Thursday, August 12, 2010

8/12/10: Thursday's Weather Report

Issued at 2:55 PM CDT, Thursday, August 12th, 2010

Weather Tidbits:

*7 days so far this month have featured a high temperature of at least 80 degrees in Duluth, Minnesota.

*Today marks the 44th consecutive day with a high temperature of at least 70 degrees in Duluth, Minnesota. The record of 46 days straight days set in 1877 looks like it will be broken!

Weather Headlines:

-Severe weather/heavy rain threat beginning Tonight and lasting through Friday Evening

-Major pattern change takes place late this weekend into the middle of next week

-Snow expected to fall in the mountains of Montana Tonight/Friday

Forecast Discussion for Northeast Minnesota and Northwest Wisconsin

Today's Weather:

Skies were cloudier then expected Today, as a result high temperatures did not get quite as warm as what was predicted 24 hours ago. Highs Today were in the 70s and 80s with plenty of moisture still in place with dewpoints This Afternoon in the 60s to lower 70s. The real intense heat featuring 90+ degree high temperatures, 75-80 degree dewpoints and heat index values of 100 degrees or warmer covered the South half of Minnesota and Iowa Today. A warm front was centered across Southern Minnesota This Afternoon with a 1002 mb low between Dupree and Pierre in Central South Dakota. Warm and moist advection pattern aided by a 30 knot southerly low level jet has been causing scattered showers and isolated thunderstorms Today generally along and north of a line from Leader to Ely with some brief heavy downpours at times, especially in portions of Cass County Minnesota. Skies across our local area were partly sunny-overcast Today with winds out of the south, north or east under 20 mph.

Today's Upper Level Analysis:

Southwest flow aloft was in place across the Upper Midwest Today per water vapor satellite imagery and RUC model analysis. A potent upper level trough was digging south/east across Western Canada/Pacific Northwest and Northern Rockies Today with 12 hour 500 mb height falls of 30 meters covering portions of the Northern Plains/Northern Rockies/and Upper Midwest This Afternoon out ahead of this H5 trough. Note: *Winter Weather Advisories* have been issued for portions of Western Montana late Tonight and early Friday where up to 3" of snow accumulation is possible for elevations at or above 7, 000 feet!

Tonight:

Low pressure will remain over the Central-Eastern parts of South Dakota with a warm front draped over Southern Minnesota while lifting slowly toward the north through the night. A southerly low level jet of around 30-35 knots will persist Tonight across the Upper Midwest with a warm/moist advection pattern continuing along and ahead of the low/warm front...This will lead to occasional showers and thunderstorms over all of our local area Tonight.

With dewpoints in the 60s to around 70 degrees, 850 mb td's increasing to around +14 degrees C and PWS nearing 1.50"...Locally heavy rainfall will be possible which could lead to areas of flooding.

The potential also exists for a few severe thunderstorms This Evening and Overnight, mainly west of a line from Ely to Pine City Minnesota, including the counties of Pine, Aitkin, Crow Wing, Cass, Itasca, Koochiching and Western-Northern St. Louis. Extreme instability consisting of CAPES >5500 j/kg and Lifted Indices as low as -12 degrees C covered parts of Eastern South Dakota, Southern Minnesota and Iowa This Afternoon and some of this instability will continue to get drawn north through the night with CAPE values around our local area around 1000-2000 j/kg with Lifted Indices around -2/-5 degrees C. This along with around 30-40 knots of SW winds at 500 mb and SHEAR of 30-50 knots will be more then supportive of organized thunderstorms Tonight, especially in Western-Southern portions of our area. Damaging wind and large hail will be the main threats from any severe weather that does develop Tonight.

Mostly cloudy skies with areas of fog can be expected in our area with lows in the 60s to lower 70s along with south or east winds under 15 mph Tonight.

Friday and Friday Night:

An upper level trough will head east out of the Northern Rockies/Northern Plains during this period while a cold front moves into the Upper Midwest and passes through our local area from west to east Friday Afternoon into Friday Night. A couple of upper level disturbances embedded within the SW 500 mb flow will also lift northeast into the Upper Midwest through this period. Lift associated with the upper trough, surface cold front and upper level disturbances in conjunction with a very moist and unstable atmosphere will go on to produce occasional showers and thunderstorms in Northern Minnesota and Northwest Wisconsin Tomorrow and Tomorrow Evening with precipitation tapering off from west to east Friday Evening or Overnight Friday the way it looks now.

Heavy rainfall will remain a possibility through Friday Evening as dewpoints hold in the 65-75 degree range, 850 mb td's >14 degrees C with PWS at or above 1.50"!

Severe chances will depend on just how much cloud-cover there is on Friday and also on smaller scale features such as outflow boundaries that will be left behind from Tonight's convection. At this time, it looks like the greater chance for severe thunderstorms will be along and south of a line from Grand Rapids to Two Harbors, including all of Eastcentral Minnesota and all of Northwestern Wisconsin, but this threat may shift a bit more to the south if clouds are widespread during the day and also depending on where those outflow boundaries set-up during the day.

Partly sunny-mostly cloudy skies are forecast on Friday with partly-mostly cloudy skies Friday Night. Highs Tomorrow will be in the 70s and 80s with lows Tomorrow Night in the 50s and 60s. Winds will be out of the south, east or southwest around 20 mph or less during this period.

Extended Forecast:

Low pressure will deepen this weekend across Central-Northern Ontario Province Canada while one cold front exits to our east early Saturday only to be replaced by a secondary cold front which looks to pass through our area from late Saturday into early Sunday. A much cooler airmass will plunge south into our area behind that secondary boundary with 850 mb temperatures dropping to between +2/+6 degrees C from late this weekend into early next week, keep in mind that our 850 mb temps as of late have been hovering around +20 degrees C!

The possibility does exist for a few showers at times both Saturday and Sunday, mainly in Northern Minnesota, but also in Northwest Wisconsin on Saturday. High temperatures will be in the 70s and 80s for Saturday with lows in the 50s. Highs on Sunday will drop into the 60s and 70s with lows in the 40s and 50s.

A cool/northwest flow aloft looks like it will linger through about the middle of next week, thereafter the pattern could shift again leading to warmer weather once again for the Upper Midwest.

5 Day Forecast for Duluth/Superior

.Tonight... Humid. Mostly cloudy with scattered showers and thunderstorms developing. Locally heavy rainfall is possible. Low 63 to 68. Wind southeast at 5 to 15 mph. Chance of rain 60%.

.Friday... Humid. Scattered showers and thunderstorms under mostly cloudy skies. A few storms could be severe with heavy rainfall also possible. High 78 to 83. Wind southeast at 10 to 15 mph. Chance of rain 60%.

.Friday Night... Humid. Scattered showers and thunderstorms, especially during the Evening. Mostly cloudy. Low 60 to 65. Wind becoming west to southwest at 5 to 15 mph. Chance of rain 40%.

.Saturday... Partly sunny. Turning less humid. High 75 to 80.

.Saturday Night... Partly cloudy. Low 55 to 60.

.Sunday... Partly sunny. High 70 to 75.

.Sunday Night... Partly to mostly cloudy. Low 50 to 55.

.Monday... Variable cloudiness. High 65 to 70.

Normal High Temperature Today 75 degrees

Normal Low Temperature Today 55 degrees

Tim