHORT WAVE OVER THE
SOUTHERN PLAINS AT H850 IS DRIVING WARM AIR AND RATHER HIGH MOISTURE
INTO IOWA AND SURROUNDING STATES. A LARGE POOL OF 15C DEW POINTS
EXTENDS FROM EASTERN KS... COVERING ALL OF IOWA AND NORTHERN MO AS
WELL AS EASTERN MN AND WESTERN WI. CLOUDS HAVE BEEN DEVELOPING AT
MID LEVELS OVER SOUTHERN IOWA IN RESPONSE TO THIS MOISTURE AND A
WEAK SFC BOUNDARY/ZONE OF H850 30KT LLJ MOVING ACROSS THE AREA. SO
FAR THERE IS TOO MUCH CIN TO REALLY LET ANYTHING GO AT THIS TIME.
NORTHWEST OF US A PRONOUNCED H700 SHORTWAVE CURRENTLY IN WY/MT WILL
SHIFT EAST SOUTHEAST TODAY. AHEAD OF IT A WEAKER WAVE IS PRODUCING A
SMALL AREA OF CONVECTION OVER EASTERN SOUTH DAKOTA ALONG A RATHER
MINOR TROUGH AT H850 THAT EXTENDS FROM SUPERIOR/DULUTH BACK
SOUTHWESTWARD TO HURON AND RAPID CITY. IT IS EXPECTED THAT THIS AREA
OF CONVECTION WILL WEAKEN AND CONTINUE TO MOVE SOUTHEAST AND IMPACT
NORTHERN PORTIONS OF THE FORECAST AREA THIS MORNING PRIOR TO NOON.
THE WESTERN EDGE OF THE CONVECTION THOUGH...IS EXPECTED TO INTENSIFY
BY LATE MORNING IN RESPONSE TO THE APPROACHING STRONGER H700 WAVE
AND H500 WESTERLIES INCREASING TO 50KTS BY 00Z AND H300 WINDS
NEARING 70 TO 85KTS BY 00Z OVER IOWA.

THIS MORNING A WEAK SFC LOW OVER SOUTHWEST IOWA WILL DRIFT SOUTHEAST
INTO NORTHERN MO DURING THE AFTERNOON HOURS. A PRONOUNCED 2500 TO
3500 J/KG MLCAPE MAX WILL BE OVER THE SOUTHERN TWO TIER COUNTIES BY
18Z...WITH HEATING INCREASING INSTABILITY TO 3500 J/KG NEAR DES
MOINES TO 5500 J/KG JUST SOUTH OF THE IA/MO BORDER.  HRRR MODEL
SUGGESTS THAT A SMALL CLUSTER OF STORMS SHOULD BE ONGOING IN
NORTHEAST/EAST NEBRASKA WHILE THE NMM/ARW SUGGEST THAT THE
CONVECTION OVER NEBRASKA WILL DISSIPATE AND REDEVLOP OVER FAR
SOUTHERN IA/MO.  HOPWRF ALSO SHOWS EASTERN NEBRASKA CONVECTION
CONTINUING TO INTENSIFY WITH TIME THIS AFTERNOON MOVING ESE. THIS IS
SUPPORTED BY THE MEAN AND FORWARD PROPAGATING CORFIDI VECTORS...WITH
TRANSLATION ABOUT 30 TO 40 KTS. WITH THE WEAK BOUNDARY OVER THE
IOWA/MISSOURI BORDER BY 00Z...ANY CONVECTION THAT DEVELOPS TO OUR
WEST WILL RAPIDLY INTENSIFY INTO THE AXIS OF HIGH CAPE THIS
AFTERNOON. GIVEN THE VARIOUS SOLUTIONS...AM LEANING TOWARD
CONVECTION DEVELOPING IN NORTHEAST/EAST NEBRASKA AND STRENGTHENING
RAPIDLY THIS AFTERNOON AS IT INTERACTS WITH THE MOISTURE POOL IN AND
NEAR IOWA TO THE SOUTH. HAVE INCREASED POP ACROSS THIS AREA TO
REFLECT THAT SCENARIO.  THE SOUTH IS OUTLOOKED FOR A SLIGHT
RISK...LOOKS VERY REASONABLE WITH THE POTENTIAL OF A STRENGTHENING
FORWARD PROPAGATING CONVECTIVE COMPLEX NEAR/JUST NORTH OF THE
BOUNDARY LATER TODAY THROUGH EITHER SOUTHERN IOWA OR NORTHERN
MISSOURI.  THERE WILL BE A POTENTIAL FOR HIGHER IMPACT CONVECTIVE
WINDS IF THE SYSTEM GETS STRONG ENOUGH PRIOR TO MOVING SOUTH/EAST OF
THE AREA THIS EVENING. PRECIPITABLE WATER INCREASES TO OVER TWO
INCHES SOUTH OF INTERSTATE 80 THIS AFTERNOON WITH WARM CLOUD DEPTHS
OF 13 TO 14KFT TODAY AS WELL. IN ANY STRONGER STORMS THAT DEVELOP...
A QUICK 1 TO +2 INCHES IS VERY POSSIBLE DESPITE THE PROJECTED FAST
MOVEMENT OF THE STORMS. HIGHS WILL AGAIN BE WARM SOUTH IN THE UPPER
80S TO NEAR 90 WITH LOWER TO MID 80S ACROSS THE NORTH. WINDS WILL
NOT BE APPRECIABLE STRONG AND GENERALLY OUT OF THE NORTHEAST.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 345 AM CDT SAT JUL 26 2014

NEARLY ALL OF THE CONCERNS IN THIS PERIOD WILL BE EARLY ON...THIS
EVENING. THE AIRMASS WILL BE THERMODYNAMICALLY PRIMED DURING PEAK
HEATING WITH THE GFS/NAM SUGGESTING MLCAPES 4K J/KG OR GREATER AND
LITTLE CINH. ONLY QUESTION WILL BE WHETHER A TRIGGER MECHANISM WILL
BE IN PLACE AND THAT SEEMS TO BE LESS AND LESS OF A CONCERN
JUDGING FROM CURRENT UPSTREAM CONDITIONS. RAP OBJECTIVE ANALYSIS
AND WATER VAPOR LOOP SHOW SEVERAL SHORT WAVES/PV ANOMALIES
TOPPING THE SWRN CONUS RIDGE AND EMBEDDED IN THE SEASONALLY FAST
PACIFIC NW TO NRN PLAINS UPPER FLOW. THIS KINEMATIC FORCING IS
CURRENTLY DRIVING SMALL WRN KS AND SD CONVECTIVE CLUSTERS IN
AREAS OF WEAK THERMODYNAMIC SUPPORT. THUS EXPECT REMNANTS OF THESE
FEATURES AND ASSOCIATED FORCING TO BE TRAVERSING SRN IA/NRN MO
DURING PEAK HEATING IN THE VICINITY OF CURRENT SURFACE
FRONT...NOTED ALONG SRN ONE/TWO TIERS OF IA COUNTIES PER 07Z
ANALYSIS. OPERATIONAL AND HI RES MODELS SUGGEST CONVERGENCE
ASSOCIATED WITH THIS BOUNDARY WILL BE INTO MO BY 00Z...BUT
EXISTING CONVECTION FROM EARLIER IN THE DAY MAY ALSO BE IN PLACE
JUST NORTH OF THE BOUNDARY AS WELL AS MENTIONED IN SHORT TERM
DISCUSSION.  ALTHOUGH THE SHALLOW SHEAR IS WEAK...THE DEEP SHEAR
SHOULD BE IN THE 50KT RANGE SUGGESTING ANYTHING THAT DOES NEWLY DEVELOP
COULD BE SUPERCELLULAR INITIALLY. ALTHOUGH THE 0-1KM KINEMATICS
ARE WEAK...THE DEGREE OF DEEP AND 0-3KM INSTABILITY MAY KEEP A FEW
THERMODYNAMICALLY DOMINATE TORNADOES IN THE PICTURE AS WELL...IN
ADDITION TO THE WIND AND HAIL THREAT AS SYSTEM EVOLVES AND LIKELY
BECOMES MORE LINEAR. WHATEVER DOES OCCUR WILL EITHER MOVE OUT OF
OUR FORECAST AREA QUICKLY...OR STAY INTO NRN MO SO OUR WINDOW WILL
BE BRIEF WITH DRY CONDITIONS OVERNIGHT.

COOLER TEMPERATURES WILL THEN BE THE PRIMARY WEATHER STORY INTO
EARLY NEXT WEEK. THERE IS LITTLE IN THE WAY OF FORCING OR WARM
ADVECTION RIGHT ON THROUGH THE EXTENDED...AND EITHER UNIFORM NW
SURFACE FLOW OR LIGHT AND VARIABLE WINDS SHOULD LEAD TO MINIMAL LOW
LEVEL CONVERGENCE. STEEP LAPSE RATES NEAR THE CORE OF THE CURRENT
SASKATCHEWAN AND EVENTUALLY WRN GREAT LAKES UPPER LOW MAY DEVELOP
SOME SHOWERS NE DURING PEAK HEATING SUN...BUT OTHERWISE HAVE EITHER
A DRY FORECAST OR ONLY SLIGHTS FOR THE REMAINDER OF THE FORECAST.
TEMPS STILL LOOK BELOW NORMAL WITH HIGHS OFTEN IN THE 70S AND NO
BETTER THAN THE LOW 80S. LOWS SHOULD OFTEN BE IN THE 50S OR LOWER
60S. ALTHOUGH UPPER LEVEL WINDS WILL EVENTUALLY DIMINISH WITH SOME
HEIGHT RISES...THE OVERALL PATTERN /MORE POSITIVE PNA/ WILL
CHANGE LITTLE INTO NEXT WEEKEND WITH WRN CONUS RIDGE/ERN TROUGH.

&&

.AVIATION...26/12Z
ISSUED AT 623 AM CDT SAT JUL 26 2014

PATCHY DENSE FOG WILL CONTINUE OVER THE AREA FOR THE NEXT 1 TO 2
HOURS. LIGHT SHOWERS/SPRINKLES HAVE DEVELOPED ACROSS THE AREA THIS
MORNING BUT THE MAIN CONCERN THIS AFTERNOON/EVENING SOUTH AS
STRONGER WINDS ALOFT COMBINE WITH A WAVE DROPPING SOUTHEAST INTO
THE STATE. THIS WILL CREATE AN AREA OF THUNDERSTORMS OVER
NORTHEAST NEBRASKA AND SHOULD MOVE SOUTHEAST DURING THE AFTERNOON
AND EVENING...AFFECTING MAINLY KDSM AND KOTM. SOME UNCERTAINTY
REMAINS REGARDING THE COVERAGE...SO HAVE NOT INCLUDED CATEGORICAL
FOR KDSM AT THIS TIME. POTENTIAL FOR QUICK HEAVY RAINS AND HIGH
WIND GUSTS IN STRONGER STORMS DUE TO HIGH INSTABILITY AND
PRECIPITABLE WATER ACROSS AREA THIS AFTERNOON. NEXT UPDATE AT 18Z
SHOULD HAVE BETTER CONFIDENCE/MORE DETAILS ON DEGREE OF IMPACT FOR
SOUTHERN TAF SITES. /REV

&&

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

$$

SHORT TERM...REV
LONG TERM...SMALL
AVIATION...REV



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