Tim from Springfield (IL) Posted August 28, 2016 Share Posted August 28, 2016 Again, not sure how threadworthy this is yet (but who knows considering how August has gone for parts of this subforum), but SPC's D4-8 outlook was hinting at multiple threats of at least marginal risk of severe over parts of the sub for the upcoming Labor Day weekend. So I thought I'd get this out there as the holiday weekend and summer's "unofficial" end is approaching: http://www.spc.noaa.gov/products/exper/day4-8/ DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0347 AM CDT SUN AUG 28 2016 VALID 311200Z - 051200Z ...DISCUSSION... THE MEDIUM RANGE MODELS INCLUDING THE ECMWF AND GFS BEGIN THE DAY 4 TO 8 PERIOD WITH AN UPPER-LEVEL TROUGH OVER THE NERN STATES AND AN UPPER-LEVEL RIDGE IN THE CNTRL AND NRN HIGH PLAINS. BOTH MODELS MOVE THE UPPER-LEVEL RIDGE SLOWLY EWD ACROSS THE GREAT PLAINS ON WEDNESDAY/DAY 4 AND THURSDAY/DAY 5 AS SFC HIGH PRESSURE DOMINATES MUCH OF THE ERN THIRD OF THE NATION. THE GREATEST CHANCE FOR A MARGINAL SEVERE THREAT WOULD BE LATE THURSDAY AFTERNOON IN THE CNTRL AND NRN HIGH PLAINS WHERE AN AXIS OF INSTABILITY AND SOUTHWEST MID-LEVEL FLOW IS FORECAST IN THE WAKE OF THE UPPER-LEVEL RIDGE. ON FRIDAY/DAY 6...THE ECMWF AND GFS SOLUTIONS MOVE THE INSTABILITY AXIS EWD ACROSS THE GREAT PLAINS SUGGESTING AN ISOLATED SEVERE THREAT COULD DEVELOP THERE FRIDAY AFTERNOON. FOR SATURDAY/DAY 7...BOTH THE ECMWF AND GFS SOLUTIONS HAVE AN UPPER-LEVEL TROUGH IN THE WRN U.S. AND SOUTHWEST MID-LEVEL FLOW OVER THE NCNTRL STATES. HOWEVER...THE INSTABILITY PATTERN FOR EACH MODEL IS QUITE DIFFERENT WITH THE GFS DEVELOPING INSTABILITY MUCH FURTHER EAST. AN ENSEMBLE OF THE TWO SOLUTIONS WOULD PUT THE GREATEST POTENTIAL FOR A SEVERE THREAT SATURDAY AFTERNOON IN ERN PARTS OF THE NRN PLAINS EXTENDING EWD INTO THE MS VALLEY. THIS SAME GENERAL AREA COULD AGAIN HAVE A MARGINAL THREAT ON SUNDAY/DAY 8 IF THE MODELS ARE SOMEWHAT CLOSE TO CORRECT. OVERALL...THE ECMWF AND GFS SOLUTIONS HAVE CONSIDERABLE VARIANCE CONCERNING THE FINER-SCALE DETAILS DURING THE LATTER HALF OF THE DAY 4 TO 8 PERIOD SUGGESTING PREDICTABILITY IS LOW IN THAT TIMEFRAME. ..BROYLES.. 08/28/2016 Link to comment Share on other sites More sharing options...
Tim from Springfield (IL) Posted August 28, 2016 Author Share Posted August 28, 2016 Also, WPC isn't yet hinting at a major heavy rain event for most of the sub but the Day 7 totals through next Sunday focus upon Minnesota as hitting the rain jackpot at this time. Of course, as the last few weeks have indicated (especially here in Springfield on Aug. 12 & 15, and for the N/NW parts of the city this morning) it won't take much for at least isolated flash flooding: Link to comment Share on other sites More sharing options...
Hoosier Posted August 28, 2016 Share Posted August 28, 2016 The real dagger from a flooding aspect would be a tropical system but it's looking like 99L may scoot northeastward after getting into the Gulf as it shoots through a weakness and gets picked up by the incoming northeast trough. If it were to somehow miss the trough though then all bets are off. Link to comment Share on other sites More sharing options...
Tim from Springfield (IL) Posted September 4, 2016 Author Share Posted September 4, 2016 Slight risk for most of MN (and far western WI) tomorrow for Labor Day: http://www.spc.noaa.gov/products/outlook/day2otlk.html ...EASTERN NEB/SD INTO MN AND NORTHWEST WI... SOME EARLY DAY SHOWERS AND THUNDERSTORMS MAY BE ONGOING ACROSS PARTS OF MN/WI AND ASSOCIATED CLOUD COVER COULD INITIALLY INHIBIT HEATING. FURTHERMORE...WEAK HEIGHT RISES AND WARMING IN THE 850-700 MB LAYER WILL INHIBIT CONVECTIVE DEVELOPMENT DURING MOST OF THE DAY. HOWEVER...SOUTHERLY LOW LEVEL FLOW WILL TRANSPORT RICH BOUNDARY LAYER MOISTURE NORTHWARD WITH MID/UPPER 60S DEWPOINTS FORECAST ACROSS PORTIONS OF THE MID-MO/UPPER MS VALLEYS. MOST GUIDANCE SUGGEST INHIBITION WILL DECREASE BY 00Z AS STRONGER FORCING FOR ASCENT BEGINS TO MOVE OVER THE REGION AND WEAK HEIGHT FALLS ENSUE. WHILE THIS WILL BE SLIGHTLY OUT OF PHASE WITH PEAK HEATING...AT LEAST A SHORT WINDOW OF SURFACE-BASED CONVECTION IS EXPECTED AFTER 00Z...MAINLY NEAR THE SURFACE BOUNDARY FROM FAR NORTHEAST NEB INTO FAR EASTERN SD AND THROUGH CENTRAL MN INTO NORTHWEST WI. STEEPENING MIDLEVEL LAPSE RATES AND BULK EFFECTIVE SHEAR GREATER THAN 40 KT WILL SUPPORT SOME SUPERCELLS CAPABLE OF LARGE HAIL AND DAMAGING WINDS. A TORNADO THREAT MAY EXIST...THOUGH THIS IS A BIT MORE UNCERTAIN AT THIS TIME GIVEN THE TIMING OF CONVECTION. AN INCREASING SOUTH/SOUTHWESTERLY LLJ OVERNIGHT WILL AID IN UPSCALE GROWTH A FEW LINES/BOWING SEGMENTS MAY TRACK NORTHEAST ACROSS THE SLIGHT RISK AREA. Link to comment Share on other sites More sharing options...
Tim from Springfield (IL) Posted September 4, 2016 Author Share Posted September 4, 2016 Might as well continue this thread to at least Wednesday (Sept. 7): D3 has a Slight for most of IA (and into WI) Tuesday, as well as a D4 15% in that same area Wednesday: Tuesday: http://www.spc.noaa.gov/products/outlook/day3otlk.html ...EASTERN NEB TO WI... GUIDANCE VARIES REGARDING THE AMOUNT AND LOCATION OF ANY ONGOING CONVECTION TUESDAY MORNING...AND THIS COULD IMPACT RISK AREAS AS THESE DETAILS BECOME MORE CERTAIN. HOWEVER...GUIDANCE HAS BEEN REASONABLY CONSISTENT IN DEPICTING FAVORABLE CONDITIONS FOR CONTINUED SEVERE THREAT ALONG THE AFOREMENTIONED SURFACE BOUNDARY TUESDAY AFTERNOON/EVENING FROM THE MID-MO TO UPPER-MS VALLEY. SURFACE DEWPOINTS IN THE MID TO UPPER 60S WILL BE MAINTAINED ON SOUTHERLY LOW LEVEL FLOW AND A MODERATELY UNSTABLE AND UNCAPPED ENVIRONMENT IS DEPICTED IN FORECAST SOUNDINGS ACROSS THE REGION BY LATE AFTERNOON. STRONGEST DEEP LAYER SHEAR MAY REMAIN A BIT NORTH OF BEST THERMODYNAMIC ENVIRONMENT...BUT WILL BE SUFFICIENT TO SUPPORT INITIAL SUPERCELL STORM MODES...WITH ALL SEVERE HAZARDS POSSIBLE. UPSCALE GROWTH IS POSSIBLE INTO THE EVENING/OVERNIGHT ONCE AGAIN WHEN STRONGER UPPER FORCING/HEIGHT FALLS ENSUE IN CONJUNCTION WITH BOUNDARY PARALLEL FLOW. Wednesday: http://www.spc.noaa.gov/products/exper/day4-8/ DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0310 AM CDT SUN SEP 04 2016 VALID 071200Z - 121200Z ...DISCUSSION... ...DAY 4/WED - CENTRAL PLAINS TO UPPER MIDWEST... MEDIUM RANGE GUIDANCE CONTINUES TO INDICATE SEVERE POTENTIAL ACROSS PARTS OF THE CENTRAL PLAINS TO UPPER MS VALLEY WILL PERSIST INTO DAY 4/WED. THE WESTERN UPPER TROUGH WILL FINALLY EMERGE OVER THE PLAINS WED NIGHT INTO THURSDAY...LEADING TO MORE PRONOUNCED UPPER FORCING ACROSS THE REGION. OVERALL THERMODYNAMIC AND KINEMATIC CONDITIONS WILL BE SIMILAR TO THOSE FORECAST IN THE DAYS LEADING UP TO WEDNESDAY...WITH A MOIST AND UNSTABLE BOUNDARY LAYER IN PLACE BENEATH BELT OF ENHANCED SOUTHWESTERLY FLOW ALOFT. AS THE UPPER SYSTEM TRACKS EASTWARD. THIS SHOULD FOCUS STRONG TO SEVERE STORMS ACROSS PARTS OF THE CENTRAL PLAINS TO THE UPPER MIDWEST ALONG/AHEAD OF A SURFACE COLD FRONT. BEYOND DAY 4...GUIDANCE BEGINS TO DIVERGE QUITE A BIT IN THE EVOLUTION OF THE UPPER TROUGH ACROSS THE CENTRAL U.S...RESULTING IN GREATER UNCERTAINTY IN WHERE ANY SEVERE THREAT MAY UNFOLD LATER IN THE PERIOD. ..LEITMAN.. 09/04/2016 Link to comment Share on other sites More sharing options...
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