National Weather Service Raw Text Product

294 
FXUS63 KMPX 221705
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1205 PM CDT THU JUL 22 2010

.DISCUSSION...

THUNDERSTORM COVERAGE...DURATION...AND INTENSITY ARE THE PRIMARY
CHALLENGES ACROSS THE FORECAST AREA THROUGH TONIGHT...WITH
PARTICULAR EMPHASIS ON SOUTHERN MINNESOTA...GIVEN THE PRESENCE OF
HEAVY RAIN/FLASH FLOODING AND SEVERE WEATHER THREATS.

SYNOPSIS...VERY IMPRESSIVE HEAVY RAIN PRODUCING MCV AND TRAILING
STORM CLUSTERS ONGOING EARLY THIS MORNING ACROSS FAR NORTHERN IA
AND BACK TO THE SD/NE BORDER. THE GOES IR CHANNEL HAS INDICATED 
CLOUD TOPS UP TO AN ASTOUNDING -80C. THIS IS ON THE NORTHERN
PERIPHERY OF A JUICY AIRMASS WITH PRECIPITABLE WATERS ANALYZED IN
EXCESS OF TWO INCHES. AT THE SURFACE...HIGH MOISTURE IS ALSO
PRESENT WITH DEW POINTS IN EXCESS OF 70F KNOCKING ON THE DOOR OF
SOUTHERN MN ONCE AGAIN. THESE ARE BEHIND A WELL DEFINED WARM FRONT
WHICH ORIGINATES BACK TO A BROAD 1006MB SURFACE LOW IN WESTERN
NE/KS. ALSO...SMALL SCALE MESO-LOW ASSOCIATED WITH MCV IS TRACKING
EAST ALONG THE STATE LINE AND CAUSING SPORADIC WIND GUSTS OF 40
MPH PLUS IN SOUTHERN MN.

THIS MORNING...DIFFERENTIAL DIVERGENCE BETWEEN A RIGHT ENTRANCE
REGION OF A DEPARTING UPPER JET STREAK AND A 45 KT VEERING LOW
LEVEL JET WILL CONTINUE TO FEED THUNDERSTORM CLUSTERS THROUGH THE
MORNING ACROSS SOUTHERN MN AND LIKELY NORTHEAST TOWARDS THE
EASTERN METRO AND WISCONSIN. A BULK OF THE MOISTURE TRANSPORT
WILL BE ABSORBED IN NORTHERN IA AND FAR SOUTHERN MN WHERE THE
GREATEST THREAT OF HEAVY RAIN IS...BUT ENOUGH ISENTROPIC ASCENT
AND NORTHWARD DRAW OF INSTABILITY WILL PRESENT SCATTERED TO
NUMEROUS THUNDERSTORMS FROM WEST TO EAST ACROSS THE REMAINDER OF
THE FORECAST AREA. ISOLATED SEVERE THREAT WILL EXIST FOR DAMAGING
WINDS AND POSSIBLY EVEN SOME LARGE HAIL...MAINLY IN SOUTHERN MN. 
RAINFALL AMOUNTS OF ONE TO TWO INCHES ARE MOST PROBABLE BY
NOON...WITH SOME AREAS IN SOUTH CENTRAL MN SEEING TWO TO THREE.
FLASH FLOOD GUIDANCE VALUES WOULD LIKELY NOT BE TOPPED...BUT
ADDITIONAL ACTIVITY LATER ON ADDED TO THIS IS THE CONCERN. HAVE
KEPT GRIDDED FORECAST HOURLY TEMPERATURES FROM CLIMBING MUCH AT
ALL THIS MORNING.

THIS AFTERNOON AND THIS EVENING...FOR THIS TIME PERIOD THE
NUMERICAL GUIDANCE IS IN FAIRLY GOOD AGREEMENT...HOWEVER A LOT
WILL DEPEND ON WHERE THE PRIMARY WARM FRONT AND OUTFLOW BOUNDARIES
RESIDE DURING AFTERNOON HEATING. THE MEAN OF AN ENVELOPE OF MODEL
GUIDANCE BRINGS THE PRIMARY SYNOPTIC BOUNDARY TO THE STATE LINE BY
21Z TO 23Z. THE LOW LEVEL JET IS FORECAST TO WEAKEN GRADUALLY
DURING THE AFTERNOON...AND MAY BE ENOUGH TO REGENERATE ELEVATED
CONVECTION BETWEEN THE SURFACE AND 850-700MB BOUNDARY THROUGH THE
AFTERNOON. MODERATE MLCAPE VALUES INCREASING TO STRONG LATE IN THE
AFTERNOON ALONG WITH SUFFICIENT DEEP LAYER SHEAR SUFFICES FOR
SUPERCELLS AND SEVERE POTENTIAL. IF CONVECTION CAN FIRE ON OR
BECOME ROOTED NEAR THE SURFACE BOUNDARY IN SOUTHERN MN THEN THERE
IS A TORNADO THREAT...ESPECIALLY WITH LOW LCLS AND 0-1 KM SHEAR
STILL AT 20-25 KTS WITH GOOD VEERING AND HELICITY IN THE 0-0.5 KM
FLOW. LOCAL TORNADIC REGRESSION FROM THE NAM MODEL INDICATES
PROBABILITIES OF NEAR 50 PERCENT JUST NORTH OF THE STATE LINE BY
LATE AFTERNOON. THIS WILL NEED TO BE MONITORED CLOSELY AND BY
LATE MORNING THERE SHOULD BE A BETTER IDEA ON WHERE BOUNDARY
/INCLUDING OUTFLOWS/ WILL BE IN THAT 21Z- 23Z TIME FRAME. HAVE
OPTED TO MENTION SEVERE IN THE FORECAST FROM MID-AFTERNOON THROUGH
EVENING IN SOUTH CENTRAL MN. THE CONVECTION THROUGH THIS PERIOD
SHOULD BE ORIENTED PARALLEL TO THE BOUNDARY FROM SOUTHWEST TO EAST
NORTHEAST AND AGAIN POSE A TRAINING THREAT IN FAR SOUTHERN MN.
GIVEN THE PRECIPITABLE WATERS FORECAST TO BE 2.15 OR GREATER...A 
FLASH FLOOD WATCH IS NECESSARY FOR PARTS OF SOUTHERN MN.
AGAIN...THE CONCERN IS MORE SO FOR THIS AFTERNOON AND EVENING WITH
GREATER RAIN ON TOP OF WHAT WILL FALL THROUGH THE MORNING HOURS.
BESIDES THAT TONIGHT...TEMPERATURES WILL NOT FALL MUCH...BUT WITH
HIGH DEW POINT AIR AND LIGHT WINDS...THE LIKELIHOOD OF FOG
EXISTS...SOME OF WHICH MAY BE DENSE.

FRIDAY THROUGH SATURDAY...THE MAIN BOUNDARY WILL SHIFT SOUTH OF
THE AREA BY FRIDAY. NVA IS FORECAST THROUGH THE MORNING AND
POSSIBLY INTO THE AFTERNOON BY SOME OF THE SLOWER GUIDANCE. A
STRONG UPPER TROUGH APPROACHES THE AREA IN THE WESTERLY FLOW BY
FRIDAY NIGHT. NUMERICAL MODELS DIFFER GREATLY IN SPEED YET ARE
SIMILAR ON ORIENTATION...WHICH WARRANTS LIKELY POPS WITH ITS
PASSAGE. HAVE CONTINUED TO DO SO IN THE FORECAST. COULD ALSO BE A
SEVERE THREAT GIVEN THE LINGERING INSTABILITY AND INCOMING PV
ANOMALY. THIS WOULD MAINLY BE PRESENT IN SOUTHERN MN. SATURDAY
WILL SEE A COLD FRONTAL PASSAGE...MORE THAN LIKELY EARLY GIVEN THE
MODEL ENVELOPE AND THE MORE CONSISTENT GFS AS OF RECENTLY. THE 
UPPER VORT MAY STILL PROMOTE SOME SHOWERS ON SATURDAY AFTERNOON.
1020 MB PLUS HIGH THEN BUILDS IN FOR SATURDAY NIGHT INTO EARLY
MONDAY.

BEYOND...ALL BUT NO SHIFTS MADE TO THIS PORTION OF THE FORECAST.
THE ACTIVE PATTERN MAY BE TOUGH TO BREAK AS LONG RANGE GUIDANCE
INDICATES THE RETURN OF WARM AND MOIST AIR IN THE MIDDLE OF NEXT
WEEK AND THETA-E BOUNDARY FURTHER NORTH INTO CENTRAL MN.

&&

.AVIATION.../18Z TAF ISSUANCE/ 

MAIN AVIATION CONCERNS IN THE FIRST 6 HRS DEALS WITH LOW CLDS AND
POSSIBLE CBS IN AXN AREA...WITH LINGERING SHRA AT RNH/EAU. AS OF
17Z...WEAK CIRCULATION IN SE MN HAS KEPT WEAK E/NE FLOW ACROSS
MSP/RNH/EAU FOR MOST OF THE MORNING WHICH WILL LIKELY CONTINUE AS
THIS WEAK CIRCULATION SLOWLY MOVES EASTWARD ACROSS WESTERN
WISCONSIN THIS AFTN. VWP ACROSS THE REGION IS ALSO SHOWING THIS
CIRCULATION WITH WNDS GENERALLY VEERING TO THE SE/S ACROSS THE
SOUTHWESTERN HALF OF FA. THIS WILL BE PROBLEMATIC IN TERMS OF LOW
LEVEL MOISTURE FROM RETREATING MCS ACROSS WESTERN WISCONSIN.
THEREFORE...WILL CONTINUE MVFR CEILINGS AT MOST OF THE TAF
SITES...ESPECIALLY FOR RNH/EAU/MSP DUE TO LOWER LCLS AND CLOSER TO
THE DEEPER MOISTURE FROM THE MCS. THERE REMAINS A LOW PROBABILITY
OF VFR CEILINGS...SO HAVE INTRODUCE THIS SCENARIO FOR MSP. AFT
00Z...THE FORECAST CONCERNS TURN TO BR/FG OVERNIGHT ALONG WITH
LIFR CEILINGS TOWARD DAWN. EVENTUALLY W/NW DRIER AIR WILL FILTER
ACROSS THE FA BY LATE TONIGHT/FRIDAY MORNING. HOWEVER...IN THE
SHORT TERM...WEAK FLOW AT LOW LEVELS AND THE CONTINUED VERY HIGH
WATER CONTENT NEAR THE SFC...HAVE CONTINUED THE PROBABILITY OF
THESE LOWER CEILINGS/VSBY DURING THE 09-14Z TIME FRAME. LATER
SHIFTS CAN UPDATE TO TEMPORARY PERIOD OR PREDOMINATE IF CONDITIONS
WARRANT.

MSP...WNDS WILL BE GENERALLY FROM THE E/NE FOR THE NEXT 3-6 HRS
WITH WNDS BECOMING MORE SE/S BY THIS EVENING. CEILINGS SHOULD
REMAIN MVFR THRU 00Z...WITH A TEMPORARY PERIOD OF LOW VFR ARND
4000 FT LATER THIS AFTN. NOT TOO CONFIDENT ON LIFR/IFR
CEILINGS/VSBY TOWARD FRIDAY MORNING. HOWEVER...THERE REMAINS
ENOUGH UNCERTAINTY FOR CONTINUING A CHC OF THIS DEVELOPMENT.
AGAIN...LATER SHIFTS CAN UPDATE DEPENDING UPON CONDITIONS. WNDS
WILL BECOME W/NW BY FRIDAY MORNING AS DRIER AIR BEGINS TO FILTER
IN. RAINFALL CHC WILL HOLD OFF UNTIL LATE FRIDAY EVENING FOR THE
NEXT EVENT. ..JLT..

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...FLASH FLOOD WATCH THROUGH THIS EVENING FOR FARIBAULT-FREEBORN-
     STEELE.

WI...NONE.
&&

$$

MTF/JLT