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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Thursday
• 
• High: 88 °
• Low: 50 °
• Chance of T-Storms

• Friday
• 
• High: 77 °
• Low: 57 °
• Chance of T-Storms

• Saturday
• 
• High: 72 °
• Low: 52 °
• Chance of T-Storms

• Sunday
• 
• High: 93 °
• Low: 63 °
• Partly Cloudy

• Monday
• 
• High: 84 °
• Low: 48 °
• Chance of T-Storms

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
922 PM CDT Wednesday may 23 2012 


Updated to expand on severe threat tomorrow... 


&& 


Discussion... 
/updated/ 
a powerful upper level jet currently crossing the 4 corners 
region will round the base of the upper level trough and head 
towards the upper Mississippi River valley. As it arrives...a 
surface low will deepen and track along the Wisconsin/Minnesota 
border. Southesterly flow in the warm sector of the surface low 
combined with the approaching upper level jet will great a 
favorable deep shear environment supportive of supercells capable 
of producing all modes of severe weather. The tornadic threat 
may be limited by the fact that the low level flow will be fairly 
unidirectional...an the large dewpoint depressions. 
None the less...50kts at 850 is a cause for concern...and will 
continue to monitor the sitation and the role tonights convection 
plays in tomorrows weather. 


/Previous discussion issued at 427 PM CDT Wednesday may 24 2012/ 
tonight and Thursday...slow-progressing surface cold front over northwest Minnesota into 
eastern South Dakota and eastern NE will slowly plod eastward overnight into Thursday then 
become stalled near the Minnesota/WI state line. Aloft...deep southwesterly flow 
aligned along and ahead of the front on the leading edge of an 
incoming upper trough will bring plenty of moisture at multiple 
levels from the deep south into the northern plains and upper 
Mississippi River valley regions. A surface low over the Southern 
Plains will be lifted north-northeast tonight along the front and become 
further enhanced by the negatively-tilting trough tonight through 
tmrw. This will greatly increase lift within the deeply moist 
atmos /pwats have increased to near 1.5 inches over western MN/. With 
the approach of the front and vorticity maximum lobes...widespread rain 
will develop overnight through tmrw. Some of the rain will be heavy 
at times over south-central Minnesota...mainly through central portions of 
the weather forecast office mpx County warning forecast area...including the Twin Cities metropolitan. Have 
maintained probability of precipitation near 100 percent with quantitative precipitation forecast well over 1 inch for 
much of the area...and possibly as high as 3-4 inches in a 
localized fashion through Thursday. The cold front will eventually push 
into WI by late Thursday afternoon...allowing the rainfall to taper off late 
in the day. Beyond the heavy rain threat...there still remains a 
slight risk of severe thunderstorms in far southern Minnesota ahead of the fnt. MUCAPES 
increase to near 500 j/kg with virtually no capping this afternoon and 
evening. Have already received a couple of 1 inch hail reports from 
short-lived thunderstorms this afternoon. Though getting storms to have high 
surface-based instability will be difficult due to extensive cloud 
cover and the heavy rain...there still may be an isolated storm that 
may reach severe limits through the daylight hours today with generic 
thunderstorms possible overnight into Thursday. Speaking of cloud cover...a few 
breaks in the overcast allowed temperatures in southern-eastern Minnesota to soar into 
the middle 80s to near 90 this afternoon. The slow progression of the fnt 
will keep mild temperatures for eastern Minnesota into western WI overnight while a wind 
shift behind the fnt will bring in cooler temperatures to western-central Minnesota. 
Highs tmrw will then not rise much above the overnight lows...with 
some diurnal spreads only in the 5-8 degree range. 


Thursday night through Saturday...the upper level trough will 
continue its negative tilt through southern Canada...dragging the surface low 
over NE Minnesota and Lake Superior while the cold front shifts S and east Thursday 
night. A secondary dry cold front will push through the region Friday...then 
will stall out over NE-IA-IL while weak high pressure slides across 
the Dakotas-MN-WI Friday night into Sat. This drying out period will 
be mainly in the lowest levels as clouds will still be fairly 
plentiful during the day on Friday. Moisture returns Friday night into Sat 
as the stalled fnt transitions into a warm front. A deep upper level 
high rotating over the southeast states will Open A plume of moisture 
from the Gomex into the upper plains. Isentropic lift with the 
warm front will spread another good dosing of rain over the region 
Saturday. Warm temperatures will return from the S Friday and especially 
Sat...but the slow progression of the warm front may well create a 
large spread of high temperatures from north to S on Saturday. 


Sunday through Tuesday...the active pattern will continue for the 
start of next week as a large digging trough coming onshore the 
socal coast will shift across The Rockies over the weekend and pick 
up a surface low over Colorado. This low will shift NE into sun... 
becoming more developed and again bringing additional Gulf 
moisture and warm air to the region. Highs look to shoot into the 
middle and upper 80s on sun as the weather forecast office mpx County warning forecast area is slotted into the 
warm sector of the system. The system exits Sun night into Monday... 
which is reflected in probability of precipitation which are maxed out Sun night then go 
on a diminishing trend Monday into Tuesday. Cooler air also follows into 
the region for the start of the workweek. 


&& 


Aviation.../00z taf issuance/ 
a surface cold front was moving southeast across the state this 
evening and was the focus for showers and thunderstorms. Ahead of 
the front winds are southeast at 20g30kt...while behind the front 
winds are northwest at 5g15kt. Showers and thunderstorms are 
expected to continue to develop along and behind the front 
overnight...especially at krwf...kstc...kmsp...and krnh. There 
will be reduced visbys under the heavier thunderstorms...but dont 
anticipate substantial wind gusts. Hopeful to see a break during 
the late morning hours...with potential for redevelopment later 
tomorrow afternoon. 


Kmsp...showers and thunderstorm will spread overhead shortly and 
continue off and on for the next several hours. Will likely see 
visbys temporarily drop below 3sm at times...but didnt have the 
confidence to include in the tafs at one particular time. Looks 
like thunderstorms are possible throughout the period...but tried 
to find a thunder-free period early tomorrow morning. Dont not 
have high confidence that this will indeed occur. 


/Outlook/ 
Friday...VFR. Winds southwest at 10g15kt. 
Saturday...mvrf with thunderstorms and rain possible. Winds east-southeast at 15g20kt. 
Sunday...VFR with thunderstorms and rain possible. Winds south-southwest at 20g25kt. 


&& 


Mpx watches/warnings/advisories... 
Minnesota...Flash Flood Watch through Thursday afternoon for Anoka-Benton- 
Blue Earth-Brown-Carver-Chisago-Dakota-Hennepin-Isanti- 
Kanabec-Kandiyohi-Le Sueur-Martin-McLeod-Meeker-Mille Lacs- 
Morrison-Nicollet-Ramsey-Redwood-Renville-Scott-Sherburne- 
Sibley-Stearns-Washington-Watonwan-Wright. 


WI...none. 
&& 


$$ 


Jpc/jrb