I kind of feel like Noah with this forecast — gather two of every animal! A warm front will be pushing northward, bringing some very moist tropical air with it, throughout the day on Wednesday and will set up some heavy rains by Wednesday Night for the area. That, combined with a slow moving low pressure center, will allow heavy rains to continue to plague the area throughout the day Thursday before finally the skies close up the rain shop sometime Thursday Night. This rain will definitely be more typical of a June soaker, especially due to all the tropical moisture surging northward with it. We definitely cannot rule out minor flooding throughout the event, and will have to watch small rivers and streams the next few days for flooding. There is even the possibility that we will have to watch the larger rivers for minor flooding as the weekend rolls around. Some of the models are printing out 1-3″+ of rainfall, with one of the largest amounts I’ve seen for the STC area being just under 3.5″ (thanks NAM/WRF!) — and the possibilities of areas getting over 4″ of rain! Same for the Twin Cities…
NAM precip forecast from 12z September 21
Meanwhile, a good site to watch for the latest on ground flooding possibilities is the Flash Flood Guidance portion of the National Weather Service. Current guidance shows that Stearns County could likely withstand 3.2″ within an hour, 3.8″ within 3 hours, or 4.4″ in 6 hours before having a lot of flooding concerns. I would not be surprised, though, to see Flash Flood Watches in place by late Wednesday across a good portion of the state.
This rain is not good for a number of reasons, including the farmers in the field trying to harvest their crops, and the fall foliage. A drier fall would lead to more vibrant colors, but when we get a lot of rainfall (whether all at once or spread out) it likes to dull the colors a bit. Here’s hoping the colors will still look good! And of course it’s not good for those having to walk outside, say to get to class or something like that!
The chance during Wednesday also brings with it a chance of some severe storms, with a Slight Risk setting up shop from STC southward. Large hail and damaging winds appear to be the main threat, especially from the Twin Cities southward, but an isolated tornado cannot be ruled out (mainly in the first few tiers of counties along the southern MN border where the warm front will be situated IF the storms can stay with the warm front).
Today's Slight Risk Area
All in all, prepare for a lot of rain in about 36 hours of time between Wednesday evening and Thursday Night. Make sure you have umbrella, poncho and boots on hand to dredge your way through the moisture. Or, quickly build your Ark and make sure you have two of every animal on board (okay, don’t be THAT extreme… it’s not gonna be that bad of a rain!). Just prepare to get soaked!
HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
257 PM CDT TUE SEP 21 2010
…HEAVY RAIN WILL OCCUR ACROSS MUCH OF CENTRAL AND SOUTHERN
MINNESOTA AS WELL AS WEST CENTRAL WISCONSIN WEDNESDAY EVENING THROUGH
THURSDAY NIGHT…
A STRONG LOW PRESSURE SYSTEM WILL MOVE OUT OF THE CENTRAL ROCKIES
AND INTO THE NORTHERN PLAINS WEDNESDAY NIGHT AND INTO THURSDAY.
AHEAD OF THIS SYSTEM…THE COLD FRONT THAT MOVED THROUGH THE AREA
EARLY THIS MORNING…WILL LIFT BACK NORTH AS A WARM FRONT. THIS
WARM FRONT WILL ACT AS A FOCUS FOR SHOWER AND THUNDERSTORM
DEVELOPMENT BEGINNING IN SOUTHWEST AND WEST CENTRAL
MINNESOTA…WEDNESDAY AFTERNOON. THE ACTIVITY WILL SPREAD ACROSS
THE ENTIRE AREA WEDNESDAY EVENING. THE RAIN WILL CONTINUE ACROSS
THE REGION ON THURSDAY AS THE LOW MOVES ACROSS SOUTHERN
MINNESOTA. THE RAIN TAPER OFF FROM WEST TO EAST…THURSDAY NIGHT
AS THE LOW MOVES INTO THE GREAT LAKES.
AS THE WARM FRONT LIFTS NORTH AND WE TAP INTO THE GULF…MOISTURE
LEVELS WILL DRAMATICALLY INCREASE TO MUCH ABOVE NORMAL LEVELS FOR
LATE SEPTEMBER. HENCE LOCALIZED INTENSE RAINFALL CAN BE EXPECTED
IN THUNDERSTORMS. AT THIS TIME…AMOUNTS ARE EXPECTED TO RANGE FROM
AROUND 2 INCHES IN FAR SOUTH CENTRAL MINNESOTA…TO 2.5 TO AROUND
3 INCHES ACROSS CENTRAL MINNESOTA AND WEST CENTRAL WISCONSIN.
HIGHER AMOUNTS WILL BE POSSIBLE THOUGH ESPECIALLY IN AREAS THAT
RECEIVE ANY CONTINUOUS OR TRAINING THUNDERSTORMS.
WITH THE SOIL ALREADY NEAR SATURATION FROM ABOVE NORMAL
PRECIPITATION OVER THE PAST SEVERAL MONTHS…LOCALIZED FLOODING IS
POSSIBLE WEDNESDAY NIGHT INTO THURSDAY…IN SMALLER CREEKS AND
STREAMS. THE CONCERN WILL SHIFT FOR RIVER FLOODING THIS WEEKEND.
WITH RIVER LEVELS ALREADY RUNNING ABOVE NORMAL…SIGNIFICANT
RISES…ESPECIALLY IN WEST CENTRAL WISCONSIN…ARE POSSIBLE.
MUCH UNCERTAINTY STILL EXISTS FOR THE TOTAL AMOUNTS AND
PLACEMENTS OF THE HEAVIER BANDS OF RAINFALL. AS CONFIDENCE
INCREASES ON THESE DETAILS…WATCHES AND WARNINGS MAY BE ISSUED.
PERSONS WITH INTERESTS ALONG THE MINNESOTA RIVER AND ITS ADJACENT
TRIBUTARIES SHOULD CONTINUE TO MONITOR THE LATEST STATEMENTS AND
FORECASTS.
St. Cloud Area Weather 
