AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 341 PM CDT FRI OCT 4 2013 .SHORT TERM.../TONIGHT/... ISSUED AT 330 PM CDT FRI OCT 4 2013 FORECAST CONCERN REMAINS SEVERE THUNDERSTORM CHANCES THROUGH THE OVERNIGHT HOURS. SUBJECTIVE SURFACE ANALYSIS INDICATES SURFACE LOW PRESSURE LOCATED IN CENTRAL NEBRASKA WITH COLD FRONT ACROSS CENTRAL KANSAS AND WARM FRONT INTO NORTHERN IOWA. ADDITIONAL...WEAK BOUNDARY ACROSS SOUTHERN IOWA FROM PREVIOUS NIGHTS CONVECTION. ANTICIPATE SYSTEM DEVELOPMENT TO FOLLOW CLOSELY WITH HIGH RES MODEL SOLUTIONS...WITH DEVELOPMENT IN EASTERN NEBRASKA ALONG CONVERGENCE ZONE NEAR 00Z...BEFORE PUSHING QUICKLY EASTWARD INTO IOWA. STORM MOTION VECTORS AROUND 40KTS INDICATE A VERY QUICK PUSH EASTWARD...WITH A LIMITED WINDOW FOR STORMS EARLY IN THE PERIOD. SEVERE THUNDERSTORMS REMAIN POSSIBLE WITH CAPE VALUES 2000-3000 J/KG...DECREASING TO AROUND 1000 J/KG OVERNIGHT. IN ADDITION...PLENTY OF SHEAR FOR STORMS...ESPECIALLY NEAR SURFACE LOW. HOWEVER...LOW LEVEL SHEAR DECREASES AFTER 00Z...WITH LARGE HAIL AND DAMAGING WINDS THE MAIN THREATS LATER IN PERIOD. PWAT VALUES REMAIN HIGH...THOUGH GIVEN QUICK STORM MOTIONS...ONLY EXPECT TO SEE LOCALLY HEAVY RAIN WITH STORMS. .LONG TERM.../SATURDAY THROUGH FRIDAY/... ISSUED AT 330 PM CDT FRI OCT 4 2013 ANY SIGNIFICANT WEATHER WILL HAVE ENDED BY THE BEGINNING OF THE PERIOD...BUT STILL SOME SENSIBLE WEATHER TO DEAL WITH OVER THE WEEKEND. LOBE OF MAINLY MID LEVEL FORCING WILL EXTEND FROM THE SRN PLAINS THROUGH IA AND MN SAT. THIS WILL BE MAINLY ABOVE 3KM AND MOISTURE STARVED SO DO NOT SEE MUCH IN THE WAY OF PRECIP DURING THE DAY OUTSIDE OF SOMETHING LINGERING EAST. COULD BE SOME RUMBLES OF THUNDER DUE TO WEAKER ELEVATED INSTABILITY...BUT NOTHING SEVERE AS FRONTAL BOUNDARY WILL HAVE PUSHED MLCAPE AXIS EAST OUT OF FORECAST AREA. EXPECT ONLY MINOR REBOUND SAT WITH HIGHS DOWN INTO THE M50S TO M60S. UPPER SYSTEM IS EXPECTED TO SAG NW-SE ACROSS IA SAT NIGHT THROUGH SUN EVENING HOWEVER WITH INCREASED MOISTURE BUT ONLY NEUTRAL TO AT TIMES MODERATE FORCING. HAVE INCREASED POPS SOMEWHAT FOR A HIGHER POP BUT STILL LOW QPF ENVIRONMENT. TEMPS WILL BE COOL AND WELL BELOW NORMAL...ONLY REACHING THE LOW TO MID 50S. THIS WOULD NOT BE TOO FAR ABOVE NORMAL LOWS AND EASILY THE COOLEST TEMPERATURES OF THE FALL THUS FAR. TRANQUIL WEATHER AND MODERATING TEMPERATURES ARE THEN ANTICIPATED THROUGH MUCH OF THE FORECAST INTO NEXT WEEK. THE UPPER LEVEL RIDGE WILL PASS THROUGH THE MO RIVER VALLEY FOLLOWED BY ANOTHER WRN CONUS TROUGH BEING ESTABLISHED. IA WILL BE IN RELATIVELY DRY SW UPPER FLOW HOWEVER WITH A RETURN TO MILD TEMPERATURES. THE NEXT CHANCE OF PRECIP WILL HOLD OFF UNTIL FRI...AND THAT WOULD ONLY BE WESTERN PORTIONS IF THE FASTER GFS VERIFIES. ONLY SLIGHT CHANCES FOR NOW. && .AVIATION...04/18Z ISSUED AT 1230 PM CDT FRI OCT 4 2013 CEILINGS HAVE LIFTED ACROSS SITES...WITH VFR CONDITIONS PREVAILING. AREAS OF SHOWERS WILL CONTINUE TO AFFECT SOUTHERN SITES...KDSM/KALO/KOTM THROUGH 00Z. THUNDERSTORMS WILL DEVELOP ACROSS THE WEST PUSHING EASTWARD AROUND 00Z. TSRA MAY AFFECT SITES...WITH IFR CONDITIONS AT TIMES. SYSTEM WILL PUSH QUICKLY EAST...WITH ONLY SMALL WINDOW TO AFFECT SITES...HOWEVER LINGERING LOW CEILINGS AND VISIBILITIES MAY AFFECT SITES...WITH IFR OR LIFR CONDITIONS POSSIBLE...MOSTLY LIFTING BY 12Z. WINDS WILL SHIFT TO THE WEST/SOUTHWEST BEHIND SYSTEM. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. &&
Posted on: Fri, 04 Oct 2013 23:20:26 +0000