Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
146 PM CDT Sat may 25 2013 


Short term...(today and tonight) 
issued at 344 am CDT Sat may 25 2013...updated for 18z taf 
discussion. 


Initial shield of warm air advection showers that was depicted well on 310k 
isentropic surface on the NAM/GFS is fading away across western WI as this 
batch of forcing weakens and dives southeast. In its wake...we have 
warm air advection at 850 mb...but the deeper moisture has pushed east...so precipitation has 
cut off pretty quick. With the warm air advection and weak moisture 
transport...should be able to get some light showers/sprinkles 
across Minnesota this morning...but not much more than that. 


Best chance for rain today will be across southern Minnesota. Warm front now can 
be found across south central Nebraska into NE kan...with a strong low level jet 
overrunning it. This has generated an mesoscale convective system over eastern Nebraska this morning. 
Thunder starting to increase across Iowa as well as the low level jet has slowly 
worked east. Most of this thunderstorm activity will remain south of 
Minnesota through the day...but all hi-res models show some of this 
moisture from Iowa sneaking up into south central Minnesota through 
morning...where some high chance/likely probability of precipitation are continued through 
the morning hours. For the afternoon...precipitation looks to shut 
off...but we will be stuck with fairly broad cloud cover...with the 
only hope for some breaks across the NE mpx County Warning Area thanks to the 
influence of a dry surface high that will be splayed out across the 
Great Lakes. Given the cloud cover will be a cool day...with 
temperatures in south central Minnesota likely staying in the 50s thanks to 
better rain chances and thicker cloud cover. 


For tonight...all models show another round of convection riding 
along north of the warm front...kind of like what we have seen 
overnight to our southwest. Question becomes how far north does the 
activity make it. Consensus placement from the warm front places it 
by 12z Sunday morning from the Black Hills...down through 
Yankton...South Dakota and then down to the central Iowa/MO border. Once 
again...will see a low level jet overrunning this frontal feature...which 
should generate yet another mesoscale convective system. Given the fronts placement to our 
southwest...best chances for thunderstorms tonight will be south of 
the upper Minnesota river in SW Minnesota into SC Minnesota. For timing...favored highest 
probability of precipitation to after 6z...as convection should fire this evening over southeast 
sodak into NE Nebraska...then head toward SW/SC Minnesota. All of this activity 
would be elevated...so severe threat looks minimal...with the main 
impact being the potential for heavy rain...as we have seen this 
evening in Nebraska. 


Long term...(sunday through friday) 
issued at 344 am CDT Sat may 25 2013 


The long term period continues to look increasingly wet and 
stormy. This is due to the region being sandwiched between a 
building upper high along the eastern Seaboard... while a very 
deep trough pushes into the western half of the United States. 
There should be a round of convection pass across southern Minnesota 
Sunday morning...very similar to what has been ongoing overnight 
across NE/IA. The storms to our south currently have been basically 
sub severe... but very efficient rain producers... with upwards of 
1.75 inches of rain in three hours. This is the trend expected 
Sunday morning across southern Minnesota... especially the I-90 
corridor. Thereafter... a significant diminishing trend in the 
precipitation for Sunday afternoon and evening with the nmm/arw 
WRF/S in agreement. 


Memorial Day is looking a little worse now with even the European model (ecmwf) 
driving a wave of convection across the forecast area during the day and 
evening. Just general thunder indicated on swody2 which seems 
reasonable with the main warm frontal boundary meandering from the 
Central Plains to the lower Ohio Valley. Again... the concern will 
be localized heavy rainfall. The deterministic runs would also 
suggest another round of convection for US late Monday night and 
Tuesday morning... especially across southern Minnesota. 


This repeating rounds of potential convection is disturbing with 
areas of southern and especially southeast Minnesota running well above 
normal on rainfall for the month of may. The threat for flash 
flooding will be on the increase. It was pointed out on Friday 
in the weathertalk from Dr Seely at the umn that since March 
1st...(meteorological spring) it has been one of the wettest in 
history for many areas of Minnesota. Add this to the cips analogs 
for 5 days from now and one sees a very wet pattern across all of 
the region with 2 inches of rainfall exceeding 30 percent 
probability with even widespread 3 inches having a 10 percent 
probability. This is in addition to the rains Sunday through 
Tuesday. Not surprising then are the run totals from the GFS and 
European model (ecmwf) through next Friday which paint the landscape with 2 to 4 
inches of rain... with 4 inches or more south of US. Digressing 
for a moment... one of the months/years that has shown up in the 
cips analogs recently is July 1993... with record flooding in this 
part of the country. A review from ncdc showed low pressure aloft 
over the western High Plains with a strong SW jet at 250 mb across 
our area. The Bermuda high had pushed into the southeast United 
States with organized 850 mb winds from the western Gulf of Mexico 
to the western Great Lakes. Hence... the flooding potential is a 
big concern for the week ahead as the pattern in the Summer of 
1993 mimics our week ahead quite well. 


Finally... and just as important... will be the threat for severe 
weather next week as the warm front lifts north into our area 
beginning on Tuesday. Not too concern about severe on Sunday. The 
chance increases some on Monday (isolated)...especially if 
afternoon convection develops as deep layer shear rises. Then from 
Tuesday Onward there is severe potential each day. The cips 
analogs contain many severe reports for US for the middle of next 
week with severe probabilities from 15 to 30 percent for the 
entire forecast area using the top 8 analogs. A cold front may move across 
the forecast area from Friday into Saturday...diminishing the severe weather 
threat. 


&& 


Aviation...(for the 18z tafs through 18z Sunday afternoon) 
issued at 100 PM CDT Sat may 25 2013 


Remnants of mesoscale convective system which produced moderate to heavy amounts of 
precipitation over much of northern Iowa...and lighter amounts 
above far southern Minnesota continues to decrease in coverage and 
intensity as it treks into northern Illinois. Closer to home...large 
swath of strato-cumulus continues to blanket all of the taf region. 
Western half of this region dealing with MVFR...to low end 
MVFR ceilings...with VFR conditions elsewhere. Although infrared satellite 
confirming some redevelopment of lower ceilings over eastern sodak 
..loss of heating by early this evening should give green 
light to short term loss of ceilings over kaxn...kstc...and krwf 
..with redevelopment possible later this evening ahead of 
area of convection forming over central Dakotas after 03z. 
Nothing very substantial concerning forcing in respect to 
convection during the next 24 hours or so...save tonight 
over west central through south central Minnesota. With that said 
tempo groups will be the rule at most western taf locations 
with instability parameters indicating possible short term 
thunder at krwf. Light to MDT southeast flow will continue for much of 
the forecast period. VFR visibilities will be seen into Sunday afternoon 
..minus short periods of MVFR associated with possible convection. 
VFR ceilings expected at all Airport locations after 15z. 


Kmsp... 


Confidence is not high for shower activity later this evening. 
Moderate Theta-E advection and very potent 250mb divergence 
Couplets after 06z...could generate a passing shower at kmsp. 
Much better bet concerns fairly drastic lowering of VFR to 
MVFR ceilings by 23z time period. Actually have a fairly large 
area of low MVFR ceilings over west central WI at this time advecting 
in this direction. Heating should elevate ceilings as they proceed 
east. Although current forecast depicts contuinuation of MVFR ceilings 
through 15z...there is a possibility of a short term break in 
the cloud cover mentioned above between 03z and 05z. After 15z 
MDT southeast flow and VFR ceilings and visibilities should be anticipated until 
end of period. Better chances for convective activity will 
be encountered by late Sunday night. 








&& 


Mpx watches/warnings/advisories... 
Minnesota...none. 
WI...none. 
&& 


$$ 


Short term...mpg 
long term...rah 
aviation...ajz