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May 23-31 Severe Threats


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MKX discussion on possible MCS and heavy rainfall.

 

 

THURSDAY... Forecast confidence is medium.

Thursday might end up being hot and humid with quiet weather.
Southern WI will be in between shortwaves, with one exiting to our
northeast Thu morning and the next arriving Thu night.

925mb temps will be increasing to 21 or 22C by Thu afternoon. This
would yield max temps toward the mid 80s, although sunshine will be
necessary. The NAM brings remnants of an MCS through northern IL. If
this happens and southern WI stays under widespread cloud cover for
much of the day, then the max temps in the mid 80s is overdone.

There will be no focused low level jet (LLJ) or warm air advection
with the shortwave Thu night, so kept chances for storms on the
lower side.

FRIDAY THROUGH SATURDAY... Forecast confidence is medium.

Friday will bring the next good chance for showers and
thunderstorms. The closed upper low over the southwest states will
progress northeast into the upper Midwest through Saturday. Repeated
waves of vorticity advection, a steady feed of moisture from the
Gulf and the LLJ directed into southern WI support one or more
rounds of convection during this period. Expect CAPE to be around
1000 j/kg or less, but the warm profile is showing tall, skinny
CAPE. Shear will continue to be around 20 kts. These conditions
support thunderstorms with the potential for a few to grow strong.

 

 

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Next timeframe I'm watching for the possibility of more organized severe weather (beyond marginal/slight risks) would be a couple weeks from now.  Obviously that's a long way off though.

Euro weeklies have the EPO going positive while the PNA goes negative. NAO and AO stay neutral near mid-June. Better pattern incoming? Probably not the place for this, but thought I'd just comment on it. 

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Although there's still a marginal risk in the Upper Midwest, perhaps a low-end, isolated tornado threat in that part of the subforum today?

 

http://www.spc.noaa.gov/products/outlook/day1otlk.html

...UPPER MS VALLEY TO NRN MO/WRN IL REGION...   GRADUAL EXPANSION/INTENSIFICATION OF CONVECTION IS EXPECTED THROUGH   MID/LATE AFTN ACROSS THIS REGION WHILE ENTIRE REGIME SHIFTS   GENERALLY NEWD.  ONE OR MORE ARCS OF CONVECTION MAY DEVELOP FROM   NRN/ERN MO ACROSS IA TOWARD SERN MN...MOVING INTO PORTIONS IL/WI   WITH TIME.  FRAGMENTED MOISTURE FIELD AND WEAK MID/UPPER-LEVEL LAPSE   RATES SHOULD KEEP MLCAPE GENERALLY LESS THAN 1000 J/KG OVER MOST OF   THIS AREA...WHILE DEEP SHEAR REMAINS MRGL AS UPPER SYSTEM WEAKENS.    MRGLLY SVR HAIL AND LOCALLY DAMAGING GUSTS ARE POSSIBLE FROM MORE   INTENSE/PERSISTENT CELLS.  WHILE TORNADO POTENTIAL CANNOT BE RULED   OUT INVOF SLOWLY MIGRATING LOW-PRESSURE AREA...WEAKNESS OF THAT AS   WELL AS OF ASSOCIATED ISALLOBARIC FIELDS AND NEAR-SFC WIND FIELDS   SHOULD KEEP HODOGRAPHS AND LOW-LEVEL SHEAR VECTORS RELATIVELY SMALL.   EXCEPTION MAY BE WHERE LOCALIZED/LOW-PREDICTABILITY BOUNDARY OR   STORM-SCALE PROCESSES DOMINATE MESOSCALE TO SUBSYNOPTIC FORCINGS.    AS SUCH...OVERALL SVR POTENTIAL REMAINS TOO ISOLATED/CONDITIONAL FOR   MORE THAN MRGL PROBABILITIES. 
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from the SPC regarding IA, IL and WI

 

 

 

POCKETS OF MODERATE WARM SECTOR HEATING WILL OCCUR TODAY OVER
NRN/ERN IA AND ADJACENT NW IL/SW WI AND FAR SRN MN...S OF STALLED
FRONT IN MN/WI...AND W OF RESIDUAL TSTM DEBRIS IN IL. SATELLITE
SUGGESTS THAT ASCENT WITH WRN IA VORT LOBE WILL OVERSPREAD NRN AND
ERN IA FOLLOWING MAX HEATING...WITH ASSOCIATED 500 MB TEMPS AOB
MINUS 14C CONTRIBUTING TO AREAL DESTABILIZATION. ALTHOUGH GRADUAL
WEAKENING OF UPR SYSTEM WILL KEEP MEAN FLOW COMPARATIVELY MODEST
RELATIVE TO RECENT DAYS...RESIDUAL BAND OF 40+ KT SWLY 700-500 MB
FLOW ON E SIDE OF VORT LOBE WILL SUPPLY AMPLE DEEP SHEAR FOR SHORT
LINES OF SUSTAINED/ORGANIZED STORMS WITH HAIL/LOCALLY DMGG WIND.
AND...ALTHOUGH WIND PROFILES WILL ONCE AGAIN EXHIBIT VERTICAL
VEER-BACK PATTERNS...WITH SFC DEWPOINTS IN THE MID 60S F AND
ENHANCED LOW-LVL DIRECTIONAL SHEAR NEAR STALLED FRONT...CANNOT RULE
OUT THE RISK OF A TORNADO OR TWO GIVEN SOME POTENTIAL FOR FAVORABLE
STORM-BOUNDARY INTERACTION. THE SVR THREAT SHOULD DIMINISH AFTER
SUNSET.
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Watch possible for E IA, NE MO, and W IL later this afternoon (IMO probably a Thunderstorm watch even though SPC isn't ruling out the isolated tornado threat):

 

http://www.spc.noaa.gov/products/md/md0769.html

MESOSCALE DISCUSSION 0769   NWS STORM PREDICTION CENTER NORMAN OK   1237 PM CDT SAT MAY 28 2016   AREAS AFFECTED...PARTS OF NERN MISSOURI/ERN IOWA AND ADJACENT AREAS   OF IL/WI   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE    VALID 281737Z - 281930Z   PROBABILITY OF WATCH ISSUANCE...60 PERCENT   SUMMARY...THE RISK FOR SEVERE STORMS IS EXPECTED TO GRADUALLY   INCREASE THROUGH THE 20-22Z TIME FRAME.  TIMING REMAINS A BIT   UNCERTAIN...BUT A WATCH SEEMS PROBABLE AT SOME POINT THIS AFTERNOON.   DISCUSSION...AN AREA OF LARGE-SCALE ASCENT /PIVOTING AROUND THE   SOUTHEASTERN PERIPHERY OF THE MID-LEVEL CLOSED LOW OVER THE MID   MISSOURI VALLEY/ IS READILY APPARENT IN SATELLITE   IMAGERY...SPREADING NORTHEASTWARD ACROSS SOUTHERN IOWA AND NORTHERN   MISSOURI.  THIS IS ALREADY CONTRIBUTING TO SCATTERED DEEPENING   CONVECTIVE DEVELOPMENT...WHICH PROBABLY WILL CONTINUE TO GRADUALLY   INTENSIFY WHILE APPROACHING THE MISSISSIPPI RIVER THROUGH 20-22Z.   INSOLATION ACROSS NORTHEAST MISSOURI INTO EASTERN IOWA AND ADJACENT   PORTIONS OF THE MISSISSIPPI VALLEY IS CONTRIBUTING TO STEEPENING   LOW-LEVEL LAPSE RATES.  BOUNDARY LAYER INSTABILITY AS CHARACTERIZED   BY CAPE IS ALSO INCREASING DESPITE SOMEWHAT MODEST MID-LEVEL LAPSE   RATES...THOUGH DIFFERENTIAL UPWARD VERTICAL MOTION AND PERHAPS WEAK   MID-LEVEL COLD ADVECTION MAY CONTRIBUTE TO FURTHER STEEPENING   THROUGH LATE AFTERNOON.   GIVEN THESE TRENDS...IN THE PRESENCE OF SUFFICIENTLY STRONG DEEP   LAYER SHEAR FOR ORGANIZED CONVECTIVE DEVELOPMENT...AND MODEST   STRENGTHENING OF 850-700 MB FLOW TO 30-40+ KT...A GRADUAL INCREASE   IN SEVERE WEATHER POTENTIAL IS EXPECTED THROUGH THE AFTERNOON.  A   TORNADO OR TWO MAY NOT BE OUT OF THE QUESTION IN THE MORE DISCRETE   INITIAL STRONGER STORMS.  HOWEVER...THE RISK FOR MARGINALLY SEVERE   HAIL TRANSITIONING TO MORE GENERAL POTENTIALLY DAMAGING SURFACE   GUSTS APPEARS MORE PRONOUNCED...WITH UPSCALE CONVECTIVE GROWTH INTO   AN EVOLVING ORGANIZED CLUSTER OF STORMS BY LATE AFTERNOON.   ..KERR/CORFIDI.. 05/28/2016   ATTN...WFO...MKX...LSX...DVN...ARX...DMX...EAX...
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Severe t-storms into La Salle County.

SEVERE WEATHER STATEMENTNATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL841 PM CDT SAT MAY 28 2016ILC099-290215-/O.CON.KLOT.SV.W.0021.000000T0000Z-160529T0215Z/LA SALLE IL-841 PM CDT SAT MAY 28 2016...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 915 PM CDTFOR NORTHERN LA SALLE COUNTY...AT 841 PM CDT...A SEVERE THUNDERSTORM WAS LOCATED NEAR NAPLATE...ORNEAR OTTAWA...MOVING NORTHEAST AT 30 MPH.HAZARD...60 MPH WIND GUSTS AND QUARTER SIZE HAIL.SOURCE...RADAR INDICATED.IMPACT...HAIL DAMAGE TO VEHICLES IS EXPECTED. EXPECT WIND DAMAGE TO         ROOFS...SIDING...AND TREES.LOCATIONS IMPACTED INCLUDE...OTTAWA...PERU...OGLESBY...LA SALLE...UTICA...NORTH UTICA...TONICA...GRANDRIDGE...NAPLATE...CEDAR POINT AND LEONORE.THIS INCLUDES...  BUFFALO ROCK STATE PARK...ILLINOIS VALLEY COMMUNITYCOLLEGE...MATTHIESSEN STATE PARK...AND STARVED ROCK STATE PARK.INCLUDING THE FOLLOWING INTERSTATES... I-39 BETWEEN MILE MARKERS 46 AND 62. I-80 BETWEEN MILE MARKERS 77 AND 90.



			
		
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