Sunday, August 29, 2010

8/29/10: Sunday's Weather Report

Issued at 5:47 PM CDT, Sunday, August 29th, 2010

Weather Tidbits:

*4 consecutive days (8/25-8/28) and counting with no rain at Duluth, Minnesota. The last time we put together 4 days in a row without any rain was back on July 6th-9th!

*693 severe weather reports in Minnesota so far this year with 123 tornado reports! Source: Paul Douglas, St. Cloud times.

Weather History:

On this date last year the high temperature was just 56 degrees at Duluth, Minnesota.

Forecast Discussion for Northeast Minnesota and Northwest Wisconsin

Today's Weather:

Warm weather continued Today with high temperatures mainly in the 80s which is 10-20 degrees above normal for late August, however, an onshore wind developed This Afternoon around the head of Lake Superior which caused temperatures to fall back into the 60s and 70s This Afternoon. Dewpoints were still rather low Today with readings in the mid 50s to lower 60s, but a muggier airmass consisting of dewpoints in the 65-68 degree range were beginning to advect north/west from Southern-Central Wisconsin late Today. Late Afternoon PWS ranged from 0.80-1.10" in Northern Minnesota and Northwest Wisconsin. A few showers and isolated thunderstorms have developed This Afternoon in extreme Northern Minnesota, generally affecting the cities of Big Falls, Manitou, Littlefork and International Falls in Koochiching County, some brief heavy downpours and occasional lightning strikes have been occurring with this activity as it heads northeast into Southern Ontario Province. These showers have been forming in a slightly unstable environment with CAPES around 500 j/kg with Lifted Indicies around zero degrees C. Surface map early This Afternoon featured a stationary front extending from Central South Dakota to Eastcentral North Dakota to Southcentral Ontario Province with low pressure averaging 1000 mb centered in Central South Dakota.

Today's Upper Level Analysis:

A broad upper level trough covered the Western U.S. Today per RUC model analysis with a 100 knot upper level jet in place on the east side of this trough from Central Montana to Southern Saskatchewan Province. A southwest 500 mb flow covered the Upper Midwest Today while a large upper level ridge (5940 meters) was in place from the Central-Southern Great Lakes, through the Central/Southern Plains, Ohio Valley and Eastern U.S.


Another strong southwesterly low level jet of 30-55 knots will be in place across Minnesota Today out ahead of a stationary front which will remain well to our west/north Tonight. Deeper moisture will advect north into our area during the night with dewpoints climbing into the 60s while PWS rise to between 1.00-1.50" Overnight. The combination of the strong LLJ and moisture transport combined with a weak upper level disturbance lifting into the Upper Midwest could be enough to trigger isolated to scattered showers/thunderstorms Tonight across Northern/Eastern Minnesota and Northwest Wisconsin. No severe weather is expected though due to marginal instability, but some brief heavy downpours and occasional lightning strikes may accompany some of this activity during the night. Partly-mostly cloudy skies will be found in our area Tonight with lows in the 60s and lower 70s which is 10-20 degrees above average for the end of August. Winds Tonight will be out of the south at 10-20 mph with a few higher gusts.

Monday and Monday Night:

A very warm and muggy airmass will be found in our local area during this period with dewpoints in the 60s to lower 70s with PWS of 1.50-2.00"! High temperatures on Monday will be mainly in the 80s to around 90 degrees with lows Monday Night in the 60s and 70s! A stationary front will be centered to our west/north on Monday, this boundary will then begin to shift east as a cold front Monday Night, but will likely remain west of our immediate area. Low pressure will also begin to deepen from 1000 mb late Today to around 995 mb by late Monday Night as it lifts northeast from Central South Dakota. The atmosphere will become more unstable along and ahead of this boundary Tomorrow and Tomorrow Night with CAPES from 1000-1500 j/kg with Lifted Indices of zero/-4 degrees C. A southwest low level jet of 30-55 knots will persist across our area during this period along with around 30-35 knots of SHEAR while mid level winds increase to 30-40 knots in Northcentral Minnesota with a 90 knot upper level jet moving into the Northern Plains.

Scattered showers and thunderstorms should develop Monday Evening and continue through the Overnight hours along and west of a line from Grand Marais Minnesota to Shell Lake Wisconsin. A few of the thunderstorms could become severe Monday Evening, mainly in Western parts of our area...including the Counties of Crow Wing, Cass, Itasca and Koochiching. Damaging wind and large hail will be the main threats from severe storms, along with heavy rainfall and dangerous lightning in any non-severe thunderstorm.

A few showers or thunderstorms could also occur on Monday, mainly in Northern-Northeastern Minnesota.

Extended Forecast:

Low pressure deepens to between 987-993 mb during the Tuesday-Wednesday time frame as it lifts northeast into Western Hudson Bay Canada. A cold front attached to that low will continue to move east and will pass through Northern Minnesota and Northwest Wisconsin Tuesday and Tuesday Evening. A very muggy and unstable airmass will continue on Tuesday along and ahead of this front with dewpoints in the 60s and 70s along with PWS from 1.50-2.00" while CAPES range from 1000-2000 j/kg with Lifted Indices of -2/-5 degrees C. The greatest instability is forecast to set-up across Northwestern Wisconsin the way it looks now, and this area will have the best chance at seeing a few severe thunderstorms Tuesday Afternoon and Evening with a lesser threat across Northeast-Eastcentral Minnesota the way it looks now due to an earlier frontal passage. Damaging wind and large hail will be the main severe threats once again on Tuesday. The threat for precipitation will end Tuesday Night with mainly dry conditions expected for Wednesday as high pressure passes through the Upper Midwest in wake of Tuesday's cold front. High temperatures will be in the 70s and 80s on Tuesday with mainly 70s expected for Wednesday along with much lower humidity. Lows Tuesday Night will be in the 50s and 60s with mainly 50s for Wednesday Night.

The forecast models continue to be at odds as to what will happen around the Upper Midwest from mid to late week and perhaps through next weekend. Models have been exhibiting little consistency for this time period with rather large swings noted from one model run to the next.

One potential outcome will be for a complex low pressure system with one center to our south and another to our northwest phasing together as they reach the Great Lakes later this week while an upper level low/upper trough intensifies over the Upper Midwest/Great Lakes which would result in a cool and rather wet period from Wednesday Night through at least Friday.

Another possible outcome would be for a cold front to pass through the Upper Midwest with possible rain mainly Wednesday Night through about midday Thursday before things dry out.

One thing that may be giving the long range models problems is Hurricane Earl and it's forecasted track toward the far Western Atlantic, possibly even affecting portions of the far Eastern U.S. late this week, the farther west this hurricane tracks would likely cause weather systems to slow down across the Plains and Upper Midwest from mid to late week.

5 Day Forecast for Duluth/Superior

.Tonight... Partly to mostly cloudy. Mild. Scattered showers or isolated thunderstorms possible mainly late. Low 62 to 67. Wind south to southeast at 10 to 20 mph. Chance of rain 30%.

.Monday... Humid. Partly cloudy. Showers or thunderstorms possible early. Warm and breezy. High 82 to 87. Wind south at 15 to 25 mph. Chance of rain 30%.

.Monday Night... Humid and warm. Becoming mostly cloudy. Showers or thunderstorms possible after Midnight. Low 65 to 70. Wind south at 10 to 20 mph. Chance of rain 30%.

.Tuesday... Humid. Partly sunny. Showers or thunderstorms possible. High 78 to 83. Chance of rain 30%.

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

.Wednesday... Less humid. Partly cloudy. High 70 to 75.

.Wednesday Night... Partly cloudy. Low 50 to 55.

.Thursday... Mostly cloudy. Showers possible. High 65 to 70. Chance of rain 20%.

Normal High Temperature Tomorrow 70 degrees

Normal Low Temperature Tomorrow 50 degrees