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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Tuesday
• 
• High: 84 °
• Low: 63 °
• Chance of T-Storms

• Wednesday
• 
• High: 79 °
• Low: 57 °
• T-Storms

• Thursday
• 
• High: 68 °
• Low: 50 °
• T-Storms

• Friday
• 
• High: 70 °
• Low: 50 °
• Partly Cloudy

• Saturday
• 
• High: 63 °
• Low: 55 °
• Chance of Rain

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
617 PM CDT Tuesday may 22 2012 


Update... 
updated to include 00z aviation discussion below. 


&& 


Discussion... 
/issued 239 PM CDT Tuesday may 22 2012/ 
very interesting weather forecast in the next 48 hours which could 
include the first significant areal flood problems 
across portions of the forecast area. In addition...severe potential...and 
how long will this unsettled pattern continue. 


First step...a very strong late Spring jet stream continues to 
move across the Pacific northwest...and into the northern rockies early 
this afternoon. This jet will be the main player by late Wednesday 
night/Thursday morning as strong large scale ascent 
develops...with the creation of a jet couplet. Almost all models 
have the same type of signal of this jet couplet which provides 
higher confidence in rainfall potential and flooding. 


It looks as though isolated to scattered convection will be the 
rule from late tonight...through Wednesday afternoon across mainly wc/central 
Minnesota. Once a jet streak and associated surface/850 mb reflection develop 
across the plains...and move NE across the upper Midwest...this 
will create the environment of numerous rain showers with embedded thunderstorms and rain. 
Both isentropic lift along and northwest of the frontal boundary and the 
jet couplet will induce a broad area of convection. 


Latest quantitative precipitation forecast amts during the 18z Wednesday to 18z Thursday time frame have 
amts greater than two inches for a broad area from SW Minnesota...NE 
across central Minnesota. The eastern edge of this high quantitative precipitation forecast forecast will 
be based on the surface/850 mb boundary location. If these boundaries 
move further eastward...the higher amts will be further eastward 
as well. With the consideration of this broad area of heavy 
rainfall amts...an esf will be issued this afternoon...with the 
possibility of a flash Flood Advisory this evening. 


Based on the latest Storm Prediction Center thunderstorm outlook...the main severe weather 
hazard will be large hail/severe winds for mainly far SC Minnesota 
Wednesday...and wc WI Thursday afternoon. This is again dependent on the front 
location and if we see more sunshine. 


Eventually the surface boundary will move eastward and stall across Iowa 
late Thursday. Friday still remains dry for most of the forecast area...except the 
far S during the late aftn/evening. This is dependent on how far 
south this boundary stalls. As a large upper ridge develops across 
the eastern U.S. This surface boundary will lift back northward late 
Fri/Sat. This again will be the best time frame for additional 
shra/tsra. By late Sat/sun...our forecast area could be capped with the main 
front across north Minnesota. This will lead to much warmer temperatures on 
Sunday...which could approach 90 in many areas. After Sunday...the 
mean upper flow will slowly break down to a more east/west flow. 


&& 


Aviation.../00z taf issuance/ 
overall conditions will progressively deteriorate over the 
upcoming 24-36 hours as the area of low pressure currently over 
the High Plains works east ahead of an upper level trough moving 
out of The Rockies and into the plains. Gusty southerly winds will 
persist into the day on Wednesday as low pressure works northeast from 
the plains and into southern Canada. We may see some leftover 
convection from the Dakotas work its way into the western and 
central portion of the area later tonight into Wednesday morning. 
However... this should generally weaken as it moves into the area 
and outruns the better instability and forcing. But... by late 
afternoon and particularly Wednesday evening we should see activity 
redevelop over the central portion of the forecast area then work 
its way east Wednesday night. At this point it is a bit difficult to 
pin down the exact timing and location of things... but would 
expect somewhere in the central-eastern part of the area to see at 
least 6 hour window of moderate to heavy rainfall with embedded 
thunder from Wednesday evening into the overnight hours. 
Initially... ceilings should remain VFR given fairly dry low 
levels... but over time would expect to see ceilings lower and 
precipitation persists... although that will likely be after the end of 
the forecast period. MVFR and local IFR visibilities will 
certainly be a concern in heavier rain showers/thunderstorms and rain Wednesday night... but 
at this point there is too much uncertainty in timing/placement to 
put those specifics into the forecast. 


Kmsp... taf reflects overall progression of expectations... with 
some chance for rain showers/thunderstorms and rain tomorrow morning... then a better shot 
tomorrow evening. As mentioned above... uncertainty in 
timing/placement of activity makes narrowing down a window of MVFR 
or possible IFR conditions as well as thunder a bit difficult at 
this point... but later forecasts should be able to refine things. 


//Outlook for kmsp for overnight Wednesday through Saturday 
overnight Wednesday... showers and thunderstorms with MVFR 
ceilings and visibilities expected. IFR conditions possible. 
Thursday...chance of showers and thunderstorms with MVFR 
conditions expected. IFR conditions possible. 
Thursday night...MVFR ceilings possible early. 
Friday...VFR conditions expected. 
Friday night...MVFR ceilings possible late. 
Saturday...chance of showers and thunderstorms with MVFR 
conditions possible. 


&& 


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


$$ 


/Jlt/