/Issued 4:32 PM CDT, Wednesday, August 28, 2013/
…Severe thunderstorms and heavy rain possible at times Thursday/Thursday Night…
*Supercell composite forecast valid for Thursday PM per 18z WRF/NAM. Rather impressive values for supercell thunderstorms showing up in a large portion of Western and North Central Minnesota. (Source, DuPage weather site)
*Significant tornado parameter forecast valid for late Thursday Afternoon and Evening. West Central into East Central Minnesota has a pretty good chance to see some severe thunderstorms Tomorrow with even a low risk of tornadoes depending on how far north the warm front will get and how much clearing can take place during the Afternoon hours. (Source, 15z SREF model)
*Severe weather probability forecast for Thursday. Note the bright colors – maxed out values stretching from Western to Eastern Minnesota, values taper off north/south of there. (Source, SREF 15z model)
Monthly, seasonal, and yearly precipitation total update for Duluth, MN (Airport location)
August rainfall total (thru the 27th) 1.52″
Rainfall total since June 1: 7.79″
Precipitation total since January 1: 21.13″
Note: The 0.80″ rainfall total on August 27, 2013 was the heaviest calendar day precipitation total since June 21 when we picked up 1.72″ of rain.
Today’s Weather Summary for Northeast Minnesota and Northwest Wisconsin
Another warm and muggy summer day under partly sunny to mostly cloudy skies. Highs were in the 80s to around 90 degrees with dew points in the 60s to lower 70s. Near Lake Superior, temperatures were in the 70s to around 80 degrees Today due to a light onshore wind, there was also areas of dense fog which burned off during the Morning. A weak boundary covering Northern Minnesota has been generating a few showers and thunderstorms This Afternoon, mostly along the border with Ontario.
Forecast Discussion for Northeast Minnesota and Northwest Wisconsin
Short Term Forecast – Confidence: High.
Tonight (August 28)
Partly to mostly cloudy skies are expected Tonight with a few showers and thunderstorms possible, mainly affecting Northern Minnesota. Locally heavy rain will be possible with this activity with a risk for isolated strong thunderstorms as well which would be capable of producing gusty winds and hail. Wind shear is weak Tonight, but there is sufficient amounts of instability around to support convection in Northern Minnesota Tonight. The other area of concern is in the Western/Southwest part of the area where scattered thunderstorms may develop Overnight, especially after 2-3 AM. Low temperatures Tongiht will be in the 60s to around 70 degrees with south or east winds at 5 to 15 mph.
Thursday and Thursday Night (August 29)
Could be an active one at times Tomorrow and Tomorrow Night. A warm front is expected to lift N/NE reaching Central Minnesota into North Central Wisconsin by late Thursday Afternoon while a surface low moves east out of South Dakota. Note: From a synoptic standpoint the setup Tomorrow looks fairly similar to Monday.
It looks like there could be a round of showers and thunderstorms that moves west to east or slightly southeast through parts of the Northland Thursday Morning into mid-Afternoon Thursday. This activity would be focused just ahead of the cap/stronger instability and would reside north of the warm front. Result from all this is that storms that formed would probably be elevated with a heavy rain and hail threat with damaging winds being the lesser threat unless a well organized bow echo/cold pool were to develop Tomorrow Morning – if that were to happen, then the potential for wind damage would increase.
Additional thunderstorm development is expected from late Thursday Afternoon into Thursday Night as the warm front and area of low pressure remain over the Upper Midwest. Severe weather parameters look pretty good at the moment with a 30-45 knot low level jet from the south while winds in the mid levels veer westerly at around 30-40 knots. Winds near the surface should be out of the south/east. So that alone indicates that we will have a change in wind direction with height which could lead to a few rotating supercells later Thursday Afternoon/Evening. Instability looks good with CAPE of 1000-3000 j/kg along with Lifted Indices of -2 to -8C. 0-6 KM Bulk Shear and Effective Bulk Shear is expected to be in the 30-50 knot range which is more than enough to produce severe thunderstorms. 1km Helicity values also look impressive, ranging from 150 m2/s2 to 250 m2/s2 near the warm front and surface low in Central/Eastern Minnesota.
The Morning convection may actually help to strengthen the warm front through the day with strong heating occurring in Western/Southern Minnesota where temperatures in the 90s to around 100 degrees are forecast while along/north of the warm front, temperatures may hold in the 80s (possibly warmer depending on sky conditions)
At the moment I’m thinking the best chance for severe thunderstorms is along and south of a Bemidji to Two Harbors line with the Walker, Brainerd Lakes, Aitkin, Pine City and Hinckley areas under the gun the most the way it looks now.
Large hail and damaging winds are the main severe weather threats, but an isolated tornado threat could also develop late Thursday Afternoon or Thursday Evening, generally around the Brainerd Lakes/Mille Lacs Lake corridor.
The other concern this period will be the potential for heavy rain due to the deep tropical moisture that’ll remain in place with dew points in the 60s to lower 70s and PWS of 1.50-2.00″.
High temperatures in Northeast Minnesota and Northwest Wisconsin will be in the 70s and 80s on Thursday with lows mainly in the 60s. Winds will be out of the south or east Tomorrow at 10 to 20 mph with south, east or north winds Tomorrow Night at 10 to 20 mph.
*Still have a slight risk for excessive rainfall in parts of Northeast Minnesota and Northern Wisconsin on Thursday (green area on the map) Source, Weather Prediction Center.
Extended Forecast – Confidence: High.
Friday through Sunday (August 30-September 1)
Friday looks dry as low pressure moves off to our east. Saturday and Sunday will feature a strengthening area of low pressure passing north of Minnesota while a cold front tracks through the Upper Midwest Saturday Afternoon/Night. Showers and thunderstorms will be possible once again on Saturday as that cold front moves through. Dry weather should return for Sunday. High temperatures will be in the 70s and 80s Friday and Saturday with highs on Sunday in the 60s and 70s. Lows Friday Night and Saturday Night will be in the 50s and 60s.
Long Range Forecast – Confidence: High.
Near to below average temperatures are expected during this period. Dry weather for Labor Day (2nd) into Tuesday (3rd) Could see some showers mid-week (4th) and possibly again toward the 7th.
5 DAY FORECAST FOR DULUTH/SUPERIOR
.Tonight… Partly to mostly cloudy. Areas of fog possible. Low 60 to 65. Wind east to southeast at 5 to 15 mph.
.Thursday… Occasional showers and thunderstorms possible. High 80 to 85. Wind south to southeast at 10 to 20 mph.
.Thursday Night… Occasional showers and thunderstorms possible. Low 60 to 65. Wind east at 5 to 15 mph.
.Friday… Partly sunny. High 75 to 80.
.Friday Night… Partly cloudy. Low 60 to 65.
.Saturday… Partly sunny. Late Afternoon showers or thunderstorms possible. High 80 to 85.
.Saturday Night… Showers or thunderstorms possible. Mostly cloudy. Low 55 to 60.
.Sunday… Cooler and less humid. Partly to mostly cloudy. High 68 to 73.
Normal temperatures for Today
Sunrise Thursday: 6:25 AM CDT
Sunset Thursday: 7:53 PM CDT