157
FXUS63 KDMX 272344
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
644 PM CDT SUN APR 27 2025
...UPDATED FOR THE 00Z AVIATION DISCUSSION...
KEY MESSAGES
- ALTHOUGH CONDITIONAL, A MODERATE RISK (4/5) OF SEVERE WEATHER
IS IN PLACE FOR NORTHERN IOWA MONDAY AFTERNOON AND MONDAY
NIGHT WITH AN ENHANCED RISK (3/5) ELSEWHERE. CONFIDENCE IN
INITIATION IS LOW, BUT ANY STORMS THAT DO DEVELOP WOULD BE
CAPABLE OF HIGH END SEVERE WEATHER, INCLUDING
STRONG/SIGNIFICANT TORNADOES (EF2+).
- OUTSIDE THE AFOREMENTIONED WINDOW FOR SEVERE WEATHER, CHANCES
OF STORMS TONIGHT INTO MONDAY MORNING, AND THEN AGAIN MIDWEEK
BEFORE DRYING OUT THIS WEEKEND
- WARMER AND MORE HUMID MONDAY, OTHERWISE SEASONAL TEMPERATURES
THROUGH THE PERIOD
DISCUSSION
ISSUED AT 300 PM CDT SUN APR 27 2025
OUR PATTERN WILL REMAIN ACTIVE THROUGH MIDWEEK WITH BOTH
SOUTHERN AND NORTHERN STREAM INFLUENCES UNTIL THINGS CALM DOWN
TO END THE WEEK AS LESS ACTIVE NORTHWEST FLOW AND THEN UPPER
RIDGING ARRIVE. THERE ISN'T MUCH GOING ON FOR THE TIME BEING
HOWEVER, BUT THE STAGE WAS ALREADY BEING SET FOR SEVERE WEATHER
POTENTIAL. DEEP WARM AND MOIST ADVECTION WAS ALREADY OCCURRING
IN THE MATURING SOUTHWEST FLOW ALOFT AHEAD OF WHAT WILL BE OUR
PARENT SYSTEM FOR TOMORROW. SFC-700MB OBJECTIVE ANALYSIS SHOWS
MOISTURE STREAMING NORTHWARD THROUGH THE PLAINS AND MO VALLEY,
WHICH HAS ALSO RESULTED IN WIDESPREAD STRATUS IN THOSE AREAS. AN
AXIS OF H85/H7 QG FORCING MAINLY DRIVEN BY THERMO EFFECTS IS
EXPECTED TO ADVANCE INTO IA OVERNIGHT WITH SOME EXPANSION OF
ELEVATED CONVECTION, LIKELY ROOTED ABOVE 1KM. EFFECTIVE CAPES
MAY REACH 1000+ J/KG WITH BURSTS OF EFFECTIVE SHEAR TOPPING 30
KTS. ALTHOUGH IT'S NOT PERSISTENT, WHEN IT DOES OCCUR WITH
ELONGATED HODOGRAPHS THERE IS SOME PULSEY HAIL POTENTIAL WITH
LFCS NEAR THE FREEZING LEVEL.
LOOKING INTO TOMORROW IS WHEN THE REAL QUESTIONS ARRIVE, ALONG
WITH A NOTED MLCAPE AXIS OF 3000+ J/KG AS TEMPS AND DEWPOINTS
REACH THE 80S AND 60S RESPECTIVELY: POSSIBLY THE MOST WARM/HUMID
DAY OF THE SEASON THUS FAR. WITH 0-6KM SHEAR VALUES JUMPING TO
50+ KTS, THE ATMOSPHERE WILL CERTAINLY BE PRIMED FOR SEVERE
CONVECTION AND DISCRETE, ALL-MODE SUPERCELLS. THE QUESTION WILL
BE WHEN, OR IF, INITIATION OCCURS HOWEVER EITHER DUE TO CINH OR
A LACK OF A SUFFICIENT FORCING MECHANISM. WHILE THERE WILL BE
SOME WEAK SYNOPTIC SCALE LIFT ACROSS EASTERN IA FROM MO INTO THE
MS VALLEY, AND MODELS DO SUGGEST SOME WEAKER ELEVATED
CONVECTION THERE, THE MAIN QUESTION WILL BE WHETHER DEEP CONVECTIVE
INITIATION CAN OCCUR ALONG A NOTED DRY LINE OVER WESTERN IA,
WHICH DOESN'T OCCUR TOO OFTEN IN THE STATE. LOW LEVEL MASS
CONVERGENCE WILL BE WEAK WITH FLOW FAIRLY PARALLEL TO THE
DRYLINE, AND THE SURFACE LOW AND ASSOCIATED STRONG QG FORCING
MOVING FROM MN TOWARD THE GREAT LAKES. EXTENDED RANGE HI RES
MODELS AT THIS TIME YESTERDAY, SUCH AS CSHIELD AND THE NCAR
MPAS ENSEMBLE, WHERE NOTING NEARLY ALL HEALTHY CONVECTION AND
UPDRAFT HELICITY STREAKS FARTHER NORTH CLOSER TO THE TRIPLE
POINT AND ASSOCIATED WARM FRONT, CLOSE TO THE TYPICAL CONCEPTUAL
MODEL FOR TORNADO OUTBREAKS. RECENT HRRR RUNS NOW ENTERING THE
APPLICABLE WINDOW REFLECT THIS EVOLUTION AS WELL, AS DO VARIOUS
MPAS AND RRFS RUNS. HOWEVER, SOME 12Z HREF MEMBERS ACROSS THREE
DIFFERENT CORES (NAMNEST, NSSL WRF, HRW FV3) ARE NOW DEPICTING
ISOLATED WEAK TO MODERATE UPDRAFT HELICITY SWATHS ACROSS
NORTHERN IA. WHILE THE DAY 2 SPC OUTLOOK HAS SCALED BACK
PROBABILITIES SOUTH TO NORTH, A MODERATE RISK (4/5) IS STILL IN
PLACE ENCOMPASSING LOCATIONS WHERE SOME 12Z HREF MEMBERS ARE
INITIATING CONVECTION. ANY HEALTHY CONVECTION THAT DEVELOPS
COULD REALIZE A SOMEWHAT ALARMING NEAR STORM ENVIRONMENT.
EXAMINATION OF 00Z RAP SOUNDINGS EAST OF THE DRYLINE NOTE
PARAMETER SPACE QUITE CONDUCTIVE FOR STRONG TORNADOES IN SUB
1000M LCLS: 0-500M SHEAR AND SRH 30 KTS AND 326 M2/S2, AND
STREAMWISE VORTICITY AT 0.033 (96% OF TOTAL VORTICITY). SO,
UNFORTUNATELY, THE PRIMARY MESSAGE HERE NEEDS TO BE THAT
POSSIBLE OUTCOMES RANGE FROM LITTLE TO NO DEVELOPMENT THIS FAR
SOUTH, TO ISOLATED, BUT STRONG SUPERCELLS WITH LARGE HAIL AND
LONGER TRACK TORNADOES. TO COMPOUND THOSE HAZARDS, ANY STORM
THAT DEVELOPS WOULD BE MOVING RAPIDLY, LIKELY IN EXCESS OF 50
MPH WITH CONDITIONS POTENTIALLY CHANGING QUITE RAPIDLY,
STRAINING WARNING AND REACTION TIMES. NEEDLESS TO SAY, IT WOULD
BE BEST TO CONTINUE TO MONITOR FOR UPDATES INTO TOMORROW. THE
SEVERE POTENTIAL WILL MAINLY BE IN THE EARLY EVENING BUT
ADDITIONAL STORMS LINGER LATE EVENING WITH MORE DEVELOPMENT
POSSIBLE EAST AS CONVERGENCE INCREASES WITH THE MERGER OF THE
APPROACHING COLD FRONT AND LINGERING DRYLINE.
ANY PRECIPITATION SHOULD EXIT OVERNIGHT HOWEVER WITH SOME
CLEARING AND MORE SEASONAL TEMPERATURES AND HUMIDITIES FOR
TUESDAY. HOWEVER PRECIPITATION CHANCES WILL RETURN BY MIDWEEK.
AFTER A BRIEF PERIOD OF ANTI-CYCLONIC FLOW IN THE TRAILING HIGH
PRESSURE, 1-3KM THETA-E ADVECTION WILL RETURN AGAIN WEDNESDAY
WITH SOME INFLUENCES FROM WHAT'S LEFT OF OUR CURRENT UPSTREAM
SYSTEM IN THE SOUTHERN STREAM, BUT MORE SO FROM A A BIT STRONGER
NORTHERN STREAM SHORTWAVE DROPPING INTO THE NORTHERN PLAINS.
THE THERMODYNAMIC SUPPORT STARTING WEDNESDAY WILL EVENTUALLY BE
AIDED BY MORE KINEMATIC SUPPORT AS THE SHORT WAVE APPROACHES
INTO THURSDAY RESULTING IN A FEW DAYS WITH CHANCES FOR SHOWERS
AND A FEW STORMS. THE SEVERE WEATHER POTENTIAL APPEARS LOW
HOWEVER, WITH LIMITED INSTABILITY IN PLACE. THE DEPARTING TROUGH
AND FLOW WILL AMPLIFY SOMEWHAT TO END THE WEEK HOWEVER, LEAVING
US WITH EQUAL RIDGING BEHIND IN WHAT WILL BE DRY, INACTIVE
NORTHWEST FLOW AND SEASONAL TEMPERATURES.
AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 644 PM CDT SUN APR 27 2025
LOW CLOUDS WILL CONTINUE TO MOVE ACROSS THE STATE THIS EVENING,
WITH MVFR CONDITIONS GRADUALLY TURNING TO IFR AND EVEN LIFR
CONDITIONS INTO MONDAY MORNING. RAIN SHOWERS ARE POSSIBLE THIS
EVENING INTO MONDAY MORNING AS WELL, WITH THUNDERSTORM POTENTIAL
STILL FAIRLY LIMITED SO LEFT OUT AT THE TERMINALS AT THIS TIME
WITH CLOSE MONITORING CONTINUING. CEILINGS ARE EXPECTED TO
INCREASE MY LATE MORNING INTO THE AFTERNOON, THOUGH WILL SEE THE
POTENTIAL FOR ADDITIONAL SHOWERS AND STORMS TOWARDS THE END OF
THE PERIOD, SOME STORMS LIKELY BECOMING SEVERE. OUTSIDE OF LOWER
PROBABILITY MENTIONS, UNCERTAINTY REMAINS ON EXACT TIMING AND
LOCATION OF THIS ACTIVITY, SO WILL KEEP A CLOSE EYE ON THIS.
WINDS WILL REMAIN BREEZY THROUGHOUT THE PERIOD, BUT ESPECIALLY
INTO THE MID TO LATE MORNING AND AFTERNOON MONDAY WITH SOUTHERLY
WINDS GUSTING TO 30-35+ KNOTS.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...SMALL
AVIATION...BURY
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